Thermal Conversion of Cannabinoids in Hemp Flower: Decarboxylation Kinetics and Potential Accumulation of Δ9-Tetrahydrocannabinol

Abstract The thermal behavior of cannabinoids in hemp flower is critical to product efficacy, consumer safety, and regulatory oversight, particularly in the context of vaporization. This study investigates the decarboxylation kinetics of cannabidiolic acid (CBDA) and the potential accumulation of tetrahydrocannabinol (THC) in CBD-rich hemp flower under controlled dry-heat exposures spanning vaporization-range temperatures in a static, no-airflow environment. Focusing on aerosol-relevant temperatures, up to 230 °C, and whole-flower matrices, we evaluated cannabinoid transformations using ultra-high-performance liquid chromatography with diode array detection (UHPLC-DAD) and gas chromatography with flame ionization detection (GC-FID). We found that CBDA decarboxylation was rapid and essentially complete at vaporization-relevant temperatures, reaching 99.96% conversion within 1 min at 230 °C. Despite this efficient decarboxylation, total CBD content declined progressively with temperature, with losses reaching approximately 58% (relative) at 230 °C, and CBD isolate showing over 30% decomposition under the same conditions. Critically, across five hemp chemotypes spanning distinct THC:CBD ratios as well as CBD and THC isolates, no meaningful accumulation of Δ9-THC was detected following heat treatment, which contrasts with reports of CBD-to-THC conversion under acidic or GC-inlet artifact conditions elsewhere in the literature. Instead, CBN formation (up to 3% in THC-rich material) indicated that Δ9-THC formed via decarboxylation is thermally labile and is preferentially degraded to secondary products such as CBN, rather than undergoing further net accumulation via CBD-to-THC conversion. These results indicate that, under conditions representative of hemp flower vaporization, the risk of unintended increase of THC is low, with direct relevance for consumer safety and regulatory compliance assessments.