Arabian Journal of Chemistry (Aug 2023)
Oxidation characteristics and thermal stability of Butylated hydroxytoluene
Abstract
Butylated hydroxytoluene (BHT) is an excellent antioxidant widely used in food, polymer materials, and other fields. In order to understand the hazards of BHT, it is necessary to study its thermal stability, oxidation properties, and reaction products. This paper investigated BHT's oxidation characteristics and products using a mini-closed pressure vessel test (MCPVT), UV radiation reaction method, iodometric method, and gas chromatography-mass spectrometry (GC–MS). The MCPVT results showed that no chemical reaction of BHT was observed under a nitrogen atmosphere even when the temperature was increased to 450 K, which indicated that it was stable. However, BHT was readily oxidized under an oxygen atmosphere with an initial oxidation temperature of 332 K. Notably, oxidation reactions can occur as low as 293 K under 365 nm UV radiations in the atmosphere. The kinetics of the initial oxidation of BHT was investigated. The kinetics of the reaction of BHT in MCPVT was a second-order reaction with the kinetic equation lnk = -1.2194 × 104(1/T) + 21.4. And Ea = 101.4 kJ mol−1. The difference is that a pseudo-first-order reaction was shown under UV radiation, with a linear relationship between the apparent activation energy and the logarithm of the light intensity (I): Ea = -1.878 lnI + 74.56, the apparent activation energy was significantly reduced compared to the former, indicating that UV light has a great effect on the oxidation of BHT. The peroxide value of the BHT oxidation product in MCPVT was determined with the iodometric method. When the reaction was carried out at 358 K for 8 h, the peroxide value of BHT was 3.2 mmol kg−1. The main oxidation products of BHT were identified with GC–MS, such as 2, 6-di-tert-butyl-p-benzoquinone, 1-(2, 4, 6-trihydroxyphenyl) butanone, 3, 5-di-tert-butyl- 4-hydroxybenzaldehyde, 3, 5-di-tert-butyl-4-hydroxyacetophenone. Based on these oxidation products, the oxidation pathway of BHT was described. In conclusion, the oxidation characteristics of BHT were studied in detail with MCPVT, and a method for evaluating thermal stability was developed. UV radiation made BHT more susceptible to oxidation reactions. These data provided a reference for BHT's storage, transportation, and safety evaluation.
