ings, city water, and synthetic sea water in varying dilutions. Both the flame photometric and gravimetric determinations n ere performed on at least three independent samples, and the averages are given in Table VIII. The major constituents of the samples are given to show concentration of extraneous ions. I n rain water, the quantity of sulfur in the aliquot was only about 1 mg.; in lysimeter leachings, it m-as about 5 mg.; in sea water, it was from 3.5 t o 44 mg. The total concentrations of extraneous cations in the analytical samples of sea water were from 1000 to 12,600 mg. per liter. The flame photometric sulfur determinations show good agreement with those obtained gravimetrically, for each type of water represented. The sea water yielded most consistent results when 10 nil. was taken per determination, although satisfactory results were obtained also with 20 and 40 ml. of water per 100-ml. final volume. It is believed that the comparative analytical values and the corresponding standard deviations shown in Table VIII sufficiently demonstrate the satisfactory accuracy and precision of flame photometric results, as compared with their gravimetric equivalents, without a n y additional statistical analysis. The determination of total sulfur in biological materials by the spectrophoto-
Analyses,‘’ 2nd ed., Kiley,
metric method will be presented in a subsequent publicat,ion. LITERATURE CITED
(1) Adams, F., Rouse, R. D., Soil Sci. 83, 305 (1957). (2) Am. Pub. Health - h o c . , Inc., New
York, “Standard Methods for the Examination of Water, Sewage, and Industrial Wastes,” 10th ed., 1955. (3) Assoc. Offic. Agr. Chemists, “hlethods of Analysis,” p. 100, 1955. (4) Baker, G. L., Johnson, L. H., ASAL. CHEY.26, 465 (1954). (5) Bertolacini, R. J., Barney, J. E., Ibid., 29, 281 (1957). (6) Blum, ‘ifT. J., .4m. 1282 (1916).
Chem. SOC.38,
( 7 ) Britton, H. T. S., “Hydrogen Ions,” 4th ed., Vol. 11, p. 152, Van Nostrand Kew York, 1956. (8) Chemin, L., Yien, C. H., Soil Sci. SOC.Am. Proc. 15, 149 (1950). (9) Chow, T. J., Thompson, T. G., ANAL. CHEM.27, 910 (1955). (10) Clarke, F. W., U. S. Geol. Survey Bull. 491 (1911). (11) Dean, J. .4., Thompson, Clarice, ANAL.CHEM.27, 42 (1955). (12) Diamond, J. J., Ibid., 28, 328 (1956). (13) Fieldes, M., King, P. J. T., Richardson, J. P., Swindale, L. D., Soil Sci. 72, 219 (1951). (14) Fiske, C. H., J. Biol. Chem. 51, 55 (1922). (15) Fritz, J. S., Yamamura, S. S., Richard, hl. J., ANAL.CHEM.29, 158 (1957). (16) Gilbert. P. I.. Haws. R. C.. Beck‘ man, A. d.,Ibid.; 22, 772 (1950). (17) Hillebrand, F. W., Lundell, G. E. F.,
Bright, H. A., Hoffman, J. I., “Applied
(20) Hortsman, E. L., I I (1956). (21) Kolthoff, I. hI., Stenger, V. A,, hloskovitz, B., J . Am. Chem. SOC.56, 812 ( 1 934) (22) Uargoshes, M.,Vallee, B. L., +$SAL. CHEJI. 28, 180 (1956). (23) Mavrodineanu, R., A p p l . Speclroscopy 10, 51, 137 (1956). \ - - - - I
(24) hlitchell, R. L., Robertson, I. h l . , J . SOC.Chem. Ind. Trans. (London) 55, 269T (1936). (25) Roy, N., ANAL.CHEJI.28,34 (1956). (26) Schroeder, W.C., ISD.ESG.CHEJI., A N A L . ED. 5,403 (1933). ( 2 i ) Shaw, W.hl., S-eal, N. C., Scil Scz. Soc. Bm. Proc. 20, 328 (1956). (28) Snell, F. D., Snell, C. T., “Colori-
metric Methods of Analyses,’’ Vol. 11, 3rd ed., p. 307, Van Xostrand, Kew York, 1949. (29) Stadie, K m . C., Ross, E. C., J . Biol. Chem. 65, 735 (1925). (30) Strickland, R. D., hlaloney, C. hl., Am. J . Clin. Pathol. 24, 1100 (1954). (31) Watanabe, H., Kendall, K. K., Jr., Appl. Spectroscopy 9, 132 (1955). (32) Keichselbaum, T. E., F-arnep, P. L.. hlararaf. H. W.,ASAL. CHEJI.23,
68h (195T). ‘ (33) \Vest, P. W., Folse, P., Montgomery, D., Ibid., 22, 667 (1950). (34) Willard, H. H., Tang Y. K., IXD. EXG.CH EJ~..,ANAL. ED.9,’$57 (1937).
