Ammonium fluoride salt crystals

Typically, the ammonium or hydronium form of the zeolite is slurried in water and reacted with the requisite amount of the ammonium fluoride salt of either iron or titanium. Given the sparingly soluble nature of ammonium fluotitanate, the (NH )2TiF6 can be added to the zeolite slurry in slurry form, or directly as salt. Alternatively, the iron may be added to the zeolite slurry as a slurry of the ammonium fluoride salt crystals in water, or the FeF3 crystals can be mixed with a water solution of ammonium fluoride or ammonium bifluoride, such that the composition of the treatment solution contains the stoichiometry of the ammonium iron fluoride salt, (NH4)3FeF6. The (NH )3FeF6 crystals can also be added directly to the zeolite slurry. The amount of either metal ammonium fluoride salt added during the reaction is determined by the desired product composition and the anticipated completeness of the reaction. 

A different approach to the substitution of metal atoms into the framework is the secondary synthesis or post-synthesis method. This is particularly effective in synthesizing metallosilicates that are difficult to crystallize from the gels containing other metal atoms or hardly incorporate metal atoms by the direct synthesis method. Substitution of Ti for A1 goes back to the 1980s. The reaction of zeolites with an aqueous solution of ammonium fluoride salts ofTi or Fe under relatively mild conditions yields materials that are dealuminated and contain substantial amounts of either iron or titanium and are essentially free of defects [58]. However, no sufficient evidence for the Ti incorporation has been provided. 

Preferred conditions for the reaction of the zeolite with the metal ammonium fluoride are as follows. A zeolite-water slurry containing about 10-25 gm of zeolite per 100 cm3 of water is preheated to 75-95°C. When substituting Ti, the titanium salt is added to the zeolite as a water slurry containing finely divided crystals, 10 gm of (NH4>2T1F6 per 100 cm3 of water. With iron substitution, the iron salt, when added as (NH4>3FeF6, is added from a 10 wt.% solution of the salt in water. Alternatively, FeF3 can be added to a solution of NH4HF2 or NH F such that the stoichiometry of fluorine (F2) to Fe3+ is 3.0 and the total amount of salt in solution is about 10 wt.%. The addition rate of the metal ammonium fluoride salt to the zeolite slurry is about 0.005 moles of the metal ion per minute per mole of aluminum in the zeolite. 

The properties of ammonium fluoride.—According to J. C. G. de Marignac, the crystals are too deliquescent for crystallographic measurements. B. Gossner2 likewise obtained hexagonal uniaxial prisms or plates by crystallization from methyl alcohol. J. J. Berzelius says the crystals are stable in air. When differences of opinion exist as to the deliquescence or otherwise of the crystals of a salt in air, it... 

Ten grams of carbonatopentamminecobalt(III) nitrate (0.036 mol) is suspended in 25 ml. of water, and 4.5 g. of ammonium hydrogen fluoride (0.079 mol) and 15 g. of ammonium fluoride (0.405 mol) are added. The reaction mixture is kept at approximately 90° in a water bath for 1 hour, with occasional stirring. During this digestion some decomposition takes place, and noticeable quantities of ammonia are evolved. The mixture is then cooled to room temperature, 75 ml. of water being added to keep the products in solution. This solution is filtered, and 20 g. of solid ammonium nitrate (0.25 mol) is added to the filtrate. Pink crystals separate immediately after the mixture is cooled in an ice-salt bath. The product is collected on a filter, washed with 10 ml. of ice-cold water, followed by alcohol and ether, and then dried at 90°. Yield, 6 g. (58%). 

Ammonium hydrogen fluoride, NH4F,HF.—Evaporation of a solution of the normal salt at a temperature between 36° and 40° C. expels ammonia, the primary salt crystallizing out. It can also be prepared by the action of ammonia on a solution of hydrogen fluoride, a small proportion of ammonium sulphide or carbonate being added.13 It forms colourless rhombic prisms, readily soluble in water,6 with a density of 1-21114 at 12° C. 

