G~LCHRJST AND PVRVES GLYCE~OL GLUCOSIDE. 2735 CCCLXXV.-Glycerol Glumaide. By HELEN SIMPSON GILCHXIST and CLIFFORD BURROTJGH PURVES. FEW condensation reactions between reducing sugars and poly-hydric compounds of simple type have been studied possibly owing to the difKculty of producing such compounds and of purifying them when formed. As in the case of glucose and glycerol con-densation leads to a type of compound which may be regarded as analogous to a carbohydrate fat and is of physiological interest, we have taken up the investigation of this subject. Glycerol glucoside which was originally described by Fischer (Ber. 1894 27 2483) has now been obtained on the large scal 2736 GILCHRIST AND PURVES GLYCEROL GLUCOSIDE. by an improved process. The older method involving &s it does the saturation of a glycerol solution of glucose with hydrogen chloride is tedious but the same compound is more readily obtained by limiting the acid concentration to 0.25% and heating a t 100".The product in each case is a syrup possessing the properties of a glucoside but no information bearing on the composition or struc-ture of the compound has hitherto been available and it was unknown to which type the glucose residue belongs or to which part of the glycerol molecule it is attached. These questions have been solved by methylation which yielded hexametAyZ glycerol glucoside as a colourless volatile liquid b. p. 190-192"/12 mm. Hydrolysis thereafter yielded 2 3 5 6-tetramethyl glucose FIG. 1. 3 Gram8 of glucose dis8olved in 80 C.C.of ylycsrol. 3 6 9 12 15 18 21 Time in h~ur8. together with a dimethyl glycerol which was shown to be ap-di-methoxy-y- hydroxypropane. From these results the constitution of the parent glucoside is established to be : CH,( OH)*CH( OH )*CH=CH(OH)*CH( OH)*CH*O*CH,*CH( OH)*CH,*OH. The compound as prepared is a mixture of a- and p-forms and the optical values determined on hydrolysing the methylated derivatives show that glycerol y-glucosides were present only in small amount the limits in different preparations being 1-95 and 0.93%. The research was accordingly extended by varying the conditions of condensation the changes in rotation which take place when glucose is dissolved in glycerol containing hydrogen chloride being utilised to study the reaction.The concentration of -0 GILCHRIST AND PERVES GLYCEROL GLUCOSIDE. 2737 the sugar in no case exceeded 6% by weight of the glycerol employed and solutions containing more than 3% by weight of the acid were not examined. These limitations were found to be necessary as, when exceeded the high viscosity or the depth of colour resulting made polarimetric observations uncertain. For the same reason the experiments were carried out a t room temperature. In Fig. 1 the rotations observed for the condensation of glucose with glycerol are plotted against time. An unexpected feature, which comes to light is that the minjmum rotation does not appear F I ~ . 2. Solutions contain 80 C.C. of glycerol and 1.5 g r a m of hydrogen chloride. +13-3' 0 i - - s 8 8 -26.7' i3 -5234 to depend on the amount of hydrogen chIoride present.The reaction prociuct in each case was the glycerol glucoside described above as shown by the identical behaviour on methylation and subsequent hydrolysis. It was also found that on long standing the optical activity of an acid solution of glucose in glycerol reverts approximately to its original value apparently owing to the con-densation being reversed as a result of secondary reactions between the solvent and the acid. The slow speed of the condensation led to the investigation being extended to cases where glucose and fructose were dissolved in acid glycerol with the view of ascertaining if under these conditions the two sugars combined in whole or in VOL. CXXVII. 