Diazabicyclo[5.4.0]undec-7-ene Research Articles

A Greener Way of Making Cellulose Clothing

Cotton is the world's most demanding non-food crop. Cotton grows in arid countries such as India and China. However, its production consumes an enormous 250 billion tons of water annually, amplifying water scarcity. Cellulose, found in plants like wood, bamboo, and mosses, offers a sustainable alternative for textiles. Traditionally, cellulose is processed into textiles using the viscose method, which involves carbon disulfide. This process releases hydrogen sulfide, harmful to aquatic life and human health, and carbon disulfide, a hazardous pollutant affecting the reproductive system and vision. Many research groups have proposed an alternative method, which involves dissolving cellulose in dimethyl sulfoxide (DMSO) and Diazabicyclo[5.4.0]undec-7-ene (DBU) under 1 atm of CO2. DBU, with a pKaH ~ 12, deprotonates cellulose’s hydroxyl groups forming a DMSO-soluble cellulose carbonate complex that can be spun into filaments. However, DBU is costly, hazardous, and prone to hydrolysis, leading to byproducts. The objective of the research was to find a more environmentally friendly, less toxic, and cost-effective base for cellulose dissolution. Two tertiary amines, triethylamine (pKaH~9) and tripropylamine (pKaH~10.7), were tested. Due to its low basicity triethylamine failed to dissolve cellulose even under high CO2 pressure (up to 50 bar), resulting in a cloudy solution. Tripropylamine is insoluble in DMSO, therefore resulting in a phase separation of a tripropylamine layer and cellulose/DMSO layer. Additionally, 2,2,6,6-tetramethyl-piperidine was also tested at high CO2 pressure (up to 50 bar), but a biphasic solution was formed at 10 bar . This indicates that the protonated form of the base does not dissolve in DMSO. Ultimately, no alternative base was found to be sufficiently basic to deprotonate the hydroxyl groups on cellulose and promote dissolution, even at high pressure.

Preparation of porous PCL-PEG-PCL scaffolds using supercritical carbon dioxide

In this study, the Supercritical Carbon Dioxide (scCO2) gas foaming procedure was used in the preparation of scaffolds containing the model drug dexamethasone (DXMT). The method used did not include an organic solvent thus making it a safe method. The ring-opening polymerization of PCL-PEG-PCL (PCEC) triblock was conducted using an organocatalyst [1,8 diazabicyclo [5.4.0] undec-7-ene (DBU)]. After mixing 5.0 g of DXMT with 50.0 g of PCEC, hydraulic pressure was applied to compress the mixed powder into disc-like tablets. The tablet-like scaffold of the triblock containing DXMT was inserted into a scCO2 gas-foaming device. The peak porosity percentage of the synthesized triblock was found to be 55.58 %. Pressure, temperature, soaking time and the time required to depressurize were recorded as 198 bar, 50 °C, 2.0 h, and 28 min respectively. After treatment with scCO2, the scaffolds experienced an almost full release of DXMT in vitro after 30 days (83.74 ± 1.54 % vs 52.24 ± 2.03 % before scCO2 treatment). In conclusion, the results proved that the scCO2 gas foaming procedure could be employed for constructing modifiable PCEC scaffolds with plausible porosity and structural and morphological features which can manipulate drug release.

A comparative study of ionothermal treatment of rice straw using triflate and acetate-based ionic liquids

