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Yol. 19, X O . 7
INDUSTRIAL AND ESGISEERIhTG CHEMISTRY
make the total volume about 75 cc., and 10 cc. of concentrated hydrochloric acid are poured in. The titanous chloride is then pipetted into the flask. As long as chloric acid is present the Folution has a faint greenish color, which changes to a faint blue when the titanous chloride is in excess. Aftei the addition of the titanous chloride solution the contents of the flask are quickly and thoroughly stirred, and if the faint blue color persists, the thiocyanate indicator is added and the excess titanous chloride immediately titrated with ferric alum. The usual blank is run on a volume of titanous chloride equal to that used in the determination, and the difference between the blank and the titration multiplied by the chlorate factor of the ferric alum gives the weight of the chlorate in the sample. It is essential that the titanous chloride be in excess before the thiocyanate indicator is added; otherwise chloric acid will be consumed in oxidizing the thiocyanate. DETERMINATlOPr'S-The potassium chlorate used was prepared by twice recrystallizing reagent-quality potassium chlorate from distilled water and drying the resultant crystals for 24 hours a t 120" C. An accurately weighed sample of this chlorate was dissolved, the solution accurately weighed, and portions of it were weighed out on an analytical balance f:om a pipet. The results in Table I11 indicate the degree of accuracy which may be expected. All the determinations were made a t one time, the samples being weighed out together, and then titrated, one after the other, consequently the blanks are the same throughout. The ferric alum was the same as that used for the iron deter-
minations of Series A, Table I, and each cubic centimeter was equivalent to 1.802 nig. of potassium chlorate. Table 111-Determination of Chlorate REAGENT SOLUTIONS BLANK KC103 USED FERRIC KC102 TAKEN TiCh Ferric alum ALUM FOUND ERROR Mg. CC. cc. cc. ME. Mg. Per cent 7.17 8.23 10 12.21 7.17 fO.00 0.00 6.17 10.61 10 10.88 +0.27 2.54 3.96 14.67 10 14.88 +0.21 1.43 17.04 20.83 25 30.52 17.48 f0.44 2.58 19.94 19.37 25 20.10 + O . 16 0.80 18.74 21.11 25 21,24 f O . 13 0.62 15.82 26.48 25 26.48 +0.00 0.00 12.38 32.75 25 32.70 -0.05 0.15 35.62 2.5 10.76 35,59 -0.03 0.09 43.06 25 6.62 43,05 -0.01 0.02 4.94 25 45.92 46,08 +O.l6 0.35 50.39 25 2.52 50.44 +0.05 0.10 MODIFICBTlOPr'S FOR CllUSTIC APr'D HYPOCHLORITE SOZUTIoxs-This method has been found convenient for the determination of chlorates in caustic soda solutions from electrolytic cells and evaporators, and in hypochlorite solutions. For the caustic solutions, the sample is measured out, acidified with hydrochloric acid, being careful to keep the temperature of the sample solution below 40" C. during the addition of acid, the titanous chloride pipetted in, indicator added, and the excess titanous chloride titrated with ferric alum. For hypochlorite solutions, a slight excess of sodium arsenite is added over that required to reduce the hypochlorite present, the solution acidified with hydrochloric acid, the titanous chloride pipetted in, indicator added. and the excess titanous chloride titrated with ferric alum.
Direct Iodimetric Determination of Glucose' By Alexis Voorhies and A. M. Alvarado LOYOLAUNIVERSITY. S E W ORLEANS, LA.
