Reaction mechanism studies of solvolytic displacement of chloride from phosphorus

Article abstract of DOI:10.1080/10426500701734943

The extended Grunwald-Winstein equation is applied to solvolytic displacement at phosphorus. Previous studies of the solvolyses of phosphorochloridates (RO)2POCl, Ph2POCl and [(CH3)2N]2POCl are extended to cyclic phosphorochloridates, with five and six me

Full text of DOI:10.1080/10426500701734943

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Reaction Mechanism Studies
of Solvolytic Displacement of
Chloride from Phosphorus
a
a
b
Han Joong Koh , Suk Jin Kang & Dennis N. Kevill
a
Department of Science Education , Chonju
National University of Education , Chonju, Korea
b
Department of Chemistry and Biochemistry ,
Northern Illinois University , DeKalb, Illinois, USA
Published online: 21 Jun 2008.
To cite this article: Han Joong Koh , Suk Jin Kang & Dennis N. Kevill (2008) Reaction
Mechanism Studies of Solvolytic Displacement of Chloride from Phosphorus,
Phosphorus, Sulfur, and Silicon and the Related Elements, 183:2-3, 364-368, DOI:
10.1080/10426500701734943
To link to this article: http://dx.doi.org/10.1080/10426500701734943
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Phosphorus, Sulfur, and Silicon, 183:364–368, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701734943
Reaction Mechanism Studies of Solvolytic Displacement
of Chloride from Phosphorus
1
1
2
Han Joong Koh, Suk Jin Kang, and Dennis N. Kevill
1
Department of Science Education, Chonju National University of
Education, Chonju, Korea
2
Department of Chemistry and Biochemistry, Northern Illinois
University, DeKalb, Illinois, USA
The extended Grunwald-Winstein equation is applied to solvolytic displace-
ment at phosphorus. Previous studies of the solvolyses of phosphorochloridates
(
RO) POCl, Ph POCl and [(CH ) N] POCl are extended to cyclic phosphorochlo-
2
2
3 2
2
ridates, with five and six membered rings. Both kinetic and product ratio mea-
surements are made. The equation is also applied to kinetic studies of the
solvolyses of Ph PCl. The l and m sensitivity values are compared with pre-
2
vious values and with values for attack at sulfur, to give useful mechanistic
information.
Keywords Chlorodiphenylphosphine; cyclic phosphorochloridates; extended Grunwald-
Winstein equation; solvolysis
INTRODUCTION
1
The extended Grunwald-Winstein equation is used to correlate the spe-
2
cific rates of solvolysis reactions in terms of solvent ionizing power and
3
solvent nucleophilicity . In Equation (1), k and k0 represent the specific
rates of solvolysis in a given solvent and in the
log(k/k0) = lNT + mYx + c
(1)
standard solvent (80% ethanol), respectively; l represents the sen-
sitivity to changes in solvent nucleophilicity (NT); m represents the
H.J.K thanks Chonju National University of Education for the granting of a sabbatical
leave during the time that a portion of this research was performed. Acknowledgement
is made to the donors of the Petroleum Research Fund, administered by the American
Chemical Society, for partial support of this research.
Address correspondence to Dennis N. Kevill, Department of Chemistry and Bio-
chemistry, Northern Illinois University, Dekalb, Illinois, 60115-2862 USA. E-mail:
dkevill.niu.edu
364

Reaction Mechanism Studies of Solvolytic Displacement of Chloride
365
sensitivity to changes in solvent ionizing power (YX for a leaving group
X); c represents a constant (residual) term.
3
The scale was initially developed for nucleophilic attack at sp -
2
4
carbon but it has been successfully applied to attack at sp -carbon
and at phosphorus5 and sulfur. The solvolyses at phosphorus have
included rate and product studies with dimethyl phosphorochlori-
date as substrate, and a direct displacement (SN2) reaction was
proposed as the pathway.6 In the present paper, the study is ex-
tended to the solvolyses of two cyclic phosphorochloridate esters, 2-
chloro-1,3,2-dioxaphospholane-2-oxide (1) and 2-chloro-5,5-dimethyl-
–7
8
1
,3,2-dioxaphosphorinane-2-oxide (2). The study of diphenylphosphinyl
7
chloride was also explained in terms of SN2 attack and this has been ex-
tended to the phosphorus(III)-containing chlorodiphenylphosphine (3)
(
Scheme 1).
SCHEME 1
KINETIC STUDIES AND CORRELATION OF THE SPECIFIC
RATES
The specific rates of solvolysis of 1 and 2 have been measured using
a rapid response conductivity apparatus, in a wide range of solvents,
including binary mixtures of water with 2,2,2-trifluoroethanol (TFE)
◦
and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The values at 25.0 C for
1
◦
and the values at 50.0 C for 2 are determined using ethanol and
methanol and their aqueous binary mixtures plus mixtures of water
with acetone, TFE, and HFIP. These values are used in correlations
3
2,9
using eqn. 1 against literature values for N and YCl. The sensitivity
T
values together with measures of the goodness-of-fit are reported in
Table I, where they are compared with literature values for solvolytic
displacements of chloride from sulfur (VI) or phosphorus (V).
10
There have been strong indications that nucleophilic attack at a
phosphorus within a 5-membered ring shows significant pathway dif-
ferences to other situations. A large1 (sometimes enormous ) rate
acceleration is frequently observed and, whereas inversion is normally
observed, reactions of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholane-2-
1,12
11
1
2
oxide give predominantly retention of configuration. The present
analyses give no support for any special effects during solvolyses, with

