Following a suggestion by the late Lennart Eberson, we have employed the ICl-HFP (HFP being hexafluoropropan-2-ol) system in iodination reactions, and found unambiguous evidence for the occurrence of an ET-mechanism of halogenation. The evidence is based on the use of 'intelligent' substrates, which make it possible to fix the boundaries between the occurrence of an ET-mechanism and of a conventional polar mechanism. In an 'intelligent' substrate, in fact, the nature of the product(s) changes significantly depending on the operating mechanism. The ICl-HFP combination is instrumental to the onset of a one-electron oxidation with electron-rich substrates, followed by halogenation. The most prominent example is that of the electron-rich substrate durene (1,2,4,5-tetramethylbenzene, DUR), when compared to mesitylene (1,3,5-trimethylbenzene, MES): with a 'conventional' iodination system (i.e., I-2/ Ag+) and in common solvents, where the polar mechanism holds, durene is less reactive (k(MES)/k(DUR) = 46 +/- 3), but becomes more reactive (k(MES)/k(DUR) = 0.23) in HFP with ICI, where the ET-mechanism takes over. Other substrates also support the onset of ET-pathways in HFP. Finally, a preliminary survey of a biohalogenation reaction induced by laccase indicates the modest occurrence of a polar process of iodination with a few substrates.
Aromatic iodination: a new investigation on the nature of the mechanism / M., Fabbrini; Galli, Carlo; Gentili, Patrizia; D., Macchitella; H., Petride. - In: JOURNAL OF THE CHEMICAL SOCIETY. PERKIN TRANSACTIONS 2. - ISSN 1472-779X. - 9:(2001), pp. 1516-1521. [10.1039/b103758g]
Aromatic iodination: a new investigation on the nature of the mechanism
GALLI, Carlo;GENTILI, Patrizia;
2001
Abstract
Following a suggestion by the late Lennart Eberson, we have employed the ICl-HFP (HFP being hexafluoropropan-2-ol) system in iodination reactions, and found unambiguous evidence for the occurrence of an ET-mechanism of halogenation. The evidence is based on the use of 'intelligent' substrates, which make it possible to fix the boundaries between the occurrence of an ET-mechanism and of a conventional polar mechanism. In an 'intelligent' substrate, in fact, the nature of the product(s) changes significantly depending on the operating mechanism. The ICl-HFP combination is instrumental to the onset of a one-electron oxidation with electron-rich substrates, followed by halogenation. The most prominent example is that of the electron-rich substrate durene (1,2,4,5-tetramethylbenzene, DUR), when compared to mesitylene (1,3,5-trimethylbenzene, MES): with a 'conventional' iodination system (i.e., I-2/ Ag+) and in common solvents, where the polar mechanism holds, durene is less reactive (k(MES)/k(DUR) = 46 +/- 3), but becomes more reactive (k(MES)/k(DUR) = 0.23) in HFP with ICI, where the ET-mechanism takes over. Other substrates also support the onset of ET-pathways in HFP. Finally, a preliminary survey of a biohalogenation reaction induced by laccase indicates the modest occurrence of a polar process of iodination with a few substrates.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.