Tin Catalyst Research Articles

Inside Back Cover: On the Catalysis of the Cycloisomerization of 1,6‐Dienes with Tin(IV) Salts: The Important Role of a Water Molecule (ChemCatChem 2/2014)

Water gets the cat out of the tin The cover picture shows a key transition state involved in the cyclisation of 1,6-dienes catalysed by a tin catalyst. In the computations and experiments presented in their Full Paper on p. 500 ff., P. Nava et al. explain how a water molecule is necessary for reaction completion and catalyst regeneration. It is shown that the tin cation does not directly participate in the reaction but sits aside on an ester lone pair of the diene. A water molecule, strongly acidic owing to its coordination to the metal, is positioned perfectly over the substrate and transfers protons at the right places along the cyclisation process (orange dots). The catalysis and its diastereoselectivity are determined completely by this coordinated water molecule.

Nanostructured Tin Catalysts for Selective Electrochemical Reduction of Carbon Dioxide to Formate

High surface area tin oxide nanocrystals prepared by a facile hydrothermal method are evaluated as electrocatalysts toward CO2 reduction to formate. At these novel nanostructured tin catalysts, CO2 reduction occurs selectively to formate at overpotentials as low as ∼340 mV. In aqueous NaHCO3 solutions, maximum Faradaic efficiencies for formate production of >93% have been reached with high stability and current densities of >10 mA/cm(2) on graphene supports. The notable reactivity toward CO2 reduction achieved here may arise from a compromise between the strength of the interaction between CO2(•-) and the nanoscale tin surface and subsequent kinetic activation toward protonation and further reduction.

Enhanced activity of MCM-48 based tin catalyst for synthesis of 3-methylbut-3-en-1-ol by adjusting the mesochannel environment

In the present work, tin incorporated MCM-48 catalysts were prepared by different strategies and applied in the synthesis of MB-AC and MBOH. The performance of the catalysts is strongly affected by mesochannel environment and acid texture. The organic-graft method (Sn-G-MCM-48) can modify the mesochannel environment and enhance the acid intensity and concentration (0.28mmol/gcat), resulting in the improvement of the catalytic activity to the target reactions. The total yield of MB-AC and MBOH is as much as 68.4% over Sn-G-MCM-48 under mild conditions.

A DFT Study of the Conversion of CO2in Dimethylcarbonate Catalyzed by Sn(IV) Alkoxides

Density functional theory (DFT) calculations of intermediates and transition states of the reaction between CO2 and methanol over different R2Sn(OCH3)2 catalysts (R = alkyl, phenyl and halogens) were carried out. The interaction of the CO2 molecule with the tin catalyst was controlled by the entropic term, being disfavored at room temperature and atmospheric pressure. On the other hand, the insertion of the CO2 molecule into the Sn–OCH3 bond is thermodynamic favorable for all the catalysts studied. The computed free-energy of activation varied with the nature of the substituent R. Phenyl groups exhibit the smallest barrier, whereas halogen atoms the highest. Alkyl groups present intermediate barriers. The results are in agreement with recent experimental results that indicated a higher turnover number (TON) for dimethylcarbonate (DMC) formation when Ph2SnO was used as catalyst. The whole mechanistic scheme was then computed for phenyl and methyl as substituents, considering a dimer tin species.

A green approach for the production of biodiesel from fatty acids of corn deodorizer distillate

A novel alginic acid derived tin catalyst, tin alginate (Sn–Alg), was successfully synthesized, characterized and applied for methyl esterification.

Kinetic investigation of the polymerization of D,L-lactide and glycolide via differential scanning calorimetry

The kinetics of polymerization of D,L-lactide and glycolide are studied via differential scanning calorimetry at different temperatures and concentrations of the catalyst tin octanoate. For the polymerization of D,L-lactide and glycolide, the enthalpies are determined to be −17 ± 1.5 and 16.5 ± 1.5 kJ/mol, respectively. The time to attain reaction equilibration decreases from 300 to 100 min with an increase in temperature from 200 to 220°C. The time of reaction at 200°C decreases from 280 to 100 min as the concentration of the catalyst is increased from 500 to 830 ppm. When the polymerization of glycolide is conducted at temperatures below 200°C, the reaction is accompanied by crystallization of polyglycolide and an increase in the total enthalpy of the process.

