Ester F.G. Barbosa

Partial molar volumes of secondary amines in methanol. Specific interactions

Abstract Lampreia I.M.S. and Barbosa E.F.G., 1992. Partial molar volumes of secondary amines in methanol. Specific interactions. Fluid Phase Equilibria, 71: 125-142. Limiting partial molar volumes, − V ∞ B , at 25° C, for diethyl-, di- n -propyl-, di- n -butyl- and di- n -hexylamines in methanol were determined from density measurements using a vibrating tube densimeter. Contributions to − V ∞ B of the secondary amine group and of the interaction of the secondary amine group with methanol, calculated with linear hydrocarbons as reference compounds, have been derived and discussed by using an additive scheme and a hard sphere model respectively. Transference partial molar volumes from benzene to methanol have been calculated and split into various contributions including solvent effects such as the differences in size and in packing density as well as interaction terms. Complementary information about intermolecular interactions in these systems, and in the range of the dilute region studied were obtained by means of excess volumes calculated in terms of Henrys model.

Conformational studies by Raman spectroscopy and statistical analysis of gauche interactions in n-butylamine

Abstract Raman spectra of n -butylamine recorded at different temperatures show pairs of bands whose temperature-dependent intensities clearly suggest their assignment to different conformers in simultaneous equilibria. Normal coordinate analysis and i.r. spectra of n -butylamine are also used to assign the spectra. These vibrational data are interpreted and correlated with structural information obtained from a statistical analysis of gauche skeletal arrangements in n -butylamine at different temperatures.

Alkyl deoxy-arabino-hexopyranosides: Synthesis, surface properties, and biological activities

Octyl and dodecyl glycosides possessing 2-deoxy-arabino-hexopyranoside moieties belonging to the D- and L-series in their alpha- and beta-forms were synthesized by reaction of an acetyl protected glycal with octanol or dodecanol, catalyzed by triphenylphosphine hydrobromide, followed by deprotection. Their surface properties were studied and discussed in terms of the adsorption and aggregation parameters, pC(20), CMC, and gamma(CMC). The antimicrobial activities were assessed using the paper disk diffusion and broth dilution methods. Both the octyl and dodecyl 2-deoxy beta-D-glycosides inhibited significantly Enterococcus faecalis, a microbe also highly susceptible to dodecyl 2,6-dideoxy-alpha-L-arabino-hexopyranoside. This compound was particularly active against Bacillus cereus and Bacillus subtilis, presenting for both Bacillus species a minimal inhibitory concentration of the same order of magnitude and a minimal lethal concentration even smaller than that obtained for chloramphenicol, a bioactivity which remained unaltered after 1 year solution storage at 4 degrees C. In addition, activity over Listeria monocytogenes was also observed. Direct cytotoxicity and genotoxicity of the glycosides were determined by proliferative index (mitotic index) evaluation in peripheral human lymphocytes of healthy donors. All compounds induced acute toxicity effects, and the response was dose dependent for the alpha-anomer of both the alkyl 2-deoxy-arabino-hexopyranosides and for the corresponding dodecyl beta-anomer, what suggests that non-toxic but still bioactive concentrations may be found for these compounds.

Partial molar volumes of linear hydrocarbons in methanol in the very dilute region. Intermolecular interactions. H-bond effects

Limiting partial molar volumes VB∞ for the linear hydrocarbons, C5, C6 , C7, C8 and C10 in methanol were determined with a vibrating tube densimeter at 24.994°C (ITS-90). VB∞ and bV were discussed in terms of solute–solvent and solute–solute molecular interactions, focusing on H-bond cleavage, hydrocarbon short-range correlations of molecular orbitals and conformational effects. VB∞ (HS)/VB (HS) values calculated according to Lees hard-sphere mixtures model are compared with experimental values. A discussion is presented and deviations are interpreted in terms of size, shape, packing densities and H-bond effects.

