Acetone Cation Research Articles

Photocatalytic C–H Carboxylation of 1,3-Dicarbonyl Compounds with Carbon Dioxide Promoted by Nickel(II)-Sensitized α-Fe2O3 Nanoparticles

Insertion of carbon dioxide into C–H bonds under mild conditions is an industrially important yet highly challenging task. In the present study, we report the synthesis of an efficient photocatalyst consisting of a Ni(bpy)3Cl2 sensitizer supported on α-Fe2O3 nanoparticles for the CO2 insertion into C–H bonds, particularly carboxylation of 1,3-dicarbonyl compounds like acetyl acetone, methyl acetoacetate, and ethyl acetoacetate with CO2 under visible light irradiation using carbon tetrachloride as a solvent. The carboxylation of these compounds afforded the predominant formation of a single isomeric acid as confirmed by 13C NMR spectroscopy. Based on the computational studies, a possible reaction mechanism suggested the generation of CO2 radical anions at the conduction band of α-Fe2O3 through single electron transfer mediated by the nickel(II) complex that coupled with acetyl acetone cation radicals at the valence band of α-Fe2O3 to give the corresponding carboxylic acid. The protocol described in the present study presents a light-assisted approach and a low-cost material for the synthesis of carboxylic acids utilizing CO2 under mild reaction conditions.

Multifunctional Ln-MOF Luminescent Probe for Efficient Sensing of Fe3+, Ce3+, and Acetone.

A new series of five three-dimensional Ln(III) metal-organic frameworks (MOFs) formulated as [Ln4(μ6-L)2(μ-HCOO)(μ3-OH)3(μ3-O)(DMF)2(H2O)4] n {Ln3+ = Tb3+ (1), Eu3+ (2), Gd3+ (3), Dy3+ (4), and Er3+ (5)} was successfully obtained via a solvothermal reaction between the corresponding lanthanide(III) nitrates and 2-(6-carboxypyridin-3-yl)terephthalic acid (H3L). All of the obtained compounds were fully characterized, and their structures were established by single-crystal X-ray diffraction. All products are isostructural and possess porous 3D networks of the fluorite topological type, which are driven by the cubane-like [Ln4(μ3-OH)3(μ3-O)(μ-HCOO)]6+ blocks and μ6-L3- spacers. Luminescent and sensing properties of 1-5 were investigated in detail, revealing a unique capability of Tb-MOF (1) for sensing acetone and metal(III) cations (Fe3+ or Ce3+) with high efficiency and selectivity. Apart from a facile recyclability after sensing experiments, the obtained Tb-MOF material features a remarkable stability in a diversity of environments such as common solvents, aqueous solutions of metal ions, and solutions with a broad pH range from 4 to 11. In addition, compound 1 represents a very rare example of the versatile Ln-MOF probe capable of sensing Ce3+ or Fe3+ cations or acetone molecules.

Controlling tunnelling in methane loss from acetone ions by deuteration

Energetic acetone cations decay by methane or methyl radical loss. Although the methane-loss barrier to form the ketene cation is higher and the activation entropy is lower, it has a significant branching ratio at low energies thanks to quantum tunnelling. H-atom tunnelling can be selectively quenched and the methane-loss channel suppressed quantitatively by deuteration.

Decomposition of diazomeldrum's acid: a threshold photoelectron spectroscopy study.

Derivatives of meldrum's acid are known precursors for a number of reactive intermediates. Therefore, we investigate diazomeldrum's acid (DMA) and its pyrolysis products by photoionization using vacuum ultraviolet (VUV) synchrotron radiation. The threshold photoelectron spectrum of DMA yields an ionization energy (IE) of 9.68 eV. Several channels for dissociative photoionization are observed. The first one is associated with loss of CH3, leading to a daughter ion with m/z = 155. Its appearance energy AE0K was determined to be 10.65 eV by fitting the experimental data using statistical theory. A second parallel channel leads to m/z = 69, corresponding to N2CHCO, with an AE0K of 10.72 eV. Several other channels open up at higher energy, among them the formation of acetone cation, a channel expected to be the result of a Wolff-rearrangement (WR) in the cation. When diazomeldrum's acid is heated in a pyrolysis reactor, three thermal decomposition pathways are observed. The major one is well-known and yields acetone, N2 and CO as consequence of the WR. However, two further channels were identified: The formation of 2-diazoethenone, NNCCO, together with acetone and CO2 as the second channel and E-formylketene (OCCHCHCO), propyne, N2 and O2 as a third one. 2-Diazoethenone and E-formylketene were identified based on their threshold photoelectron spectra and accurate ionization energies could be determined. Ionization energies for several isomers of both molecules were also computed. One of the key findings of this study is that acetone is observed upon decomposition of DMA in the neutral as well as in the ion and both point to a Wolff rearrangement to occur. However, the ion is subject to other decomposition channels favored at lower internal energies.

