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In the early 1820s, two separate reports described a white solid with a pungent odor derived from thedistillation ofcoal tar. In 1821,John Kidd cited these two disclosures and then described many of this substance's properties and the means of its production. He proposed the namenaphthaline, as it had been derived from a kind ofnaphtha (a broad term encompassing any volatile, flammable liquid hydrocarbon mixture, including coal tar).[16] Naphthalene's chemical formula was determined byMichael Faraday in 1826. The structure of two fusedbenzene rings was proposed byEmil Erlenmeyer in 1866,[17] and confirmed byCarl Gräbe three years later.[18]
A naphthalene molecule can be viewed as the fusion of a pair ofbenzene rings. (Inorganic chemistry, rings arefused if they share two or more atoms.) As such, naphthalene is classified as a benzenoidpolycyclic aromatic hydrocarbon (PAH).[19]
The eight carbon atoms that are not shared by the two rings carry one hydrogen atom each. For purpose of the standardIUPAC nomenclature of derived compounds, those eight atoms are numbered 1 through 8 in sequence around the perimeter of the molecule, starting with a carbon atom adjacent to a shared one. The shared carbon atoms are labeled 4a (between 4 and 5) and 8a (between 8 and 1).[20]
The molecule is planar, like benzene. 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 1.37 Å (137 pm) in length, whereas the other carbon–carbon bonds are about 1.42 Å (142 pm) long. This difference, established byX-ray diffraction,[21] is consistent with thevalence bond model in naphthalene and in particular, with the theorem ofcross-conjugation. This theorem would describe naphthalene as anaromatic benzene unit bonded to adiene but not extensivelyconjugated to it (at least in theground state), which is consistent with two of its threeresonance structures.
Because of this resonance, the molecule hasbilateral symmetry across the plane of the shared carbon pair, as well as across the plane that bisects bonds C2-C3 and C6-C7, and across the plane of the carbon atoms. Thus there are two sets of equivalent hydrogen atoms: thealpha positions, numbered 1, 4, 5, and 8, and thebeta positions, 2, 3, 6, and 7. Twoisomers are then possible for mono-substituted naphthalenes, corresponding to substitution at an alpha or beta position.
Pure crystalline naphthalene is a moderate insulator at room temperature, withresistivity of about 1012Ωm. The resistivity drops more than a thousandfold on melting, to about 4 × 108 Ω m. Both in the liquid and in the solid, the resistivity depends on temperature asρ =ρ0 exp(E/(kT)), whereρ0 (Ω⋅m) andE (eV) are constant parameters,k is the Boltzmann constant (8.617 × 10−5 eV/K), andT is absolute temperature (K). The parameterE is 0.73 in the solid. However, the solid shows semiconducting character below 100 K.[23][24]
In terms ofregiochemistry, electrophiles attack at the alpha position. The selectivity for alpha over beta substitution can be rationalized in terms of the resonance structures of the intermediate: for the alpha substitution intermediate, seven resonance structures can be drawn, of which four preserve an aromatic ring. For beta substitution, the intermediate has only six resonance structures, and only two of these are aromatic.Sulfonation gives the "alpha" productnaphthalene-1-sulfonic acid as the kinetic product butnaphthalene-2-sulfonic acid as the thermodynamic product. The 1-isomer forms predominantly at 25 °C, and the 2-isomer at 160 °C.Sulfonation to give the 1- and 2-sulfonic acid occurs readily:
H2SO4 + C10H8 → C10H7SO3H + H2O
Further sulfonation give di-, tri-, and tetrasulfonic acids.
The resulting lithionaphthalene undergoes a second lithiation, in contrast to the behavior of phenyllithium. These 1,8-dilithio derivatives are precursors to a host ofperi-naphthalene derivatives.[27]
With alkali metals, naphthalene forms the dark blue-green radical anion salts such assodium naphthalene, Na+C10H− 8. The naphthalene anions are strong reducing agents.
Naphthalene can behydrogenated under high pressure in the presence of metalcatalysts to give 1,2,3,4-tetrahydronaphthalene(C 10H 12), also known astetralin. Further hydrogenation yields decahydronaphthalene ordecalin (C 10H 18).
This reaction is the basis of the main use of naphthalene.Oxidation can also be effected using conventional stoichiometricchromate orpermanganate reagents.
