摘要:

The Conjigwation of Naturally Occurring Mixed Glycerides. Part I. 7. The Con$guration of Naturally Occurring Mixed Glycerides. Part I. The Cm$guration of Oleodistearin from Various Natural Sources. By M. L. MEARA. The melting and transition points of oleodistearin isolated from six seed fats of which it is a prominent constituent have been determined. They are identical in each instance with those of p-oleodistearin and dif€erent from those of the unsymmetrical a-oleodistearin (the corresponding constants for the synthesised a-and fl-oleodistearins have recently been determined by Daubert Fricke and Longenecker J. Amer. Chem. SOL, 1943 65 2142 2144; 1944 66,289 690). THE component glycerides of a large number of animal and vegetable fats have now been determined for the most part by Hilditch and his co-workers but there has been little definitive work to determine the posi- tional configuration of these glycerides mainly owing to the difficulty in isolating individual glycerides in a sufficient state of purity and until comparatively recently the properties of synthetic mixed glycerides needful for reference purposes were not sufficiently characterised.The properties of the saturated sym-metrical and unsymmetrical mixed glycerides have now been described by Malkin and his collaborators (J. 1939 103 577 1141 1518) and the corresponding unsaturated glycerides are now being synthesised and studied by Daubert Longenecker et aE. (Eoc. cit.). From the available data it is therefore now possible to specify the configuration of a number of individual naturally occurring glycerides provided they be isolated in a state of sufficient purity.The configuration of oleodistearin which was amongst the first of the natural mixed glycerides to be isolated forms the subject of the first paper'of this series. The reported m. p.'s of the majority of specimens of oleodistearin isolated from natural products lie between 42" and 44" some authors reporting a transition point at 28-30'. An early synthesis of P-oleodistearin (Kreis and Hafner Ber. 1903 36 276) by heating aa'-distearin with oleic acid under reduced pressure gave a low yield of oleodistearin melting after crystallisation at 42" and after fusion at 28-30". A specimen isolated from cacao butter melted in similar circumstances at 4A45O and 27-28" and from this these authors concluded that the substance isolated was the unsymmetrical isomer.Later knowledge of the component glycerides of cacao butter indicates that their material consisted of the symmetrical isomer contaminated with small amounts of fully saturated glycerides. Griin (Ber. 1907 M 1778) from oleic anhydride and aa'-di- stearin obtained a product which melted at 42"; after one year however it melted at 41" and 55O and when cooled and reheated at 42". Amberger and Bromig (Biochem. Z. 1922 130 257) prepared a-oleodistearin of m. p. 42* but were unable to prepare the symmetrical isomer.. Hilditch and Saletore (J. SOC.Ckem. Ind. 1933 52 101~),from the reaction between oleyl chloride and aa'-distearin obtained a product which on oxidation gave what appeared to be a mixture of azelao-glycerides as judged from the m.p.'s of the fractions obtained by crystallisation the main fraction melting at 62-5-63.5'. Oxidation of oleodistearin from AEZan-blackia Stuhlmannii gave a product of this m. p. which remained unchanged on admixture with some of the main fraction of synthetic material. Both symmetrical and unsymmetrical oleodistearin have now been synthesised by methods which have proved trustworthy in the synthesis of saturated mixed triglycerides of known composition oxalyl chloride being used in the preparation of oleyl chloride thus eliminating the use of thionyl chloride which gives oleyl chloride in low yields and doubtful purity (Daubert and Longenecker zoc. cit.). The saturated-unsaturated mixed triglycerides resemble the saturated mixed triglycerides in exhibiting the same type of polymorphism as that described by Malkin and his collaborators (Eoc.cit.) for the saturated mixed triglycerides. Each glyceride is capable of existing in four forms a vitreous form IV two intermediate forms 111 and 11 and the stable crystalline form I (in the American nomenclature) these forms corresponding to Malkin's vitreous a-,@'- and @-forms respectively. The transition points of the three metastable forms and the m. p. of the stable forms are well defined and can be determined with comparative ease. [19451 The Colzfiguration of Natzlrally Occwring Mixed Glycerides. Part II. 23 EXPERIMENTAL. Oleodistearin has been isolated in quantity from the following seed fats by fractional crystallisation from acetone Allanblackia