GB863498A - Purifying piperazines by distillation - Google Patents

Abstract

2,3-Butylene glycol present as an impurity in either 2,3,5,6-tetramethylpiperazine or 2,3,5-trimethylpiperazine is removed therefrom by adding a co-distillation agent which, with the 2,3-butylene glycol, is then distilled off azeotropically. Specified co-distillation agents include aliphatic hydrocarbons, e.g. octane, 2-methyl octane, 3-methyl octane, 2,3-dimethyl octane, 2,7-dimethyl octane, nonane, decane, 3-methyl heptane, 4-ethyl heptane, and mixtures such as petroleum fractions containing octane, nonane and decane; cycloaliphatic hydrocarbons, e.g. ethyl cyclohexane and isopropyl cyclohexane; aromatic hydrocarbons, e.g. toluene, xylene, ethyl benzene, diethyl benzene, cumene, diisopropyl benzene, ethyl toluene, n-propyl benzene, tert-butyl benzene, and 1,3,5-trimethyl benzene; and nuclear chlorinated aromatic hydrocarbons, e.g. chlorobenzene, 2-chloro-1-methyl benzene, 3-chloro-1-methyl benzene and 4-chloro-1-methyl benzene. Co-distillation agents boiling within the range 120-170 DEG C. are preferred. The distilled azeotrope separates into two phases on cooling, the lower comprising the 2,3-butylene glycol and the upper comprising the co-distillation agent, which is returned to the column. In a batch process, when the 2,3-butylene glycol has been entirely removed, water is added to the column and the co-distillation agent is distilled off azeotropically therewith. After distilling off remaining water the purified tri- or tetra-methylpiperazine is finally distilled at 165 DEG to 168 DEG C. or at 175 DEG to 183 DEG C. In a continuous process the piperazine is removed from the base of the column and fractionated in a second column.