a process for producing a 1 , 3 - bisdisiloxane derivative represented by the general formula ## str1 ## wherein rs and r &# 39 ; s independently of one another denote methyl or phenyl or a 1 , 3 - bis - disiloxane derivative dianhydride represented by the general formula ## str2 ## wherein rs and r &# 39 ; s are as defined above , the process comprising coupling a grignard reagent of halo - o - xylene with a disubstituted halosilane represented by the general formula ## str3 ## wherein r and r &# 39 ; are as defined above and x denotes halogen , to form a dimethylphenyl represented by the general formula ## str4 ## wherein r and r &# 39 ; are as defined above , hydroxylating the dimethylphenyl to form a dimethylphenyl represented by the general formula ## str5 ## wherein r and r &# 39 ; are as defined above , to form a 1 , 3 - bis - disilane dehydrating - condensing the dimethylphenyl - disilane derivative to yield the intended 1 , 3 - bisdisiloxane derivative of general formula , or further comprising the dehydration ring closure of this product to form a 1 , 3 - bis - disiloxane derivative dianhydride of general formula , mixing the resulting isomeric mixture with an ether solvent , and recovering the formed precipitate to yield a white powder of the intended product of general formula .