Reactivity of biomass relevant esters and alcohols in acidic ionic liquids
File(s)
Author(s)
Ismail, Nur Liyana Binti
Type
Thesis
Abstract
Reactivity of biomass relevant alcohols and esters in hydrogen sulfate based ionic liquids were successfully studied. A series of alcohols; methanol, 1-butanol, 2-butanol, isopropanol, and phenol were reacted with 1-butylimidazolium hydrogen sulfate [HC4im][HSO4] to represent cellulose hydroxyl group reactivity in the selected acidic ionic liquids. Apart from phenol, all selected alcohols were found to undergo sulfation via nucleophilic substitution by [HSO4]− anion after 24 h. Mechanistic study of the nucleophilic substitution reactions of p-substituted benzyl alcohols with [HC4im][HSO4] and [C4C1im][HSO4] were done using Hammett equation. The concave upward Hammett plots suggest there is a change in mechanism, from SN1 for electron donating substituents (OMe and Me) to SN2 for electron withdrawing substituents (H, Cl, CF3 and NO2). This chapter revealed that ILs can act as a solvent as well as a nucleophile in one reaction. Most importantly, this showed that sulfation of cellulose is probable under Ionosolv pretreatment. Hydrolysis of lignin-carbohydrate linkage model compounds, BHB and THFF were carried out in [HC4im][HSO4] with varying acid and water content. The rates of hydrolysis were increasing with increasing of mol% acid. The mechanistic insights of the reactions were studied using Zucker-Hammett, Bunnett-Olsen and Eyring equations. All three resulted plots are in agreement with A2 mechanism. Transesterification reactions of BHB and ethyl lactate and methanol in [HC4im][HSO4] were found to give low yields due to the sulfation of methanol. This again showed that the [HSO4]¯anion are reactive and nucleophilic enough to undergo nucleophilic substitution reaction with alcohol at 80 – 120 °C in aqueous or non-aqueous condition.
Version
Open Access
Date Issued
2018-07
Date Awarded
2019-02
Copyright Statement
Creative Commons Attribution NonCommercial No Derivatives Licence
Advisor
Welton, Tom
Hallett, Jason
Sponsor
Universiti Teknologi MARA
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)