Chlorine
Chlorine is a chemical element with atomic number 17 located in the halogen group (group VIIA) of the periodic table of elements. Its symbol is Cl. Under normal conditions and in its pure state it forms dichloro: a toxic yellow-green gas formed by diatomic molecules (Cl2) about 2.5 times heavier than air, with an unpleasant and toxic odor. It is an abundant element in nature and is an essential chemical element for many forms of life.
Main features
In nature it is not found in its pure state, since it reacts quickly with many elements and chemical compounds. For this reason it is found in the composition of chlorides (especially in the form of sodium chloride), chlorites and chlorates, in salt mines and dissolved in seawater.
History
Chlorine (from the Greek χλωρος, meaning "pale green") was discovered in its diatomic form in 1774 by the Swede Carl Wilhelm Scheele, although he believed that it was a compound that contained oxygen. He got it from the following reaction:
In addition to its suffocating nature, he discovered that it discolored many vegetable pigments. Shortly after, Claude Louis Berthollet put this discovery into practice, for the bleaching of fabrics, using a solution of chlorine in water. Leonard Alban and Mathieu Vallet introduced a very important improvement, by dissolving chlorine in a solution of potash in water, which reduced the release of toxic vapors. For his part, Charles Tennant obtained calcium hypochlorite by reacting chlorine gas with solid lime. This material was more effective as a bleach, and easier to handle.
In 1810, the English chemist Humphry Davy proved that it was a chemical element, which he named chlorine because of its color. Chlorine gas was used in World War I, the first use of chemical weapons such as phosgene and mustard gas.
Abundance
Chlorine is found in nature combined with other elements, mainly forming ionic salts; as is the case of sodium and calcium chloride; also with most metals; from hafnium chloride to silver chloride. It could be said that chlorine naturally combines quite well with most elements, except with those of its group, halogens and noble gases, although in recent decades it has synthetically formed part of them in compounds known as fluorochlorides and xenon chlorides.
Finally, it should be noted that the vast majority of these compounds are usually found with impurities forming part of minerals such as carnalite, KMgCl3·6H2O.
Getting
Commercial chlorine is obtained by electrolysis in the alkali preparation process and expands in liquid form, it is not pure; and therefore, it has to be purified.
If hydrated manganese dioxide is treated with concentrated hydrochloric acid, a gas is produced largely free of impurities such as oxygen gas (O2(g)) and chlorine oxides.
Compounds
- Some metal chlorides are used as catalysts. For example, FeCl2, FeCl3AlCl3.
- Chloric acid, HCl. It is used in the food industry, metallurgy, disincrustant, cleaning products, floor polisher, crank uncoverer and pipes. The human stomach also segregates it to activate the pepsin involved in digestion.
- Hypochloric acid, HClO. It is used in water purification and one of its salts as a whitening agent.
- Plenty acid, HClO2. The corresponding sodium salt, NaClO2, is used to produce chlorine dioxide, ClO2which is used as a disinfectant.
- Cyric acid (HClO3). Sodium chlorate, NaClO3, can also be used to produce chlorine dioxide, used in paper laundering, as well as to obtain chlorate.
- Perchoric acid (HClO4). It is an oxidant acid and is used in the explosives industry. Sodium perchlorate, NaClO4is used as an oxidizer and in the textile and paper industry.
- Chlorine compounds such as chlorofluorocarbons (CFCs) contribute to the destruction of the ozone layer.
- Some organic chlorine compounds are used as pesticides. For example, hexachlorobenzene (HCB), the for-dichlorodiphenyltricchloroethane (DDT), toxaphene, etc.
- Many organochlorinated compounds present environmental problems due to their toxicity, such as pentachloroethane, previous pesticides, polychlorinated biphenyls (PCBs), or dioxins.
Isotopes
Two stable isotopes of chlorine are found in nature. One with a mass of 35 amu, and the other with a mass of 37 amu, with relative proportions of 3:1 respectively, giving an atomic weight for chlorine of 35.5 amu.
Chlorine has 9 isotopes with masses from 32 amu to 40 amu. Only three of these are found in nature: 35Cl, stable and with an abundance of 75.77%, 37Cl, also stable and with an abundance of 24.23%, and the radioactive isotope 36Cl. The ratio of 36Cl to stable Cl in the environment is approximately 700 × 10−15:1.
36Cl is produced in the atmosphere from 36Ar by interactions with cosmic ray protons. In the subsoil 36Cl is generated mainly by neutron capture processes of 35Cl, or by muon capture of 40Ca. 36Cl decays to 36S and 36Ar, with a combined half-life of 200,090 years.
