ELSEVIER Ultrasonics Sonochemistry 5 (1998) 27-31 SONOCHEMISTRY Sonochemical and thermal redox reactions of triphenylmethane and triphenylmethyl carbinol in nitrobenzene M. Vinatoru a.,, E. Bartha a, F. Badea b, J.L. Luche c a "C.D. Nenitzescu" Institute of Organic Chemistry, P.O. Box 15-258, 71141 Bucharest, Romania b University "Politehnica", Organic' Chemistry Department, Spl. lndependentei 313, 77326 Bucharest, Romania c Laboratoire de Chimie Molbculaire et Environnement, Universitb de Savoie-ESIGEC, 73376 Le Bourget du Lac, France Received2I October 1996 Abstract The reaction of triphenylmethane and triphenylcarbinol with nitrobenzene under thermal or ultrasonic activation was studied. It was shown beyond doubt that the thermal reaction of the aforementioned systems at 210°C occurs through electron transfer. The sonochemical reactions occur at 40°C, although slowly, while heating at the same temperature leaves the system unchanged. Electron transfers are also involved but an unexpected reductive process was evident. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Sonochemistry; Electron transfer; Triphenylmethane; Triphenylmethyl carbinol; Nitrobenzene 1. Introduction Most of the chemical effects of ultrasound originate in cavitation, i.e. the growth, then collapse of bubbles, accompanied by thermal and/or electrical effects [1-3]. Several years ago it was postulated that, under such conditions, reactions proceeding via electron transfers (ET) should be preferentially activated [4]. Thus, the interest of sonochemists has moved towards ET chemis- try, a domain of high interest for theoretical reasons and continuously developing synthetic uses [5-9]. Despite much effort, there are not yet many examples of sonochemical reactions where ET processes were unambiguously identified, but even in these cases [10], it is difficult to ascertain a pertinent explanation regard- ing the origin of such a preference. Previous work from this laboratory has shown that triphenylmethyl chloride (TMC1) 2 is oxidised by nitro- benzene (NB) to a complex mixture, in which products 3, 4, 5, 7 and 9b (see below for the numbering) predominate in the thermal process, and 3 and 4 in the sonochemical reaction [11,12]. The same reactions effected with triphenylmethyl bromide (TMBr) 1, triphe- nylmethyl carbinol (TMOH) 3 and triphenylmethane (TMH) 4, were studied [ 13]. Compounds !-4 undergo a thermal ET reaction in NB at 210°C, and the order * Corresponding author. 1350-4177/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII: S1350-4177(98)00004-2 of reactivity based on the conversion of starting material is: Ph3C - Br > Ph3C- CI>> Ph3C - OH > Ph3C- H 1 2 3 4 Ultrasonic activation of the same systems preserve the reactivity order of the halides but reverses that of the last two compounds. Ph3C-Br> Ph3C-CI>> Ph3C-H> Ph3C-OH 1 2 4 3 While the ability for ET of the first two compounds is easily understood in both processes, the relative reactivi- ties of the last two products appears less easy to explain. For this reason, further experimentation was undertaken on the thermal and sonochemical reactions of 3 and 4 in NB. 2. Experimental The experiments were carried out in a dry, oxygen- free argon atmosphere. Commercial samples of 3 and 4 (from Aldrich) were recrystallised from ethanol before use. Nitrobenzene (from Chimopar-Romania) was puri- fied by water-steam distillation, drying (CaCI2) and