Oxohalides
Key points: Nitrosyl and nitryl halides are useful halogenating agents; phosphoryl halides are important industrially in the synthesis of organo phosphorus derivatives.
Nitrogen forms all the nitrosyl halides, NOX, and the nitryl halides, NO2X. The nitrosyl halides and NO2F are prepared by direct interaction of the halogen with NO or NO2, respectively:
They are all reactive gases and the oxofluorides and oxochlorides are useful fluorinating and chlorinating agents. Phosphorus readily forms the phosphoryl halides POCl3 and POBr3 by the reaction of the trihalides PX3 with O2 at room temperature. The fluorine and iodine analogues are prepared by the reaction of POCl3 with a metal fluoride or iodide:
All the molecules are tetrahedral and contain a PO bond. POF3 is gaseous, POCl3 is a colourless liquid, POBr3 is a brown solid, and POI3 is a violet solid. They are all readily hydrolysed, fume in air, and form adducts with Lewis acids. They provide a route to the synthesis of organophosphorus compounds, which are manufactured on a large scale for use as plasticizers, oil ad ditives, pesticides, and surfactants. For example, reaction with alcohols and phenols gives (RO)3 PO and Grignard reagents (Section 12.13) yield Rn POCl3-n:
