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Polyester reinforced PTFE membranes with a nominal pore size of 0.02 μm are very effective in pervaporating HCl gas from hydrochloric acid solutions and cellulose hydrolysates. The efficiency of such membranes, which may be as high as 1.8x10−2 mmol HCl min−1 cm−2 at 40°C, is almost independent of the flow rate and the static pressure of the acidic solution but depends strongly on the acid concentration. At an acid concentration of 26% (w/v) the pervaporation of HCl is negligible at 40°C, but can be accelerated by increasing the temperature. A slow increase of temperature during the pervaporation process is proposed, as this promotes post-hydrolysis of the sugars. Lithium chloride induces structural changes in the membrane which increase efficiency without compromising performance. The use of this new technology in conjunction with the original Bergius process could improve the performance of the latter and reduce its overall costs. The use of the improved process for the hydrolysis of sugar cane bagasse could double the yields of sugar or alcohol per hectare of planted sugar cane.

Lithium chloride, in combination with commercial grade hydrochloric acid, is very effective in the hydrolysis of prehydrolysed sugar cane bagasse. After 10 min at 50°C the holocellulosic portion is completely dissolved and after 20 min most of the sugar oligomers are hydrolysed to monomers, making the time-and energy-consuming post-hydrolysis unnecessary. With longer reaction times the sugars start to reoligomerise and decompose. Zinc chloride is a milder promoter, requiring post-hydrolysis even after reaction for 30 min at 50°C. On the other hand, it does not decompose the sugars giving the highest sugar yields after prolonged reaction time and post-hydrolysis. Ferric chloride is mostly ineffective in the hydrolysis of cellulose but is a good promoter of the hydrolysis of the sugar oligomers, under the reaction conditions.

Ultrasound effectively promotes the hydrolysis of pre-hydrolysed sugar cane bagasse using 38% concentrated hydrochloric acid. In combination with lithium chloride, ultrasonic promotions as high as 62% were observed. Of the three frequencies (25, 35 and 40 kHz) studied, the lowest promoted the hydrolysis most effectively but, when in combination with lithium chloride, reoligomerised the sugars. The higher frequencies of 35 and 40 kHz required larger concentrations of lithium chloride for complete conversion. Irradiation with 40 kHz also promoted subsequent acid hydrolysis of the sugar oligomers.

It is shown that sol-gel alumina calcined at 400 0C is a very efficient catalyst for the epoxidation of cyclohexene and cyclooctene with aqueous 70 wt % hydrogen peroxide. The overall yield per g of catalyst was 0.28 mol of cyclohexene oxide in 5 cycles of 450 min each and 0.43 mol of cyclooctene oxide in 4 cycles of 750 min each. The selectivity for the epoxides was always better than 99%. However, the catalyst deactives slowly, which we believe is caused by a non-radical decomposition of hydrogen peroxide.

Commercial alumina looses some activity after the first epoxidation reaction of (S)-limonene with hydrogen peroxide, but maintains a good activity and a very high selectivity in the subsequent three reactions. After this its activity is strongly reduced, probably due to structural modifications. Aluminas obtained by sol-gel methods are normally less active than the commercial alumina. However, the use of monomeric aluminum sec-butoxide and of oxalic acid to form stable alumina mesophases allows a very active alumina to be obtained, which catalyses the epoxidation of the less reactive cyclohexene with hydrogen peroxide in 98% yield. Close to 50% of the active oxygen is used up in the formation of molecular oxygen.

A method for determination of tacticity in polypropylene (PP) using FTIR associated with multivariate analysis is presented. Blends of PP with known tacticity were prepared with isotactic, syndiotactic, and atactic polymer and analyzed by 13C-NMR. The FTIR spectra were recorded and processed through principal components regression (PCR) and partial least-squares regression (PLS), using information from several different portions of the spectra. The method was compared with the classical methods of tacticity determination by FTIR based on the intensities of the bands at 998 cm−1 (isotactic), 868 cm−1 (syndiotactic), and 975 cm−1 (internal standard), which are known to be dependent on the crystallinity of the polymer and, thus, affected by temperature and sample preparation. The models obtained with multivariate calibration, both with PCR and PLS, gave prediction errors up to fivefold smaller than that of the classical methods, and were also shown not to be heavily dependent on the bands that are affected by the crystallinity of the polymer, but rather on the methyl and methylene bendings at 1375 and 1462 cm−1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 734–745, 2002

