Patent GB-640189-A (GB)
Title: A process of preparing dihydropyridine derivatives
Filed: 1947-11-17
Abstract: Resins useful as tackifiers in rubber compositions are produced by reaction with aqueous formaldehyde of dihydropyridine derivatives containing at least four hydrocarbyl substituent groups attached to carbon atoms of the ring.  A number of such derivatives are specified.ALSO:Dihydropyridine derivatives are prepared by reacting monoketones with ammonia in the presence of a substantial proportion of a strongly alkaline catalyst such as an alkali metal hydroxide or carbonate or alkaline earth metal hydroxide. Suitable ketones have the grouping <FORM:0640189/IV (b)/1> where R is a hydrocarbyl group, and R1 is hydrogen or a hydrocarbyl group which may be saturated or unsaturated, aliphatic, alicyclic or aromatic.  Preferred ketones have not more than 10 carbon atoms and contain a methyl group directly attached to the carbonyl group.  Ketones specified are acetone, 2-butanone, 3- and 2-pentanones, 2-methyl and 2,2-dimethyl-3-butanone, 2- and 3-hexanone, 3- and 4-methyl-2-pentanone, 2-methyl and 2,2-dimethyl-3-pentanone, 2-, 3-and 4-heptanones, 2-methyl-4-hexanone, 2-octanone, 2,2,3-trimethyl-4-pentanone, 2,2,6,6-tetramethyl-4-heptanone, methyl cyclohexyl and ethyl cyclopentyl ketones, 3-cyclohexyl-2-butanone and propanone, 1-buten-3-one, 1- and 2-penten-4-ones, 1-penten-3-one, 1-hexen-4-one, 1,6 - heptadien - 4 - one, 1,4 - hexadien - 6 - one, 1-butyn-3-one, acetophenone, propionophenone, 1 - phenyl - 3 - butanone and 1,5 - diphenyl - 3-hexanone.  Compounds convertible thereto may be used.  The catalyst may be employed as an aqueous solution of at least 15 per cent, when about 0.1-1 times the volume of ketone is effective.  Solutions in such solvents as methyl or ethyl alcohol may also be used.  Preferably, 1-6 mols. of ammonia per 3 mols. of ketone are used. Temperatures may be up to 200 DEG , preferably about 70-150 DEG  C.  Any pressure may be used, but is advantageously sufficient to maintain the liquid phase.  It may be preferable to avoid prolonged contact of the reactants in the absence of the catalyst.  Continuous operation may be effected with circulation of catalyst, ketone, and ammonia through a reactor or ketone and ammonia may circulate through a non-circulating catalyst solution.  A vapour phase reaction may be effected by contacting gaseous reactants with a solid catalyst at about 100-350 DEG , preferably 200-300 DEG  C. Regeneration of catalyst by removal of water may be necessary. Dihydropyridine derivatives obtained include the 2,2,4,6-tetramethyl derivative, from acetone and ammonia, the 2,2,4,5,6-pentamethyl and 2,2,4-trimethyl-6-ethyl derivatives, from methyl ethyl ketone, mesityl oxide, and ammonia, 2,5,6-trimethyl-2,4-diethyl and 2-methyl-2,4,6-triethyl derivatives, from methyl ethyl ketone and ammonia.  Other derivatives specified are the 2,2,4,6-tetraethyl - 3,5 - dimethyl, 2,2,3,4,5,6 - hexaethyl, 2,6 - divinyl - 2,4 - dimethyl - 3 - methylene, 2,6-diallyl - 2,4 - dimethyl - 3 - vinyl, 2,6 - dimethyl - 2,4-diphenyl and 2,6 - dibenzyl - 3 - phenyl - 2,4-dimethyl derivatives.  In examples, anhydrous ammonia and aqueous caustic soda are reacted with acetone, methyl ethyl ketone, a mixture of mesityl oxide and methyl ethyl ketone, and a mixture of methyl vinyl ketone and acetone.