Amines are derivatives of ammonia with one or more alkyl groups bonded to the nitrogen. They can be classified as primary, secondary, or tertiary based on having one, two, or three alkyl groups respectively. Amines exhibit basic properties due to the lone pair on the nitrogen. The basicity depends on factors like resonance, hybridization, and substituents. Amines undergo reactions like substitution, alkylation, and reactions with carbonyl compounds to form imines. Some amines like pyridine are deactivated toward electrophilic aromatic substitution.
Aromatic amines topic includes basicity of the aromatic amine. It also includes the comparison of the basicity. It is designed according to new PCI syllabus of B. Pharmacy.
Amino compounds by dr. pramod r. padolepramod padole
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. Amines are classified as primary, secondary, or tertiary based on the number of alkyl/aryl groups attached to the nitrogen atom. Alkyl amines are more basic than ammonia due to the electron-donating inductive effect of the alkyl groups, which increases the availability of the lone pair on the nitrogen atom. Within alkyl amines, basicity decreases in the order secondary > primary > tertiary. For tertiary amines, steric effects from the three bulky groups decrease basicity. Aromatic amines like aniline are weaker bases than alkyl amines due to the electron-with
The document discusses the basicity of aromatic amines compared to aliphatic amines and ammonia. Specifically, it states that the basicity of aryl amines like aniline is significantly reduced due to delocalization of the nitrogen's lone pair electrons into the benzene ring's pi system. This delocalization makes the lone pair less available for protonation and decreases the equilibrium constant Kb, resulting in aniline being less basic. Substituents that are electron-withdrawing further decrease basicity by pulling electrons away from nitrogen, while electron-donating groups increase basicity by pushing electrons towards nitrogen.
This document discusses amines, which are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. Amines can be classified as primary, secondary, or tertiary depending on the number of hydrogen atoms replaced. They have important commercial uses as intermediates in making medicines and fibers. Diazonium salts are also discussed as intermediates used to synthesize aromatic compounds like dyes.
The document discusses the classification, nomenclature, properties, preparation, and reactions of amines. Amines are classified as primary, secondary, or tertiary depending on the number of alkyl or aryl groups bonded to the nitrogen atom. They are further divided into aliphatic, aromatic, and heterocyclic amines. Amines are named according to IUPAC nomenclature rules. They are weak bases due to resonance stabilization of the conjugate acid. Common methods for preparing amines include reduction of nitriles, amides, imines, and nitro compounds. Amines react with acids to form water-soluble salts and with nitrous acid to undergo proton-transfer and electrophilic aromatic substitution reactions.
This document discusses reaction intermediates in organic chemistry reactions. It defines reaction intermediates as transient species that exist between reactants and products but cannot be isolated. The main types of reaction intermediates discussed are:
1) Free radicals which have unpaired electrons and are reactive species
2) Carbonium ions which are carbocations with a positively charged carbon atom
3) Factors that influence the stability of carbonium ions such as substituents, conjugation, and resonance structures
This document provides an introduction to organic reaction mechanisms, focusing on carbanions. It defines carbanions as anions with a negative charge on a carbon atom. Carbanions are formed through heterolytic bond cleavage, removing a proton or other group from a carbon. They are stabilized through various effects, including induction, s-character of the carbon hybrid orbital, resonance, and aromaticity in some cyclic carbanions. Carbanions act as nucleophiles and undergo addition, substitution, and rearrangement reactions. Their configuration depends on conjugation, with unconjugated carbanions being pyramidal and conjugated ones having planar geometry.
Organic intermediates and reaction transformations discusses carbocations, carbanions, and radicals as reactive intermediates in organic reactions. Aromatics and heterocycles are examined, specifically discussing their structure and stability. Organic transformations are used to make drugs and dyes by targeting specific disease pathways.
Aromatic amines topic includes basicity of the aromatic amine. It also includes the comparison of the basicity. It is designed according to new PCI syllabus of B. Pharmacy.
Amino compounds by dr. pramod r. padolepramod padole
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. Amines are classified as primary, secondary, or tertiary based on the number of alkyl/aryl groups attached to the nitrogen atom. Alkyl amines are more basic than ammonia due to the electron-donating inductive effect of the alkyl groups, which increases the availability of the lone pair on the nitrogen atom. Within alkyl amines, basicity decreases in the order secondary > primary > tertiary. For tertiary amines, steric effects from the three bulky groups decrease basicity. Aromatic amines like aniline are weaker bases than alkyl amines due to the electron-with
The document discusses the basicity of aromatic amines compared to aliphatic amines and ammonia. Specifically, it states that the basicity of aryl amines like aniline is significantly reduced due to delocalization of the nitrogen's lone pair electrons into the benzene ring's pi system. This delocalization makes the lone pair less available for protonation and decreases the equilibrium constant Kb, resulting in aniline being less basic. Substituents that are electron-withdrawing further decrease basicity by pulling electrons away from nitrogen, while electron-donating groups increase basicity by pushing electrons towards nitrogen.
This document discusses amines, which are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. Amines can be classified as primary, secondary, or tertiary depending on the number of hydrogen atoms replaced. They have important commercial uses as intermediates in making medicines and fibers. Diazonium salts are also discussed as intermediates used to synthesize aromatic compounds like dyes.
The document discusses the classification, nomenclature, properties, preparation, and reactions of amines. Amines are classified as primary, secondary, or tertiary depending on the number of alkyl or aryl groups bonded to the nitrogen atom. They are further divided into aliphatic, aromatic, and heterocyclic amines. Amines are named according to IUPAC nomenclature rules. They are weak bases due to resonance stabilization of the conjugate acid. Common methods for preparing amines include reduction of nitriles, amides, imines, and nitro compounds. Amines react with acids to form water-soluble salts and with nitrous acid to undergo proton-transfer and electrophilic aromatic substitution reactions.
This document discusses reaction intermediates in organic chemistry reactions. It defines reaction intermediates as transient species that exist between reactants and products but cannot be isolated. The main types of reaction intermediates discussed are:
1) Free radicals which have unpaired electrons and are reactive species
2) Carbonium ions which are carbocations with a positively charged carbon atom
3) Factors that influence the stability of carbonium ions such as substituents, conjugation, and resonance structures
This document provides an introduction to organic reaction mechanisms, focusing on carbanions. It defines carbanions as anions with a negative charge on a carbon atom. Carbanions are formed through heterolytic bond cleavage, removing a proton or other group from a carbon. They are stabilized through various effects, including induction, s-character of the carbon hybrid orbital, resonance, and aromaticity in some cyclic carbanions. Carbanions act as nucleophiles and undergo addition, substitution, and rearrangement reactions. Their configuration depends on conjugation, with unconjugated carbanions being pyramidal and conjugated ones having planar geometry.
Organic intermediates and reaction transformations discusses carbocations, carbanions, and radicals as reactive intermediates in organic reactions. Aromatics and heterocycles are examined, specifically discussing their structure and stability. Organic transformations are used to make drugs and dyes by targeting specific disease pathways.
This document discusses bifunctional compounds and heterocyclic compounds. It begins by defining bifunctional compounds as organic molecules containing two different functional groups. It then covers the nomenclature of multifunctional compounds and bifunctional compounds. The document primarily focuses on heterocyclic compounds, including their preparation through various reactions as well as common reaction types of three-membered, four-membered, and five-membered heterocyclic rings.
This document discusses the classification, nomenclature, properties, preparation, and reactions of amines. Amines are classified as primary, secondary, or tertiary depending on the number of alkyl or aryl groups bonded to the nitrogen. They are further divided into aliphatic, aromatic, and heterocyclic amines. Amines are named according to IUPAC nomenclature rules. They are weak bases due to resonance stabilization of the conjugate acid. Common methods for preparing amines include reduction of nitriles, amides, imines, and nitro compounds. Amines react with acids to form salts, and with nitrous acid they undergo protonation or reaction with the nitrosyl cation.
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. They can be classified as primary, secondary, or tertiary based on the number of hydrogen atoms replaced. Amines have basic properties due to the lone pair of electrons on the nitrogen atom. Primary and secondary amines can form hydrogen bonds and have higher boiling points than tertiary amines. Amines can be prepared through reduction of nitro compounds, ammonolysis of alkyl halides, reduction of nitriles or amides, and other reactions. They undergo nucleophilic substitution and other reactions due to the lone pair on nitrogen.
