N-methylformamide Research Articles

Investigation of amine-buffered amide reagents for coulometric Karl Fischer titration

Formamide (FA), N-methylformamide (NMF), and dimethylformamide (DMF), were evaluated as solvents for coulometric Karl Fischer (KF) reagents in combination with several amine bases. Except for the effect of the iodine species (iodine or triiodide), the pH of the reagent and the position of the sulfur dioxide/hydrogen sulfite equilibrium were found to be the main factors explaining the large difference in the observed reaction rates between water and the KF reagent in these solvents. Acid–base titrations showed that hydrogen sulfite is the main sulfur reactant in these media. The results will be of great importance in finding suitable combinations of base and solvent with respect to stoichiometry, side reactions caused by active carbonyl compounds, and reagent stability.

Morphology and properties of Nafion membranes prepared by solution casting

In this study, dilute Nafion solutions consisting of solvents with various dielectric constants ɛ and solubility parameters δ, i.e. N,N′-dimethyl acetamide, N,N′-dimethyl formamide, N-methyl formamide, methanol–water mixture (4/1g/g), ethanol–water mixture (4/1g/g), and isopropanol–water mixture (4/1g/g), were freeze dried and the conformations of Nafion molecules in dilute solutions were observed using transmission electron microscope. The membranes were prepared by solution casting from these solutions and evaporating the solvents at temperatures below TG of Nafion, then annealing the membranes at 150°C which was ∼50°C above TG of Nafion. We show Nafion molecular conformations in dilute solutions are strongly influenced by δ and ɛ of solvents. And, thus the morphology, water uptake, proton conductivity, and methanol permeability of membranes prepared by solution casting are also influenced by δ and ɛ of solvents.

Kinetic study of nitrosation of methylformamide

AbstractNitrosation of methylformamide (MFA) has been studied kinetically. The results obtained show that the reaction rate is first order with respect to both the MFA and proton concentration. The absence of catalysis by nucleophilic anions and the observed general base catalysis is interpreted in terms of formation of a protonated nitrosamide intermediate, being the proton transfer the slow step of the process. The primary solvent isotope effect observed corroborates this mechanism. From this study, we were able to obtain the values of the rate constants for the nitrosation process. The catalytic constants in the presence of buffers were also obtained and the analysis of the Brönsted slopes suggests a process with a transition state more similar to the reactants than the products. The absence of electron donating groups in MFA leads to a very low value of the bimolecular rate constant of the nitrosation reaction. Copyright © 2009 John Wiley & Sons, Ltd.

Kaolinite–poly(methacrylamide) intercalated nanocomposite via in situ polymerization

The preparation and characterization of a kaolinite–methacrylamide intercalation compound was achieved by a guest-displacement method, the direct treatment of a dimethylsulfoxide (DMSO) pre-intercalate with an aqueous solution of methacrylamide under mild conditions, giving intercalation ratios up to 92% and an expansion of 0.53 nm of the interlayer space. The DMSO molecules were fully displaced from the interlayer space by methacrylamide. Only partial intercalation could be obtained with N-methylformamide (NMF) pre-intercalate. After intercalation, the monomer was thermally polymerized at 100 or 150 °C with various heating times. XRD, FTIR, 13C CP/MAS NMR, and thermogravimetric analysis confirmed that polymerization was partially achieved in the interlayer spaces, while the layered structure of kaolinite was maintained, constraining the polymer in an interlayer space of 0.57 nm in the c-direction. In good agreement with the TG data, elemental analysis gave a stoichiometry of Al2Si2O5(OH)4·(C4H7NO)0.52 for the thermally treated methacrylamide intercalate, corresponding to a ratio of one methacrylamide unit per two kaolinite structural units. The thermal stability of the methacrylamide intercalate was increased after thermal treatment and polymerization.Key words: kaolinite, intercalation, nanocomposites, aluminosilicates, layered materials, interlayer polymerization, poly(methacrylamide).

