Weruin, L. N., ANAL. CHEV.28, 849 (1956). (12) Gregory, G. F., Science 121, 169 il95Si.
( l d j Hough, L., Jones, J. K. N., Wadman,
W. H., J . Chem. SOC.1950, 1702. (14) Jeanes, Allene, Wise, C. S., Dimler, R. J., ANAL.CHERI.23, 415 (1951). (15) Laidlaw, R. A, Reid, S. G., J . Sci. Food d g r . 3, 19 (1952). (16) Montgomery, E. hl., Weakley, F. B., J . Assoc. Ofic. A g r . Chemists 3 6 ,
1096 (1953). (17) Ough, Lee D., Jeanes, Allene, Pittsley, J. E., J . Chroniatoq. 6,80 (1961). (18) Pent, Stanley, Whelan, I?'. J.,
(19) Sato, -4.,Watanabe, K., Aso, K., Chem. & Ind. (London),1958, 887. Lawley, H.G., J . Chem. SOC.1958, 724. (20) Silberman, Henri C., J . Org. Chem. 26, 1967 (1961). (21) Snyder, E. C., Kooi, E. R., Division of Agricultural and Food Chemistry, Midwest Regional Meeting, ;ZCS, Nov. 4-6, 1954; also private comniunication. (22) Sowden, John C., Spriggs, Alfred S., J . Am. Chem. SOC.78, 2503 (1956). (23) Thompson, A,, A h n o ,Kimiko, Wolfrom, M. L , Inatome, hl., Ibid., 76,1309 (1954). (24) Thompson. .I., Wolfrom, M. L., Quinn, E. J., Ibid., 75, 3003 (1953).
(25) Whistler, Roy L., Hickson, John L., ANAL. CHEM. 27, 1514 (1955). (26) Williams, Kenneth T., Bevenue, Arthur, Cereal Chem., 28, 416 (1951). (27) Wise, C. S., Dimler, R. J., Davis, H. A., Rist, c. E., AN'4L. CHE41. 27, 33 (1955). (28) Wolfrom, M . L., Thompson, .\., J . S m . Chem. SOC.77, 6403 (1955). RECEIVED for review November 13, 1961. Accepted March 12, 1962. Division of Carbohydrate Chemistry. Part A, 139th Meeting, ACS, St. Louis, &Io.) March 1961; Part B, 128th Meeting, ACS, Minneapolis, Minn., September 1955.
Determination of Chloroboranes, Diborane(6), and Hydrogen Chloride by Gas Chromatography HULON W. MYERS and ROY F. PUTNAM' Stauffer-Aerojet laboratories, Nimbus, Calif. A, chromatography procedure i s presented for the determination of mixtures obtained in the preparation o f diborane(6) from the hydrogen reduction of boron trichloride. The unstable chloroborane intermediates are successfully resolved b y employing low temperature columns. [Diborane(61, B2H5, i s the name approved b y the Advisory Committee on Nomenclature of Organic Boron Compounds.]
A
the production of diborane(6) through the hydrogenolysis of boron trichloride (4) has been investigated for many years, only one quantitative anall-tical procedure conith mixtures of interinediates cerned i~ and product purity has appeared in the literature. Mixtures of boron trichloride and dichloroborane are successfully determined by the infrarcd method of Sadeau and Oaks ( 3 ) . The procedure, however, has found limited application in this laboratory since it does not include the measurement of monochlorodiborane, hydrogen chloride, or hydrogen. The inherent accuracy and speed of gas chromatography prompted an extensive search for partition columns capable of separating components of samples obtained froin investigating chloroborane syntheses and diborane(6) production. The initial tests involved studies of the most coninion polar and nonpolar solvents currently in use, and also included evaluation of partition materials that are reported for LTHOUGH
Present address, Stauffer Chemical
Co., Research Center, Kichniond 4, Calif.