The document discusses the structure and properties of benzene. It explains Kekulé's suggestion that benzene has alternating double and single bonds in a planar cyclic structure. However, benzene's properties are better explained by the resonance hybrid model, where the pi electrons are delocalized around the ring. Aromatic compounds have delocalized pi electrons in a cyclic planar structure according to Hückel's rule of 4n+2 pi electrons. Examples of aromatic and non-aromatic compounds are given. The document also discusses the nomenclature, reactions, and properties of aromatic compounds including electrophilic aromatic substitution.
1) Amines act as bases according to both Lewis and Bronsted-Lowry theories due to their ability to donate a lone pair of electrons or accept a proton.
2) The basicity of amines depends on factors such as the stability of the conjugate acid formed, inductive effects, and hydrogen bonding capabilities. In general, aliphatic amines are stronger bases than aromatic amines.
3) Within aliphatic amines, the order of basicity from strongest to weakest is typically tertiary > secondary > primary > ammonia in the gas phase. In aqueous solution, primary amines are stronger bases due to hydrogen bonding of the conjugate acid form.
This document discusses the properties and reactions of amines. It describes how amines are moderately polar and soluble in water due to hydrogen bonding. Their boiling points are higher than non-polar compounds due to intermolecular hydrogen bonding. Amines are basic due to the lone pair of electrons on nitrogen. Common reactions of amines include salt formation, alkylation, conversion to amides, aromatic substitution, Hofmann elimination, and formation of diazonium salts. Diazonium salts can undergo replacement or coupling reactions.
Benzene and its derivatives- According to PCI Syllabus Ganesh Mote
Benzene history, nomenclature, orbital structure, resonance structure, kekule structure,synthetic evidences, structural and analytical evidences, Directive effect of benzene, structure and uses of DDT, BHC, saccharine
This document discusses the structure and properties of amines. It begins by defining amines as carbon-hydrogen-nitrogen compounds that are commonly found in living organisms. It then discusses the bonding characteristics of nitrogen atoms in organic compounds and how this relates to the structures of primary, secondary, and tertiary amines. The document also covers the physical properties, basicity, and reactions of amines, including the formation of amine salts. It concludes by discussing heterocyclic and isomeric amines.
The document discusses hydrocarbon structures and alkanes. It begins by classifying hydrocarbons and then focuses on alkanes. Alkanes are hydrocarbons where all bonds are single bonds. The structures of methane, ethane, and propane are examined. Hybridization of atomic orbitals, specifically sp3 hybridization, allows carbon to form four strong single bonds in alkanes and gives molecules like methane their tetrahedral geometry. Higher alkanes are also discussed, noting how physical properties like boiling point depend on molecular size and branching.
- The document discusses aromatic compounds, including their structure, properties, and naming conventions.
- Benzene is used as the prototypical aromatic compound. It has a planar, hexagonal structure with resonance and delocalized pi electrons. This contributes to its unusual stability.
- Other aromatic compounds are named systematically according to IUPAC rules. Heterocyclic aromatics contain other elements like nitrogen in their rings. Polycyclic aromatics have fused rings.
- The Hückel 4n+2 rule defines the number of pi electrons and molecular geometry needed for aromaticity. Systems meeting these criteria exhibit properties like stability and substitution reactivity over addition.
Introduction to benzene, orbital picture, resonance in benzene, Huckel‟s rule
Reactions of benzene - nitration, sulphonation, halogenation- reactivity, Friedel- Craft‟s alkylation- reactivity, limitations, Friedel-Craft‟s acylation.
Substituents, effect of substituents on reactivity and orientation of mono substituted benzene compounds towards electrophilic substitution reaction.
Amines, Nomenclature, Physical properties and Chemical by ShababMd. Shabab Mehebub
This document discusses amines, including their classification, nomenclature, physical properties, and chemical reactions. It notes that amines are organic derivatives of ammonia where alkyl, cycloalkyl, or aromatic groups are bonded to the nitrogen atom. Amines are classified as primary, secondary, or tertiary based on the number of groups attached to nitrogen. Their nomenclature follows IUPAC or common systems. Amines tend to be gases or liquids with odors, and can hydrogen bond. Their reactivity includes acting as bases or nucleophiles in substitution reactions. Aromatic amines undergo electrophilic substitution, and oxidation or reactions with nitrous acid are also possible.
The document summarizes the history and structure of benzene. It discusses Kekulé's proposed cyclic and resonance structures of benzene which are supported by experimental data showing equal C-C bond lengths. Benzene's stability is attributed to resonance and delocalization of π-electrons over the ring. Electrophilic aromatic substitution reactions of benzene such as nitration, sulfonation and halogenation are explained. Friedel-Crafts reactions involving benzene are also summarized.
The document summarizes key concepts in aromatic substitution reactions. It describes the electrophilic aromatic substitution mechanism where an electrophile such as the nitronium ion attacks the aromatic ring. It outlines different electrophiles used such as halogens, acyl groups, and alkyl groups. It discusses the effects of different substituents on the ring in terms of their electronic properties as either activating or deactivating groups, and whether they are ortho/para or meta directors. Examples of industrially important aromatic compounds formed by substitution reactions are also mentioned, such as TNT.
This document discusses the structure, classification, naming, physical properties, preparation, and reactions of amines. It begins by describing amines as derivatives of ammonia with hydrogens and/or alkyl groups attached to the nitrogen atom. Amines can be classified as primary, secondary, or tertiary based on the number of alkyl groups. Common methods for preparing amines include SN2 reactions with alkyl halides, reduction of nitro compounds, and reductive amination of aldehydes and ketones. The document notes that amines act as bases and undergo nucleophilic substitution, electrophilic aromatic substitution, and other reactions similar to ammonia. It provides examples of biologically active amines that function as neurotransmitters, hormones
The document provides information about organic chemistry nomenclature. It discusses the need for systematic nomenclature given the large number of known organic compounds. It introduces IUPAC nomenclature rules which allow any complex organic compound to be systematically named. The key aspects covered are:
- Root words, primary suffixes to indicate saturation/unsaturation, and secondary suffixes to indicate functional groups are used to systematically name compounds.
- Prefixes are used to indicate substituents.
- Examples demonstrate how to apply nomenclature rules to arrive at IUPAC systematic names for various organic structures.
1) The document discusses electrophilic aromatic substitution reactions (EAS), where an electrophile such as a nitronium ion or halogen attacks an aromatic ring.
2) It explains how substituents on the aromatic ring can activate or deactivate the ring towards EAS through electronic effects, directing substitution to the ortho, para, or meta positions.
3) Electron donating groups activate the ring, while electron withdrawing groups deactivate it. Donating groups stabilize ortho/para intermediates, directing to those positions, while withdrawing groups direct to the meta position.
Methyl salicylate was synthesized from methyl anthranilate using a Sandmeyer reaction involving amine diazotization. The reaction produced a diazonium salt intermediate that allowed replacement of the amino group with a hydroxyl group, forming methyl salicylate. The product was purified by steam distillation and analyzed using NMR, IR, TLC, GC, and GC-MS spectroscopy. Spectroscopic data confirmed the successful synthesis of methyl salicylate, though the yield of 21% was lower than literature values. More distillation time may have improved the yield.
The document discusses SN1 and SN2 reaction mechanisms of alcohols. Tertiary alcohols undergo SN1 reactions with hydrogen halides faster than secondary or primary alcohols due to their ability to form stable carbocation intermediates. Primary alcohols favor SN2 reactions. Polar solvents can stabilize carbocations and favor the SN1 pathway. Common reagents used to convert alcohols to alkyl halides include thionyl chloride, phosphorus halides, and halogenation using sodium halides.
This document discusses bifunctional compounds and heterocyclic compounds. It begins by defining bifunctional compounds as organic molecules containing two different functional groups. It then covers the nomenclature of multifunctional compounds and bifunctional compounds. The document primarily focuses on heterocyclic compounds, including their preparation through various reactions as well as common reaction types of three-membered, four-membered, and five-membered heterocyclic rings.
