Solubilities of Vanillin. - Industrial & Engineering Chemistry (ACS


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INDUXTRIAL A N D ENGINEERING CHEMISTRY

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all these pigments are also to be regarded as colloidal, so that the pH value may influence them in a twofold manner.

CONCLUSIONS As an important deduction from all the foregoing, it is concluded that the mooted question of influence of cane and beet pigments upon the production of off-color granulated sugar resulting from various factory processes may be accurately investigated by separating the pigments and other colloids from typical samples of the sugar produced and then reasoning a posteriori to the initial stages of the factory procedure instead of depending solely upon a priori reasoning based upon the pigments present in cane and beet juices. Since, so far as the sugar itself is concerned, one is not interested in pigments which are either previously eliminated or do not contaminate the sugar crystals, some useless labor may thus be avoided and practical results arrived a t more quickly. A research of this character is now in progress and the results will be reported in the near future.

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Vol. 16, No. 12

It is helpful, in considering the effect of colloids on sugar manufacture, to keep in mind that this consists essentially in (1) influence on viscosity and surface tension of factory liquors and (2) influence on quality of sugar, although the direct manifestations may be many and varied-e. g., slow boiling, delayed crystallization, foaming, poor filtration, reduced sugar yield, off-colored sugar, etc. The results reported in the present paper are to be regarded as a preliminary testing of the tools of colloid research as applied to sugar manufacture. The writers plan to also test other criteria, as well as to extend the studies already indicated, and have confidence that the present status of colloid chemistry makes it possible to secure constructive data of practical importance to the sugar industry. I n addition to those already mentioned, the following studies are involved: determination of isoelectric point; influence of various cane and beet colloids on viscosity of sucrose solutions within certain limits of (a) sucrose concentration, ( b ) temperature, and (c) ratio of colloid t o sucrose; effects produced by varying degree of solvation of emulsoids.

Solubilities of Vanillin' By C. E. Mange and Otto Ehler MONSANTO CHEMICAL

WORKS, ST. LOUIS, Mo.

Solubility deb-minations of alcohol-water and glycerol-water solutube% one fitting inside of lions of vanillin by both synthetic and analytical methods are described the other, a thermometer, strictions have been and data are plotted. Solubilities in glycerol-water solutions are and a stirrer. The smaller Put on the use of also determined empirically and the results illustrated by curves. tube was Provided with a alcohol, manufacturers of flavors have redoubled the The formation of a precipitate of uanillin glyceride from concen2-hole stopper, through effort that they have been trated glycerol-vanillin solutions on standing is explained and which Were inserted the methods for its prevention as well as for the recovery of vanillin thermometer and the stirrer making in the Past to reduce -a thin glass rod, the lower the alcohol content of their after such formation are given. product. There has been end of which was formed into a loop bent at a right an urgent demand for tables showing the solubility of vanillin in alcohol solutions and also angle to the rod, large enough to encircle the thermometer in glycerol, which has been used to replace part or all of the and yet fit into the tube. By working the rod up and down alcohol. No data on the solubility of vanillin in dilute efficient agitation could be obtained. A weighed portion of vanillin was put into the smaller alcohol solutions are available. The tables published by De Groote2 in 1920 on the solubility of vanillin in different tube and 10 cc. of an alcohol-water solution of known concenconcentrations of glycerol a t various temperatures have been tration were added. The tube was gently warmed to effect subject to some criticism. The purpose of this paper is to solution, the thermometer and stirrer introduced, and the furnish data on the solubility of vanillin in alcohol and in tube cooled with vigorous agitation to cause a slight separaglycerol and to point out simple methods that can be used tion of very fine crystals from the solution. The tube was to determine under what extreme conditions a particular then placed into the larger one and very slowly warmed in a water bath with continuous agitation as before. The temflavor will remain clear. The vanillin used for the solubility determinations was a perature a t which the turbidity disappeared or a t which furcommercial product of the highest purity, conforming in all ther heating produced no change in the clarity of the solurespects to the requirements of the United States Pharmaco- tion was taken as the equilibrium temperature. The equilibrium temperatures were plotted against the peia. The alcohol solutions were made from pure ethyl alcoho1 (190 proof) according to the specific gravity tables of amounts of vanillin used for each concentration of alcohol, Gilpin, Drinkwater, and Squibb,3 and the glycerol solutions and from these curves graphs were constructed, from which the maximum amount of vanillin that will dissolve in a given from Glycerine U. S. P. according to G e r l a ~ h . ~ concentration of alcohol a t various temperatures can be readSOLUBILITY I N ALCOHOL-WATER SOLUTIONS ily obtained. (Fig. 1) For the solubility determinations a synthetic method was The actual proportions such as may be derived from the used which consisted of measuring the temperature at which curves in Fig. 1 are asfollows: a weighed amount of vanillin just dissolved in a measured ----TEMPERATURE OF SOLUTION-volume of solvent. The apparatus consisted of two test Alcohol in water 4 . 4 0 c. 15.6O C. 23 9 ' C .