* Present address, Aerojet-General Corp., Solid Rocket Plant, Sacramento, Calif. 664 *
ANALYTICAL CHEMISTRY
boron hydride separations ( 2 ) . Kone of the columns gave separations that mould permit quantitative determinations. The failure of these columns to give adequate resolution emphasized some of the special problems presented by the species under study: dichloroborane and nionochlorodiborane decompose a t room temperature when concentrat>ed into pure fract'ions; all of the components ot'her than hydrogen are chemically reactive toward many commonly used partition liquids; diborane and hydrogen chloride have relatively close boiling points; and the great affinity of the chlorinated compounds ton-ard most GLC rolumn materials results in disproportionate elutions. It' became apparent, therefore, that finding a single partition column to resoli-e all of the components would be a n unrealistic goal. Thus, a,nalytical requirements were successfully met through the d e ~ d o p m e n t of several different columns with specific applications. APPARATUS A N D MATERIALS
Gas Chromatograph and Vacuum System. Because of the volatility, reactivity, and toxicity of the materials being studied, the gas chromatography unit was constructed as a n integral p a r t of a borosilicate glahigh-vacuum system of conventional design. With this arrangement, purified samples from fractionation trap. were introduced directly to the chromatography sample loop, unknon-n gas sample mixtures were admitted to the system through evacuated lines, and emerging chromatograph peaks were frozen selectively in vacuum-line fractionation traps for future identification. A section in the glass system was provided for quantitative aqueous hy-
drolysis and measurement of the resulting products: Hz, B(OH)3, and HCI. With stopcocks in the vacuum system lubricated by the low vapor pressure fluorocarbon greases, the entire apparatus was routinely evacuated to 10-5 mm. of Hg. Two different chromatography detector and recorder combinations were utilized in the investigation One unit incorporated a Gow-Mac thermistor cell (9677-AEL) with a circuit control unit designed in this laboratory and built by the Loe Engineering Co., Pasadena, Calif. (Loe drawing E-26-0). AiHristo1 recorder (Model 560) with a 1-niv. span was used. The other chromatograph arrangement consish of a Loenco unit (Model 1X) used in conjunction with a Brown-Honeywell recorder S o . 143 and a Node1 KI-3 Disc Integrator manufactured by Disc Instruments, Santa Ana, Calif. The metal portion of the vacuum system, as well as the sample inlet loop and the chromatography column, were constructed from copper tubing joined with brass SIvagelok Crawford Fittings. The connecting stainless steel valves ( S o . 32ST.1) were supplied by the Quick Khitey Research Tool Co. closure diaphragm valves (Demi, Xodel G ) manufactured by the G. K. Dah1 Co. were used in the bypass lines. The chromatography colunins operated a t low temperatures were submerged in a methanol bath within a large stainless steel Dewar flask. The methanol was maintained a t the desired temperature, * 2 O C., by employing a refrigeration unit (hfodel P61H) constructed by the Tecumseh Products Co., Tecumseh, Llich. Partition Materials and Column Preparation. The reagents used in chromatography column preparations are available commercially and were used without further purification. The materials and suppliers F-ere as follows: Silicone Oil 703, Dow Corn-
ing Corp.; Fluorolube OR-362, Hooker Electrochemical Co.; Kel-F Oil, Minnesota Mining and Manufacturing Co.; USP Mineral Oil KO.11! Standard Oil Co.; n-hexadecane, Matheson, Coleman, and Bell Co.; Teflon molding powder KO.5, E. I. d u Pont de Nemours and Co., Inc.; and C'hromosorb, Johns-?tlanville Corp. The partition liquids n-ere dissolved in a suitable solvent, and the column packing material mas (coated by the conventional procedure. After being filled, the copper tubes were coiled to the appropriate size, attached to a fast helium flow, and heated at 100" C. until a steady base-line a-as obtained. Prior to use, the colunins were dried t'horoughly by passing through several 5-ml. gas samples of boron trichloride a t 2.j0 c. Standard Sample Materials. Boron t,richloride (Stauffer Chemical Co.) was passed over boron carbide at 1000O C. t o destroy the slight phosgene and hydrogen chloride inipurit'ies. Standard fractional freezing techniques then gave a purity of 99.970. Dichloroboranc, of lcss than 10 mole Yo concentration, was obtained in solutions of boron trichloride. The actual compositions were determined for in-
a:
dividual samples by the conventional vacuum-line hydrolysis procedures (4, 5 ) . I n the samples used for this study, no disproportionation products of BzHsCl or BzHs were detected by infrared analysis. Diborane(6) was manufactured by the Stauffer-Aerojet Chemical Co. The samples used in this study were of a purity higher than 99.87,. Hydrogen (electrolytic grade) of 99.8% purity n a s obtained from the Matheson Chemical Co. Hydrogen chloride (anhydrous) received from the Matheson Chemical Co. contained carbon dioxide as a n impurity. The material n as purified by repeated fractional freezing a t - 112' C. Monochlorodiborane, obtained from various laboratory and pilot plant mixtures, 1% as purified by preparativescale gas chromatographic separation on a 0" C. silicone oil column. The normal boiling points for the pure materials are given in Table I. EXPERIMENTAL
A preliminary evaluation of organic solvents commonly used in gas-liquid chromatography shon ed that glycols, Apiezon greases, phthalates, nitriles, sulfides, and phosphates w r e chemically
I
B2H6
T I M E , MINUTES
Figure 1.
