Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3617.~
MANUFACTIJRE OF ARYL ESTERS
The present invention provides a process for maklng
aryl esters from aromatic hydrocarbons such as benzene,
naphthalene, anthracene, phenanthrene, biphenyl, terphenyls, and
the like, which comprises reacting a mixture of the aromatic
hydrocarbon, for instance benzene, a carboxylic acid, preferably
one ha~ing at least 5 carbon atoms, and molecular oxygen in the
liquid phase in the present of a catalyst consisting essentially
of palladium or a compound of palladium, a compound of antimony,
and a compound of at least one member selected from the group
consisting of chromium, cobalt, nickel, manganese, iron and
tin.
Description of the Prior Art
The manufacture of phenol by direct oxidation with
oxygen is known. There are, for instance, thermal processes
which are performed at very high temperatures in which the phenol
formed is susceptible to further oxidation so that considerable
loss of yield occurs as is
disclosed in U.S. Patent No. 2,223,383, in the presence of
catalysts~ The oxidation can be carried out at somewhat
lower temperatures as in U~S. Patent No~ 3,133,122 but the
reactions have been plagued by low conversions and
excessive pxoduction of unwanted by-products as disclosed
in U.SO Pat~nt No. 2,392,875~
It has already been proposed to mak~ phenyl acetate
and biphenyl from ben~ene and acetic acid in the liquid
phase in the presence of palladium acetate and without
added molecular oxygen by a Stoichiometric reaction in
Chem. and Ind., March 12, 1966, Page 457.
-
U.S. Patent No. 3,542j852 discloses the preparation
of hydroxy aromatic compounds by reaction of an aromatic
compound and oxygen in the presence of a catalyst composed
of iron, a noble metal or a compound of either in the
presence of a nitrate ion and a carboxylic acid. More
recently, the preparation of phenyl esters and phenols by
the reaction of benzene, molecular oxygen and a lower
aliphatic carboxylic acid in the presence of a catalyst
composed of a Group VIII metal (U.S~ Patent No~ 3,642,873
or a compound of such metal IU.S~ Patent No. 3,651,127)
have been disclosed. Similarly, variations in this type
of reaction have been disclosed 1n U.SO Patent Nos.
3,646,111; 3,651,101; 3,772,383; 3,959,352 and 3,959,354.
U.S. Patent No. 3,959,354 concludes that liquid phase
reactions of this type because of problems of catalyst
elution, etc., are disadvantageous for an industrial
process. U.S. Patent No. 3,772,383 describes a liquid
phase reaction using a very complex catalyst system which
includes the use of nitric acid and a lower aliphatic
carboxylic acid such as acetic r propionic, n-butyric,
isobutyric or caproic acid. Generally speaking, these
prior art processes deal for the most part with vapor
phase oxidation reactions, or liquid phase reactions in
which all the reactants (except oxygen in some instances)
are initially included in ~he reaction mixtures, they use
lower aliphatic carboxylic acids such as acetic and
propionic acid, and they of~en require an alkali or
alkaline earth metal carboxylate as part of the catalyst.
Moreover, in general the prior art catalytic processes
have produced very low conversions, usually 12ss than 10%,
with poor selectivity to the desired phenyl ester, and
phenol is often a primary product of the oxidation
reaction. The use of the lower saturated carboxylic
acids, primarily acetic acid, in the prior art processes
produce a highly corrosive system which can cause reaction
equipment problems and excessive recycle costs as well as
the poor conversions and selectivities ~entioned above.
None of the prior art processes disclose the continuous
addition of benzene and the continuous removal of water
from the reaction mixture as it forms.
SUMMARY OF THE INVENTI~N
We have discovered an oxidation process for the
transformation of benzene, and similar aromatic compounds,
molecular oxygen and a carboxylic acid to the
corresponding aromatic carboxylate in high conversions and
selectivities to the desired product. Our discovery is
based to some extent on the use of a relatively higher
boiling mono or poly-carboxylic acid such as lauric acid
or dodecanedioic acid as the carboxylic acid reactant in
our process. We have discovered that the use of
carboxylic acids having 5 or more carbon atoms and a
liquid reaction phase in our process as well as our
palladium-antimony-chromium type of catalyst not only
helps in dramatically increasing the conversion of benzene
and increasing the selectivity to the phenyl carboxylate
over that described in the prior art, but that these
carboxylic acids are much less corrosive and much easier
to recycle than are the lower aliphatic carboxylic acids
disclosed for similar types of reactions in the prior art.
We have also discovered in contrast to what was
previously known in the art that our catalyzed liquid
67~
phase reaction produces high conversion~ and quantitative
yields of phenyl ester when benzene is continuously added
to the reaction and water is continuously removed from the
reaction as it forms during the entire course o~ the
reaction. Excess amounts of benzene in the reaction
mixture during the oxidation reac~ion as is shown in the
prior art appear to be responsible for production of
undesirable by-products such as biphenyl. Water can be
conveniently removed in the case of benzene reactant by
continuous removal of excess benzene by azeotropic
distillation and removal of the water as it is formed in
the reaction. If water, which is a by-product of the
reaction, is allowed to remain in the reaction mixture it
can cause hydrolysis of the phenyl carboxylate to form
phenol which, in turn, can cause inactivation of the
catalyst.
