p-Cymene was prepared by the liquid phase method with turpentine as raw material and activated bentonite as catalyst.The reaction process and mechanism were investigated by Fourier infrared spectrophotometry (FT-IR)and gas chromatography-mass spectrometry (GC-MS).44 peaks were separated and 41 compounds were identified by GC-MS.The main products were p-cymene and p-menthene

with the relative contents of 56.57% and 10.46%

respectively.Complete conversion of pinene and 62.78% yield for p-cymene were obtained.Some nonvolatile products and polymeric species

such as cembrene were first identified in the products.As a result of FT-IR

the absorbance peak of the endo-double bond of α-pinene at 3022 cm-1

1655 cm-1 and ＝CH2 of β-pinene at 3067 cm-1 almost disappeared

while the peak of the stretching in aromatic rings at 1611 cm-1

1498 cm-1

1458 cm-1 and that at 815 cm-1 from p-substituent of benzene ring increased.It also meant that pinene was converted completely

mainly to p-cymene.The analysis results showed that the isomerization and intermolecular hydrogen transfer disproportionation of bicyclic terpene pinene were the main reactions.Simultaneously

some accompanying side reactions

such as further ring-opening isomerization

aquated rearrangment and polymerization reaction occurred

while isomerization and dehydrogenation as well as aquated rearrangement of sesquiterpene were observed.