Kinetic study of methoxide-promoted elimination reactions of some 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes

Article abstract of DOI:10.1002/poc.459

The methoxide-promoted elimination reaction of some 1,1,1-trichloro-2,2-bis(phenyl-substitute-d)ethanes (1) was investigated. The ortho-substituted derivatives were found to be less reactive than the corresponding ortho-unsubstituted derivatives, irrespec

Full text of DOI:10.1002/poc.459

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2002; 15: 108–114
DOI:10.1002/poc.459
Kinetic study of methoxide-promoted elimination reactions
of some 1,1,1-trichloro-2,2-bisꢀphenyl-substituted)ethanes
Gianfranco Fontana,1* Vincenzo Frenna,1 Liliana Lamartina,2 Maria Concetta Natoli1 and Renato Noto1
1Dipartimento di Chimica Organica `E. PaternoÁ ,' UniversitaÁ di Palermo, V.le delle Scienze-Parco d'Orleans II, I-90128 Palermo, Italy
2Dipartimento di Chimica e Tecnologie Farmaceutiche, UniversitaÁ di Palermo, Via Archira® 32, I-90100 Palermo, Italy
Received 15 March 2001; revised 25 August 2001; accepted 7 September 2001
ABSTRACT: The methoxide-promoted elimination reaction of some 1,1,1-trichloro-2,2-bis(phenyl-substitute-
d)ethanes (1) was investigated. The ortho-substituted derivatives were found to be less reactive than the
corresponding ortho-unsubstituted derivatives, irrespective of the nature of their substituent. The reactivity data were
correlated with the 13C NMR chemical shift values of C-b of either 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes
or 1,1-dichloro-2,2-bis(phenyl-substituted)ethenes and the better result was obtained for the former correlation.
Activation parameters for the methoxide-promoted elimination of 1 show very similar values for ortho-substituted
derivatives. The total data set seems to be more indicative, even if not compelling, of an irreversible E1cB
mechanism. Copyright  2001 John Wiley & Sons, Ltd.
KEYWORDS: 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes; reaction mechanism; base-promoted elimination;
13C NMR
INTRODUCTION
should change the steric requirements of aromatic rings,
consequently deeply affecting the elimination reaction.
The kinetic studies of dehydrochlorination of 1a–e, g
and l, which produce the corresponding 1,1-dichloro-
2,2-bis(phenyl-substituted)ethenes (2a–e, g and l), were
performed over the temperature range 30–50°C at
various concentrations (from 0.04 up to 0.4 M, depending
on the studied substrate) of sodium methoxide. Com-
pounds 1h–j showed very low reactivity under these
reaction conditions, so, in order to obtain some informa-
tion about their reactivity, Hammett’s equation was
used to calculate second-order constant values, with
compound 1f3 as a reference and assuming additive
substituent effects.
The b-elimination reaction1 is one of the most studied
reactions in organic chemistry. It is well known2 that both
the electronic and steric properties of a b-substituent
(generally an aryl-substituted ring) are able to affect the
reactivity of base-promoted elimination. Furthermore, in
some cases, the b-substituent seems to be responsible for
changing the elimination mechanism from concerted E2
to stepwise E1cB.2
We recently studied the base-promoted elimination
reaction of some 1,1,1-trihalo-2,2-bis(dimethoxyphenyl)-
ethanes in alcoholic solutions.3 The reported data did not
allow definite conclusions as regards the nature of the
reaction mechanism (i.e. irreversible E1cB or E2),
thereby confirming similarity between the two mechan-
isms.1,4 Our interest in the properties of 1,1-diarylethanes
and, in particular, the effect of ortho-substituents on the
reactivity of 1,1-diarylethanes5 prompted us to carry out a
kinetic study of the methoxide-promoted elimination
reaction of some 1,1,1-trichloro-2,2-bis(phenyl-substitu-
ted)ethanes (1a–j) with at least one ortho-substituted
aromatic ring. For comparison, we also report data for the
bis(3,4-dimethoxyphenyl) (1k) and bis(4-methoxyphe-
nyl) (1l) derivatives. Ortho-substitution on either 1k or 1l
RESULTS AND DISCUSSION
The second-order rate constants for the methoxide-
promoted elimination of 1a–l, together with the 13C
NMR chemical shift values of the C-b carbon atom for
1a–l and 2a–l, are reported in Table 1. We observed that
the introduction of an ortho-substituent on at least one
aromatic ring causes a significant decrease in the second-
order rate constant, irrespective of the electron-with-
drawing/releasing nature of the substituent. Indeed, the
substitution of one ortho-hydrogen atom of 1k by one
nitro group (1a) decreases the rate constant by a factor of
2, k1k/k1a = 2, although the electron-withdrawing effect
of the nitro group should act in the opposite direction. For
*Correspondence to: G. Fontana, Dipartimento di Chimica Organica
‘E. Paterno`,’ Universita` di Palermo, V.le delle Scienze-Parco
d’Orleans II, I-90128 Palermo, Italy.
E-mail: fontgian@unipa.it
Contract/grant sponsor: Universita` degli Studi di Palermo.
