Acid-catalysed carboxymethylation, methylation and dehydration of alcohols and phenols with dimethyl carbonate under mild conditions

Dimethyl carbonate (DMC) chemistry has been extended to include acid-catalysed reactions of different aliphatic alcohols and phenols. For the first time, p-toluenesulfonic acid (PTSA), H2SO4, AlCl3 and FeCl3 have been shown to aid carboxymethylation for primary aliphatic alcohols at catalytic loadings with quantitative conversion and selectivity. For carboxymethylation of secondary alcohols, stoichiometric PTSA and catalytic AlCl3 both gave quantitative conversion and selectivity. Stoichiometric FeCl3 and H2SO4 promoted dehydration of linear aliphatic alcohols. Additionally FeCl3 catalysed methylation of cyclohexanol, whilst AlCl3 resulted in methylation of phenolic compounds. This research expands the range of potential application for DMC in green chemistry

Challenges in the development of bio-based solvents : A case study on methyl(2,2-dimethyl-1,3-dioxolan-4-yl)methyl carbonate as an alternative aprotic solvent

Many traditional solvents have drawbacks including sustainability and toxicity issues. Legislations such as REACH is driving the move towards less hazardous chemicals and production processes. Therefore, safer bio-based solvents need to be developed. Herein, a 10 step method has been proposed for the development of new bio-based solvents that utilise a combination of in silico modelling of Hansen solubility parameters (HSPs), experimental Kamlet-Abboud-Taft parameters, selection of green synthetic routes followed by applications testing and toxicity measurements. The challenges that the chemical industry face in the development of new bio-based solvents are highlighted through a case study on methyl (2,2-dimethyl-1,3-dioxolan-4-yl) methyl carbonate (MMC) which can be synthesised from glycerol. Although MMC is an attractive candidate as a replacement solvent, simply being bio-derived is not enough for a molecule to be regarded as green. The methodology of solvent development described here is a broadly applicable protocol that will indicate if a new bio-based solvent is functionally proficient, but will also highlight the importance of early stage Kamlet-Abboud-Taft parameters determination and toxicity testing in the development of a green solvent

Synthesis, Characterization, and Physicochemical Performance of Nonionic Surfactants via PEG Modification of Epoxides of Alkyl Oleate Esters

The synthesis of surfactants from fatty acid esters via epoxide chemistry has been known for its accompanying challenges, which usually involve the use of toxic homogeneous catalysts in the ring-opening reaction step and generation of many side reaction products. This paper presents environmentally benign routes to a library of nonionic surfactants via a three-step synthesis involving transesterification of methyl oleate to alkyl oleates, epoxidation of the oleate alkene, and solventless heterogeneously catalyzed ring opening of the epoxides with poly(ethylene glycols) of varying chain length under a short reaction time (60 min). The processes were highly atom efficient and afforded a minimum surfactant yield of 80% with limited or negligible side reaction products. The intermediate molecules and synthesized surfactants were purified and comprehensively characterized, including physicochemical measurements: dynamic surface tension and equilibrium surface tension. Additionally, the hydrophilic-lipophilic balance (HLB) concept was used to comprehensively scan through the polarity behaviors of the surfactants' head and tail in solution as a prediction of their end use. The results showed that surfactants have a critical micelle concentration (CMC) lower than 0.1 mg/ml as the alkyl oleate increases in length from ethyl to decyl and that the lower-molecular-weight surfactants reached equilibrium faster than the higher-molecular-weight surfactants. HLB results showed that the surfactants can be applied as oil-in-water emulsifiers, detergents, solubilizers, and wetting agents. In general, the synthesized surfactants potentially possess switchable properties for use in industrial formulations, as the alkyl chain length and the ethylene oxide number in the surfactant's structure are varied

Application of bio-based solvents for biocatalysed synthesis of amides with Pseudomonas stutzeri lipase (PSL)

