New and surprising experimental results from the oxidation of sulfinic and sulfonic acids

Article abstract of DOI:10.1021/jp981713v

Thiourea, (H₂N)₂C=S, aminoiminomethanesulfinic acid, H₂N(HN=)CSO₂H (AIMSA), and aminoiminomethanesulfonic acid, H₂N(HN=)CSO₃H (AIMSOA) are all oxidized by mild oxidizing agents to a sulfate and an organic residue. AIMSA and AIMSOA are the postulated intermediates in the oxidation pathway of thiourea to sulfate. The oxidation of AIMSOA is accompanied by a cleavage of the C-S bond to form sulfate. Surprisingly, freshly prepared solutions of AIMSOA are oxidized by the common oxidants (oxyhalogens and halogens) at rates that are much slower than oxidation rates of AIMSA by the same oxidants. These results seem to suggest that AIMSOA may be structurally different from AIMSA and that the decomposition of AIMSOA to HSO₃^- is the prerequisite to its oxidation. The oxidation pathway of AIMSA to SO₄^2- also proceeds through the formation of HSO₃^- and not predominantly through AIMSOA.

Full text of DOI:10.1021/jp981713v

6786
J. Phys. Chem. A 1998, 102, 6786-6792
New and Surprising Experimental Results from the Oxidation of Sulfinic and Sulfonic
Acids
Sergei V. Makarov
Department of Physical Chemistry, Institute of Chemistry and Technology,
IVanoVo, Engels Str. 7, 153460 Russia
Claudius Mundoma, John H. Penn, Serge A. Svarovsky, and Reuben H. Simoyi*
Department of Chemistry, West Virginia UniVersity, Morgantown, West Virginia 26506-6045
ReceiVed: March 31, 1998; In Final Form: May 21, 1998
Thiourea, (H2N)2CdS, aminoiminomethanesulfinic acid, H2N(HNd)CSO2H (AIMSA), and aminoimino-
methanesulfonic acid, H2N(HN))CSO3H (AIMSOA) are all oxidized by mild oxidizing agents to a sulfate
and an organic residue. AIMSA and AIMSOA are the postulated intermediates in the oxidation pathway of
thiourea to sulfate. The oxidation of AIMSOA is accompanied by a cleavage of the C-S bond to form
sulfate. Surprisingly, freshly prepared solutions of AIMSOA are oxidized by the common oxidants
(oxyhalogens and halogens) at rates that are much slower than oxidation rates of AIMSA by the same oxidants.
These results seem to suggest that AIMSOA may be structurally different from AIMSA and that the
decomposition of AIMSOA to HSO3- is the prerequisite to its oxidation. The oxidation pathway of AIMSA
2-
-
to SO4 also proceeds through the formation of HSO3 and not predominantly through AIMSOA.
Introduction
Step 1 forms the sulfenic acid, which is further oxidized in the
second step to form the sulfinic acid. The sulfonic acid formed
The ongoing process of improving sulfur-abatement proce-
dures from industrial activity can only be improved if the
reaction mechanisms of sulfur reactions are better elucidated.
Furthermore, the physiological role of sulfur-based amino acids
can also be rationalized if sulfur chemistry is more well-known.2
We recently established a series of research studies that focused
primarily on the kinetics and mechanisms of the oxidations of
sulfur compounds by halogens, oxyhalogens, and transition
metal ions in an effort to address this very problem.3
The compilation of our work resulted in a general mechanism
that involves a sulfur center being oxidized, in excess oxidant,
via a nonradical two-equivalent-transfer process that produces
sulfate as a final product.4-10 For small organic sulfur
compounds, this process gives, successively, the sulfenic,
sulfinic, and sulfonic acids. Further oxidation of the sulfonic
acid will result in the cleavage of the C-S bond to give sulfate
and a urea-type residue, >CdO.4 The rate-determining step
had been established as the initial oxidation of the thio
compound to the unstable sulfenic acid. This general mecha-
nism, applicable to a variety of these small organic sulfur
compounds, can be illustrated by our proposed mechanism for
the oxidation of thiourea by aqueous bromine:8
in step 3 is finally oxidized to form SO42- in the last step, which
is accompanied by a cleavage of the C-S bond.
