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  1. 1. hydrocarbons saturated unsaturated aromatic Eg butane Eg butene Eg butyne
  2. 2. Saturated hydrocarbons contain carbon- carbon or carbon-hydrogen single bonds. If different carbon atoms are joined together to form open chain of carbon atoms with single bonds ,they are termed as alkanes. In organic compounds each carbon atoms are bonded with 4 hydrogen atoms so as to satisfy carbon’s tetravalent quality. ethane methane
  3. 3. Alkanes can be prepared by the catalytic hydrogenation of unsaturated hydrocarbons in the presence of catalyst ‘Ni’ ,nickel, or ‘pt’ ,platinum at 200⁰C to 300⁰C. FROM UNSATURATED HYDROCARBONS
  4. 4. •From alkyl halides By Wurtz Reaction: When alkyl halides are heated with sodium metal in the presence of dry ethereal, alkanes are obtained (generally having double number of C- atoms than in alkyl halides). This reaction is known as Wurtz reaction and used for the preparation of symmetrical alkanes.
  5. 5. •By reduction Alkyl halides (except fluorine) on reduction with zinc and dilute hydrochloric acid gives alkanes CH3-cl+ H2  CH4 +HCl Chloromethane in presence of Zn,H+ gives methane and HCl From carboxylic acids • By Kolbe’s electrolytic method Electrolysis of aqueous conc. solution of sodium or potassium salt of carboxylic acid gives alkanes. >>RCOONa—-Sodium salt >>RCOOK—–Potassium salt RCOONa——–> RCOO- + Na+ anion cation
  6. 6. By Heating Na-salt of Carboxylic acid When Na-salt of carboxylic acid is heated with soda lime (NaOH & CaO), alkane is obtained having one carbon less than salt by removal of a molecule of CO2. This reaction is also known as decarboxylation. RCOONa + NaOH R-H + Na2CO Sodium ethanoate (methane) This is the principle reaction for laboratory preparation of methane gas
  7. 7. 1) Combustion reaction They combust in oxygen to form carbon dioxide, water and heat. It is this heat which makes them good fuel sources. e.g. C2H6 (g) + 7/2 O2(g) → 2CO2(g) + 3H20(g) + heat C8H20 (g) + 13 O2(g) → 8CO2 (g) + 10H2O(g) + heat 2) Controlled oxidation alkanes on heating with a regulated supply of dioxygen or air at high pressure and in the presence of suitable catalysts give a variety of oxidation products. 2CH4 + O2  2CH3OH
  8. 8. 3) Substitution reaction They undergo substitution reactions with halogens in the presents of UV light. CH4(g) + Cl2(g) → CH4Cl(g) + HCl(g) CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g) Substitution reaction in cyclic compounds 4) Isomerisation n-alkanes on heating in the presence of anhydrous aluminum chloride and hydrogen chloride gas isomerise to branched chain alkanes
  9. 9. Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms. Those with at least one carbon to carbon double bond are called alkenes and those with at least one carbon to carbon triple bond are called alkynes. These carbon compounds are bonded with the required number of hydrogen so as to fulfill the valency of carbon. Trans-2-butene H H H H H H H 2-butyne H
  10. 10. From alkyles alkyles on partial reduction with calculated amount of dihydrgen in the presence of palladised charcoal partially deactivated with poisons like sulphur compounds or quinoline give alkenes From alkyl halides alkyl halides on heating with alcoholic potash eliminate one molecule of halogen acid to form alkenes. This reaction is known as DEHYDROHALOGENATION ,i.e., removal of halogen acid.
  11. 11. From alcohols by acidic dehydration In dehydration reactions, a molecule of water is eliminated from an alcohol molecule by heating the alcohol in the presence of a strong mineral acid. A double bond forms between the adjacent carbon atoms that lost the hydrogen ion and hydroxide group. Dehalogenation. Vicinal dihalides, which are alkane molecules that contain two halogen atoms on adjacent carbon atoms, can form alkenes upon reaction with zinc. From vicinal dihalides
  12. 12. Addition of dihydrogen Alkenes add up to one molecule of dihydrogen gas in the presence of finely divided nickel, palladium or platinum to form alkanes. Addition of halogens The reaction with bromine (Br2)are used as a test for alkenes. Bromine solutions are brownish red. When we add a Br2 solution to an alkene, the color of the solution disappears because the alkenes reacts with the bromine:
  13. 13. Addition of water The reaction between an alkene and water to form an alcohol is called hydration, requires a catalyst— usually a strong acid, such as sulfuric acid (H2SO4): Addition of sulphuric acid Cold conc. Sulphuric acid adds to alkenes in accordance with markovnikov rule to form alkyl hydrogen sulphate by the electrophilic addition reaction.
  14. 14. From calcium carbide Ethyne (acetylene) preparation. Ethyne, which is commonly called acetylene, is the simplest alkyne. Historically, it was prepared by reacting calcium carbide with water. From vicinal dihalides The loss of additional hydrogen and halogen atoms from the double‐bonded carbon atoms leads to alkyne formation. The halogen atoms may be located on the same carbon (ageminal dihalide) or on adjacent carbons (a vicinal dihalide).
  15. 15. An alkyne reacts with hydrogen in the presence of catalyst (Pt or Ni) at 250°C, first forming alkenes and finally alkane. Addition of hydrogen Addition of Halogens Alkynes react with halogens (Cl2 or Br2) in the dark, forming dihaloalkenes first and finally tetrahaloalkanes. The reaction gets accelerated in the presence of light or halogen carriers.
  16. 16. Addition of Halogen Acids Alkynes reacts with halogen acids according to the Markownikoff's rule i.e. the carbon atom carrying the least number of hydrogen atoms will have the negative part of the addendum attached to it. Polymerization On heating, alkynes undergo polymerization in the presence of catalyst. The nature of products depends upon the conditions. For example, When ethyne (acetylene) is passed through a hot copper tube, it polymerizes to benzene.
  17. 17. Oxidation Oxidation of alkynes gives mono or dicarboxylic acids. For example, Alkaline KMnO4 oxidizes ethyne to oxalic acid.
  18. 18. These hydrocarbons are also known s ‘arenes’ or most of such aromatic compounds are found to contain benzene ring, which are highly saturated but in most of aromatic compounds are found to unsaturated too .Aromatic compounds containing benzene rings are known as benzenoids and those not containing benzene rings are known as non-benzenoids.
  19. 19. Cyclic polymerization of ethyne Ehthyne on passing through red hot iron tube at 873k undergoes cyclic polymerization. Three molecule polymerize to form benzene ,which is the starting molecule for the preparation of derivatives of benzene, dyes, drugs and large number of other organic compounds. This is the best route for entering from aliphatic to aromatic compounds . Decarboxylation of aromatic acids Sodium salt of benzenoic acid on heating with soda lime gives benzene. Reduction of phenol Phenol is reduced to benzene by passing its vapor over heated zinc dust
  20. 20. Electrophilic substitution reactions Nitration A nitro group is introduced into benzene ring when benzene is heated with a mixture of con. Nitric acid & con sulphuric acid. Halogenations Arenes react with halogens in the presence of a Lewis acid to yield haloarenes.
  21. 21. Addition reactions Under vigorous conditions ,i.e., at high temperature and /or pressure in the presence of nickel catalyst , hydrogenation of benzene gives cyclohexane.
  22. 22. Combustion When heated in air ,benzene burns with sooty flame producing CO2 and H2O C6H6 + (15/2 )O2 6 CO2 +3 H2O