Naphthalene

strong odor of coal tar || __** Naphthalene **__ is an organic compound with formula [|C] 10 [|H] 8. It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic [|hydrocarbon], naphthalene's structure consists of a fused pair of benzene rings. It is best known as the main ingredient of traditional mothballs.
 * ~ Properties ||
 * [|Molecular formula] || C10H8 ||
 * [|Molar mass] || 128.17 g mol−1 ||
 * Appearance || White solid crystals/flakes,
 * [|Density] || 1.14 g/cm³ ||
 * [|Melting point] || 80.26 °C, 353 K, 176 °F ||
 * [|Boiling point] || 218 °C, 491 K, 424 °F ||
 * [|Solubility] in [|water] || Approximately 30 mg/L ||

__** History **__ In 1819–1820, at least two chemists reported a white solid with a pungent odor derived from the distillation of coal tar. In 1821, John Kidd described many of this substance's properties and the means of its production, and proposed the name //naphthaline//, as it had been derived from a kind of naphtha (a broad term encompassing any volatile, flammable liquid hydrocarbon mixture, including coal tar) .Naphthalene's chemical formula was determined by Michael Faraday in 1826. The structure of two fused benzene rings was proposed by Emil Erlenmeyer in 1866, and confirmed by Carl Gräbe three years later.

__**Health Effects**__ Exposure to large amounts of naphthalene may damage or destroy red blood cells. Humans, in particular children, have developed this condition, known as hemolytic anemia, after ingesting mothballs or deodorant blocks containing naphthalene. Symptoms include fatigue, lack of appetite, restlessness, and pale skin. Exposure to large amounts of naphthalene may cause confusion, nausea, vomiting, diarrhea, blood in the urine, and jaundice (yellow coloration of the skin). When the U.S. National Toxicology Program exposed male and female rats and mice to naphthalene vapors on weekdays for two years, male and female rats exhibited evidence of carcinogenic activity based on increased incidences of adenoma and neuroblastoma of the nose, female mice exhibited some evidence of carcinogenic activity based on increased incidences of alveolar and bronchiolar adenomas of the lung, and male mice exhibited no evidence of carcinogenic activity. The [|International Agency for Research on Cancer] (IARC) classifies naphthalene as possibly carcinogenic to humans and animals (Group 2B). The IARC also points out that acute exposure causes cataracts in humans, rats, rabbits, and mice; and that hemolytic anemia, described above, can occur in children and infants after oral or inhalation exposure or after maternal exposure during pregnancy. Under California's [|Proposition 65], naphthalene is listed as "known to the State to cause cancer" .Over 400 million people have an inherited condition called [|glucose-6-phosphate dehydrogenase deficiency]. Exposure to naphthalene is more harmful for these people and may cause [|hemolytic anemia] at lower doses. In China, the use of naphthalene in mothballs is forbidden. It is due partly to the health effects as well as the wide use of natural camphor as replacement.

Naphthalene base superplasticizer

__**Effect of naphthalene and aqueous crude oil extracts on the green flagellate //Chlamydomonas angulosa//. I. Growth**__ Spills of crude oil and various refined fractions are an increasing threat to organisms both in marine and in freshwater situations. The present study is concerned with the effects of aqueous crude oil extracts and naphthalene on one organism, the green flagellate //Chlamydomonas angulosa//, grown under controlled conditions. Tests were carried out under conditions allowing relatively free evaporation and volatilization of the hydrocarbons (open systems) and in closed systems in which hydrocarbon loss was minimized (closed systems).In open systems, 61% of the //Chlamydomonas angulosa// cells were killed when saturated naphthalene was initially present in the medium. The generation time of the survivors was, however, the same as the controls. In a closed system a much higher percentage of the cells was killed, but a shorter generation time was observed when growth resumed. A prolonged lag phase was characteristic of all naphthalene treatments.The effect of aqueous extracts of crude oils was also tested using different crude oils, fresh and aged extracts, as well as open and closed systems. Extracts were almost always inhibitory, but the effects were less severe than those obtained with naphthalene. The possible implications are discussed.