Although this general mechanism can explain most experi-
mental observations, there were some experimental results that
could not be rationalized by this mechanism: (a) in a compara-
tive study of the oxidation of a sulfide, sulfinic acid, and sulfonic
acid the oxidation of the sulfinic acid was the fastest while the
oxidation of the sulfonic acid was the slowest;11 (b) the oxidation
of thiourea by several oxyhalogens was bistable and produced
sulfate in a clock reaction type oxidation to give a lateral
instability that produced a traveling wave of acid and sulfate.12
Generally, the oxidation of a sulfur center has presented
nonlinear and exotic dynamics that include clock reaction
mechanisms,13 chemical oscillations,14 pH oscillations,15 and
pattern formation.16 A good grasp of the oxidation mechanisms
of a sulfur center is essential for the elucidation of the observed
nonlinear dynamics.
The reaction of chlorite with thiourea and substituted thioureas
is bistable and autocatalytic and can produce spatial inhomo-
geneities in acid concentrations in unstirred aqueous environ-
ments.17 It had been accepted that the rapid formation of the
acid is from the step that involves the cleavage of the C-S
bond in the sulfonic acid intermediate, aminoiminomethane-
sulfonic acid (AIMSOA), to form sulfate:
step 1:
step 2:
step 3:
step 4:
Br2(aq) + (H2N)2CdS + H2O f
H2N(NH)CSOH + 2H+ + 2Br-
NH2(NH)CSO3H + H2O f
Br2(aq) + H2N(NH)CSOH + H2O f
H2N(NH)CSO2H + 2H+ + 2Br-
(NH2)2CO + SO42- + 4H+ + 2e- (R1)
Further experiments have shown that sulfonic acids, in
general, are inert and slow-reacting. Organic aminosulfonic
acids, especially, are so stable that the C-S bond cannot be
cleaved to give sulfate even in the presence of very strong
oxidizing agents.18 The sulfinic acid, aminoiminomethane-
sulfinic acid (AIMSA, a precursor to AIMSOA in the oxidation
chain), is extremely reactive. It is readily oxidized by very mild
Br2(aq) + H2N(NH)CSO2H + H2O f
H2N(NH)CSO3H + 2H+ + 2Br-
Br2(aq) + H2N(NH)CSO3H + 2H2O f
(H2N)2CdO + SO42- + 4H+ + 2Br-
S1089-5639(98)01713-7 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/29/1998

Oxidation of Sulfinic and Sulfonic Acids
J. Phys. Chem. A, Vol. 102, No. 34, 1998 6787
vis spectrophotometer, and faster reactions were followed on a
Hi-Tech Scientific SF-DX2 stopped-flow spectrophotometer.
Reactions with Iodine. AIMSA reacts quite rapidly with
aqueous iodine. In excess AIMSA the reaction is complete in
less than 10 s (see Figure 1A). The stoichiometry of the reaction
is
2I2 + H2N(HNd)CSO2H + 3H2O f
(H2N)2CdO + SO42- + 4I- + 6H+ (R2)
The reaction is autoinhibitory, and iodide strongly inhibits the
reaction.3,20 In other reactions involving oxidation by iodine,
-
the formation of the relatively inert electrophile I3 has been
established as the autoinhibitory mechanism:20
I2 + I- h I3
(R3)
-
On the other hand, the oxidation of AIMSOA by aqueous
iodine is extremely slow (Figure 1B). In freshly prepared
AIMSOA solutions the reaction quickly shuts down after a few
minutes. The rate of the reaction is strongly affected by the
age of the AIMSOA solutions used. Freshly prepared AIMSOA
solutions produced the slowest rates (Figure 1B, trace a). Figure
1B shows a series of reactions performed with progressively
aged solutions. Trace i shows a solution aged for 270 min.
The reaction is now very fast. Most of the reaction is already
complete by the time the stopped-flow spectrophotometer
captures the absorbance trace.
Reactions with Bromine. Aqueous bromine reacts quite
rapidly with both AIMSA and AIMSOA (parts A and B of
Figure 2). However, the reaction with AIMSA is so much faster
and is over in about 0.01 s while the corresponding reaction
with AIMSOA will take about 0.5 s. The reaction with AIMSA
did not show any observable dependence on acid. On the other
hand, acid strongly inhibits the Br2-AIMSOA reaction (Figure
2B). The reaction does not proceed under conditions of
[H+]0 > 1.0 M. The stoichiometries of the reactions are the
same as those for the corresponding iodine reactions: 2:1 ratio
for the AIMSA reaction and a 1:1 ratio for the AIMSOA
reaction.
