N-methylmorpholine-N-oxide Research Articles

A mild CuBr–NMO oxidative system for the coupling of anilines leading to aromatic azo compounds

An efficient methodology was developed for the synthesis of aromatic azo derivatives under mild reaction conditions utilizing CuBr with N-methylmorpholine N-oxide as an oxidant.

Preparation of water-dispersible graphene using N-methylmorpholine N-oxide monohydrate and its application for the preparation of nanocomposites using PEDOT

SEM and TEM images (inset: selective area electron diffraction (SAED) pattern) of mono-layered water dispersible graphene (GPN) sheet by treatment ofN-methylmorpholineN-oxide monohydrate (NMMOm).

Binuclear ruthenium(III) bis(thiosemicarbazone) complexes: Synthesis, spectral, electrochemical studies and catalytic oxidation of alcohol

A new series of binuclear ruthenium(III) thiosemicarbazone complexes of general formula [(EPh3)2(X)2Ru-L-Ru(X)2(EPh3)2] (where E=P or As; X=Cl or Br; L=NS chelating bis(thiosemicarbazone ligands) has been synthesized and characterized by analytical and spectral (FT-IR, UV–Vis and EPR). IR spectra show that the thiosemicarbazones behave as monoanionic bidentate ligands coordinating through the azomethine nitrogen and thiolate sulphur. The electronic spectra of the complexes indicate that the presence of d–d and intense LMCT transitions in the visible region. The complexes are paramagnetic (low spin d5) in nature and all the complexes show rhombic distortion around the ruthenium ion with three different ‘g’ values (gx≠gy≠gz) at 77K. All the complexes are redox active and exhibit an irreversible metal centered redox processes (RuIII–RuIII/RuIV–RuIV; RuIII–RuIII/RuII–RuII) within the potential range of 0.38–0.86V and −0.39 to −0.66 V respectively, versus Ag/AgCl. Further, the catalytic efficiency of one of the complexes [Ru2Cl2(AsPh3)4(L1)] (4) has been investigated in the case of oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of N-methylmorpholine-N-oxide(NMO) as co-oxidant. The formation of high valent RuVO species is proposed as catalytic intermediate for the catalytic cycle.

Removable bidentate directing group assisted-recyclable metal–organic frameworks-catalyzed direct oxidative amination of Sp2 C–H bonds

Several Cu-MOFs were showed to be efficient heterogeneous catalysts for ortho-amination of benzoic acid derivative C–H bonds by N–H amines using 8-aminoquinoline as bidentate directing group. The optimal reaction conditions involve the use of Cu-MOFs (25%), N-methylmorpholine oxide (NMO) as an oxidant, secondary or primary amine coupling partner, DMF, DMA, or NMP solvent at 90–100°C. Furthermore, the Cu-MOFs catalyst could be facilely isolated from the reaction mixture and reused several times without remarkable degradation in catalytic reactivity. Contribution from homogeneous leached active copper species, if any, is negligible. To the best of our knowledge, C–H activation reactions using bidentate directing groups, which are increasingly gaining importance, under heterogeneous catalytic systems were not previously mentioned in the literature.

Dry jet-wet spinning of strong cellulose filaments from ionic liquid solution

Considerable growth is expected in the production of man-made cellulose textile fibers, which are commercially produced either via derivatization to form cellulose xanthate (viscose) or via direct dissolution in N-methylmorpholine N-oxide (Lyocell). In the study at hand, cellulosic fibers are spun from a solution in the ionic liquid [DBNH] [OAc] into water, resulting in properties equal or better than Lyocell (tensile strength 37 cN tex−1 or 550 MPa). Spinning stability is explored, and the effects of extrusion velocity, draw ratio, spinneret aspect ratio and bath temperature on mechanical properties and orientation are discussed. With the given set-up, tenacities and moduli are improved with higher draw ratios, while elongation at break, the ratio of wet to dry strength, modulus of resilience and birefringence depend little on draw ratio or extrusion velocity, elastic limit not at all. We find the process robust and simple, with stretching to a draw ratio of 5 effecting most improvement, explained by the orientation of amorphous domains along the fiber axis.

