1. H. Fernholz and F. Wunder (Farbwerk Hoechst), Ger. Pat., 1 294 956, 1970.
2. K. Kimura and H. Ito (Toa Gosei Chem.), Jpn. Pat. 46-16 728, 1972.
3. R.A. Schneider (Chevron Research), U.S. Pat., 4 165 438, 1979.
4. Vapor-phase aldol condensation of formaldehyde with acetic acid on V2O5$z.sbnd;P2O5 catalysts
5. Vapor-Phase Aldol Condensation of Formaldehyde with Propionic Acid on Vanadium Pentoxide—Phosphorus Pentoxide