Reduction of o-iodosobenzoate ion by sulfides and its oxidative regeneration

Article abstract of DOI:10.1002/(sici)1099-1395(199910)12:10<758::aid-poc200>3.0.co;2-a

o-Iodosobenzoate and o-iodoxybenzoate ion (IBA and IBX, respectively) are turnover catalysts of hydrolyses of phosphonofluoridates and non-toxic simulants. Reactions of IBA with phosphonothioates are stoichiometric because sulfides (e.g. 4-methoxybenzenet

Full text of DOI:10.1002/(sici)1099-1395(199910)12:10<758::aid-poc200>3.0.co;2-a

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 12, 758–764 (1999)
Reduction of o-iodosobenzoate ion by sul®des and its
oxidative regeneration
Clifford A Bunton,* Houshang J Foroudian and Nicholas D Gillitt
Department of Chemistry, University of California, Santa Barbara, California, 93106, USA
Received 24 May 1999; revised 13 July 1999; accepted 16 July 1999
ABSTRACT: o-Iodosobenzoate and o-iodoxybenzoate ion (IBA and IBX, respectively) are turnover catalysts of
hydrolyses of phosphonofluoridates and non-toxic simulants. Reactions of IBA with phosphonothioates are
stoichiometric because sulfides (e.g. 4-methoxybenzenethiol) reduce IBA to o-iodobenzoate ion. Oxidants, e.g.
HSO5 , as OXONE, and magnesium peroxyphthalate, MPPA, regenerate IBA and gradually oxidize it to IBX, which
eventually decomposes. The procedure was tested on hydrolyses of p-nitrophenyl diphenylphosphate (pNPDPP) and
4-nitrobenzenesulfonyl fluoride, 1, catalyzed by IBA, and the catalyzed hydrolysis of 1 was examined. Some of the
oxidation products of 4-methoxybenzene thiol were identified by 1H NMR spectroscopy and oxidative decomposition
of IBX was monitored. Periodate ion slowly oxidized o-iodobenzoate ion to IBA and IBX. Copyright 1999 John
Wiley & Sons, Ltd.
KEYWORDS: o-iodosobenzoate; o-iodoxybenzoate; sulfonyl fluorides; dephosphorylation; peroxymonosulfate;
peroxyphthalate; hydrolysis
INTRODUCTION
react as nucleophiles and oxidants, e.g. hypochlorite ion
and N-chloroamines,1 but they are aggressive reagents.
Peroxy acids, e.g. HSO5 , are good oxidants at sulfur,5
and peroxycarboxylate ions are effective nucleophiles
towards phosphoryl centers,6 but these reactions occur at
different pH values. The combination of a turnover
nucleophile, e.g. IBA, and a peroxy acid may therefore
provide a system which oxidizes at sulfur, and reacts
nucleophilically at phosphorus. The requirements are that
the oxidant be effective towards sulfur compounds and
capable of re-oxidizing o-iodobenzoate ion, IB, to IBA
and/or IBX. Peroxy acids are obvious candidates for this
purpose, but periodate ion oxidizes sulfides7 and might
also oxidize IB.
Nerve agents, both phosphonofluoridates, e.g. GB (Sarin)
and phosphonothioates, e.g. VX, react readily with
nucleophiles.1 o-Iodoso- and o-iodoxybenzoate, IBA
and IBX respectively, are effective nucleophiles towards
toxic phosphonofluoridates and nontoxic model com-
pounds, e.g. triarylphosphates.2,3 The reactions of IBA
and IBX are catalytic, whereas many nucleophiles react
stoichiometrically. However, the reaction of IBA with
phosphonothioate simulants of VX is not catalytic
because IBA is reduced by thiols and their derivatives.4
The chlorosulfide blister agents, e.g. HD and Mustard
Gas, do not react bimolecularly with nucleophiles or
bases except in forcing conditions, but, like VX, they are
readily decontaminated by oxidation.1 A few compounds
We planned to use HSO5 , as OXONE (2KHSO5
KHSO4 K2SO4),5 or magnesium peroxyphthalate,
MPPA, as oxidants, the latter is convenient because its
peroxy anion is an effective dephosphorylating agent.6 p-
Nitrophenyl diphenylphosphate (pNPDPP) is often used
as a model for the toxic fluoridates in reactions with
nucleophiles, but its low solubility in aqueous media is a
disadvantage. We therefore examined 4-nitrobenzene-
sulfonyl fluoride, 1, as a model substrate towards IBA.
