Rearrangements of pinane derivatives. Part II. Products of acid-catalysed rearrangement of α-pinene and β-pinene in acetic acid

The reactions of α-pinene and β-pinene with sulphuric acid in anhydrous acetic acid have been studied, and the results have been shown to be consistent with the addition of at least partially undissociated acid, giving an intimate ion pair in which the counter ion stabilises the carbonium ion against attack by external nucleophiles. The main mode of decomposition of the carbonium ion is thus olefin formation by loss of a proton to the counter ion. In aqueous acetic acid, the ion pair is either not formed or short lived, permitting the carbonium ion to react with external nucleophiles.