Kinetics and mechanism of the reaction of substituted O-benzoylbenzamidoximes with sodium methoxide in methanol

Article abstract of DOI:10.1002/(SICI)1099-1395(199908)12:8<626::AID-POC173>3.0.CO;2-W

The kinetics of reaction of substituted O-benzoylbenzamidoximes with sodium methoxide in methanol were studied at 25 °C. The only reaction products are substituted benzamidoximes and methyl benzoates. The slope of the dependence of rate constant on sodium methoxide concentration gradually increases, but in the presence of C₁₈ crown ether the dependence becomes linear and the rate constant is lower than in the absence of the crown ether, which means that the traction is catalysed by sodium cation The rate constants of reactions with the ion pair and with methoxide ion were determined with the presumption that the rate-limited step of the catalysed reaction is the reaction of substituted O-benzoylamidoximes with the ion pair of sodium methoxide. The rate constants of the reaction with the ion pair are about 20 times higher than those of the non-catalysed process. The slopes of the dependence of log k of the non-catalysed and catalysed reactions on the pK_a of substituted benzamidoximes are 1.05 and 0.94, respectively. These high values indicate the rate-limiting step involving the splitting off of substituted benzamidoxime from the tetrahedral intermediate. On the basis of the relatively high ρ constant of methanolysis at the benzoyl group substituted derivatives (2.17 and 1.98 for the non-catalysed and catalysed reactions, respectively), it can be presumed that the transition state structure will be close to the tetrahedral intermediate. Copyright

Full text of DOI:10.1002/(SICI)1099-1395(199908)12:8<626::AID-POC173>3.0.CO;2-W

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 12, 626–634 (1999)
Kinetics and mechanism of the reaction of substituted
O-benzoylbenzamidoximes with sodium methoxide in
methanol
Ï
Ï
Libor DusÏek, JaromõÂr KavaÂlek and Vojeslav Sterba*
Department of Organic Chemistry, Faculty of Chemical Technology, University of Pardubice, 532 10 Pardubice, Czech Republic
Received 30 July 1998; revised 28 September 1998
ABSTRACT: The kinetics of reaction of substituted O-benzoylbenzamidoximes with sodium methoxide in methanol
were studied at 25°C. The only reaction products are substituted benzamidoximes and methyl benzoates. The slope of
the dependence of rate constant on sodium methoxide concentration gradually increases, but in the presence of C18
crown ether the dependence becomes linear and the rate constant is lower than in the absence of the crown ether,
which means that the reaction is catalysed by sodium cation. The rate constants of reactions with the ion pair and with
methoxide ion were determined with the presumption that the rate-limited step of the catalysed reaction is the reaction
of substituted O-benzoylamidoximes with the ion pair of sodium methoxide. The rate constants of the reaction with
the ion pair are about 20 times higher than those of the non-catalysed process. The slopes of the dependence of log k of
the non-catalysed and catalysed reactions on the pKa of substituted benzamidoximes are 1.05 and 0.94, respectively.
These high values indicate the rate-limiting step involving the splitting off of substituted benzamidoxime from the
tetrahedral intermediate. On the basis of the relatively high r constant of methanolysis at the benzoyl group
substituted derivatives (2.17 and 1.98 for the non-catalysed and catalysed reactions, respectively), it can be presumed
that the transition state structure will be close to the tetrahedral intermediate. Copyright 1999 John Wiley & Sons,
Ltd.
KEYWORDS: O-benzoylbenzamidoximes; methanolysis kinetics; sodium cation catalysis
INTRODUCTION
catalysed by sodium cation, and to suggest a reaction
mechanism.
