Properties of Hydrochloric Acid

Hydrochloric Acid. — It was shown in Exp. 19 that hydrochloric acid contains hydrogen, and in Exp. 56 that it contains chlorine. These results should be verified by a synthesis of the acid. It will first be necessary, hcweyer, to know the characteristic properties of hydrochloric acid, so that the product of the synthesis may be readily recognized. It should be remembered that hydrochloric acid, as we have used it, is a water solution of the gas, and that the same term, hydrochloric acid, includes both the gas and its solution. 

Experiment 59. — Heat a little concentrated hydrochloric acid in a test tube, and observe the white fumes and pungent odor. The gas is so soluble in water that it draws the moisture from the air, forming thereby dense white fumes. Try the action of the gas on moistened litmus paper and on a burning match. Moisten a glass rod with ammonium hydroxide, hold it near the mouth of the test tube, and note the striking re.sult. This is a confirmatory test for hydrochloric acid gas, and should always be used to verify its presence. Summarize the characteristic properties of hydrochloric acid gas. 

TABLE XXXVn. THEBMAL PROPERTIES OF HYDROCHLORIC ACID... 

What elements changed places (5) What property of hydrochloric acid made the completion of the reaction possible ... 

The characteristic property of aliphatic nitrocompounds of the type RCHiKOj and RjCHNO, is that they are pseiido cids, I. e., whereas they are neutral in the normal form (A), they are able by tautomeric change under the influence of alkali to give the acidic hydroxy form (B) which thus in turn gives the sodium salt (C). When this sodium salt is treated with one equivalent of hydrochloric acid, the acid form (B) is at once regenerated, and then more slowly reverts to the more stable normal form (A). 

A further crystallisation from 15 ml. of hydrochloric acid gives the sulphonic acid, 5 5 g., m.p. 105°, almost devoid of deliquescent properties. 

The above simple experiments illustrate the more important properties of aliphatic acid chlorides. For characterisation, the general procedure is to hydrolyse the acid chloride by warming with dilute alkali solution, neutralise the resulting solution with dilute hydrochloric acid (phenol-phthalein), and evaporate to dryness on a water bath. The mixture of the sodium salt of the acid and sodium chloride thus obtained may be employed for the preparation of solid esters as detailed under Aliphatic Acids, Section 111,85. The anilide or p-toluidide may be prepared directly from the acid chloride (see (iii) above and Section III,85,i). 

Heating of the cyclic polymer at 250°C will also lead to the production of the linear polymer, which is rubbery and stable to 350°C. On standing, however, the material hydrolyses and after a few day loses its elastic properties and becomes hard and covered with drops of hydrochloric acid solution. 

However they are formed, and from whatever source, aqueous ions are individual species with properties not possessed by the materials from which they came. Furthermore, the properties of a particular kind of ion are independent of the source. Chloride ions from sodium chloride, NaClfsJ, have the same properties as chloride ions in an aqueous solution of hydrochloric acid, HQ. In a mixture of the two, all of the chloride ions act alike none remembers whether it entered the solution from an ionic NaQ lattice or from a gaseous HC1 molecule. 

The theory of electrolytic dissociation was not immediately recognized universally, despite the fact that it could qualitatively and quantitatively explain certain fundamental properties of electrolyte solutions. For many scientists the reasons for spontaneous dissociation of stable compounds were obscure. Thus, an energy of about 770kJ/mol is required to break up the bonds in the lattice of NaCl, and about 430kJ/mol is required to split H l bonds during the formation of hydrochloric acid solution. Yet the energy of thermal motions in these compounds is not above lOkJ/mol. It was the weak point of Arrhenius s theory that this mismatch could not be explained. 

D-Glucosone (XII), prepared from D-glucose phenylosazone (XI) by the action of concentrated hydrochloric acid, is treated in aqueous solution with potassium cyanide. The imino-D-glucoascorbic acid (XIV) which readily separates shows many of the properties of ascorbic acid. Thus it shows a strong selective absorption band in the ultra-... 

The esters of nitrous acid are characterised by their high velocities of formation and hydrolysis. They are almost instantaneously decomposed by mineral acids and in the method of preparation given this has been taken into account. The slightest excess of hydrochloric acid must be avoided. Advantage is taken of this property of the alkyl nitrites in all cases where it is desired to liberate nitrous acid in organic solvents (in which metallic nitrites are insoluble). Examples addition of N203 to olefines, preparation of solid diazonium salts (p. 286), production of isonitroso-derivatives from ketones by the action of HN02. This synthesis is often also carried out in the manner of the acetoacetic ester synthesis, with ketone, alkyl nitrite, and sodium ethylate the sodium salt of the isonitrosoketone is formed (cf. in this connexion p. 259) ... 

The property of being converted by energetic reduction into primary amines belongs to the nitro-compounds both of the aliphatic and of the aromatic series. Six atoms of hydrogen are required for the reduction of each nitro-group. In industry nitrobenzene is reduced, not with expensive tin, but with iron filings or iron powder according to the old method of Bechamp, which is still in use at the present time. The amount of hydrochloric acid indicated by the equation... 

Another chlorinated compound which, like vinyl chloride, is used only in its polymeric form, is chloroprene (2-chloro-l,3-butadiene), which is polymerized to make neoprene, first produced in 1940. As far as is known (17) y the monomer is made commercially only from acetylene via addition of hydrochloric acid to monovinylacetylene in the presence of cuprous chloride, but syntheses from butylenes or butadiene have been described. The production of chloroprene exceeded 100,000,000 pounds per year at the wartime peak and has been somewhat lower since then, but in view of the many valuable properties of the neoprene rubber it will continue to be important. 

Constitution.—Hypochlorous acid, HOC1, is a very weak acid despite the presence of the non-metal chlorine, which gives to hydrochloric acid, HC1, such powerful acidic properties. D. Vorlander,15 therefore, assumed that the constitution is not H.C1 0, since such an acid would have a strength comparable with that of hydrochloric acid he considers that the chlorine of hypochlorous acid is polyvalent and unsaturated, and accordingly writes the formula HO.Cl. This, says he, is in accord with (i) its feeble acidic properties (ii) its ready oxidizibility to chloric acid and (iii) the ease with which it is decomposed—particularly into Cl and OH. The relation between water, hypochlorous acid, and chlorine monoxide is graphically shown by the formula ... 

In the description of the properties of selenious acid it was mentioned that the acid is reduced by sulphurous acid in the presence of hydrochloric acid. In the absence of hydrochloric acid the separation of selenium may be far from complete or even entirely lacking, on account of the formation of selenotrithionic acid.2... 

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