694
V O L U M E 19, NO. 9
ing the first 7 hours, distilled water can be employed for a reference blank. Figure 3 shows no difference in the sensitivity of the reagent as compared to the acetic acid reagent, which is widely used for chromium determination. Maximum color develops within 5 minutes after addition of the reagent. The prepared reagent is added in the proportion of 1 ml. to each 10 ml. of the unknown in neutral or slightly acid solution. The pH is not critical.
SUMMARY
DEVELOPMENT OF REAGENT
In a modification of the s-diphenyl carbazide reagent for the colorimetric determination of hexavalent chromium, the major change is the substitution of phthalic anhydride for the acidic constituent. The resulting reagent is stable for weeks. It compares very well with other analytical reagents, and results in a simplified analytical procedure. The reagent is well adapted, upon the addition of glycerol, for impregnating filter papers, which are used in a direct field method for the estimation of concentrations of chromic acid mists in air.
In a series of experiments which led to the selection of the final reagent it was found that the concentration of phthalic anhydride was the most critical factor in color development. Decreasing the phthalic anhydride concentration from 10 to 0.2 gram per 100 ml. of solution progressively retarded color development in the reagent. Four grams of phthalic acid were used since, with concentrations below 4 grams per 100 ml., there was an increasing lag in the formation of the chromium complex. The concentration of s-diphenyl carbazide was not so critical; however, amounts of s-diphenyl carbazide exceeding 0.25% produce a faint color development in the reagent. The final reagent produced a chromium complex which was stable for several hours. Calculated on the basis of molarity of chromium, the ex-tinction coefficient of the complex is 3.14 X lo4. This value agrees well with that reported by Sandell (7').
(1) Cazeneuve, A., Bull. SOC. chim., (3) 23, 701 (1900); 25, 781 (1901). (2) Feigl, F.,"Laboratory Manual of Spot Tests," New York, Academic Press, 1943. (3) Hodgman, C.D.,and Holmes, H. N., "Handbook of Chemistry and Physics," 25th ed., p. 1263,Cleveland, Ohio, Chemical Rubber Publishing Go., 1941. (4) Loginov, M. E., Leningrad.Znst. Gig.Truda i Tekh. Bezopasnoati, T ~ u d iy MatWialy Byull., NOS.7-8, 42 (1931). ( 5 ) Moulin, A., Bull. SOC. chim., 31,295 (1904). (6) Rowland, GI. P., Jr., IND.EXQ.CHEM.,ANAL. ED.. 11, 442 (1939). (7) Sandell, E. B., "Colorimetric Determination of Traces of Metals,'' New York, Interscience Publishers, 1944. (8) Silverman, L., and Ege, J. F., Jr., J. I d . Hug. Tosicol. (March 1947).
I
LITERATURE CITED
Identification and Determination of o-Xylose
LOUIS E. WISE AND EVELYN K. RhTLIFF, The I n s t i t u t e of Paper Chemistry, Appleton, Vis.
N 1945, Breddy and Jones (1) showed that xylose could be identified and determined proximately in the presence of other sugars as the insoluble crystalline dibenzylidene dimethyl acetal by the action of dry methanolic hydrogen chloride and benzaldehyde on xylose, over a period of 7 days. Whereas their qualitative findings were fully confirmed, it x a s at first found impossible t o substantiate their quantitative data. This led to correspondence nith Jones (S), who stated that two points had been omitted from their original communication: ( a ) during the last 18 hours of the 7-day period the reaction mixture was kept in an ice chest and (b) their equation for computing xylose from the weight of the diacetsl derivative had been changed from the 0.055 to y = 0.526s 0.046 (where = original 21 = 0.482s the weight of xylose and z = the weight of derivative). Even a-hen these modifications were applied to the estimation of xylose, the results fluctuated over a wide range, and could not be considered as proximately quantitative. After a series of experiments, it was shown that, with the following additional precautions, reasonably satisfactory determinations of xylose could be obtained. The reagent (2.5 K hydrogen chloride in anhydrous methanol) containing purified benzaldehyde must be used shortly after its preparation. The reagent deteriorates very rapidly a t laboratorv temperatures and the titer falls quickly, owing to the chemica1"interaction of methanol with hydrogen chloride. The water formed in this reaction disturbs the equilibrium and prevents the complete separation of the dimethyl acetal.
+
+
Table I. D-Xylose Determined as Its Dibenzylidene Dimethyl Acetal Derivative Xylose Taken MQ.
MQ.
