GB647420A - Improvements in or relating to the manufacture of 1,4-dicyano-2-butene - Google Patents

Abstract

1,4-Dicyano-2-butene is obtained by reacting a dichloro or dibromo or diiodo addition product of 1,3-butadiene with an alkali metal cyanide in a liquid organic nitrile free from aliphatic unsaturation; the said liquid organic nitrile containing dissolved therein cuprous bromide, chloride or iodide. The reaction mixture should be substantially anhydrous, e.g. the nitrile reaction medium should contain not more than 2 per cent by weight of water and oxygen should also be excluded, e.g. by using an inert gas such as nitrogen or by boiling the nitrile solvent so that its vapours act as an inert atmosphere. Superatmospheric pressure may be used. Cuprous chloride is the preferred catalyst and it is not necessary that the cuprous halide used be completely dissolved in the nitrile solvent. Solvent nitriles specified are aceto-, propio-, n-butyro-, valero-, capro-, benzo-, malono- and adipo-nitrile, those preferred containing carbon, hydrogen and nitrogen only and not more than seven carbon atoms especially those having 2 to 6 carbon atoms and no substituents other than the nitrile group. Aceto-nitrile is the preferred solvent. Mixtures of nitriles may be used. Satisfactory yields are obtained by using at least two moles of alkali metal cyanide and at least 0.04 moles of cuprous halide per mol. of dichlorobutene with at least a weight of solvent nitrile equal to that of dichlorobutene at at least 50 DEG C. Best results are obtained by using 2 to 2-5 moles of cyanide and 0.06 to 0.2 moles of cuprous halide per mole of dichlorobutene at between 75 DEG C. and the boiling point of the solvent nitrile of 2 to 6 carbon atoms, the quantity of the latter being from 1.2 to 4 times the weight of the dichlorobutene, e.g. preferably for each mole of dichlorobutene 2 to 2.5 moles of sodium cyanide, 3.5 to 4 moles of aceto-nitrile and 0.1 to 0.15 moles of cuprous chloride are used at the refluxing point of the mixture, i.e. 87-90 DEG C. Lithium and potassium cyanide are also specified but sodium cyanide is preferred. Preferably a crude chlorination product of 1,3-butadiene is used containing a mixture of 3,4-dichloro-1- and 1,4-dichloro-2-butene with a minor amount of 1,2,3,4-tetrachlorobutene or a mixture of the above two specified dichlorobutenes. The amount of catalyst used varies with that of solvent nitrile. Thus with nitrile/dichlorobutene weight ratios of 3.8 to 1, and 1.25 to 1, best yields are obtained using 0.13 to 0.16 and 0.09 to 0.12 moles of catalyst per mole of dichlorobutene respectively. Other diluents such as dioxane, dibutyl ether, tetrahydrofurane, benzene, cyclohexane, methanol and ethanol may be present and should be neutral, particularly non-alkaline. The preferred temperature range is 75 DEG to 120 DEG C. when the reaction is usually complete in 18 to 20 hours. 1,4-Dicyano-2-butene may be hydrogenated to hexamethylene-diamine or hydrolysed to dihydromucic acid. In examples sodium cyanide in acetonitrile with (1) cuprous bromide as catalyst is refluxed and the air replaced with nitrogen when 1,4-dichloro-2-butene is added and after 22.5 hours the product is filtered, washed with hot acetonitrile and 1,4-dicyano-2-butene isolated from the combined filtrates by distillation under reduced pressure after removal of solvent at atmospheric pressure, with (2) cuprous chloride as catalyst and 3,4-dichloro-1-butene as reactant conditions otherwise being similar to (1), with (3) which illustrates a large scale preparation, cuprous chloride or catalyst and an approximately 50/50 mixture of the above two dichlorobutenes as reactant conditions again being similar except that the crude reaction-product after removal of acetonitrile is dissolved in chloroform, washed with 9 per cent hydrochloric acid and water to remove cuprous chloridenitrile addition products when after removal of chloroform distillation under reduced pressure yields 1,4-dicyano-butene with a small quantity of 1-chloro-4-cyano-2-butene, and in (4) sodium cyanide in n-butyronitrile or propionitrile containing cuprous bromide is refluxed and 1,4-dichloro-2-butene added when after about 5.5 hours the product is isolated as in the previous examples.