Nieuwland catalysts: investigation of structure in the solid state and in solution and performance in the dimerization of acetylene

Abstract

Catalysis by Cu salts (M n CuCl n+1 ;M=K +,NH 4 +) in concentrated aqueous solutions (approximately 5–8 M) is investigated using a flow reaction system at 75°C. Selective dimerization of acetylene gives vinylacetylene as a major product and much smaller amounts of 1,2-divinylacetylene, acetaldehyde, 1-ethynyl-1,3-butadiene, and uncharacterized black tarry products. Cooling the catalyst solution to room temperature causes the growth of a mixture of tetrahedral and needle-like colorless crystals. Observation of the crystals by microscopy and their crystallography, and analyses of the Cu compounds reveal that they are CuCl and K 2CuCl 3, respectively. Plots of the graphs of the solubility of the Cu salts in water as a function of temperature and composition of the salt show the dominant presence of KCuCl 2 in the solution. A mechanism of the reaction is proposed based on the performance of the catalyst and its structure.