DMF) And N,N-dimethylacetamide Research Articles

Enzymatic Knoevenagel condensation in dual‐functionalized water‐mimicking ionic liquids and tertiary amide solvents

AbstractBACKGROUNDKnoevenagel condensation is an important tool for building carbon–carbon (CC) bonds, especially when catalyzed by enzymes to enable a potentially high chemo‐, regio‐ and/or stereoselectivity. Although many Knoevenagel condensation reactions are carried out in aqueous solutions, insoluble hydrophobic substrates often lead to poor catalytic efficiencies. The use of water‐miscible organic solvents improves the substrate solubilization, but usually induces activity suppression or inactivation of enzymes. There is a great need to develop alternative solvents for both substrate dissolution and enzyme compatibility in CC bond formation reactions.RESULTSOur group previously developed dual‐functionalized water‐mimicking ionic liquids (ILs) for the activation and stabilization of hydrolases (e.g. lipase and protease). In the present study, we evaluated the Knoevenagel condensation of 4‐chlorobenzaldehyde with acetylacetone, and found that porcine pancreas lipase in water‐mimicking ILs carrying ammonium, imidazolium and benzimidazolium cations enabled higher reaction rates (up to 3.22 μmol min−1 g−1 lipase) and better yields than tert‐butanol, glymes and [BMIM][Tf2N]. Interestingly, tertiary amide solvents such as N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethylformamide (DMF) and N,N‐dimethylacetamide (DMAc) led to 8.2‐ to 11.1‐fold increases in the initial rate (up to 35.66 μmol min−1 g−1 lipase) when compared with dual‐functionalized ILs, which is likely due to some synergistic effect of these tertiary amides with the lipase.CONCLUSIONDual‐functionalized ILs based on ammonium, imidazolium and benzimidazolium cations improved Knoevenagel condensation reaction rates and yields when compared with tert‐butanol and glymes. Tertiary amides (NMP, DMF and DMAc) significantly increased the reaction rate. © 2024 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Improving the Performance of Flame-Retarding Sodium Bis(Oxalato)Borate in Triethyl Phosphate Electrolyte for Sodium Ion Batteries

An ever-growing demand for energy storage has highlighted potential future resource constraints for Li-ion batteries (LIBs), in particular with respect to Li.1-3 With this in mind Na-ion batteries (NIBs) hold promise as a complementary technology to LIBs, particularly for stationary energy storage.4 To be competitive with LIBs, NIBs need to become fully competitive on cost and on capacity density.5-7 NIBs can however offer more than simply a cost competitive option to LIBs, with potential to offer improvements on both safety and sustainability. A number of cathode materials exist that can avoid many of the unanswered question around the sustainability of state-of-the-art LIB cathodes.3 However, to address safety concerns of LIBs it is impossible to ignore the electrolyte. State of the art electrolyte in LIBs, regularly LiPF6 in a mix of carbonates, is both toxic (by virtue of LiPF6 and to a limited extent ethylene carbonate) and flammable (by virtue of the electrolyte solvents). Importing the Na analogue of state-of-the-art LIB electrolytes (i.e. NaPF6 in carbonates) creates the same problems of flammability and toxicity currently seen in LIBs (albeit the toxicity of NaPF6 is lower than that of LiPF6).Recently Mogensen et al.8 proposed sodium bis(oxalato)borate (NaBOB) in trimethyl phosphate (TMP) electrolyte that overcame the flammability concerns of NaPF6 in carbonate electrolytes. In addition to non-flammability, the use of NaBOB instead of NaPF6 allowed for higher temperatures to be used and produced an electrolyte that was halogen free. Switching from TMP to triethyl phosphate (TEP) allowed for a relatively less-toxic electrolyte (NaBOB and TEP are listed by the European Chemical Agency as ‘harmful if swallowed’ in comparison to ‘harmful if swallowed, in contact with skin or inhaled’ for NaPF6 in carbonates, although limited research has been conducted on the toxicity of NaBOB and so this should be received with limited certainty) without sacrificing cell performance.9 However, hurdles remain for NaBOB in organophosphate electrolytes. Principal amongst these has been the poor solubility of NaBOB in most solvents and the difficulties transferring promising low mass-loading full cell results to higher mass-loading full cells. The low solubility of NaBOB limits the concentration of NaBOB in organophosphate electrolytes to < 0.4 M, producing electrolytes with relatively low conductivities (for NaBOB in TMP, 4.5 mS/cm, and in TEP, 5 mS/cm). N-methyl pyrrolidone (NMP) has previously been shown to increase the solubility of NaBOB when used as a cosolvent with TMP, with conductivity improved to 6.5 mS/cm without sacrificing non-flammability and promising cycling shown in low mass-loading full-cells.10 A range of alternative cosolvents were here investigated to increase the solubility of NaBOB in TEP. Of these, NMP, N,N-dimethyl formamide (DMF) and N,N-dimethyl acetamide (DMAc) were evaluated as cosolvents with TEP for near-commercial mass loading full-cells (Prussian white||hard carbon at ~ 2 mAh/cm2). To maintain non-flammable characteristics, the cosolvents had to be kept below 40% (v/v) for DMAc and DMF and below 60% (v/v) for NMP, resulting in electrolyte conductivities of 5.7, 6.9 and 6.0 mS/cm respectively. These nearly doubled the conductivity we observed for NaBOB in TEP of 3.5 mS/cm. However, all electrolytes examined showed large polarisation, suspected to be due a thick, resistive SEI. A range of strategies have been employed in order to reduce this polarisation, with particular focus on improved formation protocols (studying the effects of temperature, current density and electrochemical method of formation) and their use in concert with film forming additives. Future work will aim to understand the interplay between formation conditions, the resultant SEI formation and the cell polarization in an effort to translate promising low mass-loading full cell results to near-commercial mass-loading full cells.