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 108–114

METHOXIDE-PROMOTED ELIMINATION IN 1,1,1-TRICHLORO-2,2-BIS(ARYL)ETHANES
109
example, the hydroxide ion-promoted reaction of 2-(4-
nitrophenyl)ethyl bromide is about 100 times faster than
that of phenylethyl bromide.2b
A comparison of homologous mono-ortho-substituted
compounds (1a–d) shows clearly that both the steric and
electronic effects must be responsible for the observed
reactivity order. Indeed, 1b with the bulkiest substituent,
i.e. I, is less reactive than 1d (with an electron-releasing
ortho-substituent, i.e. Me), 1a and 1c (with electron-
withdrawing ortho-substituents). It is interesting that the
same decrease in reactivity is observed on going from 1k
to 1d (i.e. from an ortho-unsubstituted to an ortho-
methyl-substituted derivative, k1d/k1k = 0.11) and from
1d to 1e (i.e., from an ortho-methyl to a bis-ortho-
methyl-substituted derivative, k1e/k1d = 0.15). The ob-
served decrease in reactivity from 1k to 1e could be a
consequence of both the steric and electronic effects of
the ortho-methyl groups in 1e.
The replacement of ortho-methyl groups in 1e by
ortho-methoxy groups (1i) causes a substantial decrease
in reactivity (k1i/k1e = 6 Â 10À3), in contrast to the result
predicted only on the grounds of differences in steric
requirements of these substituents (DEs = 0.69).6 Hence
there must be a significant and unfavourable electronic
effect that can only be explained by considering that an
elimination mechanism with a carbanionic transition
state is operating. Thus, the observed reactivity order can
be derived from the usual electronic effect of the
substituents and other ortho-effects, as in the case of
steric hindrance to conjugation.
Table 1. 13C NMR C-b chemical shift values 1ppm) for 1a±l
and 2a±l and second-order ratÀe constants 1dm3 molÀ1 sÀ1 a
)
for the 1 → 2 reaction in MeO ±MeOH at 40°C
Compound C-b of 1 C-b of 2
k
Logk
a
b
c
d
e
f
g
h
i
61.29 136.72
71.98 141.10
67.16 138.61
64.87 139.26
59.84 139.01
52.12 134.01
60.28 137.02
5.43 Â 10À4
2.61 Â 10À5
9.30 Â 10À5
1.12 Â 10À4
1.71 Â 10À5
1.77 Â 10À6b
1.21 Â 10À5
À3.26
À4.58
À4.03
À3.95
À4.77
À5.75
À4.92
51.90 134.17 ꢀ10À7; 3.86 Â 10À7c À6.41
51.54 134.06 ꢀ10À7; 6.83 Â 10À7c À6.17
51.33 134.03 ꢀ10À7b; 3.24 Â 10À7c À6.49
Indeed, if we consider that two mechanisms (i.e.
irreversible E1cB and E2) can operate in the dehydro-
chlorination of 1, the steric hindrance to conjugation of
aromatic rings with a carbanionic centre (irreversible
E1cB mechanism) should cause a decrease in reactivity,
as a consequence of a decrease in acidity of the b-
j
k
l
70.10 139.81
69.55 139.66
1.04 Â 10À3b
4.00 Â 10À4
À2.98
À3.40
a
b
c
The rate constants are accurate to within Æ3%.
From Ref. 3.
Calculated values.
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 108–114

110
G. FONTANA ET AL.
Figure 2. Plot of the logaÀrithms of the rate coef®cients for
the 1 → 2 reaction in MeO ±MeOH at 40°C versus 13C NMR
C-b chemical shifts of compounds 2. The values are reported
in Table 1
Figure 1. Plot of the logaÀrithms of the rate coef®cients for
the 1 → 2 reaction in MeO ±MeOH at 40°C versus 13C NMR
C-b chemical shifts of compounds 1. The values are reported
in Table 1
hydrogen atom. Furthermore, an ortho-substituent should
also be able to hinder the conjugation between the
aromatic ring and p-electrons of the double bond, thereby
causing an increase in the energy of the elimination
product and consequently an increase in the transition-
state energy (E2 mechanism).
Considering that the reactivity of compounds 1a–j,
though affected by ortho effects, seems to depend on
electronic factors, we attempted to correlate the reactivity
data with C-b 13C NMR chemical shift values. 13C
chemical shift values can be considered a measure of the
electron density of carbon atoms7 when the electron
excitation energy term in the Karplus–Pople8 equation is
constant for the series under examination.
According to the chemical shift values reported in
Table 1, it can be observed that the presence of one ortho-
substituent, excluding the iodo derivative, determines a
significant upfield shift for the C-b carbon atom. A
downfield shift of carbon atoms, as induced by an iodo
atom in the g-position (the effect of the ortho-iodo
substituent on C-b in our case), was observed and
accounted for by 1-iodonaphthalene.9
Figure 1 shows the result of the correlation between the
logarithm of second-order kinetic constants for meth-
oxide-promoted elimination and the C-b 13C NMR
chemical shift values of 1. As can be seen, a good
correlation (s = 0.16 Æ 0.01, i = À14.6 Æ 0.6, n = 10,
r = 0.983) was obtained and only two points, which
relate to mononitro and -iodo derivatives, deviate
significantly. Presumably these deviations are the result
of the peculiar effects exerted by ortho-iodo (see above)
and the ortho-nitro substituents on the C-b 13C NMR
chemical shift, that does not influence the reactivity of 1a
and 1b in the elimination reaction. For the ortho-nitro
group, it is possible to suppose that different preferable
conformations, i.e. coplanar and perpendicular, are
responsible for spectroscopic and reactivity behaviour.