Acetone cation chemistry under varying electron density conditions: from unimolecular decomposition to dissociative recombination processes

The chemistry of ionized acetone:Ar mixtures under varied ionizing electron density conditions has been studied using matrix-isolation techniques. Gaseous acetone diluted in excess argon gas was subjected to electron bombardment with 300 eV electrons at currents between 20 and 200 μA. Linear wire 'pin' and metal 'plate' electron collector geometries were employed, allowing a wide range of electron density conditions to be explored. The products of subsequent reaction processes were matrix isolated and analyzed by Fourier transform infrared absorption spectroscopy. Products included methane, ketene, 1-propen-2-ol (the enol isomer of acetone), CO, HCO, ethane, ethane, acetylene and CCCO. Product absolute and relative yields varied with acetone number density, the choice of anode geometry and the rate of electron bombardment. The overall chemistry observed is rationalized in terms of mechanistic steps involving unimolecular cation decomposition, ion-molecule reactions, radical-radical reactions and dissociative recombination processes.

Alkaline protease production of Bacillus cohnii APT5

An obligate alkaliphilic Bacillus strain was isolated from a soil sample and identified as Bacillus cohnii APT5 based upon phylogenetic and phenotypic analyses. The optimum growth pH of B. cohnii APT5 was 10.0. B. cohnii APT5 was also found capable of producing an extracellular alkaline protease that showed optimum activity (693,318 U/min) at 50 °C and pH 11.0 when grown in a medium containing casein. The enzyme was partially purified 3.22-fold with a yield of 78.74% after acetone precipitation and cation exchange column chromatography, respectively. The partially purified enzyme maintained its activity when incubated at 50 °C for 2 h. It was stable at pH 11.0 at room temperature for 72 h. Furthermore, the alkaline protease activity was not completely inactivated by the specific inhibitors of serine alkaline proteases and metalloproteases such as PMSF and EDTA. While 1 mM PMSF had no effect on the enzyme activity, a 10 mM concentration of PMSF slightly decreased the activity, producing a relative activity of 76%. In addition, the enzyme was found to be very stable toward surface active agents such as SDS, Tween 20, Tween 80, and Triton X-100. None of the metal ions used (Ca^{2+}, Mg^{2+}, Zn^{2+}, Fe^{2+}, and Mn^{2+}) showed an inhibitory effect on enzyme activity. On the contrary, APT5 alkaline protease activity increased 53% when treated with Mn^{+2}. It was concluded that the active center of APT5 alkaline protease required Mn^{+2} as a cofactor. Based on the thermostability, pH stability, and resistance of B. cohnii APT5 alkaline protease against inhibitors, this enzyme may be very useful in commercial applications, particularly in the detergent industry.

A multiphoton ionization study of acetone using time-of-flight mass spectrometry

The 3p Rydberg states of acetone and photodissociation of the acetone cation were studied using time-of-flight (TOF) mass spectrometry. The 3p Rydberg state spectroscopy of acetone was investigated with linearly polarized two-photon resonance enhanced multiphoton ionization (REMPI) from 320 to 337 nm. Several new transition bands were observed in the spectra. In addition to the CH3COCH3 + ion, CH3CO+ and CH3 + fragments were observed. The laser power dependences suggest that the CH3COCH3 +, CH3CO+ and CH3 + ions are produced in three-, four-, and four-photon processes, respectively. Production of CH3CO+ and CH3 +involves excitation of the ground state acetone cation by an additional photon and subsequent decomposition of the excited acetone ion. The average translational energies of CH3CO+ and CH3 + from dissociation in CH3COCH3 +(X) + hv → CH3CO+ + CH3 and CH3COCH3 +(X) + hv → CH3 + + CH3CO, respectively, were derived from the ion TOF peak profiles.

