Research Journal of Chemical Sciences ________________________________________ ISSN 2231-606X Vol. 1(5), 29-35, Aug. (2011) Res.J.Chem.Sci. International Science Congress Association 29 A comparative study of corrosion inhibitive efficiency of some newly synthesized Mannich bases with their parent amine for Al in HCl solution Sharma Pooja, Upadhyay R.K.* and Chaturvedi Alok Synthetic and Surface Science Laboratory, Department of Chemistry, Govt. College Ajmer (Raj.), INDIA Available online at: www.isca.in (Received 11th June 2011, revised 29th June 2011, accepted 20th July 2011)Abstract Weight loss and thermometric methods have been used to study the corrosion inhibition of aluminium in HCl solution by four newly synthesised Mannich bases viz 3-oxo, 3-phenyl, N,N-dimethyl propanamine hydrochloride (MB), 3,5-dioxo,5-phenyl N,N-dimethyl pentanamine hydrochloride(MB), 2,2-dimethyl,3-oxo N,N dimethyl butanamine hydrochloride (MB) and 3-oxo N,N-dimethyl butanamine hydrochloride((MB). Results of inhibition efficiencies obtained from both methods are in good agreement with each other. Efficiency of inhibitor increases with increasing concentration of inhibitor as well as that of HCl solution. The efficiencies have been compared with those of parent amine from which Mannich bases have been derived. Inhibition efficiencies of synthesized Mannich bases have been found much more than their parent amine. It was observed that inhibition efficiencies of amine increases with increasing concentration of amine whereas it decreases with increasing concentration of acid. Keywords: Efficiency, corrosion rate, reaction number, weight loss, Mannich base. IntroductionAluminium is a metal of an industrial importance. Since pure aluminium is soft and weak so it is alloyed to obtain increased strength. Aluminium is a light metal having good corrosion resistance to atmosphere and pure water but it is corroded adversely in the presence of aqueous solution of acids. It dissolves in acids liberating H2 gas. The corrosion of aluminium and its alloys in HCl solution has been extensively studied Some Schifff’s bases have also been studied corrosion inhibitors for mild steel and aluminium in acid media of different concentrations2-5 The efficiency of these compounds depends upon the electron density present around the heteroatoms. Inhibition efficiency also depends upon the number of adsorption active centres in the molecule, their charge density,molecular size, mode of adsorption and formation of metallic complexes. Heteroatoms such as N, O, S are capable of forming coordinate covalent bond with metal owing to their free electron pairs. Compounds with pi bonds also exhibit good inhibitive properties due to interaction of pi orbital with metal surface. Some other workers have studied corrosion inhibition efficiency of Mannich base for aluminium in HCl solution6-12In the present investigation the inhibitive effect of four newly synthesized Mannich bases viz 3-oxo, 3-phenyl, N,N-dimethyl propanamine hydrochloride (MB), 3, 5-dioxo, 5-phenyl N, N-dimethyl pentanamine hydrochloride (MB), 2,2-dimethyl, 3-oxo N, N dimethyl butanamine hydrochloride (MB) and 3-oxo N,N-dimethyl butanamine hydrochloride((MB) have been studied in different strength of HCl solution with various concentrations of inhibitors.Inhibition efficiencies of synthesized Mannich bases have been compared with their parent amine. Material and MethodsMannich bases were synthesised by conventional methods i.e. by refluxing equimolar quantities of ethanolic solutions of corresponding ketones, formaldehyde and secondary amines in a round bottom flask for about 4-5 hours and then adding some acetone in it and mixture was left in a refrigerator overnight. Resulting crystals were filtered and then recrystallized by acetone which were then dried and collected in pure state. Rectangular specimens of aluminium of dimension 2.0×2.0×0.03 cm containing a small hole of about 1mm diameter near the upper edge were used for studying the corrosion rate. Specimens were cleaned by buffing to produce a mirror finish and were then degreased. Intial weight of specimens were taken upto the three decimal of gm with a digital balance. The solutions of HCl were prepared using