Correlation of the rates of solvolyses of cinnamyl chloride

Article abstract of DOI:10.1002/poc.550

Solvolytic rate constants (k) at 25 °C are reported for solvolyses of cinnamyl chloride (1) in binary mixtures of water with acetone, ethanol, methanol, methanol-d and 2,2,2-trifluoroethanol (TFE), and also in TFE-ethanol mixtures; product selectivities (S) are reported for aqueous ethanol and methanol: S = [ether product]/[alcohol product] × [water]/[alcohol solvent]. A good correlation observed between log k and the parameter Y_Cl (solvent ionizing power) is improved only slightly by additional parameters (N for solvent nucleophilicity and/or I, an aromatic ring parameter). Rate ratios in solvents of the same Y_Cl value but different nucleophilicities provide measures of the minimum extent of nucleophilic solvent assistance, and the value of 1.48 for [k_40EW/k_97TFE]_Y (EW = ethanol-water) is consistent with an essentially S_N1 reaction mechanism. A linear relationship between 1/S and molar ratio of solvent was derived theoretically and validated experimentally for solvolyses of the above substrate from water up to 75% alcohol-water. The dependence of S on solvent composition and the absence of rate depression in the presence of added chloride anions are explained by product formation via a contact ion pair. Copyright

Full text of DOI:10.1002/poc.550

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2002; 15: 758–764
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.550
Correlation of the rates of solvolyses of cinnamyl chloride
1
1
1
2
3
In Sun Koo, * Sun Kyoung An, Kiyull Yang, Ikchoon Lee and T. William Bentley
1
Department of Chemical Education and Research Institute of Natural Science, Gyeongsang National University, Chinju 660-701, Korea
Department of Chemistry, Inha University, Incheon 402-751, Korea
Department of Chemistry, University of Wales, Swansea, Singleton Park, Swansea SA2 8PP, UK
2
3
Received 15 November 2001; revised 26 June 2002; accepted 5 July 2002
ABSTRACT: Solvolytic rate constants (k) at 25°C are reported for solvolyses of cinnamyl chloride (1) in binary
mixtures of water with acetone, ethanol, methanol, methanol-d and 2,2,2-trifluoroethanol (TFE), and also in TFE–
ethanol mixtures; product selectivities (S) are reported for aqueous ethanol and methanol: S = [ether product]/[alcohol
product] Â [water]/[alcohol solvent]. A good correlation observed between log k and the parameter Y (solvent
Cl
ionizing power) is improved only slightly by additional parameters (N for solvent nucleophilicity and/or I, an
aromatic ring parameter). Rate ratios in solvents of the same YCl value but different nucleophilicities provide
measures of the minimum extent of nucleophilic solvent assistance, and the value of 1.48 for [k40EW/k
]
97TFE Y
(
EW = ethanol–water) is consistent with an essentially S 1 reaction mechanism. A linear relationship between 1/S
N
and molar ratio of solvent was derived theoretically and validated experimentally for solvolyses of the above substrate
from water up to 75% alcohol–water. The dependence of S on solvent composition and the absence of rate depression
in the presence of added chloride anions are explained by product formation via a contact ion pair. Copyright  2002
John Wiley & Sons, Ltd.
KEYWORDS: cinnamyl chloride; kinetics; solvolysis; selectivity
1–4
INTRODUCTION
ecular (S 1) solvolyses are smaller than the effects of
N
solvent nucleophilicity in bimolecular (S 2) solvo-
lyses.
N
1
–5
5–8
The Grunwald–Winstein (GW) equation [Eqn. (1)] has
often been applied to the correlation of solvolysis rates; in
Eqn. (1), k is the rate constant for solvolysis in any
Kevill et al. recently showed that, since dispersion
often follows a consistent pattern, an aromatic ring
parameter (I) and the appropriate sensitivity (h) may be
added to Eqns (1) and (2) to give Eqns (3) and (4),
solvent relative to 80% ethanol–water (k ), m is the
sensitivity of the substrate to the solvent ionizing power
Y) and c is a residual intercept term. Further develop-
ments include modified Y values and the incorporation
of a term for solvent nucleophilicity [N, extended GW
0
16–19
(
respectively;
one aim of our work was to continue
6
investigations using Eqns (1)–(4).
5–8
logꢀk=k † ˆ mY ‡ hI ‡ c
ꢀ3†
ꢀ4†
equation, Eqn. (2)].
