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Strong Base (strong + base)
Selected AbstractsControlling Chemoselectivity in Reactions of Unprotected Naphthalene-1-carboxylic Acid with Strong Bases.CHEMINFORM, Issue 34 2005David Tilly Abstract For Abstract see ChemInform Abstract in Full Text. [source] Separation of amino alcohols using divalent dipeptides as counter ions in aqueous CEELECTROPHORESIS, Issue 10 2010Jakob Haglöf Abstract Divalent dipeptides have been introduced as counter ions in aqueous CZE. The dipeptides form ion pairs with amino alcohols in the BGE and facilitate the separation of amino alcohols. High concentrations of dipeptide caused reversed effective mobility for the analytes. The net charge of the dipeptide can be controlled using a buffer or a strong base, and regulates the interaction between the dipeptide and the amino alcohol. A stronger interaction and higher selectivity of amino alcohols was observed when the dipeptides were used as divalent counter ions, than in monovalent or uncharged form. Association constants for ion pairs between divalent dipeptides and amino alcohols can be used to enhance selectivity for amino alcohols in CZE. No chiral separation of amino alcohols was observed when using the dipeptides as ion-pairing chiral selectors in aqueous BGE, but addition of methanol to the BGE promoted enantioselectivity. [source] The First Stable Monomeric Triaminostannane of Composition [(Me3Si)3CSn(NHtBu)3] Containing Three Substituted NH GroupsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2003Jörg Janssen Abstract Triaminostannanes of secondary amines have been known since 1977 and are widely used in tin organic chemistry. However, the corresponding nitrogen substituted stannanes of primary amines are not cited in the literature. Herein we report on the ammonolysis reaction of [(Me3Si)3CSnCl3] with tBuNH2 in the presence of a strong base and the X-ray structural analysis of [(Me3Si)3CSn(NHtBu)3], the first monomeric triaminostannane containing protons at the nitrogen atoms. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Cation exchange in forest soils: the need for a new perspectiveEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2008D. S. Ross Summary The long-term sustainability of forest soils may be affected by the retention of exchangeable nutrient cations such as Ca2+ and the availability of potentially toxic cations such as Al3+. Many of our current concepts of cation exchange and base cation saturation are largely unchanged since the beginnings of soil chemistry over a century ago. Many of the same methods are still in use even though they were developed in a period when exchangeable aluminium (Al) and variable charge were not generally recognized. These concepts and methods are not easily applicable to acid, highly organic forest soils. The source of charge in these soils is primarily derived from organic matter (OM) but the retention of cations, especially Al species, cannot be described by simple exchange phenomena. In this review, we trace the development of modern cation exchange definitions and procedures, and focus on how these are challenged by recent research on the behaviour of acid forest soils. Although the effective cation exchange capacity (CECe) in an individual forest soil sample can be easily shown to vary with the addition of strong base or acid, it is difficult to find a pH effect in a population of different acid forest soil samples. In the very acidic pH range below ca 4.5, soils will generally have smaller concentrations of adsorbed Al3+. This can be ascribed to a reduced availability of weatherable Al-containing minerals and a large amount of weak, organic acidity. Base cation saturation calculations in this pH range do not provide a useful metric and, in fact, pH is modelled better if Al3+ is considered to be a base cation. Measurement of exchangeable Al3+ with a neutral salt represents an ill-defined but repeatable portion of organically complexed Al, affected by the pH of the extractant. Cation exchange in these soils can be modelled if assumptions are made as to the proportion of individual cations that are non-specifically bound by soil OM. Future research should recognize these challenges and focus on redefining our concepts of cation retention in these important soils. [source] Kinetic studies of hydrazine and 2-hydroxyethylhydrazine alkylation by 2-chloroethanol: Influence of a strong base in the mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2009V. Goutelle To optimize yields, the study of