Benzoic acid

About: Benzoic acid is a research topic. Over the lifetime, 11832 publications have been published within this topic receiving 167127 citations. The topic is also known as: Retardex & E210.

Photocatalytic oxidation of gaseous toluene on anatase TiO2 catalyst: mechanistic aspects and FT-IR investigation

Abstract: Photo-oxidation of toluene has been carried out in gas–solid regime by using polycrystalline anatase TiO2 as the catalyst. The reacting gaseous mixture was toluene, air and water in various molar ratios. A pyrex fixed-bed continuous photoreactor irradiated by a medium pressure Hg lamp was used for performing the photoreactivity experiments. The main oxidation product was benzaldehyde but benzene, benzyl alcohol and traces of benzoic acid, phenol and unidentified compounds were also detected. The molar conversion to benzaldehyde with respect to the initial amount of toluene was ca. 20% in the best experimental conditions. Benzene was produced only as a transient product during the first 3–4 h of irradiation. The dependence of feed composition and flow rate on the toluene fractional conversion was investigated. Selected experiments were performed by using N2 or CO2 instead of air. The presence of oxygen was essential for the occurrence of the photoreaction while water played an important role in order to maintain the catalyst activity. Moreover, a Fourier-transform infrared spectroscopy (FT-IR) investigation was carried out simulating the experimental conditions used during the photoreactivity experiments. The results indicated that toluene is weakly stabilised on the hydrated TiO2 particles by hydrogen-bonding with surface hydroxyl groups, and that it is photo-oxidised to benzaldehyde only in the presence of surface OH groups.

Influence of chemisorption on the photodecomposition of salicylic acid and related compounds using suspended TiO2 ceramic membranes

Abstract: The adsorption and photodecomposition on semiconducting membranes of molecules with different functional groups were studied. Ceramic membranes, prepared by a sol-gel technique, were employed because this technique provides some control over surface area, porosity, and crystal form of these materials, properties which affect their photochemical behavior. Salicylic acid was chosen as a prototype molecule. 3-Chlorosalicylic acid, benzoic acid, phenol, and 4-chlorophenol were also investigated. The adsorption densities of salicylic and 3-chlorosalicylic acids decreased with both increasing solution pH and membrane firing temperature, in correlation with the number of positive adsorption sites on TiO2 surface. No adsorption for benzoic acid, phenol, and 4-chlorophenol was observed. Photodecomposition rates were found to depend on the adsorption characteristics of the organic compound; for salicylic acid the degradation rate diminished with increasing pH. Benzoic acid, whose degradation products adsorb on the oxide surface, showed a similar trend. No dependence on pH was detected for phenols. Methanol was found to affect the degradation rate of salicylic acid only under conditions of high pH. It is proposed that, for chemisorbing organics, the initial step of the photodecomposition process is governed by two different mechanisms that depend on the adsorption behavior of the organic compound at a particular pH. For adsorbed salicylate, an orbital configuration of the chelate ring is proposed to interpret direct electron transfer from the organic molecule to the semiconductor.

Rhodium(I)-catalyzed carboxylation of aryl- and alkenylboronic esters with CO2.

Abstract: When the esters of arylboronic acids with 2,2-dimethylpropan-1,3-diol were treated with a catalytic amount of [Rh(OH)(cod)]2 in the presence of 1,3-bis(diphenylphosphino)propane and CsF in dioxane at 60 °C under carbon dioxide atmosphere, the benzoic acid derivatives were obtained in good yields. Reactions of alkenylboronic esters also proceeded under similar conditions to give α,β-unsaturated carboxylic acids. As these boronic esters are now easily available through coupling or direct borylation reactions, this method would be a useful method for the preparation of various functionalized aryl- and alkenyl-carboxylic acids.