Synthesis and aromatization of 2+2 cycloadducts of butadienes and tetrafluoroethylene

Passing tetrafluoroethylene (TFE) and hydrocarbon dienes down a hot tube at 600 °C with a contact time of a few seconds produces substituted fluorobenzenes. Specifically, tetrafluoroethylene and butadiene form 1,2-difluorobenzene. The aromatics produced by the pyrolysis of TFE and methyl-substituted butadienes do not necessarily result from eliminating HF from the 2+4 adducts of the starting materials. Solid-acids such as alumina or silica/alumina accelerate the ring-expansion elimination of the 2+2 cycloadducts. Aromatic products result from the preformed 2+2 cycloadducts at temperatures 200 °C lower than the corresponding thermal reaction. The solid-acids can also influence product regiochemistry.