- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Boiling point
- Density
- Solubility
- Chemical properties
- Properties of your aqueous solutions
- Other properties
- Obtaining
- Uses as a disinfectant
- In food
- On paper and cardboard that will come into contact with food
- In drinking water
- In dentistry
- In medical applications
- Other uses
- Risks
- References
The chlorine dioxide is an inorganic compound element formed by chlorine (Cl) and oxygen (O). Its chemical formula is ClO 2. It is a greenish-yellow to reddish gas. It is not found naturally in the environment.
It is extremely reactive, so it is common for it to be prepared where it is to be used. One of its most important uses is as a microbicide, antiseptic and deodorizer since it eliminates bacteria, viruses and fungi very easily and in very low concentrations.
Some foods sold in supermarkets may have been disinfected with chlorine dioxide ClO 2. Author: ElasticComputeFarm. Source: Pixabay.
Allows you to disinfect foods such as vegetables, fruits, meat, poultry and seafood. It is used to sanitize surfaces, floors, bathrooms, ventilation systems, swimming pools, laboratory equipment, dental equipment, etc.
For this reason it is used in food processing, in hospitals and clinics, in industries and businesses. It is used to purify drinking water and municipal wastewater.
It is very effective as an oxidizing agent, which is why it is used to bleach paper pulp, oils, flour, leather, textile fibers, among others.
When it is in the form of a gas, it is very dangerous, as it is highly explosive, and is used mainly in aqueous solutions. It is toxic if inhaled.
Structure
Chlorine dioxide is formed by the union of a chlorine atom (Cl) with two oxygen atoms (O). The bonds of chlorine with each oxygen are covalent and double. The chlorine in this compound has a valence of +4.
Lewis structure of chlorine dioxide ClO 2. Yikrazuul. Source: Wikimedia Commons.
It has a symmetric and angled structure, as it has free electrons. That is, they do not form a bond with any other atom.
Structure of ClO 2 in three dimensions. Green = chlorine; red = oxygen. Ben Mills and Jynto. Source: Wikimedia Commons.
Nomenclature
- Chlorine dioxide
- Chlorine oxide (iv)
Properties
Physical state
Greenish-yellow to reddish-yellow gas.
Molecular weight
67.45 g / mol.
Melting point
-59 ° C.
Boiling point
11 ° C.
Density
Liquid at 0 ° C = 1,642 g / cm 3
Gas = 2.33 (relative density to air, air = 1).
Solubility
Soluble in water: 2000 cm 3 of ClO 2 gas in 100 cm 3 of cold water or 0.8 g / 100 mL of water at 20 ° C. Soluble in alkaline solution and in sulfuric acid solution H 2 SO 4.
Chemical properties
ClO 2 is extremely reactive and can explode violently. It is a very effective oxidizing agent.
ClO 2 decomposes violently if it comes into contact with organic materials. If it is in air at a concentration greater than 10%, it can explode due to sunlight or heat.
It can also detonate in the presence of mercury (Hg) or carbon monoxide (CO).
Under the action of ultraviolet (UV) light or ozone, ClO 2 turns into chlorine hexoxide Cl 2 O 6, a very unstable compound.
Properties of your aqueous solutions
Its aqueous solutions are yellow or reddish yellow. They are stable if kept cool, well sealed and protected from sunlight. In the presence of light these solutions slowly decompose to give hydrochloric acid HCl and chloric acid HClO 3.
Aqueous solution of ClO 2 where it is observed that a yellow gas that is ClO 2 is released. Author: Materialscientist. Source: Wikimedia Commons.
In alkaline solutions, ClO 2 decomposes into chlorite ions ClO 2- and chlorate ClO 3-. In acid solutions, chlorous acid HClO 2 is formed and then this is decomposed to hydrochloric acid HCl and chloric acid HClO 3.
Other properties
The concentrated vapors of ClO 2 are potentially explosive, so it has not been possible to compress it alone or mixed with other gases. For this reason, it is preferred to prepare it on the site where it will be used.
When it is at very low temperatures in its hydrated form, which is the way it is sometimes transferred, it is a block-shaped solid similar to ice and orange in color.
It has an odor similar to chlorine. It is toxic by inhalation.
Obtaining
It can be obtained in several ways. For example, in some cases ClO 2 solutions are prepared by passing a mixture of chlorine gas (Cl 2) and air (or chlorine gas and nitrogen N 2) through a column containing granules of sodium chlorite (NaClO 2).
2 NaClO 2 + Cl 2 → 2 NaCl + 2 ClO 2
The generated product contains approximately 90% ClO 2, among other chlorine compounds.
It is also obtained from potassium chlorate (KClO 3) and sulfuric acid (H 2 SO 4) in the presence of oxalic acid as a reducing agent. In this case, carbon dioxide (CO 2) is also formed, which serves to dilute the ClO 2.
