Thermal degradation in the solid state of metal salts of methacrylic acid oligomers

Alkaline earth metal salts of methacrylic acid oligomers undergo thermal degradation at 450–500°C to yield five-membered ring cyclic ketones. Some detailed studies are described in this paper. Magnesium 1-hexene-2,5-dicarboxylate undergoes thermal tetramerization in the solid state at temperatures above 300°C, but below the temperature of decomposition of the salt, to give two tetramers, 4-dodecene-2,5,8,11-tetracarboxylate and 5-dodecene-2,5,8,11-tetracarboxylate. At 450–500°C, the tetramers are converted to 1-(3-methyl-2-oxocyclopent-3-enyl)-2-(3-methyl-2-oxocyclopentyl)ethane, which, in turn, decomposes into two cyclic ketones,2,5-dimethylcyclopentan-1-one and 2,5-dimethylcyclopent-3-en-1-one. Trimer salt, magnesium 1-nonene-2,5,8-tricarboxylate, is difficult to thermally hexamerize in the solid state and, rather, decomposes at 450–500°C directly into 3,8-dimethylbicyclo4,3,0]-nonen-2,7-dione, which yields a mixture of three ketones, 2-methylcyclopentan-1-one, 2,5-dimethylcyclopentan-1-one and 2,5-dimethylcyclopent-3-en-1-one.