[2370-18-5] · C29H41O2 · Galvinoxyl · (MW 421.70)
Physical Data: mp 158-159 °C.
Solubility: sol organic solvents adequate for applications cited.
Form Supplied in: purple crystalline needles.
Handling, Storage, and Precautions: toxicological properties not investigated thoroughly. May be harmful by inhalation, ingestion, or skin absorption. Keep in tightly closed bottles away from oxygen in a refrigerator. Use in a fume hood.
Galvinoxyl is a stable phenoxy radical5 which reacts with other radicals at a rate constant near the diffusion-controlled limit (eq 1). Scavenging of radicals leads to decolorization and colorimetric determination is a way of estimating the efficiency of radical formation. Galvinoxyl has been widely used as a probe in the study of organometallic6 and radical2 reaction mechanisms. A compilation of earlier work can be found in Kochi's monographs.2,6
In a classical example, the inhibition of the addition of alkyl boranes to a,b-unsaturated carbonyl compounds was interpreted to mean a radical pathway for this reaction.7 Other reactions that have been investigated recently, include addition of trialkylaluminum to enones,8 RuII-catalyzed Kharasch-type additions of carbon tetrachloride to alkenes,9 2,3-dichloropropene-mediated homocoupling of aryl Grignards,10 SRN1 reactions,11 carbonyl additions of acyltin reagents, and radical polymerization of styrene.
A recent example of the use of galvinoxyl to affect the course of a reaction is in the chemoselective reduction of the carbonyl group of a-bromo ketones with dibutyltin dihydride.3 Without the the radical inhibitor the reduction of the a-bromo group took place.
A more general use of free radical inhibitors in organic synthesis is illustrated by the use of galvinoxyl in the synthesis of (R)-(+)-cyclohex-3-enecarboxylic acid via a Diels-Alder reaction. The major complication arising from the Ethylaluminum Dichloride-mediated polymerizations (presumably through a radical mechanism) is suppressed by galvinoxyl (eq 2).4
T. V. (Babu) RajanBabu
The Ohio State University, Columbus, OH, USA