Patent GB-783458-A (GB)
Title: Aldehyde condensation reactions
IPC: C07C49/203
Filed: 1955-04-20
Abstract: <PICT:0783458/III/1> A catalytic reactor, for use in aldol-type condensations catalysed by a basic anion-exchange resin and/or a volatile tertiary amine (see Group IV (b)) comprises a chamber 13 divided into two compartments by an annular partition 21 which surrounds a tube 18 closed at its lower end and provided with a central conduit 24.  The compartments of the reactor chamber are connected by a liquid overflow pipe 22 and by a vapour by-pass 23. The reactor is connected to the top of a distillation column. Liquid reactants enter the reactor via opening 16, accumulate in central conduit 24 and then flow through the resin bed 19.  The reacted mixture leaves through apertures 26 in tube 18 and then passes via the overflow 22 into the lower compartment of the reactor and thence to the distillation column.  Vapours from the column pass through the lower compartment of the reactor and the by-pass 23 to a condenser (not shown), the condensate being returned to the reactor through opening 16 with fresh reagents.ALSO:<PICT:0783458/IV (a)/1> <PICT:0783458/IV (a)/2> Aldol-type condensation products are prepared by the condensation of an aldehyde with itself or another compound containing an active hydrogen atom such as another aldehyde, a ketone or a nitro paraffin in which there is at least one hydrogen atom attached to a carbon atom adjacent the carbonyl or nitro group, wherein the condensation is effected continuously in a reaction zone using, as a catalyst, a basic anion-exchange resin or a volatile tertiaryamine which is otherwise inert in the reaction, or both, the resulting mixture of condensation product, unchanged starting material(s) and amine catalyst when used is fractionally distilled under conditions such that the unchanged reactants and amine are removed as vapours from the condensation product, and the vapours are liquefied and returned together with fresh reagents to the reaction zone.  The amine catalyst may be an aliphatic, aromatic or heterocyclic tertiary amine and desirably is one forming an azeotrope with the more volatile reagent present; many are specified.  It is preferred to use the resin catalyst, especially in conjunction with the tertiary-amine catalyst, which maintains the activity of the resin.  In the absence of the amine the resulting partially deactivated catalyst may be continuously replaced by fresh catalyst or a plurality of catalyst beds may be provided whereby the deactivated beds out of use may be regenerated, e.g. by aqueous solutions of ammonia, an amine, a basic salt of a weak acid or a strong base.  The resin preferably contains more quaternary ammonium salt groups than hydroxide groups; several such resins are described. The reaction mixture should preferably be homogeneous and to this end an inert volatile solvent may be added, e.g. methanol or dioxane. The fractional distillation is preferably effected in a column in which is provided an inert liquid whose boiling-point is between those of the reactants and the condensation product, e.g. water or propanol, to prevent decomposition of the product.  The aldol-type products may be catalytically dehydrated; specified catalysts are various mineral acids, oxalic acid, toluene sulphonic acid, potassium hydrogen sulphate, iodine and zinc chloride; the acids are preferably used in aqueous solution. Various arrangements of apparatus are described.  One form comprises a reactor 13 (Fig. 2) divided into two compartments by an annular partition 21 surrounding a tube 18 which encloses a conduit 24 and a resin catalyst bed 19; the two compartments being joined by an overflow pipe 22 and a vapour bypass 23.  The reactants are fed into the reactor via line 71 (Fig. 1), accumulate in central conduit 24, then flow through the resin bed and finally leave via apertures 26 and overflow pipe 22 and pass through the lower half of the reactor to a column 11.  The unchanged reactants in the reaction product are vaporized in the column and are led via the reactor by-pass 23 to a reflux condenser 14, the condensate being returned with fresh feed to the reactor.  The stripped aldol-type product is withdrawn continuously from a reboiler 12 via line 27.  The reactor is preferably maintained at or near the boiling-point of the reactants.  Dehydration of the aldol product is effected by feeding the stripped material, together with catalyst added at 72, into a dehydrating column 28 from which the products are obtained as distillate, the residue being aqueous catalyst.  In another form of apparatus (Fig. 3, not shown), the distilled vapours of unchanged reactants pass direct from the column to a condenser, the condensate is blended with fresh reactants and passed upwardly through a resin catalyst bed and the issuing reaction products are fed to the column; this apparatus is described in conjunction with the condensation of methyl ethyl ketone and aqueous formaldehyde to give the mono-methylol derivative and means are provided whereby the relative proportions of fresh reagents fed to the reactor are automatically controlled by mechanism governed by the composition of the vapours in the column.  The stripped aldol product is then fed to a dehydration column as above described with reference to Fig. 1.  A further form of apparatus (Fig. 4, not shown) uses a single column, wherein the condensation reaction mixture is stripped in the upper part and the aldol-type product is dehydrated in the lower part, the dehydration catalyst being introduced and the dehydration product withdrawn at intermediate points.  It is stated that the apparatuses may be used for the condensation reactions using only the amine as catalyst.  Examples are given using the apparatus shown, wherein (1) methyl ethyl ketone is condensed with aqueous formaldehyde using "Amberlite" (Registered Trade Mark) IRA400 as catalyst with or without triethylamine to give 4-hydroxy-3-methyl-butanone-2 which is dehydrated with aqueous phosphoric acid yielding methyl isopropenyl ketone and some ethyl vinyl ketone; (2) methyl isopropenyl ketone is reacted as in (1) yielding as dehydration product vinyl isopropenyl ketone and (7) butyraldehyde is auto-condensed using the resin of (1) and trimethylamine as catalyst and methanol as a solvent yielding 2-ethyl-3-hydroxy-hexanol which is dehydrated to give 2-ethyl hexenal.  In a further example (6), methyl ethyl ketone and aqueous formaldehyde are condensed in the presence of triethylamine in a packed distillation column operating under total reflux; the reagents are fed with catalyst into the reflux condensate and a product stream of 4-hydroxy-3-methyl-butanone-2 and 3:3-dimethylol butanone-2 is recovered from the column reboiler.  Other condensations referred to are those of formaldehyde with acetone, methyl propyl ketone, methyl butyl ketone, ethyl propyl ketone (the ketones being preferably used in excess), acetaldehyde, butyraldehyde, isobutyraldehyde, propionaldehyde, nitromethane, nitro-propane and 1- or 2-nitrobutane and the auto-condensation of propionaldehyde, valeraldehyde and, especially, acetaldehyde to aldol yielding crotonaldehyde on dehydration.