Hydrogen bromide, standard

Yang and co-workers introduced chirality in their opening sequence by reacting (5)-glycerol acetonide (87) with 2,3,4-trifluoro, 1-nitrobenzene (45) to yield ether 88 (Scheme 4.14) (Yang et al., 1999). Deprotection of the acetonide under standard conditions delivered diol 89, which was treated with hydrogen bromide in acetic acid to give a mixture... 

In the following method a slight excess of an alcoholic solution of bromine is added to an alcoholic solution of the tautomeric mixture the excess of bromine is immediately removed by the addition of a few drops of alcoholic /3-naphthoI solution potassium iodide solution is next added, and the hydrogen iodide formed by interaction with the hydrogen bromide present reduces the bromo-ketone with liberation of free iodine, which is estimated by titration with standard thiosulphate (in absence of starch). One molecule of iodine = one molecule of enolic compound. For criticism of this method, see Ann. Rep., 1930, 100. 

Epoxy content is generally determined by wet analytical techniques. ASTM D 1652 is widely used. The most common method is based on the addition of hydrogen halide (e.g., hydrogen chloride, hydrogen bromide, or hydrogen iodide) to the epoxy group. The difference between the amount of acid added and the amount unconsumed, determined by titration with standard base, is a measure of the epoxy content. There are numerous epoxy assay methods based on this technique. The specific method used depends on the resin type being analyzed as well as on the extent to which side reactions can occur. 

The standard potential of the silver-silver bromide electrode has been determined from emf measurements of cells with hydrogen electrodes and silver-silver bromide electrodes in solutions of hydrogen bromide in mixtures of water and N-methylacetamide (NMA). The mole fractions of NMA in the mixed solvents were 0.06, 0.15, 0.25, and 0.50, and the dielectric constants varied from 87 to 110 at 25°C. The molality of HBr covered the range 0.01-0.1 mol kg 1. Data for the mixed solvents were obtained at nine temperatures from 5° to 45°C. The results were used to derive the standard emf of the cell as well as the mean ionic activity coefficients and standard thermodynamic constants for HBr. The information obtained sheds some light on the nature of ion-ion and ion-solvent interactions in this system of high dielectric constant. 

Table 9.1. Approximate standard enthalpies of steps in hydrogen-bromide reaction.

Into a Pyrex tube, 44 X 275 mm., equipped with a standard-taper 29/42 joint, is condensed 100 g. (1.25 moles) of anhydrous hydrogen bromide. To this, under an atmosphere of nitrogen, is added 60 g. (0.555 mole) phenylsilane, b.p. 119°/754 mm. The reaction tube (with its contents at —196°) is fitted with a vacuum-stopcock adapter (which is wnred firmly into position)... 

The synthesis of hydrogen bromide from the elements is also catalyzed by carbons [147]. A few preliminary experiments were performed with carbon black Corax 3. A hydrogen stream satnrated with Br2 at 273 K was passed over the samples at 423 K. At this temperatnre, thermal dissociation of HBr is negligible, and the conversion is a measnre of catalytic activity. The HBr formed was absorbed in water and titrated with standard alkali [96]. The catalytic activity of the carbon black tripled after treatment of the oxidized black with NH3 at 873 K, and doubled when heat-treated at 1273 K. This behavior agrees very well with that observed in the oxidation reactions described in this section. 

The determination of chloride involves the precipitation of chloride with silver nitrate, dissolution of the precipitate in ammonia, and determination of silver in the resulting solution by FAAS using air-acetylene or air-hydrogen flames. Standard silver nitrate solutions in ammonia are used for calibration since bromide and iodide interfere in the determination of chloride. 

High molecular-weight polypeptides were synthesized by the standard N-carboxy-o-amino acid anhydride (NCA) method. The u-carbobenzoxy groups of the polypeptide in dioxane solution were removed with hydrogen bromide gas. The water-soluble polymers were then dialyzed repeatedly against dilute HCl and finally water. The concentrations of the polypeptides were determined by microKjeldahl analyses. All CD spectra were measured on a Jasco J-10 or, more recently, J-500A spectropolarimeter (for its calibration, see Ref. 8). 

Epoxy resins are characterised by two or more epoxy groups in the structure. To cure an epoxy resin with a suitable hardener, accurate estimation of epoxy groups is crucial. Epoxy equivalent is defined as the amount of resin that contains one mole of epoxy. Epoxy equivalent of an epoxy sample is determined by a standard titration method [6] using hydrogen bromide solution in acetic acid. The method is briefly described next. 

The standard valve outlet connection in the United States and Canada for hydrogen bromide cylinders is Connection CGA 330. [8]... 

The reaction progress was followed by titrating the unreacted carboxyl groups in samples removed from the reaction mixture at different times of reaction, with a standard methanolic potassium hydroxide solution. The oxirane groups were also titrated in some of the samples, using the hydrogen bromide in glacial acetic acid titration technique (21). 

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