Patent GB-618412-A (GB)
Title: Improvements in or relating to methods of producing dibasic acids
IPC: C11C3/12
Filed: 1945-02-28
Abstract: A drying or semi-drying oil is catalytically partially hydrogenated, thereby converting di-and poly-olefinic compounds in the oil into mon-olefinic compounds containing iso-oleic type acids, the oil is split and the resulting free fatty acids recovered and subjected to disruptive oxidation, thereby forming di- and mono-basic acids from the mono-olefinic acids. Alternatively, the oil may first be split and the resulting free acids recovered, subjected to the partial hydrogenation treatment and then disruptively oxidised.  Dibasic fatty acids containing more than eleven carbon atoms are isolated from the oxidation products (see Group IV).  Starting materials mentioned are soybean oil, corn oil, cotton seed oil, linseed oil and fish oils such as sardine oil and menhaden oil.  The mono-olefinic acids produced in the hydrogenation step comprise oleic and iso-oleic type acids and the oxidation, which is preferably effected with chromic acid anhydride in aqueous sulphuric acid at below 100 DEG C., yields azelaic acid from the oleic acid and long-chain dibasic acids from the other acids, as well as mono-basic acids.  The oxidation products may be steam distilled to remove volatile mono-basic acids and the residue washed to remove dibasic acids leaving finally a mixture of the solid acids such as palmitic and stearic acids present initially in the oil and by-product acids.  If desired, the solid acids may be separated before the oxidation step, for example, as described in U.S.A.  Specification 2,293,676.  Thus the mixed acids, prior to oxidation, may be dissolved in aqueous methanol and cooled, whereupon the solid acids, mainly stearic acid, separate out.  The solid fraction usually contains also the iso-oleic acids and by oxidising this fraction and removing the dibasic and mono-basic acids formed as above, a pure stearic acid may be obtained; oleic acid is found in the liquid fraction.  Soybean oil may be so treated.  In the case of fish oil fatty acids, however, the mono-olefinic acids ultimately giving rise to the dibasic acids are found in the liquid fraction.  In examples: (1) soybean oil is partially hydrogenated using a Raney nickel catalyst to produce an oil of iodine value 61.3 which is split, the resulting free acids disruptively oxidised and the products worked up as above; (2) partially hydrogenated fish oil (iodine value 82) is saponified, the free acids liberated by treatment with sulphuric acid and separated into solid and liquid fractions by cooling in 90 per cent aqueous methanol and the liquid fraction submitted to oxidation as above.ALSO:Di-basic fatty acids having more than eleven carbon atoms in the molecule are prepared by catalytically partially hydrogenating a drying or semi-drying oil thereby converting di- and poly-olefinic compounds in the oil into mono-olefinic compounds containing iso-oleic type acids, splitting the oil and recovering the resulting free fatty acids, then subjecting the fatty acids to disruptive oxidation thereby forming di-basic and mono-basic acids from the mono-olefinic acids and finally recovering the long chain di-basic acids.  Alternatively, the drying or semi-drying oil may first be split and the resulting acids recovered, partially hydrogenated to convert the di- and poly-olefinic acids into mono-olefinic acids comprising iso-oleic type acids which are then treated as above. Typical starting materials are soybean oil, corn oil, cottonseed oil, linseed oil and fish oils such as sardine oil and menhaden oil.  The mono-olefinic acids derived from the hydrogenation treatment include oleic acid and iso-oleic type acids, and the oxidation, which is preferably effected with chromic acid anhydride in aqueous sulphuric acid at below 100 DEG  C., yields monobasic acids and azelaic acid from the oleic acid or the long chain dibasic acids from the iso-oleic type acids; saturated acids present initially are not oxidised.  The oxidation products may be steam-distilled to remove volatile mono-basic acids and the residue washed first with hot water to remove the shorter chain dibasic acids such as azelaic acid and then with a mildly alkaline aqueous solution to give a solution of the required long-chain dibasic acids which are precipitated on addition of acid; the final residue contains the solid acids such as palmitic and stearic acids present in the original oil and by-product acids. If desired, the solid acids may be separated before oxidation, for example, as described in U.S.A. Specification 2,293,676.  Thus, the mixed acids may be dissolved in aqueous methanol and cooled whereupon the solid acids, mainly stearic acid, separate out. Iso-oleic acid present is usually found in the solid acid fraction and by treating with an oxidising agent as above and removing the dibasic and monobasic acids formed, a pure stearic acid may be obtained.  The solvent fraction contains oleic acid which may be oxidised to azelaic acid.  This procedure may be applied to soybean oil.  In the case of fish oil fatty acids, however, the mono-olefinic acids giving rise ultimately to the desired dibasic acids are to be found in the liquid fraction.  In examples: (1) soybean oil is partially hydrogenated using a Raney nickel catalyst to produce an oil of iodine value 61.3 which is split and the acids obtained are disruptively oxidised with chromic acid and the oxidation products worked up as above, the recovered long chain dibasic acids having an equivalent weight of 120.7; (2) partially hydrogenated fish oil (iodine value 82) is saponified and treated with sulphuric acid, the free fatty acids separated into solid and liquid fractions as described above and the liquid fraction oxidised with chromic acid and dibasic acid mixture (equivalent weight 149) is recovered by ethereal extraction; it forms a resin with glycerine.