Acetone Enolate Research Articles

BEP-Like Correction of Nonequilibrium Thermodynamic Parameters of the Solvent-Assisted Reactions: The DFT and Ab Initio Study of Hydration, Peroxidation, and Enolization of Acetone and 1,1,1-Trifluoroacetone in Aqueous Solutions.

The mechanisms of enolization and reactions of nucleophilic addition to carbonyl compounds were analyzed by density functional theory (DFT) (PBE1PBE) and ab initio (DLPNO-CCSD(T)) level of theory using the interaction of water and hydrogen peroxide with acetone and 1,1,1-trifluoroacetone (TFA) as the reference reactions. The transition states of the studied reactions were localized within the integrated approach that includes both the dielectric continuum theory (polarizable continuum model (PCM)) and the cyclic or two-cluster explicit solvation models. The considered models provide proton transfer in the enolization, hydration, and peroxidation reactions by the Grotthuss mechanism. It is shown that the calculated activation parameters at a sufficiently high level of theory and a sufficiently flexible solvation model can be additionally refined using the Bell-Evans-Polanyi (BEP)-like correction (in a form of the Bell-Evans-Polanyi equation), which is linear scaling of the model potential energy surface according to the equilibrium parameters of the reference reaction (experiment or high-level calculation). Quite good correspondence of the corrected and reference activation parameters and the lower sensitivity of the calculation results to the choice of the solvation model indicate the high reliability of the proposed BEP-like correction technique.

Real-time monitoring of surface acetone enolization and aldolization

Real-time DRIFTS reveals the formation of acetone enolate and its subsequent aldolization via an Eley–Rideal type mechanism on Zn1Zr10Oz.

Surface acetone reactions on ZnxZryOz: A DRIFTS-MS study

We report a systematic DRIFTS-MS study of surface acetone aldolization and self-deoxygenation reactions on ZrO2 and Zn1Zr10Oz, using temperature programmed surface reactions of both acetone reactant and possible intermediate compounds including diacetone alcohol, mesityl oxide, phorone, and isophorone. DRIFTS was used to monitor the evolution of surface species while MS was used to track corresponding gas phase products, in an attempt to identify the distinct reaction pathways observed on the two catalysts as well as the role zinc plays in the corresponding reaction pathways. It is found that aldol condensation (or aldolization) of acetone occurs readily at low temperature (298 K), forming mainly acetone dimers (i.e., diacetone alcohol, DAA/mesityl oxide, MSO) on both ZrO2 and Zn1Zr10Oz with the latter being more active. At elevated temperatures, secondary MSO reactions are diverted, mainly caused by the different Lewis basicity on the two catalysts. Over ZrO2, MSO reacts with activated acetone (acetone enolate) to form a surface 4,4-dimethyl-2,6-heptadione (phorone-C), which is further converted into a stable isophorone intermediate. At temperatures above 473 K, polymerization/oligomerization of isophorone along with basic hydroxyl promoted decomposition reactions occur, leading to the formation of heavier carbonaceous surface species and gas-phase side products (methane and CO2). The addition of zinc balances the surface acid-base properties on ZnxZryOz (i.e., Zn1Zr10Oz) via not only enhancing the surface Lewis basicity but passivating the strong acidity. This balance, especially the enhanced surface Lewis basicity largely promotes the α-H abstraction of MSO to form MSO enolate on the Zn1Zr10Oz, which thus favors the aldolization of MSO enolate and acetone, a reaction tends to form 2,6-dimethyl-2,5-heptadien-4-one (phorone-A). Phorone-A then readily decomposes to produce isobutene as a major product at temperature as low as 373 K. Note that, despite the facile formation of isobutene at low temperatures, a high temperature (673 K) is still necessary to release the strongly adsorbed formate/carbonate/acetate species via CO2 formation.

Spectroscopy of Ethylenedione and Ethynediolide: A Reinvestigation

AbstractIn an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron‐photofragment coincidence (PPC) spectroscopy was applied to measure anions at m/z 56 and 57 using a pulsed discharge of glyoxal vapor and N2O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C3H4O, and acetone enolate radical, C3H5O. The spectra were also found to have features nearly identical to those reported for OCCO and HOCCO by Sanov and co‐workers. The stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C3H4O, and the acetone enolate radical, C3H5O.