Transesterification of soybean oil with methanol has been carried out in the presence of heterogenized alkylguanidines as catalysts. The alkylguanidines were anchored to modified polystyrene or siliceous MCM-41, encapsulated in the supercages of zeolite Y, or entrapped in SiO 2 sol-gel matrices. The catalytic activity of these catalysts was compared with that of their homogeneous counterparts, showing that the yields of methyl esters obtained in the homogeneous phase can be obtained with the guanidines anchored to the supports after longer reaction times. The catalysts prepared by immobilization of alkylguanidines in microporous systems showed diffusion restrictions for the vegetable oil as well as the low stability of the inorganic framework.

Impregnation of SiO2.Al2O3 (24.3% Al2O3 with 6% B2O3 increases the activity of supported Re2O7 in the ethenolysis of methyl oleate, but reduces the activity of CH3ReO3 on the same support. Re2O7/SiO2.Al2O3/B2O3-SnBu4 is shown to be an effective catalyst for the ethenolysis of methyl linoleate and of the methyl esters of olive oil, and can be recycled after calcination at least five times without loss of activity.

Titanium tetrachloride heterogenized on reduced TiO2 has been studied as a catalyst for ethylene polymerization. The catalyst has good storage stability and exhibits good activity for ethylene polymerization. The polymer chains grow linearly during ca. 1 h, giving an average molecular weight of up to 2.5 × 106 which indicates that practically no β-elimination occurs. The activity of the catalyst at 50°C, based on Ti(III), is 7.6 × 106 PE/mol Ti h bar and based on the quantity of polyethylene formed it is 1.25 × 106 g PE/mol Ti h bar. The molecular weight of the polymer can be controlled with the addition of hydrogen, under 0.5 bar hydrogen, polyethylene with a molecular weight of 411,000 and a relatively low polydispersity index of 2.2 is obtained. The catalyst shows good thermal stability; the Arrhenius activation energy is 31.8 kJ/mol for the polymerization. The catalyst is also active for propylene polymerization, giving 3 × 106 g PP/mol Ti h bar with the high isotacticity of 93%. © 1994 John Wiley & Sons, Inc.

Alkanes ( n -heptane, 2- and 3-methylhexane, cis - and trans -decalin) are readily oxidized under air in acetonitrile by the O 2 - H 2 O 2 - PCA - VO 3 − reagent at room temperature to produce alkyl hydroperoxides as main products as well as minor amounts of the corresponding alcohols and carbonyl compounds. The site selectivities of the reactions are very similar to those observed with hydroxylation of the alkanes with hydrogen peroxide under UV irradiation. The proposed mechanism involves the catalytic formation of hydroxyl radicals from hydrogen peroxide which abstract hydrogen atoms from the alkanes. The alkyl radicals react rapidly with molecular oxygen to produce peroxyl radicals which are transformed mainly into the hydroperoxides.

Zeolites are viewed by some as the “philosopher's stone” of modern chemistry.[1] They are more or less indispensable in oil refining and petrochemicals manufacture where they are widely applied as solid acid catalysts. More recently attention has been focused on their use in the manufacture of fine chemicals. The synthetic utility of zeolites and related molecular sieves (zeotypes) has been considerably extended by the incorporation of redox metals into their frameworks. The resulting redox molecular sieves catalyze a variety of selective oxidations under mild conditions in the liquid phase. Their structural diversity–including variation of the redox metal, incorporation of metal complexes, and the size and polarity of the micropores–provides the possibility of designing tailor-made solid catalysts (“mineral enzymes”) for liquid-phase oxidations with clean oxidants such as O2, H2O2, and RO2H. Hence, they have enormous potential in industrial organic synthesis as environmentally friendly alternatives to traditional oxidations employing inorganic oxidants in stoichiometric amounts. A primary aim of this review is to familiarize organic chemists with the synthetic potential of redox molecular sieves. An outline of their synthesis, structures, and chemical properties, highlighting their unique advantages, is followed by a discussion of general (mechanistic) features that influence the choice of a suitable catalyst for a particular type of oxidation. The main part of the review deals with the oxidation of various substrates of synthetic interest–such as alkanes, alkenes, (alkyl)arenes, alcohols, and amines–and emphasizes the advantages of redox molecular sieves (including selectivity and stability) over their homogeneous counterparts. New directions towards truly biomimetic solid catalysts, for example zeolite-encapsulated chiral metal complexes as heterogeneous catalysts for asymmetric oxidations, are high-lighted.