Substituted arylbenzamidoxime carbonates undergo cy-
clization in aqueous hydroxides or in aprotic solvents to
give 3-aryl-1,2,4-oxadiazol-5-ones,1,2 but their reaction
with sodium methoxide in methanol exclusively results in
a two-step methanolysis giving phenolate salts, benza-
midoximes and dimethyl carbonate.3 In addition to the
reaction with methoxide ion there also takes place a
reaction with sodium methoxide ion pair which is one
order of magnitude faster, and the methanolysis proceeds
via a concerted mechanism.3 Also, O-benzoylbenzami-
doximes (1) are cyclized in aqueous alkali metal
hydroxides and aprotic solvents to give 3,5-diaryl-1,2,4-
oxadiazole derivatives.5–8 The aim of this work was to
find out whether compounds 1 reacting with sodium
methoxide in methanol only undergo methanolysis as
aryloxime carbonates and whether the reaction is
ˇ
*Correspondence to: V. Steˇrba, Department of Organic Chemistry,
Faculty of Chemical Technology, University of Pardubice, 532 10
Pardubice, Czech Republic.
E-mail: Vojeslavsˇteˇrba@upce.cz
Contract/grant sponsor: Grant Agency of the Czech Rebublic;
Contract/grant number: 203/97/0545.
Copyright 1999 John Wiley & Sons, Ltd.
CCC 0894–3230/99/080626–09 $17.50

REACTION OF O-BENZOYLAMIDOXIMES WITH SODIUM METHOXIDE IN METHANOL
627
Table 1. Melting-points, yields of syntheses and elemental analyses of substituted O-benzoylbenzamidoximes 1a±g and O-
benzoylbenzaldoxime (2)
Calculated/found (%)a
Compound
M.p. (°C)
Yield (%)
80
Formula (MW)
C
H
N
1a
145–148
(146–148)13
149–151
C15H14N2O3
(270.3)
C14H12N2O2
(240.3)
C14H11N2O2Cl
(274.7)
C14H11N3O4
(285.3)
C15H14N2O3
(270.3)
C14H11N2O2Cl
(274.7)
C14H11N3O4
(285.3)
C14H11NO2
(225.3)
66.66
66.99
69.99
69.52
61.21
61.47
58.95
58.99
66.66
66.67
61.21
61.47
58.95
58.60
74.65
74.74
5.22
5.30
5.03
5.00
4.04
3.96
3.89
3.85
5.22
5.26
4.04
3.96
3.89
3.81
4.92
4.91
10.36
10.33
11.66
11.44
10.20
9.96
14.73
14.58
10.36
10.39
10.20
9.96
1b
1c
1d
1e
1f
1g
2
57
50
51
50
80
97
43
(148)14
172–174
(175)14
198–200
(164–166)10
149–151
(146–148)15
178–180
(174)15
199–201
14.73
14.66
6.22
(202–203)10
101–102
(101–102)11
6.21
a
Calculated values in first row, found values in second row.
Table 2. 1H NMR spectra of substituted O-benzoylbenzamidoximes 1a±g and O-benzoylbenzaldoxime (2)
Compound
H-1,5 (m)
6.90–6.92
H-2,(3),4 (m)
7.68–7.71
H-6,10 (m)
8.06–8.08
H-7,(8),9 (m)
NH2 (s)
5.16
Other positions
3.82 s (OMe)
1a
7.44–7.48
(7.55–7.59)
7.71–7.74
(7.55–7.59)
7.57–7.61
8.09–8.12
1b
7.37–7.47 (5H)
8.05–8.07
5.26
—
1c
1d
7.60–7.62
8.24–8.27
7.84–7.86
7.58–7.63
(7.71–7.73)
7.50–7.57
8.23–8.25
8.38–8.40
7.10
7.31
—
—
1e
1f
1g
2
7.79–7.82
7.81–7.84
8.19–8.21
8.02–8.04
8.48–8.51
8.11–8.14
7.09–7.11
7.74–7.76
8.38–8.41
7.79–7.81
6.97
5.12
7.17
—
3.82 s (OMe)
7.42–7.50 (5H)
—
—
—
7.54–7.59
7.44–7.51 (5H)
Table 3. Rate constants kip (s 1 mol 1 dm3), ki and kiC (s 1 mol 1 dm3) of the methanolysis of O-benzoylbenzamidoximes 1a±
18
g measured at 25°C at the wavelengths ꢀanal (nm) in methanolic solutions of sodium methoxide with or without the addition of
C
18 crown ether and the pKa values of the respective benzamidoximes in the same medium