The effect of water-miscible organic solvents on the substitution reaction of Keggin-type heteropolysilicates and -germanates with vanadium(V) ion

The substitution reaction of Keggin-type polyoxometalates, [XM 12O 40] n − (X = Si, Ge, P, or As; M = Mo or W), with vanadium(V) ion was investigated with cyclic voltammetry, Raman spectroscopy, and 31P NMR. The effect of organic solvents, such as acetonitrile (ACN), tetrahydrofuran (THF), formamide (FA), N-methylformamide (NMF), and N-methylacetoamide (NMA) on their substitution reactions was examined. In aqueous and aqueous-FA, -NMF, and -NMA solutions, the molybdenum or tungsten unit in the Keggin-anions was substituted with vanadium(V) ion to form V(V)-substituted polyoxometalates, while no substitution reaction occurred in aqueous-ACN and -THF solutions. It is suggested that this results from the relationship between the total anion charge and the permittivity of organic solvents.

Glycerol, Methyl-Formamide and Dimethyl-Formamide in Canine Semen Cryopreservation

The aim of the present work was to compare the efficiency of methyl-formamide (MF), dimethyl-formamide (DF) and glycerol (GL) as cryoprotectants in canine semen cryopreservation. For the experiment, pooled semen was submitted to one of the three cryoprotectants, with a final concentration of 3% in egg yolk-TRIS extender. Semen was subjectively evaluated for total and progressive motility, vigour and morphology. Sperm membrane functional integrity was assessed by hypo-osmotic swelling test (HOST), and longevity was assessed using the thermoresistance test (TRT). Fresh semen showed normal physical and morphological characteristics. After thawing, differences were observed between semen frozen using GL and DF, regarding total and progressive motility and vigour (p < 0.05), but not between MF and GL or MF and DF. Means for total motility, progressive motility, vigour and morphologically normal spermatozoa were, respectively, 69.0 +/- 5.4%, 61.0 +/- 7.4%, 2.9 +/- 0.5 and 57.1 +/- 5.0% for GL; 59.0 +/- 8.9%, 50.0 +/- 10.0%, 2.5 +/- 0.7 and 66.9 +/- 7.7% for MF; and 44.0 +/- 21.0%, 37.0 +/- 19.8%, 2.1 +/- 0.6 and 61.1 +/- 5.5% for DF. On HOST, GL was superior (p < 0.05) to MF and DF (57.8 +/- 12.4%, 35.8 +/- 18.4% and 34.4 +/- 9.4%, respectively). During the TRT, both GL and MF were superior to DF, with no differences between GL and MF. In conclusion, the use of MF as cryoprotectant showed results similar to GL, and can be considered as an alternative in canine semen cryopreservation. Further studies testing different concentrations of MF may improve its effects on cryopreservation of canine semen.

Studies of ion solvation and ion association of n-tetrabutylammonium hexafluorophosphate and n-tetrabutylammonium tetraphenylborate in various solvents

Conductometric investigation of n-tetrabutylammonium hexafluorophosphate (NBu 4PF 6) was performed in methanol (MeOH), ethanol (EtOH), 2-propanol (2-PrOH), acetone (ACE), 3-pentanone (PEN), tetrahydrofurane (THF), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), dichloromethane (DCM), acetonitrile (ACN) and N-methylformamide (NMF) at 298.15 K. The limiting molar conductivities ( Λ o ) and the association constants ( K A ) were derived from the Lee–Wheaton conductivity equation. The limiting ion conductivities ( λ ± o ) were evaluated using n-tetrabutylammonium tetraphenylborate (NBu 4BPh 4) as a “reference” electrolyte according to the method of Krumgalz. The Stokes’ radii ( r St ) of PF 6 − anion were estimated and used for the calculation of its solvation numbers ( S n ) in investigated solvent media. The mobility of ions was found to be completely controlled by the bulk viscosity ( η) and consequently the Walden product ( W = ηΛ o ) was found to be almost constant. Slight ionic association was found for NBu 4PF 6 in solvent media with dielectric constant ɛ > 16 while the association becomes more significant in THF which has the lowest dielectric constant ( ɛ = 7.5). The S n values indicate weak interactions between PF 6 − and solvent molecules. The only exception was found in the case of MeOH, in which the great S n value can be attributed to a hydrogen bond formation between the fluor atoms of PF 6 − and hydrogen of MeOH molecules.

