Cellulose in quaternary ammonium hydroxide solutions

An ever-increasing demand to shift away from fossil-based feedstock towards renewable resources has led to more use of bio-based materials. Cellulose being the most abundant biopolymer on Earth has received a considerable attention with a wide range of applications (in textile fibers, films, membranes, etc.), many of which requiring processing through dissolution and/or chemical functionalisation. Cellulose cannot melt when heated or dissolve in the most common aqueous and organic solvents. Thus, a lot of efforts have been made to develop new and effective solvents aiming to address some common limitations associated with the existing solvents including solution instability, low dissolution capacity, specific temperature requirement, side reactions of the solvent itself and narrow concentration range required for the dissolution. Water solution of quaternary ammonium hydroxides (QAHs), classified as relatively green and economical chemicals, show promising potential in cellulose dissolution. In this thesis, to gain deeper insight on QAHs(aq) as derivatisation and dissolution media for cellulose, cellulose etherification in benzyltrimethylammonium hydroxide (Triton B) and tetramethylammonium hydroxide (TMAH), along with NaOH(aq) as well as different mixtures of these bases was investigated. In this study the emphasis was set on in-situ monitoring of the etherification reaction combined with the spectroscopic analysis of the products. The results highlighted the impact of hydroxide base composition on cellulose etherification where QAHs either alone or in combination enhanced the reagent solubility and cellulose solution stability during the reaction compared to NaOH which resulted in a lower solution stability promoting likely side reactions of the introduced substituents. Considering the importance of the dissolution system on functionalisation, a new solvent for cellulose was developed in the next study inspired by the well-known industrially used solvent N-methylmorpholine N-oxide (NMMO). In this study, N,N--dimethyl morpholinium and hydroxide ions were coupled to synthesize N,N-dimethylomorpholinium hydroxide(aq), and the dissolution properties of cellulose in the new solvent were investigated showing mostly molecularly dissolved cellulose chains with good chemical stability upon refrigeration

Aqueous N,N-dimethylmorpholinium hydroxide as a novel solvent for cellulose

N,N-dimethylmorpholinium hydroxide was synthesized and its ability to dissolve microcrystalline cellulose and pulp was assessed for the first time. Microscopy and UV–Vis measurements showed that dissolution occurred over a range of 1–2\ua0M concentration of the solvent and a maximum solubility of 7\ua0wt% microcrystalline cellulose could be achieved. The stability of cellulose solutions was evaluated by size exclusion chromatography, which did not detect degradation to any noticeable extent. This observation was further confirmed by\ua013C NMR measurements. Finally, DLS studies confirmed that most of the cellulose was molecularly dissolved, with intrinsic viscosity values indicating cellulose chains expansion in this solvent

Investigation of cellulose dissolution in morpholinium-based solvents: impact of solvent structural features on cellulose dissolution

A series of\ua0N-methylmorpholinium salts with varying\ua0N-alkyl chains and Cl−, OAc−\ua0and OH−\ua0as counter ions have been synthesized and investigated for their ability to dissolve cellulose, aiming at elucidating solvent structural features affecting cellulose dissolution. Synthesis procedures have been developed to, to a high extent, rely on conversions in water and microwave-assisted reactions employing a reduced number of work-up steps and ion-exchange resins that can be regenerated. Water solutions of morpholinium hydroxides proved capable of dissolving cellulose, with those of them possessing alkyl chains longer than ethyl showing surprising dissolution ability at room-temperature. Morpholinium acetates behaved as ionic liquids, and were also capable of dissolving cellulose when combined with DMSO. The obtained cellulose solutions were characterized according to their chemical and colloidal stability using\ua013C NMR spectroscopy, size exclusion chromatography and flow sweep measurements, while the ethanol coagulates were investigated in terms of crystallinity using solid state NMR. In contrast, the morpholinium chlorides obtained were hygroscopic with high melting points and low solubility in common organic solvents\ua0e.g., acetone, DMSO and DMAc, thus lacking the ability to swell or dissolve cellulose

In situ monitoring of cellulose etherification in solution: probing the impact of solvent composition on the synthesis of 3-allyloxy-2-hydroxypropyl-cellulose in aqueous hydroxide systems

Etherification of cellulose using allyl glycidyl ether was carried out in aqueous alkaline solutions of benzyltrimethylammonium hydroxide, tetramethylammonium hydroxide, NaOH and different mixtures of these bases in order to study the effect of hydroxide base composition on the course of the reaction and the resulting product properties. In situ FTIR spectroscopy and time sweep shear measurements were carried out to monitor the reactions in real time. Infrared Attenuated Total Reflectance Spectroscopy and H-1 NMR confirmed the synthesis of 3-allyloxy-2-hydroxypropyl-cellulose and 2D HSQC NMR confirmed substitution on C2, C3 and C6 in all of the solvents. Quantitative C-13 NMR was used to estimate the molar substitution. Cellulose solutions in these quaternary ammonium hydroxides showed higher stability at 50 degrees C during the course of reaction, faster dissolution and hydrolysis of allyl glycidyl ether and lower molar substitution values compared to NaOH. Even though the highest molar substitution value was obtained in NaOH, the isolated product from this medium had lower solubility in DMSO-d(6) and its C-13 NMR did not differ significantly except for higher intensity of C1 and C6 compared to the other spectra. The obtained results indicated a more pronounced cascade reaction on the substitution itself in NaOH and lower temperature stability of cellulose solutions in this solvent

