Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11 75058
BACXGROUND OF THE INVENTION
i~
This invention relates to a process for the prepara-
tion of phenylene diacetate. More particularly the invention
relates to the conversion of phenyl acetate to phenylene diace-
tate by a palladium catalyst in the presence of oxygen, acetic
anhydride and acetic acid at elevated temperatures and pressures.
S~ill mcre par~icularly the invention xelate~ to a method of
preparing ~ara phenylene diac~tate as a majvr produc~. Pheny-
lene diacetate may have utility as a solvent. Preparat1on of
phenyl acetate i5 disclo~ed in U.S. Patent No. 4,156,7&3.
The acetoxylation of chlorobenz~ne by Pd~OAc)2 in
acetic acid with an oxygen atmosphere and with and without
the presence of N02 and with me a - selectivity is reported in
11 ~5~58
Acta Chemica Scandinavica B28 (1974~ 771-776, L. Eberson et al
Ac as used herein refers to the~group CH3-C-. The latter
o
also discloses the stoichiometric acetoxylation of phenyl
acetate by 2,2'-Bipy Pd(OAc) (NO3) in acetic acid at 115~C in
an oxygen atmosphere with meta-diacetoxybenzene (meta-phenylene
diacetate) the major product (60%) after a reaction period of
2 hours. The aforementioned reference, pages 597-602, states
that a heterogenous gas phase acetoxylation of amonofunctional
benzene derivative that takes place in acetic acid in the
presence of oxygen shows a reversal of the normal substitutent
effect, i.e., ortho-, ~ -directing substituents give pre-
dominantly meta-acetoxylation and meta-directing ones give
ortho-, para-acetoxylation.
Formation of methylbenzylacetate via the homogeneous
reaction between palladium(II) acetate and ~ -xylene in
acetic acid in the presence of oxygen has been studied and
reported in articles in Acta Chemica Scandinavica 27, 1973,
L. Eberson et al., pages 1162-1174, 1249-1254, 1255-1267. The
acetoxylation of phenyl acetate by potassium peroxydisulfate
with Pd~II) as a catalyst in the presence of acetic acid to
form 25~ ortho-, 42% meta- and 33% ~ -isomers of phenylene
diacetate is disclosed in Acta Chemica Scandina~ica B30 (1976
pages 361-364, Eberson et al.
The use of palladium(II) lalong with other components
such as oxidants, cooxidants) to cataly~e aromatic acetoxylation
is reported in the literature as exemplified by U.S~ Patent No.
3,772,383; Tetrahedron Letters No. 58, pp. 6123-6126, 1968,
C.H. Bushweller; ~. Org. Chem., Vol. 36, No. 14, 1971, P.M.
Henry; and ~.S C. Chem. Comm. 1974, pages 885-886, L. Eberson et al.
_ ~ _
~75~5~
The acetoxylation of benzene to phenyl acetate using
oxygen, palladium on silica or alumina in the presence of
acetic acid is reported in Erdol Und Kohle, 23, 79, 1970.
According to Journal of Grganic Chemistr~, Vol. 33,
November 11, 1968, D.R. Bryant et al. acetoxylation of
toluene in the presence of oxygen, palladium acetate and
an alkali metal carboxylate at elevated temperatures results
in a henzyl acetate and at higher conversions to ben~ylidene
diacetate.
However, none of the previously mentioned references
disclose or suggest the conversion of phenyl acetate to
phenylene diacetate via applicants' method. Further contrary
to the previously discussed reference (~cta Chemica
Scandinavica B-28, pages 597-602 and pages 771-776),
applicants' method yields predominantly the ~ phenylene
diacetate isomer.
SUMMARY
As aforestated, the process of this invention comprises
reacting phenyl acetate in the presence of acetic anyhdride,
acetic acid, an acetoxylation amount of oxygen and a
palladium catalyst at an elevated temperature and pressure
to yield phenylene diacetate in accordance with the following
reaction:
O O
O-C CH O-C-C~3
~ + 1~2 2 ~ (C~3CO)2O ~ ~ ~H3CO
O-C-CH3
o
;:. - 3 -
~sv~
Para-phenylene di.acetate is the predominant product ~ollowed ~y
.
the ortho- and m~ta-isomers.
description
The word "acetoxylation" as used in this specification
refers to the addition of an acetoxy group, CH3-C-O-, to the
o
organic compound being processed.
The process of this invention is conveniently carried
out under an acetoxylation temperatùre which is th`e temperature
which favors the formation of phenylene.diacetate. Elevated
temperatuxes of from about 100C ~o about 300C are preferred
and more preferably from about 150C to about 250C. The
reac~ion is in a liquid phase. Also an acetoxyla~ion pres~ure
is used. Reaction pressures of about up to 1500 p~ig are
preferred. The period for the reaction ranges varias consider-
ably, depending in part on the operating conditions, including
for example, relative concentration~ of materials, tempera~ures,
and pressure employed. The process can al50 be carried out in
a continuous system.
