Volume of electrostriction of the solvate-separated ions of lithium perchlorate and contact ion pair of the transition state in sulfenyl insertion

Article abstract of DOI:10.1016/j.mencom.2008.01.022

The volumes of electrostriction of the ions of lithium perchlorate are in a linear relation with the solvent electrostriction parameter ?(1/ε)/?p but the volume changes of ion pair transition state of electrophilic addition of aryl sulfenyl chloride to styrene and cyclohexene have the slope about 20 times less.

Full text of DOI:10.1016/j.mencom.2008.01.022

Mendeleev
Communications
Mendeleev Commun., 2008, 18, 59–61
Volume of electrostriction of the solvate-separated
ions of lithium perchlorate and contact ion pair
of the transition state in sulfenyl insertion
Vladimir D. Kiselev
A. M. Butlerov Chemical Institute, Kazan State University, 420008 Kazan, Russian Federation.
Fax: +7 8432 92 7278; e-mail: vladimir.kiselev@ksu.ru
DOI: 10.1016/j.mencom.2008.01.022
The volumes of electrostriction of the ions of lithium perchlorate are in a linear relation with the solvent electrostriction parameter
¶(1/e)/¶p but the volume changes of ion pair transition state of electrophilic addition of aryl sulfenyl chloride to styrene and
cyclohexene have the slope about 20 times less.
The high pressure effect on the rate and equilibrium of chemical
reactions is of interest in pure and applied chemistry.1–5 The
nonpolar Diels–Alder reaction is convenient to elucidate volume
changes in the absence of electrostriction.3,6–8 Large electronic
and steric effects of substitutions, as well as a solvent effect on
the rate of the Menshutkin reaction at ambient and elevated
pressure, have been intensively studied.5 Here the charge separa-
tion can only grow during this reaction. On the other hand, a
lot of substitution or addition processes have nonpolar initial
and final states but a polar transition state. The substitution and
solvent effects can be a reason for the transformation from
polar nature of the transition state to nearly nonpolar one.9
Sulfonium ion pair type of transition state was proposed for
the electrophilic addition of sulfenyl halides to alkenes.10 This
assumption follows from the large solvent effect on the reaction
rate and stereoselective trans-addition with formation of β-halide
thioether. The transformation of the transition state from polar
to nonpolar was proposed11 for this reaction, when polar-type
stabilization sharply decreases on going from polar to nonpolar
media.
lack in the last case and the volume of activation in a polar solvent
should be more negative. A polar solvent effect on the activation
volume of AdE reaction (Scheme 1) was published recently.12
Lithium perchlorate with high solubility in organic n-donor
solvents can be a suitable model of the ionic type of the transi-
tion state of chemical reactions. Solvent effect on the partial
molar volume (PMV) of lithium perchlorate was measured for
dilute solution.13 The details of kinetic measurements under
pressure were published elsewhere.8,12 The rate constants of
these reactions (Scheme 1) decrease in 106 times on going from
acetonitrile to n-hexane. Long monitoring time (20–50 h) of the
optical density change for p-nitrophenyl sulfenyl chloride was
necessary because of the very slow reaction of 1b with styrene
2 in n-hexane at 25 °C. The obtained rate constants were
1.80×10–5 at atmospheric pressure; 5.45×10–5 at 530 kg cm–2
and 1.16×10–4 dm3 mol–1 s–1 at 960 kg cm–2. From these data
the apparent volume of activation in n-hexane was calculated as
–49.3 cm3 mol–1.
¹
¶ln k
¶p
¶G
¶p
¹
–RT
=
= ∆Vexp
T
(1)
T
Because of the concentration of reagents (and the frequency
of collision) growth under pressure due to the solvent com-
pressibility, required correction for the second order reaction
should be made.
+
SCl
O2N
1a,b
2
S
¶ln k ¶V
¶V ¶p
¹
RT
= bTRT = –∆Vconc
(2)
NO2
Cl
4a,b
The compressibility coefficient [bT = V–1(¶V/¶P)] of n-hexane
was measured in a special high pressure vessel up to 1000 bar
at 20, 30, 40 and 50 °C. The Tait equation (3) has the best
accuracy2 in description of the Vp–p dependences.
+
1a,b
S
NO2
∆V/V0 = Cln[(B + p)/B]
(3)
Cl
3
5a,b
a ortho
b para
The coefficients C, B and bT were obtained as 0.088123,
548.50 and 160.66×10–6 bar–1 at 20 °C; 0.088342, 501.69 and
176.09×10–6 bar–1 at 30 °C; 0.087517, 451.62 and 193.78×10–6 bar–1
at 40 °C and 0.088855, 415.10 and 214.06×10–6 bar–1 at 50 °C.
From obtained dependence: bT = 137.22 + 0.93015T + 0.012125T2
Scheme 1
If a polar transition state of the reaction is the same in polar
and nonpolar media, solvent electrostriction should be in all
solvents. But in this case the volume of activation in nonpolar
solvents (n-hexane, carbon tetrachloride) should be more negative
than that in polar ones.2,5 On the other hand, if the transition
state of the reaction is polar in a polar solvent but has a nonpolar
type in a nonpolar medium, solvent electrostriction should be
(
R
= 0.999997), the value of
b
25 was calculated as 168.05×10–6 bar–1
¹
at 25 °C. Using these data ∆Vconc [equation (2)] was calculated
as –4.1 cm3 mol–1, and the corrected volume of activation
¹
¹
(∆Vexp – ∆Vconc) of the reaction (1b + 2) in n-hexane at 25 °C
was determined as –45.2 cm3 mol–1.
– 59 –
© 2008 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2008, 18, 59–61
Table 1 Rate constants (k2/dm3 mol–1 s–1) for the reaction of o-nitrophenyl
1
sulfenyl chloride 1a with cyclohexene 3 in a mixture of 1,2-dichloroethane
–10
–20
–30
–40
–50
–60
45
35
25
15
5
2
3
and carbon tetrachloride at 25 °C.
4
Mole fraction
11
12
a
of 1,2-dichloro- 105k2
ln k2
em
13
5
6
7
ethane
8
b
16
15
9
0
1.60
20.4
60.3
624
2170
5850
–11.04
–8.47
–7.41
–5.08
–3.83
–2.84
2.22
2.7
3.3
5.0
7.2
14
a
17
0.1398
0.2898
0.5521
0.7850
1
10
–5
0
10
20
30
1/e2(de/dp)
40
50
60
10.02
aThe values of e for mixtures are taken from ref. 15.