Suppression of the Methyl Radical Loss from Acetone Cation within (CH3COCH3)n{CH3COCH3}+Clusters

We have investigated the photophysics of the acetone radical cation in the vacuum ultraviolet energy region by multiphoton ionization combined with time-of-flight mass spectrometry in a cluster beam. We have found that the loss of methyl radical from the acetone radical cations is remarkably suppressed at 10.5 eV when they are solvated by a few neutral acetone molecules. The cluster ion mass spectra obtained by nanosecond and picosecond laser pulses reveal that there are intermolecular processes, occurring in several tens of picoseconds, which are responsible for the survival of the acetone cations in clusters. This remarkable solvation effect on the yield of the methyl radical loss from the acetone cation can be rationalized by the intracluster vibrational energy redistribution and the self-catalyzed enolization which compete with the methyl radical loss process.

Mechanism of [M + H] + Formation in Atmospheric Pressure Photoionization Mass Spectrometry: Identification of Propionitrile in Acetonitrile with High Mass Accuracy Measurement and Tandem Mass Spectrometry and Evidence for Its Involvement in the Protonation Phenomenon

The role of propionitrile in the production of [M+H]+ under atmospheric pressure photoionization (APPI) was investigated. In dopant-assisted APPI using acetone and anisole, protonated acetone and anisole radical cations were the most prominent ions observed. In dopant-free or direct APPI in acetonitrile, however, a major ion in acetonitrile was detected and identified as propionitrile, using high accuracy mass measurement and collision induced dissociation studies. Vaporizing ca. 10(-5) M althiazide and bendroflumethazide under direct APPI in acetonitrile produced their corresponding protonated species [M+H]+. In addition to protonated acetonitrile, its dimers, and acetonitrile/water clusters, protonated propionitrile, propionitrile dimer, and propionitrile/water clusters were also observed. The role of propionitrile, an impurity in acetonitrile and/or a possible product of ion-molecule reaction, in the production of [M+H]+ of althiazide and bendroflumethazide was further investigated in the absence of dopant using propionitrile-d5. The formation of [M+D]+ species was observed, suggesting a possible role of propionitrile in the protonation process. Additionally, an increase in the [M+H]+ signal of althiazide and bendroflumethazide was observed as a function of propionitrile concentration in acetonitrile. Theoretical data from the literature supported the assumption that one possible mechanism, among others, for the formation of [M+H]+ could be attributed to photo-initiated isomerization of propionitrile. The most stable isomers of propionitrile, based on their calculated ionization energy (IE) and relative energy (DeltaE), were assumed to undergo proton transfer to the analytes, and mechanisms were proposed.

Sterically crowded azulene-based dication salts as novel guests: synthesis and complexation studies with crown ethers and calixarenes in solution and in the gas phase

The 1,4-bis(3-guaiazulenylmethylium)benzene and 1,4-bis[1-(4,6,8-trimethylazulenylmethylium)]benzene dication salts were synthesized via an acid-catalyzed condensation/dehydration protocol with guaiazulene-terephthalaldehyde (2 : 1 ratio), and 4,6,8-trimethylazulene-terephthalaldehyde (2 : 1 ratio) respectively in one-pot processes. A similar condensation reaction with the parent azulene led to an insoluble oligomer that was shown by MALDI-TOF-MS to contain 1,4-bis[(diazulenyl)methylium]benzene as a repeating unit. Dication salts and were fully characterized by 2D NMR and NOE techniques and by electrospray-MS (ES-MS) and MALDI-TOF-MS. NMR studies confirm that the dications are best represented as bis-tropylium species. A delicate balance of electronic (inductive stabilization) and steric influence of the alkyl groups on the seven-membered ring seems to influence the chemo-/regioselectivity of the co-condensation process. NMR titration and T(1) measurements established that, despite its highly crowded structure, dication forms host-guest HG complexes with dibenzo-30-crown-10 (DB30C10) and dibenzo-24-crown-8 (DB24C8) in solution, but fails to complex with the smaller dibenzo-18-crown-6 (DB18C6). The corresponding HG cation-molecule cluster ions were also detected in the gas phase by ES-MS, showing the formation of both dication-crown 1 : 1 and 1 : 2 complexes. Similar complexation of dication salt with DB30C10 was observed via NMR titration and T(1) measurements in solution and by ES-MS in the gas phase. Although solution complexation studies (NMR titration) did not indicate stable complex formation between and p-tert-butyl-methoxycalix[8]arene, their [HG](2+) and [H(2)G](2+) clusters were detectable by ES-MS. Solution decomplexation experiments (HG(2+) --> H + G(2+)) were performed on -crown complex by addition of DMSO, acetone, silver tosylate, and tropylium cation salt. Complexation of with DB30C10 was also studied by microcalorimetric titration.

