Photochemistry of aryl tert-butyl ethers in methanol: the effect of substituents on an excited state cleavage reaction

The photolysis of a set of 10 substituted aryl tert-butyl ethers, 8a-j, in methanol gave, as the major product, the corresponding phenol along with tert-butyl-substituted phenols resulting from photo-Fries reaction. The corresponding 4-cyanophenyl 1-adamantyl ether, 9, also gave 1-methoxyadamantane 16 (16%), indicating that, at least for this ether, some of the products were ion-derived. Quenching studies with 2,3-dimethylbutadiene for the tert-butyl ethers indicated that these reactions were occurring from the singlet excited state. Rate constants for the reaction, obtained from quantum yields and singlet lifetimes, were found to correlate reasonably well with sigma(h)()(nu) values, rho = -0.77 (r = 0.975), a result that is unexpected for a reaction where the polarity of the bond breaking in the transition state is expected to be -O(delta-). C(delta+).     

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.     

Kinetics of liquid-phase synthesis of ethyl tert-butyl ether from tert-butyl alcohol and ethanol catalyzed by ion exchange resin and heteropoly acid

Synthesis of ethyl tert-butyl ether (ETBE) from ethanol (EtOH) and tert-butyl alcohol (TBA) in the liquid phase was studied by using ion exchange resin, Amberlyst 15 (A15) in the H⁺ form and heteropoly acid, H_0.5Cs_3.5SiW₁₂O₄₀(HPA). Experiments were carried out in a stirred batch reactor with different temperatures under atmospheric pressure. It was found that water will inhibit the reaction rates greatly and the dehydration of TBA could not be neglected in this study. A kinetics model which considered the inhibition of water and the decrease of volume was proposed. The experimental results agreed well with the model. © 1995 John Wiley & Sons, Inc.     

Practical and robust method for regio- and stereoselective preparation of (E)-ketene tert-butyl TMS acetals and beta-ketoester-derived tert-butyl (1Z,3E)-1,3-bis(TMS)dienol ethers

We developed an efficient, practical, robust method for the regio- and stereoselective preparation of (E)-ketene trimethylsilyl acetals (KSAs) derived from tert-butyl esters 1. The reaction was performed under convenient reaction conditions; LDA-TMSCl, 0-5 degrees C, and cyclopentyl methyl ether (CPME) solvent. Two kinds of (Z)- and (E)-KSAs derived from alpha-oxygen and alpha-nitrogen-substituted tert-butyl esters, respectively, were also obtained in good yield. The present protocol was successfully applied to a stereocontrolled preparation of useful, but highly reactive (less accessible) beta-ketoester-derived tert-butyl (1Z,3E)-1,3-bis(TMS)dienol ethers 2.     

Simultaneous determination of methyl tert-butyl ether, its degradation products and other gasoline additives in soil samples by closed-system purge-and-trap gas chromatography-mass spectrometry

A new protocol for the simultaneous determination of methyl tert-butyl ether (MTBE); its main degradation products: tert-butyl alcohol (TBA) and tert-butyl formate (TBF); other gasoline additives, oxygenate dialkyl ethers: ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) and diisopropyl ether (DIPE); aromatics: benzene, toluene, ethylbenzene and xylenes (BTEX) and other compounds causing odour events such as dicyclopentadiene (DCPD) and trichloroethylene (TCE) in soils has been developed. On the basis of US Environmental Protection Agency (EPA) method 5035A, a fully automated closed-system purge-and-trap coupled to gas chromatography/mass spectrometry (P&T-GC/MS) was optimised and permitted to detect microg/kg concentrations in solid matrices avoiding losses of volatile compounds during operation processes. Parameters optimised were the sampling procedure, sample preservation and storage, purging temperature, matrix effects and quantification mode. Using 5 g of sample, detection limits were between 0.02 and 1.63 microg/kg and acceptable method precision and accuracy was obtained provided quantification was performed using adequate internal standards. Soil samples should be analysed as soon as possible after collection, stored under -15 degrees C for not longer than 7 days if degradation products have to be analysed. The non-preservative alternative (empty vial) provided good recoveries of the most analytes when freezing the samples up to 7 day holding time, however, if biologically active soil are analysed the preservation with trisodium phosphate dodecahydrate (Na(3)PO(4).12H(2)O or TSP) is strongly recommended more than sodium bisulphate (NaHSO(4)). The method was finally applied to provide threshold and background levels of several gasoline additives in a point source and in sites not influenced by gasoline spills. The proposed method provides the directions for the future application on real samples in current monitoring programs at gasoline pollution risk sites where till now little monitoring data for MTBE in soils are available.     

