Transfer Catalyst Research Articles

Insect lipid transfer particle can facilitate net vectorial lipid transfer via a carrier-mediated mechanism.

The mechanism of facilitated lipid transfer by insect or mammalian plasma lipid transfer proteins has not been elucidated. Transfer catalysts may act as carriers of lipid between donor and acceptor lipoproteins or, alternatively, transfer may require formation of a ternary complex. This study was designed to determine if Manduca sexta hemolymph lipid transfer particle (LTP) can facilitate net vectorial transfer of lipid without concomitant contact between donor and acceptor lipoproteins and LTP. M. sexta [3H]diacylglycerol-high density lipophorin-larval ([3H]DAG-HDLp-L) and human low density lipoprotein (LDL) were covalently bound to Sepharose matrices and packed into separate columns. In incubations lacking LTP, greater than 98% of the recovered DAG remained associated with HDLp-L. An unrelated hemolymph storage protein, arylphorin, was unable to catalyze the transfer of DAG between solid-phase lipoproteins. Facilitated transfer of DAG from HDLp-L to LDL was observed when LTP was circulated between the columns. Under these conditions, facilitated transfer occurred at a rate of 2.24 ng of DAG/h (versus 0.16 microgram of DAG/h in the control), and after 16 h greater than 26% of recovered labeled DAG was transferred to LDL. This corresponds to a 14-fold rate enhancement induced by LTP. The LTP-specific transfer of DAG between physically separated lipoproteins demonstrates the ability of LTP to facilitate net lipid transfer via a carrier-mediated mechanism in the absence of a ternary complex involving donor, acceptor, and catalyst. In experiments aimed at assessing the relative contribution of ternary complex formation to DAG transfer, acceptor LDL was circulated with HDLp-L remaining immobilized. Under these conditions, LTP induced a 13-fold rate enhancement from 1.3 to 16.3 micrograms of DAG/h. The similar rate enhancements observed with both lipoproteins bound and only donor bound suggest the overall contribution of ternary complex formation to facilitated lipid transfer is insignificant. The described system should prove useful in mechanistic studies of other transfer proteins as well as studies of transfer of other lipids.

ChemInform Abstract: C‐Glycoside Syntheses. Part 2. Henry Condensations of 4,6‐O‐Alkylidene Pyranoses with a 1,3‐Proton Transfer Catalyst ‐ A Route to Blocked Aminomethyl‐C‐glycosides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

C-glycoside synthesis II: Henry condensations of 4,6-O-alkylidene pyranoses with a 1,3-proton transfer catalyst- a route to blocked aminomethyl-C-glycosides.

In the presence of a novel 1,3-proton transfer catalyst (2-hydroxypyridine (2-HP)/ 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/ molecular sieves), 4,6-O-benzylidene-D-glucopyranose (1),4,6-O-isopropylidene-D-mannose (12), and 4,6-O-isopropylidene-D-glucose (16) undergo Henry condensations with nitromethane in THF to give acetal protected nitromethyl C-glycopyranosides (2, 13, and 17, respectively), which were characterized as their O-acetyl derivatives (5, 15, and 18, respectively). The Henry product from 4,6-O-benzylidene-Dglucopyranose could be reduced, with retention of the 4,6-O-benzylidene protecting group, by a specially prepared form of elemental iron in aqueous tetrahydrofuran under CO2 to aminomethyl-C-glycopyranoside (16), characterized as N-acetyl, peracetyl, and N-Cbz derivatives (7, 8, 9, 10), and converted with diazonium salt to a triazene derivative (II). Nitroalkenes are only mechanistic intermediates in our condensations with nitromethane, but they undergo Michael additions with a second mole of nitromethane to give novel 5,7-O-alkylidene-1,2-deoxy-1 nitro-2-nitromethyl-D-heptitols (3 and 14) as side-products.