Chiral MnIII(Salen) supported on tunable phenoxyl group modified zirconium poly (styrene-phenylvinylphosphonate)-phosphate as an efficient catalyst for epoxidation of unfunctionalized olefins

We have developed a series of chiral MnIII(Salen) (chiral Jacobsen's catalyst) catalysts that were axially supported onto zirconium poly(styrene-phenylvinylphosphonate)-phosphate through tunable phenoxyl linkers of varying steric hindrance, and evaluated their performance as catalysts (Cat1–Cat3) for the epoxidation of unfunctionalized olefins using m-chloroperbenzoic acid as an oxidant. The corresponding non-supported analogues (Cat4–Cat6) were also prepared and tested under similar conditions. The results demonstrated that the incorporation of substituents at the ortho-positions of the tunable phenoxyl linkers had a critical effect on the catalytic activity. Furthermore, the enantioselectivity increased as the steric hindrance imposed by the linker increased, although this also led to a decrease in the conversions under the same reaction conditions, especially for heterogeneous epoxidation. The heterogeneous system also displayed high ee values and conversions in the absence of the axial additive N-methylmorpholine N-oxide, which is commonly required to improve the catalytic activity of epoxidation reactions, especially for the epoxidation of α-methylstyrene. The reusability of the catalyst was also evaluated over 11 catalytic cycles, with no significant reduction observed in the catalytic activity or enantioselectivity after five runs.

Manufacture and performance of O-carboxymethyl chitosan sodium salt/cellulose fibers in N-methylmorpholine-N-oxide system

A series of O-carboxymethyl chitosan sodium salt (NaCMCh) with different degree of substitution (DS) of -CH2COONa agent were successfully prepared by altering the reaction temperature and time. Both fourier transform infrared spectroscopy (FTIR) and 13C-Nuclear Magnetic Resonance (13C-NMR) were used to study the structure of NaCMCh. And the impact of DS on the antibacterial activity of NaCMCh was investigated. Then, the NaCMCh with optimal antibacterial activity was selected to prepare NaCMCh/cellulose fibers in N-methylmorpholine-N-oxide (NMMO) system. The structure, crystallization behavior, thermal property and morphology of obtained fibers were carefully studied with FTIR, Wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermal gravimetric (TG) and scanning electron microscope (SEM), respectively. Meanwhile, the antibacterial activity as well as mechanical properties of resultant fibers was also investigated. The results demonstrated that the fibers had strong antibacterial activity against Escherichia coli (E. coli), acceptable mechanical properties and good water retention.

Effect of granule organisation on the behaviour of starches in the NMMO (N-methyl morpholine N-oxide) solvent system.

The response of starches of different botanical origin to heating in 78% N-methyl morpholine N-oxide (NMMO) is compared with their behaviour in water. For all starches studied an exothermic transition is obtained in the NMMO system rather than the endothermic transition in water. In NMMO the transition temperatures are lower for A-type starches (wheat, rice and tapioca) than the C-type starches (sago and pea) and also potato which has a B-type polymorph. Observations using a hot stage microscope show two different types of initial behaviour in NMMO; erosion of the granule from the surface or disruption into fragments. In both cases the final outcome is dissolution but for the most resistant C-type starches (pea and sago) some intact granules could be seen following heating at 95 °C in 78% NMMO and subsequent precipitation in ethanol. The results are discussed in terms of what is known from previous structural studies on these six starches and the behaviour of maize starch in NMMO and ionic liquids. The work is relevant to the co-dissolution of starch and cellulose to form novel polysaccharide based materials.

