Jacobsen reaction
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The document summarizes the Jacobsen rearrangement reaction. It describes how the reaction involves the migration of an alkyl group in a sulfonic acid derived from a polyalkyl- or polyhalobenzene. It provides the historical background, noting that Josef Herzig first described a similar rearrangement in 1881, while Oscar Jacobsen studied rearrangements of polyalkylbenzenes in 1886 and the reaction is named after him. The mechanism is not completely clear but evidence indicates the migrating group is transferred between polyalkylbenzene molecules, not to the sulfonic acid. The reaction has applications in isomerizing polyalkyl benzenes.
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The document discusses aromatic electrophilic substitution reactions including the Vilsmeier-Haack formylation, Reimer-Tiemann reaction, Gattermann-Koch formylation, and diazo coupling reactions. It provides background on the reactions, their mechanisms, substrates used, and factors that influence product distribution. Examples and problems are also given to illustrate the application of these reactions in synthesis.
Claisen rearrangement
The Claisen rearrangement is a thermal rearrangement reaction discovered by Rainer Ludwig Claisen in which the allyl group of a phenolic allyl ether migrates ortho to the phenol group. Key characteristics of the Claisen rearrangement are the inversion of the migrating allyl carbon and the intramolecular, unimolecular nature of the reaction. The mechanism involves a cyclic transition state that allows for migration to the ortho position, or para if both ortho positions are blocked.
wittigreaction-140313091452-phpapp02.pdf
The Wittig reaction involves reacting an aldehyde or ketone with a triphenylphosphonium ylide to form an alkene and triphenylphosphine oxide. The reaction proceeds through betaine and oxaphosphetane intermediates. The stereochemistry of the product can be controlled by the reactants and conditions. Similar reactions are the Horner and Horner-Emmons-Wadsworth reactions, which use phosphine oxides or phosphonates in place of the ylide. The Wittig reaction is one of the most important methods for synthesizing alkenes from carbonyl compounds.
Wittig reaction
The Wittig reaction involves reacting an aldehyde or ketone with a triphenylphosphonium ylide to form an alkene and triphenylphosphine oxide. The reaction proceeds through betaine and oxaphosphetane intermediates. The stereochemistry of the product can be controlled by the reactants and conditions. Similar reactions are the Horner and Horner-Emmons-Wadsworth reactions, which use different reagents. The Wittig reaction is one of the main methods for synthesizing alkenes from carbonyl compounds.
Phenols
The class of organic compounds characterized by hydroxyl (-OH) group attached to an aromatic ring. Phenol is commonly known as carbolic acid. Phenols are aromatic components which contain one or more hydroxyl groups that are attached to an aromatic ring. Phenol is a benzene derivative and it consists of a phenyl bonded to a hydroxyl (-OH) group. General chemical formula of phenol is C6H5OH and molecular formula C6H6O.
Phenol is a monohydroxy derivative of benzene prepared by the replacing of one of the hydrogen of benzene by hydroxyl group. Phenol contain two part one part is aryl group (phenyl) and other is hydroxyl group.
On the basis of number of hydroxyl group bonded to benzene. It can be classified into di, tri, tetra hydroxyls benzene.
Name-Reaction-2 (1).pptx
The Reformatsky reaction condenses aldehydes or ketones with α-halo esters using zinc metal to form β-hydroxy esters. The reaction proceeds via an organozinc reagent or 'Reformatsky enolate' formed by treating the α-halo ester with zinc dust. This enolate then reacts with the carbonyl group in a concerted reaction involving a six-membered transition state to form the carbon-carbon bond. Workup with acid removes zinc and provides the β-hydroxy ester product. The main application is the preparation of β-hydroxy esters from aldehydes or ketones.
Common named reactions
The document discusses several carbon-carbon bond forming reactions:
1. Aldol condensation allows aldehydes and ketones to undergo self-condensation in the presence of a base to form β-hydroxy carbonyl compounds.
2. The Perkin reaction uses an acid anhydride to form α,β-unsaturated aromatic acids from aromatic aldehydes.
3. The Wittig reaction converts a carbonyl group to an alkene using a phosphonium ylide.
Biotransformation of drugs
The document summarizes various processes involved in drug biotransformation and elimination from the body. It discusses two main phases - Phase I reactions which involve oxidation, reduction and hydrolysis to make drugs more polar. Phase II reactions then conjugate these products to endogenous moieties like glucuronic acid, sulfate or glutathione to facilitate excretion. Specific reactions in each phase like aromatic hydroxylation, carbonyl reduction, glucuronidation and acetylation are explained in detail.