Ionic liquids (ILs) have found applications in the pretreatment of waste lignocellulosic biomass by interacting with the carbohydrate molecules present in the biomass materials. Pretreatment is essential before biomass conversion into valuable chemicals, fuels, and many other value-added products. This comparative study mainly focused on the pretreatment ability of four ILs having acetate or triflate as a common anion with different cations. Among various studied ILs, diazabicyclo[5.4.0]undec-7-ene (DBU)-based acidic ionic liquid when used as a dual solvocatalyst showed significant structural modifications of the rice straw (RS) sample, through C6-O bond breakage assisted by the tertiary nitrogen in DBU cation. Structural modifications due to the pretreatment were confirmed through SEM, PXRD, and FTIR analysis. The elemental analysis confirmed that carbon content in original RS is reduced to 29% and 20% upon ionothermal treatment of RS with IL at 90 °C and 120 °C, respectively. Additionally, TGA indicated that further pyrolysis could be easier with the pretreated rice straw yielding biochar up to 9% thereby reducing wastes. Conversion of RS was found to be 60% which reduced marginally to 50% after three cycles of recycling the IL. The findings of this work provide the proof of concept that studied IL with high thermal stability and recyclability should act as a potential solvocatalyst in sustainable pretreatment and other biomass applications.

Comparison of photocatalytic performances of solar-driven hybrid catalysts for hydrogen energy evolution from 1,8–Diazabicyclo[5.4.0]undec-7-ene (DBU) solution

Hydrogen is evolved from 1,8–Diazabicyclo [5.4.0]undec-7-ene (DBU) model solution which is a nitrogen-containing heterocyclic organic compound using different solar-driven hybrid photocatalysts. A characterization study is performed and the results of PL analysis show that the most promising solar-driven hybrid catalyst is graphene supported LaFeO 3 . Then, an experimental design matrix is built using the Box Behnken model to main and interaction effects of reaction parameters (pH, catalyst loading, and [H 2 O 2 ] 0 ). Based on the experimental results relatively higher hydrogen amounts are achieved using GLFO and this finding is supported by PL analysis. The highest hydrogen amount and DBU removal are determined as 3058.31 μmol/g cat and 90.3%, respectively. Statistical analysis shows that the square of catalyst loading is the only effective parameter over the produced hydrogen amount from the DBU model solution using GLFO and the R 2 of model is 92.47%. Thus, hydrogen production and wastewater treatment could be achieved via photocatalytic oxidation as concomitant. • It is the first study over photocatalytic hydrogen evolution from DBU model solution. • The most promising solar-driven hybrid catalyst was GLFO. • The highest hydrogen evolution (3118.81 μmol/g cat ) was achieved using GBFO. • The highest DBU removal (90.3%) was achieved using GLFO.

Metal-free Lewis pair catalyst synergy for fully alternating copolymerization of norbornene anhydride and epoxides: Biocompatible tests for derived polymers

Synthesis of high molecular weight alternating copolymers from epoxides and norbornene anhydride via metal-free catalyst remains a challenge in aliphatic biodegradable polyester synthesis. Metal-free Lewis pair catalyst system, consisting of Lewis acid B(C2H5)3 (triethylborane) and a Lewis base DMAP (4-dimethylaminopyridine); TBD (1, 5, 7-triazabicyclo[4.4.0]dec-5-ene) and DBU (1,8 diazabicyclo[5.4.0]undec-7-ene) as a cooperative catalyst system for fully alternating polyesters synthesis is described here. By using these simple systems we have obtained, high molecular weight (Mn = 2–31.5 kDa) polyesters with narrow molecular weight distributions (MWD’s = 1.948–1.069) via ring-opening alternating copolymerisation (ROAC) of various epoxides (e.g. CHO, cyclohexene oxide; PO, propylene oxide; tBGE, tert-butyl glycidyl ether and PGE, phenyl glycidyl ether) with cis-5 norbornene-endo 2, 3 dicarboxylic anhydride (NB). Furthermore, we demonstrated that these polyesters are biocompatible in nature when tested on human embryonic kidney cells (HEK-293) showing more than 80% cell viability in 72 h and can be used for different biological applications such as drug delivery, tissue engineering or anti-microbial polymeric coatings on biomedical devices. The use of these green functional polyesters for biological studies was realized for the first time by a metal-free Lewis pair approach.

