Study On The Chlorination Of Sucrose-6-acetate

Sucralose(referred to TGS)is the best non-nutritious sweetener to date.It has been widely used for its performance of high sweetness,good stability,no heat,non-absorption by the human body and so on.The chlorination of sucrose-6-acetate is a key step in the synthesis of sucralose by means of the single-group protection strategy,which affects the final yield and quality of sucralose.The chlorination has a complex mechanism,a lot of by-products,low purity of reactants and products,low yield.Therefore,the study of the chlorination process is of great significance to promote the development of sucralose industry.Here,the chlorination of sucrose-6-acetate to produce sucralose-6-acetate was studied and the conclusions were as follows:(1)The purification and characterization of sucrose-6-acetate and sucralose-6-acetate.The results showed that the solid sucrose-6-acetate could be obtained from the crude product after twice crystallization by 1:1(v/v)acetic acid/methanol as the crystallization solvent,and its purity increased from 82.1%to 96.5%,the isolated yield was 60.7%.The mixture(sucralose-6-acetate 51.3%)from the chlorination of sucrose-6-acetate,was extracted with ethyl acetate,followed by crystallization in ethyl acetate and water,respectively.The purity of sucralose-6-acetate could reach 99.6%,the isolated yield was 71.4%.Both of the above substances were characterized by MS,IR and NMR,and the results were in agreement with the reported data.(2)The chlorination process of sucrose-6-acetate was investigated and optimized by the single-factor test,and the optimum process condition was obtained.Under nitrogen protection,DMF as solvent andl,1,2-trichloroethane as cosolvent,6.5 mL DMF and 8.5 mL 1,1,2-trichloroethane was used per gram of sucrose-6-acetate,and the ratio of n(SOCl2)to n(sucrose-6-acetate)was 9:1.Small amount of powdered activated carbon was also added.After the material dropped,by raising the temperature of three stages,the final reaction was at 112 ? for 1 h.After the end of reaction,DMF and trichloroethane was removed firstly,then the residue was dissolved in methanol/ethyl acetate(volume ratio 1:2).After that,the mixture was neutralized to pH=7 with the ammonia solution.The yield of sucralose-6-acetate was up to 52.4%in these conditions.(3)The designedd experiment was carried out to explore the exhaust gas composition,byproducts generation and related questions of the chlorination.As the chlorinated reagent Vilsmeier reagent was synthesized by SOCl2,it was found that the escaping gas not only contained HCl and SO2,but a small amount of H2S and CO.The absorption of the escaping gas is up to 94.6%through five stages absorption.And the reaction kinetics of formation of dichloro ester was studied experimentally,and it was found that the chlorination was the fisrt-order reaction and the activation energy was 82.16 kJ/mol.In addition,it was confirmed that DMF could be decomposed into dimethylamine hydrochloride and formic acid under high temperature and acidic condition,which was one of reasons for the loss of the solvent DMF,and the high temperature favored the decomposition of DMF,and the max,imum was up to 0.44%.