0
logꢀk=k † ˆ mY ‡ lN ‡ hI ‡ c
0
logꢀk=k † ˆ mY ‡ c
ꢀ1†
ꢀ2†
0
Solvolytic reactions in alcohol–water mixtures lead to
alcohol and ether products from which selectivities can
logꢀk=k † ˆ mY ‡ lN
0
10,20–24
Dispersion (separate correlation lines observed for
be calculated using Eqn. (5):
1–5
various binary mixtures) was documented
in earlier
S ˆ ‰ether productŠ=‰alcohol productŠ
‰waterŠ=‰alcohol solventŠ
treatments, and it is now recognized that dispersion can
be associated with many factors, including leaving group
effects, solvent nucleophilicity, aromatic ring solva-
ꢀ5†
4,6
7,8
9
–11
12
tion,
solvation effects adjacent to the reaction site
Nucleophilic attack may occur on ‘free’ carbocations,
solvent-separated ion pairs, contact ion pairs or neutral
substrates, and the solvent dependence of S may be due to
changes in the nature of the intermediate leading to
13–15
and competing reactions.
In general, leaving group
effects are minimized by comparing solvolyses with the
same leaving group, and dispersion effects in unimol-
24,25
product.
An alternative explanation, involving gen-
*
Correspondence to: I. S. Koo, Department of Chemical Education,
eral base-catalysed nucleophilic attack on carbocations,
accounts for the linear relationship between 1/S and the
Gyeongsang National University, Chinju 660–701, Korea.
E-mail: iskoo@nongae.gsnu.ac.kr
Contract/grant sponsor: Korea Science and Engineering Foundation;
Contract/grant number: KOSEF 2001-1-12300-008-2.
alcohol/water molar ratio for S 1 solvolyses of p-
N
24
methoxybenzyl and diphenylmethyl chlorides.
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 758–764

CORRELATION OF RATES OF SOLVOLYSES OF CINNAMYL CHLORIDE
759
Another aim of our work was to test whether there is a
linear relationship between 1/S and the alcohol/water
molar ratio, as predicted by Eqn. (6), for the product-
Table 1. Rate constants for solvolyses of cinnamyl chloride
a
(
1) in aqueous binary mixtures at 25°C
3
À1
k  10 (s
)
determining step of S 1 reactions of carbocations.
N
%
(v/v)
MeOH
EtOH
Acetone
1
=S ˆ ꢀk =k †ꢀ‰alcohol solventŠ=‰waterŠ†
wa aw
b
1
00
0.00851
0.0435
0.225
0.722
2.28
0.000839
0.00970
0.0473
0.161
0.499
1.69
7.46
22.8
66.7
106
149
‡
kww=kaw
ꢀ6†
90
8
0
0.00215
0.0144
0.0770
0.414
1.90
8.81
32.7
61.0
Suitable substrates on which to test Eqn. (6) are those
which react only by substitution pathways via carboca-
70
60
2
4
5
4
3
2
0
0
0
0
6.31
tions. Also, the substrates should permit rapid mixing in
highly aqueous mixtures, and should not be so reactive
16.5
35.8
10
that their solvolyses are interfacial. As a suitable
substrate, we chose cinnamyl chloride (1), which is
expected to react by an S 1 pathway in view of the stable
cationic form, 1 .
72.0
10
112
149
H
2
O
149
N
‡
a
Determined conductometrically at least in duplicate; typical error Æ3%.
‡
b
À6 À1
As the positive charge on the cation 1 is highly
Solvolyses in MeOD give k = 7.62 (Æ0.10) Â 10
s , giving a kinetic
solvent isotope effect of 1.11.
delocalized, and 1 contains carbon atoms attached to both
alkene and aromatic ring carbon atoms, applications of
the GW Eqn. (1), the extended GW Eqn. (2) and the
aromatic ring parameter [Eqns (3) and (4)] to solvolyses
H O <ethanol–H O <methanol–H O. The rates increase
2
2
2
appreciably as the water content of a mixture increases;
thus the rate is higher in solvents with higher ionizing
power, Y. First-order rate constants for solvolyses of 1
9–12,16–19
of 1 will extend the scope of previous work.