Effect of casting solvent on the structure development, electrical, thermal behavior of polyvinylidene fluoride (PVDF)–carbon nanofiber (CNF) conducting binary and hybrid nanocomposites

The role of two solvents, namely N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc), on the dispersion of CNF in PVDF matrix has been studied when the composites are synthesized by non-solvent precipitation route followed by melt crystallization at 200 °C and quenching in water. The electrical conductivities of melt-crystallized PVDF–CNF, PVDF-7 wt% graphite-CNF nanocomposites synthesized using DMAc solvent are higher than that of composites synthesized using DMF solvent. Thermogravimetric analysis of PVDF-7 wt% graphite, PVDF-3 wt% CNF suggests that the onset temperature of thermal degradation of the composite synthesized using DMAc is 20 °C higher than that of the same composite synthesized by using DMF. The SEM analysis of cross section of melt-crystallized, water-quenched PVDF-3 wt% CNF clearly proves better dispersion of CNF when DMAc solvent is used. Structure development in the polymer when CNF is incorporated has been understood in terms of lattice mismatch theory. DSC analysis proves the nucleating ability of CNF when incorporated in the polymer matrix as crystallization temperature (Tc) is enhanced by 5 °C. At low frequency (40 Hz), the intergranular capacitance is more than two times higher for PVDF-3 wt% CNF composites synthesized by using DMAc solvent when compared to that of DMF employed composites. The enhancement of storage modulus at − 90 °C for PVDF-7 wt% CNF composites synthesized by using DMAc solvent when compared to that of DMF employed same composite supports better dispersion of CNF in PVDF matrix in the former case as revealed by DMA.

Development of Diallylimidazolium Methoxyacetate/DMSO (DMF/DMA) Solvents for Improving Cellulose Dissolution and Fabricating Porous Material.