The formation of fatty acid methyl esters by transesterification with methanol can be monitored by1H nuclear magnetic resonance spectroscopy; this accurate determination is simpler than chromatographic methods.

Die Cooligomerisierung von Methylencyclopropan (1) mit Allen, 1,1-Dimethylallen oder 1,2-Cyclononadien an Palladium(0)-Katalysatoren liefert nur mit Allen rein cyclische Produkte: 1,3-Dimethylencyclopentan (3) und 1,3,5-Trimethylencycloheptan (4). Mit 1,1-Dimethylallen entstehen dagegen zu etwa gleichen Teilen 1-Isopropyliden-3-methylencyclopentan (6) und 2,5-Dimethyl-3-methylen-1,5-hexadien (7), wahrend mit 1,2-Cyclononadien 2-(2-Methyl-2-propenyl)-(8) und 2-(2-Methyl-1-propenyl)-1,3-cyclononadien (9) gebildet werden. Reactions of Methylenecyclopropane, III. Cooligomerization of Methylenecyclopropane with Allenes on Palladium(0) Catalysts The cooligomerization of methylenecyclopropane (1) with allene, 1,1-dimethylallene or 1,2-cyclononadiene on a palladium(0) catalyst has been investigated. Exclusive formation of cyclic products, viz 1,3-dimethylenecyclopentane (3) and 1,3,5-trimethylenecycloheptane (4), is observed only in the reaction involving allene. In the case of 1,1-dimethylallene, approximately equal amounts of 1-isopropylidene-3-methylenecyclopentane (6) and 2,5-dimethyl-3-methylene-1,5-hexadiene (7) are formed while reaction with 1,2-cyclononadiene leads to 2-(2-methyl-2-propenyl)- (8) and 2-(2-methyl-1-propenyl)-1,3-cyclononadiene (9).

3,3-Dialkylcyclopropene [3-Ethyl-3-methylcyclopropen (2), 3,3-Diethylcyclopropen (3) und Spiro 4.2]hept-1-en (4) reagieren an phosphanfreien Palladium (0)-Katalysatoren zu den entsprechenden trans-Tricyclo[3.1.0.02,4]hexan-Derivaten 6, 7 bzw. 8 und zu den Pentacyclo-[9.1.0.02,4.05,7.08,10]dodecan-Derivaten 10, 11 und 12. Triisopropylphosphan-haltige Palladium-(0)-Katalysatoren liefern dagegen selektiv die Tetracyclo[6.1.0.02,4.05,7]nonan-Derivate 14, 15 und 16 mit uber 80% Ausbeute. Reactions of Cyclopropenes, V1) Cyclooligomerisations of 3,3-Dialkylcyclopropenes at Palladium (0) Catalysts At Phosphane free palladium(0) catalysts 3,3-dialkylcyclopropenes [3-ethyl-3-methylcyclopropene (2), 3,3-diethylcyclopropene (3), and spiro[4.2]hept-1-ene (4)] are cyclooligomerised to give the trans-tricyclo[3.1.0.02,4]hexane derivatives 6, 7, and 9, and the pentacyclo[9.1.0.02,4.05,7.08,10]-dodecane derivatives 10, 11, and 12. Contrary to this at triisopropylphosphane modified palladium(0) catalysts the tetracyclo[6.1.0.02,4.05,7]nonane derivatives 14, 15 and 16 are formed selectively in more than 80% yield.