Figure 1 Effect of the electrostriction parameter of solvents (1/e2)¶e/¶p
(a) on the partial molar volume (VLP) of lithium perchlorate, and (b) on
the volume of activation (∆Vcor.) of the studied reactions. For numeration of
the solvents see Table 2.
It is well known9 that the changes of the free energy of
activation of polar reactions at ambient pressure are caused by
the changes of solvation (∆Gsolv) of polar transition or initial
states and described as:
¹
¹
or be a result of a larger contribution of mechanical work p∆V ,
ln k = a + b(1/e)
(4)
¹
caused by more negative value ∆V . From the relation describing
High pressure induces the growth of solvent permittivity e:
the pressure effect on free energy of a charged particle (q) solvation2
¶∆Gsolv
¶p
¶ln k ¶(1/e)
¶(1/e) ¶p
¶(1/e)
¶p
Nq2 ¶(1/e)
= b
(5)
= ∆Velectr = –
,
(6)
2r
¶p
With the known value of b it is possible to estimate the effect
of the modified solvent properties, induced by pressure, on the
rate constants and compare with the apparent volumes of activa-
tion. For the reaction of styrene with o-nitrophenyl sulfenyl
chloride12 the value of b is –22 2. Nearly the same value of b
was obtained14 for the reaction of styrene with phenyl sulfenyl
chloride (–25 3). Solvent mixture effect of 1,2-dichloroethane
and carbon tetrachloride on the rate constant of the reaction of
o-nitrophenyl sulfenyl chloride with cyclohexene was studied at
25 °C (Table 1). Clear linear relation ln k2 vs. 1/e was obtained
with the slope b equal to –22.3 0.9 (r = 0.997).
it is clear that both these parameters should be indistinguishable.
Nearly the same approach to the solvent effect on the volumes of
activation of some polar reactions was discussed previously.2,8,17,18
¹
The activation volume (∆V ) refined from the solvent electro-
¹
¹
striction effect (∆Vcor. – Vel)
is nearly the same (–20.5 1.4 cm3 mol–1)
for all of the test reactions (Scheme 1) and in all solvents under
¹
consideration, with the ratio ∆V /∆Vreaction = 0.92.
It is possible to compare the effects of the values of baric
coefficient of permittivity of solvents, ¶(1/e)/¶p, as electro-
striction parameter [equation (6)], on the change of PMV of the
charge solute, lithium perchlorate (LP), and on the change of
the activation volumes of studied reactions (Table 2, Figure 1).
Note that, for polar solvents with the dielectric constant e
higher than 20, [Figure 1, line a, solvents 1–7), there is a clear
correlation (r = 0.96) of lithium perchlorate PMV and the electro-
striction parameter ¶(1/e)/¶p:
The values of equation (5) were calculated using b = –22 and
known data for the ¶(1/e)/¶p.2,16
High level of correlation (r = 0.99) of the independent values
¹
¹
¹
b¶(1/e)/¶p and Vcor. = ∆Vexp – ∆Vconc is in accordance with the
assumption that the changes of free energy of activation under
TS
pressure (¶G /¶p) are produced by solvent permittivity growth.
solv
¶(1/e)
¶p
VLP = 51.3 + 8.83×106
.
(7)
From this point of view a larger pressure effect on the rate
constant, ln(kP/k0), in nonpolar medium can be caused by a larger
change of baric coefficient of permittivity, ¶(1/e)/¶p, [equation (5)],
In spite of a high solubility of LP in tetrahydrofuran (e = 7.5),
ethyl acetate (e = 6.1) and, especially, in diethyl ether (e = 4.3,
solubility up to 6 mol dm–3 at 25 °C), the values of PMV of
lithium perchlorate in dilute solutions of these solvents (no. 5, 7
and 9, Figure 1) deviate sharply from the common line (Figure 1,
line a). From equation (7) it can be predicted that the values of
PMV of separated ions of lithium perchlorate in EtOAc, THF
and Et2O are –100, –75 and –300 cm3 mol–1, respectively. This
denotes a low degree of lithium perchlorate dissociation in
these solvents under working conditions due to low polarity.
In addition, all pressure-solvent effects on the studied reactions
of aryl sulfenyl chloride with styrene and cyclohexene (Table 2)
are in accordance with Kharasch’ preposition10 of zwitter-ionic
type of transition state in the solvents under consideration.
Because of small solvent effect on the PMV values of nonpolar
reagents,12 the differences in activation volumes can be accounted
for electrostriction of transition state. Linear dependence (Figure 1,
line b, solvents 11–17, r = 0.99) between the change of the
volume of zwitter-ionic transition state and the electrostriction
parameter of solvent ¶(1/e)/¶p) (Table 2) has the slope about
20 times less than that for separated ions of lithium perchlorate:
Table 2 Partial molar volumes of lithium perchlorate (LP) in dilute solution
¹
¹
¹
(V/cm3 mol–1, no. 1–10), corrected activation volumes (∆Vcor. = ∆Vexp – ∆Vconc
/
cm3 mol–1, no. 11–17) of studied reactions of sulfenyl chloride with alkenes
¹
and electrostriction volume (∆Vel/cm3 mol–1) at 25 °C.
¹
a
¹ b
No. Solvent
V or ∆Vcor.
–∆Vel (1/e2)¶e/¶pc ed
106be
1
2
3
4
5
6
7
8
9
Formamide
H2O
48.3
44.2
38.7
36.4
25.1
24.6
23.6
20.1
14.5
–2
3.0
7.1
0.45 (0.40) 100.5
0.57 (0.57) 80.1
39.9
45.8
49
DMSO
MeNO2
EtOAc
MeOH
THF
12.6
14.9
26.2
26.7
27.7
31.2
36.8
53.3
—
(1.0)
47.2
37.3
6.08 113
33.0 124
7.52 116
36.6 113
4.20 190
2.4 (1.9)
19.3 (18.8)
3.7 (3.7)
14.4 (15.4)
3.1 (3.1)
71.7
MeCN
Et2O
47
(44)
10 Me2CO
11 MeCN
12 Anisole
5.6 (6.4)
3.1 (3.1)
13.5 (15.8)
17.9 (7.6)
20.5 132
36.6 113
4.33 68.6
–23.3 (1a + 2) 2.8
–24.7 (1a + 2) 4.2
13 ClH2CCH2Cl –29.4 (1a + 2) 8.9
10.4
78.8
14 CCl4
15 CCl4
16 CCl4
17 n-Hexane
–39.6 (1b + 2) 19.1
–41.0 (1b + 3) 20.5
–37.8 (1a + 3) 17.3
–45.2 (1a + 2) 24.7
38
38
38
(48)
(48)
(48)
2.24 108.0
2.24 108.0
2.24 108.0
1.88 167.4
51.9 (89)
aThe values of PMV of lithium perchlorate are taken from ref. 13. bCalcu-
lated for solvents no. 1–10 from equation (7) and no. 11–17 from equation (8).
cFrom refs. 2 and 16. Data in parentheses calculated from the ratio b/e. dFrom
ref. 16. eFrom refs. 2 and 19.
¶(1/e)
¹
∆Vcor. = –20.5 + 0.49×106
.
(8)
¶p
– 60 –