The phenyl acetate should de~irably be reacted in
the presence of acetic acid and acetic anhydride. The acetic
anhydride should desirably be present in the amount of about
0.1 to about 3 times by weight of the amount of phenyl ac~tate
used with 0.3 to 1.5 preferreda The molar ratio o~ palladium
catalyst to phenyl acekate employed should be in ~he range between
from about .0001 to about 1 with .001 to 0.5 preferr~d.
Oxygen is used in applicants' acetoxylation proce~s.
The amount of oxygen is an a etoxyla~ion amount, tha~ i~, an
~sass
amount which favors th~ formation of phenylene diare~ate3,
desirably the ~ isomer, in the presence of a palladium catalyst,
acetic acid and acetic anhydride. Genexally the oxygen used
can be co~tained in an inert gas such as nitrogen and in such
a mixtuxe can be at a low concentration. For example, as reported
in the Example, a gas mix~ure containing 4~ 2 and 96~ N2 was
effectively used.
The palladium catalyst is desirably palladium on
alumina. Other palladium catalysts, eOg., palladium acetate
and palladium on other qupports, e.g., carbon and silica, which
would result in an effective reaction mixture, can be used.
Generally, applicants' method results in converting
phenyl acetate substantially to phenylene diacetate with the
isomer the predominant isomer. While a product other
than phenylene diacetate may be produced the amount will be
minor, if not merely a trace. The selectivity as to ~ -phenylene
diacetate is al~o substantial, for example, in the run in the
Example, it was 82~.
The following example is provided to illustrate ths
invention described herein.
EXAMPLE
The following reaction was run in a stirred stainless
steel autoclave using 5% palladium on alumina (2.35 mmoles) as
the catalyst, acetic anhydride (510 m~oles), phenyl acetate
(950 mmoles) and acetic acid (4200 mmoles). The autoclave was
heated to 200C under nitrogen (800 psig). Then an acetoxyla~
tion gas, 4% 2 and 96% N2 was passed through the heated mixture
for 2.5 hours at a rate of 2 liters per minute (80~ psig~. At
1175~5~3
the end of the run the autoclave was cooled to room temperature
and the products were analyzed by gas chromatography. Total
product yield was 800% based on Rd. By gas chromatograph three
products were detected: ortho-phenylene diacetate 14% selectivity,
meta-phenylene diace~ate 4~ selectivi~y and para-phenylene
diacetate 82% selectivity~ Just a trace of any acetylation product
was found. The phenylene diacetates can be recovered and separated
by known methods such as distillation and~or crystallization.
Selectivity as used herein is defined as the mole percent of one
isomer to al~ products formed.
The foregoing yield~ indicate that the ~ omer
is the major diacetate product while the ortho-isomer is a
minor diacetate product. The meta-isomer is present in a
nominal amount. These amounts can be modified by changes in
operating conditions, however, generally the ~ isomer is
favored and can be the predominant isomer.
Use of other palladium catal~st, e.g., palladium
acetate, and use of other operating conditions resulted in
analogous yields and ~electivities.
~1'750~
SUPPLEMENTARY DISCLOSUl~E
In accordance with the teaching of the Principal
Disclosure a process is provided for the acetoxylation of
phenyl acetate to prepare para-phenylene diacetate by reacting
phenyl acetate with an acetoxylating amount of oxygen in the
presence of acetic anhydride, palladium and acetic acid at
elevated temperatures and pressures.
Now, in accordance with the Supplementary
Disclosure a process is provided which romprises reacting at
elevated temperature and pressure, phenyl acetate, acetic
anhydride and acetic acid in the presence of a palladium
catalyst and a gas mixture, which gas mixture contains an
inert gas and no more than 13 volume % oxygen, to yield
phenylene diacetate in accordance with the following reaction:
O O
O-C-CH ~-C-CH3
~ ~ 1/2 2 + (~l3C)2 CH3CO2E ~ -C-CH 3C2~1
AS either acetic acid or acetic anhydride, or
both can be the source of the secsnd group which bonds to the
phenyl acetate, the foregoing reaction scheme is merely re-
presentative of the possible reactions which may occur.
Para-phenylene diacetate is the predominant product followed
by the ortho- and meta-isomers.
The process is conveniently carried out in liquid
phase under acetoxylation conditions, that is, at temperature~,
pressures and oxygen levels which favor the formation of phenyl
ene diacetate. Temperatures of from about 100C to about 300C
5D7
~175~S8
are preferred and pressures of from about 100 psig up to about
150Q psig. The reaction time may vary considerably, depending
in part on the operating conditions, including, for example,
catalyst, relative concentrations of materials, and the tem-
perature and pressure. The process can be carried out in a
batch, continuous or semi-continuous system.
The amount of acetic ~cid is not critical. A
preferred range is from 0.2 to about 5.0 moles per mole of
phenyl acetate. The amount of oxygen is an acetoxylation
amount, that is, an amount which favors the formation of
phenylene diacetates, desirably the para-isomer, rather
than the acetoxyacetophenone of copending application
373,935. Generally the oxygen is used in admixture
with an inert gas such as nitrogen. The oxygen content of
the gas mixture should be maintained at a low concentration,
for example, not more than 13 volume %, preferably about 1-8
volume %, most preferably about 3-5 volume %. Above 13
Volume % the oxy-acetylation reaction of the copending
application 373,935 will dominate.
SD8