Cellulose is the most abundant natural biopolymer, with unique properties such as biodegradability, biocompability, nontoxicity, and so on. However, its extensive application has actually been hindered, because of its insolubility in water and most solvents. Herein, highly efficient cellulose solvents were developed by coupling diallylimidazolium methoxyacetate ([A2im][CH3OCH2COO]) with polar aprotic solvents dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA). Attractively, these solvents showed extraordinarily powerful dissolution performance for cellulose (e.g., 26.1 g·100g−1) in [A2im][CH3OCH2COO]/DMSO(RDMSO = 1.01 solvent even at 25 °C), which is much more advantageous over previously reported solvents. To our knowledge, such powerful cellulose solvents have not been reported before. The cellulose dissolution mechanism is proposed to be of three combined factors: (1) The hydrogen bond interactions of the H2, H4 and H6 in [A2im]+ and the carboxyl O atom in [CH3OCH2COO]−, along with the hydroxyl H atom and O atom in cellulose, are main driving force for cellulose dissolution; (2) the dissociation of [A2im][CH3OCH2COO] by DMF increases the anion and cation concentrations and thus promotes cellulose dissolution; (3) at the same time, DMF also stabilizes the dissolved cellulose chains. Meanwhile, the porous cellulose material with a varying morphologic structure could be facially fabricated by modulating the cellulose solution concentration. Additionally, the dissolution of cellulose in the solvents is only a physical process, and the regenerated cellulose from the solvents retains sufficient thermostability and a chemical structure similar to the original cellulose. Thus, this work will provide great possibility for developing cellulose-based products at ambient temperatures or under no extra heating/freezing conditions.

Effect of chain structure on the solvent resistance in aprotic solvents and pervaporation performance of PMDA and BTDA based polyimide membranes

Pervaporation (PV) performance of polyimide (PI) membranes has been attempted for the recovery of high concentrations of aprotic solvents, such as N, N-dimethyl formamide (DMF) and N, N-dimethylacetamide (DMAc). In this work, we explored the effect of chain structure on the solvent resistance and pervaporation performance of hydrophilic pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) based polyimide membranes. According to the Hansen solubility parameters and membrane formation morphologies, we selected five aprotic solvent resistant PI membranes with different chain structures. It was found that the swelling degrees in DMF and DMAc was principally determined by the elasticity modulus of the PI membrane, and was significantly influenced by the polymer chain structure. The flexible linkages (such as –OCH2 and CH2) suppressed the PI chain packing, which resulted in the d-spacing and fractional free volume (FFV) of PMDA based PI membrane was higher than BTDA based PI membrane. BTDA-BZD membrane had the highest elasticity modulus together with the lowest d-spacing value (4.68 Å) due to its symmetric intermolecular interaction and rigid chain structure. PV experiments were conducted with DMF/water and DMAc/water mixtures over a wide range of temperatures (30–60 °C) with 90 wt% solvent concentration. The BTDA based PI (M4) composite membrane showed the highest separating factor around 275 at 30 °C in DMAc solution, which was much higher than in DMF solution (the separating factor is about 70). Furthermore, the chemical and thermal stability test for the PI composite membranes in the presence of the feed solvent under the PV process demonstrated the excellent separation stability in DMAc solution.

Vacuum ultraviolet excited state dynamics of small amides.

Time-resolved photoelectron spectroscopy in combination with ab initio quantum chemistry calculations was used to study ultrafast excited state dynamics in formamide (FOR), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) following 160 nm excitation. The particular focus was on internal conversion processes within the excited state Rydberg manifold and on how this behavior in amides compared with previous observations in small amines. All three amides exhibited extremely rapid (<100 fs) evolution from the Franck-Condon region. We argue that this is then followed by dissociation. Our calculations indicate subtle differences in how the excited state dynamics are mediated in DMA/DMF as compared to FOR. We suggest that future studies employing longer pump laser wavelengths will be useful for discerning these differences.

