INTERACTION OF ALPHA-PINENE WITH CARBOXYLIC-ACIDS

The interaction of .alpha.-d-pinene with a series of organic acids from acetic to octanoic, under a wide range of olefin to acid ratios, yields esteric and rearrangement products after ring opening to the p-menthane system and ring rearrangement to the camphane system. Evidence is presented that the esterification proceeds through 2 distinct mechanisms one of which is highly dependent on the ionizing power and the nucleophilicity of the solution. This reaction leads to .alpha.-terpinyl esters while the esterification to bornyl and .alpha.-fenchyl esters is a reaction of zero order in the organic acid that constitutes 23.6 .+-. 1.5% of total product under all conditions. Furthermore, the bicyclic esters bornyl and .alpha.-fenchyl are produced in a constant ratio (bornyl/.alpha.-fenchyl = 1.6 .+-. 0.2). The esterification to give the terpinyl esters is explained as proceeding through solvolysis of a carbonium ion after a ring bond rupture. The esterification to give bornyl .alpha.-fenchyl esters is considered to be the result of the filling of the vacant orbital created after a skeletal rearrangement with strain release from the pinane to the camphane skeletal system. The isomerization reaction is also suggested as following reaction paths, one through carbonium ion intermediates producing limonene and terpinolene and the other through nonclassical intermediates with distributed charge to produce camphene and .alpha.- and .beta.-fenchenes. For all these reactions consistent mechanistic explanations of the results are given.