4 2738 GILCHRIST AND PriRVES GLYCEROL GLUCOSIDE.pad. In this connexion it was necessary to perform a series of control experiments with solutions in glycerol of fructose alone. In A (Fig. 2) the specific rotation of fructose dissolved in glycerol containing 1.5% of anhydrous hydrogen chloride is plotten against time; the behaviour of glucose under the same conditions is shown in B (Fig. l) while in C the ordinates are the algebraic mean of the corresponding ordinates in A and B. The latter curve predicts the behaviour of solutions containing both glucose and fructose, assuming that the sugars do not react with each other and the actual experimental observations are summarised in D. The values obtained tend to be more lsvorotatory than the calculated values and this was general for all concentrations of the acid reagent employed.Eventually it was found that this discrepancy was due -to the varying quantities of water formed by the condensation of the sugars with the solvent and to the effect this produced in the optical activity of fructose solutions. E records the observations made on a solution of fructose in glycerol which had not been rendered anhydrous whilst in the experiment represented by F the amount of water has been reduced by restricting the total concentration of sugars present in the solution to 3%. The close agreement of F with C indicates that under the experimental conditions outlined the behaviour of glucose is not affected by the presence of fructose. This conclusion was supported by the results obtained from an estimation of the reducing power of the above systems.For concentrations of the sugars up to 374 by weight the percentage loss in reducing power was found to be independent of the concentration. It therefore follows that in a solution containing both sugars condensation of one sugar with the other will cause the total reducing power of the mixture to be less than the sum of the reducing powers of the individual sugars. Xo such diminution was recorded although the degree of accuracy was such that condensation even to the extent of 5% would have been readily detected. Taking the combined results into con-sideration it is unlikely that glucose or fructose can combine in hydroxylic solvents or that reactions involving the condensation of glucose and glycerol play a part in natural processes.As already indicated it has proved necessary for the purposes of the resea;rch to ascertain which isomeric form of dimethyl glycerol is produced when hexamethyl glycerol glucoside is hydrolysed and it became evident that the complete series of methylated glycerols &odd be standardbed in view of future work in natural glycerides. The processes developed in this laboratory for determining the constitution of carbohydrates are equally applicable to the struc-problems of the natural fats including the mixed glycerides QILCHRIST AND PURVES GLYCEaoL GLUC0SI.DE. 2739 Methyhtion of partly hydrolyd fats followed by hydrolysis should give pa,rtly methylatel glycerols the constitution of which would lead directly to that of the parent compound.As a-methyl glycerol has already been fully described (J. 1915,107,337) this compound has not been re-examined but we have prepamid ap-dimethyl glycerol by the action of d u m methoxide on ally1 alcohol dibromide and determined the constaats of the pure liquid. In order further to characterise the compound it has been used as a solvent in which the specific rotation of active solutes wits determined. As an additional method of identifying the ether if was converted into y-benzoyl-ap-dimethyl glycerol and ap-dimethyl glycerol malate of which the constants were determined. Attempts to prepare ay-dimethyl glycerol led to a confusing result. Accordmg to Smith (2. physikd. Chem. 1918 92 717) the prod;ct of the action of hydrochloric acid on epichlorohydrin contains nothing but the pure ay-compound.The ay-dichlorohydrin prepared by this method gave however on treatment with sodium methoxide, a dimethyl glycerol which in all respects was identical with the ap-dimethyl glycerol described above. The identity was apparent’, not only in the ethers but also in the benzoates and malates pre-pared from them. Advantage was taken of the fact referred to above that liquid isomerides may frequently be distinguished by the effect they produce on the rotation of active compounds dis-solved in them. In this respect also no distinction could be made between the compounds. Cornparison of Dimethyl Glycerols. n of [a]? of B. p. n,. benzoate. mslate. afl-Dimethyl glycerol . .. 