Patent GB-634562-A (GB)
Title: Improvements in or relating to the manufacture of acetaldol
IPC: C07C45/72
Filed: 1945-03-27
Abstract: <PICT:0634562/III/1> Acetaldehyde is distilled from a mixture consisting of a neutralized aqueous solution of aldol and acetaldehyde, prepared in specified manner (see Group IV (b)), in the presence of a volatile organic liquid which is substantially insoluble in water and inert with respect to the acetaldehyde and aldol and does not form an azeotrope with the acetaldehyde but which does form an azeotrope with water boiling at a temperature below that at which the acetaldol is dehydrated and which is easily separated from acetaldehyde by fractional distillation, in order to drive off the acetaldehyde as a head product.  As shown, the aldol-acetaldehyde solution is fed from vessel 10 to a distillation column 11 charged with benzene.  Acetaldehyde distills off from the top of the column and is withdrawn at 18; from the bottom is withdrawn a mixture of water, aldol and benzene which passed after cooling to a decanter 14. The upper benzene layer is recycled to the column and the aqueous aldol layer removed at 17.  Ethyl acetate, ethers and ketones may be used in place of the benzene.  The Specification as open to inspection under Sect. 91 includes the application of the above-described process to the treatment of solutions of any aliphatic aldehyde and the corresponding aldol, propionaldehyde and butyraldehyde being mentioned.  Mesityl oxide and propyl and isopropyl oxides (ethers) are specified as further examples of suitable volatile liquids.  This subject-matter does not appear in the Specification as accepted.ALSO:<PICT:0634562/IV (b)/1> Acetaldol is prepared from acetaldehyde by a continuous process comprising two condensation stages namely an initial stage to which acetaldehyde and an alkaline condensation catalyst are continuously supplied and from which a mixture of acetaldehyde, catalyst and acetaldol is continuously withdrawn, the reaction temperature in this stage being maintained between 35 DEG  and 21.5 DEG  C. and the concentration of acetaldol being so controlled, by control of the rate of addition of the catalyst to the reaction medium, as to maintain a concentration of acetaldol of between 40 and 50 per cent of the total weight of acetaldehyde and acetaldol in the reaction mixture, such acetaldol concentration being below the equilibrium concentration at the reaction temperature, and a subsequent stage in which the mixture withdrawn from the initial stage is supplied with a further amount of alkaline condensation catalyst, cooled, condensation allowed to proceed to produce the maximum proportion of acetaldol possible without the substantial production of higher polymers and the mixture is then neutralized. Preferably, the condensation in the initial stage is performed at a temperature which is less than 5 DEG  C. below the boiling point of the reaction mixture at the pressure of the operation.  The product is generally worked up by distillation of the aldolic solution of acetaldehyde containing water, which is normally added during the initial condensation stage or to the final product when condensation has been effected in anhydrous medium, in the presence of a volatile organic liquid which is substantially insoluble in water and inert towards the acetaldehyde and aldol and does not form an azeotrope with the acetaldehyde but does form with water an azeotrope boiling at a temperature below that at which the acetaldol is dehydrated and which is easily separated from unreacted acetaldehyde by fractional distillation, in order to drive off the acetaldehyde as a head product.  The distillation residue consists of an upper layer of volatile organic liquid and a lower layer of aqueous acetaldol which may be used as such to convert the aldol to crotonaldehyde or, by catalytic hydrogenation, to butylene glycol. According to an example employing the apparatus shown, acetaldehyde is supplied from tank 20 together with catalyst from tank 21 to a vessel 1 already containing a mixture of the aldehyde and acetaldol; the composition of the mixture is 47 per cent aldol and 53 per cent aldehyde and the temperature is maintained at 27 DEG  C. by circulating a portion of the mixture through cooling means 4.  By working under a slight pressure of inert gas, a temperature of 35 DEG C. may be used but then the conversion of acetaldehyde to aldol should not exceed 40 per cent.  The liquid in vessel 1 overflows with the continuous feeding thereto of acetaldehyde, and is passed together with a small supplemental amount of catalyst from tank 21 through cooling means 9 which constitutes the subsequent stage where aldol condensation proceeds; the temperature here is 15 DEG  C. and conversion is allowed to proceed to 53 per cent, but at 0 DEG  C. it may proceed to 60 per cent.  Finally, the mixture flows to vessel 10 where it is neutralized.  Water is normally supplied to the reaction mixture via a tank 22.  A 97 per cent yield of aldol is obtained. The solution may be worked up by a continuous method by feeding the solution from vessel 10 to a distillation column 11 charged with benzene.  Acetaldehyde is continuously withdrawn at 18 and a mixture of benzene, aldol and water is removed at 12, forwarded to a decanter 14 after cooling and the upper benzene layer returned to the column and the aqueous aldol withdrawn at 17.  In place of benzene there may be used ethyl acetate, ketones and ethers.  The Specification as open to inspection under Sect. 91 relates to a continuous process for the aldolisation of acetaldehyde and higher aliphatic aldehydes including propionaldehyde and butyraldehyde comprising introducing the aldehyde continuously into a liquid mixture of the aldehyde and corresponding aldol, the aldol content of which is kept below the content corresponding to the equilibrium concentration at the temperature prevailing, by sparingly adding a condensation agent.  In the final working up of the product, it is stated that the distillation described above may be carried out in the presence of a volatile liquid, preferably sparingly soluble in water, which is inert towards the aldol and aldehyde and does not form an acetaldehyde azeotrope, and in addition to benzene, mesityl oxide and propyl and isopropyl oxides are mentioned.  An additional example illustrates the aldolisation of propionaldehyde by the process described above using acetaldehyde.  This subject-matter does not appear in the Specification as accepted.