Elimination Of Acetic Acid Research Articles

Synthesis of tricarbonylated propargylamine and conversion to 2,5-disubstituted oxazole-4-carboxylates.

The N,O-acetal derived from diethyl mesoxalate (DEMO) undergoes elimination of acetic acid upon treatment with a base, leading to the formation of N-acylimine in situ. Lithium acetylide readily attacks the imino group to afford N,1,1-tricarbonylated propargylamines. When the resulting propargylamine reacts with butyllithium, ring closure occurs between the ethynyl and carbamoyl groups, yielding 2,5-disubstituted oxazole-4-carboxylates. This cyclization also occurs when the propargylamine is heated with ammonium acetate, resulting in double activation.

Preparation of Neptunyl and Plutonyl Acetates To Access Nonaqueous Transuranium Coordination Chemistry.

Uranyl diacetate dihydrate is a useful reagent for the preparation of uranyl (UO22+) coordination complexes, as it is a well-defined stoichiometric compound featuring moderately basic acetates that can facilitate protonolysis reactivity, unlike other anions commonly used in synthetic actinide chemistry such as halides or nitrate. Despite these attractive features, analogous neptunium (Np) and plutonium (Pu) compounds are unknown to date. Here, a modular synthetic route is reported for accessing stoichiometric neptunyl(VI) and plutonyl(VI) diacetate compounds that can serve as starting materials for transuranic coordination chemistry. The new NpO22+ and PuO22+ complexes, as well as a corresponding molecular UO22+ complex, are isomorphous in the solid state, and in solution show similar solubility properties that facilitate their use in synthesis. In both solid and solution state, the +VI oxidation state (O.S.) is maintained, as demonstrated by vibrational and optical spectroscopy, confirming that acetate anions stabilize the oxidizing, high-valent +VI states of Np and Pu as they do for the more stable U(VI). All three acetate salts readily react with a model diprotic ligand, affording incorporation of U(VI), Np(VI), and Pu(VI) cores into molecular coordination compounds that occurs concomitantly with elimination of acetic acid; the new complexes are high-valent, yet overall charge neutral, facilitating entry into nonaqueous chemistry by rational synthesis. Computational studies reveal that the dianionic ligand framework assists in stabilizing the +VI O.S. via donation to the 5f shells of the actinides, highlighting the potential usefulness of protonolysis reactivity toward preparation of stabilized high-valent transuranic species.

Light-enhancing ketone transfer hydrogenation catalyzed by diphosphine phenanthroline ruthenium complexes

The cationic phenanthroline ruthenium derivatives [Ru(OAc)(dppb)(NN)]OAc (NN = phen 1, imidazo[4,5-f][1,10]phenanthroline 2) have been obtained in high yield by reaction of the acetate [Ru(OAc)2dppb] with the corresponding NN ligand. The dinuclear cyclometalated [(dppb)(η2-OAc)(Ru(µ-NN-phenimid-NC)Ru(η2-OAc)(dppb)]OAc (3) has been prepared from 2 with [Ru(OAc)2(dppb)] via elimination of acetic acid. The characterization of these compounds has been carried out by NMR, FT-IR, UV–Vis, conductivity and cyclic voltammetry measurements. These derivatives display catalytic activity in the transfer hydrogenation of aromatic and aliphatic cyclic ketones at S/C up to 2000 in presence of NaOiPr in 2-propanol. An increase of the rate (up to 8 times) has been observed upon irradiation at 30 and 60 °C (300 W Xenon Arc Lamp light source). Control experiments show that [Ru(OiPr)2(dppb)(phen)] (1A), formed from 1 by substitution of the acetate with the isopropoxide ligand, shows a stronger emission compared to 1 and that 1A is quenched by NaOiPr, affording the dihydride [Ru(H)2(dppb)(phen)] (1C) via a photo induced β-H elimination.

Iodination of Substituted Alkynes in the Presence of Cadmium(II) Acetate

AbstractA convenient and selective method for the preparation of substituted iodoalkynes, iodoalkenes based on the interaction of propargylic compounds with iodine in the presence of readily available cadmium (II) acetate in some solvents was developed. The highest yields of iodoalkynes and iodoalkenes were recorded using DMSO as the solvent. An excess of the alkylpropargyl substrate unambiguously led to iodolkynes. By varying the reaction conditions using a twofold excess of iodine in DMSO, methanol or ethanol it was possible to achieve a one‐pot preparation of triiodoalkenes. The interaction of iodine with propargyl substrates could be represented in two ways: formation and further nucleophilic transformation of the iodonium complex under the influence of the acetate ion and generation of π‐coordinated species and elimination of acetic acid.