The catalysts of our processes are preferably
composed of palladium metal or compounds of palladium and
usually a palladium carboxlyate in conjunction with an
antimony compound and a chromium compound an~/or a
compound of cobalt, nickle, manganese, iron or tin. The
~ use of significant amounts of other materials such as
those described as being catalyst promoters in the prior
art in addition to the essen~ial palladium, antimony and
chromium or other designated metal compound components of
our catalyst i5 usually detrimental to our process. The
catalysts of this invention may be used alone or may be
supported on a carrier or carriers. Suitable carrlers
include silica, alumina, carbon, quartz, pumice,
diatomaceous earth, and the like and others which are well
known in the art.
The carboxylic acids useful in our invention include
mono and poly-carboxylic acids and preferably those having
5 or more carbon atoms which correspond to the formula
R(COOH~ n wherein n is an integer of 1 or more and R is a
hydrocarbon group having at least 5-n carbon atoms, some
carboxylic anhydride can be included with the carboxylic
acid if desired.
Our liquid phase oxidation process produces in the
case of benzene reactan~ conversions of the carhoxylic
acid in the order of 10% or greater with selectivities to
the phenyl ester in the order of 100%. Thus, our process
produces product in such significant quantities that it is
directly competitive with the best of the present day
commercial processes for the manufacture of phenyl esters
and ultimately phenol itself. The phenyl ester or phenyl
carboxylate product of our process can readily be
converted to phenol and the corresponding carboxylic acid
by known means for hydrolysis or pyrolysis. The phenol is
easily recovered by known means and the carboxylic acid,
ketene or acid anhydride is readily recycled for further
use in the oxidation reaction of this invention.
Descri tion of the Preferred Embodiment
P _ _
In a typical reaction in accordance with this
invention a mixture of benzene and the carboxylic acid is
contacted with a catalyst in an oxygen containing
atmosphere at a reaction ~emperature in the range of from
about 100 to 300~C and preferred from 140 - 200C and at
from 1 to 100, preferably 1 to 10 atmospheres but most
preferably at or near atmospheric pressure. The molecular
oxygen can be oxygen, per se, or any gaseous mixture
containing molecular oxygen. For instance, molecular
oxygen can be in the form of air for convenience. The
catalyst can be a mixture of (CH3COO~2Pd, (CH3COO)3Sb and
~CH3COO)3Cr, for instance, in molar ratio of Pd:Sb of from
1:0.1 to 1:20 and preferably 1:.1 to 1:10. The present
invention represents a significant improvement over the
invention of copending U.S. Patent Application S.N.
348,561 in that a chromium or other designated metal
compound is also included in the catalyst in the molar
ratio of from about 0.01:1 to 20:1 per mole of
palladium/antimony in the catalyst. The Pd/Sb/M (wherein
t~'~
M is chromium cobalt, nickel, manganese, iron or tin)
combination has been found by us to be unique in the sense
that the components alone, i.e., Pd, Sb, or Cr or the
combinations of any two components, i.e., Pd/Sb; Pd/M or
Sb/M, when used for this oxidation reaction under the
preferred reaction conditions resulted in much lower
conversions than those obtained with the Pd/Sb/M catalyst.
During the reaction in the liquid phase J water is
removed continuously as it forms and in the case in which
benzene is a reactant it is continuously added and some of
the benzene can be continuously removed along with the
water as it forms by azeotropic distillation. In this
case the major product (and in most cases the only product
in addition to traces of CO2), the phenyl carboxylate
obtained by the process of this invention, far exceeds the
best yields reported in the prior art with essentially
quantitative selectivity. As previously mentioned, the
phenyl carboxylate thus obtained can be hydrolyzed if so
desired to produce phenol by known means and the
carboxylic acid and catalyst can be recycled back to the
reactor.
Because essentially no phenol is produced in the
process of this invention, it is believed that catalyst
activity is maintained for long periods of time under
continuous use. The rapid removal of water from the
reaction mixture is probably at least partly responsible
for the absence of phenol in the reaction product. The
presence of phenol in the reactor is believed to be
responsible for catalyst fouling and short catalyst life
which has been minimized in our process. The process of
this invention is further demonstrated in the following
illustrative examples.
EXAMPLE 1
Each of 5 experiments was conducted according to the
following procedure. To a 500 ml glass reactor equipped
with a mechanical stirrer, Dean Stark type collector with
7~
condenser, thermometer and feed tubes for gas and liquid
feed, there were charged octanoic acidl the Pd/Sb/Cr
catalyst as ace~ates and benzene. The amounts of this
charge are given in Table 1. The resulting mixture was
stirred well and heated for 5 hours at the temperatures
shown in Table 1 (140-178C~ while oxygen was bubbled
below the surface of the mixture at a rate of 50 ml/min.
