A structure-reactivity correlation with three slopes in the elimination kinetics of 2-substituted ethyl N,N-dimethyl-carbamates in the gas phase

Article abstract of DOI:10.1002/poc.341

The elimination kinetics of 17 2-substituted ethyl N,N-dimethylcarbamates in the gas phase were determined in the temperature range of 269.5-420.2°C and the pressure range of 24-186 Torr. The reactions in a static system and in the presence of a free radical inhibitor are homogeneous and unimolecular and follow a first-order rate law. The kinetics and thermodynamic parameters are described. The use of several structure-reactivity relationship methods meaningless results, except for Taft σ* values. Three good slopes are originated at σ*(CH₃) = 0.00. Slope a: the 2-substituted alkyl groups gave a good straight line when log (k/kCH₃) vs σ* values (ρ* = - 1.94 ± 0.30, r = 0.977 at 360°C) were plotted. Slope b: Polar² substituents gave an approximate straight line with ρ* = - 0.12 ± 0.02, r = 0.936 at 360°C. Slope c:the correlation of multiple bonded and electron-withdrawing substituents interposed by a methylene group at the 2-position of ethyl N,N-dimethylcarbamate was found to give a very good straight line wirh ρ* = 0.49 ± 0.02, r = 0.991 at 360°C. Mechanisms are suggested on the basis of these relationships. The point position of the substituents phenyl (C₆H₅) and isopropenyl [CH₂=C(CH₃)] at the 2-position was found to fall far above the three slopes of the lines. These results are interpreted in terms of neighboring group participation of these substituents in the elimination process of the carbamates. However, the acidity of the benzylic and allylic C_β-H bond for a six-membered cyclic transition state may not be ignored. Copyright

Full text of DOI:10.1002/poc.341

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2001; 14: 146–158
A structure±reactivity correlation with three slopes in the
elimination kinetics of 2±substituted ethyl N,N-dimethyl-
carbamates in the gas phase
Gabriel Chuchani,1* Oswaldo NunnÄ ez,2 Norka Marcano,3 Suvighey Napolitano,3 Henry Rodriguez,3
Marianella DomõÂnguez,3 Judany Ascanio,3 Alexandra Rotinov,1 Rosa M. DomõÂnguez1 and
Armando Herize1
1Centro de QuõÂmica, Instituto Venezolano de Investigaciones Cienti®cas (IVIC), Apartado 21827, Caracas 1012-A, Venezuela
2Departamento de Procesos y Sistemas, Universidad Simo n BolõÂvar, Sartenejas, Estado Miranda, Venezuela
3Departamento de QuõÂmica, Universidad Simo n BolõÂvar, Sartenejas, Estado Miranda, Venezuela
Received 26 June 2000; revised 26 October 2000; accepted 30 October 2000
ABSTRACT: The elimination kinetics of 17 2-substituted ethyl N,N-dimethylcarbamates in the gas phase were
determined in the temperature range of 269.5–420.2°C and the pressure range of 24–186 Torr. The reactions in a
static system and in the presence of a free radical inhibitor are homogeneous and unimolecular and follow a first-order
rate law. The kinetics and thermodynamic parameters are described. The use of several structure-reactivity
relationship methods meaningless results, except for Taft s* values. Three good slopes are originated at
s*(CH3) = 0.00. Slope a: the 2-substituted alkyl groups gave a good straight line when log (k/kCH3) vs s* values
(r* = 1.94 Æ 0.30, r = 0.977 at 360°C) were plotted. Slope b: Polar2 substituents gave an approximate straight line
with r* = 0.12 Æ 0.02, r = 0.936 at 360°C. Slope c:the correlation of multiple bonded and electron-withdrawing
substituents interposed by a methylene group at the 2-position of ethyl N,N-dimethylcarbamate was found to give a
very good straight line wirh r* = 0.49 Æ 0.02, r = 0.991 at 360°C. Mechanisms are suggested on the basis of these
relationships. The point position of the substituents phenyl (C6H5) and isopropenyl [CH2=C(CH3)] at the 2-position
was found to fall far above the three slopes of the lines. These results are interpreted in terms of neighboring group
participation of these substituents in the elimination process of the carbamates. However, the acidity of the benzylic
and allylic Cb-H bond for a six-membered cyclic transition state may not be ignored. Copyright 2001 John Wiley &
Sons, Ltd.
KEYWORDS: 2-substituted ethyl N, N-dimethylcarbamates; gas-phase elimination kinetics; structure–reactivity
correlation
INTRODUCTION
bamate decomposed into N-methylaniline, ethylene and
carbon dioxide Further investigations on N,N-dimethyl-
carbamate pyrolyses led to a general accepted mechanism
of a six-membered cyclic transition state as described in
reaction (1), which is similar to the transition states
The first pyrolytic elimination of a carbamate at
subatmospheric pressure was reported by Daly and
Ziolkowski.1 The substrate ethyl N-methyl-N-phenylcar-
Form A
*Correspondence to: G. Chuchani, Centro de Qu´ımica, Instituto
Venezolano de Investigaciones Cientificas (IVIC), Apartado 21827,
Caracas 1012-A, Venezuela.
designated for the thermal decomposition of acetates,
carbonates and xanthates.2–6
In our most recent work, the branching of alkyl groups
of N,N-dimethylcarbamates enhanced the rates of
elimination in the order tert-butyl >isopropyl >ethyl.7
In addition the presence of different substituents Z other
E-mail: chuchani@quimica.ivic.ve
Contract/grant sponsor: CONICIT (Consejo Nacional de Investiga-
ciones Cientificas y Tecnolo´gicas); Contract/grant number: S1-
97000005.
Contract/grant sponsor: UGA (Unidad de Gestion Ambiental).
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

