January 15, 1930
I S D I ' S T R I A I , A S D E S G I S E E R I S G CHEMISTRY Literature Cited
(1) Barlow, J . .4m. Chem. Soc., 26, 341 (19041. (2) Burgess-Parr Co, hfoline, Ill., Booklet 108. (3) Dennis and Reed, J. Biol. C h e m . , 71, 205 (1926). (4) Kahn and Leibhoff, I b i d . , 80, 623 (1928). ( 5 ) Latshaw, J . Assocn. 0 3 c i a l Agv. Chem., 5, 136 (1921).
121
(6) LeClerc and Dubois, J . .4m Chem SOL , 26, 1105 (1904). (7) LeMatte, Boinet,and Kahane, J . p h w m . c h i m . , 5, 325, 361 (1927); Compt. r e n d . soc. b i d . 96, 1211 (1927). ( 8 ) Stockholm and Koch, J. A m . Chem. Joc., 45, 1953 (1923). (9) R-akefield, J. B i d . C h e m . , 81, 713 11029). (10) \X-olesensk>-, I N D . E X G . C H E X , , 20, 12.34 (1928).
Determination of Dextrose in the Presence of Levulose' D. T. Englis and W. J. Byer G S I V E R S I T Y OF
ILLISOIS, V R B A S A , ILL.
A study has been made of the iodometric oxidation of S 9T I S F X C T 0 R Y for dextrose. Within certain dextrose and a dextrose-levulose mixture to establish method for the deterlimits the rate of oxidation of the best conditions for the determination of the former both sugars is favored by inmination of either dexin the presence of the latter in the proportions found in crease in alkalinity. trose or levulobe in a mixture artichoke and chicory sirups. It was found that these of the two has always been Recently Levy and Doisy conditions are fulfilled by using a sodium carbonatedesirable for the analysis of (8)hare made a very interestborate buffer of pH 10.6 and about three times the calhoney and certain other food ing and iniportant study of culated amount of iodine, which gives an apparent products. Such an estimathe effect of borates upon the stoichiometric oxidation of dextrose to gluconic acid in tion is of special importance oxidation of dextrose and the presence of four times the amount of levulose in in the investigations now in other sugars bv various rea20 minutes at 26-27' C. A further study will be made progress looking toward a gents. The rate of oxidation to determine the application of the method to chicory commercial production of of many sugars ty iodine in and artichoke extracts. levulose. sodium carbonate-bicarbonBorates did not seem to exert a selective inhibition on A double temperature ate and sodium carbonatethe oxidation of levulose. polarization has been emborate buffered solutions was The rate of oxidation of the dextrose and dextroseployed for levulose, but the found not to be concerned levulose mixtures beyond the apparent stoichiometric experimental error is great with alkalinity alone, but the point is shown for the borate buffer and for 1.5 per cent for dilute solutions. This borate had a specific inhibisodium carbonate. is also true of the combined tory effect. Although a slight reduction a n d polarization oxidation of lwulose was aumethods for the two sugars. A direct chemical method parent, even in the presence of borates, the statement was has been proposed by K G s ( 0 ) . This procedure involves made that the levulose may not have been pure. Hinton and the use of Ost's ( I O ) copper bicarbonate solution as the Macara ( 5 ) have previously remarked that oxidation of levuoxidizing agent, and it is stated that under suitable tem- lose was negligible when borax n-as employed as the alkali, but perature conditions le1 d o s e is oxidized, while dextrose, they n-ere not favorably disposed towards its use because of mannose, galactose, lactose. and sucrose are not affected. the slower rate of oxidation of the dextrose. It appeared to T!iis method has been studied by the carbohydrate laboratory the writers, however, that t h e borates might hare a preferenof the Bureau of Standards ( 7 ) )but details of the modifica- tial inhibitory action on t'he oxidation of l e n l o s e and that tion adopted have not appeared. Another plan of analysis conditions might be found under Tvhich dextrose could be is possible. Since the total dextrose and levulose can be more accurately determined in its presence by the iodometestimated with considerable accuracy b y the copper reduc- ric method and the method made applicable to levulose sirups. tion method, if a good direct method for dextrose were availPlan of Experiment able the levulose could be calculated by difference. I n 1 8 9 i Roinijn (11) called attention to the fact that dextrose was Since the proportion of dextrose to levulose in the sirups apparently stoichiometrically oxidized to gluconic acid by from the hydrolysis of extracts of artichoke