CH stretching vibrational overtone spectra of tert-butylbenzene, tert-butyl chloride, and tert-butyl iodide

The vapor phase CH stretching vibrational overtone spectra of tert-butylbenzene and tert-butyl chloride are measured in the Delta upsilon(CH) = 2-7 region, while the spectrum of tert-butyl iodide is recorded in the Delta upsilon(CH) = 2-6 region. The overtone spectrum of tert-butylbenzene is too complex to make detailed spectral assignments. Local mode frequencies, omega, and anharmonicities, omegax, are obtained for tert-butyl chloride and tert-butyl iodide. The torsional dependencies of the local mode frequency, delta(omega), and anharmonicity, delta(omega)(x), are calculated for the tert-butyl halides. Nonbonded, through-space intramolecular interactions are observed in the blue-shifting of sterically hindered CH oscillators. Scaling factors are presented for relating ab initio calculated local mode parameters to experimental values for alkyl CH oscillators. Fermi resonances are observed between local mode states and local mode/normal mode combination states in tert-butyl chloride and tert-butyl iodide. Vibrational overtone transition intensities are calculated in the range Delta upsilon(CH) = 3-9 using the harmonically coupled anharmonic oscillator (HCAO) model and ab initio dipole moment functions. The resultant HCAO intensities are compared to experimental intensities at Delta upsilon(CH) = 3.     

Phase-transfer catalytic aza-Michael addition of tert-butyl benzyloxycarbamate to electron-deficient olefins

A highly efficient phase-transfer catalytic aza-Michael addition of tert-butyl benzyloxycarbamate to a wide range of electron-deficient olefins is presented (90-99%).     

Steric structure of some tert-butyl aryl sulfones

Conclusions Aryl is in a skewed position (=73±13) in tert-butyl aryl sulfones. There are no significant changes in the conformation of the sulfone molecules when methyl is replaced by the tert-butyl radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2057–2060, September, 1981.The authors thank A. N. Vereshchagin for valuable consultations and for his interest in the paper.     

Asymmetric synthesis of (1R,2S,3R)-3-methylcispentacin and (1S,2S,3R)-3-methyltranspentacin by kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate

Conjugate addition of lithium dibenzylamide to tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate occurs with high levels of stereocontrol, with preferential addition of lithium dibenzylamide to the face of the cyclic alpha,beta-unsaturated acceptor anti- to the 3-methyl substituent. High levels of enantiorecognition are observed between tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate and an excess of lithium (+/-)-N-benzyl-N-alpha-methylbenzylamide (10 eq.) (E > 140) in their mutual kinetic resolution, while the kinetic resolution of tert-butyl (+/-)-3-methylcyclopentene-1-carboxylate with lithium (S)-N-benzyl-N-alpha-methylbenzylamide proceeds to give, at 51% conversion, tert-butyl (1R,2S,3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate consistent with E > 130, and in 39% yield and 99 +/- 0.5% de after purification. Subsequent deprotection by hydrogenolysis and ester hydrolysis gives (1R,2S,3R)-3-methylcispentacin in > 98% de and 98 +/- 1% ee. Selective epimerisation of tert-butyl (1R,2S,3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate by treatment with KO'Bu in 'BuOH gives tert-butyl (1S,2S,3R,alphaS)-3-methyl-2-N-benzyl-N-alpha-methylbenzylaminocyclopentane-1-carboxylate in quantitative yield and in > 98% de, with subsequent deprotection by hydrogenolysis and ester hydrolysis giving (1S,2S,3R)-3-methyltranspentacin hydrochloride in > 98% de and 97 +/- 1% ee.     

