Koch-Haaf carboxylation

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)]. 

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°). 

Benzoyl triflate prepared from TfOH and Benzoyl Chloride is a mild and effective benzoylating agent for sterically hindered alcohols and acylative ring expansion reactions. The applications of TfOH in Koch-Haaf carboxylation, Fries rearrangement, and sequential chain extension in carbohydrates are also documented. Recent applications of TfOH in cyclization reactions have been published. ... 

Other references related to the Koch-Haaf carboxylation are cited in the literature. ... 

Koch-Haaf Carboxylations Kochi Reaction Koenigs-Knorr Synthesis Kolbe Electrolytic Synthesis Kolbe-Schmitt Reaction Komer-Contardi Reaction Kostanecki Acylation Krafft Degradation Krapcho Decarbalkoxylation... 

The epimeric 2-hydroxymethyl-5,6-exo-trimethylenenorbomanes on reaction with sulphuric acid in pentane yield 4-homoisotwistane (811). Seychellene, which possesses the homoisotwistane skeleton, on conversion to its unstable epoxide, which was stored in the presence of light and air before reduction with LiAlH4, was transformed into the abnormal oxidation product norseychelanol (812) a scheme based on dioxetan formation was proposed. Bromination or Koch-Haaf carboxylation of (811) produces the appropriate 3-substituted derivative, indicating that C-3 in (811) is at least as reactive as the 1-position in adamantane, while the 1- and 8-positions in (811) are unreactive. The 3-bromo-derivative (813) is solvolytically more reactive than 1-bromoadamantane, and reaction with sodamide in boiling toluene yielded the anti-Bredt olefin (815) which could be isolated in 52% yield (815) exhibited typical... 

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. 

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... 

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)]. 

Under standard Koch-Haaf conditions, 1,5-cyclooctadiene is converted via cation 43 to the thermodynamically favored tertiary system 44 which is captured to deliver carboxylic acid 45.10 71 When a hydrogen fluoride catalyst solvent system is utilized, however, the 2-carboxylic acid is formed instead.72 ... 

Koch-Haaf earboxylation This acid is much superior to the previously used 95 % H2SO4 for carboxylation of olefins, alcohols, and esters with CO at atmospheric pressure. The beneficial effect appears to be the higher solubility ol CO in this acid. 

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]. 

When an alcohol is heated in strong acid with carbon monoxide (CO), the initially generated cation rearranges and traps carbon monoxide to give a tertiary carboxylic acid in what is known as the Koch-Haaf... 

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

Reactions of acyclic hydrocarbons of various skeletal structures with CO in superacid media were recently studied by Yoneda and coworkers " as discussed in the previous section. Products obtained were only isomeric carboxylic acids with lower number of carbon atoms than the starting alkanes. Formation of the carboxylic acids were accounted by the reactions of parent, isomerized and fragmented alkyl cations with CO to form the oxocarbenium ion intermediates (Koch-Haaf reaction) followed by their quenching with water. No formylated products in these reactions have been identified. 

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