This document discusses the classification, nomenclature, properties, preparation, and reactions of amines. Amines are classified as primary, secondary, or tertiary depending on the number of alkyl or aryl groups bonded to the nitrogen. They are further divided into aliphatic, aromatic, and heterocyclic amines. Amines are named according to IUPAC nomenclature rules. They are weak bases due to resonance stabilization of the conjugate acid. Common methods for preparing amines include reduction of nitriles, amides, imines, and nitro compounds. Amines react with acids to form salts, and with nitrous acid they undergo protonation or reaction with the nitrosyl cation.
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. They can be classified as primary, secondary, or tertiary based on the number of hydrogen atoms replaced. Amines have basic properties due to the lone pair of electrons on the nitrogen atom. Primary and secondary amines can form hydrogen bonds and have higher boiling points than tertiary amines. Amines can be prepared through reduction of nitro compounds, ammonolysis of alkyl halides, reduction of nitriles or amides, and other reactions. They undergo nucleophilic substitution and other reactions due to the lone pair on nitrogen.
The document discusses the structure and properties of benzene. It explains Kekulé's suggestion that benzene has alternating double and single bonds in a planar cyclic structure. However, benzene's properties are better explained by the resonance hybrid model, where the pi electrons are delocalized around the ring. Aromatic compounds have delocalized pi electrons in a cyclic planar structure according to Hückel's rule of 4n+2 pi electrons. Examples of aromatic and non-aromatic compounds are given. The document also discusses the nomenclature, reactions, and properties of aromatic compounds including electrophilic aromatic substitution.
1) Amines act as bases according to both Lewis and Bronsted-Lowry theories due to their ability to donate a lone pair of electrons or accept a proton.
2) The basicity of amines depends on factors such as the stability of the conjugate acid formed, inductive effects, and hydrogen bonding capabilities. In general, aliphatic amines are stronger bases than aromatic amines.
3) Within aliphatic amines, the order of basicity from strongest to weakest is typically tertiary > secondary > primary > ammonia in the gas phase. In aqueous solution, primary amines are stronger bases due to hydrogen bonding of the conjugate acid form.
This document discusses the properties and reactions of amines. It describes how amines are moderately polar and soluble in water due to hydrogen bonding. Their boiling points are higher than non-polar compounds due to intermolecular hydrogen bonding. Amines are basic due to the lone pair of electrons on nitrogen. Common reactions of amines include salt formation, alkylation, conversion to amides, aromatic substitution, Hofmann elimination, and formation of diazonium salts. Diazonium salts can undergo replacement or coupling reactions.
Benzene and its derivatives- According to PCI Syllabus Ganesh Mote
Benzene history, nomenclature, orbital structure, resonance structure, kekule structure,synthetic evidences, structural and analytical evidences, Directive effect of benzene, structure and uses of DDT, BHC, saccharine
This document discusses the structure and properties of amines. It begins by defining amines as carbon-hydrogen-nitrogen compounds that are commonly found in living organisms. It then discusses the bonding characteristics of nitrogen atoms in organic compounds and how this relates to the structures of primary, secondary, and tertiary amines. The document also covers the physical properties, basicity, and reactions of amines, including the formation of amine salts. It concludes by discussing heterocyclic and isomeric amines.
The document discusses hydrocarbon structures and alkanes. It begins by classifying hydrocarbons and then focuses on alkanes. Alkanes are hydrocarbons where all bonds are single bonds. The structures of methane, ethane, and propane are examined. Hybridization of atomic orbitals, specifically sp3 hybridization, allows carbon to form four strong single bonds in alkanes and gives molecules like methane their tetrahedral geometry. Higher alkanes are also discussed, noting how physical properties like boiling point depend on molecular size and branching.
- The document discusses aromatic compounds, including their structure, properties, and naming conventions.
- Benzene is used as the prototypical aromatic compound. It has a planar, hexagonal structure with resonance and delocalized pi electrons. This contributes to its unusual stability.
- Other aromatic compounds are named systematically according to IUPAC rules. Heterocyclic aromatics contain other elements like nitrogen in their rings. Polycyclic aromatics have fused rings.
- The Hückel 4n+2 rule defines the number of pi electrons and molecular geometry needed for aromaticity. Systems meeting these criteria exhibit properties like stability and substitution reactivity over addition.
Introduction to benzene, orbital picture, resonance in benzene, Huckel‟s rule
Reactions of benzene - nitration, sulphonation, halogenation- reactivity, Friedel- Craft‟s alkylation- reactivity, limitations, Friedel-Craft‟s acylation.
Substituents, effect of substituents on reactivity and orientation of mono substituted benzene compounds towards electrophilic substitution reaction.
Amines, Nomenclature, Physical properties and Chemical by ShababMd. Shabab Mehebub
This document discusses amines, including their classification, nomenclature, physical properties, and chemical reactions. It notes that amines are organic derivatives of ammonia where alkyl, cycloalkyl, or aromatic groups are bonded to the nitrogen atom. Amines are classified as primary, secondary, or tertiary based on the number of groups attached to nitrogen. Their nomenclature follows IUPAC or common systems. Amines tend to be gases or liquids with odors, and can hydrogen bond. Their reactivity includes acting as bases or nucleophiles in substitution reactions. Aromatic amines undergo electrophilic substitution, and oxidation or reactions with nitrous acid are also possible.
The document summarizes the history and structure of benzene. It discusses Kekulé's proposed cyclic and resonance structures of benzene which are supported by experimental data showing equal C-C bond lengths. Benzene's stability is attributed to resonance and delocalization of π-electrons over the ring. Electrophilic aromatic substitution reactions of benzene such as nitration, sulfonation and halogenation are explained. Friedel-Crafts reactions involving benzene are also summarized.
The document summarizes key concepts in aromatic substitution reactions. It describes the electrophilic aromatic substitution mechanism where an electrophile such as the nitronium ion attacks the aromatic ring. It outlines different electrophiles used such as halogens, acyl groups, and alkyl groups. It discusses the effects of different substituents on the ring in terms of their electronic properties as either activating or deactivating groups, and whether they are ortho/para or meta directors. Examples of industrially important aromatic compounds formed by substitution reactions are also mentioned, such as TNT.
This document discusses the structure, classification, naming, physical properties, preparation, and reactions of amines. It begins by describing amines as derivatives of ammonia with hydrogens and/or alkyl groups attached to the nitrogen atom. Amines can be classified as primary, secondary, or tertiary based on the number of alkyl groups. Common methods for preparing amines include SN2 reactions with alkyl halides, reduction of nitro compounds, and reductive amination of aldehydes and ketones. The document notes that amines act as bases and undergo nucleophilic substitution, electrophilic aromatic substitution, and other reactions similar to ammonia. It provides examples of biologically active amines that function as neurotransmitters, hormones
The document provides information about organic chemistry nomenclature. It discusses the need for systematic nomenclature given the large number of known organic compounds. It introduces IUPAC nomenclature rules which allow any complex organic compound to be systematically named. The key aspects covered are:
- Root words, primary suffixes to indicate saturation/unsaturation, and secondary suffixes to indicate functional groups are used to systematically name compounds.
- Prefixes are used to indicate substituents.
- Examples demonstrate how to apply nomenclature rules to arrive at IUPAC systematic names for various organic structures.
1) The document discusses electrophilic aromatic substitution reactions (EAS), where an electrophile such as a nitronium ion or halogen attacks an aromatic ring.
2) It explains how substituents on the aromatic ring can activate or deactivate the ring towards EAS through electronic effects, directing substitution to the ortho, para, or meta positions.
3) Electron donating groups activate the ring, while electron withdrawing groups deactivate it. Donating groups stabilize ortho/para intermediates, directing to those positions, while withdrawing groups direct to the meta position.
Methyl salicylate was synthesized from methyl anthranilate using a Sandmeyer reaction involving amine diazotization. The reaction produced a diazonium salt intermediate that allowed replacement of the amino group with a hydroxyl group, forming methyl salicylate. The product was purified by steam distillation and analyzed using NMR, IR, TLC, GC, and GC-MS spectroscopy. Spectroscopic data confirmed the successful synthesis of methyl salicylate, though the yield of 21% was lower than literature values. More distillation time may have improved the yield.
