Benzophenone dimethylaniline photoreduction

The photoreduction of aromatic ketones by tertiary amines is reported [38] to proceed at rates which are substantially faster than those observed for the corresponding photoinduced hydrogen abstraction from, e.g. alcohols. A limit case is given by fluorenone, the photoreduction of which does not occur in alcohol, ether or alkane solution, but readily takes place in the presence of amines, tertiary amines being the most effective [39,40]. Xanthone has also been reported to be easily photoreduced by iV,A-dimethylaniline [41], but not by 2-propanol [42]. However, the oxidation of tertiary amines photosensitized by fluorenone and xanthone is much less efficient than when sensitized by benzophenone, apparently because of lower rates of hydrogen abstraction [43]. Fluorenone/tertiary amine systems have been used successfully to photoinitiate the polymerization of MMA, St, MA and AN [30,38,44] and rather similar results have been obtained in the photoinitiated polymerization of MA by the benzophenone/EtsN system [45]. Thus, the great variety of substrates participating in exciplex formation has been readily extended to polymer-based systems. 

Photoreduction of benzophenones and acetophenones by amines has been studied in detail. A mechanism has been derived for the reaction of benzophenone with N.A -dimethylaniline that involves a triplet exciplex in the formation of the radical ion pair, as indicated in Scheme 49. 

The data show that the dynamics of this reaction involve hydrogen bonding effects . Fs-ps laser photolysis has been deployed to follow the details of the photoreduction of excited benzophenone by N,N-dimethylaniline in acetonitrile solution . Laser flash photolysis also has been used to examine the chromophore assisted peroxy-bond breakage in the case of a benzophenone perester . ... 

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