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Патент USA US3027410

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3,027,400
atet
Patented Mar. 27, 1962
1
2
product is almost exclusively o-phthalic anhydride. At
3,027,400
higher temperatures in the presence of alcohols, the
formation of o-phthalic esters and benzoic acid esters
Art C. McKinnis, Long Beach, and William D. Schae?er,
Pomona, Cali?, assignors to Union Oil Company of
California, Los Angeles, Calif., a corporation of Cali
fornia
No Drawing. Filed Feb. 1, 1960, Ser. No. 5,631
11 Claims. (Cl. 260-475)
becomes a signi?cant factor. Essentially the same ob
servations and results are obtained when the starting
MANUFACTURE OF META- AND PARA-PHTHALIC
ACID ESTERS
material is one of the following mono-esters:
0
10
This invention relates to new methods for the mono
OOOI-I
COOK
decarboxylation of trimellitic acid, or certain of its de
rivatives, to obtain mixtures of meta- and para-phthalic
acid diesters to the substantial exclusion of o-phthalic
acid esters and benzoic acid esters. Brie?y, the method
consists in heating a trimellitate reactant from the group
consisting of trimellitic acid or its inner anhydride, or a
mono-ester of either, to a temperature of about 170°
to 310° C. in the presence of certain catalytic metal ions
COOR
COOH
COOH
OOOR
II
C————(I)
(3:0
COOR
COOH
COOH
COOR
(III)
(IV)
(V)
(VI)
In all cases it is postulated that one or more of these
compounds is an intermediate in the process, regardless
(e.g. copper or silver) while contacting the reacting mix 20 of which starting material is used. In each case the ?nal
product is a mixture of dibasic acid esters wherein the
ture with an alcohol. Preferably, a strongly basic mate
ratio of para/meta isomers is about 40/60 to 50/50.
rial such as an alkali metal hydroxide or tertiary amine
This isomeric ratio of the product esters may be con
is also included in the reaction mixture, as this is found
siderably modi?ed however by including in the reaction
not only to accelerate the reaction, but to increase the
ratio of para-phthalic/meta-phthalic acid esters formed. 25 mixture a relatively strong base, which presumably inter
acts preferentially with the l- and 4-carboxyl groups,
It is an important object of this invention to provide
economical methods for the simultaneous mono-de
carboxylation and esteri?cation of trimellitic acid or its
anhydride. It is another object to provide a decarboxyla~
thereby favoring decarboxylation in the 2-position. There
is also a marked increase in the overall rate of de
carboxylation and esteri?cation.
By using the strong
tion method which can be operated at atmospheric pres
30 base, the ratio of para/meta isomers may be increased to
sure, thus avoiding the expense of high-pressure equip
about 70/30 or higher. Also, due to its accelerating
effect, even lower temperatures may be utilized, thereby
substantially eliminating the formation of o-phthalic esters
ment. Another object is to e?’ect a selective mono-de
carboxylation of the trimellitate reactant in the 1- or
and benzoic acid esters.
The process may be carried out either bacht-wise or
2~position, and still more preferentially in the Z-pcsition,
so that the product is mainly a para-phthalic acid diester.
Still another object is to provide a continuous method for
carrying out the decarboxylation, with continuous removal
of the diesters as they are formed, whereby the catalyst
and any basic material employed may be maintained in
the reaction zone in an active state.
continuously.
A continuous operation is preferred,
wherein alcohol and the trimellitate reactant are added
continuously or incrementally to the hot reaction mix
ture, and vaporized dibasic acid esters, water, CO2, and
These and other 40 excess alcohol are continuously removed. The operative
reaction temperatures range between about 170° and
310° (1., preferably between about 200° and 280° C. At
objects are achieved by the process herein described.
The present invention is based upon our discovery
that trimellitic acid or its inner anhydride (II), when
temperatures above 280° C., the formation of o-phthalic
heated at moderate temperatures in the presence of a suit
esters and benzoic acid esters becomes signi?cant.
