Urotropine as a highly effective and versatile promoter for atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) is a transition metal complex‐catalyzed controlled/‘living’ radical process. Recently, there has been a lot of interest focused on decreasing the catalyst loading and reducing the cost of post‐polymerization purification for ATRP. In this work, urotropine was found to significantly enhance the ATRP of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (St) catalyzed by CuBr/N,N,N′,N′,N″‐pentamethyldiethylenetriamine (PMDETA) and CuBr/tris(2‐(dimethylamino)ethylamine) (Me₆TREN). With the addition of 25 times the amount of urotropine relative to CuBr, well‐controlled polymerizations of MA, MMA and St were obtained at catalyst‐to‐initiator ratios of 0.01, 0.05 and 0.05, respectively, producing the corresponding polymers with molecular weights close to theoretical values and low polydispersities. The catalyst concentration could even be reduced to ppm level at a catalyst‐to‐initiator ratio as low as 0.001 in the polymerization of MA. These results indicate that urotropine is a very effective and versatile promoter for both CuBr/PMDETA and CuBr/Me₆TREN. In the presence of urotropine, the catalyst loading could be reduced by as much as 1000 times. As PMDETA is one of the cheapest ATRP ligands, the combination of urotropine with CuBr/PMDETA could substantially reduce the catalyst loading and the cost of post‐polymerization purification at the industrial scale and thus is promising for potential industrial applications. © 2014 Society of Chemical Industry     

Reverse atom transfer radical polymerization of methyl methacrylate in different solvents

The reverse atom transfer radical polymerization of methyl methacrylate was investigated in different solvents: xylene, N,N‐dimethylformamide, and pyridine. The polymerizations were uncontrolled, using 2,2′‐bipyridine as a ligand in xylene and pyridine because the catalyst (CuBr₂/2,2′‐bipyridine complex) had poor solubility in the xylene system. In the pyridine system, the solubility of the catalyst increased, but the solvent could complex with CuBr₂, which influenced the control of the polymerization. In the N,N‐dimethylformamide system, the catalyst could be dissolved in the solvent completely, but the ? N(CH₃)₂ group in N,N‐dimethylformamide could also complex with CuBr₂, so the polymerization could not be well controlled. The ligand of 4,4′‐di(5‐nonyl)‐2,2′‐bipyridine was also investigated in xylene; the introduction of the ? CH(C₄H₉)₂ group enabled the CuBr₂/4,4′‐di(5‐nonyl)‐2,2′‐bipyridine complex to easily dissolve in xylene, and the polymerizations were well controlled. The number‐average molecular weight increased linearly with the monomer conversion from 4280 to 14,700. During the whole polymerization, the polydispersities were quite low (1.07–1.10). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A green procedure for the protection of carbonyls catalyzed by novel task-specific room-temperature ionic liquid

A cheap and recyclable task-specific ionic liquid N,N,N-trimethyl-N-propanesulfonic acid ammonium hydrogen sulfate [TMPSA]HSO₄ was synthesized as dual solvent–catalyst for the protection of carbonyls via formation of acetals or ketals. The satisfactory results were obtained for the protection of carbonyls as cycloacetals or ketals with diols under the mild conditions. The products could be separated from the catalyst simply by decantation and the catalyst could be recycled and reused for several times without noticeably decreasing the catalytic activity after removal of the water.     

A practical and efficient synthesis of quinoxaline derivatives catalyzed by task-specific ionic liquid

A cheap and recyclable task-specific ionic liquid N, N, N-trimethyl-N-propanesulfic acid ammonium hydrogen sulfate [TMPSA] · HSO₄ was used as the catalyst for the synthesis of quinoxaline derivatives. The reaction could be accomplished in water as well as organic solvent, and the satisfactory results were obtained under the mild conditions. The products could be separated from the catalyst simply by filtration and the catalyst could be recycled and reused for several times without noticeably decreasing the catalytic activity.     

Palladium‐Catalyzed Regioselective and Stereoselective Oxidative Heck Arylation of Allylamines with Arylboronic Acids

A general and convenient palladium‐catalyzed oxidative Heck arylation of both N‐protected and N,N‐diprotected allylic amines with arylboronic acids under mild conditions has been developed. The catalyst system, consisting of Pd(OAc)₂ (palladium acetate), AgOAc (silver acetate) and KHF₂ (potassium hydrogen fluoride), could efficiently catalyze the coupling reaction in acetone without the aid of any ligand, leading exclusively to the γ‐arylated allylic amine products in good to excellent yields. This method is highlighted with excellent regio‐ and stereocontrol and remarkable functional group tolerance. The carbamate moiety in allylic amine substrates is of crucial importance to the catalytic performance, and the chelation between the carbonyl O (oxygen) and Pd (palladium) atoms is believed to be responsible for the high regioselectivity and stereoselectivity observed.     

