Showing papers on "Ether published in 1999"
TL;DR: Diels-Alder reactions in neutral ionic liquids (such as 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1- butyl- 3methyloride-imidazolate hexafluorophosphate) were reported in this paper, where rate enhancements and selectivities similar to those of reactions performed in lithium perchlorate-diethyl ether mixtures were observed.
452 citations
TL;DR: In this article, it was shown that Pd complexes with sterically hindered alkylphosphines accelerate reductive elimination of diaryl ethers and protected phenols from unactivated aryl halides.
Abstract: The reductive elimination of ethers from transition metal complexes is a rare elementary reaction that is limited to special cases. The importance of aryl ether substructures has created a synthetic challenge to prepare the aryl-oxygen linkage in a general fashion under mild conditions. Pd-catalyzed C-O coupling could be a solution to this synthetic problem, but the reductive elimination of acyclic ethers that is the crucial step for this catalytic process has been limited to palladium complexes with aromatic systems that are highly activated and undergo direct, uncatalyzed nucleophilic aromatic substitution chemistry. Thus, it is unactivated aryl halides that are crucial substrates to include in transition metal-catalyzed C-O coupling chemistry, and they report that Pd complexes with sterically hindered alkylphosphines (1) undergo thermal reductive elimination to form the C-O bond in diaryl ethers from complexes with unactivated metal-bound aryl groups and (2) catalyze the formation of diaryl ethers and protected phenols from unactivated aryl halides. These findings demonstrate the concept that sterically hindered alkylphosphines accelerate reductive elimination.
347 citations
TL;DR: In this article, polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry.
Abstract: Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis.
340 citations
TL;DR: In this paper, the reactivity of organic compounds composed of C, H, and O, dyes, amides, and water-soluble polymers was correlated well with their carbon content in the molecule (C/MW).
Abstract: The wet oxidation of organic compounds composed only of C, H, and O, dyes, amides, and water-soluble polymers is discussed to clarify the basic nature of this process. The reactivity of the organic compounds composed of C, H, and O, dyes, and some amides was correlated well with their carbon content in the molecule (C/MW) or carbon content in their skeletal structure (C/MW‘). This C/MW index can be applied to roughly estimate the behavior of wastewaters containing various organic compounds. Polymers are easily decomposed by the wet oxidation because they can undergo intramolecular hydrogen abstraction in the chain-propagation step. The biodegradability of polymers and amides was improved by wet oxidation treatment, indicating an asset of this process. The function of homogeneous copper salts and the effect of hydrogen peroxide are discussed. The action of Co/Bi composite oxide designed for the treatment of refractory carboxylic acids, Mn/Ce composite oxide for ammonia and other organic compounds, and Ru/C...
277 citations
TL;DR: A pincer-type SCS ligand containing Pd(II) is a simple, robust catalyst for Heck chemistry using a variety of alkene acceptors and aryl iodides as discussed by the authors.
Abstract: A new pincer-type SCS ligand containing Pd(II) is a simple, robust catalyst for Heck chemistry using a variety of alkene acceptors and aryl iodides. It is less active with aryl bromides. While certain palladium(II) species insert slowly into the aryl C−H bond of an unsubstituted version of this ligand, the introduction of activating groups into the 5 position of the aromatic ring readily allows quantitative metal insertion. These ligands were synthesized and attached to soluble polymers by simple modification of inexpensive starting materials. For example, both 5-oxy and 5-amido SCS ligands were successfully appended to 5000 Mn poly(ethylene glycol) via ether or amide linkages, respectively. Both the 5-oxo and 5-amido complexes are active as Heck catalysts in DMF solution in air. The PEG-bound 5-amido-SCS−Pd complex was recycled via solvent precipitation three times with no observed catalyst deactivation. While the 5-amido-SCS−Pd complexes are very robust, their 5-oxo counterparts decompose slowly under c...