Kinetic Analysis of a Solid Base-Catalyzed Reaction in Sub- and Supercritical Water Using Aldol Condensation with Mg(OH)2 as a Model

The kinetics of aldol condensation between acetone and benzaldehyde catalyzed by Mg(OH)2 in sub- and supercritical water at various temperatures (250–450 °C) and pressures (23–31 MPa) was investigated to elucidate the effects of water properties on solid base catalysis. The kinetics obey the Eley–Rideal (ER) mechanism, in which the reaction occurs between acetone enolate adsorbed on the catalyst and benzaldehyde in the bulk phase. Minimal benzaldehyde is adsorbed on the catalyst because of competitive adsorption with water; thus, benzaldehyde in the bulk phase mainly precipitates. The pressure dependence indicates that the reaction rate is affected by the competitive adsorption of water and acetone, as expected for the ER mechanism, and by changes in the solvent properties of supercritical water. The increase in the activation energy and the decrease in the amount of adsorbed acetone with increasing pressure are plausible effects of the solvent properties.

ABE Condensation over Monometallic Catalysts: Catalyst Characterization and Kinetics

AbstractHerein, we present work on the catalyst development and the kinetics of acetone‐butanol‐ethanol (ABE) condensation. After examining multiple combinations of metal and basic catalysts reported in the literature, Cu supported on calcined hydrotalcites (HT) was found to be the optimal catalyst for the ABE condensation. This catalyst gave a six‐fold increase in reaction rates over previously reported catalysts. Kinetic analysis of the reaction over CuHT and HT revealed that the rate‐determining step is the C−H bond activation of alkoxides that are formed from alcohols on the Cu surface. This step is followed by the addition of the resulting aldehydes to an acetone enolate formed by deprotonation of the acetone over basic sites on the HT surface. The presence of alcohols reduces aldol condensation rates, as a result of the coverage of catalytic sites by alkoxides.

Computational Reaction Mechanism Study of the Elimination of 2-pentanone

Theoretical studies for reaction mechanism of the gas phase elimination of 2-petnanone were carried out at B3LYP/6-31+g(d) level of theory. The mechanism for elemination is Norrish type II. The elimination reaction proceeds via a six-membered cyclic transition state with the formation of ethelene and propen-2-ol (acetone enol), which rearranges to the ketone. The calculated kinetic and thermodynamic parameters are in reasonable agreement with the reported experimental values. Analysis of the progress along the reaction coordinate, in terms of geometrical parameters suggest these reactions are dominated by the abstraction of a hydrogen atom from the - carbon by the carbonyl oxygen to give the diradical, and together with an important cleavage of Cα-Cβ bond in the transition state through concerted reaction mechanism.

Insights into Acetone Photochemistry on Rutile TiO2(110). 2. New Photodesorption Channel with CH3 Ejection along the Surface Normal

Angle-resolved photon-stimulated desorption (PSD) combined with infrared reflection–absorption spectroscopy and temperature-programmed desorption reveal two distinct channels in the photochemistry of acetone on rutile TiO2(110). During UV irradiation of coadsorbed oxygen and acetone molecules, nonthermal methyl radicals (CH3) are ejected in two different directions: (i) normal to the surface and (ii) off-normal at ∼±66° to the surface normal in the [11̅0] azimuth (i.e., perpendicular to the O and Ti rows). The direction of the “off-normal” PSD component is consistent with the orientation of the C–CH3 bonds in the η2-acetone diolate—a photoactive form of acetone chemisorption on the oxidized TiO2(110) surface proposed in earlier studies. The direction of the “normal” PSD component requires an orientation of a C–CH3 bond which is not consistent with the η2-acetone diolate structure. The “off-normal” PSD component dominates at lower acetone coverage (<0.2 ML), but does not increase at higher coverages in accord with the acetone diolate peak intensity in the infrared reflection–absorption spectra. The “normal” PSD component grows with the acetone coverage up to 0.6 ML. Based on the H/D exchange experiments, the newly discovered “normal” PSD channel is tentatively assigned to a photoproduced η2- acetone enolate as a precursor.