Parallel kinetic resolution of tert-butyl (RS)-3-alkyl-cyclopentene-1-carboxylates for the asymmetric synthesis of 3-alkyl-cispentacin derivatives

The double mutual kinetic resolution of tert-butyl (RS)-3-benzyl-cyclopentene-1-carboxylate with a 50 : 50 mixture of lithium (RS)-N-benzyl-N-alpha-methylbenzylamide and lithium (RS)-N-3,4-dimethoxybenzyl-N-alpha-methylbenzylamide gives, after protonation with 2,6-di-tert-butylphenol, a 50 : 50 mixture of the readily separable N-benzyl-(1SR,2RS,3RS,alphaRS)- and N-3,4-dimethoxybenzyl-(1SR,2RS,3RS,alphaRS)-beta-amino esters in >98% de in each case. This product distribution indicates that these amides react at very similar rates and with no mutual interference to furnish readily separable products, and are thus ideal for parallel kinetic resolution. The efficient parallel kinetic resolution (E > 65) of a range of tert-butyl (RS)-3-alkyl-cyclopentene-1-carboxylates with a pseudoenantiomeric mixture of homochiral lithium (S)-N-benzyl-N-alpha-methylbenzylamide and lithium (R)-N-3,4-dimethoxybenzyl-N-alpha-methylbenzylamide gives, after separation and N-deprotection, a range of carboxylate protected 3-alkyl-cispentacin derivatives in >98% de and >95% ee.     

Regiocontrolled nitration of di(tert-butyl)phenols

The nitration of 2,4-di(tert-butyl)phenol and 2,6-di(tert-butyl)phenol is accompanied by oxidative processes, leading to products of the oxidative coupling of the starting di(tert-butyl)phenols. On the other hand, the corresponding nitrophenols are formed in quantitative yield in the substitutive nitration of 6-XCH₂- and 4-XCH₂-di(tert-butyl)phenols (X-OH, OR, NR₂).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2381–2383, October, 1991.     

Ruthenium-catalyzed oxidation of alkanes with tert-butyl hydroperoxide and peracetic acid

The ruthenium-catalyzed oxidation of alkanes with tert-butyl hydroperoxide and peracetic acid gives the corresponding ketones and alcohols highly efficiently at room temperature. The former catalytic system, RuCl(2)(PPh(3))(3)-t-BuOOH, is preferable to the oxidation of alkylated arenes to give aryl ketones. The latter system, Ru/C-CH(3)CO(3)H, is suitable especially for the synthesis of ketones and alcohols from alkanes. The ruthenium-catalyzed oxidation of cyclohexane with CH(3)CO(3)H in trifluoroacetic acid/CH(2)Cl(2) at room temperature gave cyclohexyl trifluoroacetate and cyclohexanone with 90% conversion and 90% selectivity (85:15). The mechanistic study indicates that these catalytic oxidations of hydrocarbons involve oxo-ruthenium species as key intermediates.     