The document discusses SN1 and SN2 reaction mechanisms of alcohols. Tertiary alcohols undergo SN1 reactions with hydrogen halides faster than secondary or primary alcohols due to their ability to form stable carbocation intermediates. Primary alcohols favor SN2 reactions. Polar solvents can stabilize carbocations and favor the SN1 pathway. Common reagents used to convert alcohols to alkyl halides include thionyl chloride, phosphorus halides, and halogenation using sodium halides.
Ethers are compounds with two organic groups bonded to the same oxygen atom. They can be synthesized by acid-catalyzed dehydration of alcohols, Williamson ether synthesis, or alkoxymercuration of alkenes. Ethers undergo acidic cleavage reactions and Claisen rearrangement. Cyclic ethers such as epoxides undergo ring-opening reactions with acid or base to form diols. Crown ethers complex alkali metal cations and are useful for solubilizing inorganic salts in organic solvents.
Organic chemistry: Hydrocarbons, Alkyl Halides and alcoholsIndra Yudhipratama
This document outlines topics in organic chemistry including hydrocarbons, alkyl halides, and alcohols. It discusses the reactions and properties of alkanes such as combustion and free radical reactions. Alkenes and alkynes are introduced along with elimination and addition reactions. Alkyl halides are explored with substitution reactions. Finally, the document covers alcohols and their elimination through dehydration and oxidation reactions.
The document summarizes key concepts from Chapter 6 of an Organic Chemistry textbook about alkyl halides and their reactions. It covers classes of alkyl halides, nomenclature, properties, preparation methods including free radical halogenation and allylic halogenation, and substitution and elimination reaction mechanisms including SN1, SN2, E1 and E2. It also discusses factors that influence the reactivity and selectivity of these reactions such as nucleophile strength, solvent effects, and substrate structure.
This document summarizes different types of substitution reactions in aliphatic and aromatic compounds. It describes three main types of substitution reactions: free radical substitution, electrophilic substitution, and nucleophilic substitution. Free radical substitution involves radicals and occurs in non-polar solvents. Electrophilic substitution can be aliphatic or aromatic and involves attack by an electrophile. Nucleophilic substitution involves displacement by a nucleophile and can proceed by SN1, SN2, or addition-elimination mechanisms. The document provides examples and details of the mechanisms and factors that influence each type of substitution reaction.
The reaction of a tertiary alkyl halide will proceed by an SN1 or E1 mechanism to give a mixture of products. In the absence of a strong nucleophile or base, the rate-determining step is formation of the tertiary carbocation intermediate. Rearrangements and elimination may then occur to form substituted alkene products.
The document discusses the physical and chemical properties of amines. It describes how amines have higher boiling points than compounds of similar molar mass due to their ability to form hydrogen bonds between nitrogen atoms and hydrogen atoms of other molecules. However, their boiling points are lower than alcohols and carboxylic acids which form stronger hydrogen bonds. The basicity of amines increases with increasing alkyl substituents due to an inductive effect. However, the order of basicity in aqueous solution is altered by hydration and steric effects. Aromatic amines are less basic than ammonia due to resonance delocalization of the nitrogen lone pair.
This document provides an overview of amines, including:
- Amines are organic derivatives of ammonia where hydrogen atoms are replaced by alkyl or aryl groups.
- Amines are classified as primary, secondary, or tertiary based on the number of groups attached to the nitrogen atom.
- The lone pair of electrons on the nitrogen atom makes amines basic and nucleophilic. Tertiary amines are the most basic due to stabilization of the conjugate acid by alkyl groups.
- Common reactions of amines include salt formation, amide formation, and reactions with acid chlorides and anhydrides to form amides. Reduction of nitriles and nitrobenzenes provides methods to synt
This chapter discusses the structure, classification, nomenclature, physical properties and reactions of amines. Amines are classified as primary, secondary or tertiary depending on the number of carbon groups bonded to the nitrogen atom. The chapter describes various amine structures including aliphatic, aromatic, heterocyclic aliphatic and heterocyclic aromatic amines. It also discusses IUPAC nomenclature rules for naming amines and provides examples of common amine names. The chapter notes that amines are polar compounds that can form hydrogen bonds. It describes amines as weak bases and explains how their basicity depends on their structure. The chapter concludes by giving an example reaction of an amine reacting with an acid to
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. They can be classified as primary, secondary, or tertiary depending on the number of alkyl/aryl groups attached to the nitrogen atom. Aromatic amines have an amine group directly attached to an aromatic ring. Amines can act as bases by accepting protons. Their basicity depends on factors like substitution, with electron-donating groups increasing basicity. Amines undergo reactions like salt formation with acids, nitrosoamine formation with nitrous acid, amide formation with acyl chlorides/anhydrides, and halogenation of aromatic amines.
Importance of amines, classification of amines, Preparation of amines, Physical properties, Chemical properties, Basic nature, tests of amines, Carbylamine test, Hinsberg's test, reactions with nitrous acid, electrophilic reactions, -NH2 group protection, Diazonium salts, Uses, Some important conversions, short questions with answers.
This document discusses amines, which are carbon-hydrogen-nitrogen compounds that occur widely in living organisms. Amines are classified as primary, secondary, or tertiary based on how many hydrocarbon groups are bonded to the nitrogen atom. Primary amines have one hydrocarbon group and two hydrogen atoms bonded to nitrogen. Secondary amines have two hydrocarbon groups and one hydrogen bonded to nitrogen. Tertiary amines have three hydrocarbon groups bonded to nitrogen. Amines behave as weak bases and react with acids to form amine salts. Heterocyclic amines contain nitrogen atoms in aromatic or nonaromatic ring structures. Isomerism in amines can arise from different carbon chain arrangements or positioning of the nitrogen atom.
This document discusses amines, which are carbon-hydrogen-nitrogen compounds that occur widely in living organisms. Amines are classified as primary, secondary, or tertiary based on how many hydrocarbon groups are bonded to the nitrogen atom. Primary amines have one hydrocarbon group and two hydrogen atoms bonded to nitrogen. Secondary amines have two hydrocarbon groups and one hydrogen bonded to nitrogen. Tertiary amines have three hydrocarbon groups bonded to nitrogen. Amines behave as weak bases and react with acids to form amine salts. Heterocyclic amines contain nitrogen atoms in aromatic or nonaromatic ring structures. Isomerism in amines can arise from different carbon chain arrangements or positioning of the nitrogen atom.
1. Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl groups. This document discusses the nomenclature, preparation, and reactions of amines.
2. Amines are named based on whether they contain one, two, or three alkyl groups bonded to the nitrogen atom (primary, secondary, tertiary). Aromatic amines are named after the parent aromatic compound with the suffix -amine.
3. Amines can be prepared through reduction of nitro compounds, halides, amides, nitriles, or amides via Hoffman degradation. Common reducing agents include lithium aluminum hydride and catalytic hydrogenation.
This document discusses the properties and reactions of amines. It defines amines as organic derivatives of ammonia with one or more alkyl or aryl groups bonded to the nitrogen atom. Amines are classified as primary, secondary, or tertiary depending on the number of alkyl or aryl groups attached to the nitrogen. The document discusses nomenclature, physical properties, basicity, reactions including salt formation and reactions with acids, and uses of amines such as in the synthesis of nylon and azo dyes.
1. Organic chemistry deals with carbon compounds. Naming organic compounds involves identifying the carbon chain, functional group, and structure. (2)
2. Alkanes have single bonds between carbons and are generally unreactive except for combustion and halogen substitution reactions. Alkenes contain double bonds and undergo addition reactions. (3)
3. Physical properties like boiling point depend on molecular mass and structure. Functional groups determine solubility and chemical reactivity. Structural isomers have the same molecular formula but different bonding arrangements. (3)
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. They can be classified as primary, secondary, or tertiary depending on the number of alkyl/aryl groups attached to the nitrogen atom. Amines exhibit hydrogen bonding and have higher boiling points than comparable alkanes. They act as bases and react with acids to form salts. Primary amines react with nitrous acid to form nitrogen gas and alcohols/alkenes, while secondary amines form nitrosamines. Aromatic amines are used to synthesize azo dyes through diazonium salt formation. Nylon is produced by condensation polymerization of diamines and dic
1. The document discusses different types of organic compounds including alkanes, alkenes, alkynes, aromatics, alcohols, and halogen substituents.
