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10CHEMISTRY SCIENCES
STUDY OF MOLYBDENUM(VI) ION COMPLEXATION WITH CATIONIC SURFACTANTS
Abdullaeva K.
PhD in Chemistry, assistant "University of Oil and Industry", Baku, Azerbaijan DOI: 10.5281/zenodo.7148209
Abstract
Taking into account features of complexformation of molibden (VI) with azoderivates of pyroqallol we have synthesized highly sensitive reagent - bis-(2,3,4-threehydroxyphenilazo)-benzidin (R, H6R) and the given reagent has been used in direct spectrophotometry determination of molibden (VI) in clay. Complexformation of molibden (VI) with H6R is studied and it has been established, that at pH 2, Vax=490 nm intensively colored binary complex is formed. For increasing analytical parameters the influence of the third components-cation surface-active substance (CSAS) on complexformation has been studied. It is established, that during the influence of CSAS the maximum exit of different ligand complexes is observed in strongly acid medium and also decreases the limit of detection of the molibden (VI) on reaction of complexformation with H6L-CSAS and increase constants of stability of their complexes. The influence of foreign ions and masking substances on complexformation is studied. The worked out method has been used in photometric determination of molibden (VI) in Masazyr clay.
Keywords: Molybdenum (VI), thickening, sorption, desorption, prihallol.
For the determination of microgram amounts of molybdenium in various standard and natural objects, the photometric method is considered to be the simplest and most express method in analytical practice [1-3]. The literature contains information on numerous organic reagents with various functional groups. Taking into account that molybdenum ( VI ) belongs to a number of metals that has a stronger bond with oxygen than with nitrogen, and also the ability of this metal to form very strong chelate complexes with nitrogen-containing reagents [ 4 ], it can be predicted with confidence that the azo derivative of pyrogallol bis -(2,3,4-trihy-droxyphenylazo) benzidine - R can be proposed as a promising photometric reagent in the determination of
HO OH
molybdenum( VI ) in analytical chemistry. However, in the case of complex formation with reagents modified with surfactants, a sharp improvement in the analytical parameters of the reaction is observed.
In this work, the interaction of molybdenum( VI ) -bis (2,3,4-trihydroxyphenylazo)-benzidine in the presence and absence of cationic surfactants (SAS)-cetylpyridinium bromide - CP Br, cetyltrime-thylammonium bromide-CTM A In r.
EXPERIMENTAL PART Reagents. Reagent H 6 R was synthesized according to the known method [5], its composition and structure were established by IR and NMR spectroscopy [6].
HO OH
IR spectra (cm -1) 1440 (- N = N -), 3600-4000 (Ar-OH)
The resulting reagent is highly soluble in ethanol. We used 1 -10 -3 M ethanolic solution of H 6 R, CPV r, 1 -10 -2 M CTMABr, as well as 1 -10 -4 M solution of mo-lybdenum( VI ) which was prepared by dissolving an accurate sample of (NH4)2MoO4 in distilled water [9]. Fixanal was used to create the required pH values. HCl ( pH 1-2) and ammonium acetate buffer solutions ( pH 3-11). All reagents used were of at least analytical grade.
Equipment. The optical density of the solutions was measured on spectrophotometer " Lambda 40" ( PERKIN ELMER ) and photocolorimeter KF K -2 in a cuvette with a layer thickness of l=1cm. The pH value of the solutions was controlled using an I-130 ion meter with a glass electrode.
Sample Preparation Method. For analysis, a clay sample was taken from the Masazir village of the Republic of Azerbaijan. The content of molybdenum(
VI ) in the sample was determined by the photometric method and the results were verified by the addition method (Table 2).
1,000 g is taken from the sample and dissolved in a graphite bowl in HF + H 2 SO 4 (3:1) on an electric stove, gradually raising the temperature until the SO 3 is completely distilled off. Then washed 3-4 times with distilled water. Add HCl (1:1), transfer to a flask cap. 50 ml and dilute to the mark with water.
Research results and discussion Dissociation constants. Previously, it was found that the H 6 R reagent is a six-basic weak acid [6] and, depending on the pH of the medium, can be in molecular and anionic forms (Fig. 1).
It can be seen from Fig. 1 that in a strongly acidic medium (up to pH 3) the reagent exists only in the molecular form H 6 R (pK 1 = 4.36), and then slowly dissociates and at pH 5 in H 4 R 2 form (a%=55)
Fig.1. H6R Reagent Distribution Diagram vs Medium pH
Absorption spectra. To study the effect of surfactants on complexation, we first studied the ligand-lig-and interaction, i.e. associate formation. For this purpose, the light absorption spectra of the reagent and associates were taken. Maximum light absorption H 6 R is observed at 1 max = 429 nm. It is known that an azo compound containing o, o ' - dioxy groups during the interaction of surfactants in the light absorption spectrum, the appearance of new absorption bands is observed,
which are located in the region of longer wavelengths than the bands of the corresponding form of the reagent [8]. In these cases, lass is equal to 449, 461 nm respectively H 6 R-CPBr, H 6 R-CTMABr. From these data it can be seen that, 1 acc are very close to each other and this proves that, the position of maximum light absorption associates strongly depends on the nature of surfactants, i.e. on the length of the surfactant hydrocarbon radical.
420
430
440
450
460
470
Fig.1. Accordance spectra of the reagent and its associates at pHopt. 1. H6R 2. H6R-
CPBr 3. H6R-CTMABr
light absorption spectra of the binary and mixed-ligand complexes were also taken at pH opt and are indicated in Table 1. It can be seen from the data that homogeneous- and mixed -ligand complexes of molyb-denum( VI ) have absorption maxima that shift batho-chromically with respect to the absorption maximum of the reagent. On the other hand, when a surfactant is introduced into a binary system, a hypsochromic shift is observed in the absorption spectra. Analyzing all these spectral data, we can say that, in the Mo( V I ) R -CSAS
system, a ligand-ligand or more precisely hydrophobic interaction.