A Homodimer of Withaferin A Formed by Base-Promoted Elimination of Acetic Acid from 27-O-Acetylwithaferin A Followed by a Diels-Alder Reaction.

Treatment of 27-O-acetylwithaferin A (2) with the non-nucleophilic base, 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), afforded 5β,6β-epoxy-4β-hydroxy-1-oxo-witha-2(3),23(24),25(27)-trienolide (3) and 4, a homodimer of withaferin A resulting from a Diels-Alder [4 + 2] type cycloaddition of the intermediate α,β-dimethylene-δ-lactone (9). Structures of 3 and 4 were elucidated using HRMS and 1D and 2D NMR spectroscopic data. The structure of 4 was also confirmed by single crystal X-ray crystallographic analysis of its bis-4-O-p-nitrobenzoate (8). Formation of withaferin A homodimer (4) as the major product suggests regio- and stereoselectivity of the Diels-Alder [4 + 2] cycloaddition reaction of 9. Acetylation of 2-4 afforded their acetyl derivatives 5-7, respectively. Compounds 2-4 and 6-8 were evaluated for their cytotoxic activities against four prostate cancer (PC) cell lines (LNCaP, 22Rv1, DU-145, and PC-3) and normal human foreskin fibroblast (HFF) cells. Significantly, 4 exhibited improved activity compared to the other compounds for most of the tested cell lines.

Copolymers and terpolymers of vinyl phosphonic acid, acrylonitrile, methyl acrylate, and vinyl acetate. Thermal oxidative stabilization and their nanofiber

ABSTRACT Copolymers and terpolymers of acrylonitrile (AN), methyl acrylate (MA), vinyl acetate (VA), and vinyl phosphonic acid (VPA) were synthesized. Thermal gravimetric analysis studies showed that the decomposition of PANMAVPA and PANVAVPA terpolymers started at lower temperatures than PANMA and PANVA copolymers. VPA and MA caused an increase in the ring formation of pendant nitrile groups and the total ash content of PANMAVPA terpolymer. During the thermal oxidative treatment (TOS) of PANVAVPA, the phosphonic acid moiety accelerated double bond formation via acetic acid elimination. 151–340 nm nanofibers were successfully produced from copolymers and terpolymers.

Synthesis of Bis(functionalized) Aminals via Successive Nucleophilic Amidation and Amination

The central carbonyl group of diethyl mesoxalate (DEMO) exhibits high electrophilicity that allows it to be attacked by versatile nucleophiles. Even a less nucleophilic acid amide serves as a nucleophile to produce N,O-acetal upon treatment with DEMO in the presence of acetic anhydride. When the obtained N,O-acetal was treated with a base, the elimination of acetic acid generated N-acylimine in situ. N-Acylimine is also highly electrophilic, allowing it to accept the second nucleophilic addition by an amine, resulting in α,α-bis(functionalized) aminals. This protocol facilitates the modification of the two different amino groups by altering nucleophiles, resulting in the production of tetra-functionalized methane derivatives on demand. The ring closure between the amide moiety and the amino group was achieved using the structural features to form a six-membered ring.

Mechanistic Insights into Palladium(II)-Catalyzed Carboxylation of Thiophene and Carbon Dioxide

The mechanism in palladium-catalyzed carboxylation of thiophene and CO2 is investigated using the density functional theory (DFT) calculations, including three consecutive steps of the formation of carbanion through breaking the C–H bond(s) via the palladium acetate, the elimination of acetic acid and the nucleophile attacking the weak electrophile CO2 to form C–C bond. Results show that the C–C bond is formed through taking the three-membered cyclic conformation arrangement involving the interaction of the transition metal and the CO2, and the CO2 insertion step is the rate-determining step for this entire reaction process. Aiming to precisely disclose what factor determine the origin of the activation energy barrier in this carboxylation reaction, the distortion/interaction analysis is performed along with the entire reaction coordinate.

Supercritical CO2 assisted strategy for acetic acid elimination from industrial cellulose acetate–water mixtures

A critical analysis of the major steps involved in the cellulose acetate industrial process is performed, with the aim of proposing possible improvements using supercritical CO2 based sub-processes. Once highlighted the main weakness of the traditional process, related to the (i) fine modulation of the acetylation reaction to obtain 2.5 acetate, (ii) acetic acid removal from the acetic dope, and (iii) treatment of the diluted acetic acid–water solution, the most attractive alternative resulted the adoption of a supercritical antisolvent extraction (SAE) performed on the acetic dope. Operating in this way, the problems related to the use of large quantities of water to remove acetic acid from the acetic dope are resolved, since it will be directly extracted by supercritical CO2. Micro- and nanoparticles, or filaments, of cellulose acetate can be produced. Finally, an acetic acid residue of 23 ppm, in the supercritical CO2 treated cellulose acetate, confirmed the success of this alternative process configuration.