2. Key topics include naming conventions for branched and cyclic alkanes, geometric and structural isomers, benzene and aromatic compounds, functional groups like alcohols and halocarbons.
3. Examples are given of petroleum and natural gas as sources of hydrocarbons and how chlorofluorocarbons deplete the ozone layer.
Carboxylic acids and amines are named using IUPAC or common systems. Carboxylic acids contain a -COOH functional group and are named by replacing the "-ane" ending with "-oic acid". Amines are derived from NH3 and named by adding "-amine" or treating the nitrogen as the main part. Carboxylic acids have higher boiling points than hydrocarbons and amines have higher boiling points than hydrocarbons of the same size. Amines are generally basic in nature.
Carboxylic acids and amines are named using IUPAC or common systems. Carboxylic acids contain a -COOH functional group and are named by replacing the "-ane" ending with "-oic acid". Amines are derived from NH3 and named by adding "amine" or treating the N as the main part. Amines are generally more basic than their hydrocarbon counterparts.
Proteins are composed of amino acids linked by peptide bonds. They have four levels of structure - primary, secondary, tertiary, and quaternary. The primary structure is the amino acid sequence. Secondary structures include alpha helices and beta sheets formed by hydrogen bonding. Tertiary structure is the overall 3D shape formed by interactions between secondary structures. Quaternary structure refers to the arrangement of multiple polypeptide subunits in a protein.
The document provides an introduction to organic chemistry and hydrocarbons. It discusses how hydrocarbons are composed of only carbon and hydrogen and can be classified as alkanes, alkenes, alkynes, and arenes based on their bonding structure. Alkanes contain only single carbon-carbon bonds and include compounds such as methane and ethane. The structures, naming conventions, and properties of alkanes are described.
Chemistry of aromatic amines, Classification of amines, Preparation, reactions of amines, synthetic uses of aromatic amines, basicity of aromatic amines and factor affecting basicity amine.
Amines are organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. They can be classified as primary, secondary, or tertiary based on the number of hydrogen atoms replaced. Amines have basic properties due to the lone pair of electrons on the nitrogen atom. Common methods for synthesizing amines include reduction of nitro compounds, ammonolysis of alkyl halides, and reduction of nitriles or amides. Amines undergo electrophilic substitution and acylation reactions. Primary amines react with nitrous acid to form diazonium salts.
The document discusses the IUPAC system of nomenclature for naming organic compounds. It explains the key concepts of word roots, prefixes, suffixes, functional groups and rules for naming compounds. The longest carbon chain is identified and numbered from the end closest to the first branch or substituent. Functional groups and multiple bonds are given priority in numbering over substituents.
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1. Amines
Amines are derivatives of ammonia with one or more alkyl groups bonded to
the nitrogen.
Amines can be classified as primary, secondary or tertiary, meaning one,
two and three alkyl groups bonded to the nitrogen respectively.
E.g.
CH 3
Primary NH 2 H3C C NH 2
Amines
CH 3
CH 3
Secondary N-H
N:
Amines
H
CH 3
Tertiary N:
Amines N
CH 3
Quaternary ammonium salts have four alkyl groups bonded to the nitrogen,
and the nitrogen bears a full positive charge.
E.g.
CH 2CH 3
+ - +
N CH 2CH 2CH 3
H3CH 2C N CH 2CH 3 I
CH 2CH 3 Br-
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2. Amines are a very common functional group in organic chemistry, and
especially so for naturally occurring compounds.
E.g.
CH 3
N O OCH
C 3
N
H CH 3
O C Ph N
H O
Nomenclature
The IUPAC nomenclature is analogous to that for alcohols, where the -e of
the alkane ending is replaced with -amine.
Other substituents on the carbon chain are given numbers, and the prefix N-
is used for each substituent on nitrogen.
E.g.
NH 2 CH 3 NH 2 NH-CH 3
CH 3CH 2 C CH 3 H3C C CH 2 CH 2 CH 3CH 2 C CH 3
H H H
2-butanamine 3-methyl-1-butanamine N-methyl-2-butanamine
H CH 3
CH 3CH 2 C CH CH 3
N(CH 3)2
2,N,N-trimethyl-3-pentanamine
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3. Aromatic amines are called by their historical/trivial names, with
phenylamine being called aniline. Other nitrogen heterocycles have ring
system names that need to be learned also. (The N is normally considered to
be numbered 1).
Aziridine, pyrrole, pyrrolidine, imidizole, pyridine, piperidine, pyrimidine
Structures of Amines
Previously we have seen that ammonia (NH3) has a slightly distorted
tetrahedral shape, due the compression of the ideal 109.5° angle by lone
pair-bond pair repulsion.
This effect is less pronounced with alkyl groups, and trimethylamine has
bond angles closer to the perfect sp3 arrangement than ammonia.
Since an amine has three substituents and a lone pair, the question of
chirality arises. If an amine has three different substituents (and its lone pair)
can we resolve the amine into enantiomers? In most cases, this is not
possible since the enantiomers can interconvert through a low energy
pathway. The interconversion takes place through a nitrogen inversion,
where the lone pair moves from one face of the molecule to the other, and
back.
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4. The lone pair starts off in an sp3 orbital, but in the transition state of the
inversion, the nitrogen can rehybridize to sp2, with the lone pair in a p
orbital.
This is not a high energy situation, and only requires 6kcal of energy to
achieve this TS (therefore easy at room temperature).
At the TS, the inversion can occur or return back to the original enantiomer -
single enantiomers cannot be resolved in most cases.
Exceptions
There are certain special cases where amines are chiral.
(In the C-I-P convention, lone pairs have the lowest priority).
Case 1: Amines whose chirality stems from the presence of chiral carbon
atoms. E.g. 2-butanamine.
NH2 NH2
C CH2CH3 H3CH2C C
H3C H H CH3
(S) (R)
Case 2: Quaternary ammonium salts with chiral nitrogen atoms. Here the
nitrogen inversion is impossible since there are four substituents on the N,
and no lone pair.
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5. Case 3: Certain amines cannot attain the sp2 hybridization required for
nitrogen inversion.
Examples of this include nitrogen atoms in small rings (aziridines).
The required bond angle of 120° is unobtainable in the strained system, and
so the TS required for nitrogen inversion is of too high energy, and thus
chiral aziridines can be resolved into enantiomers.
Physical Properties
The N-H hydrogen bond is not as strong as the O-H hydrogen bond in
analogous molecules. Primary amines will have lower mp and bp than the
corresponding primary alcohol. Secondary amines, which have NH groups,
will have higher mp and bp than the corresponding ether.
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6. Basicity of Amines
The nitrogen atom of amines has a lone pair of electrons, and this gives rise
to characteristics of nucleophilicity and basicity (a Lewis base).
Amine as a nucleophile:
H H
+ -
R N: H3C I R N CH3 I
H H
Amine as a base:
H H
R N: H X +
R N H X-
H H
Amines are basic, and therefore their aqueous solutions are basic (pH>7),
and recall that base strength is talked of it terms of base-dissociation
constant (Kb).
The values of Kb for most amines are small (10-3), but still basic.
Since amine basicity values span many orders of magnitude, discussion of
pKb values is more common.
Remember pKb = -log10 Kb
And that KaKb=Kw = 10-14
E.g.
Table 19-3 (SLIDE)
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7. Effects on Amine Basicity
Consider the energy level diagram for the reaction of a general amine with
water.
Any feature that stabilizes the ammonium ion relative to the free amine
helps shift the equilibrium to the right, and therefore makes the amine a
stronger base (and vice versa).
(a) Alkyl group substitution
If we consider the relative basicities ammonia and methylamine, then we
might expect the electron donating abilities of the alkyl group to help
stabilize the ammonium cation produced, thus making methylamine a
stronger base than ammonia.
