398
G.D. YADAV AND D.V. SATOSKAR
Although the epoxidation process with peroxyacids has
EXPERIMENTAL PROCEDURES
been extensively studied and often is the method of choice for
laboratory-scale work, it has not been widely applied on a
commercial scale. This may be partly due to the hazards as-
sociated with handling peroxyacids on an industrial scale. In
these processes, the yield of epoxides is poor, especially when
unreactive α-olefins are employed, and thus their scope is
rather limited. On the other hand, catalytic epoxidation by or-
ganic hydroperoxides, such as CHP, TBHP and EBHP, pos-
sesses many advantages. Alkyl hydroperoxides are relatively
easier to handle than organic peroxyacids. A wide variety of
olefinic compounds has been epoxidized, including relatively
unreactive α-olefin, by hydroperoxides. Moreover, acid-labile
epoxides, such as epoxides of styrene, α-methyl styrene and
α-pinene, which cannot be prepared satisfactorily with per-
oxyacids, have been prepared in excellent yields with hy-
droperoxides (9).
Of all methods, the following three were considered under
the purview of this study: (i) preformed peroxyacetic acid as
epoxidizing agent, (ii) in situ-generated peroxyacetic acid as
epoxidizing agent, and (iii) phase transfer-catalyzed epoxida-
tion with hydrogen peroxide and heteropoly acids. The rea-
son for the above choices was as follows:
Industrially, various peroxyacids are available, such as
peroxyacetic acid, peroxybenzoic acid, peroxyfluoroacetic
acid, m-chloroperoxybenzoic acid and m-nitroperoxybenzoic
acid, from which peroxyacetic acid was selected due to
its easy availability, low price, high epoxidation efficiency,
and reasonable stability at ordinary temperatures. Besides,
epoxidation with peroxyacetic acid can be conducted in
aqueous, nonaqueous, homogeneous, and heterogeneous
media. However, the peroxyacetic acid has to be prepared
separately and stored at low temperature to avoid hazards of
its decomposition.
Using the in situ-generated peroxyacetic acid has certain
advantages, such as minimum amounts of reactants are
needed to prepare the epoxidizing reagent and convenient
safe preparation and handling of peroxyacetic acid. Homoge-
neous acids, such as sulfuric acid and p-toluene sulfonic acid,
can be avoided by using heterogeneous catalysts, such as ion
exchange resins, which would avoid disposal of strong acids.
The catalyst can be recycled, shows better selectivity, and
avoids side reactions.
PTC epoxidations have caught attention due to excellent
conversions and yields associated with the process. The reac-
tions are conducted in a two-phase system (8,10–12). Phase
transfer catalysts can be heterogenized, to make them
reusuable and to avoid disposal and effluent problems com-
pletely. Higher temperatures can be employed because all cat-
alysts are stable at higher temperatures, resulting in higher
conversions in less time and making the process commer-
cially viable. The method has been reported to be excellent
for unreactive α-olefins, which are difficult to epoxidize
owing to heterogeneity of the reaction medium. However, the
PTC method has not yet been studied for terminally unsatu-
rated acids, such as undecylenic acid and its esters.
Chemicals and catalysts. Tricapryl methyl ammonium chlo-
ride (Aliquat 336) (AR grade) was obtained from SISCO
Laboratories (Mumbai, India). Dodecatungstophosphoric
acid (AR grade), 50% aqueous hydrogen peroxide (AR
grade), and chloroform (AR grade) were obtained from
s.d.Fine Chem (Mumbai, India). Glacial acetic acid was a
laboratory-grade reagent. Undecylenic acid (98% pure) was
obtained from M/s Jayant Oil Mills Ltd. (Bombay, India).
HBr in acetic acid was obtained from S. Merck and diluted
with acetic acid to prepare 0.1 N HBr. All other chemicals
were obtained from reputed firms. Indion 130, a cation ex-
change resin catalyst, was obtained from Ion Exchange
(India) (Mumbai, India).
Methyl undecylenate. Undecylenic acid was esterified with
methanol to prepare the ester. Calculated quantities of unde-
cylenic acid and alcohol were placed in an electrically heated
three-necked flask, and the esterification was carried out under
reflux with 1% p-toluene sulfonic acid as the catalyst. The
reaction was continued for 3 h. The course of the reaction was
followed by analyzing samples that were withdrawn peri-
odically for acid value. At the end of the reaction, the catalyst
was neutralized, and the excess alcohol was removed by dis-
tillation. The isolated ester was dried over anhydrous sodium
sulfate and purified by distillation under reduced pressure.
Ethyl undecylenate. The same procedure as above was fol-
lowed for the synthesis of ethyl undecylenate, except that the
reaction was continued for 6 h.
Preformed peroxyacetic acid. The method reported by
Schmitz and Wallace (13) was followed for the synthesis of
preformed peroxyacetic acid: 300 g of glacial acetic acid, 3 g
of concentrated sulfuric acid, and 34 g (0.5 mole) of 50%
aqueous hydrogen peroxide were held at room temperature
for 24 h. The solution contained 3.16 g (9.6%) of unreacted
hydrogen peroxide and 33.1 g (87.2% conversion) of peroxy-
acetic acid. After 24 h, the sulfuric acid was neutralized with
an equivalent amount of solid sodium acetate. The contents
were then filtered to remove sodium sulfate. The peroxyacetic
acid thus prepared was used for epoxidation.
Epoxidation with preformed peroxyacetic acid. Unde-
cylenic acid or its esters (0.14 gmol) were put in a reactor,
which was allowed to reach the desired temperature. Pre-
formed peroxyacetic acid (70 g) was added to it. Samples were
withdrawn periodically and analyzed for oxirane content and
for unsaturation by iodine value (14) during the initial part of
research. Confirmation was by gas chromatography (GC).
Epoxidation with in-situ preparation of peroxyacetic acid.
The method reported by Swern (9) was used. The required
amount of undecylenic acid or its esters was placed in the
reactor mentioned above. Calculated amounts of acetic acid
and H2SO4 were added, and the mixture was stirred for 30
min. The 30% aqueous solution of H2O2 was added dropwise
by means of a dropping funnel for 30 min. After the addition
was completed, the reaction was allowed to continue further
for 6 h.
JAOCS, Vol. 74, no. 4 (1997)