At
able catalyst and an alcohol, will decarboxylate prefer 45 temperatures below the boiling point of the phthalate
entially in the l- or 2-positions, as follows:
esters formed, an excess of the alcohol may be used to
assist in sweeping the esters out of the reaction mixture.
(1)
coon
00011
coon
50
0:0
-——>
‘(1)
Other inert gases may also be used for this purpose, or
reduced pressures may be employed.
i1)
0-?
It is normally preferable to employ a high-boiling
solvent or diluent to facilitate contacting during the reac
+ ZROH
——>
tion. Suitable solvents include for example the phethalate
diesters themselves, or other high-boiling esters, prefer
00011
55
(II)
"'“}-ooon
+ CO2 + 21120
000R
ably of the same alcohol used in the reaction. Alterna
tively, we may use high-boiling ethers, alcohols, sulfones,
N,N-dialkyl amides, or the like. Alcohols will of course
become at least partially esteri?ed with the phthalic acids,
but this does not critically affect the process. A partic
ularly useful class of alcohol solvents consists of the high
boiling mono-others of polyalkylene glycols, e.g. hexa~
ethylene glycol mono-methyl ether, ‘for the para-phthalic
In the absence of alcohol, little or no decarboxylation
occurs at the moderate temperatures employed, while
acid esters are quite soluble therein.
at higher temperatures in the absence of alcohol the
pressure, but sub-atmospheric and super-atmospheric
The reaction is preferably conducted at atmospheric
3,027,400
A
reaction zone and to separate from the product esters.
Also, they sometimes tend to give a dark and/or tarry
pressures are also contemplated. At atmospheric or sub
atrnospheric pressures, the alcohol reactant may vaporize
at the reaction temperature, but the solubility of the
product.
Any amounts of the alkaline materials are effective in
quate amount can be retained therein by continuously 5 some degree, but optimum results are generally obtained
by maintaining about 0.5 to 2 moles thereof in the re
adding liquid or vaporized alcohol to the mixture. At
action mixture per mole of unreacted trimellitate reactant.
super-atmospheric pressures, reaction rates are enhanced.
The substantial absence of water during reaction is
Temperatures above about 310° C. generally result in
normally desirable, for if water is present free dibasic
lowering the amount of dissolved alcohol to a point which
permits some decarboxylation to occur in the 4-position, 10 acids will be formed which are not volatile under the re
action conditions. However, water in the starting mate
unless super-atmospheric pressures are employed, or un
rial is not harmful, since at atmospheric pressure, sub
' lms a high boiling alcohol is used.
stantially all Water is vaporized before reaction tempera
We normally prefer to use lower alkanols in the
ture is reached. Also, the conversion to trimellitic acid
reaction, e.g. methanol, ethanol, propanol, isopropanol, 15 to
its anhydride, with elimination of Water, is usually com
isobutanol, and the like. The lower alcohols form rela~
plete before decarboxylation temperatures are reached.
tively volatile phthalate esters which may easily be
The water of esteri?cation is insumcient to affect the re
vaporized or swept from the reaction mixture, and also
action materially, especially where it is continuously re
these lower alkanol esters are normally desired in the
with the product esters.
principal industrial applications as solvents, intermediates 20 moved
The following examples are cited to illustrate the in
for alkyd resins and the like. However, higher alcohols
vention, but should not be considered limiting in scope:
may also be used, e.g. hexyl, cyclohexyl, dodecyl, benzyl
and the like, particularly where high-boiling esters for
EXAMPLE I
use as plasticizers and the like are desired. 'The high
To compare the elfect of various catalysts, several batch
boiling esters may be recovered from the reaction mixture 25 experiments were carried out as follows:
by vacuum distillation, steam distillation, solvent Washing
To a 250 ml. 3-necked ?ask equipped with a re?ux
or the like. In general, any alkanol, cycloalkanol, or
condenser was added about 20 grams of 4-carbometh-oxy
arylalkanol containing between 1 and about 20 carbon
phthalic anhydride (the methyl ester of trimellitic acid
atoms may be utilized.
