ESTIMATION OF HYDROXYL GROUPS IN ALCOHOL

1. ESTIMATION OF HYDROXYL GROUPS IN ALCOHOL PRINCIPLE: ACETYLATION METHOD: The number of hydroxyl groups in an alcohol on phenol can be estimated by acetylation. A known weight of the alcohol is acetylated with freshly distilled acetic anhydride and dry pyridine and excess of the anhydride is hydrolyzed with water. Acetic acid produced is titrated against standard alkali solution in order to determine the amount of unreacted acetic anhydride. PROCEDURE: First prepare the acetylation mixture by mixing volume(10ml) of acetic anhydride and 3 volumes (40ml) of dry pyridine in a clear round bottomed flask fill a clean dry burette with this mixture and cool it. In a 250ml round bottomed flask equipped with a water condenser. Weigh accurately(by transference method) 1-1.3g sample (phenol, n-hexanol,cyclohexanol benzyl alcohol) and add 9ml acetylating mixture from the burette, stir and reflex the contents on a water bath for 45 min after replacing the condenser. Remove condenser and shake to ensure complete hydrolysis of the remaining acetic anhydride cool the flask and titrate the contents against NAOH using phenolphthalin as indicator standardize the alcoholic NAOH solution with standard O.5N HCL carry out a blank simultaneously using the above procedure with 9ml of the acetylating mixture REPORT: The phenolic compound contains 0.004 OH groups/molecules.