reaction kinetics related to the synthesis of 2-hydroxyethylhydrazine (HEH) obtained from the alkylation of N2H4 by 2-chloroethanol (CletOH) was carried out with and without sodium hydroxide. In both cases, the main reaction of HEH formation was followed by a consecutive, parallel reaction of HEH alkylation (or dialkylation of N2H4), leading to the formation of two isomers: 1,1-di(hydroxyethyl)hydrazine and 1,2-di(hydroxyethyl)hydrazine. In this study, hydrazine and hydroxyalkylhydrazine alkylations followed SN2 reactions triggered directly by CletOH or indirectly in the presence of a strong base by ethylene oxide, an intermediate compound. The kinetics was studied in diluted mediums by quantifying HEH and CletOH by gas chromatography and gas chromatography coupled with mass spectrometry (GC-MS). The activation parameters of each reaction and the influence of a strong base present in the medium on the reaction mechanisms were established. A global mathematical treatment was applied for each alternative. It allowed modeling the reactions as a function of reagent concentrations and temperature. In the case of direct alkylation by CletOH, simulation was established for semi-batch and batch syntheses and was confirmed in experiments for concentrated mediums (1.0 M , [CletOH]0 , 3.2 M and 15.7 M , [N2H4]0 , 18.8 M). Simulation therefore permits the prediction of the instantaneous concentration of reagents and products, in particular ethylene oxide concentration in the case of indirect alkylation, which must be as weak as possible. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 382,393, 2009 [source] Kinetics of elimination reactions of 1,2-diphenyl ethyl substrates in acetonitrile: A mechanistic change in the presence of a strong baseINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2008D. Santhosh Kumar Kinetics of elimination of methanesulfonic acid from 1,2-diphenylethylmethane sulfonate and its 1- p -methylphenyl- and 1- p -chlorophenyl-substituted derivatives is studied. The results show that the elimination reaction is unimolecular (E1) as reported in the case of 1-chloro-1-(4-methoxyphenyl)-2-phenylethane. The rate of the elimination reaction in the presence of added weak base pyridine is independent of the concentration of the base, but in the presence of a strong base piperidine the rate shows a linear upward drift and this is due to the appearance of a bimolecular component along with the unimolecular pathway. The shift from the unimolecular to bimolecular process takes place independently of the nature of the leaving group and the parasubstituent in the 1,2-diphenylethyl substrate. © 2008 Wiley Periodicals, Inc. 40: 481,487, 2008 [source] Reactivity studies of ethyl(Z)- N -(2-amino-1,2-dicyanovinyl) formimidate with carbonyl compounds in the presence of base,JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2000M. Joséalves The reaction of ethyl(Z)- N -(2-amino-1,2-dicyanovinyl)formimidate 6 with carbonyl compounds in the presence of triethyl amine occurs with formation of the Schiff s base and intramolecular hydrolysis of the adjacent cyano group to give the alkylideneamino derivatives 8a-f. When the ,-carbon of the ketone has at least one proton, the prolonged contact of 8a-f with triethylamine causes intramolecular cyclization between this carbon and the imidate carbon atom to form a seven membered ring. This is followed by cyclization of the cyano and amido groups, leading to the pyrrolo[4,3- b][1,4]diazepines 9. If a strong base is used the first ring to be formed is the pyrrole ring as evidenced in the reaction of 8a with 1,8-diazabicyclo[5.4.0]undec-7-ene leading to 14. The subsequent addition of methyl amine to the reaction mixture, caused cleavage of the alkylideneamino unit and formation of the amidine function from the imi date (15). The addition of acid to the imidates 8a and 8f led to the diazepine compounds 10a and 10f respectively. A suspension of compound 8e in ethanol and triethylamine evolved to a pyrazinone structure 12 under kinetic conditions (4 hours, room temperature) and to the pyrrolo[4,3- b][1,4]diazepine 9e under thermodynamic conditions (48 hours, room temperature). [source] Feasibility of the spontaneous gas-phase proton transfer equilibria between neutral Brřnsted acids and Brřnsted basesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7-8 2008Peeter Burk Abstract The computational investigation of interactions of different acid,base pairs regarding the nature and extent of spontaneous proton transfer was carried out at B3LYP/6-311,+,G** level. The