Ammonium halide route

The major previously used routes to the higher cages (i.e. where n > 4) involved elimination reactions between aluminium alkyls and primary amines or the reaction of an aluminium hydride species, e.g.. MesN AlHs orLiAlH4 with primary amines or primary ammonium halides. A number of other routes had also been used among which was the reaction between a nitrile and aluminium hydride, Equation (8.7). 

Anhydrous lanthanide halides are ionic substances with high melting points which take up water immediately when exposed to air to form hydrates (r>Br >Ch) [48]. Straightforward synthetic access and a favorable complexation/solva-tion behavior make the lanthanide halides the most common precursors in organolanthanide chemistry. Many important Ln-X bonds (X=C, Si, Ge, Sn, N, P, As, Sb, Bi, O, S, Se, Te) can be generated via simple salt metathesis reactions [4,8]. The so-called ammonium chloride route either starting from the lanthanide oxides or... 

A common and most easily to foUow way to prepare rare-earth hahdes, even in large quantities, is the so-called ammonium haUde route (Reed et al. 1939, Meyer and Ax 1982, Meyer 1989). Two steps are involved in this procedure. In the first step, the respective rare earth (most commonly the sesquioxide, R2O3) is converted into a ternary anunonium halide, (NIl4)3RX<, or (NH4)2RXs, which is, in the second step, decomposed to the respective rare-earth trihalide RX3 recovering ammonium halide (box 1). The first step may be carried out by dissolving the oxide and ammonium halide in hydochloric... 

Although anhydrous lanthanide halides have long been synthesized from oxides by the ammonium halide/hydrohahc acid route (Taylor 1962), only recently has the reaction mechanism for halide synthesis been established definitively. 

When it is not possible to produce the desired anion directly from the quaternization reaction (Step I), two other different routes are possible (Scheme 2.15). An ammonium halide [R R3N] X can for example be treated with a Lewis acid MXy to give the ionic liquid [R RsN] [MXy+i] (Step Ila). The halide ion X can alternatively, (Step Ilb) be exchanged with the desired anion by either addition of a metal salt M [A] over an ion exchanger, or removal of the halide ion using a strong acid H [A] (Scheme 2.15). 

The oxidation of NH3 to NH2OH forms the basis of a process for the ammoximation of cyclohexanone to the oxime because the NH2OH formed in solution readily reacts with the ketone (non-catalytically) to give the oxime (231). Table XXX (165) illustrates the conversions and selectivites obtained for a few typical ketones and aldehydes. The ammoximation of aldehydes is faster than that of ketones. The oxime selectivity is also higher. The ammoximation of cyclohexanone by this method offers a more eco-friendly alternative route to the cyclohexanone oxime intermediate for the production of Nylon-6. The current route coproduces large quantities of ammonium sulfate and involves the use of hazardous chemicals such as oleum, halides, and oxides of nitrogen. 

The production of a quaternary ammonium salt from a tertiary amine and an alkyl halide forms the synthetic route to decamethonium, the first of a range of synthetic muscle relaxants having an action like the natural materials found in the arrow-poison curare. Decamethonium is actually a di-quaternary salt, as are more modem analogues, such as suxamethonium. Suxamethonium superseded decamethonium as a drug because it has a shorter and more desirable duration of action in the body. This arise because it can be metabolized by ester-hydrolysing enzymes (esterases) (see also Box 6.9). 

Typical synthetic procedures include the reaction of alkyl halides with the silver salts of carboxylic acids, the reaction of carboxylate anions in alkali with an excess of a dialkyl sulphate, (especially dimethyl sulphate), and heating tertiary184 or quaternary ammonium salts of carboxylic acids. These routes are particularly valuable for the preparation of esters of seriously sterically hindered acids. For example, Fuson et al.iK made the methyl ester of 2,4,6-triethylbenzoic acid by heating the tetramethyl ammonium salt to 200-250°C, viz. 

Solvent free methods have also impacted on the preparation of other alternative reaction media. Namely, a range of ionic liquids (ILs) was prepared (including imidazolium, pyridinium and phosphonium salts) through halidetrapping anion metathesis reactions (Figure 2.17). The alkyl halide by-product was easily removed by vacuum or distillation and the products were obtained quantitatively in high purity. In addition to being solvent free, this route is more atom economic than the usual route to room temperature ionic liquids (RTILs) as it does not use silver(i), alkali metal or ammonium salts which are normally used in an anion metathesis reaction. 

