Rate Of Diels-Alder Reaction Research Articles

Study and optimization of Diels-Alder reaction of piperine in aqueous ionic solutions using Gn.HCl as a catalyst

Study and optimization of Diels-Alder reaction of piperine in aqueous ionic solutions using Gn.HCl as a catalyst

Diels-Alder Reaction in microemulsions with ionic liquid

The Diels-Alder Reaction (DAR) between N-ethylmaleimide and 2,3-dimethyl-1,3-butadiene was studied in microemulsions with ionic liquid (IL) for the first time. The apparent second-order rate constants were determined by spectrophotometry in the microemulsion. The effect of solvent on the DAR rate was investigated and interpreted. The experimental results showed that the reaction rate in the microemulsion with IL was enhanced and it was faster than that in pure isooctane and in generic AOT microemulsion. The effect of the IL on the apparent second rate constant (k2) was explained. The effect of temperature on the reaction rate was studied, and values of apparent activation energy were estimated in various microemulsion with IL. Copyright © 2012 John Wiley & Sons, Ltd.

Thermally reversible Diels–Alder-based polymerization: an experimental and theoretical assessment

A pair of monomers capable of undergoing reversible polymerization—based on reversible Diels–Alder (DA) chemistry—as a function of the applied reaction temperature is presented. Specifically, the reaction of isophorone bis(sorbic carbamate), a difunctional diene, with 1,4-phenylenebis(methylene)bis((diethoxyphosphoryl)methanedithioformate), a difunctional dithioester, was studied in detail. Various factors, including the monomer concentration, the type of solvent, and the presence of a Lewis acid, that influence this step-growth polymerization were evaluated. The solvent type was found to have a significant effect on the DA reaction rate. Under the optimized conditions, which are 1.8 g mol−1 of each monomer in acetonitrile with 1.1 equivalents of zinc chloride at 50 °C for 4 h, a polymer with a peak molecular weight of 9600 g mol−1 (relative to poly(styrene) standards) was obtained. The resulting polymer was employed to investigate the correlation between time, temperature, and percentage of debonded monomers achieved during the retro DA (rDA) reaction. In addition, theoretical predictions of the rDA temperature were obtained via ab initio quantum chemical calculations. The monomeric diene and dienophile system was employed for the calculations of the equilibrium constants at various rDA reaction temperatures to correlate the percentage of bonded molecules with the applied temperature. It was calculated that 60% of the polymer becomes debonded at a temperature (Tqc) of around 220 °C, a result that agrees well with that obtained experimentally (Texp = 219 °C).

Correlation of Isoprene-Maleic Anhydride Reaction Rate Constants in Mixed Solvents

Correlation of the Diels-Alder reaction rate constants of dilute solution for isoprene-maleic anhydride in the pure solvents such as hexane, ethyl acetate, toluene, monochlorobenzene and nitrobenzene, and the binary mixed solvents obtained by the authors are reviewed. For correlating the reaction rate constants in binary mixed solvents an empirical method based on the Arrhenius equation coupled with a Redlich-Kister type excess function introduced to obtain the excess activation energy in the mixed solvents is proposed. It is shown that the present model can correlate the reaction rate constants with a good agreement for the binary mixed solvents. Further, the applicability for the prediction of the excess activation energy for multicomponent mixed solvents by the addition of those for the constituent binary mixed solvents is presented.

Experimental evidence to support viscosity dependence of rates of Diels-Alder reactions in solvent media.

This note is aimed at ascertaining whether rates of Diels-Alder reactions depend on the viscosity of solvent media in which the reactions are performed. On the basis of the data collected from the literature and in this laboratory, it is seen in general that the rates increase in the solvents with their viscosities ranging up to approximately 1.2 cP. In solvents possessing viscosities above 1.2 cP, a drop in the reaction rates is observed in all cases. The effect of temperature on the above phenomena is also examined.

Kinetics study and theoretical modeling of the Diels-Alder reactions of cyclopentadiene and cyclohexadiene with methyl vinyl ketone. The effects of a novel organotungsten catalyst.

