How many delocalized electrons in naphthalene

naphthalene

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naphthalene (from Greek naphtha = Petroleum, name according to IUPAC: Naphthalene) is a colorless solid with the empirical formula C.10H8that sublimes even at room temperature. It is a bicyclic aromatic hydrocarbon with a characteristic odor of moth powder / tar. Naphthalene is harmful to health and the environment.

history

In 1819, naphthalene was isolated from coal tar by the British chemist Alexander Garden. In 1866 Emil Erlenmeyer established the naphthalene formula for the first time. Traditionally, naphthalene is also counted among the polycyclic aromatic hydrocarbons (PAHs). The naphthalene molecule consists of two fused benzene rings; its chemical behavior is similar to that of the other PAHs.

Occurrence in nature

Traces of naphthalene are produced by magnolias and some species of deer. The substance was also found in a species of termite that apparently uses it as a defense against natural enemies such as ants and poisonous fungi.

Extraction and presentation

Naphthalene is obtained from the middle oil fraction of the coal tar (up to 11%), as well as lignite and wood tar, crack gas oil or from coal, if this is coked. In terms of quantity, it is the largest component in coal tar. It is also found in petroleum and other fossil fuels and is also formed when wood or tobacco is burned. Naphthalene is emitted by gasworks and wood impregnation plants, and it is also produced in landfills.

In 1987 about one million tons of naphthalene was produced. Western Europe is the main producer of naphthalene with 250,000 tons, followed by Eastern Europe (200,000 tons), Japan (200,000 tons) and the USA (125,000 tons).

properties

Physical Properties

Naphthalene is largely insoluble in water; only 0.032 g of naphthalene dissolves in one liter of water at room temperature.[1] It is poorly soluble in short-chain alcohols, but readily soluble in non-polar solvents such as benzene (1.130 g / l), carbon sulfide, ether, toluene (910 g / l), xylene (783 g / l), and chloroform. Naphthalene forms white crystal flakes that melt at 80 ° C to a colorless liquid that boils at 218 ° C. It has a characteristic, intensely aromatic, tar-like odor; the odor threshold is 0.14 to 125 mg / m depending on the person3. Naphthalene has a burning taste. The vapors are flammable, the flash point is 80 ° C and the ignition temperature is 540 ° C.[1] The density is 1.14 g / cm3, hence naphthalene sinks in water.[1]

Chemical properties

Naphthalene burns with a glowing, sooty flame. It reacts violently with oxidizing agents such as chromium trioxide and nitrogen oxides. The chemical behavior is very similar to that of benzene, but due to its molecular structure it is more reactive than benzene, but less reactive than tricyclic aromatics such as anthracene. The naphthalene molecule has 10 π electrons. Like benzene, it enters into electrophilic substitution reactions. Azulene, also an aromatic hydrocarbon, is an isomer of naphthalene, it consists of a five and a seven carbon ring; however, due to a dipolar structure, it is deep blue and significantly more reactive than naphthalene.

Under moderate conditions, naphthalene can turn into tetralin (C.10H12) are hydrogenated. Further hydrogenation under more drastic conditions leads to decalin (C.10H18).

The salts of naphthalene are orange- or red-red, the ion of naphthalene is called the naphthyl radical and has the empirical formula C.10H7. With concentrated nitric acid, naphthalene forms 1-nitronaphthalene or 2-nitronaphthalene, depending on the reaction conditions chosen.

proof

Oxidation with chromates and permanganates or, on an industrial scale, with oxygen over a catalyst produces phthalic acid. Naphthalene can be detected using UV spectroscopy or a high-performance liquid chromatography method. Traces of naphthalene are detected by GC / MS.

use

Naphthalene used to be the main component of mothballs, but is now often replaced by other substances because of its unpleasant smell. Furthermore, naphthalene is hardly insecticidal. It is also hardly effective for disinfecting collections of insects, although it has been used for a long time.[4]

Naphthalene was also found in the luminous gas used at the beginning of the 20th century and often clogged the gas pipes because it separated out as a solid. Despite its potential health hazards, it was used medically, for example, to disinfect the intestines.