69-5-70-5”/15 mm. 1.4219 1-5075 - 10.48” Presumed ay-dimethyl glycerol ...............70.5-71-5”/18 mm. 1-4219 1.5075 - 10.60 Solvent. Solute. IaIIl. ab-Dimethyl glycerol Ethyl tartrate + 11-22O ay- 9 9 s 9 9 Y ? + 11.19 4- 9 9 ?7 Nicotine - 152.94 ay- 29 1 s $7 - 153.44 Comparison of the above data leaves no doubt that the com-pounds are identical and not isomeric. It has not yet been ascer-tained whether in this instance the action of sodium methoxide causes migration of the methyl groups but the following result suggests that Smith’s ay-dichlorohydrin is interchangeable with the a@-isomeride. It was expected that p-monomethyl glycerol could be obtained from ay-dichlorohydrin which when subjected t o methylation by the silver oxide reaction yielded a monomethyl dichlorohydrin. In such it compound the halogen atoms would 4 Y 2740 GILCHRIST AND PURVES GLYCEROL GLUCOSIDE.presumably occupy the ay-positions but on heating with an aqueous alcoholic solution of potassium acetate followed by hydrolysis of the acetyl groups the a-monomethyl glycerol described by W e and Macdonald (Zoc. cit.) was obtained. The result is comparable with that recorded by Fischer (Ber. 1920 53 1625) who starting from y-iodo-ap-distearyl glycerol replaced halogen successively by acetyl and hydroxyl and obtained not ap-distearyl glycerol, but the ay-isomeride. Trimethyl glycerol was prepared by the cont-hued action of methyl sulphate in alkaline solution on glycerol at 70". The product formed a constant-boiling mixture with water which distilled a t 92" whilst the distillate formed a homogeneous system with ether.The pure compound was a mobile liquid b. p. 148'1 765.4 mm. n = 1.4069. Ethyl tartrate dissolved in trimethyl glycerol gave [a] = + 5-99'. E X P E R I M E s T A L. Prepamtion of Glycerol G1ucoside.-A 5% solution of 20 g. of glucose in anhydrous glycerol containing 0.25% of dry hydrogen chloride was heated in a sealed tube at 100" until it no longer reduced Fehling's solution. The product isolated on the lines described by Fischer (loc. cit.) was a thick syrup containing barium chloride and glycerol. The glucoside was extracted with absolute alcohol and purified by precipitation with ether but this effected only partial separation of the impurities and the composition was determined through the methylated derivative.Methykction of Glycerol G1ucoside.-Only one typical experiment need be described. The syrup (16 g.) was methylated by the gradual addition of 72 g. of methyl sulphate and 55 g. of sodium hydroxide in 40% solution. The unchanged glycerol was thus converted into trimethyl glycerol which volatilised during the final heating to 100". The product (11 g.) was remethylated twice by means of the silver oxide reaction; the refractive index was then constant and on distillation a clear colourless mobile liquid was obtained b. p. 190-192"/12 mm. n = 14497 (Found C, 53-1 ; H 8.9. Hexamethyl glycerol glucoside CI5H3O8 requires C,%53.25; H 8.9%). With this compound as with many other derivatives of glycerol analysis by the ordinary combustion process gave variable results.The r' wet " process of Simonis and Thies (Chem. Ztg. 1912,97 917) gave however satisfactory values for carbon. Hydrolysis of Hexamethyl Glycerol GZuco.side.-A 7 ?$ solution of the glucoside in 8% aqueous hydrochloric acid was hydrolysed by heating a t 100" for 45 minutes the course of the reaction bein GILCHRIST AND PWVES GLYCEROL GLUCOSIDE. 