A novel one-pot strategy to prepare β-cyclodextrin functionalized capillary monoliths for enantioseparation of basic drugs

With native β-cyclodextrin (β-CD) added into the polymerization mixture directly, a novel, convenient and low-cost one-pot strategy was developed to prepare the β-CD functionalized organic polymer monolithic capillary column. Diazabicyclo[5.4.0]undec-7-ene (DBU) as a basic catalyst for the ring opening reaction between β-CD and glycidyl methacrylate (GMA) was introduced into the polymerization system for the first time. Thereby, two consecutive reactions namely the in situ methacrylation of β-CD and copolymerization reaction can be achieved in one pot. The preparation conditions including the type and composition of porogens，the ratio of functional monomer to crosslinker and amount of 2-acrylamido-2-methyl propane sulfonic acid (AMPS) were optimized. The specific surface area and morphology of the prepared monolith were characterized using scanning electron microscopy (SEM) and nitrogen adsorption analysis, respectively. Raman spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed that β-CD was covalently bonded onto the monolith successfully. Then, the monolithic column was applied to enantioseparation of six basic drugs in capillary electrochromatography (CEC). Under the optimal conditions, tropicamide, homatropine, homatropine methylbromide, brompheniramine, chlorpheniramine and clorprenaline were all totally separated with the resolution (Rs) values of 2.84, 4.70, 4.61, 3.01, 2.57 and 2.33, respectively. Furthermore, the column demonstrated satisfactory stability and repeatability of retention time and enantioselectivity using homatropine as model analyte.

New acid/base salts as co‐catalysts for the organocatalyzed ring opening polymerization of lactide

ABSTRACT(R)‐(+)‐binaphathyl‐diyl hydrogen phosphate (BNPH)/ diazabicyclo[5.4.0]undec‐7‐ene (DBU) and (1R)‐(−)−10‐camphorsulfonic acid (CSA)/4‐dimethylaminopyridine (DMAP) acid–base salts were synthesized and assessed for the ring‐opening polymerization of rac‐lactide. They were found to be inactive toward the polymerization in the presence of a protic initiator. When used in combination with a base such as DBU or DMAP and a protic initiator, these acid/base conjugates led to well‐controlled polymerization in mild conditions (DM < 1.1 in all cases). With DBU, the presence of the salt was found to lead to narrower molecular weight distributions than those obtained using the base alone, and to prevent undesirable transesterification reactions occurring at the end of the reaction. An increase in activity was observed using the salts in combination with DMAP as compared with DMAP alone, together with an improvement of the control over the molecular weight. The results were discussed on the basis of 1H nuclear magnetic resonance analyzes including acid/base equilibria involving the use of two different bases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 659–664

ChemInform Abstract: Poly(4‐vinylimidazolium)s/Diazabicyclo[5.4.0]undec‐7‐ene/Zinc(II) Bromide‐Catalyzed Cycloaddition of Carbon Dioxide to Epoxides.

Poly(4-vinylimidazolium)s, derived from the self-immobilization of 4-vinylimidazoliums, with diazabicyclo[5.4.0]undec-7-ene (DBU) and zinc bromide (ZnBr2) are used as a highly efficient catalyst for the chemical fixation of carbon dioxide. This catalytic system has been applied for the preparation of cyclic carbonates from terminal epoxides and carbon dioxide. Many functional groups, including chloro, vinyl, ether, and hydroxy groups are well tolerated in the reactions. Moreover, the catalytic system was found to catalyze the conversion of more sterically congested epoxides which are generally considered to be challenging substrates for fabricating the cyclic organic carbonates. In addition, the disubstituted epoxides are found to react with retention of configuration. The polymer precatalyst is easily recovered and reused. A plausible reaction mechanism is proposed.

