Determination of Deuterium in Water Conversion to Methyl Deuteride and Methane and Measurement by Mass Spectrometer MILTON ORCHIN, IRVING WENDER, AND R. A. FRIEDEL O f i c e of Synthetic Liquid Fuels, U. S. Bureau of Mines, Pittsburgh, Pa. A mixture of a hydrocarbon of relatively high molecular weight whose hydrogen atoms are of mass one and the same hydrocarbon containing some deuterium atoms should provide a nearly ideal solution suitable for the evaluation of distillation columns operating under reduced pressure. Such mixtures can be analyzed for deuterium by burning the hydrocarbons to water and converting the water to methane and methyl deuteridt. This gaseous mixture can then be analyzed with great accuracy by means of the mass spectrometer.
P
REPARATIOX of a binary test mixture suitable for the evaluation of laboratory distillation columns operating a t reduced pressure has been under investigation in this laboratory for some time ( d ) . A mixture of a hydrocarbon of relatively high molecular weight whose hydrogen atoms are of mass one and the same hydrocarbon containing some deuterium atoms should provide a nearly ideal solution. This idea xas first suggested to the authors by 11.S. Sewman. The use of such a solution requires a method for determining the concentration of deuterated hydrocarbons in the mixture. Preliminary experiments disclosed that, when the hydi ocarbons of high molecular weight were analyzed for deuterium content directly by the mass spectrometer, the results were not sufficiently accurate. A search was then instituted for another analytical method or for a simple but more accurate mass sprctrometric method. Because a precise procedure for burning hydrocarbons to w :iter has been described ( 4 ) , it was thought that the deuterium content of the hydrocarbon mixture could be determined by combustion and analysis of the R-ater for deuterium, either by direct mash spectrometric measurement or by one of the usual methods involving the measurement of physical constants. However, because adsorbed water vapor is always present on the inner glass surfaces of a mass-spectrometer vacuum system, exchange reactions complicate the direct determination of deuterium in water. Furthermore, determination of deuterium in water by the usual physical methods requires a relatively large sample and careful techniques to avoid contamination. The recent paper by Fischer, Potter, and Voskuyl (5)describes a method for determining deuterium in water involving equilibration of the water sample with hydrogen gas and subsequent analysis of the equilibrated gas on the spectrometer. The most dilute deuterium solution analyzed contained 26.1 mole ?' & deuterium and the experimentally determined deuterium concentrations deviated 1 to 1.9% on an absolute basis from the actual deuterium concentration in the five analpes presented. Five milliliters of water were used for each analysis. This procedure, however, can probably be extended to small samples of low deuterium content. The present paper describes a method for the quantitative determination of deuterium in water by the reaction of excess methyl magnesium iodide with the water and subsequent analysis of the methanemethyl deuteride mixture by the mass spectrometer. Pure methyl deuteride for mass spectrometric investigation has been prepared by Evans, Bauer, and Beach ( 1 ) and by Turkevich, Friedman, Solomon, and Krightson (6) by using pure deuterium oxide with the Grignard reagent. The measurement of the methane generated by the reaction of methyl magnesium iodide nith compounds containing active hydrogen is the basis of
the Zerewitinoff determination ('7). The equations for the reaction of methyl magnesium iodide with water may be written:
OH
CH,i\lgI
+ H20 +CH4 + hfgI
(1)
I
I
i Theoretically, 2 mules of methane are generated for 1 mole of water, but, in conformity with published results, the authors experienced difficulty in obtaining theoretical yields of gas. This difficulty is due to the formation of a solid hygroscopic product during the reaction; tjhe total added water does not have intimate contact with the Grignard reagent after the first hydrogen has reacted. In the present work, gas samples were taken after the initial vigorous reaction had coinpletely subsided and no attempt was made to secure theoretical yields of methane. The authors assumed that the proportion of deuterium in any unreacted material was the same as in the reacted portion. This method of determining deuterium in water can be successfully employed with as little as 10 to 20 mg. of water, is capable of high accuracy, and can be carried out without any unusual precautions to guard against dust or other inert impurities. EXPERIMENTAL PROCEDURE AND RESULTS
Methyl deuteride (,CHaD) was prepared using the apparatus and injection technique previously described (6). Immediately before use, the apparatus was warmed with a flame in a current of nitrogen and allowed to cool with a strong stream of nitrogen flowing through the'apparatus. There were then injected into the methyl magnesium iodide solution 50 to 100 mg. of 99.87% deuterium oxide. After the reaction had subsided, a gas sample Table I. Mass
17 16 15 14 13 12
Mass Spectral Patterns and Sensitivities for Methane and Methyl Deuteride B" 1oo:o 86.5 17.7 9.0 2.9 53.9
CHI E
1oo:o
CHID T
B
E
T
100.0
100.0
100.0 78.2 22.3 8.8 5.0 2.5 65.0
1oo:o 78.6 76.0 22.9 22.5 83.1 83.5 17.1 17.0 9.5 9.4 8.2 5.5 5.2 8.3 2.4 2.8 2.4 2.6 Sensitivity Equal to 81.8 53.1 Equalto of parent CHnD CHI to mass t o 1% 1% B Bureau of Mines: E = Evans, Bruer, and Beach; T Turkevich. Friedman, Solomon, and Wrightson.