The life span of this nonreactive, hydrophilic isotope makes it useful for geological dating in the range of 60,000 to a million years. In addition, large amounts of 36Cl were produced by the irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of 36Cl in the atmosphere is about a week. Thus, it is a marker for surface and groundwater from the 1950s, and is also useful for dating water that is less than 50 years old. 36Cl has been used in other areas of geological sciences, including the dating of ice and sediments.
| Núclido | Abundance | Masa | Espín | Semi-deintegration period | Disintegration product |
| 32Cl | - | 31,9857 | 1 | 642 ms | ε |
| 33Cl | - | 32,9775 | 3/2 | 2.51 s | ε |
| 34Cl | - | 33,9738 | 0 | 1.53 s | ε |
| 35Cl | 75.77 | 34,9689 | 3/2 | - | - |
| 36Cl | - | 35,9683 | 2 | 301000 a | β- |
| 37Cl | 24,23 | 36,9659 | 3/2 | - | - |
| 38Cl | - | 37,9680 | 2 | 37.2 min | β- |
| 39Cl | - | 38,9680 | 3/2 | 55.6 min | β- |
| 40Cl | - | 39,9704 | 2 | 1,38 min | β- |
| 41Cl | - | 40,9707 | n.m. | 34 s | β- |
| 42Cl | - | 41,9732 | n.m. | 6.8 s | β- |
| 43Cl | - | 42,9742 | n.m. | 3.3 s | β- |
Applications and uses
Production of industrial inputs and for consumption
The main applications of chlorine are in the production of a wide range of industrial and consumer products. For example, it is used in the manufacture of plastics, solvents for dry cleaning, degreasing of metals, production of agrochemicals, drugs, insecticides, dyes and dyes, etc.
Purification and disinfection
Chlorine is an important chemical for water purification (as in water treatment plants), in disinfectants, and in bleach. Chlorine in water is more than three times more effective as a disinfecting agent against Escherichia coli than an equivalent concentration of bromine, and more than six times more effective than an equivalent concentration of iodine.
Chlorine as an antiseptic was introduced in 1835 by Holmes (in Boston) and in 1847 by Semmelweis (in Vienna). Chlorine is used as a disinfectant in furniture, equipment, instruments, and hospital areas. Chlorine is often used in the form of hypochlorous acid to kill bacteria, fungi, parasites, and viruses in drinking water supplies and public swimming pools. In most private pools, chlorine itself is not used, but rather sodium hypochlorite, formed from chlorine and sodium hydroxide, or solid tablets of chlorinated isocyanurates. Even small water supplies are now routinely chlorinated. (See also chlorination)
It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into water, and compounds such as sodium dichloro-S-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-S-triazinetrione, sometimes referred to as "trichlor". These compounds are stable in the solid state, and can be used in powder, granular, or tablet form. When added in small amounts to swimming pool water or industrial water systems, the chlorine atoms are hydrolyzed from the rest of the molecule, forming hypochlorous acid (HClO), which acts as a general biocide, killing germs, microorganisms, algae, among others. others, hence its importance in the use in endodontics as an irrigating agent for root canals, being addressed as a solution in the form of sodium hypochlorite in different concentrations, be it 0.5% or 0.2%, the most frequently used. Chlorine is also used as a detergent for bacteria such as Bacillus repridentius or Martelianus marticus.
Chemistry
Elemental chlorine is an oxidizer. It is involved in substitution reactions, where it displaces the minor halogens from their salts. For example, chlorine gas bubbled through a solution of bromide or iodide anions oxidizes them to bromine and iodine, respectively.
Like the other halogens, chlorine participates in the radical substitution reaction with organic compounds that contain hydrogen. This reaction is frequently—but not invariably—non-regioselective, and may result in a mixture of isomeric products. Control of the degree of substitution is also often difficult, so multiple substitutions are common. If the different products of the reaction can be easily separated, for example by distillation, substitutive radical chlorination (in some cases accompanied by concurrent thermal dechlorination) may be a useful synthetic route. Some industrial examples of this are the production of methyl chloride, methylene chloride, chloroform, and carbon tetrachloride from methane, allyl chloride from propylene, and trichloroethylene and tetrachloroethylene from 1,2-dichloroethane.
As with the other halides, chlorine participates in electrophilic addition reactions, most notably, the chlorination of alkenes and aromatics, with a Lewis acid catalyst. Organic chlorine compounds tend to be less reactive in the nucleophilic substitution reaction than the corresponding bromine or iodine derivatives, but tend to be cheaper. They can be activated by substitution with a tosylate group, or by the use of a catalytic amount of sodium iodide.
Chlorine is used extensively in organic chemistry and inorganic chemistry as an oxidizing agent, and in substitution reactions, because chlorine often imparts desired properties to an organic compound, due to its electronegativity.
Chlorine compounds are used as intermediates in the production of a large number of important industrial products that do not contain chlorine. Some examples are: polycarbonates, polyurethanes, silicones, polytetrafluoroethylene, carboxymethylcellulose and propylene oxide.
Geology
Hydrochloric acid reacts with carbonates, this allows it to be a highly useful substance in the identification of minerals with the presence of carbonates, such as Calcite. Some common rocks that contain carbonates are limestone, marl, and marble.