Poly(4‐vinylimidazolium)s/Diazabicyclo[5.4.0]undec‐7‐ene/Zinc(II) Bromide‐Catalyzed Cycloaddition of Carbon Dioxide to Epoxides

AbstractPoly(4‐vinylimidazolium)s, derived from the self‐immobilization of 4‐vinylimidazoliums, with diazabicyclo[5.4.0]undec‐7‐ene (DBU) and zinc bromide (ZnBr2) are used as a highly efficient catalyst for the chemical fixation of carbon dioxide. This catalytic system has been applied for the preparation of cyclic carbonates from terminal epoxides and carbon dioxide. Many functional groups, including chloro, vinyl, ether, and hydroxy groups are well tolerated in the reactions. Moreover, the catalytic system was found to catalyze the conversion of more sterically congested epoxides which are generally considered to be challenging substrates for fabricating the cyclic organic carbonates. In addition, the disubstituted epoxides are found to react with retention of configuration. The polymer precatalyst is easily recovered and reused. A plausible reaction mechanism is proposed.magnified image

A DBU–diheteroaryl halide adduct as the fastest current N-diheteroarylating agent

An unexpected diazabicyclo[5.4.0]undec-7-ene (DBU) catalysed rate enhancement of N-arylation of amines with diheteroaryl halides is reported. DBU is found to activate the Ar–Cl bond of a diheteroaryl halide, forming a green coloured adduct under neat conditions. The activated green coloured adduct was used for the arylation of amines under neat conditions and was found to be the fastest diheteroarylating agent reported to date.

Convenient Synthesis of 1,4-Dihydroxy-2-(ω-Hydroxyalkoxy)Anthracene- 9,10-Diones and their Conjugation with D-Glucal

Purpurin, 1,2,4-trihydroxyanthraquinone, was regioselectively alkylated under basic conditions using bromoalcohol of varying chain length. As a base, potassium carbonate, tetrabutylammonium hydroxide or 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU) was used. The reaction of alkylation proceeded exclusively on the 2-hydroxyl group of the purpurin molecule. Addition of the obtained 2-(ω-hydroxyalkoxy)purpurins to protected D-glucal catalysed by triphenylphosphine hydrobromide gave an access to new glycoconjugates with high enantioselectivity. In parallel experiments, the same substrates reacted in the presence of boron trifluoride etherate yielding the appropriate unsaturated adducts as a result of Ferrier rearrangement. Keywords: Addition reaction, alkylation, bromoalcohols, D-glucal, glycoconjugates, purpurin, aluminium, iron, protease, cordifolia.

Direct fixation of [11C]-CO2by amines: formation of [11C-carbonyl]-methylcarbamates

[(11)C-Carbonyl]-methylcarbamates can be synthesised directly from [(11)C]-CO(2) and primary or secondary amines in a one-pot, two-step reaction. The use of either diazabicyclo[5.4.0]undec-7-ene (DBU) or 2-tert-butylimino-2-diethylamino-1,3-dimethyl-perhydro-1,3,2-diazaphosphorine (BEMP) enables efficient trapping of [(11)C]-CO(2) in small volumes of DMF as [(11)C]-carbamate salts. Subsequent reaction with a variety of methylating agents rapidly generates the desired [(11)C-carbonyl]-methylcarbamates in high radiochemical yields. The usefulness of the method is illustrated by the efficient radiosynthesis of a kappa opioid receptor imaging radiotracer, useful in positron emission tomography (PET).

CO2 -binding organic liquids (CO2 BOLs) for post-combustion CO2 capture

Abstract CO 2 -binding organic liquids (CO 2 BOLs) chemically bind and release CO 2 more efficiently than aqueous alkanolamine systems. CO 2 BOLs are comprised of alcohols and organic amidine or guanidine bases, which chemically bind CO 2 as liquid amidinium or guanidinium alkylcarbonate salts. CO 2 BOLs have high CO 2 binding capacities (19% by weight, 147 g CO 2 /L) compared to that of 30% monoethanolamine solution in water (7% by weight, 108 g CO 2 /L) because they are liquid with or without bound CO 2 and do not require any added solvent such as water. The dissolution of CO 2 into and out of the liquid phase limits the rate of CO 2 capture and release. Absorption of CO 2 is selective over nitrogen in both concentrated and dilute gas streams making these systems applicable to post- and pre-combustion CO 2 capture. The free energy of CO 2 binding in these systems is small and is independent of the choice of alcohol. The free energies of these systems are dependent on the choice of base; −9 kJ/mol for diazabicyclo[5.4.0]undec-7-ene (DBU) and Barton’s base and +2 kJ/mol for 1,1,3,3-tetramethylguanidine. The specific heats of the organic CO 2 BOLs are over 50% lower than that of water, resulting in a 50% reduction in the energy needed to strip out CO 2 as compared to aqueous alkanolamine solutions. CO 2 BOLs have been recycled for five cycles without losing activity or selectivity towards CO 2 .