Role of end-groups and catalyst in polyester cyclodepolymerization and cycle-chain equilibria

The influence of polyesters end-groups on cyclic oligoester formation is investigated using a series of hydroxy-, carboxy- and methylester-terminated aliphatic polyesters, in the presence of various ester interchange catalysts. The presence of hydroxy end-groups is the preponderant factor on cyclodepolymerization kinetics. This indicates that the main reaction is the intramolecular hydroxy–ester interchange reaction between hydroxy end-groups and ester functions in the chain. Carboxy-ester and ester–ester interchanges play a minor role, as the cycle-chain equilibrium is reached only very slowly when carboxy- or ester-terminated polyesters are reacted. High temperature and the presence of tin catalysts are also favorable factors, while, as expected, dilution shifts the equilibrium toward the formation of high yields of cyclic oligoesters. A mechanism is proposed, based on the reverse of the “coordination-insertion” mechanism established for the ring-opening polymerization of lactones.

Long-chain polyesters and polyamides from biochemically derived fatty acids

Here, we describe the use of biochemically derived fatty acid derivatives (ω- and ω-1 hydroxy fatty acid methyl esters) as starting materials for renewable polyesters and polyamides. The required long-chain monomers were obtained by chemical derivatization of biochemically derived fatty acids. Thus, a long chain diester and a ω-amino fatty acid methyl ester were synthesized and used to prepare polyester PE 32–34:32–34 and polyamide PA 16. The polyester was prepared by transesterification using 5mol% of the catalyst tin(II) 2-ethylhexanoate (Sn(Oct)2), leading to an average molecular weight of Mn=7.4kDa and a melting point of 109°C. PA 16 was prepared by amidation using TBD as catalyst and resulting in an average molecular weight of Mn=20.3kDa and a melting point of 166°C.

Dehydrocoupling of amine boranes via tin(IV) and tin(II) catalysts

Catalytic dehydrocoupling of primary and secondary amine boranes and ammonia borane using tin(IV) and tin(II) catalysts is presented. These tin compounds have been demonstrated to dehydrocouple phosphines where catalytic activity was dependent on metal oxidation state. In contrast, the mechanism of amine borane dehydrocoupling appears to be substrate dependent. The most sterically encumbered substrate, tBuNH2BH3, appears to engage in β-hydrogen elimination based on the observation of tBuN = BH2, whereas Me2NHBH3 appears to be involved in a chain-growth process as evidenced by linear diborazane and the absence of amino borane. Though these tin catalysts are moderately active in the spectrum of amine borane dehydrocoupling catalysts, the dependence of mechanism on substrate appears to be unique.

Heterogeneous Tin Catalysts Applied to the Esterification and Transesterification Reactions

The interest in the development of efficient and environmentally benign catalysts for esters synthesis has increased exponentially, mainly due to the demand for biodiesel. In general, fatty esters are used as bioadditive, cosmetic ingredients, polymers, and, more recently, biofuel. Nevertheless, most of the production processes use nonrecyclable and homogenous alkaline catalysts, which results in the reactors corrosion, large generation of effluents, and residues on the steps of separation and catalyst neutralization. Heterogeneous acid catalysts can answer these demands and are an environmentally benign alternative extensively explored. Remarkably, solid acid catalysts based on tin have been shown highly attractive for the biodiesel production, mainly via FFA esterification reactions. This review describes important features related to be the synthesis, stability to, and activity of heterogeneous tin catalysts in biodiesel production reactions.

Kinetic Analysis of the Living Ring‐Opening Polymerisation of L‐Lactide with Tin(II) Initiators

AbstractA general kinetic model to describe the initiation and monomer depletion phases of the metal‐catalysed living ring‐opening polymerisation (ROP) of cyclic esters is presented. The model allows the description of ROP reactions in terms of rates of initiation (ki) and propagation (kp) and is in principle applicable to all metal‐mediated ROP reactions. The model was validated by curve‐fitting of data obtained for the living ROP of L‐lactide catalysed by a variety of tin(II) catalysts. The catalyst was chosen from tin(II) diisopropoxide or from heteroleptic complexes of the type (LOx)Sn(OR), in which (LOx) is an amino or aminoether phenolate ancillary ligand and OR is isopropoxide or O‐tert‐butyl lactate. All tested catalysts promote the controlled, living polymerisation of L‐lactide. No initiation phase was discerned for any of the considered catalysts in polymerisations performed at 60 °C, whereas at 25 °C initiation is an order of magnitude slower than propagation and, therefore, the inclusion of ki is required for an accurate kinetic description. Tin diisopropoxide is polymeric in the solid state, but it is dimeric in toluene solution. [Sn(OiPr)2]2 is an excellent example of an aggregated catalyst precursor and is catalytically more active than the heteroleptic (LOx)Sn(OR). As dissociation of the inactive dimer into a catalytically active monomeric complex is required, half‐order dependence on [metal] is to be expected and was indeed found. A method to estimate the related monomer–dimer equilibrium constant KD under polymerisation conditions is also provided.