2741 followed polarimetrically. After neutralisation with barium c a r h a t e the product waa extracted with chloroform and on distillation of the solvent crystalline tetramethyl glucose was obtained (yield 65%). After one recrystallisation from light petroleum the melting point mas 88" and a mixed melting point with tetramethyl glucose showed no depression. Evaporation of the light petroleum mother-liquors gave a solid the optical values of which were determined.In one preparation [a]D = + 75-65'. These results show that the corresponding glycerol y-glucosides may be present to an extent varying between 0.93 and 1095%. In order to isolate the methylafed. glycerol formed during hydrolysis, the aqueous layer was concentrated by distillation through an efficient column. The concentrated solution was extracted with ether and on evaporation of the solvent gave a/3-dimethyl glycerol as a colourless mobile liquid showing the correct physical constants for this compound. Pohrimetric Examination of the Condensartion of Glucose tdth Glycerol.-The glycerol used was redistilled under diminished pressure and the k e l y powdered glucose kept for some days in an evacuated desiccator over sulphuric acid.The sugar (3 g.) was dissolved in glycerol by heating at 90" for 2 hours the solution when cold showing a specific rotation of 52.3" and a reducing power equivalent to the glucose it contained. Dry hydrogen chloride was drawn into the solution until the necessary increase of weight was obtained (8-10 minutes) and a further 15-20 minutes elapsed before the turbidity of the liquid had decreased sufficiently to make possible even a rough determination of its optical rotation. The following typical results are recorded the complete figures being embodied in the curves shown in the introduction. Observed rotations 2 = 1 t = 15". Cone. of gIucose 3%. HC1 1%. HCI 1.576. Hcl 1-63?;. HCI 2:/0. HCI 2.53%. HCI 3%. - A +- e b - A H r s . a .Hm. a. Hrs. a. Hrs. Q. H~s. a. - . a . 0 1-95' 0 1-95' 0 1-95' 0 1-95" 0 1.95' 0 1.95" 1 1.7 1.5 1.7 2.25 1.35 2.5 1.2 2 1.15 1 1.1-1.4 2 1.6 2.5 1-3 3 1.3 3-75 0.95 2.5 1 1.75 0.8 10 1.3 4 1.2 4 1.15 5 0.8 4 0.8 3 0.6 26.5 1.0 5.5 1.0 9 0.9 6 0-8 5-5 0.7 4 0.7 48 0.75 7.5 0-8 20 0.55 7-5 0.7 20 0.6 7-5 0.7 10 0.7 9.8 0.7 29 0-7 9 0.7 23 0.6 33-5 0-5 44 1.0 23 0.65 73.5 0-8 53 1.1 114 1.1 260 1.8 400 1-8 The reversion of the rotation to practically the initial value is clearly evident in the experiments with 2% and 2.53% H a while the minimurn specific rotation in all cases is about 15" 2742 Gn;CfFB;fST AND PURVES GLYCEROL GLUCOSIDE. Condensation of G l w e math Glycerd in presence of Fructose.-The optical behaviour of solutions containing glucose and fructose in acid glycerol was studied by methods similar to those described in detail in the case of glucose alone.Solutions containing equal weights of both sugars dissolved in anhydrous glycerol possessed initially a specific rotation of - 21" to - 22" the corresponding value for the ketose alone being from - 96" to - 97". Dry hydrogen chloride was then introduced as already described until the acid concentration wm 1.5%. C.C. of Fehling's solution. 10.3 G. of 3% glucose solution reduced ............ 10.3 G. , fructose solution reduced ......... Sum of final reducing powers ........................ 10.6 G. of 3% glucose-3% fructose solution reduced ................................................ 10.15 G. of 1.5% glucose solution reduced ......10.15 G. , fructose solution reduced ...... Sum of final reducing powers ........................ 10.3 G. of 1.5% g l u c o ~ e - l - 5 ~ ~ fructose solutioii reduced ................................................ Initially. After 23 hours. 60 21.5 60 1.5 23 120 22.6 30 10.2 30 0-5 10.7 60 10.3 Observed Rotations I = 1 t = 15". In each case the sugars were dissolved in 100 g . or 80 C.C. of glycerol. S o . 1. Fructose 3?