According to the hypothesis that the methoxide-
promoted dehydrochlorination reaction of 1 occurs via
an E2 mechanism, reactivity data were also correlated
with the C-b 13C NMR chemical shift values of 2 (Fig. 2).
Points relating in this case to 2a and b deviate
significantly and, moreover, this correlation (s = 0.47
Æ 0.05, i = À69 Æ 8, n = 10, r = 0.948) is worse than the
previous one.
In our opinion, the linear correlation obtained for 1
could be considered as an indication that the compounds
under investigation in this study react as the same
reaction mechanism. The positive value of the slope
probably indicates that the reaction mechanism is
carbanionic in nature (E1cb or E2): the greater the
electron density on the C-b carbon atom in the ground
state (upfield chemical shift), the more difficult is the
formation of a negative charge on C-b.
The activation parameters of methoxide-promoted
elimination for 1a–e and k are reported in Table 2. Both
the enthalpy and entropy values for ortho-substituted
compounds 1a–e are not much higher than those for 1k.
However, the ortho-substituted compounds have very
similar activation parameters [the activation enthalpy
values do not differ by more than 1 kcal molÀ1
(1 kcal = 4.184 kJ) and the activation entropy values
differ by more than 3 entropy units (e.u.) on going from
the more reactive 1a to the less reactive 1e]. This seems
to indicate that the differences in reactivity among these
compounds are essentially electronic in nature. We could
expect large but random variations in entropic factors
when the steric effects are operative. For example, in the
methoxide-promoted dehydrochlorination of 1-chloro-
1,1-difluoro-2-phenylethanes,10 the presence of bulky
ortho-substituents causes a decrease in the activation
entropy values that ranges from À0.5 to À9.2 e.u.
Finally, the enthalpy values similar to those that we
calculated have been reported for the methoxide-
promoted irreversible E1cB elimination of some 1,1,1-
trichloro-2,2-diphenyl-substituted ethanes.2a Conversely,
Copyright  2001 John Wiley & Sons, Ltd.
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METHOXIDE-PROMOTED ELIMINATION IN 1,1,1-TRICHLORO-2,2-BIS(ARYL)ETHANES
111
Table 2. Activation parametersa for the 1 → 2 reaction in
substituted phenyl ring. Kinetic experiments were
performed on a Beckman DU 650 UV–visible spectro-
photometer.
MeO˱MeOH
DH‡b
ÀDS‡a,c
Compound
(kcal molÀ1
)
(cal KÀ1 molÀ1
)
Materials. Silica gel 60 (Merck, 0.06–0.2 mm) was used
for column chromatography. The solvent MeOH12 and
the base solutions were purified and prepared as reported.
Compounds 1e, 2e,13 1f, 2f, 1k, 2k,14 1g,15 1h,16 1j,17
1l and 2l18 were prepared by published methods. For
these compounds we now report the 13C NMR ꢀ values.
1a
1b
1c
1d
1e
1k
19.7
20.5
19.8
20.4
22.2
17.2d
11
14
14
11
10
17d
a
Calculated from kinetic data collected in the temperature range 30–50°C.
b
c
d
Calculated at 40°C; experimental error ꢀ700 cal molÀ1
.
1,1,1-Trichloro-2,2-bisꢀ4,5-dimethoxy-2-methylphe-
nyl)ethane ꢀ1e). 13C NMR, ꢀ: 20.15 (2 CH3); 55.51 (2
OCH3); 55.84 (2 OCH3); 59.84 (C-b); 103.62 (C-a);
112.65 (2 C-6); 113.36 (2 C-3); 128.29 (2 C-1); 129.77 (2
C-2); 146.34 and 147.88 (2 C-4 and 2 C-5).
Calculated at 40°C; experimental error ꢀ2 cal KÀ1 molÀ1
.
From Ref. 3.
enthalpy and entropy values for ethoxide-promoted E2
eliminations of 1-bromo-2-phenylethane and -propane11
are lower and higher, respectively, than those reported
here. Hence we can suppose that the substrates studied in
this work probably react in their dehydrochlorination
reaction via an irreversible E1cB mechanism.
1,1-Dichloro-2,2-bisꢀ4,5-dimethoxy-2-methylphenyl)-
ethene ꢀ2e). 13C NMR, ꢀ: 19.57 (2 CH3); 55.65 (2
OCH3); 55.91 (2 OCH3); 112.05 (2 C-6); 113.15 (2 C-3);
120.20 (C-a); 128.38 (2 C-2); 130.58 (2 C-1); 139.01 (C-
b); 146.61 and 148.49 (2 C-4 and 2 C-5).
This conclusion could also be supported by the fact
that the C-b 13C NMR chemical shift values of 1 describe
reactivity data better than those of 2, as shown by the
results of relative correlations. This fact is interesting
because it is usually difficult to predict the reactivity of
polysubstituted aromatic compounds. It seems possible to
estimate the reactivity of compounds such as 1 versus the
dehydrochlorination reaction by means of a unique
parameter which is linked to the overall effect of the
substituents, that is, the C-b 13C NMR chemical shift
values.
