Note: Descriptions are shown in the official language in which they were submitted.
1058636
This invention relates to the preparation of the an-
hydrides of carboxylic acids, more particularly mono-carboxylic
acids, and especially the anhydrides of lower alkanoic acids,
such as acetic anhydride, by carbonylation.
Acetic anhydride has been known as an industrial
chemical for many years and large amounts are used in the manu-
facture of cellulose acetate. It has commonly been produced
on an industrial scale by the reaction of ketone and acetic
acid. It is also known that acetic anhydride can be produced
by the decomposition of ethylidene diacetate, as well as by
the oxidation of acetaldehyde, for example. Each of these
"classic" processes has well-known drawbacks and disadvantages
and the search for an improved process for the production of
acetic anhydride has been a continuing one. Proposals for
producing anhydrides by the action of carbon monoxide upon
various reactants (carbonylation) have been described, for
example, in Reppe et al. U.S. Patents 2,729,561, 2,730,546
and 2,789,137. However, such prior proposals involving car-
bonylation reactions have required the use of very high pressure.
Carbonylation at lower pressures has been proposed but as a
route to the preparation of acetic acid. French Patent
1,573,130, for example, describes the carbonylation of methanol
and mixtures of methanol with methyl acetate in the presence
of compounds of iridium, platinum, palladium, osmium and
ruthenium and inthe presence of bromine or iodide under more
moderate pressures than those contemplated by Reppe et al.
Similarly, South African Patent 68/2174 produces acetic acid
~rom the same reactants using a rhodium component with bromine
or iodide. More recently, Schultz (U.S. Patents 3,689,533
and 3,717,670) has disclosed a vapor-phase process for acetic
acid production employing various catalysts comprising a
- 2 -
1058636
rhodium component dispersed on a carrier. None of these
relatively recent carbonylation disclosures, however, refers
to or contemplates the preparation of acetic anhydride or other
carboxylic acid anhydrides.
Improved processes for preparing carboxylic acid,
anhydrides, including acetic anhydride, are disclosed in
Canadian patent of Colin Hewlett 1,033,761, issued July 4,
1978 wherein there is disclosed the use of promotors which
are elements having atomic weights greater than 5 of Groups IA,
IIA, IIIA, IVB, and VIB, the non-noble metals of Group VIII,
and the metals of the lanthanide and actinide groups of the
Periodic Table, and their compounds.
It is an object of the present invention to provide
a further improved process for the manufacture of carboxylic
acid anhydrides, especially lower alkanoic anhydrides, such
as acetic anhydride.
In accordance with the invention, a carboxylic ester
and/or a hydrocarbyl ether are carbonylated under substantial-
ly anhydrous conditions in the presence of a Group VIII noble
metal catalyst, in the presence of a halide which is an iodide
or a bromide and in the presence of promoters comprising at
least one metal of Groups IVB, VB and VIB or a non-noble metal
of Group VIII, or their compounds, in combination with an
organo-nitrogen compound or an organo-phosphorus compound
wherein the nitrogen and phosphorus are trivalent. It has been
discovered that this catalyst-multiple promoter system makes
possible reduced pressures, especially carbon monoxide partial
pressures, lower catalyst concentrations, lower temperatures
and shorter contact times. The rate of reaction and the
product concentration realized from this catalyst-multiple
promoter combination have been found to be exceptionally high.
Moreover, it has also been found that the promoters stabilize
10S~636
the catalyst, and inhibit corrosion.
Thus, in accordance with the invention, carbon monoxide
is reacted with a carboxylate ester, especially a lower alkyl
alkanoate, or a hydrocarbyl ether such as a loweralkyl ether,
to produce a carboxylic anhydride, such as a lower alkanoic
anhydride, the carbonylation taking p~ace in the presence of
an iodide or bromide, e.g., a hydrocarbyl halide, especially
a lower alkyl halide, which is an iodide or a bromide, such
as methyl iodide. Thus, acetic anhydride, for example, can
be effectively prepared in a representative case by subjecting
methyl acetate or dimethyl ether to carbonylation in the
presence of methyl iodide. In all cases, the carbonylation is
carried out under anhydrous conditions in the presence of
the catalyst-multiple promoter system described above. As
indicated, an ester-ether mixture can be carbonylated if
desired.