Application of solid-phase microextraction and gas chromatography–mass spectrometry for measuring chemicals in saliva of synthetic leather workers

Saliva is of interest as a diagnostic aid for oral and systemic diseases, to monitor therapeutic drugs, and detect illicit drug abuse. It is also attractive for biological monitoring of exposure to hazardous solvents. The major advantage of this indicator over other biological monitoring targets is that the saliva is noninvasive and less confidential in comparison with blood and urine. Salivary analysis is generally acceptable by study subjects and can be applied to investigation of a wide variety of compounds. However, very few studies have been conducted on the saliva matrix to monitor exposure to hazardous solvents. The aim of this study is to establish an analytical method, headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS), by which the saliva matrix can be monitored for multiple compounds with various polarities, such as methyl ethyl ketone (MEK), isopropyl alcohol (IPA), and N, N-dimethyl formamide (DMF) (common solvents used in synthetic leather manufacture), as well as acetone (ACE) and N-methyl formamide (NMF) (metabolites of IPA and DMF, respectively). We studied this technique as an alternative biological monitoring method for investigating exposure to hazardous solvents. A Carboxen/Polydimethylsiloxane (CAR/PDMS 75 μm) fiber coating was employed for this study, and various extraction and desorption parameters were evaluated. The extraction efficiency and reproducibility of analyses was improved by pre-incubation. The limits of detection were 0.004, 0.003, 0.006, 0.05, and 0.10 μg/mL for ACE, MEK, IPA, DMF, and NMF, respectively. Method validation was performed on standards spiked in blank saliva, and a correlation was made between HS-SPME and traditional solvent pretreatment methods. It was found that correlation coefficients ( r) were greater than 0.996 for each analyte, with no significant differences ( p > 0.05) between two methods. However, the SPME method achieved lower limits of detection, with good accuracy (recovery 95.3–109.2%) and precision (1.17–8.22% CV) for both intra- and inter-assay, when quality control samples were analyzed for all five compounds. The partition coefficient for each compound between the headspace of the saliva sample and the CAR/PDMS fiber coating was 90.9, 170.1, 36.4, 3.70 and 0.92 for ACE, MEK, IPA, DMF and NMF, respectively. Real sample analyses were performed on workers in a synthetic leather factory. In summary, the SPME method is a highly versatile and flexible technique for chemical measurement, and we demonstrate its application for monitoring biological exposure to hazardous solvents. Saliva monitoring using sensitive SPME approaches for determining workplace exposure should prove useful as an alternative exposure monitoring method.

Solution Rheology of a Strongly Charged Polyelectrolyte in Good Solvent

Solution rheology of poly(2-vinylpyridine) and a random copolymer of 60% N-methyl-2-vinylpyridinium iodide and 40% 2-vinylpyridine in N-methylformamide (NMF) was studied over wide ranges of concentration. The fraction of monomers bearing an effective charge f = 0.31 of these copolymers was measured using dielectric spectroscopy. This low fraction of effectively charged monomers suggests that the polyion disrupts the hydrogen-bonding alignment of NMF that makes the dielectric constant of the pure solvent anomalously large. NMF is a good solvent for neutral poly(2-vinylpyridine) but has a significant quantity of ionic impurities even when freshly distilled. The specific viscosity and relaxation time of dilute and semidilute unentangled solutions exhibit the scaling with concentration expected by theory if cs ≈ 1 mM residual salt is present, identified from the change in slope of viscosity−concentration power laws from 5/4 to 1/2 at concentration c = 2cs/f = 9.5 × 10−3 M (moles of monomer per liter). The spe...

