liquids containing 99.96 nig. of uranium (IV, VI) oxide (100.1, 99.7, 100.07 mg.) and 48.47 mg. of phosphorus pentoxide (48.83, 48.08, 48.49 mg.) analyzed b y this method gave : C'~0.9~ Mg. 99.3 98.9 100.7
PzOa, Mg. 48.34 48.28 48.28
This gives a n average deviation from the known value of 0.8270 for uranium (IV, VI) oxide and 0.357, for phosphorus pentoxide. When a sample containing 299.88 nig. of uranium(IV, VI) oxide was analyzed after phosphate and molybdenum had been removed as usual, the result was: 300.0 nig. of uranium (IV, VI) oxide. Results of a complete meta-autunite [Ca(UOz)~(P04)2.6 1 / ~ H ~ Oanalysis ] are presented in Table I as an example (3).
Table I. Analysis and Theoretical Composition of Meta-autunite Strontian Meta-autunite. Theoret. Daybreak Mine, Compn. Mt. Spokane, M = Wash. 887.27 CaO 5.16 6.32 SrOa 1.38 0.22 NsO KzO 0.33 uo3 63.92 64.48 pi05 15.54 16.00 SiOz 0.39 HzO 13.36 13.20 Rest* 0.14 100.44 100.00 SrO determined by H. A. Vincent flamespectrophotometrically (Beckman Model DU) using method of standard addition described by Chow and Thompson (I). *FezOs All08 = 0.03%; insol. = 0.11%; MgO = O.OO'%; BaO = O . O O ~ o ; Cu = no blue coloration in ammonium hydroxide filtrate, not detected spectrographically.
+
Because of the method used. traces of alkalies from the reagents and glassware used which accumulate :it the end of the analysis usually give ilightly higher values for sodium and potassium. The error is in the 0.05 to O . l O ~ o range for these elements if approximately 5oo-mg. batches are used. LITERATURE CITED
(1) Chow, T. J., Thompson, T. G., AI^. CHEM.27,18 (1955). ( 2 ) Fisher, D. J., Volborth, X., -4m Mineralogist, in press. (3) Volborth, -4., Zbid., 44, KO.7-8, 702 (1909). (4) Volborth, A,, Ann. Acad. Sci. Fennicae, Ser. A 111, 39 (1954). (5) Volborth, A., Bull. Geol. SOC.A.m. 69, KO.12, part 2, 1657 (1958). (6) Volborth, A,, 2. anorg. u . allgem. Chem. 276, 159 (1954). A. H. VOLBORTH h'evada Mining Analytical Laboratory University of Nevada Reno, Nevada
Microdetermination of 2,2-Dinitropropane by Zinc Amalgam Reduction to Nitrite SIR: I n neutral or alkaline solution, 2,2-dinitropropane undergoes electrolytic reduction according t o the equation : This dinitroparaffin may be determined polarographically, coulometrically, or as nitrite after electrolytic reduction (9). The easy absorptiometric determination of nitrite prompted the search for a simple chemical reductant t o replace electrolysis. This led to the development of a rapid method for the microdetermination of 2.2-dinitropropane, either alone or admixed with 2-nitropropane. The nitrite ion is liberated b y zinc amalgam reduction a t controlled PH.
Liquid Zinc Amalgam. First 100 grams of reagent grade zinc metal (20mesh) were quickly washed with 4111 hydrochloric acid and transferred t o a beaker containing 2000 grams of mercury and about 1 ml. of 1241 hydrochloric acid. The mixture was stirred on a steam bath for 1 hour, cooled, and washed with 0.1M hydrochloric acid; then the amalgam was run off and stored under 0.1M hydrochloric acid. Smaller quantities of other liquid amalgams were prepared similarly. Solid zinc amalgam was prepared from 20-mesh zinc in the usual manner (8). Sulfanilic acid, 1-naphthylamine hydrochloride, and standard sodium nitrite solutions mere prepared as described b y Rider and Mellon (7). Buffer solutions were those of McIlvaine and of Britton and Robinson (6).
REAGENTS AND APPARATUS
PROCEDURE
A11 absorbance measurements were made at 520 mk ~ i t ah Beckman Model B spectrophotometer using 1-cm. Corex cells. 2,2-Dinitropropane (Commercial Solvents Corp.) was recrystallized from methanol and maintained just above the melting point (53.5' C., uncorrected) for 1 hour. It was used as 0.10OJ1 stock solution in 80% ethyl alcohol. I-Nitropropane and 2-nitropropane (Matheson Co.) w r e washed several times, dried over calcium chloride, and distilled. Fractions of boiling points 130.5'to 131.5" C. and 120' to 121" C., respectively, were collected and used to make 1Ji stock solutions in 80% ethyl alcohol.
For liquid amalgam reduction, about 50 grams (3.7 to 4 ml.) of the amalgam were dried with filter paper and transferred a t once to a 250-ml. glass-stoppered Erlenmeyer flask containing 100 ml. of a buffered solution which was from 10-6 t o 10-2M with respect to 2,2dinitropropane. After shaking for a fixed time at about 4 times per second, a n aliquot of the solution was diluted t o a nitrite concentration of from 0.1 to 0.6 p.p.m. The same portion of amalgam was well washed between runs and was used repeatedly. Fresh zinc was introduced when the concentration fell below about 370. Jones reductor runs on 5-ml. portions of solution were made Kith a 25-ml.
