Koch-Haaf

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] ... 

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. 

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 acid-catalyzed hydrocarboxylation of an alkene is known as the Koch Reaction. When the source of both the CO and the H20 is formic acid, the process is called the Koch-Haaf Carbonylation. 

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... 

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... 

The Koch-Haaf reaction397 for the preparation of carboxylic acids from alkenes uses formic acid or carbon monoxide in strongly acidic solutions. The reaction between carbocations and carbon monoxide affording oxo-carbenium ions (acyl cations) is a... 

Whereas the C2—C4 alcohols are not carboxylated under the usual Koch-Haaf conditions, carboxylation can be achieved in the HF-SbF5 superacid system under extremely mild conditions.400 Moreover, Olah and co-workers401 have shown that even methyl alcohol and dimethyl ether can be carboxylated with the superacidic HF-BF3 system to form methyl acetate and acetic acid. In the carboxylation of methyl alcohol the quantity of acetic acid increased at the expense of methyl acetate with increase in reaction time and temperature. The quantity of the byproduct dimethyl ether, in turn, decreased. Dimethyl ether gave the desired products in about 90% yield at 250°C (90% conversion, catalyst/substrate ratio =1 1, 6h). On the basis of experimental observations, first methyl alcohol is dehydrated to dimethyl ether. Protonated dimethyl ether then reacts with CO to yield methyl acetate [Eq. (5.154)]. The most probable pathway suggested to explain the formation of acetic acid involves the intermediate formation of acetic anhydride through acid-catalyzed ester cleavage without the intervention of CO followed by cleavage with HF [Eq. (5.155)]. 

While studying the reaction of adamantane with carbon monoxide under super-acidic catalysis, formylation (formation of 1-adamantanecarboxaldehyde) was found by Olah and co-workers447 to effectively compete with Koch—Haaf carboxylation (formation of 1-adamantanecarboxylie acid, major product formed in 60-75% yield). On the basis of results acquired by the reaction of 1,3,5,7-tetradeuteroadamantane, formylation was interpreted by insertion of the formyl cation into the tertiary C—H cr-bond [Eq. (5.163)]. 

Dialkyl-S-vaJerolaetones.1 Reaction of primary, tertiary-1,4-diols (1) with formic acid and 97-100% sulfuric acid (Koch-Haaf carboxylation2) provides 2,2-dialkyl-S-valerolactones (2) in high yield. 

Thus, in contrast with the results in SbF5-S02,2-methyl-2-adamantanol undergoes extensive rearrangement in concentrated sulfuric acid 63> 64 The results are summarized in Eq. (17). Similar rearrangements are observed S7> 65) during Koch-Haaf carboxylation reactions carried out in sulfuric acid 66K The intermolecular nature of these reactions is indicated by the fact that high dilution conditions suppress the rearrangements s7 ... 

Similar results are obtained with 2-adamantanol which rearranges to 1 -ada-mantanol (> 98 %) at 28°C in sulfuric acid. An equilibrium mixture containing small amounts of 2-adamantanol is rapidly achieved fromeither direction67 6 K This isomerization is one of the mechanistic bases for the preparation of ada-mantanone by the reaction of adamantane with sulfuric acid at 77°C (see Section V.A.l) 57> 67> 691. The Koch-Haaf carboxylation of 2-adamantanol similarly results in predominant 1-adamantyl carboxylic acid formation unless highly dilute reaction conditions are employed 57> 7°). 

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