Chemical Weapon
World War I
Chlorine gas, also known as bertholite, was used as a weapon in World War I by Germany on April 22, 1915, at the Second Battle of Ypres. As described by the soldiers, it had a distinctive odor of a mix between pepper and pineapple. It also tasted metallic and stung the back of my throat and chest. Chlorine can react with water in the lining of the lungs to form hydrochloric acid, an irritant that can be fatal. The damage done by chlorine gas can be prevented by a gas mask, or other filtration methods, which make the overall chance of dying from chlorine gas much lower than from other chemical weapons. It was designed by Fritz Haber, a German scientist at the Kaiser Wilhelm Society in Berlin, later a Nobel Prize laureate, in collaboration with the German chemical conglomerate IG Farben, who developed methods to discharge chlorine gas into an enemy trench. Haber's role in the use of chlorine as a deadly weapon is alleged to have driven his wife, Clara Immerwahr, to suicide.[citation needed] After its first use, chlorine was used by both sides as a chemical weapon, but was soon replaced by the more deadly gases phosgene and mustard gas.
Iraq War
Chlorine gas has also been used by insurgents against local people and coalition forces in the Iraq war, in the form of chlorine bombs. On March 17, 2007, for example, three tanks filled with chlorine were detonated in Anbar province, killing two people, and sickening more than 350. Other chlorine bomb attacks resulted in higher death tolls, with more than 30 deaths on two separate occasions. Most of the deaths were caused by the force of the explosions, rather than the effects of chlorine, as the toxic gas is rapidly dispersed into the atmosphere by the explosion. The Iraqi authorities have increased security for the handling of chlorine, which is essential to provide safe drinking water for the population.
Other uses
Chlorine is used in the manufacture of numerous chlorinated organic compounds, the most significant in terms of production volume being 1,2-dichloroethane and vinyl chloride, intermediates in the production of PVC. Other particularly important organochlorines are methyl chloride, methylene chloride, chloroform, vinylidene chloride, trichloroethylene, tetrachloroethylene, allyl chloride, epichlorohydrin, chlorobenzene, dichlorobenzenes and trichlorobenzenes.
Chlorine is also used in the production of chlorates and in the extraction of bromine.
Respiratory toxicity
| ||||||||||||||||||||
Chlorine inhalation produces significant direct chemical toxicity of the respiratory tract:
- Continuous exposure at low chlorine levels: It causes irritation and inflammation of the airways and significantly increases the risk of developing asthma, chronic bronchitis and isolated attacks of wheezing. In adolescents with atopia, the risk of developing allergic rhinitis increases.
- Inhalation poisoning of high chlorine levels: It can cause acute lung injury, acute respiratory distress syndrome and, up to 1 % of cases, death. Symptoms and signs of obstruction of the airways derived from intoxication include cough, chest tightness, dyspnea, wheezing, stenders, lung inflammation (with or without associated infection), pulmonary edema or hypoxemia.
The forms of chlorine involved in respiratory toxicity are not limited to gaseous chlorine but also to compounds formed by its combination with other substances, such as hypochlorous acid, chlorine dioxide, and chloramine. In fact, because gaseous chlorine is moderately soluble in water, when it comes into contact with the mucous membranes of the respiratory tract it can form hypochlorous acid, hydrochloric acid, and various highly reactive oxidants as it dissolves in the liquid of the respiratory tract. airway surface. This causes lesions that are not limited to the lower respiratory tract, but can also affect the eyes, skin, and upper respiratory tract. The airway is especially affected from the nose to the level of the bronchi. Oxidative damage to the airways may not appear immediately, but may develop delayed, during any stage of the disease (days and even weeks after chlorine exposure).
Normal airway function may not return to normal after chlorine inhalation injury, leaving permanent sequelae such as asthma, nonspecific airway hyperresponsiveness, reactive airway dysfunction syndrome, fibrosis lung and mucosal hyperplasia. A single exposure at high levels is sufficient to cause permanent sequelae.
Exposure in swimming pools
In addition to professional activities related to the industry and handling of chlorine, a notable activity in which exposure to this substance occurs is swimming. Both swimmers and people who work in swimming pools (coaches, monitors, rescuers...) are exposed to significant direct chemical toxicity in the respiratory tracts by inhaling environmental chlorine. This toxicity (and its effects on health) is produced by the two routes described in the previous section: continuous exposure to low levels of chlorine and occasional involuntary peaks of high levels (acute exposures). Exposures at the highest levels are due to occasional failures in the automatic chlorination systems and negligence of maintenance operators, due to lack of knowledge or lack of safety culture. Other causes that lead to the release of chlorine into the air with accumulation of excessive levels, even though the chlorine level in the water is within the regulations, include insufficient ventilation, activities with great agitation of the water (such as intense training, children playing) and the presence of a large number of users.
Accidents due to inhalation of chemical products in swimming pools are not unusual occurrences. Some examples are detailed below.
In Spain, in 1992, a ten-year-old girl died of suffocation from inhaling chlorine in an indoor heated pool. Eleven other children were poisoned in the same incident and suffered lung injuries, two of them very serious. The events occurred as a result of negligence in handling the water purification systems.
Between the years 2008 to 2012, 41 accidents in swimming pools due to chemical substances were documented, with a total of 428 victims, one of them fatal (an operator) and at least 1750 people evacuated. The number of victims in a single incident ranged from a single person affected to more than 80 intoxicated (Asturias, 2010). Most of the accidents occurred in municipal swimming pools.