Nitrogen Analysis of Nitrate Esters by Micro-Dumas Combustion P. Borda and L. D. Hayward Department of Chemistry, University of British Columbia, Vancouver 8, Canada
IN THIS LABORATORY analyses of compounds with multiple 0-nitro groups (1-3) by the micro-Dumas method according to Pregl(4) and as modified by Noguchi (2, 3,5)(the addition to the sample of small amounts of glucose or sucrose), gave low and scattered nitrogen values and these were only slightly improved by the use of the Coleman Analyzer (1) with or without added carbohydrate ( 5 ) and vanadium pentoxide (4) (Table I). We report here modifications of the microDumas combustion based on the “reversed capsule” method of Klimova and Dubinina (6)and the use of cobalto-cobaltic oxide (7) which yielded satisfactory results for mono- t o octanitrate esters (Table 11). EXPERIMENTAL
Apparatus. As shown in Figure 1 a silica combustion tube (b) was equipped with a fixed electric furnace (c) t o maintain the temperature of the permanent filling a t 650” C and a movable furnace ( d ) to effect pyrolysis of the sample at 700-750” C . The remainder of the combustion train was assembled from standard components (4, 8). Reagents. Technical cobalto-cobaltic oxide, Co304,.was prepared by the method of Gawargious and Macdonald (9); other reagents were of analytical grade. Procedure. From 2 t o 5 mg of sample, depending on the nitrogen content, is placed in a silica capsule 9 cm long and 4 mm i.d., followed by 50 mg of finely powdered Co304 (Figure 1). [With shorter capsules (about 6 cm) or when Cos04was omitted, low results were obtained.] The capsule is stoppered and shaken, then filled with a mixture of copper oxide and cobalto-cobaltic oxide 4 :1 by volume, and placed in the combustion tube 5 cm from the permanent filling,
Table I. Nitrogen Analyses of D-Mannitol Hexanitrate. by the Micro-Dumas Method of Noguchi and by Coleman Nitrogen Analyzer Theoretical value
DumasNoguchi
18.59
17.88 18.01 17.56 17.60 17.51 17.81
18.56 17.75 17.12 17.59 18.79 18.18
18.34 18.13 17.74 17.87 18.80 17.84
17.63 17.92 17.90 17.89 17.62 ...
Av.
17.73
18.00
18.12
17.79
a Carbon-hydrogen analyses were within *0.2x of the calculated values. * I n series A the normal Coleman Analyzer procedure was followed; in series B, glucose and vanadium pentoxide were mixed with the sample.
Table 11. Nitrogen Analyses of Polynitrate Esters by CobaltoCobaltic Oxide and Reversed Capsule Method
Compound
Theoretical
Cholesteryl nitrate
3.25
d,l-Hydrobenzoin dinitrate
9.21
meso-Hydrobenzoin dinitrate
9.21
Xylitol pentanitrate (1) P. P. Wheeler and M. I. Fauth, Microchem. J., 9, 309 (1965). (2) W. E. Elias and L. D. Hayward, Tappi, 41,246 (1958). (3) W. E. Elias, Ph.D. Thesis, University of British Columbia, 1956. (4) AI Steyermark, “Quantitative Organic Microanalysis,” 2nd ed., Academic Press, New York, 1961. (5) J. Noguchi, Sei. Papers Osaka Unio., 22, l(1951). (6) V. A. Klimova and I. F. Dubinina, “Methods in Microanalysis, Vol. I. Simultaneous Rapid Combustion,” J. A. Kuck, Ed., Gordon and Breach, New York, p. 274, 1964. (7) M. Vecera, Collection Czech. Chem. Commuti., 26, 2308 (1961). (8) E. B. Hershberg and G. W. Wellwood, IND. ENG. CHEM., ANAL.ED., 9, 303 (1937). (9) Y . A. Gawargious and A. M. G. Macdonald, Microchem. J . Symp. Ser., 2, 397 (1962).
Coleman Analyzer* Series A SeriesB
18.57
D,L-Galactitol-l,2,4,5,6-
pentanitrate
17.20
D-Mannitol-l,2,4,5,6-
pentanitrate
17.20
Allitol hexanitrate
18.59
Galactitol hexanitrate
18.59
D-Mannitol hexanitrate
18.59
myo-Inositol hexanitrate
18.67
Cellobiose octanitrate
15.95
Figure 1. Microcombustion train for modified Dumas analysis of nitrate esters For details of (a) to (e), see text
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ANALYTICAL CHEMISTRY
Found 3.43 3.35 9.34 9.25 9.21 9.21 18.63 18.63 17.11 17.30 17.31 17.01 18.69 18.57 18.79 18.74 18.58 18.67 18.81 18.69 15.92 15.82
Difference from average value +O. 14 +O, 08
0.00
$0.06 0.00
-0.04 +O .04 +O. 18
+0.04 $0.08 -0.08
with the open end facing the mouth of the combustion tube (Figure 1). After replacement of the air in the system by COS,the stopcock between the combustion tube (b) and COS generator (a) is closed and the preheated pyrolysis furnace (6)is moved slowly toward the sample. The rate of combustion is regulated by the movement of (4 in such a way that bubbles come through into the nitrometer ( e ) at a rate of one per second or less. When the sample is completely burnedLe., when evolution of bubbles has stopped-(d) is moved over the capsule, the stopcock between ( a ) and (b) is opened, and the nitrogen is swept into ( e ) at a rate of 2 to 3 bubbles per second. Results a1.e calculated according to Pregl ( 4 ) .
