J. S. Lomas

The kinetics and mechanisms of aromatic halogen substitution. Part XXIV. The stereochemistry of addition of chlorine to naphthalene

The reaction of chlorine with naphthalene in acetic acid gives products of substitution (mainly 1-chloronaphthalene); products of addition of chlorine (mainly naphthalene-α-tetrachloride, m. p. 182°); and other products of addition (mainly an acetoxytrichloride). In the presence of added lithium chloride, the mixture of tetrachlorides contains a major proportion of the stereoisomeric δ-isomer, m. p. 96°. Light-catalysed addition in carbon tetrachloride gives a mixture of isomers, the least soluble being naphthalene-γ-tetrachloride, m. p. 134°, and the major part of the remainder being a new isomer, naphthalene-Iµ-tetrachloride, m. p. 85–87°. The configurations and conformations of the γ-, δ-, and Iµ-tetrachlorides and of the acetoxytrichloride have been established by proton magnetic resonance spectroscopy. The results establish that the α-tetrachloride is not formed through capture of a carbonium ionic intermediate by chloride ion from the environment.

Kinetics and mechanisms of aromatic halogen substitution. Part XXVIII. Environmental effects on rates and products of chlorination of some aromatic hydrocarbons

Chlorination of phenanthrene in acetic acid gives a mixture of products of substitution and addition, in which cis-9-acetoxy-10-chloro-9,10-dihydrophenanthrene has been found and estimated by n.m.r. spectroscopy, and 1-, 3-, and 4-chlorophenanthrene have been identified and estimated approximately by infrared spectroscopy. The effects of added electrolytes, and of change in solvent, on the rate of chlorination and on the proportions of adducts and products of substitution have been studied. The results suggest complexities analogous to those involved in the product-determining stages of other reactions involving carbonium ionic intermediates. The effects of added electrolytes on rates and products of the chlorination of biphenyl have also been investigated. Comparison of the effects of change in solvent on the rates and products of chlorination of naphthalene with the corresponding results for phenanthrene establish that the transition state leading to cis-addition can have considerable carbonium ionic character.

The alkaline dehydrochlorination of some naphthalene tetrachlorides and related compounds

The rates and products of alkaline dehydrochlorination of the four known naphthalene tetrachlorides have been investigated, one for the first time and the others in more detail than has previously been recorded. The results are compared with those reported for the benzene tetrachlorides; they throw light on the accessibility of the various possible modes of elimination in chloro-substituted cyclohexenes and derived systems.

The kinetics and mechanisms of aromatic halogen substitution. Part XXV. The chlorination of 2-methylnaphthalene

The chlorination of 2-methylnaphthalene in acetic acid is generally similar to that of naphthalene, in that products of substitution are accompanied by those of addition. The main components of the reaction mixture have been separated, and the structures of a crystalline tetrachloride, m.p. 99–99·5°, and of an acetoxytrichloride, m. p. 130°, have been deduced from studies of their proton magnetic resonance spectra and of their behaviour on alkaline dehydrochlorination. Their properties are compared with those of a 1-chloro-2-methylnaphthalene tetrachloride, m. p. 153°, and of various related compounds. The synthesis of 1,4-dichloro-2-methylnaphthalene is described.