5
vary 2 Â 10 -fold in alcohol–water mixtures. These
RESULTS
results are very similar to those of solvolytic reactions
1
4,26,27
of p-methoxybenzoyl chloride
and of p-methoxy-
see Fig. 1, which shows that the
primary substrate 2 is a very good similarity model
26,28
Rate constants for solvolyses of 1 in aqueous binary
mixtures of acetone, ethanol, methanol, methanol-d,
water, 2,2,2-trifluoroethanol (TFE)–water (%, w/w) and
TFE–ethanol (%, v/v) at 25.0°C are reported in Tables 1
benzyl chloride (2):
12
(Ysim ) for rate constants for solvolyses of 1, including
TFE-rich mixtures. Rate constants for solvolyses of 2
also correlate well with YBnCl, but with deviations for
and 2, and salt effects for NaClO , NaCl, and LiCl in 90%
4
2
8
methanol–water are given in Table 3. Results at various
temperatures are given in Table 4 along with the
corresponding Arrhenius parameters. Selectivity data,
obtained from product analyses as soon as possible after
completion of 10 half-lives of reaction, are given in
Table 5 for solvolyses of 1 in ethanol–water and
methanol–water mixtures at 25.0°C.
100% TFE and other TFE-rich solvent mixtures. The
Table 2. Rate constants for solvolyses of cinnamyl chloride
a
24
(
1) in 2,2,2-tri¯uoroethanol binary mixtures at 25°C
TFE–H O TFE–EtOH
% v/v
k  10 (s
2
3
À1
3
À1
%
(w/w)
k  10 (s
)
)
1
9
9
00TFE
4.70
80TFE-20EtOH 0.848
60TFE-40EtOH 0.104
40TFE-60EtOH 0.0191
20TFE-80EtOH 0.00353
DISCUSSION
Kinetic data
b
7TFE-3H O
5.05
2
0TFE-10H O 5.90
70TFE-30H O 12.0
2
2
5
0TFE-50H O 25.6
2
For binary solvents having the same % (v/v) water, the
rate constants (Table 1) increase in the order acetone–
a
Determined conductometrically at least in duplicate; typical error Æ3%.
b
k
40EW/k97TFE = 1.48 (k40EW taken from Table 1).
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 758–764

7
60
I. S. KOO ET AL.
Table 3. Rate constants for solvolyses of cinnamyl chloride
1) in salt solution in 90% methanol±10% water binary
(
a
mixtures at 25°C
5
À1
Added salt
k  10 (s
)
0
0
1
1
.1 M NaClO4
4.51
4.56
5.33
5.12
.1 M NaCl
.0 M LiCl
.0 M NaClO4
a
Determined titrimetrically at least in duplicate; typical error Æ3%.
Table 4. Additional rate constants for solvolyses of cinnamyl
chloride (1) in aqueous alcohol mixtures and activation
parameters calculated using data at 35 and 45°C
DH≠
DS
≠
T
(°C)
k
À1
À1 a
À1 À1 a
Solvent
(s
)
(kcal mol ) (cal mol
K )
À3
À2
À2
À1
À2
À2
À1
À1
5
5
3
3
5
5
3
3
0% EtOH 35 5.42 Â 10
0% EtOH 45 1.41 Â 10
0% EtOH 35 6.06 Â 10
0% EtOH 45 1.43 Â 10
0% MeOH 35 1.80 Â 10
0% MeOH 45 4.36 Â 10
0% MeOH 35 1.03 Â 10
0% MeOH 45 2.54 Â 10
19.3
16.1
17.0
17.2
À6.5
À11.9
Figure 1. Logarithms of rate constants for solvolyses of
cinnamyl chloride vs solvolyses of p-methoxybenzyl chloride
at 25°C. Slope = 1.01, r = 0.997. Solvents: *, methanol; *,
À11.4
À7.4
ethanol; ~, acetone; &, TFE±H O; &, TFE±EtOH
2
(m = 0.90, r > 0.999). Also, the data points for TFE–
a
1
cal = 4.184 J).
water and TFE–ethanol show no major deviations from
the other correlations.
Rate ratios in two solvents having the same YCl value,
i.e. the same degree of solvent assistance for bond
cleavage, but different nucleophilicities, provide
measures of the minimum extent of nucleophilic solvent
results indicate that the rate-determining step for
solvolyses of 1 involves extensive bond breaking during
formation of the transition state. Additional supporting
evidence is the similar kinetic solvent isotope effects
6,30
assistance,
and a small value is observed for
26
(
KSIE) in methanol (1.22 for 2 and 1.11 for 1; see
footnote to Table 1), although many solvolyses give
29
similar low values for KSIE.
