Hydration and acetoxylation of monoterpenes catalyzed by heteropoly acid

The liquid-phase hydration and acetoxylation of limonene (1), P-pinene (2) and alpha -pinene (3) catalyzed by dissolved or silica-supported heteropoly acid H3PW12O40 (PW) in acetic acid and acetic acid/water solutions have be en studied. All three substrates give alpha -terpineol (4) as the main prod uct along with alpha -terpenyl acetate (5). The reaction rate increases in the order: limonene < alpha -pinene < beta -pinene. Synthetically useful ho mogeneous and heterogeneous acetoxylation and hydration of 1, 2 and 3 into 4 and 5 have been developed. At room temperature under optimized conditions , 2 and 3 form a mixture of 4 and 5 with 85% selectivity at 90% substrate c onversion. 1 gives 4 and 5 with 85% selectivity at 50% conversion, with the main product being ester 5 in acetic acid (4/5 similar to 30/70) and alcoh ol 4 in HOAc/H2O (90/10 v/v) solutions (4/5 similar to 85/15). Virtually no oligomerization of monoterpenes occurs under the optimized conditions. The catalyst can be separated without neutralization and may be reused. The PW shows a much higher catalytic activity than conventional acid catalysts su ch as H2SO4 and Amberlyst- 15. (C) 2001 Elsevier Science B.V. All rights re served.