Codistillation separation with a 1 00-cm. powdered Teflon column
DIBORAhE
lvlONOCHLORODl BORANE
TIhlE, AlIhUTES
Figure 2.
Chromatographic separation on a 0" C. silicone oil column
Table I.
Boiling Points
Boiling Point, Compound Formula O C. BC13 12.5 Boron trichloride B& -02 5 Diborane( 6) BHCI? 0.20 Dichloroborane Hf -252.8 Hydrogen HC1 -83 i Hydrogen chloride Monochlorodiborane BJHbCl - 11 Ob a Estimation from vapor-liquid equilibrium data for BHCl,-BCI? mixtures. * Extrapolation of vtapor pressure data.
reactive toward one or more of thc gas sample components a t 25" C. and 40" C. Molecular Sieve, carbon, boron hydride polymers, Tide, and silica gel columns retained large quantities of the gases a t room t'emperature, and only in the cases of hydrogen chloride and boron t'richloride could gases be released a i t h out decomposition or reaction a t higher temperatures. Codistillation. Since the react'ivity and thermal instability of the components wrre a major problem in these separations, t h e use of low temper:iture chromatographj. appeared to be a logical approach. I n initial investigations, a variation of t h e low temperature fractional codistill'A t 'ion procedure outlined by Cady and Siegn-arth ( 1 ) was applied to niixturrs containing combinations of boron trichloride, dichloroborane, diborane, a i d hydrogen rhloridc. Colunins of incah and inch copper 0.d. tubing from 10 cm. to 40 feet in length were tried empty and filled with Teflon, boron carbide, or powdered glass. The best separation as obt'ained by using a 100-em. length of l/d-inch 0.d. column filled with 18- to 32-mesh powdered Teflon. A\fter the sample was frozen a t the colunin ent,rance, the temperature was raised slowly from - 195" C. to room temper:iturc in a flow of helium. -4lthough the separations on this type of r-olunin xould bc expected to follow vapor pressure rrlationships only, HC1 invariably enicrgrs earlier than B2Hs n-hicsli has the lower boiling point. A chromatogram for the separation is given in Figure I . Traces of B2H&'1 w r e also present in this mixture. It c:innot be sfen hcre, however, because of the particular attenuations chosen. -\lthough this technique could not be used for yuantitative analyses, because of the nonreproducible temperatui,e rise and changing base line, i t dit1 point the n-ay to successful del-elopmcnt of n. column operated a t -78" C. Analytical Procedure. The manipulations involved in introducing a sample for analysis or column evaluation were relatively simple. With a conventional valving system, helium flow was directed through the bypass valve, and a gas sample from t h e steel container or a vacuum-line storage volume was admitted to t h e previously evacuated sample loop. After the gas pressure was recorded (=t0.1 mm. of Hg) and the sample isolated, the connecting lines were evacuated. VOL. 34, NO. 6, MAY 1962
8
665
DIBORANE HVDROGEl
L3l
J. -/----I
l
l
I
0
!
I
I
I
Figure 3. Chromatographic separation for a tion: 0" C. silicone oil column
Helium was then admitted to the sample loop and the bypass valve was quickly closed as the sample was swept into the column. Since dichloroborane could not be introduced or recovered in a pure state, samples containing known concentrations of BHClz in Bel3 were used for evaluation and calibration. To confirm that the chromatogram for the -78" C. column was a result of BHClz separation, numerous samples were collected from the center portion of the emerging peak. Although considerable disproportionation occurred before
I
,In
I
I
I
I
vacuum-line hydrolysis was begun, the over-all elemental analysis gave the expected ratio of 1 to 1 to 2 for boron, hydrogen, and chlorine. I n several instances, the BHClz peak was analyzed by immediately directing the collected sample into an infrared cell operated a t -30" C. illthough some disproportionation had occurred even under these conditions, the technique was sufficient for a positive qualitative identification. One of the major sampling problems encountered originally concerned the transfer of boron trichloride. The
~
10 TI?'E
Figure 4.
