PREPARATION OF SALTS

Whenever possible, salts are obtained by simply mining them. Many kinds of salts can be obtained by evaporating water from a few salt-rich inland sea waters or from brines pumped from beneath the ground. However, most salts cannot be obtained so directly, and must be made by chemical processes. Some of these processes will be discussed here. 

One way of making salts already discussed in this chapter is to react an acid and a base to produce a salt and water. Calcium propionate, which is used to preserve bread, is made by reacting calcium hydroxide and propionic acid, HC3H5O2  

Almost any salt can be made by the reaction of the appropriate acid and base. In some cases, a metal and a nonmetal will react directly to make a salt. If a strip of 

Metals react with acids to produce a salt and hydrogen gas. Calcium placed in sulfuric acid will yield calcium sulfate  

Some metals react with strong bases to produce salts. Aluminum metal reacts with sodium hydroxide to yield sodium aluminate, NagAlOj  

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Fluorides. Tantalum pentafluoride [7783-71-3] TaF, (mp = 96.8° C, bp = 229.5° C) is used in petrochemistry as an isomerization and alkalation catalyst. In addition, the fluoride can be utilized as a fluorination catalyst for the production of fluorinated hydrocarbons. The pentafluoride is produced by the direct fluorination of tantalum metal or by reacting anhydrous hydrogen fluoride with the corresponding pentoxide or oxychloride in the presence of a suitable dehydrating agent (71). The ability of TaF to act as a fluoride ion acceptor in anhydrous HF has been used in the preparation of salts of the AsH, H S, and PH ions (72). The oxyfluorides TaOF [20263-47-2] and Ta02F [13597-27-8] do not find any industrial appHcation. 

The chlorohydrin process (24) has been used for the preparation of acetyl-P-alkylcholine chloride (25). The preparation of salts may be carried out mote economically by the neutralization of choline produced by the chlorohydrin synthesis. A modification produces choline carbonate as an intermediate that is converted to the desired salt (26). The most practical production procedure is that in which 300 parts of a 20% solution of trimethyl amine is neutralized with 100 parts of concentrated hydrochloric acid, and the solution is treated for 3 h with 50 parts of ethylene oxide under pressure at 60°C (27). 

The generated polysulfide dianions of different chain-lengths then establish a complex equilibrium mixture with all members up to the octasulfide at least see Eqs. (5) and (6). For this reason, it is not possible to separate the polysulfide dianions by ion chromatography [6]. The maximum possible chain-length can be estimated from the preparation of salts with these anions in various solvents (see above). However, since the reactions at Eqs. (22) and (23) are reversible and Sg precipitates from such solutions if the pH is lowered below a value of 6, the nonasulfide ion must be present also to generate the Sg molecules by the reverse of the reaction at Eq. (22). The latter reaction (precipitation of Sg on acidification) may be used for the gravimetric determination of polysulfides [11]. There is no evidence for the presence of monoprotonated polysulfide ions HS - in aqueous solutions [67, 72]. 

Uses The highest value inorganic acid marketed in the U.S. and second in value to sulfuric acid. Used primarily for the preparation of salts used as fertilizers (ammonium and calcium salts), water softeners and detergents, animal feeds, and baking powder. Food-grade phosphoric acid is used to acidify soft drinks, e.g.. Coca Cola. Organic phosphates are used in flame retardants. 

The preparation of salts of organic compounds is one of the most important tools available to the for-mulator. Compounds for both IM and IV solutions may require high solubility in order for the drug to be incorporated into acceptable volumes for bolus administration (see Table 1). Sodium and potassium salts of weak acids and hydrochloride and sulfate salts of weak bases are widely used in parenterals requiring highly soluble compounds, based on their overall safety and history of clinical acceptance. 

Previous methods for the preparation of salts of geranyl diphosphate and other allylic isoprenoid diphosphates are based on condensation between the alcohol and inorganic phosphate by trichloroacetonitrile as originally reported by Cramer and modified by Popjak The reaction generates a complex mixture of organic and inorganic polyphosphates which must be separated by chromatography. The desired diphosphate ester has been prepared on small... 

The preparation of salts containing the [Cr(en)3]3+ cation from anhydrous chromium sulfate has been described previously in Inorganic Syntheses,1 and the merits of this, and other, methods have been reviewed.9 A more rapid route to this cation involves refluxing CrCl3 6H20 in methanol with ethylenediamine and zinc metal, which allows the substitution to proceed by way of the kineti-cally labile chromium(II) species.10 All of these preparations yield hydrated salts the procedure described below leads to anhydrous [Cr(en)3] Br3. 

