When the aromatic group is further substituted by an atom or group other than carboxy or a group which carries a carboxy group, the preferred substituents are selected from halogen (especially F or Cl); ???NO2; ???CF3; ???CN; ???SO3H, ???PO3H2; or a C1-6-alkyl, C2-6-alkenyl, C5-8-cycloalkyl or C1-6-calkoxy group optionally substituted by ???OH, ???NH2, ???NO2 -SO3H, ???PO3H2 or halogen; a group of