Cationic Ring Opening Polymerization of Glycolide Catalysed by a Montmorillonite Clay Catalyst

The ring opening bulk polymerization of glycolide catalyzed by Maghnite-H⁺ was reported. Maghnite-H⁺ is a montmorillonite sheet silicate clay, exchanged with protons. The effect of the amount of Maghnite-H⁺ and the temperature on polymerisation was studied. Increasing Maghnite-H⁺ proportion and temperature produced the increase in glycolide conversion. The kinetics indicated that the polymerization rate is first order with respect to monomer concentration. Mechanism studies showed that monomer inserted into the growing chains with the acyl–oxygen bond scission rather than the break of alkyl–oxygen bond.     

Synthesis and Characterization of New Organometallic Hybrid Material LCP-1 Based on MOF (Metal–Organic Framework) and Maghnite-H<Superscript>+</Superscript>, a Protons Exchanged Montmorillonite Clay,as Catalytic Support

In this work, a new 3D crystalline metal–organic framework formulated as [Zn₂(BTC)₄, (BTC: 1,2,4,5-Benzenetetracarboxylate)] and called LCP-1 (LCP: Laboratoire de Chimie des Polymères), with unsaturated coordinated Zn(II) sites as metal ion and pyromellitic acid (H₄BTC: 1,2,4,5-Benzenetetracarboxylic acid) as organic ligand, has been successfully synthesized under solvothermal conditions. In-Situ polymerization of this material was also carried out using an amount of clay called Maghnite-H⁺, an acid-exchanged montmorillonite, as an eco-catalyst with the aim to respect the principles of green chemistry, to give a new hybrid composite material LCP-1/Mag-H⁺ with a better yield, a significantly reduced time and temperature reaction than those of LCP-1. LCP-1 and LCP-1/Mag-H⁺ have been structurally characterized and established by fourier transform infrared spectroscopy (FT-IR). The morphology of these compounds was studied by the X-ray diffraction (XRD) and revealed a highly crystalline and ordered structure for both LCP-1 and LCP-1/Mag-H⁺. FT-IR and XRD spectra showed also that the stability and structural integrity of LCP-1 and LCP-1/Mag-H⁺ was maintained even after being evacuated from the DMF solvent molecules. The thermal stability identified by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) showed that Maghnite-H⁺, as inorganic support, has also improved the thermal stability of LCP-1 compound.     

Synthesis of Biodegradable Diblock Copolymers of Glycolide and Poly(oxyethylene) Using a Montmorillonite Clay as Catalyst

Biodegradable diblock copolymers were prepared from glycolide and poly(oxyethylene) of M_n=600 (POE 600), 1500 (POE 1500) and 2000 (POE 2000). The copolymerization of glycolide and POE was induced in heterogeneous phase by “Maghnite-H⁺” under suitable conditions. Maghnite-H⁺ is a montmorillonite sheet silicate clay exchanged with protons. Various techniques, including ¹H NMR, ¹³C NMR, IR, DSC and Ubbelohde viscometer were used to elucidate structural characteristics and thermal properties of the resulting copolymers. The effect of the [glycolide]/[POE] molar ratio on the rate of copolymerization and on intrinsic viscosity of the resulting copolymers was studied. Data showed that the rate of copolymerization and intrinsic viscosity of copolymers increase with increasing [glycolide]/[POE] molar ratio.     

Bulk polycondensation of lactic acid by Maghnite-H+ a non-toxic catalyst

In this study, we report a novel approach to preparing poly (D, L-lactic acid) (PLA) as a biodegradable polymer. PLA was prepared by direct polycondensation of D, L-lactic acid using Maghnite-H⁺, a non-toxic proton exchanged Montmorillonite clay, as catalyst. We investigated in detail, the reaction conditions for the simple direct polycondensation of D,L-lactic acid, including the reaction times, temperatures, and catalyst amount. The molecular weight of synthesized PLA is dependent on both the reaction temperature, amount of catalyst and time. Kinetics indicated that the polycondensation of lactic acid behaves as second-order reaction mechanism. The method for PLA synthesis established here will facilitate production of PLA of various molecular weights, which may have a potential utility as biomaterials.     

Maghnite-H, an ecocatalyst for cationic polymerization of N-vinyl-2-pyrrolidone

The polymerization of N-vinyl-2-pyrrolidone catalyzed by the Maghnite-H⁺ (Mag-H) was investigated. Mag-H is a montmorillonite sheet silicate clay, exchanged with protons. It was found that the cationic polymerization of N-vinyl-2-pyrrolidone (NVP) is initiated by Mag-H at 30 °C in bulk and in solution. The effect of the amount of Mag-H, the temperature and the solvent was studied. The polymerization rate increased with increase in the temperature and the proportion of catalyst, and it was larger in nitrobenzene than that in toluene. These results indicated the cationic nature of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from Mag-H.     

