Investigation of dl-glyceraldehyde–dihydroxyacetone interconversion by FTIR spectroscopy

Interconversion of dihydroxyacetone and dl-glyceraldehyde was studied in different solvents and temperatures by FTIR spectroscopy. Dissolution in water or triethylamine, and increasing temperatures caused the dissociation of the dimeric forms of both compounds into monomers and subsequently inter-conversion of dihydroxyacetone and dl-glyceraldehyde. Dioxane, on the other hand, did not initiate such inter-conversions. FTIR analysis in different solvents has also indicated that monomeric dl-glyceraldehyde can exist in two distinct intramolecularly H-bonded forms. A five-membered ring form was predominant in aqueous solutions of the dissociated dl-glyceraldehyde dimer, whereas a six-membered ring form was preferred in triethylamine solution or in aqueous solution of dissociated dihydroxyacetone dimer. However, in aqueous solutions of dl-glyceraldehyde dimer, the five-membered ring conformation was slowly transformed into the six-membered ring form under slightly basic pH. In addition, dihydroxyacetone predominantly converted into the six-membered H-bonded conformation of glyceraldehyde when dissolved in water. This was attributed to the preferential formation of the trans- or E-enediol as an intermediate. Temperature-dependent spectra have also indicated that increasing the temperature favored the formation of glyceraldehyde in the aqueous equilibrium mixtures of dimeric dl-glyceraldehyde and dihydroxyacetone.