Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 1(9), 11-16, Dec. (2011) Res.J.Chem.Sci. International Science Congress Association 11 Effect of Hydrogen Bonding and Solvation of 5-Substituted Indole Carboxldehydes in Methanol-Benzene Heda L.C., Sharma Rashmi and Chaudhari Pramod B.*Research Laboratory, S. D. Govt. College, Beawar, 305901, Rajasthan, INDIA Available online at: www.isca.in (Received 8th August 2011, revised 25st August 2011, accepted, 8th November 2011)Abstract Effect of hydrogen bonding of 5-substituted indole carboxaldehyde has been investigated by viscometric measurement. The viscosity of the system increases with the increase in concentration. The Trend Change Point (TCP) values have been determined by intersection of two straight lines, which are found to be dependent on the composition of solvent mixtures. The study confirms that the nature of synthesized compounds forms clusters in methanol-benzene mixture. The viscometric data have been analyzed in terms of Einstein, Vand, Moulik and Jones-Dole equations. These well known equations have been successfully applied to explain the results of viscosity measurements and the viscometric parameters show that the behavior of compound changes in alcohol-benzene. These results show that the formation of cluster depends on the methanol concentration. This indicates that the observed methanol concentration effect on the formation of clusters interferences in formation of hydrogen bonding of methanol with molecule. Keywords: Hydrogen bonding, viscosity, molar volume, indole Introduction The increasing knowledge of the structures if aggregates in organic solvents are stimulating research into the role that the different possible aggregates play in defining the reaction mechanism in solutionMolecular self-assembly is of much interest, and recently it has been found to occur readily in solution since non covalent interactions, such as hydrogen bonding, dipole-dipole, hydrophobic interactions etc, lead to the formation of molecular clusters. N H N NH H O O H CH H3C It has been observed that indole interacts with alcohols and aromatic hydrocarbons like benzene. In order to know the nature and extent of solute-solute and solute solvent interactions3,4. Viscosity behavior in dilute solutions is very sensitive to predict solute-solute and solute solvent interactions. Never the less several papers have focused on the fluorescent behaviour of indolic compounds in non aqueous environments, in particular, the effect of small amounts of alcohols in non polar solvent produce dramatic changes in the emission spectra of indole and its derivatives 6,7,8. The presence of polar co solvents has been explained through the formation of exiplexes between one indole molecule and one or several molecules of the polar additive. It was observed that non polar aromatics such as benzene also have dramatic effect on the emission of indole and some of its derivatives. This was attributed to the formation of an excited state complex in benzene solution and it was found that an N-H bond in indole ring is essential for this to happen. Hydrogen bonded complexes of indole in methanol, ethanol aromatics benzene, toluene, and p- xylene.In this case they are forming hydrogen bonds10,11. Indole forms this type of hydrogen bond in the ground state has been shown by several authors using IR spectroscopy and constitutes the mechanism of indole auto association. At higher benzene concentration the presence of multiple benzene molecules in the complex have been reported12-13N-substituted indole does not show this types of complex formation, where there is no N-H moiety is available14. In the view of the potential applications of these compounds, present work has been undertaken to explain colloid chemical behavior in mixed solvents. Benzene and methanol has been chosen as the co solvents in this study. The mixed solvents have a tendency to interact with compounds, which affect the aggregation of molecules. The viscosity data based on various equations have been extensively used to furnish Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(9), 11-16, Dec. (2011) Res.J.Chem.SciInternational Science Congress Association 12 information concerning the structural changes in solution trend change point (TCP) and nature of molecule-solvent interaction. This vital information plays an important role in their selection for various industrial and biological applications. Material and MethodsThe compounds are synthesized using known protocol. The synthesis begins from the commercially available indole, we were able to synthesis of 5-substituted indoles in three steps15. The further formylation with DMF/POCL by Wilsmeyer-Hack method to obtain indole -3-carboxaldehydes in good yield16. Correlating melting point, H NMR and IR data for corresponding compounds the structural assignments were made17. N R R - H , B r , C l , I DMF/POCl N R R-H,Br,Cl,I C H O Compounds - RCompound A- HCompound B- BrCompound C- ClCompound D- ISolubility of compounds in methanol and benzene was determined. The calculated amount of the compound was weighed in standard flask and the solution was made by adding the required amount of benzene and methanol. In this way, a number of solutions were prepared