A study of hydrogen abstraction by CH3 radicals from CH3COOCH3 in the temperature range
116-224°, and from CD3COOCH3 in the range 117-234°, has yielded data on the reactions:
CH3 + CH3COOCH3 → CH4 + [C3H5O2] (4)
CH3 + CH3COOCH3 → CH4 + CH2COOCH3 (5)
CH3 + CH3COOCH3 → CH4 + CH3COOCH2 (6)
CH3 + CD3COOCH3 → CH3D + CD2COOCH3 (7)
The corresponding rate constants, based dn the value of 1013.34 cm3 mol-1 s-1 for the recombination
of CH3 radicals, are given by (k in cm3 mol-1 s-1 and E in J mol-1):
logk4 = (11.56 ± 0.12) - (44430 ± 970)/19.145T (4)
logk5 = (11.17 ± 0.22) - (42900 ± 1760)/19.145T (5)
logk6 = (11.44 ± 0.16) - (46980 ± 1290)/19.145T (6)
logk7 = (11.39 ± 0.04) - (52110 ± 330)/19.145T (7)
At 400 K, 64% of abstraction occurs from the acetyl group, and 36% from the methoxy group.
The kinetic isotope effect at 400 K for attack on the acetyl group is 9.6; this is mainly due to a
difference in activation energies since the quotient of A factors is close to unity.
Isotopic labelling has been employed to determine the position and extent of hydrogen abstraction from the formyl and methoxyl sites in methyl formate by methyl and trifluoromethyl radicals. Attack is principally at the formyl group, but at 182" a significant proportion of abstraction occurs from the methoxyl ; 15 % for attack by CH3 and 25 % for attack by CF3. Values for rate constants (at 182") and for Arrhenius parameters are as follows : reaction pre-exponential velocity log10 log10 activation factor constant at 182OC (A/cn$ mole-1 sec-1) (k/cm3 mole-1 sec-1) energy CH3+HC02CH3 +CH4+[CzOzH3]*
The reactions of CF3 radicals with dimethylether and diethylether and of CH3 radicals with dimethylether and diisopropylether have been studied. The photolyses of acetone and hexafluoroacetone were used as radical sources; all rate constants are based on the rate constants for radical dimerization. The Arrhenius parameters measured are as follows[Formula: see text]
Hydrogen abstraction from
(CH3),S and CH3COCH3 by CH3
radicals
CH3+CH3SCH3 → CH4+CH3SCH2
CH3 + CH3COCH3 → CH4 +
CH3COCH2
has been studied in the
temperature range 120-245�. The rate constants, based on the value of 1013.34cm3
mol-l s-1 for the recombination of CH3
radicals, are given by (k in cm3 mol-1 s-1, E
in kJ mol-1, R = 0.008314 kJ K-1 mol-1):
logk1 = (11.62 �
0.08) ? (38.35 � 0.68)/2.303RT
logk3 = (11.61 �
0.05) ? (40.48 � 0.46)/2.303RT
Combination of the results
for (1) with thermochemical data gives a calculated value of
Logk-1 = (11.8
-63.7/2.303RT
for the rate constant of
the reverse reaction. The results for CH3+(CH3)2S
are compared with all of the available data for hydrogen abstraction by free
radicals from both sulphur-containing compounds, and
molecules of the type (CH3)xM.
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