A heterogeneous catalytic process to mitigate the acidity of bio-oils caused by the presence of volatile organic acids

The removal of the acidity produced by the presence of volatile organic acids in bio-oils, such as acetic acid, assisted by heterogeneous catalysts was investigated. For this purpose, CaO and alumina-supported catalysts were prepared, and silver nanoparticles were used as promoter. The prepared catalysts, both fresh and post-reaction, were characterized by several techniques: N2 physisorption (BET), SEM-EDS, TEM, XRD, and TPR. All catalysts were tested in the elimination of acetic acid, employing two different reaction systems: batch microreactors and a pressurized batch reactor. An appreciable CH3COOH elimination of ~60%–70% was obtained at low temperature (150–200 °C) using the CaO-Al2O3 system. The addition of silver improved the removal percentage. Silver-supported catalysts were also tested in a pressure-controlled system, achieving an excellent percentage of acetic acid removed (~97.5%). Silver would promote the incipient reactions of catalytic ketonization and aldol condensation.

A new approach in adsorption modeling using random forest regression, Bayesian multiple linear regression, and multiple linear regression: 2,4-D adsorption by a green adsorbent.

The mathematical model's usage in water quality prediction has received more interest recently. In this research, the potential of random forest regression (RFR), Bayesian multiple linear regression (BMLR), and multiple linear regression (MLR) were examined to predict the amount of 2,4-dichlorophenoxy acetic acid (2,4-D) elimination by rice husk biochar from synthetic wastewater, using five input operating parameters including initial 2,4-D concentration, adsorbent dosage, pH, reaction time, and temperature. The equilibrium and kinetic adsorption data were fitted best to the Freundlich and pseudo-first-order models. The thermodynamic parameters also indicated the exothermic and spontaneous nature of adsorption. The modeling results indicated an R2 of 0.994, 0.992, and 0.945 and RMSE of 1.92, 6.17, and 2.10 for the relationship between the model-estimated and measured values of 2,4-D removal for RFR, BMLR, and MLR, respectively. Overall performances indicated more proficiency of RFR than the BMLR and MLR models due to its capability in capturing the non-linear relationships between input data and their associated removal capacities. The sensitivity analysis demonstrated that the 2,4-D adsorption process is more sensitive to initial 2,4-D concentration and adsorbent dosage. Thus, it is possible to permanently monitor waters more cost-effectively with the suggested model application.

Use of Phenols as Nucleophiles in the Zbiral Oxidative Deamination of N-Acetyl Neuraminic Acid: Isolation and Characterization of Tricyclic 3-Keto-2-deoxy-nonulosonic Acid (KDN) Derivatives via an Intermediate Vinyl Diazonium Ion.

It is well established that the N-nitrosoamide derived from peracetylated derivatives of N-acetyl neuraminic acid on treatment with a mixture of sodium isopropoxide and trifluoroethanol, followed by the addition of acetic acid, gives an oxidative deamination product, in which the AcN(NO)-C5 bond is replaced with a AcO-C5 bond with the retention of configuration, affording a practical synthesis of 2-keto-3-deoxy-d-glycero-d-galactononulosonic acid (KDN) derivatives. Application of other strong acids, including hydrogen fluoride, thioacetic acid, trifluoromethanesulfonic acid, and hydrogen azide, functions similarly to afford KDN derivatives functionalized at the 5-position. We describe our attempts to extend the range of useful nucleophiles employed in this oxidative deamination process to include phenols and thiophenols, resulting in the discovery of a new branch of the general reaction and the formation of a series of products resulting from substitution of the 5-acetamido group and of the 4-acetoxy group from neuraminic acid. A mechanistic rationale for the formation of these products is advanced according to which, in the absence of acids of pKa ≤ 8, the intermediate diazonium ion resulting from the elimination of acetic acid and nitrogen from the nitrosoacetamide undergoes elimination of acetic acid from the 4-position to afford a highly electrophilic alkenediazonium ion. Reversible conjugate addition of the nucleophile to the 4-position then initiates the reaction cascade leading to the ultimate products.

Ring Opening of 4-Arylamino-2-tert-butyl-5-oxo-2,5-dihydrofuran-2-yl Acetates with Aromatic and Heterocyclic Amines

Reactions of 4-arylamino-2-tert-butyl-5-oxo-2,5-dihydrofuran-2-yl acetates with an equimolar amount of aromatic or heterocyclic amine in toluene involves initial attack of the amine on the C2 atom of the furan ring, followed by opening of the furan ring and elimination of acetic acid to give N-aryl(hetaryl)-2-arylamino-5,5-dimethyl-4-oxohex-2-enamides.

