Chapter 20: Carboxylic Acid Derivatives. Nucleophilic Acyl Substitution

Carboxylic Acid Derivative Answers
 

Qu1:	Hydrolysis is a nucleophilic acyl substitution reaction, typical of carboxylic acid derivatives.
	First task should be to identify the functional groups in each molecule then use the reactivity order. It can be rationalised based on (i) the interaction of the substituent and the carbonyl group, and, (ii) the ability of the substituent to function as a leaving group. CH3COCl >  CH3COOCOCH3 >  CH3COOCH3 >  CH3CON(CH3)2 acid chloride anhydride  ester amide
Qu2:	All the carboxylic acids in Qu 1 are derivatives of ethanoic acid, so they all give the same carboxylic acid...
	(a) CH3CO2H  (b) 2 moles CH3CO2H  (c) CH3CO2H  and CH3OH (d) CH3CO2H  and HN(CH3)2
Qu3:	LiAlH4 is a source of H- (a nucleophile) which functions as a reducing agent.
	First task should be to identify the functional groups : carboxylic acid, ketone, aldehyde, ester. The aldehyde and ketone will undergo nucleophilic addition, the acid and the ester nucleophilic acyl substitution. Consider the electrophilicity of the carbonyl group in each compound in each pair. Aldehydes are more reactive than ketones (chapter 17) as they are less hindered and the alkyl group in the ketone is a weak electron donor. Under the reaction condition s the carboxylic acid will deprotonate to give the carboxylate which is a very poor electrophile (after all, it has a negative charge !) so the ester is more reactive than the acid. Now combine the two pairs. Since the -OR group is a stronger electron donor (resonance) than the alkyl group of the ketone, the ester is less reactive than the ketone... so we get :
	(b) The aldehyde, carboxylic acid and ester will be reduced to the same product, benzyl alcohol.      The ketone will be reduced to 1-phenylethanol, C6H5CH(OH)CH3
Qu4:	The answers the these questions involve materials from this chapter and review from chapters 10 and 19

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© Dr. Ian Hunt, Department of Chemistry