From the 1960s until the 1990s, significant amounts of naphthalene were produced from heavypetroleum fractions duringrefining, but present-day production is mainly fromcoal tar.[28] As of 2023[update], the global napthalene market was 2.25 million tons.[29]
Naphthalene is the most abundant single component of coal tar.[30] The composition of coal tar varies with coal type and processing, but typical coal tar is about 10% naphthalene by weight.[31] In industrial practice,distillation of coal tar yields an oil containing about 50% naphthalene, along with twelve otheraromatic compounds.[30] This oil, after being washed with aqueoussodium hydroxide to removeacidic components (chiefly variousphenols), and with sulfuric acid to removebasic components, undergoesfractional distillation to isolate naphthalene. The crude naphthalene resulting from this process is about 95% naphthalene by weight. The chief impurities are the sulfur-containing aromatic compoundbenzothiophene (< 2%),indane (0.2%),indene (< 2%), andmethylnaphthalene (< 2%). Petroleum-derived naphthalene is usually purer than that derived from coal tar. Where required, crude naphthalene can be further purified byrecrystallization from any of a variety of solvents, resulting in 99% naphthalene by weight, referred to as 80 °C (melting point).[25]
InNorth America, the coal tar producers areKoppers Inc., Ruetgers Canada Inc. and Recochem Inc., and the primary petroleum producer is Monument Chemical Inc. In Western Europe the well-known producers are Koppers, Ruetgers, and Deza. InEastern Europe, naphthalene is produced by a variety of integratedmetallurgy complexes (Severstal, Evraz, Mechel, MMK) inRussia, dedicated naphthalene and phenol makers INKOR, Yenakievsky Metallurgy plant inUkraine and ArcelorMittal Temirtau inKazakhstan.
Naphthalene is used mainly as a precursor to derivative chemicals. The single largest use of naphthalene is the industrial production ofphthalic anhydride, although more phthalic anhydride is made fromo-xylene.
Naphthalene has been used as afumigant. It was once the primary ingredient inmothballs, although its use has largely been replaced in favor of alternatives such as1,4-dichlorobenzene. In a sealed container containing naphthalene pellets, naphthalene vapors build up to levels toxic to both the adult and larval forms of manymoths that attack textiles. Otherfumigant uses of naphthalene include use in soil as a fumigantpesticide, inattic spaces to repelinsects and animals such asopossums,[34] and in museum storage-drawers and cupboards to protect the contents from attack by insect pests.
Molten naphthalene provides an excellent solubilizing medium for poorly soluble aromatic compounds. In many cases it is more efficient than other high-boiling solvents, such asdichlorobenzene,benzonitrile,nitrobenzene anddurene. The reaction ofC60 withanthracene is conveniently conducted in refluxing naphthalene to give the 1:1Diels–Alder adduct.[35] The aromatization of hydroporphyrins has been achieved using a solution ofDDQ in naphthalene.[36]
Manynaphthalenesulfonic acids and sulfonates are useful. Naphthalenesulfonic acids are used in the synthesis of1-naphthol and2-naphthol, precursors for various dyestuffs, pigments, rubber processing chemicals and other chemicals and pharmaceuticals.[25] They are also used as dispersants in synthetic and natural rubbers, in agriculturalpesticides, in dyes, and inlead–acid battery plates. Naphthalenedisulfonic acids such asArmstrong's acid are used as precursors and to form pharmaceutical salts such asCFT.
Alkylnaphthalene sulfonates (ANS) are used in many industrial applications as nondetergentsurfactants (wetting agents) that effectively disperse colloidal systems in aqueous media. The major commercial applications are in the agricultural chemical industry, which uses ANS for wettable powder and wettable granular (dry-flowable) formulations, and in the textile and fabric industry, which uses the wetting and defoaming properties of ANS for bleaching and dyeing operations.
