A heat sensitive recording material, comprising a) at least one colour forming compound, and b) at least one developer of formula (1), wherein R1 is unsubstituted or substituted phenyl, naphthyl or C1-C20 alkyl, X is a group of formula (i), (ii) or (iii), A is unsubstituted or substituted phenylene, naphthylene or C1-C12 alkylene, or is an unsubstituted or substituted heterocyclic group, B is a linking group of formula -O-SO2-, -SO2-O-, -NH-SO2-, -SO2-NH-, -S-SO2-, -O-CO-, -O-CO-NH-, -NH-CO-, -NH-CO-O-, -S-CO-NH-, -S-CS-NH-, -CO-NH-SO2-, -O-CO-NH-SO2-, -NH=CH-, -CO-NH-CO-, -S-, -CO-, -O-, -SO2-NH-CO-, -O-CO-O- and -O-PO-(OR2)2, and R2 is unsubstituted or substituted aryl or benzyl or C1-C20alkyl, with the proviso, that, if B is not a linking group of formula -O-SO2-, R2 is unsubstituted or substituted phenyl, naphthyl or C1-C8 alkyl and that, if B is -O-, R2 is not alkyl.