GB2165844A - Pyridine from 1,3-propane dinitrile - Google Patents

Abstract

Pyridine is produced by reacting 1,3 propane dinitrile in the presence of hydrogen over a palladium on silica catalyst which has been prepared by impregnating silica gel with a solution of a palladium compound in either a volatile alcohol or volatile chlorinated hydrocarbon, drying and reducing the palladium to free metal.

Description

SPECIFICATION Production of Heterocyclic compounds The present invention relates to the production of heterocyclic compounds and more particularly to a process for the production of pyridine.

In UK Patent specification No 1, 393,086 there is described and claimed a process for the manufacture of a palladium on silica catalyst which comprises preparing silica gel impregnated with a palladium compound by impregnating the gel with a solution, free from undissolved matter, of the said palladium compound in a volatile chlorinated hydrocarbon, for example chloroform, drying the impregnated silica gel and reducing the palladium to free metal.

UK Patent Specification No 1,393, 087 describes and claims a rather similar process for the manufacture of a palladium on silica catalyst which comprises preparing silica gel impregnated with a palladium compound by impregnating the gel with a solution, free from undissolved matter, of the said palladium compound in a volatile alcohol which is anhydrous or, when water miscible, contains not more than 50- by weight of water, drying the impregnated silica gel and reducing the palladium to free metal.

According to the present invention a process for the production of pyridine comprises reacting 1,3 propane dinitrile in the presence of hydrogen over a palladium on silica catalyst prepared by impregnating silica gel with a solution, free from undissolved matter, of a palladium compound in either a volatile alcohol or a volatile chlorinated hydrocarbon, drying the impregnated silica gel and reducing the palladium to free metal, to obtain pyridine.

The process of the invention is preferably carried out in a single stage without any separation of intermediate products. If desired, however, the process may be operated as a two-stage process in which 1,3 propane dinitrile is reacted over the palladium-on-silica catalyst to form 1,5 diaminopentane as an intermediate product, some or all of which is separated and further reacted over a dehydrogenation catalyst, preferably the palladiumon-silica catalyst used in the first stage, to obtain pyridine.

Preferably, the process, whether in its singlestage or two-stage embodiment, is carried out at a temperature in the range 350"C to 400"C, more preferably in the range 360 to 380"C the amount of hydrogen used being in the range 1 to 100 times excess over the stoichiometric amount.

The process of this invention is further illustrated by the following example.

Example The reactor used was a 1cm diameter glass column surrounded by a furnace. A palladium-on-silica catalyst was prepared by impregnating silica gel with a solution, free from undissolved matter, of palladium acetate in a chloroform/ ethanol solvent. The impregnated silica gel was dried and the palladium reduced to the free metal.

The catalyst was spaced along the length of the reactor column in 5 x 1cm bands, the bands being 1cm apart. A solution of 100 microlitres of glutaronitrile in 350 microlitres benzene was injected at the top of the column at a rate of 20 microlitres1 minute in 5 microlitre portions. Hydrogen was flowed concurrently at a rate of 2 litres/hour and the reactor column was maintained at a temperature of 368"C by heat from the furnace.

The product was analysed by gas-liquid chromatography which confirmed the production of pyridine. No residual glutaronitrile was detected in the product.

1. A process for the production of pyridine which comprises racting 1,3 propane dinitrile in the presence of hydrogen over a palladium on silica catalyst prepared by impregnating silica gel with a solution, free from undissolved matter, of a palladium compound in either a volatile alcohol or a volatiel chlorinated hydrocarbon, drying the impregnated silica gel and reducing the palladium to free metal, to obtain pyridine.

2. A process as claimed in claim 1 wherein the process is carried out in a singie stage without any separation of intermediate products.

3. A process as claimed in claim 1 wherein the process is carried out as a two-stage process in which 1,3 propane dinitrile is reacted over the palladium-on-silica catalyst to form an intermediate product comprising 1,5 diaminopentane, some or all of said 1,5 diaminopentane is separated and further reacted over a dehydrogenation catalyst to obtain pyridine.

4. A process as claimed in claim 3 wherein said second-stage dehydrogenation catalyst is the palladium-on-silica catalyst used in the first stage of the process.

5. A process as claimed in any one of the preceding claims wherein the process is carried out at a temperature in the range 350 to 400 C.

