Stoichiometric and catalytic oxidation of organic substrates with in-situ-generated peracids

Full text of DOI:10.1021/jo960457k

J . Org. Chem. 1996, 61, 5693-5696
5693
sulfoxide.13 These substituent variations and kinetic
studies have led to a mechanism5 involving nucleophilic
attack on the peracid by the sulfide or sulfoxide with
simultaneous proton transfer to the carbonyl.
Stoich iom etr ic a n d Ca ta lytic Oxid a tion of
Or ga n ic Su bstr a tes w ith in -Situ -Gen er a ted
P er a cid s
The oxidation of thioethers using a polymer-supported
peroxyacid has been reported.14 A 1:1 ratio of tetrahy-
drothiophene or L-methionine and oxidant yielded both
the corresponding sulfoxides and sulfones. Higher yields
of the sulfones were obtained when a 2:1 oxidant-to-
substrate ratio was used.
Russell S. Drago,* Alfredo L. M. L. Mateus, and
Douglas Patton
Department of Chemistry, University of Florida,
Gainesville, Florida 32611-7200
Transition metal-catalyzed oxidations by peroxyacids
have received little attention. Thioethers are oxidized
to the corresponding sulfones in the presence of a
catalytic amount of Mn(acac)3 using H2O2 in acetic acid.15
The reactive oxidant was suggested to be peroxyacetic
acid. In the presence of a catalytic amount of the
catalyst, [Fe(CH3CN)4[ClO4]2, m-chloroperoxybenzoic acid
oxidized diphenyl sulfide and diphenyl sulfoxide to the
corresponding sulfoxide and sulfone, with 51-71% ef-
ficiencies in peroxyacid utilization.16
Reactions of peroxy acids with alkenes result in ep-
oxidation and hydroxylation reactions.17 The mechanism
for epoxidation reactions has been discussed in detail
recently.18 The epoxide, formed by nucleophilic attack
by the alkene, may react with the carboxylic acid formed
from the peroxyacid to yield the monocarboxylate of the
diol, which forms the diol upon hydrolysis. Acid-
catalyzed ring-opening of epoxides also yield diols. Per-
benzoic acid gives good yields of epoxide with octenes and
other high molcular weight olefins.4 Monoperphthalic
acid has also been used to epoxidize alkenes, but reac-
tions are generally slower. The use of peracetic acid in
epoxidation reactions generally is carried out in acetic
acid and produces diols and their monoacetates. Good
yields of epoxides are obtained2,3 in inert solvents.
Subsequently, it was shown that good yields of epoxides
resulted if the reaction was carried out at 20-25 °C, short
reaction times were employed, and strong acids were
avoided.
Received March 5, 1996
In tr od u ction
The replacement of hypochlorite and alkyl hydroper-
oxides as oxidants by hydrogen peroxide is being driven
by environmental and economic considerations, respec-
tively. The byproduct when peroxide behaves as an
oxidant is water. Though peroxide is a potent oxidant,
it is very slow reacting and needs to be activated.
One possible route to activation of H2O2 involves its
conversion to peroxyacids. Organic peroxyacids are more
effective oxidants than H2O2 and are reported to oxidize
a variety of substrates under mild conditions.1-5 Some
of the peroxyacids used as oxidants include peroxyacetic
acid, m-chloroperoxybenzoic acid, monoperoxyphthalic
acid, peroxymaleic acid, and trifluoroperoxyacetic acid.
As the electron-withdrawing nature of the substituent
increases, the peracid becomes more reactive. Peroxy-
acids have been used exclusively as stoichiometric oxi-
dants.
Organic sulfides are important substrates to oxidize.
One important application involves oxidation of bis(2-
chloroethyl) sulfide, HD, or mustard for decontamination
and stock pile destruction.6 When less reactive organic
peroxyacids are used, thioethers are converted to sulfox-
ides, and the further oxidation of sulfoxides to the
corresponding sulfones occurs at a slower rate.7-9 Per-
oxymaleic acid, prepared by the reaction of maleic
anhydride and 90% H2O2 in an inert solvent, oxidized10
diallyl sulfoxide to the corresponding sulfone in an 87%
yield in methylene chloride at 0 °C.