A new catalytic transesterification for the synthesis of N, N-dimethylaminoethyl acrylate with organotin catalyst

A new transesterification method for preparing N, N-dimethylaminoethyl acrylate (DMAEA) from methyl acrylate (MA) and dimethylaminoethanol (DMAE) was carried out in the presence of organotin catalyst. Among the catalysts examined, (C₈H₁₇)₂Sn(OCOC₁₁H₂₃)₂(TD) is the most active one for the reaction. The products were characterized by gas chromatography, IR spectroscopy, NMR spectroscopy and Mass spectroscopy. The effects of various reaction conditions such as the different catalysts, the reactants ratio, the amount of catalyst, the reaction time on the DMAE conversion, the selectivity to DMAEA and the DMAEA yield were investigated. Experimental results indicated that the sort of catalyst is vital to improving DMAEA yield. The reactants ratio could effect on the DMAE conversion, the selectivity to DMAEA and the DMAEA yield. The 96.28% conversion of DMAE was obtained over catalyst TD, the yield of DMAEA could reach 94.65%, the selectivity is 98.68%. A possible catalytic mechanism of transesterification of DMAE and MA with organotin catalysts was also presumed.     

Study on Copper-based Catalysts for Synthesis of N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine from Reductive Alkylation of p-Nitroaniline with 5-Methyl-2-hexanone

The reductive alkylation of p-nitroaniline with 5-methyl-2-hexanone over copper-based catalysts was investigated. Furthermore, the catalysts were characterized using the techniques of XRD, H₂–N₂O titration, H₂-TPR, NH₃-TPD and pyridine-FTIR. The results showed that the addition of Mn, Ba and La into Cu–SiO₂ catalyst played an important role in the improvement of the selectivity towards N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine (BMPPD). The highest selectivity towards BMPPD over 58CuO–9MnO₂–BaO–1La₂O₃–30SiO₂ (wt.%) catalyst could be ascribed to the best dispersion of copper (i.e., the highest hydrogenation ability) and the most amounts of the surface Lewis acidic sites.     

A convenient synthesis of macroporous polymer‐supported supernucleophilic reagent and linear macromolecules

N,N′‐Bis(4‐pyridinyl)piperazine and N‐(4‐pyridinyl)piperazine have been prepared by treatment of piperazine with 4‐chloropyridine. N,N′‐Bis(4‐pyridinyl)piperazine (bis‐DMAP) is similar to a couple of 4‐(N,N‐dimethylamino)pyridine (DMAP). N‐(4‐Pyridinyl)piperazine as reactive group can be linked onto the macroporous polymeric carrier producing a polymer‐bound catalyst. A linear epoxy polymer containing the supernucleophilic functional groups have been synthesized by reaction of epichlorohydrin and 4‐aminopyridine. The linear polymeric catalysts have been braced by the macroporous resin to obtain a polymer‐supported linear polymeric catalyst. It is found that catalytic activity of bis‐DMAP approaches that of DMAP. The activity of the polymer‐supported linear polymeric catalyst is higher than that of the polymer‐bound catalyst in the acetylation of tert‐butyl alcohol, as monitored by gas–liquid chromatography. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 593–597, 2000     

An environmentally friendly FeTiSOx catalyst with a broad operation-temperature window for the NH3-SCR of NOx

A novel FeTiSO_x catalyst prepared by a simple hydrolysis coprecipitation method was used for the selective catalytic reduction (SCR) of NO_x with NH₃, which exhibited high catalytic activity (NO_x conversion of >97% and N₂ selectivity of >95%) and tolerance for both H₂O and SO₂ at a broad temperature window of ~325–475°C. The characterization results showed that the formation of Fe–O–Ti and Fe–O–S species could significantly enhance the acidic sites of the catalyst, which play an important role in NH₃ absorption and their catalytic activity. The Fe³⁺ ions in the bulk anatase TiO₂ could significantly enhance the redox properties for the SCR reaction and suppress the side reaction of NH₃ oxidation to NO or N₂O. In addition, the reaction mechanism was discussed based on in situ diffuse reflectance infrared Fourier transform spectroscopy measurements and kinetic investigation, indicating that the reaction was dominated by the Eley–Rideal mechanism over the FeTiSO_x catalyst.     