The GW plots [Eqn. (1)] of the rate constants in Tables
1
and 2, presented in Fig. 2 using the solvent ionizing
6
power scale Y , based on 1-adamantyl chloride, show
Cl
significant dispersion for the aqueous acetone mixtures,
with relatively large slopes for alcohol–water (m = 0.75,
correlation coefficient r > 0.998) and acetone–water
Table 5. Selectivities (S) for solvolyses of cinnamyl chloride in
aqueous binary mixtures at 25°C
Methanol–water
Ethanol–water
%
(v/v) [Ether]/[alcohol]
S
[Ether]/[alcohol]
S
9
8
7
7
6
6
5
5
4
4
0
12.8
6.65
5.22
4.38
3.64
3.28
2.71
2.80
2.01
1.66
3.20
3.73
3.90
4.21
4.40
4.91
4.99
5.36
5.51
5.61
3.41
1.23
1.47
1.54
1.71
1.84
2.05
2.18
2.36
2.56
2.77
0
5
0
5
0
5
0
5
0
1.82
1.43
1.23
1.05
0.950
0.824
0.729
0.648
0.361
Figure 2. Logarithms of ®rst-order rate constants for
solvolyses of cinnamyl chloride at 25°C: log (k/k ) vs Y .
0
Cl
Solvents: *, methanol; *, ethanol; ~, acetone; &, TFE±
H O; &, TFE±EtOH
2
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 758–764

CORRELATION OF RATES OF SOLVOLYSES OF CINNAMYL CHLORIDE
Table 6. Correlation analyses against different Y, N, I and Ysim
761
a
a
a
Parameter
n
r
m (SD)
l (SD)
h (SD)
YCl
37
35
24
23
22
23
25
0.988
0.988
0.988
0.988
0.992
0.992
0.997
0.76 (0.014)
0.79 (0.022)
0.80 (0.033)
0.81 (0.031)
0.87 (0.028)
0.88 (0.041)
1.01 (0.014)
Y , N
0.06 (0.056)
0.06 (0.059)
Cl
OTs
Y , N
Cl
T
Y , I
0.27 (0.16)
0.88 (0.19)
0.56 (0.19)
Cl
YCl, NOTs, I
Y , N , I
0.34 (0.071)
0.23 (0.073)
Cl
T
b
Ysim
a
Standard deviation.
Log (k/k ) for p-methoxybenzyl chloride; data from Refs 26 and 28.
0
b
and h is ca 0.6 [it has previously been found that l values
obtained using Eqn. (4) are more positive than those
16
calculated using Eqn. (2)].
The product-determining step
The S values are similar to, but slightly lower, than those
observed for solvolyses of p-methoxybenzyl chloride
2
4
(
2). Constant S values would be expected for competing
31
second-order reactions, and S is very close to constant
for solvolyses of 1-adamantyl substrates and for SN1
reactions of acid chlorides, solvolysing via solvent-
10,31
separated ion pairs (SSIP).
During the formation of
an SSIP, the nucleophile (alcohol or water) must insert
between two ions, and ethanol is less effective than water
or methanol (i.e. S < 1), whereas S > 1 for solvolyses in
10
methanol–water. For solvolyses of 1, S values for
methanol–water mixtures are greater than those for
Figure 3. Plot of log(k/k ) for cinnamyl chloride against
0
31–34
ethanol–water, as observed in general.
The constant
0
.81Y ‡ 0.27I À 0.16; r = 0.988. Solvents: *, methanol; *,
S values for product formation from an SSIP may be
ethanol; ~, acetone; &, TFE±H O; &, TFE±EtOH
2
explained by nucleophilic attack by the solvent with
3
5
general base-catalysed assistance by the counteranion.
solvolyses of 1 (e.g. [k40EW/k97TFE]Y = 1.48, EW = etha-
nol–water, Table 2, footnote b). Also, the extended GW
Eqn. (2) gives a negligible value for l (Table 6). The
results imply that solvolyses of 1 in the binary mixtures
proceed by an S 1 pathway channel with little or no
N
nucleophilic solvent assistance.
Inclusion of the ring parameter (I) gives only a minor
improvement to correlations of the solvolyses of 1 using
Eqn. (3); although the data for acetone–water again show
dispersion (see Fig. 3), the effect is slightly smaller than
for Eqn. (1) (see Fig. 2). Dispersions in GW correlations
depends on the number of electrons adjacent to the
reaction site, with a smaller effect for ethylene and
1
2,16
acetylene derivatives than for aromatic systems,
and
the low sensitivity to I (h = 0.27 Æ 0.16) is similar to the
value of 0.35 for solvolyses of a,g-dimethylallyl
16
chloride. As Eqn. (4) contains four freely adjustable
28
parameters, the results should be interpreted cautiously;
m = 0.88 Æ 0.04 [similar to the value obtained using Eqn.