Produced water treatment by advanced oxidation processes

Different Advanced Oxidation Processes (AOPs) such as photocatalysis, Fenton-based processes and ozonation were studied to include one of these technologies within an integrated solution for produced water (PW) polishing. Synthetic PW was prepared adding toluene, xylene, naphthalene, phenol, acetic and malonic acids to a seawater matrix. Despite that in all AOPs studied in this work BTEX and naphthalene were removed, the efficiency (in terms of TOC removal) of each treatment varied largely. Among these techniques, photocatalysis was found to be the less effective for the treatment of PW, as TOC removals lower than 20% were obtained for the best scenario after 4 h treatment. In the contrary, best results were obtained by ozonation combined with H2O2, where all the organic components were removed, including a high percentage of acetic acid, which was not abated by the rest of the AOPs studied. The optimum conditions for ozonation were 4 g h−1 O3 and 1500 mg L−1 H2O2 at pH 10, where after 2 h a 74% of TOC removal was achieved and the acetic acid elimination was 78%. This condition enabled that ozonation process accounted for the lowest electric energy consumption per order of target compound destruction regarding total organic carbon (TOC).

Electrospray ionization tandem mass spectrometry of labdane-type acid diterpenes.

Copaifera (Leguminoseae) species produce a commercially interesting oleoresin that displays several biological activities, including antimicrobial and anti-inflammatory properties. Labdane-type diterpenes are the main chemical constituents of these oleoresins, and copalic acid is the only compound that has been detected in all Copaifera oleoresins. In this study, we investigate some aspects of the gas-phase fragmentation reactions involved in the formation of the product ions from the deprotonated compounds (-)-ent-copalic acid (1), (-)-ent-3β-hydroxy-copalic acid (2), (-)-ent-3β-acetoxy-copalic acid (3), and (-)-ent-agathic acid (4) by electrospray ionization tandem mass spectrometry (ESI-MS/MS) and multiple stage mass spectrometry (MSn ). Our results reveal that the product ion with m/z 99 is common to all the analyzed compounds, whereas the product ion with m/z 217 is diagnostic for compounds 2 and 3. Moreover, only compound 4 undergoes CO2 (44 u) and acetic acid (60 u) elimination from the precursor ion. Thermochemical data obtained by computational chemistry at the B3LYP/6-31G(d) level of theory support the proposed ion structures. These data helped us to identify these compounds in a crude commercial Copaifera langsdorffii oleoresin by selective multiple reaction monitoring (MRM). Finally, a precursor ion scan (PIS) strategy aided screening of labdane-type acid diterpenes other than 1 to 4 in the same Copaifera oleoresin sample and led us to propose the structures of 8,17-dihydro-ent-agathic acid (5) and 3-keto-ent-copalic acid (6), which have not been previously reported in Copaifera oleoresins.

Microwave assisted one pot conversion of aromatic aldehydes to nitriles

Nitriles are versatile organic precursors in organic synthesis and have numerous applications. An efficient microwave assisted method for conversion of aromatic aldehydes to the corresponding nitriles is reported. Aldehydes are readily converted to oxime followed by acetylation and acetic acid elimination to provide nitriles in good yields within minutes. The method proved to be efficient for the synthesis of aromatic and heterocyclic nitriles. The reaction proceeds smoothly by microwave at 150 °C for 5 minutes. The obtained products are isolated simply by filtration or extraction.

Thermo-oxidative decomposition of lime, bergamot and cardamom essential oils

The thermal decomposition of three essential oils has been studied at 300 °C, using a 9% oxygen in nitrogen atmosphere, to mimic the thermal environment of flavours under low-temperature tobacco heating conditions. The starting compositions of the lime, bergamot and cardamom oils were determined by gas chromatography/mass spectrometry (GC/MS). The thermo-oxidative decomposition was evaluated by applying on-line pyrolysis-GC/MS. The main constituents of the oils studied were cyclic and linear monoterpenoids; however, the relative intensities of these components were characteristically different between oils. Lime oil was dominated by monoterpene hydrocarbons, while the other citrus oil, bergamot oil contained in addition a significant number of esters and alcohols. Oxygen-containing monoterpenoids were the dominant constituents of cardamom oil. The relative proportion of the constituents of all three essential oil samples significantly altered during oxidative pyrolysis at 300 °C. The strained rings of bicyclic monoterpenes (pinenes, sabinene, and thujene) underwent scission, resulting in the formation of monocyclic monoterpenes (limonene etc.). Both linear and cyclic terpene acetates decomposed via elimination of acetic acid, so linalyl acetate produced myrcene and ocimene, while terpinyl acetate formed mostly limonene and terpinolene. The relative intensities of linalool and eucalyptol were reduced during pyrolysis, which can be explained by dehydration reactions resulting in the formation of myrcene and ocimene, or limonene and terpinolene, respectively. The chemical reactions that occurred were explained by bond splitting and intramolecular rearrangement mechanisms, with oxygen playing a role in the initiation processes.