Moving-Bed Process for Residue Hydrotreating

A lot of chemical, petrochemical or refining processes require contact between three phases : a liquid feed, a gaseous reactant and a solid catalyst. Frequently, the catalyst activity is reduced by poisoning of active sites or coke deposits. This is especially the case with the processes used in heavy residual oils hydrotreating. As the catalyst life is reduced, the substitution or regeneration of the inactive catalyst is frequently necessary. Various solutions, such, as fixed beds used with swing reactors, fluidized beds, or moving beds with down flow of the catalyst and co-current or counter-current of the feed, can be proposed to perform this task with a minimum of time and production losses. A theoretical comparison between the performances of the various technologies has been made by means of a detailed simulation of the behaviour of each of these catalytic beds over a long period. Of course, in the models, some assumptions are necessary, like the ideal fluid and solids flows. Nevertheless, the problem remains complex because hydrodynamic, kinetic, catalyst deactivation, or thermal effects occur simultaneously, within the particules and/or in the bed as a whole. Various pilot plant data are of course used in order to build the kinetic part of the models. This comparison shows a marked advantage for the moving bed with counter-current flow between feed and catalyst owing to the systematic optimum use of the catalyst potential. Consequently, a series of experiments was made on various sized cold mockups designed to simulate counter-current movind beds. These experiments were necessary to demonstrate the feasability of the process, to specify the relations among gas and liquid superficial velocities, particles and fluids properties, and hydrodynamic regimes, and to develop the scale-up rules. The main goal is to secure a uniform distribution of the two fluids through out the whole bed of catalyst, and at the same time a regular progression of the solid particles during the sequential withdrawal. It is the reason why the movement of the solid and, moreover, the residence time distribution of the catalyst particles have been especially followed. To this end, a new technique has been developed to measure the concentration of magnetically marked particles. Furthermore, a specific effort has been devoted to technological problems such as selection and developement of special valves able to insure efficient tightness between the various sections at elevated temperatures and pressures in the presence of solid particles. Another study has been devoted to the operation of addition and withdrawal of the catalyst to and from the reactor running at high pressure and temperature. The solid flows and the catalyst transfer conditions have been carefully studied and tested. Finally a demonstration unit has been built at a semi-industrial scale in a mini-refinery. It was a convincing way to check all the conclusions drawed from the developement step with models, smaller scale pilots and mock-ups. As the fluids and the catalyst were real industrial products, the feasibility of the whole process has been demonstrated. Therefore, a new industrial process using the countercurrent moving bed is now available and permits a very efficient use of the catalyst particles.

Evaluation of magnesium aluminate spinel as a sulfur dioxide transfer catalyst

Infrared spectroscopy and vacuum microbalance techniques have been used to study the sulfation of magnesium aluminate spinel, MgAl 2O 4, by oxidation of sulfur dioxide in excess oxygen at temperatures from 300 to 550°C. The results have been compared with those previously obtained for sulfated Al 2O 3, TiO 2, ZrO 2 and MgO with a view to evaluating which material would be a superior SO x transfer catalyst. For low doses of sulfur dioxide, surface sulfates on spinel are mainly formed which are covalently bonded to the surface but, at higher doses, ionic sulfates are incorporated into the bulk of the spinel. At least two types of surface sulfate species have been identified and that formed preferentially at low coverages has the probable structure (−0) 3SO, as was found previously for SO 2 oxidation on Al 2O 3 and TiO 2. All sulfate species are thermally stable to evacuation up to 800°C but are removed between about 800–900°C. They are also readily removed following reduction in excess hydrogen in a relatively narrow temperature range from about 550 to 640°C. On a very low surface area spinel, only bulk sulfate is formed. Relative to the other oxides studied, sulfated spinel has a high thermal stability, the sulfates are easily reduced in hydrogen and it has a high sorption capacity by virtue of its ability to form bulk sulfate species (not observed under the same conditions on Al 2O 3, TiO 2, or ZrO 2). These favorable characteristics account for the use of spinel as a transfer catalyst for reducing SO x emissions.

Thermogravimetric study of bastnaesite under simulated SO x transfer conditions

One way of reducing sulphur oxide (SO x ) emissions from Fluidized Catalytic Cracking (FCC) units is to mix an SO x transfer catalyst with the FCC-catalyst. A basic understanding of the SO x transfer mechanism is needed if optimal SO x transfer conditions are to be found. With the aid of thermogravimetry the reactions of bastnaesite, essentially a mixture of rare-earth-element fluorocarbonates, were studied during SO x transfer to determine its properties as a potential SO x transfer catalyst. The fast absorption of SO 2 in air at 700°C gives a rare-earth sulphate compound. However, much of the cerium (III) is oxidized during absorption and CeO 2 is formed which is not active in SO x transfer. H 2S is the important gaseous species in the slow regeneration of the SO x transfer catalyst. The regeneration of the SO x transfer catalyst in the reactor/stripper has been found to involve the formation of gaseous sulphur and an oxosulphate. The rare-earth oxosulphates are considered to be the active SO 2 absorbing compounds in the regeneration of the cracking catalyst. According to the thermogravimetric measurements the rate of regeneration reaches a maximum when approximately one third of the SO 2 absorbing capacity has been utilized. Increased H 2S partial pressure, higher temperature and longer solids residence time in the (reactor)/stripper, are other factors that should increase the conversion of sulphate to sulphur and oxosulphate.

