SOLUBILITIES CT FATTX ACIDS IX Ffi»SD
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SOLUBILITIES CT FATTX ACIDS IX f f i » S D OROAMIC SQLVKWT8 AT 209 W r B ITW M DISSERTATION Pr«i«at«d In Partial Polflllatnt of tho Rofolromato Per the Degree Doctor of Philosophy in the Gtradaate Seheel of the Ohio State University By- Dor la KolLhe B.So • 0 M»Se* It The Ohio State Baieerelty 1953 Approved hyt ACEHOVLEDGMEHT To Dr* J, B» Brown go my sincerest thank# for his helpful counsel and his constant smile of encouragement* 1 also wish to thank Dr* M* S. Bowman, who kindly consented to act as my co-adviser. I am grateful to the University for the fellowship which for the past three years has been granted to me from funds allocated by the Research Foundation for fundamental research* 11 A 16487 TABLE OP CONTENTS Fag* I* STATEMENT CEF PROBIEM 1 XI • HISTORICAL 2 A. Review of Methods for Separating Fatty AcI da and Their Compound* 2 B. Development of the Low Temperature Crystallization Technique 19 C. Review of Previous Work on Fatty A d d Solubilities 23 III. EXPERIMENTAL 38 A. Plan of Investigation 36 B. Preparation of Fatty Aolds 1^2 C. Analyses Used for Criteria of Purity 59 D. Purification of Solvents 62 E. Procedure for Measuring Solubilities 62 IV. SOLUBILITY DATA ?0 V. DISCUSSION 85 VI. SUGGESTIONS FOR FUTURE WORK 100 SUMMARY 101 BIBLIOGRAPHY 101*. 111 INDEX TO TABLES P*g» 1. Fatty Aold Solubilities as Complied by Brown In 1941 29 2. Solubilities of the Saturated Acids 31 3* Solubilities of the Unsaturated Acids 32 4* Solubility Ratios of Fatty Acids Under Various Conditions 33 5» Typical Data of Singleton 34 6* Solubilities of Hoerr and Harwood for Oleic Acid 36 7. Solubilities of Hoerr and Harwood for Llnolele Aold 37 8* Fractional Distillation of the Methyl Eaters of OU ts Oil kS 9* Fractional Distillation of the Methyl Esters from Rapeseed Oil 52 10* Analytical Constants of the Fatty Acids 61 11. Sample Data Showing Change of Solubility with Time 69 12* Solubility Data on Fatty Acids In Various Solvents 71 13. Fatty Acid Solubilities In Various Hydro carbon Solvents % 14. Comparison of Solubilities with Data Previously Reported by Other Investigators 97 iv XVXXSX TO ILLtJSTRATIOKS Page 1 , Low Temperature Crystallisation Apparatus J+7 2 * Preparation of Methyl Oleate by Crystallization of the C^0 Methyl Esters of Olive Oil lj.8 3 * Preparation of Methyl Erucate by Crystallization of the C2 2 Methyl Esters of Rapeseed Oil 53 l\.m Preparation of Methyl Eleosenoate by Crystal* 11sation of the Con Methyl Esters of Rapeseed Oil 55 5* Crystallisation of Hormel Llnoleie Aold 58 6 . Constant Low Temperature Apparatus 6l(. 7* Apparatus for Removing Samples of Saturated Solution 6? 8. Solubility of Fatty Acids in Methanol 7l|. 9. Solubility of Fatty Aelds in Ethyl Aoetate 75 1 0 * Solubility of Fatty Acids In n*Heptane 76 11* Solubility of Fatty Aelds in Acetone 77 1 2 * Solubility of Fatty Aelds in Diethyl Ether 76 13* Solubility of Fatty Acids in Toluene 79 lit* Solubility of Stearle Aold In Various Solvents 80 15* Solubility of Olele Acid in Various Solvents 61 1 6 . Solubility of Llnoleie Acid in Various Solvents 82 I* STATEMENT OF PROBLEM In 1937 there appeared the first papers of a series by Brown and coworkers (l, 2) dealing with the technique of fractional crystallization at low temperatures as a means for separating fatty acid mixtures* These Investi gators worked with dilute solutions of fatty acids in organic solvents and within the range of temperatures obtainable with dry ice. Low temperature crystallization has since found wide application as a means for separating and purifying fatty acids, particularly the unsaturated acids. It may well be considered one of the most useful yet simplest tools at the disposal of the fat chemist. The utility of the method has been somewhat limited, however, by the fact that so little information is avail able relating to the solubility behavior of the fatty acids at such low temperatures. It has been the purpose of this investigation to carry out an extended study of the solubilities of a number of highly purified fatty acids in various organic solvents at low temperatures. This endeavor has first necessitated the preparation of the fatty acids themselves, since materials of the degree of purity required for such a study are not commercially available. Solubility measurements have then been taken with the aid of an 2 apparatus designed to maintain constant temperatures down to -7f>° C. It is hoped that these data will not only Till one of the very obvious gaps in our knowledge of the physical behavior of the fatty acids but will also serve as a guide for more advantageous utilization of the method of low temperature crystallization* II. HISTORICAL A. Review of Methods for Separating Fatty Acids and Their Compounds* The separation of the various component fatty acids occurring in a natural fat or oil is one of the most im portant problems in fat chemistry* The process is usually a difficult one* especially if the separation must be carried out at all quantitatively* The mixed fatty acids from a given source often Include some acids of widely different chemical properties as well as others which have almost identical chemical characteristics and differ only slightly in their physical behavior* There are a number of methods available for resolv ing fatty acid mixtures* The methods include both chemical and physical means of separation* and they vary in degree of efficiency* convenience* and applicability to a given separation problem* Usually a combination of several methods comprises the best procedure* particularly if the . 