(4) Gueron, J., Yaffee, L., Ibid., 160, 575
To verify this hypothesis, aremelted buttons were prepared with proximate compositions of 4, 40, and 90 wt. 70 uranium in molybdenum. The apparent uranium content of these buttons as determined by the “hydriding” technique was 0.04,0.20, and 9270 uranium, respectively.
,.
flaA7\ ~_”_.
(5) Hans:n, M., “Constitution of Binary Alloys, p. 978, McGraw-Hill, New Yark. 1958. (6) XaUmann, S., private communication, Ledoux and Co., Teaneck, N. J., 1965. (7) Lyon, W. I,., “The Messurement of Oxygen t o Metal Ratios in Solid Solu-
tions of Uranium and Plutonium Dioxides.’’ U. S. Atomic Energy Comm.
ACKNOWLEDGMENT
The authors thank N. P. Fairbanks, R. E. Fryxell, C. S. Wukusick, and\%’. R. Yario for specimen preparation; C. A. Asaud and F. T. Williams, Jr., for metallographic examination; D. K. Conley for electron microprobe examination; and P. F. Elliot and A. F. Rosenberg for some of the hydride analyses. LITERATURE CITED
(1) Aitken, E. A,, Brassfield, H. C., Fryxell, R. E., “Symposium on Thermodynamics with Emphasis on Nuclear Materials and Atomic Transport in
Figure 7. Sintered 80% U02-20% Thol Slorting material: arracelved
UO1 (250X,
0%
polishedl (See Tabla V, DB-8 for sample heatmen?)
Solids, IAEA, Paper SM-6683, Vienna,
Austria, 1965. (2) Aitken, E. A., Brassfield, H. C., McGurty, J. A., ANS Trans. 1963, p. 153. (3) Anderson, J. S., Sawyer, J . O., Warner, H. W., Willis, G. M., Bannister, M. J., Nature 185, 915 (1960).
Rept. GEAP-4271 (1963). (8) Mulford, R. N. R., Ellinger, F. H., Zachariasen, W. H., J. Am. C h . SOC. 76,297 (1954). (9) Robins, R. G., J . Nucl. Male?. 7, 218 IlQR%l ~-”--,. (10) Rothwell, E., Ibid., 5,241 (1962).
(11) Ibid.,. 6 , 229 (1962). (12) Wilkmaon, W. D., “Uranium Metallurgy,” Vol. 2, p. 775, Interscience, New York, 1962. (13) Zachariasen, W. H., Acta C q ~ t 6, . 393 (1953).
RECEIVEDfor review May 11, 1966. Accepted August 22, 1966. Work sponsored by the Fuels and Materials Develop ment Branch, U. S. Atomic Energy Commission, Contract AT(40-1>2847.
Gas Volumetric Method for the Determination of Dialkylaluminum Hydride and Volatile Alkyl Groups D. F. HAGEN,’ J. 1. HOYT, and W. D. LESLIE
Research ond Development Deparfmenf, Confinenfol Oil Co., Ponca City, Oklo.
b The hydride content of dialkyloluminurn hydride, trialkylaluminum, and dialkylaluminum halide mixtures can b e estimated by utilizing the obility of the aluminum-hydrogen bond to reduce azo-methine linkages in reagenk such a s pyridine or isoquinoline. One oliguot of the sample is reacted with the azo-methine reagent and a second aliquot is diluted with xylene. These aliquots a r e hydrolyzed and the quantities of evolved gases are measured in a g a s buret. Hydrolysis of the xylene diluted somple gives total hydrogen plus volatile alkanes while the aliquot which was reocted with the ozo-methine reagent yields only the volatile alkanes. Less than 0.3y0 molecular hydrogen i s present in the hydrolysis gases after reaction with the azolnethine reagent.
