Potassium bromide, complex

A. Dibromomalononitrile-potassium bromide complex. In a 2-1. three-necked flask equipped with an efficient stirrer, a dropping funnel, and a thermometer are placed 900 ml. of cold water, 99 g. (1.5 moles) of malononitrile (Note 1), and 75 g. (0.63 mole) of potassium bromide. The flask is then placed in an ice-water bath, the stirrer is started, and the thermometer is adjusted to extend into the liquid but not into the path of the stirrer. When the temperature of the mixture has dropped to 5-10° (much solid crystallizes), 488 g. (158 ml. at 25°, 3.05 moles) of bromine is added over a period of 2.5 hours. The stirring is continued for an additional 2 hours, while the temperature is held at 5-10°. The precipitated solid complex is collected on a Buchner funnel, washed with 150 ml. of ice-cold water and sucked as dry as possible for about 1 hour (Notes 2 and 3). The grainy product is then dried to constant weight in a vacuum desiccator over phosphorus pentoxide, at the pressure obtained with an aspirator (Notes 4 and 5). The yield of light-yellow product is 324 340 g. (85-90%) (Note 3). 

The vapors of dibromomalononitrile-potassium bromide complex are irritating to the eyes and nose. The solid causes discoloration of the skin on contact. Manipulations should be carried out with gloves in a hood. 

Preparation. Bromine is added in the course of 2.5 hrs. to a mixture of malonyl-nitrile and potassium bromide in 900 ml. of water to produce the solid dibromo-malononitrile-potassium bromide complex. A mixture of this complex with benzene is stirred, precipitated copper powder is added, and the mixture is stirred and... 

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). 

Aromatic Ketones The DIOP-Rh [116] and DBPP-Rh [117] complexes, in conjunction with a tertiary amine, have been employed in the asymmetric hydrogenation of acetophenone, albeit with moderate enantioselectivity (80 and 82% respectively Tab. 1.10). The asymmetric hydrogenation of aromatic ketones was significantly improved by using the Me-PennPhos-Rh complex, with which enantioselectivities of up to 96% ee were achieved [36]. Interestingly, the additives 2,6-lutidine and potassium bromide were again found to be crucial for optimum selectivity, although their specific role has not been determined. 

Aliphatic Ketones The asymmetric hydrogenation of simple aliphatic ketones remains a challenging problem. This may be attributed to the difficulty with which the chiral catalyst differentiates between the two-alkyl substituents of the ketone. Promising results have been obtained in asymmetric hydrogenation of aliphatic ketones using the PennPhos-Rh complex in combinahon with 2,6-lutidine and potassium bromide (Tab. 1.11) [36]. For example, the asymmetric hydrogenation of tert-butyl methyl ketone affords the requisite secondary alcohol in 94% ee. Similarly, isopropyl, Butyl, and cyclohexyl methyl ketones have been reduced to the corresponding secondary alcohols with 85% ee, 75% ee, and 92% ee respectively. 

In a second procedure, useful for forming reversal or direct X-ray emulsions, a high concentration of ammonia is used to form a complex precipitate with silver bromide, by mixing ammoniacal silver nitrate and ammoniacal potassium bromide. Dilution with water decomposes the ammonia complex, and silver bromide grains form.9... 

Anhydrous hydrazine dssolves many salts, thus, 100 parts of solvent at 12-5°-13° dissolve 12-2 parts of sodium chloride 8 5, of potassium chloride 56-4, of potassium bromide 135-7, of potassium iodide 26-6, of sodium nitrate 21-7, of potassium nitrate and 814, of barium nitrate. The hydrazine seemed to unite with sodium chloride with a warm soln. of ammonium chloride, ammonia is evolved, and in the cold, there seems to be a state of equilibrium a complex salt seems to be formed with lead nitrate. An aq. soln. of hydrazine hydrate also dissolves a number of salts, potassium bromide and iodide, ammonium sulphate, potassium cyanide, barium nitrate, magnesium sulphate, etc. According to T. W. B. Welsh and H. J. Broderson, the solubility of the metal haloids seems to... 

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