GB614316A - Improvements in and relating to processes for the separation of organic nitro compounds - Google Patents

Abstract

A process for the separation or concentration of the nitration products of aliphatic monoolefines or of alicyclic mono-olefines having at least 5 carbon atoms in the ring comprises bringing the liquid mixture in attenuated liquid form in contact with a heat transfer surface, allowing it to flow over the latter and subjecting it to reduced pressure while thus flowing in order to evaporate off the more volatile components in the mixture and obtain the bulk of the more volatile compounds in the residual liquid which may be fractionated to isolate individual compounds. Suitable mixtures for this treatment are those obtainable by nitration of olefines by means of nitrogen trioxide or tetroxide as described in Specifications 580,260, 587,992, [both in Group IV], 608,758, 609,022 and 613,853, [all in Group IV (b)]. Products recovered include dinitro compounds, nitronitrates and nitro-alcohols while the volatile components include nitrogen tetroxide, solvents and highly volatile nitration products, if present. The process may be effected by passing the liquid mixture from a storage vessel at atmospheric pressure into a film evaporator maintained at a controlled temperature at a sub-atmospheric pressure, the volatiles then being led through a condenser and the residual liquid collected in a cooled receiver. The evaporator may be a single or multi-tube evaporator or a double surface condenser. The liquid film may be maintained on the inner or outer surfaces of the tubes. In examples, the mixtures obtained by reacting propylene, isobutylene and cyclohexene respectively with nitrogen tetroxide in methylated ether (see Group IV) are passed through a film evaporator at 50 DEG C. and 15 mms. pressure whereby the ether and excess nitrogen tetroxide are volatilized off.ALSO:A process for the separation or concentration of the nitration products of aliphatic mono-olefines or of alicyclic mono-olefines having at least 5 carbon atoms in the ring comprises bringing the liquid mixture in attenuated liquid form in contact with a heat transfer surface, allowing it to flow over the latter and subjecting it to reduced pressure while thus flowing in order to evaporate off the more volatile components in the mixture and obtain the bulk of the less volatile compounds in the residual liquid which may be fractionated to isolate individual compounds. Mixtures which may be so treated are those obtainable by nitration of olefines by means of nitrogen trioxide or tetroxide with or without oxygen present as described in Specifications 580,260, 587,992, 608,758, 609,022 and 613,853. Examples of nitro-compounds which may thus be recovered are dinitro-compounds, nitro-alcohols and nitronitrate compounds, while the volatile components may be highly volatile nitration products, if present, and nitrogen tetroxide and/or solvent. The liquid mixture treated is preferably at atmospheric pressure initially and is then subjected as a thin film to sub-atmospheric pressure. Desirably, the stripped liquid is cooled; where the product contains unstable nitro-nitrites it is preferably dropped into an excess of water or an alcohol. The heat transfer surface may comprise a film evaporator such as a double surface condenser or a single or multi-tube evaporator. In examples, mixtures obtained by reacting isobutene with nitrogen tetroxide in methylated ether and propylene or cyclohexene with nitrogen tetroxide in methylated ether while passing in oxygen are passed through a film evaporator cooled by water at 50 DEG C. and under 15 mms. mercury pressure, whereby the ether and excess nitrogen tetroxide is volatilized off and the stripped product is dropped into ice-cold water to decompose nitro-nitrites present into nitro-alcohols.