s
methods employing reagents such as isoquincline and benzalaniline (1, 3, 4) have been used to determine hydride content of alkylaluminum mixtures. These methods are based on the formation of a highly colored 2: 1 reagenehydride complex in the presence of the slightly colored 1: 1 alkyl complex. A thermometric titration has also been reported PECTROPHOTOMETRIC
as a differentiating technique by Everson and Ramirez (2). Neumann (6) has utilized a gas-volumetric technique to estimate dialkylaluminum hydride. His method is based on the reaction between secondary amines (N-methylaniline) and aluminum-hydrogen bonds to release molecular hydrogen. However, this reaction must be carefully controlled to prevent an analogous reaction with the amine and trialkylaluminum, thus releasing volatile alkanes. The gas-volumetric method to be described is relatively simple and is based on the ability of dialkylaluminum hydride to reduce an azo-methine linkage forming an alkylaluminum amide. Hydrolysis of dialkylaluminum hydride results in the formation of molecular hydrogen plus the alkanes corresponding to the original alkyl groups bonded to the aluminum atom. However, hydrolysis of the alkylaluminum amide releases the alkanes but the hydrogen is no longer bonded to the aluminum atom; therefore, no hydrogen is found in the gases. The alkylaluminum samples are pyrophoric and all sample manipulations must be performed with anhydrous reagents in the absence of air.
EXPERIMENTAL
Apparatus. Analytical samples are contained in rubber septum capped vials which have been filled in a dry box containing a nitrogen atmosphere. Smooth bore syringes with plungers made of Teflon (3) are used to transfer the pyrophoric samples for dilution and analysis. The gas buret has a capacity of 600 ml. and the buret liquid is a saturated sodium chloride solution. A small trap partially filled with Nujol is inserted between the hydrolysis cell and the buret to prevent small particles of aluminum oxide from plugging the stopcocks. The hydrolysis cell is a 50-ml. Erlenmeyer flask with a rubber septum port for the introduction of sample. It contains a bar for magnetic stirring and is connected to the trap with a ground glass joint. Reagents. Xylene is used as a dilution solvent and it is dried with calcium hydride, distilled, and then stored over Linde 5A molecular sieves. The azo-methine reagent is prepared with this dry xylene by dissolving enough reagent to give a 40 wt. Yo solution. Molecular sieves are also Present address, the 3M Co., St. Paul, Minn. VOL 38, NO. 12, NOVEMBER 1966
1691
hydrolysis cell and the cell is connected to the gas buret set-up. Nitrogen is used to purge air from the buret lines and the cell before adjusting the leveling bulbs. The stirrer is turned on and the sample is injected dropwise through the rubber septum port into the hydrolysis medium. The leveling bulb is lowered as necessary and sample is added until the approximate volume of gas desired is collected. The sample syringe needle is then withdrawn from the septum, capped with the silicone rubber plug, and weighed to determine the amount of sample used to obtain the gas in the buret. The sample in the hydrolysis cell is allowed to react until no more gas is given off, and the system is cooled to room temperature. The usual corrections for pressure, temperature, and aliquot sample volume are applied to calculate the volume of gas obtained per gram of original sample. An aliquot is hydrolyzed prior to the actual analysis to allow for gas equilibration with the buret liquids and then two or three successive aliquots may be hydrolyzed without changing the hydrolysis solution. The volumes obtained for the complexed us. uncomplexed aliquots of a given sample were not corrected for solvent vapor pressures or changes in gas solubility with successive hydrolyses.
added to this solution to help eliminate interference from water. Procedure. Twenty milliliters of the dry xylene are transferred t o a tared, dry, rubber septum capped, 1-ounce bottle. The bottle is purged with nitrogen to remove air and then weighed to obtain the amount of xylene present. A bubbler containing Nujol is flushed with nitrogen and connected to the dilution bottle via a hypodermic needle to act as a pressure release system. Enough sample (4 ml.) is added to the xylene from a hypodermic syringe to make a final concentration of 15 to 20 wt. % (cap the syringe needle with a silicone rubber plug). The bottle is then reweighed to obtain the amount of sample which has been added to the xylene. A second aliquot (via syringe) of the original sample is diluted with the azomethine reagent in the same manner except that this dilution requires cooling the reagent bottle during the addition of sample. A good deal of heat is evolved in this dilution, and the sample should be added slowly enough to prevent temperature buildup. These samples are thoroughly mixed and a portion is drawn into a syringe for the hydrolysis step. Fifteen milliliters of 1 : 4 sulfuric acid are added to the
Table I. Hydrolysis Data for Alkylaluminum Samples Vol. of Vol. of RH, Hq RH.