selected acid,base pairs include the interactions of strong base (K2O) with acids of different strength (HClO4, HCl, and HF), and strong acid (HClO4) with bases ranging from K2O (GB,=,322.8,kcal/mol) to H2O (GB,=,157.6,kcal/mol). It was shown that spontaneus, unassisted proton transfer can take place in the gas-phase reactions of strong neutral Brřnsted acids and bases. The reaction might be barrierless as in case of interactions between strong acids and bases, for example perchloric acid and alkali metal oxides or potassium oxide and halogen hydrides, or involve the encounter complex (hydrogen bonded acid,base cluster), which is separated from ion-pair by the transition state. Copyright © 2008 John Wiley & Sons, Ltd. [source] Synthesis and structural analysis of 1,4-bis[n -(N,N -dimethylamino)phenyl]buta-1,3-diynes and charge-transfer complexes with TCNEJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2001J. Gonzalo Rodríguez Abstract n -(N,N -Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between chloromethylene(triphenyl)phosphine ylide and the appropriate n -(N,N -dimethylamino)benzaldehyde, followed by dehydrochlorination with a strong base. The conjugate dimers 1,4-bis[n -(N,N -dimethylamino)phenyl]buta-1,3-diyne were obtained by oxidative dimerization with copper(I) chloride. X-ray molecular structure analysis of the dimer 1,4-bis[2 -(N,N -dimethylamino)phenyl]buta-1,3-diyne corroborated the resonance contribution of the o -dimethylamino substituent, which was confirmed in the solid state by the molecular crystalline packing. Both o - and p -(N,N -dimethylamino) conjugate dimers develop 1:1 charge-transfer complexes with TCNE and their structure was identified by NMR, IR and UV,visible spectroscopic data. Differential scanning calorimetric analyses of the 1,3-diynes showed an irreversible transformation to a thermopolymer as a unimolecular reaction. Copyright © 2001 John Wiley & Sons, Ltd. [source] Sequence, Structure and Energy Transfer in DNA,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2007Thomas M. Nordlund Excitation energy transfer in DNA has similarities to charge transfer, but the transport is of an excited state, not of mass or charge. Use of the fluorescent, modified adenine base 2-aminopurine (2AP) as an energy trap in short (3- to 20-base) single- and double-stranded DNA oligomers is reviewed. Variation of 2AP's neighboring sequence shows (1) relatively efficient transfer from adenine compared to that from cytosine and thymine, (2) efficient transfer from guanine, but only when 2AP is at the 3, end, (3) approximate equality of efficiencies for 3, to 5, and 5, to 3, directional transfer in adenine tracks. The overall, average transfer distance at room temperature is about four adenine bases or less before de-excitation. The transfer fluorescence excitation spectral shape is similar to that of the absorption spectrum of the neighboring normal bases, confirming that initial excitation of the normal bases, followed by emission from 2AP (i.e. energy transfer), is occurring. Transfer apparently may take place both along one strand and cross-strand, depending on the oligomer sequence. Efficiency increases when the temperature is decreased, rising above 50% (overall efficiency) in decamers of adenine below ,60°C (frozen media). Modeling of the efficiencies of transfer from the nearest several adenine neighbors of 2AP in these oligomers suggests that the nearest two neighbors transfer with near 100% efficiency. As bases in B DNA, as well as in single-stranded DNA, are separated by less than 5 Ĺ (less than the size of a base), standard Förster transfer theory should not apply. Indeed, while both theory and experiment show efficiency decreasing with donor,acceptor distance, the experimental dependence clearly disagrees with Förster 1/r6 dependence. It is not yet clear what the best theoretical approach is, but any calculation must deal accurately with the excited states of bases, including strong base,base interactions and structural fluctuations, and should reflect the increase of efficiency with temperature decrease and the relative insensitivity to strandedness (single, double). Attempts to use DNA as a molecular "fiber optic" face three primary challenges. First, reasonable efficiency over more than a base or two occurs only in adenine stretches at temperatures well below freezing. Second, transfer in these adenine tracks is efficient in both directions. Third, absorption of UV light occurs randomly, making excitation at a specific site on this "fiber