The oxidation of propenoidic phenols by molecular oxygen, catalysed by [N,N'-bis(salicylidene)ethane-1,2-diaminato]cobalt(II) [Co(salen)], was studied in different solvents and for variously substituted phenols to find processes alternative to those reported for the removal of polyphenols from waste waters in the paper industry. The reaction of methyl E-4-hydroxy-3-methoxycinnamate (E-methyl ferulate) selectively gave the corresponding 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde; yields are highest in chloroform, good in methanol and very low in pyridine. Conversion was high with E-methyl ferulate, lower with methyl E-4-hydroxycinnamate, while the other phenols, methyl E-3-hydroxy-4-methoxycinnamate (E-methyl isoferulate) and methyl E-3-chloro-4-hydroxycinnamate, did not react. An EPR investigation of the reaction mixtures, performed on samples taken at different reaction times, demonstrated that the most probable mechanism involves reactions (i)-(iii). The (i) [Co-II(salen)] + ROH + O-2 reversible arrow [Co-III(salen)(ROH)(O-2)](-) (ii) [Co-III(salen)(ROH)O-2)](-) + ROH reversible arrow [Co-III(salen)(ROH)(RO.)] + HO2- (iii) [Co-III(salen)(ROH)(RO.)] + HO2- reversible arrow [Co-III(salen)(RO-)(RO.)] + H2O2 superoxocobalt radical, [Co-III(salen)(ROH)(O-2,)](-), and the phenoxy cobalt radical, [Co-III(salen)(RO-)(RO .)], are the EPR-active species; RO . is suggested easily to dissociate from [Co-III(salen)(RO-)(RO.)] and, reacting with O, at the beta-carbon of the allyl substituent, probably gives a dioxethane. This decomposes to aldehyde and acid. The phenol electron-donor properties promote the formation of the superoxocobalt derivative and consequently favour the formation of the phenoxy cobalt radical; a too high stability of this radical does not favour its evolution into oxidation products

Bolzacchini, E., Canevali, C., Morazzoni, F., Orlandi, M., Rindone, B., Scotti, R. (1997). Spectromagnetic investigation of the active species in the oxidation of propenoidic phenols catalysed by [N,N′-bis(salicylidene)-ethane-1,2-diaminato]cobalt(II). JOURNAL OF THE CHEMICAL SOCIETY DALTON TRANSACTIONS, 1997-12-21(24), 4695-4699 [10.1039/a705188c].

Spectromagnetic investigation of the active species in the oxidation of propenoidic phenols catalysed by [N,N′-bis(salicylidene)-ethane-1,2-diaminato]cobalt(II)

BOLZACCHINI, EZIO;CANEVALI, CARMEN;MORAZZONI, FRANCA;ORLANDI, MARCO EMILIO;RINDONE, BRUNO;SCOTTI, ROBERTO
1997

Abstract

The oxidation of propenoidic phenols by molecular oxygen, catalysed by [N,N'-bis(salicylidene)ethane-1,2-diaminato]cobalt(II) [Co(salen)], was studied in different solvents and for variously substituted phenols to find processes alternative to those reported for the removal of polyphenols from waste waters in the paper industry. The reaction of methyl E-4-hydroxy-3-methoxycinnamate (E-methyl ferulate) selectively gave the corresponding 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde; yields are highest in chloroform, good in methanol and very low in pyridine. Conversion was high with E-methyl ferulate, lower with methyl E-4-hydroxycinnamate, while the other phenols, methyl E-3-hydroxy-4-methoxycinnamate (E-methyl isoferulate) and methyl E-3-chloro-4-hydroxycinnamate, did not react. An EPR investigation of the reaction mixtures, performed on samples taken at different reaction times, demonstrated that the most probable mechanism involves reactions (i)-(iii). The (i) [Co-II(salen)] + ROH + O-2 reversible arrow [Co-III(salen)(ROH)(O-2)](-) (ii) [Co-III(salen)(ROH)O-2)](-) + ROH reversible arrow [Co-III(salen)(ROH)(RO.)] + HO2- (iii) [Co-III(salen)(ROH)(RO.)] + HO2- reversible arrow [Co-III(salen)(RO-)(RO.)] + H2O2 superoxocobalt radical, [Co-III(salen)(ROH)(O-2,)](-), and the phenoxy cobalt radical, [Co-III(salen)(RO-)(RO .)], are the EPR-active species; RO . is suggested easily to dissociate from [Co-III(salen)(RO-)(RO.)] and, reacting with O, at the beta-carbon of the allyl substituent, probably gives a dioxethane. This decomposes to aldehyde and acid. The phenol electron-donor properties promote the formation of the superoxocobalt derivative and consequently favour the formation of the phenoxy cobalt radical; a too high stability of this radical does not favour its evolution into oxidation products
Articolo in rivista - Articolo scientifico
EPR, phenols, radicals, catalysts
English
1997
1997-12-21
24
4695
4699
none
Bolzacchini, E., Canevali, C., Morazzoni, F., Orlandi, M., Rindone, B., Scotti, R. (1997). Spectromagnetic investigation of the active species in the oxidation of propenoidic phenols catalysed by [N,N′-bis(salicylidene)-ethane-1,2-diaminato]cobalt(II). JOURNAL OF THE CHEMICAL SOCIETY DALTON TRANSACTIONS, 1997-12-21(24), 4695-4699 [10.1039/a705188c].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/8091
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