Alcohol oxidation reactions catalyzed by ruthenium–carbonyl complexes of thioarylazoimidazoles

Alcohols are oxidized by N‐methylmorpholine‐N‐oxide (NMO), ButOOH and H2O2 to the corresponding aldehydes or ketones in the presence of catalyst, [RuH(CO)(PPh3)2(SRaaiNR′)]PF6 (2) and [RuCl(CO)(PPh3)(SκRaaiNR′)]PF6 (3) (SRaaiNR′ (1) = 1‐alkyl‐2‐{(o‐thioalkyl)phenylazo}imidazole, a bidentate N(imidazolyl) (N), N(azo) (N′) chelator and SκRaaiNR′ is a tridentate N(imidazolyl) (N), N(azo) (N′), Sκ‐R is tridentate chelator; R and R′ are Me and Et). The single‐crystal X‐ray structures of [RuH(CO)(PPh3)2(SMeaaiNMe)]PF6 (2a) (SMeaaiNMe = 1‐methyl‐2‐{(o‐thioethyl)phenylazo}imidazole) and [RuH(CO)(PPh3)2(SEtaaiNEt)]PF6 (2b) (SEtaaiNEt = 1‐ethyl‐2‐{(o‐thioethyl)phenylazo}imidazole) show bidentate N,N′ chelation, while in [RuCl(CO)(PPh3)(SκEtaaiNEt)]PF6 (3b) the ligand SκEtaaiNEt serves as tridentate N,N′,S chelator. The cyclic voltammogram shows RuIII/RuII (~1.1 V) and RuIV/RuIII (~1.7 V) couples of the complexes 2 while RuIII/RuII (1.26 V) couple is observed only in 3 along with azo reductions in the potential window +2.0 to −2.0 V. DFT computation has been used to explain the spectra and redox properties of the complexes. In the oxidation reaction NMO acts as best oxidant and [RuCl(CO)(PPh3)(SκRaaiNR′)](PF6) (3) is the best catalyst. The formation of high‐valent RuIV=O species as a catalytic intermediate is proposed for the oxidation process. Copyright © 2014 John Wiley & Sons, Ltd.

Ruthenium tetroxide and perruthenate chemistry. Recent advances and related transformations mediated by other transition metal oxo-species.

In the last years ruthenium tetroxide is increasingly being used in organic synthesis. Thanks to the fine tuning of the reaction conditions, including pH control of the medium and the use of a wider range of co-oxidants, this species has proven to be a reagent able to catalyse useful synthetic transformations which are either a valuable alternative to established methods or even, in some cases, the method of choice. Protocols for oxidation of hydrocarbons, oxidative cleavage of C–C double bonds, even stopping the process at the aldehyde stage, oxidative cleavage of terminal and internal alkynes, oxidation of alcohols to carboxylic acids, dihydroxylation of alkenes, oxidative degradation of phenyl and other heteroaromatic nuclei, oxidative cyclization of dienes, have now reached a good level of improvement and are more and more included into complex synthetic sequences. The perruthenate ion is a ruthenium (VII) oxo-species. Since its introduction in the mid-eighties, tetrapropylammonium perruthenate (TPAP) has reached a great popularity among organic chemists and it is mostly employed in catalytic amounts in conjunction with N-methylmorpholine N-oxide (NMO) for the mild oxidation of primary and secondary alcohols to carbonyl compounds. Its use in the oxidation of other functionalities is known and recently, its utility in new synthetic transformations has been demonstrated. New processes, synthetic applications, theoretical studies and unusual transformations, published in the last eight years (2006–2013), in the chemistry of these two oxo-species, will be covered in this review with the aim of offering a clear picture of their reactivity. When appropriate, related oxidative transformations mediated by other metal oxo-species will be presented to highlight similarities and differences. An historical overview of some aspects of the ruthenium tetroxide chemistry will be presented as well.

Synthesis of Open-Cage Ketolactam Derivatives of Fullerene C60 Encapsulating a Hydrogen Molecule

A novel open-cage fullerene C60 derivative having a bis(hemiketal) moiety was synthesized by the reaction of C60-N-MEM-ketolactam (MEM: 2-methoxyethoxymethyl) with N-methylmorpholine N-oxide in the presence of water. The structure was clearly determined by single crystal X-ray analysis. Further enlargement of the opening was performed by treatment with trifluoroacetic anhydride to give the tetraketo derivative having a 15-membered ring opening. For H2-insertion into the cage, the derivative was exposed to a high pressure of H2. After the encapsulation, the opening size was reduced to the original one while keeping the hydrogen molecule inside the cage. This compound can be a possible precursor for endohedral azafullerenes encapsulating a hydrogen molecule.

