Chlorine and Hydrochloric Acid: They Touch Our Lives Daily prepared by
J. Chem. Educ. Staff CsHs + Clt benzene
Overview Chlorine and hydrochloric acid are produced industrially in huge amounts and are used in a great many products that are essential to our health, well being or convenience. However, both are health hazards if present in large enough amounts. The ultimate products from chlorine include clothing, jewelry, paints, food, paper, tires and toys. In 1975, 11million tons of chlorine and 2.4 million tons of hydrochloric acid were produced in the U.S. About half of the chlorine produced each year is used to make organic chemicals (including pesticides, pharmaceuticals, refrigeration fluids and fireproofing agents), about 20 percent of it is used to make plastics, resins (film formers, as in varnishes) and fibers (including polyvinyl chloride plastics and acrylic fibers). Some chlorine is used to extract copper, zinc, lead, nickel, gold, and platinum from their ores. The rest is used in bleaches for paper and textiles, in purifying water and treating sewage, and to prepare inorganic chemicals. The per capita consumption of chlorine in the U.S. is about 45 kglpersonlyear. The largest uses of hydrochloric acid are in the metal, chemical, food and petroleum industries. Metal industries use about 47 percent, and chemical and pharmaceutical manufacturing and processing use about 33 percent of the acid produced.
Preparation of Chlorine About 95 percent of the chlorine produced comes from the electrolysis of sodium chloride (brine) solutions. The reaction can he represented by 2Nat
-
CsH&l chlorobenzene (used in dye manufacture)
Other industrial chlorine producing processes are a ) elecirolysis of potassium chloride solutions to give potassium nydroxide, hydrogen and chlorine; b) electrolysis of anhydrous nolten sodium chloride to give sodium metal and chlorine; and c) oxidation of hydrogen chloride produced when chlorine :eacts with organic chemicals. Most chlorine is packed and shipped as liquid in steel cylnders, tank cars or barges. In 1975, chlorine was manufac;wed in 67 plants in 23 of the United States.
Preparation of Hydrochloric Acid More than 90 percent of the hydrochloric acid manufac;wed is produced as a by-product in the reaction of chlorine ~ i t organic h suhstances. An example is 166 / Journal of Chemical Education
hydrochloric acid)
-
Because of its corrosive effects on metals, hydrochloric acid is stored and transported in rubber-lined steel tanks.
Organic Chemicals from Chlorine Reactions of chlorine with organic suhstances produce a large number of important chlorinated organic products. Some of these are used directly; others are converted to useful products that contain no chlorine. Important chlorinated organic suhstances are found in or used to make plastics, rubbers, dyes, high pressure lubricants, fireproofing agents for textiles and plastics, detergents, insect-, moisture-, flameand acid-proofing materials for wood, fabrics, wire and cable, herbicides, soil fumigants, refrigerants and pharmaceuticals. Specific examples of useful chlorinated organic suhstances are
H
+ 2C1- + 2H20 +Clz + Ha + 2NaOHc.,)
ITS
water to give
Other industrial processes for hydrochloric acid manufacture are Hz+ Clz 2HCI (1)
direct current
Note that both hydrogen and sodium hydroxide also are produced in this reaction. Two types of electrolytic cells are employed by industry. Both cells produce chlorine a t their modes. The cells differ in the chemical reactions occurring at their cathodes. In the diaphragm cell, water is decomposed on a steel cathode to produce hydrogen gas and hydroxide ions. In the mercury cell, sodium ions are reduced a t a mercury cathode, producing sodium atoms in a mercury amalgam. The sodium itoms then react with water to give hydrogen and sodium hydroxide. Safety and environmental problems have led to ~ncreasinguse of diaphragm rather than mercury cells in the
+ HCI (this is dissolved in
NHCOCHCI,
Chloromycetin
(has widespread antibacterial
activity)
Librium (tranquilizer)
tetrachloroethene (non-flammable dry cleaning solvent)
-. 2,4-D (herbicide)
(fumigant)
(C%-CH),
I
polyvinylchloride, PVC (plastic)
An example of the preparation of an important chlorinated organic substance is that of the refrigerant, dichlorodifluoromethane from methane. This can he represented by the reaction sequence
The chlorine oxidlzes the organic mattrr and key cumponrnts of the m~croorganisms.The taste of rhlorinared water (an be improved in some cases by adding ammonia. The reaction 2NH3 + Clp
CCb + ~ H F % CCIXFZ + 2HCI
Inorganic Chemicals from Chlorine Inorganic compounds of chlorine are used as sanitizingand disinfecting agents in municipal water supplies and swimming pools, in waste and sewage treatment, in household and commercial bleaches, as detergents for automatic dishwashers, in scouring powders, cleaners, and sanitizers. Examples of some of these substances are NaClOz sodium chlorite (bleach for paper)
NaClO ICI sodium hypochlorite iodine monochloride (disinfectantand (antiseptic) deodorant in dairies, water su~dies.sewage dispod and for households; as laundry bleach) KNsCsOaC12 Ca(C10)z potassium dichlorowxyanurate calcium hypochlorite (bleachingpowder) (scouringpowder, sanitizer, detergent)
Sodium hypochlorite, NaCIO, is prepared commercially in the reaction
-
2NaOH + Cln
NaOCl + NaCl + H20
Uses of Hydrochloric Acid The major use of this acid is in steel pickling (removing mill scale-oxide coating-from the surface of steel). In food processing industries i t is used in refining sugar, in brewing ales and beers, and in the manufacture of gelatin and sodium glutamate (a taste enhancer). It also is used to produce a great many metallic chlorides and other inorganic chemicals, including paint pigments. An important new industrial reaction of hydrochloric acid is the preparation of chloromethanes in the reaction 2CH4+ 6HC1-
2CHCh + 6Hz0 Chloroform (solvent and pharmaceutical; intermediate for refrigerants)
Chlorine in Water Purification Organic material and harmful microoreanisms not removed from municipal water supplies by coagulation, filtration and aeration can be removed by treating the water with chlorine.