Regioselective control of the nickel-mediated coupling of acetylene and carbon dioxide – A DFT study

The nickel-mediated coupling of asymmetric alkynes with carbon dioxide is known to be highly regioselective with respect to the formation of nickelacycle intermediates and α,β-unsaturated carboxylic acid products. Using density functional theory (DFT), we have investigated the effect that parameters such as acetylene-substituent, ancillary ligand and solvent have on the potential energy surface of the nickelacycle coupling reaction. 3-R-substituted nickelacycles are the thermodynamically preferred product in all cases surveyed, however, the transition structure characterised by the attack of CO 2 on the alkyne carbon distal from the R-group is generally lower in energy, making the 2-R-substituted nickelacycle the kinetically favoured product. Ligating the zerovalent nickel species with the diazabicyclo[5.4.0]undec-7-ene (DBU) ancillary ligand in preference to 2,2′-bipyridine (BIPY) leads to lower activation energies for the coupling reaction and products that are less susceptible to steric bulk in the 2-position of the nickelacycle. Solvation with dimethylformamide (DMF) has the advantage of lowering the activation barrier for the coupling reaction when compared to tetrahydrofuran (THF).

The DBU-H2O complex as a new catalyst for aldol condensation reactions

Abstract Finding new Bronsted-type basic catalysts that can perform condensation reactions of interest to fine chemistry with good activities and selectivities is a constant challenge. In this communication we report the activity of the DBU-H2O system as a basic catalyst for aldol condensation reactions. Diazabicyclo [5.4.0] undec-7-ene (DBU) is a non-nucleophilic, strong tertiary amine base that is widely used in organic synthesis. We demonstrate that DBU, which has Lewis basic properties is inactive for aldol condensation reactions. However when it reacts with equimolar amounts of water it transforms towards a second resonance structure with Bronsted basic properties and therefore, high activity for these reactions. Besides, the DBU-H2O complex is found to be very efficient with reusability for several times.

Novel michael addition networks containing urethane hydrogen bonding

AbstractCovalently crosslinked networks based on poly(propylene glycol) bis(acetoacetate) with either neopentyl glycol diacrylate or hydroxyethyl acrylate derivatized bis(4‐isocyanatocyclohexyl)methane (HMDI) were prepared utilizing the Michael addition reaction in the presence of catalytic quantities of diazabicyclo[5.4.0]undec‐7‐ene (DBU). These networks were prepared in the absence of solvent at 23 °C without the formation of byproducts. Mechanical and thermal analyses of the networks were performed utilizing DMA, tensile testing, and TGA. Tensile analysis revealed that the introduction of hydrogen‐bonding urethane linkages in the diacrylate segment resulted in higher tensile strengths and elongation to break compared with nonhydrogen‐bonding analogs. All crosslinked products exhibited high gel fractions and excellent thermomechanical properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4118–4128, 2007