It can be prepared at the site of use starting from sodium chlorate (NaClO 3), sulfuric acid (H 2 SO 4) and methanol (CH 3 OH).
In industry it is obtained by means of sodium chlorate (NaClO 3) and sulfur dioxide (SO 2) in the presence of sulfuric acid.
2 NaClO 3 + SO 2 + H 2 SO 4 → 2 ClO 2 + 2 NaHSO 4
Uses as a disinfectant
It can be used as a powerful antimicrobial agent. It has been found to be highly effective against various microorganisms, such as Escherichia coli and Staphylococcus aureus.
With the latter, a concentration of only 5 ppm of ClO 2 is enough to eliminate 100% of them. It is bactericidal, antiseptic and deodorizing. It is effective over a wide pH range.
In food
It is used as an antimicrobial agent in water to fumigate fruits and vegetables, in the processing of poultry, red meat, both pieces of meat and organs, and marine products such as shellfish.
Red meat from supermarkets may have been treated with chlorine dioxide to disinfect it. Author: Karamo. Source: Pixabay.
Chlorine dioxide solutions should be used at a concentration that does not exceed 3 ppm (parts per million) of residual ClO 2 so that it will not have an effect on food.
After treatment with ClO 2 all food must be thoroughly rinsed with potable water, or it must be used for blanching, cooking or canning.
In the case of marine products, the ClO 2 solution should be used in water and ice used in rinsing, washing, thawing, transport or storage. Raw shellfish should then be thoroughly washed with potable water before consumption.
Cold water and ice in which seafood is kept contain small amounts of ClO 2. Author: PublicDomainPictures. Source: Pixabay.
On paper and cardboard that will come into contact with food
ClO 2 solutions are used to eliminate slime-causing microorganisms (such as algae, bacteria and fungi) in the process water used in the manufacture of paper and cardboard that will come into contact with food.
In drinking water
It is used to purify water and make it drinkable (safe to drink). It is used in the pretreatment of water that will later be bottled for drinking or water that will be used as an ingredient in the manufacture of beverages or soft drinks.
Some processed sodas may contain water treated with ClO 2. Susan Slater. Source: Wikimedia Commons.
In dentistry
It is used in the instruments used by the dentist or dentist to disinfect them and destroy pathogenic organisms in them.
In medical applications
Aqueous solutions of ClO 2 have been used to treat oral candidiasis (infection in the mouth). Candidiasis is an infection by the fungus Candida albicans.
Appearance of the fungus Candida albicans in a laboratory culture. CDC / Dr. William Kaplan. Source: Wikimedia Commons.
Chlorine dioxide kills mouth fungus and significantly improves the appearance of oral tissues without side effects.
Some medical researchers indicate that ClO 2 solutions applied to surgical wounds can reduce or suppress adhesion formation without affecting adhesion healing, with the additional advantage of its antiseptic properties.
Other uses
Due to its oxidizing and microbicidal properties, ClO 2 is used to:
- Whiten the cellulose of the wood in the manufacture of pulp and paper, providing a stable shine.
- Bleaching fats and oils, leather, bleaching flour and textiles.
- Agricultural applications such as disinfecting hard surfaces, equipment, water systems and mushroom greenhouses.
- Applications in industries, shops and hospitals such as disinfecting hard surfaces (walls, floors, bathrooms), ventilation systems, laboratory equipment.
- Disinfect floors and bathrooms of homes, air conditioning systems, swimming pool water circulation systems.
- Municipal and industrial wastewater treatment.
- Cleaning of contamination of oil fields.
- Manufacture of chloride salts (Cl -).
Risks
- ClO 2 concentrated vapors are potentially explosive.
- It is toxic by inhalation and ingestion. It is irritating to the eyes, nose and throat, it can cause pulmonary edema and chronic bronchitis.
- According to the sources consulted, ClO 2 does not cause mutations in DNA or cause cancer in humans.
References
- US National Library of Medicine. (2019). Chlorine dioxide. Recovered from pubchem.ncbi.nlm.nih.gov.
- Dean, JA (editor). (1973). Lange's Handbook of Chemistry (Eleventh Edition). McGraw-Hill Book Company.
- Ullmann's Encyclopedia of Industrial Chemistry. (1990). Fifth Edition. VCH Verlagsgesellschaft mbH.
- Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
- Bajpai, P. (2012). Chlorine Dioxide Bleaching. Effect of Chlorine Dioxide Bleaching on Pulp Quality. In Environmentally Benign Approaches for Pulp Bleaching (Second Edition). Recovered from sciencedirect.com.
- Moran, S. (2018). Water chemistry. Chlorine dioxide. In An Applied Guide to Water and Effluent Treatment Plant Design. Recovered from sciencedirect.com.
- McKeen, L. (2012). Introduction to Food Irradiation and Medical Sterilization. Gaseous Chlorine Dioxide. In The Effect of Sterilization on Plastics and Elastomers (Third Edition). Recovered from sciencedirect.com.