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Title:Aqueous reactions of ozone with primary aromatic amines
Author(s):Chan, Wayne Fai
Doctoral Committee Chair(s):Larson, Richard A.
Department / Program:Civil and Environmental Engineering
Discipline:Environmental Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Sanitary and Municipal
Abstract:Ozone reacts readily with primary aromatic amines (aniline, 3-methylaniline, 3-chloroaniline, 4-bromoaniline, 4-nitroaniline) in dilute aqueous solutions (10$\sp{-5}$-10$\sp{-4}$ M). The major isolated reaction products identified by GC/MS were nitrosobenzenes, nitrobenzenes, azobenzenes, azoxybenzenes, benzidines, aminodiphenylamines, and phenazines. The N-substituted polyaromatic compounds (NPACs), azobenzenes, azoxybenzenes, and benzidines, were the products of interest because of their potential toxicity. When the reactions were conducted under experimental conditions approximating drinking water treatment ((aniline) = 1.00 $\times$ 10$\sp{-5}$ M and (O$\sb3$) = 2.00 $\times$ 10$\sp{-5}$ M, (CO$\sb3\rbrack \sb{\rm T}$ = 1.00 $\times$ 10$\sp{-2}$ M, pH 8.2), the yields of azobenzene and azoxybenzene were 0.78% and 0.15%, respectively. The experimental data showed that the reaction mechanisms for the formation of these NPACs mainly, but not exclusively, involve free radicals initiated by hydroxyl radical. Addition of mannitol, a $\cdot$OH scavenger, in most cases, significantly reduced NPACs formation. The actual reduction in the yield of azobenzene by the addition of mannitol was close to the values predicted by kinetic analysis. Hydrogen ion concentrations (pH 7.25-10.65), the selection of inorganic buffer (phosphate or carbonate), and aniline concentrations (0.10-1.00 $\times$ 10$\sp{-4}$ M) affected the yields of these NPACs. Raising the pH increased the yields of azobenzene and azoxybenzene by increasing $\cdot$OH formation. The reaction mixture with the carbonate buffer showed even a greater increase in these products due to the shift of the oxidation mechanism to the highly selective carbonate radical pathway. Additionally, lowering the relative concentration of aniline to the carbonate buffer increased the yields of azobenzene and azoxybenzene. However, the formation of benzidine was higher at pH 8.25 than at pH 10.65. The presence of dissolved organic and inorganic matter in the reaction systems significantly reduced the yield of azobenzene, azoxybenzene, and benzidine without affecting aniline removal.
When the aqueous ozonolysis of aniline was conducted in the presence of nitrite ion, 2-, 3-, and 4-nitroaniline were formed in addition to those products described above. Experimental data suggest that radical intermediates are involved in the nitration reaction pathways. The hydroxyl radical pathway is initiated by ozone decomposition and is favored at high pH whereas the pernitrous acid pathway predominates at lower pH. Lowering the pH from 10.65 to 7.25 increased the formation of nitroanilines. The higher yields of nitroanilines at lower pH is probably attributed to the more efficient formation of radicals via the pernitrous acid pathway. Carbonate buffer was able to inhibit these free radical nitration reactions.
Phenolic compounds were also susceptible to ozone induced radical nitration whereas methoxybenzene and naphthalene were not. It appears that if the concentration of nitrite ion and aromatic compounds are comparable, aromatic compounds whose reaction rates with ozone are greater than that of ozone with nitrite ion, are susceptible to the nitration reaction.
Issue Date:1991
Rights Information:Copyright 1991 Chan, Wayne Fai
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9210759
OCLC Identifier:(UMI)AAI9210759

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