a
Compound
ki  10
kiC Â 10
kip
ꢀanal
pKa
18
1a
1b
1c
1d
1e
1f
0.521 Æ 0.071
0.802 Æ 0.049
1.069 Æ 0.092
3.487 Æ 0.352
0.156 Æ 0.030
3.199 Æ 0.374
35.599 Æ 3.942
0.578 Æ 0.012
0.787 Æ 0.036
1.186 Æ 0.075
3.345 Æ 0.055
0.144 Æ 0.071
3.343 Æ 0.097
34.077 Æ 2.072
1.467 Æ 0.069
1.599 Æ 0.033
2.538 Æ 0.086
6.556 Æ 0.346
0.384 Æ 0.018
4.305 Æ 0.360
57.122 Æ 6.845
270
300
264
300
280
266
300
16.83 Æ 0.03
16.67 Æ 0.02
16.48 Æ 0.03
16.10 Æ 0.02
—
—
—
1g
a
Ref. 3.
triles with hydroxylamine in aqueous alcohol.1 O-
Benzoylbenzaldoxime (2) was obtained by acylation of
benzaldoxime11 obtained by reaction of benzaldehyde
with hydroxylamine in aqueous sodium acetate.12 The
purity of all the substances synthesized was checked by
EXPERIMENTAL
4,4'-Substituted O-benzoylbenzamidoximes 1a–g were
obtained by acylation of the corresponding benzamidox-
imes9,10 prepared by reactions of the respective benzoni-
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)

ˇ
´
ˇ
ˇ
628
L. DUSEK, J. KAVALEK AND V. STERBA
Scheme 1.
their melting-points and elemental analyses (Table 1).
The structure of the compounds prepared was confirmed
by 1H NMR spectroscopy (Table 2).
entirely on the side of the E configuration.16–18
Amidoximes with a free amino group or one alkyl group
only are in the Z configuration. The E configuration has
never been isolated.14,19 The stability of the Z form could
arise from steric effects but the presence of an internal H-
bond, which has been observed in crystalline structure
studies, is also a major factor.19 Attempts to convert the Z
into the E configuration photochemically failed, maybe
because the E form, once formed, can convert rapidly to
the Z form via a prototropic shift, which is not possible in
N, N-dialkyl derivatives.18,19 In the case of substituted O-
benzoyl-N, N-dialkylbenzamidoximes, only the E iso-
mers were isolated and measured in solution.18 O-
Benzoyl derivatives with a free amino group exist in
the Z configuration.14
The melting-points were measured on a Kofler
apparatus and were not corrected. Electron spectra were
measured on a Hewlett-Packard 8453 diode-array instru-
1
ment at 25°C. H NMR spectra were measured on a
Bruker AMX 360 spectrometer at 360.14 MHz at 25°C in
deuterochloroform. The chemical shifts are referenced to
the signals of the non-deuterated solvent [ꢁ (1H) 7.25,
CHCl3]. The identification of the reaction products and
intermediates was carried out on a Waters 616 liquid
chromatograph combined with a VG-Platform Fison-
ESP-3000Da spectrometer.
Kinetic measurements. A 1 cm quartz cell with a lid
placed in the thermostated compartment of the spectro-
photometer was charged with 2 ml of methanolic sodium
The reaction kinetics were studied in a large excess of
sodium methoxide, hence the methanolysis proceeded
kinetically as a reaction of pseudo-first order. The slopes
of the dependence of observed rate constants kobs (s 1) on
sodium methoxide concentration showed an increasing
trend in all cases (Fig. 1), although the transition state
does not allow the participation of a second methoxide
ion.