optic" a challenge. [source] Chemical and enzymatic hydrolysis of anthraquinone glycosides from madder rootsPHYTOCHEMICAL ANALYSIS, Issue 3 2003Goverdina C. H. Derksen Abstract For the production of a commercially useful dye extract from madder, the glycoside ruberythric acid has to be hydrolysed to the aglycone alizarin which is the main dye component. An intrinsic problem is the simultaneous hydrolysis of the glycoside lucidin primeveroside to the unwanted mutagenic aglycone lucidin. Madder root was treated with strong acid, strong base or enzymes to convert ruberythric acid into alizarin and the anthraquinone compositions of the suspensions were analysed by HPLC. A cheap and easy method to hydrolyse ruberythric acid in madder root to alizarin without the formation of lucidin turned out to be the stirring of dried madder roots in water at room temperature for 90 min: this gave a suspension containing pseudopurpurin, munjistin, alizarin and nordamnacanthal. Native enzymes are responsible for the hydrolysis, after which lucidin is converted to nordamnacanthal by an endogenous oxidase. Copyright © 2003 John Wiley & Sons, Ltd. [source] On Law and Disagreement.RATIO JURIS, Issue 2 2003Some Comments on "Interpretative Pluralism" According to both Michelman and Waldron, the epistemic indeterminacy of interpretation,that is, the fact that principles do not possess stable meanings beyond, and independent of, their application to concrete cases,puts its finger on a point of the contractualist and prevailing political theory. But, if neither the legitimacy of any democratic order nor the standard of internal criticism can be founded on a broad background consensus on constitutional essentials, "what else makes a deliberative process of legislation and adjudication a generator of legitimacy so that citizens are induced to accept controversial results as ,worthy of respect'?" The route pursued goes beyond all views that require legitimacy to be based on sharing a set of "thick" ethical beliefs. In this perspective, the author argues that the performative meaning of constitution-making "provides a thin yet sufficiently strong base," which corresponds to the minimal requirements inherent in the very practice of framing a constitution. [source] Facilitating student understanding of buffering by an integration of mathematics and chemical concepts,BIOCHEMISTRY AND MOLECULAR BIOLOGY EDUCATION, Issue 2 2004Robert Curtright Abstract We describe a simple undergraduate exercise involving the titration of a weak acid by a strong base using a pH meter and a micropipette. Students then use their data and carry out graphical analyses with a spreadsheet. The analyses involve using mathematical concepts such as first-derivative and semi-log plots and provide an opportunity for collaboration between biochemistry and mathematics instructors. By focusing on titration data, rather than the titration process, and using a variety of graphical transformations, we believe that students achieve a deeper understanding of the concept of buffering. [source] Titration of poly(dA-dT) · poly(dA-dT) in solution at variable NaCl concentrationBIOPOLYMERS, Issue 2 2004Marta Airoldi Abstract CD and uv absorption data showed that high molecular weight poly(dA-dT) · poly(dA-dT), at 298 K, undergoes an acid-induced transition from B-double helix to random coil in NaCl solutions of different concentrations, ranging from 0.005 to 0.600M. Similarly, titration of the polynucleotide with a strong base causes duplex-to-single strands transition. The base- and acid-induced transitions were both reversible by back-titration (with an acid or, respectively, with a base): the apparent pKa were the same in both directions. However, the number of protons per titratable site (adenine N1) required to reach half-denaturation was in great excess over the stoichiometric value; to a much larger extent, the same effect was observed also for the deprotonation of the N3H sites of thymine. Moreover, in the basic denaturation experiments, at low salt concentrations ([NaCl],0.300M) less acid than calculated was needed to back-titrate the base excess to half-denaturation. Both effects could be qualitatively justified on the basis of the counterion condensation theory of polyelectrolytes and considering the energy barrier created by the negatively charged phosphodiester groups to the penetration of the OH, ions inside the double helix and the screening effect of the Na+ ions on such charges, in the deprotonation experiments. