Naphthalene: What is it? Characteristics, Structure, Uses, Production, Danger and Safety

It is a white, solid, aromatic, crystalline hydrocarbon, best known as the main ingredient in mothballs.

Naphthalene is also known as naphthalene, mothball, tar camphor, white tar, or albocarbon.

Naphthalene is volatile, forming a flammable vapor. Each molecule of this substance consists of two fused benzene rings.

As its most abundant single component, it is obtained from coal tar and converted into phthalic anhydride for the manufacture of plastics, dyes and solvents.

It is also used as an antiseptic and insecticide, especially in mothballs (p-dichlorobenzene can be used instead of naphthalene as a substitute for mothballs). Naphthalene easily sublimates at room temperature.

Occurrence in nature

Trace amounts of naphthalene are produced by magnolias and certain types of deer. Furthermore, this chemical has been found in the subterranean Formosan termite, possibly as a repellent against “ants, poisonous fungi, and nematode worms.”

Naphthalene’s molecular formula, C 10 H 8, was determined by Michael Faraday in 1826.

Notable features

Structure

As noted above, a naphthalene molecule is made up of two fused benzene rings (in organic chemistry, the rings “fuse” if they share two or more atoms. Naphthalene is therefore classified as a polyaromatic hydrocarbon (PAH) of benzenoid.

Reactivity profile

Vigorous reactions, sometimes equivalent to explosions, can result from contact between aromatic hydrocarbons, such as naphthalene, and strong oxidizing agents. They can react exothermically with bases and with diazo compounds.

Substitution on the benzene nucleus occurs by halogenation (acid catalyst), nitration, sulfonation, and the Friedel-Crafts reaction. Naphthalene, camphor, glycerol, or turpentine react violently with chromic anhydride.

The Friedel-Crafts acylation of naphthalene with benzoyl chloride, catalyzed by AlCl3, must be carried out above the melting point of the mixture, or the reaction may be violent.

Like benzene, naphthalene can undergo electrophilic aromatic substitution. For many electrophilic aromatic substitution reactions, naphthalene is more reactive than benzene and reacts under milder conditions than benzene.

Naphthalene mono-substitution has two possible isomeric products, corresponding to substitution at an alpha or beta position, respectively. Usually the main product has the electrophile in the alpha position.

The selectivity for alpha over beta substitution can be rationalized in terms of the intermediate resonance structures, for intermediate alpha substitution, seven resonance structures can be drawn, of which four retain an aromatic ring.

For beta substitution, the intermediate has only six resonance structures, and only two of them are aromatic.

However, sulfonation provides a mixture of the 1-naphthalenesulfonic acid of the “alpha” product and the 2-naphthalenesulfonic acid of the “beta” product, with the proportion dependent on the reaction conditions.

Naphthalene can be hydrogenated under high pressure or with a suitable catalyst to give 1,2,3,4-tetrahydronaphthalene, a solvent sold under the trade name Tetralin.

Additional hydrogenation produces decahydronaphthalene or decalin (C 10 H 18, also known as bicyclodecane).

Oxidation of naphthalene with chromate or permanganate, or catalytic oxidation with O 2 and a vanadium catalyst, gives phthalic acid.

Naphthalene production

Most of the naphthalene is derived from coal tar.

From the 1960s to the 1990s, significant amounts of naphthalene were also produced from heavy oil fractions during oil refining, but today, petroleum-derived naphthalene accounts for only a minor component of oil production. naphthalene.

Although the composition of coal tar varies with the coal from which it is produced, typical coal tar is about 10% by weight of naphthalene.

In industrial practice, coal tar distillation produces an oil that contains approximately 50 percent naphthalene, along with a variety of other aromatic compounds.

This oil, after being washed with aqueous sodium hydroxide to remove the acid components, mainly various phenols, and with sulfuric acid to remove the basic components, is fractionally distilled to isolate the naphthalene.

The crude naphthalene resulting from this process is approximately 95 percent naphthalene by weight. The main impurity is the aromatic sulfur-containing compound, benzothiophene. Naphthalene derived from petroleum is generally purer than that derived from coal tar.

