Acids Halogens

The halogen acids, of course, bear the same relation to the halogen aldehydes and the halogen alcohols (halogen hydrines) that unsubstituted acids do to the unsubstituled aldehydes and alcohols. That is, they are the direct oxidation products. 

This reaction of oxidation often takes place, as has been referred to in the case of tri-chlor aldehyde, or chloral, which yields tri-chlor acetic acid on oxidation. But this is not the ordinary method of preparation of the halogen acids. The commoh method of preparing these compounds is by the direct halogenation of the acids themselves. 

Halogenation of Acids.—Several facts are of especial importance in connection with the halogenation of the saturated acids. In most cases the introduction of the halogen element into the acid takes place with comparative ease. It may be by the direct action of the halogen. 

The bromine then acts directly upon the acid bromide forming brom acetyl bromide, which, by the action of water, is hydrolyzed yielding brom acetic acid, as follows  

By the method of halogenation just described the halogen always enters the alpha position. In the case of isomeric branched chain compounds, in which the alpha carbon has no remaining hydrogen atom united to it, direct substitution does not take place. To form halogen acids from acids of this character other methods of preparation must be employed. 

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Strictly speaking the alkyl halides are esters of the halogen acids, but since they enter into many reactions (t.g., formation of Grignard reagents, reaction with potassium cyanide to yield nitriles, etc.) which cannot be brought about by the other eaters, the alkyl halides are usually distinguished from the esters of the other inorganic acids. The preparation of a number of these is described below. 

The a-halogenated acids or their esters (105) also react with thiourea to give 2-amino-4-hydroxythiazoles (106a) or their 2-amino-4-thiazolone (106b) (1, 247, 254, 530) or 2-imino-4-oxathia2olidine (106c) tautomers (Scheme 47). 

The most important of the halogenated derivatives of acetic acid is chloroacetic acid. Fluorine, chlorine, bromine, and iodine derivatives are all known, as are mixed halogenated acids. For a discussion of the fluorine derivatives see Fluorine compounds, organic. 

Reaction with Other Inorganic Halogen Compounds. Anhydrous HCl forms addition compounds at lower temperatures with halogen acids such as HBr and HI, and also with HCN. These compounds are stable at room temperature. 

Halogen acids and strong organic acids, such as tynitrobenzoic acid and tricliloroacetic acid, fomi ciy staUine salts (4), witli alkanolamines. 

Reaction with Organic Compounds. Aluminum is not attacked by saturated or unsaturated, aUphatic or aromatic hydrocarbons. Halogenated derivatives of hydrocarbons do not generally react with aluminum except in the presence of water, which leads to the forma tion of halogen acids. The chemical stabiUty of aluminum in the presence of alcohols is very good and stabiUty is excellent in the presence of aldehydes, ketones, and quinones. 

Displacement of the hydroxyl group is exemplified by the production of isopropyl haUdes, eg, isopropyl bromide [75-26-3] by refluxing isopropyl alcohol with a halogen acid, eg, hydrobromic acid [10035-10-6] (12). 

Tin does not react directly with nitrogen, hydrogen, carbon dioxide, or gaseous ammonia. Sulfur dioxide, when moist, attacks tin. Chlorine, bromine, and iodine readily react with tin with fluorine, the action is slow at room temperature. The halogen acids attack tin, particularly when hot and concentrated. Hot sulfuric acid dissolves tin, especially in the presence of oxidizers. Although cold nitric acid attacks tin only slowly, hot concentrated nitric acid converts it to an insoluble hydrated stannic oxide. Sulfurous, chlorosulfuric, and pyrosulfiiric acids react rapidly with tin. Phosphoric acid dissolves tin less readily than the other mineral acids. Organic acids such as lactic, citric, tartaric, and oxaUc attack tin slowly in the presence of air or oxidizing substances. 

Halogenation. Halogens and halogen acids add readily to the unsaturated carbon linkages of the cyclopentadiene molecule. By such additions a series of halogenated derivatives range, in the case of the chloride, from 3-chlotocydopentene to tetrachlorocyclopentane. Of all the possible chloto derivatives of CPD, only hexachlorocyclopentadiene [77-47-4] ever reached commercial status. It was used as an insecticide, but this use has been discontinued because of its toxicity (see Chlorocarbons and chlorohydrocarbons, toxic aromatics). It can be prepared by a Hquid phase chlorination of CPD below 50°C (29). 

In an analogous manner, DCPD reacts with alcohols and phenols to form ether derivatives, and with halogen acids, thiocyanic acid, and various carboxyhc acids to form esters. These esters are used as perfume components (67). Dicyclopentadiene alcohol and a number of the ethers, esters, and glycol adducts have been claimed as coal and ore flotation aids (68). 

The halogen acids also produce alkyl hahdes. 

Test on gases evolved during combustion of materials from cables Determination of the amount of halogen acid gas BS 6425-1/1990... 

Fig. 1 Schematic diagram of a chromatogram of halogen acids and halogen oxyacids Chloride (1), chlorate (2), perchlorate (3), bromide (4), bromate (5), iodide (6), iodate (7).

Annotinine, C gHjjOjN, (1). M.p. 232° perchlorate, m.p. 267°. In a later paper (1947) Manske and Marion record the results of the action of alkali and of halogen acids on annotinine, and of the oxidation of the base and discuss the reaction products. They conclude that two of the oxygen atoms are present as a lactone group and that the third oxygen may form an ether bridge in a 5- or 6-membered ring. 

It was pointed out earlier that the low nucleophilicity of fluoride ion and its low concentration in HF solutions can create circumstances not commonly observed with the other halogen acids. Under such conditions rearrangement reactions either of a concerted nature or via a true carbonium ion may compete with nucleophilic attack by fluoride ion. To favor the latter the addition of oxygen bases, e.g., tetrahydrofuran, to the medium in the proper concentration can provide the required increase in fluoride ion concentration without harmful reduction in the acidity of the medium. 

However, in the case of a-substituted unsaturated esters (4), as for example methacrylic or tiglic acid esters, diazomethane addition results in the formation of stable A pyrazolines (5). The latter products require halogen acids for conversion to the isomeric nonconjugated A -pyrazolines (6). 

The authors found that on elimination of the halogen acid from this compound, rhodinol, and not citronellol, is regenerated, dextro-rhodinol from dextro-citroneUol, and laevo-rhodinol from the laevo-rotatory alcohol from oil of rosesior geranium, the two bodies, in the latter case being identical. 

Fig. 2-4. The enantiomeric separation of a-hydroxy/halogen acids on ristocetin A CSP (250 x 4.6 mm) with the same mobile phase composition methanol with 0.02 % acetic acid and 0.01 % triethylamine (v/v). The flow rate was 1.0 mL min at ambient temperature (23 °C).

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