or r 3 in orthoesters ib ketals iib within the group of orthoesters ib the process according to the invention can be used especially to prepare orthoesters of formula ic wherein r 1 is hydrogen or c 1 to c 6 alkyl and r 2 r 3 and r 4 are methyl or ethyl orthoesters ic starting from ketals ii in which the radicals are defined as follows r 5 and r 10 are as defined for r 1 in orthoesters ic and r 6 to r 9 are as defined for r 2 or r 3 in orthoesters ic ketals iic in the ketals iib and iic the radicals r 5 and r 10 preferably have the same definition the process according to the invention can be used to very particular advantage to prepare methyl orthoformate tmof or ethyl orthoformate or methyl or ethyl orthoacetate orthoesters id the corresponding starting compounds being 1 1 2 2 tetramethoxyethane tme or 1 1 2 2 tetraethoxyethane ketals iid in the electrolyte the molar ratio of the sum of the orthoesters o and the ketals k to the alcohols a is 0 2 1 to 5 1 preferably 0 2 1 u2013 2 1 and particularly preferably 0 3 1 to.