Process for Preparing Allylic Esters of Carboxylic Acids and Allylic Alcohols

This invention relates to a process for preparing allylic esters of carboxylic acids and allylic alcohols which comprises reacting an olefin having an allylic carbon-hydrogen bond, a lower alkyl carboxylate ester, water and oxygen in the presence of a catalyst system comprising an oxidation catalyst and an acidic co-catalyst. This invention additionally relates to an improved process for preparing butanediol.

Allylic esters of carboxylic acids have been prepared by a number of different methods. A useful method of preparing allyl acetate, for example, is by contacting propylene with a palladium catalyst in the presence of oxygen and acetic acid. This is illustrated by U.S. Pat. Nos. 3,190,912, 3,275,608, and 3,670,014 and South African Pat. No. 701,077, for example. Allyl acetate is useful as an intermediate for the manufacture of polymers, plasticizers and other valuable materials.

The previously known routes to the allylic alcohols are substantially different from that described above. Allyl alcohol, for example, is commonly prepared by the hydrolysis of allyl chloride, by the rearrangement of propylene oxide, and by the dehydration of propylene glycol. It is used as an intermediate in the manufacture of plasticizers and other organic chemicals.

Butanediol has been prepared by a number of different methods as summarized in copending applications A and B, Ser. Nos. 365,228 and 365,231, both of William E. Smith and both filed May 30, 1973, now both abandoned. Applications A and B are assigned to the same assignee as the present invention and are incorporated herein by reference.

It has been discovered that allylic esters of carboxylic acids and allylic alcohols may be prepared in a novel way, using lower alkyl carboxylate esters and olefins having an allylic carbon-hydrogen bond in the presence of a catalyst system comprising an oxidation catalyst and an acidic co-catalyst.

Another important object of this invention is to make possible an improved process for preparing butanediol from inexpensive starting materials as compared with the prior art, i.e., propylene, carbon monoxide, hydrogen and oxygen, by way of several intermediate steps, mediated by a lower alkyl carboxylate ester (methyl acetate in this process) which is not consumed in the overall reaction.

A primary object of the present invention concerns a process for preparing allylic esters of carboxylic acids and allylic alcohols which comprises reacting an olefin having an allylic carbon-hydrogen bond, a lower alkyl carboxylate ester, water and oxygen in the presence of a catalyst system comprising an oxidation catalyst and an acidic co-catalyst. Preferably, the lower alkyl carboxylate is methyl acetate.

The key element of the process may be illustrated, taking the formation of allyl acetate as an example, by equation 1: ##EQU1##

This transformation is actually the net of the processes represented in equations 2 and 3: ##EQU2##

The hydrolysis depicted in equation 2 is promoted by the acidic co-catalyst, providing substantial amounts of the acetic acid needed for the oxidation process represented by equation 3.

The allylic alcohols are produced by alcoholysis or hydrolysis of the allylic esters, as illustrated by equation 4: ##EQU3##

The lower alkyl carboxylate esters which may be employed in the instant invention are illustrated by the following structure: ##EQU4## wherein R.sub.1 and R.sub.2 can contain from one to about eight carbon atoms. The preferred lower alkyl carboxylate ester is methyl acetate.

The olefins which may be employed in the instant invention are those having an allylic carbon-hydrogen bond, as illustrated by the following structure: ##EQU5## wherein R.sub.1, R.sub.2 and R.sub.3 are independently selected from the group consisting of hydrogen, alkyl of 1-8 carbon atoms, aryl of 6-10 carbon atoms, aralkyl of 7 to 10 carbon atoms and the radical --CHR.sub.4 R.sub.5, and wherein R.sub.4 and R.sub.5 are hydrogen, alkyl of 1-8 carbon atoms, aryl of 6-10 carbon atoms, and aralkyl of 7 to 10 carbon atoms. Preferred olefins are propylene and isobutylene.