In the presence of a small surplus of crown ether, the
dependence of kobs on methoxide concentration was
linear (Fig. 2) and the kobs values always were lower than
the corresponding values obtained in the absence of the
crown ether. This can be interpreted by catalytic
participation of sodium ion in the methanolysis of the
substrate, similar to the methanolysis of arylbenzami-
doxime carbonates.3
3
methoxide (5 Â 10 –1.4 Â 10 1 mol l 1). In the ex-
periments with C18 crown ether, the concentration of the
1
latter was always 2 Â 10 3 mol l higher than that of
sodium methoxide. Then 10–20 ml of a methanolic
solution of substrate 1 or 2 (1 Â 10 2 mol l 1) was
injected, and after mixing the absorbance of the mixture
was measured at 260 nm (2) or at the ꢀanal wavelengths
given in Table 3 (1a–g).
RESULTS AND DISCUSSION
Catalytic effect of sodium cation
The gradually increasing slope of the dependence of
kobs on sodium methoxide concentration can be explained
by parallel reactions of the substrate with methoxide
anion and with the ion pair (which is more reactive than
the anion alone) (Scheme 2).
In Scheme 2, ki and kip are rate constants of reactions of
the substrate with the anion and with the ion pair,
respectively, and Kip (= 7.5)20 is the equilibrium constant
The reaction of sodium methoxide with O-benzoylben-
zamidoximes 1a–g in methanol results exclusively in
methanolysis, giving substituted benzamidoximes and
methyl esters of substituted benzoic acids (Scheme 1).
Amidoximes can exist in two configurations, E and Z.
N,N-Dialkylamidoximes exist in both configurations and
they were also isolated in some cases. The equlibrium lies
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)

REACTION OF O-BENZOYLAMIDOXIMES WITH SODIUM METHOXIDE IN METHANOL
629
Figure 1. Dependence of observed rate constants kobs (s 1) of methanolysis of (&) 1a, (&) 1b, (*) 1c and (*) 1d on sodium
methoxide concentration cMeO (mol l 1) in the absence of C18 crown ether. Experimental points are shown together with
theoretical curves calculated from Eqn. (3)
Figure 2. Dependence of observed rate constants kobs (s 1) of methanolysis of (&) 1a, (&) 1b, (*) 1c and (*) 1d on sodium
methoxide concentration cMeO (mol l 1) in the presence of C18 crown ether
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)

ˇ
´
ˇ
ˇ
630
L. DUSEK, J. KAVALEK AND V. STERBA
The observed rate constant in the absence of crown ether
is given by
kobs ˆ ki‰MeO Š ‡ kip‰MeONaŠ
2
2
ˆ ki‰MeO Š ‡ kipKip‰MeO Š ꢀꢂ †
ꢀ3†
Æ
The actual concentration of methoxide ion was calculated
with the equation
q
2
1 ‡ 1 ‡ 4cMeO Kipꢀꢂ †
Æ
‰MeO Š ˆ
ꢀ4†
2
2Kipꢀꢂ †
Æ
Scheme 2.
The dependence of kobs/[MeO ] on Kip [MeO ] (g )2 is
linear with slope kip and intercept ki (Fig. 3). The values
of ki and kip (Table 3) were calculated by multiple non-
linear regression using Eqn. (3).
The ki values obtained from the measurements in the
presence of the crown ether are also presented in Table 3.