666
5
~IIUUTF\
Chromatographic separation on a -78" C. Teflon column
ANALYTICAL CHEMISTRY
-
low hydrogen chloride concentra-
BORON TRlCHLORi3E ! X 100)
15
t
material is hydrolyzed so easily that, once a connecting line to the sample container is exposed to the atmosphere, even baking under a vacuum a t 250' C. will not completely prevent hydrogen chloride formation when boron trichloride is passed through initially. Since hydrogen chloride determinations in the range of 0.01% (mole) were often required, the situation could not be tolerated. The problem was eliminated by admitting and discarding several samples before the actual analysis; but, a more practical solution was finally found by employing direct tube connections between the analytical vacuum-line and the pilot plant reaction vessel. Thus, breaking connections and atmosphere exposure were avoided. Since the analytical vacuum-line was used for various other materials, it was advisable to fill the system to 400 mm. of boron trichloride pressure, heat to 100" C., and evacuate before standard samples were introduced. Retention times and peak identifications were usually determined by introducing samples of known purity. In the earlier investigations, however, unexpected peaks appeared and were collected for identification by trapping a large number of samples a t -195" C. in the relatively standard manner. The emerging gas stream was directed through one of the fractionation trains in the glass vacuum system, and the specific unknown peak was retained in a U-trap for future elemental analysis or infrared identification. Relative retention volumes for the components on various columns are given in Table 11. RESULTS AND DISCUSSION
In actual pilot plant operations, monitoring final purification steps and establishing the purity of the diborane(6) produced were considered to be the most important analytical problems. The gas samples commonly encountered during the final purification stages contained mixtures of hydrogen, hydrogen chloride, diborane(6), and monochlorodiborane. By employing a 33 foot long by '/4 inch 0.d. chromatographic column containing 60- to 80-mesh Chromosorb coated with 20% (wt.) silicone oil, these mixtures were completely resolved a t 0" C. A chromatogram illustrating the typical separation with a helium flow of 100 ml. per minute is shown in Figure 2. It is interesting to note that, although the carrier gas was helium, positive hydrogen peaks were invariably recorded and precise calibrations were obtained. Apparently the hydrogen segment leaving the 0' C. column becomes warmer than the helium stream before it reaches the ambient temperature detector. Subsequently, the temperature of the hydrogen becomes more important than thermal conductivity properties. At the thermistor, then, less heat is conducted to the hydrogen segment than is lost to the cold helium flow, and a positive peak results. Once a constant
T
Figure
I\-TZ
5. Chromatographic separations on a 40" C. n-hexadecane column helium flow is established, the temperature gradient between column exit and detector remains constant. A chromatogram illustrating the use of a longer 0" C. silicone oil column (40 feet) for trace analysis of hydrogen chloride in diborane(6) is given in Figure 3. Early stages in the hydrogenolysis of boron trichloride yield quantities of dichloroborane in mixtures of hydrogen chloride and boron trichloride. Since dichloroborane is extremely unstable and can only be isolated a t low temperatures, use of a -78" C. chromatography column for analysis was necessary. Thc column most successfully employed for this separation was a 10-foot length of '/4 inch 0.d. copper tubing filled with 42- t o 60-mesh uncoated Teflon powder. -4 typical chromatogram for an analysis is given in Figure 4. Hydrogen chloride values in the range of 0.01 to 5.0 mole % were determined with this column by peak height measurements. Analyses
BORON T R I C H L O R I D E
m w
HYDROGEN C H L O R I D E
z 0 a
m Lli w [r
P
0 w w
+
n
Table
I
2' ,
10
5
I
-
0
TIME, M I N U T E S
Figure 6. Chromatographic separation on a oil column
25" C. mineral
II.
Relative Retention Volumes
Column SiliTeflon, cone Fluoro- n-HexaCorn-78" oil, lube, decane, ponent C. 0" C. 25" C. 40" C. H, ... 0.46 0.95 ... . .. B2"HB .. . 0.62 ... 0.97 HC1 1.00 1.00 1.00 1.00 BzHsC1 . . . 4.05 ... 2.65 BHC12 1 . 8 1 . . . ... 4.70 BCl, 4.54 . . . 2.72 6.30
VOL. 34, NO. 6, MAY 1962
667
of dicliloroborane were obtained from planimeter measurements of the area outlined in Figure 4. The shape of the BC13 peak in this chromatogram is a result of overloading the column. When colunin overloading does not occur, tlie BC13 peak appears at' 5 minutes. In Littempt's to effect a better separation a t -78" C, variations in colmnn length (from 4 to 200 feet), inside tube di:tnicter (from 0.02 to 0.5 inchpsj, Teflon particle size (from - 100 to 19 mesh) , and sample size [from 0.1 to 5.0 nil. (STP)] IT-ere eva1u:ited witliout noticeable iniprovement. Another chromatographic separation niedium found for mixtures containing dicliloroborane was based on the fact that this compound is more stable in the presence of boron trichloride. If t'he partition liquid remained saturated witli boron trichloride, i t \vas discoT-ered that dichloroborane and nionoclilorodiborane could be resolved even a t 40" C. TKOchromat~ograms illustrat'ing this type of separation are shown in Figure 5 . The '&~cli diameter column was 18 feet in length and filled with 60 to 80 mesh Chromosorb coated with 307, (n-t.) n-hesadecane containing residual boron trichloride from a previous sample. The colunin w s operated a t 40" CI. with a helium flow of 400 ml. per minute. Since 13C13was soon flushed froni the colunin under these relatively drastic conditione, column performance n-as found t o be reproducible only n-hen snmples vere introduced a t regular intervals. Suc.h a technique ~vould, therefore, he more practical for use in :i continuously operating plant stream analyzer. Although the area of the unsymmetrical boron trichloride peak obtained i n :i -78" C. separation was used for quant'itative estimations, more precise gas cliromatography methods were
BORON TRICHLORIDE
+
Table 111.
