Reactivity of sulfur centered nucleophiles in photoinduced reactions with 1-bromonaphthalene

JUAN E. ARGÜELLO; LUCIANA C. SCHMIDT; ALICIA B. PEÑÉÑORY

Arkivoc

ARKAT USA, Inc

Año: 2003 p. 411 - 419

1424-6376

The reactivity of S2- (1), -SCN (2) and -SCNH(NH2) (3) in photoinduced substitution reactions with 1-bromonaphthalene (5) in DMSO was studied. The photostimulated reaction of ion 1 with 5 renders after quenching with MeI 1-(methylthio)naphthalene (16%), bis (1-naphthyl) sulfide (17.5%) and naphthalene (42%). The lack of reaction in the dark and the inhibition of the photoinduced one by the presence of di-tert-butylnitroxide (DTBN) and p-dinitrobenzene (p-DNB) are evidence of a radical chain mechanism for these substitution reactions. On the other hand, ion 2 was unreactive towards 5, both as an electron donor under photostimulation and as a nucleophile. Finally the thiourea anion (3) affords after a photoinduced reaction with 5 and quenching with MeI, 1-methylthionaphthalene (50%), bis (1-naphthyl) sulfide (22%) and naphthalene (9%). This reaction does not occur in the dark and is inhibited in the presence of DTBN. By using hydrogen abstraction from DMSO as competitive reaction, the absolute rate constants for the addition of ions 1, 3 and benzene thiolate ions (4) to 1-naphthyl radicals have been determined to be 0.5 x 109 M-1s-1, 1.0 x 109 M-1s-1 and 5.1 x 109 M-1s-1 respectively.