PYROLYSIS AND MASS-SPECTRA OF TRIMETHYLSILYL DERIVATIVES OF MONOSACCHARIDES

The pyrolysis of trimethylsilyl derivatives of saccharides (1) was inv estigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG curves sho wed that the pyrolysis of 1 occurred in one stage. The exothermic peak s were due to sublimation or thermal decomposition by vaporization. Th e cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination of the side-chain, 2) cleavage sf the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of t he pyranose ring and side-chain at the same time. The mass-spectrum fo r 1 revealed the main common four fragment ions, such as m/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions w ere detected with a similar retention time in the gas cromatogram by G C/MS or TG-GC/MS. The retention time for 1 increased in the sequence a ldopentose < ketohexose < aldohexose. This result indicates that the t rimethylsilyl derivatives are thermally stable. Subsequently, the pyro lysis regime for 1 obeyed apparent 1/2-order kinetics and their appare nt activation energy was estimated as 75-100 kJ/mole.