Potassium halides

Mix together 1 0 g. of pure p-naphthol and the theoretical quantity of 50 per cent, potassium hydroxide solution, add 0-5 g. of the halide, followed by sufficient rectified spirit to produce a clear solution. For alkyl chlorides, the addition of a little potassium iodide is recommended. Heat the mixture under reflux for 15 minutes, and dissolve any potassium halide by the addition of a few drops of water. The p-naphthyl ether usually crystallises out on cooling if it does not, dilute the solution with 10 per cent, sodium hydroxide solution untU precipitation occurs. Dissolve the p-naphthyl ether in the minimum volume of hot alcohol and add the calculated quantity of picric acid dissolved in hot alcohol. The picrate separates out on cooling. Recrystallise it from rectified spirit. 

Table 8 1 illustrates an application of each of these to a functional group transfer matron The anionic portion of the salt substitutes for the halogen of an alkyl halide The metal cation portion becomes a lithium sodium or potassium halide... 

Perfluoroallyl fluorosulfonate is converted to perfluoroallyl bromide or iodide in 56 or 75% yield, respectively, by reaction with the potassium halide in mono-glyme at room temperature [S5]... 

These reactions occur with similar rates to those carried out in dipolar aprotic solvents such as DMF or DMSO. An advantage of using the room-temperature ionic liquid for this reaction is that the lower reaction temperatures result in higher selec-tivities for substitution on the oxygen or nitrogen atoms. The by-product (sodium or potassium halide) of the reaction can be extracted with water and the ionic liquid recycled. 

Fig. 20.5 Electrocapillary curves for KNO3, and different potassium halides showing how the former approximates to a parabola...

The conception of the formation of hetero-ligand complexes and the nature of anion-anion interactions can be clarified using IR spectra of K2TaF7 - KX mixtures, where X = Cl, Br or I [356, 360]. Fig. 78 shows the spectral transformation due to the dilution of molten K2TaF7 with potassium halide. 

The resultant mixture can be separated by fractional crystallization as the trans-isomer is more soluble the m-isomer can be resolved into its enantiomers using optically active anions like a-bromocamphor 7r-sulphonate. These chlorides can be converted into the bromide or iodide complex by refluxing with a solution of the appropriate potassium halide. 

I 5.89 Account for the observation that solubility in water i,-. uerallv increases from chloride to iodide for ionic halides v, h low covalent character (such as the potassium halides)... 

The conversion of benzaldoxime [157] into benzonitrile and benzamide by catalytic amounts of potassium halides and cyanide has also been attributed to proton abstraction by the anion (Rasmussen, 1977). Nucleophilic addition was thought to be unlikely, since the anion reactivities in (26) in acetonitrile with... 

The alkyl methanesulphonate (50 mmol), the appropriate potassium halide (50 mmol) and Aliquat (ll.27 g, 2.5 mmol) in H20 (5 ml) are stirred at ca. 100°C. The aqueous phase is separated and extracted with n-C,HI2 (50 ml). The combined organic solutions are washed sequentially with H20, cone. H2S04, and H20, dried (CaCl2), and fractionally distilled to yield the haloalkane [e.g. n-C8H,7CI (74%) from n-C8Hn0S02Me after 90 min n-C8HI7Br (73%) after 30 min n-C8H,7I (70%) after 20 min]. 

Optically pure alcohols are converted via their mesylates into the corresponding chiral haloalkanes with the opposite configuration (>70% with an optical purity 90%) by a liquiddiquid phase-transfer catalysed SN2 reaction (2.1.5) with the appropriate potassium halide [7]. The preparation of chiral fluorides normally requires more vigorous conditions (160°C, 14 h in an autoclave). By-products of the reaction are the alcohol and alkene. 

Substituted l,2,4-thiadiazol-5-yl diazonium tetrafluoroborates (314) react with potassium halides in acetonitrile in the absence of catalysts to afford the corresponding 5-halogeno compounds (315) in excellent yields.169 The isomeric 5-phenyl-l,2,4-thiadiazol-3-yl diazonium salts, however, resist substitution by this procedure, except with iodide ions by taking advantage of the catalytic effect of copper... 

J6 The ammonium km is about the same size (r+ = 151 pm) as the potassium ion ir. 152 pm) and this is a usef ul fact to remember when explaining the resemblance in properties between these two tuns. For example, (he solubilities of ammonium salts arc similar to those of potassium sails. Explain the relation between ionic radius and soloWiiy. On the other hand, all of the potassium halides crystallize in the NaClstrocture with C.N. = 6 (see Chapter 4). but none of the ammonium halides does so. The coordination numbers of the ammonium halides are either four or eight- Suggest an explanation. 

When an electrolyte which is without action on vanadium at ordinary temperatures (for example, dilute solutions of mineral acids, of oxalic acid, or of potassium halides) is electrolysed with a vanadium anode, a complex tetravalent vanadium ion is produced. Similarly, electrolysis at 100° C. and in molten chlorides of sodium or zinc gives rise to complex tetravalent vanadium ions. The E.M.F. in each case is found to be independent of the nature of the electrolyte. When, however, solutions of caustic soda or of caustic potash are employed, the vanadium dissolves as a pentavalent ion, irrespective of variations... 

Fig. 23. Volume changes of gels upon addition of sodium and potassium halides. The efficiency of anions are in order of the ionic radii, while there are also markedly greater values for the divalent anions, sulfate and carbonate...

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