ELIMINATION KINETICS OF 2-SUBSTITUTED ETHYL N,N-DIMETHYLCARBAMATES
147
Table 1. Ratio of ®nal (Pf) to initial (P0) pressurea
Temperature
Po
(Torr)
Pf
(Torr)
Substrate
(°)
Pf/Po
Average
Ethyl N,N-dimethylcarbamate
359.6
370.4
380.8
390.1
73
88
118
97
215
257
254
285
2.95
2.92
3.02
2.94
2.96 Æ 0.04
2.96 Æ 0.06
2.41 Æ 0.15
2.98 Æ 0.02
2.93 Æ 0.05
2.95 Æ 0.02
2.95 Æ 0.01
3.10 Æ 0.04
3.04 Æ 0.04
2.95 Æ 0.02
2.97 Æ 0.03
2.98 Æ 0.10
2.83 Æ 0.03
2.32 Æ 0.07
Propyl N,N-dimethylcarbamate
362.8
370.0
380.1
389.9
90
64
68
57.5
258
193
201
171
2.87
3.01
2.96
2.98
1-Butyl N,N-dimethylcarbamate
361.0
371.0
379.0
400.0
68
71
78
72
179.5
169
181
2.64
2.38
2.32
2.30
167
3-Methyl-1-butyl N,N-dimethylcarbamate
3,3 Dimethyl-1-butyl N,N-dimethylcarbamate
2-Chloroethyl N,N-dimethylcarbamate
2-Bromoethyl N,N-dimethylcarbamate
2-Methoxyethyl N,N-dimethylcarbamate
2-Butoxyethyl N,N-dimethylcarbamate
3-Phenylpropyl N,N-dimethylcarbamate
3-Chloropropyl N,N-dimethylcarbamate
3-Phenoxypropyl N,N-dimethylcarbamate
2-Dimethylaminoethyl N,N-dimethylcarbamate
3-Butyn-1-yl N,N-dimethylcarbamate
350.6
370.5
380.5
390.7
50
61
56
44
150
182
165
132
3.00
2.98
2.95
3.00
339.7
350.7
370.2
390.3
44
48
38
37
130
142
112
106
2.96
2.96
2.95
2.85
379.6
390.6
400.5
420.2
27
80
232
275
265
2.96
2.92
2.97
2.96
79.5
92.5
89.5
360.8
370.7
400.6
410.4
94
95
92
98
277
279
271
288
2.95
2.94
2.95
2.94
385.6
410.3
419.9
430.1
55
40
41
39
171
120.5
129
3.11
3.01
3.15
3.13
122
389.6
401.1
410.0
420.5
56
43
47
67
172
130
145
201
3.07
3.02
3.08
3.00
340.5
360.4
380.6
400.6
89
98
84
92
263
291
249
269
2.95
2.96
2.96
2.92
360.4
370.5
380.2
390.5
69
72
112
114.5
202
215
335
342
2.93
2.99
2.99
2.99
350.1
370.4
380.9
390.4
32.5
49.5
41
97
2.98
2.84
3.05
3.05
138
125
122
40
380.7
389.9
400.0
409.7
76
76
71.5
70
214
218
201.5
176
2.82
2.87
2.82
2.81
329.7
340.0
349.0
360.0
98
103
114.5
112
220
2.24
2.32
2.32
2.40
238.5
265.5
269
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

148
G. CHUCHANI ET AL.
Table 1 continued.
Temperature
Po
(Torr)
Pf
(Torr)
Substrate
(°)
Pf/Po
Average
2-Cyanoethyl N,N-dimethylcarbamate
290.0
309.6
319.0
329.6
54.5
34
30.5
61
140
92
77.5
156
2.63
2.71
2.54
2.56
2.61 Æ 0.08
2-Phenylethyl N,N-dimethylcarbamate
310.1
321.0
330.2
341.7
44
46
65
76
131
135
194
227
2.98
2.93
2.98
2.99
2.97 Æ 0.03
2.26 Æ 0.21
3-Methyl-3-buten-1-yl N,N-dimethylcarbamate
339.6
349.6
360.9
370.1
63
67.5
67
159
157
138.5
147
2.52
2.33
2.07
2.10
70
aTemperature <360°C, cyclohexene inhibitor; >360°C, toluene inhibitor.
than carbon in ZCOOCH2CH3 gave a good correlation
when using the Taft–Topsom method.7 In relation to this
result, the field (inductive) effect of the substituent has
the greatest influence on rate enhancement, whereas the
polarizability (steric) and resonance factors favor the
elimination process very little.
mechanisms of the gas-phase elimination of 2-substituted
ethyl acetates, the present work was addressed at
examining a considerable number of 2-substituted ethyl
N,N dimethylcarbamates [(CH3)2NCOOCH2CH2Z,
Z = substituent] in order to establish whether a similar
or different linear relationships are obtained for the
mechanistic considerations illustrated in reaction (1).
A considerable number of the database of substituents
at the 2-position of ethyl acetates (CH3COOCH2CH2Z)
8
were examined in correlation studies . The pyrolysis of
the acetates with alkyl and polar substituents attached to
the Ca—O bond by at least three methylene group was
found to be affected by steric acceleration. The log (k/k0)
vs Hancock’s steric parameter Esc gave a ꢀ = 0.12,
r = 0.916 at 400°C. However, electron-withdrawing
substituents at the 2-position of ethyl acetates showed
an approximate linear relationship with the Taft original
inductive parameter s*.9a,b The r* value was 0.19
(r = 0.961 at 400°C). Likewise, plotting log k/k0 against
s1 value also gave a good straight line with slope
r1 = 1.03 (r = 0.960 at 400°C). Further examination of
the influence of these alkyls and a polar group separated
by at least a three methylene chain in CH3COOCH2CH2Z
was carried out by using the Taft–Topsom method of
substituent effects. The result was log (k/ko) =
(0.450 Æ 0.004) sa (1.29 Æ 0.11) sF (r = 0.959 at
400°C).8 The negative value of ra suggests that the
elimination process is favored by the polarizability of the
2-substituent Z, while the size of the negative rF implies
the stabilization of the transition state by field/inductive
effects. The influence of the resonance factor sR was
found to be insignificant. Multiple bonded substituents Z
at the 2-position of ethyl acetates led to a very good Taft–
Topsom correlation log (k/k0) = (1.81 Æ 0.02) sa
(0.38 Æ 0.03) sF ‡ (7.34 Æ 0.12) ꢁR (r = 0.999 at
400°C). This result suggests significant polarizability
and resonance effects on the elimination rates.
RESULTS AND DISCUSSION
The products of the gas-phase elimination of 2-sub-
stituted ethyl N,N-dimethylcarbamates are the corre-
sponding olefin, dimethylamine and carbon dioxide
[reaction (1)]. The stoichiometry based on reaction (1),
demands that for long reaction times Pf/P0 = 3, where
Pf and P0 are the final and initial pressure, respectively
(Table 1). The average Pf/P0 values at four temperatures
and ten half-lives were, within the experimental errors,
nearly 3.0. However, a departure of Pf/P0 < 3.0 for
1-butyl, 2-dimethylaminoethyl, 3-butyn-1-yl, 2-cyano-
ethyl and 3-methyl-3-buten-1-yl N,N-dimethylcarba-
mates was due to polymerization of the corresponding
olefinic product. These pure unsaturated products when
introduced in the reaction vessel give rise to a decrease in
pressure and formation of a solid polymer product.
Further examination for the verification of
the stroichiometry in reaction (1), up to 50–77%
reaction, was made by comparing the extent of decom-
position of the substrate from pressure measurements
with that obtained from quantitative gas–liquid chroma-
tographic (GLC) analyses of the corresponding olefin
formation or from the unreacted amount of the carbamate
(Table 2).
The pyrolytic elimination of reaction (1) was found to
be homogeneous, since no significant variations in rates
were obtained in these experiments when using both
clean Pyrex and seasoned vessels with a surface-to-
Because various correlations of substituent effects had
to be used to obtain some reasonable explanation of the
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

