Heteropolyacids as catalysts for synthesis of methyl tert-butyl ether

The influence of the composition and structure of heteropolyacids (HPA) on their catalytic activity in the liquid phase synthesis of methyl tert-butyl ether (MTBE) at 42 °C has been studied. The activity of HPA is compared with that of other acid catalysts. The most active are HPA's of the Dawson structure, then come HPA's of the Keggin and Dexter-Silverton structures. HPA salts have low activity in the synthesis of MTBE.

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() () 42°C. . , -. .

     

N-to-C solid-phase peptide and peptide trifluoromethylketone synthesis using amino acid tert-butyl esters

Solid-phase peptide synthesis in the N-to-C direction, opposite to the classical C-to-N direction of peptide synthesis, provides the synthetically versatile C-terminal carboxyl group for further modification into C-terminally modified peptide mimetics. These are of general interest as potential bioactive agents, particularly as protease inhibitors. Elaboration of peptide mimetics on the solid-phase would facilitate synthesis of peptide mimetic combinatorial libraries. This report describes an effective strategy for solid-phase inverse peptide synthesis based on readily available amino acid tert-butyl esters. The potential of this approach for peptide mimetic synthesis is demonstrated by the solid-phase synthesis of two peptide trifluoromethylketones.     

Dual capillary gas chromatographic analysis of alcohols and methyl tert-butyl ether in gasolines

A gas chromatographic method has been developed for the identification and direct determination of alcohols and methyl tert-butyl ether (MTBE) in gasolines. The technique involves simultaneous injection of the gasoline without any sample preparation onto two fused silica capillary columns of differing polarities. The method permits simultaneous determinations of methanol, ethanol, 2-propanol, tert-butanol, 1-propanol, sec-butanol, 1-butanol, and MTBE. By using an automatic sampler in combination with electronic pressure programming and BASIC programming, the determinations were performed automatically and reproducibly with a relatively short analysis time.     

Simple and efficient synthesis of thysanone methyl ether

The synthesis of thysanone methyl ether is achieved by employing semivioxanthin methyl ether, which in turn is prepared by the tandem Michael addition of an anion of orsellinate to a substituted dihydropyrone.     

Highly efficient preparation of aryl beta-diketo acids with tert-butyl methyl oxalate

An improved and efficient oxalylation of aryl methyl ketones was accomplished with tert-butyl methyl oxalate. This is the key step in constructing the pharmacophore of aryl beta-diketo acids, which represent a promising new class of HIV-1 integrase inhibitors. Structurally diverse aryl beta-diketo acids, including bisdiketo acids, can be prepared rapidly in impressive yields under mild conditions with this method. Advantages over conventional methods with dimethyl (or diethyl) oxalate were observed in both yield and reaction time.     

A convenient synthesis of amino acid methyl esters

A series of amino acid methyl ester hydrochlorides were prepared in good to excellent yields by the room temperature reaction of amino acids with methanol in the presence of trimethylchlorosilane. This method is not only compatible with natural amino acids, but also with other aromatic and aliphatic amino acids.     

Decomposition of methyl tert-butyl ether on zeolites

The H-forms of mordenite, ZSM-11 and ZSM-5 zeolites were employed for the decomposition of methyl tert-butyl ether to methanol and isobutene. It was found that even at low temperatures the zeolites exhibit an extremely high and relatively very stable activity and selectivity in this decomposition compared with the amorphous silica-based catalysts.

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- ZSM-11 ZSM-5 -.- . , , , .

     

Determination of low level methyl tert-butyl ether, ethyl tert-butyl ether and methyl tert-amyl ether in human urine by HS-SPME gas chromatography/mass spectrometry

Methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) are oxygenated compounds added to gasoline to enhance octane rating and to improve combustion. They may be found as pollutants of living and working environments. In this work a robotized method for the quantification of low level MTBE, ETBE and TAME in human urine was developed and validated. The analytes were sampled in the headspace of urine by SPME in the presence of MTBE-d12 as internal standard. Different fibers were compared for their linearity and extraction efficiency: carboxen/polydimethylsiloxane, polydimethylsiloxane/divinylbenzene, and polydimethylsiloxane. The first, although highly efficient, was discarded due to deviation of linearity for competitive displacement, and the polydimethylsiloxane/divinylbenzene fiber was chosen instead. The analysis was performed by GC/MS operating in the electron impact mode. The method is very specific, with range of linearity 30-4600 ng L⁻¹, within- and between-run precision, as coefficient of variation, <22 and <16%, accuracy within 20% the theoretical level, and limit of detection of 6 ng L⁻¹ for all the analytes. The influence of the matrix on the quantification of these ethers was evaluated analysing the specimens of seven traffic policemen exposed to autovehicular emissions: using the calibration curve and the method of standard additions comparable levels of MTBE (68-528 ng L⁻¹), ETBE (<6 ng L⁻¹), and TAME (<6 ng L⁻¹) were obtained.     

Biomimetic synthesis of esters of natural amino acids

A method for the synthesis of Gly, Ala, Phe, and Thr esters is proposed and considered as being a stage of possible biomimetic synthesis of peptides. The methyl esters of the said amino acids are obtained via intervention of 2‐hydroxypropyl phosphonate. The resulting aminoacyl phosphonates reacts with methanol to produce the amino acid methyl esters, with the release of phosphoric acid. The reaction is carried out at room temperature in water. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:252–255, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20427     

An efficient chiral synthesis of fluoro-containing amino acids: N-benzyloxycarbonyl-2-amino-4,4-difluorobutyric acid methyl ester and its analogs

Fluoro-containing amino acids, N-benzyloxycarbonyl-2-amino-4,4-difluorobutyric acid methyl ester and analogs, were prepared in high enantiomeric excess. Incorporation of 2-amino-4,4-difluoro butyric acid as P1 group provided a potent HCV NS3 protease inhibitor.     

An efficient method for demethylation of aryl methyl ethers

A new efficient method for demethylation of aryl methyl ethers using iodocyclohexane in DMF under reflux condition is described.     

An efficient synthesis of silyl ethers of primary alcohols, secondary alcohols, phenols and oximes with a hydrosilane using InBr3 as a catalyst

An efficient method for the preparation of silyl ethers by InBr₃ catalyzed silylation of primary alcohols, secondary alcohols, phenols and oxime with a hydrosilane is described.     

An efficient one-pot synthesis of unsymmetrical ethers: a directly reductive deoxygenation of esters using an InBr3/Et3SiH catalytic system

This study describes a novel one-pot procedure for a directly reductive conversion of the carbonyl function of esters to the corresponding ethers by Et3SiH in the presence of a catalytic amount of InBr3.     

Kinetics of liquid phase synthesis of methyl tert-butyl ether from tert-butyl alcohol and methanol catalyzed by ion exchange resin

Synthesis of methyl tert-butyl ether (abbreviated as MTBE) from methanol (MeOH) and tert-butyl alcohol (TBA) in the liquid phase was studied by using Amberlyst 15 in the H⁺ form as an acid catalyst. Experiments were carried out in a stirred batch reactor at different temperatures (313, 318, and 323 K) under atmospheric pressure. It was found that catalyst sizes and rotation speeds had no significant effects on reaction rates. Mechanism studies showed that three reactions took place simultaneously. It was also found that dehydration of TBA could not be neglected. The experimental concentration profiles with time could be simulated well by simple kinetics. Finally, rate constants could be expressed by Arrhenius equations. © 1993 John Wiley & Sons, Inc.     

Cinnamyl alcohols and methyl esters of fatty acids from Wedelia prostrata callus cultures

Two methyl esters of fatty acids, namely octadecanoic acid methyl ester (methyl stearate) and hexadecanoic acid methyl ester (methyl palmitate), in addition to four cinnamyl alcohol derivatives, sinapyl alcohol, coniferyl alcohol, p-coumaryl alcohol and coniferyl alcohol 4-O-glucoside (coniferin), were isolated from callus cultures of Wedelia prostrata. The structure of coniferin was established by spectroscopic and chemical methods, while the other compounds were identified by gas chromatography-mass spectrometry and thin layer chromatography in comparison with standards.