A one-step production of fine chemicals using supercritical water: an environmental benign application to the synthesis of monoterpene alcohol

Abstract

A one-step synthesis of monoterpene alcohols such as lavandulol (Scheme3, 5), linalool(8), and geraniol(7)/nerol(10) and α -terpineol(6) from hemiterpene alcohols proceeds efficiently in supercritical water (scH 2 O) without any catalyst. Our device of a microreaction ( μ -reaction) system that can heat up very quickly an ambient substrate solution to the scH 2 O state and then can quench rapidly to sufficiently low temperatures after the reaction achieves the selectivity to (5) and the yield reached 82% and 59%, respectively; even at a short reaction time of 7.7 s at 30 MPa and 375 ∘ C in the near-critical region. The yield was superior to the conventional method promoted by organometallic catalysts in which the reaction time of 7.25 h is needed to obtain 54% yield. When the reaction was carried out at a lower temperature of 300 ∘ C in hot water, we obtained only 15% yield even at a reaction time of 38 s. The acidic ability of H 2 O peculiar to supercritical conditions is thus considered to promote the desired pathway alone, and so the scH 2 O μ -reaction system could conveniently prevent side reactions such as dehydration and hydrolysis. It is further noteworthy that the presence of methanol in a high-temperature water medium completely suppresses the (5) production. This seems to be due to its own acidic ability peculiar to scH 2 O state.