There is disclosed a process for the preparation of a compound of general formula (I), wherein Y and Z each independently represent a fluorine atom or a hydroxy group, and a, b, c and d independently represent 0, 1, 2 or 3 provided that the sum of a, b, c, and d is 1, 2, 3 or 4; the process comprising treating a compound of general formula (II), wherein a, b, c, and d are as described above and L1 and L2 each independently represent an active group provided that either Y and L1 are different or Z and L2 are different, with a fluorinating system in the presence of oxygen. A preferred compound of general formula (I) is 4,4′-difluorobenzophenone which may be prepared from 4,4′-dinitrophenylmethane using tetramethylammonium fluoride.