Polyvinylpolypyrrolidone-Supported Chlorosulfonic Acid: An Efficient Catalyst for One-Pot Synthesis of Dihydropyrimidinones and Octahydroquinazolin-2,5-diones

Polyvinylpolypyrrolidone-supported chlorosulfonic acid has been successfully applied to perform one-pot reaction of arylaldehydes, urea, ethylacetoacetate, or cyclic 1,3-diketo compounds under solvent-free condition at 70°C to provide a series of dihydropyrimidinones and octahydroquinazolin-2,5-diones in good to excellent yields. The method offers several advantages such as high yield, short reaction time, simple workup, easy preparation, and reusability of the catalyst. The [PVPP-SO₃H]⁺Cl^? catalyst was characterized via Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). Moreover, the catalyst could be recycled several times without significant loss of its catalytic activity. Clean methodologies, easy work-up procedure, high yield, and simple preparation of the catalyst are some advantages of this article.     

Rhodium‐Catalyzed Enantioselective Intramolecular [4+2] Cycloaddition using a Chiral Phosphine‐Phosphite Ligand: Importance of Microwave‐Assisted Catalyst Conditioning

The use of modular α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL)‐ and 1,1′‐bi‐2‐naphthol (BINOL)‐derived phosphine‐phosphite ligands (L₂*) in the asymmetric rhodium‐catalyzed intramolecular [4+2] cycloaddition (“neutral” Diels–Alder reaction) of (E,E)‐1,6,8‐decatriene derivatives (including a 4‐oxa and a 4‐aza analogue) was investigated. Initial screening of a small ligand library led to the identification of a most promising, TADDOL‐derived ligand bearing a phenyl group adjacent to the phosphite moiety at the arene backbone. In the course of further optimization studies, the formation of a new, more selective catalyst species during the reaction time was observed. By irradiating the pre‐catalyst with microwaves prior to substrate addition high enantioselectivities (up to 93% ee) were achieved. The new cyclization protocol was successfully applied to all three substrates investigated to give the bicyclic products in good yield and selectivity. ³¹P NMR and ESI‐MS measurements indicated the formation of a [Rh(L₂*)₂]⁺ species as the more selective (pre‐) catalyst.     

Catalytic hydrogenation of soybean oil with Rh(l) dihydride complexes as catalysts

Cationic rhodium(I) complexes of the type [NBD Rh L₂]⁺[C1O₄]⁻ (NBD = norbornadiene and L = diphenylphosphinoethane or triphenylphosphine) have been studied as catalysts for the hydrogenation of soybean oil. These catalysts give a good yield of products with cis-configuration. Indeed, hydrogenation could be performed under mild conditions (30 C, 1 atm hydrogen pressure) to an iodine value of 80 with not more than 12% oftrans monoenes and only 5% conjugated isomers formed. The results obtained are interpreted on the basis of the equilibrium H₂RhL _n ⁺ ⇌HRhL_n+H⁺. By the addition of acid (HClO₄ ) the bishydrido form of the catalyst could be studied. With this system only small amounts of trans monoenes were formed and no othertrans isomers could be detected. By the addition of a base such as triethylamine, the monohydridic form of the catalyst could be studied. In contrast to the bishydrido complex, this system gave large amounts oftrans monoenes, together withcis-trans andtrans-trans forms of the 18:2 acid. With both forms of the catalyst system, conjugated isomers were formed.     

Synthesis of copolymer from 1,3,5‐trioxane and 1,3‐dioxolane catalyzed by Maghnite‐H+

Copolymers (polyoxymethylene) were prepared by cationic copolymerization of 1,3,5‐trioxane (TOX) with 1,3‐dioxolane (DOX) in the presence of Maghnite‐H⁺ (Mag‐H⁺) in solution. Maghnite is a Montmorillonite sheet silicate clay, with exchanged protons to produce Mag‐H⁺. Various techniques, including ¹H‐NMR, ¹³C‐NMR, FT‐IR spectroscopy, and Ubbelohde viscometer were used to elucidate structural characteristics properties of the resulting copolymers. The influence of the amount of catalyst, of dioxolane (DOX), temperature, solvent, and time of copolymerization on yield and on intrinsic viscosity of copolymers was studied. The yield of copolymerization depends on the amount of Mag‐H⁺ used and the reaction time. We also propose mechanisms involved in the synthesis of copolymer (polyoxymethylene). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Prediction of catalyst stability in naphtha reforming

