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Chemicals from Aromatic Hydrocarbons
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Oxidizing toluene to benzaldehyde (C6H5CHO) is a catalyzed reaction in which a selective catalyst limits further oxidation to benzoic acid. In the first step, benzyl alcohol is formed and then oxidized to benzaldehyde. Further oxidation produces benzoic acid: C6H5CH3+[O]→C6H5CH2OHC6H5CH2OH[O]→C6H5CHO
List of Chemical Substances
Published in T.S.S. Dikshith, and Safety, 2016
Benzaldehyde is a colorless to yellow, oily liquid with an odor of bitter almonds. Benzaldehyde is commercially available in two grades: (i) pure benzaldehyde and (ii) and double-distilled benzaldehyde. The latter has applications in the pharmaceutical, perfume, and flavor industries. Benzaldehyde may contain trace amounts of chlorine, water, ben-zoic acid, benzyl chloride, benzyl alcohol, and/or nitrobenzene. Benzaldehyde is ignited relatively easily on contact with hot surfaces. This has been attributed to the property of very low auto-ignition temperature. Benzaldehyde also undergoes autoxidation in air and is liable to self-heat. Benzaldehyde exists in nature, occurring in combined and uncom-bined forms in many plants. Benzaldehyde is also the main constituent of the essential oils obtained by pressing the kernels of peaches, cherries, apricots, and other fruits. Benzaldehyde is released into the environment in emissions from combustion processes, such as gasoline and diesel engines, incinerators, and wood burning. It is formed in the atmosphere through photochemical oxidation of toluene and other aromatic hydrocarbons. Benzaldehyde is corrosive to gray and ductile cast iron (10% solution), and all concentrations of lead. However, pure benzaldehyde is not corrosive to cast iron. Benzaldehyde does not attack most of the common metals, like stainless steels, aluminum, aluminum bronze, nickel and nickel-base alloys, bronze, naval brass, tantalum, titanium, and zirconium. On decomposition, benzaldehyde releases peroxybenzoic acid and benzoic acid.
Keggin-type polyoxometalate-based supramolecular complex for selective oxidation of styrene to benzaldehyde
Published in Journal of Coordination Chemistry, 2020
Wen-Jing Cui, Qing Zhao, Hao-Tian Zhu, Na Hu, Yuan-Yuan Ma, Zhan-Gang Han, Yang-Guang Li
Benzaldehyde is an important chemical intermediate in pharmaceuticals, foods, pesticides and spices production. The catalytic performance of 1 was evaluated by employing the model reaction of selective oxidation of styrene to benzaldehyde. The conditions of the catalytic oxidation experiment were referred to our previous work [38], in which the reaction was performed in an acetonitrile media at 70 °C with hydrogen peroxide as green oxidant. The corresponding oxidized products were detected by using GC technique. As shown in Figure 4 and Table 2, 1 displays good catalytic activity on selective oxidation of styrene. The styrene can achieve almost 98% conversion within 4 h with 99% selectivity toward benzaldehyde. Without the presence of 1 as catalyst, the blank experiment shows only 5% conversion of styrene, indicating that 1 has high catalytic activity for the selective oxidation of styrene (Table 2, entry 2). To understand the origin of catalytic performance of 1, a series of comparative experiments with single component or mixed components as catalysts were carried out under the same conditions (Figure 5 and Table 2). When using single-component precursor Co(OAc)2·4H2O as catalyst, the conversion of styrene can only reach 16% after reacting for 4 h with about 90% selectivity of benzaldehyde (Figure 5(a,b)). While employing POMs precursor K5BW12O40 as catalyst, it could achieve 21% conversion of styrene in 4 h and the selectivity of benzaldehyde was 78% (Figure 5(c)). As for Co(OAc)2·4H2O and K5BW12O40, the former shows the relatively high selectivity to benzaldehyde, which may be due to its specific coordinated activation mode to substrate. When choosing the physical mixture of Co(OAc)2·4H2O and K5BW12O40 with same equivalents, the maximum conversion of styrene was 34% for 4 h reaction and almost 83% of benzaldehyde selectivity was obtained. This result demonstrates the potential synergistic effect may occur when POM precursor K5BW12O40 meets transition metal Co2+ ion. Compared with these control samples, 1 displays better catalytic activity, which is almost five times more than the catalytic activities of the single components (Co(OAc)2·4H2O or K5BW12O40). From the above results, it can be speculated that the high catalytic performance of 1 may stem from amplification of the synergistic effect of metal sites and polyoxoanions in 3-D supramolecular frameworks.