It will be understood that the hydrocarbyl halide may
be formed in situ and the halide may thus be supplied to the
system not only as the hydrocarbyl halide but the halogen
moiety may also be supplied as another organic halide or as
the hydrohalide or other inorganic halide, e.g., salts, such
as the alkali metal or other metal salts, or even as elemental
iodine or bromide. Following the reaction the organic com-
ponents of the reaction mixture are readily separated from
one another, as by fractional distillation.
In like manner, other lower alkanoic anhydrides, i.e.,
anhydrides of lower alkanoic acids, such as propionic anhydride,
butyric anhydrides and valeric anhydrides, can be produced
by carbonylating the corresponding lower alkyl alkanoate or
a lower alkyl ether. Similarly, other carboxylic acid an-
hydrides, e.g., the anhydrides of other alkanOic acids, such
~058636
as those containing up to 12 carbon atoms, for example capric
anhydrides, caprylic anhydrides and lauric anhydrides, and
like higher anhydrides are produced by carbonylating the corres-
ponding ester, e.g. alkyl alkanoates containing up to 11 carbon
atoms in the alkyl group up to 12 carbon atoms in the car-
boxylate group, or aryl esters, or the corresponding ether, such
as heptyl caprylate, nonyl decanoate, undecyl laurate, phenyl
benzoate, heptyl ether, nonyl ether, phenyl ether, and the
like.
It is preferred that the reactants be selected so that
the resulting anhydride will be a symmetrical anhydride, i.e.,
having two identical acyl groups, viz., wherein R in equations
(1) and (2) is the same in each instance, but it is within
the scope of the invention tQ produce non-symmetrical or mixed
anhydrides and this can be readily effected by using different
combinations of reactants, i.e., by using compounds having
different R groups in the foregoing reactions, as will be
obvious to persons s~illed in the art.
The above described reaction can be expressed as
follows:
CO + RCOOR ~ (RCO) 2 (l)
2CO + ROR - - ~ (RCO) 2 (2)
wherein R is a hydrocarbyl radical which may be satur-
ated, e.g., alkyl of
1 to 11 carbon atoms, or monocyclic aryl, e.g.,
phenyl, or alkaryl, e.g., benzyl. Preferably, R is lower
alkyl, i.e., an alkyl group of l to 4 carbon atoms, such
as methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl,
and t-butyl.
The hydrocarbyl radical may be substituted with
substituents which are inert in the reactions of the invention.
The more volatile alkyl halide, by-product acyl halide and
~058636
unreacted ether or ester in the final produce mixture can be
readily removed, as by distillation, for recycling, and the
net yield of product is substantially exclusively the
desired carboxylic anhydride. In the case of liquid-phase
reaction, which is preferred, the organic compounds are
easily separated from the metal-containing components, as by
distillation. The reaction is suitably carried out in a
reaction zone to which the carbon monoxide, the ester or
ether, the halide and the noble metal catalyst and the pro-
moters are fed. No water is produced in the above-described
reactions and anhydrous or ~ubstantially anhydrous conditions
are employed.
In carrying out the process of the invention, a
wide range of temperatures, e.g., 25 to 350C are suitable
but temperatures of 100 to 250C are preferably employed and
the more preferred temperatures generally lie in the range of
125 to 225C. Temperatures lower than those mentioned can be
used but they tend to lead to reduced reaction rates, and
higher temperatures may also be employed but there is no
particular advantage in their use. The time of reactiQn is
also not a parameter of the process and depends largely
upon the temperature employed, but typical residence times,
by way of example will generally fall in the range of 0.1
to 20 hours. The reaction is carried out under super-atmos-
pheric pressure but, as previously mentioned, it is a feature
of the invention that excessively high pressures, which require
special high-pressure equipment, are not necessary. In
general, the reaction is effectively carried out by employ-
ing a carbon monoxide partial pressure which is preferably
15 to 1000 p.s.i., and most preferably 30to 200 p.s.i.,
although carbon monoxide partial pressure of 1 to 10,000
p.s.i. can also be employed. By maintaining the partial
1058636
pressure of carbon monoxide at the values specified, adequate
amounts of this reactant are always present. The total pres-
sure is preferably that required to maintain the liquid phase
and in this case the reaction can be advantageously carried
out in an autoclave or similar apparatus. The final reaction
mixture will normally contain an acyl halide and a hydrocarbyl
halide along with the product anhydride and these halides,
after separation from the anhydride, can be recycled to the
reaction. At the end of the desired residence time, the
reaction mixture is separated into its several constituents,
as by distillation. Preferably, the reaction product is
introduced into a distillation zone, which may be a fractional
distillation column, or a series of columns, effective to
separate the hydrocarbyl halide, acyl halide and the ester
or ether, free organic promoter and the product anhydride.