The preparation of salts of this series in the pure state is difficult. The dithiouates are most easily prepared, and from these pure bromides are obtained. 

Crystallographic studies of the bis oxalates of chromium(III) are not abundant. However, the structure of both tarns904 and cis905 isomers has been confirmed crystallographically. Potassium tams-bis(oxalato)diaquachromate(III) is monoclinic (space group P2/c) the oxalates are strictly coplanar. The crystal structure of the complex salt [Cr(en)2(ox)][Cr(en)(ox)2] has been determined 905 this red salt is obtained as an intermediate in the preparation of salts of mixed ethylenediamine/oxalate chromium(III) complexes. The structure consists of discrete complex ions linked by H bonding to water molecules and neighbouring ions. 

Various otlior processes for tlio preparation of Salt ... 

The cis/trans isomerization reaction, Eq. (24), has been applied in the preparation of salts of the cis isomers of the chromium(III) complexes with L3 = (NH3)3 or tacn (319). For these species Eq. (24) equilibrium is shifted to the right, while the corresponding equilibria with the diaqua or dihydroxo species, respectively, are shifted to the left (Table X). The increased stability of the cis aqua hydroxo species can be explained in terms of intramolecular hydrogen bond formations (Section VI,C). As mentioned above, the corresponding cobalt(III) and rhodium(III) complexes have been isolated as salts only in the case of the trans-(H20)L3M(0H)2ML3(H20)4+ cations, but it seems very probable that their cis isomers could be prepared by reaction Eq. (24). 

A typical pyrilium salt synthesis is illustrated by the preparation of salt 9.12. The precursor to 9.12 is pyran 9.11, available by dehydration of 1,5-diketone 9.10. Note the similarity of this sequence to the Hantzch pyridine synthesis, Chapter 5. Also, the dehydrative cyclisation of a diketone to oxygen heterocycle 9.11 is reminiscent of furan synthesis, Chapter 2. 

Recently, the preparation of salts of the bis(tetrathiotungsto)nickelate (II) ion, Ni(WS4)J2, has been reported and the tetraphenylphosphonium and -arsonium salts isolated. The structure shown in Fig. 17 has been proposed for this anion196. ... 

When generating the ylide from the corresponding phosphonium salt, the choice of the method of formation is important for the stereochemistry of the reaction. With the original application of lithium alkyls as bases one equivalent of lithium halogenide is always formed this lowers the stereoselectivity. Not before the development of methods for the preparation of salt-free ylide solutions, such as the sodium amide... 

In contrast, Sr(NCS)2(HMPA) and SrIjIHMPA) were not prepared by dissolution of their respective anhydrous salts by base, but rather by reaction of NH4X (X = SCN or 1) with Sr metal in the presence of base. The main advantage of this method is that it yields anhydrous compounds. In addition, this method is useful in the preparation of salt adducts when the dissolution method fails for kinetic reasons (i.e., when the metal coordination sites of [MX2l are inaccessible to the base). 

Several preparations of salts of the czs-dinitrobis(ethyl-enediamine)cobalt(III) ion have been reported in the literature. The most usual is that of Werner/ modified by Holtzclaw, Sheetz, and McCarty, beginning with potassium hexanitrocobaltate(III). However, this method makes use of a starting material which is difficult to prepare in high purity and to dry thoroughly, involves critical temperature control, and produces a yield of about 15%. The following procedure, which utilizes ethylenedi-amine)cobalt(III) chloride as the starting material, provides a 60% yield of cfs-dinitrobis(ethylenediamine)cobalt-(III) nitrite. The nitrite is then easily converted to the nitrate. 

Benzisoselenazoles 2 were prepared, in a similar manner to isoselenazoles, by the addition of bromine followed by ammonia to 2-(methylselanyl)benzaldehydes or 2-(methylselanyl)phenyl ketones 97 <1973JHC267>. When the aldehyde 97 (R= H) was treated with ethyl carbamate and then with bromine, A -acyl benzisoselenazolinium salt 6 (R = H) was produced. The alternative method for preparation of salt 6 is based on the A -acylation of benzisoselenazoles 2 with ethyl chloroformate (Scheme 34) <1989BSB395>. 

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