1)] and c = À0.09 (small, as expected), but l is ca 0.30
Scheme 1. General base-catalysed reactions for nucleophilic
attack on carbocations
(
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 758–764

7
62
I. S. KOO ET AL.
reactions shown in Scheme 1 are given by third-order rate
constants multiplied by the appropriate bulk molar
concentrations of solvent, so we do not allow for any
solvent clustering or microenvironments. In a recent
search we found no evidence for changes in solvent
composition (solvent clustering) at the reaction site, as
solvolyses of p-methoxybenzoyl chloride (i.e. a neutral
substrate, reacting via a very short-lived cationic
intermediate) gave almost constant selectivities through-
1
0,37
out wide ranges of alcohol–water mixtures.
In
contrast, there is mass spectrometric evidence for
tropylium cations solvated by clusters of acetonitrile
38
and alcohols,
but these results are not directly
comparable to ours.
In highly aqueous media, kaw[water][ROH]
2
ꢁ
k [ROH] , the relationship given in Eqn. (6) can
aa
34
readily be derived. The intercept of Eqn. (6) implies
that the maximum S value in highly aqueous media is
determined by the ratio of third-order rate constants
kaw/kww; this ratio represents the rate constant for
nucleophilic attack by alcohol compared with the rate
constant for nucleophilic attack by water, in water as
solvent and with water acting as a general base catalyst.
Plots of 1/S versus the alcohol/water molar ratio [Eqn.
Figure 4. Plot of 1/S vs molar ratio of solvents, [alcohol]/
water], for solvolyses of cinnamyl chloride at 25°C. Solvents:
, methanol; *, ethanol, S values from Table 5. For
[
*
ethanol±water, slope = 0.395, intercept = 0.298, r = 0.982.
For methanol±water, slope = 0.078, intercept = 0.153,
r = 0.996
(6)] are linear from 10% to at least 70% alcohol–water
mixtures and thereafter curvature is significant (Fig. 4),
which is consistent with increasing contributions from
the kaa term (Scheme 1).
The selectivities for methanol–water are significantly
greater than those for ethanol–water, and the slopes of 1/S
plots are lower for methanol–water than for ethanol–
water (Fig. 4). These trends can be explained by the kaw
term, which, compared with the kwa term, is greater for
methanol–water than for ethanol–water. The intercept of
Eqn. (6) is determined by the ratio of third-order rate
However, values of S are rarely constant over a range
of compositions of binary aqueous mixtures; usually S
values increase as water is added to alcohol (as for
solvolyses of 1, Table 5), so an explanation is required.
We propose that the product-determining step is third
order, and nucleophilic attack by one solvent molecule is
assisted by a second molecule of solvent acting as general
base; in alcohol–water mixtures there will then be four
competing product-determining steps (Scheme 1) defined
by the following third-order rate constants: kww, where
constants kww/k , so nucleophilic attack by methanol
aw
assisted by water is 6.5 times more favourable than
nucleophilic attack by water assisted by water.
water is both nucleophile and general base; k , where
aw
the alcohol solvent acts as nucleophile and water acts as
Unlike solvolyses of p-methoxybenzyl chloride (2),
which shows common ion rate depression for solvolyses
general base; k , where water acts as nucleophile and
wa
39
40
alcohol acts as general base; and k , where alcohol acts
in 50% TFE–water and ethanol–water, there is no
common ion depression for solvolyses of cinnamyl
chloride (Table 3). Therefore, the product-determining
steps must differ. Product formation via a ‘free’
carbocation is consistent with solvolyses showing a
common ion rate depression (e.g. for solvolyses of p-
methoxybenzyl chloride, 2). Nucleophilic attack on an
SSIP gives a constant selectivity with S <1 for ethanol–
water mixtures (see above), so the results for solvolyses
of 1 [Eqn. (6) is obeyed, but the common ion effect is
absent] require another explanation, probably nucleo-
philic attack on a contact ion pair.
aa
24
as both nucleophile and general base.
Scheme 1 is of the same kinetic form as the one we
33,34
34,36
have previously derived for acyl
and sulfonyl
transfer reactions, which are shown to proceed by S 2 or
N
33,34
addition–elimination reaction mechanisms.
