Patent GB-956382-A (GB)
Title: Oxidation of organic compounds
IPC: C07C51/27
Filed: 1961-01-23
Abstract: Organic compounds are oxidized by introducing gaseous nitrogen dioxide at a temperature of at least 160 DEG C. into the compounds or solutions thereof, oxygen and/or air being absent and water formed being continuously removed to prevent nitration.  Specified temperatures are between 160 and 230 DEG C., although temperatures up to the decomposition points of the reactants or products or the vaporization temperature of the solvent may be employed.  The following reactions are exemplified:  (1) oxidation of paraxylene in trichlorobenzene solution at 160 to 170 DEG C. to form paratoluic acid which is then further oxidized at 190 to 200 DEG C. to terephthalic acid. Reflux is provided in each stage and the filtrate from the second stage may be recycled with addition or further additions of paraxylene. The effluent gases may be treated to reform nitrogen dioxide for recycling.  The reaction may also be performed in a single stage at 190 to 200 DEG C. to form terephthalic acid directly; (2) Paratoluic acid starting material is similarly converted to phthalic acid; (3) Paracymene is employed in place of xylene; (4) Pseudo-cumene is oxidized in trichlorobenzene solution at 165 to 192 DEG C. to pyromellitic acid; (5) Examples are given in which 1:6-dimethyl naphthalene and 2:3-dimethyl naphthalene are oxidized between 160 and 200 DEG C. in trichlorobenzene solution to give the corresponding dibasic acid or anhydride. In one case an intermediate product is formed which by oxidation with hypochlorite gives a final acid or anhydride; (6) 2-methyl-6-aceto-naphthalene is oxidized by means of hypochlorite to 2-methyl-6-carboxy naphthalene and the latter is converted in trichlorobenzene solution at 190 DEG C. to give the dicarboxy naphthalene; (7) Acenaphthene in trichlorobenzene solution is oxidized at 190 to 195 DEG C. to give acenaphthene quinone which with alkaline peroxide gives naphthalic anhydride; in another example the acenaphthene quinone is precipitated by cooling, recrystallized from nitrobenzene and washed with methyl alcohol, the filtrate being recycled and the product converted with hypochlorite to naphthalic anhydride; (8) 3:4-acenaphthene dicarboxylic acid dissolved in trichlorobenzene is oxidized at 190 DEG C. to give an intermediate product which with hypochlorite gives a naphthalene tetracarboxylic acid plus the dianhydride; (9) Anthracene is converted at 195 DEG C. in trichlorobenzene solution to anthraquinone: it is stated that the reaction may take place at up to 250 DEG C. if desired with superatmospheric pressure; (10) Fluorene is converted at 190 DEG C. in benzene trichloride solution to fluorenone; (11) Toluene is converted similarly to benzoic acid, and paranitrotoluene and parachlorotoluene are converted respectively at 195 to 190 DEG C. in trichlorobenzene solution to the corresponding benzoic acids.  The following reactions are also referred to:-Oxidation of ortho-xylene and ortho-toluic acid to phthalic acid; meta-xylene and meta-toluic acid to isophthalic acid; durene to pyro-mellitic acid; alkylphenanthrenes and anthracenes and mixtures of dialkylnaphthalenes may be oxidized; acetaldehyde is said to be oxidized to glyoxal; benzyl alcohol to benzaldehyde; diphenyl methane to benzoquinone; and camphor to camphorquinone.  In a modification of the invention, selenium dioxide is present in the reaction mixture and appears to function as the oxidizing agent, being continuously regenerated by the nitrogen dioxide. Examples are given under (5) and (6) above, and in another example, ethylene is oxidized to glyoxal in trichlorobenzene solution at 195 DEG C. in the presence of SeO2. When selenium dioxide is added it is indicated that the colour of the product is improved and may be removed altogether by treatment with hypochlorite.  In the above examples isooctane, naphtha and benzene are used as the wash liquids.  Alternative solvents are chlorobenzenes containing 1-4-chlorine atoms, nitrobenzene, diphenyl and chlorinated diphenyl.ALSO:Organic compounds are oxidized by introducing gaseous nitrogen dioxide at a temperature of at least 160 DEG C. into the compound or a solution thereof, oxygen and/or air being absent and water being removed to prevent nitration.  Specified temperatures are between 160 and 230  DEG C. although temperatures up to the decomposition points of the reactants or products or the vaporization temperature of the solvent, may be employed.  In a modification of the invention, selenium dioxide is present in the reaction mixture and appears to function as the oxidizing agent, being continuously regenerated by the nitrogen dioxide.  Numerous specific examples are given, together with an indication of other oxidations which may be thus performed (see Division C2).