PREPARATION, CRYSTAL-STRUCTURE AND THERMAL-DECOMPOSITION STUDY OF SOME TRIMETHYLSILYL ESTERS OF DICARBAMIC ACIDS

Some new trimethylsilylated dicarbamic acid esters 1-9 and 10 were pre pared. Their thermal decomposition was studied in n-alkanes as media. The reactions were monitored by gas chromatography (GC) and gas chroma tography-mass spectrometry (GC-MS), respectively. Some N-silylated cyc lic ureas 11-15 were also prepared from the corresponding esters 2-6 b y thermolysis. The crystal structures of 2, 5 and 8 are also discussed . The crystal and molecular structures of 2 and 5 have very similar ch aracteristics. Both molecules are sited via their molecular centre of symmetry on crystallographic inversion centres, The carbamate groups a re planar in all three cases as expected. An analysis of the data show ed that the force due to Si-O conjugation which constrains the Si atom into the plane of the carbamate group is comparable to the crystal pa cking forces with a small out-of-plane movement being not unfavourable .