Catalyst Activation with Cp*RhIII/IrIII–1,2,3-Triazole-Based Organochalcogen Ligand Complexes: Transfer Hydrogenation via Loss of Cp* andN-MethylmorpholineN-Oxide Based vs Oppenauer-Type Oxidation

The reactions of 1-benzyl-4-((phenylthio/phenylseleno)methyl)-1H-1,2,3-triazole (L1/L2) and 4-phenyl-1-((phenylthio/phenylseleno)methyl)-1H-1,2,3-triazole (L3/L4), synthesized using the click reaction, with [(η5-Cp*)RhCl(μ-Cl)]2 and [(η5-Cp*)IrCl(μ-Cl)]2 at room temperature followed by treatment with NH4PF6 result in complexes of the type [[(η5-Cp*)M(L)Cl] (1–8). Their HR-MS and 1H, 13C{1H}, and 77Se{1H} NMR spectra have been found characteristic. The single-crystal structures of 2, 3, and 6 have been established by X-ray crystallography. There is a pseudo-octahedral “piano-stool” disposition of donor atoms around Rh/Ir. In 1, 2, 5, and 6 N(3) of the triazole skeleton coordinates with Rh/Ir, whereas in the other four complexes the nitrogen involved is N(2). These complexes have been explored as catalysts for N-methylmorpholine N-oxide (NMO) based and Oppenauer-type oxidation of alcohols and transfer hydrogenation (TH) of carbonyl compounds with 2-propanol. Oppenauer type oxidation is somewhat slower than that based on NMO. The homogeneous nature of TH is supported by a poisoning test. The catalytic processes are more efficient with Rh complexes than the corresponding Ir complexes. The complexes having N(2) coordinated with the metal have shown better activity than those in which N(3) is involved in ligation. The reactivity with respect to ligands is in the order Se > S. In TH the species formed with loss of Cp* appears to be involved in catalysis with Rh as well as Ir complexes. Such a loss is noticed in the case of Rh for the first time. Generally results of DFT calculations are consistent with the experimental results.

Synthesis, spectral and catalytic dehydrogenation studies of ruthenium complexes containing NO bidentate ligands

The synthesis and characterization of ruthenium mononuclear complexes containing NO bidentate ligands are reported. The complexes cis-[RuII(bpy)2L](PF6)n (1a–c), [RuIIICl(L)2(H2O)] (2a–b) and [RuIIICl2(L)2]Cl (2c) were prepared by the reaction of cis-[RuIICl2(bpy)2]·2H2O (bpy=2,2′-bipyridine) and/or RuCl3·nH2O with the Ligands: 2-aminophenol (2-aph), 8-hydroxyquinoline (8-hq) and 4-aminoantipyrine (4-apy). These complexes were characterized by elemental analysis, spectroscopic (IR, UV–Vis, 1H NMR, ESR) and magnetic susceptibility measurements. The ligand field parameters, Δo (splitting parameter), B (Racah parameter of interelectronic repulsion), and β (nephelauxetic ratio) were calculated. The redox properties were also investigated electrochemically by cyclic voltammetry. The complexes cis-[RuII(bpy)2(8-hq)](PF6)2 (1b) and [RuIIICl(8-hq)2(H2O)] (2b) have been investigated in conjunction with N-methylmorpholine-N-oxide (NMO) as co-oxidant for the catalytic dehydrogenation of benzyl amine, p-methyl benzylamine and p-nitrobenzylamine to their respective nitriles.

