hydrogen phthalate (Mathieson, Coleman/Bell). 18-Crown-6
ether (Parish Chemicals) was recrystallized from acetonitrile and
stored over P2O5 in vacuo prior to use. Dicyclohexyl-18-crown-6
ether, [2.2.2]cryptand and [2.1.1]cryptand were Aldrich products
which were used without further purification.
water bath coupled to a McPherson monochromator and Can-
Tech transient recorder. Spectral traces were displayed on a
Hewlett-Packard oscilloscope; the data were treated directly
by computer. The kmax of the phenoxide ion being monitored
was obtained in a separate experiment, prior to the kinetic
determinations. Run solutions were generally made up just
before the kinetic experiments; the kinetic experiments were
performed in replicate and were followed for ca. 10 half-lives.
First-order constants, kobs, were reckoned from linear plots of
ln(A∞ − At) vs. time. The kobs values are presented as in the
supplementary information.
Synthesis of substrates
The substituted aryl methyl phenyl phosphinate esters investi-
gated in this study were synthesized from the parent phenols and
phenyl methyl phosphinyl chloride (13), the latter compound
being obtained through a series of known reactions according
to eqn. (11).
Acknowledgements
Support for this research by grants from the Natural Sciences
and Engineering Research Council of Canada (NSERC) is
gratefully acknowledged. KGA is the recipient of the Queen’s
University Graduate Student Fellowship.
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(11)
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◦
1
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Kinetic method
The rates of reaction in anhydrous EtOH were investigated
spectrophotometrically by monitoring the formation of the
appropriate phenoxide ion at 25 ◦C under pseudo first-order
conditions, with substrate concentrations in at least 20-fold
deficit of the base. Kinetic measurements were performed, in
part, using a Beckman DU-8 or Perkin-Elmer Lambda-5 spec-
trophotometer, equipped with thermostatted cell holders which
maintained the temperature in the 10 mm quartz cuvette at 25
0.1 ◦C. Relatively fast kinetics experiments were measured using
a Hi-Tech stopped-flow module equipped with a thermostatted
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1 4 7 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 4 6 8 – 1 4 7 5