Thermolysis of 2,4,6-trichlorophenol chemisorbed on aluminium oxides as example of fly ash mediated surface catalysis reaction in PCDD/PCDF formation.
The influence of aluminium cation as a strong electrophilic centre on the thermolysis of chlorophenols chemisorbed on Al(OH)3 surface was investigated. If thermolysis is carried out at 300 degrees C the spontaneous rupture of the bond between aluminium and oxygen of phenol takes place in the temperature range of 260-280 degrees C. The thermolysis of chlorophenoxy aluminium compounds occurs through homolytic and heterolytic bond cleavage. In the case of heterolytic cleavage the leaving chlorophenoxy anion causes a simultaneous formation of the aluminium cation, which is the driving force for the rearrangement of the unstable intermediate. By homolytic cleavage of the Al-O bond the chlorophenoxy radical is formed. The isolation of reaction products of the thermolysis of the system AI(OH)3/2,4,6-trichlorophenol gave five isomers of dimeric compounds of resonance stabilised 2,4,6-trichlorophenoxy radical. The compounds are stable in nonaqueous, aprotic solution, but they are very sensitive to acid catalysis. They quickly transform into aromatic hydroxydiphenyl ethers. The process of dechlorination and aromatisation of cyclohexadienone dimers gives PCDD/PCDF.
Voncina
Ernest
E
Public Health Institute, Maribor, Slovenia. ernest.voncina@zzv.mb.si
Solmajer
Tomaz
T
D000327:Adsorption; D000535:Aluminum / Q000737:chemistry; D001572:Benzofurans / Q000032:analysis; D002384:Catalysis; D002733:Chlorophenols / Q000032:analysis / Q000737:chemistry*; D000072338:Dibenzofurans, Polychlorinated; D017745:Incineration; D013058:Mass Spectrometry; D009153:Mutagens / Q000032:analysis / Q000737:chemistry*; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000032:analysis; D012037:Refuse Disposal; D012989:Soil Pollutants / Q000032:analysis; D013696:Temperature
D001572:Benzofurans; D002733:Chlorophenols; D000072338:Dibenzofurans, Polychlorinated; D009153:Mutagens; D000072317:Polychlorinated Dibenzodioxins; D012989:Soil Pollutants; D000535:Aluminum; C024564:2,4,6-trichlorophenol