Polynuclear aromatic compound• Polycyclic aromatic hydrocarbons (PAHs), also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents.• Napthalene is the simplest example of a PAH.• PAHs occur in oil, coal, and tar deposits, and are produced as byproducts of fuel burning.• As a pollutant, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic.
Polynuclear aromatic compound• The simplest PAHs, are phenanthrene and anthracene, which both contain three fused aromatic rings.• PAHs may contain four-, five-, six- or seven- member rings, but those with five or six are most common.• Naphthalene, consisting of two coplanar six- membered rings sharing an edge, is another aromatic hydrocarbon. By formal convention, it is not a true PAH, though is referred to as a bicyclic aromatic hydrocarbon.
Napthalene-Properties• Molecular Formula • C10H8• Molar Mass • 128.17 g/mol• Appearance • White solid• Density • 1.14 g/cc• Melting Point • 80.26 oC• Boiling Point • 218 oC
Napthalene Properties• Naphthalene, also known as naphthalin, bicyclo[4.4.0]deca-1,3,5,7,9-pentene or antimite is a crystalline, aromatic, white, solid hydrocarbon with formula C10H8 and the structure of two fused benzene rings.• It is volatile, forming a flammable vapor, and readily sublimes at room temperature, producing a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass.
Structure and Reactivity• A naphthalene molecule is derived by the fusion of a pair of benzene rings.• Unlike benzene, the carbon-carbon bonds in naphthalene are not of the same length.• Like benzene, naphthalene can undergo electrophilic aromatic substitution.• For many electrophilic aromatic substitution reactions, naphthalene reacts under milder conditions than does benzene.• For example, whereas both benzene and naphthalene react with chlorine in the presence of a ferric chloride or aluminium chloride catalyst, naphthalene and chlorine can react to form 1- chloronaphthalene even without a catalyst.• Similarly, whereas both benzene and naphthalene can be alkylated using Friedel-Crafts reactions,• naphthalene can also be alkylated by reaction with alkenes or alcohols, with sulfuric or phosphoric acid as the catalyst.
• Like benzene, naphthalene can undergo electrophilic aromatic substitution.