Synthesis and reactivity of μ-butadienyl diruthenium cations

Propargyl alcohols HCCCR 2OH (R=H, Me or Ph) react with [Ru 2(CO)(MeCN)(μ-CO)(μ-CH 2)(η-C 5H 5) 2] ( 2) to form the allylidene complexes [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CR 2OH)CHCH 2}(η-C 5H 5) 2] ( 4a, R=H; 4b, R=Me; 4c, R=Ph). Treatment of complexes 4a– c with HBF 4 removes the hydroxide group as water, giving the 2-butadienyl complexes [Ru 2(CO)(μ-CO)(μ-η 2,η 3-CR 2CCHCH 2)(η-C 5H 5) 2][BF 4] ( 5a, R=H; 5b, R=Me; 5c, R=Ph). The reactivity of 5a– c towards nucleophiles and bases is described. With hydride, 5a– c undergo nucleophilic attack at the C(R 2) carbon to give the allylidene complexes [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CR 2H)CHCH 2}(η-C 5H 5) 2] ( 6a, R=H; 7, R=Me; 11, R=Ph) and, in the case of 5c, the butadiene complex [Ru 2(CO) 2(μ-η 2,η 2-CPh 2CHCHCH 2)(η-C 5H 5) 2] ( 12) and the allene complex [Ru 2(CO) 2(μ-η 2,η 2-CPh 2CCHMe)(η-C 5H 5) 2] ( 13), formally due to attack at the μ-C and CH 2 carbons, respectively. The complexes 5a– c react with methyl lithium to undergo nucleophilic attack predominantly at the C(R 2) carbon, giving methylated allylidene complexes [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CR 2Me)CHCH 2}(η-C 5H 5) 2] ( 6b, R=Me; 9, R=Me; 14, R=Ph). With 5b and 5c methyl lithium also acts as a base, abstracting protons to give the novel divinylcarbene complex [Ru 2(CO)(μ-CO){μ-η 1,η 3-C(CMeCH 2)CHCH 2}(η-C 5H 5) 2] ( 8) and the μ-butatriene complex [Ru 2(CO) 2(μ-η 2,η 2-CPh 2CCCH 2)(η-C 5H 5) 2] ( 15), respectively. Complexes 8 and 15 are formed exclusively by treating 5b and 5c, respectively, with diazabicyclo[5.4.0]undec-7-ene (DBU). Complexes 8 and 9 were also prepared in good yield by reaction of complex 2 with 2-methyl-1-buten-3-yne {CH 2C(Me)CCH} and t-butylacetylene, respectively. Treatment of complex 8 with HBF 4 resulted in protonation at each of the methylene groups, affording 5b and isomeric [Ru 2(CO)(μ-CO){μ-η 2,η 3-CH(Me)CC(Me)CH 2}(η-C 5H 5) 2][BF 4] ( 10). The structures of 5b, 5c and 8 were established by X-ray diffraction.

The case for configurational stability of H-phosphonate diesters in the presence of diazabicyclo[5.4.0]undec-7-ene (DBU)

Configurational stability of dinucleoside H-phosphonates and the stereochemical course of their sulfurisation in the presence of diazabicyclo[5.4.0]undec-7-ene (DBU) were investigated using 31P NMR spectroscopy. It was found that under the reaction conditions and irrespective of the type of protecting groups present in the nucleoside moieties, the H-phosphonate diesters investigated did not undergo any detectable epimerisation at the phosphorus centre, and their sulfurisation with elemental sulfur in the presence of DBU, proceeded stereospecifically. Thus, we could not confirm reports from another laboratory on a stereoselective course of sulfurisation of H-phosphonate diesters and the corresponding acylphosphonates in the presence of DBU.

Regioselective bisaddition to C 60 with bis(β-keto esters)

Abstract Reaction of C60 with bis(β-keto esters) in the presence of iodine and diazabicyclo[5.4.0]undec-7-ene (DBU) in toluene provides covalent bisadducts of C60 with high regioselectivity.

Cyclopropanation of C 60 with malonic acid mono-esters

Reaction of C 60 with malonic acid mono-esters in the presence of iodine and diazabicyclo[5.4.0]undec-7-ene (DBU) provides the corresponding 61-iodo-1,2-methano[60]fullerene-61-carboxylates. This cyclopropanation of C 60 seems to occur via a carbenoid intermediate.