Handbook of Inorganic Chemicals
Hydrogen chloride, HCl, is a colorless, fuming, highly toxic gas that is soluble in water, alcohol, and ether. It is used in polymerization, isomerization, and the synthesis of vinyl chloride and alkyl chloride.
Hydrochloric acid is one of the most important industrial chemicals and has numerous applications. Both anhydrous hydrogen chloride and aqueous acid are used to produce a large number of chloride salts. The acid also is a common laboratory reagent. Some major applications of hydrochloric acid include processing of ores and extraction of metals from their minerals; in metal cleaning, particularly in steel pickling to dissolve oxide impurities; production of alumina, titanium dioxide, and other metal oxides by various hydrometallurgical processes; production of hydrogen; synthesis of chlorine dioxide; removal of heavy metal impurities from carbon black; activation of bentonite clays; etching of concrete surfaces for finishing operations; and as a catalyst in several organic reactions such as inversion of sugar, hydrolysis of starch to obtain sugar syrup, and esterification of aromatic acids.
Anhydrous hydrogen chloride gas is used to produce phosphonium chloride, PH4Cl, which is a flame retardant for cotton textiles. Other major applications include manufacture of a number of high purity metal chlorides, ammonium chloride, chlorosulfuric acid; recovery of waste metals; preparation of alkyl chlorides and chloroacetic acids; and as a chlorinating agent in organic syntheses.
In the production of chlorides; refining ore in the production of tin and tantalum; for the neutralization of basic systems; as laboratory reagent; hydrolyzing of starch and proteins in the preparation of various food products; pickling and cleaning of metal products; as catalyst and solvent in organic syntheses. Also used for oil- and gas-well treament and in removing scale from boilers and heat-exchange equipment. Pharmaceutic aid (acidifier).
Air & Water Reactions
Fumes strongly in moist air. Soluble in water with evolution of heat.
ChEBI: A mononuclear parent hydride consisting of covalently bonded hydrogen and chlorine atoms.
ANHYDROUS HYDROGEN CHLORIDE is an anhydrous (no water) strong acid. Reacts rapidly and exothermically with bases of all kinds (including amines and amides). Reacts exothermically with carbonates (including limestone and building materials containing limestone) and hydrogen carbonates to generate carbon dioxide. Reacts with sulfides, carbides, borides, and phosphides to generate toxic or flammable gases. Reacts with many metals (including aluminum, zinc, calcium, magnesium, iron, tin and all of the alkali metals) to generate flammable hydrogen gas. Reacts violently with acetic anhydride, 2-aminoethanol, ammonium hydroxide, calcium phosphide, chlorosulfonic acid, 1,1-difluoroethylene, ethylenediamine, ethyleneimine, oleum, perchloric acid, b-propiolactone, propylene oxide, silver perchlorate/carbon tetrachloride mixture, sodium hydroxide, uranium(IV) phosphide, vinyl acetate, calcium carbide, rubidium carbide, cesium acetylide, rubidium acetylide, magnesium boride, mercury(II) sulfate [Lewis]. Undergoes a very energetic reaction with calcium phosphide [Mellor 8:841(1946-1947)]. Corrosive to metals and tissues and irritating to the eyes and respiratory system. Corrodes galvanized or copper-alloy metals (brass, bronze); fittings of stainless steel or mild or cast steel must therefore be used. Reacts with calcium carbide with incandescence [Mellor 5:862(1946-1947]. Absorption on mercuric sulfate becomes violent at 125°C. [Mellor 2, Supp. 1:462(1956)].
Pass it through conc H2SO4, then over activated charcoal and silica gel. It fumes in moist air. Hydrogen chloride in gas cylinders contains ethylene, 1,1-dichloroethane and ethyl chloride. The latter two may be removed by fractionating the HCl through a trap cooled to -112o. Ethylene is difficult to remove. HCl fumes in moist air. HARMFUL VAPOURS. Its solubility in H2O is 82% at 0o. A constant boiling aqueous solution (azeotrope) has b 108.6o/760mm with an HCl concentration of ~20%, and is called Hydrochloric acid (muriatic acid) (see above). [Schmeisser in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 280-282 1963.]