Dielectric Relaxation Studies of Binary Mixtures of N-Methylformamide and Tetramethylurea in Benzene Using Microwave Absorption Data

The dielectric relaxation time (τ ) and dipole moment (μ) of binary mixtures of different molar concentrations of N-methylformamide (NMF) in binary mixtures of NMF and tetramethylurea (TMU) in benzene have been calculated at 25, 30, 35 and 40 ◦C using standard standing wave microwave techniques and following the single frequency (9.885 GHz) concentration variational method of Gopala Krishna. The energy parameters (ΔH ε , ΔF ε , ΔS ε ) for the dielectric relaxation process of binary mixtures containing 30 mol% of NMF have been calculated at different temperatures, and comparison has been made with the corresponding energy parameters (ΔH η , ΔF η , ΔS η ) for the viscous flow process. Based on these studies, it was inferred that the dielectric relaxation process can be treated as a rate process just like the viscous flow process. Solute-solvent and solute-solute molecular associations have been proposed.

A model study of dickite intercalated with formamide and N-methylformamide

Local geometry and orientation of intercalated molecules of formamide (FA) and N-methylformamide (NMFA) in the clay mineral dickite (D) was studied by means of Density Functional Theory (DFT) calculations. Ten configurations with different orientation of the intercalated molecule were investigated for both D_FA and D_NMFA intercalates. Four groups of relaxed structures sorted by the calculated total electronic energy were found in both cases. The experimental geometry of the D_FA intercalate was denoted as the most stable structure from the investigated models. The differences in the total electronic energy of all D_FA configurations are within the interval of ∼92 kJ/mol. On one hand FA forms intercalates specifically and a close relation between the orientation of the FA molecules in the interlayer space and the stability of a particular configuration has been observed. On the other hand, N-methylformamide forms intercalated structures non-specifically. Small differences in the total energy, not larger than 18 kJ/mol, are observed for different orientations of the NMFA molecules The reorientation of the intercalated molecules has only a small effect on the stabilization of the D_NMFA intercalate what is in contrast with the D_FA intercalate. It was also observed that the experimental D_NMFA configuration is not the most stable. A small variation of the total electronic energy of different configurations correlates with small changes of the orientation of the dipole moment of the intercalated NMFA molecule.

Hydration of Simple Amides. FTIR Spectra of HDO and Theoretical Studies

The hydration of formamide (F), N-methylformamide (NMF), N,N-dimethylformamide (DMF), acetamide (A), N-methylacetamide (NMA), and N,N-dimethylacetamide (DMA) has been studied in aqueous solutions by means of FTIR spectra of HDO isotopically diluted in H2O. The difference spectra procedure has been applied to remove the contribution of bulk water and thus to separate the spectra of solute-affected HDO. To facilitate the interpretation of obtained spectral results, DFT calculations of aqueous amide clusters were performed. Molecular dynamics (MD) simulation for the cis and trans forms of NMA was also carried out for the SPC model of water. Infrared spectra reveal that only two to three water molecules from the surrounding of the amides are statistically affected, from among ca. 30 molecules present in the first hydration sphere. The structural-energetic characteristic of these solute-affected water molecules differs only slightly from that in the bulk and corresponds to the clathrate-like hydrogen-bonded cage typical for hydrophobic hydration, with the possible exception of F. MD simulations confirm such organization of water molecules in the first hydration sphere of NMA and indicate a practical lack of orientation and energetic effects beyond this sphere. The geometry of hydrogen-bonded water molecules in the first hydration sphere is very similar to that in the bulk phase, but MD simulations have affirmed subtle differences recognized by the spectral method and enabled their understanding. The spectral data and simulations results are highly compatible. In the case of F, NMF, and A, there is a visible spectral effect of water interactions with N-H groups, which have destabilizing influence on the amides hydration shell. There is no spectral sign of such interaction for NMA as the solute. The energetic stability of water H-bonds in the amide hydration sphere and in the bulk fulfills the order: NMA > DMA > A > NMF > bulk > DMF > F. Microscopic parameters of water organization around the amides obtained from the spectra, which have been used in the hydration model based on volumetric data, confirm the more hydrophobic character of the first three amides in this sequence. The increased stability of the hydration sphere of NMA relative to DMA and of NMF relative to DMF seems to have its origin in different geometries, and so the stability, of water cages containing the amides.

