Potassium bromid

Crim F F, Bente FI B and Fisk G A 1974 Inelastio soattering of vibrationally exoited potassium bromide by polyatomio partners J. Rhys. Chem. 78 2438-42... 

Calculate the standard enthalpy of formation. AH potassium bromide. 

In the laboratory, bromine is prepared by oxidation of bromide ion the oxidation is carried out by mixing solid potassium bromide with manganese(IV) oxide and distilling with concentrated sulphuric acid ... 

Note. (1) Most sulphur compounds are completely oxidised if the tube is heated under the conditions described for the estimation of halogens. Sul-phonic acids and sulphones are more difficult to oxidise completely and the tube should be slowly heated to 300 and maintained at this temperature for at least 6 hours. The oxidation may be facilitated by adding a few crystals of sodium or potassium bromide to the organic material in the small tube, so that bromine shall be present to intensify the oxidation during the heating. 

Method 2 (from potassium bromide and sulphuric acid). Potassium bromide (240 g.) is dissolved in water (400 ml.) in a litre flask, and the latter is cooled in ice or in a bath of cold water. Concentrated sulphuric acid (180 ml.) is then slowly added. Care must be taken that the temperature does not rise above 75° otherwise a little bromine may be formed. The solution is cooled to room temperature and the potassium bisulphate, which has separated, is removed by flltration through a hardened Alter paper in a Buchner funnel or through a sintered glass funnel. The flltrate is distilled from a litre distilling flask, and the fraction b.p. 124 127° is collected this contains traces of sulphate. Pure constant boiling point hydrobromic acid is obtained by redistillation from a little barium bromide. The yield is about 285 g. or 85 per cent, of the theoretical. 

Bromine. The commercial product may be dried (and partially purified) by shaking with an equal volume of concentrated sulphuric acid, and then separating the acid. Chlorine, If present, may be removed by fractionation in an all-glass apparatus from pure potassium bromide the b.p. is 59°/760 mm. The analytical reagent grade is satisfactory for most purposes where pure bromine is required. 

SO, + 2H,0 + Br, — HjSO, + 2HBr Alternatively, the acid mixture may be obtained from the reaction between potassium bromide solution and concentrated sulphuric acid below 76° the potassium hydrogen sulphate crystallises out and is removed by filtration ... 

Dissolve 30 g. of potassium bromide in 50 ml. of water in a 350 ml. conical flask gerUle warming may be necessary. Cool the flask with running water from the tap so that the contents attain room temperature. Add 25 ml. of concentrated sulphuric acid slowly and with constant rotation of the flask to ensure thorough mixing cool under the tap from... 

IR spectra can be recorded on a sample regardless of its physical state—solid liquid gas or dissolved m some solvent The spectrum m Eigure 13 31 was taken on the neat sample meaning the pure liquid A drop or two of hexane was placed between two sodium chloride disks through which the IR beam is passed Solids may be dis solved m a suitable solvent such as carbon tetrachloride or chloroform More commonly though a solid sample is mixed with potassium bromide and the mixture pressed into a thin wafer which is placed m the path of the IR beam... 

Table 2 Hsts examples of compounds with taste and their associated sensory quaUties. Sour taste is primarily produced by the presence of hydrogen ion slightly modified by the types of anions present in the solution, eg, acetic acid is more sour than citric acid at the same pH or molar concentration (43). Saltiness is due to the salts of alkaU metals, the most common of which is sodium chloride. However, salts such as cesium chloride and potassium iodide are bitter potassium bromide has a mixed taste, ie, salty and bitter (44). Thus saltiness, like sourness, is modified by the presence of different anions but is a direct result of a small number of cations.

Ferrous Sulfdte Titration. For deterrnination of nitric acid in mixed acid or for nitrates that are free from interferences, ferrous sulfate titration, the nitrometer method, and Devarda s method give excellent results. The deterrnination of nitric acid and nitrates in mixed acid is based on the oxidation of ferrous sulfate [7720-78-7] by nitric acid and may be subject to interference by other materials that reduce nitric acid or oxidize ferrous sulfate. Small amounts of sodium chloride, potassium bromide, or potassium iodide may be tolerated without serious interference, as can nitrous acid up to 50% of the total amount of nitric acid present. Strong oxidizing agents, eg, chlorates, iodates, and bromates, interfere by oxidizing the standardized ferrous sulfate. 

Potassium Bromide. Potassium bromide [7758-02-3] KBr, can be prepared by a variation of the process by which bromine is absorbed from ocean water. Potassium carbonate is used instead of sodium carbonate ... 

Potassium bromide is extensively used in photography (qv) and engra ving. It is the usual source of bromine in organic synthesis. In medicine, it is a classic sedative. 

Instrumental Interface. Gc/fdr instmmentation has developed around two different types of interfacing. The most common is the on-the-fly or flow cell interface in which gc effluent is dkected into a gold-coated cell or light pipe where the sample is subjected to infrared radiation (see Infrared and raman spectroscopy). Infrared transparent windows, usually made of potassium bromide, are fastened to the ends of the flow cell and the radiation is then dkected to a detector having a very fast response-time. In this light pipe type of interface, infrared spectra are generated by ratioing reference scans obtained when only carrier gas is in the cell to sample scans when a gc peak appears. 

Electrochemical Process. Applying an electrical current to a brine solution containing propylene results in oxidation of propylene to propylene oxide. The chemistry is essentially the same as for the halohydrin process. AH of the chemistry takes place in one reactor. Most of the reported work uses sodium or potassium bromide as the electrolyte. Bromine, generated from bromide ions at the anode, reacts with propylene and water to form propylene bromohydrin. Hydroxide generated at the cathode then reacts with the bromohydrin to yield propylene oxide (217—219). The net reaction involves transfer of two electrons ... 

Silver bromide crystals, formed from stoichiometric amounts of silver nitrate and potassium bromide, are characterized by a cubic stmcture having interionic distances of 0.29 nm. If, however, an excess of either ion is present, octahedral crystals tend to form. The yellow color of silver bromide has been attributed to ionic deformation, an indication of its partially covalent character. Silver bromide melts at 434°C and dissociates when heated above 500°C. 

Electrophilic mercuration of isoxazoles parallels that of pyridine and other azole derivatives. The reaction of 3,5-disubstituted isoxazoles with raercury(II) acetate results in a very high yield of 4-acetoxymercury derivatives which can be converted into 4-broraoisoxazoles. Thus, the reaction of 5-phenylisoxazole (64) with mercury(II) acetate gave mercuriacetate (88) (in 90% yield), which after treatment with potassium bromide and bromine gave 4-bromo-5-phenylisoxazole (89) in 65% yield. The unsubstituted isoxazole, however, is oxidized under the same reaction conditions, giving mercury(I) salts. 

Rate differences observed between the same bromophenylcarbene (241) when prepared by two different routes, diazirine photolysis and the reaction of benzylidene dibromide with potassium r-butoxide, vanish when a crown ether is added to the basic solution in the latter experiment. In this case the complexing potassium bromide is taken over by the crown ether, and selectivity towards alkenes reaches the values of the photolytic runs (74JA5632). 

Potassium bromide [7758-02-3] M 119.0, m 734°, d 2.75. Crystd from distilled water (ImL/g) between 100° and 0°. Washed with 95% EtOH, followed by Et20. Dried in air, then heated at 115° for Ih, pulverised and heated in a vacuum oven at 130° for 4h. Has also been crystd from aqueous 30% EtOH, or EtOH, and dried over P2O5 under vacuum before heating in an oven. 

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