Abstract: Phthalic anhydride is prepared in a multiple tube reactor provided with separate salt baths, the temperature of the salt bath used for cooling the first layer of catalyst, as regarded in the direction of flow of the reaction mixture, being from 2.degree. to 20.degree. C. higher than that of the salt bath(s) associated with the following layer(s).

Abstract: Anhydrous or substantially anhydrous formic acid is prepared by hydrolyzing methyl formate in the presence of a formamide and then obtaining the formic acid from the hydrolysis mixture by distillation, by a method in which the hydrolysis is carried out in the presence of 0.5-3 moles, per mole of methyl formate, of a water-soluble formamide of the general formula I ##STR1## where R.sup.1 and R.sup.2 are each alkyl or together form an alkylene group, giving a 5-membered to 7-membered ring, with the proviso that the sum of the carbon atoms in R.sup.1 and R.sup.2 is 5 or 6 and, in the case of an alkylene group, a carbon atom which is not directly bonded to the N atom can be replaced by an oxygen atom.

Abstract: Very pure maleic anhydride having a stable color is obtained by fractional distillation of crude maleic anhydride by a method in which the maleic anhydride vapor separated off from low boilers and high boilers is partially condensed so that from 0.5 to 15% by weight of the maleic anydride vapor is separated off from the vapor phase as a liquid precondensate, and the remaining very pure maleic anhydride vapor is then completely condensed.

Abstract: Process for obtaining maleic anhydride that is not prone to discolor by treating crude maleic anhydride with oxygen, a gas mixture containing oxygen, or a substance that releases oxygen before or while it is distilled.

Abstract: A process for the continuous isolation of phthalic anhydride and maleic anhydride from the reaction gases obtained by catalytic oxidation of o-xylene or naphthalene with air, wherein the reaction gases are treated with a hydrocarbon of boiling range from 115.degree. to 175.degree. C. as the solvent in a column, and are then treated with an organic solvent of boiling range from 180.degree. to 290.degree. C. in a second column, the phthalic anhydride and maleic anhydride being isolated from the liquid bottom product of the first column.

Abstract: A process for the preparation of phthalic anhydride (PA) of catalytic oxidation of naphthalene or o-xylene with air, a preheated mixture of air and naphthalene or o-xylene being passed into a reactor charged with the catalyst, and the reaction gas leaving the reactor being passed through a separator in which the PA is separated out as a solid, in which process the air fed to the reactor is preheated, before or after the admixture of naphthalene or of o-xylene, by using it to cool the reaction gas in the PA separator.

Abstract: Formic acid is prepared by hydrolyzing methyl formate, the hydrolysis being carried out in the presence of from 0.5 to 3.0 moles, per mole of methyl formate, of a base which contains tertiary nitrogen atoms, boils at not less than 180.degree. C. under atmospheric pressure and has a pKa from 4 to 9, N-substituted imidazole derivatives being the preferred bases.

Abstract: Carboxylic acids of the general formula IR.sup.1 -COOH Iwhere R.sup.1 is hydrogen, methyl, ethyl or vinyl, are isolated from their dilute aqueous solutions by extraction followed by distillation of the mixtures obtained, the extractant used being a secondary amide of the general formula II ##STR1## where R.sup.2 and R.sup.3 are alkyl, cycloalkyl, aryl or aralkyl or conjointly are 1,4- or 1,5-alkylene, in each case of not more than 8 carbon atoms, with the proviso that the sum of the carbon atoms of R.sup.2 and R.sup.3 is from 7 to 14 and that only one of these radicals is aryl, and where R.sup.4 is one of the radicals R.sup.1.

Abstract: Formic acid is purified by extractive distillation of its aqueous solutions using a basic extractant, followed by distillation of the bottom mixture first obtained, the extractant used being N-formylmorpholine.