This invention relates to a process for the isomerization of a vinyl glycol to an unsaturated diol. It is known that certain unsaturated alcohols when heated or subjected to acidic or basic conditions undergo an isomerization identified as an allyl rearrangement in which the migration of a hydroxyl group in a beta-position takes place with the displacement of the carbon-carbon double bond. Substances known to promote such an isomerization include water-soluble mercuric salts employed under acidic conditions such as disclosed in U.S. Patent 2,911 ,445; metal iodides such as disclosed in Japanese Patent 59-084,831 and Japanese Patent 82-002,227; and calcium compounds such as disclosed in Japanese Patent 79-073,710.

To date, such rearrangement reactions of unsaturated alcohols have not found prominent use in industrial processes due to poor selectivity or poor yield or a combination thereof. It would therefore be desirable to provide for a reaction procedure using a catalyst which is able to provide for a greater selectivity and preferably in combination with an enhanced yield.

A substance of prime industrial importance is 1 ,4-butanediol which can be obtained by the hydrogenation of 2-butene-1 ,4-diol. Accordingly, it would be desirable to develop a process for the manufacture of 1 ,4-butanediol employing the rearrangement reaction of an unsaturated alcohol to provide, as intermediate, 2-butene-1 ,4-diol. 1 ,4-Butanediol is an important industrial commodity of value in the polymer industry and in the pharmaceutical industry.

In a first aspect, this invention relates to a process for the isomerization of a vinyl glycol of the general formula

HO-CHR-CHOH-CH=CR'H (I) wherein R and R' independently represent hydrogen or a lower alkyl to an unsaturated diol of the general formula

HO-CHR-CH=CH-CHR'-OH (II) wherein R and R' independently represent hydrogen or a lower alkyl which comprises contacting the vinyl glycol with rhenium, a rhenium compound and mixtures thereof. In a second aspect, this invention relates to a process for the preparation of

2-butene-1 ,4-diol by isomerization of 3-butene-1 ,2-diol in the presence of a supported

transition metal catalyst characterized in that the catalyst is selected from the group consisting of rhenium, a rhenium compound and mixtures thereof and is supported by a zeolite type carrier comprising silicon and aluminum in an atom ratio of from 1 to 1 to 1000 to 1. In a third aspect, this invention relates to a process for the preparation of

1 ,4-butanediol comprising the step of isomerizing 3-butene-1 ,2-diol to 2-butene-1 ,4-diol in the presence of a supported transition metal catalyst characterized in that the catalyst is selected from the group consisting of rhenium, a rhenium compound and mixtures thereof and is supported by a zeolite type carrier comprising silicon and aluminum in an atom ratio of from 1 to 1 to 1000 to 1.

In a fourth aspect, this invention relates to a catalyst, suitable for the conversion of a vinyl glycol to an unsaturated diol, which comprises a transition metal on a carrier characterized in that, the carrier is a faujasite type zeolite which contains silicon and aluminum in an atom ratio of from 1 to 1 to 1000 to 1 ; and in that the transition metal is rhenium or a rhenium compound and mixtures thereof present in an amount of from 0.1 to 50 weight percent based on total combined weight of the carrier and of the rhenium or rhenium compound and mixtures thereof.

Applicants have found that such rhenium-based catalyst are able to promote the rearrangement of vinyl glycols to unsaturated diols at a surprisingly high selectivity.

According to the present invention, the isomerization of a vinyl glycol to the unsaturated diol is carried out in the presence of a supported transition metal catalyst. The transition metal of preference is rhenium present as rhenium metal, a rhenium compound and mixtures thereof, preferably supported by a silica-based carrier. Advantageously, the supported catalyst consists substantially of rhenium metal, or a rhenium compound. Based on the combined total weight of the carrier and transition metal, the rhenium or rhenium compound is present in an amount of from 0.1 to about 50, preferably from 1 to 30, and more preferably from 5 to 25, and yet more preferably from 8 to 20 weight percent.

The support, or carrier, is a silica-based substance having a structure recognized as being a faujasite type zeolite, which comprises silicon and aluminum in an atom ratio of from 1 to 1 to 1000 to 1 preferably a Y type zeolite with a silicon and aluminum ratio of 1.5 to 1 to about 200 to 1 , and more preferably an ultra-stabilized faujasite type zeolite with a Si/AI ratio of from 5 to 1 to 100 to 1. Exemplary of suitable carriers include

zeolites such as the product CBV-780 available from Pennsylvania Quartz Corporation and understood to be a Y type zeolite with a Si/AI ratio of 40 to 1.

