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Polyhalogen Compounds – Definition, Properties, Uses

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Hydrocarbons having one or more hydrogen atoms substituted by halogen atoms are known as haloalkanes and haloarenes. Haloalkanes and haloarenes are distinguished by the fact that haloalkanes are formed from open-chain hydrocarbons (alkanes), whereas haloarenes are derived from aromatic hydrocarbons.

Polyhalogen Compounds

Polyhalogen compounds are carbon compounds with more than one halogen atom. These chemicals are beneficial in the domains of industry and agriculture. The usage and impacts of various polyhalogens on the environment are discussed.

Dichloromethane (Methylene Chloride) CH2Cl2

Methylene chloride is a clear, sweet-smelling liquid with no colour. It’s a flammable liquid with a low boiling point of 312.75 degrees Celsius and a specific gravity of 1.37.

Harmful Effect of Dichloromethane

Methylene chloride is recognised to be toxic to the central nervous system of humans. Methylene chloride exposure at low concentrations might cause minor hearing and visual loss. High doses of methylene chloride, on the other hand, might produce dizziness, nausea, tingling, and numbness in the fingers and toes. Methylene chloride produces intense stinging and minor reddening in humans when it comes into close contact with the skin. Direct contact with the eyes may cause corneal burns. When animals were exposed to methylene chloride vapours, their corneas were shown to be injured.

Uses of Dichloromethane

  1. It’s utilised as a paint removal solvent, as well as a metal cleaning and a finish solvent.
  2. It is an excellent solvent for extraction in pharmaceutical goods in the manufacturing of medications and in the food sector due to its low boiling point and low flammability.
  3. It’s also utilised in aerosols as a propellant.
  4. It is used as a dewaxing agent and a refrigerant.

Chloroform (Trichloromethane) CHCl3

Chloroform has the chemical formula CHCl3. Trichloromethane is the IUPAC designation for CHCl3. A CHCl3 molecule is created by overlapping a C atom’s hybrid sp3 orbital with the 1s orbital of the H atom, and three C atom’s hybrid sp3 orbitals with the partially-filled p-orbitals of three Cl atoms. The structure of CHCl3 is tetrahedral.

Preparation of Chloroform

Chloroform is made in the lab by distilling a combination of ethanol and bleaching powder solution.

CaOCl2 + H2O → Ca(OH)2 + Cl2


CH3CHO + 3Cl2 → Cl3CCHO + 3HCl

2Cl3CHO + Ca(OH)2 → 2CHCl3 + (HCOO)2Ca

Properties of Chloroform

  1. It’s a colourless, oily liquid with a strange odour and a scorching flavour.
  2. It has a higher density than water.
  3. It is only slightly soluble in water, but it dissolves readily in organic solvents like ethanol and ether.
  4. It’s a poisonous substance. The inhalation of vapours renders the person unconscious. Chloroform is used as an anaesthetic.
  5. In the presence of air or light, chloroform progressively oxidises to the deadly chemical phosgene.

CHCl3 + 1/2O2 → COCl2 + HCl

Uses of Chloroform

  • Chloroform is a common solvent in business, notably for lipids, alkaloids, iodine, waxes, rubber, and other materials.
  • It’s a type of anaesthetic. However, alternative anaesthetics, such as ether, have mostly supplanted it in recent years; it is inherently exceedingly poisonous.
  • It is utilised as a reagent in laboratories.
  • It’s used to make chloropicrin, chloretone and other chemicals.
  • It’s employed in pharmaceuticals.
  • Used in Freon Refrigerant Manufacture, R–22.

Environmental Effect of Chloroform

  1. The central nervous system is irritated by inhaling chloroform vapours.
  2. Even if just for a short period, inhaling roughly 900ppm chloroform can produce dizziness, weariness, and headaches.
  3. Long-term exposure to chloroform can harm the liver and kidneys (where chloroform is converted to phosgene).
  4. Skin wounds result from direct and sustained contact with chloroform.
  5. In the presence of light, chloroform slowly oxidises in the air to generate phosgene, also known as carbonyl chloride, an exceedingly poisonous gas.

Iodoform (Tri-iodomethane) CHI3

Iodoform has the chemical formula CHI3 and the IUPAC name triiodomethane. One sp3 hybrid orbital of the C atom interacts with the 1s orbital of the H atom during the production of iodoform (CHI3), while the other three sp3 hybrid orbitals of the same C atom overlap with partly filled p-orbitals of iodine.

Preparation of Iodoform

In the lab, iodoform is made by heating ethanol or acetone with iodine and a Na2CO3 or alkali solution.

CH3CH2OH+ 4I2 + 6NaOH → CHI3 + 5NaI + HCOONa + 5H2O

Properties of Iodoform

  1. Iodoform is a light yellow crystalline solid with a melting temperature of 392 K and a distinct odour.
  2. It is water-insoluble, however, it dissolves readily in ethyl alcohol and ether. Due to the release of free iodine, it has an antibacterial effect.

Uses of Iodoform

  • The iodine released, rather than the iodoform itself, is utilised as an antiseptic. However, due to its strong odour, it has been phased out in favour of alternative iodine-based formulations.
  • It’s a chemical that’s utilised to make pharmaceuticals.

Carbon tetrachloride (Tetrachloromethane) CCl4

Carbon tetrachloride is a colourless, oily liquid with a sickening odour that is insoluble in water but soluble in organic solvents like ether and alcohol. It has a boiling point of 350 K. It is combustible.

