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Chlorinated naphthalenes


CAS No.: 70776-03-3
Registry name: Chlorinated naphthalenes
Chemical name: Chlorinated naphthalenes
Synonyms, Trade names; Chloronaphthalene, chloronaphthalene derivatives, PCN, Halowax
Chemical name (German): Chlorierte Naphthaline
Chemical name (French): Naphthalènes chlorés
Appearance: Except for 1-monochloronaphthalene, which is a liquid at room temperature, pure chlorinated naphthalenes are colourless, crystalline compounds


Empirical formula: C10H8-nCln (n=1-8)
Rel. molecular mass: 162.5-404.0 g
Density: 1.2 - 2.0 g/cm3
Boiling point: 250 - 440°C
Melting point: -25 - 197°C
Flash point: 135 - >430°C
Solvolysis/solubility: soluble in aromatic solvents


The chemical structure of the molecules results in 75 chlorinated naphthalene congeners. The physical and chemical properties are dependent on the degree of chlorination. Whereas the melting and boiling point increase with an increase in the number of chlorine atoms, there is a simultaneous reduction in vapour pressure and water solubility.


Chlorinated naphthalenes are used in the electrical industry and as additives. Only isomeric mixtures characterised by their chlorine content are commercially available.

The substances are not found naturally. They are obtained by batchwise chlorination of naphthalene in the presence of ferric chloride as a catalyst.

Production figures:
Worldwide approximately 5,000 t per annum with a declining tendency (acc. KOCH, 1989).


Humans: TCLo 30 mg/m3, inhalation (trichloronaphthalene) acc. KOCH, 1989
Rat: LD50 1,540 mg/kg, oral acc. KOCH, 1989
LD50 868 mg/kg, oral (2-chloronaphthalene) acc. KOCH, 1989
Mouse: LD50 1,091 mg/kg, oral acc. KOCH, 1989
LD50 2,087 mg/kg, oral (2-chloronaphthalene) acc. KOCH, 1989

Characteristic effects:

Humans/mammals: Poisoning is due to oral application (foodstuffs) or inhalation. The toxicity is largely governed by the degree of chlorination. Chloracne and liver damage are especially caused by pentachloro- and hexachloronaphthalene while chlorinated naphthalenes with 1 to 3 chlorine atoms hardly have any toxic effects.


Chlorinated naphthalenes are very resistant to degradation. Mobility is slight in water and soil, but there is a pronounced tendency towards bioaccumulation and geoaccumulation depending on the degree of chlorination. Highly chlorinated naphthalenes are very persistent. Incomplete combustion results in the formation of polychlorinated dibenzodioxins and -furans (PCDD/F).


Recommended limits in the USA for drinking water (acc. KOCH, 1989):
Trichloronaphthalene isomers: 3.9 m g/l
Tetrachloronaphthalene isomers: 1.5 m g/l
Pentachloronaphthalene isomers: 0.39 m g/l
Hexachloronaphthalene isomers: 0.15 m g/l
Octachloronaphthalene isomers: 0.08 m g/l
(Refer also to 'naphthalene')

Comparison/reference values

Medium/origin Country Value Source
Air   up to 25 ng/m3 acc. KOCH, 1989
Surface water   up to 200 ng/l acc. KOCH, 1989
Seawater   up to 20 ng/l acc. KOCH, 1989
Sediments/soil   up to 100 µg/kg acc. KOCH, 1989
Fish   up to 0.12 µg/kg acc. KOCH, 1989
Birds   up to 70 µg/kg acc. KOCH, 1989
Humans (fatty tissue)   up to 15 µg/kg acc. KOCH, 1989


Similarly to chlorinated biphenyls, the toxicity and the environmental persistence of chlorinated naphthalenes increase with the degree of chlorination. The use of naphthalene with a high degree of chlorination should therefore be kept to a minimum.

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