ISSN-1680-9955 Pak. J. Anal. Envir. Chem. Vol. 7, No. 1, (2006) 62 � 67 Lewis Acid Nature of SnCl4 and n-Bu2SnCl2 Determined by Adduct Formation with 3-Methyl-1-Indanone MUHAMMAD DANISH1*, C.M. ASHRAF2, ALI MOHAMMAD3 AND FAIZ-UR-REHMAN3 1*Department of Chemistry, University of Sargodha, Sargodha, Pakistan 2Department of Chemistry, F.C. College University, Lahore, Pakistan 3Department of Chemistry, University of the Punjab, Lahore, Pakistan Abstract Lewis acid nature of SnCl4 and n-Bu2SnCl2 has been studied using 3-methyl-1-indanone. The equilibrium constant has been calculated for both the tin moieties. It has been found that Lewis acid character of SnCl4 is fourteen times greater than that of n-Bu2SnCl2. Key words: Lewis Acid Nature, Adduct Formation, 3-Methyl-1-Indanone Introduction Tin is inert and does not react with air or water at room temperature. However, at elevated temperatures, it forms a very thin oxide layer on the surface. Tin behaves in an amphoteric way and this nature depends upon concentration and temperature of the medium [1,2]. There are numerous reports on synthesis and applications of organotin compounds [3-8]; however, study of Lewis acid nature of tin halides and organotin halides covers the academic interest. In tin halides, organotin halides and most of organotin compounds, the tin center behaves as Lewis acid. Crystallographic data show, that tin center may show coordination number up to seven [10]. If a donor atom is much away from tin, it does not affect the coordination number and this state is also retained in non coordinating solvents [7,8,12]. Due to Lewis acid character of tin center, it can be used to study basic properties of compounds containing donor atoms. Compounds containing carbonyl group fit in this category as they act as Lewis bases. In the present work, 3-methyl-1-indanone has been selected to study acidic properties of SnCl4 and n-Bu2SnCl2. Furthermore, it is an important ligand in the synthesis of various tricarbonyl chromium complexes [13-15]. Experimental All the chemicals were of analytical reagent grade (purchased from Merck) and used without further purification. Fresh distilled benzene was used whenever required. Preparation of 3-methyl-1-indanone Dry benzene (50 cm3) [16] was taken in a two-necked round bottom flask equipped with a water condenser and magnetic stirrer. Crotonic acid (6.5 g) was then added followed by portionwise addition of anhydrous AlCl3 (31.8 g), under inert atmosphere. The reaction being exothermic started without heating. Afterwards, the reaction mixture was refluxed for five hours. The reaction mixture was cooled, extracted in dry benzene, washed with distilled water to remove un- reacted AICl3. The organic layer was separated and treated with an aqueous solution of sodium *Author for Correspondence Pak. J. Anal. Envir. Chem. Vol. 7, No. 1, (2006) 63 bicarbonate to remove un-reacted crotonic acid and -phenyl butyric acid (by product). The organic layer was separated and washed twice with distilled water. The benzene extract was dried over MgSO4 for several hours and filtered. Benzene was removed under reduced pressure. The residue was dissolved in dry. ether (100 cm3), stirred with activated charcoal for several hours and filtered through alumina. The filtrate was concentrated to half of its volume and kept overnight. The 3- Methyl-1-indanone was obtained as a crude mass, which was purified by distillation under reduced pressure [17]. Measurement of absorption and equilibrium constant A stock solution of indanone (3.8x10-3 M) was prepared. Its molar concentration was kept constant throughout the experiment with both tin halides. The molar concentration of tin halides was varied for each determination. Stoichiometric amounts of indanone and tin halide were mixed and absorption was measured at various wavelengths using UV-6000 UV-Vis-spectropho- tometer, R&M Marketing, England. The absorbance was calculated using Beer-Lambert law. Discussion ortho-Dichlorobenzene was chosen as the solvent for studying the basicity of the ketone towards tin halides. Concentration of ketone was maintained constant while the concentration of SnC14 or n-Bu2SnCl2 was varied as far as