GB812064A - Improvements in or relating to the production of aromatic aldehydes - Google Patents

Abstract

<PICT:0812064/III/1> A reaction mixture containing an aldehydeboron trifluoride-hydrofluoric acid complex and obtained from a continuous aromatic aldehyde synthesis using an aromatic hydrocarbon, carbon monoxide and a boron trifluoride-hydrofluoric acid catalyst, is treated with at least the stoichiometrically correct quantity of barium fluoride or strontium fluoride which is required to combine the boron trifluoride to form the metal fluoborate and at the same time to liberate hydrofluoric acid from the complex in an anhydrous state. The liberated hydrofluoric acid may be removed from the mixture by distillation or evaporation before or after the metal fluoborate is removed, and condensed and recycled to the synthesis. The fluoborate may be heated in a revolving drum to liberate the metal fluoride and boron trifluoride both of which may be used again. In a preferred embodiment, complex from aldehyde synthesis reactor 1 is depressurized in 2 and continuously run into each of the stirrer vessels 3 or 3a in turn. In 3 or 3a barium fluoride in toluene from 4 is run in to combine with the boron trifluoride only. Liberated hydrofluoric acid is drawn off by vacuum and condensed in cooler 7 and recycled to the synthesis at 1. The fluorborate slurry is run out of 3 or 3a, centrifuged in 10 and the filtrate processed to recover aldehyde. The fluoborate is heated in drum 12 to liberate boron trifluoride which may be recycled to the synthesis and barium fluoride which may be recycled to the decomposition. An example is given.ALSO:In a continuous process for making aromatic aldehydes from aromatic hydrocarbons and carbon monoxide in the presence of boron trifluoride and hydrofluoric acid as catalysts, the reaction mixture comprising an organic aldehyde-boron trifluoride-hydrofluoric acid complex, excess hydrofluoric acid and aromatic hydrocarbon and discharged from the reaction zone is treated with at least the stoichiometrically correct quantity of barium fluoride or strontium fluoride which is required to combine with the boron trifluoride to form a metal fluoborate and at the same time to liberate hydrofluoric acid from the complex in an anhydrous state. The liberated hydrofluoric acid may be removed from the mixture by distillation or by a vacuum pump either before or after the metal fluoborate is removed by centrifuging or filtration. The recovered fluoborate may be heated in a revolving drum to liberate the metal fluoride and boron trifluoride both of which may be used in the process again. The hydrofluoric acid may be condensed and recycled to the synthesis. The metal fluoride may be added to the reaction mixture in an inert vehicle such as toluene or benzene. In a preferred embodiment, the reaction mixture from the aldehyde synthesis is run continuously into each of at least two vessels in turn. One of these vessels is always in operation decomposing the complex, the reaction mixture being discharged continuously into one or other of the vessels. The calculated amount of barium or strontium fluoride is added to the reaction mixture in the vessel with stirring, free hydrofluoric acid is removed under vacuum and with slight heating and the mixture is run out of the vessel. The metal fluoborate is removed and the aldehyde obtained from the filtrate by distillation. An example illustrating the preparation of p-tolualdehyde from toluene is given. The aldehyde synthesis is conducted by continuously injecting the aromatic hydrocarbon, anhydrous hydrofluoric acid, gaseous boron trifluoride and carbon monoxide into a reactor vessel under 50-150 atmospheres pressure, the reaction mixture being continuously pumped through a condenser connected across the reaction vessel and maintained at -30 DEG to +20 DEG C.