An ecotoxicological study on tin- and bismuth-catalysed PDMS based coatings containing a surface-active polymer

Novel films were prepared by condensation curing reaction of a poly(dimethyl siloxane) (PDMS) matrix with bismuth neodecanoate and dibutyltin diacetate catalysts. An ecotoxicological study was performed on the leachates of the coatings using the bacterium Vibrio fischeri, the unicellular alga Dunaliella tertiolecta, the crustacean Artemia salina and the fish Sparus aurata (larvae) as testing organisms. A copper-based self-polishing commercial paint was also tested as reference. The results showed that the tin-catalysed coatings and the copper paint were highly toxic against at least two of the four test organisms, whereas bismuth-catalysed coatings did not show any toxic effect. Moreover, the same biological assessment was also carried out on PDMS coatings containing a surface-active fluorinated polymer. The toxicity of the entire polymeric system resulted only from the tin catalyst used for the condensation curing reaction, as the bismuth catalysed coatings incorporating the surface-active polymer remained atoxic toward all the tested organisms.

Micromachined catalytic combustion type gas sensor for hydrogen detection

A catalytic combustion hydrogen sensor has been fabricated using the microelectromechanical system technology. The application of hafnium oxide thin films as the insulating layer has been deposited by electron beam evaporation. The semiconductor combustion catalyst tin oxide layer was prepared by chemical vapour deposition. It is a novel application of semiconductor material to a catalytic combustion gas sensor. The resistivity of hafnium dioxide thin film is about 3 × 1012 Ω cm at 900°C. Both the sensing elements and the reference elements could be connected in a suitable circuit such as a Wheatstone configuration with low power consumption. The catalytic combustion sensor shows high response to hydrogen at an operating voltage of 4 V and has a higher relative sensitivity and a good linearity for concentrations of hydrogen ranging from 0 to 4% in volume. Good consistency and high accuracy of the micromachined catalytic combustion gas sensor were achieved.

Preparation of High-Molecular-Weight Poly(glycolic acid) by Direct Melt Polycondensation from Glycolic Acid

Relatively high molecular weight poly(glycolic acid)(PGA) was prepared by improved melting polycondensation of glycolic acid. Firstly, two kinds of catalyst, zinc acetate dihydrate and tin dichloride dehydrate, were utilized respectively, and a selection was made according to the molecular weight of final product. It has been found that the tin catalyst was the better one. Then the catalyst usage, the heating program, the polymerization time, as well as the vacuum condition were optimized. It was found that the high vacuum at 220~230°C contributed much to the molecular weight to the polymer, however, the polymerization time should be less than 1.5hr to avoid the discolor of the product. Finally, the PGA with a weight average molecular weight of 45,000g/mol were obtained directly without solid phase polycondensation, which was rather higher than some reported previously. The structure and properties of PGA were also characterized by means of intrinsic viscosity, FTIR, NMR and DSC testing.

Novel and Highly Efficient SnBr2-Catalyzed Esterification Reactions of Fatty Acids: The Notable Anion Ligand Effect

In this work, the efficiency of Lewis acid catalysts, SnX2 (X = F−, Cl−, Br−, or −OAc), was investigated on the esterification reactions of fatty acids (i.e., myristic, palmitic, stearic, oleic, linoleic, and linoleic) with different alcohols (i.e., methyl, ethyl, propyl, isopropyl, and butyl alcohol). Tin(II) bromide was the most active catalyst in all reactions studied. We investigated the effects of main reaction parameters, such as catalyst concentration, temperature, and nature of alcohol and fatty acid. The highest activity of SnBr2 catalyst was discussed in terms of its lower activation energy, higher Lewis acid strength, and higher softness of anionic ligand. Finally, the SnBr2 catalyst can be easily recovered and reused without loss of catalytic activity. Effect of the tin catalyst nature on the oleic acid esterification with ethyl alcohol.