A method to predict catalyst activity (RON) and selectivity (ηc5⁺, liquid yield) of naphtha-reforming catalysts during normal operation is described. It involves performing experiments at normal operational conditions and testing accelerated deactivation. These last experiments have a severe intermediate period at lower pressure. Carbon formation is related to time and the decrease in RON and ηc5⁺ is related to carbon at normal operation. The accelerated deactivation produces a similar coke to the one at normal conditions for an equal amount of coke. Therefore for each time at normal conditions there is a corresponding pressure in the accelerated deactivation test. Power law-equations fit the data well and combining them results in the following relations: P = at^b; Δ_NRON = cP^d; Δ_Nηc5⁺ = eP^f. The coefficients a, b, c, d, e and f depend on the catalyst and are calculated from four or six experiments (half at normal conditions and half accelerated deactivation tests); b, d and f bare negative. The value of pressure for the time at which it is desired to predict catalyst activity and selectivity is calculated from the first equation. This value when applied to the second and third equations gives the activity and selectivity, respectively, that the catalyst will have after time t.     

Preparation of In,H-ZSM-5 for DeNOx reactions by solid-state ion exchange

A simple method is proposed to prepare In,H-ZSM-5 catalyst for DeNOx reactions. This consists of mechanically mixing the fine powders of In₂O₃ and H-ZSM-5 followed by heating in oxygen free inert gas flow to 580 °C where indium undergoes thermal auto-reduction and moves into exchange positions as In⁺ without destroying the crystalline structure of the zeolite.It was evidenced by IR, temperature-programmed reduction (TPR) and reoxidation that, once In⁺ was introduced into the lattice either by reductive solid-state ion exchange (RSSIE) or by thermal auto-reductive SSIE, it can be oxidized by O₂ or in the DeNOx reaction to (InO)⁺. The formed (InO)⁺ can easily be reduced to In⁺ suggesting that In,H-ZSM-5 might be a good catalyst for reactions where a redox cycle in the catalyst is involved in the reaction mechanism.Selective catalytic reduction (SCR) by methane proved that only a small fraction of In exchanged, together with some acid sites of the zeolite formed the active center for the catalytic reaction. XRD, XPS and FT-IR using pyridine proved that the structure of the zeolite and these centers are stable under reaction conditions and In is mainly in the form of (InO)⁺ in the used catalyst.     

Study of glycolysis of poly(ethylene terephthalate) recycled from postconsumer soft‐drink bottles. III. Further investigation

A modified glycolysis reaction of recycled poly(ethylene terephthalate) (PET) bottles by ethylene glycol (EG) was investigated. Influences of the glycolysis temperature, the glycolysis time, and the amount of catalysts (per kg of recycled PET) were illustrated in this study. The manganese acetate was used as a glycolysis catalyst in this study. Bis‐2‐hydroxyethyl terephthalate (BHET) and its dimer were predominately glycolysis products. It was found the optimum glycolysis temperature is 190°C. And the best glycolysis condition is 190°C of glycolysis temperature, 1.5 h of glycolysis time, and 0.025 moles of manganese acetate based on per kg of recycled PET. If the best glycolysis condition is conducted, the glycolysis conversion may be as high as 100%. For a given reaction time (1.0 h), the ln(% glycolysis conversion) is linear to 1/T (K^?1) and the activation energy (E) of glycolysis reaction is around 92.175 kJ/(g mole). The glycolysis conversion rate increases significantly with increasing the glycolysis temperature, the glycolysis time, or the amount of manganese acetate (glycolysis catalyst). Thermal analyses of glycolysis products were examined by a differential scanning calorimetry (DSC) and a thermogravimetric analysis (TGA). According to the definition of a 2³ factorial experimental design, the sequence of the main effects on the glycolysis conversion of the recycled PET, in ascending order, is the glycolysis time (0.18) < the amount of catalyst per kg of the recycled PET (0.34) < the glycolysis temperature (0.40). Meanwhile, the prediction equation of glycolysis conversion from the result of a 2³ factorial experimental design is ? = 0.259+0.20X₁+0.09X₂+0.17X₃+0.06X₁ X₂+0.145X₁X₃+0.05X₂X₃+0.035X₁X₂X₃. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2004–2010, 2003     

Esterification of Renewable Levulinic Acid to n‐Butyl Levulinate over Modified H‐ZSM‐5

