Hydrogen halide salts

A simple and atom-economical synthesis of hydrogen halide salts of primary amines directly from the corresponding halides, which avoids the production of significant amounts of secondary amine side products, has been described by researchers from Bristol-Myers Squibb [227]. Microwave irradiation of a variety of alkyl halides or tosylates in a commercially available 7 m solution of ammonia in methanol at 100-130 °C for 15 min to 2.5 h followed by evaporation of the solvent provided the corre-... 

Oxo-3,4-dihydro-2//-pyrido[l,2-ci]pyrimidines (142) and their hydrogen halide salts can be prepared by reacting 2-aminopyridine or methyl-substituted 2-aminopyridines with alkyl 3-halopropionates,20,196-200 3-halopropionic acids,200-203 or alkyl acrylates18,20 197,204 205... 

Here, we restrict attention to ring-halogenated compounds as opposed to any hydrogen halide salts, dihalogen complexes, or even N-halogenated species. 

In the solid state though not in solution, the halide ions in the hydrogen halide salt of ll,12-bis(diethylaminomethyl)-9,10-dihydro-9,10-ethenoanthracene are observed to cause heavy atom effects. 

The solubilities of inorganic substances in HF resemble those in water, with some marked differences. Most elements are not dissolved, except the active metals, which react with evolution of hydrogen gas. Alkali metal and some alkaline earth salts are soluble, but many react liberating weaker acids in solution. Alkali metal halides evolve the nearly insoluble hydrogen halides. Salts of transition metals are at most... 

Gattermann s reaction A variation of the Sandmeyer reaction copper powder and hydrogen halide are allowed to react with the diazonium salt solution and halogen is introduced into the aromatic nucleus in place of an amino group. 

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... 

It is not difficult to incorporate this result into the general mechanism for hydrogen halide additions. These products are formed as the result of solvent competing with halide ion as the nucleophilic component in the addition. Solvent addition can occur via a concerted mechanism or by capture of a carbocation intermediate. Addition of a halide salt increases the likelihood of capture of a carbocation intermediate by halide ion. The effect of added halide salt can be detected kinetically. For example, the presence of tetramethylammonium... 

Wastewater occasionally contains hydrogen sulfide and nitrites. These contribute to higher halogen demands. Many of these reactions reduce halogens to halide salts. 

In the following procedure, use is made of the basic character of epoxides. In the presence of phosphonium salts, ethylene oxide removes hydrogen halide and the alkylidenetriphenylphosphorane is produced. If a suitable carbonyl compound is present in the reaction mixture, its reaction with the in situ generated phosphorane proceeds readily to give the Wittig product. 

As a consequence of facile homolytic cleavages, sulfonyl halides (I > Br > Cl F unsuitable) are able to add to unsaturated C—C systems. To prevent (or reduce) competing polymerizations, the additions of sulfonyl chlorides have been recommended to be carried out in the presence of copper(I/II) salts (Asscher-Vofsi reaction ). Comprehensive surveys have been published on the resulting j8-halogeno sulfones (or their vinyloguous compounds) as well as on their dehalogenation products (vinyl sulfones, 1-sulfonyl-l, 3-dienes, etc.). Table 5 reviews a series of sulfonyl halide additions and facile hydrogen halide eliminations. 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

There are many ways in which the hydrogen halides can be prepared. Heating a salt containing the halide ion with a nonvolatile acid is the usual way in which HF, HC1, and HBr are obtained in laboratory experiments. 

The reactions of the halide salts, in the solid state, with concentrated sulphuric acid vary in relation to the reducing power of the hydrogen halides produced. 

The cross-coupling alternative yields halide salts as co-products. During the preparation of aryl halides from the aromatic ring and dihalogen also one equivalent of halide salt is produced and thus there is further room for improvement if we could directly substitute a hydrogen atom by the hetero atoms mentioned ... 

By far the most common method for preparation of amides is the reaction of ammonia or a primary or secondary amine with one of the reactive reagents described in Section 3.4.1. When acyl halides are used, some provision for neutralizing the hydrogen halide is necessary, because it will otherwise react with the reagent amine to form the corresponding salt. Acid anhydrides give rapid acylation of most amines and are convenient if available. The Schotten-Bauman conditions, which involve shaking an amine with excess anhydride or acyl chloride and an alkaline aqueous solution, provide a very satisfactory method for preparation of simple amides. 

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