RECEIVED for review Xovember 6, 1957. Accepted April 29,1958.
Determination of Silicon, Germanium, and Tin in Their Volatile Organo Compounds MICHAEL P. BROWN and GERALD W. A. FOWLES Chemistry Department, Southampton University, Southampton, England
b A rapid dry combustion method of analysis has been developed for the determination of silicon, germanium, and tin in their volatile organo compounds. Some 13 compounds have been analyzed b y this procedure, with an average error of 0.370;.An analysis could normally be completed in 3 to 4 hours.
D
are encountered whenever volatile organo compounds of silicon, germanium, and tin, such as hexamethyldisilane, hexamethyldigermane, and hexamethyldistannane compounds are analyzed by the standard techniques available for organo compounds of these elements. I n general, the available methods may be classified according to the type of approach used, IFFICULTIES
such as wet oxidation, fusion, and dry combustion. Wet Oxidation. I n this method, which is t h e most commonly used, t h e organo compound is completely oxidized-for example, b y a mixture of fuming nitric and sulfuric acids, ignited, and weighed as t h e oxide. Although this method is useful for t h e analysis of nonvolatile organosilicon ( 2 ) and organogernianium (4, 7) compounds. it is unreliable for volatile compounds because material can easily be lost \\-hen the sample is introduced. There is also a strong tendency for organosilicon compounds to form the carbide instead of the oxide, because of incomplete oxidation before or during evaporation of the acids. With germanium compounds-e.g., ethylger-
nianiuni derivatives-complete oxidation is obtained only after prolonged treatment with the acids ( 6 ) , often refluxing for a veek or more. Moreover, if the solution is evaporated too soon, volatile germanium compounds are formed and lost from the solution. Although organotin compounds are on the n hole more easily oxidized, analysis of volatile substances by this method (3, 8) is still experimentally difficult. Fusion. Oxidation b y fusion procedures with sodium peroxide in Parrtype bombs has been extensively carried out v i t h organosilicon compounds (1, 9, 12) only. For volatile substances, this method is the most reliable but requires about 24 hours for completion. VOL. 30,
NO. 10,
OCTOBER 1958
1689
According to Krause and Johnson (7), the use of the Parr bomb for analysis of organogermanium compounds gave inconclusive results in preliminary experiments, and its use does not seem to have been extended to organotin compounds. Dry Combustion. Rochow (10, 11) suggests a dry combustion method for t h e analysis of silicone polymers b y burning t h e sample, contained in a silica tube, in a stream of oxygen. Volatile constituents driven from the sample are oxidized by passage over platinum gauze and the silica formed is trapped by a plug of glass wool. Carbon and hydrogen are determined simultaneously. Although McHard, Servais, and Clark (9) report that this method is slow for the analysis of the polymers, and that the formation of carbide cannot always be avoided, it seems to be suitable in principle for the analysis of volatile substances, and the following procedure has been developed.
EXPERIMENTAL
Procedure. Oxygen is passed through a weighed sample of t h e substance, and t h e vapor is carried into a weighed silica tube, a n d ignited in a plug of carefully packed asbestos (of the type suitable for Gooch crucibles). I n earlier experiments a layer of platinized asbestos was incorporated in the packing, but this was unnecessary, because, even with ordinary asbestos, there is complete combustion to the oxide, provided the supply of oxygen is adequate. N h e n the sample is completely carried over, the tube is reweighed, and the weight of the oxide (silicon, germanium, or tin oxide) obtained. The apparatus is illustrated in Figure 1, The silica combustion tube, A , which has a B14 (S.T. 14/20) socket at one end, has a n internal diameter of 8 mm. for most of its length (-30 cm.), but the exit end, G, is of 1-mm. internal bore. Sample tube, B, constructed from borosilicate glass, has two short lengths of neoprene tubing ( E and F ) complete with screw clips and a n exit B14 (S.T. 14/20) cone. A is filled for two thirds of its length m-ith asbestos, C, by adding it in small amounts, shaking, and packing lightly but firmly with a glass rod. The tube and its contents are then heated to constant weight a t about 800" C. in a muffle furnace. Part H of the tube is strongly heated with a Meker burner. The sample tube, B, stoppered with a rubber stopper a t the ground joint, is weighed empty, the tubing and clip at E are rcmoved, and the sample (0.1 to 0.4 gram) is introduced into the bottom of the tube by means of a capillary pipet. E is closed by the tubing and clip, and
