diethoxybutane (2,3-dimer) was 2.57 units, that of the 1,3-dimer was 10.09 units, and the 1,Cdimer was not observed. Similarly, G(ethy1 sec-butyl ether) = 0.74 and G(ethy1 n-butyl ether) = 0.03. There is some doubt about the exact yields of the minor products, but the results indicate that the value of the ratio of the steady-state concentration of CH&HOC2H5 to that of CHzCH2OCzHS was about 40 to 1. If this difference is
attributed to the difference in the activation energies of the two abstraction reactions R
+ CH3CH20C2Hs-+R H + CH,CHOC,H, --+R H + CH2CH20C2H5
(24) (25)
then A E = (Ez5 - E Z 4 )= 2.4 kcal./mole. This is in good agreement with the corresponding value AE = 2.7 kcal./mole in the ethanol ~ y s t e m . ~
Radiolysis of Diethyl Ether. 11. Deuterium-Substituted Ethers in the Gas and Liquid Phases' Mark K. M. Ng and Gordon R. Freeman Contribution f r o m the Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada. Received December 5 , 1964
The G values of the major products of the y-radiolysis of diethyl ether vapor at 25" and a dose of 3 X l o z oe.v./g. are: hydrogen, 6.4; 2,3-diethoxybutane, 2.4; ethylene, 2.1; acetaldehyde, 1.4; methane, 1.3; ethyl isopropyl ether, 1 .O; formaldehyde, 0.9; ethyl sec-butyl ether, 0.8; ethanol, 0.7; G ( - C 2 H 5 0 C 2 H 5 )= 11.2, based on the carbon in the measured products; G(excess H Z in products) = 1.7. The yields of acetaldehyde and ethyl vinyl ether (G = 0.4 at 19 X 1020 e.v./g.) decreased with increasing dose. The value of G(-ether) in the vapor phase is nearly the same as that in the liquid phase, although the product distribution is quite different in the two phases. Ether molecules, on the average, break into smaller fragments in the gas than in the liquid phase ka
radiolysis. For the reactions R f M
+
dose rate = 3 X 1017 e.v./g. hr. ( N 2 0dosimetry), dose = 10I8e.v./g. Experimental Most of the materials and procedures were described earlier.2 Only new materials and techniques will be described here. Three deuterated ethers were obtained from Merck Sharp and Dohme of Canada Ltd: (CzD5)z0(etherdlo); (CD3CHz)20 (ether-/3-d6); (CH3CD2)20 (ethera-d4). The isotopic impurities of the ethers were measured by n.m.r. analysis and are listed in Table I. Table I. Isotopic Impurities in the Deuterated Ethers
R H f R'
kc
and R f R --.c Rz,k,/kc is smaller in the vapor than in the liquid phase. Comparison of the product yields f r o m the radiolysis of (CZHs)zo, ( C D 3 C H 2 ) 2 0(, C I f 3 C D 2 ) 2 0 , and (CZD&O showed that a-C-H bond cleavage was most important in hydrogen and methane formation, and P-C-H cleavage was most important in ethylene formation although both types of cleavage made sign$cant contributions to the formation of all three products.
Introduction The y-radiolysis of liquid diethyl ether was reported earlier.2 The present article describes a brief study of the y-radiolysis of the ether in the gas phase and also reports the influence of phase on the hydrogen-deuterium content of some of the gaseous products from various deuterium-substituted diethyl ethers. Baxendale and Gilbert3 found the values G(Hz) = 6.75 f 0.05 and G(CH4) = 3.55 f 0.15 for the yradiolysis of diethyl ether vapor. The yields of the other products were not measured. The conditions of the experiments were 116", 140 and 470 mm. pressure, (1) This work received financial assistance from the National Research Council of Canada. (2) M. K. M. Ng and G . R. Freeman, J . A m . Chem. Soc., 87, 1635 (1965). (3) J . H. Baxendale and G. P. Gilbert, DfscussfonsFaraday Soc., 36, 186 (1963).
