First-principle predictions of absolute pKa's of organic acids in dimethyl sulfoxide solution

MP2/6-311++G(d,p) and B3LYP/6-311++G(2df,p) methods were found to be able to predict the gas-phase acidities of various organic acids with a precision of 2.2 and 2.3 kcal/mol. A PCM cluster-continuum solvation method was developed that could predict the solvation free energies of various neutral, cationic, and anionic organic species in DMSO with a precision of about 2.0 kcal/mol. Using these carefully tested methods, we successfully predicted the pKa's of 105 organic acids in DMSO with a precision of 1.7-1.8 pKa units. We also predicted the pKa's of a variety of organosilanes in DMSO for the first time using the newly developed methods. This study was one of the first that employed first-principle methods for calculating pKa's of unrelated compounds in organic solutions.     

Quantum-chemical predictions of absolute standard redox potentials of diverse organic molecules and free radicals in acetonitrile

A calibrated B3LYP/6-311++G(2df,2p)//B3LYP/6-31+G(d) method was found to be able to predict the gas-phase adiabatic ionization potentials of 160 structurally unrelated organic molecules with a precision of 0.14 eV. A PCM solvation model was benchmarked that could predict the pK(a)'s of 15 organic acids in acetonitrile with a precision of 1.0 pK(a) unit. Combining the above two methods, we developed a generally applicable protocol that could successfully predict the standard redox potentials of 270 structurally unrelated organic molecules in acetonitrile. The standard deviation of the predictions was 0.17 V. The study demonstrated that computational electrochemistry could become a powerful tool for the organic chemical community. It also confirmed that the continuum solvation theory could correctly predict the solvation energies of organic radicals. Finally, with the help of the newly developed protocol we were able to establish a scale of standard redox potentials for diverse types of organic free radicals for the first time. Knowledge about these redox potentials should be of great value for understanding the numerous electron-transfer reactions in organic and bioorganic chemistry.     

Highly efficient Cu-catalyzed oxidative coupling of tertiary amines and siloxyfurans

A mild, selective, and efficient protocol for the synthesis of γ-aminoalkyl butenolides via the oxidative coupling between tertiary amines and siloxyfurans catalyzed by simple copper salts was developed. Compared with the reported method, our method employs copper catalyst instead of the expensive rhodium catalyst. Besides TBHP, both O₂ and H₂O₂ can also be utilized as oxidant to effect the coupling.     

Sensitive fluorescent detection and Lewis basicity of aliphatic amines

In this contribution is reported the sensitive properties of the Zn(II) Schiff base complex, 1, in dichloromethane with respect a series of primary, secondary, and tertiary aliphatic amines through the study of fluorescence enhancement upon amine coordination to the Lewis acidic Zn(II) metal center with formation of 1:1 adducts. It is found that complex 1 exhibits selectivity and nanomolar sensitivity for primary and alicyclic amines. A distinct selectivity is also observed along the series of secondary or tertiary amines, paralleling the increasing steric hindrance at the nitrogen atom. The binding interaction can be related to the Lewis basicity of the coordinating amine; thus, complex 1 represents a suitable reference Lewis acid, and estimated binding constants within the investigated amine series can be related to their relative Lewis basicity. A relative order of the Lewis basicity can be established for acyclic amines, primary > secondary > tertiary, while an inverted order, tertiary > secondary ≈ primary (acyclic), is found in the case of alicyclic amines. The present approach represents a simple, suitable method to ranking the relative Lewis basicity of aliphatic amines in low-polarity, nonprotogenic solvents.     

Three-component reaction of secondary phosphines with elemental selenium and amines

Russian Journal of Organic Chemistry -     

Self-consistent spectrophotometric basicity scale in acetonitrile covering the range between pyridine and DBU

A self-consistent spectrophotometric basicity scale in acetonitrile, including DBU, ten (arylimino)tris(1-pyrrolidinyl)phosphoranes, two (arylimino)tris(dimethylamino)phosphoranes, 2-phenyl-1,1,3, 3-tetramethylguanidine, 1-(2-tolyl)biguanide, benzylamine, two substituted benzimidazoles, pyridine, and ten substituted pyridines, has been created. The span of the scale is almost 12 pK(a) units. Altogether, 29 different bases were studied and 53 independent equilibrium constant measurements were carried out, each describing the relative basicity of two bases. The scale is anchored to the pK(a) value of pyridine of 12.33 that has been measured by Coetzee et al. Comparison of the basicity data of phenyliminophosphoranes and phenyltetramethylguanidines implies that the P=N bond in the (arylimino)tris(1-pyrrolidinyl)phosphoranes involves contribution from the ylidic (zwitterionic) structure analogous to that found in phosphorus ylides.     

