Penta-chlor benzene

Mono-chlor benzene, CeHaCl.. Penta-chlor benzene, CeHCU.. 

Hexa-chlor benzene is formed by the chlorination not only of benzene itself, but also of other more complex hydrocarbons, e.g, naphthalene, anthracene, phenanthrene, di-phenyl methane (but not diphenyl). Penta-chlor benzene is of interest because it was at one time supposed to exist in isomeric forms which is contrary to the Kekule theory. 

Chlor Naphthalenes.—Another series of reactions which support the view just discussed, that in naphthalene there are present two nuclei either one of which is a benzene ring, is found in Laurent s work on the chlorine substitution products of naphthalene. When naphthalene is chlorinated it yields different chlor naphthalenes. Two of these are important in this place, viz., a tetra-chlor naphthalene, C10H4CI4 and a penta-chlor naphthalene, C10H3CI5. Now the first one must have all four chlorines linked to one nucleus because on oxidation it yields ortho-phthalic acid, as below. The penta-chlor compound must of necessity have at least one of the chlorines linked to the second nucleus as only four are possible of being linked to one nucleus. Now this compound on oxidation yields not mono-chlor phthalic acid but tetra-chlor phthalic acid. The reactions may be represented as follows ... 

Substitution Products.— The halogen derivatives of naphthalene include both substitution and addition products. The tetra- and penta-chlor substituted naphthalenes have already been referred to as furnishing proof that in naphthalene there are present two benzene nucleii (p. 771). Other halogen substituted naphthalenes are known but none need be discussed in detail. ... 

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