Investigations on the formose reaction with partial formaldehyde conversion: A chance for the production of synthetic carbohydrates

The formose reaction currently seems to be the only possible system for the production of synthetic carbohydrates in one step. This reaction has been intensively investigated during the 1960s, 70s and 80s without a significant progress in production of edible carbohydrates due to very high complexity of the reaction and product toxicity. It seems that complexity and toxicity can be avoided by conducting formose reaction only under partial conversion of HCHO. However, only few investigations addressed exactly this issue showing very limited information. Thus, in the present work it was the aim to explore this subject taking the influence of some qualitative parameters (degree of conversion, introduction of catalyst) into account. The selective production of partially edible C3-carbohydrates was of particular interest. Under the present conditions, no selectivity regarding straight-chain lower molecular weight monosaccharides was observed. Surprisingly, this result was not in agreement with the reported data. Decreasing the degree of HCHO conversion and lowering reaction temperature might enhance the selectivity in C3-carbohydrates. Concerning problems in analyzing formose carbohydrates, the extent of the cross-Cannizzaro reaction that leads to branched-chain polyols, may be estimated based on stoichiometric considerations as presented in this work. One strategy of the present work was also to follow the preferable production of C6- carbohydrates (glucose) on the basis of older published data at an elevated temperature of 98°C. Although many trials under different conditions (at this temperature) were conducted, a production of glucose with high selectivity was not achieved. Simultaneously, the investigations showed clearly that the preferable (selective) synthesis of individual compounds may occur only under very specific reaction conditions. Further investigations with regard to the synthesis of partially edible lower molecular weight carbohydrates are necessary, since the situation still is not clarified.