Hydrohalide

Except in the case of the 4,5-diphenyl derivatives, these compounds are obtained as their hydrohalide salts tvith yields of 70 to 90% the free heterocyclic base is obtained by treatment with weak alkali. 

When the preceding rules lead to inconvenient names, then (1) the unaltered name of the base may be used followed by the name of the anion or (2) for salts of hydrohalogen acids only the unaltered name of the base is used followed by the name of the hydrohalide. An example of the latter would be 2-ethyl-p-phenylenediamine monohydrochloride. 

For this reaction to proceed it is obviously necessary to remove the hydrochloric acid formed, preferably by means of hydrohalide acceptor. 

Greater success has been achieved with organic solvents which are also hydrohalide acceptors, pyridine being a specific example. 

Because of the cost of pyridine the phosgenation process may be carried out with a mixture of pyridine and a non-hydrohalide-accepting solvent for the polymer and the growing complexes. Suitable solvents include methylene dichloride, tetrachlorethane and chloroform. Although unsubstituted aromatic hydrocarbons may dissolve the solvent they are not effective solvents for the acid chloride-pyridine complexes. 

The hydrohalide is usually prepared by passing hydrogen chloride into a solution of masticated high-grade raw rubber in benzene at 10°C for about six hours. Excess acid is then neutralised and plasticisers and stabilisers are added. The benzene is removed by steam distillation and the product washed and dried. Alternatively the solution is cast on to a polychloroprene rubber belt, leaving a tough film after evaporation of the solvent. 

The hydrohalide is liable to dehydrochlorination, particularly when moist acid is used in its preparation, so that hydrochloric acid acceptors such as lead carbonate are useful stabilisers. Dibutyl phthalate and tritolyl phosphate are effective plasticisers. Rubber hydrochloride is used as a packaging film (Pliofilm) and as a rubber-to-metal bonding agent (e.g. Typly). 

The compounds B2X4 are spontaneously flammable in air and react with H2 to give BHX2, B2H6 and related hydrohalides they form adducts with Lewis bases (B2CI4L2 more stable than B2F4L2) and add across C-C multiple bonds, e.g. 

In contrast to aromatic halonitro compounds, selective removal of halogen in aliphatic halonitro compounds presents little problem. The reaction can be done by hydrogenation over palladium-on-carbon in the presence of a hydrohalide acceptor 46,73). 

The scope of the reactions of phosphazenes with alkyl halides and, subsequently, water, as a preparative route to secondary amines (as their hydrohalides) has been investigated ... 

Amine-phosphorus halide reactions involve hydrogen halide (or amine hydrohalide) formation. They can be complicated through acid catalysis or side reactions. Thus, the possible formation of skeletally stabilized products through transamination reactions in which no hydrohalide products are obtained is of interest. 

Condensations of amine hydrohalides with potassium thiocyanate (KSCN) provide both the primary thioureas and symmetrical 7V,7V -disubstituted thioureas. Selectivity in the product was achieved by changing the concentration of KSCN as shown in the diagram (Scheme 50).131... 

The oxides have been converted to the trihalides by reaction with amine hydrohalides with mp <200°C (e.g., PhNH2, MeNH2, Me2NH, EtNH2, Et NH, etc.). A double salt was formed from the reaction with the hydrohalide, which served both as solvent and halogenating agent. The reaction mixture was heated to vaporize the solvent and decompose the double salt, leaving the anhydrous halide (85). 

Although the synthesis is completed in very few steps, oxidation of 1,4-xylene to the corresponding terephthalic acid does not afford a uniform product. Partial dihalogenation gives rise to side products. The condensation reaction requires two equivalents of arylamine per halogen atom. One equivalent is needed to neutralize the generated hydrohalogen acid, which is subsequently separated as aryl-amine-hydrohalide and recycled as hydrohalide and arylamine. 

