4-Dimethylaminobenzaldehyde condenses with 3-dimethylaminobenzoic
acid in the presence of acetic anhydride to yield 3-(4-dimethylaminophenyl)-6-dimethylamin0phthalide.25
Subsequent oxidation, preferably with
3-nitrobenzenesulfonic acid,26 yields the bisdimethylaminobenzophenonecarboxylic
acid, which then is treated with dimethylaniline in acetic anhydride
to form CVL.26,27 A variation for the preparation of the intermediate
phthalide by treatment of 2-formyl-5-dimethylaminobenzoic acid with
dimethylaniline has also been described.28 However, the difficulty in preparing
this former starting material renders this route less attractive. It has
also been shown29 that treatment of the phthalide intermediate with
dimethylaniline in the presence of a Friedel–Crafts catalyst yields leuco
CVL, which may then be oxidized as described for Scheme 2. The development
of CVL as a color former for carbonless copying papers was a result
of the deficiencies of the readily available Malachite Green lactone