Halogenated/ Organohalogen Compounds

A halogenated compound can be defined as a compound that has halogen such as fluorine, chlorine, bromine or iodine linked to it. Many organic compounds contain halogens in their molecule structure. The halogenated compounds can easily contaminate the water, soil and air as well as plants and animals and can also harm the ozone layer. The decomposition of the compound can give rise to inorganic compounds that may have a direct impact on plants and animals near the source of emission and can also cause acid rain. 

Organohalogen compounds are organic compounds containing halogen atoms as part of their molecule. Haloalkanes (alkyl halides), haloarenes (aryl halides) and acid halides are some of the important classes of these compounds.  

Properties of Halogenated Compound 

• The electronegativity of halogens decreases from fluorine down the group towards iodine. As a result, the bonds between these elements and others vary in their polarity. 
• Bonds between the halogen atoms and carbon would show a similar pattern, with the most polarised bonds occurring between carbon and fluorine. On the contrary, molecules containing carbon to halogen bonds will have different dipoles. 
• In certain cases where fluorine or chlorine is present, the molecular dipole moments can be quite large, altering the solubility of a compound in water and affecting its melting and boiling point dramatically.    
• This broad category of chemicals has the potential to have a wide range of health and environmental consequences. The risks of cancer and genetic diseases, as well as the possibility of altering fertility or the unborn child, are the most significant.
• Most of the compounds are dangerous to aquatic life and have long-term repercussions, and some of them fit the criteria for persistence, bioaccumulation, and toxicity (PBT).

Examples of Halogenated Compounds 

Halogenated compounds are organic compounds that consist of halogens such as fluorine, chlorine or bromine. Examples of Halogenated Compounds are 1-chloro-2-bromoethane, benzyl bromide, captan, vinyl chloride, vinylidene chloride, methylene chloride, chloroform, iodoacetic acid, mustard gas, carbon tetrachloride.

Functions and uses of Halogenated compounds 

Halogenated Compounds can have a variety of functions that includes flame-retarding, plasticising, biocidal, fat-dissolving, water-repellent, cooling and lubricating. Contrary to flammable materials, which mainly consist of hydrogen and carbon, brominated flame retardants are much more difficult to ignite and can be incorporated into materials in several ways to give fire protection. 

Chloroparaffins such as SCCP can act as plasticisers, lubricants, or flame retardants. Chlorophenols such as PCP have mainly been used as a multifunctional biocide.

Example of Organohalogen Compounds 

The general term of Organohalogen refers to compounds with covalent carbon-halogen bonds Substances such as bromomethane (CH3Br) and chloroethane (CH3CH2Cl )are examples of organohalogen compounds, whereas others such as methylammonium chloride salt, which have no carbon-halogen bonds, are not. 

Organohalogen chemicals have a wide range of applications in both everyday life and industry. They are employed as laboratory and industrial solvents (such as chloroform, carbon tetrachloride, westron, and westrosol); as precursors to other organic compounds; as anaesthetics (e.g. halothane); as refrigerants (such as freons); and so on.

Typhoid fever is treated with chloramphenicol, an antibiotic containing halogen. Thyroid glands create thyroxine, an iodine-containing hormone. PVC (polyvinyl chloride) is a chlorine-containing polymer.

Simple organohalogens, such as alkyl halides, are made by substituting one or more H atoms in hydrocarbons with X atom(s). The hybridization of the carbon to which the halogen is bound can be used to classify these compounds.

Class of Organohalogens Compounds 

• Alkyl Halides (or haloalkanes) 
• Allylic Halides 
• Benzylic Halides 

Alkyl Halides 

Alkyl Halides or Haloalkanes are represented by R-X. The X atom is bonded to sp3 hybridised carbon of an alkyl group R that is derived from an alkane. Mono Haloalkanes are represented by the general formula CnH2n+1X  .These are obtained by replacing one of the hydrogen from alkane by halogen. 

Allylic Halides

In allylic halides, the halogen is bonded to an sp3 – hybridised carbon atom, which is adjacent to a C=C. This carbon is also known as allylic carbon. For example, allyl chloride. They also show a special trend in reactivity because of the stability of allyl carbocation.  

Benzylic Halides

The halogen group, in benzylic halides is bonded to an sp3 – hybridised benzylic carbon atom, which in return is bonded to an aromatic ring. For example, Benzyl bromide. They are also more reactive than normal haloalkanes due to the stability of benzyl carbocations.

Conclusion 

Organic compounds with halogen atoms in their molecules are known as organohalogen compounds. Haloalkanes (alkyl halides), haloarenes (aryl halides), and acid halides are examples of these compounds. A polar C-X functional group is present in their molecules, with X being a halogen atom such as F, Cl, Br, or I. The carbon atom has a partial positive charge, whereas the halogen atom, which is more electronegative than carbon, has a partial negative charge. Halogenated compounds are those that contain a halogen element, such as chlorine, bromine, fluorine, iodine, and so on.