anhydride), and the catalyst to be tested. The mixture
The operative catalysts for use herein comprise mate 30 was then heated to reaction temperature, ‘and methanol
rials capable of yielding copper, silver, nickel, cadmium
was slowly added through the side-arm in small increments
or thallium ions in the reaction mixture. This includes
until su?‘icient CO2 could be collected from the off-gases
the oxides, hydroxides and salts of these metals. In
to measure the half-life of the trimellitate reactant.
general, the nature of the salt anion is immaterial, for in
Methanol and product esters were continuously re?uxed
any case the operative catalyst is probably a trimellitate 35 back into the reaction ?ask. At the end of each run, the
or phthalate salt of the catalyst metal. Suitable catalysts
reaction mixture was distilled to recover the product
alcohols in the reaction mixture is su?icient that an ade
include for example cupric acetate, cupric sulfate, cupric
esters, which were then analyzed to determine the ratio
of para- meta-phthalic esters formed. The results were
naphthenate, cupric trimellitate, cupric chloride, cupric
nitrate, cupric oxide, silver acetate, silver benzoate, silver
as follows:
naphthenate, silver trimellitate, silver chloride, silver 40
nitrate, silver sul?de, silver oxide, nickel nitrate, nickel
acetate, nickel trimellitate, cadmium hydroxide, cadmium
acetate, cadmium trimellitate, thallium acetate, thallium
Run
No.
hydroxide, thallium nitrate, thallium trimellitate and the
like.
Cuprous salts may also be used. The preferred
catalysts are the copper and silver compounds, and es
Table 1
T emp.
Catalyst
° 0.
utes
or no eifect.
phthalic pelgter in
esters 2
1I_1-, p
mixture
290
260
290
290
290
Any amounts of catalyst tare operative to some extent,
mercury have been tried, but were found to have little
Yielddoip- Pelrlrcent
- thalic
rn- an
45
pecially copper. Nickel, cadmium and thallium are less
active than copper or silver. Silver compounds are quite
active, but tend to become reduced to the free metal.
but preferably amounts between about 0.001% and 2%
by weight, based on the trimellitate reactant, are used.
Other metal salts, including salts of gold, zinc and
io,
Min-
____
290
(3)
50
90
30
80
______ _.
0
________ __
95+
95+
95+
95+
46
48
53
48
0
________ ._
1 Reaction is zero order; hence half-life of trimellitate reagent is canal to
one-half the time required for complete reaction.
2 Based on trimellitate reactant consumed.
‘
a After one hour of heating, substantially the only product was a small
55 quantity of trrmellrtlc acid esters. N o decarboxylation occurred.
The preferred alkalis or bases to be used in conjunction
with the foregoing catalysts are the alkali metal hydroxides,
carbonates or other alkaline salts thereof, e.g. lithium
It is hence apparent that, at moderate temperatures, the
catalysts of this invention are capable of effecting a sub
stantially complete conversion to dibasic acid esters in
hydroxide, sodium hydroxide, sodium carbonate, sodium
1-2 hours, while in the absence of a catalyst, no
trimellitate, potassium hydroxide, potassium carbonate, 60 about
decarboxylation occurs.
potassium trimellitate, rubidium hydroxide, rubidium car
The 4-carbomethoxy phthalic anhydride used in this
bonate, rubidium trimellitate, cesium hydroxide, cesium
example was prepared by heating trimellitic acid anhy
carbonate, cesium trimellitate, and the like, including the
dride at atmospheric pressure and 270—320° C. while
corresponding sul?des, acetates, phosphates, etc. The
adding methanol in small increments under a re?ux con
rubidium and cesium salts are especially preferred, for 65 denser which allowed H20 and excess methanol to escape.
