Features of thermolysis of Cu and La maleates

Salts of carboxylic acids are widely used in organic synthesis, in the preparation of catalysts and nanocomposites of metals in the carbon matrix by thermolysis of maleates, acrylates or acetylenedicarboxylates of these metals; however, the studies of the thermal destruction process of such compounds are fragmentary. The processes of multi-stage decomposition of Cu and La maleates in an inert atmosphere were studied by the method of simultaneous thermal analysis with the analysis of the composition of evolved gases. Reaction mechanisms have been suggested that correspond to the gaseous products and the final solid decomposition product determined during the thermal steps of mass loss. The formation of nano-dispersed copper oxides and lanthanum oxocarbonate included in the porous carbon matrix has been shown. The results of thermal analysis have allowed us to identify common features of the maleate thermolysis. First, the decomposition of maleate ion or maleic acid is always accompanied by the formation, along with water and carbon dioxide, of two products containing a double or triple C-C bond: acrylic acid and acetylene in approximately equal amounts. Second, the presence of multiple bonds in the molecules of the initial substances and in the molecules of the gaseous products of thermolysis leads to their polymerization and further to formation of the carbon residue. The amount of this residue is the highest in the case of decomposition of lanthanum maleate and the lowest in the case of copper maleate. Third, the thermolysis of metal maleate results in a matrix consisting of a carbon polymer with particles of metals (Cu) or metal oxides / carbonates in the form of nanodispersed crystals evenly distributed in this matrix. With the use of electron microscopy the morphology and particle size of the products of the thermolysis of La and Cu maleates were determined. The thermolysis products are composites of spherical La2O2(CO3) particles (2-5 µm in diameter) and Cu2O, CuO, Cu (10-500 nm in diameter), evenly distributed in the carbon matrix. The analysis of the thermolysis mechanism on the basis of the data on the magnitude of mass loss at each stage, thermal effects, as well as on the composition of gaseous products and on the phase composition of the final solid products of thermolysis allowed us to suggest a consistent initial formula of La and Cu maleates.