Me& (N02)*+2e-+ Me&.NOz- 3- XOZ-
buret packed with a 15-cm. length of solid zinc amalgam. At a flow rate of 4 t o 5 ml. per minute, result,9 were identical with those obtained when 100 ml. of solution mere passed through a larger reductor. RESULTS
Reduction of 2,Z-Dinitropropane by Liquid Amalgams. I n 0 . l M sodium hydroxide, 2,2-dinitropropane solutions between and 10-2M gave reproducible yields of nitrite Ivith zinc amalgam, provided that the shaking time was not less than 2 minutes. T h e yields were not changed when the reduction was carried out under nitrogen. -4lthough cadmium and lead amalgams gave similar results, their action was considerably slower; bismuth amalgam was inactive. The reaction time \vas longer in 0.01M and shorter in 1.1.1 sodium hydroxide. Use of Jones Reactor. I n 1il1 sodium hydroyide, 2,2-dinitropropane solutions between l o p 4and l O - 3 ; M gave results that were precise and accurate t o within 1%. Kith l O - * X solutions, the yield of nitrite was about 27, high. Mercuric ion is reported to cause color intensification in the Griess-Ilosvay reaction ('i'), but the results mere unaffected by the addition of up to mole of mercuric chloride. Determination of 2,2-Dinitropropane in Mixtures with 2-Nitropropane. 2-Kitropropane in alkaline solution passes into the nonreducible aci-form VOL 32, NO. 7, JUNE 1960
883
(4, 6) and should not interfere with the determination of 2,2-dinitropropane. This was so in 0.1M sodium hydroxide when the ratio of 2-nitropropane to 2,2-dinitropropane did not exceed about 5 to 1. An increasing positive error appeared as the ratio was progressively increased. Replacement of sodium hydroxide by buffer solutions gave satisfactory results within the approximate limits p H 5 t o 8 with liquid zinc amalgam, or p H 5 to 7 with cadmium amalgam (Figure 1). Under these conditions, a Jones reductor gave results of poor reproducibility. Results obtained in the liquid zinc amalgam determination of 2,2-dinitropropane in a pH 6.4 McIlvaine buffer containing 2-nitropropane are given in Table I. h Britton-Robinson buffer of the same p H was equally effective. Table I. Determination of 1.00 X 1 O-4M 2,2-Dinitropropane in Presence of Nitropropanes
Nitropropane Concn., M x 104 2-Nitropropane
2,2-Dinitropropane Found, M x 104
0
0.99 1.00 1.00 1.00 1.00
0.5 1
10 20 50
100 300 500
800 1000
1.oo 1.01
0.99 0.95 0.8“
0.6‘
1-Nitropropane 0 1
10
l o b
10” 30 50
1.00 1.oo
1.01 0.19 0.21 0.9O
1.oa
100 1.O” a Reproducibility not better than about 10%. b In 0.1M NaOH. In 1M NaOH. 0
Determination of 2,2-Dinitropropane i n Mixtures with I-Nitropropane. I n strongly alkaline solution, the presence of 1-nitropropane caused very low results in t h e determination of 2,2-dinitropropane. Reduction with zinc amalgam a t p H 6.4 gave results t h a t were moderately satisfactory and reproducible t o within about 5y0 when the ratio of l-nitro-
884
ANALYTICAL CHEMISTRY
Figure 1. Effect of pH upon determination of 2,2-dinitropropane admixed with 2-nitropropane 1. 1 O-4M 2,2-dinitropropane and 1 O-3M 2-nitropropane, zinc amalgam 2. Same as 1 , but cadmium amalgam
propane to 2,2-dinitropropane did not exceed 10 (Table I).
2,2-dinitropropane in mixtures with 1nitropropane are therefore to be expected.
DISCUSSION ACKNOWLEDGMENl
Because Bose ( I ) has claimed that mononitroparaffins may be detected by nitrite formation on treatment with alkali, high results are to be expected for 2,2-dinitropropane when mixed with a mononitropropane and subjected to reduction in sodium hydroxide solution. I n the case of 2-nitropropaneJ slowness of attack presumably limits the interference unless the relative concentration of this nitroparaffin is considerable. I n nearly neutral solution, the attack becomes slower, so that a large excess of 2-nitropropane may be tolerated. I n strongly alkaline solution, 1nitropropane passes more rapidly into the aci- form than does the 2- isomer ( 4 ) and yields little or no nitrite ion (8). Under the slightly acid conditions used for the Griess-Ilosvay reaction, primary nitroparaffins couple with diazotized sulfanilic acid (IO). Although this coupling product is colored, its absorbance above 500 mM is practically zero ( 2 ) . This product, formed in competition with the normal GriessIlosvay product, thus contributes nothing to the measured nitrite concentrations. The erratic results obtained for
The 2,2-dinitropropane was donated by the Commercial Solvents Corp. LITERATURE CITED
(1) Bose, P. K., Analyst 5 6 , 504 (1931).
(2) Cohen, I. R., Altshuller, A. P., ANAL.CHEM.31, 1638 (1959). (3) Fischer, R. B., “Quantitative Chemical Analysis,” p. 287, W. B. Saunders Co., Philadelphia, 1956. (4) Miller, E. m., Arnold, A. P., Astle, AI. J., J. Am. Chem. SOC.70, 3971 (1948). ( 5 ) Muller, 0. H., “The Polarographic Method of Analysis,” appendix, Chemical Education Publishing Co., Easton, Pa., 1951. (6) Petre, F., Collection Czechoslou. Chem. Communs. 12, 620 (1947). (7) Rider, B. F., hlellon, M. G., IND. ENG.CHEM.,ANAL.ED.18,96 (1946). (8) Shinozuka, F., unpublished data. (9) Stock, J. T., J . Chem. SOC.1957, 4532. (10) Turba, F., Haul, R., Uhlen, G., Angew. Chem. 61, 74 (1949). FUJIKO SHINOZUKA JOHN T. STOCK Department of Chemistry University of Connecticut Storm, Conn. WORKsupportedin part by the U. S. Atomic Energy Commission.