3
66
H. J. Koh et al.
TABLE I Grunwald-Winstein Correlations for Attack at
Phosphorus and Sulfur
na
T C
o
lb
mb
Rc
Substrate
(
(
(
Me2N)2POCld
31
18
28
27
28
27
25
37
19
26
25.0
25.0
25.0
25.0
25.0
50.0
25.0
25.0
25.0
25.0
1.20 ± 0.07
1.27 ± 0.14
1.17 ± 0.07
1.42 ± 0.10
1.16 ± 0.06
1.03 ± 0.05
1.25 ± 0.09
1.10 ± 0.17
1.28 ± 0.05
1.17 ± 0.06
0.69 ± 0.04
0.47 ± 0.08
0.56 ± 0.03
0.54 ± 0.07
0.60 ± 0.03
0.43 ± 0.02
0.46 ± 0.06
0.61 ± 0.04
0.64 ± 0.03
0.70 ± 0.04
0.958
0.941
0.966
0.956
0.974
0.974
0.954
0.959
0.988
0.975
d
MeO)2POCl
d
MeO)2PSCl
d
Ph2POCl
1
2
3
p-MeOC6H4SO2Cl
i-PrSO2Cle
Me2NSO2Cle
e
a
b
c
Number of data points; from Eq. (1); correlation coefficient;
d
e
from Ref. 7; and from Ref. 8.
the l and m values for 1 being similar to those for other entries within
Table I. Also, a comparison of the specific rates (Table II) shows 1 only
modestly more reactive than the open-chain analog.
The phosphorus(III)- containing compound Ph2PCl (3) not only
shows l and m values very similar to the phosphorus(V)- containing
7
compound Ph2POCl but the actual specific rates in a given solvent are
◦
very similar. For example, at 25.0 C, the specific rates in ethanol are
−3
−1
−3 −1
8
.09 × 10
s
and 7.02 × 10
s
and, in 97% HFIP, they are 6.16 ×
−
6
−1
−6 −1
10
s
and 5.91 × 10
s , respectively. Studies with the replacement
of phenyl by other groupings are needed to explore the generality of this
◦
TABLE II Specific Rates of Solvolysis at 25.0 C,
in a Few Typical Solvents, for Dimethyl
Phosphorochloridate, 1 and 2
4
10 k[(CH3O)2POCl]a
4
b
4
b
Solvent
10 k(1)
10 k(2)
1
8
1
8
9
5
7
00%EtOH
0%EtOH
00%MeOH
0%MeOH
7%TFE
2.96
28.5
11.3
49.6
0.036
18.6
0.71
37.8
328
48.7
480
1.13
259
55.4
0.13c
0.27c
0.12c
—
—
—
0%TFE
0%HFIP
—
a
b
c
From ref. 6; this Work; and extrapolated using 3 or 4
values determined at higher temperatures.

Reaction Mechanism Studies of Solvolytic Displacement of Chloride
367
a
◦
TABLE III Selectivity Values (S) in Solvolyses of 2 at 50.0 C
Solventb:
S(2):
90E 70E 50E 20E 90M 70M 40M 20M 80T 70T 50T
1.97 1.43 1.37 2.01 2.20 1.91 1.32 1.66 0.23 0.09 0.07
S[(CH3O)2POCl]: 0.36c 0.56c 0.85c
a
b
From Eq.. (3); E, M, T represent ethanol, methanol, and TFE, with its percentage
component given (remainder water); ethanol-water and methanol-water on
◦
c
◦
volume-volume basis at 25.0 C and TFE-water on weight-weight basis; at 25.0 C.
observation. The acid catalysis frequently observed in substitutions at
phosphorus (III)13 appears not to operate.
PRODUCT SELECTIVITY
The reactions of 1 were sufficiently fast for appreciable reaction to occur
during mixing. For 2 infinity titers could be used to determine the prod-
uct partitioning [Equation (2)]. These values can be used in conjuction
with the composition of a water-alcohol mixture to
arrive at selectivity values (S) defined as in Equation 3. Values for the
selectivity are
[
[
ester in product][H O in solvent]
2
acid in product][ROH in solvent]
S =
(3)
compared to those previously observed for dimethyl phosphorochlori-
date in Table III. The values in aqueous ethanol and aqueous methanol
for the open-chain compound are slightly below unity as opposed to
slightly above unity for 2. However, the variation in the energy differ-
ence between the two pathways of Equation 2 would only have to be
small to account for these changes in S value. As expected, TFE does
not compete effectively against water.
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[
[
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3
68
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[
[
[
[
[
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[
[
10] A. J. Kirby and S. G. Warren, The Organic Chemistry of Phosphorus (Elsevier, New
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[
[
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[
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