Bio-based solvents were investigated for the biocatalysed amidation reactions of various ester-amine combinations by Pseudomonas stutzeri lipase (PSL). Reactions were undertaken in a range of green and potentially bio-based solvents including terpinolene, p-cymene, limonene, 2-methyl THF, ɣ-valerolactone, propylene carbonate, dimethyl isosorbide, glycerol triacetate and water. Solvent screenings demonstrated the importance and potential of using non-polar bio-based solvents for favouring aminolysis over hydrolysis; whilst substrate screenings highlighted the unfavourable impact of reactants bearing bulky para- or 4-substituents. Renewable terpene-based solvents (terpinolene, p-cymene, D-limonene) were demonstrated to be suitable bio-based media for PSL amidation reactions. Such solvents could provide a greener and more sustainable alternative to traditional petrochemical derived non-polar solvents. Importantly, once the enzyme (either PSL or CALB) binds with a bulky para-substituted substrate, only small reagents are able to access the active site. This therefore limits the possibility for aminolysis to take place, thereby promoting the hydrolysis. This mechanism of binding supports the widely accepted 'Ping Pong - Bi Bi' mechanism used to describe enzyme kinetics. The work highlights the need to further investigate enzyme activity in relation to para- or 4-substituted substrates. A priority in PSL chemistry remains a methodology to tackle the competing hydrolysis reaction

DFT and experimental analysis of aluminium chloride as a Lewis acid proton carrier catalyst for dimethyl carbonate carboxymethylation of alcohols

The Lewis acid catalysed mechanism of dimethyl carbonate (DMC) mediated carboxymethylation of alcohol was investigated experimentally and through computational chemistry methods including density functional theory (DFT). Experimental data showed that catalytic loading of AlCl3 enabled the quantitative carboxymethylation of octanol in less than 20 h, while in the absence of a catalyst only trace product was observed. The geometry of the identified transition states and related energy barriers indicate that the activation energies in AlCl3 catalysed pathways are significantly lower than those in catalyst-free pathways. Theoretical quantum chemistry methods were utilised to explore and analyse the complex of DMC with AlCl3. Natural bond orbital theory analysis and molecular orbital analysis demonstrated that the dipole present in Al-Cl covalent bonding plays a vital role in assisting the proton-transfer process. Most importantly, the reaction mechanism disclosed in this research can aid in the exploration of new Lewis acid catalysed processes in the field of dialkyl carbonate chemistry

Dialkyl carbonates: scale-up synthesis and application as green solvents for PVDF membranes preparation

Dialkyl carbonates (DACs) are well-known green solvents and reagents that have been extensively investigated as safe alternatives to chlorine-based compounds. In fact, they can replace alkyl halides and dimethyl sulfate in alkylation and carbonylation reactions as well as phosgene and its derivatives in alkoxycarbonylation ones. Recently we have developed a high yielding scale-up synthesis of non-commercially available or expensive DACs via transcarbonylation reactions of an alcohol with dimethyl carbonate (DMC) promoted by the nitrogen-based organocatalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD. Compared to previously published works, the proposed procedure has been customized for DACs large scale production (up to 100 mL of product obtained). Purification of these compounds has been achieved by fractional distillation and the exceeding reagents have been recovered and recycled. Selected DACs for this study include both symmetrical and unsymmetrical compounds, incorporating several alkyl, alkoxyalkyl, alkylamino and alkylthio functional groups. Chemical-physical properties of the new DACs have been also evaluated, as well as their water solubility. Furthermore, biodegradability and cytotoxicity tests have been carried out to investigate the effects of the different substituents on the greenness of these potential solvents and reagents. DACs application as green solvents for membrane preparation was next investigated, using non-solvent induced phase separation (NIPS) and vapor induced phase separation (VIPS) techniques, achieving both porous and plain membranes [4]. Morphology, additives effect, physical-chemical and mechanical proprieties as well as their performances in terms of water permeability and rejection were evaluated and compared to membranes obtained using commercially available cyclic carbonates (namely ethylene carbonate – EC and propylene carbonate – PC)

Valorization of spruce needle waste via supercritical extraction of waxes and facile isolation of nonacosan-10-ol

