Graham W. Burton

Naphthalene tetrachlorides and related compounds. Part IV. Photochemical chlorination of 1-chloronaphthalene

The photochemical chlorination of 1-chloronaphthalene gives a mixture of dichlorides, which on further chlorination give several new 1-chloronaphthalene tetrachlorides. The structures of the latter have been elucidated by using 1H n.m.r. spectroscopy and by isomerisation with aluminium trichloride as the 1,1,r-2,t-3,c-4- and 1,1,r-2,-c-3,t-4-pentachlorotetralins; and the r-1,t-2,t-3,c-4,5-; r-1,t-2,c-3,c-4,5-; and r-1,t-2,c-3,t-4,5-pentachlorotetralins. Evidence is presented to suggest that the last compound, because of internal non-bonding strain, exists predominantly in an unusual ‘half-boat’ conformation. The results are compared with those obtained by heterocyclic chlorination, from which another isomer, r-1,c-2,t-3,t-4,5-pentachlorotetralin, is a minor product. The course and products of alkaline dehydrochlorination have been used to support some of the assignments of structure. The heterolytic chlorination of 1,2-dichloronaphthalene has been examined also; the major product is r-1,t-2,c-3,t-4,5,6-hexachlorotetralin, which also exists in a ‘half-boat’ conformation.

Naphthalene tetrachlorides and related compounds. Part V. Chlorination of 1,5-dichloronaphthalene; conformations affected by intramolecular non-bonding repulsions

The chlorination of 1,5-dichloronaphthalene in chloroform or in dichloromethane is heterolytic in character, but gives little or no trichloronaphthalene. The main tetrachloride product is 1,1,r-2,t-3,c-4,5-hexachlorotetralin, previously thought to be its t-4-isomer. The latter compound has been prepared by isomerisation of the former with aluminium trichloride. The structures have been established by using 1H n.m.r. spectroscopy together with reactions with aluminium trichloride and with sodium methoxide. The former tetrachloride exists in a deformed conformation as the result of intramolecular non-bonding repulsions. trans-1,2,4,8-Tetrachloro-1,2-dihydronaphthalene is an intermediate in the chlorination.

Naphthalene dichloride and its derivatives. Part II. 1,2,3-Trichloro-1,2-dihydronaphthalene from the dehydrochlorination of naphthalene δ-tetrachloride; a comparison of vicinal coupling constants in the 1H nuclear magnetic resonance spectra of some 1,2-dihydronaphthalenes, tetralins, and related compounds

1,2,3-Trichloro-1,2-dihydronaphthalene has been prepared by the partial dehydrochlorination of naphthalene δ-tetrachloride, and has been characterised spectroscopically and kinetically. Vicinal coupling constants in the 1H n.m.r. spectra of some 1,2-dihydronaphthalenes are compared with related values for other systems.

Naphthalene dichloride and its derivatives. Part III. trans-1,2-Dichloro-1,2-dihydronaphthalene and a new naphthalene tetrachloride, r-1,c-2,c-3,t-4-tetrachlorotetralin

The photochemical chlorination of naphthalene with equimolar amounts of chlorine in carbon disulphide at low temperatures gives trans-1,2-dichloro-1,2-dihydronaphthalene, which on heterolytic chlorination in methylene chloride gives a new (fifth) geometric isomer of naphthalene tetrachloride, r-1,c-2,c-3,t-4-tetrachlorotetralin. On alkaline dehydrochlorination in a mixture of methanol and acetone this tetrachloride gives, as the main intermediate,trans-1,2,4-trichloro-1,2-dihydronaphthalene. Some reaction through other intermediates, one of which can decompose unimolecularly, is indicated also. Further dehydrochlorination of trans-1,2,4-trichloro-1,2-dihydronaphthalene gives approximately equal amounts of 1,3- and 1,4-dichloronaphthalene by a bimolecular route, which is accompanied by a unimolecular pathway giving nearly exclusively 1,4-dichloronaphthalene. The results throw new light on the courses taken in the dehydrochlorination of the naphthalene tetrachlorides; comparisons are made of the reactivities of some naphthalene trans-dichlorides in bimolecular and unimolecular eliminations. Treatment of the new naphthalene tetrachloride with aluminium trichloride in nitrobenzene effects nearly complete conversion into naphthalene Iµ-tetrachloride, consistent with the view that this isomerisation involves heterolysis of 1- and 4-, but not of 2- and 3-chlorine substituents.

Dehydrochlorination of some naphthalene tetrachlorides and related compounds. Part III. Structure and dehydrochlorination of a 1,2,3,4-tetrachloro-1-phenyltetralin

Chlorine reacts with 1-phenylnaphthalene in chloroform to give, among other products, a tetrachloride which has been characterised from its 1H n.m.r. spectrum as r-1,c-2,t-3,t-4-tetrachloro-1-phenyltetralin. On alkaline dehydrochlorination, it gives 2,3-dichloro-1-phenylnaphthalene almost exclusively; when heated in carbon disulphide or when treated in nitromethane with an excess of aluminium trichloride, it gives 2,4-dichloro-1-phenylnaphthalene and 2,3-dichloro-1-phenylnaphthalene in a ratio of ca. 2 : 1 or greater. The mechanistic implications of these results are discussed.

The kinetics and mechanisms of aromatic halogen substitution. Part XXX. Chlorination of triphenylene: linear free-energy relationships in chlorinations of some aromatic hydrocarbons

A study of the rates of chlorination of p-xylene, m-xylene, mesitylene, triphenylene, naphthalene, and phenanthrene by molecular chlorine in acetic acid, and of the proportions and nature of the products, allows a reassessment of the applicability of linear free-energy correlations with related data for other electrophilic reactions and with theoretical parameters. Similar relationships for the reactions of acidified hypochlorous acid in aqueous dioxan with a range of hydrocarbons are also discussed.

The alkaline dehydrochlorination of some naphthalene tetrachlorides and related compounds. Part II. 1,1,2,3,4-Pentachlorotetralin

The rates and products of alkaline dehydrochlorination of 1,1,2,3,4-pentachlorotetralin and its 2- and 4-deuterio-derivatives have been examined; they establish that the primary kinetic isotope effect on both the first and second stage of the reaction is large (kH:kD > 7). Evidence for a small secondary deuterium isotope effect for hydrogen atoms α- to the displaced halogen (kH:kD= 1·12) is also obtained. Comparison with corresponding kinetic measurements on naphthalene α-tetrachloride and its octadeuterio-derivative throws light on the conformations and reaction paths involved in these reactions. The alternative paths available for dehydrochlorination, though not much affected by temperature, are substantially dependent on the solvent, in a way which indicates complex formation between certain aromatic solvents and the organic substrate, and can be correlated with solvent effects on the chemical shifts of the 1H n.m.r. signals from the alicyclic hydrogen atoms.