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Elemental tellurium originally was put on the list of "extremely hazardous substances," but a review of the study by the Environmental Protection Agency indicated that sodium tellurate was used instead of tellurium. The LD50 is now given as 5,000 mg per kg for mice. Ingestion of tellurium by humans causes garlic-like "tellurium breath" because of the formation of dimethyl telluride. Tellurium compounds in microgram amounts occur fairly widely in plants (for example, onions, peas, and tea leaves), and larger quantities (3173 µg per g) are found in garlic buds. My interest in tellurium came as the result of an attempt to prepare telluracyclobutene, a four-membered cyclic compound with one tellurium atom and a carbon-carbon double bond, to be used as an electron donor in semiconductor formation. Treatment of epichlorohydrin (chloromethyloxirane) with sulfide ion gave 3-hydroxythiacyclobutane, a precursor of thiacy-clobutene (which does form a semiconducting material), but treatment with telluride ion gave allyl alcohol and elemental tellurium. This represents a nucleophilic reduction in which the powerful nucleophilic telluride ions, Te2 or Ten2, are oxidized and the organic compound is formally reduced. The first nucleophilic reduction by telluride ion, reported by W. V. Farrar and J. Masson Gulland (J. Chem. Soc. 1945, 1114), was the unexpected conversion of 1,2-dibromoethane to ethylene by sodium telluride, with elemental tellurium also being produced. The driving force for these reactions is caused by the high nucleophilicity of Te2 and the thermodynamic instability of Te2 with respect to elemental tellurium. Nucleophilic attack by telluride ion on an organic compound with an electrophilic site or sites opens a pathway whereby oxidation to the element occurs with concomitant transformation of the original organic compound to a new compound. My coworkers found that Sharpless-Katsuki asymmetric epoxidation of primary allylic alcohols; conversion of the alcohol function to an electrophilic site with a good leaving group, typically a tosylate or mesylate; followed by treatment with telluride ion obtained by reduction of elemental tellurium produce new chiral secondary and tertiary allylic alcohols [J. Org. Chem., 58, 718 (1993)]. Similar results for the synthesis of allylic amine derivatives have been obtained via O-tosylates of aziridinemethanols or oxazolidinonemethanols [J. Org. Chem., 62, 7920 (1997); Tetrahedron Lett., 40, 2255 (1999); and 42, 5789 (2001)]. Müller's discovery is an interesting element whose unique properties, which may be inferred from its position in the periodic table, make it useful in a variety of organic chemical transformations as well as in the construction of alloys and other solid-state materials such as semiconductors and solar cells.
Donald C. Dittmer is a professor emeritus at Syracuse University. His research interests include telluride-induced nucleophilic reductions.
Chemical & Engineering News
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