259 citations
TL;DR: In this article, the depolymerization of Kraft and organosolv-derived lignins by KOH in supercritical methanol or ethanol was studied in rapidly heated batch microreactors.
256 citations
TL;DR: The hypothesis that plasmalogens, through the vinyl ether, act as antioxidants to protect cells against ROS is supported and might protect cells from ROS-mediated damage during events such as chemical hypoxia.
Abstract: Exposure of plasmalogen-deficient variants of the murine cell line RAW 264.7 to short-term (0-100 min) treatment with electron transport inhibitors antimycin A or cyanide (chemical hypoxia) resulted in a more rapid loss of viability than in the parent strain. Results suggested that plasmalogen-deficient cells were more sensitive to reactive oxygen species (ROS) generated during chemical hypoxia; the mutants could be rescued from chemical hypoxia by using the antioxidant Trolox, an alpha-tocopherol analogue, and they were more sensitive to ROS generation by plumbagin or by rose bengal treatment coupled with irradiation. In addition, the use of buffers containing 2H2O greatly enhanced the cytotoxic effect of chemical hypoxia, suggesting the involvement of singlet oxygen. We used the unique enzymic deficiencies displayed by the mutants to differentially restore either plasmenylethanolamine (the major plasmalogen species normally found in this cell line) or its biosynthetic precursor, plasmanylethanolamine. Restoration of plasmenylethanolamine, which contains the vinyl ether, resulted in wild-type-like resistance to chemical hypoxia and ROS generators, whereas increasing levels of its precursor, which bears the saturated ether, had no effect on cell survival. These findings identify the vinyl ether double bond as a crucial element in cellular protection under these conditions and support the hypothesis that plasmalogens, through the vinyl ether, act as antioxidants to protect cells against ROS. These phospholipids might protect cells from ROS-mediated damage during events such as chemical hypoxia.
205 citations
TL;DR: Wright et al. as discussed by the authors reported the first examples of kinetic resolution of epoxides with phenols, with the isolation of 1-aryloxy 2-alcohols (1) in high ee's and yields
Abstract: Department of Chemistry and Chemical Biology HarVard UniVersity, Cambridge, Massachusetts 02138 ReceiVed April 6, 1999 Enantiopure R-aryloxy alcohols (1) are valuable targets for asymmetric synthesis as a result of their role as key synthetic intermediates in a variety of pharmaceutically important compounds1 In principle, access to these building blocks may be provided by several routes, including asymmetric reduction of aryloxy ketones2 or the ring opening of enantiopure terminal epoxides with phenols Of these, the latter is probably the most versatile and direct, but available methods for the addition of phenols to epoxides are extremely limited No catalytic methods have been devised for phenolic opening of terminal epoxides,3 and forcing conditions are required for the uncatalyzed reaction, such as heating epoxide in the presence of a phenoxide salt to high temperatures in a polar solvent These thermal methods are generally low-yielding and are particularly unsuitable for sensitive substrates Thus, despite the recent discovery of general methods for accessing terminal epoxides in high optical purity,4 the development of routes to enantiopure R-aryloxy alcohols via epoxide ring-opening with phenols remains an unsolved problem The ready accessibility of terminal epoxides in racemic form renders kinetic resolution of terminal epoxides with phenols a potentially attractive route to 1 (Scheme 1, Nu ) OAr) The high selectivities obtained in the recently reported hydrolytic kinetic resolution of terminal epoxides with catalyst 3b4 (Scheme 1, Nu ) OH) suggested that (salen)Co(III) complexes might also serve as effective catalysts for the enantioselective addition of phenols