and chicory alkaline iodine solutions while levulose was scarcely affected. is in a ratio of 1 to 3 or 4, the experiments were designed for Many articles have since appeared in which the effect of a mixture of this character. The general analytical protemperature. time, alkalinity, concentration of iodine and cedure used by Levy and Doisy was folloTvetl. Their resugar, and other factors haT7-e been studied. A detailed dis- sults indicated that' a sodium carbonate-borate buffer, 0.15 cussion is not necessary here as the earlier work is well re- and 0.05 molar, respectively, gave very nearly stoichiometric viewed in the later publications ( 1 , 3, d , 5 ) . oxidation of dextrose in 60 minutes. Since this is about There are some differences of opinion as to whether the the maximum interval to be allowed for convenience of dereaction with dextrose is stoichiometric or can be made ap- termination, this buffer concentration (pH 10.6) was selected parently so and whether or not fructose is affected by the for a comparison of the dextrose alone with tiext;rose-.levulose reagent. Many of those differences can be attributed to the (1:4) mixture. varying conditions of experimentation and others to the uncerFurthermore, since Cajori ( 3 ) states that an alkalinity tain purity of the sugars studied. On the whole the evidence equivalent to 1 to 1.5 per cent of sodium carbonate proseems rather conclusive that a small amount of levulose is duces no enolization of dextrose and that under his condioxidized but that the rate is yery slon- in comparison to that tions of determination no levulose was oxidized, experiments 1 ReceiLed July 1 6 , 1929. were also run in the absence of borates a t the higher alkalinity.
A
A S A L YTICAL EDI T I O S
122 Experimental Procedure
SUGARS-The dextrose was purified by the method of Hudson and Dale (6). A stock solution was made by dissolving 1.800 grams in 200 cc. A sample of Pfanstiehl, 90 per cent levulose was recrystallized from glacial acetic acid, washed with absolute alcohol, and dried in a vacuum oven. The crystals were perfectly white and the purity by polarization using Vosburgh's (22) formula was 99.7 per cent. The stock solution of the sugar contained 7.2 grams in 100 cc. BUFFERSoLuTIoNs-The borate buffer was made by dissolving 15.46 grams of boric acid and 79.50 grams of sodium carbonate in distilled water and diluting to 1 liter. The sodium carbonate buffer contained 150 grams per liter. The iodine solution was 0.1436 normal. For these esperiments the reagents were measured out in the volume and order indicated below, thoroughly mixed, and made up to 250 cc. The zero interval of the react'ion was fixed as the time of introduction of the alkaline reagent into the mixture. REAGENT
EXPT.A
EXPT.B
EXPT.C
EXPT.D
CC.
Cc. 100
CC.
50
30
70
CC. 100 50 25 45
25
25
100 50
Iodine Dextrose Levulose Water Borate buffer Carbonate buffer
...
100
25
45 50
20
'
...
50
...
...
EXPT.A
BXPT.B
EXFT.
C
EXPT.D
0.02872
0.02872
0.02872 0.01000
0.02872 0.01000 0.0400 11.5
0.01000
......
10.6
0.01000
......
0,0400 10.6
11.5
iodine in the presence of the borate buffer a t pH 10.6 in 60 minutes. When the quantity of levulose present is four times that' of the dextrose (experiment B) an apparent theoretical value is obtained in 20 minutes. Under these conditions the method niay be applied to the determination of dextrose in the lenlose sirups from artichoke and chicory extracts, if the sirups either do not contain, or if containing may be freed by proper defecation of! other substances which may be oxidized by iodine under the same conditions. Further experiments will be conducted to make certain of' the application of the method to such extracts. of Dextrose by I o d i n e in Presence of S o d i u m Carbonate Experiment C: 0 01 .If dextrose and 0.1414 .!,f sodium carbonate; p1-I = 11.5
T a b l e 111-Oxidation
I O D I N E .kBSORBED I S TERXS OF
TIME
THIOSULF.ATE
M inul es
CC.
of Dextrose by I o d i n e in Presence of Borates 0.01 M dextrose and borate buffer; p H = 10.6 I O D I N E ABSORBED I O D I N E TO IX TERMS OF 1 GRAMOF THIOSULFATE GLUCOSE OXIDATION cc. Gram Per cent
T a b l e I-Oxidation Experiment A:
TIME
EXPERIMEKT A I
1.051
74.6
6 10 20 60 120
6.62 7.53 8.33 8.88 9.03
6 10 20 60 120 135
6.58 7.39
1.046 1.li2
74.1 83.2
s: 91 8.98 8.98
1,427 1.427
i:4i5
100:2 101,l 101.1
1.196
1,323 1.410
1.435
Grams
OXIDATION Per cent
Z X P S R I M B h T C1
8 85 8 03 8.96 9.20 9.34
6 5 10.0 21.0 120.0 130,O
1 410 1 418 1 422 1 476 1.483
100 0 100 3 100 8 104 6 103 1
EXPERIMENT C!