The catalyst system of the instant invention comprises an oxidation catalyst and an acidic co-catalyst. The oxidation component of the catalyst may be selected from the group consisting of a Group VIII noble metal, or its salts, or its oxides, or mixtures thereof. Specific examples of such catalysts include metals such as palladium, ruthenium, rhodium, platinum, osmium, and iridium as well as oxides and salts such as palladous propionate, palladous benzoate, palladous chloride, palladous bromide, palladous oxides, etc., ruthenium acetate, etc., rhodium acetate, etc., platinous benzoate, platinum dichloride, platinum oxide, etc. iridium chloride, etc., and the like and mixtures thereof.

The preferred oxidation catalyst is a mixture of the Group VIII noble metal and its salt. A more preferred oxidation catalyst is a mixture of palladium and palladous acetate.

The acidic co-catalyst may be an acidic support material such as alumina or silica or the like or may be a more active substance present in smaller amounts.

A promoter may be added to the catalyst system which influences activity and selectivity. Among the preferred promoters are the alkali metal and alkaline earth metal carboxylates, the transition metals, their salts, gold or copper.

The catalyst may be prepared in a number of different ways. For example, a support such as aluminum oxide is impregnated with a palladium acetyl acetonate solution in benzene and dried. The resulting material is then impregnated with a solution of potassium acetate in water and dried. The catalyst is then treated with propylene, which reduces the palladium to the metallic state. The catalyst thus obtained contains palladium metal and potassium acetate in about 1:10 parts.

Varying amount of the catalyst can be used within the scope of this invention. Amounts as low as about .1% based on weight of support have been found to be effective.

Water serves the dual function of hydrolyzing the lower alkyl carboxylate and moderating the oxidation reaction.

The working temperature is in the range of from about 100.degree.C. to about 200.degree.C. For optimum production of the allylic ester, the temperature is in the range from about 125.degree.C. to about 160.degree.C. At higher temperatures, significant quantities of the allylic alcohol are produced. The working pressure is in the range from about atmospheric to about 150 psi. Somewhat higher or lower temperatures and pressures may, however, be used within the scope of the invention.

The oxygen in the instant process may be used in pure elementary form or in admixture with inert gases, for example, in the form of air. However, it is preferred to work with concentrated oxygen.

The olefin in the instant process may be used in pure form or in admixture with inert compounds, for example, saturated hydrocarbons.

In carrying out the allylic ester formation aspect of the invention, propylene and methyl acetate, for example, are passed through a bed of the catalyst in a tube reactor with water and oxygen at temperatures of from about 100.degree.C. to about 160.degree.C. at about 80 psi. Upon leaving the reaction zone, the products are condensed and a two phase mixture forms. The upper phase is a mixture of, in this case, methyl acetate, allyl acetate and methanol. The lower phase is principally water and methanol, with a small amount of allyl acetate. Traces of allyl alcohol are present in both phases. Direct distillation of the mixture affords the methanol and methyl acetate for recycle, leaving a two phase mixture of allyl acetate and water. The allyl acetate phase is decanted in a form suitable for further use.

The amount of allyl alcohol produced can be significally increased by increasing the temperature and the activity of the hydrolysis-methanolysis component of the catalyst.

The ester starting material (for example methyl acetate) may be supplemented with the carboxylic acid (for example acetic acid) itself, with equally satisfactory results.

The present invention is also concerned with an improved overall process for the production of butanediol from propylene, which is based on the hydrolysis-oxidation sequence described above and is represented in equations 5-7: ##EQU6##

The methyl acetate formed in the methanolysis reacting (equation 7) can be recycled to the hydrolysis-oxidation step (equation 5). Preferably, the methyl acetate is isolated and recycled as its azeotrope with methanol.

Specifically, the improved process for the production of butanediol comprises: (a) reacting propylene, methyl acetate, water and oxygen in the presence of a catalyst system comprising an oxidation catalyst and an acidic co-catalyst to form allyl acetate; (b) converting the allyl acetate under hydroformylation-hydrogenation conditions to a mixture comprising the monoacetate esters of 1,4-butanediol, 2-methyl-1,3-propanediol and 1,2-butanediol and their respective diol and diacetate disproportionation products; (c) de-esterifying the mixture of the acetate esters of the butanediols so produced under methanolysis conditions to produce the corresponding butanediols and methyl acetate; (d) isolating the methyl acetate from the butanediols in a form suitable for use in (a).

