Editing Naphthalene (section)

== Chemical properties ==

=== Reactions with electrophiles ===
In [[Electrophile|electrophilic]] aromatic [[substitution reaction]]s, naphthalene reacts more readily than benzene. For example, chlorination and bromination of naphthalene proceeds without a [[Catalysis|catalyst]] to give [[1-chloronaphthalene]] and [[1-Bromonaphthalene|1-bromonaphthalene]], respectively. Likewise, whereas both benzene and naphthalene can be [[alkylated naphthalene|alkylated]] using [[Friedel–Crafts reaction]] conditions, naphthalene can also be easily alkylated by reaction with [[alkene]]s or [[Alcohol (chemistry)|alcohol]]s, using [[sulfuric acid|sulfuric]] or [[phosphoric acid]] catalysts.<ref name=Ullmann/>  Contrariwise, anhydrous [[aluminium chloride]] reacts with naphthalene to give a hexamer, in which one ring of each naphthalene monomer loses aromaticity, linking to the other monomers at the 1 and 4 positions.<ref>{{cite journal|doi=10.1246/bcsj.42.779|date=March 1969|pages=779–781|journal=Bulletin of the Chemical Society of Japan|volume=42|title=Polymerization of napthalene and reactions of polynaphthalene|author1=Minato Hiroshi|author2=Higosaki Nobuyuki|author3=Isobe Chieko|orig-date=July 13, 1968|issue=3}}</ref>  

In terms of [[regiochemistry]], 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. [[Friedel-Crafts reaction#Friedel–Crafts dealkylation|Sulfonation]] gives the "alpha" product [[naphthalene-1-sulfonic acid]] as the kinetic product but [[naphthalene-2-sulfonic acid]] as the thermodynamic product. The 1-isomer forms predominantly at 25&nbsp;°C, and the 2-isomer at 160&nbsp;°C.
[[Friedel-Crafts reaction#Friedel–Crafts dealkylation|Sulfonation]] to give the 1- and 2-sulfonic acid occurs readily:
: {{chem2|H2SO4 + C10H8 → C10H7SO3H + H2O}}
Further sulfonation give di-, tri-, and tetrasulfonic acids.

=== Lithiation ===
Analogous to the synthesis of [[phenyllithium]] is the conversion of 1-bromonaphthalene to 1-lithionaphthalene, by [[lithium–halogen exchange]]:
: C<sub>10</sub>H<sub>7</sub>Br + BuLi  →   C<sub>10</sub>H<sub>7</sub>Li + BuBr
The resulting lithionaphthalene undergoes a second lithiation, in contrast to the behavior of phenyllithium. These 1,8-dilithio derivatives are precursors to a host of [[peri-naphthalene]] derivatives.<ref>{{cite journal | vauthors = van Soolingen J, de Lang RJ, den Besten R, Klusener PA, Veldman N, Spek AL, Brandsma L |display-authors=3| year = 1995 | title = A simple procedure for the preparation of 1,8-bis(diphenylphosphino)naphthalene | journal = Synthetic Communications | volume = 25 | issue = 11 | pages = 1741–1744 | doi = 10.1080/00397919508015858 }}</ref>

=== Reduction and oxidation ===
With alkali metals, naphthalene forms the dark blue-green radical anion salts such as [[sodium naphthalene]], Na<sup>+</sup>C<sub>10</sub>H{{su|b=8|p=−|lh=1}}. The naphthalene anions are strong reducing agents.

Naphthalene can be [[hydrogenate]]d under high pressure in the presence of metal [[catalyst]]s to give 1,2,3,4-tetrahydronaphthalene({{chem|C|10|H|12}}), also known as [[tetralin]]. Further hydrogenation yields decahydronaphthalene or [[decalin]] ({{chem|C|10|H|18}}).

Oxidation with {{chem|O|2}} in the presence of [[vanadium pentoxide]] as [[catalyst]] gives [[phthalic anhydride]]:
:C<sub>10</sub>H<sub>8</sub>  +  4.5 O<sub>2</sub>   →   C<sub>6</sub>H<sub>4</sub>(CO)<sub>2</sub>O  +  2 CO<sub>2</sub>  +  2 H<sub>2</sub>O
This reaction is the basis of the main use of naphthalene. [[Oxidation]] can also be effected using conventional stoichiometric [[Chromate and dichromate|chromate]] or [[permanganate]] reagents.