Patent GB-920834-A (GB)
Title: Process of purifying ª ,ª -unsaturated aliphatic aldehydes resulting from aldol condensation
IPC: C07C45/85
Filed: 1959-05-25
Abstract: <PICT:0920834/III/1> Alpha, beta-unsaturated aliphatic aldehydes having from 4 to 12 carbon atoms per molecule and produced by the aldol condensation of aliphatic aldehydes having from 2 to 6 carbon atoms per molecule, followed by dehydration of the resulting diols, are purified by separating the organic layer from the aldol condensation and steam distilling it from an aqueous caustic alkali solution of from 0,1 to 10% by weight concentration.  The steam distillation decomposes impurities which, in the absence of alkali, would distil over in the same temperature range as the aldehydes (enals) and thus contaminate any saturated alcohols (anols) prepared therefrom by hydrogenation.  Such alcohols are desired free from colour for the preparation of esters suitable for use in the plastics industry.  Enals exemplified are crotonaldehyde; 2,4-dimethylbuten-2-al; 2-ethylhexen-2-al; 2-methylpenten-2-al; 2-ethylisohexen-2-al; 2-propylhepten-2-al; 2-propyl-4-methylhexen-2-al; 2-isopropyl-5-methylhexen-2-al; 2,4-dimethylpenten-2-al; 2-ethyl-4-methylhexen-2-al; and 4-butylocten-2-al.  As shown, the organic layer of the products resulting from aldol condensation and dehydration are fed by line 1 into a steam distillation column 2 operated at a base temperature of 90 DEG -100 DEG C. while a solution of caustic soda or caustic potash of preferably 1% to 3% by weight concentration is fed into the column near its top by line 7.  The distillate from column 2 passes to a decanter 5 by way of a condenser 4, and the desired organic layer is withdrawn from the decanter 5 by line 6, the aqueous layer returning to the column 2 via line 7.  The caustic alkali solution withdrawn at the base of column 2 passes via line 8 to a heat-exchanger 9 and is returned to column 2 partly via the line 10 and partly via the pump 12 and line 13.ALSO:Alpha, beta-unsaturated aliphatic aldehydes having from 4 to 12 carbon atoms per molecule and produced by the aldol condensation of aliphatic aldehydes having from 2 to 6 carbon atoms per molecule, followed by dehydration of the resulting diols, are purified by separating the organic layer from the aldol condensation and steam distilling it from an aqueous caustic alkali solution of from 0.1 to 10% by weight concentration.  The steam distillation decomposes impurities which, in the absence of alkali, would distil over in the same temperature range as the aldehydes (enals) and thus contaminate any saturated alcohols (anols) prepared therefrom by hydrogenation.  Such alcohols are desired free from colour for the preparation of esters suitable for use in the plastics industry.  Enals exemplified are crotonaldehyde; 2,4 - dimethylbuten - 2 - al; 2-ethylhexen-2-al; 2-methylpenten-2-al; 2-ethylisohexen-2-al; 2-propylhepten-2-al; 2-propyl-4-methylhexen-2-al; 2-isopropyl-5-methylhexen-2-al; 2,4-dimethylpenten-2-al; 2-ethyl-4-methylhexen-2-al; and 4-butylocten-2-al.  As shown, the organic layer of the products resulting from aldol condensation and dehydration are fed by line 1 into a steam distillation column 2 operated at a base temperature of 90-100 DEG C. while a solution of caustic soda or caustic potash of preferably 1% to 3% by weight concentration is fed into the column near its top by line 7.  The distillate from column 2 passes via a condenser 4 to a decanter 5, whence the desired products are withdrawn via line 6, the aqueous layer returning to column 2 via line 7.  The caustic alkali solution withdrawn at the base of column 2 passes via line 8 to a heatexchanger 9 and is returned to column 2 partly via the line 10 and partly by the pump 12 and line 13.