Process for manufacture of fluoran dyes
View Patent ↗The invention teaches an improved process for the manufacture of useful fluoran dyes of the structure according to formula 1 comprising condensing in an alkanesulfonic acid or an arenesulfonic acid to acid according to formula 2 with an aminodiphenylamine of formula 3 wherein R, R 1 -R 6 are as defined in the specification.
1. 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.
2. The process according to claim 1 wherein the keto acid is first dissolved in methanesulfonic acid.
3. The process according to claim 2 wherein dissolution is accomplished by heating to at least 30° C.
4. The process according to claim 2 wherein after dissolving the keto acid, the aminodiphenylamine is added with stirring and the reaction mixture is reacted for a time and temperature sufficient to form the fluoran of formula 1.
5. The process according to claim 4 wherein the mixture is made alkaline and the formed fluoran recovered by extraction with a solvent.
6. The process according to claim 5 wherein the solvent is toluene.
7. The process according to claim 1 wherein the alkanesulfonic acid is selected from methanesulfonic acid or ethanesulfonic acid.
8. The process according to claim 1 wherein the arenesulfonic acid is selected from benzenesulfonic acid, 1-napthalenesulfonic acid, or 2-naphthalenesulfonic acid.
9. The process according to claim 1 wherein the aminodiphenylamine is 3-methoxy-4′-dimethylaminodiphenylamine.