Photochemistry of 4-chlorophenol on cellulose and silica.
The photochemistry of 4-chlorophenol (4-CP) was studied on silica and cellulose, using time-resolved diffuse reflectance techniques and product degradation analysis. The results have shown that the photochemistry of 4-CP depends on the support, on the concentration, and also on the sample preparation method. Transient absorption and photoproduct results can be understood by assuming the formation of the carbene 4-oxocyclohexa-2,5-dienylidene in both supports. On cellulose, at concentrations lower than 10 micromol g(-1), the carbene leads to the unsubstituted phenoxyl radical, and phenol is the main degradation product. At higher concentrations a new transient resulting from phenoxyl radicals coupling was also observed, and dihydroxybiphenyls are also formed. The reaction of the carbene with ground-state 4-CP was also detected through the formation of 5-chloro-2,4'-dihydroxybiphenyl. 4-Chlorophenoxyl radical and degradations products resulting from its coupling were also detected. Oxygen has little effect on the photochemistry of 4-CP on cellulose. On silica the transient benzoquinone O-oxide was formed in the presence of oxygen. Benzoquinone and hydroquinone are the main degradation products. In well-dried samples the formation of hydroquinone is reduced. At higher concentrations the same products as detected on cellulose were observed. 4-CP undergoes slow photochemical decomposition under solar radiation in both supports. The same main degradation products were observed in these conditions.
Da Silva
José P
JP
Centro de Química-Física Molecular, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. jpsilva@ualg.pt
Vieira Ferreira
Luis F
LF
Da Silva
Abílio M
AM
Oliveira
Anabela S
AS
D000327:Adsorption; D002482:Cellulose / Q000737:chemistry; D002733:Chlorophenols / Q000737:chemistry*; D004785:Environmental Pollutants; D010777:Photochemistry; D012388:Root Canal Irrigants / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry
D002733:Chlorophenols; D004785:Environmental Pollutants; D012388:Root Canal Irrigants; C029107:4-chlorophenol; D012822:Silicon Dioxide; D002482:Cellulose