Catalyst system for the preparation of an ester and processes employing this ester

A process for the preparation of an ester, at least based on

• a. at least one alcohol component,
• b. at least one carboxylic acid component,
• c. optionally further additives,
• d. at least two different catalysts, and
• e. max 20 wt. % of a solvent;
• as process components, comprising, in a reactor, the process steps:
• i. provision of the process components,
• ii. reaction of the process components to give an ester A,
• iii. optionally after-treatment of the ester A,
• wherein at least in each case one of the at least two different catalysts is an electron donor and a further catalyst of the at least two different catalysts is a sulphur-containing proton donor;
• wherein
• aa. sulphuric acid, or
• bb. an aliphatic, cycloaliphatic or aromatic C1 to C10-sulphuric acid, or a combination of two or more of these, is chosen as the sulphur-containing proton donor;
• and
• wherein a metal, a metal compound, or a reducing acid, or a combination of two or more of these is employed as the electron donor.