Determination of paclitaxel in rat plasma by LC-MS-MS

A simple, rapid, and sensitive liquid chromatography-mass spectrometry (MS)-MS method for quantitating paclitaxel in rat plasma is developed. Liquid-liquid extraction with tert-butyl methyl ether is used for sample preparation, and docetaxel is used as the internal standard. Paclitaxel and docetaxel are separated on a C18 column and quantitated using a triple-quadrupole MS operating in positive ion electrospray selective reaction monitoring mode with a total run time of 6.0 min. The peak area of the m/z 876.3 --> 307.9 transition of paclitaxel is measured versus that of the m/z 830.3 --> 549.1 transition of docetaxel to generate the standard curve. The standard curve is linear over the concentration range of 0.2008-1004 ng/mL for rat plasma. The method has high extraction recovery (> 90%) and accuracy (> 90%), with the intra- and interday precision < 15%. Frozen stability, freeze-and-thaw stability, extracted stability, and room temperature solution stability are also examined. This assay is used to support a pharmacokinetic study of paclitaxel self-assembled nanoliposome in rats.     

Kinetic resolution of tert-butyl (RS)-3-alkylcyclopentene-1-carboxylates for the synthesis of homochiral 3-alkyl-cispentacin and 3-alkyl-transpentacin derivatives

High levels of stereocontrol are observed in the conjugate addition of lithium dibenzylamide to tert-butyl (RS)-3-alkylcyclopentene-1-carboxylates (alkyl = Et, Bn), with addition occurring exclusively anti- to the 3-alkyl substituent. Treatment of a range of tert-butyl (RS)-3-alkylcyclopentene-1-carboxylates (alkyl = Et, Bn, (i)Pr, (t)Bu) with lithium (RS)-N-benzyl-N-[small alpha]-methylbenzylamide indicates that good enantiorecognition is observed (E > 80) in their mutual kinetic resolution. In these reactions, conjugate addition of the lithium amide occurs exclusively anti- to the 3-alkyl substituent, with subsequent C(1)-protonation occurring preferably anti- to the 2-amino group in the 3-Et, 3-Bn and 3-(i)Pr cases, giving predominantly the corresponding 1,2-syn-2,3-anti-diastereoisomers. Conjugate addition to (RS)-3-tert-butyl cyclopentene-1-carboxylate results in exclusive 2,3-anti -addition and a reversal in C(1)-protonation selectivity, giving predominantly the 1,2-anti-2,3-anti-diastereoisomer. Furthermore, the kinetic resolution of the tert-butyl (RS)-3-alkylcyclopentene-1-carboxylates (alkyl = Et, Bn, (i)Pr, (t)Bu) with lithium (S)-N-benzyl-N-alpha-methylbenzylamide proceeds efficiently, giving, at between 47 and 51% conversion, the resolved 3-alkylcyclopentene-1-carboxylates in >85 to >98% ee and the beta-amino ester products of conjugate addition in high de, consistent with E > 80 in each case. Subsequent deprotection of the 1,2-syn-2,3-anti-3-alkyl-beta-amino esters (alkyl = Et, Bn, (i)Pr) by hydrogenolysis and ester hydrolysis gives the corresponding 1,2-syn-2,3-anti-3-alkylcispentacins in >98% de and 98 +/- 1% ee. Selective epimerisation of the 1,2-syn-2,3-anti-3-alkyl-beta-amino esters (alkyl = Et, Bn, (i)Pr, (t)Bu) by treatment with KO(t)Bu in (t)BuOH gives the corresponding 1,2-anti-2,3-anti-3-alkyl-beta-amino esters in quantitative yield and in >98% de, with subsequent deprotection by hydrogenolysis and ester hydrolysis giving the corresponding 1,2-anti-2,3-anti-3-alkylcispentacin hydrochlorides in >98% de.     

Solvent effect on standard electrode potential: Part V. Silver-silver chloride electrode in tert-butyl alcohol + water mixtures

The electromotive force measurements of the cell Pt, H₂ (gas, 1 atm); HCl (m), X % Bu ^tOH, Y% H₂O; AgCl, Ag, at nine different temperatures ranging from 15 to 55°C at 5° intervals, have been used to determine the standard potentials of the silver-silver chloride electrode in eighteen tert-butyl alcohol+water solvent mixtures containing up to 90 wt. % alcohol. The standard molal potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HCl, and the standard thermodynamic quantities for the transfer of one mole of HCl from water to tert-butyl alcohol+water media have been evaluated. The results have been discussed in the light of ion-solvent interactions as well as the structural changes of the solvents.     

