Table IV. Effects of Various Added Impurities on the Analysis of Triisobutylaluminum Nature of impurity: wt Oh:
None
-
Tri-2-methylpentylaluminum 4.3
n-Hexane
5.7
[isoBu~AlOisoBu] 8.3
[(~soBu~AI)~~] 5.4
Component, wt %
Methane as Me3AI Ethane as Et3AI Propane as n-PrsAl lsobutane as isoBu3Al n-Butane as n-Bu3Al Isobutylene Hydrogen as A I H 3 Number of runs averaged Wt YOaluminum, calculated Wt YO aluminum, found
0.1
0.1
0.1 0.2 96.5 0.2 2.3 0.6 2 13.8 13.7
0.1
and bis-oxides-has been demonstrated for a sample of commercial grade triisobutylaluminum, and the results are shown in Table IV. It was observed that the hydrolysis gas composition is generally unaffected by any of these types of impurities. Their presence was indicated, however, by marked changes in the found wt Yo aluminum. Positive confirmation of t h e specific nature and quantity of impurities in aluminum alkyls requires more detailed analytical procedures, as previously described. In summary, a rapid hydrolysis method for indirect analysis of aluminum and zinc alkyls has been developed and found to perform as well as the more involved and lengthy methods of hydrolysis. The rapid method has reduced hydrolysis time and equipment cost considerably while maintaining the same accuracy and precision of the previous methods. The method permits calculation of the expected wt ’70 metal content, which can be compared with the actual found wt % value for indication of sample purity. In general, the closer the agreement, the greater the purity of the metal alkyl.
APPENDIX I Estimation of Wt YO Aluminum in Alkylaluminum Halides. Assume for the purposes of the calculation that alkvlaluminum halides are s i m d e mixtures of RsAl and AL?3. The contribution of the aiuminum in the components can be obtained from the hydrolysis gas analysis by the method shown in Table I. This value is called the “uncorrected calculated wt ’70 aluminum” and given the symbol (AI).
0.1 0.1 0.2 96.5 0.2 2.3 0.6 2 13.8
0.2 96.4 0.3 2.3
0.6 2 13.8 12.8
0.1
0.1 0.1 0.2 96.5 0.2 2.3 0.6 2 13.8 13.5
13.4
0.1 0.2 96.5
0.2 2.3 0.6
2 13.8 13.9
The aluminum in the A H 3 component (Az) is assumed to be theory for AlX3 ( e . g . , 20.238 for AlC13). Then the “calculated wt % aluminum” (AT) equals the weighted average of A1 and Aa.
A,
=
Al(l-F)
+
A,(F)
where F = the wt fraction of AlX, in the total sample (Mol Wt of MX,) F=B + 100 3 (Atomic Wt of X ) For example, a sample of diethylaluminum chloride (DEAC) gave the following results: A1 = 23.4 = Uncorrected wt 90A1 from hydrolysis gas analysis B = 29.01 = wt % chloride (experimentally determined from tridicate analysis) (133’346i - (29.01) 3 (35.453) x 100 -
= (29.01)
X
(0.012537)
= 0.3637
Therefore.
+
AT = 23.4(1 - 0.3637) 20.238 (0.3637) = 14.89 7.36 = 22.2 = calculated wt % aluminum in DEAC
+
Actual found wt % aluminum in this sample of DEAC by EDTA titration was 22.0. Received for review February 16, 1973. Accepted May 2, 1973.
Simple Device for Preparing Ethereal Diazomethane without Resorting to Codistillation H. M. Fales and T. M. Jaouni Laboratory of Chemistry, National Heart and Lung Institute, National institutes of Health, Bethesda, Md. 20074
J. F. Babashak Kontes Glass
Co., Vineland, N.J.
