Лако-красочные материалы — производство

Camphene can be obtained from a-pinene through acid-catalysed rearrangement. The details of the mechanism are shown in Scheme 4.26. It was study of this reaction and related conversions that led to the elucidation of the Wagner-Meerwein rearrangement. Acid-catalysed addition of acetic acid to camphene gives isobornyl acetate; the first carbocation formed in this conversion is identical to that from which camphene was formed. In the conversion of a-pinene into camphene, no good nucleophile is present and so the cation eliminates a proton. In the second reaction, the presence of acetic acid allows the cation to be trapped as the acetate. In such carbocationic rearrangements, the outcome of the reaction is usually determined by a delicate balance of steric and thermodynamic factors and by the nature of other species present in the medium. Hydrolysis of isobornyl acetate gives iso — borneol, which can be oxidized to give camphor. Camphor can also be

isolated from camphorwood, of which it is the major volatile con­stituent. The synthetic material is usually the less expensive. Camphor, isoborneol and isobornyl acetate are all used for their woody odours.

Another bicyclic monoterpene of use in perfumery is nopyl acetate, which has a sweet woody-fruity odour. Prins reaction of /?-pinene with formaldehyde gives nopol which is easily esterified to the acetate (Scheme 4.27).

Isobomyl acetate