Mass spectrometry for characterization of homologous piperidine alkaloids and their activity as acetylcholinesterase inhibitors.

Piperidine alkaloids from Senna spectabilis constitute a rare class of natural products with several biological activities. However, the absence of chromophores makes their structural elucidation by conventional methods a great challenge. In this context, mass spectrometry emerges as a powerful tool for metabolomics studies. The piperidine alkaloids (-)-cassine and (-)-spectaline and the semisynthetic derivatives (-)-3-O-acetylcassine and (-)-3-O-acetylspectaline were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in the positive mode and electron ionization mass spectrometry (EI-MS). ESI fragmentation studies were performed with a quadrupole time-of-flight instrument; N2 was used as collision gas. The acetylcholinesterase inhibitory activity of the investigated compounds was evaluated by bioautography and microplate screening assays. ESI-MS/MS and EI-MS provided valuable and complementary information about the structure of the piperidine compounds. Collision-induced dissociation experiments (MS/MS) revealed that neutral elimination of water or acetic acid is the major fragmentation pathway, which agrees with the stereochemistry proposed for (-)-cassine and (-)-spectaline and the semisynthetic derivatives (-)-3-O-acetylcassine and (-)-3-O-acetylspectaline. The ESI-MS/MS and EI-MS studies allowed us to propose fragmentation mechanisms for piperidine alkaloids and derivatives. Therefore, mass spectrometry is an important tool for characterizing the structure of these compounds and for supporting further metabolomics studies.

Unprecedented Cyclization Catalyzed by a Cytochrome P450 in Benzastatin Biosynthesis.

Benzastatins have unique structures probably derived from geranylated p-aminobenzoic acids. The indoline and tetrahydroquinoline scaffolds are presumably formed by cyclization of the geranyl moiety, but the cyclization mechanism was unknown. We studied the benzastatin biosynthetic gene cluster of Streptomyces sp. RI18; functions of the six enzymes encoded by it were analyzed by gene disruption in a heterologous host and in vitro enzyme assays. We propose the biosynthetic pathway for benzastatins in which a cytochrome P450 (BezE) is responsible for the cyclization of geranylated p-acetoxyaminobenzoic acids; BezE catalyzes elimination of acetic acid to form an iron nitrenoid, nitrene transfer to form an aziridine ring, and nucleophilic addition of hydroxide ion to C-10 and chloride ion to C-9 to generate the indoline and tetrahydroquinoline scaffolds, respectively. Discovery of this enzyme, which should be termed cytochrome P450 nitrene transferase, provides an important insight into the functional diversity of cytochrome P450.

Production of polyimide ceria nanocomposites by development of molecular hook technology in nano-sonochemistry

Poly(amic acid), the precursor of polyimide (PI), was used for the preparation of PI/CeO2 nanocomposites (NC)s by ultrasonic assisted technique via insertion of the surface modified CeO2 nanoparticles (NP)s into PI matrix. In the preparation stages, in the first, the modifications of CeO2 NPs by using hexadecyltrimethoxysilane (HDTMS) as a binder were targeted using ultrasonic waves. In the second step, newly designed PI structure was formed from the sonochemical imidization process as a molecular hook. In this step two different reactions were occurred. The acetic acid elimination reaction in the main chain of macromolecule, and the acetylation reaction in the side chains of poly(amic acid) were accomplished. By acetylation process the hook structure was created for trapping of the modified nanoparticles. In the final step the preparation of PI NCs were achieved by sonochemical process. The structural and thermal properties of pure PI and PI/CeO2 NCs were studied by several techniques such as fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and thermal analyses. FT-IR and 1H NMR spectra confirmed the success in preparation of PI matrix. The FE-SEM, TEM, and AFM analyses showed the uniform distribution of CeO2 NPs in PI matrix. The XRD patterns of NCs show the presence of crystalline CeO2 NPs in amorphous PI matrix. The thermal analysis results reveal that, with increases in the content of CeO2 NPs in PI matrix, the thermally stability factors of samples were improved.