The catalytic effect of quaternary ammonium salts in the basic liquid liquid two-phase alkylation of amines [1-3] is somewhat unexpected in view of the low acidity of most amines (pKfl>30). Aqueous sodium hydroxide is not a sufficiently strong base to deprotonate non-activated amines in aqueous solution and the hydroxide ion is not readily transferred into the organic phase to facilitate the homogeneous alkylation (see Chapter 1). Additionally, it is known that ion-pairs of quaternary ammonium cations with deprotonated amines are decomposed extremely rapidly by traces of water [4]. However, under solidrliquid two-phase conditions, the addition of a quaternary ammonium salt has been found to increase the rate of alkylation of non-activated amines by a factor of ca. 3-4 [5]. Similarly, the alkylation of aromatic amines is accelerated by the addition of the quaternary ammonium salt the reaction is accelerated even in the absence of an inorganic base, although under such conditions the amine is deactivated by the formation of the hydrohalide salt, and the rate of the reaction gradually decreases. Hence, the addition of even a weak base, such as... 

Hofmann rearrangement org chem A chemical rearrangement of the hydrohalides of N-alkylanilines upon heating to give aminoalkyl benzenes. haf man. res ran)-mont ... 

Alkylation of 2-amino-5-(alkyl, aryl, hetaryl)-l,3,4-oxadiazoles is said to occur at the ring N atom (N-3) (94HOU526), but this report remains doubtful. In addition, as others have pointed out, the very low basicity of imidazo[2,l-b][l,3,4]oxadiazoles precludes the isolation of hydrohalides of type 20. 2,6-Diaryl-imidazo[2,l-ft][l,3,4]oxadiazoles 22 can be obtained directly by treatment of 2-amino-5-aryl-l,3,4-oxadiazoles 21 with phenacyl-bromides in ethanol [reflux in a water bath at 70°C ( ) for 5 h] (84MI1). 

Only a few reactions of imidazo[2,l-h][l,3,4]oxadiazoles have been reported. The basicity of these compounds is rather low hydrohalides cannot be isolated (69ZC337). Protonation of 23 with strong acids occurs at position 7, giving, for example, 24 (mp 212°C with explosion ). With aqueous base 24 is converted back to 23 (72BSF3968). On alkylation of 23 the quaternary salts 25 are obtained (72BSF3968). Reaction of 25 (R = Et) with ethyl cyanoacetate (Et3N/EtOH) yields 26, albeit in low yield (3.8%) (72BSF3968). 

In contrast to imidazo[2,l-h][l,3,4]oxadiazoles (see Section III), im-idazo[2,l-h][l,3,4]thiadiazoles form stable salts (hydrohalides, perchlorates, picrates, picronolates). Hydrohalides are often the primary products of the cyclization reaction. 

Kaupp et al. also exploited heterogeneous reactions with CICN and BrCN in the quantitative synthesis of cyanamides, cyanates, thiocyanates and derivatives [26]. Gaseous acids were shown to form salts with strong and weak solid nitrogen bases. Solid hydrohalides are formed quantitatively by reaction with vapours of HCl, HBr and HI the same applies to di-bases such as o-phenylen-diamines. The products are much more easily handled than when they are formed in solution. The solid products can in turn be used in reactions with gaseous acetone to form the corresponding dihydrohalides of 1,5-benzodi-azepines [27]. 

Equally important is the salt formation of solid bases with gaseous acids. An example has been cited above (30 31). This type of reaction is quite general. Strong and very weak bases react quantitatively and the gas-solid technique does not have problems with moisture. Amino acids such as L-phenylalanine, D-penicillamine (42), DL-penicillamine, L-cysteine, L-leucine, L-proline, DL-ty-rosine and others are quantitatively converted into their hydrohalides with... 

Methyl-1,2,4-triazolo[ 1,5-a]pyrimidin-7-on is amphoteric and can be titrated with perchloric acid in glacial acetic acid (61JOC3834). Some derivatives form isolable hydrohalides (75PHA134). Glier et al. (72T5789) formulated a cationic structure at pH 1 from the UV spectrum contrary to that of Hill et al. (61JOC3834). 

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