Recovery
%
81.6 163.1 87.9 176.7 200 100.9 504.4 500 91.2 456.9 600 99.6 696.9 700 99.3 7nn 695.0 . _. Values calculated from the more recent Breddy-Jones equation. 200
a
Xylose Founda
The reaction must be carried out at 20" C. for 6 days and finally a t 4' C. for 18 to 24 hours. Provided no crystallization has occurred within the first 24 hours, the mixture must be seeded with the derivative. After filtration, the xylose derivative should be washed with 200 cc. of ice water, follon-ed by washing with methanol saturated with the derivative. The washed precipitate should be dried no more than 1 hour a t 100" to 105' (despite the fact that this drying period may not ensure constant weight). When these precautions avere observed, the results given in Table I were obtained. The importance of seeding the xylose-methanolic hydrogen chloride-benzaldehyde mixture within 48 hours (provided crystallization has not occurred spontaneously) is illustrated in the following experiment.
A 500-mg. sample of xylose was treated with 10 cc. of the Breddy-Jones reagent a t 20" C. and seeded within 48 hours. In this case, the xylose found after 7 days was 97.2% of the theoretical (based on the Breddy-Jones equation). A similar mixture, not seeded, remained liquid for 6 days. Crystallization was then induced by scratching the sides of the flask. In this case only 23% of the original xylose was recovered. Breddy and Jones have shown that the following carbohydrates form no crystalline deposit with the xylose reagent: glucose, mannose, galactose, fructose, sorbose, maltose, sucrose, methyl a-mannoside, methyl a-glucoside, rhamnose, and arabinose. To this list may be added D-glucurcme and D-galacturonic acid. On the other hand, Irxylose also gives a crystalline derivative. The method thus furnishes an excellent, highly specific qualitative test for xylose, which has been used in identifying the sugar separated from the hydrolysis products of the hemicelluloses of overcup oak and slash pine. Breddy and Jones recrystallized their dimethyl acetal of dibenzylidene xylose from chloroform-ligroin, reporting a melting 9" (chloroform), It was found more point of 211" and satisfactory to recrystallize the product from anhydrous methanol, thus obtaining silky needles, melting a t 211-12" (corrected), - 6.65" (chloroform).
-
SEPTEMBER 1947
698
The analogous Gxylose derivative, after recrystallization from methanol, melted a t 210-11 O ; 6.56' (chloroform). Calculated for C21H2406: C 67.7; H 6.5; M e 0 16.65'%. Found: C 67.5 and 67.4; H 6.7 and 6.6; M e 0 16.3%. Inasmuch as anhydrous conditions must be maintained, the new xylose method appears less practical for most purposes than does the microbiological assay for xylose (4) (which also requires much smaller samples). In the hope of discovering some analogous xylose derivative better suited for its quantitative determination, CHI other aldehydes of higher molecular weight were used in place of benzaldehyde, using correspondingly larger amounts of each aldehyde. In other respects, the reaction was carried out as previously outlined-ie., in the presence of 2.5 A- methanolic hydrogen chloride. The aldehydes CHa used were o-chlorobenzaldehyde, m-nitrobenzaldehyde, veratraldehyde, vanillin, and p-isopropylbenzaldehyde. Of these only p-isopropylbenzaldehyde gave an insoluble crystalline product, analogous to that obtained by Breddy and Jones. [ I n the case of m-nitrobenzaldehyde, an oil separated which, after standing a t 4' C. for about 3 months, crystallized partially. The upper methanolic layer was decanted off and the lower oilycrystalline layer was washed successively with ice water, aqueous bicarbonate, and ice water. The residual crystals were filtered; after recrystallization from methanol, the compound melted a t 203-3.5"; the yield mas 25 mg. Calculated for C2,H2~O1oN2: C 54.54; H 4.76%. Found: C 54.44, 54.35; H 4.81, 4.98%. Evidently the compound is the analogous di(m-nitrobenzylidene) dimethyl acetal of D-xylose.] Under the best conditions, 500 mg. of xylose yielded 1.113 grams of the (crude) isopropylbenzylidene derivative, n-hich, after repeated crystallizations from benzene, melted at 190.5" to 191.5". The white crystalline, odorless compound, when heated XTith dilute sulfuric acid, gives the typical unpleasant odor of isopropylbenzaldehyde, thus indicating rapid hydrolvsis. It is evidently a di(isopropvlbenzy1idene) dinieth\ 1 acetal of D-uvlose.