Optical Properties and Colloidal Stability Mechanism of Bismuth Nanoparticles Prepared by Q-switched Nd:Yag Laser Ablation in Liquid

Bismuth is semimetal with unique properties such as magnetoresistance and thermoelectric behaviors due to high electron mobility, low carrier density and highly anisotropic Fermi surface. In addition, bismuth NPs undergoes a semimetal to semiconductor transition due to size induced quantum confinement effect. Therefore, bismuth NPs are potentially useful for optical and electro optical devices. In addition, bismuth NPs are interesting as green lubricant and thermoelectric materials. Recently, laser ablation is extensively employed to synthesis of metal NPs by laser target interaction in liquid environment. The aim of this work is the synthesis of stable bismuth colloidal NPs by Q-switched laser ablation in acetone. A Q-switched Nd:YAG laser with the fundamental wavelength at 1064nm,energy of 118mJ/pulse and 12ns pulse duration was employed for bismuth target ablation. The laser was operated for 5min at repetition rate of 10Hz. Colloidal stability, particle size, crystal structure and optical properties of the NPs were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-visible spectroscopy respectively. The bismuth NPs were rather spherical and with the particle size of 27±9nm. The XRD pattern of NPs was consistent with a bismuth rhombohedral crystal structure. Colloidal bismuth NPs in acetone is in light brown color. UV-Visible spectra were measured in 6 months shows perfect stability of colloidal samples without any precipitation. Optical extinction without plasmon resonance pick in visible wavelengths is the optical characteristic of bismuth NPs and reveal perfect dispersion of NPs without agglomeration or coupling of NPs in liquid. According to the FT-IR result as the stability of NPs is related to the large dipole moment of acetone molecule and acetone enolate formation on the surface of bismuth NPs.

Density Functional Theory Study of Mixed Aldol Condensation Catalyzed by Acidic Zeolites HZSM-5 and HY

We applied density functional theory to investigate the mixed aldol condensation of acetone and formaldehyde in acid zeolites HZSM-5 and HY, as a prototypical bond-forming reaction in biofuel production. We modeled the acid-catalyzed reaction in HZSM-5 and HY in two steps: keto–enol tautomerization of acetone and bimolecular condensation between formaldehyde and the acetone enol. For both acid zeolites, the keto–enol tautomerization of acetone was found to be the rate-determining step, consistent with the accepted mechanism in homogeneous acid-catalysis. Convergence studies of the activation energy for keto–enol tautomerization, with respect to cluster sizes of HZSM-5 and HY, exhibit rather different convergence properties for the two zeolites. The keto–enol activation energy was found to converge in HY to ∼20 kcal/mol for a cluster with 11 tetrahedral atoms (11T cluster), which does not complete the HY supercage. In contrast, the activation energy for HZSM-5 reaches an initial plateau at a value of ∼28 kcal/mol for clusters smaller than 20T and then converges to ∼20 kcal/mol for clusters of size 26T or greater, well beyond the completion of the HZSM-5 pore. As such, completing a zeolite pore surrounding a Brønsted acid site may be insufficient to converge activation energies; instead, we recommend an approach based on converging active-site charge.

Thiamine pyrophosphate stimulates acetone activation by Desulfococcus biacutus as monitored by a fluorogenic ATP analogue.

Acetone can be degraded by aerobic and anaerobic microorganisms. Studies with the strictly anaerobic sulfate-reducing bacterium Desulfococcus biacutus indicate that acetone degradation by these bacteria starts with an ATP-dependent carbonylation reaction leading to acetoacetaldehyde as the first reaction product. The reaction represents the second example of a carbonylation reaction in the biochemistry of strictly anaerobic bacteria, but the exact mechanism and dependence on cofactors are still unclear. Here, we use a novel fluorogenic ATP analogue to investigate its mechanism. We find that thiamine pyrophosphate is a cofactor of this ATP-dependent reaction. The products of ATP cleavage are AMP and pyrophosphate, providing first insights into the reaction mechanism by indicating that the reaction proceeds without intermediate formation of acetone enol phosphate.