A Simple Approach to Unsymmetric Atropoisomeric Bipyridine N,N′‐Dioxides and Their Application in Enantioselective Allylation of Aldehydes

The [2+2+2] cyclotrimerization of 1‐isoquinolinyl‐1,7‐octadiyne with benzonitrile catalyzed by CpCo(CO)₂ opened a new pathway for a synthesis of unsymmetrical axially chiral bipyridine N,N′‐dioxides. The N,N′‐dioxide 3a was found to be highly catalytically active and enantioselective for the asymmetric allylation of aldehydes with allyltrichlorosilane. The allylation took place with even 1 % of the catalyst with an enantioselectivity up to 87 % ee.     

Effect of pretreatment and regeneration conditions of Ru/γ-Al2O3 catalysts for N2O decomposition and/or reduction in O2-rich atmospheres and in the presence of NOX, SO2 and H2O

The effect of the pretreatment (inert, oxidative, and reducing) of Ru/γ-Al₂O₃ catalyst on its activity and stability in the decomposition of N₂O in the absence or presence of O₂, SO₂, H₂O and NO_X was studied in the present work. Decomposition of pure N₂O was slightly enhanced by the H₂-pretreated catalyst (metallic Ru) compared to the O₂- or He-pretreated ones, owing to a cyclic oxidation–reduction pathway of metallic Ru. The observed decrease of activity by O₂ or H₂O addition was reversible compared to SO₂ which caused a strong, irreversible deactivation of the catalyst, irrespective of the type of pretreatment. This was attributed to the formation of stable sulphates, mainly those on RuO₂ surface, which could only be removed by regeneration under reducing (H₂ in He) atmosphere at temperatures of ca. 500 °C. Oxidative or inert regeneration required very high temperatures (i.e. >700 °C) in order to decompose these sulphates. A method of retaining N₂O conversion activity very high (≥98%) for long reaction times is suggested and is based on frequent and short-time (ca. 10 min) regenerations of the catalyst under reducing atmosphere (ca. 5% H₂ in He). The effect of co-feeding various reducing agents, such as CO or C₃H₆, on the N₂O conversion activity in the presence of O₂, SO₂, H₂O and NO_X is negligible, mainly because they are oxidized at relatively low temperatures in the O₂-rich feeds used in this study.     

Controlled polymerization of methylmethacrylate from fumed SiO2 nanoparticles through atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) is a promising method to synthesize well‐defined polymer/inorganic nanoparticles. However, the surface‐initiated ATRP from commercially mass produced inorganic nanoparticles has seldom been studied. In this study, the surface‐initiated ATRP of methylmethacrylate (MMA) from commercially mass produced fumed silica (SiO₂) nanoparticles was investigated. Unlike the ATRP of MMA initiated from a free initiator, the controllability of ATRP of MMA from the surface of fumed silica nanoparticles was much better using ligand 2,2'‐bipyridine (bpy) than N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) as the initiator was immobilized on the surface of the SiO₂ nanoparticles and the presence of the SiO₂ nanoparticles made the CuCl/bpy catalyst system a homogeneous catalyst system and CuCl/PMDETA a heterogeneous one. The appropriate molar ratio of monomer and initiator was essential for preparing controlled PMMA/SiO₂ nanoparticles. The entire process of ATRP of MMA from the surface of SiO₂ nanoparticles was controllable when using bpy as ligand, xylene as solvent and with a monomer to initiator ratio of 300:1. The ¹H NMR results indicated that the PMMA on the surface of the SiO₂ was prepared via ATRP initiated from 4‐(chloromethyl)phenyltrimethoxysilane. The well‐defined PMMA/SiO₂ nanoparticles obtained have good thermal stability and are well dispersed in organic media as proved by TGA, dynamic light scattering and transmission electron microscopy. © 2013 Society of Chemical Industry     

Recovery of Wilkinson’s Catalyst from Hydrogenated Nitrile Butadiene Rubber Latex Nanoparticles

Three different chelating ligands were used to separate Wilkinson’s catalyst from HNBR nanoparticles in latices. N,N,N′,N′,N′′-pentamethyldiethylenetriamine was found to be very effective in removing the catalyst. HNBR particle size and the extraction temperature on catalyst removal were investigated. The mechanism involved in the separation process was elucidated. This study promotes the possible commercialization of the green latex direct hydrogenation technique.