6. A process as claimed in claim 5 wherein the process is carried out at a temperature in the range 360 to 380 C.

7. A process as claimed in any one of the preceding claims wherein the amount of hydrogen used is in the range 1 to 100 times excess over the stoichiometric amount.

8. A process for the production of pyridine substantially as hereinbefore described with reference to the Example.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Production of Heterocyclic compounds The present invention relates to the production of heterocyclic compounds and more particularly to a process for the production of pyridine. In UK Patent specification No 1, 393,086 there is described and claimed a process for the manufacture of a palladium on silica catalyst which comprises preparing silica gel impregnated with a palladium compound by impregnating the gel with a solution, free from undissolved matter, of the said palladium compound in a volatile chlorinated hydrocarbon, for example chloroform, drying the impregnated silica gel and reducing the palladium to free metal. UK Patent Specification No 1,393, 087 describes and claims a rather similar process for the manufacture of a palladium on silica catalyst which comprises preparing silica gel impregnated with a palladium compound by impregnating the gel with a solution, free from undissolved matter, of the said palladium compound in a volatile alcohol which is anhydrous or, when water miscible, contains not more than 50- by weight of water, drying the impregnated silica gel and reducing the palladium to free metal. According to the present invention a process for the production of pyridine comprises reacting 1,3 propane dinitrile in the presence of hydrogen over a palladium on silica catalyst prepared by impregnating silica gel with a solution, free from undissolved matter, of a palladium compound in either a volatile alcohol or a volatile chlorinated hydrocarbon, drying the impregnated silica gel and reducing the palladium to free metal, to obtain pyridine. The process of the invention is preferably carried out in a single stage without any separation of intermediate products. If desired, however, the process may be operated as a two-stage process in which 1,3 propane dinitrile is reacted over the palladium-on-silica catalyst to form 1,5 diaminopentane as an intermediate product, some or all of which is separated and further reacted over a dehydrogenation catalyst, preferably the palladiumon-silica catalyst used in the first stage, to obtain pyridine. Preferably, the process, whether in its singlestage or two-stage embodiment, is carried out at a temperature in the range 350"C to 400"C, more preferably in the range 360 to 380"C the amount of hydrogen used being in the range 1 to 100 times excess over the stoichiometric amount. The process of this invention is further illustrated by the following example. Example The reactor used was a 1cm diameter glass column surrounded by a furnace. A palladium-on-silica catalyst was prepared by impregnating silica gel with a solution, free from undissolved matter, of palladium acetate in a chloroform/ ethanol solvent. The impregnated silica gel was dried and the palladium reduced to the free metal. The catalyst was spaced along the length of the reactor column in 5 x 1cm bands, the bands being 1cm apart. A solution of 100 microlitres of glutaronitrile in 350 microlitres benzene was injected at the top of the column at a rate of 20 microlitres1 minute in 5 microlitre portions. Hydrogen was flowed concurrently at a rate of 2 litres/hour and the reactor column was maintained at a temperature of 368"C by heat from the furnace. The product was analysed by gas-liquid chromatography which confirmed the production of pyridine. No residual glutaronitrile was detected in the product. CLAIMS

1. A process for the production of pyridine which comprises racting 1,3 propane dinitrile in the presence of hydrogen over a palladium on silica catalyst prepared by impregnating silica gel with a solution, free from undissolved matter, of a palladium compound in either a volatile alcohol or a volatiel chlorinated hydrocarbon, drying the impregnated silica gel and reducing the palladium to free metal, to obtain pyridine.

2. A process as claimed in claim 1 wherein the process is carried out in a singie stage without any separation of intermediate products.

3. A process as claimed in claim 1 wherein the process is carried out as a two-stage process in which 1,3 propane dinitrile is reacted over the palladium-on-silica catalyst to form an intermediate product comprising 1,5 diaminopentane, some or all of said 1,5 diaminopentane is separated and further reacted over a dehydrogenation catalyst to obtain pyridine.

4. A process as claimed in claim 3 wherein said second-stage dehydrogenation catalyst is the palladium-on-silica catalyst used in the first stage of the process.

5. A process as claimed in any one of the preceding claims wherein the process is carried out at a temperature in the range 350 to 400 C.

6. A process as claimed in claim 5 wherein the process is carried out at a temperature in the range 360 to 380 C.

7. A process as claimed in any one of the preceding claims wherein the amount of hydrogen used is in the range 1 to 100 times excess over the stoichiometric amount.

8. A process for the production of pyridine substantially as hereinbefore described with reference to the Example.