Abstract
In the previous papers, the influences of water contents on the stability of vitamin A acetate and its related compounds in aqueous ethanolic solutions were reported. Similar investigations were carried out on vitamin A aldehyde and the results are described in this paper. Vitamin A aldehyde solutions in absolute ethanol or aqueous ethanol with various water contents were stored at various temperatures. When the remaining rates were estimated by a spectrophotometric method, vitamin A aldehyde in 60〜90% aqueous ethanolic solutions was found to be more stable than vitamin A alcohol solution in the corresponding solutions. The observed transformation patterns of vitamin A aldehyde were the isomerization of all-trans into 13-cis and the others including decomposition. By applying the method using nuclear magnetic resonance (NMR), all-trans vitamin A aldehyde in solutions was confirmed to be isomerized into 13-cds isomer until it reached the equilibrium of all-trans and 13-cis (1 : 0.4). When the stored vitamin A aldehyde solutions were subjected to a thin-layer chromatography, those in 60〜90% aqueous ethanol gave five spots including the two due to all-trans and 13-cis isomers while that in absolute ethanol gave the spots and an additional one (R_F 0.74). The chemical structure of the R_F 0.74 substance was investigated after purifying by a silica gel column chromatography and then it was assigned to have an acetal structure (1) from the results of NMR, UV and mass spectra. Other minor products have not been investigated.