REVIEW of the literature shows that most of the important methods for the determination of glucose are copper reduction methods, which, with sundry variations and modifications, are essentially the same as the original procedure devised by Fehling in 1848. rlniong the modifications of Fehling's method are Kendall's2 in which the alkaline tartrate solution is replaced by an alkaline salicylate solution, and that of Benedict,3 in which the alkaline tartrate is replaced by an alkaline citrate solution. One of the main difficulties in a volumetric copper reduction method for glucose is the accurate determination of the end point. Daggett, Campbell, and Whitman4 have proposed the electrometric determination of this end point. Recently Lane and Ey16 have developed a method using methylene blue as an internal indicator. I n seeking, if not a more accurate, at least a simpler, method of determining glucose, the writers have been led to the use of iodine directly as the oxidizing agent. The results here presented are merely preliminary and further work is being done on the problem. Theoretical
A
When glucose is treated with an alkaline solution of metallic salts, the aldehyde group in the sugar molecule should be oxidized to an acid carboxyl group. This oxidation Received March 14, 1927 Z J A m Chsm S o c , 34, 317 (1912) 3 J A m Med A s s o c , 61, 1193 (1911) 4 J A m Chem Soc, 46, 1043 (1923) s l n r e r n Sugor J 26, 143 (1923)
1
is only t'he beginning of bhe reaction, however, for the oxidation is attended by the breaking down of the carbon chain, bhe products of decomposition varying in proportion according to the conditions of experiment.6 It was hoped that by using an oxidizing agent of the type of iodine and working a t room temperatures the oxidation would proceed only to the gluconic acid stage. The general reaction is represented by the following equation: -C / O \H
+
I*
--f
-c
\OH
+
2HI
By removing the H I formed the reaction should proceed to completion to the right. By examining this equation we can see that 90.06 grams of pure anhydrous glucose are equivalent to 126 grams of iodine. Therefore, a solution containing 9.006 grams of anhydrous glucose per liter would be exactly 0.1 normal. Apparatus and Materials All burets and other measuring apparatus were carefully calibrated in the usual way. SODIUM THIOSULFATE-C. P. reagent quality. A 0.1 71'2 solution was made up and carefully standardized against C. P. reagent quality potassium iodate. IODINE-C. P. resublimed quality. A 0.1 N solution was prepared and the concentration checked daily against the thiosulfate. Gr.ueosS=C. F. anhydruus quality. A 0.1 N solution was prepared by dissolving 0.9006 gram of the anhydrous glucose in boiled and cooled distilled water and making up t o 100 cc. e Browne, Handbook of Sugar Analysis. p. 335.
The concentration of this solution was checked daily by the polariscope Procedure About 30 cc. of 0.1 S iodine solution were added to 2 1 95 cc. of 0 1 glucose solution; 6 S sodium hydroxide was added until the color of the solution changed to a light yellow.. After standing for a definite length of time the solution was acidified with 6 S hydrochloric acid. The excess of iodine was titrated with sodium thiosulfate using starch as the indicator Discussion of R e s u l t s A \ 7
PROCEDURE-About 30 cc. of 0.1 IV iodine were added t o 21.95 cc. of 0.1 &Vglucose. The mixture was allowed t o stand 2 minutes, and 25 cc. of 1 A' sodium bicarbonate were added. The mixture was heated t o 70" C. for a definite period of time, then cooled, acidified with 6 -V hydrochloric acid, and the excess of iodine titrated with thiosulfate using starch as the indicator. Table I1 (24.95 cc. 0.1 S glucose; initial temperature, 70" C . )
EQUIVALEXT TIMEOF EO.
1
2 3
The results are shown in Table I. (24 0 5 cc S O .
1 2 3
4
6
7 8 0 10
11 12
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I N D U S T R I A L A N D ENGI,YEERI,VG C H E M I S T R Y
July, 1927
Table I 0 1 S glucose, temperature, 22'
0 1 S IODINE E Q U I V ~ L E N TTIMEOF ADDED I O D I N E REDUCEDS T A N D I N G cc. CC Mznufes 22,19 33.38 33.31 25.67 32.81 25.86 33.03 25.68 29,96 25.10 24.05 30.01 24.91 35.25 35.16 25.38 24.14 30.86 25.40 35.04 25.05 30.88 3B. 09 24 07
C.) GLUCOSE (IXIDI7ED BY I O D I N E
Per r e n t