In-Line Monitoring of Carbon Dioxide Capture with Sodium Hydroxide in a Customized 3D-Printed Reactor without Forced Mixing

Many industrial processes make use of sodium because sodium is the fifth most abundant metal and the seventh most abundant element on Earth. Consequently, there are many sodium-containing industrial wastes that could potentially be used for carbon capture, paving the way towards a circular and biobased economy. For example, a common industrial chemical is NaOH, which is found in black liquor, a by-product of the paper and pulp industry. Nonetheless, the literature available on CO2\ua0absorption capacity of aqueous NaOH is scarce for making a fair comparison with sodium-containing waste. Therefore, to fill this gap and set the foundation for future research on carbon capture, the CO2\ua0absorption capacity of NaOH solutions in a concentration range of 1–8\ua0w/w% was evaluated, a wider range compared with currently available data. The data set presented here enables evaluating the performance of sodium-based wastes, which are complex mixtures and might contain other compounds that enhance or worsen their carbon capture capacity. We designed a customized reactor using a 3D-printer to facilitate in-line measurements and proper mixing between phases without the energy of stirring. The mixing performance was confirmed by computational fluid dynamics simulations. The CO2\ua0absorption capacity was measured via weight analysis and the progress of carbonation using a pH meter and an FTIR probe in-line. At 5\ua0w/w% NaOH and higher, the reaction resulted in precipitation. The solids were analyzed with X-ray diffraction and scanning electron microscope, and nahcolite and natrite were identified. With our setup, we achieved absorption capacities in the range of 9.5 to 78.9 g CO2/L for 1\ua0w/w% and 8\ua0w/w% of NaOH, respectively. The results are in fair agreement with previously reported literature, suggesting that non-forced mixing reactors function for carbon capture without the need of stirring equipment and a possible lower energy consumption

Facile epoxidation of α, β-unsaturated ketones with urea-2, 2- dihydroperoxypropane as a new oxidant

Various aromatic\ua0α, β-unsaturated ketones were successfully transformed into their corresponding epoxides using urea-2,2-dihydroperoxypropane as the oxygen source for the first time. The reactions were carried out under mild alkaline conditions at room temperature in high yields and short reaction times

Urea-2,2-dihydroperoxypropane as a novel and high oxygen content alternative to dihydroperoxypropane in several oxidation reactions

Urea-2,2-dihydroperoxypropane (UDHPP)- a white crystalline solid oxidant which is formed when urea is recrystallized from dihydroperoxypropane- was applied as the terminal oxidant in several oxidative procedures namely epoxidation of α, βunsaturated ketones and alkenes, oxidation of sulfides to sulfoxides and sulfones, bayer-villeger reaction, bromination and iodation of aniline and phenol derivatives, oxidative esterification, oxidative amidation of aromatic aldehydes, thiocyanation of aromatic compounds, and oxidation of pyridines, oxidation of secondary, allylic and benzylic alcohols. All the approaches were carried out under mild conditions and short reaction times and afforded the corresponding products in high yields

1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane: An efficient and high oxygen content oxidant in various oxidative reactions

Several oxidative approaches namely thiocyanation of\ua0aromatic compounds,\ua0epoxidation\ua0of\ua0alkenes,\ua0amidation\ua0of aromatic\ua0aldehydes, epoxidation of α, β-unsaturated\ua0ketones, oxidation of\ua0sulfides\ua0to\ua0sulfoxides\ua0and\ua0sulfones, bayer-villeger\ua0reaction, bromination\ua0and\ua0iodation\ua0of\ua0aniline\ua0and\ua0phenol\ua0derivatives oxidative\ua0esterification, oxidation of\ua0pyridines\ua0and oxidation of secondary, allylic and benzyllic\ua0alcohols\ua0were carried out using 1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane as the potential solid\ua0oxidant\ua0which can be stored for several months without any loss in its activity. All of the procedures were accomplished via mild reaction conditions and the products were afforded in high yields and short reaction times

Alkanedisulfamic acid functionalized silica-coated magnetic nanoparticles as a reusable efficient nanocatalyst for synthesis of gem-dihydroperoxides and 1,2,4,5-tetraoxanes”, Iranian Journal of Catalysis

Alkanedisulfamic acid functionalized silica-coated magnetic nanoparticles (ADSA-MNPs) were used as effective, low-cost and reusable solid heterogeneous nanomagnetic catalysts for conversion of aldehydes and ketones to correspondinggem dihydroperoxides and 1, 2, 4, 5-tetraoxanes using aqueous hydrogen peroxide (30% w/w in H2O) at room temperature. These compounds are important key intermediates in preparation of anti-malaria drugs. The reactions proceeded in high rates and excellent yields. Since the catalyst was separated facilely from the reaction mixture by an external magnet and was reused six times without considerable loss of catalytic activity, this methodology is environmentally friendly. It is notable that it is the first report on using a nanocatalyst in the synthesis ofgem -dihydroperoxides and 1, 2, 4, 5-tetraoxanes from aldehydes and ketones up to now