Ruka Nakashima

Formose reactions: IX. Selective formation of branched sugar alcohols in a modified formose reaction and factors affecting the selectivity☆

Abstract In the course of kinetic studies of the calcium hydroxide-catalyzed formose reaction, which usually gives a complex mixture of sugar products, a selective formose reaction was found to occur giving three kinds of branched sugar alcohols, 2-C-hydroxymethyl glycerol, 2,4-C-dihydroxymethyl pentitol, and most probably a diasteremeric mixture of 3-C-hydroxymethyl pentitol, when the major part of the dissolved calcium ions were removed as sparingly soluble salts or chelate complexes at the end of the induction period. Oxalic and phosphoric acids were found to be effective for removing the dissolved calcium ion as well as a chelating agent such as ethylenediamine-tetraacetic acid (EDTA). Various factors affecting this selective formose reaction were investigated. The addition of Mg(OH) 2 , Fe(OH) 3 , and FeO gave the same selectivity, while the addition of Pb 2 O(OH) 2 resulted in a different type of selectivity. Other factors, such as the reaction pH and the time of adding the acid, were also found to be important for the selective reaction.

Formose reactions: VIII. Solvent effects in the formose reaction

Effects of aqueous and nonaqueous alcoholic solvents and polar aprotic solvents on the CaO-catalyzed formose reaction were examined. The reaction occurs only in hydroxylic solvents. In alcohol-water solvent systems, the induction period of the reaction was found to correlate with their Z values and with the concentration of dissolved calcium ion. The formose reaction in 90 and 100% methanol was analyzed in some detail, suggesting that the formation of a formaldehyde hemiacetal was essential for the formose reaction in nonaqueous alcoholic solvents and that competitions among the Cannizzaro, sugar formation, and sugar decomposition reactions are important factors affecting the sugar yield.

The Selective Formose Reaction in Dimethylformamide in the Presence of Vitamin B1

Abstract The formose which was obtained from formaldehyde in the presence of base was a mixture of sugars and sugar alcohols containing over 30 components. The formose reaction has drawn much attention for 122 years from several standpoints; the chemical synthesis of edible carbohydrates from C1 compounds, an important process in the recycling of carbon sources during sustained space flights, and as a model for the prebiotic synthesis of monosaccharides. Nevertheless, because of the complexity of this product mixture (Fig. 1b), the formose reaction has not been completely elucidated and the product (so called formose) has not been useful yet. During the long formose history few products were isolated from the formose mixture and identified, except in work from our laboratories.

Formose reactions: XVI. Some factors affecting the selective formation of 2,4-di-C-(hydroxymethyl)-3-pentulose

Abstract The formose reaction catalyzed by BaCl 2 ue5f8-KOH in methanol was found to give 2,4-di-C-(hydroxymethyl)-3-pentulose (2,4-DH-3-P) with high selectivity. The yield of 2,4-DH-3-P increased with a decrease in the amount of barium ion, however, at less than 0.001 M of barium ion, the formose reaction was no longer allowed to proceed. The rate of the formaldehyde consumption decreased with a decrease in the pH of the reaction mixture. The yield of 2,4-DH-3-P was largely dependent on pH. 2,4-DH-3-P was obtained in higher yield by adjusting the initial pH ∗ of the reaction mixture to 12.0–13.0 than that obtained by the continuous adjustment of the pH ∗ to 13.0 during the reaction. The conversion rate of 2,4-DH-3-P into 2,4-di-C-(hydroxymethyl)-pentitol (2,4-DHP) was much slower in methanol than that in aqueous media and decreased with decreases in the pH of the reaction mixture and the formaldehyde concentration. A conventional mechanism for the formation of this branched ketose (2,4-DH-3-P) was suggested, which involved a cumulative aldol condensation of formaldehyde.