SEPTEMBER 1947
698
The analogous Gxylose derivative, after recrystallization from 6.56' (chloroform). Calcumethanol, melted a t 210-11 lated 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. O;
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) Breddy, L. J., and Jones, J. K. K., J . Chem. so,., 1945,735-9. (2) Rirst, E. L., and Peat, S., Ann. Repts. Prog. Chem., 1935, 279. (3) Jones. J. K. N.. orivate communication. .lueust 1946.. (4) 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, D e p a r t m e n t of Agricultural C h e m i s t r y , 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 4) to added and then a few drops of ammonium hydroxide (1 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.
Calcium Values C
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
Digestion B (PhosAshing Digestion phorus) % % 70 A
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 % 4-0.38
A to C
t0.79 +2.17 4-0.37
+0.11 +1,14 +1.47 +6.10 +1.39 1-1.20 $0.86 + 2 , 78 +4.40
+5.08
t0.41 +0.85 i o . 15 t2.50 +6.59
% +0.22
696
V O L U M E 19, NO. 9
furic acid are added. The solution is brought to 80” to 90” C. for titration with 0.050 N potassium permanganate. For samples of low calcium content, two to four digests of 500mg. samples can be combined. Since only 500-mg. samples are used the feed, food, or other products analyzed should be finely ground and well mixed, so that uniform samples can be taken.
and that all the calcium in the ash was brought inta solution only by long standing in hydrochloric acid. Thus it appears that the digestion methods might be preferable to the ashing method. The combined vanadate-phosphorus and calcium methods of digested samples have been used for a number of feed and food samples with much saving of time.
DISCUSSION OF RESULTS
LITERATURE CITED
The data in Table I show the results obtained on several materials and the per cent difference of the two digestion methods as compared to the official ashing method. The results with the digestion methods obtained with 500-mg. samples are slightly higher than those with the ashing method; hiorris, Nelson, and Palmer ( 4 ) found that in the case of certain materials the calcium values obtained by the regular nshing method Tvere slightly low
(1) Assoc. Official Agr. Chem., Official and Tentative Methods of .&nalysis, 6th ed., p. 127 (1940). and Stamberg, 0. E., IKD. ENG. CHEW.,ANAL. ( 2 ) Bolin, D . W., ED., 16, 345 (1944). (3) Koenig, R . A., and Johnson, C. R., Ibid., 14, 155 (1942). (4) Morris, H . P . , Selson, J. IT., and Palmer, L. S.,Ibid., 3, 164 (1931). PUBLISHED with the approval of the director of the Agricultural Experiment Station as Research Paper 254.
C 0 R R E S P 0 N D E N.C E Explosion in Determination of Cobalt as Potassium Cobaltinitrite SIR: I was interested to read in the January issue of ASALYTICAL CHEMISTRY [19, 72 (1947)l of the occurrence of an explosion during the determination of cobalt as potassium cobaltinitrite. Some years ago as a student I was preparing sodium cobaltinitrite by the usual method (Bilts, Hall, and Blanchard, “Laboratory Methods of Inorganic Chemistry,” New T o r k , John W l e y 8: Sons). The salt failed to precipitate out, so the solution was concentrated by evaporation. During evaporation the solution turned purple, frothed considerably, and, on cooling, solidified in the form of a solid foam. Another student was carrying out flame tests and, Tyishing to obtain a sample of the substance, touched the surface with a hot platinum wire, whereupon i t exploded with some violence, covering everyone with a sooty powder. At the time this was regarded merely a s an interesting phenomenon and it was not until I read of this rather similar occurrence t h a t I recalled i t to mind. R. J. GOWSES Veterinary Research Laboratory Vom. P.O. Bukuru Xorth Nigeria
Pressure Regulators SIR: An article published in your AKALYTICAL EDITION[ b ~ ENG. . CHEM.,ANAL.ED., 18, 156 (1946)l describes a “Variable Pressure Manostat” based on t h e same principle as Kewman [Ibid., 12, 274 (1940)l. Unfortunately, simple as the apparatus looks, it does not fulfill the purpose of a pressure regulator and calling it a manos t a t is erroneous. 811 vacuum pumps work irregularly, and a manos t a t should serve to keep t h e pressure of t h e evacuated system. Several such devices have been described in your journal, all of which should give satisfactory results [Ibid., 13, 418, 908 (1941) ; 15, 283 (1943); 18,214 (1946)l. The principle of this device is theoretically wrong, because all pressure changes of the vacuum pump are fully transmitted t o t h e system. The constant level of the liquid in the apparatus does not equalize pressure changes caused by the irregular working of t h e pump. 48 Hopetoun Ave. x-aucluse, N.S.W., Australia
ERNEST CHALLEN
vacuum pump, and pressure changes of the pump are therefore transmitted to the system. I n our experience, however, a good commercial pump, kept in proper working condition, will deliver a constant vacuum, and by using a New-man-type regulator in conjunction with such a pump we have been able consistently t o conduct distillations at constant pressure for several days a t a time. HUGH B . DOXAHOE University of Kansas Lawrence, Kans.
ROBERTR. RVSSELL C. A. VANDERWERF
SIR: Challen’s point concerning the use of t h e word “manostat” is well taken. If the word “regulator” had been used, all would have been well. T h e success of the devices described depends on the vacuum pump’s being used. I can check VanderWerf’s statement t h a t a constant pressure can be maintained with a good pump protected by a dry ice-cooled trap. Ohio State CniversitjColumbus, Ohio
MELVINS. XEWJIAN
Determination of Olefins, Aromatics, Paraffins, and NapMhenes in Gasoline SIR: I n the article on “Determination of Olefins, Aromatics, Paraffins, and Naphthenes in Gasoline” [ANAL.CHEX., 19, 178 (1947)l the following paragraph appears: Recently Groennings has suggested t h a t the 0.16 factor recommended by Grosse and \Tackher for correcting the specific dispersion for olefinic unsaturation should be replaced by a value read from a curve of correction factor 21s. boiling point. Groennings in deriving his correction assumed t h a t there was a 50-50 distribution betw-een cyclic and noncyclic olefins throughout the boiling range. T h e last sentence is slightly misleading, since Groennings [IKD. ENG.
CHEM., AXAL.ED.,17,361 (1945) I recommends the assumptionof a 5050 distribution between cyclic and noncyclic olefins only in case there is no information concerning the type of olefin present and no basis for a n y better approximation than the 50-50 approximation. Groennings does not assume such a distribution in all cases. V e regret t h a t in attempting to discuss a complex subject briefly a slightly misleading statement was made concerning Groennings’ valuable paper. S. S.KL-RTZ. JR. I. IT,MILLS
c. c. 5 1 . 4 R T I S
SIR: T h e Newman-type regulator is obriously designed t o maintain a constant pressure differential between the system as a whole and the
Sun Oil Co. Sorwood and Marcus Hook, Pa.
TT T. HARVEY l f . R.LIPKIN
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