CC BY
5UOT 543.49.062:546.56
Gasanova N.S. Dissertator, Laboratory Assistant, Faculty of Chemical Technology, Department of Petrochemical Technology and Industrial Ecology, Azerbaijan State Oil and Industry University, Baku, Republic of Azerbaijan Гасанова Н.С. диссертант, лаборант, химико-технологический факультет, кафедра «Нефтехимическая технология и промышленная экология», Азербайджанский государственный университет нефти и промышленности,
Баку, Азербайджанская Республика E-mail: hesenova.1969@inbox.ru
Investigation of chromium (VI) complexes using 2-hydroxy-5-bromothyophenol Исследование комплексов хрома (VI) С применением 2-гидрокси-5-бромтиофенола
Abstract: When chromium (VI) interact with 2-hydroxy-5-bromothyophenol, chloroform extractable multi-ligand complexes are formed. O-xylidine (o-Xyl) and m-xylidine (m-Xyl) were used as hydrophobic amine. The conditions of extraction-photometric determination of chromium are found. It is established that multi-ligand complexes are formed at pHopt = 2.8-5.1. The maximum in the light absorption spectrum of chromium (VI) is observed at 437-438 nm, respectively. It was determined that Cr(VI) is reduced to Cr(III) by the reagent itself upon formation of a complex with 2-hydroxy-5-bromothyophenol.
Аннотация: При взаимодействии хрома (VI) с 2-гидрокси-5-бромтиофенолом образуются экстрагируемые хлороформом разнолигандные комплексы. В качестве гидрофобного амина использованы о-ксилидин (о-Ксил) и м-ксилидин (м-Ксил). Найдены условия экстракционно-фотометрического определения хрома. Установлено, что разнолигандные комплексы образуются при рНопт = 2.8-5.1. Максимум в спектре светопоглощения хрома (VI) наблюдается при 437-438 нм соответственно. Определено, что Cr (VI) при образовании комплекса с 2-гидрокси-5-бромтиофенолом восстанавливается до Cr (III) самим реагентом.
Keywords: chromium; 2-hydroxy-5-bromothyophenol; complexation; extraction; aniline; ligand; multi-ligand complexes.
Ключевые слова: хром; 2-гидрокси-5-бромтиофенол; комплексо-образование; экстракция; анилин; лиганд; разнолигандные комплексы.
Introduction. This work is devoted to the study of the conditions of interaction of chromium (VI) with 2-hydroxy-5-bromothyophenol (HBTF, H2L). In the presence of hydrophobic amines, the extraction of these compounds into the organic phase in the form of a multi-ligand complex (MLC) is observed. O-xylidine (o-Xyl) and m-xylidine (m-Xyl) were used from hydrophobic amines.
The most successful solution of the problems to date is associated with the use of hydroxytiophenols, in particular 2-hydroxy-5-bromothyophenols absorbed in the visible region of the spectrum, for the photometric determination of metal ions.
Multi-ligand complexes have found wide application in the photometric determination of elements [1]. Organic reagents are widely used in spectrophotometric analysis methods, their selectivity depends on the nature of the complexing agent, the basicity of the ligand, and the stoichiometry of the components in the complex. Numerous methods of photometric determination of chromium (VI) using various classes of organic reagents in the form of multi-ligand complexes are known.
We have investigated multi-ligand complexes of chromium with thiophenols (L) derivatives: 2-hydroxy-5-chlorophenyl, 2-hydroxy-5-bromothyophenol, 2-hydroxy-5-iodothyophenol and anilines (An), then developed methods for its extraction-photometric determination.
Experimental Part
Initial solutions (1 mg/ml) of Cr (VI) were prepared from chemically pure salts of K2Cr2O7 h.d.a. The concentration of chromium(VI) solutions was determined by titrimetric [2]. 0.01 M solutions of thiophenol (L) and aniline (An) in chloroform were used in the work. 0.1 M solutions of KOH and HCl were used to create optimal acidity. Purified chloroform was used as an extractant. All reagents and solvents used had the qualification of "o.c." or "h.c." and were used without additional purification.
Up to 90 micrograms of chromium, 2.0-2.5 ml of 0.01M solution of thiophenol (L) and 2.0-2.5 ml of aniline (An) were injected into graduated tubes with a capacity of 50 ml. The required pH value was set by adding 1M HCl solution. The volume of the organic phase was adjusted to 5 ml with chloroform, and the aqueous phase was adjusted to 20 ml with distilled water. The mixture was shaken for 2 minutes. After 10 minutes, the organic layer was separated and its optical density was measured at room temperature at KFK-2 at 440 nm.