Effect of pH. The study of the dependence of complex formation on pH (1-8) showed that the yield of the binary complex Mo( V I ) R maximum at pH 2. It is known that, in the presence of surfactants in complex formation, the interaction interval is extended with a shift to a more acidic medium [ 8 ]. This is due to the fact that stable hydrophobic associates are formed in an acidic or weakly acidic environment and this correlates with the formation of the corresponding chelate. The
maximum yield of mixed- ligand complexes is observed at pH 1.
Influence of reagent concentration and third components. To select the optimal conditions for complex formation, the influence of the concentrations of the reactants was studied. The output of the binary complex is maximum at a concentration of 1 -10 -4 M R, Mo( V I ) R -CTMA Br at 1 -10 -4 M R, 4 -10 -4 M CTAB and Mo( V I ) R -CP Br 0.8 -10 -4 M R and 4 -10 -5 M CP Br.
Stoichiometry and stability constants of complexes. Homogeneous and mixed ligand complexes of vanadium are formed immediately after mixing the components. To determine the ratio of the reacting components in the complexes, we used the Starik-Barbanel relative yield method, equilibrium shift, isomolar series, and equal to 1:2, 1:2:2 [ 9 ]. As follows from the data obtained (Table 1), the addition of surfactants to the H 6 R chelate with Mo( V I ) leads to an
Influence of foreign ions. The direct determination of 1.22 ^g/ml of molybdenum in the form of a mixed ligand complex with an error +of 5% is not interfered with by 3500-fold amounts of alkali and alkaline earth metals, as well as 1200 -fold amounts of Ni ( II ), Mn ( II ), Cd ( II ), Zn ( II ), 200-fold - Al, 6-45-fold - Fe ( III ), Ti ( IV ), 10-15-fold - Bi ( III ), Cu ( II ), W ( VI ) and 1-5-fold Zr ( IV ) and W ( VI ).
References
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5. Gambarov D.G. A new class of photometric reagents - azo compounds based on pyrogallol. // Diss. on the soysk. scientist step. doc. chem. Sciences. M. 1984. 295 p.
increase in the stability constants of the complexes. It is known that surfactants form stable associates, and this, in turn, affects the stability of the chelate, i.e. the higher the stability of associates, the more stable their complexes. Taking into account the molar ratio of the components in the composition of the complexes, the stability constants of the complexes were calculated [ 9 ] (Table 1).
Grading chart. A series of solutions containing 0.096-1.92 ^g/ml (homogeneous), 0.077-3.84 ^g/ml ( mixed- ligand ) Mo( V I ) was prepared and their light absorption was measured at Xopt = 490 nm relative to the solution of the control experiment. The concentration intervals were established where the Beer law and the molar absorption coefficients of the complexes are observed from the saturation curves [ 9 ] (Table 1).
Tab. 1.
Definitions of Mo( V I ) in clay. When determining Mo( V I ) by the photometric method, an aliquot of the prepared solution is placed in a flask cap. 25 ml, add 2 ml of 1 10 -3 M solution of H 6 R, 1 ml of 1 10 -3 M solution of CPBr and diluted to the mark with pH 1 buffer solution. relative to the control solution. The results of the analysis were verified by the method of additions and are given in Table 2.
Tab. 2.
6. Alieva R.A., Gadzhieva S.R., Valiev V.N., Chiragov F.M. // factory lab. Mother diagnostics. 2007. V.73. No. 8. P.20-23
7. Korostelev P.P. Preparation of solutions for chemical-analytical work. Moscow: Chemistry, 1964. 386 p.
8. Savvin S.B., Chernova R.K., Shtykov S.N. Surfactants. M.: Nauka, 1991. 251 p.
9. Bulatov M.I., Kalinkin I.P. A practical guide to photometric and spectrophotometry methods of analysis. L.: Chemistry, 1972, 407 p.
10. Abbaszade G.G. Application of mixed- ligand complex compounds of vanadium( V ) with pyrogallol azo derivatives and N-, O -containing reagents in photometric analysis. // Diss. on the soysk. scientist step. can. chem. Sciences. Abstract. Baku, 2004.
Main photometric characteristics of vanadium( V ) complexes
Reagent p H Xmax, nm Respectively -schenie comp. Smax X 10 Interval under-Beer's law, mcg /ml lgß
R 2 4 29 1 : 2 7.0+ 0.02 0.096-1.92 9.18 +0.03
R + CTMA Br 1 435 1 : 2 : 2 7.75 +0.01 0.077-3.84 21.05 +0.04
R + CPU Br 1 440 1 : 2 : 2 8.20 +0.01 0.077-3.84 1 9.77 +0.02
L 1 + R 2 Cl [3 ] 4.7 420 - 2.2 <3.56 -
R 3 + CTMA Br [10] 5 379 1 : 2 : 1 4.00 0.051-1.224 5.90 +0.24
Li -4-nitrocatechol, R2 - neotetrazol chloride, R3 -1-phenyl, 2,3 -dimethylpyrazolone-5-azopyrogallol.
Results of determination of Mo( VI ) in clay (%). n =3
Sample clay Photometric method METHOD of additions
( aliquot ) mcg/ml ( 10 -2 %) mcg/ml ( 10 -2 %)
I 0.290 0.12 0.33 0.13
II 0.255 0.09 0.28 0.1
III 0.267 0, 11 0.290 0.12