For makeup of process losses, the methyl acetate may be supplemented with acetic acid in various proportions.

In copending application A, Ser. No. 365,228 of William E. Smith, filed May 30, 1973, and assigned to the same assignee as the present invention, there is disclosed and claimed a process for making butanediols by reacting propylene, oxygen and a carboxylic acid to produce an allyl carboxylate which is then hydroformylated to produce the mixture of the corresponding aldehydes. Hydrogenation of the mixture produces a mixture of the esters of the corresponding diols. In copending application B, Ser. No. 365,231 of William E. Smith, filed May 30, 1973, and assigned to the same assignee as the present invention, there is disclosed and claimed a process wherein the hydrogenation is accomplished concurrently with the hydroformylation reaction. De-esterification of the diol ester mixture produces the desired butanediols which can be separated by distillation. These copending applications A and B are incorporated herein by reference.

The process of converting the allyl acetate under hydroformylation-hydrogenation conditions to a mixture comprising the monoacetate esters of 1,4-butanediol, 2-methyl-1,3-propanediol and 1,2-butanediol and their respective diol and diacetate disproportionation products, i.e., step (b) of the overall process of preparing butanediol, is fully set forth in copending applications A and B described above, and incorporated herein by reference.

Methanolysis conditions that may be used in step (c) above are fully set forth in copending application C, Ser. No. 365,230, of Will Dockery Merritt, Jr., filed May 30, 1973, now abandoned, and copending application D, Ser. No. 365,239 of John E. Corn et al, filed May 30, 1973, now U.S. Pat. No. 3,880,939, both assigned to the same assignee as the present invention. Application C describes alcoholysis using a base catalyst while application D discloses alcoholysis in the presence of an acidic cationic exchange material. Applications C and D are incorporated herein by reference.

The following examples are set forth to illustrate more clearly the principle and practice of this invention to those skilled in the art. Unless otherwise specified, where parts or percents are mentioned, they are parts or percents by weight.

An 8 ft. .times. 1 in. diameter stainless steel tube is charged with one liter (1000 grams) of catalyst composed of alumina impregnated with palladium (0.3%) and potassium acetate (3%). The reactor temperature is maintained at 155.degree.C. (circulating oil jacket) while a mixture per hour of 2000 grams of propylene, 740 grams of methyl acetate, 900 grams of water and 170 grams of oxygen is passed through under a pressure of about 80 psi. The output per hour is a mixture (two liquid phases) of about 310 grams of allyl acetate, 92 grams of methanol, 490 grams of unconverted methyl acetate, 860 grams of water, traces of allyl alcohol and acetic acid, and the excess propylene. These results, determined by quantitative glpc analysis of the effluent, indicate a conversion of about 34% of the methyl acetate, and a yield of allyl acetate on that basis of about 92%.

The tube, catalyst and general procedure described in Example 1 are employed, the reagent quantities differing only in the amount of water which is doubled to 1800 grams. Analysis of the effluent in this case shows the presence of 390 grams of unconverted methyl acetate (53% recovery), 440 grams of allyl acetate (93% yield based on 47% conversion) and 130 grams of methanol (86% yield).

The tube, catalyst and procedure described in Example 1 are employed, with substitution of 910 grams of methyl acetate-methanol azeotrope (composed of 740 grams of methyl acetate and 170 grams of methanol) for the pure methyl acetate. Analysis of the effluent reveals the presence of 580 grams of unconverted methyl acetate (78% recovery), 210 grams of allyl acetate (95% yield based on 22% conversion), and 230 grams of methanol.

Direct distillation of the mixture yields the methanol and methyl acetate-methanol azeotrope for recycle, and leaves another two phase mixture as the residue. The lower phase is water while the upper phase is substantially pure allyl acetate.

The tube, catalyst and general procedure described in the above examples are employed, with use of 910 grams of the methyl acetate-methanol azeotrope described in Example 3 and 1800 grams of water. Analysis of the effluent shows the presence of 520 grams of unconverted methyl acetate (70% recovery), 280 grams of allyl acetate (93% yield based on 30% conversion), and 240 grams of methanol.