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source] Bifunctional Heterogeneous Catalysis of Silica,Alumina-Supported Tertiary Amines with Controlled Acid,Base Interactions for Efficient 1,4-Addition ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 41 2009Ken Motokura Dr. Abstract We report the first tunable bifunctional surface of silica,alumina-supported tertiary amines (SA,NEt2) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon,carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA,NEt2) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA,NEt2 catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA,NEt2 catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time 13C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid,base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid,base interactions. [source] Stressing the (Other) Three Rs in the Search for Empirically Supported Treatments: Review Procedures, Research Quality, Relevance to Practice and the Public InterestCLINICAL PSYCHOLOGY: SCIENCE AND PRACTICE, Issue 3 2000John R. Weisz The Society of Clinical Psychology's task forces on psychological intervention developed criteria for evaluating clinical trials, applied those criteria, and generated lists of empirically supported treatments. Building on this strong base, the task force successor, the Committee on Science and Practice, now pursues a three-part agenda: (a) evolution of review and classification procedures with an emphasis on reliability across reviewers, (b) an active role as gadfly in promoting improved research, and (c) a dissemination program (with an evolving web site) to make our process, findings, and data base accessible to practitioners, researchers, policy makers, and the public. We seek to link practitioners and researchers in the shared goal of improving mental health care by encouraging evidence-based practice and training. [source] Estimation of the soil,water partition coefficient normalized to organic carbon for ionizable organic chemicals,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2008Antonio Franco Abstract The sorption of organic electrolytes to soil was investigated. A dataset consisting of 164 electrolytes, composed of 93 acids, 65 bases, and six amphoters, was collected from literature and databases. The partition coefficient log KOW of the neutral molecule and the dissociation constant pKa were calculated by the software ACD/Labs®. The Henderson-Hasselbalch equation was applied to calculate dissociation. Regressions were developed to predict separately for the neutral and the ionic molecule species the distribution coefficient (Kd) normalized to organic carbon (KOC) from log KOW and pKa. The log KOC of strong acids (pKa < 4) was not correlated to these parameters. The regressions derived for weak acids and bases (undissociated at environmental pH) were similar. The highest sorption was found for strong bases (pKa > 7.5), probably due to electrical interactions. Nonetheless, their log KOC was highly correlated to log KOW. For bases, a nonlinear regression was developed, too. The new regression equations are applicable in the whole pKa range of acids, bases, and amphoters and are useful in particular for relatively strong bases and amphoters, for which no predictive methods specifically have been developed so far. [source] Buttressing Effects Rerouting the Deprotonation and Functionalization of 1,3-Dichloro- and 1,3-DibromobenzeneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2003Christophe Heiss Abstract A systematic comparison between 1,3-difluorobenzene, 1,3-dichlorobenzene, and 1,3-dibromobenzene did not reveal major differences in their behavior towards strong bases such as lithium diisopropylamide or lithium 2,2,6,6-tetramethylpiperidide. Thus, all 2,6-dihalobenzoic acids 1 are directly accessible by consecutive treatment with a suitable base and dry ice. In contrast, (2,6-dichlorophenyl)- and (2,6-bromophenyl)triethylsilane (2a and 2b) were found to undergo deprotonation at the 5-position (affording acids 3 and, after deprotection, 4), whereas the 1,3-difluoro analog is known to react at the 4-position. The 2,4-dihalobenzoic acids 7 were selectively prepared from either the silanes 2 (by bromination at the 4-position, metalation and carboxylation of the neighboring position, followed by desilylation and debromination) or the 1,3-dihalo-2-iodobenzenes 8 (by base-promoted migration of iodine to the 4-position followed by iodine/magnesium permutation and subsequent carboxylation). