Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (6): 598-617.doi: 10.3866/PKU.WHXB201711231

• REVIEW • Previous Articles     Next Articles

How to Synthesize Vitamin E

Zhe WANG,Shanjun MAO,Haoran LI,Yong WANG*()   

  • Received:2017-10-11 Published:2018-03-20
  • Contact: Yong WANG E-mail:chemwy@zju.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21622308);the National Natural Science Foundation of China(91534114);the National Natural Science Foundation of China(21376208)

Abstract:

Vitamin E compounds are biologically active and are frequently used as antioxidants. The demand for Vitamin E compounds has increased significantly in recent years, and at present, more than 80% of the market demand for Vitamin E is fulfilled by its synthetic counterparts. Therefore, it is imperative to increase the production of Vitamin E. Vitamin E compounds contain tocopherol and tocotrienol derivatives, and α-tocopherol, which dominates the sound, is the most biologically active. This review covers the methods of preparation of α-tocopherol, focusing on the synthesis routes, chemical reactions, and corresponding catalysts. The synthesis of Vitamin E, including preparation of 2, 3, 5-trimethylhydroquinone (TMHQ), preparation of isophytol, and condensation of TMHQ and isophytol are discussed in detail. The disadvantages and issues related to the preparation methods are also included. In general, the preparation of TMHQ comprises three steps: (1) methylation of m-cresol to 2, 3, 6-trimethylphenol, (2) oxidation of 2, 3, 6-trimethylphenol to 2, 3, 5-trimethylbenzoquione (TMBQ), and (3) hydrogenation of TMBQ to TMHQ. Recently, a novel and attractive method using isophorone, which can be produced by self-condensation of acetone, as a source for synthesizing TMHQ has been developed. Among these procedures, it is important to attain high selectivity in the oxidative reactions, including oxidation of 2, 3, 6-trimethylphenol and isophorone (α-isophorone or β-isophorone), and to replace H2O2, a common oxidant, by oxygen or air. One of the methods of preparation of isophytol using citral as a source has been abandoned because of shortage of oil of litsea cubeba, which is a natural source of citral. Linalool, produced from 6-methyl-5-hepten-2-one, is a key intermediate in the main process of preparation of isophytol. Both BASF SE and Roche have developed effective methods for the preparation of 6-methyl-5-hepten-2-one, respectively. Semi-hydrogenation of alkynols plays a key role in the whole process. The selectivity, especially at high conversion is directly related to the profit; therefore, it is of great importance for industries. The condensation of TMHQ and isophytol is essentially a Friedel-Crafts alkylation reaction catalyzed by acids. Similar reactions include methylation of m-cresol. Bronsted acids are usually effective for these reactions; however, it is difficult to recover these catalysts from the homogeneous systems. Therefore solid acid has a great potential in this area and it is also a promising topic to reduce the loss of acid sites when using acid-immobilized catalysts. The supply of various sources of the reactants and the local policy need to be considered while choosing an appropriate method for the preparation of Vitamin E.

Key words: Vitamin E, Tocopherol, 2, 3, 5-trimethylhydroquinone, Isophytol, Catalyst