acetate) CH -CH =CH-CHO CH -CH=CH-CH OH crotonaldehyde (i)LiAlH crotyl alcohol (but- -enal) (but- -en- -ol) When two or more functional groups are present in a molecule a less vigorous sodium borohydride is used as a reducing agent to reduce the more reactive group. For example, if a compound contains both carbonyl and carboxyl group, it preferentially reduces the carbonyl group. RCOCH CH COOH RCHOH-CH CH COOH NaBH4 H O -alkyl- - hydroxybutanoic acid XII U11-Hydroxy XII U11-Hydroxy - - - - Preparation of glycol We have already learnt that the hydroxylation of ethylene using cold alkaline solution of potassium permanganate (Baeyer’s reagent) gives ethylene glycol. CH = CH + H O Cold alkaline KMnO ethene ethane- , -diol [O] Preparation of glycerol Glycerol occurs in many natural fats and it is also found in long chain fatty acids in the form of glyceryl esters (Triglycerides).
The alkaline hydrolysis of these fats gives glycerol and the reaction is known as saponification. (CH ) CH (CH ) (CH ) + 3NaOH triglyceride) CH + 3NaO (CH ) Glycerol Sodium palmitate (propane- , , -triol) Sodiumhexadeconoate Glycerylpalmitate (a D Evaluate Yourself? . Suggest a suitable carbonyl compound for the preparation of pent- -en- -ol using LiAlH .
. -methylpropene H SO /H O ? . How will you prepare the following using Grignard reagent.
i ) t-butyl alcohol ii ) allyl alcohol Methods to differentiate primary, secondary and tertiary alcohols. The following tests are used to distinguish between , and ° ° ° alcohols. a) Lucas test: When alcohols are treated with Lucas agent (a mixture of concentrated HCl and anhydrous ZnCl ) at room temperature, tertiary alcohols react immediately to form a turbidity due to the formation of alkyl chloride which is insoluble in the medium. Secondary alcohols react within minutes to form a turbidity of alkyl chloride where primary alcohols do not react at room temperature.
XII U11-Hydroxy XII U11-Hydroxy - - - - CH - C -