Solubility modelling, solvent effect and preferential solvation of 6-chloropurine in several aqueous co-solvent mixtures between 283.15 K and 328.15 K

The mole fraction solubility of 6-chloropurine in aqueous mixtures of methanol, ethanol, N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) was measured by a saturation shake-flask method over the temperature range of (283.15–328.15) K at pressure of 101.2 kPa. The solubility of 6-chloropurine increased positively with increasing temperature at a given solvent composition and decreased with increasing mass fraction of water in each binary system. The maximum solubility was found in neat methanol, ethanol, DMF and DMA. Given the same temperature and mass fraction of the organic solvent, the solubility of 6-chloropurine was greater in (DMF + water) than in the other three solvent mixtures. The X-ray power diffraction (XPRD) analysis showed that no polymorphic transformation, solvate formation or crystal transition took place during the experiments. Linear solvation energy relationships concept was used to describe the variation in the solubility based on the solvent effect. The preferential solvation parameters were derived from their thermodynamic solution properties using inverse Kirkwood–Buff integrals. The preferential solvation parameters (δx1,3) for methanol, ethanol, DMF and DMA were negative in the four solvent mixtures with water-rich compositions, which indicated that 6-chloropurine was preferentially solvated by water. Temperature has little effect on the preferential solvation magnitudes. The higher solvation by water could be explained in terms of the higher acidic behavior of the solvents interacting with the Lewis basic groups of the 6-chloropurine. Furthermore, several mathematical cosolvency models were adopted to correlate the measured solubility values. The relative average deviation and root-mean-square deviation were no more than 2.36% and 1.026 × 10−3, respectively.

Vapor–liquid equilibrium in the ternary system isobutyl alcohol + isobutyl acetate + N, N-dimethyl acetamide and the binary systems isobutyl alcohol + N, N-dimethyl acetamide, isobutyl acetate + N, N-dimethyl acetamide at 101.3 kPa

The isobaric Vapor-Liquid Equilibrium (VLE) data at 101.3 kPa were measured for the binary systems isobutyl alcohol + N, N-dimethyl acetamide (DMAC), isobutyl acetate + N, N-dimethyl acetamide and the ternary system isobutyl alcohol + isobutyl acetate + N, N-dimethyl acetamide using an all glass dynamics recirculating still. The isobutyl alcohol + DMAC system exhibits negative deviation from Raoult's law and isobutyl acetate + DMAC system deviates positively from ideal solution. The thermodynamic consistency of the binary VLE data was checked by Herington method and Wisniak point-to-point method. The NRTL, UNIQUAC and Wilson activity coefficient models were used to correlate the binary VLE data in order to obtain the binary interaction parameters which were used to predict ternary VLE data. The predicted results agree well with the experimental data. The results indicate that the solvent DMAC can greatly enhance the relative volatility of isobutyl acetate to isobutyl alcohol, and azeotrope of isobutyl acetate and isobutyl alcohol will be broken if the mole fraction of DMAC is greater than 0.361. The effects of the solvents 1-hexanol, butyl propionate (BUP), N, N-dimethyl formamide (DMF) and N, N-dimethyl acetamide (DMAC) were compared, and the selectivity of DMAC was the largest. The solvent DMAC is a promising extractive agent for the separation of mixtures of isobutyl alcohol and isobutyl acetate by extractive distillation.

Volumetric Properties of (Difurylmethane + an Amide) Binary Mixtures at 293.15K, 298.15K and 303.15 K

Densities (&rho;) of pure difuryl methane (DFM), N-methylformamide (NMF), N-ethylformamide (NEF), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) and those of [DFM + (NMF or NEF or DMF or DMA] binary mixtures over the entire composition range, have been measured at (<i>T</i> = 293.15, 298.15 and 303.15) K and atmospheric pressure. Excess molar volumes (<img width="18" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image001.png" />), of each binary system were calculated and correlated by the Redlich-Kister equation. <img width="18" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image001.png" /> values for each binary system were negative at each of the three temperatures investigated (<i>T</i> = 293.15, 298.15 and 303.15) K. The <img width="18" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image001.png" /> values decreased with temperature increase for each of the binary systems investigated. Sign and magnitude of <img width="18" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image001.png" /> are discussed in-terms of type and nature of intermolecular interactions that occur in a binary mixture. The <img width="18" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image001.png" /> data have been used to derive excess partial molar volumes (<img width="18" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image002.png" />), limiting excess partial molar volumes (<img width="32" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image003.png" />) and limiting partial molar volumes at infinite dilute region (<img width="20" height="16" src="http://article.sciencepublishinggroup.com/journal/128/1281027/image004.png" />) of each component of the binary mixture. Results are discussed in terms of possible intermolecular interactions and structural effects that occur in the binary mixtures.