Ether
For example, 100(a-H)/(a-H purity in the CY position.
Impurity
Atom
%"
+ CY-D)is the atom
of H im-
The gas phase radiolysis cells were 500-ml. Pyrex bulbs with break-seals. Each cell contained about 0.7 g. (0.5 atm.) of sample. The irradiation temperature was 25 f 3", and the dose rate was 6 X 1019e.v./g. hr. Unless otherwise stated, the liquid and the vapor samples received a dose of 3.5 X IOzo e.v./g. Liquid phase dosimetry was done with the Fricke dosimeter. Vapor phase dosimetry was done with ethylene, using G(H2) = 1.28.4 Sufficient ethylene was placed in the bulb that the electron denshy of ethylene was approximately the same as that of ether in the ether samples. The products were analyzed by the same techniques as those reported in the previous paper,* except that the gaseous products were analyzed by mass spectrom(4) R. A . Back, T. W. Woodward, and K. A. McLauchlan, Can. J . Chem.,40, 1380(1962).
Ng, Freeman
1 Radiolysis of Deuterium-Substituted Ethers
1639
2.0 1.5 1 .a
Ob
c)
(35 0.4
03 0.2 0.1 0
2
1
6
8
2
4
6
8
1
0 0
EpXlO Figure 1. Gaseous product yields as a function of 1,3-pentadiene concentration (gas phase radiolysis). The dashed lines refer to = 3.5 X lozoe.v./g.; sp = electron fraction of G e r p e c r c ~Dose ~. 1.3-pentadiene. A : Hz. B : 0, CH,; 0,CzH4. C : 0, CO; 2 , CzHs.
etry instead of by gas chromatography. For formaldehyde analysis of the vapor samples, the sample cell was cooled in ice water before it was opened. After breaking open the cell, 5 ml. of distilled water was introduced into it, the cell shaken, and the ether allowed to evaporate. The solution was analyzed by a chromotropic acid method.5 Freezing the sample was avoided to prevent polymerization of the formaldehyde.
ether had t o be measured a t higher doses. The yield of acetaldehyde decreased from G = 1.4 a t 5 X lozo e.v./g. t o 1.0 a t 19 X 1020 e.v./g. The yield of ethyl vinyl ether was G = 0.4 a t 19 X 1020 e.v./g.; i.e., the final ethyl vinyl ether concentration was 0.09 electron %. However, when diethyl ether was radiolyzed in the presence of 0.3 % of ethyl vinyl ether, the latter was destroyed a t a rate which corresponded to G = 0.74 at 5.0 X IOzo e.v./g. The steady-state concentration of ethyl vinyl ether in diethyl ether under these conditions of radiolysis was in the vicinity of 0.2%. Thus, the value of G(ethyl vinyl ether) would be greater than 0.4 a t doses below 19 X lozoe.v./g. The product yields from the liquid phase radiolysis of diethyl ether2 are included in Table I1 for comparison. The product distribution is quite different in the two phases. The effects of 1,3-pentadiene on the gaseous product yields are shown in Figure 1. The formation of ethylene and of carbon monoxide is slightly inhibited, whereas the formation of hydrogen, methane, and ethane is greatly inhibited. The inhibition of the formation of three major liquid products is shown in Table 111. The yields of all three products are greatly reduced by 1,3-pentadiene. Table 111. Inhibition of Liquid Product Formation in Gas Phase Radiolysis G -
Results
Gar Phase Radiolysis of “Light” Diethyl Ether. Most of the product yields were measured a t doses of 1.0, 2.0, and 3.5 X 1020 e.v./g. and were independent of dose over this range. The G values listed in Table I1
EP
Product 2,3-Diethoxybutane Ethyl sec-buty, ether Ethanol
=
0
ep =
0086
7
ep =
ep =
0 23
0 32
2 38 0 83
(0 2
0 14
