Thermal stability and pathways for the oxidation of four 3-phenyl-2-propene compounds

• Published in: RSC advances 2021-10, Vol.11 (52), p.32654-3267
• Main Authors: Yu, Chang, Liang, Min, Dai, Su-Yi, Cheng, Hai-Jun, Ma, Li, Lai, Fang, Liu, Xiong-Min, Li, Wei-Guang
• Format: Article
• Language: English
• Subjects: Acids; Alcohol; Benzaldehyde; Benzoic acid; Carbon; Carboxyl group; Chemistry; Cinnamaldehyde; Cinnamic acid; Gas chromatography; Mass spectrometry; Oxidation; Pressure vessel design; Pressure vessels; Reaction kinetics; Thermal stability
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d1ra04836h

Cinnamaldehyde, cinnamyl alcohol, β-methylstyrene and cinnamic acid are four important biomass 3-phenyl-2-propene compounds. In the field of perfume and organic synthesis, their thermal stability and oxidation pathways deserve attention. This paper reports a new attempt to investigate the thermal stability and reactivity by a custom-designed mini closed pressure vessel test (MCPVT). The pressure and temperature behaviors were measured by MCPVT under nitrogen and oxygen atmosphere. The temperature of initial oxygen absorption ( T a ) and rapid oxidation ( T R ) were calculated. The results showed that four 3-phenyl-2-propene compounds were stable under nitrogen atmosphere. The T a of cinnamaldehyde, cinnamyl alcohol, β-methylstyrene, and cinnamic acid was 271.25 K, 292.375 K, 323.125 K, and 363.875 K, and their T R was 301.125 K, 332.75 K, 357.91 K, and 385.375 K, respectively. The oxidation reactivity order was derived to be cinnamaldehyde > cinnamyl alcohol > β-methylstyrene > cinnamic acid. The oxidation kinetics were determined using n versus time ( n - t ) plots, which showed a second-order reaction. Peroxide was determined by iodimetry, and the oxidation products were analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that the peroxide value of cinnamaldehyde, cinnamyl alcohol, β-methylstyrene, and cinnamic acid reached 18.88, 15.07, 9.62, and 4.24 mmol kg −1 at 373 K for 6 h, respectively. The common oxidation products of four 3-phenyl-2-propene compounds were benzaldehyde, benzoic acid, and epoxide, which resulted from the carbon-carbon double bond oxidation. The substituents' oxidation products were obtained from the oxidation of cinnamaldehyde, cinnamyl alcohol, and β-methylstyrene. In particular, the difference is that no oxidation products of the carboxyl group of cinnamic acid were detected. The common oxidation products of the four 3-phenyl-2-propene compounds were benzaldehyde, benzoic acid, and epoxide, which resulted from the carbon-carbon double bond oxidation. The substituents' oxidation products were caught in the oxidation of cinnamaldehyde, cinnamyl alcohol, and β-methylstyrene. In particular, the difference is that no oxidation products of the carboxyl group of cinnamic acid were detected. According to the complex oxidation products, important insights into the oxidation pathways were provided. A new attempt to investigate the thermal stability and reactivity of four 3-phenyl-2-propene compounds with oxygen b