Determination of the absolute values of Gibbs energy of hydration or solvation ΔG0 abs(M+ or X-)h or s of monovalent (alkali metal and halide) ions and other thermodynamic parameters in aqueous and non-aqueous solvents using a single standard state and analysis of ΔG0 abs(M+ or X-)h or s values based on cluster-ion solvation method

or X - ) h or s and other thermodynamic parameters in aqueous and non-aqueous solvents (methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, propylene carbonate (PC), N-methyl formamide (NMF), acetone, tetrahydrofuran (THF), 1,4-dioxan, acetonitrile) were determined directly using modified Born equation and a single standard state [i.e. AG° and ΔH 0 (but not ΔS 0 ) of H 2 gas and other elements to be zero in their elementary standard states at 1 atm. pressure (1 bar) and 298 K]. The ΔH 0 abs (M + or X - ) h or s and ΔG 0 (M + or X - ) h or s values are calculated considering ion-dipole, ion-quadrupole interactions and without considering the interaction terms. Very few data are available in non-aqueous solvents for comparison. Most of the single ion values (particularly for the anions) suffer from limitations associated with the erroneous principle of division of solvation energies ΔG 0 h or s (MX) or ΔΗ 0 h or s (MX) of electrolytes into single ion values. ΔG 0 (M + or X - ) h values determined using cluster-ion solvation data have also been presented. The values have been claimed to be most accurate in recent years. However, the method involves a number of assumptions of doubtful validity and the values cannot be regarded to be equivalent to ΔG 0 (Μ + or X - ) h or determined by other workers using different methods. Coupling the values of ΔG 0 (M + or X - ) h or s and ΔH 0 (M + or X - ) h or s with ΔG 0 (M + or X - ) g and ΔH 0 (M + or X - ) g values in the gaseous state, ΔG 0 (M + or X - ) Water or org. solvent' ΔH 0 (Μ + or X - ) water or org. solvent and ΔS 0 (M + or X - ) water or org. solvent [values in water and in organic solvents] are determined.

Catalytic Effect of Various Kaolinite Forms on the Emulsion Polymerization of Vinylacetate Using Acetone Sodium Bisulfite as Initiator

Kaolinite was intercalated with N-methylformamide (NMF) and dimethylsulphoxide (DMSO), separately. The intercalation of these species expanded the basal space of kaolinite from 0.72 to 1.08 and 1.13 nm, respectively as shown by the X-ray diffraction (XRD). Emulsion polymerization of vinylacetate (VAc) was carried out at different temperatures (60–80°C) using acetone sodium bisulfite as initiator in the absence and presence of untreated as well as the modified forrms of kaolinite (K-NMF, K-DMSO). The results revealed that the presence of kaolinite decreased the rate of polymerization (Rp) by factor of 4 at 60 and 70°C and 7 at 80°C and also the activation energy of polymerization (E a ) was decreased from 43.35 × 104 to 10.32 × 104 J mole−1 if compared with the polymerization of VAc in absence of kaolinite. Using the modified forms of kaolinite (K-NMF, K-DMSO) enhanced the Rp and reduced effectively the E a to − 27.92 and − 55.78, respectively. Conversely to untreated kaolinite, the Rp was declining with increasing the temperature in these cases. In all cases, Rp was the highest in the absence of any kaolinite form but in the same time the E a was also the highest. These results were discussed and explained on the basis of the catalytic activity of the different forms, radical scavenging nature of the kaolinite, and chain transfer.

Dielectric relaxation studies of binary mixtures of N-methylacetamide and N-methylformamide in benzene solutions using microwave absorption data

Using standard microwave X-band technique and by following Gopala Krishna's single frequency (9.90 GHz) concentration variational method, the dielectric relaxation times (τ) and the dipole moments (μ) of dilute solution of N-methylacetamide (NMA), N-methylformamide (NMF) and NMA + NMF binary mixtures in benzene solutions have been calculated at different temperatures. The energy parameters for the dielectric relaxation process for NMA + NMF binary mixture containing 30 mol% NMF have been calculated at 25, 30, 35 and 40°C and compared with the corresponding viscosity parameters. A good agreement between the free energy of activation from these two sets of values shows that the dielectric relaxation process like the viscous flow process can be treated as the rate process. From relaxation time behavior of NMA and NMF binary mixture in benzene solution, solute–solute types of the molecular association has been proposed.

