Bromine titration method

This technique, called bromine titration method , was extensively used by K.H. Meyer in the early twentieth century.18 It was later extended to determine the enol content of simple ketones using faster flow methods combined with more sensitive potentiometric measurements of bromine uptake, but this technique sometimes produced apparent enol contents that were far too high, such as the enol content of acetone of 2.5 x 10 4% that is frequently quoted in older textbooks of organic chemistry. The excessive values so obtained have been attributed to the presence of small amounts of impurities reacting with bromine. 

Bromine titration has been applied to several heteroaromatic compounds, but it is not a reliable method. The assumption is often made that oxo structures react very slowly with bromine whereas the hydroxy forms react rapidly. Thus, 3,4-diphenylisoxazol-5-one when freshly dissolved in ethanol was found to react with 0.5 mole of bromine, but after standing it reacted with almost 1 mole. These observations led to the conclusion that the solid was in the CH... 

The amount of oil in a sample is determined by Scott oil analysis (AOAC, 1990e). This is a bromination reaction previously used to determine the number of fatty acid double bonds. This titration method quantifies the recoverable oil in fruits and fruit products based on the release of Br2 and the formation of limonene tetrabromide (Braddock, 1999). Figure Gl.5.3 illustrates the chemical reaction for the bromination of limonene. Other monoterpenes (a-pinene and citral) also react however, the method is accurate to within 10 ppm limonene (Scott and Valdhuis, 1966). For this procedure, limonene is co-distilled with isopropanol and titrated with a potassium bromide/bromate solution. 

Purification in many applications the use of unrecrystallized material has led to erratic results. Material stored for extended periods often contains significant amounts of molecular bromine and is easily purified by recrystallization from H2O (AcOFI has also been used). In an efficient fume hood (caution bromine evolution), an impure sample of NBS (200 g) is dissolved as quickly as possible in 2.5 L of preheated water at 90-95 °C. As filtration is usually unnecessary, the solution is then chilled well in an ice hath to effect crystallization. After most of the aqueous portion has been decanted, the white crystals are collected by filtration through a bed of ice and washed well with water. The crystals are dried on the filter and then in vacuo. The purity of NBS may be determined by the standard iodide-thiosulfate titration method. 

The bromine index can be measured by electrometric and coulomelric titration. In the electrometric titration method, a sample is titrated with bromide-bromate solution (0.1 N solution of mixture of potassium bromide and potassium bromate) until the end-point increase in potential remains steady for 30 s. In coulometric titration, a potassium bromide solution is used to titrate the solvent until the bromine concentration increases because it is no longer being consumed by the unsaturation of the solvent. ... 

Bromine... The method used here was virtually identical with that described for iodine, but the latter was replaced with 30 ml of 0.029M Br2 (chitin) or the mixture of 27 ml of 0.05M Br2 and 3 ml of IN HCl (H-alg.). After storing for 5 h (chitin) or 6 days (H-alg.) in the dark, the amount of bromine consumed by the sample was examined both by absorbance at 394 nm and titration with O.IN Na2S203. Ca-alg. beads prepared with 30 ml of 0.02M Ca(N03)2 and 20 ml of 0.4% Na-alg. were immersed into the mixture of 20 ml of 0.025M Br2 and 2 ml of IN HCl. Several parallel experiments using different concentrations of Br2 in the solution were carried out. 

In acidic medium, potassium bromide and potassium bromate produce bromine stoichiometrically, and this is the basis of a titration method [82], which has been used to determine double bonds in polymethylacrylate. After bromination, excess bromine is estimated by the addition of potassium iodide and the iodine produced by the reaction is titrated with standard sodium thiosulfate to the starch end-point. 

A number of unsaturated organic compounds have been determined by coulometric bromination. This method has been used successfully to titrate such compounds as styrene, monochlorostyrene, allyl alcohol, vinyl toluene, divinylbenzene, N-vinylpyrrolidone, vinylbenzyl methyl-ammonium chloride, and other similar compounds. It can be used to determine micro-amounts of such compounds, but has proved equally useful for the determination of assay amounts. It has also been used to determine bromine numbers and iodine numbers of petroleum and natural products. 

In this section, we study the titration methods involving the bromine element. 

Biuret acyl-, 194 alkyl-, 197 formyl-, 194, 195 preparation of, 194 reactions of, 195, 200 Bromine titration, as method to study tautomerism, 1... 

Effluents have been analysed following a previously published procedure (5). It consists in separating the water from the oil phase by decantation, then by filtrating the aqueous phase through 1.2 micron (Millipore) filters. For polymer, the concentration was determined with a colorimetric titration method (8) based on the reaction of acrylamide with bromine. Calcium and magnesium were measured by a colorimetric method (Lange-LASAaqua). 