to epoxides This strategy has proven successful, and we report here the first examples of kinetic resolution of epoxides with phenols, with the isolation of 1-aryloxy 2-alcohols (1) in high ee’s and yields Reaction of 22 equiv of (()-1,2-epoxyhexane (2a) with phenol (4a) in the presence of (salen)Co(OAc) complex 3b (0044 equiv) in tert-butyl methyl ether (TBME) led to 61% conversion of phenol after 55 h at room temperature, with 1-phenoxy-2-hexanol (1a) generated in 94% ee Encouraged by the observation of high enantioselectivity in this reaction, we evaluated a variety of reaction parameters with the goal of identifying a more reactive system The identity of the counterion for the (salen)cobalt complex proved to be important in this context, with the perfluoro tert-butoxide complex displaying superior reactivity Thus, the use of complex 3c5 under conditions otherwise identical to those outlined above resulted in 80% conversion of phenol in 18 h and formation of 1-phenoxy-2-hexanol as the major product in 96% ee Small amounts of 1,2-diol were also generated, presumably as a result of epoxide hydrolysis with adventitious water,4 but this pathway could be suppressed easily by the inclusion of 3 A molecular sieves in the reaction mixture The optimized procedure afforded the product in 97% isolated yield based on phenol and 98% ee (Table 1, entry 1)6,7 A series of terminal epoxides were screened in the kinetic resolution with phenol, and results are summarized in Table 1 Both electron-rich (entries 1 and 4) and electron-poor (entries 2,3,5 and 6) epoxides as well as epoxides with a range of steric properties reacted with complete regioselectivity to provide the corresponding R-aryloxy alcohols in excellent yields and ee’s In contrast, reaction with styrene oxide resulted in a mixture of regioisomeric ring-opened products (entry 7) In general, the stereoselectivities in the kinetic resolution displayed a strong temperature dependence, such that reactions providing moderate ee’s at room temperature could be rendered significantly more selective simply by lowering the reaction temperature For example, in the reaction of phenol with methyl glycidate, the following data were obtained: 25 °C, 85% ee; 4 °C, 90% ee; -20 °C, 96% ee There was correspondingly little effect of temperature on reaction rate, with all of the above reactions reaching completion within 16-24 h The phenolic kinetic resolution was found to have a broad substrate scope with respect to the phenol (Table 2) Alkyl (1) (a) Wright, J L; Gregory, T F; Heffner, T G; MacKenzie, R G; Pugsley, T A; Meulen, S V; Wise, L D Bioorg Med Chem Lett 1997, 7, 1377 (b) Baker, N R; Byrne, N G; Economides, A P; Javeld, T Chem Pharm Bull 1995, 1045 (c) Kirkup, M P; Rizvi, R; Shankar, B B; Dugar, S; Clader, J; McCombie, S W; Lin, S; Yumibe, N; Huie, K; Heek, M; Compton, D S; Davis, H, R; McPhail, A T Bioorg Med Chem Lett 1996, 6, 2069 (2) For examples of asymmetric reductions of R-arlyoxy ketones, see: (a) Takahashi, H; Sakuraba, S; Takea, H; Achiwa, K J Am Chem Soc 1990, 112, 5877 (b) Gooding, O; Colin, B; Cooper, G; Jackson, D J Org Chem 1993, 58, 3681 (c) Yuan, R; Watanabe, S; Kuwabata, S; Yoneyama, H J Org Chem 1997, 62, 2494 (d) Kang, S B; Ahn, E J; Kim, Y; Kim, Y H Tetrahedron Lett 1996, 37, 9317 (e) Guanti, G; Banfi, L; Narisano, E Tetrahedron Lett 1986, 27, 3547 (3) Shibasaki has reported the asymmetric catalytic ring opening of meso epoxides with 4-methoxyphenol using a Ga(BINOL) catalyst system: Lida, T; Yamamoto, N; Matsunaga, S; Shigeki, M; Woo, H; Shibasaki, M Angew Chem, Int Ed 1998, 37, 2223 (4) Tokunaga, M; Larrow, J F; Kakiuchi, F; Jacobsen E N Science 1997, 277, 936 (5) Commercially available (salen)Co complex 3a was effectively oxidized to (salen)Co(III) complex 3c simply by stirring 3a and (CF3)3COH in CH2Cl2 open to the atmosphere for 45 min and then removing the solvent by rotary evaporation See Supporting Information (6) General procedure for the