     

Mannich reaction in water using acidic ionic liquid as recoverable and reusable catalyst

The task-specific room-temperature ionic liquid (TSIL) N, N, N-trimethyl-N-butanesulfonic acid ammonium hydrogen sulfate [TMBSA]HSO₄ was synthesized as a cheap and recyclable catalyst for one-pot three-component Mannich reaction in water. Sixteen β-amino carbonyl compounds were obtained in good yields under the mild conditions. The products could simply be separated from the catalyst/water, and the catalyst could be reused at least 7 times without noticeably decreasing the catalytic activity.      

Catalytic reduction of N2O by H2 over well-characterized Pt surfaces

A 0.65% Pt/SiO₂ catalyst has been prepared using an ion exchange technique and extensively characterized prior to being used for continuous catalytic N₂O reduction by H₂ at very low temperatures, such as 363 K. The supported Pt with a high dispersion of 92% gave no presence of O atoms remaining on an H-covered Pt _s , based on in situ DRIFTS spectra of CO adsorbed on Pt _s after either N₂O decomposition at 363 K or subsequent exposure to H₂ for more than 1 h; thus the residual uptake gravimetrically observed even after the hydrogen titration on an O-covered surface is associated with H₂O produced by introducing H₂ at 363 K onto the oxidized Pt _s . Dissociative N₂O adsorption at 363 K on Pt _s was not inhibited by the H₂O_(ad) on the silica surface but not on Pt _s , as acquired by IR peaks at 3,437 and 1,641 cm⁻¹, in very consistent with the same hydrogen coverage, established via H₂-N₂O titration on a reduced Pt _s , as that revealed upon the titration reaction with a fully wet surface on which all bands and their position in IR spectra for CO are very similar to that obtained after H2 titration on a reduced Pt _s . Based on the characterization using chemisorption and in situ DRIFTS and TPD measurements, the complete loss in the rate of N₂O decomposition at 363 K after a certain on-stream hour, depending significantly on N₂O concentrations used, is due to self-poisoning by the strong chemisorption of O atoms on Pt _s , while the presence of H₂ as a reductant could readily catalyze continuous N₂O reduction at 363 K that is a greatly lower temperature than that reported earlier in the literature.     

Formylation with “Supercritical” CO2: Efficient Ruthenium-Catalyzed Synthesis of N-Formylmorpholine

Formylation of morpholine with supercritical CO₂ using the bidentate ruthenium catalyst RuCl₂(dppe)₂ affords high N-formylmorpholine production rate at almost 100% selectivity. The solventless reaction could be an interesting alternative to the present N-formylmorpholine synthesis routes, which are based on environmentally harmful formylation agents. Video monitoring of the reaction mixture during reaction revealed a complex phase behavior, including the formation of solid carbamate, which was most prominent at low conversion and gradually disappeared with higher conversion, i.e., with the formation of N-formylmorpholine and water as a by-product. Addition of water as an additive suppressed solid carbamate formation and enhanced the reaction rate. Infrared spectroscopy was applied to follow the changes in the liquid and dense gas phase. The ruthenium catalyst was confined to the liquid phase, containing morpholine, N-formylmorpholine, water, dissolved carbon dioxide and hydrogen. Although the solubility of the ruthenium catalyst in the liquid phase decreased with increasing conversion, good performance in the synthesis of N-formylmorpholine could be achieved.     

Organic–inorganic composite materials as photoinitiator for controlling/living polymerization

Titanium dioxide (TiO₂)/graphitic carbon nitride (g‐C₃N₄) composites were first used as photoinitiator for photochemically mediated controlled/living polymerization of methyl methacrylate. The polymerization was successfully carried out in polyethylene glycol at room temperature with FeCl₃·6H₂O/N,N,N ′,N ′,N ″‐pentamethyldiethylenetriamine as complex catalyst and ethyl 2‐bromoisobutyrate as initiator in this case. A pseudo‐first‐order dependence of the monomer concentration on the polymerization time was observed. TiO₂/g‐C₃N₄ was verified to be an efficient photoinitiator. The polymerization was controlled to produce poly(methyl methacrylate) with narrow molecular weight distribution and controlled number average molecular weight (M_n,GPC). The M_n,GPC matched well with the theoretical values when using both UV and sunlight irradiation as light source. The effects of reaction conditions on the polymerization were investigated. The polymerization could be started and stopped through periodically switching on/off the light. The living nature was further supported by the chain extension experiments. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42891.     

