[7783-09-7] · H2Te · Hydrogen Telluride · (MW 129.62)
(mild reducing agent for aromatic nitro, azoxy, azo, nitroso, hydroxylamino, imino, and aldehyde groups, and the carbon-carbon double bonds of enamines and electron-deficient alkenes; useful in reductive alkylation of amines with aldehydes and ketones)
Physical Data: bp -2.2 °C; mp -51.2 °C; d 5.81 g L-1; pK
Solubility: sol alkali, water (dec), ether, benzene.
Preparative Method: hydrolysis of Al2Te3 in an atmosphere of CO2.1 Can be generated in situ.
Handling, Storage, and Precautions: a malodorous, colorless gas. Use in a well-ventilated fume hood. Decomposes completely to elemental Tellurium and hydrogen above 0 °C. Unstable to heat and light. Oxidizes very rapidly in air to Te0. Flammable. Corrosive (H2Te is a stronger acid than HF). Irritant. Highly toxic, but the ready decomposition of H2Te to relatively nontoxic elemental Te suggests it is unlikely to be a serious hazard if precautions are taken. (Ingestion or inhalation of small amounts of elemental tellurium produces transient, garlic-like breath that is said to be eliminated by oral dosage with vitamin C.) Hydrogen telluride is a strong reducing agent and may react explosively with strong oxidants. Forms insoluble heavy metal tellurides. Possible contaminants are H2S, H2Se, and HCl.
Aromatic nitro compounds are reduced to amines (47-94%) by addition of powdered Al2Te3 to a THF solution of the nitro derivative under N2. Water is added gradually to the warmed solution to generate H2Te in situ, and the mixture is refluxed (eq 1).2 Likewise, phenylhydroxylamine gives aniline (98%); nitrosobenzene, azobenzene, and azoxybenzene give hydrazobenzene (63%, 96%, and 86%, respectively). Imines and enamines (eq 2) may be reduced at lower temperatures by the in situ procedure.3 Addition of Triethylamine improves yields in reduction of imines. A convenient reductive alkylation of amines with carbonyl compounds involves in situ generation of both imine and H2Te (eq 3).3 Yields varied from a low of 12%
Donald C. Dittmer Syracuse University, NY, USA
Donald C. Dittmer
Syracuse University, NY, USA