Carboxylic acids from alkene hydrocarboxylation

Higher olefins inherently show distinct chemical and physical differences from ethylene, which result in a number of obstacles when producing carboxylic acids from them. Additionally, the hydrocarboxylation of higher alkenes gives mixtures of the saturated acids (eq. (19)) ... 

Non-oxidative hydrocarboxylation of alkenes to carboxylic acids with CO and H20 is catalyzed by palladium complexes such as PdCl2(PhCN)2 or PdCl2(PPh3)2, and a-methyl acids predominate in the presence of HC1.374,443 A recent improvement of this reaction consisted of the use of a PdCl2/CuCl2/HCl catalyst under oxidative conditions.377 Almost quantitative yields of a-methyl carboxylic acids and dicarboxylic acids were obtained from terminal alkenes and terminal dialkenes respectively, at room temperature and atmospheric pressure (equation 174).377... 

Catalytic hydrocarboxylations and related esterifications as well as amidations of alkenes belong to a family of carbonylation reactions which has attracted considerable industrial interest. Minor changes in the catalyst system as well as in reaction conditions can lead to simple carboxylic acids, diacids, polyketones, or unsaturated acids as products (Scheme 1). Most importantly, these methods provide routes to monocarboxylic acids, e.g., ethylene to propanoic acid (see Section 2.1.2.2), or 1-olefins (readily available from the oligomerization of ethylene discussed in Section 2.3.1.3) to higher carboxylic acids. 

Diphasic hydrocarboxylations of alkenes yield carboxylic acids with a typical linear to branched (n/i) ratio which ranges from 1 to 1.4 (Scheme 5). 

Nonoxidative hydrocarboxylation of alkenes to carboxylic acids with CO and water catalyzed by Pd catalysts is greatly improved in the presence of oxygen (Scheme 16). Almost quantitative yields of mono- and dicarboxylic adds were obtained from the corresponding terminal alkenes and terminal dialkenes, respectively, under atmospheric pressure at room temperature. ... 

Branched acids and esters are obtained from the palladium-catalyzed reaction in the absence of phosphines, and in the presence of copper chloride and HC1.79 The mild reaction conditions and the regio-specificity make this a very attractive carboxylation procedure (entry 5, Table 5). Internal straight chain alkenes can be hydrocarboxylated, but the rates are slower and the reaction is not regiospecific. 

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