Adsorption and Tautomerization Reaction of Acetone on Acidic Zeolites: The Confinement Effect in Different Types of Zeolites

The adsorption and tautomerization reaction of acetone in H-FER, H-ZSM-5, and H-MCM-22 zeolites has been studied using full quantum calculations at the M06-2X/6-311+G(2df,2p) level of theory. The combination of a large quantum cluster and this meta-hybrid density functional results in reasonably accurate adsorption energies of −26.9, −28.1, and −23.9 kcal/mol for acetone adsorption in H-FER, H-ZSM-5, and H-MCM-22, respectively. Due to the acidity of the zeolite and the framework confinement effect, the tautomerization of acetone proceeds through a much lower activation barrier than in the isolated gas phase or in the presence of water molecules alone. The activation energies are calculated to be 24.9, 20.5, and 16.6 kcal/mol in H-FER, H-ZSM-5 and H-MCM-22, respectively. The endothermic reaction energy decreases with increasing of the zeolite pore sizes and amounts to 22.7, 17.6, and 15.9 kcal/mol for the reaction in H-FER, H-ZSM-5 and H-MCM-22, respectively. In addition, the adsorbed acetone enol is found to be highly unstable in the zeolite framework and readily reverse-transforms to adsorbed acetone with a very small activation energy. The activity trend and relative stabilities of the adsorbed keto and enol forms are well correlated with the interactions within the Brønsted acid site.

Quantum-chemical investigation of the formation of 1,3-diiodoacetone at the photoinitiated disproportionation of 1-iodoacetone

In the framework of ab initio and DFT methods potential energy surfaces (PES) of 1-iodoacetone disproportionation S0, T1, and S1 were investigated. The first stage of the reaction proceeds in the S1 state and leads to the formation of a bimolecular system involving 1,3-diiodoacetone and acetone enol form. The subsequent enol-ketone rearrangement with a high probability occurs in the ground state.

A useful synthetic equivalent of an acetone enolate

2-Methoxymethoxy-3-chloropropene derived organometallics act as synthetic equivalents of an acetone enolate. Indium-promoted reaction of this reagent with aldehydes affords aldol adducts in moderate to excellent yields. When the reaction was performed with zinc, aldol products were isolated in protected form as the corresponding MOM-enol ethers.

Activation energies of sigmatropic shifts in propene and acetone enolate from the anti-Hermitian contracted Schrödinger equation

The hydrogen [1,3]-sigmatropic shift in propene is predicted by the Woodward-Hoffman rules to occur by an antarafacial pathway, yet the lack of experimental evidence suggests that this pathway is not favorable. Two natural questions arise: (i) can the [1,3]-shift be made more favorable by a symmetry-forbidden multistep pathway, and (ii) can the energetics be influenced by a substituent on propene? As in many chemical reactions, describing the energetics of these reactions requires a balanced treatment of both single-reference and multireference electron correlations, and yet traditional wave function methods often excel in treating only one kind of correlation. An equitable description of correlation effects, however, can be achieved, at a cost similar to efficient single-reference methods, by computing the two-electron reduced density matrix (2-RDM) from the anti-Hermitian part of the contracted Schrödinger equation (ACSE) [D. A. Mazziotti, Phys. Rev. Lett. 97, 143002 (2006)]. As with the contracted Schrödinger equation, the indeterminacy of the ACSE is removed without the many-electron wave function by reconstructing the 3-RDM from the 2-RDM via cumulant theory [D. A. Mazziotti, Chem. Phys. Lett. 289, 419 (1998)]. In this paper we apply the ACSE to study sigmatropic shifts in both propene and acetone enolate while extending its formalism to treat doublet spin states. In the 6-311G(**) basis set the ACSE predicts the activation energy of the trimethylene-to-propene rearrangement to be 8.8 kcal/mol while multireference perturbation theory yields a smaller barrier of 2.2 kcal/mol and coupled cluster singles-doubles predicts a negative barrier. We further find that the [1,3]-shift in acetone enolate is more favorable by approximately 30 kcal/mol than the [1,3]-shift in propene, which is consistent with a prior theoretical investigation as well as experimental observations of these shifts in 2-butanone enolate.