Mendeleev Commun., 2008, 18, 59–61
7
8
9
V. D. Kiselev, A. I. Konovalov, T. Asano, G. G. Iskhakova, E. A. Kashaeva,
Note that the change of PMV of lithium perchlorate in the
solvents of low polarity (no. 5, 7 and 9, Table 2) located with
nearly the same slope on the zwitter-ionic line (Figure 2, line b).
M. S. Shihaab and M. D. Medvedeva, J. Phys. Org. Chem., 2001, 14, 636.
V. D. Kiselev, E. A. Kashaeva and A. I. Konovalov, Tetrahedron, 1999,
55, 1153.
Ch. Reichardt, Solvents and Solvent Effects in Organic Chemistry,
VCH, Weinheim, 1988.
This work was supported by the Russian Foundation for
Basic Research (project no. 05-03-32583a), the US Civilian
Research and Development Foundation (CRDF), and the Ministry
of Science and Education of the Russian Federation (grant
no. REC-007).
10 W. L. Orr and N. Kharasch, J. Am. Chem. Soc., 1953, 75, 6030.
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Izv. Akad. Nauk, Ser. Khim., 2007, 477 (Russ. Chem. Bull., Int. Ed.,
2007, 56, 494).
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Received: 13th June 2007; Com. 07/2962
– 61 –