The boiling points of these several compounds are sufficiently
far apart that their separation by conventional distillation
presents no particular problem. Likewise, the higher boiling
organic components can be readily distilled away from the
noble metal catalyst, the metal-containing promoter, and any
organic promoter which may be in the form of a relatively
non-volatile complex. The hydrocarbyl halide and the noble
metal catalyst, as well as the acyl halide and the promoters,
can then be combined with fresh amounts of ester or ether and
carbon monoxide and reacted to produce additional quantities
of anhydride.
The ratio of ester or ether to the halide in the
reaction system can vary over a wide range. Typically, there
are used 0.1 to 1000 moles of the ester or ether per mole
of halide, preferably 1 to 30 moles per mole.
The process is advantageously carried out in the
1058636
presence of a solvent or diluent, particularly when the
reactant has a relatively low boiling point, as in the case
of di-methyl ether. The presence of a higher boiling solvent
or diluent, which may be the product anhydride itself, e.g.,
acetic anhydride in the case of di-methyl ether, or which may
be the corresponding ester, e.g., methyl acetate, again in
the case of methyl ether, will make it possible to employ
more moderate total pressure. Alternatively, the solvent or
diluent may be any organic solvent which is inert in the en-
vironment of the process such as hydrocarbons, e.g., octane,
benzene, toluene, or carboxylic acids, e.g., acetic acid,
and the like. The carboxylic acid, when used, shou~d pre-
ferably correspond to the anhydride being produced. A solvent
or diluent is suitably selected which has a boiling paint
sufficiently different from the desired product in the reaction
mixture so that it can be readily separated, as will be ap-
parent to persons skilled in the art.
The Group VIII noble metal catalyst, i.e., iridium,
osmium, platinum, palladium, rhodium, and ruthenium can be
employed in any convenient form, viz~, in the zero valent
state or in any higher valent form. For example, the catalyst
to be added may be the metal itself in finely divided form,
or as a metal carbonate, oxide, hydroxide, bromide, iodide,
chloride, lower alkoxide (methoxide), phenoxide or metal
carboxylate wherein the carboxylate ion is derived from an
alkanoic acid of 1 to 20 carbon atoms. Similarly, complexes
of the metals can be employed, for example the metal carbonyls,
such as iridium carbonyls and rhodium carbonyls, e.g., hexa-
rhodium hexadecacarbonyl, or as other complexes such as the
carbonyl halides, e.g., iridium tri-carbonyl chloride
[Ir(CO)3Cl]2 or chlorodicarbonyl rhodium dimer, or the
acetylacetonates, e.g., rhodium acetylacetonate RH(C5H702)3.
-- 8 --
~058636
Other suitable forms of the Group VIII noble metal include
trichloro trispyridine rhodium, hydrido carbonyl tris(tri-
phenyl phosphine)rhodium, dirhodium octacarbonyl, chlorotris
(triphenyl phosphine) rhodium, chlorocarbonyl bis(triphenyl
phosphine)rhodium, and corresponding forms of other Group VIII
noble metals, e.g., corresponding palladium compounds. In-
cluded among the catalysts listed above are complexes of the
Group VIII noble metal with organic promoter ligands derived
from the organic promoters hereinafter described. It will be
understood that the foregoing compounds and complexes are
merely illustrative of suitable forms of the Group VIII noble
metal catalyst and are not intended to be limiting.
The carbon monoxide is preferably employed in sub-
stantially pure form, as available commercially, but inert
diluents such as carbon dioxide, nitrogen, methane, and
noble gases can be present if desired. The presence of inert
diluents does not affect the carbonylation reaction but their
presence makes it necessary to increase the total pressure in
order to maintain the desired CO partial pressure. The
carbon monoxide, like other reactants should, however, be
essentially dry, i.e., the CO and the other reactants should
be reason~bly free from water. The presence of minor amounts
of water such as may be found in the commercial forms of
the reactants is, however, entirely acceptable. Hydrogen
which may be present in very small (trace) amounts as an im-
purity is not objectionable and even may tend to stabilize the
catalyst, but significant amounts may tend to affect radically
the character of the products produced during the
carbonylation, as disclosed in the commonly assigned Canadian
application of Nabil Rizkalla and C.N. Winnick entitled
"Process for Preparing Ethylidene Diacetate" S.N. 246,466
filed February 24, 1976.
