Pyrazolopyrimidine herbicides

The invention provides certain herbicidal pyrazolopyrimidine derivatives, processes for their preparation, and compositions containing them, the compounds being of the formula: and salts thereof, where: R' and R2, which may be the same or different, each represent hydrogen, hydroxy, halo, substituted or unsubstituted alkyl, alkoxy, alkylthio, alkenyl, alkynyl or phenyl, or heterocyclyl;R6 represents hydrogen, halo, cyano, carboxy, alkoxycarbonyl, or substituted or unsubstituted alkyl or carbamoyl; or R6 and one of R' and R2 together represent an alkylene chain of 3 or 4 carbon atoms:R3 represents hydrogen, alkyl, aryl, aralkyl, carboxy, substituted or unsubstituted alkoxycarbonyl, carbamoyl or thiocarbamoyl, cyano or nitro; X represents -NR-SO2-, -S02-0-, -S02-NR- or -S(O)n-CR'R"-, where n is 0, 1 or 2 and R, R' and R" each represent hydrogen, or substituted or unsubstituted alkyl, alkenyl, alkynyl, alkoxycarbonyl, acyl, alkylsulphonyl or arylsulphonyl; and R4 represents hydrogen, heterocyclyl, or a substituted or unsubstituted alkyl or aryl group.