ELIMINATION KINETICS OF 2-SUBSTITUTED ETHYL N,N-DIMETHYLCARBAMATES
Table 2. Stoichiometry of the reaction.a
149
Temperature
Substrate
(C°C)
Parameter
Time (min)
Value
Ethyl N,N-dimethylcarbamate
380.8
370.0
379.0
370.0
360.1
390.3
400.0
380.3
390.0
370.0
350.3
360.8
379.6
329.8
300.3
300.0
339.6
4
5
7
9
12
Reaction (%) (pressure)
Ethylene (%) (GLC)
28
33.5 43.3 50.8 65.1
28.2 33.5 44.7 50.2 64.1
Propyl N,N-dimethylcarbamate
Time (min)
Reaction (%) (pressure)
Propene (%) (GLC)
8
12.5 20 46 300
20.6 30.8 41.2 60.8 72.5
20.9 32.4 42.0 59.2 72.0
1-Butyl N,N-dimethylcarbamate
Time (min)
Reaction (%) (pressure)
Butene (%) (GLC)
4
6
8
11
16
22.8 33.3 38.5 50.0 63.5
22.9 33.5 37.8 50.1 63.9
3-Methyl-1-butyl N,N-dimethylcarbamate
3,3 Dimethyl-1-butyl N,N-dimethylcarbamate
2-Chloroethyl N,N-dimethylcarbamate
2-Bromoethyl N,N-dimethylcarbamate
2-Methoxyethyl N,N-dimethylcarbamate
2-Butoxyethyl N,N-dimethylcarbamate
3-Phenylpropyl N,N-dimethylcarbamate
3-Chloropropyl N,N-dimethylcarbamate
3-Phenoxypropyl N,N-dimethylcarbamate
2-Dimethylaminoethyl N,N-dimethylcarbamate
3-Butyn-1-yl N,N-dimethylcarbamate
2-Cyanoethyl N,N-dimethylcarbamate
2-Phenylethyl N,N-dimethylcarbamate
3-Methyl-3-buten-1-yl N,N-dimethylcarbamate
Time (min)
Reaction (%) (pressure)
3-Methyl-1-butene (%) (GLC)
4
6
10
12
16
21.9 34.2 45.5 52.0 62.5
21.5 33.4 48.0 52.3 62.0
Time (min)
Reaction (%) (pressure)
4
6
8
11
16
22.8 33.3 38.5 50.0 63.5
3,3-Dimethyl-1-butene (%) (GLC) 22.9 33.5 37.8 50.1 63.9
Time (min)
Reaction (%) (pressure)
Vinyl chloride (%) (GLC)
6
10
24.3 39.2 50.7 61.8 73
21.1 39.9 50 62.2 67.7
10 13
16
40 150
Time (min)
Reaction (%) (pressure)
Vinyl bromide (%) (GLC)
4
6
8
21.4 30.6 39.6 49.7 64.9
20.3 30.2 40.2 51.1 65.1
Time (min)
Reaction (%) (pressure)
Methyl vinyl ether (%) (GLC)
10
20
30
40
60
22.1 31.9 41.9 54.6 69.6
21.1 34.5 44.4 53.8 66.6
Time (min)
Reaction (%) (pressure)
Butyl methyl ether (%) (GLC)
6
12
18
25
35
15.3 29.7 36.3 45.1 73.4
15.7 28.6 35.8 45.3 74.5
Time (min)
Reaction (%) (pressure)
3-Phenyl-1-propene (%) (GLC)
2
4
6
9
12
11.4 21.9 31.1 42.9 51.8
11.5 21.4 30.9 42.6 51.8
Time (min)
Reaction (%) (pressure)
3-Chloro-1-propene (%) (GLC)
6
10
18
22
30
19.2 28.5 37.8 72.6 60.6
19.1 28.5 38.0 51.9 59.3
Time (min)
Reaction (%) (pressure)
Allyl phenyl ether (%) (GLC)
2
5
10
14
22
10.7 22.1 37.8 47.4 63.0
10.6 24.3 37.2 48.0 61.5
Time (min)
Reaction (%) (pressure)
Substrate (%) (GLC)
4
7
9
15
18.7 32.7 41.7 50.4
19.1 34.2 42.3 51.7
Time (min)
Reaction (%) (pressure)
Substrate (%) (GLC)
4
7
10
13
19.4 31.7 41.6 56.0
17.6 29.5 42.8 55.3
Time (min)
Reaction (%) (pressure)
Acrylonitrile (%) (GLC)
4
7
12
19
18.8 30.3 45.7 58.7
18.6 28.1 43.1 55.8
Time (min)
Reaction (%) (pressure)
Styrene (%) (GLC)
5
15
20
28
35
14.6 34.2 44.8 53.5 75.4
14.8 34.6 45.1 53.2 76.8
Time (min)
Reaction (%) (pressure)
Substrate (%) (GLC)
6
8
10
12
15
23.2 28.6 40.4 47.4 57.1
22.2 30.6 38.4 49.2 59.1
aTemperature <360°C, cyclohexene inhibitor; >360°C, toluene inhibitor.
volume ratio of 6.0 relative to that of the normal vessel,
which is equal to 1.0. The effect of the addition of
different proportions of the free radical suppressor
cyclohexene or toluene is shown in Table 3. Never-
theless, the pyrolysis experiments were carried out in the
presence of at least twice the amount of the inhibitor in
Copyright 2001 John Wiley & Sons, Ltd.
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150
G. CHUCHANI ET AL.
Table 3. Effect of the free radical inhibitor on rates.a
Temperature
PS
(Torr)
Pi
(Torr)
104 k1
1
Substrate
(°C)
Pi/PS
(s
)
Ethyl N,N-dimethyl carbamate
370.4
380.0
379.0
400.5
360.1
420.2
390.3
410.4
400.1
350.8
360.4
360.6
379.6
340.0
93
74
66
52
—
30
86
—
0.4
1.3
2.2
8.11
8.02
7.98
8.09
114
Propyl N,N-dimethylcarbamate
77
98
73
47
—
89
111
129
—
0.9
1.5
2.7
9.40
9.39
9.43
9.38
1-Butyl N,N-dimethylcarbamate
72
116
78
—
78
103
178
—
0.7
1.3
2.5
9.92
10.00
10.24
10.19
71
3-Methyl-1-butyl N,N-dimethylcarbamate
3,3 Dimethyl-1-butyl N,N-dimethylcarbamate
2-Chloroethyl N,N-dimethylcarbamateb
2-Bromoethyl N,N-dimethylcarbamate
2-Methoxyethyl N,N-dimethylcarbamate
2-Butoxyethyl N,N-dimethylcarbamate
3-Phenylpropyl N,N-dimethylcarbamate
3-Chloropropyl N,N-dimethylcarbamate
3-Phenoxypropyl N,N-dimethylcarbamate
2-Dimethylaminoethyl N,N-dimethylcarbamate
3-Butyn-1-yl N,N-dimethylcarbamate
73
56
41
28
—
100
89
—
1.8
2.2
3.1
49.31
49.81
49.68
48.85
86
44
69.5
75
—
66
164
139
—
1.0
2.2
3.2
11.11
10.31
10.99
10.60
43.5
60
37
39
32
—
—
1.0
1.7
2.6
38.67
37.19
38.62
37.95
38.5
66.5
84
103
88
85
—
52
86
—
0.6
1.0
2.0
8.96
8.85
8.90
8.88
84
165
49
40
33
28
—
—
1.5
2.1
2.5
14.61
14.72
14.63
14.58
59.5
81.5
72.5
94
92
90
91
—
64
78
—
0.7
0.9
1.3
21.52
21.65
21.33
21.50
118
85
84
68
82
—
55
101
159
—
0.7
1.5
1.9
3.32
3.32
3.33
3.31
62
66.5
69
—
49
107
163
—
0.7
1.6
2.3
9.36
9.46
9.30
9.41
71
49
83.5
46
—
61
87
—
0.7
1.9
2.9
7.05
7.58
7.50
7.47
45
131
62
119
76
—
65
105
117
—
0.5
1.4
2.6
9.42
9.27
9.44
9.88
45
95
103
66.5
87
—
—
0.8
1.1
2.2
15.53
15.60
15.49
15.64
79.5
72.5
186.5
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

