Note: Descriptions are shown in the official language in which they were submitted.
W092/0955~ ~C'~ ~ 7 ~3 ~ PCT/US90/06860
PROCESS FOR THE PREPARATION
OF PHENYL CARBONATES
The present invention relates to a process for
the preparation of phenyl carbonates. More
particularly, the present invention allows for the
preparation of phenyl carbonates utilizing as reactants
a phenol; acetic anhydride; carbon monoxide; and oxygen.
In U.S. Patent 4,533,504 an integrated proce~s
for the preparation of aromatic carbonates was di-~closed
wherein the methyl acetate by-product formed in the
tran~esterification of a phenyl ester with a dialkyl
carbonate was recycled by heating the alkyl ester to
form a ketene and subsequently such ketene was
reconverted by reaction with a phenol to form additional
quantities of the phenyl ester.
Preparation of a ketene intermediate has proven
costly and inefficient due to the high temperatures
involved. Recoveries on the order of only about 80
percent of theoretical or less are typical leading to
the need to develop a more efficient means of generating
phenyl carbonate precursors and disposing of alkyl ester
by-products.
W092/095~ 2 Q 9 'i 7 ~ J PCT/US90/06860
According to the present invention, there is
now provided a process for producing an aromatic
carbonate comprising the steps of:
A. reacting acetic anhydride with a phenol to
produce a phenyl acetate and acetic acid
and ~eparating the phenyl acetate;
B. reacting dimethyl carbonate with at least a
portion of the phenyl acetate from step A
to produce a phenyl carbonate and methyl
acetate and separating the methyl acetate;
C. reacting the methyl acetate with carbon
monoxide in the presence of a catalyst to
prepare acetic anhydride; and
D. employing the acetic anhydride as at least
a portion of the acetic anhydrlde reactant
of step A.
The reaction of phenols with acetic anhydride
to form a phenyl acetate and acetic acid, step A of the
present invention, is a well known acetylation reaction.
Suitable process conditions are disclo~ed, for example,
in U.S. Patent 4,374,263. By the term "phenol" is
included hydroxy benzene and C1_14 alkyl or halo
substituted phenols, however, the preferred reactant is
hydroxybenzene. In schematic form, the reaction of a
phenol and acetic anhydride may be depicted by the
following illustration.
`
wos2/osss; 2 ~ ~ 1 7 Q ~ PCT~USsO/06860
O O O
,. .. ..
ArOH + (CH3C)20 - > ArOCCH3 + HOCCH3
wherein Ar represents a C6_20 aryl group or alkyl or
halo substituted aryl group, particularly phenyl.
The reaction is conducted at moderate
temperatures from 25C to 180C, more preferably 75C to
150C. The products are easily separated by fractional
distillation or other suitable technique. While
5 numerous catalysts are known for the esterification
process, preferred catalysts are acids, especially
heterogeneous macroporous ion exchange re~ins in the
acid form.
The dimethyl carbonate reactant for step B may
be prepared by the reaction between methanol, carbon
monoxide and oxygen, according to any suitable
procedure. Suitable are those processes disclosed in
25 V.S. Patents 3,846,468, 3,980,690, 4,452,690, 4,533,504,
and 4,360,477. The reaction is generally expedited by
the use of a catalyst, particularly a copper or cobalt
complex and the use of elevated temperatures and
pressures. Preferred catalysts are cuprous chloride
30 complexed with an organic base such as pyridine,
dipyridyl, imidazole, alkyl or aryl phosphines, etc.
Preferred temperatures are from 20 to 75C, more
preferably 25 to 50C. Preferred pressures of 2 and CO
are from atmospheric to 20 atmospheres pressure.
.
W092/09ss~ 2 Q ~ ~ 7 o 9 PCT/US90/06860
Reaction of dimethyl carbonate and a phenyl
acetate to give the desired phenyl carbonate and by-
product alkyl acetate is a known chemical
tranqformation. This step of the proceqs may be
illustrated schematically by the following diagram.
O O
ll ll
2 ArOCCH3 + (CH3)2C03 > ArOC02Ar + 2 CH30CCH3
wherein Ar is as previously defined.
The above reaction has been previously
diqclosed, for example, in U.S. Patent 4,182, 726, and
U.S. Patent 4,533,504. In a highly desirable embodiment
of the preqent invention, this reaction is conducted in
the presence of a catalyqt, particularly a Lewis acid,
such as AlC13, or stannate or titanate catalysts.
Temperatures of the reaction are from 100C to 350C,
preferably from 150C to 300C. Pressures are generally
from atmospheric to 25 atmospheres, more preferably 5 to
25 10 atmospheres-
The phenyl carbonate product is a highlydesired article of commerce for conversion into
polycarbonate resins. Processes for such conversion are
alqo well known having been disclosed in U.S. Patents
3,625,920, 3, 888, 826 and 4,330,664. Included in the
synthesized product may be a mixture of both the mono-
and ditransesterified products, that is both the
35 diphenyl carbonate and phenyl methyl carbonate products
are formed.
. , ................................ ~ .
.
. ,~ ' . ,
W092/0955~ 2 Q ~ ~ 7 0 9 PCT/US90/0686~
--5--
The phenyl carbonate product and methyl acetate
are readily separated by use of standard distillation
techniques and the by-product, methyl acetate, is
recycled by means of a reaction with carbon monoxide to
produce acetic anhydride that is used in step A.
Suitable proces3es for such reaction between methyl
acetate and carbon monoxide are known and previouQly
disclosed in the art, for example, in U.S. Patents
4,374,070, 4,559,183, and 4,046,807 and in S. W.
Polichnowski, J. CHEM. ED., 63, 206 (1986). A preferred
process utilizes a noble metal catalyst and temperatures
from 50C to 250C, preferably 100C to 200C, and
pressures from atmospheric to 500 atmospheres,
preferably 10 to 250 atmospheres.
It may be readily observed that the present
process scheme allows for the overall conversion of a
phenol to the corresponding phenyl carbonate utilizing
as reactants acetic anhydride, carbon monoxide and
oxygen. The recycle of methyl acetate intermediate
allows for great economy and simplicity in the resulting
process compared to the generation of a ketene
intermediate. The present process utilizes much lower
reaction temperatures and results in greatly improved
efficiency of operation. Moreover, intermediate by-
product acetic acid may also be recycled if desired by
reaction with additional methanol to form methyl acetate
and then carbonylated as above explained to form acetic
3 anhydride. Alternatively, the acetic acid, which
represents a significant increase in value over the
starting material, methanol, may be sold.
