Ammonium halides

Towards a simple Lewis base, for example the proton, phosphine is a poorer electron donor than ammonia, the larger phosphorus atom being less able to form a stable covalent bond with the acceptor atom or molecule. Phosphine is, therefore, a much weaker base than ammonia and there is no series of phosphonium salts corresponding to the ammonium salts but phosphonium halides. PH4X (X = Cl, Br, I) can be prepared by the direct combination of phosphine with the appropriate hydrogen halide. These compounds are much more easily dissociated than ammonium halides, the most stable being the iodide, but even this dissociates at 333 K PH4I = PH3 -t- HI... 

Reaction of Na2Se and Na2Sc2 with Se in the presence of ethanolic solutions of tetraalkyl-ammonium halides and catalytic amounts of I2 yields dark green or black crystalline polyselenides (jc = 3,5-9) depending on the conditions used and the particular cation selected. Tetraphenylphosphonium salts and crown ether complexes of alkali or alkaline earth cations in dimethylformamide solution can also be used. " )... 

These considerations also explain the occurrence of cases of dimorphism involving the sodium chloride and cesium chloride structures. It would be expected that increase in thermal agitation of the ions would smooth out the repulsive forces, that is, would decrease the value of the exponent n. Hence the cesium chloride structure would be expected to be stable in the low temperature region, and the sodium chloride structure in the high-temperature region. This result may be tested by comparison with the data for the ammonium halides, if we assume the ammonium ion to approximate closely to spherical symmetry. The low-temperature form of all three salts, ammonium chloride, bromide and iodide, has the cesium chloride structure, and the high-temperature form the sodium chloride structure. Cesium chloride and bromide are also dimorphous, changing into another form (presumably with the sociium chloride structure) at temperatures of about 500°. 

A very small hump in the heat capacity curve at —30° was also found for ammonium fluoride the interpretation of this is uncertain (the structure of this crystal is not the same as that of the other ammonium halides). 

In some cases, the Q ions have such a low solubility in water that virtually all remain in the organic phase. ° In such cases, the exchange of ions (equilibrium 3) takes place across the interface. Still another mechanism the interfacial mechanism) can operate where OH extracts a proton from an organic substrate. In this mechanism, the OH ions remain in the aqueous phase and the substrate in the organic phase the deprotonation takes place at the interface. Thermal stability of the quaternary ammonium salt is a problem, limiting the use of some catalysts. The trialkylacyl ammonium halide 95 is thermally stable, however, even at high reaction temperatures." The use of molten quaternary ammonium salts as ionic reaction media for substitution reactions has also been reported. " " ... 

When quaternary ammonium halides are treated with strong bases (e.g., PhLi, KNH2 in liquid an elimination can occur that is similar in products, though not in... 

The cationic monomer can be a diallyldimethyl ammonium halide, a di-methylaminoethyl acrylate quaternary salt, or a dimethylaminoethyl methacrylate quaternary salt [1635]. The copolymers may be in solid, dispersion, latex, or solution form. 

They find that heating cyclotri- and cyclotetrasilazanes with ammonium halide catalysts at temperatures of 160°C for 6-8 h results in a condensation polymerization process that evolves ammonia and leads to the formation of waxy polysilazanes. Analytical results suggest that these polysilazanes consist of rings linked by silyl bridges as illustrated by the following structure ... 

Information available regarding the chemistry of lead in air is limited. Before the ban on sales of leaded gasoline, lead particles were emitted to the atmosphere from automobiles as lead halides (mostly PbBrCl) and as double salts with ammonium halides (e.g., 2PbBrCl NH4Cl. Pb3[P04]2, and PbS04 [Biggins and Harrison 1979 Ter Haar and Bayard 1971]). After 18 hours, approximately 75% of the bromine and 30-40% of the chlorine disappeared, and lead carbonates, oxycarbonates and oxides were produced. 

See Bromine trifluoride Ammonium halides Bromine pentafluoride Acids, etc. 

The phase-transfer catalyst (Q+X-) is usually a quaternary ammonium halide (R4N+X ) such as tetrabutylammonium halide (CH3CH2CH2CH2)4N+X. ... 

Another approach for ion-sensing (here copper and zinc) is based on the water-soluble ligand zincon and the ion pair with quaternary ammonium halides shown in Figure 17 which can be homogeneously dissolved in polymers such as plasticized poly(vinyl acetate), ethyl cellulose, and polyurethane. 

Ammonium halides, 2 714-715 vapor pressure, 2 715t Ammonium hydrosulfide, 2 728 Ammonium hydroxide, for fermentation, 11 38... 

Trihalides can be produced by heating the oxide with an excess of ammonium halide at a high temperature. The excess ammonium halide is sublimed off in N2, He (12), or in vacuo (39, 77-84). 

---