This work is concerned with the in-situ generation of
organic peroxyacids from carboxylic acids and anhydrides
with aqueous H2O2 in the solvent 1-methyl-2-pyrrolidi-
none. Conditions are examined to make peracid forma-
tion catalytic in the carboxylic acid. This oxidant system
is studied for the oxidation of both sulfides and alkenes
with and without transition metal cocatalysts.
The oxidation of p,p-dichlorobenzyl sulfide11 and diphe-
nyl sulfide12 using a series of para-substituted peroxy-
benzoic acids11 showed an increased oxidation rate when
electron-withdrawing groups were used on the peracid
and a decreased oxidation rate with electron-donating
groups. In both acidic and alkaline media, substitution
of electron-withdrawing groups on the oxidant led to an
increase in the rates of oxidation of p-tolyl methyl
Resu lts a n d Discu ssion
Su lfid e Oxid a tion s. When maleic anhydride (MAnh)
(1.6 × 10-2 mol) and 30% aqueous H2O2 are added to 10
mL of N-methylpyrrolidinone (NMP), a very efficient
oxidant is produced for sulfide oxidation. A 0.2 M
solution of n-butyl sulfide is completely oxidized in 1 h
at ambient temperature, as shown in Table 1. By using
a 10-fold excess of maleic anhydride and varying the
(1) Uemura, S. In Comprehensive Organic Synthesis; Trost, B. M.,
Ed.; Pergamon Press: Oxford, 1991; Vol. 7, p 758.
(2) Sawaki, Y. In Organic Peroxides; Ando, W., Ed.; Wiley: New
York, 1992; p 426.
(3) Swern, D. In Organic Peroxides; Swern, D., Ed.; Wiley-Inter-
science: New York, 1971; pp 355-533.
(4) Heaney, H. In Top. Curr. Chem.; 1993, 164, 1-19.
(5) Syntheses of Sulphones, Sulphoxides and Cyclic Sulphydes; Patai,
S., Rapoport, Z., Eds.; Wiley: New York, 1994.
(6) Yang, Y. C.; Baker, J . A.; Ward, J . R. Chem. Rev. 1992, 92, 1729-
1743.
(13) Curci, R.; Giovine, A.; Modena, G. Tetrahedron 1966, 22, 1235.
(14) Harrison, C. R.; Hodge, P. J . Chem Soc., Perkin Trans. 1 1976,
21, 2252.
(7) Cerniani, A.; Modena, G.; Todesco, P. E. Gazz. Chim. 1959, 89,
843.
(8) Greco, A.; Modena, G.; Todesco, P. E. Gazz. Chim. 1960, 90, 671.
(9) Kresze, G.; Schramm, W.; Cerc, G. Chem. Ber. 1961, 94, 2060.
(10) White, R. W.; Emmons, W. D. Tetrahedron 1962, 17, 31.
(11) Overberger, C. G.; Cummins, R. W. J . Am. Chem. Soc. 1953,
75, 4250.
(15) Doumaux, A. R.; McKeon, J . E.; Trecker, D. J . J . Am. Chem.
Soc. 1969, 91, 3992.
(16) Sugimoto, H.; Sawyer, D. T. J . Am. Chem. Soc. 1985, 107, 5712.
(17) Swern, D. In Organic Reactions; Adams, R., Ed.; Wiley: New
York, 1953; Vol. 7, pp 378-401.
(18) Yamabe, S.; Kondou, C.; Minato, T. J . Org. Chem. 1996, 61,
616-620 and references therein.
(12) Szmant, H. H.; J armberger, H. F.; Krahe, F. J . Am. Chem. Soc.
1954, 76, 2185.
(19) Cooper, M. S.; Heavey, H.; Newbold, A. J .; Sowdersor, W. R.
SYNLETT 1990, 533.
