Aromatic Nitro- Compounds Aryl Halides & Ethers

The compounds which contain the functional group NO2 are called nitro compounds. Depending on the alkyl or the aryl group, they are classified into aromatic and non-aromatic compounds. They can easily be converted into nitriles with the help of appropriate reagents. Most are generally phosphorus (III) compounds, like phosphorus trichloride. 

Aromatic nitro compounds are reduced by various nitroreductases. The nitroreductases are flavoprotein enzymes used in the catalyzation of up to 6 electrons. The main usage of aromatic nitro compounds is in cancer chemotherapy.

Definition and uses of the aromatic nitro compounds

Aromatic nitro compounds are the chemical compounds that are obtained through nitration. For conducting the following procedure, nitric acid and sulphuric acid are mixed. Nitronium ion (NO2) is produced as one of the products. The nitration product, which is synthesised on the largest scale today, is benzene.

The most important and expansive use of the aromatic nitro compounds is in the chemotherapy of cancer patients. They are used widely as radiosensitisers as they are quite efficient in inducing cell death in a hypoxic environment, even in the absence of radiation. They usually exist in the form of yellow liquids or solids and have distinctive smells. Nitrobenzene is one of the finest examples of aromatic nitro compounds.

Aromatic nitro compounds can be easily prepared by nitration, using a nitrating mixture of concentrated nitric acid and concentrated sulphuric acid.

Aryl halides

Aryl halides are known to be the halogen derivatives of aromatic alkanes. They are the chemical compounds containing arenes and have one or more hydrogen atoms connected with the aromatic rings and are replaced by halogens. These compounds are usually denoted by “Ar-X”. X signifies the halogen atom, whereas Ar denotes the aryl group.

Aryl halides are widely used in the making of compound libraries. One major use of chlorobenzene is as a solvent for the dispersion of herbicides. Hexamethylphosphoric triamide is a phosphoramide that has a role as a mutagen and an insect sterilant.

The aryl halide nitration reaction is one of the major chemical reactions. In this process, sulphuric acid and nitric acid are used, which produce NO2. Due to the presence of two electronegative oxygen molecules, the ortho and para positions are attacked. Thus, we get para isomer and ortho isomer as the products.

Friedel-Crafts Reaction

Due to a positive charge on the carbon atom, the carbonyl or the alkyl group behaves as an electrophile. The ortho and para positions are electrons rich and, thus, are the sites of attack in the aryl halides. Para and ortho isomers are produced in different quantities at the end of the reaction. This reaction came into existence in 1877 with the motive of attaching the substituents to the aromatic rings. They are basically of two types – alkylation and acylation. 

We can take an example of the acylation reaction.

Here, aluminium trichloride acts as the Lewis acid. AlCl3 is a stable compound. Here, phosphorus chloride reacts with aromatic hydrocarbons in the presence of AlCl3.

Sodium borohydride is commercially produced with the help of the Brown-Schlesinger process and the Bayer process.

Ethers

Ethers can be defined as the derivatives of hydrocarbons, where the hydrogen atom gets replaced by an alkoxy (-Or) group. It can also be replaced by the arolaxy group (-OAr). The oxygen atom is connected with two aryl or alkyl groups. The general formula for ethers is – R-O-R, R-O-R’, Ar-O-Ar, or R-O-Ar. Here, R denotes the alkyl group, and Ar denotes the aryl group.

Ethers are generally highly flammable when subjected to high pressure and room temperature. It has C-O-C linkages. Ethers have various uses in the chemical as well as other industries. They are used as insecticides, miticides and fumigants for soil. They are widely used for agricultural purposes to safeguard the food grains and harvesting or harvested crops.

There are various important properties of ethers. Some of them are:

• They are easily soluble in water. This happens because the lone pair of electrons on the oxygen atom forms a hydrogen bond with the hydrogen atoms in the water molecules.
• They have lesser boiling points than analogous alcohols. Due to strong intermolecular hydrogen bonding, their boiling points are closer to their corresponding alkanes.

Conclusion

Many chemical compounds are crucial for various chemical reactions, which are necessary for various industrial processes. Some important chemical compounds are – phosphorus trichloride, hexamethylphosphorous triamide and sodium borohydride. Aromatic nitro compounds, aryl halides and ethers, cumulatively, are important parts of chemistry and involve several chemical equations. Some of them are – Williamson Synthesis, Friedel-Crafts reaction, etc. The nitration between them results in the formation of NO2, which takes the chemical equation to the next step.