Uses of Carbon Tetrachloride

  1. It’s widely used in the manufacture of aerosol can refrigerants and propellants.
  2. It’s used to make chlorofluorocarbons (freons) and other chemical compounds as a starting ingredient.
  3. It’s a solvent used in the manufacturing of medications.
  4. It’s a solvent for a variety of substances, including oils, fats, and waxes.
  5. Pyrene is a chemical that may be used to put out fires. Dry cleaning is done with carbon tetrachloride.

The Hazardous Effect of Carbon Tetrachloride on Human Being

Humans get liver cancer after being exposed to carbon tetrachloride. The most common adverse effects are dizziness, lightheadedness, nausea, and vomiting, which can irreversibly damage nerve cells. In severe circumstances, these consequences can swiftly progress to stupor, coma, unconsciousness, or even death. Your heartbeat may become erratic or stop if you are exposed to carbon tetrachloride vapours. It’s possible that it’ll irritate your eyes after coming into touch with them.

Environmental Effect of Carbon Tetrachloride

It also has negative consequences for the ecosystem. Carbon tetrachloride rises into the sky and depletes the ozone layer when discharged into the environment. Human exposure to UV radiation is increased when the ozone layer depletes, leading to a rise in skin cancer, eye illnesses and disorders, and perhaps compromised immune systems.

Freons and Ozone layer depletion

Freons are the chlorofluoro compounds of methane and ethane that are grouped together. These are non-flammable, non-toxic, non-corrosive, readily liquefied, and highly non-reactive substances that are exceptionally stable at low concentrations. They are used as refrigerants because they are stable even at high pressures and temperatures. Because of its commercial application, dichlorodifluoromethane (CCl2F2), often known as Freon-12, is the most significant constituent in this family. Through the Swarts reaction, antimony fluoride forms it on carbon tetrachloride in the presence of antimony pentachloride.

Uses of Freons

  1. Freons are refrigerants that are utilised in refrigerators and air conditioners, thus the name.
  2. These have also been widely utilised as propellants for deodorants, detergents, shaving creams, hairsprays, and insecticides in aerosols and foams.

Ozone Layer Depletion due to Freons

Freons degrade the protective ozone layer that surrounds our planet through photochemical breakdown and moderate radical change processes in the stratosphere. As a result, several nations have banned or severely restricted the use of freons as a propellant or refrigerant.

Dichloro-Diphenyl Trichloroethane (D.D.T.)

In water, D.D.T. is almost insoluble, although it is somewhat soluble in polar solvents. It’s a strong pesticide that’s extensively used to kill mosquitoes and other insects. Heat a combination of chloral (1mol) and chlorobenzene (2mol) in the presence of concentrated H2SO4 to make D.D.T. It was initially created in 1874, but Paul Muller of Geigy Pharmaceuticals in Switzerland found its usefulness as an insecticide in 1939. Paul Muller was awarded the Nobel Prize in Medicine and Physiology in 1948 for this discovery.

Side Effects of D.D.T.

One of the most potent and efficient pesticides is D.D.T. Because of its efficiency against malaria-transmitting mosquitos and typhus-transmitting lice, the usage of D.D.T. skyrocketed after WWII. Excessive usage of D.D.T., on the other hand, has been warned to cause a slew of issues.

Many insect species evolved resistance to D.D.T., and D.D.T. was also manufactured at a high toxicity level for fish. D.D.T. has high chemical stability and fat solubility. It is not readily digested by animals, but it is deposited and retained in adipose tissue, posing serious health risks, which is why it is prohibited in the United States. Despite its hazardous side effects, DDT is still widely utilised in India and other Asian nations due to a lack of alternative pesticides.

Sample Questions

Question 1: What are polyhalogen compounds?


Polyhalogen compounds are carbon compounds that include more than one halogen atom.

Question 2: What are Polyhalides?


Polyhalides are metal halides with more than one halogen atom. Potassium triiodide, for example (Kl3).

Question 3: Which polyhalogen chemical is utilised in industrial and dry cleaning as a solvent?


In manufacturing and dry cleaning, carbon tetrachloride is utilised as a solvent.

Question 4: What are the uses of Freons?


  • The term comes from the fact that freons are refrigerants used in refrigerators and air conditioners.
  • Deodorants, detergents, shaving creams, hairsprays, and insecticides in aerosols and foams have all used these as propellants.

Question 5: What are the uses of Carbon Tetrachloride?


  • It’s frequently utilised in the production of refrigerants and propellants for aerosol cans.
  • As a starting material, it’s used to generate chlorofluorocarbons (freons) and other chemical compounds.
  • It’s a solvent utilised in the pharmaceutical industry.
  • It may be used to dissolve a wide range of compounds, including oils, fats, and waxes.
  • Pyrene is a flammable liquid that may be used to extinguish flames. Carbon tetrachloride is used for dry cleaning.

Question 6: What are the effect of Carbon Tetrachloride on the Environment?


It also has harmful effects on the environment. When carbon tetrachloride is released into the atmosphere, it climbs into the sky and depletes the ozone layer. When the ozone layer depletes, human exposure to UV radiation increases, leading to an increase in skin cancer, eye illnesses and disorders, and perhaps impaired immune systems.

Question 7: What are the properties of Iodoform?


  • Iodoform is a crystalline light yellow solid with a melting point of 392 K and a strong odour.
  • It is insoluble in water, but quickly dissolves in ethyl alcohol and ether. It has an antimicrobial effect due to the release of free iodine.

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Last Updated : 30 Jan, 2022
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