Evaluating Poly(lactic acid) Fiber Reinforcement with Modified Tannins

PLA fibers with high tannin content are prepared by melt spinning PLA with tannin acetate (TanAc) prepared from a condensed tannin. PLA with up to 50% TanAc content can be readily processed, giving melt spun fibers suitable for further processing as textile fibers or for carbonization. The PLA molecular weight profile is not impacted by blending with TanAc. Melt processing does not de-esterify the TanAc nor lead to transesterification between tannin and PLA chains in the presence of a tin catalyst. PLA polymer properties and NMR relaxation parameters suggest higher TanAc content gives greater change to PLA molecular mobility and reduced crystallinity, particularly in the presence of the transesterification catalyst.

Sn–bentonite-induced Baeyer–Villiger oxidation of 2-heptylcyclopentanone to δ-dodecalactone with aqueous hydrogen peroxide

A tin ion-exchanged bentonite seems to be a rather efficient and highly selective catalyst for Baeyer–Villiger oxidation of 2-heptylcyclopentanone to δ-dodecalactone using aqueous hydrogen peroxide (35 wt%) as a clean oxidant. The bentonite-supported tin catalyst was characterized by IR spectroscopy, X-ray diffraction spectroscopy, and scanning electron microscopy. Methanesulfonic acid and sodium dodecyl sulfate promoted conversion of 2-heptylcyclopentanone to δ-dodecalactone in high (81 %) yield.

Recycling of polyamide (PA) from scrap tires as composites and blends

Mechanical recycling is a way to decrease trouble caused by polymeric waste such as residues of polyamide derived from milling of scrap tires. However, mechanical recycling of polymeric materials is not a trivial process, depending strongly of degradation stage and degree of contamination of the wastes. The aim of this study was evaluate the possibility of mechanical recycling of polyamide waste (W-PA) derived from scrap tires in the form of composites with glass fiber and blends with polyethylene terephthalate (PET) wastes (W-PET). W-PA was previously treated for separation of rubber particles and processed by extrusion for preparation of composites with glass fiber and by reactive extrusion with tin catalyst for preparation of blends with W-PET. The reinforcement of glass fiber produced excellent improvement of mechanical properties of W-PA, while the best result of blends W-PA/W-PET was verified for composition with 25/75wt%.

Preparation of Cellulose Stearate and Cellulose Acetate Stearate in 1-Butyl-3-Methylimidazolium Chloride

Cellulose stearates were prepared in a 1-butyl-3-metylimidazolium chloride ionic liquid. The addition of base pyridine as well as catalyst Tin octoate sufficiently increases the degree of hydroxyl group substitution. The new path for preparation of cellulose mixed esters, namely cellulose acetate stearate (CAS), is performed. The 1H NMR data confirmed the structure of obtained mono- and mix- cellulose esters.

Reversible hydrogen storage properties of NaAlH4 enhanced with TiN catalyst

Hydrogen storage properties of commercial NaAlH4 doped efficient TiN catalyst have been systematically investigated. The dehydrogenation and reversibility of the 2mol% TiN-doped NaAlH4 (2%TiN–NaAlH4) system have been studied. It is found that TiN catalyst improves the dehydrogenation kinetics and decreases the dehydrogenation temperature of NaAlH4. Interestingly, the onset dehydrogenation temperature of 2%TiN–NaAlH4 system gets lowered to about 130.0°C with a faster kinetics, and the dehydrogenation rate reaches a maximum value at 183.5°C. The apparent activation energy for the first and the second dehydrogenation step of TiN–NaAlH4 system is estimated to be 91.70kJmol−1 and 99.93kJmol−1, respectively. The dehydrogenation and hydrogenation behaviors of 2%TiN–NaAlH4 are investigated under different hydrogen pressures using high-pressure differential scanning calorimetry (HP-DSC). The 2%TiN–NaAlH4 system exhibits excellent reversibility at moderate conditions. Moreover, the dehydrogenation and hydrogenation processes of the 2%TiN–NaAlH4 system are also discussed.