Abstract: Process for the preparation of pure 2,3-pyridinedicarboxylic acids of the formula I which are substituted in position 4 and/or 5 and/or 6 by R1, where R1 is hydrogen, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkoxy-C1-C4 alkyl, halogen, hydroxyl or nitro, from quinolines of the formula II in which R1 is as defined above, and which are substituted in position 6 and/or 7 by R2, where R2 is hydrogen, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkoxy-C1-C4 alkyl, halogen, hydroxyl, nitro or amino, which are reacted in the first step in aqueous sulfuric acid or nitric acid solution with ozone in the ratio of from 1:2 to 1:3 at temperatures from 0 to +50° C., and the resulting peroxide solution is then reacted at temperatures of from +0 to +100° C. in the presence of 0.5-4.0 mol of oxidizing agent per mole of ozonolysis product formed, after which the pH of the reaction solution is adjusted to 0.2 to 3, the mixture is cooled to 0 to 30° C.

Abstract: Process for the preparation of pure 2,3-pyridinedicarboxylic acids of the formula I 1

Abstract: Process for preparing glyoxylic esters or their hydrates in which a water-soluble salt of a maleic or fumaric monoester or a mixture thereof is reacted with ozone in aqueous solution at temperatures of from 0 to 50.degree. C., and the corresponding glyoxylic ester or its hydrate is isolated from the resulting reaction mixture.

Abstract: Process for the purification of o-phthalaldehyde in which an alcoholic solution containing the crude, unpurified o-phthalaldehyde is adjusted to a pH between 0 and 3 at a temperature between 0.degree. and 60.degree. C., then an alkaline solution is added, and the corresponding dialkoxyphthalan is extracted from the organic phase and purified by distillation and, when required, converted into the purified o-phthalaldehyde by hydrolysis.

Abstract: A process for preparing an aqueous o-phthalaldehyde-glutaraldehyde solution which comprises converting an acetal of the o-phthalaldehyde in a 10 to 60% strength aqueous glutaraldehyde solution into o-phthalaldehyde at room temperature up to 100.degree. C. by eliminating the corresponding alcohol, and removing the eliminated alcohol to give the aqueous o-phthalaldehyde-glutaraldehyde solution.

Abstract: Process for the preparation of alpha, omega-alkanedicarboxylic acids of the general formula I ##STR1## in which A is an alkylene radical having 4-14 C atoms by reacting a cycloalkene of the general formula II ##STR2## in which A has the abovementioned meaning with ozone in the presence of an inert solvent, catalytically hydrogenating the peroxide solution formed, followed by oxidation of the dialdehyde formed to the diacid of the formula I in the presence of an inert aprotic solvent.