Patent GB-655305-A (GB)
Title: Separation of by-products from isophorone and homologues thereof
Filed: 1947-10-17
Abstract: In a process for producing isophorone or homologues thereof by condensing a ketone and recovering a mixture of isophorone or a homologue thereof and lower boiling saturated and unsaturated ketone by-products such as mesityl oxide, diacetone alcohol, and possibly phorone, the isophorone or homologue thereof is substantially freed from said ketone by-products by treating the mixture with a dilute aqueous solution of a basic compound which has a hydroxyl ion concentration not exceeding that of a 1-normal aqueous solution of sodium hydroxide and which provides an excess of water over that needed to hydrate the said lower boiling by-product ketones in the mixture to the ketone used in the said condensation, the treatment being effected at a temperature above 100 DEG  C. and at super-atmospheric pressure thus selectively and catalytically reverting the said by-product ketones to the ketone used in the condensation and separating the thus formed ketone from the isophorone or homologue thereof.  The ketone starting material may be an aliphatic, alicyclic, or aliphatic-alicyclic ketone such as acetone, methyl ethyl ketone, methyl propyl ketone, diethyl ketone, methyl isopropyl ketone, methyl cyclohexyl ketone, ethyl cyclopentyl ketone, cyclohexanone, cyclopentanone and alphamethyl cyclopentanone. The by-product ketones obtained with the homo-isophorones are homologues of those produced with isophorone in its synthesis, the lower boiling point by-product ketones being homologues to mesityl oxide and diacetone alcohol and being revertible to the parent ketone in the process of the invention.  When isophorone is produced the crude material contains acetone and this may be distilled from the mixture first and only the residue treated and the separation of the acetone from the isophorone may be made either after the reversion of the lower boiling by-products or during their reversion.  Preferably the crude material is distilled in the presence of the aqueous basic solution at above 100 DEG  C. and acetone is removed as distillate during its formation by the reversion reactions.  The prepared temperature is between 130 DEG  and 200 DEG  C. and when the treatment is effected at about 150 DEG  C. and at pressures of about 75 to 150 pounds per square inch using a solution having a hydroxyl ion concentration equivalent to that of a 1 per cent by weight aqueous solution of sodium hydroxide the reaction is complete in a short time such as fifteen minutes. Specified basic-acting compounds are the alkaline - reacting metal hydroxides, carbonates and borates and especially the alkali metal and alkaline earth metal hydroxides as well as basic reacting salts of strong bases and weak acids such as the carbonates and borates.  It is preferable to employ solutions of a hydroxyl ion concentration not materially lower than that of a one-tenth normal solution of sodium hydroxide but in some cases a solution having a hydroxyl ion concentration as low as a one-hundredth normal solution of sodium hydroxide may be used. The amount of water in the solution should be in excess of that required to hydrate the ketone by-products and it may be desirable to introduce water with the feed to the still to avoid depleting the catalyst solution of water.  In order to demonstrate the reversion of the undesired ketone by-products an example is given in which a synthetic mixture of isophorone, mesityl oxide and diacetone alcohol and which approximates the composition of the crude material obtained in the synthesis of isophorone from acetone by treatment in the liquid phase at 170 DEG  C. with a 25 per cent by weight sodium hydroxide solution after removing unreacted acetone and the substances boiling higher than isophorone being omitted is used. This synthetic mixture is distilled in the presence of a 1 per cent solution of sodium hydroxide at 150-160 DEG  C., the acetone formed by the reversion being removed by the distillation.