A solution of CrO3 • 2 Py (Sarett Reagent) in methylene chloride is called the "Collins Reagent". One advantage over the Sarett Reagent is that the addition of one equivalent chromium trioxide to a stirred solution of two equivalents of pyridine in methylene chloride allows the convenient and safe preparation of the oxidant. In addition, the use of methylene chloride as solvent and stoichiometric amounts of pyridine makes the Collins Reagent less basic than the Sarett Reagent. Thus, most acid and base-sensitive substrates can be oxidized with Collins Reagent, unlike both the Sarett and Jones Reagent.
As the Collins Reagent does not contain water (compared to the Jones Reagent) and is not as hygroscopic as is the Sarett Reagent, the oxidant is especially useful for the oxidation of primary alcohols to aldehydes where traces of water can lead to overoxidation.
A full review of chromium-based reagents can be found in the book written by Tojo and Fernández (Oxidation of Alcohols to Aldehydes and Ketones, Springer Berlin, 2006, 1-97.).
Attention: Chromium (VI) compounds are toxic and must be handled with care.