Testing if the Interstitial Atom,X, of the Nitrogenase Molybdenum−Iron Cofactor Is N or C: ENDOR, ESEEM, and DFT Studies of theS=3/2Resting State in Multiple Environments

A high-resolution (1.16 A) X-ray structure of the nitrogenase molybdenum-iron (MoFe) protein revealed electron density from a single N, O, or C atom (denoted X) inside the central iron prismane ([6Fe]) of the [MoFe7S9:homocitrate] FeMo-cofactor (FeMo-co). We here extend earlier efforts to determine the identity of X through detailed tests of whether X = N or C by interlocking and mutually supportive 9 GHz electron spin echo envelope modulation (ESEEM) and 35 GHz electron-nuclear double resonance (ENDOR) measurements on 14/15N and 12/13C isotopomers of FeMo-co in three environments: (i) incorporated into the native MoFe protein environment; (ii) extracted into N-methyl formamide solution; and (iii) incorporated into the NifX protein, which acts as a chaperone during FeMo-co biosynthesis. These measurements provide powerful evidence that X not equal N/C, unless X in effect is magnetically decoupled from the S = 3/2 electron spin system of resting FeMo-co. They reveal no signals from FeMo-co in any of the three environments that can be assigned to X from either 14/15N or 13C: If X were either element, its maximum observed hyperfine coupling at all fields of measurement is estimated to be A(14/15NX) < 0.07/0.1 MHz, A(13CX) < 0.1 MHz, corresponding to intrinsic couplings of about half these values. In parallel, we have explicitly calculated the hyperfine tensors for X = 14/15N/13C/17O, nuclear quadrupole coupling constant e2qQ for X = 14N, and hyperfine constants for the Fe sites of S = 3/2 FeMo-co using density functional theory (DFT) in conjunction with the broken-symmetry (BS) approach for spin coupling. If X = C/N, then the decoupling required by experiment strongly supports the "BS7" spin coupling of the FeMo-co iron sites, in which a small X hyperfine coupling is the result of a precise balance of spin density contributions from three spin-up and three spin-down (3 upward arrow:3 downward arrow) iron atoms of the [6Fe] prismane "waist" of FeMo-co; this would rule out the "BS6" assignment (4 upward arrow:2 downward arrow for [6Fe]) suggested in earlier calculations. However, even with the BS7 scheme, the hyperfine couplings that would be observed for X near g2 are sufficiently large that they should have been detected: we suggest that the experimental results are compatible with X = N only if aiso(14/15NX) < 0.03-0.07/0.05-0.1 MHz and aiso(13CX) < 0.05-0.1 MHz, compared with calculated values of aiso(14/15NX) = 0.3/0.4 MHz and aiso(13CX) = 1 MHz. However, the DFT uncertainties are large enough that the very small hyperfine couplings required by experiment do not necessarily rule out X = N/C.

Vibrational Spectroscopic Signature Indicating the Mixing of the Cis Conformers in Liquid N-Methylformamide

For the purpose of seeking vibrational spectroscopic signatures of the mixing of the cis conformers in liquid N-methylformamide (NMF), infrared (IR) and Raman spectra are calculated by the ab initio molecular orbital method for three clusters of NMF: linear and cyclic hexamers of the trans conformers, and a cyclic trimer of the cis conformers. It is found that a small feature at ∼250 cm−1 in the observed Raman spectrum of liquid NMF corresponds to the strongly Raman-active modes calculated at 263 cm−1 for the cis cyclic trimer. Considering that there is no vibrational mode around this frequency position for the clusters of the trans conformers, it is suggested that the Raman band at ∼250 cm−1 is a marker band of hydrogen-bonded cis conformers, and the existence of a small feature at this position in the observed Raman spectrum of liquid NMF is a vibrational spectroscopic signature indicating the mixing of the cis conformers in this liquid. However, the main features of the observed low-frequency Raman spectrum (10–400 cm−1) of liquid NMF are explained by the strongly Raman-active modes of the clusters of the trans conformers, in contradiction to the suggestion in a recent x-ray diffraction study that liquid NMF is dominated by the cis conformers. The features of the IR and Raman spectra in the amide I (C=O stretching) region are also discussed.