they are found to give the maximum ratio of para-/meta
Under these conditions (in the absence of a catalyst)
phthalic esters. Other alkalis which may be used to less
there is no decarboxylation, and there is no appreciable
advantage than the alkali metal compounds, include the
esteri?cation beyond the mono-ester stage.
hydroxides, carbonates, sul?des, or other alkaline salts
of the alkaline earth metals, and of the relatively alkaline
EXAMPLE II
transitional metals, particularly those of groups 1B, 113 70
To
evaluate
the
effect
of added alkaline materials,
and VIII. Tertiary nitrogen bases are also found to be
etfective, e.g. pyridine, quinoline, trimethylamine, tri<
ethylamine, tributylamine, and the like. The nitrogen
several additional runs were carried out in a manner
analogous to that of Example I, but employing in each
case 20 grams of trimellitic acid anhydride instead of the
bases are however subject to the disadvantage of being
volatile, and thus relatively difficult to maintain in the 75 monoester. The results were as follows:
3,027,400
6
Table 2
Run
Catalyst
N o.
and Base
romp.
.
Halflite,1
Yield of Percent
m- and p- p~pl1thalio
M in-
phthalic
utcs
esters
mono-decarboxylation with resultant production of a
mixture of the diesters of meta- and para-phthalic acids
with said alcohol, said catalyst being a compound capable
ester in
of yielding ions of a metal selected from the class con
nu, p
sisting of copper, silver, nickel, cadmium and thallium,
said trimellitic acid reactant being selected from the class
iilixture
-
7 ____ __
8 .... ._
_
g gkgccm‘
9 ____ __
consisting of trimellitic acid, monoesters of trimellitic acid,
\
g. Cu(Ac)z__
Cu(Ac)2--
k
220
30
95+
}
230
30
95+
66
}
220
20
95+
73 10
trimellitic acid anhydride and monoesters of trimellitic
acid anhydride, and said alcohol being selected from the
class consisting of alkanols, cycloalkanols and arylalka
nols of l to 26 carbon atoms.
10“--
}
225
14
95+
ll_____
12.
}
}
mo
290
so
so
85
as
} 210
so
7s
is a copper compound.
3. A method as de?ned in claim 1 wherein said alcohol
15 is a lower alkanol.
57
4. A method as de?ned in claim 1 wherein said heating
}
220
so
75
58
‘
.~
1a.... {814.--"
.
’0.2 g Cu(Ae)
15_ ____
11m. (CC}(LX>3§\I
.
g.
}
H 1 C 2"
__
220
.1 g. ‘u
e 2-.
17" '"‘ {15 ml. pyridine . _ _ .
210
___,
. _ _. i
50
85
40
so
is carried out at substantially atmospheric pressure.
5. A method as de?ned in claim 4 wherein said alcohol
50
80
57
..
21c
15 ml. pyridine ________ __
2. A method as de?ned in claim 1 wherein said catalyst
>
16“.-. {(1)5 m 83,55,319)______
18___._
74
65
59
210
is a lower alkanol and is added continuously to the reac
,.
______ __
O
is 20 tion mhrture during said heating, and wherein product
61
diesters are continuously vaporized from the reaction mix
ture.
________ __
6. A method for the manufacture of diesters of meta
and para-phthalic acids, which comprises heating a tri
From the foregoing data, it will be observed that the
addition of an alkali gives markedly increased reaction 25 mellitic acid reactant in the presence of (1) an alcohol
rates, even at temperatures considerably lower than those
selected from the class consisting of alkanols, cycloalka
of Example I. The proportion of p-phthalic acid esters
nols and araylkanols of 1 to 20 carbon atoms, (2) a de
in the product is also markedly increased. Runs 9 and
carboxylation catalyst, and (3) an added alkaline ma
10 show the superiority of cesium and rubidium com
terial selected from the class consisting of tertiary nitro
pounds, as compared to sodium or potassium. Runs 11
gen bases and the oxides, hydroxides and alkaline salts of
and 12 show that cadmium hydroxide, even in small
amounts, materially increases the ratio of para-/meta
esters formed. Runs 13—17 demonstrate the ei?cacy of
nitrogen bases, and run No. 18 shows that the nitrogen
bases alone are ineffective.