With the c.xception of experiments 1, 9, and 12, all the resultb are of approximately the same order of magnitude and tend to approach the theoretical value. This shows that an alkaline solution of glucose by iodine oxidizes readily a t room temperature. The results in the last column were calculated on the assumption that the glucose is oxidized to the gluconic acid stage only. All the reqults may be divided into three groups-first, those in which not enough iodine wa5 consumed for the oxidation to the gluconic acid stage, thereby accounting for the low results; second, those in which approximately the theoretical amount of iodine was consumed for oxidation to the gluconic acid stage; and finally those results in which more iodine was consumed than was required for oxidation to the gluconic acid stage. It will be noted that high and low values appear when the time between the addition of sodium hydroxide and acidification is 10, 20, or 30 minutes. This brings out the interesting fact that the oxidation of an alkaline solution of glucose by iodine is fairly rapid, the reaction attaining a state of equilibrium in a comparatively short time. It is evident, then, that if we keep all the experimental conditions uniform it should make no difference how long we allow the alkaline glucose solution to remain in contact with the iodine, beyond the time required to attain this state of equilibrium, as the results are independent of the time of standing before acidification and removal of the excess of iodine n-ith thiosulfate. It is well recognized that such factors as time of boiling, size of vessel, concentration, and other conditions of experiment are extremely important in the determination of glucose by Fehling solution methods. Undoubtedly, these same factors are of importance in the oxidation of alkaline glucose by iodine. I n this work an effort mas made to maintain as uniform experimental conditions as possible, and so eliminate as many of these disturbing effects as possible. The deviations from the theoretical values are due to some constant factor, or factors, which are continually entering, causing the results to be in some cases high and others low. Apparently in experiment 6 ideal conditions were attained and here we find that the glucose has been completely oxidized to the gluconic acid stage. Effect of T e m p e r a t u r e
The effect of temperature on the oxidation of weakly alkaline solutions of glucose by iodine was studied
REDUCED S T A N D I N G rc. Hours 13.40 14.16 48 17.46
IODINE
FINAL GLUCOSE TEMPERATURE OXIDIZED
c.
Per c e n f 53.70 56.70 69.70
38 34 22
Table I1 s h o w that even after the reaction mixture had stood for 48 hours the oxidation was still far from complete. This indicates that the oxidation of glucose by iodine takes place readily only in a strongly alkaline medium. The effect of increased temperature was further studied, with results as shown in Table 111. Table I11 brings out the very important effect of temperature on the oxidation of weakly alkaline solutions of glucose by iodine. Cornparing the results in Tables I1 and 111, it will be seen that when the temperature is raised to 82" C. and the time is 5 minutes we get a more complete oxidation t,lian when the temperature is 70" C. and the time 1 hour. When the temperature is raised to 90" C. and the time to 10 minutes the percentage of glucose oxidized reaches 82.20. Table 111 (24.96 cc. 0.1 S glucose)
EQUIVALENT TIMEOF IODINE XO.
1 2
REDUCED CC. 15.47 20.51
S r A x m i C
Minutes 5 10
TEMPERATURE Initial Final
c.
82 90
c.
40 50
GLVCO~E OXIDIZED Peu c e n f
62.01 82.21
Effect of S o d i u m Bicarbonate t o Acidified Solution PROCEDURE-In these experiments the original procedure was modified somewhat. Sodium hydroxide was added as before to the iodine-glucose mixture. The mixture was allowed to stand 30 minutes, then acidified with 6 1V hydrochloric acid and the excess acid neutralized with 1 A' sodium bicarbonate. The sodium thiosulfate titration was carried out in a neutral medium.
The results are shown in Table IV. Table I V (24.95 cc. 0.1 .V glucose; time of standing, 30 minutes) 0.1 S IODINE 0.1 N IODINE GLUCOSE No. -4DDED REDu c E D OXIDIZED cc. cc. Per cent 24.51 1 31.05 98.24 2 4 . 1 5 32.74 100.80 2 25,2i 25.27 100.30 3
The addition of sodium bicarbonate to the acidified solution has little or 110 effect on the oxidatioii of glucose by iodine. The results are of the same order of magnitude A B those given in Table I. Conclusion
The oxidation of glucose by iodine takes place readily oiily in a strongly alkaline medium a t room temperatures. I n a weakly alkaline medium glucose is incompletely oxidized to the gluconic acid stage by iodine, even a t comparatively elevated temperatures. Further work is being done on this problem to determine the most favorable conditions of experiment for this oxidation. The Eastman Kodak Company has acquired, through its subsidiary, Kodak, Ltd., of London, the new film-manufacturing plant of the Glanz Film Aktien-Gesellschaft in Berlin -a subsidiary of the largest rayon producers in central Europe. This gives the Eastman company a major manufacturing plant in Germany, in addition to its factories in Canada, England, France, and America.
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