Patent ID: 7294724

Claim:
A process for the manufacture of a fluoran dye of the structure according to formula 1 comprising condensing in an alkanesulfonic acid or in an arenesulfonic acid a keto acid according to formula 2 with an aminodiphenylamine of formula 3 wherein R, R 1 and R 2 are each independently selected from alkyl(C 1 -C 8 ), aryl or aralkyl; wherein the aromatic ring in aryl or aralkyl may be unsubstituted or substituted with alkyl(C 1 -C 8 ), alkoxy(C 1 -C 8 ), or halogen; wherein R 1 —N—R 2 may form pyrrolidinyl, piperidinyl or morpholinyl ring moieties; wherein R 3 , R 4 , R 5 and R 6 are each independently selected from hydrogen, alkyl, cycloalkyl, alkoxy, halogen, aryl or aralkyl; wherein the aromatic ring in aryl or aralkyl may be unsubstituted or substituted with alkyl, alkoxy or halogen; the alkyl or alkoxy moieties herein being from one to eight carbons; or R 3 and R 4 , or R 4 and R 5 , or R 5 and R 6 , may form alicyclic or aromatic ring structures.