Gas Chromatographic Analysis of Aryl Grignard Reagents LLOYD V. GUILD, C. A. HOLLINGSWORTH, DARL H. McDANIEL, and JOHN H. WOTIZ Department o f Chemistry, University of Pittsburgh, Pittsburgh I 3, Pa.
b A gas chromatographic method for the analysis of Grignard reagents has been developed. This method distinguishes between the active Grignard reagent which is present at the time of analysis and that which has undergone hydrolysis prior to the time of analysis. The method has been used in the analysis of para-tert-butylphenylmagnesium bromide.
A
of aryl Grignard reagents is usually carried out by titrating the basic magnesium produced by hydrolysis of the Grignard reagent using a procedure developed by Gilman (8). RMgX HOH + RH Mg(0H)X NALYSIS
+
tetrahydrofuran solvent was stored under nitrogen in a brown bottle closed with a serum stopper. Nonane, Phillips Petroleum Co. C.P. grade, was checked chromatographically and shown to have no components with the same retention time as tert-butylbenzene. By use of a syringe, Procedure. several milliliters of the Grianard reagent were added t o the Zared sample tube. A weighed amount, approximately 1.0 ml., of an internal standard, n-nonane, was added by a syringe, and the tube again weighed. (Nonane Kas selected as an internal
g
+
This procedure does not distinguish between the active Grignard reagent present a t the time of the analysis and Grignard reagent which has undergone hydrolysis prior to the time of analysis. For some kinetic studies carried out in this laboratory it was necessary to determine the amount of active Grignard reagent in stock solutions. This paper describes a gas chromatographic method of analysis which was found to be simple and convenient. Following the conclusion of the experimental phase of this investigation, an iodometric method for the determination of active organometal in phenyllithium and other organoalkalies was described in the literature, and the authors indicated that their method might also be applicable to aryl Grignard reagents (1).
MKRO SYRINGE
Figure 1.
Sample tub*
EXPERIMENTAL
Apparatus. A prototype of the Burrell Model K-5 gas chromatograph was used. Polypropylene glycol, supported on C-LL firebrick was used as column packing. The only special apparatus required was a sample tube constructed as shown in Figure 1. This tube facilitated the transfer of samples with a minimum of exposure to the atmosphere. The total volume of the tube was approximately 10 ml. The ends of the tube were fitted with silicone seals as shown, and the gas chromatographic column was also fitted with a silicone seal. Reagents. para-tert-Butylphenylmagnesium bromide prepared from para-tertbutylbromobenzene and magnesium in a 4:l (by volume) ether to 1156
ANALYTICAL CHEMISTRY
Table 1. Analysis of para-terf-Butylphenylmagnesium Bromide
Analysis N ~ Acid . Titration
6
Grignard Reagent Moles/1000 Grams Active Reacted Original ... ... 1.37 1.36 ... ...
...
...
...
...
... ...
... ...
1.36 1.37 1.37 1.35
Gas Chromatography 1 2 3
1.15 1.15 1.16
0.21 0.21 0.21
1.36 1.36 1.37
standard because it gave complete separation from tert-butylbenzene) . The internal standard and the Grignard reagent were mixed by shaking. A microsyringe was then inserted through one of the silicone seals in the sample tube, and, after the tube was tilted to trap liquid above the seal, approximately 0.005 ml. of sample was drawn into the syringe, care being taken to free the sample of gas bubbles. With the syringe still in place the tube was positioned as shown in Figure 1 and pressed tightly against the top of the silicone seal in ttie gas chromatographic column. The needle was then forced down through the double seal (the seal on the sample tube and the seal in the top of the chromatographic column) and the sample injected for chromatographic analysis. These data were used to determine the amount of Grignard reagent that had undergone hydrolysis prior to analysis. After the above chromatograph was obtained the unreacted Grignard reagent in the column was destroyed by the addition of methanol and water to the column (0.05 ml.) which themselves were removed by elution before proceeding. Usin a syringe, excess methanol was addef to the sample tube, and 0.005ml. of sample was again injected into the chromatographic column by the technique already described. From the chromatogram the total aryl magnesium content originally present in the Grignard reagent could be obtained. A calibration curve showing the relationship between the mole ratio of tert-butylbenzene and nonane and the area ratio of the peaks on the chromatogram for these two components was constructed (by adding these two pure components in varying amounts to ether in the sample tube and obtaining chromatograms on 0.005-ml. samples as described). From the curve, the area ratios obtained for a particular sample, and the weights of sample and internal standard the amount of aryl hydrocarbon in the sample may be readily calculated. RESULTS AND DISCUSSION
The results of three separate analyses of a sample of para-tert-butylphenylmagnesium bromide by the procedure just described are shown in Table I. The samples used for the analysis by acid titration were taken by using a
10-ml syringe as a weighing pipet. The piston was sealed with silicone oil Prim to taking the mmPle, and the tip of the needle was sealed with a s& cone stopper after taking a sample. The agreement between the two methods for original Grignard reagent as R M ~ X )is excellent, and indicates that decomposition occurred only by hydrolysis. This agreement may be partially the result of using a freshly prepared Grignard reagent. On analysis of 4 year old
phenylmagnesium bromide and tolylmagnesium bromide by a gas chromatographic method (but one using vapor sampling under reflux conditions instead of the one described here) and by acid titration, the acid titration results were found to be about 20% This discrepancy may be the result of some air oxidation of the 4 Year old reagent, which had been stored under nitrogen in a brown bottle closed with a serum stopper.