ꢀClCH2CH2†2S
HD
*Correspondence to: C. A. Bunton, Department of Chemistry,
University of California, Santa Barbara, CA 93106, USA. E-mail:
bunton@chem.ucsb.edu
Copyright 1999 John Wiley & Sons, Ltd.
CCC 0894–3230/99/100758–07 $17.50

REDUCTION OF o-IODOSOBENZOATE
759
Table 1. 1H NMR chemical shifts.a
IBA
IB
8.19, d, d; 7.98, t, d; 7.89, d; 7.75, t
7.87, d; 7.42, t; 7.40, d; 7.10, t, d
4-O2NC6H4SO2F
4-O2NC6H4SO3
4-MeOC6H4SH
(4-MeOC6H4S)2
MPPA
Phthalate ion
C6H5I
8.60, d; 8.37, d
7.80, d; 7.08, d
7.30, d; 6.79, d
7.37, d; 6.91, d
7.68, m, 3H; 7.55, t, 1H
7.59, m; 7.47, m
7.69, d; 2H; 7.41, t, 1H; 7.17, t, 2H
a
In H2O–t-BuOH 7:3 v/v with TSP in D2O as external reference.
Vicinal coupling constants are 7–8 Hz, and long-range coupling
constants, where observed, are ca. 1 Hz.
This reaction can be followed spectrophotometrically and
products can be monitored by using NMR spectroscopy.8
Some of the results of this work were presented at the
ERDEC Scientific Conference on Chemical and Bio-
logical Defense Research, November 1998,8 where
Professor Moss told one of us of his new work in this
area.9 This work materially extends understanding of
reactions of IBA and IBX with thioates and their
hydrolysis products in cationic micelles.4
Figure 1. Hydrolysis of 4-nitrobenzenesulfonyl ¯uoride
catalyzed by IBA in water, pH 8.5, and 25.0°C
Reduction of IBA and its regeneration by HSO5
1
We used H NMR spectroscopy to monitor reduction of
3
IBA (5 Â 10 M) by 4-methoxybenzene thiol, 4, and the
subsequent oxidation of o-iodobenzoate ion, IB. Unless
specified all NMR reactions were carried out in H2O–t-
BuOH 7:3 v/v, 0.1 M NaHCO3, nominal pH = 7.5. This
solvent was used to solubilize the sulfide and some of its
oxidation products. We use protio solvents with signal
suppression and only monitored signals in the aromatic
region. There is overlap between 1H NMR signals of the
iodine compounds, but in order of decreasing chemical
shift the multiplicities are: for IBA, d, t, d, t, and for IBX,
RESULTS AND DISCUSSION
Hydrolysis of 4-nitrobenzenesulfonyl ¯uoride, 1
The IBA catalyzed hydrolysis of 1 was followed at pH
8.5 over a range of [IBA] (Fig. 1). The first-order rate
constant, kobs, with respect to 1 varied linearly with
[IBA]. The data point with 1 in excess over IBA fit on the
plot (Fig. 1), indicating that IBA is a turnover catalyst.
There was a small contribution from a spontaneous
1
d, d, t, t. The H NMR signals of the sulfur compounds
are all doublets, which assists identification of products
and intermediates.
3
1
hydrolysis. With [IBA] >10 M we saw an induction
The H NMR signals of IBA disappeared within the
period (<7 s) before the intermediate, 3 (Scheme 1) came
into steady state.
time of signal measurement (8–10 min); on addition of
3
5 Â 10 M thiol, 4, signals of IB appeared and those of 4
The overall reaction (Scheme 1) is shown with a
mechanism similar to that observed in dephosphoryla-
tion, where breakdown of the intermediate involves
nucleophilic attack on the iodoso residue.2,12 The second-
order rate constant is 20.4 Æ 0.5 M 1 s 1 at 25.0°C (Fig.
