Naphthalene

Naphthalene is a white crystalline volatile solid with a distinct odor that reminds many people of mothballs. At room temperature, the compound sublimes (turns from a solid to a gas) slowly, generating a highly flammable vapor. 

John Kidd (1775–1851), an English chemist and physician, was the first to extract naphthalene from coal tar in 1819. When soft coal is burned in an insufficient quantity of air, coal tar forms, which is a brown to black thick liquid. It is made up of a complex hydrocarbon mixture comparable to that found in petroleum. 

Kidd's naphthalene extraction was historically significant since it revealed that coal could be used for more than just fuel. It could potentially be used to create chemical compounds with a variety of commercial and industrial applications. 

Richard August Carl Emil Erlenmeyer (1825–1909), a German chemist, discovered the chemical structure of naphthalene. The naphthalene molecule, according to Erlenmeyer, is made up of two benzene molecules linked together. 

Natural sources of naphthalene include petroleum and coal tar. It is extracted by heating the raw material to a temperature of 200°C to 250°C (392°F to 482°F), resulting in middle oil, a mixture of hydrocarbons. After that, the middle oil is distilled to separate its many components, one of which is naphthalene. This naphthalene is cleaned by washing it in strong acid, then in a sodium hydroxide solution, and finally by steam distillation.

What is Naphthalene?

Before starting with naphthalene, first, you need to understand what an aromatic compound is. Aromatic compounds are the ring compounds that contain a double and single bond in an alternate manner, and follow the huckel rule. Let’s come to our main question, what is naphthalene? Naphthalene is an aromatic hydrocarbon, consisting of two or more fused aromatic benzene rings. These are polynuclear aromatic hydrocarbons. In short, naphthalene is fused with hydrocarbons. In this article, we have covered the all-important points about naphthalene like the use of naphthalene, structure of naphthalene, and resonance in naphthalene.

Structure of Naphthalene

Naphthalene is a member of a polynuclear aromatic hydrocarbon where two aromatic benzene rings are fused together at the ortho position.

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The bond length at the double bond position is around 1.36 Angstrom, and the bond length at the single bond position is around 1.40 angstrom. Naphthalene molecule shows the resonance in its structure. It forms a resonance hybrid. Naphthalene molecules show three resonance structures. These structures are known as canonical structures. Naphthalene forms three resonating structures. These structures are shown below for better understanding.

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In this structure, the pi electrons are delocalised from one position to another. This delocalisation phenomenon leads to the lowering of the electronic energy of the system. In the naphthalene molecule, the carbon 1 - carbon 2 bond length is shorter than the carbon 2 - carbon 3 bond length. All carbons are sp² hybridised and have unused p-orbitals with one electron. In naphthalene, the sigma bond count is eleven.

Properties of Naphthalene:

The physical properties and chemical properties of naphthalene are discussed below:

1. Naphthalene exists in crystalline form.

2. Naphthalene is generally white in color. It is also found in transparent to brownish color.

3. The molecular weight of naphthalene is 128.18 g/mol.

4. Naphthalene is insoluble in water at normal room temperature.

5. Naphthalene has an aromatic odor.

6. The vapor pressure of naphthalene is 0.087 mmHg.

Synthesis of Naphthalene

1. From Coal Tar- Naphthalene can be obtained from the coaltar, by making naphthalene crystals. These crystals can be formed by the middle oil fraction. The crystals produced in this process are subjected to sulphuric acid for the purification process. In the end, pure naphthalene crystals are formed.

2. Haworth Synthesis- In this process, benzene to naphthalene is produced. The benzene ring is first subjected to the acylation process. This reaction starts with the Friedel craft Acylation of a benzene ring with the succinic anhydride, then a series of reduction reactions undergo. Finally, a naphthalene molecule is produced by dehydrogenation.

Naphthalene in Water

The solubility of naphthalene in water can be determined by its structure. Naphthalene is a polyatomic hydrocarbon. A large number of carbon atoms makes it a hydrophobic molecule. Due to this hydrophobic structure, the naphthalene in water is insoluble. In this article naphthalene, the liquid structure is not discussed in detail.

Naphthalene in Other Solvents

Naphthalene is an organic compound with a melting point of 80℃ and a boiling point of 218℃. It sublimes upon heating and is insoluble in water.  In other solvents like ethanol, it is not completely soluble. It is very soluble in benzene, ether and chloroform. 

Different Forms of Naphthalene

1. Refined naphthalene

2. Alkyl naphthalene

3. Naphthalene solid

Refined Naphthalene- Refined naphthalene powder is raw material, used for the production of various organic compounds. It is used in agriculture and the fabric industry.

Pyrotechnic special effects such as the formation of black smoke and simulated explosions employ refined naphthalene. It's highly sublime and won't dissolve in water. It dissolves in benzene, alcohol, ethers, chloroform, and carbon disulfide. Features of Refined naphthalene include multi-sectoral uses; it has a longer shelf life and is considered effective. 

Alkyl Naphthalene- Alkyl naphthalene generally exists in a form of salt. The most common and widely used alkyl naphthalene is alkyl naphthalene sulfonate sodium salt. It occurs in powder form. The PH of this compound is generally more than 7 (slightly basic in nature). It acts as a surfactant. 

Alkyl Naphthalene is also used to make lubricants. As is expected by customers, lubricants must work even in the most difficult circumstances. Alkyl naphthalene is a choice based on features like stability for long durability and seal compatibility. 

Naphthalene Solid- Naphthalene solid is a very common form of naphthalene. It occurs white in color. It is a crystalline volatile solid. It has an odor like coal tar. 

Naphthalene is obtained from the petroleum distillation of coal tar. It is majorly used in the manufacture of phthalic anhydride. It is also used in repellents for moths. It is an organic compound and the simplest hydrocarbon. 

Use of Naphthalene

The main uses of naphthalene are discussed below:

• Naphthalene is used in making carbaryl drugs. These drugs are used in making insecticides.

• Naphthalene is used in making nadoxolol drug for beta-blocking.

• The Sulphonated form of naphthalene is used as a surfactant.

• Naphthalene is used in making synthetic dyes.

• amino naphthalene sulfonic acid is used in making different types of dyes.

• Molten naphthalene is used for making solvents for an aromatic compound.

Did You Know?

• You may be shocked to hear that naphthalene can be present in cigarette smoke, vehicle exhaust, and forest fire smoke.

• In the United States, naphthalene was first licensed as a pesticide in 1948.

• Insecticides include naphthalene.

• Naphthalene is a highly flammable material.

Interesting Facts about Naphthalene

• Naphthalene is derived from the Persian word naphtha, which means oil or pitch. 

• Naphthalene is used as a pesticide, for example. The Formosan termite, a species of insect, uses naphthalene to construct its nests. Scientists are still trying to figure out where the termites acquire their naphthalene and why they are immune to its normally lethal qualities. 

• When naphthalene is absorbed into the soil, it becomes a pollutant. Scientists discovered microorganisms capable of digesting naphthalene in the soil in 2003, decreasing the dangers it brings to the environment. 

• Napalm, a mixture of naphthalene and palmitate that ignited and burned at a very high temperature, was one of the most devastating weapons used during the Vietnam War in the 1960s and 1970s, causing widespread damage to plant life, structures, and human life.