A Double Prodrug with Improved Membrane Permeability over the Parent Chelator HBED Provides Superior Cytoprotection against Hydrogen Peroxide

The clinical use of N,N′‐bis(2‐hydroxybenzyl)ethylenediamine‐N,N′‐diacetic acid (HBED) has been hindered by its lack of bioavailability. N,N′‐bis(2‐boronic pinacol ester benzyl)ethylenediamine‐N,N′‐diacetic acid methyl, ethyl, and isopropyl esters 7 a – c , respectively, and their dimesylate salts 8 a – c , are double prodrugs that mask the two phenolate and two carboxylate donors of HBED as boronic esters and carboxylate esters, respectively. Their activation by chemical hydrolysis and oxidation, their passive diffusivity, and their cytoprotective capabilities have been investigated here. 8 a – c hydrolyzed in minimum essential medium at 37 °C with half‐lives of 0.69, 0.81, and 2.28 h, respectively. The intermediate formed, 9 [N,N′‐bis(2‐boronic acid benzyl)ethylenediamine‐N,N′‐diacetic acid], then underwent oxidative deboronation by H₂O₂ to give HBED (k=1.82 m ^?1 min^?1). Solubility measurements in mineral oil and in phosphate buffer indicated that 7 a had a better balance between lipid and aqueous solubilities than did HBED. 7 a was also able to passively diffuse across a lipid‐like silicone membrane (log flux=?0.36), whereas HBED‐HCl was not. 8 c provided better protection to retinal cells than did HBED against a lethal dose of H₂O₂ (84 % vs. 28 % protection, respectively, at 44 μm ). These results suggest that the double prodrugs have better membrane permeability than does HBED, and therefore could be therapeutically useful for improving the delivery of HBED.     

A Scrutiny on the Reductive Amination of Carbonyl Compounds Catalyzed by Homogeneous Rh(I) Diphosphane Complexes

The reductive amination of a series of aldehydes with secondary amines and H₂ in the presence of a homogeneous Rh-diphosphane catalyst was studied in order to establish a general mechanism of this reaction and to identify conditions for the improvement of the amine/alcohol ratio in the product. Several possible intermediates as constituents of changing equilibria like half-aminals, N,O-acetals and aminals were observed in the reaction mixture by means of ¹H NMR spectroscopy. In individual trials, these compounds could be successfully hydrogenated under the conditions applied for reductive amination (50 bar H₂ pressure, MeOH). Some evidence is accumulated that half-aminals and N,O-acetals might be key intermediates of the reductive amination. Moreover, it was found that the formation of the undesired product alcohol is likely based on the reduction of the starting carbonyl compound. However, due to numerous equilibria consisting of several intermediates, general conclusions are hard to be drawn. Proof will be given that, in several cases, the efficiency of the reductive amination of aliphatic aldehydes can be significantly improved by prehydrogenation of the cationic [Rh(dppb)(COD)]⁺ complex.     

New Approaches to Immobilization of Aluminum Chloride on γ-Alumina and Its Regeneration After Deactivation

The preparation of an AlCl₃ catalyst immobilized on -Al₂O₃ and its regeneration after deactivation have been studied. AlCl₃, generated by reacting CCl₄ with -Al₂O₃, was carried by N₂ to a reactor containing the -Al₂O₃ support. The immobilized AlCl₃ catalyst with meso- and macro-pore bimodal structure was shown to be suitable for isobutene oligomerization. The amount of AlCl₃ immobilized on the support in terms of AlCl _x (x = 2.2) was 7.5 wt%. The catalyst exhibited excellent catalytic properties for isobutene polymerization under mild conditions. The average molecular weight of the product was 1000–2500, and its distribution was narrow, around 2.0 in the reaction temperature range 10–40 °C. This catalyst showed nearly perfect reactive specificity to isobutene polymerization and remarkable stability. After 2000 h of continuous running, the conversion dropped from 99 to 57%, the selectivity was maintained with little change at about 90%, and the average molecular weight was within the range 1000–1200 under the conditions T = 32 ± 1 °C, LHSV = 2.0 h^-1, and P = 1.0 MPa.Reneration of the deactivated catalyst was satisfactorily accomplished by treating the used catalyst with a saturated solution of AlCl₃ in CCl₄ either in situ or ex situ. The activity recovery can be as high as 96%, and the deactivated catalyst can be regenerated repeatedly.