1, r = 0.998). The pKa of o-iodosobenzoic acid is 7.35 in
water13 and an apparent value of 7.25 was estimated from
kinetics of reactions in cationic micelles.14
were replaced by signals of the disulfide, 5 (Table 1), and
signals of an intermediate, 6a, at 7.31 and 6.44 ppm, d
[Fig. 2 (A)]. There was signal overlap, but signals had the
expected multiplicity. We then added 0.025 M HSO5 and
signals of IBA reappeared with signals of 4-methoxy-
benzenesulfonate, 7, at 7.79 and 7.04 ppm, d. Signals of
intermediate, 6a, correspondingly decreased (Fig. 2), but
those of a second intermediate, 6b, appeared at 7.54 and
Scheme 1. Hydrolysis of 4-nitrobenzenesulfonyl ¯uoride catalyzed by IBA in water, pH 8.5, and 25.0°C
Copyright 1999 John Wiley & Sons, Ltd. J. Phys. Org. Chem. 12, 758–764 (1999)

760
C. A. BUNTON ET AL.
3
3
Figure 2. Reduction of IBA (5 Â 10 M) by 4-methoxybenzene thiol (5 Â 10 M) at 21°C. (A) Initial reduction. (B) After addition
of HSO5 . Chemical shifts of the identi®ed compounds are indicated and * indicates signals of intermediates, 6a,b
Ar = 4 MeOC6H4
7.01 [Fig. 2 (B)]. Within the time required for running the
spectrum (ca. 10 min) we saw no signals of IBX, but IB
was not completely oxidized back to IBA [Fig. 2 (B)] and
there was overlap with a signal of 4.
The oxidation of IB by HSO5 is illustrated by the data
in Table 2 and Fig. 3 (A) with no sulfur compounds, and
within 10 min of mixing. Within this time there was
formation of IBA and IBX, depending on ‰HSO5 Š, but no
loss of aromatic iodo compounds. In a separate experi-
ment with 0.01 M IB and 0.102 M HSO5 the IB signal
disappeared within 65 min at 21°C and there were signals
The spectrum changed with time and after 1 day at
21°C signals of IBA had decreased and those of IBX
appeared at 8.26, d, 8.06, t and 7.91, t, ppm, each
1
corresponding to H, although there is overlap with the
signal of IBA at 8.18 ppm. The signals of the inter-
mediate sulfur compounds, 5 and 6a,b, disappeared and
were replaced by those of the sulfonate, 7. The signal-to-
noise ratio deteriorated with respect to IBA and IBX as
they gradually decomposed, but the spectrum did not
change within a further 3 days, probably because HSO5
had been used up. We then added 0.25 M HSO5 and all
signals of aromatic iodine compounds disappeared, but
those of 4-methoxybenzenesulfonate, 7, remained.
a
Table 2. Oxidation of IB by HSO5
[HSO5 ], M
[HSO5 ]/[IB]
wIB
wIBA
wIBX
0.0104
0.0174
0.0338
0.0846
0.51
0.85
1.65
4.13
0.82
0.24
—
0.18
0.63
0.78
0.71
—
0.13
0.22
0.29
—
a
In H2O–t-BuOH 7:3 v/v, pH 8.6, 0.1 M NaHCO3.
J. Phys. Org. Chem. 12, 758–764 (1999)
Copyright 1999 John Wiley & Sons, Ltd.

REDUCTION OF o-IODOSOBENZOATE
761
Figure 3. (A) Reaction of IB (0.021 M) with 0.017 M HSO5 after 20 min at 21°C. (B) Reaction of IBA (0.02 M) with equimolar
MPPA after 41 min at 21°C
of IBA and IBX in the ratio 1:1.8. On the basis of
comparison of signal areas with that of mesitoate ion the
combined concentrations of IBA‡IBX were 53% of the
original [IB], showing that IBX was decomposing before
its complete formation from IBA. Even with modest
concentration of HSO5 (ca. 0.1 M) the decomposition of
IBX (and IBA) is inconveniently rapid.
hydrolysis is relatively slow in solutions of OXONE.
Qualitative observations on the hydrolysis of pNPDPP
are described in the Experimental section.
Reactions of peroxyphthalate ion
We established regeneration of IBA as a catalyst of the
hydrolysis of 4-nitrobenzene sulfonyl fluoride. We
reduced 0.01 M IBA with 0.01 M 4-methoxybenzene
thiol, 4, then added 0.05 M HSO5 followed by 0.01 M
sulfonyl fluoride. Within the time required to collect the
19F NMR spectrum (8–10 min), the signal of the sulfonyl
fluoride had disappeared and we saw only that of F.
