Patent GB-744180-A (GB)
Title: Manufacture of esters
Inventor: COWDREY WILLIAM ARTHUR
IPC: C07C69/82
Filed: 1953-04-22
Abstract: The mixture of acid esters of terephthalic acid of formul CH3.C6H4.COO(CH2)nOOC.C6H4. COOH (I) and HOOC.C6H4.COO(CH2)nOOC.C6H4.COOH (II), wherein n is an integer from 2 to 10, prepared by oxidation of the corresponding polymethylene di-para-toluates (see Group IV (b)) are intermediates in the production of polymers.  The mixture obtained by oxidation of ethylene di-para-toluate is preferred, i.e. where n = 2.  The mixed esters (where n = 2) may be reacted with excess ethylene glycol to produce ethylene glycol mono-para-toluate and bis(beta hydroxy ethyl) terephthalate.  The latter can be separated, e.g. by aqueous extraction and on heating with ethylene glycol forms polyethylene terephthalate. Alternatively ester (II) wherein n = 2, may be separated by repeated recrystallization from the mixture of esters and converted to polyethylene terephthalate by heating with excess ethylene glycol under pressure.  As a further alternative the same ester may be reacted with ethylene oxide to give the ester of formula HO(CH2)2OOC.C6H4.COO(CH2)2OOC. C6H4.COO(CH2)2OH which on heating under pressure, preferably in presence of ethylene glycol, yields polyethylene terephthalate.ALSO:Esters of terephthalic acid are prepared by passing oxygen, air or other mixtures of oxygen-containing gases into a liquid polymethylene dipara-toluate having the general formula <FORM:0744180/IV(a)/1> , wherein n is an integer from 2 to 10 inclusive, at an elevated temperature, preferably in the presence of an oxidation catalyst. The esters have the formul  <FORM:0744180/IV(a)/2> and <FORM:0744180/IV(a)/3> The temperature of the oxidation process is conveniently from 160 DEG  to 180 DEG  C.  Any catalyst used in the liquid phase oxidation of alkyl benzenes to the corresponding carboxylic acids may be used. Specified oxidation catalysts are oil-soluble compounds of cobalt and oxides or salts of cobalt, lead, barium, iron, manganese, chromium, copper and nickel, or mixtures thereof.  The polymethylene di-para-toluates are made by an ester interchange reaction between a glycol of formula HO(CH2)nOH and an ester of para-toluic acid derived from an alcohol having a lower boiling-point than that of the glycol.  An ester interchange catalyst such as lead oxide, calcium acetate, zinc acetate, or mercuric acetate-boron trifluoride etherate may be used. Ethylene di-para-toluate may also be made by reacting para-toluic acid with ethylene oxide.  The mixture of esters (I) and (II) obtained by the oxidation, especially of ethylene di-paratoluate, are useful as intermediates in the manufacture of polymers (see Group IV (a)).  In examples: (1) ethylene di-para-toluate is prepared by ester interchange between methyl para-toluate and ethylene glycol; (2) ethylene di-para-toluate is prepared by reaction between para-toluic acid and ethylene oxide; (3) ethylene di-para-toluate is oxidized with air using cobalt naphthenate as catalyst at 165-175 DEG  C. for 36 hours, to give a mixture of acid esters (I) and (II) where n=2. This may be reacted with excess ethylene glycol to produce a mixture of ethylene glycol mono-para-toluate and bis-(beta-hydroxy ethyl) terephthalate, which may be separated, e.g. by extraction with water. Residual ethylene glycol mono-para-toluate may be reacted with para-toluic acid to form the di-para-toluate for further oxidation. Acid ester (II) where n=2, may be separated, by repeated crystallization, from the reaction product, and reacted with ethylene oxide to form the ester HO(CH2)2OOC.C6H4. COO(CH2)2OOC.C6H4.. COO.(CH2)2OH.