C O ~ U I I I IHJ ~ Teflon ... ... ... Silicone oil 8'3.8 7.2 9.8 Fliioro~. lulic .., ...
... 1'l.b
86.7
668
.,. ...
TIN5
Figure 7.
d e d o p e d for mistures in which hydrogen chloride and boron trichloride were t'he only components. Two different ambient temperature columns were used for routine analysis of these mixt'ures. One colunin consisted of mineral oil (20y0,wt.) on Chroinosorli and tlie other used Fluorolube (lo%, ivt'.) on Teflon. Khen using the 12-foot by ,4-inch 0.d. mineral oil column! IThich was operated a t 25" C.with :I 230 nil. per minute helium flow, analyses n-ere based on peak height nieasurenients. A typical rhromatogram for the separat'ion is given in Figure 6. The most precise measurements for boron t'richloride were obtained by peak area determinations with t,he 4-foot by &ich o.d. Fluorolube column.
10.2 . . . ... 3.5 . . . . . .
...
81.2
BCl, 03.8 93.1 89.9
...
...
91 1
... ...
H, , , ,
, . ,
, . .
-(9.1
, , ,
.
, ,
24.9
...
,
2.6
,..
,,.
97.4
, . .
, . .
ANALYTICAL CHEMISTRY
..
0
...
..
,
3.5
i4.2
2.7
9.8 80.7
,.. .. ... ,
,..
..,
,..
. ,, ,..
., .,.
25.2 95.7
, , ,
,
The chromatogram for a hydrogen chloride and boron trichloride separation is given in Figure 7 . If dichloroborane is present, however, it disproportionates during separation, and the result is an uneven base line between the two peaks. The quantitative results obtained for a reixwentative number of experimental mixtures are giren in Table 111. ACKNOWLEDGMENT
The authors are indebted to A. J. Cranley, -4. I. Goldford, and R. P. Tessen for their capable assistance in performing the experimental operations. LITERATURE CITED
(1) Cady, G . H., Siegnarth, L). P., A\
i ~ .
CHEW31,618 (1959). (2) Kaufman, J. J., Todd, J. E., Koshi, W S.,Ibtd., 29, 1032 (1957) (3) Nadeau. H. G.. Oaks. D. AI.. Jr.. Zbid., 32, 1480 (1960). ( 4 ) Schlesinger, H. I., Burg, A. B., J . Avz. Cheni. SOC.53, 4321 (19311. (5) Stock, A, "Hydrides of Boron and ,
Found, Mole % B?H,- BHBIH, HC1 C1 C1, BC1, , , , 1 . 4 . . . 4 . 7 92.0 ... 3 . 7 . . . 3 . 0 95.6 ... 0.54 , . . 9 . 1 88.0
7 . 3 11.7 1 0 . 3 86.1
5 MINUTES
Chromatographic separation on a 25" C. Fluorolube column
Quantitative Determinations for Experimental Mixtures
Knoxn, Mole C,G B?Hj- BHB2HF HC1 C1 C1, ... 1.2 . . . 5.0 ... 4.0 , . . 2 . 9 ... 0.50 , . . '3.6
~
m
IS
I
Silicon," p. 108, Cornel1 Cniversity
Press, Ithaca, S. Y . , 1033.
RECEIVED for review October 6, 1961. Accepted l\larch 5, 1962. Work described herein was performed under Contract S o . AF33(600)-35780 with the United
States Air Force, Aeronautical Systems Division, llanufacturing Technology Laboratory, Kright-Patterson .4ir Force Base, Ohio. Charles Tanis was Air Force Project Engineer. This article appears as Contribution 50.229 from the Cheniical Ilivibion of -4erojet-General Corp.
