Process for preparing carboxylic acids

Allyl alcohol is reacted with carbon monoxide in the presence of a catalytically effective amount of a heterogeneous catalyst composition comprising zero valent palladium and a catalyst promoting amount of hydrogen halide to provide a mixture of products predominantly made up of carboxylic acids containing four and five carbon atoms, e.g., 3-butenoic acid, crotonic acid, butyric acid, isobutyric acid, glutaric acid and methyl succinic acid and possibly minor amounts of other oxygenated compounds such as allyl ether and allyl 3-butenoate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the field of processes for preparing acyclic 
carboxylic acids and, more particularly, to such processes featuring the 
reaction of an olefinic compound and carbon monoxide in the presence of 
palladium-containing catalyst (i.e., carbonylation). 
2. Description of the Prior Art 
The C.sub. 4 and C.sub. 5 carboxylic acids, e.g., 3-butenoic acid 
(vinylacetic acid), crotonic acid, butyric acid, isobutyric acid, glutaric 
acid and methyl succinic acid are industrially important compounds useful 
as intermediates for the manufacture of numerous chemical products. It is 
known at present that carboxylic acids and/or carboxylic acid esters can 
be prepared by the reaction of an olefinically unsaturated compound and 
carbon monoxide (i.e., carbonylation) in the presence of 
palladium-containing catalysts. U.S. Pat. No. 3,427,344 to Tsuji, et al. 
describes the reaction of allyl alcohol with carbon monoxide in the 
presence of palladium chloride catalyst. Among the products formed are 
ethyl-3-butenoate and 3-butenoic anhydride. U.S. Pat. No. 3,437,676 to von 
Kutepow, et al. describes the reaction of allyl alcohol, carbon monoxide 
and water in the presence of a homogenous palladium complex such as 
bistriphenylphosphine palladium dichloride to provide carboxylic acids. 
U.S. Pat. No. 4,140,806 to Fernholz, et al. describes the reaction of an 
allyl compound substituted by oxygen functions, e.g., allyl alcohol, with 
carbon monoxide in the presence of a heavy metal catalyst such as 
elemental palladium and methyl iodide or palladium iodide as co-catalyst 
to provide vinylacetic acid. Patentees disclose that isometric C.sub.4 
acids, such as cis- and trans- crotonic acid, are not formed, or form in a 
small amount only, in contrast to known proceses. U.S. Pat. No. 4,189,608 
to Kurkov describes the reaction of allyl alcohol with carbon monoxide in 
the presence of a palladium chloride catalyst and in a substantially 
anhydrous C.sub.2 -C.sub.10 carboxylic acid liquid solvent to provide 
3-butenoic acid (i.e., vinylacetic acid). 
SUMMARY OF THE INVENTION 
It has now been discovered that allyl alcohol and carbon monoxide can be 
reacted, usually at elevated temperature and pressure, in the presence of 
a catalytically effective amount of a heterogeneous catalyst composition 
comprising zero valent palladium and a catalyst promoting amount of 
haloacid to provide a mixture of products predominantly made up of 
carboxylic acids containing four and five carbon atoms. Among such acids 
are 3-butenoic acid, crotonic acid, butyric acid, isobutyric acid, 
glutaric acid and methyl sussinic acid. In addition to the foregoing 
reaction products, smaller quantities of other oxygenated compounds may be 
produced such as glutaric anhydride, methyl succinic anhydride, allyl 
ether, allyl vinyl acetate, and so forth. Such compounds also posses 
utility as intermediates for the manufacture of a variety of industrially 
useful products. 
Unlike many of the palladium-containing catalyst systems of the prior art 
which are soluble in the reaction medium, e.g., the palladium complex 
described by U.S. Pat No. 3,437,676 to von Kutepow, et al., the 
acid-promoted zero valent palladium catalysts of the present invention 
remain insoluble in the reaction mixture thereby greatly facilitating 
their separation from the reaction products and subsequent use for further 
carbonylation of allyl alcohol. Contrary to what one skilled in the art 
would expect based upon the disclosure of U.S. Pat. No. 4,140,805 to 
Fernholz, et al., substantial quantities of C.sub.4 and C.sub.5 acids 
result from the process of the present invention. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The process of the present invention contemplates the use of allyl alcohol 
and carbon monoxide in the commercially available grades, i.e., containing 
minor amounts of one or more impurities which do not appreciably interfere 
with the progress of the reaction herein. The molar ratios of allyl 
alcohol and carbon monoxide can vary widely, it generally being preferred 
to employ carbon monoxide in substantial molar excess, e.g., from about 
1.5 to about 10 moles carbon monoxide per mole of allyl alcohol. 
