WO1988000189A1

WO1988000189A1 - A process for the preparation of nitrogen-containing heterocyclic compounds

Info

Publication number: WO1988000189A1
Application number: PCT/EP1987/000362
Authority: WO
Inventors: Lucio Forni
Original assignee: Bracco Industria Chimica S.P.A.
Priority date: 1986-07-08
Filing date: 1987-07-03
Publication date: 1988-01-14
Also published as: IT8621066A1; KR880701714A; IT8621066A0; AU7644587A; IT1196480B

Abstract

The use of a Zn catalyst containing Cr and Pd, in the synthesis of pyrazines from diols and diamines, allows to obtain high conversions and selectivities, as well as a long-lasting action of the catalyst itself.

Description

A PROCESS FOR THE PREPARATION OF NITR0GEN-CONTAINING HETEROCYCLIC COMPOUNDS.

The present invention relates to a process for the preparation of pyrazines, by contact reaction of diols and diamines in gaseous phase, in the presence of a zinc catalyst. Pirazines, particularly 2-aIkyl-pyrazines, such as

2-methyIpyrazine, are used as essences, perfumes, flavours, and are moreover valuable as intermediates in the preparation of medicaments, fertilizers or other chemicals useful in agriculture. Due to the wideness of applicative possibilities of pyrazines, it appears evident the need to obtain pyrazines cheaply, by means of a process suitable for industrial application on a large scale.

In order to overcome the restrictions and drawbacks affecting the conventional preparation method, based on dehydrogenation of piperazines, processes consisting in the catalytic reaction of diols and diamines have been developed.

Said methods allow to use economic starting materials, which are easily available; however, to be considered convenient, they have to fullfil the following requirements:

- high conversions and selectivities, with minimal or no formation of side-products;

- low cost and long-lasting action of the catalyst. Researches have been therefore facused on the improvement of the catalysts, in order to attain the above mentioned requirements. First, the use of catalysts based on alumina or copper-chromium, having a low selectivity and short duration, was proposed. Moreover, the obtained product was difficult to purify due to the presence of side-products. British Patent Specification GB 1 565 117 discloses a catalyst based on zinc, particularly zinc oxide, optionally containing other elements selected from the group consisting of cobalt, nickel, iron, aluminum and chromium, optionally supported on silica, alumina, diatomaceous earth, etc. The disclosed catalysts show satisfying yields and selectivities, but a short duration: a decrease in their performances already appearing after 20 hours.

To prove the uncomplete attainment of the above mentioned goals, the same research group discloses, in the subsequent Japanese Patent Application n. 79 132 588, a catalyst based on zinc, added with one or more substances selected from the group consisting of cerium, manganese, iron, palladium, lead, phosphorus and boron.

In comparison with the above cited british patent, transition metals are therefore excluted, with the exception of iron, in the search of further improvements in conversion and selectivity yietds. The problem of the catalyst duration remains therefore unsolved.

Now it has been found that the above cited objects may be attained, overcoming the restrictions and drawbacks of the known methods, by the use of a catalyst based on zinc added with a chromite and palladium.

The catalyst object of the presente invention preferably comprises zinc oxide and zinc chromite, added with Pd, preferably in form of Pd SO₄. Zinc/chromium ratio is preferably 3:1, whilst Pd SO₄ weight percentage may vary from 0.5 to 5%, preferably from about 1 to about 3%.

The catalyst may be prepared according to conventional techniques, such as those described by G. Natta in "Catalysis" (P. H. Emmett, Ed.) Vol. 3, Reinhold, New York, 1955, p. 349, Bowker et al. in J. Catal. 84, 252 (1983) and by A.B. Stiles in "Catalyst Manufacture", Dekker, New York (1983).