In the case of methanolysis of carbonates,3 for the
reaction with an ion pair the presence of an NH2 group
was necessary and in order to prove this in the case of the
substrates studied here, we determined the rate constant
of the reaction of 2 with methoxide both in the presence
and in the absence of the crown ether. In both the cases
the dependence of kobs on methoxide concentration was
linear and the kobs values were equal at equal methoxide
Æ
‡
of association of Na cation with MeO anion:
‰MeONaŠ
‰MeO Š‰Na Šꢀꢂ †
‰MeONaŠ
Kip ˆ
ˆ
ꢀ1†
2
2
2
‡
‰MeO Š ꢀꢂ †
Æ
Æ
The activity coefficient of the ion pair is presumed to be
equal to 1, hence the activity of the ion pair is equal to its
concentration. The activity coefficients of sodium and
methoxide ions were obtained from the equation21
p
1:69 I
p
log ꢂ ˆ
ꢀ2†
Æ
1 ‡ 2:5 I
concentrations (ki = 3.60 Æ 0.17 and kiC = 3.53 Æ 0.14
18
Figure 3. Dependence of kobs/[MeO ] on Kip [MeO ] (g )2 with slope kip and intercept ki for methanolysis of O-
Æ
benzoylbenzamidoximes (&) 1a, (&) 1b, (*) 1c and (*) 1d
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)

REACTION OF O-BENZOYLAMIDOXIMES WITH SODIUM METHOXIDE IN METHANOL
631
‡
complexes A‡ and A‡M , respectively, and K'ip is the
association constant of formation of the complex of the
sodium ion with the transition state A‡ of the non-
catalysed reaction. On the basis of the respective
thermodynamic cycle, it is possible to calculate this
virtual association constant.
Since, according to the activated complex theory, the
concentrations of activated complexes are in equilibrium
with those of reactants and, at the same time, both starting
ions are in equilibrium with the ion pair, the two activated
complexes are also in equilibrium, although there is no
direct dynamic equilibrium between them.22
Scheme 3.
For a rate constant we can write
z
kT ÁG
kT
h
k ˆ
e
ˆ
Kz
ꢀ5†
RT
h
s
1 mol 1 dm3, ꢀanal = 260 nm). We presume that for 1a–
g there takes place a complex formation of the sodium
cation of the ion pair with the oxygen atom of the
carbonyl group and the electron pair of the partially
negatively charged, doubly bonded nitrogen atom, as in
the case of arylbenzamidoxime carbonates.
so that K'ip can be calculated from
kipKip
Ki0p ˆ
ꢀ6†
ki
According to the transition state theory, the kinetic
data can be divided into a contribution of stabilization by
sodium cation in the starting (ground) state and in the
transition state. The degree of stabilization of the
activated complex can be evaluated by the method
developed by Kurz22–24 (Scheme 3).
The change in the Gibbs energy, ꢁ Gip, of formation of the
ion pair was calculated from
ꢁGip ˆ RT ln Kip
ꢀ7†
The catalysis takes place if the metal cation stabilizes the
activated complex more than the ground state (Fig. 4). In
the opposite case inhibition occurs. The resulting
K‡ and K‡ are the equilibrium constants of the
ip
ip
catalysed and non-catalysed formation of the activated
Figure 4. Relative changes in Gibbs energies (kJ mol 1) of the species indicated for methanolysis of O-benzoylbenzamidoxime
1b referenced to the zero energy level of starting reactants
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)

ˇ
´
ˇ
ˇ
632
L. DUSEK, J. KAVALEK AND V. STERBA
Scheme 4.
catalytic effect DGcat is given by
the blg values (obtained from the dependence of log k on
pKa of the conjugated acid of the leaving group34) range
from 0.1 to 0.3 if the formation of the intermediate is rate-
limiting and from 0.8 to 1.3 if the decomposition of the
intermediate into products is rate-limiting. For concerted
mechanisms these values vary in the range 0.4–0.6,26,35–
ÁGcat ˆ ÁGzcat ÁGzu ˆ ꢁGts ꢁGip
ꢀ
ꢁ
ꢀ
ꢁ
Ki0p
Kip
kip
ki
ˆ
RT ln
ˆ
RT ln
ꢀ8†
exceptionally reaching up to about 0.8.27
37
The log ki and log kip values of splitting off anions of
substituted benzamidoximes were correlated with the pKa
values of their conjugated acids measured in methanol.
The slope values blg = 1.05 (found in the correlation of ki,
i.e. those found in the presence of crown ether) and
blg = 0.94 (found in the correlation of kip) indicate that the
reaction takes the addition–elimination mechanism and
the rate-limiting step is splitting off of anions of
substituted benzamidoximes (see Scheme 4 for the
reaction in the presence of crown ether).