1058636
In accordance with the invention, the activity of
the Group VIII noble metal catalysts described above is
significantly improved, particularly with respect to
reaction rate and product concentration, catalyst stability
and corrosion inhibition, by the concurrent use of a promoter
combination or co-promoter system containing a metal component
which is a metal of Groups IVB, VB and VIB, and the non-noble
metals of Group VIII in association or combination with an
organo-nitrogen compound or an organo-phosphorus compound
wherein the nitrogen and the phosphorus are trivalent. In
the case of the metal component, particularly preferred are
the lower atomic weight metals of each of these groups, e.g.,
those having atomic weights lower than 100, and especially
preferred are the metals of Group VIB, and the non-noble metals
of Group VIII. In general, the most suitable elements are
chromium, iron, cobalt and nickel. Most preferred is chromium.
The promoters may be used in their elemental form, e.g., as
finely-divided or powdered metals, or they may be employed
as compounds of various types, both organic and inorganic,
which are effective to introduce the element into the reaction
system. Thus, typical compounds of the promoter elements
include oxides, hydroxides, halides, e.g., bromides and
iodides, oxyhalides, hydrides, alkoxides, and the like.
Especially preferred organic-metal compounds are the salts of
organic mono-carboxylic acids, e.g., alkanoates such as
acetates, butyrates, decanoates, laurates, benzoates, and
the like. Other compounds include the metal alkyls and
carbonyl compounds as well as chelates, association compounds
and enol salts. Particularly preferred are the elemental forms,
compounds which are bromides or iodides, and organic salts,
e.g., salts of the mono-carboxylic acid corresponding to the
anhydride being produced. Mixtures of promoters can be used,
-- 10 --
1058636
if desired, especially mixtures of elements from different
Groups of the Periodic Table. The exact mechanism of the
effect of the promoter, or the exact form in which the promoter
acts, is not known but it has been noted that when the
promoter is added in elemental form, e.g., as a finely-
divided metal, a slight induction period is observed.
The metals employed may contain impurities normally
associated with the commercially available metal or metal
compounds, and need not be purified any further. Thus, the
commerically available metal or metal compound is suitably
employed in the case of the Group VIII noble metal catalyst
and in the case of the metal promoter.
The organic co-promoter can, in its broader sense,
be any organo-nitrogen or argano-phosphorus compound wherein
the nitrogen and phosphorus are trivalent. Preferably,
however, the organo-nitrogen co-promoter is an amine, especial-
ly a tertiary amine of the formula ~N-R wherein R , R
and R are the same or different and are alkyl, rycloalkyl,
aryl or acyl groups which may be substituted by non-interfering
groups, preferably having up to 20 carbon atoms, such as tri-
methylamine, triethylamine, triphenylamine, ethylenediamine,
tetraacetic acid, and the like, or a heterocyclic amine such
as pyridine, picoline, quinoline, methylquinoline, hydroxy
quinoline, pyrrole, pyrrolidine, pyrrolidone, and the like,
or an imidazole, such as imidazole, methyl imidazole and
the like, or an imide of a carboxylic acid which may be mono-
basic or polybasic and which may be aliphatic or aromatic and
preferably contain up to 20 carbon atoms, such as acetic acid,
succinic acid, phthalic acid, pyromellitic acid, e.g.
N,N-dimethylacetamide, succinimide, phthalimide and pyromellitic
diimide, or a nitrile or amide which may be aliphatic or
aromatic and preferably contain up to 20 carbon atoms, e.g.,
~058636
acetonitrile, hexamethyl phosphoric triamide, and like imides,
nitriles, and amides, or an oxime such as cyclohexanone oxime,
and the like. It will be understood, however, that higher
molecular weight promoters e.g., polymeric forms of the
organo-nitrogen compounds, may be used such as polyvinyl-
pyridine, polyvinyl pyrrolidone, and the like.