Ab initio study of the isomerization and photodissociation of the C 3H 6O + [rad] cation radicals

We have performed ab initio (using Gaussian-2 (G2M) method) calculations for the reactant, intermediates, transition states, and photofragmentation products of the C 3H 6O + cation radicals in order to elucidate its unimolecular photofragmentation and isomerization mechanisms. We have identified nine photofragmentation pathways, 39 stable intermediates, and 61 transition states for the acetone cation radical C H 3 COC H 3 + as an initial state by ab initio calculations. The isomerization pathways among them are also characterized. It was found that the photofragmentation and isomerization pathways are intertwined through various transition states. Two of the nine pathways contain only one transition state with high energy (70–80 kcal/mol) just after the reactant. In the other ones, the reactant acetone cation radical is transformed into an enol structure via one transition state, and enol and ether isomers undergo many-step isomerizations. From the ab initio calculation, the reaction pathways found in this work have energy barriers higher than those obtained by Heinrich et al. [J. Am. Chem. Soc. 110 (1988) 8183]. In general, the photofragmentation species not investigated previously are found to have high energies, which coincides with the fact that the previous experiments conducted with low laser intensity and short wavelength do not reveal such species.

Surface-induced dissociation of acetone cations from self-assembled monolayer surface of fluorinated alkyl thiol on Au (1 1 1) substrate at low collision energies

We have studied the dissociation of acetone molecular cations to acetyl cations following collision with a monolayer surface of fluorinated alkyl thiol (FC 12) self-assembled on Au (1 1 1) substrate at 13, 25.2 and 49.6 eV kinetic energies. Three energetically distinct dissociation processes contribute to total dissociation in this energy range. At all energies there is a common dissociation pathway involving loss of nearly all of the parent ion’s kinetic energy in the collision process. Fragment ions resulting from this dissociation mechanism are scattered over a wide range of angles. The second pathway, observed at 25.2 and 49.6 eV kinetic energy is delayed dissociation of collisionally excited acetone cations after only a small fraction of the ion’s kinetic energy is lost in the collision process. Fragment ions resulting from this unique dynamics feature are scattered close to the surface parallel. These dissociations take place after the excited ions have passed through the collision region and the energy analyzer and prior to their entering the mass analyzer. At 49.6 eV kinetic energy, a small intensity fragment ion peak appears at intermediate kinetic energy spectra between the low energy loss and the highly inelastic scattering peaks.

A Study of Ion—molecule Reactions in the Xe+ + Acetone System by Flow Technique Mass Spectrometry

