Chemistry Reference
In-Depth Information
Table 4.2 Rate constants from the literature for the reactions from Scheme 4.2.
Constant
Value
Units
Notes
Ref.
1.5
10
5
M
1
s
1
k
1Z
At 25 1C, in tert-butanol
15, 16
2.2
10
7
s
1
k
1Z
At 25 1C, in tert-butanol
2.0
10
5
M
1
s
1
k
1E
At 25 1C, in tert-butanol
1.5
10
8
s
1
k
1E
At 25 1C, in tert-butanol
4.5
10
6
M
1
s
1
k
1Z
¼
k
1E
Liposomes in water pH
¼
60
3.5
10
6
M
1
s
1
k
1Z
—
21
7.0
10
7
M
1
s
1
21
a
k
1Z
—
3.0
10
5
s
1
k
1Z
¼
k
1E
—
20, 21
(0.2-6)
10
7
M
1
s
1
k
d
At 30 1C. Depends on
solvent polarity.
22
1.1
10
7
M
1
s
1
k
d
At 22 1C in 1.2 M pyridine
in benzene.
23
0.8
10
7
M
1
s
1
k
d
For primary radical
þ
t-BuSH, claims the rate
for secondary and tertiary
radicals is close
24
k
1
c
3.0
10
9
M
1
s
1
For PhS
16
b
radicals
M
1
s
1
1.0
10
5
k
1
Dinorbornene
25
M
1
s
1
1.0
10
5
k
d
—
1.0
10
6
M
1
s
1
k
t
—
(0.5-2.2)
10
5
M
1
s
1
k
1
Divinyl ether, acrylate,
vinyl silazane
25
(0.17-2.5)
10
5
M
1
s
1
k
d
2.5
10
4
M
1
s
1
k
H
Acrylic
homopolymerization
(0.3-3.1)
10
7
M
1
s
1
Bis abstraction
—
26
(1.2-1.6)
10
7
M
1
s
1
Bis abstraction
20
1
10
5
M
1
s
1
(for P-H
þ
CH
2
R) at 80 1C8
a
Ref. 21 attributed the authorship of the value to ref. 26.
b
k
t
is the termination rate constant, of the reaction of forming of a molecule from two radicals.
Despite the value for k
t
being for a thiophenyl radical, refs. 15 and 16 use it successfully to fit
the data for other thiyl radicals.
c
k
1
is an effective rate constant, depending on k
1Z
, k
1Z
, k
1E
and k
1E
.
B
k
d
subsequent reaction of hydrogen abstraction is a slow, rate-determining step.
They obtained high thiol-ene conversions without side reactions.
Lee et al.
29
investigated the reaction of vinyl acrylate with thiols under UV
light (365 nm) and demonstrated that, in this compound, the acrylate double
bond homopolymerizes, while the thiyl radical exclusively attacks the vinyl
double bonds. It was proposed that the selectivity was due to the electro-
philic nature of the thiyl radical and the low electron density of the acrylic
double bond in the vinyl acrylate. When catalyzed by primary amines, in-
stead of UV light, the acrylate double bond reaction occurred so rapidly it
could not be monitored under normal mixing conditions. The thiol-ene re-
action is not stopped by the presence of oxygen, because peroxy radical can
abstract a hydrogen atom from a thiol group.
Roper et al.
30
reported that the reactivity of alkenes follows the order
monosubstituted4disubstituted4trisubstituted. Norbornene (bicyclo[2.2.1]-
hept-2-ene) reacted faster than 1-hexene; the authors explained this with the