H H
+ -
H N: H OH H N H OH
H H pKb = 4.74
H H
+ -
H3C N: H OH H3C N H OH
H H pKb = 3.36
(Stronger base)
This is indeed the case.
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8. However the above logic implies that secondary amines should be stronger
bases than primary amines, and that tertiary amines the strongest bases of
all.
This is not true, and the real situation is more complicated involving
solvation effects and steric hindrance.
The overall net result of the combination of these three effects is that
primary, secondary and tertiary amines are all of approximately equal
basicity, and all stronger bases than ammonia itself.
(b) Resonance Effects
Aromatic amines, such as aniline, are weaker bases than normal aliphatic
amine.
This is due to the fact that the lone pair of electrons on the nitrogen are
delocalized into the aromatic system.
This stabilizes the free amine, and therefore makes the transition to the
protonated form more endothermic than the aliphatic case - and thus less
energetically favorable.
The stabilizing overlap in aniline, makes the lone pair less reactive, therefore
a weaker base.
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9. Resonance effects are also pronounced for pyrrole.
Pyrrole is a weak base since the lone pair is used in contributing to the
aromatic system.
The use of the lone pair to form a bond to hydrogen (i.e. protonation)
removes the lone pair from the system, and this makes the protonated form
no longer aromatic - this is energetically unfavorable.
E.g.
H OH OH-
+
N N
H H H pKb = 154
aromatic non-aromatic
(c) Hybridization Effects
We have already observed that electrons held in orbitals that have more s
character are held more tightly.
Therefore a lone pair held in an sp orbital will be more strongly held (i.e.
less basic) than a lone pair held in an sp3 orbital.
E.g. Pyridine, piperidine
and acetonitrile, pKb = 24
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10. Salts of Amines
When an amine is protonated, an amine salt is produced.
The amine salt consists of two parts: the cationic ammonium ion, and the
anionic counter ion.
+
CH3CH2CH2 NH2 + H-Cl CH3CH2CH2 NH3 Cl-
Simple amine salts are named as substituted ammonium salts, whereas more
complicated amine salts use the name of the amine and the acid that create
the salt.
E.g. (CH3CH2)3N: + H2SO4 (CH3CH2)3NH+ HSO4-
Triethylammonium hydrogen sulfate
O O
+
N: HO C CH3 N H
-O C CH3
Pyridinium acetate
Amines are generally volatile, smelly liquids, whereas the ammonium salts
are crystalline, high melting solids.
These ionic solids are soluble in water, but insoluble in organic solvents.
The free amines are generally insoluble in water, but soluble in organic
solvents.
This provides an excellent method for the separation and isolation of amine
compounds.
Free amines are insoluble in water, but when dilute acid is added, the
ammonium salt is produced, which dissolves.
(Formation of a soluble salt is a simple chemical analytical test for amine
functionalities).
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11. When the solution is made alkaline (by adding NaOH), the now purified free
amine is regenerated, which is insoluble in the aqueous solution and
therefore precipitates, or can be extracted into an organic solvent.
This procedure is typical/useful for the purification of all amine containing
compounds (cocaine crack, etc).
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12. Amine salts as phase transfer catalysts
Reactions of Amines
With Carbonyl Groups
We have already seen the reaction of various amines with ketones and
aldehydes to generate imines and their analogues. E.g.
Y
O HO NHY N
Y NH 2 C
R C R' R R' R C R'
ketone carbinolamine derivative
Y = H (or alkyl) = Imine
= OH = Oxime
= NHR = Hydrazone
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13. Aromatic Substitution of Aryl and Heterocyclic Amines
Aryl amines are activating, ortho/para directors in electrophilic aromatic
substitution reactions, since the lone pair stabilizes the intermediate cationic
sigma complexes formed at these two positions of attack.
Aniline and its derivatives are so reactive that if excess reagent is used, then
all the available ortho and para positions become substituted.
E.g.
NH 2 NH 2
Excess Br2 Br Br
Br
NH 2 NH 2
O2 N Excess Cl2 O2 N Cl
Cl
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14. Attention must be paid to the reaction conditions.
In strongly acidic conditions, the amino group becomes protonated, and thus
is converted to a deactivating, meta director.
+
NH2 NH3
Strong acid
Electrophilic Aromatic Substitution of Pyrrole
Pyrrole undergoes EAS more readily than benzene itself, and thus milder
and reagents and conditions may be used.
Reactions such as nitration, halogenation, FC alkylation and acylation all
work, but milder conditions must be employed.
E.g. instead of an acid chloride, an anhydride is used for acylation.
O O O
SnCl 4
H3C C O C CH 3 C CH 3 H3C C OH
N N
O
H H
Also weaker Lewis acid catalysts such as SnCl4 are employed.
Attack at the C-2 position is preferred over attack at C-3.
Figure 19-11 (SLIDE)
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15. EAS of Pyridine
Pyridine behaves like a strongly deactivated aromatic compound in EAS
reactions.
FC alkylations and acetylations fail, and other EAS reactions require
unusually harsh reaction conditions.
The deactivation arises from the electron withdrawing effect of the nitrogen
atom in the ring.
The lone pair of the nitrogen sticks out away from the system, and so
cannot be used to stabilize any positively charged intermediates.
When pyridine does react, it displays a preference for substitution in the 3
position, which is meta direction (like other deactivating substituents).
Consider attack at C-2 and C-3:
Electrophilic attack at C-2 produces a sigma complex that has one resonance
form with only 6 electrons and a positive charge on nitrogen (high energy).
In contrast, for C-3 substitution, all resonance forms of the sigma complex
have the positive charge on the less electronegative carbon atoms.
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16. EAS is further inhibited by pyridine because of the tendency of the nitrogen
atom to react directly with the electrophile, generating a pyridinium ion
(which is still aromatic).
This positively charged pyridinium ion is even more deactivated to EAS
than pyridine itself.
+ E+
N N
+
E
Examples of EAS reactions that do actually work on pyridine are shown
below (note the very harsh conditions).
o
Br2, 300 C Br
N N
Fuming H2SO4, HgSO4 SO3H
230oC
N N
Nucleophilic Aromatic Substitution
Pyridine is strongly deactivated to EAS, but is activated toward attack by
nucleophiles, i.e. NAS.
If there is a good leaving group at either the 2 or 4 position, then NAS may
occur.
NaOCH 3
N Cl N OCH 3
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17. Consider the (negatively) charged sigma complexes for attack occurring at
C-2 and C-3:
C-2 Attack
_ _
OCH 3 OCH 3 OCH 3
N
_ Cl N Cl N Cl
-
Cl
N OCH 3
Attack at C-3
_ OCH 3 OCH 3 OCH 3
Cl Cl Cl
_ _
N N N
The negative charge on the electronegative nitrogen (good) can only be
produced in resonance forms from attack at C-2 (and C-4).
Alkylation of Amines
Amines react with primary alkyl halides to give alkylated ammonium
halides.
+
R NH2 R' CH2 Br R NH2 CH2-R' Br-
(This direct alkylation usually proceeds via the SN2 mechanism, so does not
work with tertiary halides which are too hindered).
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18. Since amines are bases, this creates a problem:
The ammonium salt formed initially, can be deprotonated by the remaining
amine.
This produces a secondary amine, which can react with the alkyl halide.
Direct alkylation cannot be easily stopped at the desired level alkylation -
complex mixtures of products are observed (bad).
There are two cases where the alkylation of amines are reasonable synthetic
routes:
(1) Exhaustive alkylation to give tetra-alkylammonium salts.
If enough alkyl halide is used to alkylate the amines all the way to the tetra-
alkylammonium cations, then we get a single (exhaustively) alkylated
product.
E.g.
CH 3
+ I-
CH 3CH 2CH 2 NH 2 3 H3C I CH 3CH 2CH 2 N CH 3
CH 3
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19. (2) Reaction with a large excess of ammonia.
Since ammonia is so inexpensive, it can (acceptably) be used in large excess.
The primary alkyl halide is added slowly to the large excess of ammonia,
and so the probability of dialkylation is as low as possible.
E.g.
H
+ I-
NH3 R H2C I R-H2C N H
H
10moles 1mole
Acylation of Amines using Acid Chlorides
Primary and secondary amines react with acid halides to produce amides.
