Patent GB-844957-A (GB)
Title: A process for the purification or separation of isophthalic acids, and the monoesters and polyesters thereof
IPC: C07C51/48
Filed: 1957-08-21
Abstract: In a process for the separation of polyglycol terephthalate from waste material containing the same the waste material is treated with a dialkyl sulphoxide at a temperature above 140 DEG C., the insoluble impurities are filtered off at approximately the same temperature and the polyglycol terephthalate is recovered from the filtrate.  In an example polyglycol terephthalate is recovered from a polyglycol terephthalate foil metallised with aliminium by heating with dimethyl sulphoxide, filtering the solution and precipitating the polyester by adding methanol.ALSO:Dimethyl isophthalate is extracted from a mixture of dimethyl iso- and terephthalates by treating the mixture with a dialkyl sulphoxide at a temperature from 20 DEG C. to 150 DEG C., filtering off the undissolved dimethyl terephthalate at a temperature from 20 DEG C. to 100 DEG C. and precipitating the dimethyl isophthalate from the filtrate e.g. by diluting the filtrate with water.  Monomethyl esters of iso- and terephthalic acid and dimethyl isophthalate are separated from a mixture containing the same and dimethyl terephthalate by treating the mixture with a dialkyl sulphoxide at a temperature of from 20 to 150 DEG C and filtering off the undissolved dimethyl terephthalate at approximately the same temperature.  Terephthalic and isophthalic acids are separated from a mixture thereof by treating the mixture with a dialkyl sulphoxide at a temperature of from 20 to 150 DEG C. filtering off the undissolved terephthalic acid at approximately the same temperature and precipitating the isophthalic acid from the filtrate e.g. by diluting the filtrate with methanol and cooling. Monomethyl esters of terephthalic and isophthalic acids are separated from a mixture thereof by treating the mixture with a dialkyl sulphoxide at a temperature of from 20 to 50 DEG C. and filtering off the undissolved monomethyl terephthalate at approximately the same temperature.  A process for the separation of terephthalic acids from a mixture containing the same together with the mono- and dimethyl esters thereof comprises treating the mixture with a dialkyl sulphoxide at a temperature of from 20 to 100 DEG C. filtering off the undissolved dimethyl terephthalate at approximately the same temperature, precipitating the terephthalic acid from the filtrate e.g. by adding methanol, filtering off the precipitated terephthalic acid and precipitating the mono methyl terephthalate from the filtrate thus obtained e.g. by addition of water to the filtrate. Terephthalic acid is purified by treating the terephthalic acid with a dialkyl sulphoxide at a temperature of from 20 DEG C. to 150 DEG C., filtering off any undissolved impurities at approximately the same temperature, precipitating the terephthalic acid by cooling or by addition of water or an organic solvent and filtering off the purified terephthalic acid.  Mono-and polyesters may be produced by esterification of iso- or terephthalic acid produced by methods set forth above.  Examples relate to the separation of dimethyl terephthalate and isophthalate from a mixture thereof and to the purification of terephthalic acid containing nitrogen, the solution in dimethyl sulphoxide being boiled with fuller's earth or a active carbon and water and methanol being added to the sulphoxide solution to precipitate the terephthalic acid.  The Specification of polyglycol terephthalate is also described (see Group IV(a)).