The Partial Additive Chlorination of the Benzene Ring. II. The Isomers of Benzene Tetrachloride¹

Abstract

Five isomers of benzene tetrachloride, synthesized by the iodine-catalyzed photochlorination of benzene, have been isolated by vacuum rectification and partition chromatography, purified and characterized by melting point and infrared spectrophotometry. The steric structures of these isomers have been established by chlorination to benzene hexachloride. On the basis of the products thereby formed and of the structural relationships of the tetra-and hexachlorides, it has been possible to confirm chemically the reported configurations of the benzene hexachlorides and to assign the following structures to the benzene tetrachlorides: a, eepp; ß, peep; 7, eeep; S, eeee; e, eepe. The photocatalytic addition of chlorine to the cycloolefinic double bond has been shown to proceed by two cis and two trans mechanisms, yielding products in which the chlorine substituents thus introduced are oriented ep or pe, and ee or pp, respectively. Chemical evidence was obtained for ring conversion. B.p., 15 ram., Isomer °c.

Electrochemical reduction and anaerobic degradation of lindane

“…Gas chromatographic product analysis revealed the presence of three major components: an unidentified early eluting fraction followed by -BTC, and then by unreacted lindane. The -BTC was isolated by preparatory GC and had a melting point of 88-89 °C (Fisher-Johns apparatus) and an infrared spectrum (Beckman IR-5) in agreement with the values reported by Orloff et al (1953) Benzene formation was confirmed by synthesizing the 1,3-dinitro derivative with the following procedure. First, 15 ml of concentrated sulfuric acid was added to 5 ml of concentrated nitric acid and the mixture was cooled with ice to about 5 °C.…”

“…It is not surprising that -BTC is formed at the first step during the reduction. The conformation of the chlorines in lindane is eeeaaa (e = equatorial, a = axial) while -BTC has the conformation eeea or aaae, the former being the preferred conformation (Orloff et al, 1953). Thus, there are four equivalent positions (allowing for ring inversion) on lindane by which the loss of adjacent chlorines will generate -BTC.…”

The Stereoisomerism of Cyclohexane Derivatives.

“…If ring conversion is assumed to take place readily, then there are only eight separable steric isomers of which only one (a) has a separable pair of enantiomorphs. Chemical evidence for ring conversion (220) supports the smaller number.…”

The Tetrahydrophphalic Acids

“…Although extensive structural determinations have not been carried out. it has been possible to treat the stereochemistry of substituted cyclohexenes (21,22,23,24,77,104) in a fashion analogous to that used for cyclohexanes (103). Figure 1 shows the chair form or ''half chair" form and figure 2 the boat form or "half boat'' form which are possible for the cyclohexene ring (21).…”

“…Only carbon atoms 4 and 5 of the cyclohexene ring have well-defined equatorial bonds (e) and axial bonds fa), which before 1954 were designated as polar bonds fp). The bonds of carbon atoms 3 and 0 can be designated as either axial fa') or equatorial (e') on the basis of what they would be if the double bond were saturated (21,104).…”