E.g.
O O
R' NH2 R C Cl R C NH-R' + H-Cl
This reaction is an example of nucleophilic acyl substitution - the
replacement of a leaving group with a nucleophile on a carbonyl group.
The amine attacks the acid chloride just like any other carbonyl compound at
the electrophilic carbon.
O O- O
R C Cl +
R' NH 2 R C Cl R C NH-R'
H2N R' H
+
amide
The acid chloride is more reactive than an aldehyde or ketone since the
electronegative chlorine pulls electron density away from the carbon making
it more reactive.
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20. The tetrahedral intermediate formed is negatively charged, and since
chlorine is a good leaving group, the C=O bond reforms with the expulsion
of the good leaving group.
The amide produced is much less reactive towards (further) acylation
reactions since the lone pair on the nitrogen is delocalized onto the oxygen,
thus making amides much less nucleophilic (and basic) than amines.
O H O- H
R C N R C N
R + R
We can take advantage of this reduced basicity of amides in Friedal-Crafts
type reactions of aryl amines. The amino group of aniline is powerfully
electron donating and o/p directing in FC reactions.
However we have see that in strongly acidic media the amino group
becomes protonated and is transformed into a deactivated, meta directing
substituent.
Amides are not protonated under such conditions, and often aryl amines are
converted into their corresponding amides before EAS are performed.
E.g.
NH 2 NHCOCH 3 NHCOCH 3 NH 2
NO 2 NO 2
After the reaction, the amide group is simply hydrolyzed back to the amino
group by mild acid (or base) treatment (see later).
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21. Reaction of Amines with Sulfonyl Chlorides (Sulfonamides)
Sulfonyl chlorides are the acid chlorides of sulfonic acids.
O O
R S OH R S Cl
O O
sulfonic acid sulfonyl chloride
Just like before, amines react with displacement of the chlorine. The amides
derived from sulfonic acids are called sulfonamides.
O O
R' NH 2 R S Cl R S NHR'
O O
Amines as Leaving Groups (Hoffman Elimination)
The amino group (-NH2 or -NHR) is a poor leaving group.
However, the amino group can be converted into a very good group via
exhaustive methylation (usually using CH3-I).
CH 3
H3C I + I-
R' NH 2 R' N CH 3
CH 3
The quaternary ammonium salt is a very good leaving group since when it
leaves, it produces a neutral amine.
The elimination of the quaternary ammonium salt usually takes place via the
E2 mechanism - requires a strong base.
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22. The ammonium iodide salt is converted to the corresponding hydroxide salt
(strong base) by reaction with silver oxide.
CH 3 CH 3
+ I- Ag2O + H2O + -
2 R' N CH 3 2 R' N CH 3 OH
CH 3 CH 3
2AgI
Heating the quaternary ammonium hydroxide salt produces elimination, and
an alkene is produced.
-
OH H2O
H
N(CH 3)3
+
:N(CH 3)3
This is called the Hoffman elimination.
E.g. 2-butanamine is exhaustively methylated, converted to the hydroxide
salt and heated, thus generating a mixture of 1-butene (major) and 2-butene
(minor).
H H H H
H2C CH CH CH 3 H2C CH CH 2-CH3 H3C C C CH 3
+N(CH 3)3
H2O + :N(CH 3)3
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23. Satzyeff vs.Hofmann
In Ch 7 we saw that normally in elimination reactions, the most highly
substituted alkene was the one preferentially formed.
However here the least substituted alkene is the major product.
We say the this is a Hoffman product, and the most substituted alkene
product is the Satzyeff product.
So why does the Hoffman elimination have this (unexpected) preference for
the least substituted alkene?
There are many factors but the simplest explanation is because of the huge
steric size of the leaving group.
Recall that the E2 mechanism requires an anticoplanar arrangement of the
leaving group and the proton being removed.
The large steric bulk of the leaving group interferes with this necessary
arrangement.
For the 2-butanamine case, the leaving group is trimethylamine, and the
proton being lost either comes from C-1 or C-3.
Let us consider the loss of the proton from C-3 first. ( Satzyeff Product)
The most stable conformation for this molecule has the two largest
substituents arranged anti.
This conformation does not allow for any E2 elimination to occur.
To achieve a conformation suitable for E2 to occur, C-3 must rotate and
place a Hydrogen anti to the bulky leaving group.
Figure 19-12 (SLIDE)
(Note the book messed up its numbering scheme so use mine!)
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24. To remove the proton from C-1 ( Hoffman product), any of the three
staggered conformations allow the E2 mechanism to operate.
The Hoffman product dominates since elimination of one of the hydrogens
on C-1 involves a lower energy, and more statistically probable transition
state than the sterically hindered TS required for C-3 elimination.
Thus Hoffman elimination always gives the least substituted alkene product
(Hoffman product).
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25. Reaction of Amines with Nitrous Acid
The reaction of amines with nitrous acid (HNO2) is a very useful synthetic
reaction.
Nitrous acid is unstable and needs to be generated in situ by reaction of
sodium nitrite and hydrochloric acid.
Na+ -O-N=O + HCl H-O-N=O + Na+Cl-
In very acidic media, nitrous acid can become deprotonated and lose water
(acid catalyzed dehydration) and generate the nitrosonium ion, NO+.
H
+ H +
+
H O N O H O N O N O N O
+
Reaction with Primary Amines (Diazonium Salts)
Primary amines react with nitrous acid (actually the nitrosonium ion) to
produce compounds of the type R-N2+.
These are called diazonium cations.
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26. The diazotization procedure starts with the nucleophilic attack of the
primary amine on the nitrosonium ion.
H H2O H
+
R' NH2 N O R' N N O R' N N O
+
H N-nitrosoamine
Deprotonation of the intermediate generates an N-nitrosoamine.
Tautomerism (proton transfer from nitrogen to oxygen) generates a
compound which undergoes an acid catalyzed elimination of water, thus
generating the diazonium cation.
H H H
H+ +
R' N N O R' N N O H R' N N O H
+
H2O
H H+
+
R' N N R' N N O H R' N N O H
+
H2O
The overall balanced reaction is:
R-NH2 + NaNO2 + 2HCl R-N2+ Cl- + 2H2O + NaCl
Diazonium salts are fairly unstable, but some are very useful intermediates,
and can be converted into a whole variety of functional groups.
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27. Arenediazonium Salts
Alkyldiazonium salts are fairly unstable, yet arenediazonium salts are stable
up to temperatures of 0-10°C, and can be smoothly converted into halogens,
nitriles, phenols, azo compounds, etc.
Arenediazonium salts are formed by diazotizing primary aromatic amines
(which are prepared by reduced nitroarenes, which are prepared via nitration
of the parent aromatic).
E.g.
N
NO 2 NH 2 N+ Cl- X
CH 3 CH 3 CH 3 CH 3 CH 3
Conversion to Hydroxyl
By heating the diazonium salt in a strong aqueous acid, hydrolysis occurs,
and the product is a phenol.
NH 2 OH
1) NaNO2, HCl
2) H2SO4, H2O, heat
CH 3 CH 3
This route is generally preferable to the NAS route since much milder
conditions are employed here.
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28. The Sandmeyer Reaction (-Cl, -Br, -CN)
Copper (I) salts have a special affinity for the diazonium salts, and reaction
of CuCl (or Br or CN) generates aryl chlorides (or bromides or nitriles).
The use of copper (I) salts in the replacement of diazonium groups is known
as Sandmeyer reactions.
E.g.
NH2 Cl
1) NaNO2, HCl
2) CuCl
Fluorides and Iodides
These two halogens cannot be introduced via Sandmeyer chemistry.
To make an aryl fluoride, the diazonium salt is treated with fluoroboric acid,
causing a precipitate of the diazonium fluoroborate salt, which is then heated
to eliminate N2 and BF3, thus producing the fluorobenzene.
N
NH 2 N+ BF4- F
1) NaNO2, HCl
2) HBF4
N2 + BF3
Aryl iodides are simply prepared by heating the arenediazonium salts with a
solution of potassium iodide.
NH2 I
1) NaNO2, HCl
2) KI
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29. Reduction (Deamination)
When arenediazonium salts are treated with hypophosphorus acid, the
diazonium group is replaced with a hydrogen.
