Pyridinium dichromate

Cornforth reagent

Names
Other names Pyridinium dichromate
Identifiers
CAS Number	20039-37-6 Y
3D model (Jmol)	Interactive image
ChemSpider	2006289 N
ECHA InfoCard	100.039.511
PubChem CID	2724130
InChI InChI=1S/2C5H5N.2Cr.7O/c2*1-2-4-6-5-3-1;;;;;;;;;/h2*1-5H;;;;;;;;;/q;;;;;;;;;2*-1/p+2 N Key: LMYWWPCAXXPJFF-UHFFFAOYSA-P N InChI=1/2C5H5N.2Cr.7O/c2*1-2-4-6-5-3-1;;;;;;;;;/h2*1-5H;;;;;;;;;/q;;;;;;;;;2*-1/p+2/r2C5H5N.Cr2O7/c2*1-2-4-6-5-3-1;3-1(4,5)9-2(6,7)8/h2*1-5H;/q;;-2/p+2 Key: LMYWWPCAXXPJFF-OXLJHMOQAP
SMILES [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O.c1cc[nH+]cc1.[nH+]1ccccc1
Properties
Chemical formula	C10H12N2Cr2O7
Molar mass	376.2
Appearance	orange to brown solid
Boiling point	145 to 147 °C (293 to 297 °F; 418 to 420 K)
Solubility in water	soluble in water
Hazards
EU classification (DSD)	Toxic (T) Oxidizing (O)
R-phrases	R8 R43 R49 R50
S-phrases	(S1/2) S4 S17 S20 S24 S37 S45 S53 S57
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

The Cornforth reagent or pyridinium dichromate (PDC) is a pyridinium salt of dichromate with the chemical formula [C₅H₅NH]₂[Cr₂O₇]. This compound is named after the Australian-British chemist Sir John Warcup Cornforth (b. 1917) who introduced it in 1962. The Cornforth reagent is a strong oxidizing agent which can convert primary and secondary alcohols to aldehydes and ketones respectively. In its chemical structure and functions it is closely related to other compounds made from hexavalent chromium oxide, such as pyridinium chlorochromate and Collins reagent. Because of their toxicity, these reagents are rarely used nowadays.

The Cornforth reagent is prepared by slow addition of a concentrated aqueous solution of chromium trioxide to pyridine. The reaction may cause explosion, which is avoided by thoroughly dissolving the trioxide in water and cooling the solution by ice. The product is filtered, washed with acetone and dried, yielding an orange powder. The powder is stable in air, not particularly hygroscopic and has an almost neutral pH that facilitates its handling; it is only slightly acidic owing to the presence of pyridinium cations. The Cornforth reagent is readily soluble in water, dimethylformamide and dimethyl sulfoxide (DMSO). It is poorly soluble in acetone and chlorinated organic solvents, such as dichloromethane, and forms suspensions.

The Cornforth reagent is a strong oxidizing agent which can convert primary alcohols to aldehydes and secondary alcohols to ketones, both as a solution or suspension. This application was first mentioned in 1969, but fully developed only in 1979 by Corey and Schmidt. They mentioned that reaction of saturated primary alcohols with PDC, using dimethylformamide as solvent, results in oxidation to carboxylic acids rather than aldehydes. However, no oxidation to carboxylic acids occurs on allylic and benzylic primary alcohols.