Determination of fuel dialkyl ethers and BTEX in water using headspace solid-phase microextraction and gas chromatography-flame ionization detection

A simple procedure for the determination of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), ethyl butyl ether (EBE), tert-amyl methyl ether (TAME), benzene, toluene, ethylbenzene, and xylenes (BTEX) in water using headspace (HS) solid-phase microextraction (HS-SPME) was developed. The analysis was carried out by gas chromatography (GC) equipped with flame ionization detector (FID) and 100% dimethylpolysiloxane fused capillary column. A 2 Plackett-Burman design for screening and a central composite design (CCD) for optimizing the significant variables were applied. Fiber type, extraction temperature, sodium chloride concentration, and headspace volume were the significant variables. A 65 microm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 10 degrees C, 300 g/l, and 20 ml of headspace (in 40 ml vial) were respectively chosen for the best extraction response. An extraction time of 10 min was enough to extract the ethers and BTEX. The relative standard deviation (R.S.D.) for the procedure varied from 2.6 (benzene) to 8.5% (ethylbenzene). The method detection limits (MDLs) found were from 0.02 (toluene, ethylbenzene, and xylenes) to 1.1 microg/l (MTBE). The optimized method was applied to the analysis of the rivers, marinas and fishing harbors surface waters from Gipuzkoa (North Spain). Three sampling were done in 1 year from June 2002 to June 2003. Toluene was the most detected analyte (in 90% of the samples analyzed), with an average concentration of 0.56 microg/l. MTBE was the only dialkyl ether detected (in 15% of the samples) showing two high levels over 400 microg/l that were related to accidental fuel spill.     

Dichloromethyl tert-butyl ketone in the Darzens reaction

The condensation of dichloromethyl tert-butyl ketone (1) with benzaldehyde, para-bromobenzaldehyde, and 2,4-dichlorobenzaldehyde under conditions for the Darzens reaction gives 1-aryl-1-chloro-4,4-dimethyl-2,3-pentanediones (2–4). In the case of nitrobenzaldehydes, the reaction products are 1-aryl-2-chloro-1,2-epoxy-4,4-dimethylpentanones (5 and 6), which isomerize to -chloroketones (7 and 8) upon prolonged storage or heating at reflux in benzene.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Science Center, Russian Academy of Sciences, 420083 Kazan. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 438–441, February, 1992.     

Hydroxyalkylation of alpha-C-H bonds of tetrahydrofuran with aldehydes in the presence of triethylborane and tert-butyl hydroperoxide

The alpha-hydroxyalkylation of tetrahydrofuran with aldehydes via radical C-H abstraction was conducted using triethylborane in the presence of tert-butyl hydroperoxide. This study presents a rare instance of direct intermolecular radical addition of unactivated cyclic ether to aldehydes.     

Excess molar volumes of methyl tert-butyl ether with chloroalkanes at 30°C

Excess molar volumes are reported for binary mixtures of methyl tert-butyl ether with trichloromethane, tetrachloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane, or 1,1,1,2,2-pentachloroethane at 30°C over the entire composition range of the mixtures. Excess volumes for all the mixtures are found to be negative. A qualitative interpretation of the results in terms of O–H–C and Cl–O interactions is presented. The Prigogine-Flory-Patterson theory has been used to analyze the results.     

Highly active and stable performance of catalytic vapor phase Koch-type carbonylation of tert-butyl alcohol over H-zeolites

A high catalytic activity and excellent stability of the vapor phase Koch-type carbonylation of tert-butyl alcohol towards 2,2-dimethylpropanoic acid on a H-ZSM-5 catalyst were achieved with a yield as high as 90% without any threat of deactivation in 120 h.