Iodine with phenols

Irreversible reaction of [18] iodine with acetylsalicylic acid, aethaverine, amidopyrine, ascorbic acid, benzo-caine, quinine, dihydrocodeine, fluorescein, glycine, hydrocortisone acetate, isoni-azid, metamizole, papaverine, paracetamol, phenacetin, phenol-phthalein, piperazine, resorcinol, salicylic acid, salicylamide, sulfaguanidine, thymol, triethanolamine, tris buffer detection by reaction chromatography... 

Iodine water is added to an acetic acid sodium acetate buffered sample to reoxidise to iodate any iodine-containing substances produced by reduction of iodate by naturally occurring reducing substances present in the sample. Total iodate (i.e., iodate present in the original sample as iodate plus additional iodate produced by iodine water treatment) is then reacted with phenol solution at... 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

Procedure Weigh accurately 0.5 g of phenol and dissolve in sufficient water to produce 500 ml in a volumetric flask. Mix 25.0 ml of this solution with 25.0 ml of 0.1 N potassium bromate in a 250 ml iodine flask and add to it 1 g of powdered KI and 10.0 ml of dilute hydrochloric acid. Moisten the glass stopper with a few drops of KI solution and place it in position. Set it aside in a dark place for 20 minutes while shaking the contents frequently in between. Add to it 10 ml of KI solution, shake the contents thoroughly and allow it to stand in the dark for a further duration of 5 minutes. Wash the stopper and neck of the flask carefully with DW, add 10 ml chloroform and titrate with the liberated iodine with 0.1 N sodium thiosulphate using freshly prepared starch as an indicator. Carry out a blank titration simultaneously and incorporate any necessary correction, if required. Each ml of 0.1 N potassium bromate is equivalent to 0.001569 g of C6H60. 

By examining some typical data on donor-acceptor systems, we can illustrate the very important principal that donors ) (or acceptors) cannot be ordered according to strength unless the acid (or base) is defined. The adducts formed by the acceptors phenol and iodine with oxygen and sulphur donors illustrate the reversals in donor order that can occur as the acid is varied (Table 2). Toward iodine, the sulphur donors... 

Barluenga et al.565 have reported the selective monoiodination of arenes with bis (pyridine)iodonium(I) tetrafluoroborate [I(py2)BF4] in excess superacids (2 equiv.) [Eq. (5.210)]. Comparable results were found for activated compounds with both HBF4 and triflic acid, whereas triflic acid was more effective in the iodination of deactivated aromatics. For example, nitrobenzene and methyl benzoate are unreactive in HBF4 but give the corresponding iodo derivatives in triflic acid (83% and 84% yields, respectively, in 14 h). Iodination of phenol required low temperature (-60°C). 

The relations which exist between the potential and the pressure with which a discharged ion, like chlorine, bromine, or iodine reacts with phenol nave been determined by Zehr-lant1 with the following results ... 

The original set of E and C parameters was determined mainly with the help of enthalpies of adduct formation of iodine and phenol as acceptors with alkylamines as donors. Subsequently, the best set of E and C parameters has been obtained by computer optimization of a large data base of enthalpies and four arbitrarily fixed reference values [71, 215] E = C = for iodine, E = 1.32 for A, A -dimethylacetamide, and Cb = 7.40 for diethyl sulfane. Table 2-6 gives a selection of E and C parameters for Lewis acids and bases commonly used as solvents. 

Procedure of Kline and Acree. For the determination of the aldose present it is preferable to take an aliquot of the sugar solution, or a weighed amount of the solid substance, which will react with approximately 20 ml. of 0.1 A iodine. Titrate this solution with 0.1 A sodium hydroxide or hydrochloric acid until it is exactly neutral to phenolphthalein. Add the phenolphthalein at this point only when it is necessary to bring the solution to neutrality and use only one drop, as the alcohol introduces a potential source of error involving a loss of iodine. A water solution of this indicator or of phenol red or thymol blue might be used for this titration. Add 5 ml. of 0.1 A iodine from a buret then add drop by drop from a buret 7.5 ml. of 0.1 A sodium hydroxide. Repeat this process until 22 ml. of iodine and 35 ml. of alkali have been added. This operation takes about five to six minutes. Allow a two-minute interval for the completion of the oxidation. Acidify with 0.1 A (or 0.2 A) hydrochloric acid to free the iodine from any sodium iodate present and titrate the liberated iodine with... 

Analytical control followed the Standard Methods recommendations [ 4 ]. Metal ion concentrations were determined by a Perkin-Elmer Model 4000 Atomic Absorption Spectrophotometer with zinz lamp 303-6081, lead lamp 303-6039, and copper lamp 303-6024. Determination of dissolved sulfide was done by titrimetric iodine methods. Phenol determination was performed by distillation/ex-traction method. Total cyanide and ammonia nitrogen were detrmined by the respective distillation/titrimetric methods. 

Phenol is a reducing agent and is capable of reacting with ferric salts in neutral to acidic solutions to form a greenish-colored complex. Phenol decolorizes dilute iodine solutions, forming hydrogen iodide and iodophenol stronger solutions of iodine react with phenol to form the insoluble 2,4,6-triiodo-phenol. 

The iodination of phenols and arylamines with KI3 solution is advantageously carried out in the presence of an Hl-acceptor such as ethylamine or ethylene-... 

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