On the Microheterogeneity in Neat and Aqueous Amides: A Molecular Dynamics Study

A molecular dynamics study of three amides, namely, formamide, N-methyl formamide, and dimethyl formamide, and their mixtures with water is conducted to sort out the nature of the local microstructure of both the pure amides and the aqueous mixtures. For pure amides, both the cluster distribution and pair structure factors are investigated. The former reveals no specific cluster formation for all three amides, while the latter shows that formamide has a weak prepeak at about k ≈ 1.32 Å-1 reminiscent of that observed for water, thus enforcing the puzzle of the nature of the hydrogen-bonding self-clustering in this type of liquids. The analysis of aqueous mixtures shows that all three mixtures are strongly microheterogeneous at the nanometer/nanosecond scales. This is confirmed in two ways: the direct visual observation and through the analysis of the pair distribution functions. The observation of microheterogeneity through usually measured quantities, namely the Kirkwood−Buff integrals, is discussed in light of the present analysis, and these latter quantities are shown to be weak indicators of microheterogeneity mainly because all three aqueous amides have nearly ideal such integrals in contrast to displaying strong microheterogeneity. As a direct consequence of this fact two features are reported. First, the Kirkwood−Buff integrals of the amide−amide correlations are obtained in relatively good agreement with the experimental ones, and second, those involving correlations with water are considerably affected by the microheterogeneity beyond the 15 Å range and need prohibitively larger statistics despite the large system sizes used in this study.

Dielectric Relaxation Study of Amide-Alcohol Mixtures by Using Time Domain Reflectometry

Using time domain reflectometry (TDR), dielectric relaxation studies were carried out on binary mixtures of amides ( N-methylformamide (NMF) and N, N-dimethylformamide (DMF)) with alcohols (1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-decanol) for various concentrations over the frequency range from 10 MHz to 10 GHz at 303 K. The Kirkwood correlation factor and excess dielectric constant properties were determined and discussed to yield information on the molecular interactions of the systems. The relaxation time varied with the chain length of alcohols and substituted amides were noticed. The Bruggeman plot shows a deviation from linearity. This deviation was attributed to some sort of molecular interaction which may take place between the alcohols and substituted amides. The excess static permittivity and excess inverse relaxation time values varied from negative to positive for all the systems indicating that the solute-solvent interaction existed between alcohols and substituted amides for all the dynamics of the mixture.

Isentropic compressibilities of (amide + water) mixtures: A comparative study

The density and ultrasonic velocity of aqueous solutions of formamide (FA), N-methylformamide (NMF), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA), pyrrolidin-2-one (PYR), N-methyl-2-pyrrolidinone (NMP), and their pure phases have been measured at 298.15 K and atmospheric pressure. Densities and ultrasonic velocities in pure amides have been also measured at the temperature range 288.15 K to 308.15 K for the computation of their thermal expansivities. Isentropic compressibility, intermolecular free length, relative association, apparent molar compressibility, as well as the excess quantities, ultrasonic velocity, isentropic compressibility, intermolecular free length, have been evaluated and fitted to the Redlich–Kister type equation. The deviation from ideal mixing law in ultrasonic velocity is positive while the deviations in isentropic compressibility and intermolecular free length are negative for all (amide + water) mixtures. This behavior reveals the nature and the magnitude of intermolecular interactions between the amide–water molecules. The sequence of superimposed curves of various ultrasonic parameters vs. the amide mole fraction is related to the strength of interactions between the unlike molecules and the role of –CH 3 substitution in amides. The comparison of ultrasonic to volumetric properties reveals differences on the position of the extrema and their relation with the degree of substitution while the interpretation of these differences is discussed. Two different approaches on the computation of excess functions, applied in this work, brought out a difference in the magnitude of deviations and a partial reversion to the sequence of amides curves suggesting a different estimation in terms of deviations from ideal mixing law and therefore of the relative molecular interactions.