NH2 H
1) NaNO2, HCl
2) H3PO2
Even though this might seem pointless, it allows the removal of an amino
group which was added to activate and direct specific EAS processes.
E.g. the synthesis of 3,5-dibromotoluene.
Br Br
CH 3
Bromination of toluene gives the wrong isomers.
Br
2 Br2
FeBr3 Br Br Br
CH 3 CH 3 CH 3
Bromination of para-methylaniline gives a dibromo derivative, which on
removal of the amino groups yields the desired 3,5-dibromotoluene.
NH 2 NH 2
2 Br2 Br Br 1) NaNO2, HCl Br Br
2) H3PO2
FeBr3
CH 3 CH 3 CH 3
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30. Diazo Coupling
Arenediazonium salts are positively charged and can act as (weak)
electrophiles with powerful nucleophiles via EAS processes, generating
compounds of the general type Ar-N=N-Ar'.
The -N=N- linkage is called an azo linkage.
Azo compounds are generally bright colored compounds, and find numerous
application in the dye and coloring industries.
E.g.
-
Cl
+ N(CH 3)2
-O3S N N
-O3S N N N(CH 3)2
methyl orange
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31. Synthesis of Amines
Reductive Amination
The most general method for synthesizing amines involves the reduction of
an imine or oxime derivative of an aldehyde or ketone.
O
1) R H
C R'
N H N C R'
2) reduction R
The reduction is most commonly achieved via LiAlH4 or by catalytic
hydrogenation.
The overall effect is to add another alkyl group to the original nitrogen.
This works to make primary, secondary or tertiary amines.
Primary Amines are made from condensation of hydroxylamine (zero alkyl
groups bound to N) with a ketone or aldehyde, followed by reduction of the
oxime produced.
E.g.
OH
O H2N OH N reduction NH 2
R' C R R' C R R' CH R
+
H
primary
amine
The reduction is achieved by use of LiAlH4, NaBH3CN (sodium
cyanoborohydride - mild reducing agent) or catalytic hydrogenation.
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32. Secondary Amines are made via condensation of a primary amine (one alkyl
group) with a ketone (aldehyde), followed by reduction of the imine
produced.
E.g.
R''
O H2N R'' N reduction NHR' '
R' C R R' C R R' CH R
+
H
secondary
amine
Tertiary Amines are made via the condensation of a secondary amine (two
alkyl groups) with an aldehyde or ketone, generating an iminium salt.
The iminium salts are usually unstable, and so are reduced as they are
formed by a reducing agent already in the reaction mixture.
E.g.
R R R R
O R2N H N+ reduction N
R' C R' R' C R' R' CH R'
+
H
tertiary
amine
This reducing agent therefore cannot be so reactive to react with the ketone
or aldehyde starting material, and thus sodium cyanoborohydride
(NaBH3CN) is most commonly used.
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33. Acylation - Reduction to Amines
Again this method adds one alkyl group to the nitrogen of an amine.
The amine is acylate with an acid chloride, and the amide produced thus has
no desire to undergo further reaction (good).
E.g.
O O 1) LiAlH4
R NH2 R' C Cl R' C NHR R'-CH2 NHR
2) H2O
The amide is reduced with LiAlH4 to produce the desired amine.
This is a very general and useful synthetic method, and the only drawback is
the fact that the new C bonded to the nitrogen has to be a methylene (-CH2-).
Reduction of Nitro Compounds
Both aromatic and aliphatic nitro groups are readily reduced to amino
groups, and the most common methods are catalytic reduction or reaction of
an active metal with an acid.
H2, catalyst
R NO 2 R NH 2
or Fe, HCl
(or Sn, Zn)
Aromatic nitro compounds are reduced to anilines.
NO 2 NH 2
Zn, HCl
These anilines are useful synthetic compounds themselves, and also can be
used in diazonium type chemistry also.
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34. Direct Alkylation of Ammonia and Amines
As seen before, these reactions have a tendency to over alkylate, which gives
mixtures of products (bad).
A situation where this is a viable synthetic route is using a large excess of
ammonia to produce a primary amine.
R-CH2-X + excess NH3 R-CH2-NH2 + NH4X
We can also use NAS to make some aryl amines.
An aryl bromide can be displaced by a nucleophile if there are electron
withdrawing groups on the aromatic ring (addition/elimination mechanism).
E.g.
NO 2 NO 2
HN(CH 3)2
Br N(CH 3)2
Since aryl amines are less basic than alkyl amines there is no tendency for
over reaction (good).
Reduction of Azides and Nitriles (Primary Amines)
Amines can be produced without using ammonia, or other less substituted
amines.
We have already seen that a nitro group can be reduced to an amino group.
Essentially any nitrogen containing functionality can be reduced to an amino
group.
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35. Azides
The azide ion (N3-) is a good nucleophile, and thus can displace leaving
groups from primary and secondary alkyl halides and tosylates.
R-CH2-Cl + Na+ -N3 R-CH2-N3 + NaCl
The alkyl azides that are produced (explosive) are reduced to primary
amines either by LiAlH4 or catalytic reduction.
E.g.
+
-N N N-
_
+
CH 2-CH2-Br CH 2-CH2 N N N
1) LiAlH4 _ +
CH 2-CH2 NH 2 CH 2-CH2 N N N
2) H2O
Azides also react with a variety of other electrophiles:
E.g.
N3 NH2
NaN3 H H2, Pd H
O OH OH
H H
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36. Nitriles
Cyanide ion (-CN) is also a good nucleophile, and the products it produces
are called nitriles.
- Redn.
CN
R X R C N R CH2-NH2
Nitriles are reduced with LiAlH4 or catalytic hydrogenation to primary
amines.
Notice that when the nitrile group is reduced, an NH2 and an extra CH2 are
introduced into the molecule.
Gabriel Synthesis
In 1887, Gabriel developed a new method for the synthesis of primary
amines, which eliminated the danger of over alkylation.
His strategy of using the phthalimide anion as a protected form of ammonia
that cannot be alkylated more than once.
O O O- O
C C C C
N H N- N N
C C C C
O O O O-
The phthalimide anion is resonance stabilized and acts as a good
nucleophile.
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37. This nucleophile can be alkylated with primary alkyl halides (or tosylates) to
produce an N-alkyl phthalimide, which on heating with hydrazine generates
the desired primary amine (and phthalimide hydrazide which is very stable).
E.g.
O
O O
R-X H2N NH 2
C C NH
N- N R R NH 2
NH
C C
O O O
The Hoffman Rearrangement
If primary amides are treated with a strong base in the presence of chlorine
or bromine, then amines are produced which have lost the carbonyl group!
These chain shortened amines are produced via the Hoffman rearrangement.
O
+ X2 + 4 NaOH R-NH2 + 2NaX + Na2CO3 2H2O
R C NH2
This is a good synthetic route to produce any amines, especially tertiary
amines since the other synthetic methods generally don't work for 3° amines.
E.g.
-
H3C O Cl 2, OH CH 3
C C NH 2 C NH 2
H2O
CH 3 CH 3
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38. Mechanism
The reaction starts with the deprotonation of the amide to give a resonance
stabilized anion, that becomes brominated.
O O O- O
_ Br-Br
R C NH-H R C NH R C NH R C NH-Br
Since Br is electronegative, the N-bromo amide can also be readily
deprotonated, and this also gives a resonance stabilized anion.
O O O-
_
R C NBr-H R C N-Br R C N-Br
R N C O
The rearrangement occurs since we have a negative charge on the oxygen
and a good leaving group (bromine) on the nitrogen.
The negative charge (lone pair of electrons) reforms the carbonyl C=O
double bond, forcing the alkyl group to migrate.
It migrates to the nitrogen, displacing the good leaving group, bromine.
The product, R-N=C=O, is called an isocyanate.
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39. _
R N C O R N C O- R N C O
OH OH
H
R N C O
OH
The isocyanate reacts rapidly with water, generating carbamic acid, that
decarboxylates to give the amine and carbon dioxide.
H H _
R N C O R N C O R NH CO 2
O-H O-
R NH 2
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