The influence of selected metals and halogens on the electronic system of benzoic acid

The influence of halogens and metals on the electronic system of the aromatic ring in lithium, sodium and potassium complexes with p-halogenobenzoic acids has been investigated by means of ¹³C and ¹H NMR, IR and Raman spectroscopy and semi-empirical calculations. It has been shown that ionic potentials and electronegativities of halogens and metals are the main factors responsible for perturbations of the electronic charge distribution in the ring.     

The influence of selected metals on the electronic system of biologically important ligands

The influence of (i) halogens, (ii) different alkaline cations, Li(I), Na(I), K(I), Rb(I) and Cs(I), and (iii) lanthanide cations, Pr(III), Nd(III), Dy(III) and Er(III) on the electronic structure of the aromatic ring as well as of the carboxylic anion of the substituted benzoic acids was investigated. Systematic change (decrease or increase) in the wavenumbers of selected bands along the F-->Cl-->Br-->I series was observed. This change correlates in linear fashion with a decrease in the ionic potential of the halogens. A shift of the selected bands along with the alkaline and the lanthanide metal series was also observed and correlated with the ionic potential of the metal. It was noticed that the increase in the ionic potential of halogen atoms causes a remarkable increase in the difference (Deltanu) between the wavenumbers of nuasym(COO-) and nusym(COO-). Among the halogens the ionic potential is the lowest for iodine and this substituent brings about maximal proximity of the asymmetric and symmetric bands of the carboxylic anion. The change of cation in the molecule causes a characteristic change in the difference (Deltanu) between the wavenumbers of nuasym(COO-) and nusym(COO-) as well. Along with the lanthanide series under study (Pr-->Nd-->Dy-->Er) this difference decreases, while between alkaline cations lithium broadens these bands to the highest degree. The influence of the alkaline and the lanthanide cations on the vibrational structure of the whole molecule was analysed and compared.     

Theoretical interpretation of the electronic spectra of nitrobenzene and benzoic acid

At theoretical study is reported of the electronic spectra of nitrobenzene and benzoic acid by the CNDO/2 method (del Bene and Jaffé's version). An a     

Mobile-phase pH influence on the retention of some benzoic acid derivatives in reversed-phase chromatography

Five end-capped octadecyl RP stationary phases, among which one was a polar embedded stationary phase, were tested for the analysis of benzoic acid derivatives using two mobile phases with or without addition of formic acid (water pH was measured by a common approach; pH of water with addition of formic acid was 3.0 and without formic acid 5.8). The influence of mobile-phase pH on the retention of benzoic acid derivatives was under study. Consequently, Purospher-STAR and Alltima columns provided symmetrical peaks for benzoic acid derivatives at pH 3.0 and also at pH 5.8. Reprosil and Symmetry stationary phases showed poor peak shapes at higher pH of the mobile phase. Differences between the tested columns may be caused by surface heterogeneity. Another reason may be the presence of some atoms creating additional adsorption sites on the surface of Reprosil and Symmetry stationary phases. This can lead to enhanced silanol activity resulting in peak tailing. The addition of formic acid into the mobile phase improved peak shapes. The polar embedded C18 stationary-phase Synergi-Fusion-RP appeared as not a suitable column for the analysis of benzoic acid derivatives. Synergi-Fusion-RP provided asymmetrical peaks even if formic acid was added into the mobile phase.     

The influence of surfactants on the behaviour of heavy metals in the system n-octanol-water

The partition of heavy metals between octanol and water in the presence of surfactants has been investigated. It is shown that metal ions can be extracted from water into the organic phase, n-octanol, as a model for biological materials in the presence of various anionic surfactants. Anions such as chromate can be extracted with the help of certain cationic surfactants. It was found that the extent of extraction depends on various parameters, such as the concentration of the surfactant, ionic strength and pH. With some anionic surfactants, the K_(ow) of lead or cadmium can reach values of 200 from waters of low ionic strength, decreasing as the ionic strength increases.     

Study of the influence of carboxymethylcellulose on the absorption of selenium (and selected metals) in a target plant

The aim of the present paper is the study of the influence of a polysaccharide (carboxymethylcellulose, CMC) on uptake by a target plant Lactuca sativa (LS) of selenium and some metals. LS was grown on a well characterized soil: such as, treated with 1.5 mg kg⁻¹ Se(IV) only and with two levels of CMC (3 and 30 mg kg⁻¹). Similar experiments were carried out by using Se(VI) instead of Se(IV). Uptake was evaluated through the quantification of total content of Se in dried leaves and roots by a suitable technique (graphite furnace atomic absorption spectrophotometry, instrumental neutron activation analysis and differential pulse cathodic stripping voltammetry). Results evidenced as the uptake of selenium was dependent on the form of selenium added to the soil: Se(VI) is accumulated much more then Se(IV) according to its lower toxicity and higher mobility. The simultaneous presence of CMC led to a lower selenium uptake in leaves, whereas no clear influence was evidenced in roots. Furthermore, the presence of CMC influenced also the mobility process (soil→plant) of several other metals: a lower content of them was detected in plants when CMC was present in the soil.     

The effect of temperature on the solubility of benzoic acid derivatives in water

Using a laser monitoring observation technique, solubilities of o-nitro-benzoic acid, p-hydro-benzoic acid, p-methyl-benzoic acid and m-methyl-benzoic acid in water have been measured in the temperature range 290.15–323.15 K. The experimental data are regressed with the Wilson equation and the λH equation. The experimental results show that solubilities of these compounds in the range of 10⁻⁴–10⁻⁵ mole fraction in water, increase significantly with temperature. Except for o-nitro-benzoic acid, the solubility data are described adequately with the Wilson equation. The λH equation gives good agreement with all experimental data. The results indicate that the molecular structure and interactions affect the solubilities significantly.     

Electrochemical oxidation of sulfodifluoroacetic acid in the presence of halogens

The electrochemical oxidation of sulfodifluoroacetic acid (HOSO₂CF₂CO₂H) in the presence of Cl₂ or Br₂ gives halodifluoromethanesulfonic acid. The anodic oxidation of sulfodifluoromethanecarboxylate ion to form the sulfodifluoromethyl radical as an intermediate is proposed as the rate-determining step. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 246–248, July–August, 1999.     

Temperature effect on the partition and dimerization constant of benzoic acid

Making use of the regular solution theory with binary coefficients, the partition of benzole acid between aqueous benzene phases was investigated. ΔH, ΔS and ΔG thermodynamic functions associated with the hydration-corrected partition and dimerization were calculated. It was found that the partition was spontaneous at high temperatures and of the hydrates of benzoic acid, the monohydrate monomer was dominant at high temperatures.     

Adsorption and dissociation equilibrium of benzoic acid on the mercury electrode

Adsorption of benzoic acid at the mercury electrode was studied in a wide pH range. The adsorption isotherms of benzoic acid from electrocapillary and capacity measurements were calculated. From the dependence of capacitance and potential of zero charge on pH the pK_el of benzoic acid was determined.     

The uranyl-chloro-substituted benzoic acid-rhodamine b-benzene extraction system

Of the chloro-substituted benzoic acids, the 2-chloro and 2,4-dichloro compounds yield higher effective molar absorptivities than benzoic acid does in the Rhodamine B-benzene extractive spectrophotometric procedure for determination of uranium(VI). Carbonyl compounds (especially acetone) in the organic phase enhance the extraction of the ion associate. The stoichiometry of the complexes has been determined, and a method of computing the extraction constants of the ion-associates developed. A spectrophotometric method for determining uranium in the presence of interfering ions has been designed.