Chemical Synthesis of ascorbyl palmitate in [BMIM]BF 4. Junmin Ji

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1 Advanced Materials Research Online: ISSN: , Vols , pp doi:10.28/ Trans Tech Publications, Switzerland Chemical Synthesis of ascorbyl palmitate in [BMIM]BF 4 Junmin Ji School of Food Science and Engineering,Henan University of Technology, 1 Songshan South Road,52 Zhengzhou,Henan Province,Peoples Republic of China jjm77@haut.edu.cn Keywords: Esterification Palmitic acid L-ascorbic acid Ionic liquid Ascorbyl palmitate Abstract. Scorbyl palmitate is a safty and highly efficient lipophilic antioxidant.it is produced by a novel ionic liquid method: L-ascorbic acid was esterified with palmitic acid to synthesize ascorbyl palmitate,using concentrated sulfuric acid as chemical catalyst in 1-Butyl-3-methy limidazolium terafluoroborate ([BMIM]BF 4 ).The yield of ascorbyl palmitate reached 69.6±1%. Introduction L-ascorbic acid is a component of antioxudants,and possesses excellent antioxidant properities.but the use of L-ascorbic acid in lipophilic media has been limited because of its low solubility.modification of L-ascorbic acid is an effective way of solving this problem. Ascorbyl palmitate is lipophilic derivatives of L-ascorbic acid. According to previous reports,there are two synthesis routes for ascorbyl palmitate preparation: chemical synthesis and enzymatic synthesis.the chemical synthesis was the direct esterification and transesterification of L-ascorbic acid with palmitic acid (or palmitic acid methyl ester) in organic solvents, using concentrated sulfuric acid (or hydrogen fluoride) as chemical catalyst.it was an energy intensive process and results in the formation of a mixture of products with a preponderance of o-6 substitation.enzymatic synathesis was the direct esterification or transesterification of L-ascorbic acid with palmitic acid (or palmitic acid methyl ester) in organic solvents,using lipase as biocatalyst.the enzymatic method was characterized by mild reaction conditions and high regioselectivity, but it had low yields,low time efficiency.ascorbyl palmitate is produced industrially by chemical synthesis today. To prepare high-purity ascorbyl palmitate,a novel route reported in the paper,namely, esterification of L-ascorbic acid and palmitic acid catalyzed by concentrated sulfuric acid in 1-Butyl-3-methy limidazolium terafluoroborate([bmim]bf 4 ). Materials and methods Materials. L-ascorbic acid (purity approximatively 99.9%) and palmitic acid (purity opproximatively 99%) were purchased from Luoyang Haohua Chemical reagent Co.,Itd (Luoyang,China).1-Butyl-3-methy limidazolium terafluoroborate([bmim]bf 4 ) was obtained from Shanghai Chengjie Chemical Reagent Co.Ltd(Shanghai,China).All other regents were of analytical grade. Esterified of L-ascorbic acid and palmitic acid catalyzed by concentrated sulfuric acid in [BMIM]BF mg of [BMIM]BF 4 were added to a solution of 6mmol(1059mg) of L-ascorbic acid, 5mmol (molar ratio=1.2:1) of the acyl donor (palmitic acid or palmitic acid methyl ester) in 20mL concentrated sulfuric acid (98.3%).The reaction was performed 2mL round-bottom flasks on a magnetic stirring reactor at for 24h,and 0rpm.These conditions were throughout the experiments except when otherwise stated in the text. Analysis. The production of ascorbyl palmitate was separated by normal pressure chromatography using a C18 column(3.9mm 1mm). Elution was achieved successively with methanol aqueous solution (adjust to ph 5.5 by 0.01% phosphoric acid) at 0.8mL/min.The eluate was monitored at 2nm using a ultraviolet spectrum detector. Componedts in the sample would be conducted by HPLC detection, It almost had no impurity peaks. It illustrated that the product was relatively fineness. Further compared with ascorbic acid in All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-06/03/16,17:55:57)