Flow reactor technique mass spectrometry was used to study the reaction of Xe+ ions with acetone and the subsequent transformation of the product ions at a buffer gas (He) pressure of 1.1 Torr. A kinetic scheme describing the evolution of the ionic composition of the most abundant ionic constituents (up to the fourth generation) has been determined. The values of rate constants and branching ratios of the key reactions involved in the scheme have been evaluated from experimental kinetic dependences. The main channel of the Xe+ + acetone reaction (which occurs practically at each collision) is the production of the CH3CO+ fragment as the exothermicity of the charge transfer is higher than the dissociation threshold of the ground state acetone cation. The formation of a 2.5% fraction of the molecular ion via a parallel channel indicates that the production of an electronically-excited, long-lived state of the acetone cation takes place. The competition of association and particle-rearrangement processes in the reactions of the CH3CO+ ion and its CH3CO+(CH3)2CO cluster with acetone was also studied. It was found that channels in which a rearrangement of particles takes place (the production of protonated acetone for CH3CO+ and the protonated acetone dimer for CH3CO+(CH3)2CO) are slower than the association process at 1.1 Torr. Total effective rate constants (involving all the channels) for these ions are approximately several 10−10 cm3 s−1 units and the rate constant for the cluster ion is about 40% smaller. The production of slowly reacting C3H6O+ ions with an increase of acetone concentration was observed. Their structure may be ascribed to the enolic acetone cation (CH2COHCH3+). The only pathway for the loss of the ion in an exoergic reaction with acetone is the association process. The product of the process, i.e. the non-protonated ionic dimer of acetone, was also observed in the mass spectra.

Benzonitrile assisted enolization of the acetone and acetamide radical cations: proton-transport catalysis versus an intermolecular H+/· transfer mechanism

The acetamide radical cation, CH3C(=O)NH2·+, can be induced to rearrange into its more stable enol isomer, CH2=C(OH)NH2·+, by an ion–molecule interaction with benzonitrile, C6H5C≡N, under conditions of chemical ionization. (This enolization does not occur unassisted because of a prohibitively high energy barrier: 26 kcal/mol, from a CBS-QB3 calculation.) The initially formed [C6H5C≡N ⋯ acetamide]·+ adduct ion isomerizes to a stable hydrogen bridged radical cation [C6H5C≡N ⋯ H-O-C(NH2)=CH2]·+ en route to its dissociation into the enol ion. Multiple collision and deuterium labeling experiments on the acetamide/benzonitrile and the previously reported acetone/benzonitrile systems, indicate that the acetone ion enolizes by way of a base-catalyzed 1,3-proton shift (“proton-transport catalysis”) but that a different mechanism must be operative in the acetamide system. Ab initio and density functional theory calculations at the PMP3//RHF/D95∗∗ and PMP3//B3LYP/D95∗∗ level of theory support a mechanism which can be described as a consecutive H+/H·transfer between the partners of the [C6H5C≡N·+ ⋯ acetamide] encounter complex. The calculations provide a rationale for the observed isotope effects and lead to a tentative explanation for the differences in interaction of the title ions with benzonitrile.

Photodissociation of the acetone cation at 355 nm using the velocity imaging technique

Photodissociation of acetone cations, CH3COCH3+, at 355 nm has been studied by means of the ion velocity imaging technique. Acetone cations are produced via direct photoionization of a supersonic beam of acetone at 118 nm generated by frequency tripling the 355 nm laser. Only the acetyl cation, CH3CO+, could be detected as a dissociation product in the time-of-flight mass spectrometer. The acetyl ion signal depends upon the fifth power of the 355 nm laser energy, while the acetone ion signal depends upon the third power. This suggests that the fragment ion is produced via two-photon absorption of 355 nm photons by the acetone cation. The total translational energy distribution and angular distribution of acetyl cation were derived from the 2D images of CH3CO+ for the reaction CH3COCH3++2hν355 nm→CH3CO++CH3*. The translational energy distribution suggests that methyl radicals are produced in two electronically excited states, the Rydberg 3s 1 2A1′ and the valence 1 2A″ states. The anisotropy parameter β shows that the Rydberg state is formed via a perpendicular excitation and the valence state via a parallel transition.

Production, partial purification and properties of β‐mannanases obtained by solid substrate fermentation of spent soluble coffee wastes and copra paste using Aspergillus oryzae and Aspergillus niger

