The Molecular Structure of Dimethyl Sulfate

A. BORBA, GOMEZ ZAVAGLIA, ANDREA, PEDRO N.N.L. SIMÕES Y RUI FAUSTO

Funchal, Madeira

Congreso; 6th Conference on Inorganic Chemistry; 2005

Sociedad Portuguesa de Quimica

Dimethyl sulfate (DMSO4) has many industrial applications as alkylating agent, as intermediate in the manufacture of pharmaceuticals, pesticides, etc. [1,2]. Being extremely toxic, methods like gas chromatography and optical spectrometry have been applied for its determination in the environment [3]. In spite of its well-known chemical and biochemical importance, the available knowledge on structural and vibrational properties of this compound is very scarce. The relatively large computational resources required to perform reliable theoretical predictions, together with its relatively difficulty to crystallize, its easy decomposition upon heating and light exposition and its high toxicity to human beings (it was used in the first World War as war-gas [4,5], discourage studies on DMSO4. Most of these problems can be avoided by using the low temperature inert-matrix isolation technique [6].   In this work a concerted approach based on the matrix-isolation method coupled with FTIR spectroscopy and theoretical methods [DFT/B3LYP/aug-cc-pVQZ calculations] was applied, in order to investigate the molecular structure of DMSO4 and spectroscopically characterize its conformationally dependent vibrational properties.   According to calculations, conformer GG (of C2 symmetry and exhibiting O-S-O-C dihedral angles of 74.3º) was found to be the most stable conformer in both the gaseous phase and isolated in argon, occupying two substitutional sites with different stabilities in the matrix. Upon annealing of the matrix, the less stable observed conformer (GT; with C1 symmetry) quickly converts to the GG conformer, with the resulting species being embedded in a matrix-cage, which corresponds to the most stable matrix-site for GG form. Further annealing leads to extensive aggregation; however, even at 41 K, where the aggregates strongly dominate, some amount of GG monomer occupying its most stable site can still be observed. The highest energy TT conformer, which was assumed to be the most stable conformer in previous studies [3], was predicted by the calculations to have a relative energy of ca. 10 kJ mol-1 and was not observed in the spectra of the matrix-isolated compound.     [1] Du Pont, Dimethyl Sulfate Properties, Uses, Storage and Handling, Wilmington, Delaware, E.I. Du Pont de Nemours & Co., Inc. (1981) 24. [2] L. Fishbein, Washington DC, US Environmental Protection Agency Bulletin 1977, 319. [3] K. O. Christe and  E.C. Curtis, Spectrochim. Acta A, 1972, 28, 1889. [4] R. Ray, B. J. Benton, D. R. Anderson, S. L. Byers and J. P. Petrali J. Appl. Toxicol. 2000, 20, S87. [5] J. P. Petrali and S. Oglesby-Megee, Microsc. Res. Tech. 1997, 37, 221. [6] R. Fausto, Ed. “Low Temperature Molecular Spectroscopy”, Kluwer, Amsterdam, 1995.   Acknowledgements - This work was supported by the Portuguese Fundação para a Ciência e a Tecnologia (Research Project POCTI/QUI/43366/2001 and Grant FCT SFRH/BPD/11499/2002), FEDER, CONICET, and Agencia Nacional de Promoción Científica y Tecnológica-PICT 13080, Argentina.   e-mail: angoza@qui.uc.pt