S

INCE legislative re-

1 Presented before the Division of Industrial and Engineering Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 to 14, 1923. Received June 2, 1924. 2 "The American Perfumer," 1920, p. 372. * U.S.Depl. Agr., Bull. 66. 4 Van Nostrand's Chemical Annual, 1922.

Per cent 0 (water) 5 10 15 20 25

30

Grams/100 cc. Grams/100 cc. Grams/100 cc. 0.30 0.52 0.90 0.40 0.60 1.10 0.45 0.75 1 35 0.60 1.00 1.90 0.60 1.35 2.80 0.90 2 00 4.70 1.40 3.30

...

December, 1924

INDUSTRIAL A N D ENGINEERING CHEMISTRY

A number of points on the curve were confirmed by the following analytical method: An excess of vanillin was added to a known concentration of alcohol in a stoppered Erlenmeyer flask and shaken mechanically for 14 hours a t a constant temperature. The clear solution was drawn from

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50' C. the synthetic and analytical results checked fairly

closely, but at lower temperatures the solubility of vanillin differed considerably as determined by the two methods. Since neither the synthetic nor the analytical method is cairied out in a manner similar to the procedure a flavor manufacturer uses for his preparations, and since these methods gave different results, the solubility was determined in an empirical or proximate manner by making up series of tubes of various concentrations of vanillin in different concentrations of glycerol, warming'the solutions to dissolve the vanillin, and noting the stability. Water, 10, 20, 30, 50, and 70 per cent solutions of glycerol in water were used as solvents. A series of tubes containing varying quantities of vanillin was prepared for each con.centration, the amounts of vanillin being so chosen that a t the end of a month, a t which time it was assumed no further change would take place, some of the tubes would remain clear while those of higher vanillin concentration in the same series would have vanillin crystallized from them. One set of tubes was kept a t room temperature averaging about 26" C. but varying between 20" and 30' C., and the other was put into a cooler with a temperature averaging about 13" C., but varying between 9" and 17" C. The maximum solubility of vanillin in a given concentration of glycerol a t a given temperature was taken as the mean of the vanillin content of the last tube in the series, which remained clear, and the one of next higher concentration, which showed crystallization. After standing for a month, with occasional shaking, at the temperature indicated, each tube in the respective series which had remained clear was seeded with a few crystals of

FIG.~ ~ O L U B I L I T OF Y VANILLIN IN ALCOHOL-WATBR SOLUTIONS

the flask by means of a graduated pipet protected a t the tip by means of a wad of cotton to prevent crystals from being withdrawn with the solution. The vanillin was then extracted from the measured volume of solution with ether, the ether evaporated, and the vanillin weighed.

SOLUBILITY I N DILUTE GLYCEROL-WATER SOLUTIONS The same synthetic procedure that was used for the determination of the solubility of vanillin in alcohol solutions was carried out with glycerol solutions. Contrary to expectations and the belief that glycerol is a good solvent for vanillin, it was found that apparently not much more vanillin would dissolve in the glycerol solutions than was soluble in water. (Fig. 2) It was noted in the course of the experiments that because of the viscosity of glycerol the solutions supercooled considerably before crystals formed. This was especially true in the more concentrated solutions and a t the lower temperatures, it being necessary in some instances to cool as much as 20 degrees below the equilibrium point to cause a separation of crystals. The viscosity rather than real solvent power of glycerol inay account for its use commercially as a solvent, for if vanilliii is dissolved in a glycerol solution the solution may be supercooled a number of degrees and yet remain perfectly clear. The solubility of vanillin-glycerol solutions was next determined by analytical means, practically identical with the method employed by De Groote.2 An excess of vanillin was heated with the glycerol-water solution and very slowly cooled with occasional shaking. Samples were drawn from time to time and the vanillin was determined by extraction with ether. The results showed a materially higher solubility than was secured synthetically as described under the method used to determine the alcohol-water solubilities and, although indicating a slightly lower solubility of vanillin than the data published by De Groote, were in general comparable. At about

Temperature (Y ) FIG. %-SOLUBILITY

GLYCEROL-WATER SOLUTIONS. SYNTHETIC METHOD

O F VANILLIN IN

vanillin. No change was produced in the tubes held a t 25' C., but this may have been because the temperature a t the time of seeding was 2 to 5 degrees higher than the average a t which they had been held. Several of the tubes held a t 13" C., however, were supersaturated, as shown by crystallization of vanillin. Curves A and B, Fig. 3, are derived from these data and indicate the maximum amount of vanillin that can be held in

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INDUSTRIAL A N D Eh7i?INEERING CHEMISTRY

solution under the usual conditions for preparing and storing a commercial flavor-namely, by heating the glycerol-water mixture to a temperature just sufficient to dissolve the required amount, of vanillin and maintaining at temperatures of 13 a and 25 C., respectively. O

when the composition of the solutions in both flasks was identical. After 20 hours of vigorous agitation, clear solution was drawn from the flasks by means of a protected pipet, and upon extraction of the vanillin with ether was found to have the same composition in each flask. The analyses confirmed points on the curve derived by the synthetic method. These results indicate that the synthetic method carried out as described is reliable even in cases where a condition of supersaturation may be encountered as with glycerol. SOI~UTlOSSI N CONCEKTRATED

i 3

i

i

101 '.