Structure and reactivity
A naphthalene molecule can be viewed as the fusion of a pair of benzene rings. (In [|organic chemistry], rings are //fused// if they share two or more atoms.) As such, naphthalene is classified as a benozenoid [|polycyclic aromatic hydrocarbon] (PAH). There are two sets of equivalent hydrogen atoms: the //alpha// positions are positions 1, 4, 5, and 8 on the drawing below, and the //beta// positions are positions 2, 3, 6, and 7. Unlike [|benzene], the carbon-carbon bonds in naphthalene are not of the same length. The bonds C1–C2, C3–C4, C5–C6 and C7–C8 are about 1.36 Å (136 pm) in length, whereas the other carbon-carbon bonds are about 1.42 Å (142 pm) long. This difference, which was established by [|x-ray diffraction] [// [|citation needed] //], is consistent with the [|valence bond] model of bonding in naphthalene that involves three [|resonance structures] (as shown below); whereas the bonds C1–C2, C3–C4, C5–C6 and C7–C8 are double in //two// of the three structures, the others are double in only one. Like benzene, naphthalene can undergo [|electrophilic aromatic substitution]. For many electrophilic aromatic substitution reactions, naphthalene reacts under milder conditions than does benzene. For example, whereas both benzene and naphthalene react with [|chlorine] in the presence of a [|ferric chloride] or [|aluminium chloride] catalyst, naphthalene and chlorine can react to form [|1-chloronaphthalene] even without a catalyst. Likewise, whereas both benzene and naphthalene can be alkylated using [|Friedel-Crafts reactions], naphthalene can also be alkylated by reaction with [|alkenes] or [|alcohols] , with [|sulfuric] or [|phosphoric acid] as the catalyst.

As a chemical intermediate
Naphthalene is used mainly as a precursor to other chemicals. The single largest use of naphthalene is the industrial production of [|phthalic anhydride], although more phthalic anhydride is made from [|//o//-xylene]. Other naphthalene-derived chemicals include alkyl naphthalene sulfonate [|surfactants], and the [|insecticide] [|1-naphthyl-N-methylcarbamate (//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]. The hydrogenated naphthalenes tetrahydronaphthalene ( [|tetralin] ) and decahydronaphthalene ( [|decalin] ) are used as low-volatility [|solvents]. Naphthalene is also used in the synthesis of [|2-naphthol], a precursor for various dyestuffs, pigments, rubber processing chemicals and other miscellaneous chemicals and pharmaceuticals. [|[4]] Naphthalene sulfonic acids are used in the manufacture of naphthalene sulfonate polymer [|plasticizers] ( [|dispersants] ), which are used to produce [|concrete] and [|plasterboard] ( [|wallboard] or [|drywall] ). They are also used as dispersants in synthetic and natural rubbers, and as [|tanning] agents ( [|syntans] ) in leather industries, [|agricultural] formulations (dispersants for [|pesticides] ), [|dyes] and as a dispersant in [|lead–acid battery] plates. Naphthalene sulfonate polymers are produced by reacting naphthalene with sulfuric acid and then polymerizing with [|formaldehyde], followed by neutralization with [|sodium hydroxide] or [|calcium hydroxide]. These products are commercially sold in solution (water) or dry powder form. H2SO4 + C10H8 → C10H7-SO3H + H2O C10H7-SO3H + CH2-O → C10H7-SO3H-(C10H7-SO3H)n + H2SO4 C10H7-SO3H-(C10H7-SO3H)n + NaOH → C10H7-SO3Na-(C10H7-SO3Na)n + H2O + Na2SO4
 * [|Sulfonation] Step (sulfuric acid plus naphthalene):
 * [|Polymerization] Step (naphthalenesulfonic acid plus formaldehyde):
 * [|Neutralization] Step (naphthalene sulfonic acid condensate plus sodium hydroxide):