Figure 1. (A) Reaction of aminoiminomethanesulfinic acid, AIMSA,
with iodine in excess of AIMSA. [I2]0 ) 5.5 × 10-4 M; [AIMSA]0 )
6.65 × 10-3 M. The solutions were aged for (a) 0, (b) 84, (c) 139, (d)
186, and (e) 227 min. (B) Oxidation of aminoiminomethanesulfonic
acid, AIMSOA, with aqueous iodine. [I2]0 ) 1.1 × 10-3 M; [AIMSOA]0
) 1.1 × 10-2 M. The solutions were aged for (a) 2, (b) 14, (c) 34, (d)
45, (e) 70, (f) 118, (g) 138, (h) 168, and (i) 270 min.
Reactions with Chlorite. AIMSA reacts very rapidly with
chlorite over a very wide pH range.21 The reaction is followed
by the absorbance of chlorine dioxide at 360 nm. AIMSA is
initially oxidized by chlorite to give HOCl:
H2N(HNd)CSO2H + ClO2- + H+ f
H2N(HNd)CSO3H + HOCl (R4)
oxidizing agents (e.g., I2) to sulfate and urea.3 AIMSOA has
not yet been characterized and very little is known about its
reactivity.
We present, in this manuscript, a series of experiments that
suggest that there may be some fundamental differences in the
bonding, structure, and reactivity of AIMSA and AIMSOA. By
way of comparison, reactivities of hydroxymethanesulfinate
(HMSA) and hydroxymethanesulfonate (HMSOA) are also
discussed.
The chlorine dioxide is formed from an extraneous oxyhalogen
reaction22 in which the HOCl produced in reaction R4 rapidly
-
oxidizes ClO2 to produced ClO2:
2ClO2- + HOCl + H+ f 2ClO2(aq) + Cl- + H2O (R5)
The rate of production of chlorine dioxide is proportional to
the rate of reaction R4. Figure 3 shows the formation of
chlorine dioxide whose oligooscillatory behavior in this reaction
has been previously explained.23 There was no visible reaction
on a time scale of hours for the reaction of AIMSOA with
chlorite. If the reported initial step of the chlorite-AIMSA
reaction is reaction R4, we should expect similar rates for the
two reactions.
Experimental and Results
Bromine, iodine crystals, formaldehyde, aminoiminomethane-
sulfinic acid, sodium hydroxymethanesulfinate, and sodium
hydroxymethanesulfonate (Aldrich) were used without further
purification. Aminoiminomethanesulfonic acid (AIMSOA) was
prepared from a standard literature procedure.19 Conventional
kinetics experiments were performed on a Lambda 2S UV-
Hydroxymethanesulfinic Acid (HMSA) and Hydroxy-
methanesulfonic Acid (HMSOA) Reactions. A comparison

6788 J. Phys. Chem. A, Vol. 102, No. 34, 1998
Makarov et al.
(A)
Figure 3. Reaction of chlorite and AIMSA showing the rapid and
oligooscillatory production of chlorine dioxide. [ClO2-]0 ) 5.0 × 10-3
M; [AIMSA]0 ) 5.0 × 10-3 M. No observable reaction was detected
with AIMSOA.
(B)
solutions with formaldehyde (Figure 4B). Figure 4B has an
overwhelming excess of HMSOA (at least 10-fold excess),
ensuring that all iodine would be consumed at the end of the
reaction. The reaction had not reached its half-life even after
5 h. Figure 4B also shows that aged solutions with formalde-
hyde react faster than those solutions that are freshly made. The
aged solutions gave a very fast initial reaction with the quantity
of iodine consumed in this first step being proportional to the
aging period.
Reactions with Bromine. Reaction of HMSOA with bromine
is slow, but a corresponding reaction with HMSA is very fast.
Figure 5shows that the HMSA reaction is too fast to be captured
on the time scale of the HMSOA reaction. The HMSA reaction,
on a time scale of 0.02 s, is shown in the Figure 5 inset.
Reactions with Chlorite. The mechanism for the oxidation
of HMSA by chlorite was recently reported.24 The reaction is
very fast and shows oligooscillatory behavior in the concentra-
tions of chlorine dioxide (see Figure 6insert). The postulated
first step of the oxidation is
Figure 2. (A) Extremely rapid oxidation of AIMSA by aqueous
bromine. Calculated initial bromine absorbance was 0.26. The reaction
is too fast to be observed on the Hi-Tech DX2 stopped-flow spectro-
photometer. [Br2]0 ) 1.8 × 10-3 M; [AIMSA]0 ) 3.25 × 10-2 M. (B)
Oxidation of AIMSOA with aqueous bromine at variable concentrations
of acid. [Br2]0 ) 6.5 × 10-3 M; [AIMSOA]0 ) 5.0 × 10-2 M. [H+]0
values are the following: (a) 4.0 M; (b) 0.5 M; (c) 0.3 M; (d) 0.125
M; (e) 0.01 M; (f) 0.
