Preparation of Carboxylic Acids, Esters and Ketones

2-addition of H and CO2H, or CO2R to alkenes and alkynes is called hydrocarboxylation, or hydroesterification, and proceeds with catalytic amounts of 

Pd(0) complexes, Co2(CO)8 or Ni(CO)4 [1,2]. Most conveniently, Pd(0)-catalysed carbonylations of alkenes can be carried out under mild conditions in a laboratory with or without using a high pressure apparatus. Carbonylation in the presence of a small amount of HC1 is explained by the following mechanism. The first step is oxidative addition of HX to Pd(0) to generate 4. Then insertion of alkenes to H-PdX 4 gives the alkylpalladium bond 5, and the acylpalladium complex 6 is formed by subsequent CO insertion. The last step is nucleophilic attack of alcohol or water to the acylpalladium complex 6 to give the ester 7 or acid, with regeneration of H-PdX. 

However, the linear ester 12 can be prepared as a major product from 1-alkene using Pd(OAc)2 or even Pd on carbon as a catalyst and DPPB as a ligand in DME in the presence of formate, formic acid or oxalic acid under CO pressure [9]. Linear ester 13 is obtained from 1-octene as a main product using PdCl2(Ph3P)2 coordinated by SnCl2 [10]. 

Sometimes, keto esters are formed. Carbonylation of ethylene in alcohol affords propionate (14) as a main product, accompanied by a small amount of 4-oxohexanoate (15) [3]. Keto esters are obtained by the carbonylation of some dienes via insertion of alkene to an acylpalladium intermediate [11]. Carbonylation of 1,5-COD (16) in alcohols affords the mono- and diesters 17 and 18 [12], On the other hand, bicyclo[3,3,l]-2-nonen-9-one (20) is formed in 40% yield in THF by the intramolecular insertion of the alkene to the acylpalladium bond in 19 [13], 

The carbonylation of acetylene to produce acrylic acid or ester (22) catalysed by Ni(CO)4 was a historical industrial process developed by Reppe. 

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