Hydrohalogen acids

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. 

Health and Safety. Halosilane vapors react with moist air to produce the respective hydrohalogen acid mist. Federal standards have not set exposure to halosilanes, but it is generally beheved that there is no serious risk if vapor concentrations are maintained below a level that produces an irritating concentration of acid mist. The exposure threshold limit value (TLV) for HCl is 5 ppm, expressed as a ceiling limit. Because most people experience odor and irritation at or below 5 ppm, HCl is considered to have good warning properties. 

In complexing acid media (e.g. hydrohalogenic acids HX) the reduction of pertechnetate ions proreeds in a different way. In the works [11,13,15] it was shown that such a reduction occurred according to the scheme (1). 

A number of studies [42,43,52,114] have shown that [TcX6]2 " entered into reduction reactions more readily in hydrohalogenic acids at a concentration of 4-7 M than in concentrated hydrohalogenic acids. It was assumed [9,11,52] that the reduction of [TcC16]2 was promoted by their acidic hydrolysis (anation reaction) (2). 

The stability of the [Tc2X8]3 ions forming in hydrohalogenic acids is determined by the sum of the competing processes (5-7) [80,87]. 

The cluster formation reactions considered in this review occur in technetium-concentrated solutions of hydrohalogenic acids. From comparison of the data reported in [9,11,44,49,50,53,68,72,73,75,76,118] it follows that the ions [Tc2X6]2b (X = Cl,Br) are immediate precursors to polynuclear technetium... 

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 acid constants of the hydrohalogenic acids are discussed in Appendix XI. 

The strength of an acid in aqueous solution depends upon the difference in free energies of the hydrated ions and the undissociated molecules. Each of these free-energy terms is affected by the electronegativity of the halogen atom, and analysis of the problem shows that it is not unreasonable for hydrofluoric acid to be weaker than the other hydrohalogenic acids.1... 

This general reaction allows the conversion of a halogen group to an ester group without the evolution of hydrohalogen acid and therefore without the corrosion problem that would attend such evolution. The reaction is particularly useful for changing organosilicon halides to esters in order to separate them more easily. 

Problem 6.23 Arrange the following alkenes in order of increasing reactivity on addition of hydrohalogen acids a) H2C=CH2, (b) (CH3)2C=CH2, (r) CH3CH=CHCH,. ... 

Pyrolysis of chlorinated unsaturated polyhydrocarbons is in some respects similar to that of the parent polyhydrocarbon, and in some others similar to halogenated saturated hydrocarbon type polymers. The elimination of the hydrohalogenated acid takes place relatively easily, and the polymers from this class are not resistant to heating. In practice, additives that enhance the resistance to heating frequently are added. Since the elimination of the acid seems to accelerate thermal decomposition, similarly to the case of PVC, metallic oxides that scavenge the acid increase the resistance to heating. The main pyrolysis products of each polymer are not modified by the addition of these additives. 

The polymers from this group show excellent thermal stability when they do not contain hydrogens, for example, when they are perfluorinated. Compounds having both hydrogen and a halogen (such as fluorine) eliminate the hydrohalogenated acid (HF, HCI, etc.) at lower temperatures. Some literature reports on thermal decomposition for this group of compounds are indicated in Table 8.2.1 [1]. 

Water can be removed from alcohols by dehydrating agents either directly or indirectly, but the analogous removal of ammonia or an amine from primary, secondary, or tertiary amines is not generally feasible. The latter type of reaction succeeds only in individual cases when, occasionally, an olefin is formed by loss of, e.g., ammonium chloride from the salt of an amine with a hydrohalogen acid ... 

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