ELIMINATION KINETICS OF 2-SUBSTITUTED ETHYL N,N-DIMETHYLCARBAMATES
151
Table 3 continued.
Temperature
PS
(Torr)
Pi
(Torr)
104 k1
1
Substrate
(°C)
Pi/PS
(s
)
2-Cyanoethyl N,N-dimethylcarbamate
319.0
330.1
339.6
50
74
48
30.5
—
73
86
98
—
1.0
1.8
3.2
25.20
25.23
25.21
25.53
2-Phenylethyl N,N-dimethylcarbamate
85
65
89
94
—
58
94
—
0.9
1.1
1.2
14.49
14.62
14.77
14.54
115
3-Methyl-3-buten-1-yl N,N-dimethylcarbamate
60
88
72
45
—
—
0.7
1.4
2.3
8.98
7.19
7.31
7.40
66.5
101.5
103
a
Temperature <360°C, cyclohexene inhibitor; >360°C, toluene inhibitor.
PS = pressure substrate, Pi = propene inhibitor.
order to prevent any possible free radical chain reactions.
No induction period was observed. The rate coefficients
were reproducible with a relative standard deviation not
greater than 5% at a given temperature
CH3COOCH2CH2Z. However, employing this method
of correlation for the carbamates given in Table 7 gave
random points with no meaning, even when using one or
two of the contribution parameters. Moreover, the
application of various correlations9a,b such as the steric
parameters Hancock’s Esc, Taft’s Es, Charton’s v and the
inductive sI values also gave random points with no
significance for mechanistic interpretations for these
series of carbamates. However, plotting log k/kCH3) versus
s* values gives rise at the origin of s* (CH3) = 0.00 three
good slopes (Fig 1), which, means that small alterations
in the polarity of the transition state may be due to
changes in electronic transmissions at the reaction center.
This means that a simultaneous effect may be operating
during the process of elimination, especially with
electron-withdrawing and multiple-bonded substituents
at the 2-position of ethyl N,N-dimethylcarbamates. The
Taft correlation of alkyl groups gives an approximate
straight line [Fig. 1, Eqn. (3)] Thus,
The first-order rate coefficients of these carbamates,
calculated from k1 = ( 2.303 /t) log[2 P0/(3P0 Pt)], were
independent of their initial pressure (Table 4). A plot of
log (3P0 Pt) against time t gave good straight lines up
to 50–75% reaction, indicating that the elimination
process is unimolecular in nature. The variation of the
rate coefficients with temperature and the corresponding
Arrhenius equation is described in Table 5 ( 90%
confidence coefficient from a least-squares procedure).
The kinetic and thermodynamic parameters of a
significant number of 2-substituted ethyl N,N-dimethyl-
carbamates [(CH3)2NCOOCH2CH2Z, Z= substituent] are
given in Table 6. The negative entropy of activation ꢀS ≠
of these eliminations suggests a symmetrical arrange-
ment and possible planarity of the transition state, while
the enthalpy of activation DH≠ implies endothermic
processes. The log of A values between 11.4 and 12.8 are
reasonable for a six-membered cyclic transition mech-
anism.9c The indication that these carbamates elimina-
tions are not spontaneous, unstable and endergonic are
reflected by the free energy of activation DG≠ values
given in Table 6.
ꢂà ˆ 1:94 Æ 0:30 at 360ꢁC ꢀr ˆ 0:9768; SD
ˆ 0:0664†
ꢀ3†
The negative r* value suggests that a positively charged
carbon is rate determining. The greater the electron
release of the alkyl groups, the faster is the elimination
process. The reaction of this series of carbamates appears
to proceed through semi-polar six-membered cyclic
transition state mechanims (TS-1).
Electron-withdrawing susbtituents give rise at
s*(CH3) = 0.00 to another approximate straight line
[Fig 1, Eqn. (4)].
Table 7 lists a large number of pyrolyzed primary
carbamates which makes it possible to estimate ade-
quately the substituent effect of
Z
for the
(CH3)2NCOOCH2CH2Z compounds. The Taft–Topsom
treatment of substituent effects [Eqn. (2)]:
logꢀkko† ˆ ꢂꢃꢁꢃ ‡ ꢂFꢁF ‡ ꢂR ꢁR
ꢀ2†
ꢂà ˆ 0:12 Æ 0:02 at 360ꢁC ꢀr ˆ 0:9364; SD
where the contribution parameters are ꢁꢃ ˆ polarizabil-
ity effect, ꢁF ˆ field effect and ꢁR ˆ resonance effect,
was satisfactorily applied to the gas-phase elimination
ˆ 0:0571†
ꢀ4†
kinetics
of
2-substituted
ethyl
acetates,
The smaller negative r* value indicates some destabili-
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

152
G. CHUCHANI ET AL.
Table 4. Independence of the rate coef®cients from initial pressure
Temperature
Substrate
(°C)
Parameter
Value
Ethyl N,N-dimethylcarbamate
380.5
Po (Torr)
81.5
13.94
94
13.10
118
13.97
128
13.78 13.46
186
1
104 k1 (s
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
Propyl N,N-dimethylcarbamate
380.0
379.0
400.0
360.1
400.5
400.4
390.2
400.1
380.2
370.5
350.2
379.6
340.0
309.6
330.1
339.6
Po (Torr)
40
9.45
54
9.33
77
9.40
86
9.34
98
9.39
1
104 k1 (s
1-Butyl N,N-dimethylcarbamate
Po (Torr)
45
9.83
68
10.34
78.5
10.24
85
116
1
104 k1 (s
10.19 10.00
3-Methyl-1-butyl N,N-dimethylcarbamate
3,3 Dimethyl-1-butyl N,N-dimethylcarbamate
2-Chloroethyl N,N-dimethylcarbamate
2-Bromoethyl N,N-dimethylcarbamate
2-Methoxyethyl N,N-dimethylcarbamate
2-Butoxyethyl N,N-dimethylcarbamate
3-Phenylpropyl N,N-dimethylcarbamate
3-Chloropropyl N,N-dimethylcarbamate
3-Phenoxypropyl N,N-dimethylcarbamate
2-Dimethylaminoethyl N,N-dimethylcarbamate
3-Butyn-1-yl N,N-dimethylcarbamate
2-Cyanoethyl N,N-dimethylcarbamate
2-Phenylethyl N,N-dimethylcarbamate
3-Methyl-3-buten-1-yl N,N-dimethylcarbamate
Po (Torr)
28
49.85
23.5
50.21
21
49.68
56
73.5
1
104 k1 (s
49.81 49.32
Po (Torr)
24
11.05
44.5
11.11
59.5
10.91
75
10.99
1
104 k1 (s
Po (Torr)
31.5
13.37
43
13.52
53
13.48
67.5
13.60 13.42
89
1
104 k1 (s
Po (Torr)
68
15.24
85
15.26
101
15.22
121
15.25
1
104 k1 (s
Po (Torr)
26
8.53
50.5
8.64
70
8.55
78.5
8.53
86
8.48
1
104 k1 (s
Po (Torr)
46
21.45
68
21.58
83
21.42
92
110
1
104 k1 (s
21.75 21.52
101 115
16.53 16.46
142 171
16.03 16.12
Po (Torr)
72
16.24
84
16.67
93
16.33
1
104 k1 (s
Po (Torr)
42
16.13
71
16.45
119
16.43
1
104 k1 (s
Po (Torr)
42
4.45
71
4.44
80.5
4.23
127
4.80
168
4.24
1
104 k1 (s
Po (Torr)
45
9.58
57
9.27
76
9.44
97
9.34
119
9.27
1
104 k1 (s
Po (Torr)
35.5
9.25
71
8.90
101.5
9.00
134
8.80
143
9.07
1
104 k1 (s
Po (Torr)
26.5
14.26
42.5
14.51
52.5
14.87
64.5
14.51 14.47
85
1
104 k1 (s
Po (Torr)
34
14.52
59
14.32
63
14.58
72
89
1
104 k1 (s
14.40 14.46
Po (Torr)
45
7.40
52.5
7.61
72
7.27
88
7.19
147
7.01
1
104 k1 (s
zation of the Ca—O bond polarization, while the Cb—H
bond may increase in acidity and assist the O of the C=O
in the transition state (TS-2). When Z is a multiple-bond
substituent or an electron-withdrawing susbtituent inter-
posed by a CH2 at the 2-position of the ethyl ester there is
another inflection point at s*(CH3) = 0.00 with an
Form B
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