The structure of the compound has not been determined; three structures are possible, of which the following appears to be the most probable ( 2 ) : CHIO
H
/
Calculated for CZiH3606: C 71.02; H 7.95; M e 0 13.6%. Found: C 70.71, 70.56, 70.89, 70.6; H 8.01, 8.15, 7.81, 7.94; M e 0 13.49, 13.40, 13.507,.
OCHI
H!C '
C--C>-C-H
/
CHI
H-C-0
\\
O--CH2
(On the other hand, the other possibilities, which involve the 2,3- and 4,5-carbon atom pairs or the 2,6- and 3,4carbon atom pairs, are not excluded.) Because of the asymmetry of the carbon atoms attached to the isopropylphenyl nucleus and involved in the benzylidene formation, the new compound may not be stereochemically homogeneous, but may actually be a mixture of isomers. This possibility gains some support from the difficulty in obtaining constant or sharp melting points when the material is recrystallized from methanol. The new compound offers no advantages in the xylose determination over that described by Breddy and Jones. ACKh-OWLEDGMENT
Acknowledgment is made to Virginia Kest who determined carbon and hydrogen in the samples, to L. Bublitz for making methoxyl determinations, and to J. Swanson for determining the optical rotations. LITERATURE CITED (1) (2) (3) (4)
Breddy, L. J., and Jones, J. K. K.,J . Chem. so,., 1945,735-9. Rirst, E. L., and Peat, S., Ann. Repts. Prog. Chem., 1935, 279. Jones. J. K. N.. orivate communication. .lueust 1946.. Kise, L. E., and Appling, J. W., IKD.EYG.-CHEM., A N ~ LED., . 17, 182 (1945).
Rapid Digestion Method for Determination of Calcium OLOF E. STAJIBERG' AND D. W. BOLIN, Department of Agricultural Chemistry, University of Idaho, AMoscou.,Idaho digestion method for the determination of phosA RAPID phorus has been described by Bolin and Stamberg who (Z),
used a mixture of perchloric and sulfuric acids containing some sodium molybdate to digest the organic matter. The oxidation is rapid and requires only 2 to 4 minutes. This digestion method can also be used to determine calcium much faster than by the ashing method. Phosphorus and calcium can be determined on the same digest by f h t preparing the yellow phosphovanadomolybdate complex described by Koenig and Johnson (3)as used by Bolin and Stamberg. After the phosphorus reading is taken on a photoelectric colorimeter, this solution can be used for calcium determination by the usual oxalate method.
taken with a photoelectric colorimeter. ,4n aliquot of 75 ml. or less can then be used for the calcium determination. The calcium is determined by a slight modification of the official method (1): Bromocresyl green is used as indicator. In a 250-ml. beaker, ammonium hydroxide (1 4) is added to bring the color back t o yellow. The solution is then brought to boiling temperature and 10 ml. of saturated ammonium oxalate are added and then a few drops of ammonium hydroxide (1 4) to give a distinct blue color. After standing for 4 hours or more, the calcium oxalate crystals are collected by filtering through a sintered-glass crucible and washed. This crucible is returned to the beaker and 100 ml. of water and 5 to 6 ml. of concentrated sul-
+
+
Table I.
PROCEDURE
The digestion mixture is that of Bolin and Stamberg ( 2 ) and the digestion is carried out in the manner described by them. When calcium only is to be determined, the digest is made up to 100 ml. with distilled water and all or an aliquot is used for the regular oxalate procedure (1). When phosphorus is first to be determined by the vanadate method (3) about 50 ml. water are added and then 10 ml. of vanadate reagent, the solution is heated to boiling and cooled, and 10 ml. of the molybdate reagent are added. After making up to volume, the phosphorus reading is 'Present address, Red Star \-east and Products Co., Milwaukee. Win.
Sample Bone meal Defluorinated phosphate Meat meal Fish meal Dr skim milk Degydrated alfalfa Dehydrated alfalfa Dehydrated alfalfa Soybean oil meal Dry pes. meal
A Ashing
Calcium Values C Digestion B (PhosDigestion phorus)
%
%
70
31.36
31.48
31.43
27,81 6.593 2.716 1.180 1.219 1,170 1.284 0.324 0.091
28 03 6 2 1 1 1 1
27.84 6.668 2.756. 1.252 1.236 1,184 1.295 0.333 0.095
736 726 240 224 180 286 0 332 0 097
Difference8 A to B A to C % % 4-0.38 +0.22 t0.79 +2.17 4-0.37 +5.08
t0.41 +0.85 i o . 15 t2.50 +6.59
+0.11 +1,14 +1.47 +6.10 +1.39 1-1.20 $0.86 + 2 , 78 +4.40