P I G 3-sOLUBILITY

l

1

20'lo

l

i

l

i

40%

30%

i 50

i

i

l

60%

70%

Perceniaqe of GlyceroF \nWa\er

O F VANILLIN I N

G~YCEROL-WATER SOLUTIONS.

EMPIRICAL METHOD

Curve C represents the maximum solubility of vanillin in various concentrations ol glycerol under the same conditions of temperature as Curve B , but in which the several solutions were seeded with vanillin crystals. These data indicate the solubility under conditions which may be typical but the most unfavorable to which a flavor may be subjected. The following values are taken from the curves in Fig. 3 and represent, working solubilities of vanillin-glycerol-water solutions: 7 -

Glycerol in water Per cent

,

___-

TEMPERATURE OF SOLIJTION---,~ 130

26' C Grams/100 cc.

Without seeding Grams/100 cc

After seeding Grams/100 cc.

The analytical method used to confirm the vanillin solubilities in alcohol-water solutions was modified for glycerolwater solubilities so that the final equilibrium point would be approached from both the unsaturated and supersaturated conditions. In view of the high viscosity of glycerol and the importance Seidel15 placed upon equilibrium points, this added precaution was considered necessary to insure that the point of saturation had been reached. To each of two flasks containing the same concentration of glycerol and water an excessive quantity of vanillin was added. One flask was warmed above the temperature a t which the equilibrium point was to be determined so that an excess of vanillin would be in solution, while no attempt was made to effect the solution in the other. Both flasks were then mechanically skaken at constant temperature. The true equilibrium or saturation point would be reached "Solubilities of Inorganic a n d Orgamc Compounds," 2nd ed revised, p. 7.57.

Vol. 16, No. 12

GLYCEROL

SOLUTIOKS

Attempts have been made to prepare concentrated imitation vanilla flavors using glycerol as a solvent for the vanillin or using glycerol in conjunction with alcohol, and such preparations are actually on the market. Directions accompanying the flavors specify the amount of water to be added to dilute the flavor to a proper strength for use. On standing, such concentrated flavors often become turbid within a few weeks, and a heavy white precipitate forms. The precipitate is not vanillin and does not readily redissolve upon warming the flavor. The precipitate has been described by Dodge6 as vanillin glyceride, an acetal resulting from the addition of a molecule of vanillin t o a molecule of glycerol with the separation of one molecule of water. The glyceride is very easily hydrolyzed and can be converted into glycerol and vanillin by adding water and heating. By this means concentrated flavors in which a precipitation has occurred can be recovered and a more dilute flavor produced without loss of the constituents, and the amount of water necessary for this hydrolysis should be equal to the amount that wouId prevent its formation. The following test was carried out to determine this equilibrium point. A series of tubes was made up containing alcohol and vanillin glyceride which had been previously prepared and purified. To these tubes varying amounts of water were added. The compound is only sparingly soluble in alcohol, while the products of hydrolysis, vanillin and glycerol, are very soluble; thus, upon hydrolysis a clear solution would result. The tubes were kept a t an average temperature of about 25" C. for 6 weeks and shaken occasionally. Only in those tubes of higher water concentration did the compound completely decompose. It was found that water to the extent of about 62 per cent of the weight of the vanillin-glycerol compound is necessary for complete hydrolysis a t 25' C. At higher temperatures, however, a considerably less amount of water is necessary, whereas theoretically only 8 per cent of the weight of the compound is involved in the reaction. In a series of tubes containing vanillin, glycerol, alcohol, and varying amounts of water, it was found that water to the extent of only 7 per cent of the weight of vanillin will prevent the formation of the compound at 25' C., although 12 per cent is theoretically necessary. The difference in the two equilibrium points may be accounted for mainly by the supersaturating effect of glycerol and the fact that vanillin glyceride is somewhat soluble in water, alcohol, and glycerol. The hydrogen-ion concentration of the solution also has an influence on the formation of the compound. This phase of the subject is now under investigation. There are other conditions besides the water content that effect the formation of vanillin glyceride in concentrated flavors, such as the amount and nature of the constituents, and the temperature and procedure used in the preparation. It would be safe to say, however, that from the foregoing tests and general observations, if there is as much water present in the flavor as vanillin, no glyceride precipitation d l take place. 5

J . A m Chem. Soc., 44, 1406 (1922).