Highly Active Trifloaluminate Ionic Liquids as Recyclable Catalysts for Green Oxidation of 2,3,6-Trimethylphenol to Trimethyl-1,4-Benzoquinone

Abstract

An effective method for the synthesis of 2,3,6-trimethyl-1,4-benzoquinone via the oxidation of 2,3,6-trimethylphenol as the key step in the in the preparation of vitamin E was presented. An aqueous solution of H2O2 was used as the oxidant and Lewis acidic trifloaluminate ionic liquids [emim][OTf]-Al(OTf)3, χAl(OTf)3 = 0.25 or 0.15 as catalysts. Trifloaluminate ionic liquids were synthesised by the simple reaction between 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (triflate) [emim][OTf] and aluminium triflate used in sub-stoichiometric quantities. The influence of the reaction parameters on the reaction course, such as the amount and concentration of the oxidant, the amount of catalyst, the amount and the type of organic solvent, temperature, and the reaction time was investigated. Finally, 2,3,6-trimethyl-1,4-benzoquinone was obtained in high selectivity (99%) and high 2,3,6-trimethylphenol conversion (84%) at 70 °C after 2 h of oxidation using a 4-fold excess of 60% aqueous H2O2 and acetic acid as the solvent. The catalytic performance of trifloaluminate ionic liquids supported on multiwalled carbon nanotubes (loading of active phase: 9.1 wt.%) was also demonstrated. The heterogeneous ionic liquids not only retained their activity compared to the homogenous counterparts, but also proved to be a highly recyclable catalysts.

Trifloaluminate Ionic Liquids Supported UIO‐67 as Lewis Acidic Catalyst for Excellent Synthesis of Alkyl Levulinates

“…Butyl levulinate, 1 H NMR (600 MHz, CDCl 3 , TMS): δ = 0.94 (t, J = 7.40 Hz, 3H),1.39-1.62(m,2H),2.2(s,3H) 2,58 (t, J = 6.5 Hz, 2H), 2.75 (t, J = 6.6 Hz, 2H), 4.08 (t, J = 6.7 Hz,2H) 13 C NMR (151 MHz, CDCl 3 ): δ 13.56, 18.97, 27.88, 29.75,30.49, 37.85, 64.43, 172.72, 206.51 GCMS: (EI) m/z (%) 172 (3, M + * ), 157 (8), 143 (3), 130 (6), 117 (15), 99 (90), 81 (5), 74 (28),71 (12), 57 (18), 43 (100).…”

“…[13,[15][16][17][18] The metal triflates generally have medium to strong acidity, excellent water tolerance, and high activity at moderate condition but suffer from limited solubility. [13,[15][16][17][18] Recently, Lotos et al replaced the poorly soluble Al(OTf) 3 with the fully homogeneous ionic liquids with oligonuclear trifloaluminate anion (Scheme 2) as an acid catalyst towards the LAEs synthesis from α-AL. [13,16] Full α-AL conversion and unprecedented LAE selectivity (> 99 %) were achieved in shorter reaction times.…”

“…Lewis acidic metal triflates have been efficiently used in a number of chemical processes. [13,[15][16][17][18] The metal triflates generally have medium to strong acidity, excellent water tolerance, and high activity at moderate condition but suffer from limited solubility. [13,[15][16][17][18] Recently, Lotos et al replaced the poorly soluble Al(OTf) 3 with the fully homogeneous ionic liquids with oligonuclear trifloaluminate anion (Scheme 2) as an acid catalyst towards the LAEs synthesis from α-AL.…”

“…Lewis acidic metal triflates have been efficiently used in a number of chemical processes [13,15–18] . The metal triflates generally have medium to strong acidity, excellent water tolerance, and high activity at moderate condition but suffer from limited solubility [13,15–18] . Recently, Lotos et al.…”

“…A reaction network analysis reveals that the LEAs synthesis from α‐AL occurs via the formation of pseudo‐LEA intermediates (Scheme 1) and require a catalyst with sufficient acid strength. Lewis acidic metal triflates have been efficiently used in a number of chemical processes [13,15–18] . The metal triflates generally have medium to strong acidity, excellent water tolerance, and high activity at moderate condition but suffer from limited solubility [13,15–18] .…”