4-Formylbenzoic acid (p-Eormylbenzoicacid; terephthalaldehydeacid; BENZALDEHYDE-4- CARBOXYLIC ACID; 4-Carboxybenzaldehyde, 96% 100GR; 4-Carboxybenzaldehyde, 96% 25GR; 4-Carboxybenzaldehyde, 96% 5GR; 4-Carboxylbenzaldehyde; NSC 15797)[1] is also called 4-Carboxybenzaldehyde. Its molecular formula is C8H5O3, it is insoluble in water, it can be dissolved in DMF, it can undergo esterification reaction and alcohol-aldehyde condensation reaction with alcohol. An important intermediate for organic synthesis, widely used in medicine, pesticides, coatings, liquid crystal raw materials, polymer materials and perfume raw materials.[1] 

In addition, in the course of studies of the crystal structure of bis (2-hydroxyethyl) terephthalate, it became of interest to determine the structure of 4-formylbenzoic acid (4-FBA), an important intermediate in the manufacture of terephthalic acid (TPA) from p-xylene, 4-FBA is known to constitute the principal impurity in TPA which is difficult to eliminate. By Masao Haisa have studied topochemical studies of the crystal and molecular structures of two polymorphs of 4-formylbenzoic acid.[2] At the same time, solubilities of 4-Formylbenzoic Acid in Ethanoic Acid, Water, and Ethanoic Acid/Water Mixtures with Different Compositions from (303.2 to 473.2) K have been studied by Weizhen Sun et al.[3]. 4-formylbenzoic acid is regarded as the major impurity, because compared with other impurities it is hard to eliminate, due to its similarity to TPA in molecular structure. The concentration of 4-formylbenzoic acid in solid TPA is expected to be as low as possible by PX oxidation and subsequent crystallization steps in aqueous ethanoic acid. So, the solubility data of 4-formylb enzoic acid in aqueous ethanoic acid are fundamental to the design and optimization of the PX oxidation reactor and subsequent crystallizers. Meanwhile, in the field of hydrogenation of 4-carboxybenzaldehyde, some researchers have done some studies. Terephtha -lic acid is usually produced by the oxidation of p-xylene in liquid phase, which is often accompanied by impurities such as 4-carboxybenzaldehyde (4-CBA). 4-CBA can be removed via hydrogenation over a Pd/AC catalyst in a trickle bed reactor. Zhou et al.[4] introduced TiO2 nanoparticles on the surface of the CDC–SiC composite. The resulting catalyst gives a significantly enhanced activity, as well as stability for the hydrogenation of 4-CBA due to the stabilization of the highly dispersed Pd nanoparticles.

References

[1] http://m.is0513.com/ProductChemicalPropertiesCB7702071_EN.htm
[2] Haisa M, Kashino S, Ikejiri F, et al. Topochemical studies. VIII. The crystal and molecular sturtures of two polymorphs of 4-formylbenzoic acid[J]. Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry, 1976, 32(3): 857-860.
[3] Sun W, Qu W, Zhao L. Solubilities of 4-Formylbenzoic Acid in Ethanoic Acid, Water, and Ethanoic Acid/Water Mixtures with Different Compositions from (303.2 to 473.2) K[J]. Journal of Chemical & Engineering Data, 2010, 55(10): 4476-4478.
[4] Zhou Y, Lai X, Pan X, et al. A highly active and stable Pd–TiO 2/CDC–SiC catalyst for hydrogenation of 4-carboxybenzaldehyde[J]. Journal of Materials Chemistry, 2012, 22(28): 14155-14159.
[5] https://pubchem.ncbi.nlm.nih.gov/compound/2723734