Preparation of carboxymethyl cellulose superabsorbents from waste textiles

Production of superabsorbent polymers from cotton and viscose waste textiles was investigated. The cellulose wastes were carboxymethylated, crosslinked by divinylsulfone, and then converted to superabsorbent material using air-drying, freeze-drying, or air-drying after phase inversion. The separation of cellulose from synthetic polymers in the textile (polyester) was carried out by direct dissolution of cellulose in N-methylmorpholine-N-oxide (NMMO), or separation by dissolution in water after carboxymethylation of the textiles. The progress of the carboxymethylation reaction was evaluated by measurement of the degree of substitution (DS) of carboxymethyl cellulose (CMC). The DS values of 0.50–0.86 confirmed the prosperous substitution of hydrophilic carboxymethyl groups into the cellulosic chains. The water binding capacity and the swelling rate of the superabsorbents prepared under different conditions were measured. Under the best condition the superabsorbent obtained from waste textiles showed an ultimate water binding capacity of 541 g/g which was notably higher than that of the reference superabsorbent derived from cotton linter (470 g/g). The amount of absorbed water by this product exceeded that of the reference sample after 60 min immersion.

Synthesis, electronic structure and catalytic activity of ruthenium-iodo-carbonyl complexes with thioether containing NNS donor ligand

The ruthenium carbonyl complexes 1 and 2 with redox noninnocent NNS donor ligand, 1-methyl-2-{(o-thiomethyl)phenylazo}imidazole (L) have been synthesized and characterized by various analytical and spectroscopic (IR, UV–Vis and 1H NMR) techniques. The complexes exhibit a quasi-reversible one electron Ru(II)/Ru(III) oxidation couple at 1.11V for 1 and 0.76V for 2 along with two successive one electron ligand reductions. Catalytic activity of the compounds has been investigated to the oxidation of PhCH2OH to PhCHO, 2-butanol (C4H9OH) to 2-butanone, 1-phenylethanol (PhC2H4OH) to acetophenone, cyclopentanol (C5H9OH) to cyclopentanone, cyclohexanol to cyclohexanone, cycloheptanol to cycloheptanone and cycloctanol to cycloctanone using N-methylmorpholine-N-oxide (NMO) as oxidant. The catalytic efficiency of 2 is greater than complex 1 and well correlate with the metal oxidation potential. DFT, NBO and TDDFT calculations in DFT/B3LYP/6-31G(d)/lanL2TZ(f) method are employed to interpret the structural and electronic features of the complexes.

Biogas Production from N-Methylmorpholine-N-oxide (NMMO) Pretreated Forest Residues

Lignocellulosic biomass represents a great potential for biogas production. However, a suitable pretreatment is needed to improve their digestibility. This study investigates the effects of an organic solvent, N-Methylmorpholine-N-oxide (NMMO) at temperatures of 120 and 90 °C, NMMO concentrations of 75 and 85% and treatment times of 3 and 15 h on the methane yield. The long-term effects of the treatment were determined by a semicontinuous experiment. The best results were obtained using 75% NMMO at 120 °C for 15 h, resulting in 141% increase in the methane production. These conditions led to a decrease by 9% and an increase by 8% in the lignin and in the carbohydrate content, respectively. During the continuous digestion experiments, a specific biogas production rate of 92 NmL/gVS/day was achieved while the corresponding rate from the untreated sample was 53 NmL/gVS/day. The operation conditions were set at 4.4 gVS/L/day organic loading rate (OLR) and hydraulic retention time (HRT) of 20 days in both cases. NMMO pretreatment has substantially improved the digestibility of forest residues. The present study shows the possibilities of this pretreatment method; however, an economic and technical assessment of its industrial use needs to be performed in the future.

Enhanced ethanol and biogas production from pinewood by NMMO pretreatment and detailed biomass analysis.

N-Methyl morpholine-N-oxide (NMMO) is an environmentally friendly and commercially applied cellulose solvent that is suggested for pretreatment of lignocelluloses to improve biofuel productions. However, the underlying mechanisms of the improvements have been poorly understood yet. In an attempt to investigate the mechanisms, pinewood powder and chips were pretreated with 85% (w/w) NMMO at 120°C for 1–15 h. The pretreatment improved ethanol production yield from 7.2% (g/g) for the untreated wood powder to 68.1–86.1% (g/g) and from 1.7% (g/g) for the untreated wood chips to 12.6–51.2% (g/g) of theoretical yield. Similarly, the biogas yields of untreated wood chips and powder were improved from 21 and 66 (mL/g volatile solids) by 3.5–6.8- and 2.6–3.4-folds, respectively. SEM micrographs indicated major increase in the wood porosity by the pretreatment, which would confirm increase in the water swelling capacity as well as enzyme adsorption. The analysis of X-ray diffraction showed considerable reduction in the cellulose crystallinity by the pretreatment, while FTIR spectroscopy results indicated reduction of lignin on the wood surface by the pretreatment.

