Alkene Addition Reactions
A R T I C L E S
atom transfer radical cyclization reactions proceeded much more
effectively in water than in the traditional organic solvents.
were determined from the experimental growth curves of the absorption
at ca. 320 nm measured over a range of substrate concentrations,
according to eq 1. Rate constants for the alkene that did not form easily
observed products were obtained using ca. 0.0019 M sodium 4-(2-
1
6
In contrast to the relative lack of data in the organic literature,
water has long been a popular solvent for carrying out free-
2
1
propenyl)benzoate (2c) as a spectroscopic “probe” according to eq 2.
Preparation of Samples for Laser Flash Photolysis. IR SO Na (601
mg) was dissolved in 50 mL H O to make a 0.027 M stock solution.
17,18
radical polymerizations,
especially of fluorinated mono-
1
9
f
3
mers. Although most fluoropolymers are now made by
dispersion, emulsion, or suspension polymerizations in aqueous
media, there are still problems associated with this field that
make studies of absolute rates of fluoroalkyl radicals in water
of some importance. Undertaking structure-activity relation-
ships for propagation (radical addition) and chain transfer (atom,
especially H-transfer) processes of fluorinated radicals will allow
fluoropolymer scientists to develop superior initiators and
surfactants for polymerization of fluoroolefins and thus allow
them to better control the relative rates of propagation and chain
2
All the alkene substrate solutions (ca. 0.03 M) were made freshly and
used within 1.5 h after being prepared.
Using a pipet, a series of quartz cuvettes were charged with 1.5 mL
of the stock solution of IR
were then degassed by bubbling N
min. During this time, the alkene solution was prepared and degassed
by bubbling with N for 20-30 min. Varying portions of alkene solution
f
3
SO Na and sealed with rubber septa. They
2
through the solution for 10-15
2
were then added to the cuvettes using a microliter syringe. The mixtures
were shaken well, and they were then, one by one, subjected to laser
pulses at 308 nm from an excimer laser, each sample undergoing 7-9
individual flashes in order to obtain an average pseudo-first-order
growth curve for generation of the benzylic radicals, which were
monitored at ca. 320 nm by UV. The first-order rate constants were
obtained from the fitting curve with the best R value, and these rate
constants were plotted against the concentrations of alkene to give the
second-order rate constants
transfer and, hence, control the molecular weight of the
polymers.20
This initial report provides the first absolute rate data for
alkene addition processes of a fluorinated radical in water,
information which can be related to propagation processes in
polymerization of perfluoroolefins. We will soon be reporting
the first absolute rate data for H-abstraction processes of this
fluorinated radical, the rate constants of which should be related
to chain transfer processes in such polymerizations.
Sodium 5-Iodo-3-oxaoctafluoropentanesulfonate (1). NaOH (2.97
g, 74.1 mmol) was dissolved in 20 mL of H O in a 100 mL round-
2
bottom flask equipped with a condenser and stirring bar. To the flask
was added tetrafluoro-2-(tetrafluoro-2-iodoethoxy)ethanesulfonyl fluo-
Summary
2 2 2 2 2
ride (ICF CF OCF CF SO F) (15.8 g, 37.1 mmol). The reaction mixture
19
In the current study, absolute rate constants of ‚RfSO3Na
radical addition to a series of water-soluble alkenes bearing
carboxylate ion functionality in aqueous solution were measured
by LFP experiments. As was the case for previous studies in
F113 solution, thermodynamic, polar, and steric effects were
all observed to be important factors in determining the dynamics
of these addition reactions.
With comparison of the relative rates for the series with a
similar series that had been studied in F113, it was apparent
that steric and thermodynamic factors were similar and es-
sentially independent of the nature of solvent. On the other hand,
the rate constants for the series in water, although nearing
diffusion control, were all considerably larger than those of their
counterparts in F113, with rate factors of 3-9-fold being
observed, despite the expected retardation of the additions by
Coulombic repulsion. We conclude that these rate enhancements
most probably derive from more effective stabilization of the
polar transition state for addition of the electrophilic perfluoro-
n-alkyl radical to alkenes by the polar solvent, water, than by
the nonpolar organic solvent, F113.
was stirred overnight at 95 °C. F NMR showed the complete
consumption of the starting material. The pH of this solution was 7.
