Patent GB-714883-A (GB)
Title: Improvements relating to the production of unsaturated aliphatic aldehydes
Filed: 1952-04-17
Abstract: Unsaturated aldehydes are made by continuously flowing through a distilling column a reaction mixture containing 100 parts by weight of a saturated aliphatic aldehyde which has a straight chain or a branched chain branched on a carbon atom other than that in alpha position, and having at least 3 carbon atoms per molecule, and an aqueous solution of at least 5 parts by weight of an inorganic alkaline condensation catalyst, while maintaining a temperature of above 90 DEG  C. in at least part of the column, the rate of flow being such that the reaction mixture traverses the length of the column in not more than 10 minutes.  When a single aldehyde is used as starting material the product contains twice as many carbon atoms per molecule as the starting aldehyde.  When a mixture of two aldehydes is used the product contains per molecule a number of carbon atoms equal to the sum of the number of carbon atoms in the two starting aldehydes.  The flow should be maintained substantially uniform and without mechanical agitation.  Preferably the starting aldehydes contain 3-10, especially 3-7, carbon atoms per molecule, those specified being propionaldehyde, n-butyraldehyde, isovaleraldehyde and oenanthol. Preferably the catalyst is used in quantities of 5-25 per cent by weight.  Sodium hydroxide may be used in the form of a 5 to 30 per cent aqueous solution, other specified catalyst being potassium and calcium hydroxide and sodium carbonate or mixtures of these substances.  Pressures of 1-5, preferably 3 atmos., may be applied so that the reaction is completed in a little over a minute.  Reaction may be effected by continuously introducing the saturated aldehyde and an aqueous solution of the catalyst into the head of a distillation column heated at its base, the vapours from the top being condensed and the condensate refluxed, and liquid containing the product is continuously withdrawn from the base at a rate corresponding to the feed rate.  The withdrawn stream is preferably allowed to separate into aqueous and non-aqueous layers the former layer being recycled after adjustment for catalyst concentration and the latter layer treated for product recovery.  It may be advantageous to effect the separation whilst hot, e.g. in a reservoir at the foot of the column.  The starting aldehyde may be introduced a few plates below the top one.  In examples, butyraldehyde is treated at atmospheric pressure with aqueous sodium hydroxide in (1) and (4) and with aqueous sodium hydroxide and carbonate in (3) to yield alpha-ethyl betapropyl acrolein with some butyraldol and in (8) at 3 atmos., and (10) 5 atmos. with aqueous sodium hydroxide to yield the acrolein of (1) and together with acetaldehyde at atmospheric pressure in the presence of (5) aqueous sodium, and (6) potassium hydroxides to yield alpha-ethyl beta-methyl, alpha-ethyl beta-propyl and alpha-propyl acrolein and at 3 atmos. in (9) in the presence of aqueous sodium hydroxide to yield the same acroleins, in (2) propionaldehyde at atmospheric pressure with aqueous sodium hydroxide yields alpha-methyl beta-ethyl acrolein and some propionaldol, in (7) oenanthol at atmospheric pressure with aqueous potassium hydroxide yields pentylnonenal also obtained from the same aldehyde in (11) at 5 atmos. with aqueous sodium hydroxide and in (12) and (13) isovaleraldehyde with aqueous sodium hydroxide at atmospheric and 5 atmos. pressure respectively to yield isopropyl-isoheptenal.