35
EXAMPLE iii
A continuous run was carried out as follows: Into a
the alkali metals, at a reaction temperature between
about 170° and 310° C. to eifect esteri?cation and mono
decarboxylation with resultant production of a mixture of
the diesters of meta- and para-phthalic acids with said
alcohol, said mixture predominating in p-phthalic esters,
said catalyst being a compound capable of yielding ions of
a metal selected from the class consisting of copper, silver,
nickel, cadmium, and thallium, and said trimellitic acid
reactant being selected from the class consisting of trimel
1 liter reaction flask equipped with a stirrer, dropping
funnel and heated vapor outlet line, was placed 13.8 40 litic acid, monoesters of trimellitic acid, trimellitic acid
grams of K2CO3, 0.2 grams Cu(acetate)2, 100 grams of
anhydride and monoesters of trimellitic acid anhydride,
dimethyl isophthalate (solvent), ‘and 19 grams of trimel
the concentration of said alkaline material in the reaction
litic acid anhydride. A separate feed mixture was pre
mixture being maintained at a value below about 2 moles
pared by disolving 190 grams of trimellitic acid anhydride
thereof per mole of unreacted trimellitate reactant.
in 1 liter of methanol. The contents of the reaction ?ask 45
7. A method as de?ned in claim 6 wherein said alkaline
were then heated to about 235° C., and the feed mixture
material is selected from the class consisting of the oxides,
was admitted through the dropping funnel at the rate of
hydroxides and alkaline salts of rubidium and cesium.
about 1 ml. per minute. The vaporized product plus
8. A method as de?ned in claim 6 wherein said catalyst
is a copper compound.
carbon dioxide and excess methanol was continuously
50
taken off and condensed into a product receiver. The
9. A method as de?ned in claim 6 wherein said alcohol
is a lower alkanol.
total yield of meta- and para-phthalic acid dimethyl esters
was about 95 percent, based on trimellitic acid anhydride
10. A method as de?ned in claim 6 wherein said heat
ing is carried out at substantially atmospheric pressure.
consumed. The ratio of para-/meta-esters was about
63/37.
11. A method as de?ned in claim 10 wherein said alco
55
hol is a lower alkanol and is added continuously to the
It is thus apparent that the process of this invention
provides a simple and economical method for converting
trimellitic acid to the diesters of meta- and para-phthalic
reaction mixture during said heating, and wherein product
diesters are continuously vaporized from the reaction mix
acids. It is not intended that the invention should be
limited to the details described above. Other catalysts,
bases, and alcohols within the purview of this speci?ca
tion can be substituted in the above examples to obtain
analogous results as to conversions, yields, reaction ve
locities and isomeric product distribution. The true
scope of the invention is intended to be embraced by the 65
following claims:
We claim:
1. A method for the manufacture of diesters of meta
and para-phthalic acids, which comprises heating a tri
mellitic acid reactant in the presence of an alcohol and a
decarboxylation catalyst at a reaction temperature be 70
tween about 170° and 310° C. to effect esteri?cation and
ture.
References Cited in the file of this patent
UNITED STATES PATENTS
2,864,854
McKinnis ____________ .__ Dec. 16, 1958
OTHER REFERENCES
Fieser and Fieser: Organic Chemistry, 3rd Ed., page 178
(1956).
Noller: Chemistry of Organic Compounds, 2nd Ed.,
page 170 (1957).
Gould: Structure and Mechanism in Organic Chemistry,
pages 314-15, 342-53 (1959).
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