Stuhlnurnnii (Hilditch and Saletore loc.cit.) Allanblackia fEoribunda and Allanblackia Pawiflora (Meara and Zaky,J. SOC.Chcm. Ind. 1940 59 25) Palaquium oblongifolium (Hilditch and Stainsby ibid. 1934 !S 197~).Garcinia Indica (Hilditch and Murti ibid. 1941 55 16) and Pentadesma butyracea (Hilditch and Saletore zb& 1931 50 468~). The oleodistearin from the above fats was recrystallised several times from pure redistilled B.G.S. acetone (15-25 ml. per g.) the flasks being well lagged with cotton wool and suspended in a room the temperature of which was main-tained as constant as possible. The deposited crystals were filtered off and dried in an desiccator for several days. The m. p.of the stable crystalline form was obtained in a capillary tube in the normal way. The form I11 transition point was obtained by allowing the molten mass to solidiry and redetermining the m. p. On keeping the specimen at this temperature for a short time it soliditied and on raising the temperature of the bath it remelted at form I1 trans-ition point. If this operation was carried out too slowly the m. p. of the stable form was obtained since form I1 had been converted into form I. The transition point of form I1 was checked by immersing the capillary tube with the specimen in form I11 into a beaker of water the temperature of which was adjusted so that the specimen just melted prolonged immersion causing it to change over again to form I. The transition point of form IV was obtained by immersing the capillary tube containing the molten specimen first in a freezing mixture and then in a beaker of water the temperature being adjusted and the process repeated until the substance gave rise to a definite change in appearance due either to expansion and filling up of the cracks caused by cooling or to melting followed by rapid re-solidification.Transition and melting points of different specimens of oleodistearin. IV. 111. 11. I. From Allanblackia floribunda ..................... 23 -23.5" 29.5" 37.0" 43-3-43-6" , .. ParvifZora ..................... 23 -24 291 -30 36.0 43-0-43.3 3P * , Stuhlmannii .................. 23 -24 29 -30 37-5 43-0-43.3 .. Garcinia Indica .............................. 23-5-24-5 29 -29.5 37.5 43-3-43.5 ..Pentadesma butyracea ........................ 23-5-24 29-3-29-6 37-0 43.5-4343 .. Palaquium oblongifolium .................. 32 -23 29 -29.5 37.5 43.0-43-6 Synthetic /3-oleodistearin * ........................ 22-3 29-8 37-3 7.6 41.6 , a-, * ........:... ............ ? ? ? 38.5 * Daubert et al. (locc. cit.). Discussion.-It is seen from the above data that the transition and melting points of all the specimens of oleodistearin examined lie very near to those given for synthetic P-oleodistearin and that of form I differs markedly from that recorded for a-oleodistearin. This taken in conjunction with the evidence available from oxidation of synthetic ang naturally occurring p-oleodistearin makes it conclusive that the oleodistearins so far examined occurring in the above seed fats consist entirely of symmetrical p-oleodistearin.Little can yet be said in regard to the seeming paradox that concurrently with a very pronounced tendency to elaborate glycerides of as mixed a character (i.e. containing as many different acyl groups) as possible the oleodistearin in this group of fats is restricted to one configurational fo'm only. It may be pointed out however that the proportion of oleic acid in all the fats under consideration (cf. table below) is of a similar order and that It is less than that of the saturated acids (of which stearic is the main component). Whether this feature is of any significance in determining the position taken by the oleic group in oleodistearin remains to be seen. Compownt acids of the fats studied (weight yo).Seed fat. Myristic. Palmitic. Stearic. Oleic. Linoleic. Allanblackia goribunda ........................... 0.2 3-2 56.8 . 39.4 0-4 .. paruiflora ........................... -3-5 52-7 43.8 - Stuhlmannii ........................ 3-1 52-6 44-1 0-2 I Garcinia Indica .................................... -2.5 56-4 39.4 1-7 Pentadesma butyracea -5-4 46-1 48-5 -.............................. Palaquium oblongifolium ........................ 0.2 5.9 54-0 39-9 - It is not practicable to define the configuration of the stearodiolein which accompanies oleodistearin in these fats until further refinements now under investigation can be added to the technique of separation of the lower-melting glycerides in a sufficient state of purity for thermal investigation. LIVERPOOL. [Received October 26th 1944.J THE UNIVERSITY

ISSN:0368-1769    

DOI:10.1039/JR9450000022

出版商:RSC    

年代:1945

数据来源: RSC