experimentally possible. The absorption data are given in Tables 1 and 2. The absorption spectra of neat of 3-methyl- 1-indanone and with tin moieties are shown in Figs. 1 and 2. On adding SnC14 or n- Bu2SnC12 (as solution in ortho-dichlorobenzene), Table 1. Absorption data for 3-methyl-1-indanone* with SnCl4. Concentration of SnC14 (M) S. No. Wave Length (nm) 0 1.86×10-3 3.73×10-3 7.45×10-3 14.91×10-3 1 380 0.065 0.252 0.264 .285 0.325 2 390 0.048 0.237 0.252 0.276 0.320 3 400 0.044 0.235 0.247 0.284 0.336 4 410 0.032 0.223 0.250 0.293 0.354 5 420 0.022 0.210 0.256 0.302 0.376 6 430 0.017 0.202 0.260 0.310 0.392 7 440 0.013 0.190 0.230 0.304 0.380 8 450 0.010 0.174 0.202 0.285 0.356 9 460 0.008 0.163 0.177 0.250 0.315 10 470 0.007 0.149 0.156 0.190 0.248 11 480 0.006 0.133 0.140 0.150 0.192 12 490 0.004 0.116 0.124 0.130 0.162 13 500 0.002 0.103 0.114 0.122 0.146 14 510 0.000 0.096 0.107 0.114 0.130 15 520 0.000 0.089 0.101 0.106 0.118 16 530 0.000 0.087 0.098 0.104 0.109 17 540 0.000 0.084 0.086 0.102 0.104 * Concentration of 3-methyl-1-indanone taken each time is 3.84 × 10-3M Pak. J. Anal. Envir. Chem. Vol. 7, No. 1, (2006) 64 Table 2. Absorption data for 3-methyl-1-indanone* with n-Bu2SnCl2. Concentration of n-Bu2SnC12 (M) S No. Wave Length (nm) 0 1.8×10-2 5.4×10-2 10.8×10-2 16.3×10-2 1 380 0.078 0.085 0.100 0.103 0.108 2 390 0.054 0.060 0.071 0.075 0.084 3 400 0.041 0.050 0.060 0.064 0.068 4 410 0.025 0.029 0.039 0.043 0.048 5 420 0.011 0 .020 0.026 0.029 0.032 6 430 0.005 0.014 0.020 0.022 0.028 7 440 0.001 0.010 0.016 0.018 0.023 8 450 0.000 0.008 0.012 0.014 0.021 9 460 0.000 0.005 0.011 0.013 0.018 10 470 0.000 0.004 0.009 0.011 0.016 11 480 0.000 0.003 0.007 0.009 0.014 12 490 0.000 0.002 0.006 0.008 0.011 13 500 0.000 0.001 0.005 0.006 0.009 14 510 0.000 0.000 0.004 0.005 0.007 15 520 0.000 0 .000 0.002 0.004 0.005 16 530 0.000 0.000 0.003 0.003 0.004 17 540 0.000 0.000 0.000 0.001 0.002 * Concentration of 3-methyl-1-indanone taken each time is 3.84 × 10-3M Figure 1. Absorption spectra of 3-methyl-1-indanone (3.84×10-3 M) in presence of varying amounts of SnCl4 using o-dichlorobenzene as solvent. A b sa rb an ce Wavelength (nm) Pak. J. Anal. Envir. Chem. Vol. 7, No. 1, (2006) 65 Figure 2. Absorption spectra of 3-methyl-1-indanone (3.84x10-3 M) in presence of varying amounts of n-Bu2SnCl2 using o-dichlorobenzene as solvent. Table 3. Concentration and absorption data of the ligand with SnCl4 Conc. of SnCl4 Absorption at 430 nm D-Do [SnCl4] / D-Do 1/D 1.86 × 10-3M 0.202 0.185 10.05 × 10-3 4.950 3.73 × 10-3M 0.260 0.243 15.35 × 10-3 3.850 7.45 × 10-3M 0.310 0.293 25.43 × 10-3 3.230 14.91 × 10-3M 0.292 0.375 39.76 × 10-3 2.550 Concentration of indanone (base) = 3.84×10-3M Absorption of pure indanone solution at 430 nm = Do = 0.017 Relation:- [SnCl4] / D-Do = -1/K × 1/D + 1/KD∞ Where Do=Absorption of pure indanone solution D=Absorption at a given concentration of alkyltin halide D∞=Absorption for complete aduct formation K=Equilibrium constant From graph (Fig. 3) K = 69.7 A b sa rb an ce Wavelength (nm) Pak. J. Anal. Envir. Chem. Vol. 7, No. 1, (2006) 66 Table 4. Concentration and absorption data of the ligand with n-Bu2SnCl2. Conc. of Bu2SnCl2 Absorption at 420 nm D-Do [Bu2SnCl2] / D-Do 1/D 1.81 × 10-2M 0.020 0.009 2.640 50.00 5.44 × 10-2M 0.026 0.015 3.630 38.46 10.87 × 10-2M 0.029 0.018 5.040 34.48 16.31 × 10-2M 0.033 0.022 7.410 30.30 Concentration of indanone (base) = 3.84×10-3M Absorption of pure indanone solution at 420 nm = Do = 0.011 Relation:- [n-Bu2SnCl2] / D-Do = -1/K × 1/D + 1/KD∞ From graph (Fig. 4) K = 4.6 Figure 3. Plot of [SnCl4]/D-Do Vs 1/D for the interaction of 3-methyl-1- indanone with SnCl4. Figure 4. Plot of [n-Bu2SnCl2]/D-Do Vs 1/D for the interaction of 3-methyl-1-indanone with n-Bu2SnCl2. [S n C l 4 ]/ D -D 0 1/D [n -B u 2 S n C l 2 ]/ D -D 1/D Pak. J. Anal. Envir. Chem. Vol. 7, No. 1, (2006) 67 the absorption increased. Absorption maxima were observed at 430 and 380 nm for SnC14 and n- Bu2SnCl2 respectively. Further increase in SnC14 or n-Bu2SnCl2 concentration was not possible experimentally because of weaker interaction between ketone and tin moieties. 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