Koch carbonylation

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 HF-SbFs system works well in the Gattermann-Koch formylatlon of arenes and the Koch carbonylation of alkanes [54]. For instance, biphenyl is diformylated in HF-SbFs-CO to afford 4,4 -diformylbiphenyl as a major isomer (Scheme 14.20). The carbonylation of alkanes with C5-C9 carbon atoms in the HF-SbFs-CO system affords mixtures of C3-C8 carboxylic acids after hydrolysis of the generated secondary carbenium ions [55]. Successive treatment of methylcyclopentane with CO in HF-SbF and with water produces cyclohexanecarboxylic acid as a major product (Scheme 14.21) [56]. It seems that a tertiary methylcyclopentyl cation readily isomerizes to the more stable cyclohexyl cation before being trapped by CO. Bicyclic a, -unsaturated ketones are functionahzed by HF-SbF or FSOsH-SbFs under a CO atmosphere to give saturated keto esters after methanolysis (Scheme 14.22) [57]. Alcohols with short carbon chains also react with CO in HF-SbFs to give the corresponding methyl esters [58]. y-Butyrolactones are carboxy-lated under the same conditions to afford 1,5-dicarboxyhc acids [59]. 

GATTERMAN - KOCH Carbonylation Synthesis of aromatic aldehydes or ketones using cyanide salts or CO - HCI and Lewis acids. 

Koch carbonylation. Tertiary alcohols give carboxylic acids on treatment with the sulfated zirconia (a solid superacid) under carbon monoxide at 150°. 

Commercial petrochemical processes using syngas or carbon monoxide are based on four principal classes of reactions phosgenation, Reppe chemistry, hydroformylations, and Koch carbonylations. Phosgenation is a key step in the manufacture of polyurethanes, polycarbonates, and monoisocyanates. Reppe chemistry is the basis for acetic acid and acetic anhydride production as well as formic acid and methyl methacrylate synthesis. Hydroformylations utilize syngas in the oxo synthesis to make a wide variety of aldehydes and long-chain alcohols. The fourth class of reactions are Koch carbonylations. Koch carbonylations are used commercially to produce neo acids which are specialty products that serve markets similar to 0X0 alcohols. 

The term carbonylation was first used by W.Reppe while working with syngas and carbon monoxide chemistry at BASF during the 1930s and 1940s. Carbonylations are catalytic reactions in which carbon monoxide, alone or with other compounds, is incorporated in an organic substrate. There are three general types of carbonylation reactions Reppe reactions, hydroformylations, and Koch carbonylations. 

Koch carbonylations use strong acid catalysts to react olefins with carbon monoxide and water to form branched isomers of carboxylic acids. Neo acids produced by Exxon Chemical and Versatic acids produced by Shell Chemical are examples of commercial processes utilizing Koch carbonylation chemistry [9]. 

Hydroformylation is the reaction of carbon monoxide and hydrogen with olefins to produce aldehydes and derivative alcohols. It is also known as 0X0 chemistry and the alcohol products produced by this method are known as 0X0 alcohols. Of all three types of carbon monoxide reactions, Reppe reactions, Koch carbonylations, and hydroformylations, oxo chemistry currently has the greatest commercial importance. An extremely broad range of products and end use markets are served by the aldehydes, alcohols, and derivatives produced by hydroformylation. The list of products shown in Table 6 illustrates the range of oxo chemical products. 

Neo Acids. Neo acids are actually not made by the 0x0 process but are products of Koch carbonylation. They are frequently included with the family of 0x0 chemicals because their end use products serve similar markets. For instance, pivaloyl chloride made from neo pentanoic acid is used as a precursor for several herbicides, pesticides, and pharmaceutical products. Neodecanoic acids are used as drying agents for paint and as a heat stabilizer for PVC. Latex paint additives are made from vinyl and glycidyl esters which are derived from neodecanoic acid. 

The isolation of saturated and unsaturated acetic acid derivatives in the manganese(m) acetate oxidation of olefins has been reported earlier examples of this oxidation led solely to y-lactones. A one-step synthesis of aeo-di-carboxylic acid diesters has been reported, based on Kolbe electrolysis of oxalic and malonic half-esters in the presence of olefins, and is exemplified in Scheme 2. As part of a study of insect hormone activity, Kolbe electrolysis has been utilized in the preparation of aj9-unsaturated Cj4—Cj7 acid esters with a terminal quaternary alkyl group. The utility of liquid hydrogen fluoride in the Koch carbonylation of olefins has been descried, as has a general study of this reaction. ... 

Koch carbonylation reaction (Koch-Haaf carbonylation reaction)... 

One method of converting alcohols into carboxylic acids, known as Koch carbonylation, is mediated by AgOTf in the presence of weak and soft Lewis acids (eq 11). Alkenes can be similarly carbonylated albeit in much lower yields (eq 12). ... 

Addic ILs promote the carbonylation of tertiary alcohols with CO (Koch carbonyl-ation. Scheme 6.6) [66]. The reaction is performed in a biphasic mode, using decane as a second phase, therefore allowing the separation of reaction products. The pivalic acid yield reaches 23% at 150 °C and 80 bar CO. 

Scheme 6.6 Koch carbonylation of -BuOH in acidic IL medium.

---