S0022-3263(96)00457-4 CCC: $12.00 © 1996 American Chemical Society

5694 J . Org. Chem., Vol. 61, No. 16, 1996
Notes
Ta ble 1. n -Bu tyl Su lfid e Oxid a tion s Usin g Ma leic
Sch em e 1
a
An h yd r id e a n d H2O2
amt of
amt of
substrate (mol)
H2O2 (mol)
time (min)
product (%)
1.6 × 10-3 b
1.6 × 10-3
5
30
60
240
360
600
720
840
5
R2SO (12)
R2SO (21)
R2SO (29)
R2SO (62)
R2SO (79)
R2SO (94)
R2SO (97)
R2SO (100)
R2SO (35)
R2SO2 (57)
R2SO (10)
R2SO2 (88)
R2SO2 (95)
R2SO (73)
R2SO2 (27)
R2SO (67)
R2SO2 (33)
R2SO (75)
R2SO2 (11)
1.6 × 10-3 b
4.9 × 10-3
30
Ta ble 2. Tr a n sition Meta l-Ca ta lyzed n -Bu tyl Su lfid e
a
Oxid a tion s Usin g Ma leic An h yd r id e a n d H2O2
60
5
3.2 × 10-2 b,d
5.0 × 10-2 b,d
3.2 × 10-2 b
3.2 × 10-2
5.0 × 10-2
3.2 × 10-2
cocatalyst
none
time (min)
5
products (%)
R2SO (35)
R2SO2 (57)
5
5
30
R2SO (10)
R2SO2 (88)
a
The amount of MAnh in all experiments was 1.6 × 10-2 mol;
30% aqueous H2O2 was used. The reactions were studied under
N2 at 25 °C unless otherwise indicated. 10 mL of NMP was used.
4 mL of NMP was used. Run under air instead of N2.
60
5
R2SO2 (95)
R2SO (2)
R2SO2 (93)
R2SO (1)
b
RuCl3‚3H2O
c
d
30
amount of H2O2, selective production of sulfoxide or
sulfone can result. In the first reaction listed in Table
1, a 1:1 ratio of H2O2 to sulfide is used, resulting in 100%
conversion to sulfoxide and 100% efficiency in the utiliza-
tion of peroxide. In an analogous reaction in which
maleic anhydride is omitted, only a 7% conversion to
sulfoxide occurred. This result demonstrates the involve-
ment of a much stronger oxidant than H2O2, i.e., the
peroxyacid, in the previous reaction. The use of a 3:1
excess of H2O2 to sulfide results in the complete conver-
sion of the sulfide to sulfone in 1 h.
Using a 3:1 H2O2-to-substrate ratio, the less nucleo-
philic thioether, diphenyl sulfide, also reacts with the
maleic anhydride/H2O2 system, leading to the complete
oxidation of the substrate to sulfoxide (14%) and sulfone
(84%) in 1 h. No oxidation products were observed in
an analogous reaction containing no maleic anhydride.
It should be emphasized that conversion of the diphe-
nyl sulfide to sulfone requires the peracid formed to be a
strong enough electrophile to oxidize the sulfur of the
weak nucleophile diphenyl sulfoxide.
R2SO2 (98)
60
5
5
R2SO2 (100)
R2SO2 (100)
R2SO (2)
Mo(O)2(acac)2
ReCl3
R2SO2 (92)
30
R2SO (1)
R2SO (99)
60
5
R2SO2 (100)
R2SO2 (100)
NiCl2‚6H2O
Reaction conditions: substrate (1.6 × 10-3 mol), 1.6 × 10-4
a
mol of metal compounds, H2O2 (4.9 × 10-3 mol, 30% aqueous
solution), MAnh (1.6 × 10-2 mol), NMP (10 mL), run under N2 at
ambient conditions.
addition of the H2O2 to these solutions, containing the
acid anhydride and the substrate, results in a very
exothermic reaction, with temperatures of >75 °C being
observed. Since the reaction vessels were open to the
atmosphere, it is most likely that the solvent, 1-methyl-
2-pyrrolidinone, reacted with atmospheric oxygen to form
the corresponding N-alkylamide hydroperoxide, which
would result in the further oxidation of the sulfide and/
or sulfoxide. Under an N2 atmosphere, an analogous
reaction showed a 97% efficient use of the H2O2 (Table
1). A blank run with no maleic anhydride was carried
out under air. Butyl sulfide (3.2 × 10-2 mol) was reacted
with H2O2 (1:1 ratio) at room temperature using 4.1 mL
of NMP as solvent. This reaction produced only 9%
sulfoxide in 5 min and 16% in 30 min.