containing different concentration of compound and varying compositions of benzene and methanol. Ostwald’s type viscometer was used to measure the viscosity of the solutions. The accuracy of the results was checked by determining the viscosity of known solutions and the agreement was found to be good and the difference was below 0.5%. All measurements were made at a constant temperature 30 ± 0.1ºC in thermostat. The viscosity results are expressed in centipoises. Results and Discussion The flow of characterization of solutions in terms of viscometric measurements has been employed as a tool to find out the TCP of molecule in benzene - methanol mixtures. The viscosity of solutions of varying composition of benzene- methanol mixtures increases with the increase in the concentration. The increase in viscosity with the increase in concentration may be due to the increasing tendency of molecules to associate in the form of clustering entity in the solvent system. The numbers of workers have reported the molecular interaction and characterizing aspects of physicochemical behavior of binary liquid mixtures and mixed solvent. The difference in the viscosities of solutions in varying composition of benzene methanol mixtures is mainly due to the difference in the viscosities of the solvent mixtures. The plots of viscosity () against concentration (C) are characterized by an intersection of two straight lines at a definite concentration corresponding to TCP of the molecule (figure1-4) of course this is the maximum concentration of molecular dispersion where balancing of the internal forces causes the formation of aggregates. It is apparent from the data that the values of TCP are dependent on the composition of solvent mixtures. The values of TCP in the solution containing benzene below 50% are lower as compared to those containing higher volume percent of benzene. This may be attributed to the change in the mobility of the molecules due to change in the dielectric constant of the solvent mixture having different composition of benzene-methanol. Further it is suggested that predominance of lipophilic character in the solvent mixture plays a pertinent role in the clustering alignment of the solute molecules. Thus there is delay in the aggregation due to increase in the interaction between lipophilic solvent and solute molecules. The viscosity of solutions as well as those of the solvent mixtures increases as the volume percent of benzene increases which may be attributed to the cumulative effect of the variation of dielectric constant, degree of aggregation and the nature of the agglomerate. The values of specific viscosity (sp) of solutions in varying compositions of benzene-methanol mixtures also increase with the increase in the concentration. The nature of curves and TCP values are in good agreement with those observed for viscosity data. The fluidity of solutions in benzene methanol mixtures decreases with the increase in the concentration as well as with the increase in volume percent of benzene (figure 3). A perusal of table-2 indicates that TCP values are in good agreement with those derived from viscosity and specific viscosity curves and are dependent on the solvent composition. The viscosity results have been explained in terms of equations proposed by Einstein18 and Thomas19. Einstein: sp = 2.5 V C Thomas: (-1)/C = 2.5 + (10.05 ) C Where V, C, Q, , and sp are molar volume, concentration, interaction coefficient, viscosity of the solution, viscosity of solvent and specific viscosity respectively. The plots of specific viscosity (sp) against concentration (C) are characterized by an intersection of two straight lines at a definite concentration, which corresponds to the TCP. The plots with intercept almost equal to zero are linear below TCP, which shows that the equation proposed by Einstein is applicable to dilute solutions. It is observed that the values of molar volume V obtained from the plots of Einstein equation and Vand equation. It is interesting to note that the values of molar volume enumerated from these equations are almost equal and the trend remains unaltered irrespective of the type of equation applied. The Moulik equation.20 also fits well to the solutions, as the plots (vs. C are almost linear. (/ ) = M + KC2 Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(9), 11-16, Dec. (2011) Res.J.Chem.SciInternational Science Congress Association 13 Where M and K are constants. The values of M and K have been calculated from the intercepts and slopes of the () vs. C plots and are recorded in table-3. Table-1 Viscosity of compounds A-D in methanol –benzene Compound % methanol Concentration 0.0002 0.0004 0.0006 0.0008 0.0010 0.0012 0.0014 Compound A 40 0.57526 0.58630 0.59600 0.60060 0.60630 0.61171 0.61726 60 0.55439 0.56310 0.57000 0.57374 0.58130 0.58842 0.59703 80 0.53592 0.54120 0.54752 0.55280 0.55702 0.56126 0.56654 100 0.51773 0.52250 0.52880 0.52910 0.53219 0.53530 0.53841 Compound B 40 0.57743 0.58750 0.59810 0.60190 0.60800 0.61396 0.61952 60 0.55549 0.56310 0.57200 0.57690 0.58440 0.59003 0.59867 80 0.53803 0.54750 0.55560 0.55810 0.56130 0.56440 0.56885 100 0.51878 0.52440 0.53130 0.53380 0.53600 0.53753 0.54068 Compound C 40 0.57856 0.58750 0.59750 0.60310 0.61130 