Mechanism Of Diels-Alder Reaction Research Articles

ChemInform Abstract: Synthesis of 2‐Trifluoromethyl Quinoline (III) by the Reaction of Fluorinated Imine with Alkyne Catalyzed by Indium(III) Triflate.

AbstractDeuterium labeling studies support the Diels—Alder reaction mechanism proposed.

Mechanism of wet sewage sludge pyrolysis in a tubular furnace

The main objective of this work was to develop a preliminary mechanistic understanding of wet sewage sludge decomposition from starting constituents to final products, including intermediates formed during the pyrolysis process. Sewage sludge with a moisture content of 84.2 wt% was pyrolyzed at different temperatures in a tubular furnace, the pyrolysis products (hydrogen-rich fuel gas, tar and solid char) were detected by micro-GC, GC-MS, and FTIR, respectively. The high moisture content of wet sewage sludge generated a steam-rich atmosphere at high temperatures, leading to an in situ steam reforming of the volatile compounds and a partial gasification of the solid char, which contributed to the production of hydrogen-rich fuel gas. The pyrolysis process can be divided into two steps: at a relatively low temperature (<600 °C), the breaking of the C–H bonds of alkyl gave rise to the release of CH 4 and C 2 hydrocarbons, and a large amount of CO and CO 2 evolved as the result of C O decreasing, both processes indicated the decomposition of volatile compounds. The increasing absorbance amount of C–O and C–H aromatic demonstrated the formation of tar. As temperature increased further, the diminishing IR absorbance of C–O and C–H aromatic was accompanied by a significant reduction of tar yield and an increase of H 2. H 2 was considered as an indicator for the occurrence of tar cracking. The Diels–Alder reaction mechanism followed by dehydrogenation was employed to explain the PAHs formation.

Aqueous syntheses of [(Cp-R)M(CO) 3] type complexes (Cp = cyclopentadienyl, M = Mn, 99mTc, Re) with bioactive functionalities

We describe reactions of [ 99mTc(H 2O) 3(CO) 3)] + ( 1) with Diels–Alder products of cyclopentadiene such as “Thiele’s acid” (HCp-COOH) 2 ( 2) and derivatives thereof in which the corresponding [(Cp-COOH) 99mTc(CO) 3)] ( 3) complex did form in water. We propose a metal mediated Diels–Alder reaction mechanism. To show that this reaction was not limited to carboxylate groups, we synthesized conjugates of 2 (HCp-CONHR) 2 ( 4a–c) ( 4a, R = benzyl amine; 4b, R = N α-Boc- l-2,3-diaminopropionic acid and 4c, R = glycine). The corresponding 99mTc complexes [( 4a) 99mTc(CO) 3)] 6a, [( 4b) 99mTc(CO) 3)] 6b and [( 4c) 99mTc(CO) 3)] 6c have been prepared along the same route as for Thiele’s acid in aqueous media demonstrating the general applicability of this synthetic strategy. The authenticity of the 99mTc complexes on the no carrier added level have been confirmed by chromatographic comparison with the structurally characterized manganese or rhenium complexes. Studies of the reaction of 1 with Thiele’s acid bound to a solid phase resin demonstrated the formation of [(Cp-COOH) 99mTc(CO) 3)] 3 in a heterogeneous reaction. This is the first evidence for the formation of no carrier added 99mTc radiopharmaceuticals containing cyclopentadienyl ligands via solid phase syntheses. Macroscopically, the manganese analogue 5a and the rhenium complexes 5b–c have been prepared and characterized by IR, NMR, ESI-MS and X-ray crystallography for 5a (monoclinic, P2 1/ c, a = 9.8696(2) Å, b = 25.8533(4) Å, c = 11.8414(2) Å, β = 98.7322(17)°) in order to unambiguously assign the authenticity of the corresponding 99mTc complexes.

Surface modification of polyacrylonitrile-based carbon fiber and its interaction with imide

In this work, sized polyacrylonitrile (PAN)-based carbon fibers were chemically modified with nitric acid and maleic anhydride (MA) in order to improve the interaction between carbon fiber surface and polyimide matrix. Bismaleimide (BMI) was selected as a model compound of polyimide to react with modified carbon fiber. The surface characteristic changing after modification and surface reaction was investigated by element analysis (EA), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and surface enhanced Raman scattering (SERS). The results indicated that the modification of carbon fiber surface with MA might follow the Diels Alder reaction mechanism. In the surface reaction between modified fibers and BMI, among the various surface functional groups, the hydroxyl group provided from phenolic hydroxyl group and bridged structure on carbon fiber may be the most effective group reacted with imide structure. The results may shed some light on the design of the appropriate surface structure, which could react with polyimide, and the manufacture of the carbon fiber-reinforced polyimide matrix composites.

