Effect of solvents on the kinetics and mechanism of the acidic and alkaline hydrolysis of hydroxamic acids

The acid catalyzed hydrolysis of N-phenylbenzohydroxamic acid (PEHA) C6H5C( =0)N(OH)C6H5 has been studied in aq. dioxane, acetone, dimethylsulphoxide, dimethylformamide, methanol, ethanol and 2-propanol mixtures. Dioxane and m ethanol have a rate enhancing effect but DMF, acetone, ethanol and 2-propan ol exert a rate decreasing effect. In DMSO an increase is followed by a dec rease i.e. a rate maximum is observed. An attempt has also been made to stu dy the alkaline hydrolysis of PBHA and two of its derivatives (X-C6H4C(=0)N (OH)C6H5; X=4-NO2, 4-Cl) in aq. dioxane. In all case the pseudo first order rate constant increase with increasing dioxane content. The activation par ameters Delta H-double dagger, Delta S-double dagger and Delta GH(double da gger) have been calculated. An attempt has been made to correlate rate data for acidic hydrolysis in terms of solvatochromic parameters and linear fre e energy relationships.