The Diels-Alder reaction rate constants of methyl vinyl ketone with cyclopentadiene and cyclohexadiene in the presence of a novel organotungsten catalyst, [P(2-py)(3)W(CO)(NO)(2)](2+), have been measured experimentally and modeled theoretically at several temperatures. The uncatalyzed systems were also studied for direct comparison. When 0.0022 M of catalyst is present at room temperature, the rate constants were found to be approximately 5.3 and 5300 times higher than the corresponding uncatalyzed reactions for cyclopentadiene and cyclohexadiene systems, respectively. Experimental data suggested that the catalyst reduced the activation energies by 5-10 kcal/mol. However, the preexponential factors showed reduction of more than 3 orders of magnitude upon catalysis due to the entropic effects. The energy barriers and the rate constants of the uncatalyzed systems were accurately modeled by correlated electronic structure and dual-level variational transition state theory calculation. The calculated endo selectivity is in good agreement with the observed product distribution. Theoretical calculation also suggested the catalyzed reactions proceeded in a highly asynchronous or even stepwise fashion.

Effect of Elevated External Pressure on the Rate of the Diels-Alder Reaction of 9-Methylanthracene with Acrylonitrile, Catalyzed by Gallium Chloride

External pressure was found to similarly affect the rate of a gallium chloride-catalyzed Diels-Alder reaction between 9-methylanthracene with acrylonitrile and a noncatalyzed reaction of 9,10-dimethylanthracene with acrylonitrile. The observation of equal activation volumes is consistent with the assumption that elevated pressure very weakly affects the bond energy in the n,η complex of acrylonitrile with gallium chloride.

Diels—Alder reaction. Effect of internal and external factors on the reactivity of diene—dienophile systems

The key factors influencing the Diels—Alder reaction rate at ambient and elevated pressures were elucidated using data on the reactivity of various diene—dienophile systems in usual and Lewis acid-catalyzed Diels—Alder reactions, the reaction enthalpy, complex formation, dissolution, and solvation, and the donor-acceptor properties of the reactants. It was found that taking account of both the orbital interaction energy and the balance of bond rupture and formation energies allows correct prediction of the reaction rate in the absence or in the presence of Lewis acids.

Rate acceleration and subsequent retardation of Diels-Alder reactions in LiClO4-diethyl ether: an experimental investigation.

The experimental kinetic data for several Diels-Alder reactions show why a 5 M LiClO(4)-diethyl ether (LPDE) solution offers maximum enhancement of reaction rates, endo/exo ratios, and yields. These reactions, if carried out in LPDE solutions of concentrations higher than 5 M, show a substantial decrease in these kinetic parameters. This decrease is attributed to the very high viscosity of LPDE solutions near saturation, though this interpretation is not consistent when considered in terms of sizes of the diene and dienophile. The monoetherates, dietherates, and higher other clusters in LPDE solutions and their relationship with the Lewis acid catalysis by Li+ offer a more plausible explanation of both the enhancement and the decrease of the rate of Diels-Alder reactions in this medium.

Differences in rates of Diels-Alder reactions as experimental indicators of synchronous or asynchronous transition states

Assessment of the relative rates of the Diels-Alder reactions of the unsymmetrical diene 2-(trimethylsilyloxy)-1,3-cyclohexadiene ( 1) and its 6,6- and 5,5-dimethyl analogs 2 and 3 indicated that with symmetrical, ethylenic dienophiles ( para-benzoquinone, maleic anhydride and N-phenylmaleimide) the Diels-Alder reaction is almost synchronous, but with tetracyanoethylene and with diethyl acetylenedicarboxylate the addition is sufficiently asynchronous as to lead to different rates of reaction with dimethyl-dienes 2 and 3.

