Preparation of O-substituted hydroxylammonium salts I (L=halogen, hydrogensulfate; X=H, alkyl; R.sup.1 =unsubst. or subst. phenyl, thienyl, furanyl, pyrrolyl or --CR.sup.2 .dbd.CR.sup.3 R.sup.4 ; R.sup.2, R.sup.3, R.sup.4 =H, halogen or alkyl) by reaction of an acetone oxime O-allyl or --O--benzyl ether II ##STR1## with water and a mineral acid H--L with continuous removal of the acetone formed in this process, by carrying out the hydrolysis batchwise at 0.degree.-50.degree. C. and under a pressure of 10-500 mbar is described. The O-substituted hydroxylammonium salts I are intermediates for plant protection agents and pharmaceuticals.

p-Hydroxyaniline derivatives of the formula I ##STR1## where the substituents have the following meanings: R.sup.1 is hydrogen, or unsubstituted or substituted alkyl; R.sup.2 and R.sup.3 independently of one another are halogen, alkyl, haloalkyl, alkoxy or haloalkoxy; R.sup.4 is unsubstituted or substituted alkyl, alkenyl, cycloalkyl, cycloalkenyl or aryl, OR.sup.5 or NR.sup.6 R.sup.7, where R.sup.5, R.sup.6 are unsubstituted or substituted alkyl, alkenyl, cycloalkyl, cycloalkenyl or aryl, and R.sup.7 is hydrogen or alkyl, and their salts, processes for their preparation, compositions containing them and their use for controlling harmful fungi or pests, and also compounds of the formula VI ##STR2## and their salts, processes for their preparation, compositions containing them and their use as intermediates and for controlling pests are described.