The support can be loaded with the rhenium or rhenium compound by any method generally employed for the loading of such supports. Such methods include bringing the support into contact with an aqueous metal salt solution, subsequently drying the support and optionally calcining. For the present disclosure, suitable metal salts include water soluble rhenium-containing substances including HReO ₄ , KReO ₄ , NaReO ₄ and other ReO ₄ salts, ReCI ₅ , ReCI ₄ , ReCI ₃ , ReF ₆ , Re.O ₇ and preferably NH ₄ ReO ₄ .

The above described supported catalyst is found to be of particular value for promoting the rearrangement of a vinyl glycol to an unsaturated diol. The vinyl glycols include substances of the following general formula;

HO-CHR-CHOH-CH=CR'H (I) wherein R and R' independently represent hydrogen or a lower alkyl. By lower alkyl it is understood moieties containing from 1 to 6 carbon atoms. R and R' can also be a part of an alicyclic structure. For the present invention the preferred vinyl glycol is where both R and R' is hydrogen, as exemplified by 3-butene-1 ,2-diol.

The unsaturated diols obtained according to this invention are characterized by the following general formula:

HO-CHR-CH=CH-CHR'-OH (II) wherein R and R' independently represent hydrogen or a lower alkyl and as described for the vinyl glycol. When the starting vinyl glycol is 3-butene-1 ,2-diol, the resulting diol is 2-butene-1 ,4-diol.

As mentioned above, one aspect of this invention is to provide a procedure for the manufacture of 1 ,4-butanediol employing an intermediate step of isomerizing 3-butene-1 ,2-diol to 2-butene-1 ,4-diol. The following reaction scheme illustrates a procedure for the manufacture of 1 ,4-butanediol starting from 1 ,3-butadiene, a widely available industrial feedstock, and involving the discussed isomerization reaction:

Step 1 : Conversion of 1 ,3-butadiene to 1 ,2-epoxy-3-butene;

Step 2: Hydrolysis of 1 ,2-epoxy-3-butene to 3-butene-1 ,2-diol; Step 3: Isomerization of 3-butene-1 ,2-diol to 2-butene-1 ,4-diol;

Step 4: Hydrogenation of 2-butene-1 ,4-diol to 1 ,4-butanediol.

For Step 1 , 1 ,3-butadiene can be converted to 1 ,2-epoxy-3-butene by an appropriate epoxidizing agent. Such agents include hydrogen peroxide in the presence of an acid catalyst such as disclosed in German Patent 2,734,240; oxygen in the presence of a silver catalyst such as disclosed in U.S. Patent 5,117,012; hydrogen peroxide/alcohol/water mixtures in the presence of an organorheniu catalyst such as disclosed in

U.S. Patent 5,166,372; hydrogen peroxide in the presence of Ti/Si catalysts as disclosed in European Patent 190,609.

For Step 2, 1 ,2-epoxy-3-butene can be hydrolyzed to obtain 3-butene-1 ,2-diol by an appropriate hydrolyzing agent. Such agents and procedures include acid catalyzed solvolysis such as disclosed in the publication Tetrahedron Asymmetry page 15-16, Vol. 6, 1995; water as disclosed in German Patent 4,342,030; water in the presence of SiO/TiO- F as disclosed in German Patent 4,429,699; water in the presence of rhenium oxide (Re ₂ O ₇ ) as disclosed in German Patent 4,429,700.

For Step 3, isomerization of 3-butene-1 ,2-diol to 2-butene-1 ,4-diol in the presence of the supported rhenium catalyst as described above.

For Step 4, 2-butene-1 ,4-diol can be hydrogenated by procedures employing hydrogen over nickel catalysts such as disclosed in Japanese Patent 53-127,405; Japanese Patent 62-054,788; Japanese Patent 74-049,910; Japanese Patent 79-061 ,108.

The preparation of 1 ,4-butanediol is presented as a four step procedure, however a person skilled in the art of organic synthesis will be aware that Steps 1 and 2 can be combined.

The following examples are presented to illustrate the invention. Unless otherwise specified all amounts are given in parts by weight.

Example 1 {a) Preparation of Catalyst 1

A rhenium-containing catalyst is prepared by mixing 60 parts of an ultrastablo Zeolite Y carrier US-Y CBV-780, available from the Pennsylvania Quartz Corp. and having a Si/AI ratio of 40 to 1 , with 8.6 parts of NH ₄ ReO ₄ dissolved in 60 parts of water at 40°C. The resulting slurry is then placed in an oven and dried by progressively increasing the temperature at the rate of 1 °C per minute from 20°C to 100°C and subsequently maintaining it at 100°C for one hour. The oven temperature is then increased at a rate of 3°C/min to

250°C and the dried slurry calcined for a period of 5 hours. The resulting catalyst contains 10 weight percent Re(VII)oxide.

