Reactions of α- and β-pinenes
in pressurized hot water
were examined in a batch reactor made of a SS316 1/2-in. tube at temperatures
of 250–400 °C, pressures of 4–30 MPa, and reaction
times of 1–30 min in the absence of any additive under an argon
atmosphere. The maximum yields of limonene from α-pinene were
ca. 70% in 20 min at 300 °C or 1 min at 400 °C. Limonene
was obtained from β-pinene in ca. 16% yield for 30 min at 300
°C and 1 min at 400 °C. Reversible production of myrcene
in 14% yield and formation of unidentified C20 dimer fractions
were noted for 1 min at 370 °C from β-pinene. The conversion
of α-pinene to limonene took place under anhydrous conditions,
albeit at slightly lower yield of 65% compared to processes conducted
in the presence of water, where increased limonene yield of 70% was
observed for 1 min at 400 °C. The conversion of β-pinene
to limonene under anhydrous conditions was limited to 6.1% in contrast
to 11.9% in the presence of water for 7 min at 370 °C. In the
presence of oxygen, p-cymene was formed in 23% and
24% yield at the expense of limonene from α- and β-pinenes,
respectively, for 30 min at 400 °C.
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