Monitoring the rate of hydrolysis of aminophosphonic acid esters by UV-VIS- and NMR-spectroscopy

Two aminophosphonic acid dimethylesters 1 and 3 bearing COOH functions atta ched to W-VIS absorbing groups were hydrolysed by aqueous NaOH to yield the corresponding monomethylesters 2 and 4. The rates of hydrolysis were monit ored by UV-VIS methods. The type of reaction observed is of pseudo first or der with rate constants k(1)[1 mol(-1)s(-1)] of 1.92.10(-6) (1, 25 degrees C), 4.96.10(-5) (1, 50 degrees C) and 4.63.10(-5) (3, 50 degrees C). Hydrol ysis is sufficiently slow to enable the practically undisturbed determinati on of dissociation constants for 1-(4-carboxyphenyl)-1-(N-t. butyl)-aminome thylphosphonic acid dimethylester (1) and 1-(4-benzoic-acid)-1-(N-4-phenyl- azo-phenylene)-aminomethylphosphonic acid dimethyl ester (3).