1,1,1-Trichloro-2,2-bisꢀ2,5-dimethoxyphenyl)ethane
ꢀ1f). 13C NMR, ꢀ: 52.12 (C-b); 55.55 (2 OCH3); 56.62 (2
OCH3); 102.15 (C-a); 112.32 (2 C-3); 112.64 (2 C-4);
116.46 (2 C-6); 128.33 (2 C-1); 152.00 (2 C-2); 152.98 (2
C-5).
1,1-Dichloro-2,2-bisꢀ2,5-dimethoxyphenyl)ethene
ꢀ2f). 13C NMR, ꢀ: 55.63 (2 OCH3); 56.18 (2 OCH3);
112.25 (2 C-3); 113.88 (2 C-4); 116.00 (2 C-6); 121.56
(C-a); 129.06 (2 C-1); 134.01 (C-b); 150.41 (2 C-2);
153.18 (2 C-5).
1,1,1-Trichloro-2-ꢀ2-methoxyphenyl)-2-ꢀ4-methoxy-
phenyl)ethane ꢀ1g). 13C NMR, ꢀ: 55.11 (OCH3); 55.73
(OCH3); 60.28 (C-b); 102.60 (C-a); 111.02 (C-3); 113.24
(C-3',5'); 120.22 (C-5); 127.76 (C-1); 128.36 and 128.66
(C-4 and C-6); 129.84 (C-1'); 132.00 (C-2',6'); 156.71
(C-2); 159.00 (C-4').
EXPERIMENTAL
Melting-points were measured on a Bu¨chi 510 melting-
point apparatus and are uncorrected. High-resolution
mass spectrometry (HRMS) spectra were performed on
an AutoSpec O-TOF instrument (Micromass) at a
resolving power of 10 000 with an accuracy of
Æ10 ppm. IR spectra were obtained with a Perkin-Elmer
1,1,1-Trichloro-2,2-bisꢀ2-methoxy-5-methylphenyl)-
ethane ꢀ1h). 13C NMR, ꢀ: 20.94 (2 CH3); 51.90 (C-b);
56.11 (2 OCH3); 102.58 (C-a); 111.26 (2 C-3); 127.22 (2
C-1); 129.00 and 130.19 (2 C-4 and 2 C-6); 129.12 (2 C-
5); 155.60 (2 C-2).
Model 1310 IR spectrophotometer. H and 13C NMR
1
spectra were recorded on a Bruker AC-E 250 MHz
spectrometer in deuterochloform solutions. Chemical
shifts are reported as ꢀ values (ppm) relative to residual
CHCl3 (7.27 ppm) for 1H NMR. 13C NMR chemical shift
values are reported as ꢀ values (ppm) with respect to
solvent central peak signals (77.00 ppm) and were taken
from fully decoupled spectra. C-b carbon signals assign-
ment was made on the ground of known substituent
effects and, when necessary, mult-ellipticities were also
determined by ‘proton gated’ decoupled experiments. For
1a–d and 2a–d H' and C' refer to protons and carbons of
the 3,4-dimethoxy-substituted phenyl ring. For 1g and 2g,
H' and C' refer to protons and carbons of 4-methoxy-
1,1,1-Trichloro-2,2-bisꢀ2,4-dimethoxyphenyl)ethane
ꢀ1j). 13C NMR, ꢀ: 51.33 (C-b); 55.17 (2 OCH3); 55.87 (2
OCH3); 98.74 (2 C-3); 103.27 (C-a); 104.05 (2 C-5);
120.36 (2 C-1); 130.14 (2 C-6); 158.65 (2 C-2); 159.98 (2
C-4).
1,1,1-Trichloro-2,2-bisꢀ3,4-dimethoxyphenyl)ethane
ꢀ1k). 13C NMR, ꢀ: 55.74 (2 OCH3); 55.95 (2 OCH3);
70.10 (C-b); 102.35 (C-a); 110.95 (2 C-5); 113.76 (2 C-
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 108–114

112
G. FONTANA ET AL.
2); 122.48 (2 C-6); 130.85 (2 C-1); 148.56 and 148.82 (2
C-3 and 2 C-4).
3.83 (3 H, s, OCH3); 3.84 (3 H, s, OCH3); 3.86 (3 H, s,
OCH3); 3.89 (3 H, s, OCH3); 5.47 (1 H, s, H-b); 6.82 (1
H, d, Jo = 8.2 Hz, H-5'); 7.14 (1 H, d, Jm = 2.0 Hz, H-2');
7.18 (1 H, dd, Jo = 8.2 Hz, Jm = 2.0 Hz, H-6'); 7.26 (1 H,
s, H-3); 7.67 (1 H, s, H-6). 13C NMR, ꢀ: 55.61 (OCH3);
55.80 (OCH3); 55.85 (OCH3); 55.88 (OCH3); 71.98 (C-
b); 91.79 (C-2); 102.11 (C-a); 110.47 (C-5'); 111.26
(C-6); 113.99 (C-2'); 121.84 (C-3); 122.99 (C-6'); 128.86
(C-1'); 133.38 (C-1); 148.16, 148.70, 148.78 and 148.83
1,1-dichloro-2,2-bisꢀ3,4-dimethoxyphenyl)ethene
ꢀ2k). 13C NMR, ꢀ: 55.65 (2 OCH3); 55.76 (2 OCH3);
110.46 (2 C-5); 112.50 (2 C-2); 117.77 (C-a); 122.19 (2
C-6); 131.89 (2 C-1); 139.81 (C-b); 148.24 and 148.57 (2
C-3 and 2 C-4).
