甲酰胺对有序介孔二氧化硅形貌的影响

At room temperature and in acidic solution, ordered mesoporous silicas with particular morphology were synthesized using cetylpyridinium chloride as the template and formamide as the cosolvent. Scanning electron microscope (SEM), small angle X-ray diffraction (SXRD), and nitrogen adsorption techniques were used to characterize the as-synthesized and calcined samples. Results showed that the samples had hexagonal mesostructure analogous to MCM-41 and relatively narrow pore-size distributions (BJH). Besides, BET surface areas of the samples were in the range of 1 000～1 250 m²·g^-1 and high total pore volumes were up to 1.367 cm³·g^-1. Addition of formamide affected obviously mesostructures and the morphology of the mesoporous silica. Furthermore, with the increase of the concentration of formamide, the unit-cell constant decreased and particle shape changed from gyroids to fibers.     

Enthalpies of dilution of aqueous solutions of amides and alcohols

Enthalpies of dilution of aqueous systems containing formamide, dimethyl-formamide, the mixture of these amides, and each amide separately with mannitol, inositol, and cyclohexanol have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle and in combination with literature data. New values for the methylene-amide, carbinol-amide, and amide-amide group interaction enthalpies are presented. These may be used with data on a wider variety of solute systems to obtain interaction enthalpies for new groups.     

Thallium-205 NMR spectroscopy. Solvation of the thallous ion in dilute aqueous-amide and amide-amide binary solvent systems of formamide,N-methylformamide,andN-ethylformamide

Solvation of the thallous ion in dilute solutions of six binary solvent systems (formamide/water,N-methylformamide/water,N-ethylformamide/water, formamide/N-methylformamide, formamide/N-ethylformamide, andN-methylformamide/N-ethylformamide) was studied with²⁰⁵Tl NMR spectroscopy. An attempt was made to separate solvation effects related to the electrondonating ability (Lewis basicity) of the solvents from effects resulting from structural changes in the solvation sphere. Structural effects were found to be greatest in theN-methylformamide/water system and least in theN-methylformamide/formamide system.     

Electrical conductivities of halide salts in aqueous formamide solutions

The electrical conductivities of sodium chloride and sodium iodide solutions in formamide-water mixtures of different composition have been measured at 25°C. From these data, the limiting equivalent conductances for these salts have been determined. The correspondingWalden products are compared together with the one reported for sodium bromide in the same solvent mixtures, and they are analysed as functions of the anion size. Further, the limiting ionic equivalent conductances are estimated for the different ions. The variation of the ionicWalden products with solvent composition is discussed in terms of ionic solvation and solvent structure.

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Elektrische Leitfähigkeit von Halogensalzen in wäßrigen Formamid-Lösungen

Zusammenfassung Es wurden die elektrischen Leitfähigkeiten von Natriumchlorid- und Natriumjodidlösungen in Formamid-Wasser-Mischungen verschiedener Zusammensetzung bei 25°C gemessen. Aus diesen Daten wurden die Grenzäquivalenzleitfähigkeiten für diese Salze bestimmt. Die entsprechendenWalden-Produkte wurden mit den für Natriumbromid in den gleichen Lösungsmittelgemischen berichteten verglichen und hinsichtlich der Anionengrößen analysiert. Außerdem wurden die ionischen Grenzäquivalenzleitfähigkeiten für die einzelnen Ionen abgeschätzt. Die Variation der ionischenWalden-Produkte mit der Lösungsmittelzusammensetzung wurde bezüglich Ionensolvatation und Lösungsmittelstruktur diskutiert.

     

The structure of diluted binary solutions of amides according to the heat capacity data

The specific heat capacities of hexamethylphosphoric triamide, diethylpropionamide, their aqueous solutions, and mixtures of hexamethylphosphoric triamide with formamide were measured in the temperature range from 288.15 to 318.15 K. The dependences of the partial molar heat capacity of aqueous solutions of amides on the composition of the mixture have maxima in the region of 0.02–0.04 molar fractions of amide. The maximum on a similar dependence for solutions of hexamethylphosphoric triamide corresponds to the concentration of 0.01 molar fractions. The conclusion on the formation of solvates (hydrates) in the systems studied was made. The heat capacity coefficients of pair and triple interactions were calculated in terms of the McMillan-Mayer theory. A change in the heat capacity characteristics with the temperature change was analyzed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2479–2483, December, 1998.     

