Carboxylic acid conversions

The most appar ent chemical property of car boxylic acids, then- acidity, has already been examined in earlier sections of this chapter. Three reactions of carboxylic acids—conversion to acyl chlorides, reduction, and esterification—have been encountered in previous chapters and are reviewed in Table 19.5. Acid-catalyzed esterification of carboxylic acids is one of the fundfflnental reactions of organic chemistry, and this portion of the chapter begins with an exanination of the mechanism by which it occurs. Later, in Sections 19.16 and 19.17, two new reactions of carboxylic acids that are of synthetic value will be described. 

Fluorobenzene to fluorodihydrocatechol and fluorocatechol Conversion of 2,5-dimethyl pyrazine to 5-metyl pyrazine-2-carboxylic acid, conversion of 5-ethyl-2-methyl pyridine to... 

Carbonation of Grignard reagent, 282, 294 Carboxylic acid, conversion to acid chloride, with PCh, 56, 83, 186 with PCh, 41, 209 with SOCh, 258, 283 Chichibabin reaction, 16... 

Pyridine side-chain carboxylic acids, conversion to condensed heterocycles, 353-355, 476, 500... 

The decarboxylation of free carboxylic acids is often difficult except for some activated acids such as aryl carboxylic acid. Conversion of the free carboxylic acids into proper derivatives snch as acid anhydrides or esters makes the transition metal-catalysed decarboxylation reaction easy and these have also been applied to various coupling reactions. Water in a snpercritical stage (374°C, 22 MPa) was used for decarboxylation of free carboxylic acids using 10 wt% Pd on active carbon in a closed pot (Matsnbara et al., 2004) (Scheme 3.14). 

---