Koch-Haaf acid synthesis

Alkyl cations can also be generated by decarbonylation of tertiary acylium ions, like the pivaloyl cation 26 [Eq. (3.20)].91 This reaction corresponds to the reverse of Koch-Haaf acid synthesis, which is known to involve carbocation intermediates. Indeed the reaction of the terf-butyl cation with carbon monoxide gives the pivaloyl cation.91 135... 

This is unlikely to be a dominant factor. Steric effects have been observed in the Koch-Haaf synthesis of carboxylic acids (Pincock et al., 1959 Stork and Bersohn, 1960 Peters and Vs,n Bekkum, 1971), but these are ascribed to the steric requirements of the protonated carboxyl group (—COOHj) and not to those of the oxocarbonium group (—CO+). In FHSOs—SbFs, the product is the alkyloxocarbonium ion. 

The reaction is also called hydrocarboxylation. According to a later modification, the alkene first reacts with carbon monoxide in the presence of the acid to form an acyl cation, which then is hydrolyzed with water to give the carboxylic acid.97 The advantage of this two-step synthesis is that it requires only medium pressure (100 atm). Aqueous HF (85-95%) gave good results in the carboxylation of alkenes and cycloalkenes.98 Phosphoric acid is also effective in the carboxylation of terminal alkenes and isobutylene, but it causes substantial oligomerization as well.99 100 Neocarboxylic acids are manufactured industrially with this process (see Section 7.2.4). The addition may also be performed with formic acid as the source of CO (Koch-Haaf reaction).101 102 The mechanism involves carbocation formation via protonation of the alkene97 103 [Eq. (7.10)]. It then reacts with carbon monoxide... 

Synthesis of carboxylic acids with formic acid Koch-Haaf synthesis... 

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