Patent GB-744809-A (GB)
Title: Improvements in or relating to the production of aromatic dicarboxylic acids
IPC: C07C51/215
Filed: 1951-11-22
Abstract: Benzene dicarboxylic acids and C1-4 fatty acids are prepared by reacting toluene under alkylating conditions with a fraction comprising olefines having up to 12 carbon atoms per molecule, obtained by distillation of olefinically unsaturated polymers of propylene and/or at least one butene, fractionally distilling the hydrocarbon product to separate a mono-alkyl substituted toluene fraction containing at least one mono-non-tertiary alkyl substituted toluene, oxidizing this fraction in the liquid phase at a temperature above 120 DEG  C. by direct contact with a molecular oxygen containing gas until benzene dicarboxylic acids and fatty acids are formed and thereafter treating the oxidation product for the separate recovery of benzene dicarboxylic acids and fatty acids of 1 to 4 carbon atoms per molecule, the fatty acids being recovered individually or as a mixture thereof.  The expression "mono-non-tertiary alkyl substituted toluene" is used to denote mono-alkyl substituted toluene in which the carbon atom of the alkyl group by which the latter is attached to the benzene ring, also has attached thereto, at least one hydrogen atom.  The benzene dicarboxylic acids obtained comprise terephthalic acid and minor amounts of o- and m-benzene dicarboxylic acids.  In the alkylation step, the toluene:olefine molar ratio preferably lies in the range 2:1 to 20:1; the preferred catalysts are sulphuric acid, hydrofluoric acid and aluminium chloride, the last-mentioned being used as described in Specification 633,985.  Oxidation of the alkylated toluene is generally effected by air blowing at temperatures in the range 135 DEG  to 200 DEG  C., under elevated pressure and batchwise or continuously.  Catalysts may be present such as organic acid salts of cobalt, lead, iron, nickel and manganese, e.g. the stearic, oleic, ethyl hexoic or nonanoic acid salts, co-ordination compounds of metals such as cobalt, and manganese compounds such as potassium permanganate and manganese dioxide. The oxidation mixture may be fractionally distilled to recover C1-4 fatty acids, the residue being further distilled to remove as successive fractions, neutral oxidation products and unoxidized hydrocarbons, toluic acids and others having more than 4 carbon atoms formed in the oxidation and to recover a residue comprising the benzene dicarboxylic acids, the by-product fractions being wholly or partially recycled to the oxidation stage.  Alternatively, after removal of the C1-4 acids, the residue may be cooled to separate the benzene dicarboxylic acids which are filtered off, the residue being used in further oxidations. In a further modification, after removal of the C1-4 acids and neutral products, the residue is esterified with a lower alcohol, e.g. methanol, and the esters fractionated for separation of the benzene dicarboxylic acid esters.  Another recovery method comprises extracting the crude oxidate with aqueous alkali to remove the acids, the residue oil being recycled to the oxidation step; the extract is acidified and filtered to remove the benzene dicarboxylic acids, distilled to recover C1-4 acids and the residue of toluic and other acids recovered for further oxidation.  The toluic acid may be isolated. In examples (1) toluene is alkylated with propylene trimer using sulphuric acid as catalyst and the product distilled to recover a nonyl toluene fraction B.P. 93-121 DEG  C. at 2 mm. which is oxidized by air blowing at 170 DEG  C. under 450-500 p.s.i. in the presence of manganese stearate catalyst; the oxidate is treated with diethyl ether yielding a solid phase of crude terephthalic acid, an aqueous phase yielding formic, acetic and higher acids on distillation and an ethereal phase; (2) the ethereal phase of (1) is stripped of ether leaving a two-phase mixture, the organic phase of which on distillation yields more formic and acetic acids and also propionic and butyric acids, the other phase being re-oxidized to yield more terephthalic acid.  Specifications 666,709 and 685,498 also are referred to.