Reaktionssteuerung durch die Struktur eines Phasentransfer‐Katalysators bei Tribrommethyl‐Anion‐/Dibromcarben‐Umsetzungen

Control of Reactions with Tribromomethyl Anions/Dibromocarbene by the Nature of the Phase Transfer CatalystConversion of (substituted) allyl bromides with bromoform/sodium hydroxide/phase transfer catalyst may be directed towards dibromocarbene addition or substitution by tribromomethyl anion by choice of the catalyst. The observed effects (addition: substitution in the primary step variable between maximally 92:1 and 1:91) are by far the largest reported for specific catalyst influences. Small, hard cations favor the carbene route, sterically shielded and highly delocalized ones favor the substitution process.

ChemInform Abstract: Electrochemical Oxidation of Malonic Acid Esters in the Presence of Iodides as Transfer Catalysts.

AbstractElectrochemical oxidation of the malonic acid esters (I) in the corresponding alcohols (II) in the presence of iodides gives mixtures of the dimers (III) ‐ (V) and the trimer (VI).

Development and the Environment—A Third World Perspective

Sustainable economic development and the environment are the two sides of a coin. The World Bank as the largest financier of the Third World development must seek not only a decent return on its investment, but it must also ensure that development projects are appropriate and in the best interests of developing countries. To achieve these goals, the Third World must be allowed to make its own decisions on development issues. This requires the substantial dilution of the World Bank's power and an enhanced role for the Third World technical manpower to act as catalysts for development and technology transfer. Sustainable economic development will remain as a theoretical concept unless this orientation is brought about in the World Bank. Without changes, the World Bank has the potential of becoming the largest agent of environmental degradation in the world.

ChemInform Abstract: Synthesis of Z‐2‐Benzylidene‐4‐phenyl‐1,3‐diselenole from Metallic Selenium and Phenylacetylene Under Phase‐Transfer Catalysis.

AbstractThe title compound (III) is formed from metallic selenium (II) and phenylacetylene (I) in aqueous alkali only in the presence of a phase‐ transfer catalyst.

ChemInform Abstract: Reactivity and Application of Soluble and Polymer‐Supported Phase‐ Transfer Catalysts

ChemInformVolume 18, Issue 42 Reviews ChemInform Abstract: Reactivity and Application of Soluble and Polymer-Supported Phase- Transfer Catalysts F. MONTANARI, F. MONTANARI Centro CNR, Univ., Milano, ItalySearch for more papers by this authorD. LANDINI, D. LANDINI Centro CNR, Univ., Milano, ItalySearch for more papers by this authorA. MAIA, A. MAIA Centro CNR, Univ., Milano, ItalySearch for more papers by this authorS. QUICI, S. QUICI Centro CNR, Univ., Milano, ItalySearch for more papers by this authorP. L. ANELLI, P. L. ANELLI Centro CNR, Univ., Milano, ItalySearch for more papers by this author F. MONTANARI, F. MONTANARI Centro CNR, Univ., Milano, ItalySearch for more papers by this authorD. LANDINI, D. LANDINI Centro CNR, Univ., Milano, ItalySearch for more papers by this authorA. MAIA, A. MAIA Centro CNR, Univ., Milano, ItalySearch for more papers by this authorS. QUICI, S. QUICI Centro CNR, Univ., Milano, ItalySearch for more papers by this authorP. L. ANELLI, P. L. ANELLI Centro CNR, Univ., Milano, ItalySearch for more papers by this author First published: October 20, 1987 https://doi.org/10.1002/chin.198742378Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue42October 20, 1987 RelatedInformation

The structure and stability of sulfated alumina and titania

The oxidation of H 2S or SO 2 in excess O 2 over Al 2O 3 or TiO 2 (anatase) yields, for either catalyst under anhydrous conditions, an infrared spectrum which is characterized by an intense sharp band near 1380 cm −1 and a broad band or doublet near 1040 cm −1. The same spectrum arises from the impregnation of Al 2O 3 with either (NH 4) 2SO 4 or Al 2(SO 4) 3 · 18H 2O or of TiO 2 with (NH 4) 2SO 4 or TiOSO 4 and heating the dried mixture at 450 °C under vacuum. The sulfated surface does not exchange with 18O 2 but does with H 2 18O and only one new shifted high-wavenumber band is produced for partial or complete oxygen-18 exchange. The infrared spectrum changes in the presence of H 2O at 20 °C and resembles that of a more traditional bidentate type sulfate species and we postulate that, in the absence of OH groups or water the sulfate has a structure resembling ( M 3 O 3) S O [ M = Al or Ti], whereas in the presence of H 2O or excess surface OH groups this is converted to ▪ type groups, thus accounting for the increased Brønsted acidity. Finally, the sulfated Al 2O 3 surface is more thermally stable and more resistant to reduction in H 2 than is the TiO 2 surface and the ramifications are discussed in terms of the use of these oxides for SO x transfer catalysts or in air pollution abatement.

