Uses
Diethyl D(-)-tartrate is mainly used in chiral pharmaceuticals, chiral intermediates and chiral catalysts. It can be used with titanium in enolic asymmetric epoxidization. The compound d-alpha-tocopherol is the principal compound present in natural vitamin E sources. At present, d-alpha-tocopherol and other tocopherol derivatives are used in pharmaceuticals, foods and animal feeds. It is used as a food additive.
Synthesis
[Refining Procedure No. 1]: In a reactor equipped with a thermometer and a stirrer, 60.0 g of D-tartaric acid (containing 0.20% malic acid and 0.07% fumaric acid) and 36.0 g of ethanol were added, and stirred for 2 hr. at 10° C. The reaction was completed by filtration. After completion of the reaction, 48.1 g of D-tartaric acid was recovered by filtration. [Method 1]: [1st refining step] Dried D-tartaric acid was mixed with 28.8 g of ethanol, 1.9 g of 35% hydrochloric acid was added, and the reaction was carried out at 80°C. Subsequently, the same amount of ethanol and 35% hydrochloric acid was added again at 70 °C, and the reaction was concentrated. The moisture content was confirmed to be 0.1% by weight, and the first esterification reaction solution was obtained. [Method 2]: Ethanol was added to the first esterification reaction solution for stirring, and then 11.4 g of thionyl chloride was added, and the reaction was carried out at 30-40 °C. The reaction was concentrated after completion to obtain the second esterification reaction solution. [Method 3]: Sodium bicarbonate was added to the second esterification reaction solution, and the filtrate was filtered after the reaction to obtain the filtrate (diethyl D-tartrate, 97% yield). Finally, diethyl D-(-)-tartaric acid with an optical purity of 99.8% ee was isolated by film distillation (hot medium temperature 145 °C) under reduced pressure, with diethyl malate and diethyl fumarate contents of less than 0.01%. In addition, the contents of diethyl sulfite and monoethyl tartrate were less than 0.01% and 0.02%, respectively.
Purification Methods
Distil the esters under high vacuum and store them under vacuum or in an inert atmosphere in a desiccator in round bottomed flasks equiped with a vacuum stopcock. They have also been distilled by Kügelrohr distillation and/or by 'wiped-film' molecular distillation. They are slightly soluble in H2O but miscible with EtOH and Et2O. [Gao et al. J Am Chem Soc 109 5770 (5771) 1987, IR: Pristera Anal Chem 25 844 1953, Beilstein 3 III 1025 for D-(-), 3 IV 1232 for L(+).]
References
[1] Tetrahedron, 2007, vol. 63, # 27, p. 6346 - 6357
[2] Tetrahedron Asymmetry, 2011, vol. 22, # 3, p. 257 - 263
[3] RSC Advances, 2014, vol. 4, # 90, p. 48827 - 48835
[4] RSC Advances, 2013, vol. 3, # 43, p. 20298 - 20307
[5] Patent: CN104003883, 2016, B. Location in patent: Paragraph 0165-0170