The tube, catalyst and procedure described in Example 3 are employed, with the operating temperature increased to 180.degree.C. Analysis of the effluent shows the collection of (per hour) 61 grams of allyl alcohol, as well as 285 grams of allyl acetate and 481 grams of unconverted methyl acetate.

A miniplant is constructed and operated for the production of butanediol from propylene via the disclosed cyclic process. The hydrolysis-oxidation tube reactor and basic procedure described in Example 4 is employed for the production of allyl acetate at the rate of about 500 grams per hour. The product stream of allyl acetate, methyl acetate, methanol, water and acetic acid forms two phases when condensed. The mixture is distilled directly using a conventional distilling column. The methyl acetate and methanol are taken overhead, leaving the allyl acetate, water and a small amount of acetic acid as the bottoms product. Distillation of the overhead affords the unconverted methyl acetate and methyl acetate-methanol azeotrope (suitable for direct recycle in allyl acetate production) and methanol (suitable for use in the butanediol acetate methanolysis to be described). The allyl acetate-water-acetic acid distillation residue is cooled; the upper phase, essentially pure allyl acetate, is decanted and used directly in the next stage of the process.

A two liter stirred autoclave heated at 125.degree.C. is pressurized with 3000 psi of 2:1 hydrogen/carbon monoxide and charged with a mixture of 400 grams of the allyl acetate, 8.0 grams of cobalt octacarbonyl and 400 ml. of benzene. An exothermic reaction and gas uptake ensue. After 15 minutes at 125.degree.-145.degree.C. the product mixture is pumped from the autoclave, cooled and vented. It is then decobalted by heating at 110.degree.C. for 10 minutes in a closed vessel, the addition of acetic acid being unnecessary because of its presence as a decomposition product. (The cobaltous acetate which forms is filtered off and transformed to cobalt octacarbonyl by subjection to hydrogen/carbon monoxide at elevated temperature and pressure ([160.degree.C., 3000 psi]). The benzene solution is concentrated and the products are flash distilled affording 474 grams (91% yield) of oxo aldehydes containing minor amounts of the butanediol acetate compounds. A glpc analysis indicates the presence of 4-acetoxybutyraldehyde, 3-acetoxy-2-methylpropionaldehyde and 2 -acetoxybutyraldehyde in 7 : 1.5 : 1.5 ratio.

The aldehyde mixture is combined in a stirred autoclave with 50 grams of a 30% cobalt on silica catalyst, subjected to 1000 psi of hydrogen, and heated for 30 minutes at 150.degree.C. Reduction to the diol derivatives is complete, in essentially quantitative yield.

After removal of the hydrogenation catalyst by filtration, the product mixture is examined by glpc and found to contain 4-acetoxybutanol, 3-acetoxy-2-methylpropanol and 2-acetoxybutanol, and small amounts of their respective diacetate and diol disproportionation products.

The low boiling components of the hydrogenation mixture (principally water, acetic acid and hydrogenation products derived from methacrolein and allyl acetate) are distilled off under reduced pressure. The residue is combined with 500 grams of methanol containing 2.5 grams of sodium hydroxide, in a static mixer leading to a 4 ft. .times. 1 in. diameter Goodloe distillation column. The methanolysis reaction takes place in a 2 ft. long packed section below the feed. Methyl acetate and most of the excess methanol are taken overhead and subsequently fractionated affording the methyl acetate-methanol azeotrope and pure methanol, both suitable for direct recycle.

The bottoms product contains, according to glpc analysis, 241 grams of 1,4-butanediol (67% yield in the conversion from allyl acetate), 14 grams of 2-methyl-1,3-propanediol (4% yield), and 51 grams of 1,2-butanediol (14% yield). The mixture is flash distilled, leaving a residue of partially deactivated catalyst. Fractionation of the diols through a 4 ft. .times. 1 in. diameter Goodloe column affords the three separated isomers -- 1,4-butanediol (bp 144.degree.C/20mm), 2-methyl-1,3-propanediol (bp 132.degree.C/20 mm), and 1,2-butanediol (bp 121.degree.C/20 mm).

The process as described is operated semi-continuously to provide butanediol at about one pound per hour.

Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.