Reaction of catalytic enantioselective reductive aminolysis of δ 2-oxazolin-5-ones as a method of asymmetric synthesis of α-amino acids

This investigation is devoted to the interaction of Δ 2-oxazolin-5-ones, S(—)-α-phenylethy lamine and H 2 in the presence of PdCl 2 which yields α-phenylethylamides of acylamino acids of the S,S configuration, hydrolysis of the latter compounds resulting in the formation of optically pure amino acids and providing for chiral amine recycling. In DME, double bond saturation and ring opening in Δ 2-oxazolin-5-one occur within the catalytic complex sphere without the intermediate formation of saturated oxazolinones or unsaturated amides. In t-BuOH, saturated oxazolinones are formed as intermediates. The catalyst formed in situ was shown to be a zero-valent Pd complex with S(—)-α-phenylethylamine stabilized by substrate coordination. The stereochemical pathway of the reactions has been traced. Reductive aminolysis involves cis-addition of H 2, while in reductive methanolysis H 2 trarns-addition occurs. The suggested process mechanism accounts for the ratio of aminolysis and racemization rates for saturated oxazolinones and the ratio of diastereomers of α-phenylethylamides of acylamino acids obtained by reacting unsaturated Δ 2oxazolin-5-ones with S(—)-α-phenyl-ethylamine. In agreement with the postulated mechanism, the catalyst enantioselectivity is observed at the steps of substrate addition to the catalyst and proton transfer to the α-C-center, provided the process is carried out in DME. In the case of t-BuOH, the enantiodifferentiating action of the catalyst vanishes as a result of racemization, and process stereo selectivity appears at the step of saturated oxazolinone aminolysis with a chiral amine.

Hydrogen isotope exchange between fluoroform (CF3H) and water. 3. Catalysis by −OH-type anion exchange resins, and the effect of added dimethyl sulfoxide

Anion exchange resins like Rexyn 201(OH) and Amberlyst A-26 have been shown to be active catalysts for deuterium transfer between water and fluoroform. Under stirred slurry conditions at 50 °C the Rexyn 201 is 25 × more effective than NaOH on a per-hydroxide-ion basis. Addition of DMSO to the aqueous slurry produces an increase in Rexyn 201 reactivity, but the resin advantage over homogeneous −OH declines to zero by ~30 mol% DMSO. At 70 mol% DMSO the resin is less effective by a factor of ~100. Local fluoroform solubility and hydroxide ion solvation effects, including phase separation, in the pore liquid of the resin beads appear to be responsible for the observed behaviour.

Phase transfer and rhodium (I) catalyzed isomerization of allylaromatics and cognate systems

Allylaromatics undergo isomerization by the use of chlorodicarbonylrhodium(I) dimer as the metal catalyst and phase transfer catalysis conditions [benzene or methylene chloride as the organic phase, aqueous NaOH, and a quarternary ammonium salt as the phase transfer catalyst]. Isomerization of allyl amines and sulfones occurred as well, but the rhodium(I) complex was not required in the latter case.

Kinetics of polymerization of nitroethylene. II. Study of molecular weights (by cryoscopic method)

AbstractThe study of the polymerization of nitroethylene in methyl ethyl ketone and catalyzed by bases of the pyridine series—as reported in part I—was extended in the present work. The MW of a number of polymers was determined by a semimicro cryoscopic method, which is described in detail. Of all the reaction parameters, at 20°C., the MW was found to depend only on the initial monomer concentration. To account for this dependence, an additional step was included in the three‐step mechanism suggested earlier, namely, that of catalyst transfer to monomer. Spectroscopic examination of the polymers support the suggestion that termination, or transfer, is accompanied by ring closure and the formation of cyclic structures.

Studies in chain transfer. III. Determination of chain transfer coefficients from catalyzed polymerization data

AbstractBased on a general equation correlating DP and rate for catalyzed polymerization in the presence of solvents, an experimental method has been devised for determining all three transfer coefficients, viz. monomer transfer (CM), solvent transfer (CS), and catalyst transfer (CI), in a simple and straightforward way. Three types of methods are possible for solvent transfer determination: (1) by determining the slope of at constant 1 (catalyst): M (monomer) ratio; (2) by determining the intercept of at constant S/M; and (3) by direct use of the general equation, especially using a catalyst whose CI is known to be zero. It has been further shown that the existing method (slope of 1/P versus S/M) in uncatalyzed polymerization would give correct results for all solvents only over the range in which the rate of uncatalyzed polymerization is proportional to the square of monomer concentration. It has also been pointed out that, in systems in which the more usual rate equation, RP = KP (ki/kt)1/2I1/2M3/2 is valid, the slope of 1/P versus S/M (at constant I/M) would give correct CS values for catalyzed polymerization also.