In order to achieve a higher added value of two galactomannan-containing wastes, copra paste and spent coffee from the soluble coffee industry (SCW), solid substrate fermentation (SSF) was used. Filamentous fungi Aspergillus oryzae and A niger were used to evaluate the feasibility of producing β-mannanase by SSF. A 23 factorial design was used to select the best interaction among the two fungi, the two substrates and two fermentation times. The treatment ‘A niger–copra–2.5 days’ produced a significantly higher (p < 0.05) β-mannanase activity, having five different isoforms of the enzyme, one of which was partially purified to a specific activity of 764 U mg−1 (U = nmol of mannose released per second from a galactomannan substrate). Copra paste had a higher mannose/galactose ratio (14:1) than SCW (6:1), and low oil content, which led to higher β-mannanase production from SSF. A β-mannanase from SSF of copra produced by A oryzae was highly purified using acetone precipitation and cation exchange and size exclusion chromatographies. This enzyme had an MW of 110 kDa, a pI between 3.5 and 4.5 and a specific activity of 1760 U mg−1; purification achieved was 90.7 times. The temperature and pH for optimal activity were 40 °C and 6.0 respectively. The optimal temperature was lower and the optimal pH higher than others previously reported (produced by submerged fermentation), which could be important for viscosity reduction of concentrated coffee extract in instant coffee manufacture. Copra is an interesting alternative for β-mannanase production, since it is readily available in Mexico; moreover, the residue after SSF has a reduced galactomannan content and may be used for monogastric animal feed. © 2000 Society of Chemical Industry

Collision-induced dissociation dynamics of the enolic acetone cation: evidence for non-ergodic behavior

Angle- and energy-resolved collision-induced dissociation (CID) of the enolic acetone cation to an acetyl cation plus methyl radical has been studied using the crossed-beam technique. The results, presented in the form of center-of-mass velocity contour plots, suggest that a single dynamical mechanism is followed in the CID of enolic acetone cation as the collision energy is increased from 3.4 eV to 41 eV (CM). When interpreted according to the usual two-step model for CID, our data show that energy deposition from translational to internal modes is about 2.6 ± 0.5 eV and is independent of collision energy. We also find that angular scattering is characterized by a constant reduced scattering angle, τ = E cm θ cm. The only decomposition path induced by collision with Ar and He in this energy range is the reaction producing acetyl cation and methyl radical. The simplest interpretation for this relatively large energy deposition and moderate reduced scattering angle parameter is that collisional activation proceeds mainly by electronic excitation, followed by rapid evolution of products onto the ground electronic state hypersurface of the keto ion. However, a low energy tail observed in the fragment ion kinetic energy distributions indicates that a significant fraction of collisionally activated ions survive for 2 to 10 μs before undergoing dissociation. This delayed CID is postulated to follow the same mechanism responsible for the unimolecular metastable dissociation of enolic acetone cations.

Theoretical study of the unimolecular dissociation of the acetone cation radical

Theoretical study of the unimolecular dissociation of the acetone cation radical

Theoretical study of the unimolecular dissociation of the acetone cation radical

Two parallel unimolecular dissociation channels of the acetone cation radical are known experimentally. Methyl loss is the dominant reaction channel for high internal energies of the reactant ion whereas methane elimination is the major reaction channel for low internal energies. However, there exists a controversy about the mechanisms of dissociation of acetone cation radical. High level ab initio MP3/6-311G(d, p)//MP3/6-311G(d,p) calculations have been carried out to investigate the most relevant parts of the C3H6O+·ground state potential energy surface. Reactant and transition state frequencies also have been obtained at the MP3/ 6-311G(d, p) level to include zero-point energy effects. These energy results reinforce the idea that methane elimination at low internal energies may take place only via a tunnelling mechanism through the hydrogen transfer energy barrier. To analyse the influence of the entropic contribution on the mechanism the Gibbs free energy was calculated. Variational calculations at the hydrogen transfer region indicate that conventional transition state theory correctly describes the main features of the system at that bottleneck.

Low energy reactive and dissociative collisions of the acetone cation CH 3COCH 3+ and its fragment ion CH 3CO + with a surface

The interaction of the parent acetone cation CH 3COCH 3 + and its ionic fragment CH 3CO + with a stainless steel surface covered with hydrocarbons has been studied as a function of the collision energy from about 0 up to 50 eV. In the case of CH 3COCH 3 + as projectile ion, the collisional interaction with the surface leads to the formation of protonated acetone and with increasing collision energies to fragment ions originating from both the protonated acetone ion (in particular, the production of CH 2OH +) as well as the parent ion. These results have been confirmed using deuterated acetone ions. In the case of collisions of CH 3CO + with the surface only simple dissociative reactions of the projectile ion are observed.