STUDIES ON REACTIONS RELATING TO CARBOHYDRATES AND POLYSACCHARIDES: LII. THE PREPARATION, SEPARATION AND IDENTIFICATION OF THE ISOMERIC PROPYLIDENE, ISOBUTYLIDENE, t-AMYLIDENE AND DIBROMOETHYLIDENE GLYCEROLS AND THE GENERAL PROPERTIES OF GLYCEROL CYCLIC ACETALS

Abstract

The condensation of propionaldehyde, isobutyraldehyde, trimethylacetaldehyde and dibromoacetaldehyde with glycerol has been carried out in the presence of a catalyst (40% sulphuric acid) at 90 °C., and the resulting products have been shown to consist in each case of a mixture of the five- and six-membered cyclic acetals. The separation of these isomers from the acetal mixture was rendered possible by the difference in the physical properties of their benzoates. The structure of the latter was proved by saponification, methylation, hydrolysis and isolation of the resulting glycerol α- and glycerol β-methyl ethers respectively.With the isomers from dibromoacetaldehyde this method could not be used, owing to the labile character of the bromine atoms in presence of alkali. Their structures were proved by direct synthesis of the five-membered acetal benzoate from glycerol α-benzoate and dibromoacetaldehyde.The data obtained provide additional evidence of the marked influence exerted by the polar character of the aldehyde on the extent and character of acetal condensation. Increase in the electronegative character increases the amount formed of the five-membered acetal and decreases that of the six-membered. Trimethylacetaldehyde condensed readily with glycerol in absence of a catalyst. Lowering of temperature, in presence of the catalyst, favored the formation of the six-membered acetals, in agreement with the earlier work of van Roon. The results further confirm the Hibbert-Michael Ring Partition Principle.A general comparison is made of the physical properties of the ethylidene–, propylidene–, isobutylidene–, t–amylidene–, bromoethylidene–, and dibromoethylidene glycerol acetals.By substituting diphenylamine for aniline in the synthesis of trimethylacetaldehyde from trimethylpyruvic acid the yield is increased from 25 to 40%.