Efficient aldol condensation in aqueous biphasic system under microfluidic conditions

A microfluidic system was applied to aldol reaction in aqueous biphasic medium. Advantageous aspects of microfluidic conditions, that is, efficient mixing, fast heat transfer, and residence time control led to the high-yielding reaction of acetone enolate with even α-proton-containing aldehydes in biphasic aqueous-acetone system, by minimizing the formation of self-condensation products.

On the Mechanism of Reaction of Radicals with Tirapazamine

Ketyl radicals produced by photolysis of ketones or di-tert-butyl peroxide (DTBP) in alcohol solvents react rapidly with tirapazamine (TPZ). The acetone ketyl radical (ACOH) reacts with TPZ with an absolute second-order rate constant of (9.7 +/- 0.4) x 108 M-1 s-1. The reaction kinetics can be followed by monitoring the bleaching of TPZ absorption at 475 nm or the formation of a reaction product which absorbs at 320 and 410 nm. The ACOD radical reacts with TPZ in 2-propanol-OD with an absolute rate constant of (6.7 +/- 0.5) x 108 M-1 s-1, corresponding to a kinetic isotope effect (KIE) of 1.4. Deuteration of the radical on carbon (ACOH-d6) retards the reaction of the radical with TPZ even further (absolute rate constant = (4.8 +/- 0.04) x 108 M-1 s-1). This result corresponds to a KIE of 2.0. Radicals derived from dioxane and diisopropyl ether by flash photolysis of DTBP in ethereal solvent react with TPZ more slowly than do ketyl radicals. It is concluded that ketyl radicals react, in part, with TPZ in organic solvents by transfer of a hydrogen atom from the OH and CH3 groups of the ketyl radical to the oxygen atom at the N4 position of TPZ to form acetone or acetone enol and a radical derivative of TPZ (TPZH). The latter species absorbs at 320 and 405 nm, has a lifetime of hundreds of microseconds in alcohol solvents, and decays by disproportionation to form TPZ and a reduced heterocycle. The reduced heterocycle eventually forms a desoxytirapazamine by a polar mechanism. The results are supported by density functional theory calculations. It is proposed that dioxanyl radical will also react, in part, with TPZ by transfer of a hydrogen atom from the carbon adjacent to the radical center to the oxygen atom at the N4 position of TPZ. This produces the enol ether and the previously mentioned TPZH radical. It is further posited that ether radicals react a bit more slowly than ketyl radicals because they lack the second mode of hydrogen transfer (from the OH group) that is present in the ACOH radical. Our data are permissive of the possibility that ether radicals add to TPZ at a rate that is competitive with beta-hydrogen atom transfer.

Secondary N-nitrosocarbamate anions: Structure and alkylation reactions. A DFT study

The current article reports theoretical studies (DFT: B3LYP/6-31+G(d)) on the structure and alkylation reactions of the anions of some secondary N-nitrosocarbamates, a class of ambident nucleophiles whose chemistry has been little explored. Several anions ( 1– 4), with an increasing size of the carbamate alkyl (aryl) group were investigated, in an attempt to establish the influence of the size of that group on the thermal stability and regioselectivity of alkylation of the title anions. The conclusion is that thermal stability and the mode of reaction are affected significantly only in the presence of very large and branched carbamate groups. The thermal decomposition studies at the B3LYP/6-31+G(d) level of theory yield quantitative results that are in very good or excellent agreement with experimental data. A detailed study of N- vs. O-alkylation reactions was conducted, in an attempt to reveal the nature and origin of regioselectivity. Several factors seem to play prominent role: (1) charge distribution within the N-nitrosocarbamate anion; (2) exothermicity of alkylation; (3) size of electrophile and (4) size of the carbamate alkyl (aryl) group. Computational results on the alkylation reactions of N-nitrosocarbamate anions are compared to results for alkylation of the acetone enolate ion, the outcome for the latter being in sharp contrast to earlier, lower-level calculations. In addition, alkylation studies were conducted on the Z-isomers of the title anions and the results indicate that they undergo O-alkylation with significantly lower barriers compared to the E-isomers. However, Z-isomers are 5–6 kcal/mol less stable thermodynamically and application of the Curtin–Hammett principle leads to the conclusion that O-alkylation occurs almost exclusively on the E-isomers.