‡
1,1,1-Trichloro-2,2-bisꢀ4-methoxyphenyl)ethane ꢀ1l).
13C NMR, ꢀ: 55.04 (2 OCH3); 69.55 (C-b); 102.48 (C-
a); 113.50 (2 C-3, 5); 130.46 (2 C-1); 131.00 (2 C-2, 6);
158.95 (2 C-4).
(C-4, C-5, C-3' and C-4'); HRMS (M ), m/z calc. for
C18H18Cl3IO4: 529.9315. Found: 529.9261.
1,1,1-Trichloro-2-ꢀ2-bromo-4,5-dimethoxyphenyl)-2-
ꢀ3,4-dimethoxyphenyl)ethane ꢀ1c). A solution of 1k
(2.03 g, 5 mmol) in chloroform (10 ml) was stirred at
room temperature during the dropwise addition of a
solution of bromine (0.8 g, 5 mmol) in chloroform
(10 ml). The solution was set aside at room temperature
until the evolution of hydrogen bromine gas was
complete (48 h). After solvent removal in vacuo, the
crude product was chromatographed over silica gel,
employing light petroleum (b.p. 40–60°C)–diethyl ether
(80:20) as eluent, to give pure 1c (yield 85%) as white
crystals from 1:1 light petroleum (b.p. 40–60°C)–diethyl
ether, m.p. 99°C. 1H NMR, ꢀ: 3.85 (6 H, s, 2 OCH3); 3.87
(3 H, s, OCH3); 3.91 (3 H, s, OCH3); 5.62 (1 H, s, H-b);
6.84 (1 H, d, Jo = 8.4 Hz, H-5'); 7.05 (1 H, s, H-3); 7.12 (1
H, d, Jm = 2.0 Hz, H-2'); 7.17 (1 H, dd, Jo = 8.4 Hz,
Jm = 2.0 Hz, H-6'); 7.69 (1 H, s, H-6). 13C NMR, ꢀ: 55.67
(OCH3); 55.87 (OCH3); 55.95 (OCH3); 56.05 (OCH3);
67.16 (C-b); 101.96 (C-a); 110.56 (C-5'); 111.92 (C-6);
114.02 (C-2'); 115.56 (C-3); 116.29 (C-2); 123.02 (C-6');
129.03 (C-1'); 129.97 (C-1); 148.01, 148.28, 148.80 and
1,1-Dichloro-2,2-bisꢀ4-methoxyphenyl)ethene ꢀ2l). 13C
NMR, ꢀ: 55.18 (2 OCH3); 113.47 (2 C-3, 5); 117.62 (C-
a); 130.79 (2 C-2, 6); 132.03 (2 C-1); 139.66 (C-b);
159.11 (2 C-4).
1,1,1-Trichloro-2-ꢀ4,5-dimethoxy-2-nitrophenyl)-2-
ꢀ3,4-dimethoxyphenyl)ethane ꢀ1a). A solution of 1k
(2.03 g, 5 mmol) in acetic anhydride (100 ml) was placed
in a two-necked round-bottomed flask fitted with a
mechanical stirrer and a reflux condenser protected by a
CaCl2 tube. Cu(NO3)2Á3H2O (0.604 g, 2.5 mmol) was
added to the stirred solution. The mixture was heated at
40–50°C for 0.5 h. The cold mixture was poured into
water, then extracted with chloroform, neutralized, dried
and evaporated in vacuo. Cristallization of the crude
product from ethanol afforded pure 1a as yellow crystals
1
(yield 98%), m.p. 149°C. H NMR, ꢀ: 3.88 (6H, s, 2
OCH3); 3.93 (3H, s, OCH3); 3.94 (3H, s, OCH3); 6.28
(1H, s, H-b); 6.86 (1H, d, Jo = 8.4 Hz, H-5'); 7.18 (1H, d,
Jm = 1.9 Hz, H-2'); 7.27 (1H, dd, Jo = 8.4 Hz, Jm = 1.9 Hz,
H-6'); 7.47 (1H, s, H-6); 7.57 (1H, s, H-3). 13C NMR, ꢀ:
55.73 (OCH3); 55.93 (OCH3); 56.25 (2 OCH3); 61.29 (C-
b); 101.31 (C-a); 108.14 (C-3); 110.70 (C-5'); 112.32
(C-6); 113.84 (C-2'); 122.28 (C-6'); 126.44 (C-1); 129.04
(C-1'); 143.17 (C-2); 148.13, 148.54 and 148.93 (C-4, C-
‡
148.91 (C-4, C-5, C-3' and C-4'). HRMS (M ), m/z calc.
for C18H18Cl3BrO4: 481.9454. Found: 481.9503.
1,1,1-Trichloro-2-ꢀ3,4-dimethoxyphenyl)-2-ethanol.
LiAlH4 (1.14 g, 0.03 mol) was added to a suspension
of 2,2,2-trichloro-3',4'-dimethoxyacetophenone19 (8.5 g,
0.03 mol) in anhydrous diethyl ether (75 ml) and after
normal work-up 83% of 1,1,1-trichloro-2-(3,4-dimeth-
oxyphenyl)-2-ethanol was obtained. The compound was
recrystallized from ethanol, m.p. 135°C. IR (Nujol),
ꢁmax: 3420 cmÀ1 (OH). 1H NMR, ꢀ: 3.34 (1 H, d,
J = 3.6 Hz, exchangeable with D2O, OH); 3.90 (6 H, s, 2
OCH3); 5.17 (1 H, d, J = 3.6 Hz, singlet after exchange
with D2O, CHCCl3); 6.87 (1 H, d, Jo = 8.1 Hz, H-5);
7.14 (1H, dd, Jo = 8.1 Hz, Jm = 2.0 Hz, H-6); 7.17
‡
3' and C-4'); 151.78 (C-5). HRMS (M ), m/z calc. for
C18H18Cl3NO6; 449.0200. Found: 449.0244.