2 Advanced Materials Research Vols the same conditions, it can be seen that the retention time of product and ascorbic acid was inconsistent, so we could eliminated ascorbic acid interference with the product fineness. Purification of ascorbyl palmitate. At end of the reaction, remaining ascorbic acid was eliminated by water washing and joining ethyl acetate and ice water mixture, mixing quickly, then obtained white crystallization. The reaction media was filtered and constantly washing to neutral, The fractions containing the desired products were pooled,and concentrated to dryness under reduced pressure and low temperature. The crude products extractant using toluene and ascorbyl palmitate was isolated by recrystallization in mixed solvents (hexane and anhydrous alcohol). Results and discussion Comparison between the direct esterification and transesterification in [BMIM]BF 4 Using concentrated sulfuric acid catalyzed acylation of L-ascorbic acid was performed in the presence of palmitic acid(direct esterification) or methyl palmitate(transesterification),and these two reaction were operated in 1-Butyl-3-methy limidazolium terafluoroborate([bmim]bf 4 ).Four reactions led to only one product identified as 6-O-palmitoyl L-ascorbic acid by comparison with a commercial sample. yields of ascorbyl palmitate(%) a b c d Fig. 1 Effect of yields of ascorbyl palmitate in the direct esterification and transesterification of L- ascorbic acid with palmitic acid (or palmitic acid methyl ester) in [BMIM]BF 4,using concentrated sulfuric acid as chemical catalyst (a is direct esterification using concentrated sulfuric acid as chemical catalyst,b is transesterification using concentrated sulfuric acid as chemical catalyst,c is direct esterification using concentrated sulfuric acid as chemical catalyst in [BMIM]BF 4, d is transesterification using concentrated sulfuric acid as chemical catalyst in [BMIM]BF 4 ) Transesterification methods need synthesize palmitic acid methyl ester.this reaction process was complicated,and the separation process conditions was complicated,and yields of ascorbyl palmitate less than that of direct esterification while in the direct esterification there were many palmitic acid hadn t dissolved, even had been emulsified when the reactiong no using [BMIM]BF 4.Yields of ascorbyl palmitate in the direct esterification,was improved greatly, and palmitic acid could be well dissolved in [BMIM]BF 4. These results indicated that the polar mediun [BMIM]BF 4 can improve the ascorbyl palmitate Yield,which is attributed to the higher solubility of [BMIM]BF 4 for L-ascorbic acid.besides this performance, [BMIM]BF 4 also showed many advantage as reaction medium.replacing pressure solvent such as negligible volatile pressure and chemical and thermal stability.considering the environmentally benign processing technology and the glyceryl ferulate yield, [BMIM]BF 4 was the best choice for ascorbyl palmitate preparation. Effect of mass ratio of [BMIM]BF 4 to ascorbic acid Direct esterification of L-ascorbic acid with palmitic acid in [BMIM]BF 4, using concentrated sulfuric acid as chemical catalyst as a function of mass ratio of [BMIM]BF 4 to ascorbic acid was studied

3 1964 Application of Chemical Engineering at,for 24h.Esterification extent increased with increasing mass ratio of [BMIM]BF 4 to ascorbic acid with maximal conversion achieved with 3% mass of ascorbic acid,at mass ratios greater than 3%,a decrease in conversion was observed,possibly owing to substrate inhibition. y i e l d s o f a s c o r b y l p a l m i t a t e ( % ) mass ratio of [BMIM]BF 4 to ascorbic acid(%) Fig. 2 Effect of varying mass rotio of [BMIM]BF 4 to ascorbic acid on the direct esterification of L- ascorbic acid with palmitic acid in [BMIM]BF 4,using concentrated sulfuric acid as chemical catalyst at for 24h. Effect of temperature The reaction temperature has a profound effect on the direct esterification rates.in the present case, the initial reaction rates were found to increase directly with temperature with maximal rate obtained at. 80 y i e l d s o f a s c o r b y l p a l m i t a t e ( % ) temperature( ) Fig.3 Effect of temperature on the direct esterification of 6mmol L-ascorbic acid with 5mmol palmitic acid in 31.76mg [BMIM]BF 4,using 20mL concentrated sulfuric acid as chemical catalyst for 24h. Conclusions The novel Chemical synthesis of ascorbyl palmitate in [BMIM]BF 4 was established in the study with a higher yield(69.58±1%) of ascorbyl palmitate.replacing organic solvents with ionic liquids ([BMIM]BF 4 ) makes ascorbyl palmitate synthesis more efficient and greener.a continuation study is in progress,where the effects of various parameters on the direct esterification are being studied.

4 Advanced Materials Research Vols Acknowledgements This work was financially supported by the double production planning of edible vegetable oil of Henan Province. References [1] Humeau C,Girardin M,Rovel B,Miclo A. Effect of the thermodynamic water activity and the reaction medium hydrophobicity on the enzymatic synthesis of ascrobyl palmitate[j]. Journal of Biotechnology, 63:1-8(1998). [2] Youchun Y, Uwe T, Schmid. Lipase-catalyzed synthesis of vitamin C fatty acid esters[j]. Biotechnology Letters,21: (1999). [3] Lu hong TANG, Hao ZHANG.Selection of suitable reaction media and lipase: synthesize of lascorbyl palmitate catalyzed by lipase[j]. Journal of Wuxi University of Light Industry,19(2): (2000). (In Chinese) [4] Nickels,Helmut,et al.preparation fatty acid esters of ascorbic acid [P].US :45869(1987). [5] S.Bradoo,R.K.Saxena,R.Gupta.High yields of ascorbyl palmitate by thermostable lipase-mediated esterification.jaocs, 77(11): (1999). [6] Yinyu Gao,Zhanlan Lei, Herong XieStudy on Antioxidation Effect of Ascorbyl Palmitate[J]. Food Science, 28(11):-62(2007).(In Chinese)

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