Homogeneously catalyzed formaldehyde condensation to carbohydrates II. Instabilities and Cannizzaro effects

Abstract Cannizzaro reaction of formaldehyde proceeds in alkaline medium in conjunction with the “formose” condensation reaction to produce aldoses and ketoses. The ratio of the two reactions is a function of the catalyst used. In studies with Ca(OH) 2 catalyst at conversion levels below 4%, HCHO disappearance rate by Cannizzaro is triple that by formose condensation. Near 50% conversion, which is where the stoichiometry of the Cannizzaro reaction requires that its absolute rate pass through a maximum, HCHO disappearance by Cannizzaro is only 5% of that by formose. Reaction instabilities occur both at low and high Ca(OH) 2 concentration levels at fixed HCHO feed rate in a continuous stirred tank reactor (CSTR). As catalyst concentration is increased, reaction pH drops from 12 to 10.5 in the range of 0 to 100% HCHO conversion. Inordinate levels of Ca(OH) 2 catalyst (2 moles/mole HCHO) quench both the formose and Cannizzaro reactions—an unexpected result. The ratio of branched chain carbohydrate products, such as hydroxymethylglyceraldehyde and apiose, or straight chain species such as erythrose and arabinose, can be controlled by manipulation of operating conditions; the branched species are so subject to reduction by cross-Cannizzaro reaction with HCHO that species such as hydroxy-methylglycerol are made in large quantities by HCHO condensation in the presence of NaOH.