ELIMINATION KINETICS OF 2-SUBSTITUTED ETHYL N,N-DIMETHYLCARBAMATES
153
Form C
approximate straight line as described by Eqn. (5) (Fig 1).
The mechanism of the formation of dimethylamine and
CO2 gas from the unstable N,N-dimethylcarbamic acid
intemediate in the gas-phase elimination of 2-substituted
ethyl N,N-dimethylcarbamates [reaction (1)] may be
rationalized in terms of a four-membered cyclic transition
state as described in reaction (7).
ꢂà ˆ 0:49 Æ 0:03 at 360ꢁC ꢀr ˆ 0:9907; SD
ˆ 0:1036†
ꢀ5†
This result suggests that a negative carbon reaction center
is being developed in the transition state. Apparently, the
negative charge from the Cb—H bond polarization, in the
EXPERIMENTAL
ꢀ
sense of Cb ...Hꢀ‡, may be rate-determining step (TS-
General procedure. Method A: the 2-substituted ethyl
esters of N,N-dimethylcarbamic acid were prepared by
adding 0.15 mol of the corresponding alcohol to 0.15
mole of N,N-dimethylcarbamyl chloride (Aldrich) in
45 ml of anhydrous pyridine. The reaction mixture was
heated in a 100 ml sealed vessel as described.15
Method B: the substituted alcohol (0.15 mol) was
added to N,N-dimethylcarbamyl chloride (0.15 mol) in
50 ml of carbon tetrachloride until no more HCl gas was
evolved.
3).
The point position for Z = phenyl (C6H5, and iso-
propenyl [CH2=C(CH3)], falls far above the slopes of
the lines (Fig.1) which leads to the consideration of
neighboring group participation of these substituents for
rate enhancement. According to the transition state TS-4.
the p-electrons of the aromatic ring stabilize the bond
ꢀ‡
polarization Ca ...Oꢀ , thus causing a faster elimination
process. This interpretation appears to find support from
the gas-phase pyrolytic elimination of 2-phenylethyl
chloride.10 The presence of the OCH3 at the 4-position of
phenylethyl chloride confirms the participation of the
aromatic nuclei by a significant increase in the rate of
HCl elimination. Along this line of consideration, the
phenyl substituent also assisted anchimerically in the gas-
phase elimination of 2-phenylethyl methanesulfonate.11
In addition to this reference, a classical study with
convincing evidence neighboring double bond participa-
tion was described for the acetolysis of 4-methyl-3-
pentenyl tosylate.12 In association with this study, the
influence of an olefinic double bond in alkenyl chloride
pyrolyses has been assessed.13,14 The vinyl substituent
showed a significant rate enhancement effect in several 4-
chloro-1-butene substrates. By analogy, the rate enhance-
ment of 3-methyl-1-buten-1-yl N,N-dimethylcarbamate
(Fig 1) may also be due to the anchimeric assistance of
the neighboring double bond for elimination. The mech-
anism may be explained according to reaction (6).
However, the acidity of the benzylic and allylic Cb—H
bond for a six-membered cyclic transition state may not
be ignored.
Ethyl N,N-dimethylcarbamate. Method A was employed
for the synthesis of this substrate (b.p. 38°C at 10 Torr
(1 Torr=133.3 Pa), lit.16 74°C at 80 Torr, yield 71%).
Several distillations gave 97.0% purity by GLC (Porapak
Q, 80–100 mesh).
1-Butyl N,N-dimethylcarbamate. This substrate, ob-
tained by Method A, was distilled several times to 90%
purity by GLC (Porapak Q, 80–100 mesh). B.p. 48°C at
10 Torr, yield 63%. 1H NMR, ꢀ 0.9 (t, 3H, ꢀ), 1.3 (m, 2H,
CH2CH2), 1.5 (m, 2H, CH2CH2), 2.8 (s, 6H, 2CH3), 4.0
‡
‡
(t, 2H, OCH2). MS, m/z 145 (M ), 88 [(CH3)2NCOO ],
‡
‡
72
[(CH3)2NCO ],
57
(CH3CH2CH2CH2 ),44
‡
(CH3)2N ).
Form D
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

