GB810916A - Utilization of by-products from manufacture of 2,5-dimethyl-piperazine - Google Patents

Abstract

In the manufacture of 2.5-dimethyl-piperazines by heating isopropanolamine with an hydrogenation catalyst, the 2.5-dimethyl-piperazines are separated from the higher boiling material which is heated with a hydrogenation catalyst at a temperature in the range 130-300 DEG C. to give at least one of the compounds 2.5-dimethyl-pyrazine and 2.5-dimethyl-piperazines. The relative yields of 2.5-dimethylpyrazine and 2.5-dimethyl-piperazines is dependent partly on the hydrogenation catalyst used. For example, copper chromite, copper powder and the less active nickel catalysts favour the formation of 2.5-dimethyl-pyrazine whereas the more active nickel catalysts, e.g. Raney nickel and the finely-divided nickel formed by the reduction of precipitated nickel hydroxide, favour the formation of cis- and trans-2.5-dimethyl-piperazines. If some of the by-product material is mixed with isopropanolamine and heated with an hydrogenation catalyst to a temperature in the range 130-300 DEG C. less of the by-product material is formed than when the isopropanolamine is used alone. The high-boiling by-product material may be heated at atmospheric or superatmospheric pressure and preferably 5 to 15 per cent of catalyst is used based on the combined weight of the catalyst and by-product material. The process may be carried out continuously by recycling the higher boiling by-products but advantageously from one quarter to half of the high boiling by-product is withdrawn from the system and may be treated separately. In the examples: (a) a high-boiling fraction of the residue obtained after separating 2.5-dimethyl-piperazines from a mixture obtained by heating isopropanolamine with a hydrogenation catalyst is heated at 200 DEG C. under pressure with Raney nickel to give 2.5-dimethyl-pyrazine and 2.5-dimethyl-piperazines; (b) a mixture of isopropanolamine, a high-boiling residue from a previous reaction and Raney nickel is heated to 200 DEG C. to give 2.5-dimethyl-piperazines with very little high-boiling residue; (c) a higher-boiling fraction from a previous reaction, isopropanolamine and reduced nickel hydroxide are heated to 200 DEG C. to give 2.5-dimethyl-pyrazine, and 2.5-dimethyl-piperazines with a very little high-boiling residue; (d) isopropanolamine, a high-boiling residue from a previous reaction, and copper powder are heated to 200 DEG C. to give 2.5-dimethyl-pyrazine and 2.5-dimethyl-piperazines with very little higher boiling residue; (e) isopropanolamine, a high-boiling residue from a previous reaction and a supported nickel catalyst are heated to 200 DEG C. to give 2.5-dimethyl-pyrazine, 2.5-dimethyl-piperazines and a small amount of high-boiling residue; (f) isopropanolamine, a high-boiling residue from a previous reaction and Raney nicel are heated to 200 DEG C. to give mainly 2.5-dimethylpiperazines; and (g) the process of (f) is carried out continuously at 195-205 DEG C. to give mainly 2.5-dimethylpiperazines.