Supercritical carbon dioxide was utilized as a sustainable alternative to solvent extraction of waxes from the waste needles of two spruce species, namely Norwegian and Sitka spruce. These extracts were rich in nonacosan-10-ol, an organic compound with hydrophobic properties that lends its use in the preparation of superhydrophobic coatings. The highest crude yields were 1.7% w/w of needles obtained at 400 bar and 60 °C, while nonacosan-10-ol was selectively extracted at 200 bar and 60 °C (8070 ± 91.1 μg/g of needles). Purification of nonacosan-10-ol from the wax extracts was conducted using a simple rapid green recrystallization technique. This yielded a recovery of 44.6% ± 2% and 48.4% ± 2% of the total nonacosan-10-ol from the original crude Sitka (3600 μg/g of needles) and Norwegian wax (1920 μg/g of needles) respectively. Application of nonacosan-10-ol to a filter paper led to the formation of highly hydrophobic surfaces, with preliminary contact angles of up to 149°. This sustainable production method may develop opportunities to valorize forestry waste within a holistic biorefinery

Integrated biorefinery approach to valorise Saccharina latissima biomass : Combined sustainable processing to produce biologically active fucoxanthin, mannitol, fucoidans and alginates

The feasibility of European seaweed farming depends on the valorisation of algal biomass harvested. In the present work we have combined sequential extraction processes from Saccharina latissima to produce a range of products, focusing on the extraction of fucoxanthin using supercritical CO2 followed by different valorisation routes. We optimised the conditions the for extraction of fucoxanthin (40 MPa, temperature has little impact on extraction) and the extracts obtained were tested on cancer cell cultures to determine the antiproliferative effects of this pigment. We established that the supercritical CO2 extracts have an antiproliferative effect similar to that of commercial fucoxanthin (concentrations 0.1–0.4 mg/mL) and showed that the active compound in the extracts is fucoxanthin. In order to integrate this process with a holistic valorisation of the algal biomass, we explored the extraction of mannitol using a microwave-assisted protocol (4.15 wt % yield). We also evaluated the potential extraction of fucoidans and alginates from the solids remaining after supercritical CO2 extraction (67.27 to 69.38 % of alginates). A life cycle analysis of the supercritical CO2 extraction proposed shows that the drying process of algal biomass and the energy used to compress the CO2 are the elements with the highest environmental impact (over 90% of CO2 eq/g of extract) in this the process, indicating routes for reducing the environmental footprint. Combining supercritical CO2 extraction and microwave-assisted extraction methods would enable European seaweed producers to obtain multiple marketable products from algal biomass

Recent developments in key biorefinery areas

To meet decarbonisation goals and implement a more sustainable circular economy model, the chemical industry needs to transition from fossil to renewable sources of carbon. Current chemical production is dominated by petroleum, where this broadly uniform feedstock is separated using a single, simple process to give a small range of heteroatom-free molecules that are the platform to a myriad of products. In a biorefinery, however, many feedstocks of widely varying composition using markedly different technologies are processed to give one or two of a wide range of bioderived platform molecules. Here, recent publications are used to highlight selection of the most suitable second or third generation feedstocks, converted using integrated, complementary processes to generate multiple products. This approach generates a range of chemicals, more fully using the carbon source of choice in a sustainable manner, generating more value, which together makes the realisation of the biorefinery concept draw ever closer

Economic Assessment of Supercritical CO2 Extraction of Waxes as Part of a Maize Stover Biorefinery

To date limited work has focused on assessing the economic viability of scCO2 extraction to obtain waxes as part of a biorefinery. This work estimates the economic costs for wax extraction from maize stover. The cost of manufacture (COM) for maize stover wax extraction was found to be €88.89 per kg of wax, with the fixed capital investment (FCI) and utility costs (CUT) contributing significantly to the COM. However, this value is based solely on scCO2 extraction of waxes and does not take into account the downstream processing of the biomass following extraction. The cost of extracting wax from maize stover can be reduced by utilizing pelletized leaves and combusting the residual biomass to generate electricity. This would lead to an overall cost of €10.87 per kg of wax (based on 27% combustion efficiency for electricity generation) and €4.56 per kg of wax (based on 43% combustion efficiency for electricity generation). A sensitivity analysis study showed that utility costs (cost of electricity) had the greatest effect on the COM