Compounds of formula : wherein: R1 represents hydrogen, a halogen or alkyl, R1a represents hydrogen or alkyl, R2 represents hydrogen, a halogen or hydroxy, A represents NR4, R3 represents hydrogen, alkyl or cycloalkyl, R4 represents hydrogen or alkyl, X is as defined in the description, their isomers, and also addition salts thereof. In accordance with the invention, the separation chamber is made in multistage form, with the first stage of the separation chamber serving the accumulation of the water drops, the second stage of the separation chamber serving the deposition of the accumulated water drops and the third stage of the separation chamber serving the extraction of the air mass flow. The spinning tumbler is preferably rotated about its longitudinal axis by a motor. the transformer and when the circuit wire-to-ground voltage exceeds an appropriately-established dynamic sensitivity voltage value. The plasma tube assembly also has a plasma-sustaining region defined by an upstream plurality of plasma traps and a downstream plurality of plasma traps.