Kinetic study of the mutarotation of D-glucose in concentrated aqueous solution by gas-liquid chromatography

Growth is the most important step of industrial seeded crystallisation. The overall laws that govern alpha -D-glucose monohydrate crystal growth shoul d depend upon mutarotation. This parameter could become a limiting Factor, as it is the case for diffusion or the integration of molecules at the surf ace of crystal. Consequently, it was considered essential to obtain additio nal information on mutarotation kinetics, under temperature and concentrati on conditions close to solution saturation. Composition of D-glucose concen trated solutions was studied, using GC procedure after trimethylsilylation in pyridine. This is commonly used to obtain directly the anomeric composit ion of alpha and beta -D-glucopyranose in solution. Moreover, minor compone nts, such as D-glucofuranose, can be evidenced. GC has one main and obvious advantage over polarimetric measurement as it can be applied to turbid sol utions, which is the case for concentrated syrups. Admitting that mutarotat ion is a first order kinetics reaction, it was found that concentration has no significant effect on the rate constant for mutarotation, whereas incre asing temperature enhanced the mutarotation rate of D-glucose solution. Res ults show that the proportion of the alpha -anomer at equilibrium increases slightly with both saturation and temperature, whatever the anomer (alpha or beta) in the original solution. These results agree with previous studie s by Kraus and Nyvlt, who have established kinetic parameters of mutarotati on at higher temperatures. (C) 2001 Elsevier Science Ltd. All rights reserv ed.