N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) reactions with NO3, OH and Cl: A theoretical study of the kinetics and mechanisms

A theoretical study of the kinetics and the mechanism of the hydrogen abstraction by OH, Cl and NO3 radicals from two amides (DMF and DMA) has been investigated. Calculations were carried out using DFT B3LYP/6-311++G(2d,pd)/CBS-QB3 and transition-state theory. This work provides the first theoretical determination of the rate coefficients and detailed mechanism for the reactions of OH, NO3 radicals and chlorine atoms with DMF/DMA, over a temperature range 273–380K and at atmospheric pressure. The obtained rate coefficients are in reasonable agreement with experiments. Results indicate that the mechanism of the Cl and NO3 reactions with amides goes preferentially through H-abstraction from (C(O)H) and (C(O)CH3) groups. Meanwhile the mechanism of the OH with amides (DMF, DMA) is dominated by H-abstraction from the N-methyl groups.

Thermochemical Characteristics of the Dissolution of d-Valine in Aqueous Solutions of Some Amides at T = 298.15 K

Enthalpies of the dissolution of d-valine in the mixtures of water with formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) with the mole fraction (x2) of amides ranging up to 0.3 have been measured at T = 298.15 K. The standard enthalpies of the dissolution (ΔsolH°) and the transfer enthalpies (ΔtrH°) of d-valine have been calculated. On the basis of McMillan–Mayer’s theory, the enthalpic coefficients of pairwise interaction (hxy) have been calculated. The enthalpic coefficients (hxy) of the solute–amide pairwise interaction in the water proved to be positive and increasing in the series: FA < MFA < DMF. It is associated with the increasing of the hydrophobic properties of amides and the energy of intermolecular interactions between components of water+organic mixtures in the same sequence.

Binding to Redox-Inactive Alkali and Alkaline Earth Metal Ions Strongly Deactivates the C-H Bonds of Tertiary Amides toward Hydrogen Atom Transfer to Reactive Oxygen Centered Radicals.

The effect of alkali and alkaline earth metal ions on the reactions of the cumyloxyl radical (CumO(•)) with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) was studied by laser flash photolysis. In acetonitrile, a >2 order of magnitude decrease in the rate constant for hydrogen atom transfer (HAT) from the C-H bonds of these substrates (kH) was measured after addition of Li(+). This behavior was explained in terms of a strong interaction between Li(+) and the oxygen atom of both DMF and DMA that increases the extent of positive charge on the amide, leading to C-H bond deactivation toward HAT to the electrophilic radical CumO(•). Similar effects were observed after addition of Ca(2+), which was shown to strongly bind up to four equivalents of the amide substrates. With Mg(2+), weak C-H deactivation was observed for the first two substrate equivalents followed by stronger deactivation for two additional equivalents. No C-H deactivation was observed in DMSO after addition of Li(+) and Mg(2+). These results point toward the important role played by metal ion Lewis acidity and solvent Lewis basicity, indicating that C-H deactivation can be modulated by varying the nature of the metal cation and solvent and allowing for careful control over the HAT reactivity of amide substrates.

Determination and Correlation of Solubility of N-tert-Butylacrylamide in Seven Different Solvents at Temperatures between (279.15 and 353.15) K

The solubility data of N-tert-butylacrylamide (TBA) in the ethyl acetate, ethanol,dichloromethane, water, formamide, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAC) at temperatures ranging from (279.15 to 353.15) K were measured by synthetic method. The experimental data were correlated by the van’t Hoff plot, modified Apelblat equation, and two local composition models (NRTL and UNIQUAC), respectively. It was found that modified Apelblat equation could obtain the better correlation results than the other three models. In addition, the standard enthalpy, standard entropy and Gibbs free energy change for the solution process were calculated from the solubility data by the van’t Hoff analysis. Furthermore, on the basis of the NRTL model and experimental data, the thermodynamic excess functions (GE,SE,HE) of TBA + solvents (ethyl acetate, ethanol, dichloromethane, water, formamide, DMF, DMAC) systems were determined.