-
NHzCI ehloramine (disinfectant,less objectionable than Cln)
+ NH&I
Industrial History of CI, and HCl
..
Althoueh a natent for the bleachine" annlication of chlorine was issue; in i798, large scale electrolytic production of this element was delaved nearlv 100 veam until eauinment became available to proiuce the iarge amounts of direct current required. Nearly all basic discoveries and inventions related to the diaphragm and mercury-cell processes for the electrolysis of hrine that are used today were made between 1883 and 1893. Hydrogen chloride was discovered in the 15th century. Commercial production of hydrochloric acid began in England in the last half of the 18th century when legislation was passed prohibiting discharge of hydrogen chloride (a by-product in the manufacture of soda ash, Na2C03) into the atmosphere.
Safety and Health Factors Chlorine is a respiratory irritant. Its presence is readily detected by its characteristic, penetrating odor and its greenish-yellow color that is visible when high concentrations are present. When present in 1 ppm in air C12 can produce slight symptoms of irritated mucous membranes after several hours exposure. Odor is detectable when chlorine is present in 3.5 ppm; 4 ppm is the maximum that can be inhaled for one hour without serious irritation. Throat irritation occurs a t 15.1 ppm, coughing is provoked a t 30.2 ppm. At levels of 40-60 ppm, Clp is dangerous to health in 30-60 minutes; 1000 ppm is lethal. Hydrochloric acid is a strong acid. In high concentrations, it must be kept away from the eyes, nose, throat, and other sensitive tissue. A laree fraction of chlorine-containine orzanic comoounds are potentially toxic. More and more restrictions are being olaced on the uses of these substances. For examole. the use bf tetrachloroethene, the most widely used dry-cieaning solvent, may he curtailed because of its carcinogenic properties. References Kirk-othmer,"Encycbpedisofchemical T e c h n a l o ~ad , Ed.: John Wileyand sons, New York, 1978. Vol. I, pp. 799882. (21 Shreve. R.N.. and Brink, Jr., J. A.,"ChemicalPrmessIndusL~i~s,4lh Ed.."McCraw-Hill (1)
BookCo., New York. 1977,Chapters 13and 20. (3) Lorenheim,F. A.,end Moran,M. K.,"lndustrialChemicals:4thEd.. Sone. New York, 1975, pp. 24&2.53and 464461.
John Wileysnd
Dates of Fluorocarbon Aerosol Phaseout Beginning December 15, 1978, the government will prohibit the manufacture of virtually all aerosol products using chlorofluorocarbons (commonly called fluorocarbons) as propellants. Among the products affected are deodorants, anti-
for nonessenikl propellant uses in the products they regulate. On April (5,1979, thk Food and Drug Administration will stop interstate shipment of nonessential aerosol products containing fluorocarbonsthat come within its jurisdiction (roughly 85 percent). The three agencies agreed to take regulatory action in 1976. The National Academy of Sciences examined the theory that fluorocarbon gases might deplete the ozone layer in the atmosphere that protects earth from the sun's harmful ultraviolet rays. Since 1976,many manufacturers have switched to alternative types of dispensers. The amount of fluorocarbonsreleased into the atmosphere from the use of aerosols has dropped from about 511 million pounds in 1973 to about 300 million in 1977, the government estimates. Volume 55, Number 7. July 1978 / 467