Reactions of alkyl halides with diethyl phosphite in the presence of ammonium acetate/sulfur and acidic aluminia using microwave irradiation provide a simple and general route to thiophosphates. Two diastereoisomers of 1,3,2-dithiadiphosphetane 2-sulfide (19) have been isolated for the first time via the reaction of thioketones (20) with Lawesson s reagent (Figure 5). ... 

The achiral 14-membered trans-diimine macrocycle (f , S )-102, in the presence of trifluoroacetic acid, rearranges quantitatively into the chiral seven-membered monoimine ( )-103 (Section Ill.C.l.h)". If the rearrangement of (i , S )-102 is carried out in methanol containing a suspension of ( )-(—)-78, an orange solution is obtained from which pure [I ,(Sas,I as)] ( )-1 6 can be isolated by the addition of ammonium hexafluorophosphate. The yield of the complex was ca 50%. The addition of more acid and halide in an attempt to facilitate racemization of the free arsine and thereby promote the further crystallization of the complex by second-order asymmetric transformation was unsuccessful. Nevertheless, this highly stereoselective synthesis of [H,(Sas,IIas)] ( ) 106 is a more expedient route to (R,I )-(—)-102 than the one involving resolution of the benzyl alcohol complex (R, SA.)-(-)-92a. 

Chlorobenzene is employed in the synthesis of certain amino-containing vat dye intermediates. When reacted with phthalic anhydride, the product is 2-chloroanthraquinone, which, with ammonia, is converted readily into 2-aminoanthraquinone (61). Other routes include replacement of halogen by amino groups, with ammonia or ammonium salts of urea, and alkyl- and aryl amines to afford secondary amines. Modification of the amino group by alkylation, with dimethyl sulfate, alkyl halides or esters of toluenesul-fonic acids, is of synthetic value. Arylation of the amino groups is of importance only in the reaction between aminoanthraquinones and nitro- or chloroanthraquinones to yield dianthraquinonylamines, or anthrimides48. For example, the reaction between 62 and 63 yields 64, which can then be converted into carbazole 65, Cl Vat Brown R (Scheme 14). Amination of haloanthraquinones such as l-amino-4-bromoanthraquinone-2-sulfonic acid (bromamine acid) (66), prepared from 1-aminoanthraquinone, is of industrial use. 

Unfortunately, this route is expensive and forms a large amount of silver halide as by-product. Complete precipitation of silver halides from organic solvents can also be quite slow, leading to silver-contaminated products. The nature of the precipitate can also be troublesome in some cases the silver halide forms as submicron particles which are difficult to filter. For these reasons, the preferred and most common metathesis approach is still to carry out the reaction in aqueous solution with either the free acid of the appropriate anion, or its ammonium or alkali metal salt as described in Sect. 2.1.1. 

Primary amines can also be synthesized by alkylaton of ammonia. Haloalkanes react with amines to give a corresponding alkyl-substituted amine, with the release of a halogen acid. Such reactions, which are most useful for alkyl iodides and bromides, are rarely employed because the degree of alkylation is difficult to control. If the reacting amine is tertiary, a quaternary ammonium cation results. Many quaternary ammonium salts can be prepared by this route with diverse R groups and many halide and pseudohalide anions. 

The yield and ratio of the two Stevens rearrangement products are dependent on both the base and the solvent however, the ortho-rearrangement product was only detected when butyllithium was used in hexane. Variation of the halide ion had only a small effect on the ratio of rearrangement products. Several mechanisms were considered 93) as routes to the formation of the rearrangement products, 1) ion-pairs, 2) cationic rearrangement, 3) carbenoid, 4) dimetallated intermediates, 5) free-radical, 6) predissociation of the ammonium salt and, 7) sigmatropic shift. 

In principle, deprotonation of any of the sulfanes gives polysulfide anions In practice, this route is not employed and rather fewer anions are known compared with the sulfanes. It was established last century that sulfur dissolves in basic media to give intensely colored (often blue) solutions. The well-known polysulfide solution [NH4]2Sjt, which contains mostly X = 4 and 5, is obtained by bubbling H2S through a suspension of sulfur in ammonium hydroxide. It is accepted nowadays that the blue coloration of many of these solutions is a consequence of the 83 radical. This species has characteristic EPR, visible, and Raman spectra that have enabled its detection in a variety of solutions including liquid ammonia,DMF, and HMPA. 82 can be introduced as an impurity into alkali metal halides. In lapis lazuli (lazurite that is made synthetically as ultramarine blue Na8[Al68i6024]8 , n = 2-4), the blue color is due to the presence of 83 radicals, which has also been identified by Resonance Raman Spectroscopy ... 

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