How-
ever, we have reported that the new relationship between
S and solvent composition also applied to S 1 reactions
N
involving nucleophilic attack on carbocations assisted by
24
general base catalysis. It should be noted that in an SN2
process the rate-determining and product-determining
steps are the same, whereas in an S 1 process the rate
N
depends on the ionizing power of the solvent but the
product is determined by the attack of solvent on the
cationic intermediate, R , i.e. the rate-determining and
It has been suggested previously that solvolyses of
4
1
1-(4-methylphenyl)ethyl chloride in TFE–water and
‡
42
1-phenylethyl chloride in methanol react through
product-determining steps are not the same.
nucleophilic attack on contact ion pairs. Differences in
product-determining steps may be explained by the
We assume that the rates of the product-determining
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 758–764

CORRELATION OF RATES OF SOLVOLYSES OF CINNAMYL CHLORIDE
763
lifetimes of carbocations, which have been investigated
by laser flash photolyses. First-order rates of reaction of
calibrations, area ratios from solvolyses of 1 in pure
alcohol and in 40% acetonitrile–water mixtures were
used. The eluent was 78% methanol–water and the flow-
43
the following cations with hexafluoro-2-propanol at 20°C
2
À1
À1
are as follows: p-methoxybenzyl 3 Â 10 s , 1-(4-
rate was adjusted to 1 ml min . The HPLC system was a
4
À1
methylphenyl)ethyl 5 Â 10
s
and 1-phenylethyl
Hewlett-Packard 1050 Series instrument with
a
5
À1 43
6
 10 s . Rate constants are much greater in more
250 Â 4 mm i.d. Spherisorb ODS reversed-phase column.
43
nucleophilic media, but the order of reactivity is not
30
expected to change; the greater lifetime (smaller rate
constant) for the p-methoxybenzyl cation is consistent
with reaction via nucleophilic attack on a free cation,
whereas the other two phenylethyl cations are shorter
lived and react via contact ion pairs. Although no data are
available for the lifetimes of cinnamyl cations, it is
Acknowledgements
This research was supported by grant No. KOSEF 2001-
1-12300-008-2 from the Korea Science and Engineering
Foundation. We are also grateful to D. N. Kevill for
helpful discussions.
‡
reasonable to suppose that the cinnamyl cation (1 ) is
more like a phenethyl cation (and not so stabilized as the
‡
p-methoxybenzyl cation), and so 1 reacts via a contact
ion pair.
REFERENCES
1
2
3
4
. Winstein S, Grunwald E. J. Am. Chem. Soc. 1948; 70: 846–854.
. Fainberg AH, Winstein S. J. Am. Chem. Soc. 1957; 79: 1957–1608.
. Fainberg AH, Winstein S. J. Am. Chem. Soc. 1957; 79: 1608–1612.
. Winstein S, Fainberg A, Grunwald E. J. Am. Chem. Soc. 1957; 79:
CONCLUSIONS
4
146–4155.
. Winstein S, Grunwald E, Jones HW. J. Am. Chem. Soc. 1951; 73:
700–2707.
Solvolyses of cinnamyl chloride (1) respond almost
identically with those of p-methoxybenzyl chloride (2) to
changes in solvent ionizing power and solvent nucleo-
philicity (Fig. 1), and products of solvolyses in ethanol–
and methanol–water mixtures both obey Eqn. (6). Rates
of solvolyses of p-methoxybenzoyl chloride also respond
to solvent changes very similarly, but the product
selectivities are constant for a wide range of ethanol–and
methanol–water mixtures.
these three substrates solvolyse by very similar rate-
determining steps, it appears that each substrate has a
different product-determining step; solvolyses of 1 are
explained by product formation by general base-cata-
lysed nucleophilic attack on a contact ion pair.
5
2
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Consequently, although
3639–3641.
1
1
1
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1
1
1
EXPERIMENTAL
2
6
303–6312.
Materials. Methanol, ethanol and acetone were of Merck
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3
973–980.
obtained from Aldrich. Distilled water was redistilled
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UHQ PS to obtain a specific conductivity of less than
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1
7
À6
À1
1
 10
mho cm . Cinnamyl chloride (Aldrich GR
9
grade, 99%) was used without further purification.
2
1
Rate measurements and product selectivities. Rate
constants were measured conductometrically at 25
1
2
(
Æ0.03)°C at least in duplicate, as described pre-
1
15,26,44
viously,
1
with concentrations of substrate ca
À3
7
0
M. The solvolysis products, ether and alcohol, were
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determined by HPLC analysis as described pre-
34,45
viously
and the product selectivities, S, were
2
2
calculated with Eqn. (5). The S values were calculated
from the observed peak area ratios of ether and alcohol,
divided by the appropriate response factor. For response
2
181–2185.
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