Stereoselectivities and reaction rates in Diels-Alder reactions promoted by non-aqueous solvents and their aqueous mixtures: Correlations with non-adjustable parameters

Stereoselectivities and rates of Diels-Alder reactions in different solvents were correlated with a parameter, Q, defined based on internal pressure, which is normalized with respect to a polarity scale. The polarity scale or index, although purely empirical in nature, can be calculated from the refractive index of the solvent. These correlations were linear for both stereoselectivities and reaction rates. Using expressions derived in this study, it is possible to represent the kinetic profiles of several Diels-Alder reactions in about 75 pure and mixed solvent media. The activation volume of a reaction can be directly estimated from the regression of data on rates and Q in various solvents using the proposed correlations.

Unusual stability of N-methylmaleimide cycloadducts: characterization of isobenzofuran retro-Diels-Alder reactions

Many years ago Diels and Thiele noted the unusual stability of maleic anhydride cycloadducts and employed the feature in scavenging anthracene generated in a retro-[4+2] reaction. N-methyl-maleimide, although nearly identical to maleic anhydride in rates of Diels-Alder reactions, forms even more stable cycloadducts. The rate constants for the four reactions that characterize the furan/N-methylmaleimide system were measured under the conditions used by Lee and Herndon to study the furan/maleic anhydride system. Comparison of the two dienophiles indicates that N-methylmaleimide adducts are ca. 3 kcal.mol -1 more stable than the corresponding exo- and endo-maleic anhydride adducts. Somewhat larger (ca- 4±0.5 kcal.mol -1 ) differences in stability were found for the cycloadducts of the much more reactive diene isobenzofuran

Rate Enhancement in Ethanolic Aqueous Buffer. The Diels-Alder Reaction

Abstract We have observed a 2.5-3-fold increase in the rate of Diels-Alder reactions when done in aqueous ethanol, where the aqueous solution was prepared with a pH 7 buffer. This is a simple, inexpensive and convenient method for modest acceleration of the Diels-Alder reaction, in addition to the rate increase normally observed in aqueous media.

Vinylboranes are omniphilic dienophiles. Some unusual and useful properties of vinylboranes in diels-alder reactions

The rate of Diels-Alder reactions with vinyl-9-BBN is uniquely insensitive to diene substituent effects, and high reactivity is observed with both electron-rich and electron-poor dienes. The regioselectivity of these reactions is controlled mainly by steric effects.

Zur Reaktivität des Silaethens Me2Si = C(SiMe3)2: Relative Geschwindigkeiten der Diels‐Alder‐Reaktionen mit organischen Dienen1,2)

On the Reactivity of the Silaethene Me2Si = C(SiMe3)2: Relative Rates of Diels‐Alder Reactions with Organic Dienes1,2)[4 + 2] Cycloaddition of dienes to silaethene Me2Si = C(SiMe3)2 is accelerated in the directions: (i) butadiene < isoprene < CH2 = CR – CH = CH2 with R = CH2SiMe2CH‐ (SiMe3)2 (increase in electron donation of the diene substiuents), (ii) trans‐piperylene < 2,3‐dimethylbutadiene (DMB) < isoprene (decrease in steric hindrance of diene substituents), (iii) cis‐piperylene or cis,trans‐hexadiene < trans‐piperylene and trans,trans‐hexadiene (decrease in equilibrium concentration of the cisoid conformer).

ChemInform Abstract: Changes of Stereoselectivity and Rate in Diels‐Alder Reactions by Hydrophobic Solvent Effects and by Bovine Serum Albumin.

Abstract The use of water instead of benzene as the solvent can strongly influence the stereoselectivity and the rate of Diels-Alder reactions of 1,4-naphthoquinone derivatives with different dienes. Enantiomeric excess (e.e.) up to 38% is reached in the presence of a catalytic amount of bovine serum albumin.

Changes of stereoselectivity and rate in diels-alder reactions by hydrophobic solvent effects and by bovine serum albumin

The use of water instead of benzene as the solvent can strongly influence the stereoselectivity and the rate of Diels-Alder reactions of 1,4-naphthoquinone derivatives with different dienes. Enantiomeric excess (e.e.) up to 38% is reached in the presence of a catalytic amount of bovine serum albumin.