kinetic resolutions in Table 1 and Table 2: A 10 mL flask was charged with 86 mg (0100 mmol) of 3c and 100 mg MS 3A Epoxide (500 mmol) and phenol (225 mmol) were added at the indicated reaction temperature, and then TBME (015 mL) was added The reaction was stirred at the indicated temperature until GC analysis indicated complete conversion of phenol, at which time 75 mg (030 mmol) pyridinium p-toluenesulfonate was added The reaction mixture was filtered through a pad of silica and washed with 50% EtOAc/hexanes The filtrate was concentrated and purified by chromatography on silica gel with EtOAc/hexanes or Kugelrohr distillation under reduced pressure The enatiomeric purity was determined by GC or HPLC (7) Full experimental procedures, spectral data for new compounds, and ee determinations are presented in the Supporting Information Scheme 1
179 citations
Patent•
12 May 1999
TL;DR: In this article, the authors proposed a refrigerating machine oil composition which is less apt to cause capillary tube clogging in the case where a hydrofluorocarbon, hydrocarbon, ether, carbon dioxide, or ammonia refrigerant is used.
Abstract: A refrigerating machine oil composition which is less apt to cause capillary tube clogging in the case where a hydrofluorocarbon, hydrocarbon, ether, carbon dioxide, or ammonia refrigerant is used. The composition comprises a base oil comprising at least one oxygenic synthetic oil selected among polyvinyl ethers and polyol esters and either a specific polyalkylene glycol alkyl ether or an alkylbenzene having a number-average molecular weight of 100 to 1,000, the amounts of the ether and the alkylbenzene being 1 to 20 wt.% and 1 to 40 wt.%, respectively, based on the whole composition.
175 citations
TL;DR: 15N-1H dipolar couplings measured for ubiquitin over the 2.3–10.4pH range indicate that this protein retains a backbone conformation which is very similar to its structure at pH 6.5 over this entire range.
Abstract: It is demonstrated that mixtures of ditetradecyl-phosphatidylcholine or didodecyl-phoshatidylcholine and dihexyl-phosphatidylcholine in water from lyotropic liquid crystalline phases under similar conditions as previously reported for bicelles consisting of dimyristoyl-phosphatidylcholine (DMPC) and dihexanoyl-phosphatidylcholine (DHPC). The carboxy-ester bonds present in DMPC and DHPC are replaced by ether linkages in their alkyl analogs, which prevents acid- or base-catalyzed hydrolysis of these compounds. 15N-1H dipolar couplings measured for ubiquitin over the 2.3-10.4 pH range indicate that this protein retains a backbone conformation which is very similar to its structure at pH 6.5 over this entire range.
172 citations
TL;DR: In this paper, the secondary alcohols (1g,h) and tertiary alcohol 1i, as well as tertiary alkyl ether 4i, did not react with the HSiEt 3 ( B(C 6 F 5 ) 3 reducing reagent at all.
TL;DR: In this article, the surface tension results were analyzed on the basis of a treatment that considers the relation between the activity coefficients according to the Gibbs−Duhem equation, and the results were compared with Rubingh's treatment, which considers the activation coefficients given by the regular solution theory.
Abstract: The mixed micelles C12E4 (tetraethylene glycol mono-n-dodecyl ether)/CTAB (hexadecyltrimethylammonium bromide) were studied. The surface tension results were analyzed on the basis of a treatment that considers the relation between the activity coefficients according to the Gibbs−Duhem equation. The results are compared with Rubingh's treatment, which considers the activity coefficients given by the regular solution theory. The conductivity of the samples and the aggregation numbers at low mixture concentration are also given.
TL;DR: In this article, a strategy for the enantioselective construction of medium-ring cyclic ethers by merging the asymmetric aldol addition of glycolates with a ring-closing metathesis reaction is described.