The catalyst may of course be used on appropriate supports such as silica, alumina, diatomaceous earth, etc. The reaction between diols and diamines is also carried out according to known techniques, for instance as described in the above cited patents. A diol, such as ethylene glycol, 1,2-propylene glycol, 1,2-butanedioI, etc. and a diamine such as ethylenediamine, 1,2-diaminopropane, 1,2-diaminobutane etc. are reacted at high temperatures, 300 to 600° C, optionally diluted with inert gases or solvents. Diol and diamine are generally present in equimolecular amounts in the reactor, and temperature is preferably kept from 400 to 500° C.

Working up of the reaction mixture for recovering the pure product is generally carried out according to conventional procedures, such as distillation or extration. According to the process, object of the present invention, remarkably high yields and selectivities may be obtained, the catalyst life being markedly longer than the one of known catalysts. This longer life appears to be mainly due to chromite addition to zinc oxide, and it was not foreseeable from the prior art. The simultaneous improvement in duration and selectivities, obtained by adding the two additives, chromite and palladium, was neither foreseeable.

The following non-limiting Examples illustrate the invention and its effects.

COMPARATIVE EXAMPLE 1

Eff ect of Zn chromite addition to ZnO.

0,75 ml/hr of a 50% by weight aqueous solution of an equimolecular mixture of ethylenediamine and 1,2-propylene glycol were fed into a fixed-bed continuous reactor, under standard conditions of 430°C and atmospheric pressure. 0.5 g of fresh catalyst was used for each batch. The reaction was carried on for 24 hours, effecting at various times samplings which were subjected to gas-chromatographic analysis.

The following Table reports the obtained results for ethylenediamine conversion (% mol) and for selectivity to 2-methyl-pyrazine (% mol) after 1 and 24 hours, using ZnO and ZnO-ZnCr₂O₄ as the catalysts.

* C₁ and C₂₄: conversion at 1 and 24 hours.

** S₁ and S₂₄: selectivity at 1 and 24 hours COMPARATIVE EXAMPLE 2

Effect of Pd addition to ZnO. Under the same conditions as in Example 1, using a catalyst of pure ZnO added with 2% by weight of PdSO₄, a conversion and a selectivity of 81 and 48%, respectively, were attained, after 24 hours.

EXAMPLE 1

Operating analogously to the above examples, but using a ZnO-ZnCr₂O₄ (3:1) catalyst added with 1% Pd, a conversion and a selectivity of 80 and 56%, respectively, were attained.

Similar resu lts were obtained in the synthesis of other pyrazines, starting from the following compounds:

Diol Diamine Obtained p yr azine ethyleneglycoI ethyl e n edia mine pyrazine

1,2-butanediol ethylenediamine 2-ethyl-pyrazine 2,3-butanedioI ethylenediamine 2,3-dimethyIpyrazine 1,2-propyleneglycol 1,2-diaminopropane 2,5 and 2,6-dimethylpyrazine

Claims

1. A process for the preparation of pyrazines, by reacting diols and diamines in the presence of a zinc-based catalyst, characterized in that said catalyst comprises also Cr and Pd.

2. A process according to claim 1, wherein the catalyst is based on zinc oxide.

3. A process according to claims 1 or 2, wherein chromium is present as zinc chromite.

4. A process according to claim 3, wherein ZnO:ZnCr₂O₄ weight ratio is about 3:1.

5. A process according to any one of the preceding claims, wherein palladium is added to the catalyst in form of PdSO₄, in an amount ranging from 0.5 to 5% by weight, preferably from 1 to 3% by weight.

6. A process according to claim 1, wherein a

ZnO:ZnCr₂O₄ (3:1) catalyst containing 1% by weight of

PdSO₄ is used.

7. A catalyst based on zinc for use in dehydration- dehydrogenation processes, characterized in containing Cr and Pd.

8. A catalyst according to claim 7, wherein chromium is in form of zinc chromite.

9. A catalyst according to claim 8, comprising a ZnO-ZnCr₂O₄ mixture in an about 3:1 ratio, added with Pd.

10. A catalyst according to claim 9, wherein Pd is added in form of a salt thereof, such as PdSO₄, in weight percentages from 0.5 to 5%, preferably from 1 to 3%.