Basicity of some organic superbases in acetonitrile

[structure: see text] It is shown that the pK(a) values of strong neutral organic (super)bases in acetonitrile are well described by the density functional theory (DFT) employing the isodensity polarization continuum model (IPCM) for treating solvent-solute interactions. High pK(a) values are predicted for two model compounds, and their synthesis is strongly recommended.     

Thermometric titrations of amines with nitrosyl perchlorate in acetonitrile solvent

Thirteen aliphatic and four aromatic amines, namely diethylamine, triethylamine, n-propylamine, di-n-propylamine, tri-n-butylamine, isopropylamine, di-isopropylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, aniline, N,N-dimethylaniline, 2-nitroaniline and 4-nitroaniline were titrated thermometrically with nitrosyl perchlorate in acetonitrile solvent. All the aliphatic amines gave very well-shaped thermometric titration curves. The calculated recovery values of the amines were very good. In comparison, the aromatic amines, aniline and N,N-dimethylaniline gave rather well-shaped titration curves, but the recovery values were fairly low. 2-Nitro- and 4-nitro anilines gave no thermometric response at all. The heats of reaction of the amines with nitrosyl perchlorate are rather high. However, the average heat of reaction of the aromatic amines is approximately two-thirds that of the average heat of the aliphatic amines. To support this method all the amines were also titrated potentiometrically and very similar results to those obtained with the thermometric method are seen. The nitrosyl ion is a Lewis acid, strong enough to titrate quantitatively aliphatic amines in acetonitrile solvent, but not strong enough to titrate aromatic amines at the required level in the same solvent.     

Extension of the self-consistent spectrophotometric basicity scale in acetonitrile to a full span of 28 pKa units: unification of different basicity scales

The earlier compiled self-consistent spectrophotometric basicity scale in acetonitrile (AN) was expanded to range from 3.8 to 32.0 pK(a) units, that is 28 orders of magnitude. Altogether 54 new relative basicity measurements (DeltapK(a) measurements) were carried out and 37 new compounds were introduced to the scale (it now includes altogether 89 bases). The relative basicity of any two bases in the scale can be obtained by combining at least two independent sets of measurements. Multiple overlapping measurements make the results more reliable. The overall consistency (as defined earlier) of the measurements is s = 0.03 pK(a) units. Thorough analysis of all of our experimental data (DeltapK(a) values of this and earlier works) and experimental pK(a) data in AN available in the literature (works from the groups of Coetzee and Padmanabhan, Kolthoff and Chantooni, Jr., the Schwesinger group, Bren' et al. and some others, altogether 19 papers) was carried out. On the basis of this analysis the anchor point of the scale-pyridine-was shifted upward by 0.20 pK(a) units thereby also revising the absolute pK(a) values of all the bases on the scale. This way very good agreement between our relative data and the absolute pK(a) values of the abovementioned authors was obtained. The revised basicity scale was interconnected with the earlier published self-consistent acidity scale by DeltapK(a) measurements between acids and bases. The rms deviation between the directly measured DeltapK(a) values and the absolute pK(a) values of the compounds was 0.10 pK(a) units.     

Correlation between basicity and quantum chemical indices of some aliphatic amines

Conclusions The change in the pK values of solutions of aliphatic amines (C₂H₅)₂NCH₂CH₂X in acetic acid is linear and opposite to the change in the energies of the upper filled molecular orbitals, which were calculated by the CNDO/2 method.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1908–1909, August, 1979.The authors are indebted to L. A. Piruzyan for his constant interest in the work.     