The organo-phosphorus co-promoter is preferably a
phosphine of the formula ,P-R wherein R , R and R
may be the same or different and are alkyl, cycloalkyl, aryl
groups, amide groups or halogen atoms, preferably containing
up to 1 to 20 carbon atoms in the case of alkyl and cyclo-
alkyl groups and 6 to 18 carbon atoms in the case of aryl
groups. Typical phosphines include trimethylphosphine, tri-
propylphosphine, tricyclohexylphosphine and triphenylphosphine.
Although it is preferred that the organic promoters
be added separately to the catalyst system, it is possible to
add them as complexes with the Group VIII noble metal such
as the trichloro trispyridine rhodium, tris(triphenyl phos-
phine) rhodium, chlorotris(triphenyl phosphine) rhodium, and
chlorocarbonyl bis (triphenyl phosphine) rhodium previously
mentioned. Both free organic promoters and complexed pro-
moters can also be used. Indeed, when a complex of the or-
ganic promoter and the Group VIII noble metal is used, it is
desirable to add free organic promoter as well.
The amount of Group VIII nobel metal catalyst is in
no way critical and is not a parameter of the process of the
invention and can vary over a wide range. As is well known to
persons skilled in the art, the amount of catalyst used is
that which will provide the desired suitable and reasonable
reaction rate since reaction rate is influenced by the amount
of catalyst. However, essentially any amount of catalyst will
~058636
facilitate the basic reaction and can be considered a
catalytically-effective quantity. Typically, however, the
catalyst is employed in the amount of 1 mol per 10 to 100,000
mols of ester or ether, preferably 1 mol per 100 to 10,000
mols of ester or ether, and most preferably 1 mol per 500 to
2000 mols of ester or ether.
The quantity of metal promoter can vary widely.
Typically, it is one mole per 10,000 moles of ester or ether,
preferably it is used in the amount of 1 mole per 20 to
2000 moles, most preferably 1 mole per 50 to 500 moles of ester
or ether. The quantity of organic promoter can also vary widely
but typically it is used in the amounts of 1 mole per 1 to
10,000 moles of ester or ether, preferably 1 mole per 10 to
1000, most preferably 15 to 200 moles of ester or ether.
In the working up of the reaction mixtures, e.g.,
by distillation, as discussed above, the metal promoter general-
ly remains with the Group VIII noble metal catalyst, i.e.,
as one of the least volatile components, and is suitably
recycled or otherwise handled along with the catalyst. The
organic promoter can also be recovered and recycled.
It will be apparent that the above-described reactions
}end themselves readily to continuous operation in which the
reactants and catalyst, preferably in combination with the
promoter combination are continuously supplied to the
appropriate reaction zone and the reaction mixture continuously
distilled to separate the volatile organic constituents and
to provide a net product consisting essentially of carboxylic
acid anhydride, with the other organic components being
recycled and, in the case of liquid-phase reaction, a residual
Group VIII noble metal-containing (and promoter-containing)
fraction also bein~ recycled. In the case of such continuous
operation, it will be apparent that the halogen moiety remains
1058636
in the system at all times subject only to occasional handling
losses or purges. The small amount of halogen makeup which
may be needed from time to time is preferably effected by
supplying the halogen in the form of the hydrocarbyl halide
but, as pointed out above, the halogen moiety may also
be supplied as another organic halide or as the hydrogen
halide or other inorganic halide, e.g., salts, such as the
alkali metal or other metal salts, or as elemental iodine or
bromine.
As previously indicated, the carbonylation
reaction involved in the process of the invention can
be carried out in the vapor phase, if desired, by
appropriate control of the total pressure in relation
to the temperature so that the reactants are in vapor
form when in contact with the catalyst. In the case of
vapor-phase operation, and in the case of liquid-phase operation,
if desired, the catalyst and promoter, i.e., the catalyst com-
ponents, may be supported, i.e., they may be dispersed on a
carrier of conventional type such as alumina, silica, silicon
carbide, zirconia, carbon, bauxite, attapulgus clay, ana the
like. The catalyst components can be applied to the carriers
in conventional manner, e.g., by impregnation of the carrier
with a solution of the catalyst, or the catalyst and promoter,
followed by drying. Catalyst component concentrations upon
the carrier may vary widely, e.g., 0.01 weight percent to 10
weight percent, or higher. The organic promoter can be either
fed with the reactants or complexed with the catalyst. Typical
operating conditions for vapor-phase operation are a tempera-
ture of 100 to 350C, preferably 150 to 275 and most pre-
ferably 175 to 255C, a pressure of 1 to 5000 p.s.i.a.,
preferably 50 to 1500 p.s.i.a. and most preferably 150 to
500 p.s.i.a., with space velocities of 50 to 10,000 hr. 1,
-- 14 --
1058636
preferably 200 to 6,000 hr. 1 and most preferably 500 to
4000 hr. (STP).