Modern instrumental techniques often require the conversion of acidic and phenolic groups to their methyl esters and ethers for purposes of volatility, solubility, or merely for functional group identification. Although ether 2302
solutions of diazomethane are stable for weeks in the freezer, a pale yellow color may finally develop that obscures the fact that diazomethane is no longer present. Furthermore, in a t least one case, methylation of meth-
ANALYTICAL C H E M I S T R Y , VOL. 45, NO. 13, N O V E M B E R 1973
acrylic acid, use of an aged solution led to complications ( I ) and freshly prepared solutions are generally recommended. Common practice involves generation of diazomethane by the action of alkali on N-methyl-N-nitrosourea ( 2 ) or N-methyl-N-nitroso-N1-nitroguanidine ( 3 ) or N-methyl-N-nitroso-p-toluenesulfonamide ( 4 ) in the presence of ether and codistillation of the product using a hot water bath. However, it has been noted that "most diazomethane explosions take place during its distillation. Hence, diazomethane should not be distilled unless the need justifies it" ( 4 ) . Distillation can be avoided by entraining the diazomethane in an inert gas passed through its solutions ( 5 ) . To avoid the necessity for distillation or entrainment apparatus, we have constructed the apparatus shown in Figure 1 (available in this and a smaller size from Kontes Glass Co., Vineland, N.J.) where diazomethane, generated in the inside tube from the action of alkali on N methyl-N-nitroso-Iln-nitroguanidine(Aldrich Chemical Co.) escapes from a vent and is collected in ether or another solvent in the bottom of the outside tube. The whole apparatus is sealed during the entire preparation. Thus, 1 mmole (133 mg) or less of the reagent is placed in the inside tube through its screw cap opening along with YZ ml of water to dissipate any heat generated (6). Ether (-3 ml) is placed in the outside tube and the two parts are assembled with a butyl O-ring and held with a pinch-type clamp. The lower part is immersed in an ice bath and about 0.6 ml of 5N sodium hydroxide is injected through the silicone rubber septum via a syringe with a narrow gauge (No. 22) needle to prevent leakage around the shank. The yield of diazomethane depends in part on the length of time allowed for the gas to collect in the cold ether. Experiments with benzoic acid, analyzing the methyl benzoate formed by gas chromatography, showed that about 15 min is sufficient to produce approximately 20%, while up to 45 min is required to achieve a maximum of -60% (lit. 73% (3)). N-methyl-N-nitroso-p-toluenesulfonamideis the preferred reagent but it reacts too slowly a t room temperature, even in the presence of methanol, to be useful in this apparatus. N-methyl-N-nitrosourea reacts rapidly at room temperature and presumably would also be satisfactory. Diazoethane, from N-ethyl-N-nitroso-W-nitroguanidine (Aldrich Chemical Co.), works equally well in spite of its (1) J. W. Wheeler, R. H. Chung, S. K. Oh, E. F. Benfield. and S. E. Neff, Ann. Entomol. SOC.Amer., 63, 469 (1970). (2) F. Arndt in "Organic Syntheses," Coll. VoI. II, A. H. Blatt, Ed., Wiley, New York, N.Y., 1950, p 165. (3) A. F. McKay, J. Amer. Chem. SOC., 70, 1974 (1948). (4) Th. J. de Boer and H . J. Backer in "Organic Synthesis," Coll. Vol. I V . N. Rabjohn, Ed., Wiley, New York, N.Y., 1963, p 250. (5) H . Schlenk and J. L. Gellerman, Anal. Chem., 32, 1412 (1960). (6) B. Eistert in "Newer Methods of Preparative Organic Chemistry," Interscience, New York, N.Y., 1947, p 518.
V
0
"0" Ring
Figure 1. Apparatus for
W
preparing diazornethane
lower volatility. A further advantage of the system is that the diazomethane can be collected in solvents other than ether. Since the apparatus is entirely enclosed, it may also be advantageous where radioactive diazomethane is required. To prepare tritiated methyl esters, it should only be necessary to use tritiated sodium hydroxide since the hydrogens on diazomethane are easily exchanged in alkali (7). The degree of labeling achieved in such experiments was determined by using deuterated sodium hydroxide. In the case of methyl benzoate (from benzoic acid preequilibrated with deuteriomethanol), the methyl group showed conversion to 50% CD3, 35% CD3 H, 15% CDHZ, 0% CH3 by mass spectrometry, i.e., an overall 71% deuteration of the methyl group, undoubtedly sufficient for many purposes. We have been using the apparatus routinely for over 1 year without difficulty. Ground glass joints were avoided because of reports they cause explosions (2). The syringe and O-ring tend to relieve any excessive pressure during preparation, but it is obvious that if local construction is attempted, stout-walled strain-free glass should be used for the outer tubes. Received for review April 6, 1973. Accepted June 11, 1973. (7) W. B. Denrnore, H. D. Pritchard, and N. Davidson, J. Amer. Chem. SOC., 81, 5874 ('1959).
ANALYTICAL C H E M I S T R Y , VOL. 45, NO. 13, N O V E M B E R 1973
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