d by fluorine, chlorine or bromine atoms; and, R4 is a hydrogen atom, an alkyl group with 1 to 4 carbon atoms, an alkenyl or alkynyl group having 3 to 6 carbon atoms; or, R3 and R4 together with the nitrogen atom between them form a pyrrolidino, piperidino, hexamethyleneimino or morpholino group; or, a pharmaceutically acceptable acid addition salt thereof. 2.