Koch-Haaf reaction

The reaction of trivalent carbocations with carbon monoxide giving acyl cations is the key step in the well-known and industrially used Koch-Haaf reaction of preparing branched carboxylic acids from al-kenes or alcohols. For example, in this way, isobutylene or tert-hutyi alcohol is converted into pivalic acid. In contrast, based on the superacidic activation of electrophiles leading the superelectrophiles (see Chapter 12), we found it possible to formylate isoalkanes to aldehydes, which subsequently rearrange to their corresponding branched ketones. 

Olefins are carbonylated in concentrated sulfuric acid at moderate temperatures (0—40°C) and low pressures with formic acid, which serves as the source of carbon monoxide (Koch-Haaf reaction) (187). Liquid hydrogen fluoride, preferably in the presence of boron trifluoride, is an equally good catalyst and solvent system (see Carboxylic acids). 

The hydrocarboxylation of an olefin, catalyzed by strong mineralic acids (Koch-Haaf reaction), leads to branched carboxylic acids [57] ... 

Koch-Haaf reaction, acylium ions, 42 160 Koch reaction, 34 126 Kolbel-Engelhardt reaction, 31 59 Kolbe reaction, 40 160-161 chemical identity of adsorbed intermediates, 38 18-19... 

Koch-Haaf reaction, 17, 3 Kornblum oxidation, 39, 3 Kostaneki synthesis of chromanes, flavones, and isoflavones, 8, 3... 

The acid-catalyzed hydrocarboxylation of olefins (the Koch reaction) can be performed in a number of ways.565 In one method, the olefin is treated with carbon monoxide and water at 100 to 350°C and 500 to 1000 atm pressure with a mineral-acid catalyst. However, the reaction can also be performed under milder conditions. If the olefin is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0 to 50°C and 1 to 100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.566 The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 0-103). Nearly all olefins can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. 

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... 

In the Koch-Haaf reaction, a superacid/CO mixture leads to carbonylation of the alkane. A variety of products were obtained, e.g. BuKTOaH, IVCHCOMe and Pr CHaCOBu, from isobutane using this product. Usually the method is only useful for alkanes containing a tertiary C—H bond, but Sommer has introduced a modification that sdlows secondary C—H bonds to be functionalized, although only with 4% conversion (equation 3S). ... 

An interesting but rather unusual reaction involves the direct carbonylation of carbocations to carboxylic acid derivatives. Carbenium ions can be generated from alkenes or alkanes in strong acidic media. Thus, tertiary carboxylic acids can be produced from C4 or higher alkenes Koch-Haaf reaction) [39] (e.g., eq. (8)). Interestingly, Koch carbonylations are known to be catalyzed by copper or silver cations [40]. 

The reaction of isobutane with carbon monoxide in the presence of an excess of AICI3 was first reported by Nenitzescu et al. to yield a complex mixture of products, mainly carboxylic acids (Koch-Haaf reaction), but also some methyl isopropyl ketone, a formylation product. Later, Olah et al. louiid " that in the reaction of adamantane (26) with carbon monoxide under superacidic catalysis, formylation (formation of 1-adamantanecarboxaldehyde) effectively competes with Koch-Haaf carboxylation (formation of 1 -adamantanecarboxyUc acid). On the basis of results acquired by the reaction of 1,3,5,7-tetradeu-teroadamantane, formylation was interpreted by a-insertion of the formyl cation into the tertiary C-H bond [Eq. (6.47)]. 

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