Silver(I) complexation with tertiary amines in toluene

The extent of complexation between silver(I) nitrate and triethylamine and tri-n-butylamine in toluene solutions at 23 °C has been determined by infrared spectroscopy. Both amines produced a mixture of monoamine and diamine silver complexes, and the second stepwise formation constants (K2) are reported. Infrared and atomic absorption experiments on solutions saturated with silver nitrate also yielded formal values of the first formation constant (K1) and of the solubility product (Ks) of silver nitrate in toluene. The results showed that Et3N coordinates more strongly with silver(I) in toluene than does Bu3nN. The values of K1 in toluene were found to be 4–5 powers of ten higher than in protic and dipolar aprotic solvents, while the values of K2 were smaller. Structural and solvation reasons are given to explain these results.

Catalysed quaternization of coordinated tertiary amines by ethyl iodide: kinetics and mechanism

Abstract A kinetic study of the joint homogeneous–heterogeneous catalysis for the quaternization of silver (I)-coordinated triethylamine and tributilamine by ethyl iodide was performed in toluene. The data obtained substantiated the superficial molecular arrangement, previously proposed by Barbosa and Spiro, and exposed a new competitive reaction of the non-coordinated soluble silver salt with the alkyl halide in the solvent under study. Estimates of the solution rate constants were obtained for both systems and evidence of a surface effect is also presented.

Catalysed quaternization of coordinated triethylamine by ethyl iodide: further developments in the kinetic analysis

A new approach in the kinetic analysis of the joint homogeneous–heterogeneous catalysis of the quaternization of silver(I) coordinated triethylamine by ethyl iodide in toluene is presented. This complex competitive process was thoroughly scrutinized and the set of solution and surface rate equations were integrated under a novel perspective thus leading to the calculation of solution rate constants as well as guesstimates of the superficial quaternization rate. Testing the rate equations developed herein also required the performance of kinetic runs over a wider range of experimental conditions, than those previously reported.

Heterogeneous catalysis in solution. Part 20.1—Catalysis by silver bromide and other solids of the solvolysis of t-butyl bromide in 80 vol% ethanol + water

The SN1 solvolysis of 2-bromo-2-methylpropane (t-butyl bromide) in 80 vol%(55.2 mol%) EtOH + H2O at 25 °C was found to be catalysed by silver and several insoluble silver and mercury salts but not by BaSO4, SiO2 or platinum. The relative catalytic effectiveness of these solids could be largely explained by Pearsons SHAB concept. The kinetics of the AgBr-catalysed process were studied in detail by a pH-stat technique. The results fitted a model in which t-BuBr molecules and product Br– ions competitively adsorbed on the surface according to Langmuir isotherms. Calculations showed the surface reaction to be ca. 105 times faster than the homogeneous solvolysis and to possess a much lower activation energy. The heterogeneous reaction was found to be selective, forming no alkene product and a higher ratio t-BuOEt:t-BuOH than in the bulk solution. These findings have been discussed in terms of the structure of the interfacial region.

Interactions in the systems Et3N/AgNO3/C6H6 and Et3N/AgNO3/CH3COCH3. The effect on the catalysed quaternization of Et3N with EtI

Abstract A strong catalytic effect having been observed due to the presence of AgNO 3 in a Menschutkin reaction mixture in benzene [1] and acetone [2], it has been considered of interest to study more deeply this effect. Studies of interactions in the systems Et 3 N/AgNO 3 /solvent are required to understand the mechanism and rate law of the proposed catalysed reaction. The studies started benzene and acetone as solvents. Density measurements in the binary mixtures Et 3 N/C 6 H 6 and Et 3 N/AgNO 3 /CH 3 COCH 3 as well as in the ternary mixtures Et 3 N/AgNO 3 /C 6 H 6 and Et 3 N/AgNO 3 /CH 3 COCH 3 have been undertaken in this laboratory using a Digital Anton Paar DMA O2D Density Meter. Computation of partial molal volumes were made. Discussion of the foregoing results together with infrared spectroscopic information and the analysis of data found in the literature [3–7] led us to propose structural models for the investigated mixtures and to make correlations with the experimental rates measured for the catalysed reactions.

Joint homogeneous and heterogeneous catalysis: a new synergistic effect

An increase of the order of 104 in the rate of the Menschutkin reaction was achieved at reaction sites created by the adsorption of silver ions on silver iodide or carbon surfaces.