Basilus Valentinus of Italy was first to isolate the acid and reported it under the name spiritus salis in the fifteenth century. Glauber prepared this acid by the reaction of sulfuric acid with common salt in 1648. Lavoisier proposed the name muriatic acid in 1789 after muriate, the term referring to a chlorine-containing inorganic substance. Sir Humphrey Davy proved the gas was composed of only hydrogen and chlorine in 1810. Subsequently, the gas was named hydrogen chloride.
Dilute hydrochloric acid occurs in the stomachs of mammals. Gaseous hydrogen chloride occurs in trace concentrations in the atmosphere.
Fire may produce irritating or poisonous gases. Containers may explode in heat of fire. At high temperatures, Hydrochloric acid decomposes into hydrogen and chlorine. The following materials should be avoided: Mercuric sulfate -- violent reaction with gaseous hydrochloric acid at 250F. Sodium -- reacts vigorously with gaseous hydrochloric acid. Acetic anhydride, 2-aminoethanol, ammonium hydroxide, chlorosulfonic acid, ethylene diamine, ethyleneimine, oleum, propiolactone, sodium hydroxide, sulfuric acid, and vinyl acetate -- increase in temperature and pressure when mixed with hydrochloric acid. Calcium phosphide -- energetic reaction with hydrochloric acid. Silver perchlorate and carbon tetrachloride -- when mixed in combination with hydrochloric acid forms a compound that detonates at 105F. Formaldehyde -- when mixed with hydrochloric acid forms a human carcinogen. Material reacts violently with bases and is corrosive with the generation of heat. Reacts with base metals, forming combustible gas (hydrogen). Reacts violently with strong oxidants forming toxic gas (chlorine). Avoid heat; at high temperatures Hydrochloric acid will decompose into hydrogen and chlorine.
Gas concentrations of 50 to 100 ppm are tolerable for 1 hour. Concentrations of 1,000 to 2,000 ppm are dangerous, even for brief exposures. More severe exposures will result in serious respiratory distress and prolonged exposures will result in death. Mists of hydrochloric acid are considered less harmful than anhydrous hydrochloric acid, because droplets have no dehydrating action. Individuals with respiratory problems and digestive diseases may be adversely affected by low level exposures to the gas or mist.
Hydrochloric acid can be produced by several methods. It is obtained from the reaction of sodium chloride and sulfuric acid in a cast iron retort at elevated temperature. Although reaction starts at 150°C, the complete reaction occurs at about 600°C:
2NaCl + H2SO4→ Na2SO4 + 2HCl
Hydrochloric acid also is made by the Hargreaves process in which a mixture of salt, sulfur dioxide, oxygen, and water are heated at elevated temperatures, between 430 to 540°C. The reaction is exothermic and becomes selfsustaining:
4NaCl + SO2 + O2 + 2H2O→ 2Na2SO4 + 4HCl
Hydrochloric acid may be produced by hydrolysis of metal chlorides such as titanium(IV) chloride:
TiCl4 + 2H2O →TiO2 + 4HCl
High purity HCl for commerce is made directly from hydrogen and chlorine:
H2 + Cl2→ 2HCl
The above reaction is highly exothermic. The stoichiometric proportion of gaseous mixture at equilibrium flame temperature is cooled to 200°C, whereupon the elements combine rapidly to form HCl with over 99% yield.
HCl also may be prepared by several other methods including thermal dissociation of aluminum chloride hexahydrate, AlCl3•6H2O, and as a by-product of manufacturing many organic compounds.
Crude HCl gas mixture may be purified by cooling and drying over concentrated sulfuric acid, which also removes organic unsaturated contaminants.
Organic contaminants may be removed further by adsorption over molecular sieves, polystyrene foam, active carbon, or scrubbing with a high-boiling point organic liquid.
Commercial grade, concentrated hydrochloric acid is about 37.5% HCl by weight and has a normality of 12 and specific gravity 1.19.
Hydrogen chloride gas may be stored in steel cylinders free of contaminants. Monel, pure nickel, or its alloy, inconel, may also be used for storage and transportation up to 500°C. Hydrochloric acid may be stored in glass bottles or in containers made up of tantalum or tantalum-molybdenum alloys, or other alloys of zirconium, molybdenum, and tungsten.