R9 is a hydrogen atom or an alkyl group of 1 to 4 carbon atoms which may be substituted by a hydroxy, cyano, carboxy, sulfo, sulfato, carbomethoxy or carbethoxy group or a phenyl radical, or is a phenyl radical which may be substituted by alkyl of 1 to 4 carbon atoms, alkoxy of 1 to 4 carbon atoms, chlorine and/or sulfo,