1690
ANALYTICAL CHEMISTRY
'
yr
A D
vc4 4
TH Figure 1. Apparatus for determination of silicon, germanium, and tin in their volatile organo compounds
the whole weighed. The bottom of the sample tube is then immediately frozen out in liquid oxygen to prevent loss of the sample as vapor when the rubber stopper is removed prior to the connection of B to A. The aspirator is turned on, the rubber stopper is removed from D, and the two tubes are connected by the ground joint. End E is connected to a supply of oxygen, a t a pressure just below atmospheric, by removing the clip and slipping a rubber lead over the neoprene tubing. A bubbler, containing concentrated sulfuric acid, indicates approximately the rate of flow of oxygen, and the aspirator is adjusted until this rate is about one bubble per second (the diameter of the bubbler tube being 6 mm.). A screw clip a t F then closes the bypass and oxygen bubbles through the sample, carrying the vapor through the silica tube, where it is ignited to the oxide. K h e n the sample has evaporated completely, usually after about 90 minutes, oxygen is passed for a further 15 minutes. The silica tube is then disconnected and heated to constant weight in the muffle furnace, and the tube and its contents are allowed to cool in a desiccator prior to weighing. When highly volatile substances are used-eg., tetramethylgermane, boiling bottom of the point 42-4" C.-the sample tube may be immersed in a cold bath to slow the rate of evaporation. Alternatively, a bleed of oxygen may be admitted through the bypass by adjustment of the screw clip a t F . For higher boiling materials-e.g., hexamethyldigermane, boiling point 135-6' C.evaporation is assisted by irradiating the apparatus with an infrared lamp. Substances such as dimethyldichlorosilane, which on hydrolysis form relatively nonvolatile products, give low results because unavoidable hydrolysis occurs in the sample tube. A modification of the procedure is satisfactory for these substances. Modified Procedure. A 11-eighed glass capsule (Figure 2) is filled by placing it in a tube (with a constriction) containing the sample, evacuating briefly, and then admitting d r y air. T h e capsule is removed, t h e outside cleaned, and i t is then reweighed. It is placed in t h e silica
Figure 2. Method filling glass capsule
of
tube, the capillary end just touching the plug of asbestos. The tube is fitted with a supply of oxygen and that part of the tube containing the capsule is surrounded by a small electric furnace, the tube being heated at H by a Meker burner. Over a period of about 90 minutes, the temperature of the furnace is gradually increased from room temperature to above the boiling point of the sample and the sample is gradually expelled from the capsule. The furnace is removed and the capsule carefully brought to dull red heat by means of another burner, thus oxidizing traces of nonvolatile material. The silica tube is disconnected, and all parts of the tube, except that part containing the glass capsule, are heated strongly. Finally the tube and capsule are heated in a mufie at about 500" C., cooled, and weighed. The gain in weight is equal to the weight of oxide plus the weight of the capsule. The capsules used generally weigh about 0.3 gram, and the change in weight during this treatment is negligible as shown by reweighing after the complete determination. Materials. Details of the preparation of hexmethyldisilane (boiling point 112" C.) and heuamethyldigermane (a new compound boiling point 135-136" C.) will be publishpd later. Hexamethyldistannane (melting point 23" C.) was prepared by the method of Ki-aus and Sessions (6) and was purified by recrystallization at -78" C. Tetramethylgermane (boiling point 42-44" C.) and tetramethyltin (boiling
point 77.5" C.) were made b y the Grignard reaction and purified by fractionation Tetramethylgermane was shaken Kith cold concentrated sulfuric acid before distilling. Hexamethyldisilosane (boiling point 99-100"), trimethylethoxysilane (boiling point 75-76"), dimethyldiethosysilane (boiling point 112-114"), methyltriethoxysilane (boiling point 142-143'), trimethvlchlorosilane (boiling point 57 ") , dimethvldichlorosilane (boiling point 69-70"), methyltrichlorosilane (boiling point G4--66"), and cyclohexyltrichlorosilane (boiling point about 206') !';ere obtained from Hopkin and Williams, Ikd., and were stated to be of 99% purity. Asbestos (of the tvwe suitable for Gooch crucibles) was brkated with concentrated hydrochloric acid, washed with n-ater, and ignited in a muffle furnace a t 800" to 900" C.
Table 1.
Determination of Silicon, Germanium, and Tin Using Bubbler-Type Sample Tube
Boiling Point, ' C.
Substance ( CH3)6Si,
Detd.
% Mi* Calcd.