The synthesis of n‐butyl levulinate, one of the most important biodiesel additives, by catalytic esterification of biomass‐derived levulinic acid (LA) with n‐butanol over modified H‐ZSM‐5 (micro/meso‐HZ‐5) in a closed‐batch system is reported for the first time. The optimization of the reaction conditions such as the reactant molar ratio, the catalyst loading, the reaction time and the temperature was performed in view to maximize the yield of n‐butyl levulinate. Micro/meso‐HZ‐5 was found to be the most efficient catalyst, with 98 % yield of n‐butyl levulinate and a reusability for six cycles, which is higher than reported in the literature. A possible catalytic mechanism for the esterification reaction is also proposed. A second‐order pseudo‐homogeneous model with R² > 0.97 confirmed that the esterification reaction is performed in the kinetic regime due to the high activation energy of 23.84 kJ mol^?1.     

Dehydration of fructose into 5-hydroxymethylfurfural in the presence of ionic liquids

The acid-catalyzed dehydration of fructose was performed in a microbatch reactor at 80 °C using two commercially available ionic liquids, a hydrophilic one, 1-butyl 3-methyl imidazolium tetrafluoroborate (BMIM⁺BF₄⁻), and a hydrophobic one, 1-butyl 3-methyl imidazolium hexafluorophosphate (BMIM⁺PF₆⁻). When the reaction is carried out in 1-butyl 3-methyl imidazolium tetrafluoroborate as solvent and Amberlyst-15 as catalyst, a yield up to 50% in 5-hydroxymethylfurfural (HMF) is obtained within around 3 h. When the reaction is carried out now in 1-butyl 3-methyl imidazolium tetrafluoroborate and in 1-butyl 3-methyl imidazolium hexafluorophosphate as solvents and Amberlyst-15 as catalyst, DMSO is used as a co-solvent, in order, in particular, to solubilize fructose in the hydrophobic ionic liquid. Under these conditions, both ionic liquids allow the reaction to work more rapidly than in DMSO alone and with yields in HMF close to 80% within 24 h.     

Influence of Rare-Earth and Bimetallic Promoters on Various VPO Catalysts for Partial Oxidation of n-Butane

Vanadium phosphorous oxide (VPO) catalyst was prepared using dihydrate method and tested for the potential use in selective oxidation of n-butane to maleic anhydride. The catalysts were doped by La, Ce and combined components Ce + Co and Ce + Bi through impregnation. The effect of promoters on catalyst morphology and the development of acid and redox sites were studied through XRD, BET, SEM, H₂-TPR and TPRn reaction of n-butane/He. Addition of rare-earth element to VPO formulation and drying of catalyst precursor by microwave irradiation increased the fall width at half maximum (FWHM) and reduced the crystallite size of the Vanadyl hydrogen phosphate hemihydrate (VOHPO₄ · 1/2 H₂O, VHP) precursor phase and thus led to the production of final catalysts with larger surface area. The Ce doped VPO catalyst which, assisted by the microwave heating method, exhibited the highest surface area. Moreover, the addition of promoters significantly increased catalyst activity and selectivity as compared to undoped VPO catalyst in the oxidation reaction of n-butane. The H₂-TPR and TPRn reaction profiles showed that the highest amount of active oxygen species, i.e., the V⁴⁺–O^? pair, was removed from the bimetallic (Ce + Bi) promoted catalyst. This pair is responsible for n-butane activation. Furthermore, based on catalytic test results, it was demonstrated that the catalyst promoted with Ce and Bi (VPOD1) was the most active and selective catalyst among the produced catalysts with 52% reaction yield. This suggests that the rare earth metal promoted vanadium phosphate catalyst is a promising method to improve the catalytic properties of VPO for the partial oxidation of n-butane to maleic anhydride.     

Efficient Addition Reaction of Dibutylphosphane Oxide with Alkynes: New Mechanistic Proposal Involving a Duo of Palladium and Brønsted Acid

The addition reaction of dibutylphosphane oxide [Bu₂P(O)H] with alkynes proceeds efficiently in the presence of palladium‐chelating phosphane–Brønsted acid catalyst systems. Terminal alkynes afford branched‐structured products selectively. On the other hand, the same reaction using monodentate phosphane ligands or the reaction run in the absence of a Brønsted acid affords a much lower yield. A mechanistic study has revealed that Brønsted acids (XOH) interact with oxygen in M P(O)R₂ species (M=Pd, Pt) through hydrogen bonding to transform them to ionic M⁺←PR₂(OH⋅⋅⋅O⁻X) species, which was confirmed by NMR spectroscopy and X‐ray crystallography. The phosphane‐like PR₂(OH⋅⋅⋅O⁻X) moiety is coordinatively labile, as substantiated by the ligand exchange reaction with tert‐butyl isocyanide. A new mechanism that accommodates these observations has been proposed to rationalize the enhancement of catalytic activity and the regioselectivity induced by the Brønsted acid.     

