Chloramines reactions with phenols

Bromide ion reacts with a dilute solution of sodium / -1 o 1 uc nc sulfo nc h 1 o ra -mide (chloramine-T) and is oxidized to bromine which readily reacts with phenol red at pH 4.5 to 4.7. The bromination reaction with phenol red produces a color that ranges from red to violet, depending on the concentration of bromide ion. An acetate buffer solution is used to maintain the pH between 4.5 and 4.7. The presence of high concentration of chloride ions in the sample may seriously interfere in the test. In such cases, the addition of chloride to the pH buffer solution or the dilution of the sample may reduce such interference effect. Remove free chlorine in the sample by adding Na C solution. In addition, the presence of oxidizing and reducing agents in the sample may interfere in the test. 

Chloramine reacts with phenolate in the presence of sodium nitroprusside as catalyst and in several reaction steps forms the dye indophenol blue, which is yellow in the non-dissociated and blue in the dissociated state. This reaction can be represented by the following empirical formula ... 

Kanno et al. (1982) studied the aqueous reaction of phenol and other substituted aromatic hydrocarbons (aniline, toluidine, 1-naphthylamine, cresol, pyrocatechol, resorcinol, hydroquinone, and 1-naphthol) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride (Kanno et al., 1982). The amount of cyanogen chloride formed increased at lower pHs. At pH 6, the greatest amount of cyanogen chloride was formed when the reaction mixture contained ammonium ion and hypochlorous acid at a ratio of 2 3 (Kanno et al., 1982). 

As shown by the downward swing of the curve, the reactions that occur between point B and the breakpoint are all breakdown reactions. Snbstances that have been formed before reaching point B are destroyed in this range of dosage of chlorine. In other words, the chloro-organics that have been formed, the organic chloramines that have been formed, the ammonia chloramines that have formed, and all other snbstances that have been formed from reactions with compounds such as phenols and fnlvic acids are all broken down within this range. These breakdown reactions have been collectively called breakpoint reactions. 

The hydroxyl group of a phenol can be replaced with iodine. The reaction of phenol with a boronic ester and a palladium catalyst, followed by reaction with Nal and chloramine-T converts phenol to iodobenzene. " ... 

Chloramine, which is formed as the first step of the reaction, reacts with phenol to yield quinonechloramine. This reacts with another phenol molecule to give indophenol. The blue colour is due to the indophenol anion, formed in alkaline medium. The intensity of the blue colour is greatly increased by adding a little acetone (-0.2 ml of acetone per 25 ml of solution). The molar absorptivity at A.max = 625 nm is 4.5T0 (a = 0.32). 

Fluorine ions are evidenced by the destruction of the zirconium-alizarin complex (see Chap. 30). Revealing bromide ions in the presence of chloride ions is trickier. It is carried out with chloramine T and phenol red. The reaction is performed at pH = 5.2. The bromide ions are oxidized by chloramine T into bromine, which reacts by substitution with phenol red. A purple color appears. Normally, a pure solution of phenol red is yellow. 

When all the sodium has dissolved, the phenoxide-phenol mixture is heated to 150°. With the oil bath or heating mantle still surrounding the flask, and with a protective shield between the reaction vessel and the operator (Note 3), the cold ethereal chloramine solution is added with rapid stirring in a thin stream from the dropping funnel at such a rate that the temperature of the reaction mixture does not drop below 125°. Best results are obtained if the thin stream of ether solution can be added directly to the molten mass without first touching the walls of the flask. 

Chlorination and chloramination of a widely used antibacterial additive, triclo-san, which is used in many household personal care products, results in the formation of chloroform, 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol, 2, 4-dichlorophenol, and 2,4,6-trichlorophenol [119]. The reaction of triclosan with monochloramine is slow, however, compared to chlorine [120]. The chlorophenox-yphenols are formed via bimolecular electrophilic substitution of triclosan. 

Ring expansion of phenols. Theilacker heated the sodium salt of 2,6-dimethyl-phenol with chloramine in a fusion with an excess of the dimethylphenol and obtained in about 50% yield a crystalline product originally assumed to be the O-arylhydroxylamine, ArONH, but recognized by Paquette as a l,3-dihydro-2H-azepin-2-one (see 3, below). The reaction is generally applicable to 2,6-disub-stituted phenols. A procedure by Paquette for the conversion of 2,4,6-trimethyl-phenol (1) into l,3-dihydro-3,5,7-trimethyl-2-H-azepine-2-one (3) is as follows. 

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