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Are Oxazolidinones Really Unproductive, Parasitic Species in Proline Catalysis?HELVETICA CHIMICA ACTA, Issue 3 2007Experiments Pointing to an Alternative View, Thoughts Abstract The N,O-acetal and N,O-ketal derivatives (oxazolidinones) formed from proline, and aldehydes or ketones are well-known today, and they are detectable in reaction mixtures involving proline catalysis, where they have been considered ,parasitic dead ends'. We disclose results of experiments performed in the early 1970's, and we describe more recent findings about the isolation, characterization, and reactions of the oxazolidinone derived from proline and cyclohexanone. This oxazolidinone reacts (THF, room temperature) with the electrophiles , -nitrostyrene and chloral (=trichloroacetaldehyde), to give the Michael and aldol adduct, respectively, after aqueous workup (Scheme,5). The reactions occur even at ,75° when catalyzed with bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or EtN(i-Pr)2 (DIPEA) (10%; Table,1). It is shown by NMR (Figs.,1 and 3) and IR analysis (Figs.,2 and 4) that the primarily detectable product (before hydrolysis) of the reaction with the nitro-olefin is again an oxazolidinone. When dissolved in hydroxylic solvents such as MeOH, ,hexafluoroisopropanol' ((CF3)2CHOH; HFIP), AcOH, CF3COOH, or in LiBr-saturated THF, the ring of the oxazolidinone from cyclohexanone and proline opens up to the corresponding iminium ion (Tables,2,4), and when treated with strong bases such as DBU (in (D8)THF) the enamino-carboxylate derived from proline and cyclohexanone is formed (Scheme,8). Thus, the two hitherto putative participants (iminium ion and enamine) of the catalytic cycle (Scheme,9) have been characterized for the first time. The commonly accepted mechanism of the stereoselective C,C- or C,X-bond-forming step (i.e., A,D) of this cycle is discussed and challenged by thoughts about an alternative model with a pivotal role of oxazolidinones in the regio- and diastereoselective formation of the intermediate enamino acid (by elimination) and in the subsequent reaction with an electrophile (by trans -addition with lactonization; Schemes,11,14). The stereochemical bias between endo - and exo -space of the bicyclo[3.3.0]octane-type oxazolidinone structure (Figs.,5 and 6) is considered to possibly be decisive for the stereochemical course of events. Finally, the remarkable consistency, with which the diastereotopic Re -face of the double bond of pyrrolidino-enamines (derived from proline) is attacked by electrophiles (Schemes,1 and 15), and the likewise consistent reversal to the Si -face with bulky (Aryl)2C-substituents on the pyrrolidine ring (Scheme,16) are discussed by invoking stereoelectronic assistance from the lone pair of pyramidalized enamine N-atoms. [source] Biodegradable Polymer Nanocylinders Fabricated by Transverse Fragmentation of Electrospun Nanofibers through AminolysisMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2008Taek Gyoung Kim Abstract Biodegradable polymeric nanocylinders were fabricated by segmental degradation of electrospun nanofibers. Poly(L -lactic acid) (PLA) was electrospun to produce non-crystalline nanofibers that were immediately treated with amino group-containing strong bases to fabricate semi-crystalline PLA nanocylinders with tunable aspect ratio. The formation of PLA nanocylinders was attributed to two concurrent events occurring during the aminolysis reaction: (i) development of stacked lamellae and (ii) transversely oriented degradation and fragmentation of the amorphous gaps between lamellae, both responsible for the fragmentation of PLA nanofibers into uniformly shaped nanocylinders. The aspect ratio of PLA nanocylinders was tunable by varying aminolysis time and controlling nanofiber diameter. [source] An Environmentally Benign Access to Dimethylated 1,6-Dihydropyrimidines Using Dimethyl Carbonate as Methylating Agent under MicrowaveCHINESE JOURNAL OF CHEMISTRY, Issue 2 2008Xi-Cun WANG Abstract An environmentally benign procedure for dimethylated 1,6-dihydropyrimidines has been developed by the reaction of 1,2,3,4-tetrahydropyrimidine-2-thiones with dimethyl carbonate, a non-toxic and environmentally friendly reagent. The methylation of 1,2,3,4-tetrahydropyrimidine-2-thione was promoted by MgO and tetrabutylammonium bromide (TBAB) under microwave. This protocol avoids the use of strong bases and highly toxic methylating agents such as methyl halide or dimethyl sulfate. Additionally, the possible role of MgO/TBAB in the reaction was also presented. [source] | |||||||||||||||||||||||||