An alternative method to produce PTA directly via oxidation of p-cymene, a compound that can be easily prepared from limonene or terpenes, has been studied more recently (Scheme 6). The oxidation produces various intermediates including p-cymenol, p-methylacetophenone, and p-toluic acid, all of which are eventually further oxidized into PTA. Quantitative conversion with 38% PTA selectivity has been reported. Life cycle assessment analyses revealed that this method is greener compared to the isobutanol route or the HMF route, largely due to p-cymene being readily available from biomass waste. 86 Scheme 6. Preparation of PTA from p-cymene.