Triorganylphosphan-modifizierte Palladium(0)-Verbindungen katalysieren die Codimerisierung von Methylencyclopropan (1) mit Ethylen, Norbornen, Dicyclopentadien oder Norbornadien unter Offnung des Dreirings zwischen C2 und C3 zu den substituierten Methylencyclopentan-Derivaten 3 – 7. 1-Alkene, wie auch Alkene mit mittelstandiger Doppelbindung oder Cycloalkene, die keine gespannte Doppelbindung enthalten, gehen diese Reaktion nicht ein. Ebensowenig erfolgreich waren Versuche einer Codimerisierung von 1 mit Alkinen oder 1,3-Butadien. Reactions of Methylenecyclopropane, IV. Palladium(0)-catalyzed Codimerization of Methylenecyclopropane with Alkenes Triorganylphosphane-modified palladium(0) compounds catalyze the codimerization of methylenecyclopropane (1) with ethylene, norbornene, dicyclopentadiene or norbornadiene to give substituted methylenecyclopentane derivatives 3 – 7. In all of these reactions the three-membered ring of 1 is opened between C2 and C3. 1-Alkenes, alkenes with an internal double bond and unstrained cycloalkenes as well as alkynes and 1,3-butadiene do not react in this manner.

Triorganylphosphan-haltige Palladium(0)-Verbindungen katalysieren die Codimerisierung des Methylencyclopropans (1) mit Acrylsaure-, trans-Crotonsaure- oder trans-Zimtsaure-methyl-estern sowie mit Fumarsaure-diethylester und Maleinsaure-dimethylester zu den entsprechenden Methylencyclopentancarbonsaureestern 3, 4, 5 bzw. den Methylencyclopentadicarbonsaureestern 12. Mit Maleinsaure-diethylester entstehen neben 12b auch Cooligomere, die zwei mol 1 und ein (cis/trans-14) oder zwei mol (cis/trans-15) des Diesters enthalten. Reactions of Methylenecyclopropanes, V1) Palladium (0)-catalyzed Codimerisation of Methylenecyclopropane with Methyl Acrylates and 1,2-Ethylenedicarbonic Esters Triorganylphosphane-modified palladium(0) compounds catalyze the codimerization of methylenecyclopropane (1) with methyl acrylate, methyl trans-crotonate or trans-cinnamate to give the methylenecyclopentanecarboxylic esters 3, 4, 5; diethyl fumarate or dimethyl maleate and 1 lead to the methylenecyclopentanedicarbonic esters 12. With diethyl maleate besides cis/trans- 12b also oligomers containing two mols of 1 and one cis/trans-14) or two mols of the diester cis/trans-15 are formed.

Pyridin (py) bildet mit den Methyl(methylthio)boranen (CH3)3−nB(SCH3)n stabilere 1: 1-Addukte als Timethylamin. Die Aciditat der Borane sinkt mit steigender Zahl von CH3S-Gruppen im Molekul. Mit CH3Cl2 reagieren die Pyridin-Addukte zu den Boroniumsalzen [(CH 3)2Bpy2]Cl bzw. [CH3B(SCH3)py2]Cl. Aus B(SCH3)3, 2,2′-Bipyridyl (bpy) und CH2Cl2 wurde [(CH3S)2Bbpy]Cl erhalten. Die Bildung der Boroniumsalze wird diskutiert. Contributions to the Chemistry of Boron, LXVI. Amine Adducts and Boronium Salts from Methyl(methylthio) boranes Pyridine and methyl(Methylthio) boranes yield 1: 1 adducts which are more stable than the corresponding trimethylamine adducts. The acidity of the boranes under consideration decreases as the number of CH3S groups increases. CH2Cl2 reacts with the pyridine adducts to form the boronium salts [(CH3)2Bpy2]Cl and [ CH3B(SCH3py2]Cl, respectively. [(CH3S)2-Bbpy]Cl is obtained from ( B(SCH3)3, 2,2′-bipyridyl and CH2Cl2. The formation of the boronium salts is discussed.

A new method for the rapid preparation of methyl esters from vegetable oils and fats, using tetramethylguanidine as catalyst, has been developed. This method is compared with the traditional method (Ce 2–66, using 20% BF3 in methanol) and that proposed by Hartman and Lago (using NH4Cl/H2SO4 in methanol). It is shown that the new method produces the methyl esters in quantitative yields and has certain advantages, as it is simpler, cheaper and does not result in isomerization of the fatty acids.