The photochemical behavior of three aryl alkyl sulÐdes, thioanisole (TA), benzyl phenyl sulÐde (BPS) and 4-methoxybenzyl phenyl sulÐde (MBPS), sensitized by triplet chloranil (CA), was investigated by nanosecond laser Ñash photolysis and steady-state irradiation in CH and MeCN. The nature of the transients detected 2Cl2 upon 355-nm laser excitation was independent of the molecular structure of the aryl alkyl sulÐdes but strongly a ected by the solvent polarity. In particular, in CH the quenching process of triplet CA by aryl alkyl 2Cl2 sulÐdes was accompanied by H-transfer, with formation of the CAH~ and TA(-H)~/BPS(-H)~/MBPS(-H)~ radicals. In contrast, a charge transfer process between triplet CA and aryl alkyl sulÐdes, with formation of the radical anion CA~~ and radical cations of aryl alkyl sulÐdes, occurred in MeCN. In this solvent, a transient detected at long delay time was tentatively assigned to the anion CAH~ formed by H-transfer between radical ions. In all experiments, transient species were characterized in terms of second-order decay rate constants and quantum yields of formation. Steady-state irradiation of the CA/TA system led to the stable photoadduct C in both and MeCN with quantum yields of 0.033 and 0.27, respectively. In 6H5SCH2OC6Cl4OH CH2Cl2 contrast, aldehydes, thioacetals, and disulÐdes were the main products obtained upon irradiation of the CA/BPS and CA/MBPS systems. The photoaddition products were not observed, probably owing to their low stability. The nature of the photoproducts formed by irradiation of CA/aryl alkyl sulÐdes was independent of solvent properties, even though the reactivity was higher in MeCN than in CH2Cl2 .
Photoinduced hydrogen- and electron-transfer processes between chloranil and aryl alkyl sulfides in organic solvents. Steady-state and time-resolved studies
DEL GIACCO, Tiziana;ELISEI, Fausto;
2000
Abstract
The photochemical behavior of three aryl alkyl sulÐdes, thioanisole (TA), benzyl phenyl sulÐde (BPS) and 4-methoxybenzyl phenyl sulÐde (MBPS), sensitized by triplet chloranil (CA), was investigated by nanosecond laser Ñash photolysis and steady-state irradiation in CH and MeCN. The nature of the transients detected 2Cl2 upon 355-nm laser excitation was independent of the molecular structure of the aryl alkyl sulÐdes but strongly a ected by the solvent polarity. In particular, in CH the quenching process of triplet CA by aryl alkyl 2Cl2 sulÐdes was accompanied by H-transfer, with formation of the CAH~ and TA(-H)~/BPS(-H)~/MBPS(-H)~ radicals. In contrast, a charge transfer process between triplet CA and aryl alkyl sulÐdes, with formation of the radical anion CA~~ and radical cations of aryl alkyl sulÐdes, occurred in MeCN. In this solvent, a transient detected at long delay time was tentatively assigned to the anion CAH~ formed by H-transfer between radical ions. In all experiments, transient species were characterized in terms of second-order decay rate constants and quantum yields of formation. Steady-state irradiation of the CA/TA system led to the stable photoadduct C in both and MeCN with quantum yields of 0.033 and 0.27, respectively. In 6H5SCH2OC6Cl4OH CH2Cl2 contrast, aldehydes, thioacetals, and disulÐdes were the main products obtained upon irradiation of the CA/BPS and CA/MBPS systems. The photoaddition products were not observed, probably owing to their low stability. The nature of the photoproducts formed by irradiation of CA/aryl alkyl sulÐdes was independent of solvent properties, even though the reactivity was higher in MeCN than in CH2Cl2 .I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