Ca ta lytic Su lfid e Oxid a tion . In order for the reac-
tion to be catalytic in maleic anhydride, the maleic acid
formed after oxygen atom transfer from the peracid
would have to react with H2O2 to regenerate the peracid,
as illustrated in Scheme 1 and eqs 1-3. To evaluate this
(RCO)2O + H2O2 f RC(O)OH + RC(O)OOH (1)
RC(O)OOH + S f products + RC(O)OH
RC(O)OH + H2O2 f RC(O)OOH + H2O
(2)
(3)
Effect of Tr a n sition Meta l Ca ta lysts. The activa-
tion of H2O2 in the solvent, 1-methyl-2-pyrrolidinone, was
pursued using maleic anhydride in the presence of
transition metal cocatalysts. The addition of 5 × 10-3
mol of H2O2 and 1.6 × 10-2 mol of maleic anhydride to
10 mL of 1-methyl-2-pyrrolidinone led to ∼90% oxidation
of 1.6 × 10-3 mol of n-butyl sulfide to the sulfone in 30
min (Table 2). Several transition metal compounds
increased the activity of this system. The addition of Mo-
(O)2(acac)2 to the above reaction led to complete oxidation
of the sulfide to the sulfone in 5 min (Table 2). An
possibility, a 20-fold increase in n-butyl sulfide concen-
tration over that in Table 1 was oxidized using a 1:1
H2O2-to-substrate molar ratio at ambient conditions. This
produces reactant molarities that are 2 times that of
maleic anhydride. After 5 min of reaction, complete
oxidation of the substrate had occurred. A similar result
was obtained when a 3:1 reactant-to-maleic anhydride
ratio was employed. The results obtained for these
experiments show >100% efficient use of H2O2. The

Notes
J . Org. Chem., Vol. 61, No. 16, 1996 5695
analogous reaction containing Mo(O)2(acac)2 but no ma-
leic anhydride required 48 h to oxidize the sulfide to the
sulfone.
Complete oxidation of the sulfide to the sulfone also
occurred in 5 min when NiCl2‚6H2O was added to the
peroxyacid system. The use of H2O2 as the oxidant in
an analogous reaction with NiCl2‚6H2O but with no
maleic anhydride led to only 10% substrate conversion
to the sulfone in 48 h. The reaction was accompanied
by nonproductive peroxide decomposition.
The catalysts RuCl3‚3H2O and ReCl3 enhanced the
activity but were less effective than the molybdenum-
(VI) and nickel(II) catalysts. No increase in activity was
observed with V(O)(acac)2, CoCl2‚6H2O, and FeCl3‚6H2O,
and metal-catalyzed peroxide decomposition becomes a
factor.
After 1 h at 65 °C, 37% of the initial olefin was converted
to the epoxide, with a selectivity of 93%.
Phthalic acid (2 mmol) was used instead of the anhy-
dride in the oxidation of cyclooctene (3 mmol), using UHP
(5 mmol) as the oxidant and 10 mL of NMP as solvent.
After 1 h at 65 °C, little consumption of the olefin (<5%)
and no epoxide were observed. This result indicates that
the epoxidation reaction would not be catalytic in anhy-
dride.
A series of experiments were carried out in N-meth-
ylpyrrolidinone using benzoic acid, 3-chlorobenzoic acid,
and 3,5-dichlorobenzoic acid. The purpose of these
experiments was to study the regeneration step with
increasingly electron-withdrawing substituents. In all
instances, the decrease in octene in 3 h at 65 °C was 5%
or less.