/, HCI 1.3;;. Hours 0 1.25 2 3.25 5.5 8.5 19 23 a - 3-6O - 1.25" - 1.20 - 1.3" - 1.50 - 1.70 - 2.20 - 2.40 [a] -96" -33.3" -32" -34.7" -40" -45.3" -58.To -64" Xo. 2. Fructose 1-50//, HC1 l-59;//,. Hours 0 2.5 3-25 4 5.5 10 21 a - 1.8' - 0.7"f - 0.65" - 0.650 - 0.70 - 0.850 - 1-10 [a] -96" -37.3"? -34.7' -34.j" -37.3" -45.3" -58.7" No.3. Glucose 3:/, fructoss 3?& HC1 1G./,. Hours 0 1 2 3 4 6 8 22-5 a - 1.6" +ve. - 0.20 - 0.4" - 0.50 - 1-40 - 1.50 - 2.40 [a] -21.3" +ve. - 2.7" - 5-3" - 6.7" -18.7" -20" -32" No. 4. Glucose 1.50;/, fructose 1.5" HC1 1.5"/. Hours 0 2 3-75 3-5 4.3 6 10 21-5 a - 0.8" + 0.2" + 0.1" + 0.05' 0.0" - 0.25" -0*453 -0.85" [a] -21.3" + 5.3" + 2-6" + 1.3" 0.0" - 6.5" -12" -22.7' No. 5. Fructose 376 HC1 1*5:& moisture. Hours 0 0.5 0.76 1-0 1.5 2 3 5 a - 3-6" - 1.0" - 1.0" - 1.0" - 0.8" - 1-10 - 1.45 - 1.6" [a] -96" -26.7" -26.7" -26.7" -21.3" -20.3' -27.33 -42.7 Hours 9 23 a - 2.20 - 3.00 [a] -58.7" -80-0" Blackening GILCHRIST AND PURVES GLYCEROL GLUCOSIDE. 2743 up-DamethyZ GZyceroZ.-z~-Dibromohydrin was prepared by Michael and Norton's method (Amer.Chern. J. 1880 2 18) 20 g. of ally1 alcohol giving 51.4 g. of product b. p. 110-112"/15 mm. To this were added 11 g. of sodium dissolved in methyl alcohol. Sodium bromide was immediately deposited. The reaction pro-ceeded slowly initially but afterwards suddenly became very rapid the methyl alcohol boiling vigorously. (It is possible to control the reaction if the solutions are dilute and the mixture is kept initially in ice-cold water for several hours. Completion of the reaction is ensured by heating for a considerable time as other-wise it is extremely di6cult to remove the last traces of bromine.) After neutralbation with carbon dioxide the dimethyl glycerol was extracted with ether and distilled as a clear colourless liquid, Dimethyl glycerol C5H1203 requires [R& 30.10 (Found C, 49-4; H 9.8.C5Hl2O3 requires C 50-0; H 10.0%). of ethyl tartrate and nicotine in up-dimethyl glycerol as solvent = + 11.22' (c = 13.37) and - 152.94" (c = 13-46) respectively. y- Benzoyl ap-Dimeihyl Glycerol.-The benzoate was prepared by the standard method. Dimethyl glycerol (3.6 g. ; 1 mol.) was acted on by 7.5 g. of benzoyl chloride (1.67 mols.) and 2.9 g. of sodium hydrosde (2.5 mols.) in 10% solution at + 5' to - 5". The product isolated by extraction with ether was a fairly mobile oil, b. p. 162"/12 mm. nD 1-5075 (Found benzoic acid 50.0. Benzoyl dimethyl glycerol C1,HI6O4 requires benzoic acid 54.5%). ap-Dimethyl Glycerol M&te.-Malic acid (4 g.; 0.6 g. in excess of 1 mol.) was esterified with 6 g.of dimethyl glycerol in presence of gaseous hydrogen chloride a t room temperature. The product was poured into a large quantity of water neutralised with barium carbonate filtered and the filtrate extracted with ether for several hours. The ethereal solution was dried the solvent evaporated, and the residue distilled (yield 5.6 g.). The ester b. p. 2OOo/0-5 mm., is a viscous oil insoluble in water or alcohol but readily dissolved by chloroform. Attempted Preparation of cry-Dimethyl G1ymroZ.-ay-Dichloro-hy& wit8 obtained in the manner described by Smith (Zoc. cit.), b. p. 175-5-176"/733 mm. nD = 1.4827 whilst the treatment with sodium methoxide was carried out as in the case of the ap-isomeride. The identity of the product with afi-dimethyl glycerol is referred to in the introduction.p-.MonometAyl uy-Dic~ohydrin.-uy-Dichlorohydrin (1 1.3 g. ; 1 mol.) wit8 dissolved in 56.8 g. of methyl iodide (4 mols.) and methyhted in the usual m w e r by the addition of 46-4 g. of silver oxide (2 mols.). The reaction which was spontaneous was b. p. 69*5-70.5"/15 mm. nD 1.4219 &? = 1.016 [R& 30.02. [u]:' in chloroform = - 10-60" (c = 9.05) 2744 GILCHRBT AND PURVES GLYCEROL GLUCOSIDE. continued by warming on a water-bath under a reflux condenser for 8 hours an additional 10 C.C. of methyl iodide being added when the mixture became pasty. Ether was used as the extracting agent. The product was a clear colourless liquid (11 g.) b. p. 58"/14 mm. nD 1.4560 (Found Cl 49.7. Monomethyl dichloro-hydrin C,H80C1, requires C1 49065%).Attempted Prepradion of p-Nonomethyl Glycerol.