The water formed as the by-product of the reaction was
distilled off with benzene and collected in the Dean-Stark
collector. More benzene was fed continuously but at a
slow rate into the reactor during the entire course of the
reaction. After the reaction had been run for 5 hours,
the reaction mixture was cooled to rGom temperature and
analyzed by GLC which showed the formation of phenyl ester
of octanoic acid. The amounts of the phenyl ester formed
varied depending upon the reaction temperature and are
given in Table 1. It can be seen that as the temperature
increased, the amount of phenyl ester also increased.
EXAMPLE 2
Six experiments were carried out exactly as in
Example 1 except that the amounts of catalyst tcatalyst
level) were varied systematically from 2 mole% to 0.03
mole%. The reactions were carried out for 5 hours in each
case, and the reaction mixtures were analyzed by GLC.
Results are given in Table 2 which clearly demonstrate
that as the amount of catalyst was decreased from 2 mole%
to 0.06 mole%, the catalytic turnover numbers increased.
This suggests that the part of the catalyst at higher
catalyst level was ineffective in catalysis, i.e., was not
being used. Thus, various levels of catalyst may be used
according to the need.
XAMPLE 3
This set of ten experiments were carried out exactly
as in Example 1 except that the ratios of Pd/Sb/Cr were
varied in order to demonstrate the wide range as well as
its effect on the reaction rate. All these reactions were
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carried out for 5 hours and the products were analyzed by
GLC. Catalytic turnover numbers as high as 90.4 were
achieved. The results are given in Table 3.
EXAMPLE 4
This set of experiments ~ere carried out in a similar
manner as in Example 1 except that chromium was replaced
with other metal salts. In a typical experiment, 6 m
moles of palladium acetate, 7 m moles of antimony acetate
and 0.28 m moles of nickel acetate were mixed with 276 m
moles of octanoic acid in the reactor. ~bout 5 ml of
benzene was charged initially and the reaction mixture was
stirred and heated to 160C while bubbling oxygen at a
rate 50 ml/minute. Additional benzene was pumped in
slowly and the reaction was carried out for 5 hrs. during
which time, 220 m moles of total benzene were charged.
GLC analysis showed that about 17.5~ of the octanoic acid
charged was converted to produce 52 m moles of the phenyl
ester of octanoic acid. The catalytic turnover number was
calculated ~o be 8.7. Results of other reactions are
given in Table 4.
EXAMPLE 5
To the reactor fit~ed with a stirrer, thermometer,
Dean-Stark tube with condenser and oxygen inlet, there
were charged 300 m moles of octanoic acid, 76 m moles of
naphthalene, 0.75 m moles of palladium acetate, 0.75 m
moles of antimony acetate, 0.75 m moles of chromium
acetate, and 10 ml of heptane. The resulting mixture was
stirred and heated at 170 + 5C for 4 hrs. with oxygen
passing into the reactor at a rate of 50 ml/min. The
water produced was removed azeo~ropically with heptane and
collected in the Dean-Stark tube.
Analysis of the reaction mixture after 4 hrs. showed that
64% of naphthalene was converted to produce 48 m moles of
the naphthyl ester of octanoic acid.
E~AMPLE 6
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This set of experiments were carried out exactly as
in Example 1 except that various other carboxylic acids
were used instead of octanoic acid. The results of these
experiments are given in Table 5.
EXAMPLE 7
To a 500 ml reactor equipped as in Example 1, was
charged 1128 m moles of octanoic acid, 3 m moles of
palladium acetate, 3 m moles of antimony acetate, 3 m
moles of chromium acetate and 10 ml of benzene. The
reaction mixture was stirred and heated at 170-5C while
adding oxygen at a rate of 75 ml/minute. The reaction was
carried out for 24 hrs. and additional benzene was fed
slowly during the course of the reaction. The total
benzene introduced was about 700m moles. Samples of the
reaction mixture were withdrawn at ~arious time intervals
and analyzed by GLC. The results which are given below
clearly demonstrate a continuous production of phenyl
esters.
Reaction Reaction
Time wt% Phenyl Time wt% Phenyl
(hrs) ~ster (hrs) Ester
2 8 12 27
3 12.4 15 30
6 lB.5 18 32.3
9 23 2~ 38.5
EXAMPLE 8
r
Experiments were conducted in a high pressure
reactor equipped with either a built-in high-pressure
condenser or a high-pressure condenser connected to a
reactor at the outsideO Typically, the reactor was
charged with 208 m moles of octanoic acid, 0.5 m moles of
palladium acetate, o.5 m moles of antimony acetate, 0.5 m
moles of chromium acetate and 100 m moles of benzene. The
reactor was pressurized to 20 psig with oxygen. The
reaction mixture was stirred and hea~ed at 170~5C. The
atmosphere of the reactor was continuously vented and
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pressuriæed with fresh oxygen. The reactio~ was carried
out for 4 hrs. and the analysis showed that 7 m moles of
phenyl ester were produced. The catalytic turnover
numbers were calculated to be 14.
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