154
G. CHUCHANI ET AL.
Table 5. Variation of rate coef®cients with temperaturea
Substrate
Parameter
Value
Ethyl N,N-dimethylcarbamate
Temperature (°C) 340.6
350.5 359.6 370.4 380.8 390.1
1
104 k1 (s
)
1.43
2.68
4.57
8.07
13.97 23.28
Rate equation: log k1 (s 1) = (12.23 Æ 0.30) (188.8 Æ 3.3) kJ mol
1
1
(2.303 RT) r = 0.99981, SD = 0.0097
Propyl N,N-dimethylcarbamate
Temperature (°C) 349.5
362.8 370.0 380.0 390.0
1
104 k1 (s
)
1.64
3.66
5.67
9.63
16.67
Rate equation: log k1 (s 1) = (12.68 Æ 0.30) (192.2 Æ 3.7) kJ mol
(2.303
(2.303
1
RT) 1 r = 0.99989, SD = 0.0067
1-Butyl N,N-dimethylcarbamate
Temperature (°C) 351.6
361.2 371.6 379.0 390.3 400.2
1
104 k1 (s
)
2.23
4.08
6.80
10.03 17.44 31.31
1
Rate equation: log k1 (s 1) = (11.91 Æ 0.29) (186.0 Æ 3.6) kJ mol
RT) 1 r = 0.99926, SD = 0.0179
3-Methyl-1-butyl N,N-dimethylcarbamate
3,3 Dimethyl-1-butyl N,N-dimethylcarbamate
2-Chloroethyl N,N-dimethylcarbamate
2-Bromoethyl N,N-dimethylcarbamate
2-Methoxyethyl N,N-dimethylcarbamate
2-Butoxyethyl N,N-dimethylcarbamate
3-Phenylpropyl N,N-dimethylcarbamate
3-Chloropropyl N,N-dimethylcarbamate
3-Phenoxypropyl N,N-dimethylcarbamate
Temperature (°C) 340.2
350.2 360.5 370.0 380.2 390.6 400.5
1
104 k1 (s
)
2.03
3.46
6.53
10.70 17.62 33.06 49.57
Rate equation: log k1 (s 1) = (12.16 Æ 0.15) (186.1 Æ 1.8) kJ mol
(2.303
1
RT) 1 r = 0.99954, SD = 0.0169
Temperature (°C) 330.2
339.7 350.7 360.1 370.2 380.6 390.3
1
104 k1 (s
)
2.26
3.76
6.56
10.62 18.99 32.51 52.57
Rate equation: log k1 (s 1) = (11.48 Æ 0.20) (174.9 Æ 3.2) kJ mol
(2.303
(2.303
1
RT) 1 r = 0.99950, SD = 0.0172
Temperature (°C) 369.8
380.1 390.3 400.5 410.0 420.1
4.46
1
104 k1 (s
)
2.57
7.67
13.48 21.81 38.12
Rate equation: log k1 (s 1) = (12.51 Æ 0.38) (198.3 Æ 4.9) kJ mol
1
RT) 1 r = 0.99972, SD = 0.0115
Temperature (°C) 360.8
370.7 380.4 390.3 400.5 410.5 420.2
1
104 k1 (s
)
1.69
2.96
5.13
8.86
15.25 26.24 45.44
Rate equation: log k1 (s 1) = (12.83 Æ 0.15) (201.6 Æ 1.9) kJ mol
(2.303
(2.303
(2.303
1
RT) 1 r = 0.99978, SD = 0.0119
Temperature (°C) 360.1
370.0 380.2 385.3 390.0 400.5
2.82
1
104 k1 (s
)
1.62
5.00
6.75
8.52
14.66
Rate equation: log k1 (s 1) = (12.23 Æ 0.20) (194.2 Æ 2.5) kJ mol
1
RT) 1 r = 0.99992, SD = 0.0050
Temperature (°C) 370.0
380.2 390.1 401.0 410.1
7.49
1
104 k1 (s
)
4.40
12.78 21.73 37.26
Rate equation: log k1 (s 1) = (12.30 Æ 0.69) (192.9 Æ 8.7) kJ mol
1
RT) 1 r = 0.99933, SD = 0.0156
Temperature (°C) 340.4
350.8 360.7 370.0 380.1 390.3 400.5
1
104 k1 (s
)
1.96
3.32
5.86
10.17 16.55 27.83 44.95
Rate equation: log k1 (s 1) = (11.71 Æ 0.26) (181.2 Æ 3.2) kJ mol
(2.303
1
RT) 1 r = 0.99974, SD = 0.0124
Temperature (°C) 330.5
340.2 350.4 360.4 370.5 380.2 390.5
1
104 k1 (s
)
1.59
3.20
5.30
9.37
16.28 27.07 46.09
Rate equation: log k1 (s 1) = (12.17 Æ 0.20) (184.3 Æ 2.5) kJ mol
(2.303
1
RT) 1 r = 0.99955, SD = 0.0170
Temperature (°C) 330.5
340.1 350.1 360.5 370.5 380.5 390.5
1
104 k1 (s
)
1.19
2.12
4.34
7.32
12.46 22.19 38.26
Rate equation: log k1 (s 1) = (12.60 Æ 0.23) (190.8 Æ 2.8) kJ mol
(2.303
(2.303
(2.303
1
RT) 1 r = 0.99951, SD = 0.0186
2-Dimethylaminoethyl N,N-dimethylcarbamate Temperature (°C) 361.0
369.5 380.7 389.9 400.0 410.0
5.26
1
104 k1 (s
)
3.00
9.44
15.76 25.80 43.89
Rate equation: log k1 (s 1) = (12.53 Æ 0.40) (194.7 Æ 5.1) kJ mol
1
RT) 1 r = 0.99966, SD = 0.0126
3-Butyn-1-yl N,N-dimethylcarbamate
Temperature (°C) 310.3
319.5 329.8 340.0 349.7 360.0
4.67
1
104 k1 (s
)
2.61
8.81
15.64 26.79 47.15
Rate equation: log k1 (s 1) = (12.39 Æ 0.14) (178.3 Æ 1.6) kJ mol
1
RT) 1 r = 0.99996, SD = 0.0047
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