Reaction mechanism, substituent effect
Until recently, nucleophilic substitution reactions on
carbonyl carbon atoms were presumed to proceed
exclusively by the addition–elimination mechanism via
a tetrahedral intermediate. It was subsequently found that
in a number of cases the splitting of a bond and the
formation of a new bond can be simultaneous (concerted,
one-step mechanism).25 A transition from a two-step,
addition–elimination mechanism to a one-step, concerted
mechanism is realized when the tetrahedral intermediate
becomes so unstable that there is no significant barrier to
its decomposition (it does not exist for a period of several
vibrations) and so it becomes an activated complex.25
For instance, in reactions of negatively charged oxygen
nucleophiles with substituted phenyl acetates in aqueous
solution, the presumed intermediate has too short a
lifetime to exist for a significant period, and the reaction
takes the concerted pathway.26 If the leaving oxyanion
has a pKa above ca 11, the intermediate is stable enough
and the reaction proceeds via the adition–elimination
mechanism.27,28
The stability of the intermediate also depends on the
structure of the acyl group, e.g. replacement of MeCO by
MeOCO decreases the stability of the intermediate
considerably, so that in some cases the addition–
elimination mechanism changes to the concerted me-
chanism.29–32 The concerted mechanism is preferred
when the polarity of the medium (expressed by
quantitative values of solvatochromic parameters, e.g.
p* and a or ETN) decreases.33
The values of blg for ki and kip are almost identical, in
accordance with the findings38 concerning alkali metal
ion catalysis in nucleophilic displacement reactions of
phosphorus-, sulphur- and carbon-based esters by lithium
and potassium ethoxides in ethanol, where the rate
constant values of reaction with the ion pair are almost
the same with lithium ethoxide as with ethoxide ion
alone, being ca 10% lower with potassium ethoxide than
with ethoxide alone; in our case the situation is similar.
On the basis of this finding, Pregel et al.38 came to an
important conclusion, viz. that the alkali metal ions do
not significantly change the activated complex structure.
The situation is different with substituted methyl
benzamidoximecarbonates,3 where blg = 0.85 for the
reaction with methoxide ion but 0.53 for that with the
ion pair, i.e. a value lower by almost 40%. This relatively
large difference in blg values indicates a considerably
different structure of the activated complex and supports
the idea of a change in the reaction mechanism from
addition–elimination in the presence of the crown ether to
concerted in the reaction with the ion pair. Replacement
of a phenyl group (substituted O-benzoylbenzamidox-
imes) by a methoxy group (methyl benzamidoximecar-
bonates) caused such a decrease in the lifetime of the
tetrahedral intermediate that it did not exist for a period of
One of the ways of determining a reaction mechanism
consists in the quantitative evaluation of substituent
effects (LFER). In an addition–elimination mechanism,
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)

REACTION OF O-BENZOYLAMIDOXIMES WITH SODIUM METHOXIDE IN METHANOL
633
several vibrations, and the mechanism changed from
addition–elimination to concerted. The splitting off of the
benzamidoxime anion from the tetrahedral intermediate
in the rate-limiting step is surprising as both the
nucleophile (MeO ) and the leaving group are oxygen
anions, and the pKa of methanol (18.31) is about 1.5–2
times higher than those of substituted benzamidoximes
(Table 1). On the other hand, the nucleophilicity of
benzamidoxime anions as nucleophiles with an a effect is
substantially higher than that of normal oxygen nucleo-
philes with similar pKa values.39 Also, the delocalization
of the electron pair on oxygen to the carbonyl group,
which would favour the reversible splitting off of the
methoxy group in the intermediate, is supported by
repulsion from the electron pair of the adjacent nitrogen
atom,3,40 which is further strengthened by the partial
charge at the nitrogen atom due to delocalization of
electrons from the NH2 group.
structure is close to that of the intermediate, and that the
bond splitting between the carbonyl carbon atom and the
benzamidoxime oxygen has hardly advanced. This is
apparently in contradiction with the high value of
blg = 1.05 found. In substituted phenyl acetates,43,44 the
oxygen atom of the phenoxy group bears an ‘effective
charge’ of 0.7. In substituted O-benzoylamidoximes, the
effective charge at the oxygen atom of substituted
benzamidoximes is probably still higher because the
negative charge transfer to the carbonyl oxygen atom is
supported by repulsion from the electron pair of the
adjacent nitrogen atom bearing a partial negative charge.
