Kinetics of CBD, Δ⁹-THC Degradation and Cannabinol Formation in Cannabis Resin at Various Temperature and pH Conditions

Introduction: Cannabidiol (CBD), cannabinol (CBN), and Δ⁹-tetrahydrocannabinol (Δ⁹-THC) are major cannabinoids in cannabis resin and products. The kinetic of the chemical reaction of resin cannabis is important for product development and storage. A few reports are available in the literature on the rate of CBD and Δ⁹-THC degradation, and CBN formation in dried resin and solutions of various pH. Materials and Methods: Thermal degradation of CBD, Δ⁹-THC, and formation of CBN was studied at 50°C, 60°C, 70°C, and 80°C for dried cannabis resin. The effect of pH and temperature on cannabinoids transformation in cannabis solution was also examined at pH 2, 4, 6, 8, 10, and 12 and at 40°C, 50°C, 60°C, and 70°C. High-performance chromatography coupled with diode-array detection (HPLC-DAD) was used for the analysis of CBD, CBN, and Δ⁹-THC transformation. The values of activation energies (E_a), shelf-life (t_90% - t_110%), and rate constant (k) were calculated for the CBD, Δ⁹-THC, and CBN. The effect of temperature and pH on the dried cannabis resin was adequately modeled with the Arrhenius equation. Results: The results indicated that the chemical kinetics in the thermal degradation of CBD, Δ⁹-THC, and formation of CBN were the zero-order, pseudo-zero-order, and first-order reactions, respectively, in cannabis resin. The first-order and pseudo-first-order degradation kinetics were evidenced for CBD and Δ⁹-THC, respectively, in cannabis solutions, whereas the zero-order formation kinetic was detected for the CBN. The transformation rate of the CBD, CBN, and Δ⁹-THC increased with increasing temperature, especially as temperature increased to 70°C at pH 2.0. The optimum pH for CBD stability was between pH 4 and 6, whereas the optimum pH for Δ⁹-THC stability was between pH 4 and 12. Conclusion: The major cannabinoids (CBD, CBN, and Δ⁹-THC) reacted more quickly at high temperature and in an acidic solution. Especially, the minimum transformation of CBD, CBN, and Δ⁹-THC was achieved by using on a low temperature, slightly to moderately acidic pH values, and short-time processing. These results may help to improve the storage condition of CBD, CBN, and Δ⁹-THC products and in the manufacturing process.