Aromatic rearrangements
The document discusses several aromatic rearrangement reactions including the Fries rearrangement, photo-Fries rearrangement, Reimer-Tiemann reaction, Gattermann-Koch reaction, Gattermann aldehyde synthesis, and Vilsmeier-Haack reaction. The Fries rearrangement involves the rearrangement of phenolic esters to ortho- and para-substituted phenolic ketones/aldehydes using Lewis or Brønsted acids. The photo-Fries rearrangement is similar but uses light instead of acids. The Reimer-Tiemann, Gattermann-Koch, and Vilsmeier-Haack reactions all involve the formylation of aromatic compounds to produce
Group transfer reactions
For PG students of Chemistry, Applied Chemistry YouTube link for the same video Lecture is
https://youtu.be/dqgHOypef_M
Electrophilic substitution reaction..ncert HYDROCARBONS
Electrophilic substitution reactions involve replacing a hydrogen atom in an aromatic ring with an electrophilic group such as nitro, halogen, sulfonic acid or alkyl/acyl groups. This is done using electrophiles generated in situ with a Lewis acid catalyst. It proceeds by generation of an electrophile, formation of a carbocation intermediate through attack on the aromatic ring, and removal of a proton. Ortho/para directing groups activate the ring towards substitution at those positions, while meta directing groups deactivate the ring at ortho/para positions. Polynuclear aromatic hydrocarbons with more than two fused benzene rings can be carcinogenic if inhaled from incomplete combustion.
Electrophilicsubstitutionreaction
Electrophilic substitution reactions involve replacing a hydrogen atom in an aromatic ring with an electrophilic group. Nitration replaces hydrogen with a nitro group using nitric and sulfuric acid. Halogenation uses a halogen and Lewis acid. Sulphonation uses fuming sulfuric acid and oleum. Friedel-Crafts alkylation and acylation use an alkyl or acyl halide with aluminum chloride to add those groups. The mechanism involves generating an electrophile, forming a carbocation intermediate, and removing a proton. Ortho and para directing groups increase electron density, favoring substitution at those positions, while meta directing groups decrease electron density, favoring meta position. Polynuclear hydrocarbons from
Aromatic compounds
Kekulé had a dream in which he envisioned snakes grasping their own tails and forming rings, inspiring his hypothesis that carbon atoms in benzene are arranged in a ring structure with alternating single and double bonds. This ring structure explains benzene's stability and resistance to addition reactions compared to open-chain alkenes. Aromatic compounds are named for many originally having pleasant aromas, though the term now refers to chemical stability conferred by conjugated planar ring structures like benzene that allow for resonance. These compounds are important industrially as precursors to dyes, drugs, polymers, and other chemicals.
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Electrophilic substitution reaction..ncert HYDROCARBONS
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Jacobsen reaction
- 1. St. Joseph’s College, (Autonomous) Thiruchirappalli-620002 NAME : F.LESLIN DANIEL . DEPARTMENT : CHEMISTRY D.N0 : 18PCH101 SUBJECT : ORGANIC CHEMISTRY
- 2. Jacobsen rearrangement: The Jacobsen rearrangement is a chemical reaction, commonly described as the migration of an alkyl group in a sulfonic acid derived from a polyalkyl- or polyhalobenzene:
- 3. HISTORICAL VIEW: It was Herzig who described this type of rearrangement for the first time in 1881 using polyhalogenated benzenesulfonic acids. But the reaction took the name of the German chemist Oscar Jacobsen, who described the rearrangement of polyalkylbenzene derivatives in 1886.
- 4. Oscar Georg Friedrich Jacobsen and Josef Herzig:
- 5. The exact reaction mechanism is not completely clear, but evidence indicates that the rearrangement occurs intermolecularly and that the migrating group is transferred to a polyalkylbenzene, not to the sulfonic acid (sulfonation only takes place after migration). The intermolecular mechanism is partially illustrated by the side products found in the following example:
- 6. When a polyalkyl or polyhalo benzenes are treated with sulfuric acid , the ring is sulfonated and rearrangement also takes place. This reaction limited to benzene ring that have at least four substituents, which can be any combination of alkyl and halo groups. When isopropyl or t-butyl group are on the ring cleaved to give olefins. Jacobsen reaction used as a means of rearranging the polyalkyl benzenes.
- 7. Reaction: As we discussed early the mechanism of this rearrangement is not established, but there is a evidence at least for polymenthyl benzenes, that the rearrangement is intermolecular, And that species to which the menthyl group migrates is polymenthyl benzene ,not a sulfonic acid. Sulfonation takes place after the migration. It is shown by labelling that ethyl groups migrate without internal rearrangement.
- 8. REACTION:
- 9. APPLICATIONS: This reaction can be used for the isomerisation of polyalkyl benzenes. For example: Durene on sulfonation rearranges to prehnitenesulfonic acid ,which on desulfonation affords prehnitene.
- 10. Another important application is isomerisation of octahydroanthracene to otctahydrophenantherene.
- 11. REFFERENCE: ADVANCED ORGANIC CHEMISTRY (REACTIONS, MECHANISMS AND STRUCTURE) 4TH EDITION BY JERRY MARCH ORGANIC REACTION MECHANISM 4TH EDITION BY V.K .AHLUWALIA.