III International Conference

PP-I-47growth stages (2) and (3) – condensation of lower carbohydrates with each other andformaldehyde. The confluent branching of the reaction takes place on stage (1) – two newactive species capable of continuation of the chain elongation are formed from one of thereaction products.Thus, the formose reaction is a unique example of the process with its mechanism whichis analogous to the chain mechanism with confluent branching but does not involve freeradicals.We have thoroughly investigated the kinetics and products of the formose reaction in thepresence of various initiators. The kinetics and products of stage (3) for the condensation oflower carbohydrates – glycolaldehyde, glyceraldehyde and dihydroxyacetone, with each otherwas investigated as well. It turned out that the most of the carbohydrates present in the finalcomposition of the formose products can be formed in the course of condensation of lowercarbohydrates with each other. The rates of the condensation of lower carbohydrates arerelatively high; e.g., the typical time of the 90 % conversion of 5 mM glycolaldehyde withitself is about 1 min. If the reaction time is prolonged, higher monosaccharides formed fromglycolaldehyde are breaking up into lower carbohydrates and glycolaldehyde is formed again.Finally the detailed model of the formose reaction based on the condensation of the lowercarbohydrates and formaldehyde was created. The computer program assigned for themodeling of the kinetics of the formose reaction was developed. This program was adaptedfor the solution of the reverse kinetic problem – to compute the kinetic rate constants of someindividual stages of the process basing on the experimental data. Thus few apparent rateconstants for several condensation reactions were determined. Besides, it was shown that aring-chain rearrangement of higher carbohydrates which stabilize them to prevent their furthertransformations may play an important role in the formose mechanism. Thus theserearrangements have to be taken into account and their exclusion from the overall kineticmodel of the formose reaction leads to the incorrect results.The financial support of RFBR (Grant No. 05-03-32862), program of the Presidium ofRAS «Origin and evolution of biosphere», grant RNP.2.1.1.1969 and «Scientific schools ofRussia» (Grant No.N.Sh. 6526.2006.3) is gratefully acknowledged.References1. Khomenko, T.I., Sakharov, M.M., Golovina O.A. // Usp. Khim. 69. 1079–1105. 1980 (in Russian).2. Breslow R. // Tetrahedron Letters. C.22-26. 1959.3. de Bruijn J.M., Kieboom A.P.G. and van Bekkum H. // J. Carbohydrate Chemistry. 5 (4). 19864. Simonov A.N., Pestunova O.P., Matvienko L.G., Parmon V.N. // Kin.Cat., No.2, 2007. In press.(in Russian).94