Control experiments confirmed that the spontaneous
Magnesium peroxyphthalate, MPPA, behaves similarly
to HSO5 in its reactions. When 0.01 M 4-methoxyben-
zene thiol, 4, was mixed with equimolar MPPA, signals
of 4 disappeared and new signals (doublets) of disulfide,
5, appeared at 7.37 and 6.91 ppm, and those of the
sulfonate, 7, appeared at 7.80 and 7.08 ppm. We did not
see signals at 7.31 and 6.44 ppm of the intermediate, 6,
which was formed in the reaction with HSO5 (Fig. 2),
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 758–764 (1999)

762
C. A. BUNTON ET AL.
Table 3. Oxidations by MPPAa
ates in the course of reaction. Initially thiol, 4, was
oxidized to disulfide, 5, by IBA, and intermediate, 6a,
appeared, probably by oxidation of disulfide, 5. On
addition of HSO5 a second intermediate, 6b, appeared at
the expense of 6a. (Fig. 2), and sulfonate, 7, was formed.
A possible reaction sequence is shown in Scheme 2, in
which disulfide is oxidized to the thiol arenesulfinate, 6a,
and HSO5 oxidizes 6a to the thiol arenesulfonate, 6b.
The sulfonate, 7, could be generated by hydrolyses of
6a,b, which would reform thiol, 4, and 4 would be
recycled oxidatively. Alternatively the esters 6a,b could
be oxidized to anhydrides which would be rapidly
hydrolyzed to an arenesulfinate ion (which would then
be rapidly oxidized), or to 7. Our hypothesis that 6a is a
sulfinate and 6b a sulfonate is consistent with the latter
having higher chemical shifts (Fig. 2), but we recognize
that these assignments are speculative.
Yield (mol %)b
Time
[MPPA]/[IB] [MPPA]/[IBA] (min)
IB
IBA
IBX
1c
41
48
31
0.44 0.44 0.12
0.09 0.68 0.23
1.97c
10d
—
—
0.24
a
In H2O–t-BuOH 7:3 v/v, pH 7.4, 0.1 M NaHCO3, 21°C;
b Yields are calculated from relative areas of the 1H NMR signals and
that of mesitoate ion;
c
0.021 M IB;
d 0.01 M IBA.
a
Table 4. Oxidation of IB by IO4
Time (h)
0
0.68
9.94
2.95
25.7
147
103 [IB] (M) 10.6
9.65 6.78 (3)b 1.22 (0.7)b
1
We did not see H NMR signals of 6a,b in reactions
a
3
In H2O, pH 6.1, 21.4°C with initially 0.1 M NaIO4 and 5 Â 10
M
with MPPA (Fig. 3), consistent with the formation of
sulfinate or sulfonate esters, which would react rapidly
with a nucleophilic peroxyphthalate dianion to readily
give hydrolyzable mixed anhydrides. These reactions
would not occur with HSO5 which is a weak nucleophile.
The postulated reaction sequence is shown in Scheme
2, although the overall reactions probably include
hydrolyses of 6a,b. The scheme includes the observed
chemical shifts, ppm, (Fig. 2).
mesitoate ion;
b Values in parentheses are [IBA]/[IBX].
and some of the disulfide could have formed by air
oxidation.
o-Iodobenzoate ion is oxidized to IBA and then to IBX
by MPPA [Table 3, and Fig. 3 (B)]. As in other
experiments, extents of the reaction were estimated from
signal areas relative to that of mesitoate ion. In the
experiment illustrated in Fig. 3 (B) there was some
residual peroxyphthalate with a signal at ca. 7.70, m, and
another signal under that of phthalate ion.
With equimolar reactants there was no loss of aromatic
iodine compounds, but the situation was different with
more concentrated MPPA and IBA (Table 3). With
0.01 M IBA and 0.1 M MPPA we saw no 1H NMR signals
of IBA after 31 min at 21°C, and areas of signals of IBX
were only 24% of those of the original IBA (Table 3).
The degradation of IBX by MPPA was greater than with
HSO5 under similar conditions (Tables 2 and 3). Signals
in the aromatic region disappeared and that of t-BuOH
was so large that we have no information on possible
structures of the aliphatic products. Oxidation of ethane
thiol by IBA gave the disulfide, rather than the sulfonate,
as the final product.9
Decomposition of IBX
We did not observe quantitative formation of IBX
1
starting from either IBA or IB and oxidant, because H
signals in the aromatic region decreased with time and
finally disappeared, indicating that IBX reacts with both
HSO5 and MPPA. Reaction probably involves further
oxidation at iodine, although such an intermediate must
be short-lived, because we saw no new 1H NMR signals.
