44 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS THE CHEMISTRY OF ACETOGLYCERIDES AND THEIR USES IN COSMETICS H. G. NEWMAN* INTRODUCTION ACETOGLYCERmES HAVE been the subject of much research and investigation during recent years, and are currently attracting considerable attention. They are relatively inexpensive compounds, readily available in commercial quantities and they combine a number of remarkable features which are of undoubted value in the formulation of a wide variety of products. The potentialities of acetoglycerides ,are indeed great, and since their original introduction they have found particular application in cosmetics formulation. Their use has facilitated the production of many improved cosmetic and toilet preparations, and the properties outlined below will give some indication of their scope in this particular field. Extensive studies have been conducted and published'-' on the general properties, formulation, etc., of the acetoglyceride compounds and it is felt that a useful purpose will be served by summarising those physical characteristics which make the greatest contribution to their effectiveness in cosmetics manufacture. Included in the summary which follows is much information (hitherto unpublished) obtained as a result of investiga- tions carried out in the ABRAC laboratories. CHEMICAL AND PHYSICAL PROPERTIES The term "acetoglyceride" covers a vast number of substances which are obtained by the substitution, by acetate groups, of one or more of the fatty acid groups occurring in triglycerides. Any triglyceride can be converted to either a mono-acetate or a di-acetate, and the changes in chemical structure are illustrated by the following example of the conversion of glycerol tri-stearate. Glycerol Glycerol Glycerol a-mono-acetate a/•-di-acetate tri-stearate di-stearate monostearate CH•OOC.C,,Ha• CH•OOC.C,,H• CH•OOC.C,,H.•, CH.OOC.C,,H,G CH.OOC.Cx,Ha, CH.OOC.CH.• CH,OOC.C,,Ha• CH,OOC.CHa CH,OOC.CH• The acetoglycerides offered commercially are substantially mixtures of mono- and di-acetates, but variations in manufacturing techniques, plus * A. Boake, Roberts & Co. Ltd.

CHEMISTRY OF ACETOGLYCERIDES AND THEIR USES IN COSMETICS 45 the wide choice of raw materials, make possible the production of an almost infinite number of different compounds--each possessing the same desirable properties, but in varying degrees of intensity. For the sake of simplicity, only the • form of the mono-acetate and the • form of the di-acetate have been illustrated abSve. It will be appreciated that the • form of the mono-acetate and the •' form of the di-acetate are also possible, and by the normal methods of preparation, mixtures of these are formed. As each component of the blend can exist in more than one crystalline form, it is quite obvious that a great deal of research has been necessary in order to assess the many grades and to arrive at methods of standardising the composition of those selected for specific uses. As a result of this investigation, a limited number of grades have been judged pre-eminently suitable for cosmetic and pharmaceutical applications and these have formed the basis of a more comprehensive study. The properties of these selected grades are given in the following table. (The product names employed are those given to the standardised grades manufactured by A. Boake, Roberts & Co. Ltd.) Aceto- Softening t Specific Iodine Saponifica- Acid glyceride point gravity value tion values øC. (max) value (max) ..... S/C 30 ø to 32 ø 0.925-0-935•60 ø C. 2.0 330-345 1.0 S/C/1 43-5 ø to 45.5 ø 0.918-0.928•60 ø C. 2-0 325-340 1-0 S/C/4' 42ø•to 44 ø 0.930-0.940•60 ø C. 4.0 290-305 6.0 L/C --9 ø to --5 ø C.967-0.977•25 ø C. 10-22 390-405 0.8 (cloud point) * S/C/4 is a self-emulsifying grade. t Softening points have been determined by the A S.T.M. Ring and Ball method. $ The number of milligrams of potassium hydroxide required to neutralise one gram of sample. RHEOLOGICAL CHARACTERISTICS The rheological characteristics of the acetoglycerides are probably the most important of the various properties which have led to the use of these materials in cosmetic formulations. Certain blends of acetoglycerides with oils and waxes exhibit unusual rheological properties, in that they retain their initial texture and plasticity over a wide temperature range. Under warm conditions, such blends remain firm and do not readily deform whilst at low temperatures, they do not become unduly brittle. This can be explained by a micro-crystalline structure of the various constituents, and presumably by changes in their natural solubility under various conditions of temperature. It appears that a type of thixotropic gel is formed.