When more pure naphthalene is required, crude naphthalene can be further purified by recrystallizing it from any of a variety of solvents.

Naphthalene Uses

The most familiar use for mothballs is as a household fumigant, as in mothballs. In a sealed container of naphthalene granules, naphthalene vapors accumulate to levels toxic to adult and larval forms of many moths that are destructive to textiles.

Other fumigant uses of naphthalene include use in the soil as a pesticide fumigant, and in attic spaces to repel animals.

In the past, naphthalene was administered orally to kill parasitic worms in livestock.

Large volumes of naphthalene are used as a chemical intermediate to produce other chemicals. The most important use of naphthalene is the industrial production of phthalic anhydride, although more phthalic anhydride is manufactured from o-xylene than from naphthalene.

Other chemicals derived from naphthalene include alkyl naphthalenesulfonate surfactants and the insecticide carbaryl.

Naphthalenes substituted with combinations of strongly electron-donating functional groups, such as alcohols and amines, and strongly electron-withdrawing groups, especially sulfonic acids, are intermediates in the preparation of many synthetic dyes.

Hydrogenated naphthalenes tetrahydronaphthalene (tetralin) and decahydronaphthalene (decalin) are used as low volatility solvents.

Mothballs can also slow the appearance of rust, and therefore mothballs are sometimes used in places like a toolbox.

It’s also used to help make insecticides, artificial tanners, and dyes, and if you’ve ever wondered why a public bathroom (especially men’s) sometimes actually smells like mothballs, it’s because naphthalene is used in some types. of deodorants for bathrooms.

I’m not sure which smells worse though, that or body waste.

Naphthalene is also used to make something called phthalic anhydride. This chemical is used to make, among other things, artificial resins, such as glyptals, and pharmaceuticals, as well. Naphthalene also helps make a very famous type of plastic, polyvinyl chloride (PVC).

Health effects

Hazards and safety

And that’s where the problem lies, the fact that naphthalene is used in so many places to make so many different products.

This means that employees involved in the manufacture of these products and end users, such as consumers, can be exposed to the potentially harmful effects of naphthalene.

In humans, exposure to large amounts of naphthalene can damage or destroy red blood cells. This could cause the body to have too few red blood cells until it replaces the destroyed cells.

Humans, especially children, have developed this condition after ingesting mothballs or deodorant blocks that contain mothballs. Some of the symptoms of this condition are fatigue, poor appetite, restlessness, and pale skin.

Exposure to large amounts of naphthalene can also cause nausea, vomiting, diarrhea, blood in the urine, and jaundice (yellowing of the skin).

Researchers from the US National Toxicology Program exposed male and female rats and mice to mothballs during weekdays for two years.

They found that female mice exhibited some evidence of carcinogenic activity, based on a higher incidence of alveolar and bronchiolar adenomas of the lung; but male mice showed no evidence of carcinogenic activity.

In both male and female mice, naphthalene led to increased incidences and severity of chronic inflammation and abnormalities in the tissues that line the nose and lungs.

Regarding rats, they found clear evidence of carcinogenic activity of naphthalene in male and female rats based on the increased incidence of respiratory epithelial adenoma and olfactory epithelial neuroblastoma of the nose.

Naphthalene exposure caused significant increases in the incidence of non-neoplastic lesions of the nose in both male and female rats.
More than 400 million people have an inherited condition called glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency).

People exposed to naphthalene, especially in large amounts or over a long period of time, can experience one of many different types of side effects, including:

Hemolytic anemia – This is where red blood cells pop like a balloon. This includes hemolytic anemia in babies born to a mother who ate or smelled mothballs while pregnant.

Other conditions are:

  • Hepatic injury.
  • Damage to the nervous system.
  • Allergic skin reactions.
  • Falls, thus limiting your ability to see.

The International Agency for Research on Cancer (IARC) classifies naphthalene as possibly carcinogenic to humans. It also notes that acute exposure causes cataracts in humans, rats, rabbits, and mice.

Additionally, hemolytic anemia can occur in children and infants after oral or inhalation exposure, or after maternal exposure during pregnancy.

Other places you can find mothballs in use include:

  • Abrasives.
  • Fuels
  • Paint additives.
  • Adhesives.