On the restoration of Cr (VI) to Cr(III). Thiophenols (L) in an acidic environment have reducing properties [3]. To find out whether the valence of chromium does not change when interacting with thiophenol (L), two series of experiments were conducted. The reaction with thiophenol (L) Cr(III) obtained by reduction of SnCl2 and KI was carried out in hydrochloric acid solution and without the use of additional reducing agents. The products of both reactions had light absorption maxima at 440 nm. Consequently, Cr (VI) upon formation of a complex with thiophenol (L) is reduced to Cr (III) by the reagent itself.
Results and Discussion
Alcohols (butyl, amyl, benzyl), aromatic hydrocarbons (benzene, toluene, xylene), esters (isoamyl acetate, ethyl benzoate), ketones (methylbutyl ketone, cyclohexanone), halide derivatives of hydrocarbons (chlorobenzene, chloroform, 1,2-dichloroethane) were tested as organic solvents. With a single extraction with chloroform, 97.5-99.5% of chromium is extracted in the form of a multi-ligand complex. Further studies were carried out with chloroform. The chromium content in the organic phase was determined by photometric diphenylcarbazide [4] after reextraction, and in the aqueous phase by the difference.
Electronic absorption spectra of chloroform extracts of a multi-ligand complex taken at different pH values show that chromium (VI) with thiophenol (L) and aniline (An) forms one compound. Chromium (VI) thiophenol (L) and aniline (An) form multi-ligand complexes in the pH range 1.2-7.9. Optimal conditions for the formation and extraction of Cr (VI) complexes with 2-hydroxy-5-chlorophenol and aniline are
pH 3.5- 4.8, with 2-hydroxy-5-bromothyophenol and aniline - pH 3.3- 4.6, with 2-hydroxy-5-iodothyophenol and aniline - pH 3.1-4.5.
At the beginning, with an increase in the acidity of the initial solution, the extraction of Cr (III) increases, and with a further increase it gradually decreases, which is obviously due to a decrease in the concentration of the ionized form of H2L and most likely it is in an undissociated form in the solution. With an increase in pH > 7, the formation of multi-ligand complexes is practically not observed, which is probably due to a decrease in the degree of protonization of aniline.
The optimal condition for the formation and extraction of these compounds is the concentration of (1.3-1.5) x10-3 M (L) and (1.2 - 1.5) x 10-3 M (An). Extracts of the multi-ligand complex Cr obey the basic law of light absorption at concentrations of 0.2-20 micrograms/ml. The multi-ligand complexes are stable in aqueous and organic solvents and do not decompose for three days, and after extraction for more than a month. The maximum optical density of chromium (III) complexes is reached within 10 min.
Similar results were obtained by the methods of relative yield and equilibrium shift (fig.1). The Nazarenko method established that the complexing form of chromium (III) is Cr3+ [5].
A
420 430 440 450 460 ?shm
Figure 1 — Absorption spectra of chloroform extracts of chromium (III) complexes with L
and An.
1 — Cr — 2-hydroxy-5-chlorophenol (HCTF) - An, 2 — Cr - 2-hydroxy-5-bromothyophenol (HBTF) - An, 3 - Cr - 2-hydroxy-5-iodothyophenol (HITF) - An Ccr(III) = 3.84x10-5 M, Cr= (1.3-1.5) xl0-3 M; Cah= (1.2-1.5) xl0-3 M; pHonx, C^-26, 1= 1.0 CM
The disappearance of a pronounced band at 2580 cm-1 (SH) and in the region of 3200-3600 cm-1 with a maximum at 3450 cm-1 (OH), observed in the spectrum of thiophenol (L), suggests that -SH and -OH groups are involved in the formation of the complex. Absorption bands at 1380 cm-1 indicate the presence of protonated aniline [6].
Table 1 shows the analytical characteristics of chromium complexes with thiophenol (L) and aniline (An).
