Kinetic and mechanistic study of Lilestralis, a synthetic muguet fragrance molecule

• Main Author: Scott, Laura-Marie
• Published: University of Aberdeen 2011
• Subjects: 547.6; Perfumes : Toilet preparations : Perfumes industry : Essences and essential oils
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540544

In the multi-step synthesis of Lilestralis, a synthetic muguet fragrance, the kinetics and mechanism of the formation of 3-(3-t-butylphenyl)-2-methylpropan-1-ol (m-LOL) and 4-(3-t-butylphenyl)-2-methylpropan-1-ol (p-LOL) from 2-methyl-3-phenylpropan-1-ol (MPP) and isobutylene using concentrated liquid phosphoric acid as a catalyst was investigated. By-products that include phosphate esters of MPP, m-LOL and p-LOL and oligomers of isobutylene were produced during this reaction and their role within the kinetics and mechanism was also investigated. When crystalline phosphoric acid is dissolved in water, it can form equilibrium polyphosphate mixtures at high acid concentrations. The phosphate species have the general formula Hn+2PnO3n+1 and consist of species such as orthophosphoric acid (H3PO4), pyrophosphoric acid (H4P2O7) and triphosphoric acid (H5P3010). The presence of polyphosphate within liquid phosphoric acid solutions used in this study was investigated using 31P NMR. To investigate the influence of water on the reaction, a number of experiments were performed using 1,4-dioxane as a solvent. This was chosen as the boiling points and density are similar to water, although it is classified as an aprotic solvent. Phosphate esters of MPP, m-LOL and p-LOL are produced as by-products and can potentially undergo hydrolysis when water is present, therefore reactions using aqueous phosphoric acid solutions may not give a true reflection of the concentration of phosphate esters produced. The use of heterogeneous catalysts was also investigated in order to improve yield and selectivity for p-LOL and m-LOL. These include acid catalysts such as solid phosphoric acid supported on Kieselguhr (SPA), sulphated zirconia and ultra stable zeolite-Y (H-USY).