Process for the production of macrocyclic esters and lactones utilizing mixed metal catalysts

A process for the production of macrocyclic compounds having 8 to 20 carbon atoms in the ring and selected from the group consisting of ##STR8## where R' is a bivalent aliphatic hydrocarbon radical having 1 to 16 carbon atoms, R" is a saturated bivalent aliphatic hydrocarbon radical having from 2 to 12 carbon atoms, R"' is a bivalent aliphatic hydrocarbon radical having 6 to 18 carbon atoms and x is an integer from 1 to 4 by thermal depolymerization of the corresponding linear polyester which comprises heating the polyester at a temperature from 200.degree. C. to 400.degree. C. and pressure less than 50 mm Hg. in the presence of 0.01% to 20% by weight, based on the polyester, of a mixed metal catalyst comprising:

• (a) an aluminum alkoxide or aluminum carboxylate corresponding to the formula ##STR9## where m is an integer from 1 to 22, R.sub.1 is hydrogen, an alkoxy or polyalkoxy radical having from 1 to 16 carbon atoms and R.sub.2 is an alkyl group having from 2 to 22 carbon atoms, phenyl or substituted phenyl having 7 to 20 carbon atoms;
• and
• (b) from 0.05 to 8 moles, per mole of (a), of an alkali metal or magnesium alkoxide or carboxylate corresponding to the formula ##STR10## wherein R.sub.1, R.sub.2 and m are the same as defined above, M is lithium, sodium, potassium or magnesium and y is 1 when M is lithium, sodium or potassium, and 2 when M is magnesium.