N-oxyl mediated free radical donor-acceptor co- and terpolymerization of styrene, cyclic maleimide monomers andn-butyl methacrylate

The N-oxyl mediated donor-acceptor copolymerization of styrene as a donor and the maleimides N-phenylmaleimide (NPI), N-benzylmaleimide (BMI), and N-cyclohexylmaleimide (CMI) as acceptor monomers is studied, using 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as reversible capping agent and benzoyl peroxide (BPO) as initiator. These copolymerizations are characterized by high polymerization rates and very short induction periods. In bulk, a control of the molecular weights and the polydispersity is only possible for the weakest acceptor CMI. For the stronger acceptors BMI and NPI the polymerizations have to be performed in solution (anisol) to realize a linear increase of the molecular weight with conversion and polydispersities below Mw/Mn 1.55. The polymerization rates (NPI > BMI > CMI), the induction periods (CMI > BMI > NPI) and the total number of polymer chains (NPI > BMI > CMI) of the TEMPO mediated free radical donor-acceptor copolymerizations are a function of the acceptor strength of the maleimide monomers. As the main reason for the observed high reactivity, an “acceptor depending self-initiation”, proceeding via a Diels-Alder reaction mechanism, is discussed. Additionally, the concept of the “acceptor depending self-initiation” is used for the rate of acceleration of S/BuMA copolymerizations leading to poly(S-co-BuMA-co-maleimide) terpolymers with well-controlled molecular weights and narrow molecular weight distributions.

On the mechanism of the Diels-Alder reaction of enal dienophiles. Competitive reactivity and ab initio calculations using a transannular probe

A sterically unbiased macrocyclic probe has been used to study the Diels-Alder reaction mechanism of enal dienophiles. All the results, theoretical as well as kinetical, converge to the conclusion that a virtually non-concerted zwitterionic mechanism is possible for certain cases of Lewis acid catalysis. This conclusion was reached because the zwitterionic limit intermediates obtained after the first step could arise either from favored [6.11] or disfavored [7.10] bicycle formation. These two opposite effects could assist or counteract asynchronicity. The analysis of these effects showed that asynchronicity highly stabilizes the Diels-Alder reaction transition state if the latter is geometrically favorable such as in the case of a [6.11] zwitterionic limit intermediate. Altogether, these results on the Diels-Alder cycloaddition involving enal dienophiles demonstrate the extreme sensitivity in transition state geometry in response to the most subtle structural changes in substrates.

The role of proton transfer in acid-catalyzed diels-alder reactions: A theoretical study

The role of proton transfer in the mechanism of Diels-Alder reactions of acrolein with 1-hydroxybutadiene and 1-methylbutadiene catalyzed by NH 4 + is theoretically studied by means of the MINDO/3 method. It is found that the catalyst strengthens the asynchronous formation of the two new C-C bonds. In the catalyzed reaction these bonds are formed in two clearly differentiated steps, through a stable intermediate, in which there is a total proton transfer from the catalyst to the dienophile.

Evidence for the concerted mechanism of the Diels-Alder reaction of butadiene with ethylene

Diels-Alder reactions of substituted dienes and dienophiles have been found to cccur by both concerted and stepwise mechanisms.’.* The nature of the mechanism of the prototype Diels-Alder reaction of butadiene with ethylene to form cyclohexene is not only of fundamental interest but has generated fervid fulminations for favorite We wish to report new experimental evidence that is compatible only with the concerted mechanism, as well as further theoretical evidence for the synchronicity of this concerted mechanism.6 The reactions of 1,1,4,4-tetradeuterio-1,3-butadiene with cisor trans-1,2-dideuterioethylene were carried out at 185 “ C for 36 h at a pressure of 1800 psi in a stainless steel b~mb.~-’O Infrared spectra of the unreacted dideuterioethylenes indicate that they do not isomerize under the conditions of the reaction. Each cyclohexene product was separated from butadiene dimers by preparative GLC” and was then epoxidized with m-chloroperbenzoic acid (Figure 1). The N M R spectrum of cyclohexene oxide (Figure 2A) has resonances for the protons at C, and C, at 6 1.19 and 1.38, corresponding to protons that are cis and trans to the epoxide oxygen.12 The proton NMR spectra of the epoxides obtained from the reactions of cis and trans-dideuterioethylenes are clearly different. The DH couplings were partially eliminated by irradiation of the C3 and C6 deuteriums to give the spectra shown in Figure 2. The cis-dideuterio compound has a singlet resonance at d 1.19, due to the product with C4 and Cs hydrogens cis to the epoxide, and a second singlet a t 6 1.38, due to the

SCF MO CNDO/2 considerations on the Diels-Alder reaction : An ethylene- cis-butadiene system

The semi-empirical SCF MO CNDO/2 theory was applied to the addition reaction of ethylene and cis-butadiene and theoretical investigations on the Diels-Alder reaction mechanism were performed. In the calculations of the system, molecular structures (bond lengths and hybridization conditions of atoms) and geometrical relationship of reactant molecules were determined so that the total energy of the system was minimized. Variations of interaction energy, molecular and electronic structures, and geometrical relationship of two molecules were obtained along the reaction process.