Hydrogenation of naphthalene gives tetrahydronaphthalene (tetralin) and decahydronaphthalene (decalin), which are used as low-volatilitysolvents. Tetralin is used as a hydrogen-donor solvent.[25]
Several uses stem from naphthalene's high volatility: it is used to create artificial pores in the manufacture of high-porositygrinding wheels; it is used in engineering studies of heat transfer using masssublimation; and it has been explored as a sublimable propellant for cold gas satellite thrusters.[38][39]
Exposure to large amounts of naphthalene may damage or destroyred blood cells, most commonly in people with the inherited condition known asglucose-6-phosphate dehydrogenase (G6PD) deficiency,[40] from which approximately 400 million people suffer.[41] Humans, in particular children, have developed the condition known ashemolytic anemia, after ingesting mothballs or deodorant blocks containing naphthalene. Symptoms includefatigue, lack of appetite, restlessness, and pale skin. Exposure to large amounts of naphthalene may causeconfusion,nausea,vomiting,diarrhea,blood in theurine, andjaundice (yellow coloration of the skin due to dysfunction of theliver).[42]
The USNational Toxicology Program (NTP) held an experiment where male and female rats and mice were exposed to naphthalene vapors on weekdays for two years.[43] Both male and female rats exhibited evidence ofcarcinogenesis with increased incidences ofadenoma andneuroblastoma of the nose. Female mice exhibited some evidence of carcinogenesis based on increased incidences ofalveolar andbronchiolaradenomas of thelung, while male mice exhibited no evidence of carcinogenesis.
TheInternational Agency for Research on Cancer (IARC)[44] classifies naphthalene as possibly carcinogenic to humans and animals (Group 2B). The IARC also points out that acute exposure causescataracts in humans,rats,rabbits, andmice; and that hemolytic anemia (described above) can occur in children and infants after oral or inhalation exposure or after maternal exposure during pregnancy. A probable mechanism for the carcinogenic effects of mothballs and some types of air fresheners containing naphthalene has been identified.[45][46]
Mothballs and other products containing naphthalene have been banned within theEU since 2008.[49][50]
InChina, the use of naphthalene in mothballs is forbidden.[51] Danger to human health and the common use of naturalcamphor are cited as reasons for the ban.
^abNaphthalene in Linstrom, Peter J.; Mallard, William G. (eds.);NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD) (retrieved 2014-05-24)
^Amoore JE, Hautala E (1983). "Odor as an aid to chemical safety: Odor thresholds compared with threshold limit values and volatiles for 214 industrial chemicals in air and water dilution".J Appl Toxicol.3 (6):272–290.doi:10.1002/jat.2550030603.PMID6376602.S2CID36525625.
^John Kidd (1821). "Observations on Naphthalene, a peculiar substance resembling a concrete essential oil, which is produced during the decomposition of coal tar, by exposure to a red heat".Philosophical Transactions.111:209–221.doi:10.1098/rstl.1821.0017.S2CID97798085.
^Cruickshank, D. W. J.; Sparks, R. A. (18 October 1960). "Experimental and Theoretical Determinations of Bond Lengths in Naphthalene, Anthracene and Other Hydrocarbons".Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.258 (1293):270–285.Bibcode:1960RSPSA.258..270C.doi:10.1098/rspa.1960.0187.S2CID96765335.
^Dieter Cremer; Thomas Schmidt; Charles W. Bock (1985). "Theoretical determination of molecular structure and conformation. 14. Is bicyclo[6.2.0]decapentaene aromatic or antiaromatic?".J. Org. Chem.50 (15):2684–2688.doi:10.1021/jo00215a018.
^Minato Hiroshi; Higosaki Nobuyuki; Isobe Chieko (March 1969) [July 13, 1968]. "Polymerization of napthalene and reactions of polynaphthalene".Bulletin of the Chemical Society of Japan.42 (3):779–781.doi:10.1246/bcsj.42.779.
^van Soolingen J, de Lang RJ, den Besten R, et al. (1995). "A simple procedure for the preparation of 1,8-bis(diphenylphosphino)naphthalene".Synthetic Communications.25 (11):1741–1744.doi:10.1080/00397919508015858.
^K. Komatsua; Y. Murataa; N. Sugitaa; et al. (1993). "Use of naphthalene as a solvent for selective formation of the 1:1 Diels–Alder adduct of C60 with anthracene".Tetrahedron Letters.34 (52):8473–8476.doi:10.1016/S0040-4039(00)61362-X.
^M.A. Filatov; A.V. Cheprakov (2011). "The synthesis of new tetrabenzo- and tetranaphthoporphyrins via the addition reactions of 4,7-dihydroisoindole".Tetrahedron.67 (19):3559–3566.doi:10.1016/j.tet.2011.01.052.
^"NTP Technical Reports 410 and 500".NTP Technical Reports 410 and 500, available from NTP: Long-Term Abstracts & Reports.Archived from the original on October 24, 2004. RetrievedMarch 6, 2005.
