Alicyclic hydrocarbons

General Introduction, Physical Properties, Chemical Properties

1. Alicyclic Hydrocarbons By Priyanka

2. General Introduction Alicyclic Hydrocarbons are those carboxylic compounds in which the carbon atoms are joined together to form a ring. In this carbon atoms are joined together to form a ring. In saturated alicyclic hydrocarbons methylene groups joined together to form a cyclic structure, hence they are also known as polymethylene. According to IUPAC system, they are named as cycloalkanes or cycloparaffins. They resemble with the aliphatic compound in their properties.

3. Methods of preparation of Alicyclic Hydrocarbons From Dihalides : The reaction is an extension of Wurtz reaction in which terminal dihalides are treated with sodium or zinc to give cycloalkanes. Three to six membered cycloalkanes can be prepared by this reaction by using appropriate dihalide

4. Methods of preparation of Alicyclic Hydrocarbons From Calcium salts of Dicarboxilic Acids : When the calcium salts of Dicarboxylic acids are heated one carbon less cyclic ketones are formed, which can be readily converted into the corresponding cycloaokanes by Clemmensen reduction.

5. Methods of preparation of Alicyclic Hydrocarbons From the Esters of Dicarboxylic acids [Dieckmann Reaction]: When ester of Dicarboxylic acids are leaked with sodium intermolecular condensation takes place to give β-keto esters. β—keto esters are first hydrolysed to give β-keto acid and then decarboxylated to give cyclic keone. Cyclic ketones on Clemmensen reduction give cyclo alkanes.

6. Methods of preparation of Alicyclic Hydrocarbons From Aromatic Hydrocarbons: Benzene and its derivatives on catalytic reduction are converted to six membered cycloalkanes.

7. Methods of preparation of Alicyclic Hydrocarbons From Alkenes: [preparation of cycloproparne derivatives]: Alkene when treated with methylene iodide in presence of Zn-Cu couple in ether, give cyclopropane derivatives.(Simmons-Smith Reaction )

8. Physical Properties Cycloalkanes are liquids at room temperature except cyclopropane and cyclobutane which are gases at room temperature. Their melting and boiling points are gradually increase with increase in molecular weights. Cycloalkanes are insoluble in water but soluble in ethanol and ether.

9. Chemical Properties Cycloalkanes resemble with alkanes in several chemical properties. But the lower members, cyclopropene and cyclobutene are the exceptions. They form addition compounds with the ring fusion. Thus cycloalkanes behave both like alkanes as well as alkenes.

10. Reactions of Cycloalkanes Substitution with Cl2 and Br2 : In presence of UV light cycloalkane react with Cl2 or Br2 to give substitution products.

11. Reactions of Cycloalkanes Addition of Cl2 and Br2 : Cyclopropane reacts with Cl2 or Br2 indark and in CCl4 as a solvent to give addition product with the opening of ring.Cyclo butane and other higher members do not give this reaction.

12. Reactions of Cycloalkanes Addition of Hydrogen: Cyclopropane and Cyclobutane react with Hydrogen in the presence of Ni Catalyst to give corresponding normal alkanes .i.e. propane and n-butane.

13. Reactions of Cycloalkanes Addition of HBr and HI : Cyclopropane gives open chain addition product with concentrated HBr and HI.Higher members do not give this reaction.

14. Reactions of Cycloalkanes Oxidation: Cyclo alkanes when treated with hot alkaline KMnO4 yield dicarboxylic acid with the cleavage of ring.