Multi‐Step Controlled Kinetics of the Transesterification of Crude Soybean Oil with Methanol by Mg(OCH3)2

This work focuses on a kinetic model that can be expressed as three significant controlled regions, i.e., a mass transfer controlled region in the internal surface of a heterogeneous catalyst, an irreversible chemical reaction controlled region in the pseudo‐homogenous fluid body and a reversible equilibrium chemical reaction controlled region near to the transesterification equilibrium stage. With the help of MATLAB7.0 software, the apparent reaction rate constants, k₂, k₂⁺ and k₂^–, were calculated and the corresponding apparent activation energies were calculated to be 67.450, 60.680 and 58.279 kJ·mol^–1, respectively. According to the confirmation experiments, it is indicated that the results can be applied for predicting the FAME yield at other reaction temperatures.     

Study of the Alkylation of Phenol with Methanol on Zn(H)-Exchanged NaY Zeolites

Abstract  

The gas-phase alkylation of phenol with methanol was studied at 473 K on zeolite NaY exchanged with Zn⁺² (samples Zn(x)NaY) or H⁺ (samples Na(x)HY) cations. Zeolite NaY contained only weak and medium Lewis acid sites. The addition of Zn⁺² formed essentially strong Lewis acid sites. In contrast, the exchange of NaY with H⁺ generated Br?nsted acid sites and decreased the density of Lewis acid sites. Zeolite NaY was inactive at 473 K, but after its exchange with Zn²⁺ efficiently promoted the phenol methylation reaction. Phenol conversion and the selectivities to o- and p-cresols increased with the Zn content in the sample. The exchange of Na⁺ with H⁺ also activated the parent NaY zeolite. At similar phenol conversion levels, Na(x)HY samples formed more anisole and less cresols than Zn(x)NaY. All the Zn(x)NaY and Na(x)HY samples deactivated on stream, but the catalyst activity decay increased with the exchange degree.     

Two-step synthesis and characterization of urea–isobutyraldehyde–formaldehyde resins

Urea–isobutyraldehyde–formaldehyde (UIF) resins were synthesized from urea, isobutyraldehyde and formaldehyde using sulfuric acid as catalyst by two-step method. The effect of molar ratio of isobutyraldehyde to formaldehyde (n(I)/n(F)), molar ratio of aldehyde to urea (n(A)/n(U)), catalyst concentration and reaction time on the yield, hydroxyl value and softening point of UIF resins were investigated. The UIF resins were characterized by Fourier transform infrared spectroscopy (FT-IR), ¹H-nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC) and thermogravimetric (TG). The results showed that the yield, hydroxyl value and softening point of the UIF resin were 76.5%, 90 °C and 32 mgKOH/g, respectively, when the molar ratio of urea to isobutyraldehyde to formaldehyde (n(U)/n(I)/n(F)) was 1.0/3.6/2.4, catalyst concentration was 6.0%, and reaction time in the second step reaction was 3.0 h. FT-IR and ¹H NMR results showed that α-H in isobutyraldehyde participated in the synthesis reaction of UIF resins, and the reaction was Mannich reaction. The amount of aldehyde groups in UIF resins increased with the increase of the amount of isobutyraldehyde. GPC results showed that the UIF resins had narrow molecular weight distribution and TG results indicated that the UIF resin had excellent heat resistance.     

Catalytic Activity of Rhodium Complexes Supported on Al2O3–ZrO2 in Isomerization and Hydroformylation of 1-Hexene

Two new nanostructured Al₂O₃–ZrO₂ mixed oxides supports, A and B, have been prepared by sol–gel process and characterized by TEM, XRD and XPS methods. The freeze-dried gel gave support A whereas the support B was obtained by drying of gel at ambient temperature. Both supports reacted with Rh(acac)(CO)₂ complex, producing Rh(CO)₂ ⁺ tethered species, characterized by ν(CO) at 2011 and 2083 cm^?1. The Rh(CO)₂ ⁺/A applied as catalyst for reaction of 1-hexene at 80 °C with H₂/CO = 1, at 10 atm was found as active for isomerization (ca. 90% of 2-hexene after 6 h) and relatively poor catalyst of hydroformylation (<10% of aldehydes). At the presence of stoichiometric amount of PPh₃ the yield of aldehydes increased up to 65%. The selectivity of the reaction was strongly dependent on the catalyst pre-treatment with CO or CO/H₂ mixture.