ClO2- + HOCH2SO2H + H+ f
HOCl + HOCH2SO3H (R6)
This is then followed by the oxidation of HOCH2SO3H to give
sulfate and the organic residues:
ClO2- + HOCH2SO3H f
was also made between the reactions of HMSA and HMSOA.
The relationship between HMSA and HMSOA is the same as
that for AIMSA and AIMSOA. The oxidation of HMSA is
very facile and rapid.24,25 The products, in excess oxidants, are
sulfate with either formaldehyde, formic acid, or carbon dioxide,
depending on the strength and abundance of the oxidant. It
has been postulated that the oxidation of HMSA passes through
HMSOA as an intermediate before proceeding to give prod-
ucts.24,25
Reaction with Iodine. Oxidation of HMSOA by iodine is
extremely slow (Figure 4A), but a corresponding oxidation of
HMSA is complete within the dead-time of the instrument. The
HMSOA-iodine reaction shown in Figure 4A had a half-life
of over 1000 s. The reactions are even slower in reaction
HOCl + SO42- + HCHO + H+ (R7)
The oxyhalogen reaction, reaction R5, is also responsible for
the production of chlorine dioxide, and thus, the formation of
chlorine dioxide can be used as an indicator of the rate of
reaction R4.
Figure 6 shows that the chlorite oxidation of HMSA is much
faster than the oxidation of HMSOA. If reaction R6 is the rate-
determining step (as has been assumed), then the rate of
oxidation of HMSOA should be faster than that for HMSA. If
reaction R7 is the rate-determining step, we should have a
reverse situation.

Oxidation of Sulfinic and Sulfonic Acids
J. Phys. Chem. A, Vol. 102, No. 34, 1998 6789
(A)
Figure 5. Reactions of HMSOA and HMSA with aqueous bromine.
The reaction of HMSA is so fast that it cannot be captured by the Hi-
Tech DX2 stopped-flow spectrophotometer on the 1 s time scale. The
inset shows the HMSA reaction on a 0.02 s time scale. [Br2]0 ) 5.0 ×
10-4 M; [HMSA]0 ) 1.1 × 10-4 M.
(B)
Figure 4. (A) Reaction of HMSOA with aqueous iodine. [I2]0 ) 5.0
× 10-4 M; [HMSOA]0 ) 5.0 × 10-4 M. (B) Effect of formaldehyde
in the iodine HMSOA reaction. [I2]0 ) 1.1 × 10-3 M; [HMSOA]0 )
1.1 × 10-2 M. Trace a is from fresh solution of HMSOA, and trace b
is from solutions aged for 180 min.
Figure 6. Comparison between the reactions of chlorite with HMSOA
and with HMSA. The reaction with HMSA is so fast that it is not
possible to catch the first stage of the reaction on the time scale of the
HMSOA reaction. This detail is shown in the inset. [ClO2-]0 ) 1.1 ×
10-3 M; [HMSOA]0 ) [HMSA]0 ) 1.1 × 10-3 M.
The data shown in Figures 1-6 indicate that either (a) the
oxidation of sulfinic acids does not pass through a sulfonic acid
intermediate or (b) there is a fundamental difference in the
bonding and structure of sulfinic and sulfonic acids.
Further Experimental Data: Effect of Formaldehyde. Only
the iodine oxidations were tested for the effects of formaldehyde.
The substrates used were AIMSA and AIMSOA. The rapid
oxidation of formaldehyde by aqueous bromine did not allow
the same set of experiments to be set up for bromine oxidations.
Figure 7A shows a series of experiments run with 0.01 M
formaldehyde. This concentration is comparable to the con-
centration of AIMSOA in solution (0.011 M). The aged
solutions reacted more rapidly. The effect of aging is not as
large as in the case with solutions without formaldehyde.
Figure 7B shows another series of experiments run with
overwhelming excess of formaldehyde (12.3 M). In this case,
aging the reaction solutions does not seem to have any effect
on the rate of reaction.
Discussion
HMSA is a well-known industrial chemical that is used in
the textile industry. HMSOA has been implicated in atmo-
spheric chemistry as a pathway for the stabilization of sulfur
dioxide.26 It is prepared from the reaction of formaldehyde and
sodium bisulfite27 and not from the oxidation of a sulfinic acid.