3 mixture Is at all complex* The techniques which are available can be roughly divided into processes Involving (l) distillation, (2) adsorption and extraction, and (3 ) methods dependent upon solubility. 1 . Distillation Procedures. As applied to the separation of fatty acids and their derivatives there are three distinct distillation techniques, each useful in performing a particular type of separation* These are the methods of steam distillation, vacuum distillation, and molecular distillation. Steam distillation is used to separate the fatty acids of such materials as milk fats, containing acids such as butyric and caproic, which volatilize readily with steam* The method may serve as a means for partial separation of the shorter chain from the longer chain acids; however, in order to obtain any kind of efficient separation it is necessary to employ some type of frac tionating column. The history of vacuum distillation, with respect to fats, dates back to the work of Chevreul (3 ) during the early part of the nineteenth century* A review of the extensive work that has appeared on the subject since that time, and particularly within recent years, is quite beyond the scope of this paper* Since there are numerous texts (I4-, 5 , 6 ) dealing with both theoretical and practical aspects of fractional distillation under vacuum, the technique need be discussed only briefly here* In general the distillation unit consists of the following essential parts: (l) a boiler or still pot equipped with a source of heat, (2 ) a fractionating column, including packing and Insulation, (3) a still head, equipped with a condenser and a device for reflux control, (4.) a fraction cutter of some sort, with a set of receiving vessels, and (5) a means for producing and controlling the vacuum in the system* Much Ingenuity has been exercised In designing modifications of these various parts. Probably the most attention has been directed toward the column Itself and the development of various types of packing materials. These have Included various types of rings, tubes, Jack chains, and BB shot, straight and bent carding teeth, Vigreux Indentations, wire and glass helices, spiral coils, crimped wire, and the conical type of wire gauze packing developed by Stedman* Industrial columns are usually of the bubble-cap type, while a modified spinning band column, with minimum pressure drop, has been used in the laboratory by Murray (7 ) with excellent results. Distillation was first applied to fat materials by direct distillation of the oils themselves, then later by attempted fractionation of their mixed fatty acids.. Some investigators were able to distill certain glycerides, but they had little success in achieving fractionation by this method. This Is not surprising in view of the present picture of the heterogeneous nature of the glycerides comprising natural fats and oils. Work with the free acids was largely unsuccessful because of their tendency to decompose on prolonged heating. In addition, since the acids tend to associate even in the vapor phase, such separations as were obtained were poor. The use of methyl ester distillation was first reported In 1906 (8 ). This method permitted distillation at lower temperatures and largely eliminated the dangers of association and decomposition. Ester distillation has since been used In the investigation of a vast number of fatty substances, and, although other esters have some times been used, the methyl esters are the ones most commonly employed. Fractional ester distillation, carried out under vacuum with an efficient column, Is probably the best technique available for separating fatty acids according to chain length. Ordinarily, however, there Is little or no separation of saturated from unsaturated components accomplished by distillation. For this reason ester distillation is generally used in conjunction with some other means of separation when more complete resolution 6 • • Is desired. Molecular distillation differs from ordinary vacuum distillation In that the system must be much more highly evacuated (ca. 0 .0 0 1 mm.) and the distillation path ex tremely short, with only 1 -2 cm. distance between evapora tion surface and condensation surface* By using this method It is possible to distill many normally non- di3tillable substances.