Abstract: A strategy is described for the enantioselective construction of medium-ring cyclic ethers by merging the asymmetric aldol addition of glycolates with a ring-closing metathesis reaction. Cyclic ethers of seven-, eight-, and nine-membered rings are readily available through a ring-closing metathesis without cyclic conformational constraints, by exploiting the acyclic conformational bias of the gauche effect. A short formal synthesis of the eight-membered ether (+)-laurencin, a red algae metabolite, has been accomplished utilizing the aldol−metathesis combination.
TL;DR: The mechanism by which heated tetramethylammonium hydroxide (TMAH) degrades the lignin biopolymer was investigated and substantiate the base-catalyzed reactions previously postulated by Gierer (1970) to explain alkali wood pulping and explain the facile formation and distribution of lignIn derivatives obtained in the TMAH thermochemolysis of natural samples.
TL;DR: In this article, a hybrid of poly(ether imide) and silica was prepared by in situ growth of the inorganic network by hydrolysis and condensation of TEOS.
TL;DR: The thermal decomposition pathways leading to the formation of volatile compounds and to char residue in poly(bisphenol A carbonate) (PC), poly(resorcinol carbonate), and poly(hydroquinone carbonate, PHC) have been investigated by mass spectrometry as mentioned in this paper.
Abstract: The thermal decomposition pathways leading to the formation of volatile compounds and to char residue in poly(bisphenol A carbonate) (PC), poly(resorcinol carbonate) (PRC), and poly(hydroquinone carbonate) (PHC) have been investigated by mass spectrometry. The structure of the volatile compounds obtained in the temperature range 300−700 °C, by direct pyrolysis mass spectrometry (DPMS), suggests that these polycarbonates undergo thermal decomposition by a number of different pyrolysis processes. In the initial stage of the thermal degradation are generated cyclic oligomers by an intramolecular exchange reaction, whereas the evolution of CO2 and H2O is spread over all the pyrolysis temperature range, being responsible for the formation of ether bridges (decarboxylation) and phenolic end groups (hydrolysis). A disproportionation reaction of the BPA isopropylidene bridges of PC itself takes place at higher temperature yielding phenyl and isopropylidene end groups, whereas pyrolysis products containing dibenzo...
TL;DR: In this paper, six perfluoroalkyl-activated bishalo monomers 4a,b−6a, b have been synthesized successfully using Pd(0)-catalyzed cross-coupling reaction of 4-chloro- or 4-fluoro-3-trifluoromethylphenylboronic acid with 1,4-dibromobenzene, 2,6-Dibromopyridine, and 2,5-diberromothiophene.
Abstract: Six novel perfluoroalkyl-activated bishalo monomers 4a,b−6a,b have been synthesized successfully using Pd(0)-catalyzed cross-coupling reaction of 4-chloro- or 4-fluoro-3-trifluoromethylphenylboronic acid with 1,4-dibromobenzene, 2,6-dibromopyridine, and 2,5-dibromothiophene. These monomers were converted to poly(arylene ether)s by nucleophilic displacement of the halogen atoms on the benzene ring with several bisphenols. The products obtained by displacement of the fluorine atoms exhibit weight-average molar masses up to 3.52 × 105 g mol-1 in GPC. Displacement of the chlorine atoms from the analogous monomer structures by bisphenols was not successful in obtaining high molar mass products. These poly(arylene ether)s showed very high thermal stability even up to 536 °C for 5% weight loss in TGA in synthetic air. Comparatively low thermal stability for the thiophene ring containing polymers was attributed to the oxidation of the sulfur atom of the thiophene ring at high temperature in air, which destroyed t...
TL;DR: In this paper, the isolated homoleptic dinuclear Pd0 and Pt0 compounds Pd2(C7H12)3 (1), Pd 2(C6H10O)3·C6HO10O (2) and Pt 2(c7H11O)2 (3) were obtained in solution.
