Patent GB-799059-A (GB)
Title: Preparation of di-(2-hydroxyethyl) terephthalate
Inventor: HADLEY DAVID JAMES
IPC: C07C69/82
Filed: 1956-06-08
Abstract: Di - (2 - hydroxyethyl) terephthalate is prepared by heating diammonium terephthalate with ethylene glycol and removing the liberated ammonia.  The molar ratio of glycol to diammonium terephthalate is between 7:1 and 15:1.  The process may be carried out at temperatures between 150 DEG  and 200 DEG  C. preferably at the temperature of reflux of the reaction mixture at atmospheric pressure.  Reduced or increased pressure may also be used.  The reaction is preferably carried out in the absence of oxygen, e.g. by passing a stream of an inert gas such as nitrogen through the reaction mixture.  A catalyst such as an alkali or alkaline earth metal oxide, hydroxide, alcoholate, carbonate or bicarbonate, or the salts of these metals with weak inorganic or organic acids such as silicates, borates, aluminates, acetates, propionates, stearates, palmitates and oleates may be present.  Specific catalysts mentioned are magnesia, sodium methoxide and sodium terephthalate.  Amounts of catalyst up to 1 per cent by weight of the diammonium terephthalate may be used.  The reaction may be carried out batchwise or continuously.  In the latter case, after the recovery of the di-(2-hydroxyethyl) terephthalate, the remainder of the reaction mixture, together with further amounts of diammonium terephthalate, ethylene glycol and catalyst, as necessary, are recycled to the reactor.  The di-(2-hydroxyethyl) terephthalate may be recovered from the reaction mixture by cooling and filtering, or if an insoluble catalyst is present by first dissolving in a suitable solvent, filtering and then recrystallizing the di-(2-hydroxyethyl) terephthalate.  The di-(2-hydroxyethyl) terephthalate may be directly converted into polyesters by heating the reaction product at temperatures above the boiling point of the ethylene glycol, and under such conditions that the excess glycol is removed from the reaction zone.  Examples illustrating the effect of using varying proportions of glycol to diammonium terephthalate in the presence and absence of a catalyst, are given.ALSO:Polyethylene terephthalate may be prepared by heating di(2-hydroxyethyl) terephthalate (which has been prepared by heating diammonium terephthalate with ethylene glycol the molar ratio of glycol to diammonium terephthalate being between 7 : 1 and 15 : 1 and removing the liberated ammonia) at temperatures above the boiling point of the ethylene glycol, and under such conditions that the excess glycol is removed from the reaction zone.  The di(2-hydroxyethyl) terephthalate need not be recovered from the original reaction mixture before being further heated. The first part of the process leading to the formation of the monomer may be carried out at 150-200 DEG  C., preferably at the temperature of reflux of the reaction mixture at atmospheric pressure.  Reduced or increased pressure may also be used.  The reaction is preferably carried out in the absence of oxygen, e.g. by passing a stream of an inert gas such as nitrogen through the reaction mixture.  A catalyst such as an alkali or alkaline earth metal oxide, hydroxide, alcoholate, carbonate or bicarbonate, or the salts of these metals with weak inorganic or organic acids such as silicates, borates, aluminates, acetates, propionates, stearates, palmitates and oleates may be present.  Specific catalysts mentioned are magnesia, sodium methoxide and sodium terephthalate.  Amounts of catalyst up to 1 per cent by weight of the diammonium terephthalate may be used.