We considered a reaction in which a hypervalent
iodine compound is hydrolyzed to salicylate ion, but we
1
did not see its H NMR signals at 7.88, d, 7.40, t, and
6.92, m, and there was no diminution of these signals
relative to those of mesitoate, when salicylate ion,
0.02 M, was left with 0.2 M HSO5 for 1 day at 21.4°C
in H2O–t-BuOH 7:3 v/v, pH 7.4. Iodobenzene was
oxidized by HSO5 to iodoxybenzene [Fig. 3 (A)]. In the
reaction conditions used for salicylate ion, and with
mesitoate ion as a quantitative marker, there was 70%
reaction after 1 h at 21°C, with no loss of aromatic
signals and after 3.7 h we saw only signals of iodoxy-
benzene at 8.04, d, 2H 7.78, m, 3H. With 0.02 M reactants
Oxidation of 4-methoxybenzene thiol
The final oxidation product, 4-methoxybenzene sulfonate
ion, 7, survived oxidation,15 but we detected intermedi-
!
!
!
!
2ArSH
ArSSAr
ArSO:SAr
ArSO2:SAr
2ArSO3
4; ꢀ ˆ 7:30; 6:79
5; ꢀ ˆ 6:91; 7:37
6a; ꢀ ˆ 7:31; 6:44
6b; ꢀ ˆ 7:54; 7:01
7; ꢀ ˆ 7:79; 7:04
Scheme 2
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 758–764 (1999)

REDUCTION OF o-IODOSOBENZOATE
763
Scheme 3
in the above conditions we saw the same 1H NMR signals
and 3%, 13% and 13% reaction after 0.1, 2 and 22 h,
respectively, probably because HSO5 gradually decom-
posed. There was no decrease in the 1H aromatic signals
relative to that of mesitoate ion.
These observations indicate that the acyl residue is
involved in the decomposition of IBX. The carbonyl
group in the cyclic form of IBX (and IBA) is conjugated
with the aromatic residue and a hypervalent iodo
compound generated by oxidation of IBX could lose its
aromatic character. Possible reactions, shown in Scheme
3 would generate dienes which should react with peroxy
acids to form aliphatic compounds. We could not identify
1H NMR signals of these hypothetical products because
of the very large signal of the CH3 groups of t-BuOH, and
we have no evidence on the step-wise or concerted nature
of the hypothetical reactions shown in Scheme 3.
phosphorus (V) esters and sulfonyl fluorides at mildly
alkaline pH in the presence of sulfides. In these
conditions peroxyphthalate ion is an effective depho-
sphorylating agent. Periodate ion oxidizes o-iodobenzo-
ate ion, but this reaction is too slow to be practically
useful. There is considerable decomposition of aromatic
iodine compounds with [peroxyacid] >0.1 M.
EXPERIMENTAL
Materials
Magnesium peroxyphthalate (Lancaster), OXONE (Al-
drich), IBA (ACROS), iodobenzene (TCI), o-iodoben-
zoic acid (ACROS), and 4-methoxybenzene thiol
(ACROS), 4-nitrobenzenesulfonyl fluoride (Aldrich)
were used as received and pNPDPP had been used in
earlier work.6 The peroxy contents of OXONE and
peroxyphthalate, determined iodometrically, were 80%
and 73% of theoretical, respectively, and concentrations
were corrected accordingly. Solutions were made up with
redistilled, deionized water in H2O–t-BuOH 7:3 v/v to
allow solubilization of the substrates and oxidation
products of the sulfides.
Reaction of periodate ion and IB
Periodate ion oxidizes aryl sulfides,7 although it is less
reactive than HSO5 in these reactions,5b,16 and we
examined its reaction with IB at 21.4°C. The experiment
was made with 0.1 M NaIO4 and 0.011 M IB in H2O,
initial pH = 6.4, and 0.005 M mesitoate ion as reference.