Stereoselective Synthesis of Polyhydroxylated Amines Using (<i>S</i>)-Pyroglutamic Acid Derivatives

Naturally occurring polyhydroxylated amines such as (+)-1-deoxynojirimycin, polyoxamic acid, anisomycin, (-)swainsonine, and alexine stereoisomers, which have interesting biological activities including glucosidase- and mannosidase-inhibitory activity, immunoregulatory activity, and antibacterial effects, were synthesized stereoselectively starting from (S)-pyroglutamic acid derivatives. α,β-Unsaturated lactams ((S)-5-hydroxymethyl-2-oxo-3-pyrroline derivatives), α,β-unsaturated δ-lactone ((S)-4-amino-2-penten-5-olide derivative), and E-olefin ((S,E)-methyl-4-amino-5-hydroxypent-2-enoate derivative) from (S)-pyroglutamic acid derivatives were dihydroxylated using OsO4 in the presence of N-methyl morpholine N-oxide (NMO) to afford various chiral building blocks with different configurations. The stereoselectivity of cis-dihydroxylation for α,β-unsaturated lactams and α,β-unsaturated δ-lactone was very high, while the stereoselectivity was low for E-olefin. Therefore, the double asymmetric induction of E-olefin using K2OsO4 with chiral ligands was successively applied to yield high stereoselectivity. (2R,3S)-2-Hydroxymethyl-3-hydroxypyrrolidine and Gaissman-Weiss lactone, important intermediates for the preparation of pyrrolizidine alkaloids, were synthesized from a (3R,4R,5R)-3,4-dihydroxy-5-hydroxymethyl-2-pyrrolidinone derivative derived from α,β-unsatulated lactam. (+)-1-Deoxynojirimycin was synthesized from a (2S,3R,4R)-methyl 4-amino-2,3,5-trihydroxypentanoate derivative of E-olefin. (-)-Swainsonine and its stereoisomers were synthesized from (2R,3S,4R)- or (2R,3R,4R)-2-hydroxymethyl-3,4-dihydroxypyrrolidine derivatives of α,β-unsaturated δ-lactone or α,β-unsaturated lactam. The key reaction was diastereoselective allylation of the aldehyde derived from the corresponding 2-hydroxymethylpyrrolidine derivatives with various allylation reagents. The high diastereoselectivity could be explained by cyclic chelate formation between metals and the α-aminocarbonyl group or β-alkoxycarbonyl group, in which the nucleophile approaches from the less hindered face. Four alexine stereoisomers were synthesized from (2R,3R,4S,5R)- and (2R,3R,4S,5S)-2,3-dihydroxymethyl-3,4-dihydroxyl pyrrolidine derivatives of α,β-unsaturated lactam.

In situ precipitation of amorphous and crystalline calcium sulphates in cellulose thin films

Cellulose films regenerated with calcium sulphate are fabricated using N-methylmorpholine N-oxide as a solvent and capping agent for polysaccharide dissolution and nanoparticle stabilization, respectively.

Nonstabilised Azomethine Ylids from N-Oxides: Unravelling the Deprotonation of N-Methylmorpholine N-Oxide

Nonstabilised azomethine ylids (NAYs) are useful 1,3-dipoles, but their synthetic applications are restricted by the high temperatures often needed for their generation, and by an incomplete understanding of the effect of heteroatoms in cyclic systems. We have examined the behaviour of N-methylmorpholine N-oxide (NMO) as a NAY precursor in the Roussi reaction (low-temperature reaction of an N-oxide with strong base). The choice of base is critical to achieving cycloadduct formation. We report synthetic and computational (density functional theory) investigations of the products obtained with different bases and their mechanisms of formation.