AsCl5

AsCl5, or arsenic pentachloride, is a covalent compound consisting of arsenic and chlorine with the formula AsCl5. Arsenic is in the +5 oxidation state. The compound is moisture sensitive and hydrolyzes readily in water or moist air.

Preparation and occurrence

AsCl5 can be prepared by chlorinating arsenic trichloride: AsCl3 + Cl2 → AsCl5. It can also be generated in situ by chlorinating AsCl3 under controlled conditions. It is not a widely used commercial reagent and is typically produced in the laboratory for chlorination chemistry or as a Lewis acid source.

Structure and bonding

In the gas phase, AsCl5 is described as a trigonal bipyramidal molecule, analogous to PF5. In the condensed phase, it tends to form polymeric networks or stabilize as adducts with halide donors, providing species such as [AsCl6]− when treated with chloride sources. AsCl5 behaves as a Lewis acid, capable of accepting halide or other donors to form adducts.

Reactions

AsCl5 is highly reactive with nucleophiles and moisture. It hydrolyzes to arsenic acid and hydrochloric acid according to the reaction: AsCl5 + 4 H2O → H3AsO4 + 5 HCl. It also reacts with bases and other nucleophiles to form chloride-containing adducts and various coordination compounds.

Safety and handling

AsCl5 is highly toxic and corrosive. It fumes in air and reacts exothermically with water, releasing HCl and arsenic-containing oxides or acids. It must be handled under strictly controlled, moisture-free conditions, using appropriate protective equipment and in a fume hood.