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.