The salt so purified may contain some ammonium fluoride, which can be removed only by recrystallization of the product from water. This is a wasteful process due to the great solubility of the fluophosphate. The salt is dissolved in water (50 g./lOO ml.) and the filtered solution evaporated in a platinum dish on a steam bath until crystals appear in the hot solution. The mixture is chilled in ice, and the crystals are collected on a sintered-glass suction filter, washed with a few milliliters of ice water, sucked free from adhering moisture, and dried in a desiccator over sulfuric acid. 

A challenge for industrial syntheses of perfluoroalkanesulfonate tetraalkylammonium salts is the impurities present in technical perfluorooctanesulfonyl fluoride. These impurities cause side reactions that result in tar formation, thus lowering the production yield. One patent claims the preparation of the desired perfluoroalkanesulfonate tetraalkylammonium salts in excellent yields and good purities by reaction of the sulfonyl fluoride with alkoxysilanes (e.g., triethoxymethylsilane) and trial-kylamines (e.g., triethylamine) in a suitable organic solvent (e.g., chlorobenzene, ether, or toluene) as outlined in Scheme 18.1. Under these conditions, the ammonium salts crystallize from the reaction mixture, whereas the fluorosilane by-products remain dissolved in the organic solvent. 

In 1914 Lemaire [64] proposed the use of a sheath made of incombustible and inexplosive substances in explosive charges. As an inert material he recommended milled sand, salts containing water of crystallization (e.g. sodium sulphate), salts volatilizing at high temperatures (e.g. sodium chloride, sodium fluoride, cryolite), salts decomposing at high temperatures (e.g. ammonium chloride). Sheaths were made by placing the substance between the dual walls of a paper tube. 

Single crystals of difluoromethane bis(sulfinic acid) anhydride 17 were isolated, after the cesium salt 119 was stored in the presence of traces of water vapor for several weeks <1998JFC(89)55>. Treatment of difluoromethane-l,l-bis(sulfonyl fluoride) 120 with liquid ammonia led to the formation of the cyclic ammonium imide 121 <1997ZNB359, 1997WO9731909>, while reaction of sulfamide 122 with trifluoroacetaldehyde O-ethyl hemiacetal afforded the cyclic aminal 60 (Scheme 41) < 1999S1731 >. 

Ammonium tetrathiocyanatomercurate(II)-cobalt sulphate test This test is similar to that described under reaction 8, except that a minute amount of a dilute solution of a cobalt salt (nitrate, sulphate or acetate) is added. Coprecipitation of the cobalt tetrathiocyanatomercurate(II) yields a blue precipitate composed of mixed crystals of Zn[Hg(SCN)4] + Co[Hg(SCN)4], Iron(II) salts give a red colouration but this can be eliminated by the addition of a little alkali fluoride (colourless [FeF6]3- ions are formed). Copper salts should be absent. 

A number of fluoride complexes have been made, both by crystallization for the ammonium salts like (NH4)4CeFg, which has square-antiprismatic coordination of cerium, also found in the (CeF6 )oo chains in (NH4)2CeF6, its thermal decomposition product. (NH4)3CeF7-H20 acquires dodecahedral eight-coordination by dimerization. (NH4)4[CeFg] can... 

Table CLH gives the values of d d U for different ammonium salts together with the values of P calculated by means of equation hi. It is interesting to notice that the values increase in the order I, Br, Cl and F, and that the value for the fluoride is significantly greater than the other values. NH4CI, NH4Br, NH4I crystallize in lattices of the sodium chloride and caesium chloride type. The lattice of NH4F, however, is of the tetrahedral, wurtzite type. The NH4 ion is tetrahedral and in NH4F,...

Molybdenum Hexafluoride, MoFg, the only fluoride known vith certainty to exist, is best prepared by the action of fluorine on the finely divided metal at 60° to 70° C., the product being collected in a vessel cooled by a mixture of solid carbon dioxide and alcohol. It forms white crystals which melt at 17° C., the boLling-poiiit of the liquid being 35° C. It is decomposed by water, yielding the blue oxide (see p. 131), but does not react with chlorine, sul2ihur dioxide, or dry air it is absorbed by alkali or ammonium hydroxides, and fomis double salts vith alkali fluorides. It also reacts with ammonia, vith 2>roduction of a brown powder. 

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