Dec., 1938
STABILITY OF AROMATIC AND ALIPHATIC 8-MONOGLYCERIDES
[CONTRIBUTIONN O . 370 FROM
THE
DEPARTMENT OF CHEMISTRY, UNIVERSITY
300.3
O F PITTSBURGH]
The Relative Stability of Aromatic and Aliphatic Monoglycerides BY B. F. DAUBERT AND C. G. KING Since the early investigations of Fischer' and associates, it has been evident that aliphatic Pmonoglycerides tend to rearrange to the corresponding a-isomers, but there has been very little information available concerning the factors that accelerate the change, or concerning the relative ease of migration of the acyl group in aromatic Pmono esters. Helferich and Sieber2>$ prepared the 8-monobenzoate of glycerol from a,a'-di-(triphenylmethyl)-P-benzoylglycerol by treatment with hydrogen bromide in glacial acetic acid, apparently with no evidence of migration. Bergmann and Carter4reported no shift of the P-monobenzoate, during treatment with anhydrous hydrogen chloride for drying. Hibbert and CarterJ6however, observed a rearrangement of the @-monobenzoate, p-p-bromobenzoate, and P-p-nitrobenzoate to the a-isomers in 0.025 N hydrochloric acid during hydrolysis of the benzylidene compounds in 50% alcoholic solution a t 80". Jackson and King6 observed a complete 8- to a-shift of the palmityl group a t temperatures as low as -30" when removing (hydrogen bromide in acetic acid) the triphenylmethyl group from the a-trityl ether of 1,2-dipalmitin. In agreement with Helferich and Sieber, however, no shift was observed when the ether group was hydrolyzed from analogous aromatic esters by the use of cold hydrogen bromide-acetic acid solution. Stimmel and King7 found that P-monopalmitin rearranged quantitatively to the a-isomer on standing for twentyfour hours a t room temperature in an alcoholic solutioii of 0.05 N hydrochloric acid or 0.1 N ammonium hydroxide. A number of important observations concerning changes in the molecular structure of 8-glycerides have been made by Verkade and associates* and by Fairbourne.g During the course of the present investigation, (1) (2) (3) (4)
Fischer, B e y . , 63 1621 (1920). Helferich and Sieber, 2. physio2. Chem., 170, 31 (1927). Helferich and Sieber, ibid., 116, 311 (1928). Bergmann and Carter, ibid., 191, 211 (1930). ( 5 ) Hibbert and Carter, THISJOURNAL, 61, 1601 (1929). (6) Jackson and King, ibid., 66, 678 (1933). (7) Stimmel and King, ibid., 66, 1724 (1934). (8)Verkade, Van der Lee and Meerburg, Rcc. Irau. chim., 66, 365, (i13, 716 (1937); Verkade and Van der Lee, PYOC. Roy. Soc. Amsteudarn, 31, 812 (1034). (!I) I'airhourne, J . Chcrn. .So
