Moisture induced solid phase degradation of l-ascorbic acid part 3, structural characterisation of the degradation...

The influence of moisture on the solid phase degradation of l-ascorbic acid and the chemical characteristics of the degradation products have been investigated previously [Shephard et al. (1998) (in press)]. Moisture induced degradation in the solid phase leads to severe discolouration. This paper describes the isolation of the compounds responsible for the discolouration and their partial chemical identification. Eight different degradation compounds were found to be present in a severely discoloured sample [Shepherd et al. (1998) (in press)]. Three of the compounds were present at levels above 1% of the total chromatography peak area with the major degradation peak present at 29% in a sample with 5% v/w moisture present when stored at 60 degrees C for 42 days. The major impurity was isolated and was found to exhibit a lambda(max) at 280 nm with further absorbance to 600 nm. This material was pyrolysed at 300, 500, and 600 degrees C. Amongst the volatile pyrolysates tentatively identified were furfural, 2-furancarboxylic acid, 1-(2-furanyl)-ethanone, tetrahydrofuran and 1-(2-furanyl)-1-propanone along with some aromatic compounds such as benzene and phenol. The periodate consumption of the major impurity was examined and the products of the reaction investigated. Estimation of hydroxyl and carbonyl group content by acetyl group determination of the acetate and reduced acetate showed that for every five repeating units there was one hydroxyl group and for every four repeating units there was one carbonyl group. Elemental analysis gave 46.26% carbon, 5.42% hydrogen and 48.32% oxygen giving an empirical formula of CH(2)O.