Abstract: New compounds have the formula I: ##STR1## wherein R is a C.sub.1 -C.sub.12 straight or branched chain alkyl residue, a C.sub.2 -C.sub.12 straight or branched chain alkenyl residue, a C.sub.5 -C.sub.12 cycloalkyl residue, a C.sub.6 -C.sub.10 aryl residue or a C.sub.7 -C.sub.12 aralkyl residue; and X is a C.sub.1 -C.sub.10 straight or branched alkylene residue, a C.sub.2 -C.sub.10 straight or branched chain alkenylene residue or a C.sub.6 -C.sub.10 arylene residue; as well as derivatives of the compounds of formula I; and enantiomers, racemic mixtures, and mixtures of diastereomers.The new compounds are useful e.g. as corrosion inhibitors in aqueous systems.