By forming the tetrahedral intermediate, this effective
charge at oxygen is cancelled, and blg has a large negative
value even if the CO bond splitting has hardly advanced.
Acknowledgements
The evaluation of substituent effects in O-benzoyl-
bezamidoximes 1a–g is more complex. The reaction
involves both bond formation and bond splitting at
carbonyl carbon atoms, and the reaction product,
substituted methylbenzoate, has a zero charge like the
starting substrate, hence the change of charge at the
carbonyl carbon is greater in the activated complex than
in the product. The structure of the activated complex
approaches that of a tetrahedral intermediate, the
hybridization at the carbonyl carbon atom with the
This work was supported by research grant No. 203/97/
0545 from the Grant Agency of the Czech Republic.
REFERENCES
1. F. Eloy and R. Lenaers, Chem. Rev. 62, 155 (1962).
2. H. Berger and A. E. Siegrist, Helv. Chim. Acta 62, 1411 (1979).
ˇ
3. L. Dusˇek, J. Kava´lek and V. Steˇrba, Collect. Czech. Chem.
Commun. 64, 265 (1999).
strongly polar C
=O bond being partially changed (from
4. H. Mu¨ller, Chem. Ber. 22, 2401 (1889).
5. F. Tiemann and P. Kru¨ger, Chem. Ber. 18, 727 (1885).
6. F. Tiemann, Chem. Ber. 18, 2456 (1885).
7. R. Buyle, R. Lenaers and F. Eloy, Helv. Chim. Acta 46, 1073
(1963).
sp2 to sp3). This change is considerably affected by
substituents in the benzene ring. The addition of water to
substituted benzaldehydes, which produces the corre-
sponding neutral diol, exhibits41 a constant of the
equilibrium reaction req equal to 1.71, although two
neutral molecules form a neutral product! The addition of
OH to substituted benzaldehydes giving the anion of the
corresponding diol exhibits42 ꢃeq = 2.76, which means
that the r value of dissociation of the diol (1.05) is similar
to that of substituted benzoic acids. The r value found for
the reaction with methoxide ion is 2.17 and that for the
reaction with the ion pair is 1.98, i.e. again lower by about
10%. This lowering is, as in the previous examples,
obviously predominantly due to the presence of metal
cation in the activated compex.
8. F. Grambal, J. Lasovsky and V. Beka´rek, Collect. Czech. Chem.
´
Commun. 43, 2008 (1978).
9. J. A. Duren and D. L. Heywood, J. Org. Chem. 30, 4359 (1965).
10. A. V. Evangelia and E. D. Micromastoras, Collect. Czech. Chem.
Commun. 48, 596 (1983).
11. C. R. Hauser and G. Vermilion, J. Am. Chem. Soc. 63, 1224 (1964).
12. K. Kahr and C. Berther, Chem. Ber. 93, 132 (1960).
13. L. I. Belenkii, D. B. Brokhovetskii and M. M. Kraynshkin,
Tetrahedron 46, 1659 (1990).
14. O. Exner and N. Motekov, Collect. Czech. Chem. Commun. 43,
2746 (1978).
15. F. Grambal, Chem. Zvesti 33, 371 (1979).
16. K. J. Dignam, A. F. Hegarty and P. L. Quain, J. Chem. Soc., Perkin
Trans. 2 1457 (1991).
17. H. Gozlan, R. Michelot, C. Riche and R. Rips, Tetrahedron 33,
2535 (1977).