Ep oxid a tion of Alk en es. In view of the excellent
reactivity observed for sulfide oxidations, the maleic
anhydride/H2O2 system of Table 1 was used to attempt
the epoxidation of olefins. The liquid olefin 1-octene was
selected as the substrate because of its similarity to
propene but greater ease of handling. Terminal olefins
tend to be difficult to selectively epoxidize. When the
same conditions used for the noncatalytic thioether
oxidations were used for the 1-octene epoxidation, only
a small consumption of olefin (9%) was observed after
16 h. The epoxide peak could not be observed in this run
because the maleic anhydride has similar retention
times. Phthalic anhydride was used in the place of
maleic anhydride under similar conditions, and after 3
h, no consumption of olefin or formation of epoxide was
observed.
Phthalic anhydride was used for the epoxidation of
1-octene under the conditions used for the catalytic
sulfide oxidations. A biphasic system resulted, and no
products could be observed in either of the phases after
3 h of reaction. When reacting 5 mmol of the olefin, 3
mmol of 50% aqueous hydrogen peroxide, and 1 mmol of
phthalic anhydride at 65 °C, only one phase was ob-
served. After 3 h, very little olefin disappeared, and no
epoxide could be found by GC. Addition of NiCl2 did not
increase the rate of epoxidation to the extent required
to react at the peracid concentrations in this system.
Commercial magnesium monoperphthalate (MgMMP,
2 mmol) was employed as the oxidant for 1-octene (5
mmol) with 3 mmol of 50% H2O2 in 10 mL of NMP. In
this reaction, 26% of the initial olefin was consumed, and
a 23% yield of epoxide was obtained after 1 h of reaction.
The olefin consumption corresponds to utilization of 65%
of the MgMPP used. None of the hydrogen peroxide
reacts with the phthalate anion to regenerate the peracid
at these conditions.
The poor reactivity of 1-octene in contrast to sulfide
and sulfone is attributed to the poor nucleophilicity of
1-octene. Accordingly, the epoxidation of cis-cyclooctene
was tried next at 65 °C. Cyclooctene (3 mmol) was
reacted with phthalic anhydride (2 mmol) and 50%
aqueous hydrogen peroxide (5 mmol) in 10 mL of NMP.
After 1 h, 20% of the initial olefin was converted to the
epoxide, with a selectivity of 85%.
To increase reactivity, aqueous 50% hydrogen peroxide
was substituted by the urea hydrogen peroxide adduct
(UHP) in the same reaction to increase the equilibrium
concentration of peracid by decreasing the excess water
in the system (eq 3). In this reaction, 2 mmol of phthalic
anhydride was added to a solution containing 5 mmol of
UHP and 3 mmol of cis-cyclooctene in 10 mL of NMP.
Since UHP provides a good and safe source of anhy-
drous hydrogen peroxide18 and increases the conversion
of cyclooctene, attempts were made to oxidize 1-octene
with this system. First, 40 mmol of UHP was reacted
with 10 mmol of phthalic anhydride in 25 mL of NMP at
40 or 80 °C. After 30 min, 4 mmol of 1-octene was added.
The reaction at 40 °C gave an 18% decrease on the olefin
and a similar amount of epoxide after 3 h. The reaction
at 80 °C, run 10, gave a 38% decrease of the olefin but
only 13% epoxide after 3 h. This difference is due to the
reaction of phthalic acid and epoxide to form the car-
boxylate of the diol.
The more facile reaction of sulfides than alkenes with
the peracid generated in this system is readily under-
stood in terms of their nucleophilicity. Much higher
concentrations of peracid are needed for epoxidation than
for sulfide oxidation. These concentrations are not
produced at room temperature with phthalic anhydride
and 50% aqueous H2O2, so little or no reaction occurs.
Attempts to facilitate peracid formation by acid catalysis
also catalyze ring-opening hydrolysis.
