Chlorine dioxide reaction with phenols

In some examples of reactions with phenolic compounds, it seems that acidic solutions of chlorite give about the same products as chlorine dioxide (41), whereas in other instamces there is quite a difference (105, 149). This brings up a most serious question concerning the species responsible for the various steps in what must certainly be multistep reactions. 

Toxic or malodorous pollutants can be removed from industrial gas streams by reaction with hydrogen peroxide (174,175). Many Hquid-phase methods have been patented for the removal of NO gases (138,142,174,176—178), sulfur dioxide, reduced sulfur compounds, amines (154,171,172), and phenols (169). Other effluent treatments include the reduction of biological oxygen demand (BOD) and COD, color, odor (142,179,180), and chlorine concentration. 

Oxidation of phenols with chlorine dioxide or chlorine produces chlorinated aromatic intermediates before ring rupture. Oxidation of phenols with either chlorine dioxide or ozone produces oxidized aromatic compounds as intermediates which undergo ring rupture upon treatment with more oxidant and/or longer reaction times. In many cases, the same nonchlorinated, ringruptured aliphatic products are produced using ozone or chlorine dioxide. 

Aside from oxygen and the activated oxygen species,there are several other oxidants that cause abiotic oxidation reactions involving environmental contaminants. In engineered systems, these include chlorine (49), chlorine dioxide (50-52), permanganate (53, 54) and ferrate (55, 56). At highly contaminated sites, anthropogenic oxidants such as chromate, arsenate, and selenate may react with co-contaminants such as phenols (57, 58). 

Thielemann [105] has used thin layer chromatography to study the effect of chlorine dioxide on 1- and 2-naphthols in potable water. The coloured products obtained are thought to be condensation products of chloroderivatives of 1,2- or 2,6-naphthaquinone. Thielemann applied paper chromatography to a study of the reaction products of polyhydric phenols with chlorine dioxide. 

In contrast to aliphatic alcohols, which are mostly less acidic than phenol, phenol forms salts with aqueous alkali hydroxide solutions. At room temperature, phenol can be liberated from the salts even with carbon dioxide. At temperatures near the boiling point of phenol, it can displace carboxylic acids, e.g. acetic acid, from their salts, and then phenolates are formed. The contribution of ortho- and -quinonoid resonance structures allows electrophilic substitution reactions such as chlorination, sulphonation, nitration, nitrosation and mercuration. The introduction of two or three nitro groups into the benzene ring can only be achieved indirectly because of the sensitivity of phenol towards oxidation. Nitrosation in the para position can be carried out even at ice bath temperature. Phenol readily reacts with carbonyl compounds in the presence of acid or basic catalysts. Formaldehyde reacts with phenol to yield hydroxybenzyl alcohols, and synthetic resins on further reaction. Reaction of acetone with phenol yields bisphenol A [2,2-bis(4-hydroxyphenyl)propane]. 

In other work related to bleaching chemistry, the reactions of chlorine dioxide with monomeric [44] and dimeric [45] lignin model compounds have been studied computationally. These studies closely parallel experimental work in which oxidation mechanisms were proposed [46-51]. In accord with the experimental work, which reports higher reactivity of phenolic compounds, the heats of reaction for these compounds are lower than those for etherified models. The experimentally based mechanisms were generally found to be energetically feasible, but in some cases the electronic results were not consistent with the proposed mechanisms. 

Ni, Y, X. Shen, and A. R. P. van Heiningen. 1994. Studies on the reactions of phenolic and non-phenolic lignin model compounds with chlorine dioxide. J. Wood Sci. Technol. 14 243-262. 

FIGURE 11.19 Reaction mechanism for oxidation of a phenolic lignin nnit with chlorine dioxide. 

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