Naphthalene is mainly used for the synthesis of phthalic anhydride, which is processed into solvents, plastics and fuels. It is also required for the production of the solvents and fuel additives decalin and tetralin, for the production of azo dyes, for the synthesis of the wood preservative chloronaphthalene, insecticides (carbamates) and PVC plasticizer intermediates, as well as for the production of alkylnapththalene sulfates, which are used as soaps . Further industrially important derivatives are the naphthols, bromonaphthalenes, naphthylamines and nitronaphthalenes.

Biological importance

In the microsomes of human liver cells, naphthalene is metabolized by cytochrome P450. The oxidation leads to the primary metabolites via the short-lived epoxide intermediate:[5]

  • trans-1,2-dihydro-1,2-naphthalenediol ("dihydrodiol")
  • 1-naphthol and
  • 2-naphthol

The cytochrome subtype CYP1A2 mainly produces the dihydrodiol and 1-naphthol, while the subtype CYP3A4 mainly produces 2-naphthol. 2,6- and 1,7-dihydroxynaphthalene are formed directly from 2-naphthol as secondary metabolites. In contrast, dihydrodiol and 1-naphthol are no longer broken down in the microsomes.

safety instructions

Naphthalene causes severe irritation and dermatitis on the skin. Naphthalene can damage red blood cells. Inhalation can cause irritation of the mucous membranes, headache and nausea, vomiting and confusion. If ingested, it leads to gastrointestinal disorders, respiratory paralysis, cramps and tremors. Despite its low solubility in water, it is highly hazardous to water (WGK 3).[1] Damage to the cornea, liver and kidneys is possible. It forms explosive mixtures between an air volume fraction of 0.9 to 5.9%.[1] A carcinogenic effect is suspected.

Derivatives

Numbering of the substituent positions in naphthalene
Surname Molecular formulaMolar mass [g / mol] M.p. [° C] Bp [° C] Density [g / cm3] Refractive index
1-naphthoic acid C.11H8O2 172,18 157 300
1-naphthoic acid chloride C.11H7ClO 190,63 16–19 190 (35 torr) 1,265 1,6552
1-naphthol C.10H8O 144,17 94–96 278 1,224
1-naphthaldehyde C.11H8O 156,18 1–2 160 (15 torr)
1-nitronaphthalene C.10H7NO2 173,17 53–57 340 1,22
1-fluoronaphthalene C.10H7F. 146,16 −19 215 1,323 1,593
1-chloronaphthalene C.10H7Cl 162,62 −6 259 1,194 1,632
2-chloronaphthalene C.10H7Cl 162,62 59,5 256 1,138
1-bromonaphthalene C.10H7Br 207,07 −2 279 1,489 1,670

See also

literature

  • BUA - Substance reports 39. Naphthalene. Wiley / VCH, Weinheim 1989, ISBN 3-527-28066-9.
  • Harald Derner: Investigations on the resonance Raman effect on anthracene, naphthalene and p-nitro-p-dimethylamino-azobenzene. Freiburg (Breisgau), Univ., Diss., 1986, ISBN 3-8107-2217-0.

Individual evidence

  1. 1,001,011,021,031,041,051,061,071,081,091,101,111,12Entry to naphthalene in the GESTIS substance database of the IFA, accessed on May 13, 2012 (JavaScript required).
  2. 2,02,1Entry from the CLP regulation too CAS no. 91-20-3 in the GESTIS substance database of the IFA (JavaScript required)
  3. ↑ Since December 1, 2012, only GHS hazardous substance labeling has been permitted for substances. The R-phrases of this substance may still be used to classify preparations until June 1, 2015, after which the EU hazardous substance labeling is of purely historical interest.
  4. ↑ Gerfried Deschka: The disinfection of small collections of insects according to newer criteria, Self-published by Steyrer Entomologenrunde, Steyr 1987.
  5. ↑ T. M. Cho, R. L. Rose, E. Hodgson: In vitro metabolism of naphthalene by human liver microsomal cytochrome P450 enzymes, Drug Metab Dispos., 2006 Jan; 34 (1): pp. 176-183; PMID 16243959.

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