Question

Write a note about any three polyhalogen compounds.Give answer of the question in detail.

Answer 1

Polyhalogen compounds are Carbon compounds having more than one halogen (elements present in the group 17 of the modern periodic table) atom. Common uses of polyhalogen compounds are in agriculture and industrial sectors. They are popularly used for many purposes such as solvents, anaesthetics pesticides, etc.
Few very important polyhalogen compounds are methylene chloride, chloroform, carbon tetrachloride, iodoform, DDT, benzene hexachloride among many others. In this article, we will discuss some of the most prominent polyhalogen compounds.

1) Methylene chloride (Dichloromethane)

Dichloromethane, also known as methylene chloride, is one of the polyhalogen compounds present in form of solvent. It is popularly known for its uses in many purposes such as a paint remover, as a process solvent during drug manufacturing processes, as a propellant in aerosols, as a cleaning solvent, and as a finishing solvent.
Low levels of methylene chloride exposure in the air can cause slight hearing and vision impairment. High levels of methylene chloride exposure in the air can lead to nausea, dizziness, tingling, and numbness in an individual’s fingers and toes. Direct skin contact of humans with this solvent is highly injurious. It can cause harmful effects such as mild redness of the skin, intense burning, etc. Direct eye contact can lead to burning of the cornea.


2) Chloroform (Trichloromethane)

Trichloromethane, also known as Chloroform, is a colourless polyhalogen compound present in liquid form. It has a characteristic sweet smell. The boiling point of chloroform is 334 K. However, chloroform can slowly oxidize by air and form a poisonous gas “phosgene” in the presence of light.
Therefore, it is necessary to store chloroform bottles away from sunlight. It should be completely filled to the brim in order to keep the air out of the bottle. Phosgene is the common name for the chemical carbonyl chloride, (COCl2). However, the addition of little ethanol to chloroform can convert toxic phosgene to a nontoxic compound known as ethyl carbonate.
Chloroform act as a solvent for many substances such as fats, iodine, alkaloids, etc. One of the major use of chloroform in the present day for the manufacturing of Freon refrigerant R-22. Chloroform depresses the Central Nervous System. Initially, chloroform was used as the general anaesthetic for surgical purposes. However,  now much safer options are available like ether.
Breathing 900 parts per million concentration of chloroform can lead to fatigue, dizziness, and headache. Chronic exposure of the compound can cause liver damage (due to the metabolism of chloroform and formation of poisonous gas phosgene) and kidney damage. Development of sores is one of the effects on immersion of skin in the chloroform.

Laboratory Uses of Chloroform

Chloroform act as a detection agent of primary amines during isocyanide test, also known as Carbylamine test. In the test, chloroform is heated with the mixture of amines with alcoholic NaOH. The reaction results in the formation of a foul-smelling isocyanide gas. It helps in the detection of aliphatic and aromatic primary amines.


3) Iodoform (Triiodomethane)

The IUPAC name of Iodoform is triiodomethane. It is a pale yellow solid with the presence of a distinct smell. Initially, the polyhalogen compound was used as an antiseptic. However, the antiseptic property of the compound was due to the release of free iodine rather than iodoform which led to the release of objectionable smell. Therefore, now a day other iodine-containing formulations are in use rather than iodoform.