1,1,1-Trichloro-2-ꢀ4,5-dimethoxy-2-iodophenyl)-2-
ꢀ3,4-dimethoxyphenyl)ethane ꢀ1b). To a solution of 1k
(2.03 g, 5 mmol) in chloroform (30 ml) was added silver
trifluoroacetate (1.10 g, 5 mmol). To this stirred mixture,
a solution of iodine (1.27 g, 5 mmol) in chloroform
(50 ml) was added dropwise. The mixture was left to stir
overnight, then filtered to eliminate silver iodide and the
resulting solution was poured into water. The aqueous
layer was extracted twice with chloroform and the
combined organic phase was neutralized, dried and
evaporated in vacuo. The crude product was chromato-
graphed over silica gel, employing light petroleum (b.p.
40–60°C)–diethyl ether (80:20) as eluent, to give pure 1b
(yield 95%) as white crystals from 1:1 light petroleum
‡
(1 H, d, Jm = 2.0 Hz, H-2). HRMS (M ), m/z calc. for
C10H11Cl3O3: 283.9774. Found: 283.9802.
1,1,1-Trichloro-2-ꢀ4,5-dimethoxy-2-methylphenyl)-2-
ꢀ3,4-dimethoxyphenyl)ethane ꢀ1d). A solution of 1,1,1-
trichloro-2-(3,4-dimethoxyphenyl)-2-ethanol (6 g, 0.021
mol) in glacial acetic acid (50 ml) was added dropwise to
a stirred solution of 3,4-dimethoxytoluene (3.20 g,
0.021 mol) in glacial acetic acid–98% sulphuric acid
1
(b.p. 40–60°C)–diethyl ether, m.p. 84°C. H NMR, ꢀ:
Copyright  2001 John Wiley & Sons, Ltd.
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METHOXIDE-PROMOTED ELIMINATION IN 1,1,1-TRICHLORO-2,2-BIS(ARYL)ETHANES
113
(1:1, v/v) (10 ml), while the temperature was maintained
below 20°C. After standing at room temperature over-
night, the mixture was poured on to crushed ice and the
oil obtained was extracted with ethyl acetate, neutralized,
dried and evaporated in vacuo. The oil obtained was
chromatographed on silica gel, employing light petro-
leum (b.p. 40–60°C)–ethyl acetate (80:20) as eluent,
gave pure 1d (yield 55%), as white crystals from 1:1 light
petroleum ether (b.p. 40–60°C)–diethyl ether, m.p. 83°C.
1H NMR, ꢀ: 2.30 (3H, s, CH3); 3.86 (9H, s, 3 OCH3); 3.91
(3H, s, OCH3); 5.20 (1H, s, H-b); 6.67 (1H, s, H-3); 6.82
(1H, d, Jo = 8.0 Hz, H-5'); 7.09 (1H, d, Jm = 2.0 Hz, H-2');
7.11 (1H, dd, Jo = 8.0 Hz, Jm = 2.0 Hz, H-6'); 7.65 (1H, s,
H-6). 13C NMR, ꢀ: 19.83 (CH3); 55.62 (OCH3); 55.70
(OCH3); 55.86 (OCH3); 56.10 (OCH3); 64.87 (C-b);
102.71 (C-a); 110.47 (C-5'); 111.37 (C-6); 113.69 (C-3);
114.12 (C-2'); 123.50 (C-6'); 129.20 (C-2); 129.20 (C-1');
129.58 (C-1); 146.61 (C-4); 147.91 (C-5); 148.24 and
H-2'); 7.68 (1H, s, H-3). 13C NMR, ꢀ: 55.76 (OCH3);
55.94 (OCH3); 56.35 (OCH3); 56.61 (OCH3); 107.91
(C-3); 110.42 (C-5'); 112.59 (C-6); 113.02 (C-2'); 119.35
(C-a); 122.07 (C-6'); 128.98 and 129.26 (C-1 and C-1');
136.72 (C-b); 139.80 (C-2); 148.28 and 148.64 (C-4 and
‡
C-3'); 149.12 (C-4'); 153.20 (C-5). HRMS (M ), m/z
calc. for C18H17Cl2NO6: 413.0433. Found: 413.0471.