ACKNOWLEDGMENT
We thank the Burrell Corp. for providing the chromatograph for this research and the Research Corp. for the supplies used in this research. LITERATURE CITED
( 1 ) Clifford, A. F., Olsen, R. R., ANAL. CHEM. 32,544 (1960). (2) Gilman, H., J. Am. Chem. SOC.51, 1576 (1929).
RECEIVED for review February 16, 1961. Accepted April 6, 1961.
Separation and Analysis of Chlorobenzenes in Mixtures by Gas Chromatography HERBERT G. NADEAU and DUDLEY OAKS, Jr. Olin Research Center, Olin Mathieson Chemical Corp., New Haven, Conn.
b A gas chromatographic method for the separation and analysis of a series of increasingly substituted isomeric aromatic compounds is described. The procedure utilizes a temperatureprogrammed chromatograph jo separate all components over a column temperature range of 75" to 260" C. A new partitioning material possessing high selectivity for aromatic compounds and ethers is described and compared to a conventional hightemperature silicone column.
C
MIXTURES of chlorinated benzenes, including some nitro derivatives, have been analyzed for some time by infrared methods (16). It has not always been possible to determine all components prcsent in these mixtures because of the complexity of the infrared spectrum resulting from the numerous similar compounds present and because of a general lack of sensitivity for small concentrations. I n some cases, even qualitative detection is not possible. Gas chromatographic methods of separation and analysis have been reported for various chlorohydrocarbons (IO, 1I ) , including alkyl halides ( I @ , chloronitrobenzenes (Z), and chloroaromatics ( I , 4). These methods demonstrate the extreme utility of gas chromatographic techniques for the separation and analysis of chlorinated organics, but were not as much suited for application to the following series of wide boiling range chlorinated organics, which are in some cases isomeric : benzene, monochlorobenzene (MCB), 0- and p-dichlorobenzene (DCB), 1,2,4 and 1,2,3-trichlorobenzene (TCB), sym- and oictetrachlorobenzene (tetra CB), penta-
RUDE
chlorobenzene (PCB), hexachlorobenzene (HCB), and pentachloronitrobenzene (PCNB) The published methods dealt primarily with separations of relatively low-boiling compounds as compared to the components comprising the mixtures with which this work is concerned (Table I). The various partitioning materials used, unfortunately, were materials which would not stand high temperatures. The wide range in boiling points between isomeric chlorinated benzenes dictated that the gas chromatographic separation would be more effective if it were performed on a high-temperature limit partitioning material and if it were temperature-programmed. Temperature-programmed separations are most
.
Table 1.
applicable where speed and flexibility of operation are requisite in dealing with compounds or groups of compounds possessing a wide spread in boiling points, as in this case. Temperatureprogrammed column heating and some of its applications have been covered adequately in the published literature (3). The method presented effectively utilizes two different high-temperature partitioning agents, either of which is suitable for separation and analysis of these mixtures performed under temperature-programmed conditions. EXPERIMENTAL
Apparatus. F & M linear programmed gas chromatograph, Model 202. A 4-foot column of silicone
Retention Time (Uncorrected) and Response Factors for Compounds on Silicone and High-Boiling Ether Columns
Compound Benzene MCB
p-DCB
o-DCB
1,2,iTCB 1,2,3-TCB
sym-Tetra CB uic-Tetra CB PCB HCB PCNB 1,4-DNTCB
(Response factors are relative t o monochlorobenzene) Retention Time, Minutes Response Factors HighHighboiling boiling Boiling Pt., O C. Silicone ether Silicone ether 80.1 132.0 180.4 174.4 213.0 128 to 219 240 to 246 254 275 t o 277 309 (742 mm. Hg) 328
...
3.0 7.6 13.4 15.0 19.5 20.6 24.1 25.4 31 .O 36.1 37.5 37.8
2.0 6.2 11.0 12.0 16.5 17.5 21.3 22.5 27.0 32.0 36.0
...
1 .oo 1.30 1.10 1.30 1.30 1.25 1.42 1.49 1.51 2.70
...
VOL 33, NO. 9, AUGUST 1961
1 .oo 1.23 1.11 1.26 1.20 1.30 1.41 1.44 1.54 2.67
...
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