Process for preparing bromochloromethane

A process for preparing chlorobromomethane, comprising

• a) reacting dibromomethane and dichloromethane with at least one catalyst selected from the group consisting of aluminum trichloride, aluminum tribromide, iron (II) chloride, iron (III) chloride, nickel chloride, zinc chloride, boron trifluoride, tetraalkylphosphonium halide, tetraalkylphosphonium tosylate, tetraalkylphosphonium mesylate, tetraalkylphosphonium triflate, tetraarylphosphonium halide, tetraarylphosphonium tosylate, tetraarylphosphonium mesylate and tetraarylphosphonium triflate, whereby a first crude mixture comprising at least dibromomethane, dichloromethane and bromochloromethane is obtained, and
• b i) adding at least one alcohol to the first crude mixture obtained in step a), resulting in the formation of a monophasic second crude mixture, which comprises an organic phase comprising at least alcohol, dibromomethane, dichloromethane and bromochloromethane, or
• b ii) adding water and optionally at least one alcohol to the first crude mixture obtained in step a), resulting in the formation of a biphasic second crude mixture, which comprises an organic phase comprising at least dibromomethane, dichloromethane and bromochloromethane, and an aqueous phase, and the organic phase is separated off from the aqueous phase,
• c) separating the components dibromomethane, dichloromethane and bromochloromethane from one another from the monophasic second crude mixture from step b i), or from the separated organic phase of the second crude mixture from step b ii) by
• c i) firstly separating off dichloromethane as a first distillate over a first distillation column, said first distillate comprising dichloromethane at a content of 95 to 99.9% by weight based on the total mass of the distillate, from the monophasic second crude mixture from step b i) and/or from the separated organic phase of the second crude mixture from step b ii), and
• c ii) subsequently feeding a bottom portion from the distillation of step c i) into a second distillation column, the bottom portion comprising dibromomethane at a content of from 25 to 40% by weight based on total mass of the bottom portion and bromochloromethand at a content of 60 to 76% by weight based on total mass of the bottom portion,
• isolating bromochloromethane as a second distillate with a content of from 95 to 99.9% by weight based on the total mass of the second distillate and
• isolating dibromomethane as a bottom portion of from the distillation step c ii) in a content of 95 to 99.5% by weight based on the total weight of the bottom portion from distillation step c ii), and
• d) using the dichloromethane obtained from step c i) and the dibromomethane obtained from step c ii) in step a) of a subsequent preparation of bromochloromethane that comprises said steps a) to c).