+
Sample AlRzH AlRzH AlRzH AlRs AlRzH AIR3 AlRzH AlRs AlRzH AlRs AlRzH AlRs AlRzH AlRzH AlRa AlRs AlRzCl R = CzH6
+++ +++
xylene ’ dilution, ml./gram
azo-methine dilution, ml./gram
753.9 752.4 732.0 712.2 669.9 637.8 628.5 601.1 602.1 587.1 564.4 338.7
503.1 499.5 500.0 525.0 528.6 535.5 544.9 565.2 548.6 588.5 563.6 335.1
Mole % ’ AlRlH Expected Found Difference 0.0 0.8 3.4 3.7 2.3 0.6 4.9 6.7 2.7 -0.7 0.4 3.2
100.0
100.0 100.0 91.7 82.6 65.6 47.5 46.2 24.6 24.0
100.8 95.1 78.9 63.3 48.1 41.3 17.9 26.7 -0.7 0.4 3.2
0.0 0.0 0.0
Table II. Repeatability Data for Gas Volumetric Method
+
Sample AlRzH
AlRa
R
1692
=
Hz RH, xylene dilution, ml./gram 750.8 745.3 747.0 748.5 756.7 Mean 749.7 553.0 553.0 551.4 556.0 548.9 Mean 552.5
CzHs
ANALYTICAL CHEMISTRY
Deviation from mean
RH, azo-methine dilution, ml./gram
Deviation from mean
+1.1 -4.4 -2.7 -1.2 f7.0 23.3 +0.5 f0.5 -1.1 +3.5 -3.6 et1.8
497.9 502.6 500.7 501.3 504.3 501.4 554.7 552.1 554.4 553.3 554.4 553.8
-3.5 $1.2 -0.7 -0.1 +2.9 21.7 +0.9 -1.7 +0.7 -0.5 -0.6 AO.9
For a given sample, however, the volume and composition of the hydrolysis gases should be essentially identical except for the absence of hydrogen in the complexed sample. The difference in gas volumes obtained for the azomethine reagent and xylene dilution is due to molecular hydrogen from the hydrolysis of aluminum-hydrogen bonds, and this is directly proportional to the quantity of dialkylaluminum hydride present in the original sample. RESULTS
The data shown in Table I for the mixtures were obtained by blending diethylaluminum hydride with triethylaluminum. Isoquinoline was used as the azo-methine reagent and several of the resulting alkylaluminum amides were hydrolyzed for analysis by gasliquid chromatography. The resulting gases contained less than 0.3 mole % molecular hydrogen indicating that the reduction reaction readily goes to completion under the conditions outlined. Table I1 gives the repeatability data for xylene and isoquinoline dilutions of diethylaluminum hydride and triethylaluminum samples. The two samples were diluted as described in the procedures and six hydrolyses were carried out for each dilution. The first value of each series was rejected. The mean value of the series was used to calculate the mole % hydride as follows: Al(CzHa)& 3(749.7
-
501.4) X 100 749.7 99.4 mole
3(552.5
- 553.8) 552.5
yoAl&H
X 100 -
-0.7 mole yoA E 2 H Other azo-methine reagents which have been tested include pyridine and benzalaniline. The alkylaluminum amide formed with benzalaniline converts to a secondary amine upon hydrolysis and the acid salt of this compound forms a rather voluminous precipitate in the cell. Twenty-five weight per cent sodium hydroxide was used as the hydrolysis medium to eliminate this interference, but the hydrolysis reaction is relatively slow in basic media. Curve A in Figure 1 shows the theoretical quantities of gas expected for triethylaluminum and diethylaluminum hydride mixtures when subjected to the azo-methine and xylene dilutions. Curve B illustrates the experimental data obtained using isoquinoline for the reagent. The samples used to make these blends were partially oxidized and contained some solvent. The gas volumes which were obtained