Influence of the composition of water–organic mixtures and of organic solvents properties on solvation of glycyl-L-tyrosine at 298.15 K

Enthalpies of dissolution of glycyl-L-tyrosine in the mixtures of water with methanol (MeOH), ethanol (EtOH), propanol (1-PrOH), 2-propanol (2-PrOH), acetonitrile (AN), 1,4-dioxane (DO),acetone (AN), dimethylsulfoxide (DMSO), formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) have been measured at 298.15K. The standard enthalpies of the solution (ΔsolH∘) and transfer (ΔtrH∘) of glycol-L-tyrosine from water into aqueous solution of organic co-solvents as well as the enthalpy coefficients of pairwise interaction (hxy) have been calculated. The interrelation between the enthalpy characteristics of dissolution (transfer) of glycyl-L-tyrosine and the composition of aqueous organic mixtures was established. Contributions of the organic co-solvent properties (molar volume, cohesion energy density, dipolarity/polarizability, acidity and basicity) to the energy of pairwise interactions were estimated quantitatively by means of a modified Kamlet–Taft equation. Some characteristics of intermolecular interactions of glycyl-L-tyrosine with the molecules of organic co-solvents with the analogous characteristics of glycylglycine and diglycylglycine were compared.

Study of assorted interactions of an ionic liquid in significant solvent systems using compensated equation of Fuoss conductance and vibrational mode

Qualitative and quantitative analyses of molecular interaction prevailing in ionic liquid tetrabutylphosphonium methanesulfonate [Bu4PMS] in dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF) and N,N-dimethyl acetamide (DMA) probed by electrical conductances and Fourier transform infrared (FT-IR) measurements have been reported at 298.15 K. Corresponding conductance data have been analysed using the Fuoss conductance-concentration equation (1978) for ion pair formation. The limiting ionic conductances (λo±) have been estimated from the appropriate division of the limiting molar conductivity value of tetrabutylammonium tetraphenylborate [Bu4NBPh4] as the ‘reference electrolyte’. The diffusion coefficient (D) has been obtained from Stokes-Einstein relation and the ionic mobility (i) for [Bu4P]+ and MS− using appropriate equation. The results have been discussed in terms of dipole-dipole interactions, hydrogen bond formation and structural aspect of the solvents and configurational theory. The FT-IR spectra have also been studied to predict the interactions occurring in the system.

Thermochemistry of the dissolution of DL-α-alanyl-DL-norleucine in aqueous solutions of amides at 298.15 K

Enthalpies of the dissolution of DL-α-alanyl-DL-norleucine are determined by calorimetry in aqueous solutions of formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) at a concentration of amides of x2 = 0–0.4 molar parts and T = 298.15 K. Standard values of enthalpies of dissolution ΔsolHo and ΔtrHo of DL-α-alanyl-DL-norleucine transfer from water to binary solvent are calculated, along with the enthalpy coefficients of pair interactions hxy of DL-α-alanyl-DL-norleucine with amide molecules. The effect of the composition of water-organic mixtures and the structure of amides on the enthalpy characteristics of dissolution and transition of DL-α-alanyl-DL-norleucine is considered. Quantitative estimates of the contributions to energy from DL-α-alanyl-DL-norleucine-amides pair interactions determined by the polarity, polarizability, and electron acceptor and electron donor ability of organic cosolvents are given using the Kamlet-Taft correlation equation.

