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 caprolactam as obtained by Beckmann transposition or by nitrosation of cyclohexyl compounds, characterized in that it comprises the following steps:(a) the caprolactam oil is treated with ammonia to obtain a pH in the 8 to 10 range;(b) the caprolactam in water-ammonia solution yielded by (a) is extracted with toluene;(c.sub.1) any caprolactam still in the toluene solution yielded by (b) is treated with NaOH;(C.sub.2) the aqueous phase left over from the extraction with toluene (b) is removed.

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.

Abstract: A process for the purification of raw caprolactam obtained by extraction h alkylated phenols from its sulphuric solution, re-extraction with water, oxidation preferably with KMnO.sub.4, evaporation of water and distillation, comprises, before the oxidation treatment, a "fast distillation", in the presence of an alkali. The oxidation is conducted at 0.degree.-80.degree. C. and at atmospheric pressure with 0.005-0.5% by weight of KMnO.sub.4. The amount of alkali (NaOH) used in the fast distillation is comprised between 0.05 and 0.5% by weight.

Abstract: A process for purifying caprolactame by continuous and/or discontinuous (or atch) vacuum distillation comprises a first stage fast vacuum distillation of the raw caprolactame possibly in the presence of an alkaline and/or alkaline-earth hydroxide, a second stage consisting of a vacuum rectification distillation of the caprolactame obtained in the first stage and a third stage consisting of the fast vacuum distillation of the caprolactame yielded from the second stage, in the presence of an alkaline and/or alkaline-earth hydroxide. The hydroxide amount in the third and possibly the first stage distillation as well varies from 0.05 to 5% preferably from 0.1% to 1%.

Abstract: A method for the purification of raw caprolactam containing primary amides f the formula ##STR1## wherein R is a hydrocarbon radical having 1-14 carbon atoms is described. The raw caprolactam is treated with at least one compound containing at least one hydroxyl group, in an amount of at least 20% by weight with respect to the raw caprolactam, at a temperature equal to or higher than that at which the ammonia, which is a part of the amide of formula I, is liberated. The caprolactam is then separated and isolated from the hydroxyl containing compound by known methods.

Abstract: A method for purifying raw caprolactam containing, as impurities, primary amides of the formula ##STR1## R being a hydrocarbon radical having 1-14 carbon atoms, and other by-products is described. The operations, carried out in the following order, consist in (a) treating a solution of raw caprolactam in a water insoluble organic solvent with water to extract most of the caprolactam in purified form, (b) separating the aqueous caprolactam solution and isolating the caprolactam, (c) treating the remaining organic solution with mineral acid to cause the formation of two phases, (d) separating these phases into a heavy phase containing the mineral acid, dilution water and most of the amides and by-products and a light phase containing the organic solvent and any residual amides and by-products, and (e) preferably recycling the light phase to (a). Further object of the invention is the purified caprolactam thus obtained.