CH2(OH)2 + HSO3- h CH2(OH)SO3- + H2O (R8)
The adduct HMSOA is much more stable in acidic conditions
and quickly decomposes when above pH 7. The equilibrium
constant of this reaction has been established as 7.82 × 106
M-1 at pH 6.27 The rate of attainment of equilibrium when

6790 J. Phys. Chem. A, Vol. 102, No. 34, 1998
Makarov et al.
HMSOA. Addition of formaldehyde suppresses the dissociation
of HMSOA to give HSO3-. The reaction is expected to be
retarded by formaldehyde. This retardation has been observed
in our experiments (see Figure 4).
Reactions of AIMSA and AIMSOA. The solid-state
structure of AIMSA is well-known.28 The structure of AIMSOA
was recently obtained in our laboratory.29 In its zwitterionic
form AIMSOA is strictly planar with a tetrahedral sulfur atom
with three nearly equivalent S-O bonds. Because of its efficient
packing, the density of AIMSOA is 1.948 g cm-3
. Both
structures of AIMSA and AIMSOA show extensive hydrogen
bonding.28,29 The biggest difference between the structures of
AIMSA and AIMSOA lies in the C-S bond lengths. AIMSA’s
C-S bond length is anomalously long at 0.1867 nm, while that
of AIMSOA is 0.1815 nm. The geometry around the sulfur
atom in AIMSA is planar, while that in AIMSOA is tetrahedral.
It is expected that in aqueous solution the AIMSOA zwitterion
will be more stable than the corresponding zwitterion from
AIMSA. The stronger electron-withdrawing properties of the
-
-
-SO3 group over the -SO2 group as well as the lower
basicity of the -SO3- oxygens on AIMSOA make the AIMSOA
zwitterion more preferable in solution over the AIMSA zwit-
terion. The zwitterion is susceptible to nucleophilic attack from
the solvent because of the formally positive charge resident on
the carbon atom. This very small difference in the sulfinic and
sulfonic acids imparts a vast difference in their reactivities.
Effect of Acid. Acid stabilizes the zwitterion of AIMSOA.
We could not detect products of AIMSOA decomposition (NH4+
and HSO3-) under conditions of pH less than 1.00 even after
incubating the AIMSOA solutions for more than 2 days.29
-
Production of HSO3 will increase the rate of consumption of
Br2 in the AIMSOA-Br2 reaction (see Figure 2B). This
especially holds under conditions where [AIMSOA]0 . [Br2]0.
Under these conditions, complete decomposition of the AIM-
SOA is not necessary for the generation of sufficient HSO3- to
consume bromine. Initial bromine absorbances were the same
for all reaction solutions shown in Figure 2B. The amount of
bromine rapidly consumed at the beginning of the reaction is
-
proportional to the amount of HSO3 in solution.
Figure 7. (A) Reaction traces at 465 nm of the oxidation of AIMSOA
by iodine in the presence of 1.1 × 10-2 M HCHO. [I2]0 ) 1.1 × 10-3
M; [AIMSOA]0 ) 1.1 × 10-2 M. The age of the solutions is as
follows: (a) 2 min; (b) 40 min; (c) 260 min; (d) 363 min. (B) Reaction
traces with overwhelming excess of formaldehyde, 12.3 M. [I2]0 ) 1.1
× 10-3 M; [AIMSOA]0 ) 1.1 × 10-2 M. The age of the solutions is
as follows: (a) 2 min; (b) 30 min; (c) 70 min; (d) 120 min; (e) 300
min.
HSO3- + Br2(aq) + H2O f
SO42- + 2Br- + 3H+ [fast] (R10)
The trace with no acid, trace f, has enough HSO3- to consume
all the bromine during the initial very fast reaction phase.
Data in Figure 1B can also be explained by evoking the
decomposition of the AIMSOA zwitterion. Longer-aged solu-
starting with pure HMSOA is about 45-75 min at this pH.27
Upon dissolving HMSOA in water, we expect a slow equilib-
rium process to occur in which formaldehyde and bisulfite are
formed. The oxidation of bisulfite to sulfate is fast:
-
tions contain more HSO3 and hence consume iodine much
more rapidly. Figure 1A shows that aging the AIMSA solution
has no significant effect on the rate of reaction. AIMSA, upon
being dissolved, will predominantly exist in neutral form with
a CdN double bond:
HSO3- + H2O f SO42- + 3H+ + 2e-
(R9)
If all the HMSOA decomposed to give the bisulfite, then the
observed oxidation rate upon addition of oxidant would be fast.
