Patent GB-744746-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 fatty acids are prepared by reacting toluene with a normal mono-olefine having 2-12 carbon atoms or a hydrocarbon mixture comprising said olefine under alkylating conditions, fractionally distilling the product to separate a mono-alkyl substituted toluene fraction therefrom, oxidizing this fraction in the liquid phase at a temperature above 120 DEG  C. by direct contact with a molecular oxygen containing gas until a benzene dicarboxylic acid 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, these fatty acids being recovered individually or as a mixture thereof.  Ethylene and propylene may be used in the alkylation but n-butenes, n-pentenes and the higher n-olefines are preferred whereby p-benzene dicarboxylic acid is formed predominantly in the oxidation step.  Olefinic fractions obtained for example from the cracking of gas oil, wax and wax distillates, thermal reforming of naphthas and synthesis from carbon monoxide and hydrogen may be used.  Suitable catalysts for the alkylation include sulphuric acid, hydrofluoric acid and aluminium chloride, the last-mentioned being used as described in Specification 633,985.  Toluene: olefine molar ratios of from 2:1 to 20:1 are generally employed.  The oxidation may be effected at atmospheric or higher pressures, preferably by means of air-blowing at 135-200 DEG  C.  Oxidation catalysts such as cobalt, lead, iron, nickel and manganese salts, especially the stearates, ethylhexoates, oleates and nonanoates, co-ordination compounds of e.g. cobalt, and manganese compounds such as manganese dioxide and potassium permanganate may be present.  Oxidation may be operated in continuous or batchwise manner.  The oxidate may be worked up by fractionation to remove successively C1-4 fatty acids, neutral oxidation products and unoxidized hydrocarbon and toluic acid and other acids having more than 4 carbon atoms leaving a residue of benzene dicarboxylic acids; the by-products may be recycled to the oxidation stage.  Alternatively after removal of the C1-4 acids the residue may be cooled to precipitate benzene dicarboxylic acids which are filtered off and the residue returned for further oxidation, or after removal of the C1-4 acids and neutral products, the residue may be esterified with a lower alcohol, e.g. methanol and the product fractionated to separate the benzene dicarboxylic acid esters.  A modified procedure comprises extracting the oxidate with aqueous alkali to remove the acids as salts, the neutral oil residue being re-oxidized, and acidifying the extract whereby the benzene dicarboxylic acids are precipitated out and distilling to remove the C1-4 acids; the residue of toluic and other acids is subjected to further oxidation.  The toluic acid may be isolated, if desired.  In an example, toluene is alkylated with a mixture of butenes -1 and -2 using sulphuric acid as catalyst and the product is distilled to recover sec. butyl toluene which is airoxidized in an autoclave at 125-160 DEG  C. under a pressure of 200 p.s.i. using manganese stearate as catalyst; the oxidate is filtered to remove a solid phase of terephthalic acid leaving an organic acid phase and an aqueous phase, the latter being treated as described in Specification 707,153, [Group III], to separate C1-4 acids.  Specification 685,498 is referred to.