Migration of an acyl group in glycerol derivatives: I. Migration of the acyl group in monoglycerides in acid medium

For a number of pairs of isomeric α‐ and β‐monoglycerides with a carboxylic acid as component acid it is shown that these isomers mutually rearrange in ethanolic hydrogen chloride. At 25° the equilibrium mixture invariably contains about 88% of α‐ and consequently about 12% of β‐monoglyceride. From measurements of the migration rate of β‐monobenzoylglycerol in the said medium at 25° it appeared that the migration reaction shows kinetics of the first order and that the migration rate is directly proportional to the concentration of the catalyst. Addition of small quantities of water to the medium retards the migration reaction to a very great extent. The determination of α‐monoglyceride in mixtures of α‐ and β‐monoglyceride was effected by periodic‐acid oxidation, as described previously. The migration rate constant of a number of β‐monoglycerides was determined under identical experimental conditions. The nature of the acyl group has great influence on the migration rate, but not ‐ see above – on the position of the equilibrium. The mechanism of this intramolecular rearrangement of the monoglycerides is discussed and used for an explanation of the facts observed. Monoglycerides with a sulphonic acid as component acid do not show any tendency towards rearrangement under the same experimental conditions.