活性白土上松节油直接制备对伞花烃的反应过程

Reaction process of direct preparation of p-cymene from turpentine over activated bentonite

以自制活性白土为催化剂,松节油为原料液相法直接制备对伞花烃,采用傅里叶红外光谱(FT-IR)和气相色谱-质谱联用技术(GC-MS)对反应产物进行了分析鉴定,研究其反应过程并探讨了反应机理。GC-MS分析共分离出44个峰,鉴定出41种化合物,其中主要产物为对伞花烃和3-对孟烯,相对质量分数分别为56.57%和10.46%;松节油主要成分蒎烯的转化率为100%,对伞花烃收率为62.78%;首次鉴定出松节油歧化产物中非挥发性物质和聚合物如西松烯的存在。FT-IR分析显示,产物中蒎烯环内双键的3022、1655cm-1特征峰及=CH2的3067cm-1特征峰基本消失,1611、1498、1458cm-1处的苯环骨架振动及815cm-1苯环对位双取代单峰的强度增大,也表明蒎烯已完全反应,主要生成对伞花烃。对活性白土催化松节油的反应过程进行了探讨,双环单萜蒎烯的异构及分子间氢转移歧化反应为主反应,并伴随深度开环异构、水合重排、聚合等副反应,倍半萜发生异构、脱氢及水合重排等反应。

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.