Abstract: The complexes (cod)MCl2 (M = Pd, Pt; cod = cis,cis-1,5-cyclooctadiene) react with Li2(cot) (cot = cyclooctatetraene) in a 1,6-diene/diethyl ether mixture (1,6-diene = hepta-1,6-diene, diallyl ether, dvds (1,3-divinyl-1,1,3,3-tetramethyldisiloxane)) to afford the isolated homoleptic dinuclear Pd0 and Pt0 compounds Pd2(C7H12)3 (1), Pd2(C6H10O)3·C6H10O (2‘; 2: Pd2(C6H10O)3), Pd2(dvds)3 (3), and Pt2(C7H12)3 (4). When 1−4 are treated with additional 1,6-diene the equally homoleptic but mononuclear derivatives of type M(1,6-diene)2 (5−8) and with ethene the mixed alkene complexes (C2H4)M(1,6-diene) (9−12) are obtained in solution. Complexes 1−12 react with donor ligands such as phosphanes, phosphites, or tBuNC to give isolated complexes of types L−M(1,6-diene) (13−41), which have also been prepared by other routes. In all complexes the metal centers are TP-3 coordinated: complexes 1−4 contain chelating and bridging 1,6-diene ligands, whereas the other complexes contain a chelating 1,6-diene ligand and an η2-a...
TL;DR: In this paper, the bond energies of the metal-crown complexes have been analyzed by using a guided ion beam tandem mass spectrometer, and the experimental and theoretical results provided an extensive thermochemical database for evaluation.
TL;DR: In this article, the Baylis-Hillman reaction was accelerated in the presence of a catalytic amount of 1,4-diazabicyclo[2,2-2] octane (DABCO) and lithium perchlorate in ether.
TL;DR: In this paper, a catalytic system consisting of sodium tungstate and methyltrioctylammonium hydrogensulfate effects oxidation of simple secondary alcohols to ketones using 3-30% H2O2 without any organic solvents.
Abstract: A catalytic system consisting of sodium tungstate and methyltrioctylammonium hydrogensulfate effects oxidation of simple secondary alcohols to ketones using 3—30% H2O2 without any organic solvents. The oxidation can be conducted under entirely halide-free, mildly acidic conditions. A combination of tungstic acid and an appropriate quaternary ammonium salt also effects the alcohol dehydrogenation. The organic/aqueous biphasic reaction allows easy product/catalyst separation. The turnover number, defined as mols of product per mol of catalyst, approaches 77700 (2-octanol) or 179000 (1-phenylethanol), two orders of magnitude higher than any previously reported. Ester, alkyl and t-butyldimethylsilyl ether, epoxy, carbonyl, N-alkyl carboxamide, and nitrile groups are tolerated under the reaction conditions. Secondary alcohols are preferentially oxidized over terminal olefins. Primary alkanols are oxidized directly to carboxylic acids in a moderate to high yield. Benzylic alcohols are selectively oxidized to be...
TL;DR: The intramolecular cyclization of epoxy alcohols was catalyzed with excellent regio- and enantiocontrol by a [CoIII(salen)] complex, and the reaction of meso substrates produced novel cyclic and bicyclic ethers in good yields and high enantiopurity.
Abstract: The intramolecular cyclization of epoxy alcohols was catalyzed with excellent regio- and enantiocontrol by a [CoIII(salen)] complex. High endo selectivity was observed for the enantioselective cyclization of terminal epoxy alcohols [Eq. (a)], while the reaction of meso substrates produced novel cyclic and bicyclic ethers in good yields and high enantiopurity. TBME=tert-butyl methyl ether.
TL;DR: In this paper, the photo-induced copolymerization of electron donor/electron acceptor monomers has been studied by real-time infrared spectroscopy, and the reaction was found to proceed rapidly upon u.v. exposure in the absence of oxygen.
TL;DR: A comprehensive review of the mixtures and properties (both binary and ternary) that have been studied or are presently under study is presented in this article, where workers in the field can ascertain the mixture classes and types where sufficient data are now available and where further property measurements are required.