Con clu sion s
Thioethers, such as n-butyl sulfide, can be oxidized to
the corresponding sulfoxides and sulfones in the solvent
1-methyl-2pyrrolidinone using maleic anhydride to acti-
vate H2O2 under ambient conditions. When compared
with the analogous thioether oxidations using H2O2, the
addition of maleic anhydride to these reactions resulted
in a very pronounced increase in activity. The use of a
catalytic amount of the acid anhydride in reactions
employing 1:1 molar ratios of H2O2 to substrate led to
nearly complete oxidation of the sulfide in minutes,
demonstrating the regeneration of the organic peroxyacid
from the carboxylic acid formed from the reaction.
Catalytic amounts of transition metal complex cata-
lysts showed an increase in the activity of the peroxyacid.
These systems were considerably more active than the
analogous metal-catalyzed reaction using the oxidant
H2O2.
The amount of peracid existing in solutions of H2O2
and carboxylic acid is low in the absence of strong acids.
For the strong sulfide nucleophile, this amount is enough
for reaction, and as the peracid is consumed, this small
amount is replenished via eq 3. In the epoxidation
reactions, this small concentration leads to a very slow
reaction. Since the epoxide production is slow, secondary
reactions of the epoxide can occur. If an acid is added to
catalyze the peracid formation, it also catalyzes the ring-

5696 J . Org. Chem., Vol. 61, No. 16, 1996
Notes
H2O2 content was determined using a redox titration with Ce4+
using ferroin as an indicator. Samples were withdrawn and
diluted in 1 M H2SO4 that was cooled to 0 °C. They were then
titrated quickly with a standardized solution of CeIV(NH4)4(SO4)4
in 2.5 M H2SO4.
Su lfid e Oxid a tion s. Maleic anhydride (1.6 g, 1.6 × 10-2 mol)
and 1-methyl-2-pyrrolidinone (5.0 mL) were placed in a 100 mL
round-bottom flask equipped with magnetic stirring and an N2
atmosphere. After 5 min of stirring, the appropriate amount of
H2O2 was added dropwise to the acid anhydride solution. The
resulting colorless solution was stirred for 1 h to ensure
formation of the peroxyacid.
,
opening of the epoxide product. When a buffer is added
to protect the epoxide from solvolysis, the concentration
of the peracid in solution is decreased.
Increasing the temperature to increase the rate and
concentration of peracid in solution generated from the
carboxylic acid also leads to an increase in rate of the
competing epoxide reactions. Conditions can be found
that lead to good yields and selectivities for the stoichio-
metric reaction in which peracids are generated from
anhydrides reacting with H2O2.
1-Methyl-2-pyrrolidinone (5.0 mL) and n-butyl sulfide (0.23
g, 1.6 × 10-3 mol) were placed in a 100 mL round-bottom flask
equipped with magnetic stirring and an N2 atmosphere. After
30 min of stirring, the previously prepared peroxyacid solution
was added dropwise to the reaction solution. Samples were
analyzed periodically by GC.
Ca ta lytic Ma leic An h yd r id e. For the catalytic maleic
anhydride experiment, maleic anhydride, n-butyl sulfide, and
1-methyl-2pyrrolidinone were placed in a 100 mL round-bottom
flask equipped with magnetic stirring and stirred for 5 min.
Samples were analyzed periodically by GC.
Exp er im en ta l Section
Rea gen ts a n d Equ ip m en t. The n-butyl sulfide, n-butyl
sulfoxide, n-butyl sulfone, diphenyl sulfide, diphenyl sulfoxide,
diphenyl sulfone, and 1-methyl-2-pyrrolidinone (HPLC grade)
were obtained from Aldrich Chemical Co. and used as received.
The metal complexes Mo(O)2(acac)2, C(O)(acac)2, ReCl3, and
RuCl3‚3H2O were received from Aldrich Chemical Co. as well.
All other reagents and solvents were obtained from Fisher
Scientific and used as received.
