The Preparation and Properties of Purified Oleic Acid and some of its Salts

Abstract

NOTWITHSTANDING the large amount of work which has been done on the chemistry of oleic acid the published methods for preparing it leave much to be desired.The descriptions given of the compound itself inspire so little confidence that even the most recent edition of the Handbook of Lewkowitsch [1921] quotes melting points for oleic acid varying from 6.50 to 160, although Kirschner's conclusion [1912] that the acid is dimorphous, is accepted.Edmed [1898] by recrystallisation of Kahlbaum's oleic acid from alcohol obtained a sample of the acid which was stated to melt at 13-15°.Partington [1911] by crystallising another specimen obtained from Kahlbaum, and probably one of inferior grade, could not obtain a product melting higher than 6.50; Kirschner [1912] by following much the same procedure obtained samples of the acid which showed dimorphism and therefore two different melting points.The present authors originally hoped to devise an improved method for the estimation of oleic acid in mixtures such as are obtained by hydrolysis of natural fats and oils, but soon found that it would be necessary to study the question of preparing and characterising pure oleic acid almost ab initio.During the course of their studies, now extending over some years, the authors have been forced to retrace their steps many times, but they believe that they can now with advantage place some of their results on record and indicate with considerable confidence the probable margins of experimental error.Having tried nearly all the published devices for purifying oleic acid and numerous combinations and permutations of these and others, they have worked out a process by which oleic acid containing not more than 1 % of impurity can, with practice, be obtained with considerable certainty.Separation of salts of higher fatty acids by recrystallisation.The authors have latterly confined their experiments to the acids obtained by hydrolysis of olive oil, in which it is known that palmitic acid is the main saturated constituent.It is not intended to discuss this point in the present paper, but it may be stated that the authors have never detected the presence 'Repeated warming and cooling is sometimes necessary to obtainla granular material.m -OLEIC ACID.