If, however, HMSOA remained in the adduct form, then it will
be oxidized at a slower rate. The effect of aging our reagent
solutions is to increase the bisulfite and formaldehyde concen-
trations in solution. The longer-aged solutions attain a higher
concentration of free bisulfite. Figure 7A clearly shows the
effect of aging on our solutions.
(R11)
Effect of Formaldehyde. Formaldehyde is involved in the
decomposition of the AIMSOA zwitterion through a secondary
reaction. Addition of HCHO decreases the amount of free
bisulfite (see reaction R8), and thus, we expect a retardation of
the reaction. This is indeed the case with the data in Figure
7A, which can be compared with data in Figure 1A. In these
Effect of Formaldehyde. Formaldehyde is involved in the
equilibrium R8 that determines the formation of the adduct

Oxidation of Sulfinic and Sulfonic Acids
J. Phys. Chem. A, Vol. 102, No. 34, 1998 6791
-
data, the amount of HCHO added is not in overwhelming excess
over the AIMSOA. The rate of reaction is, however, reduced
by a factor of 100 because of the addition of formaldehyde.
However, the age of the solution still affects the rate of reaction,
with the aged solutions reacting faster because of decomposition
of AIMSOA.
The HSO2 species is readily oxidized to bisulfite:
HSO2- + H2O f HSO3- + 2H+ + 2e-
(R17)
-
HSO3 is next also easily oxidized to sulfate (reaction R9).
In Figure 7B the reaction had an overwhelming excess of
HCHO; [HCHO]0/[AIMSOA]0 > 1000. Thus, all the HSO3
Conclusion
-
In the crystalline form, small organic sulfinic and sulfonic
acids have nearly the same structure and exist in their zwitter-
ionic forms. However, upon dissolving in polar solvents, the
sulfinic acid zwitterion loses its stability to its neutral form.
The sulfonic acid zwitterion decomposes to form HSO3-, which
can be quickly oxidized to sulfate. The experimental data
presented in this manuscript show that sulfonic acids are very
stable in solution and decompose only very slowly (cf. half-
life of approximately 3 days). Their decomposition can give
an anomalous rate of oxidation depending upon the length of
time the solutions have been aged. The differences in the rates
of reaction, however, need further attention. The accepted
general mechanism of a sulfinic acid being oxidized to the
sulfonic acid before formation of sulfate may need to be revised.
It does appear that the oxidation of a sulfinic acid may be
produced is consumed by the added HCHO. The age of the
reaction no longer becomes a factor, and the reaction ceases to
respond to it. This is the observation in Figure 7B.
Possible Reaction Pathway for the Oxidation of AIMSA. The
following simple experiment was performed. A 1:1 mole ratio
of AIMSA to bromine was mixed and allowed to stand for more
than 2 h. The expected result was the oxidation of AIMSA to
AIMSOA only as expected from the following stoichiometry:
(NH2)2CSO2 + Br2 + H2O f
(NH2)2CSO3 + 2Br- + 2H+ (R12)
If the oxidation of AIMSA forms AIMSOA as an intermedi-
ate, then we expect very little or no sulfate production at all. A
test for sulfate proved that there was nearly quantitative sulfate
production based on the stoichiometry
-
proceeding through the HSO2 and HSO3-, which then are
oxidized to sulfate. There is need for more extensive experi-
mental data and analysis.
2Br2 + (NH2)2CSO2 + 3H2O f
(H2N)2CdO + SO42- + 4Br- + 6H+ (R13)
Acknowledgment. We acknowledge the National Science
Foundation, through Grant CHE-9632592 for financial support.
with the bromine concentrations being limiting. This experiment
indicates that the oxidation of AIMSA proceeds through more
than one possible pathway with one of them not involving
AIMSOA.
The preparation of AIMSOA, however, had been affected
by the use of a mild oxidizing agent peracetic acid.19 This
oxidation was also carried out in chilled solutions to slow the
reaction and to obtain a quantitative yield of AIMSOA. Product
dependency on the strength of the oxidizing agent is very
common. For example, peracetic acid can oxidize cysteine to
cysteine sulfinic acid while aqueous bromine produces cysteine
sulfonic acid and hydrogen peroxide produces the cysteine dimer
cystine.30
References and Notes
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(R14)
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The positive charge is delocalized around the two nitrogen atoms
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