ES373234A1 - Procedure for the preparation of 1-carbamoil-substituted-2-benzymidazolcarbamates. (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Process for the preparation of pyridinecarboxylic acids, by oxidation of heterocyclic compounds, which bear a pyridine nucleus and are substituted at least in one position, with nitric acid, at elevated temperature and pressure, characterized in that it comprises oxidizing the heterocyclic compounds with a pyridine nucleus, with nitric acid in an amount such that the excess of HNO3 over the amount theoretically necessary for oxidation amounts to 25-600%; reacting this mixture at temperatures up to about 370ºC, preferably 230-350ºC and pressures up to 500 atmospheres, preferably 50-300 atmospheres, with a residence time of 1-20 minutes; adjust the reaction mixture that forms to a HNO3 concentration of 10-28%; crystallize the pyridinecarboxylic acid at 0-20ºC as a hydronitrate and separate this from the acidic mother liquor; dissolve the crystallized pyridinecarboxylic acid hydronitrate in water; adjust the solution, with the corresponding starting base, to the isoelectric point of the pyridinecarboxylic acid to be obtained; separating the pyridinecarboxylic acid that thus crystallizes from the mother liquor that contains the base; reunite the two base lyes, bringing them to the starting concentration and recycling them to the process. (Machine-translation by Google Translate, not legally binding)