(b) Preparation of Catalysts 2. 3 and 4

Additional catalysts are prepared according to the same general procedure as given for Catalyst 1.

Catalyst 2 contains 1 weight percent Re(VII) oxide on the ultrastable Zeolite Y carrier US-Y CBV-780.

Catalyst 3 contains 5 weight percent Re(VII) oxide on the ultrastable Zeolite Y carrier US-Y CBV-780. Catalyst 4 contains 30 weight percent Re(VII) oxide on the ultrastable Zeolite Y carrier US-Y CBV-780.

(c) Comparative Catalysts A. B and C

Catalyst A is ultrastable Zeolite Y carrier US-Y CBV-780 in absence of a rhenium substance.

Catalyst B is Re ₂ O ₇ of 99.9 percent purity as available from Aldrich. Catalyst C is γ-AI ₂ O ₃ with a surface area of 316 m ² /g as available from Rhόne-Poulenc loaded with 10 weight percent Rhenium; prepared according to the general procedure as mentioned for Catalyst 1.

(d) Isomerization of 3-butene-1.2-diol to 2-butene-1 ,4-diol

Catalysts 1 to 4 are used to effect the conversion of 3 butene-1 ,2-diol to 2-butene-1 ,4-diol according to the following general procedure.

3-Butene-1 ,2-diol is obtained by the hydrolysis of 1 ,2-epoxy-3-butene (O.75 parts, purity 99 percent) in water (37.5 parts) at 100°C; the resulting mixture according to GC analysis, on a CP-Sil-5-column, contained 90 mole percent of 3-butene-1 ,2-diol, 8 mole percent of 2-butene-1 ,4-diol, and 2 mole percent of 2-butenal. The obtained 3-butene-1 ,2-diol mixture is brought into contact with 0.1 parts of the catalyst and heated to 150°C for an extended period of time. The isomerization of 3-butene-1 ,2-diol to 2-butene-1 ,4-diol is followed by determining the composition of the mixture using GC analysis after 1 , 3 and 5 hours. Table 1 presents the extent of mole conversion and the degree of selectivity exhibited by the catalysts.

Table

1 hour 3 hours 5 hours

Catalyst 1 Conversion (mole %) 1.5 2.0 5.5

(10 wt.% Selectivitv: 1%)

Re) 2-butene-1 ,4-diol 88.2 87 86.9

2-butenal 0.8 0.6 3.9

3-butenal 0 0 0

Catalyst 2 Conversion (mole %) 0.8 2.8 3.1

(1 wt.% Re) Selectivitv: (%.

2-butene-1 ,4-diol 64.3 52.5 0

2-butenal 35.6 47.5 68.8

3-butenal 0 0 0

Catalyst 3 Conversion (mole %) 1.2 2.0 3.1

(5 wt.% Re) Selectivitv: (%)

2-butene-1 ,4-diol 60.6 55.1 49.3

2-butenal 38.0 45.0 50.7

3-butenal 0 0 0

Catalyst 4 Conversion (mole %) 0.2 3.9 10.0

(30 wt.% Selectivitv: (%.

Re) 2-butene-1 ,4-diol 0 0 0

2-butenal 50.8 0 0

3-butenal 0 0 0

The results presented in Table I show the ability of the rhenium based catalyst to isomerize a vinyl glycol to an unsaturated diol with a large degree of selectivity. The extent of selectivity is dependent on the amount of rhenium present on the catalyst. The optimum amount of Rhenium required to be present is dependent on the vinyl glycol to be isomerized and needs to be established by routine experimentation.

Comparative Examples

As comparative examples, the rearrangement of 3-butene-1 ,2-diol was performed in the presence of 0.1 part unsupported Re ₂ O ₇ ; 0.1 part of US-Y Si/AI = 40; and 0.1 part of a catalyst containing 10 weight percent Re on a γ-AI ₂ O ₃ prepared as stated above for Catalyst 1. The results given in Table II illustrate the low selectivity for 2-butene-1 ,4-diol obtained in the presence of these catalysts.

Table II

1 hour 3 hours 5 hours

Catalyst A Conversion (mole %) 0.2 0.5 1.0 Selectivity: (%. 2-butene-1 ,4-diol 1.6 1.4 1.3 2-butenal 95.4 95.6 85 3-butenal 0 0 0

Catalyst B Conversion (mole %) 6.1 19.3 41.7 Selectivity: (%) 2-butene-1 ,4-diol 0 0 0 2-butenal 34.7 40.3 48.9 3-butenal 0 0 0

Catalyst C Conversion (mole %) 6 8 16 (10 wt.% Selectivitv: (%) Re on γ- 2-butene-1 ,4-diol 52 10 0 AI ) 2-butenal 42 65 86 3-butenal 0 0 0