-p-Monomethyl ay-dichlorohydrin (18-3 g. ; 1 mol.) was heated in 36 C.C. of an aqueous alcoholic solution of 29 g. of potassium acetate (2 mols. and 15% excess) in a sealed tube a t 120-140" for 12 hours. The potassium chloride that separated was removed the filtrate evapor-ated to dryness and the residue extracted with ether. On distil-lation of the ether monomethyl glycerol diacetate remained. This was hydrolysed by boiling with barium hydroxide solution for an hour neutralising with carbon dioxide and taking to dryness. The monomethyl glycerol was extracted with chloroform and dis-tilled. The product undissolved by ether was also extracted with chloroform and yielded a further quantity of monomethyl glycerol which had been produced by hydrolysis during the heating process.The monomethyl glycerol obtained was the a- and not the p-, form; b. p. 110-112"/11 mm. nD 1.4462 (Found C 45.2; H 9.4. C,H,,-,O requires C 45.3; H 904%). Trimethyl Glycerol.-The methyl sulphate reaction was the most satisfactory in the case of glycerol and one typical preparation is described. To 20 g. of glycerol (1 mol.) were added drop by drop, 186 C.C. of methyl sulphate (4.5 mols.) and 186-7 g. of sodium hydroxide in 40% solution. At first the usual method of procedure was adopted the methylating reagents being allowed to react with the glycerol at 60-70" the excess of methyl sulphate being destroyed by heating to 100". Under these conditions however the yield of methylated glycerol was very small.Afterwards the reaction was carried out in a flask provided with a mercury seal and attached to a condenser ; trimethyl glycerol and water then formed a volatile mixture which boiled vigorously during the final heating a t 100". The following process was therefore adopted After destruction of the excess of methyl sulphate the mixture was heated in a brine bath; a mixture of water and trimethyl glycerol distilled steadily at 92". This was saturated with sodium chloride and extracted with ether. On drying the ethereal solution with calcium chloride a large aqueous layer separated showing that ether water and trimethyl glycerol form a homogeneous system. The ethereal layer was separated from the calcium chloride solution dried over solid caustic soda and finally over sodium wire.This treatment has the added advantage of eliminating traces of partly substitute NOTES. 2745 glycerols. Pure trimethyl glycerd was thus obtained as a mobile, refractive liquid b. p. 148"/765.4 mm. ng* 1.4069 dt?* 0.9401, [R& 35.06. Trimethyl glycerol C,H,,O, requires [R& 34-84 (Found C 53.3 ; H 10-2. C,H,,O requires C 53.7 ; H 10.45%). Great dif€iculty was experienced in the analysis of the methylated glycerols and although many variations of the usual combustion process have been employed the results obtained are not yet entirely satisfactory. The figures are however sufliciently close to the calculated values to show that each of the compounds possesses the composition ascribed to it. Determination of the methoxyl content by Zeisel's method leads as has already been pointed out in the case of the a-monomethyl ether (Irvine and Macdonald Zoc. cit.) to the formation of isopropyl iodide in varying amount and therefore cannot be regarded as an accurat'e analytical factor. For purposes of comparison the rotatory power of ethyl tartrate in trimethyl glycerol was ascertained. [a] = 5-99 (c = 13-36). The authors desire to acknowledge their indebtedness to the Food Investigation Board and to the Carnegie Trust for the facilities provided during the foregoing research. They also take this opportunityof expressing their gratitude to Principal Sir James C. Irvine C.B.E. F.R.S. for the invaluable help which he has given. THE UNKERSITY ST. ASDREWS. [Receired October Sth 1925.