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

Catalysis by Cu salts (MnCuCln+1; M = K+, NH4(+)) in concentrated aqueous s olutions (approximately 5-8 M) is investigated using a flow reaction system at 75 degreesC. Selective dimerization of acetylene gives vinylacetylene a s a major product and much smaller amounts of 1,2-divinylacetylene, acetald ehyde, 1-ethynyl-1,3-butadiene, and uncharacterized black tarry products. C ooling the catalyst solution to room temperature causes the growth of a mix ture of tetrahedral and needle-like colorless crystals. Observation of the crystals by microscopy and their crystallography, and analyses of the Cu co mpounds reveal that they are CuCl and K2CUCl3, respectively. Plots of the g raphs of the solubility of the Cu salts in water as a function of temperatu re and composition of the salt show the dominant presence of KCUCl2 in the solution. A mechanism of the reaction is proposed based on the performance of the catalyst and its structure. (C) 2001 Elsevier Science B.V. All right s reserved.