The following examples will serve to provide a fuller
understanding of the invention, but it is to be understood
that they are given for illustrative purposes only, and ar@
not to be construed as limitative of the invention. In
the examples, all parts and percentages are by weight, unless
otherwise indicated.
In the examples, the various reactants and catalyst
components are charged to the reaction vessel which is then
closed and brought to the reaction temperature indicated.
The initial carbon monoxide partial pressure specified is the
calculated value at reaction temperature at the beginning of
the reaction, i.e., at zero conversion. The total pressure
is maintained by introducing additional carbon monoxide as the
reaction proceeds.
EXAMPLE I
Methyl acetate (350 parts), rhodium trichloride
hydrate (2.25 parts), methyl iodide (57 parts), pyridine
(15 parts), chromium hexacarbonyl (7.5 parts) and acetic acid
(90 parts) were heated at 175C in a stirred Hastelloy pressure
vessel, under an atmosphere of carbon monoxide (continuous
total pressure 350 p.s.i.g.; initial partial pressure of
carbon monoxide 66 p.s.i.). GC analysis o the reaction
mixture after one-hour reaction time showed it to contain 54
acetic anhydride (331 parts).
EXAMPLE II
Methyl acetate (350 parts), rhodium trichloride
hydrate (0.2 parts), pyridine (15 parts), methyl iodide (114
parts), chromic iodide (15 parts) and acetic acid (90 parts)
were heated at 175C in a stirred Hastelloy pressure vessel,
under an atmosphere of carbon monoxide (continuous total
1058636
pressure 350 p.s.i.g.; initial carbon monoxide partial
pressure 66 p.s.i.). GC analysis of the reaction mixture after
one-hour reaction time showed it to contain 26% acetic anhydride
(160 parts).
EL~MPLE III
Methyl acetate (300 parts), rhodium trichloride
hydrate (2 parts), pyridine (13 parts), methyl iodide (50
parts), and chromium hexacarbonyl (6.4 parts) were heated at
175C in a stirred Hastelloy-lined autoclave under an
atmosphere of carbon monoxide (total pressure 350 p.s.i.g.;
initial carbon monoxide partial pressure 65 p.s.i.). After
1-1/2 hours reaction time a GC analysis of the reaction mixture
showed it to contain 62.9% acetic anhydride (282 parts).
EX~LE IV
Methyl acetate (350 parts), rhodium trichloride
hydrate (2.25 parts), methyl iodide (57 parts-), 2-picoline
(17 parts) and chromium hexacarbonyl (7.5 parts) were heated
at 175C in a stirred Hastelloy pressure vessel, under an
atmosphere of carbon monoxide (continuous total pressure 350
p.s.i.g.; initial partial pressure of carbon monoxide 66 p.s.i.).
GC analysis of the reaction mixture after one-hour reaction
time showed it to contain 72.4% acetic anhydride (383 parts).
EXA~LE V
Methyl acetate (100 parts), rhodium trichloride
hydrate (0.75 parts), methyl iodide (18 parts), methyl
imidazole (.5 parts), chromium carbonyl (2.5 parts) and acetic
acid (50 parts) were heated at 175C in a stirred glass
lined pressure vessel, under an atmosphere of carbon monoxide
(continuous total pressure 350 p.s.i.g.; initial partial
pressure of carbon monoxide 66 p.s.i.). G.C. analysis of the
reaction mixture after one-hour reaction time showed it to
contain 38.7% acetic anhydride (76 parts).
- 16 -
1058636
EXAMPLE VI
Methyl acetate (100 parts), rhodium trichloride hydrate
(0.2 part), methyl iodide (36 parts), pyromellitic diimide
(5 parts), chromium hexacarbonyl (5 parts) and acetic acid (50
parts) were heated at 175C in a stirred glass-lined pressure
vessel, under an atmosphere of carbon monoxide (continuous
total pressure 350 p.s.i.g.; initial partial pressure of car-
bon monoxide 66 p.s,i.). GC analysis of the reaction mixture
after one-hour reaction time showed it to contain 32.4%
acetic anhydride (70 parts).
