Collins reagent

Collins reagent is the complex of chromium(VI) oxide with pyridine in dichloromethane. It is used to selectively oxidize primary alcohols to the aldehyde, and will tolerate many other functional groups within the molecule. It can be used as an alternative to the Jones reagent and pyridinium chlorochromate when oxidising secondary alcohols to ketones. Moreover, the Collins reagent is especially useful for oxidations of acid sensitive compounds.

This complex is both difficult and dangerous to prepare, as it is very hygroscopic and can inflame during preparation. It is typically used in a sixfold excess in order to complete the reaction.