-
1072
-
V O L U M E 21, NO. 9, S E P T E M B E R 1 9 4 9
1073
Table 11. Analysis of Deuterium in Water Gas
Sample 1
L
% N1
Present 32.7
?& Air
Present 3.3
1.1
0.6
6.9
0.2
I
20.3
P
3.7
1
22.6
2
12.8
5 Air presumably collected and before
Experimental, hloie % D (as CHPD) 1.37 1 .37 1 .27 1.26 2.73 2.72
Experimental Average, Mole % D 1.32
Calculated, Mole % D (as Dz0) 1 42
2.70
2.83
26.3"
4.71 4.75 4.84 4.70 0.3 4.80 4.78 26.ga 14.54 14.63 14.79 14.62 25.8" 14.60 14.68 leaked into gas sampling bulb aftrr sample had been analysis was made.
ages of 55, and pattern values were corrected for C13 content (1.1%). The pattern values compare favorably; the fragmentation values from the present work are slightly higher, possibly because of a higher ionization chamber temperature. The sensitivity difference between methane and methyl deuteride for thi8 work (methyl deuteride lower than methane by 1.5%) comparea more favorably with that of Evans et al. (sensitivities equal within 1%) than with those of Turkevich et al. (methyl deuteride higher than methalie by 5%). A series of water standards of known isotopic composition was prepared by weight dilution methods, using normal distilled water and 99.87% deuterium oxide as the ingredients. Using the same apparatus and technique as in the preparation of methyl deuteride, two successive gas samples were prepared from each water standard. Two analyses of each sample were made, using the mass spectrometer. Table I1 shows that air or nitrogen or both are present in large amounts in four of the eight samples. From the good results obtained, it is apparent that no special precautions need to be taken to prevent this contamination. LITERATURE CITED
was taken. Without removing the syringe from the neoprene serum stopper, 50 to 100 mg. of water were injected and a second gas sample was taken. Additional samples of gas were taken without removing the syringe. The mass spectral patterns of nine samples of methyl deuteride, prepared in three batches from two different vials of deuterium oxide, did not vary by more than 0.2 for the 16 mass peak and not more than 0.1 for the other mass peaks.
(1) Evans, Yl.,Bauer,, N.,and
Comparisons of patterns and sensitivities for methane arid methyl deuteride with those of Evans et al. ( 1 ) and of Turkevich et al. (6) are given in Table I. All three sets of data were obtained o n Consolidated mass spectrometers at electron-accelerating volt-
(6) Turkevich, J., Friedman, L., Solomon, E., and Wrightson, F. M.: J . Am. Chem. Soc., 70, 2638 (1948). ( 7 ) Zerewitinoff, Ber., 40, 2023 (1907).
(1946). -,
Beach, J. Y . , J . Chem. Phgs., 14, 701
\--
(2)
Feldman, J., Myles. M., Wender, I., and Orchin, M.,I d . Eng.
Chem., 41, 1032 (1949). (3) Fisher, R. B., Potter, R. A,, and Voskuyl, R. J., ANAL.CHEM.. 20, 571 (1948). (4) Keston, A. S., Rittenberg, D.. Chem., 122, 227 (1937).
and Schoenheimer, R. J., J . Riol.
( 5 ) Orchin, M., and Wender, I., h s a ~CHEM., . 21, 875 (1949).
RECEIVEDJanuary 18. 1949.
Determination of Acrylonitrile and Alpha, Beta-Unsaturated Carbonyl Compounds Using Dodecanethiol DONALD W. BEESING, WILLARD P. TYLER, DONALD M. KURTZ, AND STUART A. HARRISON' The B. F. Goodrich Research Center, Brecksville, Ohio Methods are described for the determination of from 2 to 200 mg. of acrylonitrile and a,@-unsaturatedaldehydes and esters by the addition of excess primary mercaptan and determination of the unreacted mercaptan iodometrically or amperometrically. The salts of the corresponding acids do not react with the mercaptan under the conditions employed and other unsaturated compounds in general do not interfere.
N
0 CHEMICAL method for determining acrylonitrile in ap-
preciable quantities has been described in the literature. A method for determining small amounts in air by hydrolysis to ammonia was developed by Petersen and Radke (11) and a physical method by infrared spectroscopy was described recently by Dinsmore and Smith (9). In studying the disappearance of mercaptan (thiol) in butadiene-acrylonitrile copolymerizations, it was found that primary mercaptans disappeared rapidly in the presence of a base; the 1 Present address, Research Laboratories, General Mills. Inc., Minneapolis. Mion.
primary mercaptan had reacted with the scryloiiitrile in what appeared to be a quantitative manner. At about the same time, the reaction of acrylonitrile as well as other open-chain a,@-unsaturated nitriles with certain organic mercaptans was patented by Harman (4). Since that time, Hurd and Gerahbein (6) have reported that acrylonitrile and alkanethiols or thiophenols react practically quantitatively in the presence of a small amount of alkaline condensing agent. This paper describes the conditions under which acrylonitrile and some a,@-unsaturated esters and aldehydes can be determined accurately by adding an excess of n-dodecyl or other pri-