On the dissociation of the 2-pentanone ion studied by threshold photoelectron photoion coincidence spectroscopy

The photodissociation of 2-pentanone has been studied by threshold photoelectron photoion coincidence (TPEPICO) spectroscopy, in which ion time-of-flight (TOF) mass spectra are recorded as a function of the photon energy in the range of 9.6–12.2 eV. 2-Pentanone ions dissociate via four competitive channels: ethylene (C 2H 4) loss to produce the propen-2-ol ion, n-propyl ( C 3H 7) loss to produce the acetyl ion, and two parallel methyl ( CH 3) loss channels, producing the butanoyl ion at low energies and the but-3-en-2-ol ion at higher energies. The latter dissociates further via ethylene (C 2H 4) loss providing a second pathway to the acetyl ion. This final dissociation channel is observed experimentally by the appearance of an asymmetric ion peak in the time-of-flight (TOF) distribution at photon energies greater than 11.5 eV. The ion TOF distributions and breakdown diagram have been modeled in terms of the statistical RRKM theory for unimolecular reactions, yielding the 0 K dissociation onsets of 10.239 ± 0.015 eV for the butanoyl ion and 10.259 ± 0.019 eV for the propen-2-ol (acetone enolate) ion. By relating the measured onsets with other well established heats of formation, the 298 K heat of formation of the butanoyl and propen-2-ol ions were determined to be 586.9 ± 2.1 and 680.7 ± 1.8 kJ/mol, respectively. The acetone enolate ion is thus 37 kJ/mol more stable than the acetone ion, a value supported by G3B3, and CBS-QB3 calculations. The but-3-en-2-ol ion was found to lose ethylene to produce the acetyl ion without an energy barrier.

ATP-Dependent Enolization of Acetone by Acetone Carboxylase from Rhodobacter capsulatus

Acetone carboxylase catalyzes the carboxylation of acetone to acetoacetate with concomitant hydrolysis of ATP to AMP and two inorganic phosphates. The biochemical, molecular, and genetic properties of acetone carboxylase suggest it represents a fundamentally new class of carboxylase. As the initial step in catalysis, an alpha-proton from an inherently basic (pK(a) = 20) methyl group is abstracted to generate the requisite carbanion for attack on CO(2). In the present study alpha-proton abstraction from acetone has been investigated by using gas chromatography/mass spectrometry to follow proton-deuteron exchange between D(6)-acetone and water. Acetone carboxylase-catalyzed proton-deuteron exchange was dependent upon the presence of ATP, Mg(2+), and a monovalent cation (K(+), Rb(+), NH(4)(+)), and produced mixtures of isotopomers, ranging from singly exchanged H(1)D(5)- to fully exchanged H(6)-acetone. The initial rate of isotopic exchange was higher than k(cat) for acetone carboxylation. The time course of isotopic exchange showed that multiple exchange events occur for each acetone-binding event, and there was a 1:1 stoichiometric relationship between molecules of ATP hydrolyzed and the sum of new acetone isotopomers formed. ADP rather than AMP was formed as the predominant product of ATP hydrolysis during isotopic exchange. The stimulation of H(+)(-)D(+) exchange and ATP hydrolysis by K(+) followed saturation kinetics, with apparent K(m) values of 13.6 and 14.2 mM for the two activities, respectively. The rate of H(+) exchange into D(6)-acetone was greater than the rate of D(+) exchange into H(6)-acetone. There was an observable solvent (H(2)O vs D(2)O) isotope effect (1.7) for acetone carboxylation but no discernible substrate (H(6)- vs D(6)-acetone) isotope effect. It is proposed that alpha-proton abstraction from acetone occurs in concert with transfer of the gamma-phosphoryl group of ATP to the carbonyl oxygen, generating phosphoenol acetone as the activated nucleophile for attack on CO(2).