[39078-30-3] · C6H5Cl2PSe · Phenyl(seleno)phosphonic Dichloride · (MW 257.94)
Physical Data: bp 60 °C/0.01 mmHg; suffers progressive decomposition into PhPCl2 and Se on being heated.
Solubility: sol most inert solvents; most useful are xylene, toluene, benzene, dichloromethane.
Preparative Methods: PhPCl2 is treated at ambient temperature with ca. 6 mol % Aluminum Chloride under dry N2 followed by Selenium powder. The resulting PhP(Se)Cl2 is distilled in a good vacuum.2 More convenient is to heat PhPCl2 with a 20 mol % excess of powdered black Se at 170-175 °C under dry N2 for 40 min.1 The PhP(Se)Cl2, which is formed quantitatively, is cooled and dissolved in dry xylene. The mixture is filtered through a glass frit to remove the excess Se and sufficient additional xylene is added to give a 2 M solution. Other inert solvents may be used in place of xylene.
Handling, Storage, and Precautions: PhP(Se)Cl2, alone or in solution, is sensitive to moisture. Solutions of PhP(Se)Cl2 should be stored in dark bottles which are tightly closed by crown or screw caps fitted with a septum. Required volumes are transferred by means of graduated syringes. For best results, PhP(Se)Cl2 and solutions thereof should be used within 2-3 days after preparation. Reactions involving prolonged times should be carried out in a dry inert atmosphere.
Various types of carbonyl compounds in which the carbonyl group is highly polarized undergo O-Se exchange reactions with PhP(Se)Cl2. The carbonyl substrate is allowed to react with an aliquot of a 2 M solution of PhP(Se)Cl2 in xylene, either with or without addition of more xylene or a different inert solvent. Tertiary amides of aliphatic1, aromatic1, and electron-rich heterocyclic carboxylic acids3 are converted into the corresponding selenocarboxamides (eqs 1-4), and N-substituted lactams yield the corresponding N-substituted selenolactams (eq 5).1
A recommended workup procedure for small-scale (<25 mmol) reactions is to add chromatographic alumina (activity I-II) to the reaction solution, transfer the resulting slurry to a column of alumina (activity II-III), and elute. Unreacted PhP(Se)Cl2 and its reaction product PhP(O)Cl2 are retained on the basic column.
Indolizine-1- and 3-carbaldehydes are converted into the corresponding indolizineselenocarbaldehydes at room temperature (eq 6).1 In one case a 1,2-dithiol-3-one was converted into the corresponding 1,2-dithiol-3-selone (eq 7).1
1-Oxa-6,6al4-dithiapentalenes and 6-oxa-6al4-thia-1,2-diazapentalenes, which are masked carbonyl compounds, react at room temperature with PhP(Se)Cl2 in the presence of Triethylamine to give the corresponding Se-containing heterocycles (eqs 8 and 9).1 The Et3N suppresses acid-catalyzed side-reactions of the substrates.
David H. Reid
University of the Witwatersrand, Johannesburg, South Africa