1,1-Dichloro-2-ꢀ4,5-dimethoxy-2-iodophenyl)-2-ꢀ3,4-
dimethoxyphenyl)ethene ꢀ2b). Reaction time 72 h, yield
50%, white crystals from ethanol, m.p. 143°C. 1H NMR,
ꢀ: 3.85 (3 H, s, OCH3); 3.86 (3 H, s, OCH3); 3.88 (6 H, s,
2 OCH3); 6.72 (1 H, s, H-6); 6.81 (1 H, d, Jo = 8.4 Hz, H-
5'); 6.95 (1 H, dd, Jo = 8.4 Hz, Jm = 2.0 Hz, H-6'); 7.08
(1H, d, Jm = 2.0 Hz, H-2'); 7.27 (1H, s, H-3). 13C NMR, ꢀ:
55.80 (OCH3); 55.96 (OCH3); 56.09 (OCH3); 56.11
(OCH3); 86.88 (C-2); 110.54 (C-5'); 112.39 (C-6);
112.99 (C-2'); 121.05 (C-a); 121.63 (C-3); 122.39 (C-
6'); 129.47 (C-1'); 137.28 (C-1); 141.10 (C-b); 148.25,
148.97, 149.09 and 149.52 (C-4, C-5, C-3' and C-4').
‡
148.66 (C-3' and C-4'). HRMS (M ), m/z calc. for
C19H21Cl3O4: 418.0505. Found: 418.0544.
‡
HRMS (M ), m/z calc. for C18H17Cl2IO4: 493.9549.
1,1,1-Trichloro-2,2-bisꢀ2,4,5-trimethoxyphenyl)ethane
ꢀ1i). To a stirred solution of 1,2,4-trimethoxybenzene
(20.17 g, 0.12 mol) and chloral hydrate (4 g, 0.024 mol)
in glacial acetic acid (50 ml), 98% sulphuric acid (30 ml)
was added dropwise, while the temperature was main-
tained below 30°C. After standing at room temperature
overnight, the mixture was poured on to crushed ice and
the precipitate obtained was filtered, neutralized and
dried. Crystallization of the crude product from ethanol
afforded 1i as white crystals (yield 90%), m.p. 106°C. 1H
NMR, ꢀ: 3.82 (6H, s, 2 OCH3); 3.84 (6 H, s, 2 OCH3);
3.87 (6 H, s, 2 OCH3); 6.34 (1 H, s, H-a); 6.53 (2 H, s, 2
H-3); 7.47 (2 H, s, 2 H-6). 13C NMR, ꢀ: 51.54 (C-b);
55.81 (2 OCH3); 56.64 (2 OCH3); 57.05 (2 OCH3); 97.95
(2 C-3); 103.16 (C-a); 113.68 (2 C-6); 118.97 (2 C-1);
142.56 (2 C-5); 149.16 (2 C-4); 152.34 (2 C-2). HRMS
Found: 493.9450.
1,1-Dichloro-2-ꢀ2-bromo-4,5-dimethoxyphenyl)-2-
ꢀ3,4-dimethoxyphenyl)ethene ꢀ2c). Reaction time 72 h,
yield 60%, white crystals from ethanol, m.p. 133°C. H
1
NMR, ꢀ: 3.86 (6 H, s, 2 OCH3); 3.88 (3 H, s, OCH3);
3.89 (3H, s, OCH3); 6.73 (1 H, s, H-6); 6.82 (1 H, d,
Jo = 8.3 Hz, H-5'); 6.93 (1 H, dd, Jo = 8.3 Hz, Jm = 2.1 Hz,
H-6'); 7.04 (1H, d, Jm = 2.1 Hz, H-2'); 7.07 (1H, s, H-3).
13C NMR, ꢀ: 55.80 (OCH3); 55.90 (OCH3); 56.00
(OCH3); 56.10 (OCH3); 110.46 (C-5'); 112.47 (C-2');
112.59 (C-6); 113.25 (C-2); 115.46 (C-3); 121.00 (C-a);
122.01 (C-6'); 129.69 (C-1'); 132.73 (C-1); 138.61 (C-b);
148.19, 148.48, 148.81 and 149.23 (C-4, C-5, C-3' and
‡
C-4'). HRMS (M ), m/z calc. for C18H17Cl2BrO4:
445.9687. Found: 445.9732.
‡
(M ), m/z calc. for C20H23Cl3O6: 464.0560. Found:
464.0514.
1,1-Dichloro-2-ꢀ4,5-dimethoxy-2-methylphenyl)-2-
ꢀ3,4-dimethoxyphenyl)ethene ꢀ2d). Reaction time 72 h,
1
Reaction products. Compounds 1a–d and 1g–j (1
equiv.), were dehydrochlorinated by heating under reflux
with a solution of CH3ONa (2 equiv.) in dry CH3OH.
Reaction times for each compound are reported below.
The crude dehydrohalogenated compounds 2a–d and 2g–
j were purified by chromatography over silica gel
employing mixtures of light petroleum (b.p. 40–60°C)–
ethyl acetate as eluents. The physical properties and
spectral data for each compound are reported below.
