Mao Haifang, Zhang Chiyuan, Meng Tao, Wang Hongzhao, Hu Xiaojun, Xiao Zuobing, Wang Chaoyang, Liu Jibo
School of Chemical and Environmental Engineering, Shanghai Institute of Technology, 100 Haiquan Road, Shanghai 201418, China.
School of Perfume and Aroma Technology, Shanghai Institute of Technology, 100 Haiquan Road, 201418 Shanghai, China.
ACS Omega. 2020 Sep 17;5(38):24526-24536. doi: 10.1021/acsomega.0c03003. eCollection 2020 Sep 29.
3-methoxy-4-hydroxymandelic acid (VMA) was the critical intermediate for the synthesis of vanillin by the glyoxylic acid method. Meanwhile, a valuable byproduct (2-hydroxy-3-methoxy-mandelic acid, -VMA) was obtained during the reaction. Al was found to be a helpful catalyst in increasing the selectivity for VMA and -VMA. In the presence of Al, the selectivity for VMA and -VMA increased from 83 to 88% and from 3 to 8%, respectively, while that of the helpless byproduct 2-hydroxy-3-methoxy-1,5-mandelic acid (di-VMA) decreased from 14% to less than 4%. The kinetics based on the kinetic equation of the condensation reaction was studied by the initial concentration method. The results indicated that the involvement of Al could reduce the activation energy of the reaction on the basis of the Arrhenius equation. Combined with thermogravimetric analysis, Fourier transform-infrared spectroscopy, and H NMR research, Al was found to interact with guaiacol through Al-O and Al···H, which further improved the selectivity of the VMA and -VMA and reduced the selectivity of di-VMA by adding the electronegativity of the ortho- and para-positions of hydroxyl groups of guaiacol.
3-甲氧基-4-羟基扁桃酸（VMA）是通过乙醛酸法合成香草醛的关键中间体。同时，在反应过程中还得到了一种有价值的副产物（2-羟基-3-甲氧基扁桃酸，即-VMA）。发现铝是提高VMA和-VMA选择性的有用催化剂。在铝存在下，VMA和-VMA的选择性分别从83%提高到88%和从3%提高到8%，而无助副产物2-羟基-3-甲氧基-1,5-扁桃酸（二-VMA）的选择性从14%降至4%以下。采用初始浓度法研究了基于缩合反应动力学方程的动力学。结果表明，基于阿仑尼乌斯方程，铝的参与可以降低反应的活化能。结合热重分析、傅里叶变换红外光谱和核磁共振研究，发现铝通过Al-O和Al···H与愈创木酚相互作用，通过增加愈创木酚羟基邻位和对位的电负性，进一步提高了VMA和-VMA的选择性，降低了二-VMA的选择性。
