[7783-07-5] · H2Se · Hydrogen Selenide · (MW 80.98)
Physical Data: mp -65.7 °C; bp -41.3 °C; d 3.66 g L-1; pK1 3.89; pK2 11.0.
Solubility: fairly sol water (9.88 mg mL-1 at 22.5 °C/760 mmHg).
Form Supplied in: available commercially as gas in bottles or cylinders.
Preparative Methods: H2Se is made by hydrolysis of Al2Se3, by the action of dilute mineral acids on FeSe, by the surface catalyzed reaction of gaseous Selenium and H2 above 350 °C, or by heating Se with Lithium Hydroxide or Mg(OH)2.3 Se is readily reduced to H2Se by Carbon Monoxide and H2O (water gas) in the presence of Triethylamine.4
Handling, Storage, and Precautions: colorless gas with a disagreeable odor; very toxic. It irritates the mucous membranes of the nose, eyes, and upper respiratory tract. It is easily oxidized by atmospheric oxygen and must be handled under inert gas. It burns in air and is decomposed by dust and rubber and in the presence of moisture with separation of Se. Aqueous solutions are oxidized in air with separation of red Se. Use in a fume hood.
H2Se reduces aldehydes and ketones (eq 1) under basic conditions to form diselenides.5 With photochemical activation, primary and secondary alcohols are obtained6 from aldehydes and ketones. Arylhydroxylamines, nitrosoarenes, and nitroarenes are reduced to primary aromatic amines with H2Se formed in situ from Se and water gas.7 In this reaction, only catalytic amounts of selenium need to be used since the Se formed during the reaction is reduced by the excess of water gas (eq 2).7b Acetaldehyde treated with H2Se and HCl gives intermediate bis(1-chloroethyl) selenide, which yields divinyl selenide on dehydrohalogenation (eq 3).8
Addition of H2Se to Ethylene leads to diethyl selenide as a main product, but severe reaction conditions are required.9 H2Se adds to the cyano group in nitriles or to the azomethine group in imidoyl or iminium chlorides to produce selenoamides.10 The action of H2Se on formamidines gives N-alkylselenoformamidines, while the treatment of N-alkylcyanamides or carbodiimides yields N-substituted selenoureas (eq 4).11
Treatment of adenosine, its derivatives, and analogs with H2Se in aqueous pyridine gives the corresponding 6-seleno-substituted nucleosides and nucleotides.12 The reaction of acid chlorides with H2Se leads to diacyl selenides.13 Ring opening of Ethylene Oxide with H2Se affords a modest yield of a mixture of 2-hydroxyethylselenol and bis(2-hydroxyethyl) diselenide.14
Jacek Mlochowski & Ludwik Syper
Technical University of Wroclaw, Poland