Halogen Compounds: Methods of Preparation

Introduction

When the hydrogen atom or atoms are replaced by halogen atoms, e.g., fluorine(F), chlorine(Cl), bromine(Br), iodine(I), etc., then it results in the formation of Halogen Compounds. Halogen-containing compounds are known as halogen compounds. If the halogen compound is formed by adding halogen in alkanes, it forms alkyl halides, but if it is constructed from alkynes, it is known as alkyl halides. Hydrogen Fluoride (HF), Hydrogen Chloride (HCl), Hydrogen Iodide (HI), etc., are some of the halogen compounds examples. 

Types of Halogen Compounds

1. Metal Halides

When they form a compound with metals, these halogens are called metal halides. Metal halides include highly ionic substances like sodium chloride, monomeric covalent substances like uranium hexafluoride, and polymeric covalent substances like palladium chloride. They are prepared through direct combination or neutralising a basic metal salt with a hydrohalic acid.

1. Interhalogen Compounds

When halogens react with each other, they result in the formation of Interhalogen Compounds. A molecule that contains two or more distinct halogen atoms but no atoms from any other group is known as an interhalogen complex. They are covalent and have diamagnetic properties. They have more reactive bonds compared to the diatomic halogen compounds.

Types of Interhalogen Compounds

1. Diatomic Interhalogens

The interhalogens of form XY have physical properties that are midway between those of the two-parent halogens. The covalent bond between the two atoms has an ionic character because halogen X, which is less electronegative, has been used oxidised and has a partial positive charge. All fluorine, bromine, chlorine, and iodine combinations have a recognised formula. However, They aren’t all stable. Combinations of astatine with halogen aren’t even known, and the ones that are known are extremely unstable. 

Examples of diatomic interhalogens are chlorine monofluoride, bromine monofluoride, iodine monofluoride, etc. There haven’t been any discoveries of astatine fluorides yet. The extraordinary reactivity of such compounds, including the reaction of an originally produced fluoride with the walls of the glass container to form a non-volatile product, has been speculated as to the reason for their absence. While the production of astatine fluoride is predicted to be feasible, a liquid halogen fluoride solvent may be required, which has already been utilised to characterise radon fluorides.

Tetratomic Interhalogens

Some examples of Tetra Interhalogens are Chlorine Trifluoride, Bromine Trifluoride, Iodine Trifluoride, etc. 

Hexatomic Interhalogens

In every stable hexatomic and octatomic interhalogen, a heavier halogen is linked with five or seven fluorine atoms. Unlike other halogens, fluorine atoms have a high electronegativity and a small size that allows them to be stabilised. 

Chlorine pentafluoride, Bromine pentafluoride, and Iodine pentafluoride are only known hexatonic interhalogens.

  Octatomic Interhalogens

Iodine Heptafluoride is the only known Octatomic Interhalogen. Iodine heptafluoride, a fluorinating agent, is a colourless gas. The reaction of iodine with fluorine gas produces iodine pentafluoride. The molecule’s form is a pentagonal bipyramid. This is the only interhalogen compound known in which the larger atom carries seven smaller atoms. Bromine or chlorine heptafluoride has never been synthesised. Instead, fluorine gas and bromine or chlorine pentafluoride is created.

These compounds are formed when a group 17 element reacts directly with a lower interhalogen compound under certain circumstances. They are generally used as non-aqueous solvents and as a catalyst in some of the reactions. 

       Organic Halides

• Organic halides are formed up of halogen atoms present in a variety of manufactured organic compounds, such as plastic polymers and a few natural organic molecules. Chlorine is the most abundant halogen, and it is also the only one that humans require in considerable quantities. 
• Chloride ions, for example, play an important role in brain activity through regulating the inhibitory transmitter GABA.
• They’re also used to make stomach acid by the body. Thyroid hormones like thyroxine require trace amounts of iodine to be produced. 
• On the other hand, fluorine and bromine aren’t thought to be necessary for human survival.
• The nucleophilic abstraction procedure is also used to make organohalogens. An organic fluoride is a compound that has a carbon atom bonded to a fluorine atom (C-F). 
• A carbon atom is linked to a bromine atom in the organobromine molecule. Organochlorine is a compound that consists of carbon atoms bonded to a chlorine atom. Organic Iodide is the one in which a carbon atom is bonded with an iodide atom. 
• Organic halides’ reactivity is determined by the halogen atom that is linked to the carbon atom in the molecule. 
• The most reactive are organic iodides, which can be transformed into various chemicals. Organobromine has a lower reactivity than organic iodides but a higher reactivity than organochlorines. 
• Organic Fluorides are the organic halides with the least amount of reactivity. Bromoethane, Flurocyclopentane, etc., are a few examples of organic halogen compounds. It is a halogen atom, and it is linked to a carbon atom in an organic functional group.

Polyhalogenated Compounds

Any chemical containing numerous halogen substitutions is referred to as a polyhalogenated compound (PHC). They are of particular interest and significance since they bioaccumulate in people and are part of a superset that includes several hazardous and carcinogenic industrial compounds. Polyhalogenated chemicals include PBDEs, PCBs, dioxins (PCDDs), and PFCs. They are not miscible in organic solvents or water. However, they are miscible in certain hydrocarbons, from which they are frequently derived. Automobiles, airplanes, plastics, clothing and textiles, adhesives, paints, sealants, lubricating oils, polyurethane foams, cancer therapy, and medical imaging, as well as cosmetics, pharmaceuticals, food containers, and wrappings, all contain PHCs. They’re also employed a lot in pest control.

Conclusion

Halogens and the methods of preparing them is very crucial topic. We have also discussed different types of halogen compounds and interhalogen compounds. We hope that you learned something new about halogens and the methods of preparing them.