0.61736 0.62183 60 0.55658 0.56500 0.57440 0.58000 0.58630 0.59221 0.60084 80 0.53810 0.54441 0.55182 0.55600 0.56139 0.56461 0.57000 100 0.51984 0.52630 0.53250 0.53500 0.53880 0.54167 0.54481 Compound D 40 0.58077 0.58855 0.60060 0.60630 0.61200 0.61970 0.62420 60 0.55872 0.56630 0.57500 0.57880 0.58691 0.59449 0.60423 80 0.54123 0.54657 0.55401 0.55728 0.56370 0.56697 0.57339 100 0.52192 0.52800 0.53440 0.53690 0.54060 0.54285 0.54807 Table-2 Values of molar volume ( ) in benzene – methanol derived from Einstein and Thomas equationsCompound %of methanol   \n   Thomas equation V 1 V 2 V 1 V 2 Compound A 40% 36.4804 19.5932 19.4540 32.8224 60% 28.4328 28.204 16.9032 19.4420 80% 21.8092 17.1928 13.9252 21.1656 100% 21.4760 12.1136 3.8647 13.5812 Compound B 40% 36.3504 20.8092 29.2828 33.9632 60% 30.0812 26.0012 21.3660 25.2292 80% 33.0432 13.3672 21.1028 30.8880 100% 24.2728 8.6484 8.4096 22.4204 Compound C 40% 33.3132 22.0560 31.5936 35.6056 60% 32.4564 25.0588 25.7984 29.7208 80% 25.7984 17.1328 20.1124 26.2848 100% 24.5596 12.6108 13.9388 22.3620 Compound D 40% 34.8696 21.6984 31.9536 39.2628 60% 29.6584 30.7232 31.1140 29.5628 80% 24.0532 19.5588 27.6808 26.9688 100% 24.2028 13.9616 24.2828 24.2188 Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(9), 11-16, Dec. (2011) Res.J.Chem.SciInternational Science Congress Association 14 Table-3 Viscosity parameters in benzene – methanol derived from different equations Compound % of methanol Moulik equation Jones-Dole equation M 1 M 2 K 1 K 2 A 1 A 2 B 1 B 2 Compound A 40 1.019 1.087 228952 47433 -0.721 1.049 110.940 32.882 60 1.017 1.050 176636 68193 -0.477 -0.716 84.701 81.079 80 1.012 1.055 137129 41102 -0.336 0.315 62.738 37.820 100 1.004 1.036 135019 28361 -0.755 0.110 72.618 28.532 Compound B 40 1.025 1.090 230701 50468 -0.304 1.041 98.570 36.139 60 1.018 1.065 190451 63145 -0.501 -0.075 96.608 65.793 80 1.020 1.081 206845 32244 -0.371 1.711 84.218 5.020 100 1.008 1.059 152685 20534 -0.681 1.071 77.800 5.758 Compound C 40 1.029 1.070 212037 53153 0.080 1.051 80.569 39.897 60 1.022 1.077 205747 61330 -0.279 0.372 87.912 56.282 80 1.020 1.064 163046 41028 -0.104 0.721 66.570 31.781 100 1.013 1.059 153245 29750 -0.458 0.770 73.615 19.890 Compound D 40 1.035 1.105 225902 52922 0.402 1.394 74.168 33.049 60 1.030 1.064 188667 75141 0.306 -0.462 65.427 83.329 80 1.031 1.071 153824 47031 0.231 0.578 59.827 40.050 100 1.021 1.063 152176 33475 0.005 0.822 60.167 21.907 0.500.520.540.560.580.600.620.6400.00020.00040.00060.00080.0010.00120.0014C(mol/l) Compound A Compound B Compound C Compound D 1.501.551.601.651.701.751.801.851.901.952.0000.00020.00040.00060.00080.0010.00120.0014 Compound A Compound B Compound C Compound D 0.000.020.040.060.080.100.00000.00040.00080.00120.0016spC(mol/l) compound A compound B compound C compound D 0.00.51.01.52.02.53.00.0100.0150.0200.0250.0300.0350.040 Compound A Compound B Compound C Compound DFigure-1 Plot of v/s C for Compounds A-D in benzene and methanol mixture Figure-2 Plot of v/s C for Compounds A-D in benzene and methanol mixture Figure-4 Plot of C v/s C for compounds A-D in benzene methanol mixture Figure-3 Plot of sp v/s C for Compounds A-D in benzene and methanol mixture Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 1(9), 11-16, Dec. (2011) Res.J.Chem.SciInternational Science Congress Association 15 Figure-5 Plot of (2 v/s C for compounds A-D in benzene methanol mixture The viscosity data have also been interpreted in the light of Jones-Dole equation21. /-1)/C = A + BFor convenience, the equation may be expressed as C = A + BC Where the coefficient A and B refer to solute- solute and solute-solvent interactions respectively. The plots / C vsfor the molecules studied here were found to be linear, with least scatter. These plots are characterized by two straight lines intersecting at a point corresponding to the TCP of compounds. The values of TCP are in good agreement with the values derived from the plots of , sp and vs. C. In view of the two intersecting straight lines for / C vsplots, it is logical to evaluate two values of both the coefficients below and above TCP designated as A1, B1 and A1, B1 respectively. It is observed that the values of these constants depend on the composition of the solvent mixtures. ConclusionIt has been observed that the viscosity of the system increases with the increase in concentration. The increasing trend of viscosity may be due to combined effect of the variation of dielectric constant of solvent, degree of aggregation and nature of the compound agglomerate. The TCP values obtained from different viscosity data are in good agreement and show maximum concentration of molecular dispersion at which aggregation of molecule initiates. These results show that the formation of cluster depends on the methanol concentration. This indicates that the observed methanol concentration effect on the formation of clusters interferences in formation of hydrogen bonding of methanol with molecule. It is noteworthy to point out on the basis of results obtained that the above treatment gives a phenomenological description of clustering profile and confirms the existence of aggregation in the non-aqueous mixed solvent. 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