Modification Of β-cyclodextrin With Dimethyl Carbonate

The modification of β-CD by green reagent dimethyl carbonate under normalpressure, high pressure and microwave irradiation conditions was systematicallystudied, using anhydrous potassium carbonate as alkaline catalyst and N,N-dimethylformamide as reaction medium. Different kinds of β-CD derivatives wereprepared and the effects of various factors on the reactions were investigated. Theproducts were purified through preparative HPLC, and characterized by means of IR,ESI-MS,1H NMR and13C NMR. The results were as follow:(1) The modificationforms were related to reaction temperature and pressure. When the reactions wereoperated either in the temperature range of50oC to85oC at normal pressure or in therange of60oC to90oC under microwave irradiation, methyl carbonates of β-CD withlow degree of substitution equal to1.38~3.17and1.53~2.49were obtainedrespectively, and6-mono-methoxycarbonyl-β-CD was separated with a pleasant yieldof60.91%. The methylation and methoxycarbonylation of β-CD occurredsimultaneously in the range of90oC to140oC. At the temperature range from160oCto170oC, and the pressure of approximately1.40MPa, randomly methylated β-CDwith the substitution degree range of6.97to11.49were generated with yields of80%~85%.(2) Compared with the normal pressure reactions, when equal amount ofβ-CD was methoxycarbonylated, microwave-assisted reactions could save up to50times of energy and even more, and reaction time could also be shorten by dozens oftimes.(3) Through process optimization, for normal pressure reactions, the optimallevels of reaction temperature, material ratio of dimethyl carbonate to β-CD, reactiontime, dosage of solvent and catalyst turned out to be85oC,42,10h,80mL and1.0grespectively, corresponding to10g of β-CD; with regard to high pressure reactions at160oC, the results revealed that when material ratio of dimethyl carbonate to β-CD,reaction time, dosage of catalyst and solvent were optimized to be126,6h,1.0g and160mL respectively corresponding to48mL of dimethyl carbonate, the conversionrate of β-CD was96.70%, and randomly methylated β-CD derivatives with thesubstitution degree of11.49were obtained; for microwave-assisted reactions, theoptimal material ratio of dimethyl carbonate to β-CD, reaction temperature, reactiontime, dosage of catalyst, power of microwave, rotating speed and amount of solvent proved to be21,90oC,21min,0.6g,400W,600r·min-1and90mL, respectively,corresponding to15g of β-CD, under which conditions the conversion rate of β-CDwas up to95.01%, and the substitution degree of the product was2.49.The processes presented in this paper were novel and environmentally friendly,which involved facile reaction conditions, pleasant high yields and simple operationas well.