An assessment of the extent to which the activated
complex of a particular reaction approaches the tetra-
hedral intermediate was made by comparing the r
constant of the reaction of 4-nitrophenyl esters of
substituted benzoic acids with OH ions going by
concerted mechanism (the most recent value found45 in
10% aqueous acetonitrile is ꢃ = 2.14) with the r constant
of addition of OH ion to substituted benzaldehydes
(ꢃeq = 2.76). From these values, it was concluded43 that
the activated complex structure is close to the inter-
mediate structure.
18. O. Exner and N. Motekov, Collect. Czech. Chem. Commun. 47,
814 (1982).
19. K. J. Dignam and A. F. Hegarty, J. Chem. Soc., Perkin Trans. 2 704
(1980).
20. J. Barthel, J. C. Justice and R. Wacker, Z. Phys. Chem. 84, 100
(1973).
21. J. E. Gordon, The Stereochemistry of Electrolyte Solutions, pp. 40
and 389. Wiley, New York 1975.
22. M. J. Pregel, E. J. Dunn and E. Buncel, Can. J. Chem. 68, 1846
(1990).
23. J. L. Kurz, J. Am. Chem. Soc. 85, 987 (1963).
24. E. J. Dunn and E. Buncel, Can. J. Chem. 67, 1440 (1989).
25. A. Williams, Chem. Soc. Rev. 23, 93 (1994).
26. D. Stefanidis, S. Cho, S. D. Pafanon and W. P. Jencks, J. Am.
Chem. Soc. 115, 1650 (1993).
Comparison of this value with our ꢃ = 2.17 allows the
conclusion that in our case also the activated complex
27. B. S. Saif, A. K. Luthra and A. Williams, J. Am. Chem. Soc. 111,
2647 (1989).
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)

ˇ
´
ˇ
ˇ
634
L. DUSEK, J. KAVALEK AND V. STERBA
28. E. Gutrie, J. Am. Chem. Soc. 113, 3941 (1991).
36. A. C. Satterthwait and P. W. Jencks, J. Am. Chem. Soc. 96, 7018
(1974).
29. E. A. Castro and C. J. Ureta, J. Chem. Soc., Perkin Trans. 2 63
37. D. J. Hupe and P. W. Jencks, J. Am. Chem. Soc. 99, 451 (1977).
38. M. J. Pregel, G. R. Nagelkerke, G. R. J. Thatcher and E. Buncel,
Chem. Soc. Rev. 24, 449 (1995).
39. S. Hoz and E. Buncel, Isr. J. Chem. 26, 313 (1985).
40. Y. Zhao, F. G. Bordwell, Cheng J. P. and D. Wang, J. Am. Chem.
Soc. 119, 9125 (1997).
41. R. A. McClelland and M. Coe, J. Am Chem. Soc. 105, 2178 (1983).
42. W. J. Bover and P. Zuman, J. Chem. Soc. Perkin Trans. 2, 786
(1973).
43. A. Williams, Adv. Phys. Org. Chem. 27, 1 (1992).
44. J. Gerstein and W. P. Jencks, J. Am. Chem. Soc. 86, 4655 (1964).
45. M. J. Colthurst and A. Williams, J. Chem. Soc., Perkin Trans. 2
1493 (1997).
(1991).
30. E. A. Castro, F. Ibaney, M. Salas and J. G. Santos, J. Org. Chem.
56, 4819 (1991).
31. E. A. Castro, M. Salas and J. G. Santos, J. Org. Chem. 59, 30
(1994).
32. E. Chrystiuk and A. Williams, J. Am. Chem. Soc. 109, 3040 (1987).
33. A. B. Mande and A. Williams, J. Chem. Soc., Perkin Trans. 2 179
(1997).
34. F. G. Bordwell, J. C. Branca and I. A. Tripe, Isr. J. Chem. 26, 357
(1985).
35. E. A. Castro, J. G. Santos, T. Te´llez and M. I. Umana, J. Org.
Chem. 62, 6568 (1997).
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 626–634 (1999)