Labeled tolylium ions from the decay of ring-multitritiated toluene have been allowed to react with propane in the gas phase, at pressures ranging from 20 to 744 Torr, yielding isomeric propyltoluenes as the major addn. products. The relative compn. of the n- vs. iso-propyltoluenes (σp:σs 3.2-4.7) is found to depend appreciably upon the total pressure of the system and the presence of added bases (NH3 or CH3OH). Pressure and base effects on the isomeric distribution of both n- and iso-propyltoluenes are also investigated. The results are consistent with a reaction pattern involving preliminary formation of an electrostatic adduct, wherein fast hydride-ion transfer from a secondary C-H bond of C3H8 to the arylium ion takes place. The same mechanism does not seem operative when the first interaction occurs between the tolylium ions and a primary C-H bond of the substrate. The behavior of isomeric tolylium ions towards propane is discussed and compared with related studies involving unsubstituted phenylium ions. A mechanistic model is proposed for both reactions, which accounts for the apparent discrepancy between the indiscriminate affinity of arylium ions for any kind of substrate and their abnormally high site selectivities.
Competitive Concerted and Stepwise Addition of Free Arylium Ions To Propane In the Gas-phase / Angelini, Giancarlo; C., Sparapani; Speranza, Maurizio. - In: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS II. - ISSN 0300-9580. - STAMPA. - (1988), pp. 1393-1400. [10.1039/p29880001393]
Competitive Concerted and Stepwise Addition of Free Arylium Ions To Propane In the Gas-phase
ANGELINI, Giancarlo;SPERANZA, Maurizio
1988
Abstract
Labeled tolylium ions from the decay of ring-multitritiated toluene have been allowed to react with propane in the gas phase, at pressures ranging from 20 to 744 Torr, yielding isomeric propyltoluenes as the major addn. products. The relative compn. of the n- vs. iso-propyltoluenes (σp:σs 3.2-4.7) is found to depend appreciably upon the total pressure of the system and the presence of added bases (NH3 or CH3OH). Pressure and base effects on the isomeric distribution of both n- and iso-propyltoluenes are also investigated. The results are consistent with a reaction pattern involving preliminary formation of an electrostatic adduct, wherein fast hydride-ion transfer from a secondary C-H bond of C3H8 to the arylium ion takes place. The same mechanism does not seem operative when the first interaction occurs between the tolylium ions and a primary C-H bond of the substrate. The behavior of isomeric tolylium ions towards propane is discussed and compared with related studies involving unsubstituted phenylium ions. A mechanistic model is proposed for both reactions, which accounts for the apparent discrepancy between the indiscriminate affinity of arylium ions for any kind of substrate and their abnormally high site selectivities.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.