Reactions of (CF3)3BCO with amines and phosphines

Reactions of tris(trifluoromethyl)borane carbonyl, (CF(3))(3)BCO, with ammonia yielded either a mixture of [NH(4)][(CF(3))(3)BC(O)NH(2)], [NH(4)][(CF(3))(3)BCN], and [NH(4)](2)[{(CF(3))(3)BC(O)}(2)NH] or neat [NH(4)](2)[{(CF(3))(3)BC(O)}(2)NH] depending on the reaction conditions. The salt K[(CF(3))(3)BC(O)NH(2)] was obtained as the sole product from the reaction of NH(3) with K[(CF(3))(3)BC(O)F]. A simple synthesis for cyanotris(trifluoromethyl)borates, M[(CF(3))(3)BCN], was developed by dehydration of M[(CF(3))(3)BC(O)NH(2)] (M = [NH(4)], K) using phosgene. In addition, syntheses of the tris(trifluoromethyl)boron species [(CF(3))(3)BC(O)NH(n)()Pr](-), [(CF(3))(3)BC(O)NMe(2)](-), and (CF(3))(3)BC(O)NMe(3), as well as of (CF(3))(3)BC(O)PMe(3), were performed. All species were characterized by multinuclear NMR spectroscopy. As far as neat substances resulted, IR and Raman spectra were recorded and their thermal behaviors were studied by differential scanning calorimetry. The interpretation of reaction pathways, structures, and vibrational spectra are supported by DFT calculations. The solid-state structure of K(2)[{(CF(3))(3)BC(O)}(2)NH].2MeCN was determined by single-crystal X-ray diffraction.     

Mass spectrometry of organic compounds of the group V elements. IV—new data on amines,phosphines, arsines and the corresponding acyl derivatives

Further investigations have given new data confirming differences in fragmentation under electrol impact of compounds of trivalent nitrogen and other group V elements. These data have been obtained by comparision of the fragmentation of the amines, phosphines, arsines, benzyl derivatives, geminal systems and acyl derivatives. Mass spectra of tetraethyl derivatives of the group IV elements and acetyl triethyl germane have also been taken and compared with the previous ones.     

Cathodic behaviour of nickel(II) in acetonitrile in the presence of carbon monoxide and substituted phosphines

Summary The reduction of nickel perchlorate in the presence of carbon monoxide and substituted phosphines or diphosphines has been studied in acetonitrile by cyclic voltammetry. The results show that only mono- and bis-carbonylphosphinenickel(O) complexes are formed, while no evidence for the formation of carbonyl-nickel(I) and -nickel(II) species was obtained. Although the oxidation processes are not reversible, a good correlation between the anodic peak potentials relative to nickel(O) complexes and the -donor--acceptor abilities of the phosphines employed was observed.     

Hydrogenolysis of tertiary phosphines coordinated on transition metals by hydrogen transfer from amines

Considerable amounts of benzene were formed by heating triphenylphosphine complexes of transition metals in several types of organic compounds, especially in amines; in the case of a tributylphosphine complex, n-butane was detected. In the reactions with indoline, tetrahydroquinoline or dioxane, the hydrogen consumed for the hydrogenolysis was proved to arise from the amines or the ether.     

Kinetic study of nucleophilic reactivity of heterocyclic amines with 4,6-dinitrobenzofuroxan in acetonitrile

The reaction kinetics of 4,6-dinitrobenzofuroxan with five heterocyclic amines was investigated spectrophotometrically (UV–Vis) in acetonitrile at 20 °C. It was observed that the rate constants of these reactions increased as follows: 2-aminopyrimidine > 2-aminothiazole > 2-aminobenzothiazole > 5-amino-3,4-dimethylisoxazole > 2-amino-5-trifluoromethyl-1,3,4-thiadiazole. Further, second-order rate constants (k₁) pertaining to the C–N and C–C bond forming step of these complexation processes fit to the three parameter equation log k (20 °C) = s_N (N + E), allowing the determination of the nucleophilicity parameters (N) of the five heterocyclic amines. The heterocyclic amines were subsequently ranked on the comprehensive nucleophilicity scale defined by Mayr et al. (2003), providing a direct comparison of n-, π-, and σ-nucleophiles.     

CNDO/2 calculation on gas-phase basicity of amines,alcohols and ethers

The gas-phase basicity of about seventy compounds containing N or O have been calculated by means of the CNDO/2 method. For alkylamines, alcohols, ethers and carbonyl compounds, computational results agree qualitatively with the experimental values. We have also discussed the relationships between gas-phase basicities and charge distributions and ionization potentials of these molecules.