Experimental and theoretical studies of a greener catalytic system for saturated hydrocarbon chlorination composed by trichloroisocyanuric acid and a copper(II) compound

Abstract

We are describing herein a new environmentally friendly catalytic system able to convert cyclohexane to chlorocyclohexane with 100% selectivity. The method was also applied to the chlorination of n-hexane and adamantane. The catalytic system employs thichloroisocyanuric acid (TCCA) as halogenating agent and a mononuclear copper(II) complex [Cu(BPAH)(H2O)](ClO4)2, 1, as catalyst (BPAH = 1,4-bis(propanamide)homopiperazine), whose molecular structure was solved by monocrystal X-ray diffraction. For cyclohexane, at a ratio catalyst:substrate:TCCA of 1:1000:333, the system reached a conversion of 32.0 ± 1% at 25 °C and 44.7 ± 0.4% at 50 °C, with 100% selectivity for chlorocyclohexane. With n-hexane, a similar conversion was observed at 50 °C, resulting in mixture of monochlorides. Employing adamantane as substrate, the isomers 1-chloroadamantane and 2-chloroadamante were preferentially formed, together with traces of dichloroadamantane. EPR and ESI-(+)-MS analyses indicate the formation of a Cu-hypochlorite intermediate species, which is supported by theoretical calculations.