aluminum hydride is difficult to control. This is similar to the reaction between gaseous ammonia and trialkylaluminum samples where i t is very difficult to control the reaction when the complex begins to decompose to the amide and the alkane. The reaction between dialkylaluminum hydride and azomethine reagents is shown in Equation 3. Hydrolysis of the resulting amide releases the volatile alkanes, H XYLENE DILUTION
RzAlH
( CaH. SHz)
+ R'-N
/ = C \
+
R
R'
\ /
R2Ai
AZO-METHINE
40
20 MOLE
60
% AI(CaH,l,
COMPLEX
80
100
H IN AI ( C ~ H ~ ) ~
Figure 1. Hydrolysis gas volumes for AI(CZH6)2H-AI(C2H& mixtures and the azo-methine complex
reflect this and the curves are shifted downward. The ratio of hydrogen to total gas collected should be constant regardless of dilution. The convergence of the lines at pure triethylaluminum is a result of the inability of aluminum-carbon bonds to reduce the azo-methine linkage. If nonvolatile alkanes result from the hydrolysis of the original alkyl, i t is not possible to use the calculations illustrated to express the result as mole % AlR2H. I n this case the mmoles of hydrogen per gram of sample can be related to the mmoles of aluminum present to estimate dialkylaluminum hydride content.
AlRzH
+ RzNH
+
Trialkylaluminum species undergo a similar reaction, however, as shown in Equation 2; and when the resulting alkane is volatile, a positive interference will result. A&R'
+ RzNH
+
RZA1-NRz
+ R'H
H
N-C-R"
I
(3)
H
but the hydrogen is no longer bonded to the aluminum atom and it does not appear in the hydrolysis gases. Trialkylaluminum forms a 1 : l complex with the azo-methine reagent but does not appear to add across the carbon-nitrogen double bond at room temperature. Hydrolysis of this complex releases all of the alkyl groups bonded to the aluminum atom as alkanes. It should be emphasized that this method measures those entities which are capable of reducing the carbon-nitrogen double bond and therefore is not entirely specific for the dialkylaluminum hydride For example, hydride molecule. samples when partially oxidized may contain ethylethoxyaluminum hydride and this compound could also undergo a reduction reaction with the azomethine reagent. The method is of value for estimating hydride and volatile alkyl groups for a variety of samples. The azo-methine reduction reaction may also be used to mask the dialkylaluminum hydride in gas analyses of samples containing free metals. If a mixture of AlR2H and metallic aluminum was reacted with isoquinoline and then hydrolyzed, the quantity of hydrogen in the gases obtained would be directly proportional to the aluminum metal present. LITERATURE CITED
(2)
DISCUSSION
The gas-volumetric method as d e scribed by Neumann (s) is based on the formation of molecular hydrogen when dialkylaluminum hydride is reacted with a secondary amine as illustrated in Equation l.
I
Neumann (6) found that the amide formation reaction with trialkylaluminum could be suppressed if the amine was cooled to between -20° and -40' C.prior to the addition of the sample. If the solution is too cold, the amide formation reaction with dialkyl-
(1) Bonitz, L., Chem. Ber. 88, 742 (1955).
(2) Everson, W. L., Ramirez, E. M., ANAL.&EM. 37, 806 (1965). (3) Hagen, D. F., Leslie, W. D., Ibid., 35. 814 (1963). (4) Mitchen, J. H.,Ibid., 33, 1331 (1961). (5) Neumann, W. P., Ann. Chim. 629, 23 (1960). RECEIVEDfor review July 11, 1966. Accepted September 6, 1966.
VOL 38, NO. 12, NOVEMBER 1966
1693
