The invention provides compounds of the general formula ##STR1## wherein R represents a hydrogen atom, or an optionally substituted alkyl or acyl group, or an alkenyl or alkynyl group or an inorganic or organic cation;R.sup.1 represents an alkyl, haloalkyl, alkenyl, alkynyl or optionally substituted aralkyl or phenyl group;R.sup.2 represents an optionally substituted alkyl or phenalkyl group or a cycloalkyl, alkenyl, haloalkenyl or alkynyl group;each R.sup.3 represents an optionally substituted alkyl group;one of R.sup.4 or R.sup.5 represents a hydrogen atom or an alkyl group while the other of R.sup.4 and R.sup.5 represents an optionally substituted phenyl group; together with their use as herbicides and their preparation using novel intermediates.