Error, 70
112
38 35 38 24
(CH,)&O
99-100
34 53 34 51
38 38 34 3i
( CH3),SiC1
57
25 85 25.78 61.41 61.37
25.85 25.85 61.68 61.68
-0 08 -0 36 -0 20 -0 26 0.00 -0.27 -0.44 -0 50
54 G9
5i 37
54 70 54 70
-0 02 -0 GO
66.53 66.40
66,37 66.37
4 0 24 +0.05 - 6 39" - 2 71a
135-136 42-44 77.5
38 38 60 60
(CH3)&3i(OC&), 112- 114 17.73 18.91 (CK3),SjC1, 69-70 21.17 21 76 a Low results obtained because of hydrolysis in sample tube. RI is Si, Ge, or Sn.
RESULTS A N D DISCUSSION
The results obtained using a sample tube of the bubbler type are given in Table I and are accurate to within 0.5% for all the substances tested, evcept for dimethyldichlorosilane and dimethyldiethoxysilane, hich are successfully analyzed h j the modified method. Commencing n i t h JT eighed silica tubes, complete determinations may be carried out this way in 3 to 4 hours, the manipul'itive time being much shorter Good control over the rate of evaporation and rate of oxygen supply is obtained and only in one initanre, with tetramcth? lgermane, Tyas there an! sign nf carbide formation. Thp modified method gir es results (Table 11) of about the same accuracy, although the rate of evaporation of the sample is not quite '0 easily controlled, and in some instances, the oxide deposit nas gray because of slight formation of carbide. It is essential t o increase the temperature of the furnace .lonly over the required range. Only n ith one substance. hexamethyldistannane. did this method of introducing the sample fail. Several attempts n ere necessary to avoid explosive combustion of this suhstance, which is known to be unstable a t the boiling point (6). This method has about the same over-all time requircment but the manipulative time required is greater than that of the first method. The rewlts quoted in Tables I and I1 show that this dry combustion method is applicable to the analysis of several classes of volatile organo compounds: alkyls of silicon, germa-
Table II.
Point, C.
Detd.
Calcd.
Error, $&
75-76
23.67 23.71
23.75 23.75
-0.34 -0.17
(CH,'l,Si( OC2H6),
112-114
19.02 18.91
18.94 18.94
CH,Si( OC?H,),
142- 143
15.71 15.73
( CH1)eSiC12
69-70
CH.SiCI3
64-66
CcH, >Sic13
About 206
21.81 21.86 18.74 18.91 13.03 12 95
15.76 15.76 21.76 21.7G 18.79 18.79 12 91 12.91
(CHjt6Sn?
182
72.48 72 46
72.47 72.47
+0.42 -0.16 -0.32 -0 19 + 0 . 23 $0.46 -0.27 $0.59 $0 93 $0 31 $0 01 -0 01
(
a
Determination of Silicon and Tin Using Glass Capsule Boili!g yo 3\20
Substance CH3)3Si(OC21151
321 is Si or Sn.
niuni. and tin; chloro-alkysilanes; and, siloxanes. It seems probable that the method could be uqed n i t h equal success for organo germanium and organotin compounds containing ox! gen and perhaps nitrogen. LITERATURE CITED
(1) Gilliam, K. F., Liebhafskv, €1. A , , Winslow, A. F., J . .4m. C h e m SOC.63, 801-3 (1941). ( 2 ) Gilman, H., Hofferth, B., Melvin, H. W.,Dunn, G. E , I b i d , 72, 5767 (1950). (3) Kocheshkov, K. A.. Ber. 61, 1659 (1928). (4) Kraus, C. h.,Brown, C. L., J . Am. Chenz. SOC.52, 3690 (1930). ( 5 ) Kraus, C. -4., Flood, E. A., Zbzd., 54, 1635 (1932). (6) Kraus, C. A., Sessions, IT. V., Zbid., 47,2361 (1925).
(7) Iirause, H. H., Johnson, 0. H., ANAL. CHEM.25,134 (1953). (8) Luijten, J. G. A., Van der Kerk,
G. J. RI., "Investigations in the Field of Organotin Chemistry,'' p. 82, Tin Research Institute, Middlcsex, England,
1955. (9) PIIcHard, J. *4,, Servais, P. C., Clark, H. d.,ANAL. CHEW20, 325 (1948). (10) Rochow, E. G., "Introduction to the Chemistry of the Silicones," Chap. 7, Wiley, Ken. York, 1946. (11) Rochow, E. G., Gilliam, TT'. F., J . Am. Chem. SOC.63. 798 (1941). (12) Whitmore, F. C., Fommer, I,. €I., Di Giorgio, P. -4., Strong, IT. A., Van
Strien, R. E., Bailey, D. L., Hall, H. K., Pietrusza, E. IT,, Iierr, G. T., J A4m. Chem. SOC.68, 475 (1026).
RECEIVED for review Sovember 29, 1957. Accepted RIav 22, 1958. Maintenance grant t o M. P. B. from Department of Scientific and Industrial Research.
VOL. 30, NO. 10, OCTOBER 1958
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