The ion exchange capacity (lEC) was determined by the titration method. For all the three different types of PPOBr it was attempted to achieve an lEC of 2.0 meq/g of dry polymer. However, the lEC values were different for the polymers with different degrees of bromination. Steric hindrance, due to the presence of bulky bromine groups attached to the polymer chain was expected to be the cause of lower than expected lEC values for PPOBr. The values obtained are shown in Table 11. 

PPO and PPOBr were sulfonated by reacting with chlorosulfonic acid in chloroform [49]. The degree of sulfonation was determined by acid-base titration method. Under the reaction conditions only mono-aryl substitution of PPO and PPOBr occurred. The polymers were converted to the salt form by replacing the proton of the sulfonic acid group with Na-cation. Sulfonated PPO (SPPO) and sulfonated brominated PPO (SPPOBr), both in the Na-cation form (SPPONa and NaSPPOBr), were used for water removal studies. 

Chlorine and bromine add vigorously, giving, with proper control, high yields of 1,2-dihaloethyl ethers (224). In the presence of an alcohol, halogens add as hypohaUtes, which give 2-haloacetals (225,226). With methanol and iodine this is used as a method of quantitative analysis, titrating unconsumed iodine with standard thiosulfate solution (227). 

N-Bromosuccinimide purchased from Arapahoe Chemical Company was used without purification. If the purity of the N-bromosuccinimide is in doubt, it should be titrated before use by the standard iodide-thiosulfate method and purified, if necessary, by recrystallization from 10 times its weight of water. Solutions of N-bromosuccinimide in dimethyl sulfoxide cannot be stored, since the solvent is oxidized by the brominating reagent. 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Walash et al. [10] determined primaquine and other quinoline drugs in bulk and in pharmaceuticals by a titrimetric method. The method is based on reaction with l,3-dibromo-5,5-dimethylhydantoin or TV-bromosuccinimide as the titrant. Primaquine was determined either by usual titration or by potentiometric titration with the brominating agents. The recovery was approximately 100%. The method was simple, precise, and accurate. 

Other methods for the determination of chlorine in seawater or saline waters are based on the use of barbituric acid [13] and on the use of residual chlorine electrodes [ 14] or amperometric membrane probes [15,16]. In the barbituric acid method [12], chlorine reacts rapidly in the presence of bromide and has completely disappeared after 1 minute. This result, which was verified in the range pH 7.5-9.4, proves the absence of free chlorine in seawater. A study of the colorimetric deterioration of free halogens by the diethylparaphenylene-diamine technique shows that the titration curve of the compound obtained is more like the bromine curve than that of chlorine. The author suggests... 

The classical method for the determination of iodide in seawater was described by Sugawara [5]. Various workers [6,7] have improved the original method. Matthews and Riley [6] modified the method by concentrating iodide by means of coprecipitation with chloride using silver nitrate (0.23 g per 500 ml seawater). Treatment of the precipitate with aqueous bromine and ultrasonic agitation promote recovery of iodide as iodate which [15] when reacted with excess of iodide ions under acid conditions, yields Ij, which are determined either spectrophotometrically or by photometric titration with sodium thiosulfate. Photometric titration gave a recovery of 99.0 0.4% and a coefficient of variation of 0.4% compared with 98.5 0.6% and 0.8%, respectively, for the spectrophotometric procedure. 

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. 

The substance is burned on a platinum catalyst in a stream of oxygen and the iodine liberated is oxidised to iodic acid by bromine in acetic acid. After excess bromine has been removed with formic acid, potassium iodide is added to the solution, and the iodine liberated is titrated with thiosulphate. Since the amount of iodine titrated is six times the iodine content of the substance the method yields very accurate results. 

Analysis. The titration of thiols and of disulfide by iodine and bromine has been described (3). Control experiments involving the titration of solutions containing known amounts of thiol and disulfide showed the methods to be accurate to within 2%. 

Methylene difluorocyclopropanes are relatively rare and their rearrangement chemistry has been reviewed recently [14]. In addition, electron deficient alkenes such as sesquiterpenoid methylene lactones may be competent substrates. Two crystal structures of compounds prepared in this way were reported recently [15,16]. Other relatively recent methods use dibromodifluoromethane, a relatively inexpensive and liquid precursor. Dolbier and co-workers described a simple zinc-mediated protocol [17], while Balcerzak and Jonczyk described a useful reproducible phase transfer catalysed procedure (Eq. 6) using bromo-form and dibromodifluoromethane [18]. The only problem here appears to be in separating cyclopropane products from alkene starting material (the authors recommend titration with bromine which is not particularly amenable for small scale use). Schlosser and co-workers have also described a mild ylide-based approach using dibromodifluoromethane [19] which reacts particularly well with highly nucleophilic alkenes such as enol ethers [20], and remarkably, with alkynes [21] to afford labile difluorocyclopropenes (Eq. 7). 

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