P r od u ct An a lysis. A Varian 3700 GC with an FID and
Hewlett Packard 3390A integrator was used to analyze the
products of the sulfide reactions, using a 6 ft stainless steel
column packed with Carbowax 20M (10%) on Chromosorb WHP
(80/100 mesh) for the n-butyl sulfide oxidations and a 6 ft
stainless steel column packed with SE-30 (3%) on Gas Chro-
mosorb Q (80/100 mesh) for the diphenyl sulfide oxidations. All
olefin reactions were carried out using o-dichlorobenzene as an
internal standard. Reaction products were analyzed using an
HP 5890 GC. The substrate(s) and product(s) were identified
and quantified using known standards.
P er oxym a leic Acid Sta bility. Maleic anhydride, 30%
aqueous H2O2, and the solvent 1-methyl-2-pyrrolidinone produce
peroxymaleic acid, a potent oxygen atom transfer agent. This
conversion is enhanced by the hydrogen-bonding of the product
water to the solvent. The solvent 1-methyl-2-pyrrolidinone is
readily oxidized by O2 at 75 °C, so its oxidative stability to peroxy
acids was investigated.
Metal-catalyzed sulfide oxidations were carried out by stirring
maleic anhydride (1.6 g, 1.6 × 10-2 mol) and 1-methyl-2-
pyrrolidinone (5.0 mL) in a 100 mL round-bottom flask equipped
with magnetic stirring and an N2 atmosphere for 5 min. H2O2
(4.9 × 10-3 mol, 0.5 mL of a 30% aqueous solution) was added
dropwise to the solution and stirred for 1 h. 1-Methyl-2-
pyrrolidinone (5.0 mL), n-butyl sulfide (0.23 g, 1.6 × 10-3 mol),
and the appropriate catalyst (1.6 × 10-4 mol) were placed in a
100 mL round-bottom flask equipped with magnetic stirring and
an N2 atmosphere. After 30 min of stirring, the previously
prepared peroxyacid solution was added dropwise to the reaction
solution. When 30% H2O2 was the oxidant, it was added
dropwise to the sulfide-metal complex solution in NMP. Samples
were analyzed periodically by GC.
Ep oxid a tion of Olefin s by P er a cid s. Epoxidation reac-
tions were carried out either on a Parr pressure bottle or in a
round-bottom flask equipped with a cold water condenser. Care
must be taken when using hydrogen peroxide solutions with 50%
or greater content. In general, anhydrides (1.0 × 10-3 mol) were
allowed to react with hydrogen peroxide 50% (3.0 × 10-3 mol)
in 10 mL of NMP for 0.5 h at room temperature. 1-Octene (5.0
× 10-3 mol) was then added, and the reaction flask was placed
in a silicon oil bath at 65 °C. The reaction was monitored by
collecting samples periodically and analyzing by GC using an
internal standard. Solutions of known concentration were
prepared and used to construct calibration curves to permit
quantitative determination of octene and the corresponding
epoxide.
Maleic anhydride (1.6 g, 1.6 × 10-2 mol) and 1-methyl-2-
pyrrolidinone (10 mL) were placed in a 100 mL round-bottom
flask equipped with magnetic stirring. After 5 min of stirring,
H2O2 (4.9 × 10-3 mol, 30% aqueous solution) was added dropwise
to the acid anhydride solution. After 1 h of stirring, the colorless
solution was stored under ambient conditions. The peroxyacid
solution was analyzed periodically. Under ambient conditions,
1.6 × 10-2 mol of maleic anhydride and 4.9 × 10-3 mol of H2O2
showed <5% loss of oxidation titer over a period of 168 h. The
peracid content in the solutions was determined as the difference
of the total oxidant content and the hydrogen peroxide content.
These were determined in separate titrations as follows. The
total oxidant content was determined using an iodomeric titra-
Ack n ow led gm en t. The authors acknowledge finan-
cial support of this research by the U.S. Army Research
Office and ERDEC.
tion. Samples were withdrawn and diluted in 2-propanol.
A
saturated solution of NaI in 2-propanol and acetic acid were
added, and the mixture was heated to reflux for 30 s. The iodine
was titrated with a standard sodium thiosulfate solution. The
J O960457K