yield 45%, white crystals from ethanol, m.p. 95°C. H
NMR, ꢀ: 2.17 (3 H, s, CH3); 3.84 (3 H, s, OCH3); 3.86 (3
H, s, OCH3); 3.88 (3 H, s, OCH3); 3.89 (3 H, s, OCH3);
6.67 (1 H, s, H-3); 6.71 (1H, s, H-6); 6.80 (1 H, d,
Jo = 8.4 Hz, H-5'); 6.88 (1 H, dd, Jo = 8.4 Hz, Jm = 1.9 Hz,
H-6'); 6.96 (1H, d, Jm = 1.9 Hz, H-2'). 13C NMR, ꢀ: 19.08
(CH3); 55.85 (2 OCH3); 55.94 (2 OCH3); 110.49 (C-5');
112.08 (C-6); 112.45 (C-2'); 113.15 (C-3); 118.83 (C-a);
122.22 (C-6'); 128.29 (C-2); 130.58 (C-1'); 131.46 (C-1);
139.26 (C-b); 146.93 (C-5); 148.17, 148.54 and 148.69
‡
1,1-Dichloro-2-ꢀ4,5-dimethoxy-2-nitrophenyl)-2-ꢀ3,4-
dimethoxyphenyl)ethene ꢀ2a). Reaction time 48 h, yield
80%, yellow crystals from ethanol, m.p. 122°C. 1H
NMR, ꢀ: 3.85 (3 H, s, OCH3); 3.86 (3 H, s, OCH3); 3.97
(3 H, s, OCH3); 3.99 (3 H, s, OCH3); 6.78 (1 H, d,
Jo = 8.4 Hz, H-5'); 6.81 (1 H, s, H-6); 6.85 (1 H, dd,
Jo = 8.4 Hz, Jm = 2.0 Hz, H-6'); 7.07 (1H, d, Jm = 2.0 Hz,
(C-4, C-3' and C-4'). HRMS (M ), m/z calc. for
C19H20Cl2O4: 382.0739. Found: 382.0700.
1,1-Dichloro-2-ꢀ2-methoxyphenyl)-2-ꢀ4-methoxyphe-
nyl)ethene ꢀ2g). Reaction time 72 h, yield 48%, white
crystals from 1:1 diethyl ether–light petroleum (b.p. 40–
60°C), m.p. 68°C. 1H NMR, ꢀ: 3.77 (3 H, s, OCH3); 3.79
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 108–114

114
G. FONTANA ET AL.
(3 H, s, OCH3); 6.84 (2 H, d, Jo = 8.7 Hz, H-3',5'); 6.91 (1
H, d broad, Jo = 8.6 Hz, H-3); 6.96 (1H, t broad,
Jo = 7.7 Hz, H-5); 7.18 (1 H, d broad, Jo = 7.2 Hz, H-6);
7.29 (2 H, d, Jo = 8.7 Hz, H-2',6'); 7.31 (1 H, t broad, H-
4). 13C NMR, ꢀ: 55.15 (OCH3); 55.64 (OCH3); 111.48
(C-3); 113.28 (C-3', 5'); 119.35 (C-a); 120.55 (C-5);
129.29 (C-1); 129.48 and 130.04 (C-4 and C-6); 130.20
(C-2', 6'); 131.12 (C-1'); 137.02 (C-b); 156.18 (C-2);
were placed in cuvettes that had been temperature
equilibrated for at least 15 min. The kinetics were studied
by following spectrophotometrically the appearance of
the reaction products at a wavelength where the largest
difference between the absorbance spectra of the reagents
and products was observed (1a, 296; 1b, 299; 1c, 301; 1d,
297; 1e, 300; 1g, 290; 1h, 290; 1i, 292; 1l, 290 nm).
‡
158.91 (C-4). HRMS (M ), m/z calc. for C16H14Cl2O2:
308.0370. Found: 308.0340.
Acknowledgements
1,1-Dichloro-2,2-bisꢀ2-methoxy-5-methylphenyl)-
We are grateful to the Universita` degli Studi di Palermo
for financial support.
ethene ꢀ2h). Reaction time 96 h, yield 45%, white
1
crystals from ethanol, m.p. 113°C. H NMR, ꢀ: 2.28
(6 H, s, 2 CH3); 3.84 (6 H, s, 2 OCH3); 6.82 (2 H, d,
Jo = 8.3 Hz, 2 H-3); 7.07 (2 H, d, Jo = 8.3 Hz, 2 H-4); 7.09
(2 H, s, 2 H-6). 13C NMR, ꢀ: 20.45 (2 CH3); 55.81 (2
OCH3); 111.28 (2 C-3); 120.96 (C-a); 128.42 (2 C-1);
129.58 (2 C-5); 129.58 and 130.54 (2 C-4 and 2 C-6);
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‡
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1,1-Dichloro-2,2-bisꢀ2,4,5-trimethoxyphenyl)ethene
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‡
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1,1-Dichloro-2,2-bisꢀ2,4-dimethoxyphenyl)ethene ꢀ2j).
Reaction time 96 h, yield 45% white crystals from
ethanol, m.p. 129°C. 1H NMR, ꢀ: 3.77 (6 H, s, 2
OCH3); 3.78 (6 H, s, 2 OCH3); 6.43 (2 H, d, Jm = 2.3 Hz,
2 H-3); 6.45 (2 H, dd, Jo = 8.9 Hz, Jm = 2.3 Hz, 2 H-5);
7.15 (2 H, d, Jo = 8.9 Hz, 2 H-6). 13C NMR, ꢀ: 55.28 (2
OCH3); 55.54 (2 OCH3); 98.66 (2 C-3); 104.18 (2 C-5);
120.83 (C-a); 121.44 (2 C-1); 130.75 (2 C-6); 134.03 (C-
‡
b); 157.27 (2 C-2); 160.52 (2 C-4). HRMS (M ), m/z
calc. for C18H18Cl2O4: 368.0582. Found: 368.0545.
Kinetics. Reaction mixtures for kinetic measurements
were prepared by mixing thermostated volumes of base
and substrate solutions. The substrate concentrations
used were 5 Â 10À5–1 Â 10À4 M. Reactions mixtures
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Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2002; 15: 108–114