ELIMINATION KINETICS OF 2-SUBSTITUTED ETHYL N,N-DIMETHYLCARBAMATES
155
Table 5 continued.
Substrate
Parameter
Value
2-Cyanoethyl N,N-dimethylcarbamate
2-Phenylethyl N,N-dimethylcarbamate
Temperature (°C) 269.5
279.3 290.0 300.3 309.6 319.0 329.6
1
104 k1 (s
)
1.32
2.44
4.94
8.39
14.52 25.28 44.36
Rate equation: log k1 (s 1) = (11.40 Æ 0.25) (158.7 Æ 2.8) kJ mol
(2.303
(2.303
(2.303
1
RT) 1 r = 0.99980, SD = 0.0121
Temperature (°C) 291.1
300.2 310.5 321.1 330.1 341.8
1
104 k1 (s
)
1.39
2.54
4.79
9.03
15.29 29.51
Rate equation: log k1 (s 1) = (12.21 Æ 0.24) (173.5 Æ 3.1) kJ mol
1
RT) 1 r = 0.99999, SD = 0.0025
3-Methyl-3-buten-1-yl N,N-dimethylcarbamate Temperature (°C) 320.8
329.8 339.6 349.6 360.9 370.1
1
104 k1 (s
)
2.52
4.57
7.61
13.12 23.99 40.18
Rate equation: log k1 (s 1) = (11.87 Æ 0.38) (175.8 Æ 4.5) kJ mol
1
RT) 1 r = 0.99968, SD = 0.0127
aData for s values obtained from Ref. 9.
3-Methyl-1-butyl N,N-dimethylcarbamate. This carba-
mate, prepared by Method A (b.p. 94°C at 19 Torr, yield
51%) was distilled to 99% purity as determined by GLC
(Penwalt 223). 1H NMR, ꢀ 0.9 (d, 6H, 2CH3), 1.5 (q, 2H,
CH2CH2C), 1.6 (m, H, CH), 2.9 (s, 6H, 2CH3), 4.0 (t, 2H,
n-Propyl N,N-dimethylcarbamate. This starting material
was prepared by Method A. (b.p. 70°C at 5 Torr, yield
66%). After several distillations the purity was 97.2% as
detremined by GLC (Penwalt 223). 1H NMR, ꢀ 0,6 (t, 3H,
CH3), 1.3 (m, 2H, C—CH2—C), 2.6 [s,6H, (CH3)2N], 3.7
‡
‡
‡
OCH2CH2). MS, m/z 159 (M ), 88[(CH3)2NCOO ],
(t, 3H, OCH2). MS, m/z 131 (M ), 102
‡
‡
‡
‡
‡
72[(CH3)2NCO ], 43 [(CH3)2C ].
[(CH3)2NCOOCH2 ], 72 [(CH3)2NCO ], 58 (NCOO ),
‡
43 (CH3CH2CH2 ).
3,3-Dimethyl-1-butyl N,N-dimethylcarbamate. This
compound was prepared by Method B (b.p. 70°C at
15 Torr, yield 58%). Several distillations gave a purity of
97% as determined by GLC (Carbopack C 80–100 mesh).
1H NMR, ꢀ 0.9 (s, 9H, 3CH3), 1.5 (t, 2H, CH2CH2), 2.8
2-Methoxyethyl N,N-dimethylcarbamate. Method A
was used for the preparation of this substrate (b.p.
70°C at 9 Torr, yield 48%). Several distillations gave
1
98.7% purity by GLC (Porapak R 80–100 mesh). H
NMR, ꢀ 2.5 [s, 6H, (CH3)2N], 3.1 (s, 3H, OCH3), 3.3 (t,
‡
‡
[s, 6H, (CH3)2N), 4.1 (t, 2H, OCH2). MS, m/z 179 (M ),
2H, OCH2—C), 3.9 (t, 2H, OCH2). MS, m/z 147 (M ),
‡
‡
‡
‡
88
[(CH3)2NCOO ],
72
[(CH3)2NCO ],
69
116 [(CH3)2NCOOCH2CH2 ], 72 [(CH3)2NCO ], 58
‡
‡
‡
‡
[(CH3)3CCH2 ], 57 [(CH3)3C ].
(NCOO ), 45 ( CH3OCH2 ).
Table 6. Kinetic parameters for pyrolysis of (CH3)2NCOOCH2CH2Z at 360°C
4
4
k1 Â 10
kH Â 10
Ea
(kJ mol)
LogA
DS≠
DH≠
(kJ mol
DG≠
1
1
1
1
1
1
1
1
Z
(s
)
(s
)
)
(s
)
(J mol
K
)
)
(kJ mol )
H
4.47
3.09
3.63
6.31
12.22
1.41
1.55
1.62
2.40
5.75
9.12
7.24
2.88
47.86
201.77
78.28
22.91
1.49
1.55
1.82
3.15
5.61
0.71
0.77
0.81
1.20
2.88
4.56
3.62
1.44
188.8 Æ 3.3
196.2 Æ 3.7
186.0 Æ 3.6
186.1 Æ 1.8
174.9 Æ 3.2
198.3 Æ 4.9
201.6 Æ 1.9
194.2 Æ 2.5
192.9 Æ 8.7
181.2 Æ 3.2
184.3 Æ 2.5
190.8 Æ 2.8
194.7 Æ 5.1
178.3 Æ 1.6
158.7 Æ 2.8
173.5 Æ 3.1
175.8 Æ 4.5
12.23 Æ 0.30
12.68 Æ 0.30
11.91 Æ 0.29
12.16 Æ 0.15
11.48 Æ 0.20
12.51 Æ 0.38
12.83 Æ 0.15
12.23 Æ 0.20
12.30 Æ 0.69
11.71 Æ 0.26
12.17 Æ 0.20
12.60 Æ 0.23
12.53 Æ 0.40
12.39 Æ 0.14
11.40 Æ 0.25
12.21 Æ 0.24
11.87 Æ 0.38
25.30
16.70
31.46
26.65
39.65
19.95
14.01
25.31
23.97
35.26
26.48
18.24
19.58
22.25
41.20
25.62
32.21
194.1
201.5
191.3
191.4
180.2
203.6
206.9
199.5
198.2
186.5
189.6
196.1
200.0
183.6
164.0
178.8
181.1
210.1
212.1
211.2
208.3
205.3
204.3
215.8
215.5
213.4
208.8
206.4
207.6
212.4
197.7
190.1
195.1
201.5
CH3
CH2CH3
CH(CH3)2
C(CH3)3
Cl
Br
OCH3
O(CH2)3CH3
CH2C6H5
CH2Cl
CH2OC6H5
Nꢂ(CH )
23.93
100.9
39.14
11.45
3 2
C
CꢂCH
N
C6H5
CH2
=
C(CH3)
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

156
G. CHUCHANI ET AL.
Table 7. Parameters of substituents Z in (CH3)2NCOOCH2CH2Z at 360°Ca
Log (kZ/ko)
(ko = H)
(kZ/ko)
(ko = CH3)
Z
sa
sF
sR‡
sR
s*
sI
H
0.0000
0.0171
0.0868
0.3251
0.5757
0.3219
0.2867
0.2647
0.0940
0.2862
0.4857
0.3855
0.0148
1.2057
1.8307
1.4194
0.8856
0.0171
0.0000
0.0697
0.3079
0.5586
0.3397
0.3038
0.2818
0.1111
0.2690
0.4686
0.3683
0.0319
1.1886
1.8135
1.4022
0.8684
0.00
0.35
0.49
0.62
0.75
0.43
0.59
0.17
0.26
0.70
0.54
0.94
0.44
0.55
0.46
0.81
—
0.00
0.00
0.00
0.00
0.00
0.45
0.45
0.25
0.25
0.05
0.23
0.05
0.10
0.16
0.60
0.10
—
0.00
0.08
0.07
0.07
0.06
0.17
0.15
0.42
0.46
0.05
0.05
0.03
0.64
0.16
0.00
0.22
—
0.00
0.03
0.02
0.01
0.00
0.12
0.10
0.27
0.27
0.02
0.02
0.02
0.26
0.16
0.10
0.22
—
0.49
0.00
0.10
0.19
0.30
2.94
2.80
1.67
1.65
0.215
1.05
0.85
0.62
2.13
3.64
0.60
0.36
0.00
0.046
0.055
0.064
0.074
0.50
0.44
0.27
0.27
0.08
0.11
0.40
0.06
0.35
0.56
0.08
0.058
CH3
CH2CH3
CH(CH3)2
C(CH3)3
Cl
Br
OCH3
O(CH2)3CH3
CH2C6H5
CH2Cl
CH2OC6H5
Nꢂ(CH )
3 2
C
CꢂCH
N
C6H5
CH2=C(CH3)
a
Data for s values obtained from Ref. 9.
2-Chloroethyl N,N-dimethylcarbamate. Method A was
used for this carbamatee, b.p. 110°C at 13 Torr, yield
54%. Several distillations gave 97.0% purity by GLC,
2-Bromoethyl N,N-dimethylcarbamate. This compound
obtained by Method B, was distilled several times to
99.8% purity by GLC (Penwalt 223) (b.p. 150°C at
100 Torr, yield 49.8%). 1H NMR, ꢀ 2.8 [(s, 6H,
(CH3)2N)], 3.5 (t, 2H, Br—CH2—C), 4.3 (t, 2H,
1
(Penwalt 223). H NMR, ꢀ 2.6 [s, 6H, (CH3)2N], 3.5 (t,
‡
2H, Cl—CH2—C), 4.1 (t, 2H, OCH2). MS, m/z 152 (M ),
‡
‡
‡
‡
116 [(CH3)2NCOOCH2CH2 ], 72 [(CH3)2NCO ], 58
OCH2). MS, m/z 196 (M ), 152 (COOCH2CH2Br ),
‡
‡
‡
‡
‡
(NCOO ), 49 (CH2Cl ), 44 [(CH3)2N ].
116 [(CH3)2NCOOCH2CH2 ], 72 [(CH3)2NCO ], 44
[(CH3)2N ].
‡
Figure 1. Log krel against Taft s * values for (CH3)2NCOOCH2CH2Z at 360°C
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