Group contributions to the infinite dilution partial molar volumes of alkanes, alcohols, and glycols in polar organic solvents

Densities of binary mixtures of polar organic solvents with alcohols were measured at 25‡C. The solvents studied were N,N-dimethylformamide, dimethylsulfoxide, and formamide while alcohols were butanol, pentanol, hexanol, and 1,4-butanediol. Density measurements of hydrocarbons (from pentane to dodecane and some heptane isomers) + N,N-dimethylformamide were also performed. From these data the apparent molar volumes of alcohols and hydrocarbons as functions of concentration were calculated. The standard partial molar volumes were obtained by extrapolation to infinite dilution and are discussed in terms of group contributions.     

Freezing temperatures of aqueous solutions of methyl formate and ethyl acetate with a variety of nonelectrolytes. Gibbs energy of interaction of the ester group with other functional groups

Freezing temperatures of dilute aqueous solutions of ethyl acetate and mixtures with myo-inositol, D-mannitol, formamide, 1,3,5-trioxane, 1,4-dioxane, acetamide, hexamethylenetetramine, and methyl formate have been measured. In addition, freezing temperatures of dilute aqueous solutions of methyl formate and mixtures with the above solutes have been measured. From these data, the pairwise molecular Gibbs energies of interaction between the molecules were calculated. Using the additivity principle, the pairwise functional group Gibbs energies of interaction were calculated for ester group interactions with a variety of other functional groups.     

Solvation of small hydrophobic molecules in formamide: A calorimetric study

The solubility and enthalpy of solution of benzene, cyclohexane, hexane, and heptane in formanide have been determined from titration microcalorimetric experiments at 25°C. The solution enthalpies are significantly more endothermic than in water but still the solubility is much higher. The entropy changes in formamide are small and positive and do not vary significantly with size. The enthalpies of solution of some 1-alkanols, 1-chloro- and 1,5-dichloropentane and pentane-1,5-diol were measured as functions of concentration. The solution enthalpies for 1-alkanols from methanol to decanol increase linearly with chain length. The enthalpic interaction coefficients h_xx are small and negative in formamide while they are large and positive in water. The partial molar heat capacities C _p,2 ^o for 1-propanol, 1-pentanol, benzene and cyclohexane in formamide were determined at 25°C from drop heat capacity measurements. Values of C _p,2 ^o are only slightly larger than the molar heat capacities of the liquid solutes.     

Kinetics and mechanism of trichloroisocyanuric acid/NaNO2-triggered nitration of aromatic compounds under acid-free and Vilsmeier-Haack conditions

Kinetics and mechanism of nitration of aromatic compounds using trichloroisocyanuric acid (TCCA)/NaNO₂, TCCA-N,N-dimethyl formamide (TCCA-DMF)/NaNO₂, and TCCA-N,N-dimethyl acetamide (TCCA-DMA)/NaNO₂ under acid-free and Vilsmeier-Haack conditions. Reactions followed second-order kinetics with a first-order dependence on [Phenol] and [Nitrating agent] ([TCCA], [(TCCA-DMF)], or [(TCCA-DMA)] >> [NaNO₂]). Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups, but did not fit well into the Hammett's theory of linear free energy relationship or its modified forms like Brown-Okamoto or Yukawa-Tsuno equations. Rate data were analyzed by Charton's multiple linear regression analysis. Isokinetic temperature (β) values, obtained from Exner's theory for different protocols, are 403.7 K (TCCA-NaNO₂), 365.8 K (TCCA-DMF)/NaNO₂, and 358 K (TCCA-DMA)/NaNO₂. These values are far above the experimental temperature range (303-323 K), indicating that the enthalpy factors are probably more important in controlling the reaction.     

Prebiotic Route to Thymine from Formamide—A Combined Experimental–Theoretical Study

Synthesis of RNA nucleobases from formamide is one of the recurring topics of prebiotic chemistry research. Earlier reports suggest that thymine, the substitute for uracil in DNA, may also be synthesized from formamide in the presence of catalysts enabling conversion of formamide to formaldehyde. In the current paper, we show that to a lesser extent conversion of uracil to thymine may occur even in the absence of catalysts. This is enabled by the presence of formic acid in the reaction mixture that forms as the hydrolysis product of formamide. Under the reaction conditions of our study, the disproportionation of formic acid may produce formaldehyde that hydroxymethylates uracil in the first step of the conversion process. The experiments are supplemented by quantum chemical modeling of the reaction pathway, supporting the plausibility of the mechanism suggested by Saladino and coworkers.