EXAMPLE VI I
Methyl acetate (400 parts), rhodium trichloride
hydrate (2.25 parts), methyl iodide (57 parts), triphenyl
phosphine ~10 parts), and chromium hexacarbonyl(7.5 parts)
were heated at 175C in a stirred Hastelloy pressure vessel
under an atmosphere of carbon monoxide (continuous total
pressure 350 p.s.i.g. initial partial pressure of carbon
monoxide 66 p.s.i.). GC analysis of the reaction mixture
after one-hour reaction time showed, it to contain 52.7% acetic
anhydride (294 parts).
EXAMPLE VI I I
Methyl acetate (170 parts), rhodium trichloride
hydrate ~one part), methyl iodide (25 parts), succinimide
(6.5 parts), chromium carbonyl (3.2 parts), and acetic acid
(16 parts) were heated at 175C in a stirred glass-lined
pressure vessel under an atmosphere of carbon monoxide (con-
tinuous total pressure 350 p.s.i.g.; initial Co partial pressure
66 p.s.i.). GC analysis of the reaction mixture after one-
hour reaction time showed it to contain 40~ acetic anhydride
(99 parts).
EXAMPLE IX
Methyl acetate (173 parts), rhodium trichloride
1058636
hydrate (1 part), methyl iodide (25 parts), chromium carbonyl
(3.3 parts) and triethylamine (7.5 parts) were heated at
175C in a stirred Hastelloy pressure vessel under an atmosphere
of carbon monoxide (continuous total pressure 350 p.s.i.g.;
initial CO partial pressure 66 p.s.i.). GC analysis of the
reaction mixture after one-hour reaction time showed it to
contain 32% acetic anhydride (76 parts).
EXAMPLE X
Methyl acetate (173 parts), rhodium trichloride
hydrate (1 part), methyl iodide (25 parts), chromium carbonyl
(3.3 parts), and tri-n-butyl phosphine (17 parts) were heated
at 175C in a stirred Hastelloy pressure vessel under an atmos-
phere of carbon monoxide (continuous total pressure 350
p.s.i.g.; initial partial pressure 66 p.s.i.). GC analysis
of the reaction mixture after one-hour reaction time showed
it to contain 56% acetic anhydride (147 parts).
EXAMPLE XI
Example X was repeated, using 22 parts of triphenyl
phosphine instead of the tri-n-butyl phosphine. GC analysis
of the reaction mixture after one-hour reaction time showed
it to contain 53% acetic anhydride (128 parts).
EXAMPLE XII
Dimethyl ether (109 parts), methyl acetate (175 parts),
rhodium trichloride hydrate (2 parts), methyl iodide (50
parts), 3-picoline (15 parts), and chromium carbonyl (7.5
parts) were heated at 150C in a stirred Hastelloy-C pressure
vessel under an atmosphere of carbon monoxide, (total pressure
1000 p.s.i.g., CO partial pressure 320 p.s.i.). After 3
hours reaction time, GC analysis of the reaction mixture shows
it to contain 50.6% acetic anhydride (242 parts) and 29.3%
methyl acetate (140 parts).
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1058636
EXAM~LE XIII
Methyl acetate (350 parts), rhodium trichloride
hydrate (2 parts), methyl iodide (50 parts), acetic acid
(90 parts), phthalimide (28 parts) and chromium hexacarbonyl
(7.5 parts) were heated at 175C in a stirred Hastelloy-C
pressure vessel under an atmosphere of carbon monoxide (total
pressure 350 p.s.i.g.; initial partial pressure of carbon
monoxide 70 p.s.i.). After 1 hour reaction time, GC analysis
of the reaction mixture shows it to contain 33.3% acetic
anhydride (193 parts).
EXAMPLE XIV
Methyl acetate (350 parts), rhodium trichloride
hydrate (2 parts), methyl iodide (50 parts), acetic acid
(90 parts), 2,6 lutidine (20 parts), and chromium hexacarbonyl
(7.5 parts) were heated at 175C in a stirred Hastelloy-C
pressure vessel under an atmosphere of carbon monoxide (total
pressure 350 p.s.i.g.; initial partial pressure of carbon
monoxide 70 p.s.i.). After 1 hour reaction time, GC analysis
of the reaction mixture shows it to contain ~.2% acetic
anhydride (268 parts).
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