TL;DR: In this article, a series of linear and macrocyclic comb-like poly(chloroethyl vinyl ether) (PCEVE-g-PS) polymers were synthesized.
Abstract: The grafting of polystyryllithium onto chloroethyl ether functions of poly(chloroethyl vinyl ether) (PCEVE) chains is a selective reaction which allows the complete substitution of chloride of CEVE units by polystyrene (PS) chains. Since the PCEVE polymer backbone and the PS grafts can be prepared by living cationic and anionic polymerization, respectively, it is possible to synthesize PCEVE-g-PS polymers possessing both a backbone with controlled dimensions and an adjustable number of branches of precise length. This procedure was applied to the synthesis of a series of linear and macrocyclic comblike PCEVE-g-PS based on the use of linear and cyclic PCEVE as reactive backbone, respectively. The synthesis, the characterization and the solution properties of these linear and cyclic comblike polymers are reported.
TL;DR: In this paper, 1-bromoadamantane with dihydroxybenzenes was used to produce 4-(adamantyl-1)-1,2-dihydroxybenzene and 2-(adadamyl- 1)-1.4-DHB.
TL;DR: In this article, small-angle neutron scattering has been used to study the structure and composition of mixed ionic−nonionic surfactant micelles, and a comparison between two different mixed surfactants systems, sodium dodecyl sulfate (SDS) and hexaethylene glycol monodecyl ether (C12EO6), both in 0.1 M NaCl, has been made.
Abstract: Small-angle neutron scattering has been used to study the structure and composition of mixed ionic−nonionic surfactant micelles. A comparison between two different mixed surfactant systems, sodium dodecyl sulfate (SDS) and hexaethylene glycol monododecyl ether (C12EO6) and hexadecyltrimethylammonium bromide (C16TAB) and C12EO6, both in 0.1 M NaCl, has been made. In the latter system, ideal mixing is observed, and in the former, departure from ideality, broadly consistent with regular solution theory, RST, is observed. The deviations from the predictions of RST are attributed to subtle changes in the packing of the two surfactants in the mixed micelles. For the SDS/C12EO6 mixture, the micellar aggregation number is essentially constant with composition and concentration, whereas for the C16TAB/C12EO6 mixture there is a marked micellar growth with increasing concentration and mole fraction of C12EO6 in solution. The SANS results on structure and composition are compared with the results reported for other m...
TL;DR: In this paper, density functional calcula- tions and Raman spectroscopic data were correlated with the unique cata- lytic epoxidation activity of peroxomo- lybdenum complexes (MoO(O2)2(O- ER3)) (EaN, P, As; Ra n-dodecyl) in a biphasic chloroform - 1-octene/aque- ous hydrogen peroxide system.
Abstract: Density functional calcula- tions and Raman spectroscopic data were correlated with the unique cata- lytic epoxidation activity of peroxomo- lybdenum complexes (MoO(O2)2(O- ER3)) (EaN, P, As; Ra n-dodecyl) in a biphasic chloroform - 1-octene/aque- ous hydrogen peroxide system. Crystal structure determinations on (MoO(O2)2(OPtBu3)(OCMe2)) and two complexes containing chelating hemila- bile ether - phosphane oxide and ether - arsane oxide ligands (MoO(O2)2- {iPr2E(O)CH2CH2OCH3}) (Ea P, As) are reported. A mechanistic study with these model complexes reveals the im- portance of free coordination sites for peroxide activation. Calculations and Raman spectroscopic data indicate the tendency of coordinatively unsaturated species (MoO(O2)2(L)) to dimerize in noncoordinating solvents. The catalytic activity in the presence of water as competing ligand could be correlated with the calculated proton affinity of the ligands OER3 (Ra N, P, As). Elucida- tion of the vibrational behavior of the structurally characterized peroxo com- plexes was supported by normal-coordi- nate analyses.