Table 1 — Analytical characteristics of a multi-ligand chromium complex with thiophenol (L) and aniline (An)
Parameter* Cr- HCTF-An Cr- HBTF-An Cr- HITF-An
ECG 0.0295 + 0.267x 0.0373 + 0.238x 0.0459 + 0.264x
CC 0.9983 0.9986 0.9987
LRCG, mcg/ml 0.2-20 0.2-19 0.2-18
DL, ng/cm3 9.21 9.75 9.90
LQD, ng/cm3 30.3 36.5 43.4
S, ng/cm3 2.41 2.53 2.69
*Note: ECG — Equations of calibration graphs; CC-Correlation coefficient; LRCG-Linear range of calibration graphs; DL-Detection limit; LQD-Limit of quantitative determination; S-Sensitivity.
The influence of foreign ions. The influence of a number of cations and anions on the accuracy of chromium determination has been studied. The experiments were carried out according to the recipe according to which the calibration graphs were constructed, with the only difference being that a certain amount of the corresponding ions were introduced into the solution in addition to chromium. Selectivity of spectrophotometric determination of chromium in the form of studied complexes (table 2).
Table 2 — The effect of foreign ions on the determination of chromium with thiophenol (L) and aniline (An) (40 mcg Cr (III) was taken) n = 5, P = 0,95
Ion Molar ion excess Masking reagent Found Cr, mcg; (Sr)
Cr- HCTF-An Cr- HBTF-An Cr - HITF-An
Co(II) 70 NaNO2 40.4 (0.06) 39.7(0.02) 40.1 (0.03)
Ni(II) 25 Ma^OHaT 39.9 (0.03) 40.4(0.03) 39.9 (0.04)
Fe(II) 140 P043- 40.0 (0.05) 40.3(0.03) 39.8 (0.05)
Fe(III) 10 Ascorbic acid 40.4 (0.04) 40.3(0.03) 40.2 (0.04)
Cd(II) 60 NaI 40.2 (0.05) 39.8(0.02) 39.6 (0.05)
Al(III) 10 NaF 39.9 (0.03) 40.7(0.05) 39.6 (0.03)
Bi(III) 1:1 Thiourea 39.5 (0.06) 40.3(0.03) 40.1 (0.04)
Nb(V) 40 Tartaric acid 40.2 (0.02) 39.5(0.03) 39.5 (0.02)
Zr(IV) 40 39.6 (0.03) 39.6(0.05) 39.5 (0.02)
Cu(II) 55 Thiourea 40.5 (0.03) 40.4(0.03) 39.2 (0.04)
Hg(II) 35 40.0 (0.0) 40.3(0.01) 39.6 (0.02)
Ti(IV) 20 Tartaric acid 39.6 (0.01) 39.7(0.02) 39.9 (0.04)
V(V) 70 EDTA 39.8 (0.06) 39.8(0.06) 40.4 (0.02)
W(VI) 40 39.7 (0.03) 40.6(0.03) 39.5 (0.01)
Mo(VI) 140 40.0 (0.0) 40.0(0.0) 40.0 (0.03)
Ta(V) 45 Tartaric acid 39.5 (0.03) 40.3(0.01) 40.2 (0.01)
uo2+ 50 Tartaric acid 39.7 (0.05) 50.5(0.06) 39.4 (0.04)
Th(IV) 50 Thiourea 39.6 (0.05) 50.0(0.0) 39.1 (0.03)
Mn(II) 50 39.7 (0.01) 50.0(0.0) 39.1 (0.02)
It was found that large amounts of alkaline, alkaline earth elements, REE, F ,
9 9 9
CI-, Br-, SO3 , SO4 and C2O42- - do not interfere with the determination of chromium. The selectivity of the determination increases significantly in the presence of masking substances. Conclusions
When chromium 2-hydroxy-5-bromothyophenol (HBTP) interacts, multi-ligand complexes extracted by chloroform are formed. Cr(VI) upon formation of a complex with 2-hydroxy-5-bromothyophenol (HBTP) is reduced to Cr(III) by the
reagent itself. With a single extraction with chloroform, 97.8% of chromium is extracted in the form of a multi-ligand complex. pH 2.8-4.8 nm is optimal for the formation of chromium complexes. The maximum analytical signal during complexation of Cr(III) with 2-hydroxy-5-bromothyophenol (HBTP) and Am is observed at 435-437. The molar absorption coefficients are (3.4-3.9) *104. Extracts of a multi-ligand chromium complex obey the basic law of light absorption at concentrations of 0.2-19 mcg/ml, respectively. The maximum optical density of chromium complexes is reached within 10 minutes.
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