Naphthalene
Naphthalene (IUPAC)
Colorless solid with odor of mothballs / tar
Fixed
1.14 g · cm -3
80.3 ° C
218 ° C
4 Pa ( 20 ° C)
Very poor in water ( 32 mg / l at 20 ° C)
Attention
Repealed as evidence of a carcinogenic effect
Template: Infobox chemical / molecular formula search available
Naphthalene [ naftali ː n] (from Greek = naphtha petroleum, name according to IUPAC: naphthalene ) is a colorless solid with the molecular formula C10H8, who has sublimated at room temperature. It is a bicyclic aromatic hydrocarbon with a characteristic odor of mothballs / tar. Naphthalene is harmful and dangerous for the environment.
History
Naphthalene in 1819 by the British chemist Alexander Garden was isolated from coal tar. 1866 have been prepared by Emil Erlenmeyer for the first time Naphthalinformel. Traditionally, naphthalene is also counted among the polycyclic aromatic hydrocarbons ( PAHs). The Naphthalinmolekül consists of two fused benzene rings, its chemical behavior is similar to the other PAHs.
Occurrence in nature
Traces of naphthalene are produced by magnolias and some species of deer. In addition, the material with a termite species was detected, which apparently used it as a defense agent against natural enemies such as ants and poisonous mushrooms.
Production and representation
Naphthalene is from the middle oil fraction of coal tar (up to 11 %), as well as brown coal and wood tar, cracked gas oil or coal when it is coked won. In coal tar, it is quantitatively the largest component. It also occurs in petroleum and other fossil fuels and is also formed during the combustion of wood or tobacco. Naphthalene is emitted from gas plant sites and Holzimprägnierwerken, further, it is also produced in landfills.
In 1987 approximately one million tons of naphthalene was produced. Western Europe with 250,000 tons the main producer of naphthalene, followed by Eastern Europe ( 200,000 tons ), Japan ( 200,000 tonnes) and the USA ( 125,000 tonnes).
Properties
Physical Properties
In water, naphthalene is largely insoluble at room temperature only 0.032 g of naphthalene dissolved in a liter of water. In short-chain alcohols it is bad, in nonpolar solvents such as benzene ( 1.130 g / l), carbon sulfide, ether, toluene (910 g / l), xylene ( 783 g / l), and chloroform, however, readily soluble. Naphthalene forms of white crystal flakes which melt to a colorless liquid at 80 ° C, which boils at 218 ° C. It has a characteristic, intense aromatic tar-like odor; the odor threshold is depending on the person at 0.14 to 125 mg/m3. Naphthalene has a burning taste. The vapors are flammable, flash point is 80 ° C and the ignition temperature at 540 ° C. The density is 1.14 g/cm3, therefore decreases naphthalene in water.
Chemical Properties
Naphthalene burns with a luminous, sooty flame. It reacts violently with oxidants such as chromium trioxide and nitrogen oxides. The chemical behavior of is very similar to that of benzene, however, it is more reactive than benzene, but less reactive than tricyclic aromatics due to the molecular structure, such as anthracene. The Naphthalinmolekül has 10 π - electrons. It's a like benzene electrophilic substitution reactions. Azulene, also an aromatic hydrocarbon, is an isomer of naphthalene, it consists of a five - and a seven- carbon ring; due to a dipolar structure, however, it is deep blue and significantly more reactive than naphthalene.
Naphthalene can be hydrogenated under moderate conditions to tetralin ( C10H12 ). The further hydrogenation under more drastic conditions leads to decalin ( C10H18 ).
Naphthalene represented by reduction with alkali metals in aprotic solvents ( for example tetrahydrofuran, 1,2-dimethoxyethane ) Alkalinaphthalide. With sodium results in a deep green salt. Is a radical ketyl having an ESR signal at g = 2.0. The Reduktiospotential is -2.5 V (vs. standard hydrogen electrode ( SHE) ). Cause of the green color are absorption bands at 463 and 735 nm
The anion is a strong base, it reacts with the protic solvent to dihydronaphthalene:
Forms naphthalene with concentrated nitric acid according to the reaction conditions selected 1 -nitronaphthalene and 2 -nitronaphthalene.
Proof
The oxidation with chromates and Permanganates or a large scale with oxygen over a catalyst yields phthalic acid. Naphthalene can be detected by UV spectroscopy or by high performance liquid chromatography. Traces of naphthalene can be detected by gas chromatography -mass spectrometry (GC / MS).
Use
Naphthalene was used to the main component of clay balls, but today often replaced with other substances due to its unpleasant odor. Furthermore, naphthalene is hardly effective insecticide. Also, for the disinfection of insect collections, it is unlikely to be effective, although it used a long time to do so.
Naphthalene also occurred in the early 20th century coal gas used and often clogged the gas lines because it separated out as a solid. Despite its potential health risks, it was used as medicine for intestinal disinfectant.
Mainly naphthalene for the synthesis of phthalic anhydride is used, which is further processed to solvents, plastics, and fuels. For the production of solvent and fuel additives decalin and tetralin, it is required for the preparation of azo dyes, for the synthesis of the wood preservative chloronaphthalene, insecticides ( carbamates ) and PVC plasticizer intermediates, also for the production of Alkylnapththalinsulfaten used as soaps. Other industrially important derivatives are the naphthols, bromonaphthalenes, naphthylamines and nitronaphthalenes.
Biological Significance
In the microsomes of human liver cells naphthalene is metabolized by cytochrome P450. The oxidation results on the short-lived epoxide intermediate stage to the primary metabolite:
- Trans-1 ,2 -dihydro -1 ,2- naphthalenediol ( " dihydrodiol " )
- 1 -naphthol and
- 2-naphthol
The cytochrome subtype CYP1A2 generates primarily the dihydrodiol and 1- naphthol, while the subtype CYP3A4 produces mainly 2- naphthol. Secondary metabolites are products of 2- naphthol directly 2,6 - and 1,7 -dihydroxynaphthalene. In contrast, dihydrodiol and 1- naphthol are not further degraded in the microsomes.
Safety
Naphthalene leads to the skin to strong irritation and dermatitis. Naphthalene can damage the red blood cells. When inhaled, it can lead to mucous membrane irritation, headache and nausea, vomiting, and a state of confusion. Taking it leads to gastrointestinal disorders, respiratory paralysis, convulsions and tremors. It is, despite its low solubility in water extremely hazardous for water (WGK 3). Damage to the cornea, liver, and kidneys is possible. Between an air volume fraction from 0.9 to 5.9 %, it forms explosive mixtures. A carcinogenic effect is suspected.