TL;DR: In this article, the ozone reaction with unsaturated aliphatic oxygenates has been studied at ambient T (287-297 K) and p = 1 atm. of air (RH = 55 ± 10%) with sufficient cyclohexane added to scavenge the hydroxyl radical.
Abstract: The reaction of ozone with unsaturated aliphatic oxygenates has been studied at ambient T (287–297 K) and p = 1 atm. of air (RH = 55 ± 10%) with sufficient cyclohexane added to scavenge the hydroxyl radical. Reaction rate constants, in units of 10-18 cm3 molecule-1 s-1, are 10.7 ± 1.4 for methyl trans-3-methoxy acrylate, 63.7 ± 9.9 for 4-hexen-3-one (predominantly the trans isomer), 125 ± 17 for trans-4-methoxy-3-buten-2-one, ≥148 ± 13 for cis-4-heptenal, ≥439 ± 37 for 3- methyl-2-buten-1-ol and ≥585 ± 132 for (cis + trans)-ethyl 1-propenyl ether. The influence of the oxygen-containing substituents on reactivity toward ozone is examined. Unsaturated ethers react with ozone faster than their alkene structural homologues; the reverse is observed for unsaturated esters and unsaturated carbonyls. Major reaction products have been identified by liquid chromatography with ultraviolet detection (LC-UV), particle beam-mass spectrometry (PB- MS) and gas chromatography-mass spectrometry (GC-MS) and are methyl formate and methyl glyoxylate from methyl trans-3-methoxy acrylate, acetaldehyde and 2-oxobutanal from 4-hexen-3-one, propanal and succinic dialdehyde from cis-4-heptenal, hydroxyacetaldehyde and acetone from 3-methyl-2-buten-1-ol, and ethyl formate and acetaldehyde from (cis + trans)-ethyl 1-propenyl ether. PB-MS and GC- MS were also employed to identify new reaction products and to confirm the structure of products tentatively identified in a previous study of the reaction of ozone with five unsaturated oxygenates (Grosjean and Grosjean, 1997a): formic acid and methyl glyoxylate from methyl acrylate, formic acid and formic acetic anhydride from vinyl acetate, 2-oxoethyl acetate and 3-oxopropyl acetate from cis-3-hexenyl acetate, ethyl formate and formic acid from ethyl vinyl ether, and methyl formate from trans-4-methoxy-3- buten-2-one. The nature and formation yields of the reaction products are consistent with (and supportive of) the reaction mechanism: O3 + R1R2C=CR3X → α(R1COR2 + R3C(X)OO) + (1 - α)(R3COX + R1C(R2)OO), where R1, R2 and R3 = H or alkyl, X is the oxygen-containing substituent, R1COR2 and R3COX are the primary products and R1C(R2)OO and R3C(X)OO are the carbonyl oxide biradicals. The variations of the coefficient α, which ranges from 0.25 to 0.61, are discussed in terms of the number and nature of alkyl and oxygen-containing substituents. Subsequent reactions of the alkyl-substituted biradicals R1C(R2)OO and of the biradicals R3C(X)OO that bear the oxygen-containing substituent are discussed. For the biradical CH3CHOO, the ratio ka/kb for the competing pathways of rearrangement to acetic acid (CH3CHOO → CH3C(O)OH, reaction (a) and formation of an unsaturated hydroperoxide (CH3CHOO → CH2=CH(OOH), reaction (b) is 99.9%) and comparable to that for formaldehyde (98.4%) for formic acetic anhydride and for difunctional oxygenated compounds. Uptake in water impingers was lower (19–78%) for monofunctional aldehydes and ketones.
TL;DR: In this paper, the first direct catalytic asymmetric Mannich-type reaction using unmodified ketones and an aminomethyl ether is described, achieved by the cooperative catalysis of a heterobimetallic asymmetric complex (AlLibis(binaphthoxide)) and La(OTf)3·nH2O).