Valorization of Commercially Important Essential Oils of Poaceae and Lamiaceae Families Using Heterogeneous Catalysts

<p dir="ltr">This work offers a comprehensive exploration of innovative catalytic processes designed to transform essential oil components, addressing challenges related to unwanted compounds and enhancing the value of traditionally undervalued essential oils. Each section of this thesis introduces distinct catalytic transformations, showcasing applications that span the fragrance, pharmaceutical, and chemical industries.</p><p dir="ltr">Mitigating the challenge posed by pulegone, a carcinogenic compound in dementholized oil (DMO) during menthol crystal separation, involves the introduction of two novel catalysts: 3%Pd-2.5%Al- 1.5%B/AC and 2%Pd-3%Si/AC. These catalysts facilitate the selective conversion of pulegone to thymol and menthone/isomenthone, with optimized conditions yielding impressive results (98.54% for thymol and 97.68% for menthone/isomenthone). This approach extends to pulegone-rich essential oil (CIM-Vishisth variety), demonstrating efficacy in reducing pulegone content for commercial use. </p><p dir="ltr">Targeting the transformation of citral, a major component in lemongrass essential oil (low value essential oil), and the present work introduces a novel catalytic process with a 12%Ni-HT-530 composite. This process exhibits remarkable efficiency, achieving a 99% conversion and 95% selectivity for enantiospecific (+)-citronellal. The adaptability of this process is further showcased in lemongrass oil, highlighting its potential for industrial applications. In another scheme, the selective hydrogenation of citral to nerol and geraniol is achieved using a modified Fe2O3 catalyst, 3%Ni-1.5%Pd/Fe2O3. Synthesized through various methods, the catalyst demonstrates high selectivity (97%) under optimized conditions, offering a viable route for transforming citral in lemongrass essential oil into valuable sweet smelling (nerol/geraniol) rosy note products. Describing a two-step catalytic process for the semi-synthesis of (-)-menthol from citronellal-rich essential oils, bi-acidic composites (Al-B-NaYZE or Sn-B-NaYZE) play a crucial role. These composites exhibit high selectivity (99%) for the cyclization of citronellal to isopulegol isomers. The subsequent reduction to menthol using 1%Pd/AC demonstrates efficient biobased menthol production. The spent oil after menthol separation has displayed antimicrobial activities; hence, it is used in the preparation of health-care products. In another scheme, a green process has been developed for the semi-synthesis of p-menthane-3,8-diol (PMD), a mosquito repellent, from citronellal-rich essential oils. Metal-incorporated Sulfonated biochar (SBC) catalysts (Zn, Cr, Fe & Ni) prepared via a hydrothermal process demonstrate high efficiency and selectivity. The Cr-SBC-HT catalyst achieves exceptional results, with 99% citronellal conversion and 96% PMD selectivity. This compound has displayed mosquito repellency up to 6 hours, and very closely compared with DEET (N,N-diethyl-m-toluamide).</p><p dir="ltr">Further, the bio-nano-technological synthesis of silver (Ag) and silver-copper (Ag-Cu) nanoparticles utilizing the discarded aqueous portion of Prosopis cineraria pod were used for monoterpenes epoxidations. These synthesized nanoparticles exhibit antimicrobial properties and find application in the epoxidation of alkene moieties, showcasing their potential in nano-medicine, therapeutics, and the modification of monoterpenoids for fine fragrance. Collectively, these contributions significantly advance the development of environmentally friendly and economically viable catalytic processes, offering widespread applications across diverse industries. The major advantages of novel catalytic processes include enantiospecific product selectivity, reusability, quick attainment of reaction pressure and temperature, and the production of a final product that is 100% biobased. Consequently, the finished product is considered as nature-identical. Therefore, catalytic modification of essential oil to commodity products might be suitable for commercial applications, serving the fragrance, flavor, and pharmaceutical industries.</p>