ELIMINATION KINETICS OF 2-SUBSTITUTED ETHYL N,N-DIMETHYLCARBAMATES
157
‡
‡
‡
3-Phenyl-I-propyl N,N-dimethylcarbamate. This carba-
mate was prepared by Method B (b.p. 175°C at 20 Torr,
yield 71.3%). Several distillations gave 99.8% purity by
GLC (Penwalt 223). 1H NMR, ꢀ 1.9. (m, 2H, —CH2—),
2.7 (t, 2H, CH2C6H5), 2.9 [s, 6H, (CH3)2N], 4.1 (t, 2H,
[(CH3)2NCOOCH2CH2 ], 102 [(CH3)2NCOOCH2 ], 88
‡
‡
[(CH3)2NCOO ], 72 [(CH3)2NCO ], 44 [(CH3)2N ].
3-Butyn-I-yl N,N-dimethylcarbamate. This carbamate
prepared by Method B (b.p. 109°C at 31 Torr, yield 63%)
was distilled to 99.8% purity by GLC (FFAP–Chromo-
‡
OCH2), 7.1 (m, 5H, C6H5). MS, m/z 207 (M ), 116
‡
‡
‡
[(CH3)2NCOOCH2CH2 ], 102 [(CH3)2NCOOCH2 ], 91
‡
sorb W AW 80–100 mesh). MS, m/z 141 (M ), 97
‡
‡
(CH2C6H5 ), 77 (C6H5 ), 72 [(CH3)2NCO ], 44
‡
‡
(COOCH2CH2C=CH ),
72
[(CH3)2NCO ],
53
‡
[(CH3)2N ].
‡
‡
(CH2CH2C=CH ),44 [(CH3)2N ].
3-Chloro-1-propyl N,N-dimethylcarbamate. This sub-
strate prepared according to Method B (b.p. 161°C at
5 Torr, yield 75%) was distilled several times to 99%
2-Cyanoethyl N,N-dimethylcarbamate. The preparation
of this substrate was carried out by Method B (b.p. 133°C
at 13 Torr). Several distillations gave a purity of 99.1%
1
purity by GLC (Porapak Q, 80–100 mesh). H NMR, ꢀ
‡
by GLC (Porapak R, 80–100 mesh). MS, m/z 142 (M ),
2.0 (m, 2H, C—CH2—C), 2.8 [s, 6H, (CH3)2N], 3.6 (t,
‡
‡
‡
88
[(CH3)2NCOO ],
72
[(CH3)2NCO ],
54
2H, OCH2), 4.1 (t, 2H, C—CH2Cl). MS, m/z 165 (M ),
‡
‡
‡
(CH2CH2C=N ), 44 [(CH3)2N ].
130 [(CH3)2NCOOCH2CH2CH2 ], 121 (COOCH2CH2
‡
‡
‡
CH2Cl ), 102 [(CH3)2NCOOCH2 ], 72 [(CH3)2NCO ],
‡
‡
58 (COOCH2CH2 ), 49 (CH2Cl ).
3-Methyl-3-buten-1-yl N,N,dimethylcarbamate. This
carbamate was prepared by Method B (b.p. 92–94°C at
14 Torr, yield 51%). Several distillations gave 99.9%
purity by GLC (FFAP–Chromosorb W AW, 80–100
3-Phenoxy-I-propyl N,N-dimethylcarbamate. Using
Method B, this starting material (b.p. 161°C at 5 Torr,
yield 70%) was distilled several times to 98.9% purity by
GLC (Porapak Q, 80– 100 mesh). 1H NMR, ꢀ 2.1 (m, 2H,
C—CH2—C), 2.9 [s, 6H, (CH3)2N], 4.0 (t, 2H, OCH2),
‡
‡
mesh). MS, m/z 157 (M ), 88 [(CH3)2NCOO ], 72
‡
‡
‡
[(CH3)2NCO ], 54 (CH2CH2C=N ), 40 (CH3C=CH ).
‡
4.2 (t, 2H, OCH2). MS, m/z 224 (M ), 146
Analyses. The quantitative chromatographic analyses of
the olefinic products were performed using the same
column as used for their corresponding carbamate
substrates. The identifications of substrates and products
were performed by GLC Film thickness–MS (Saturn
2000, Varian). With a DB-5MS capillary column 30 m x
0.250 mm i.d, 0.25 mm
‡
[(CH3)2NCOOCH2CH2CH2CH2 ],
130
‡
‡
[(CH3)2NCOOCH2CH2CH2 ], 107 (CH2OC6H5 ), 72
‡
[(CH3)2NCO ].
2-Phenylethyl N,N-dimethylcarbamate. This compound
was prepared by Method B (b.p. 122°C at 5 Torr, yield
75%). Several distillations gave a purity of 98% by GLC
1
(Carbopack C 80–100 mesh). H NMR, ꢀ 2.8 [s, 6H,
Kinetics. The pyrolysis kinetics were studied in a static
(CH3)2N], 3.4 (t, 2H, CH2C6H5), 4.3 (t, 2H, OCH2), 6.6
17,18
reaction system as described
with some modifica-
[t, 2H, C6H3H2(ortho)], 6.7 [d, 1H, C6H5H(para)], 7.2 [t, 2H,
tions and additions of modern electronic and electrical
devices. The temperature was controlled by a resistance
thermometer controller, Shinko DIC-PS 25RT, and an
Omega solid-state SSR240AC45, maintained with-
in Æ 0.2°C and measured with a calibrated platinum–
platinum–13% rhodium thermocouple. No temperature
gradient was found along the reaction vessel. The
carbamate substrates were injected with a syringe
through a silicone-rubber septum directly into the
reaction vessel.
‡
C6H3H2(meta)].
MS,
m/z
194
(M ),
116
‡
‡
‡
[(CH3)2NCOOCH2CH2 ], 102 [(CH3)2NCOOCH2 ], 88
[(CH3)2NCOO ], 72 [(CH3)2NCO ], 44 [(CH3)2N ].
‡
‡
2-Butoxyethyl N,N-dimethylcarbamate. This starting
material obtained by Method B (b.p. 80°C at 25 Torr,
yield 70%), was distilled several times to 98.0% purity by
1
GLC (Poparak Q 80–100 mesh). H NMR, ꢀ 1.3 (t, 3H,
CH3), 1.4 (m, 2H, OCH2—C), 1.5 (m, 2H, C—CH2—C),
2.8 [s, 6H, (CH3)2N], 3.4 (t, 2H, OCH2—), 3.5 (t, 2H,
‡
‡
‡
CH2—C), 4.1 (t, 2H, COOCH2—C). MS, m/z 190 (M ),
‡
116 [(CH3)2NCOOCH2CH2 ], 102 [(CH3)2NCOOCH2 ],
‡
‡
88 [(CH3)2NCOO ], 72 [(CH3)2NCO ], 44 [(CH3)2N ].
Acknowledgements
I-Dimethylaminoethyl N,N-dimethylcarbamate. Di-
methylcarbamyl chloride was added to 2-dimethylami-
noethanol hydrochloride according to Method B (b.p.
106°C at 693 Torr, yield 67%). Several distillation gave
We are grateful to CONICIT ( Consejo Nacional de
Investigaciones Cientı´ficas y Tecnolo´gicas) of Venezuela
for financial support, Project No. S1-97000005. The
support of UGA (Unidad de Gestion Ambiental) at Simo´n
Bolivar University is also appreciated.
98.4% purity by GLC (FFAP–Chromosorb W AW 80–
‡
100
mesh).
MS,
m/z
160
(M ),
116
Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158

158
G. CHUCHANI ET AL.
9b. Hansch C, Leo A, Taft R. Chem. Rev. 1991, 91, 165;
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Copyright 2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 146–158