Patent GB-792199-A (GB)
Title: Improvements in or relating to the preparation of aromatic dicarboxylic acids and partial alkyl esters thereof
IPC: C07C51/265
Filed: 1955-05-25
Abstract: A process for preparing an aromatic dicarboxylic acid or partial ester thereof comprises oxidizing an alkyl-substituted aromatic monocarboxylic acid or an alkyl ester thereof respectively by means of oxygen or a molecular oxygen-containing gas in the presence of one or more of the following nitrogen compounds: nitrogen dioxide and organic nitro compounds and organic nitrites, and in a substantially anhydrous liquid phase reaction mixture, e.g. a liquid reaction mixture in which no liquid aqueous phase is present.  Starting materials mentioned include the toluic, o-, m- and p-isopropylbenzoic, tertiary-butyl benzoic, and mesitylenic acids and the alkyl esters thereof. Additional substitutents such as tertiary alkyl and halogen substituents may be present in the starting materials provided that they are not themselves oxidized and do not inhibit the oxidation of the alkyl groups.  The nitrogen compound may be added to the reaction zone initially and/or continuously during the oxidation or the aromatic monocarboxylic acid may be first reacted with the nitrogen dioxide at a temperature and pressure at which nitro- or nitrite derivatives capable of being oxidized to the desired carboxylic acid are formed and thereafter the molecular oxygen-containing gas may be introduced.  Preferably the nitrogen dioxide is mixed initially with the oxygen-containing gas.  The nitrogen dioxide may be employed as pure gas or liquid or as a mixture with other gases, e.g. obtained by the thermal catalytic or non-catalytic oxidation of ammonia or cracking of nitric acid. Water is removed so quickly that the formation of a separate liquid aqueous phase cannot occur.  Organic nitrites and nitrocompounds employed may be nitrites or nitro derivatives of a hydrocarbon, e.g. corresponding to the monocarboxylic acid.  The organic nitrites and nitrocompounds may be prepared by reacting the monocarboxylic acids to be oxidized and nitrogen dioxide, e.g. the latter may be absorbed in the monocarboxylic acid at a temperature just below its boiling point. Other organic compounds and nitrites mentioned include nitroalkanes and alkyl nitrites, e.g. nitroethane, 1- and 2-nitropropane, nitrobutanes and nitro-isobutanes, amyl- and isoamyl-nitrites, tolyl nitrite, phenyl nitromethane, isomeric xylyl nitrites, tolyl-nitromethane, the corresponding carboxylic acids and the esters thereof.  A small amount of water may be introduced with one or more of the materials supplied to the reaction mixture provided such water is present only transiently and entirely in the vapour-phase in the reaction mixture.  Water may be removed from the reaction zone by condensing the vapours evolved during the reaction, separating water from the condensate and returning any organic component to the system.  An azeotroping agent may be used to remove water in this way.  Inert dehydrating agents may be used in the reaction zone. Inert organic liquid diluents or solvents may be employed to dissolve both the reactant and product or form a suspension of the latter, e.g. aromatic hydrocarbons, e.g. benzene, alkyl substituted benzenes, e.g. tert. butyl benzene, chlorobenzene and o- and p-dichlorobenzenes, aliphatic carboxylic acids, e.g. acetic and propionic acids and the methyl or ethyl esters thereof, aliphatic ketones, e.g. di-isobutyl ketone and aliphatic nitriles, e.g. aceto- and benzonitrile.  Oxidation catalysts which may be employed include inorganic and organic compounds, e.g. oxides, salts and complexes of heavy polyvalent metals, e.g. of atomic number from 23 to 82, e.g. the chlorides of vanadium, cerium, cobalt, and manganese, acetetes and naphthenates of ferric iron, cobalt, zinc, bismuth, manganese, lead and copper, cobalt and barium permanganates and mixtures thereof.  Preferred catalysts include cobalt salts of organic acids and chelates of cobalt, with, e.g. diketones, the acetate, p-toluate, naphthenate, stearate, octoate, salicylate, acetonate and isovaleryl acetonate of cobalt.  Elevated temperatures and pressures may be employed. In examples: dicarboxylic acids are obtained by passing air and nitrogen dioxide into a solution of m- and p-toluic acids in o-dichlorbenzene at 180 DEG  C. whilst the reaction mixture is maintained anhydrous by removal of water in the vapour phase; alternatively, nitrogen dioxide is generated in the reaction mixture by the addition of anhydrous nitric acid or by passing air through heated nitric acid (IA-C); air is passed into a solution of m-toluic acid in dichlorobenzene with addition of nitrogen dioxide and subsequently cobalt naphthenate during the reaction (IIA-B) toluic acid dissolved in o-dichlorobenzene containing cobalt naphthenate is oxidized with air in the presence of 2-nitropropane, nitro-p-toluic acid or products obtained by reacting toluene or p-xylene at elevated temperature with nitrogen dioxide (III); iso-amyl nitrite is employed in a similar process in the absence of cobalt naphthenate; monomethyl terephthalate is obtained by treating methyl p-toluate dissolved in o-dichlorobenzene at 153 DEG  C. with air in the presence of nitrogen dioxide and cobalt naphthenate (IV); and m-toluic acid is oxidized at 170 DEG  C. by passing vapours containing oxygen, nitrogen dioxide and water vapour obtained by heating nitric acid into the molten acid (V).