84.9 94.0 100.0 101,i
EXPERIMENT A2
of Dextrose a n d Levulose by I o d i n e i n Presence of S o d i u m C a r b o n a t e 0.01 .If dextrose, 0.04 .If levulose, and 0.1414 sodium carbonate; p H = 11.5 IODINE ABSORBED IODINE TO I S TERMS OF 1 GRAMOF THIOSCLFATE GLUCOSE OXIDATION CC. Crams Per cent 9.26 1.471 104 2 9.53 1,513 107 2 10.53 1.678 118 8 11.77 1.870 132 3
T a b l e I\'-Oxidation Experiment D:
TIME Minul es 11 5
At definite intervals 25-cc. portions of the solutions were removed. acidified with 2 cc. of 6 N sulfuric acid, and titrated with 0.05634 N sodium thiosulfate. Blanks were also run in which no sugar was present. A11 experiments xere carried out at room temperature, which varied between 26" and 27" C. The results of the titrations showing the iodine consumed and per cent oxidation of the sugar on the basis of a stoichiometric conversion into gluconic acid are given in Tables I, 11, 111, and IV.
Minutes
I O D I X E TO
1 GRAMO F G L uc DsE
...
The solutions then had the following init'ial molar concentration and pH: X0ls: Iodine Dextrose Levulose PH
Yol. 2, KO. 1
20 0
60.0 120 0
,
The desired selective inhibition of the oxidation of levulose by borates was not evident. The minimization of action in so far as this sugar is concerned seems to be related primarily t o basicity. When the alkalinity of the solution is increased to the equivalent of 1.5 per cent sodium carbonate (experiment D), much more oxidation of levulose takes place. I n all the experiments the iodine consumption increases beyond the calculated 100 per cent oxidation of the dextrose and is greater when levulose is present. Although Cajori believes that the apparent reduction of iodine by levulose can be attributed to the small losses due to the volatility of the reagent in t'he course of the reaction, if this were true experiments A and B should gire identical values. The fact that the rate and extent of oxidation of dextrose alone are greatly increased (experiment C) a t the higher alkalinity supports the conclusion first stated by Bougalt ( 2 ) that there is oxidation of the secondary alcohol groups of the sugar. The importance of fixing the proper conditions for reaction of any sugar mixt'ure is emphasized.
Table 11-Oxidation
Literature Cited
Experiment B:
Xuerbach and Bodlander, Z . angew. Chem., 36, 602 (1923). Bougalt, Compt. rend., 164, 1008 (191i). Cajori, J . B i d . Chem., 64, 616 (1922). Dekker, Arch. Suikerind., 36, 111; Afededeel. Pvoefda. J a v - S u i k e r i n d . . 1948, 699; C . A , , 24, 4268 (1928). ( 5 ) Hinton and hlacara, Analysl, 49, 2 (1924). (6) Hudson and Dale, J . A m . Chem. SOL.,39, 320 (1917). (7) Jackson,Silsbee, and Profitt, Bur. Standards, Sci. Paper 591,594 (1926). (8) Levy and Doisy, J. Bid. Chem., 77, 733 (1928). (9) Nyns, Bull. assocn. &ole sup brassevie Louuain, 26, 63 (1925); C. A , , 19, 1236 (1925). (10) Ost, C h e m . - Z f g . , 19, 1784, 1829 (1925). (11) Romijn, Z . anal. Chem., 36, 349 (1897). (12) Vosburgh, J. A m . Chem. SOL., 42, 1696 (1920).
TIME Minutes
of Dextrose a n d Levulose b y I o d i n e in Presence of B o r a t e s 0.01 ,M dextrose, 0.04 .M levulose, and borate buffer; p H = 10.6 IODINEABSORBED I O D I N E TO IN TERMS OF 1 GRAMOF THIOSULFATE GLUCOSE OXIDATION CC. Grams P e r cent 1.359 96.4 1 393 98.9 1,424 100.9 1.461 103 6 1.508 106,X
Discussion
The results of experiments A show that there is an apparent stoichiometric oxidation of dextrose to gluconic acid by
(1) (2) (3) (4)
