Hydrolysis of acid chlorides

Similar aggressive reaction conditions characterize the hydrolysis of acid chlorides, in particular when using short-chain alkyl-substituted acid chlorides such as propionic acid chloride. This fast reaction serves well as a model reaction for micro channel processing, especially for IR monitoring owing to the strong changes in the carbonyl peak absorption by reaction [21]. 

Carboxylic acids are prepared hy the hydrolysis of acid chlorides and acid anhydrides, and acid- or hase-catalysed hydrolysis (see Section 5.6.1) of esters, primary amides and nitriles (see Section 5.6.1). 

Hydrolysis of acid chlorides, acid anhydrides, esters and carboxamides leads to the carboxylic acid, although these compounds are often derived from a carboxylic acid group in the first place (Scheme 5.5). Nitriles are usually derived from amines via diazotization and reaction with copper(I) cyanide (see Chapter 8) and so the hydrolysis of a nitrile group is of more value. In all cases, alkaline hydrolysis gives the salt of the acid, from which the free acid is obtained by addition of mineral acid. 

Amides undergo hydrolysis to yield carboxylic acids plus amine on heating in either aqueous acid or aqueous base. The conditions required for amide hydrolysis are more severe than those required for the hydrolysis of acid chlorides or esters, but the mechanisms are similar. The acidic hydrolysis reaction occurs by nucleophilic addition of water to the protonated amide, followed by loss of ammonia. The basic hydrolysis occurs by nucleophilic addition of OH" to the amide carbonyl group, followed by deproto nation of the -OH group and elimination of amide ion NH2). 

Acid or base hydrolysis of acid chlorides, acid anhydrides, esters, or amides regenerates the parent carboxylic acid. 

Loss of ethanol from 33 gives oxocarbenium ion 34, and loss of the acidic proton from that species gives butanoic acid (7). The two products of the acid hydrolysis are the carboxylic acid (butanoic acid) and the alcohol (ethanol). As with the hydrolysis of acid chlorides and acid anhydrides before, this mechanism is a series of acid-base reactions. 

As with the hydrolysis of acid chlorides, the hydrolysis of acid anhydrides will occur without an added acid or base catalyst (although sometimes acid is used) therefore, the mechanism is similar to that given above. The acid-catalyzed mechanism is analogous to that with esters, discussed in the next section. 

The interphase method of polycondensation was more effective in synthesis of LC polyamides than in synthesis of polyethers. High-molecular-weigjit polyethers were only obtained in rare cases. This is due to the fact that the rate of acylation of alcohols is not as high as the rate of acylation of amines, and for this reason, the competing reaction of hydrolysis of acid chloride groups becomes more marked. 

HYDROLYSIS OF ACYL DERIVATIVES Hydrolysis of Acid Chlorides and Anhydrides Hydrolysis of Esters... 

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