Synthesis Of Biomass Vanillin

Synthesis of biomass vanillin from renewable resource eugenol was investigated. It consists of isomerization of eugenol, one-pot synthesis of vanillin from eugenol and one-step synthesis of vanillin from eugenol.Firstly, isomerization of eugenol was investigated. Using NiA14-HT [C/S (w/w)=2.0] as the catalyst and DMF as the solvent, the reaction achieved 76.7%conversion of eugenol, 21.2% selectivity for cis-isoeugenol and 78.8% selectivity for trans-isoeugenol at 152 ℃-153 ℃ for 8.0 h. Then, employing NaOH (2.0 equiv.) as the catalyst and MeOH as the solvent, the reaction achieved 99.1% conversion of eugenol,24.4% selectivity for cis-isoeugenol and 75.6% selectivity for trans-isoeugenol at 150 ℃ for 1.0 h. In contrast, the catalyst of the former was easily recovered and recycled, but the reaction obtained low selectivity for eugenol. Though the later offered higher selectivity for eugenol, the catalyst was not easily recovered and recycled. In addition, a large amount of acid was needed for the post-treatment of the later, which increased the cost.On the basis of 99.1% conversion of eugenol catalysized by NaOH, one-pot synthesis of vanillin from eugenol was found. The oxidation of isoeugenol was focused on. Under the optimal conditions, using Co(OAc)2·4H2O (0.2 mol%) as the catalyst, Ni(OAc)2·4H2O (0.2 mol%) as the co-catalyst and MeOH as the solvent, the reaction offered 53.31% and 5.49% yields of vanillin and vanillic acid under the mediation of NaOH (5.0 equiv.) and O2(0.6 atm) at 100 ℃,800 r/min for 20 h, via the investigation of various factors on the effect of the oxidation. Apart from vanillin and vanillic acid, two intermediates were separated in the reaction process. At last, several contral experiments were conducted and a possible mechanism for the intermediates was proposed.Furthermore, one-step synthesis of vanillin from eugenol, namely direct oxidation of eugenol to vanillin, was found. Under the optimal conditions, using Co(OAc)2·4H2O (0.2 mol%) as the catalyst, Co(OAc)2·4H20 (0.2 mol%) as the co-catalyst and MeOH as the solvent, the reaction offered 60.54% and 5.91% yields of vanillin and vanillic acid under the mediation of NaOH (5.0 equiv.) and O2 (0.6 atm) at 100 ℃,800 r/min for 20 h, via the investigation of various factors on the effect of the oxidation. Apart from vanillin and vanillic acid, two intermediates were separated in the reaction process. At last, several contral experiments were conducted and a possible mechanism for the intermediates was proposed.In contrast, both the intermediates and products are the same and the proposed mechanisms are similar. Compared with the former, the one-step method offered higher yields, In contrast with the traditional methods, this method offers a renewable, green, environmently friendly, simple and meanful alternative for producing vanillin without conducting the isomerization of eugenol.