Vacuum was applied to remove H O, giving a solid residue. A 20 mL
2
volume of ethanol was added to the solid to dissolve compound 1,
leaving NaF undissolved. The NaF was removed by filtration, and the
filtrate was concentrated on a rotary evaporator to give a white solid
residue. After recrystallization from water, the title compound was
obtained in 87% yield. Elemental analysis indicated the compound to
be ICF
CFCl in C
br s, 2F), -118.4 ppm (br s, 2F); MS (FAB) 469 (M + Na). Anal.
Calcd for C INaSO : C, 10.35, H, 0.43. Found: C, 10.36, H, 0.26.
2
CF
2
OCF
2
CF
2
3
SO Na‚H
O: mp 151 °C, dec; 19F NMR (D
O/
2 2
3
6 6
D
) δ -69.2 (br s, 2F), -83.0 (t, 2F, J ) 12.1 Hz), -86.4
(
H F
4 2 8
5
Unsaturated Carboxylic Acids. 4-Ethenylbenzoic acid, 4-phenyl-
3-butenoic, and 4-pentenoic acid were obtained from Aldrich and used
without further purification to prepare the sodium carboxylate salts.
4-(2-Propenyl)benzoic acid and (4-ethenylphenyl)acetic acid were
prepared according to literature procedures.2 4-(1-Propenyl)benzoic
acid was prepared by a procedure analogous to that used for 4-(2-
propenyl)benzoic acid. Details of the procedures used for these
3,24
1
13
preparations, as well as H and C NMR spectra of the compounds,
are contained in the Supporting Information.
General Procedure for Preparation of Sodium Salts 2a-f of
Unsaturated Carboxylic Acids. The following procedure is typical
of those used to prepare the sodium salts of the unsaturated carboxylic
Experimental Section
Time-Resolved Laser Flash Photolysis. The apparatus and proce-
1
2
1,22
acids (individual details, including H NMR spectra of the salts, can
dures have been described in detail elsewhere.
The rate constants
be found in the Supporting Information):
for the reactions that resulted in the formation of the benzylic radicals
Sodium p-Ethenylbenzoate (2a). p-Ethenylbenzoic acid (0.2348 g,
1.58 mmol) was dissolved in 5 mL of methanol in a 25 mL round-
bottom flask equipped with a magnetic stir bar. Two drops of
phenolphthalein solution (0.1% in ethanol) were added to the flask.
NaOH solution (0.96 M in methanol) was added to the reaction mixture
dropwise until the color of the mixture turned to light pink. Using a
rotary evaporator, methanol was removed, giving a solid residue. The
(
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Fujimoto, H. J. Am. Chem. Soc. 2000, 122, 11041-11047.
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G. C., Ledwith, A., Russo, S., Sigwalt, P., Eds.; Elsevier: Oxford, U.K.,
1
988; Vol. 3, p 261.
(
18) Van Doremaele, G. H. J.; Schoonbrood, H. A. S.; German, A. L. In
ComprehensiVe Polymer Science, first supplement ed.; Aggarwal, S. L.,
Russo, S., Eds.; Elsevier: Oxford, U.K., 1992; p 41.
(
19) Putnam, R. E. In ComprehensiVe Polymer Science; Eastmond, G. C.,
Ledwith, A., Russo, S., Sigwalt, P., Eds.; Elsevier: Oxford, U.K., 1988;
Vol. 3, p 321.
(22) Kazanis, S.; Azarani, A.; Johnston, L. J. J. Phys. Chem. 1991, 95, 4430-
(20) Feiring, A. E.; Krespan, C. G.; Resnick, P. R.; Smart, B. E. U.S. Patent
4435.
5
,182,342, 1993.
(23) Letsinger, R. L.; Hamilton, S. B. J. Am. Chem. Soc. 1959, 81, 3009.
(24) Wright, S. W.; McClure, L. D. Org. Prep. Proced. Int. 1994, 26, 602-
605.
(21) Paul, H.; Small, R. D., Jr.; Scaiano, J. C. J. Am. Chem. Soc. 1978, 100,
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J. AM. CHEM. SOC.
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