The palladium component of the catalyst is in the metal or, zero valent 
state, or, if in combined form such as palladium salt, is capable of 
undergoing reduction under the conditions of the reaction to provide zero 
valent palladium. The palladium can be used as a fine powder or, 
advantageously, supported upon a solid inert catalyst carrier such as 
carbon, silica, alumina, silica-alumina, zirconia, titania, quartz, glass 
beads, and the like. The zero valent palladium is employed in combination 
with a hydrogen halide, i.e., hydrogen fluoride, hydrogen chloride, 
hydrogen bromide, or hydrogen iodide, as catalyst promoter, generally at a 
molar ratio of HX:Pd of 10:1 to about 200:1 (X=Cl1, Br or I). Hydrochloric 
acid is an especially preferred promoter. 
The amount of palladium catalyst can vary over a wide range provided, of 
course, at least catalytically effective amount is employed. Thus, for 
example, from about 0.00001 to about 0.5, and preferably from about 0.01 
to about 0.1, molar equivalents of zero valent palladium catalyst per mole 
of allyl alcohol can be used with good results. 
Although carbon monoxide will react with allyl alcohol at room temperature 
and atmospheric pressure, reasonable reaction rates favor the use of 
temperatures and pressures which are substantially greater than those of 
the ambient surroundings. Accordingly, it is preferred to conduct the 
reaction at an eleveated temperature within the range of from about 
80.degree. C. to about 300.degree. C. Within the lower end of this range, 
i.e., from about 80.degree. C. to about 135.degree. C., the reaction has 
been observed to provide a mixture for the most part containing 3-butenoic 
acid together with some diallyl ether and allyl esters. At the upper end 
of the temperature range, i.e., from about 150.degree. C. to about 
300.degree. C., the reaction mixture will be largely that of crotonic 
acid, butyric acid, isobutyric acid, 3-butenoic acid, glutaric acid and 
methyl succinic acid. Pressures on the order of about 2,000 psig to about 
5,000 psig, and especially about 2,500 psig to about 3,500 psig, are 
preferred. 
The process of this invention is suitably conducted on a batch or 
continuous basis and contemplates the use of conventional high pressure 
equipment. 
The following examples are further illustrative of the process of this 
invention.

EXAMPLE 1 
Into a 70 ml Parr reactor was charged a mixture of 15 ml allyl alcohol, 05 
g of 5% Pd on carbon and 0.87 g anhydrous hydrogen chloride. The reactor 
was pressurized with carbon monoxide at 3000 psi and sealed. The reactor 
was shaken in an oven heated at 85.degree. C. for six hours. The reactor 
was cooled to room temperature and vented. The reaction mixture was 
filtered and analyzed. Chromatographic analysis indicated that the mixture 
contained (% by volume): 60% allyl 3-butenoate, 29% butenoic acid, 4% 
allyl ether and the balance being unconverted allyl alchol. 
EXAMPLE 2 
Example 1 was repeated, except the temperature was raised to 100.degree. C. 
The analysis gave the composition (vol. %): 73% 3-butenoic acid, 22% allyl 
3-butenoate, 2% allyl ether and the balance being unconverted allyl 
alcohol. 
EXAMPLE 3 
Example 1 was repeated, except the temperature was raised to 135.degree. C. 
and the pressure was 2800 psi. Analysis disclosed presence (vol.%) of: 14% 
mixed glutaric and methyl succinic acids, 40% allyl 3-butenoate, 44% 
3-butenoic acid and 2% ally ether. 
EXAMPLE 4 
Example 1 was repeated, except the temperature was raised to 150.degree. C. 
using 0.43 g HCl with 0.62 g triphenylarsine as promotors. The reaction 
mixture contained (vol.%): 37% 3-butenoic acid, 10% isobutyric acid, 30% 
crotonic acid, 5% butyric acid and 18% mixed glutaric and methyl succinic 
acids. 
EXAMPLE 5 
Example 4 was repeated without triphenylarsine and the temperature was 
raised to 175.degree. C. at 2850 psi CO. The reaction mixture separated 
into two layers. Analysis of the upper layer disclosed presence of 
(vol.%): 38% 3-butenoic acid, 7% isobutyric acid, 6% butyric acid, 35% 
crotonic acid and 13% mixed glutaric and methylsuccinic acids. 
EXAMPLE 6 
Example 5 was repeated except that 0.29 g HCl was used. The reaction 
mixture contained (vol.%): 45% 3-butenoic acid, 6% isobutyric acid, 4% 
butyric acid, 31% crotonic acid and 13% mixed glutaric and methylsuccinic 
acids. 
As the results of the foregoing examples show, the composition of the 
reaction products is influenced by the reaction temperature with maximum 
quantities of C.sub.4 and C.sub.5 carboxylic acids being obtained at the 
higher temperatures.