Reactions of the Cumyloxyl and Benzyloxyl Radicals with Tertiary Amides. Hydrogen Abstraction Selectivity and the Role of Specific Substrate-Radical Hydrogen Bonding

A time-resolved kinetic study in acetonitrile and a theoretical investigation of hydrogen abstraction reactions from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) by the cumyloxyl (CumO(•)) and benzyloxyl (BnO(•)) radicals was carried out. CumO(•) reacts with both substrates by direct hydrogen abstraction. With DMF, abstraction occurs from the formyl and N-methyl C-H bonds, with the formyl being the preferred abstraction site, as indicated by the measured kH/kD ratios and by theory. With DMA, abstraction preferentially occurs from the N-methyl groups, whereas abstraction from the acetyl group represents a minor pathway, in line with the computed C-H BDEs and the kH/kD ratios. The reactions of BnO(•) with both substrates were best described by the rate-limiting formation of hydrogen-bonded prereaction complexes between the BnO(•) α-C-H and the amide oxygen, followed by intramolecular hydrogen abstraction. This mechanism is consistent with the very large increases in reactivity measured on going from CumO(•) to BnO(•) and with the observation of kH/kD ratios close to unity in the reactions of BnO(•). Our modeling supports the different mechanisms proposed for the reactions of CumO(•) and BnO(•) and the importance of specific substrate/radical hydrogen bond interactions, moreover providing information on the hydrogen abstraction selectivity.

Densities, ultrasonic speeds, viscosities and excess properties of binary mixtures of methyl methacrylate with N,N-dimethylformamide and N,N-dimethylacetamide at different temperatures

The densities, ρ, ultrasonic speeds, u and viscosities, η of binary mixtures of methyl methacrylate (MMA) with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA), including those of pure liquids, over the entire composition range were measured at temperatures (288.15, 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15)K and atmospheric pressure. From the experimental results, the excess molar volume, VmE, and excess isentropic compressibility, κsE, excess isobaric coefficient of thermal expansion, αpE and excess molar isobaric expansion, Ep,mE were calculated. The excess partial molar volume, V¯m,1E and V¯m,2E and excess partial molar isentropic compressibility, K¯s,m,1E and K¯s,m,2E over the whole composition range; and partial molar volume, V¯m,1° and V¯m,2°, partial molar isentropic compressibility, K¯s,m,1° and K¯s,m,2°, excess partial molar volume, V¯m,1°E and V¯m,2°E, excess partial molar isentropic compressibility, K¯s,m,1°E and K¯s,m,2°E at infinite dilution, and excess partial molar isobaric expansion, E¯p,m,1E and E¯p,m,2E over the whole composition range have also been calculated. The variations of these parameters with composition and temperature of the mixtures are discussed in terms of molecular interaction in these mixtures. It is observed that the MMA-DMF/DMA interactions in these mixtures follow the order: DMF<DMA. Further, the viscosities of these binary mixtures were correlated theoretically by using various empirical and semi-empirical models and the results were compared with the experimental findings.

Enthalpies of solution of L-phenylalanine in aqueous solution of amides at 298.15 K

The enthalpies of solution ΔsolHm have been determined for L-phenylalanine in aqueous solutions of formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA). The measurements have been made at 298.15K and mole fraction of amide x2=(0–0.4) on the precise isothermic calorimeter. The results obtained have been used to calculate the standard enthalpies of solution (ΔsolH°) and transfer (ΔtrH°) of L-phenylalanine from water into mixtures as well as the enthalpy coefficients of pairwise interaction (hxy) of the solute with amide in aqueous media. The interrelation between enthalpy characteristics of dissolution (transfer) of L-phenylalanine and the composition of (water+amide) binary mixtures has been established. Contributions of the amides properties (molar volume, dipolarity/polarizability, acidity and basicity) to the energy of pairwise interactions have been estimated quantitatively by means of a modified Kamlet–Taft equation.

Apparent molar volumes and compressibilities of lanthanum, gadolinium, lutetium and sodium trifluoromethanesulfonates in N,N-dimethylformamide and N,N-dimethylacetamide

The concentration and temperature dependencies of density of lanthanum, gadolinium, lutetium and sodium trifluoromethanesulfonates in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) have been determined. From density data the apparent molar volumes and partial molar volumes of the salts at infinite dilution as well as the expansibilities have been evaluated. The apparent molar isentropic compressibilities of lanthanum, gadolinium, lutetium and sodium trifluoromethanesulfonates in DMF and DMA have been calculated from sound velocity data obtained at 298.15K. The results have been discussed in terms of ion–solvent interactions.