RESUL’I’S AND DISCUSSION Nitrogen analyses of compounds containing from one to eight 0-nitro groups pel*molecule by the method given above fell within acceptable limits for organic compounds (Table 11). No explosive decomposition occurred during the analyses of detonable materials and the time required for a single analysis was essentially the same as for the usual Pregl procedure. The low results obtained in the conventional Pregl method have been attributed to retention in the metal oxide tube filling of nitrogen oxides (10, 11) formed in the pyrolysis of
the samples (12). This did not occur in the present method since satisfactory analyses were obtained with samples of potassium nitrate and silver nitrate pyrolyzed at ca. 900’ C. Calcd. for K N 0 3 : 1 3 . 8 4 z N. Found: 13.75, 13.80. Calcd. for AgN03: 8 . 2 4 z N. Found: 8.20, 8.10. We conclude that the present method provides a longsought solution to the problem of low results in combustion analysis of compounds containing NOz groups.
ACKNOWLEDGMENT We thank Dr. Wilma E. Elias and Mrs. A. Aldridge for analyses. RECEIVEDfor review December 19, 1966. Accepted February 9, 1967. Work supported by the National Research Council of Canada (Grant 249). (10) W. Kirsten, “Comprehensive Analytical Chemistry, Vol, 1B. Organic Quantitative Analysis,” C. L. Wilson and D. W. Wilson, Eds., Elsevier, New York, p. 467, 1960. (11) H. Swift, Microchem. J., 11, 193 (1966). (12) L. Dauerman, G. E. Saker, and Y . A. Tajima, J . Phys. Chem., 69,3668 (1965).
Qualitative Detection of Boron via a Crystalline Derivative George Vogel Department of Chemistry, Boston College, Chestnut Hill, Mass.
A NOVEL METHOD for the detection of small amounts of boron, for example, in organi: materials, is based on the ready formation of a crystallir!e compound, triethanolamine borate ( I ) , which in addition tci its characteristic appearance can be identified unequivocally through its sharp melting point. This fact, together with the simplicity and rapidity of the procedure, represents a \,ahable advantage over the numerous other methods described in the literature (2), all of which are based on the less definite criteria of development of colors with organic reagents or the coloration of a flame. Although somewhat less sensitive, the method here described makes it possible to detect reliably amounts of boron of the order of 20 P8.
EXPERIMENTAL Prior to the reaction with triethanolamine, the sample should contain at least 20 pg of boron in the form of boric acid or boron trioxide. The nature of the material to be tested determines the first step. A nonvolatile organic com(1) H. C. Brown and E. A. Fletcher, J. Am. Chem. SOC.,73, 2808 (1951). (2) Extensive lists of references, too numerous to list individually, are found in (a) Houben-Weyl, “Methoden der organischen Chernie,” 4th ed., Vol. 11, p. 25, Georg Thieme Verlag, Stuttgart, 1953; (b) R. Fresenius End G. Jander, “Handbuch der analytischen Chemie,” Part 2, VOI. 3, p. 4, Springer-Verlag, Berlin, 1944.
02167
pound is ashed in a small platinum capsule or crucible (a suitable size is 5 mm high and 10 mm in diameter), A volatile organic compound is dropped (a larger sample is recommended here in view of the unavoidable losses by volatilization) onto a thin layer of sodium carbonate in the capsule held at red heat (alternatively, the decomposition procedure of reference 2a may be used). A solution suspected of containing boron as an inorganic borate is simply evaporated in the capsule and ignited. Unless the residue in each case is known not to be alkaline, it is acidified by moistening with concentrated hydrochloric acid, and again evaporated. It is then treated with not more than one drop of a 10% aqueous solution of commercial triethanolamine (2,2 ’,2”nitrilotriethanol), the capsule is placed on a hot plate preheated to 220” to 230” C, and within 2 to 4 seconds, a test tube partially filled with cold water is placed on top to serve as condenser. After 30 to 45 seconds, the test tube is lifted carefully. With amounts of the order of 10 to 30 pg of boron, the product usually adheres in the form of very fine needles to the bottom of the test tube, from which it can be transferred by tapping onto a cover glass for a melting point determination. With larger amounts, thicker needles are found loosely filling the space in the capsule and can be removed with a spatula. The literature ( I ) melting point of triethanolamine borate is 236.5 O to 237.5 O C. RECEIVED for review December 21, 1966. Accepted January 23, 1967. VOL. 39, NO. 4, APRIL 1967
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