[1313-85-5] · Na2Se · Sodium Selenide · (MW 124.94)
(nucleophilic agent for synthesis of organic selenides1)
Physical Data: mp 845 °C; d 2.58 g cm-3.
Solubility: readily sol water; sol ethanol, liquid ammonia; sparingly sol THF.
Form Supplied in: white, fine hygroscopic crystals.
Preparative Methods: prepared by reduction of Selenium with Sodium (molar ratio 1:2) in liquid ammonia. It can be used in solution2b,c or isolated by evaporation of ammonia.2a In aqueous medium, Na2Se is obtained by reduction of Se with Sodium Hydroxymethanesulfinate (rongalite)3 or by reduction of Na2Se2 with Sodium Dithionite.4 Na2Se (or K2Se) can also be produced by the direct reaction of Se with Na (or K) in high-boiling, polar, aprotic solvents, such as DMF, HMPA, and NMP5 or in THF in the presence of naphthalene as a catalyst.6 A combination of electrochemical reduction and ultrasound is used to produce the Se2- anion in THF, DMF, and acetonitrile.7
Handling, Storage, and Precautions: hygroscopic crystals; rapidly turns red in moist air because of the formation of polyselenides and separation of Se. From water solution, red Se separates rapidly on contact with air. It can be stored under anhydrous and oxygen-free conditions, although usually it is used as prepared without isolation. Use in a fume hood.
Sodium and potassium selenides are good nucleophiles for the synthesis of dialkyl selenides from alkyl halides or sulfates.2b,3,4,7 The alkylating agent is added directly to Na2Se (or K2Se) in solution or suspension (eq 1).7 Aliphatic diacyl selenides are obtained in 58-90% yield from the reaction of acyl chlorides with Na2Se suspended in ethyl ether.8
A general method for the preparation of symmetrical diaryl selenides involves treatment of arenediazonium salts with Na2Se or K2Se,9 or with sodium or potassium polyselenide (Na2Se
Diphenyl selenide is formed from Na2Se and iodobenzene in liquid ammonia under photochemical activation. This selenide is easily reduced to the benzeneselenolate anion (PhSe-) by addition of an excess of Na, and this provides a route to aryl methyl selenides (when Iodomethane is added) and unsymmetrical diaryl selenides (by photostimulated reaction with aryl iodides).2c
Sodium selenide is also used in the synthesis of divinyl selenides. Alkylation with diethyl iodomethylphosphate forms a selenide which gives bis(2-phenylvinyl) selenide by Horner-Wittig reaction with benzaldehyde (eq 3).12 Treatment of N-phenyldichloroimine with Na2Se gives phenyl isoselenocyanate.13
Jacek Mlochowski & Ludwik Syper
Technical University of Wroclaw, Wroctaw, Poland