[F:1][C:2]([F:16])([CH:13]([F:15])[F:14])[CH2:3][O:4][C:5]1[CH:12]=[CH:11][C:8]([CH:9]=O)=[CH:7][CH:6]=1.C([CH2:19][C:20]([OH:22])=[O:21])#N.FC(F)(C(F)F)COC1C=CC(/C=C\C#N)=CC=1.N1CCCCC1>N1C=CC=CC=1.C1(C)C(C)=CC=CC=1>[F:1][C:2]([F:16])([CH:13]([F:15])[F:14])[CH2:3][O:4][C:5]1[CH:12]=[CH:11][C:8]([CH:9]=[CH:19][C:20]([OH:22])=[O:21])=[CH:7][CH:6]=1735.0 g (3.12 mol) of 4-(2,2,3,3-tetrafluoropropoxy)benzaldehyde, 269 g of cyanoacetic acid, 660 g of cis-4-(2,2,3,3-tetrafluoropropoxy)cinnamonitrile (main fractions containing 80 to 85% by weight of cis isomer) are admixed with 750 g of xylene, 750 ml of pyridine and 750 ml of piperidine and heated to 110° C. with stirring. The mixture is allowed to react for 2 hours, and 53.8 g of cyanoacetic acid are added again and the mixture is allowed to react for a further 30 minutes. After cooling, the reaction mixture is distilled under reduced pressure and 1173 g of 4-(2,2,3,3-tetrafluoropropoxy)cinnamic acid (yield: 87% purity>95% by weight) are obtained in the form of a mixture of isomers which contains cis-4-(2,2,3,3-tetrafluoropropoxy)cinnamonitrile and trans-4-(2,2,3,3-tetrafluoropropoxy)cinnamonitrile in a molar ratio of about 1.8:1 and , in addition, about 3% by weight of piperidine and up to 2% by weight of unidentifiable impurities.
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