The solution was unbuffered because NaHCO3 salted out
the reactants. The reaction was slow, t1/2 ꢁ 412days, but 1H
NMR signals of IB decreased and those of IBA and IBX
appeared. With time there was some precipitation,
probably of o-iodoso and o-iodoxy benzoic acid. From
the relative peak areas of IB and mesitoate ion kobs was
Kinetics
4
The reaction of 10 M 4-nitrobenzenesulfonyl fluoride
(1) in water was followed in an HP 8451 diode array
spectrophotometer at 25.0°C at pH 8.5 (0.1 M NaHCO3
buffer). The sulfonyl fluoride was added in 30 ml MeCN
to 3ml of kinetic solution. The reaction was followed at
240–280 nm and in this range values of first-order rate
constants, kobs, varied by <2%, except for the fastest
reactions where values were within 5%. There is an
isobestic point at 258 nm. The turnover catalysis is shown
6
1
2 Â 10
s
and the reaction was too slow to be
practically useful. There was slow oxidation by KIO4 but
reactants were not completely soluble.
CONCLUSIONS
by the values of 103 kobs
s
1, at 240, 275 and 280 nm,
4
4
Both HSO5 and peroxyphthalate ion allow IBA and IBX
to be used as turnover catalysts of hydrolysis of activated
respectively: 1 Â 10 M 1, 1 Â 10 M IBA— 4.16,
4
4
4.24, and 4.25; and 2 Â 10 M 1, 1 Â 10 M IBA—
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 758–764 (1999)

764
C. A. BUNTON ET AL.
4.44 (4.87), 4.32 (4.95), and 4.42 (4.95). Values in
varied slightly with changes in the reaction medium
because we used external references, but there was no
effect on signal multiplicities or relative peak areas. In
most compounds that we examined, hydrogens in a given
molecule were in 1:1 ratios, which assisted identification.
The 1H NMR signals of the stock compounds are given in
Table 1.
4
parentheses were with 1.04 Â 10 M IBA.
We attempted to examine the IBA catalyzed hydrolysis
of pNPDPP in the presence of PhSH and HSO5 (as
OXONE). In MeCN–H2O 3:7 v/v, pH 8.5 (nominal),
5
0.1 M NaHCO3 buffer and 2.4 Â 10 M pNPDPP, the
second-order rate constant for reaction with IBA was
1
1
0.56 M
1.0 M
s
at 25.0°C, which is similar to the value of
1
1
s
at pH 7.0 in water.10 We could not obtain
good kinetic data spectrophotometrically in the presence
of OXONE and PhSH, because precipitates formed,
although absorbance at 400 nm increased as expected.
We made qualitative observations on the deactivation
of IBA using thioanisole, 2, and its regeneration on
addition of HSO in H2O–t-BuOH 7:3 v/v, pH 8.5, 0.1 M
Acknowledgements
This work was supported by the US Army Research
Office. We are grateful to Professor R. A. Moss for
information on the reaction of IBA and IBX with thiols
and for his prepublication manuscript.
NaHCO3. When510 M pNPDPP was added to 10
M
4
3
IBA at ca. 21°C the solution became yellow within a few
3
minutes. Addition of 10 M 2 stopped color develop-
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3
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NMR spectroscopy
Spectra were monitored typically in H2O–t–BuOH 7:3
v/v on a Varian Unity (INOVA) instrument, 400 MHz
for 1H, in isotopically normal solvents with a D2O
insert, TSP as external reference, and suppression of the
1H signal of H2O. As a result of signal suppression we
saw some ‘spikes’ in the spectra, which appeared in the
absence of reactants and were easily identified. The
breaks in NMR spectra were due to these adventitious
‘spikes’. There was a large signal of CH3 of t-BuOH and
therefore we only monitored signals in the aromatic
region. We used mesitoate (2,4,6-trimethylbenzoate) ion,
ꢀH = 6.86 ppm, s, as a calibrating standard for estimating
extents of reaction.11 The 19F signal of 4-O2NC6H4SO2F
was at 68.5 ppm and that of F was at 112.4 ppm,
relative to CF3Cl ꢀ = 0 ppm measured with CF3CO2H as
an external reference, ꢀ = 76.55 ppm.
1
There was overlap of some H signals of the iodo
compounds and of the oxidation products, but in all
conditions there were sufficient 1H signals to allow
quantification of iodo compounds, based on comparison
of peak areas with that of mesitoate ion. Chemical shifts
15. Y. C. Yang, L. L. Szafraniec, W. T. Beaudry, C. A. Bunton and A.
Kumar, J. Chem. Soc. Perkin Trans. 2, 607 (1997).
16. A. Blasko, C. A. Bunton and S. Wright, J. Phys. Chem., 97, 5435
(1993).
Copyright 1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 758–764 (1999)