Abstract: A method of preparing .omega.-lactams, in particular caprolactam, comprising: a step of premixing cycloaliphatic acids having the formula ##STR1## where n=3-13, with a dehydrating agent; the first step of reaction with a nitrosating agent; the second step of reaction with the addition of a very small amount of water corresponding to a molar ratio U=H.sub.2 O/SO.sub.3 within the 0.1 to 0.9 range; and the step of reclaiming the unreacted cycloaliphatic acid. The method affords improved output from the lactamization reaction and reduced byproducts.

Abstract: The invention is concerned with a method of purifying benzoic acid, as obtained by catalytic oxidation of toluene and purification by rectification with the secondary streams being cycled back into the oxidation reactor, characterized in that the secondary streams flowing out of the stripping column undergo the following sequential steps: (a) at least one distillation and at least one crystallization in an organic solvent; (b) scrubbing of the crystals obtained from (a) with the same solvent as in (a); (c) cycling of the mother liquors from crystallization in (a) plus the scrubbing liquors as in (b) back into the dissolver; (d) further scrubbing of the crystals from (b) with the same solvent as in (a) and cycling back of the scrubbing liquors, the crystals scrubbed as in (d) being optionally (d1) further scrubbed with water.