double distilled water. All chemicals used were of analytical reagent grade. Each specimen was suspended by a V-shaped glass hook made up of capillary tube in a beaker containing 50 mL of the test solution at 25 ± 0.1C. After the sufficient exposure, specimen was cleaned by running water and then dried by hot air dryer then final weight was taken. Duplicate experiments were performed in each case and mean values of the weight loss were determined. The percentage inhibition efficacy (%) was calculated as13 ui 100( W - W) %Wh= Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(5), 29-35, Aug. (2011) Res.J.Chem.Sci. International Science Congress Association 30 Where and i are the weight loss of metal in uninhibited and in inhibited solution respectively.The degree of surface coverage ( can be calculated as14 : = – ) / u Where and are the weight loss of the metal in uninhibited and in inhibited solution respectively.Inhibition efficacies were also calculated by thermometric technique. This involved the immersion of single specimen in an insulated reaction chamber containing 50mL of solution.Initial temperature of each test solution was taken by a thermometer upto the accuracy of 0.1C. It was observed that the temperature of the solution increased slowly initially then rapidly and attained a maximum value before falling due to exothermic nature of reaction involved in corrosion process. The maximum temperature was recorded in each case. Percentage inhibition efficacy (%) was calculated as15 ui u 100(RN - RN) RNWhere RN and RN are the reaction number in uninhibited and in inhibited solution respectively and RN (Kelvin min) is defined as- mi (T - T) RN t Where T and T are the maximum and initial temperature of test solution respectively and t is the time(in min.) required to reach the maximum temperature . Results and DiscussionWeight loss data and percentage inhibition efficacy (%) for various concentrations of acid and inhibitor are given in table1. It is clear from the table that inhibition efficacy increases with increasing concentration of inhibitor as well as that of acid. It is also evident from the table that all inhibitor show maximum efficiency at the highest concentration of acid used i.e. 2N. MB and MB2 show almost same efficiency in 2N HCl with highest concentration of inhibitor i.e. 400ppm.Corresponding variation of inhibition efficiency with the concentration of inhibitor in 2N HCl are given in figure 1. Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(5), 29-35, Aug. (2011) Res.J.Chem.Sci. International Science Congress Association 31 Table-1 Weight loss () and inhibition efficiency (%) for aluminum in HCl solution with given concentration of inhibitor Corresponding data of Reaction Number (RN) and inhibition efficacy are given in Table 2. Thermometric experiments were carried out at higher concentrations of acid i.e. 1N, 2N and 3N because no appreciable changes of  \n      Inhibition efficiency (  \n    \rFigure-1: Variation of inhibition efficiency with concentration of inhibitor for aluminium in 2N HCl \r \r \r \r Conc.of inhibitor 0.5 N HCl (72hrs.) 1N HCl (120min.) 1.5 N HCl (20min.) 2N HCl (12min.) (ppm)  \n \n \n \n  q Uninhibited 185 - - - 250 _271269 MB 100 76 58.91 0.5891 0.1564 95 62.00 0.6200 0.2125 90 66.78 0.6678 0.3032 72 73.23 0.7323 0.4370 200 70 62.16 0.6216 0.2155 92 63.20 0.6320 0.2348 80 70.47 0.7047 0.3791 56 79.18 0.7918 0.5801 300 62 66.48 0.6648 0.2973 82 67.20 0.6720 0.3114 65 76.01 0.7601 0.5008 48 82.15 0.8215 0.6629 400 60 67.56 0.6756 0.3186 78 68.80 0.6880 0.3434 50 81.54 0.8154 0.6451 22 91.82 0.9182 1.0224 MB 100 80 56.75 0.5675 0.1179 108 56.80 0.5680 0.1188 115 57.56 0.5756 0.1323 95 64.68 0.6468 0.2627 200 75 59.45 0.5945 0.1661 100 60.40 0.6040 0.1833 97 64.20 0.6420 0.2536 65 75.83 0.7583 0.4965 300 70 62.16 0.6216 0.2155 90 64.00 0.6400 0.2498 71 73.80 0.7380 0.4497 58 78.43 0.7843 0.5606 400 64 65.40 0.6540 0.2764 85 66.00 0.6600 0.2880 68 74.90 0.7490 0.4747 24 91.07 0.9107 1.0085 MB 100 82 55.65 0.5565 0.0985 110 56.00 0.5600 0.1047 112 58.67 0.5867 0.1521 108 59.85 0.5985 0.1733 200 80 56.75 0.5675 0.1179 100 60.40 0.6040 0.1833 103 61.99 0.6199 0.2124 100 62.96 0.6296 0.2303 300 75 59.45 0.5945 0.1661 94 62.40 0.6240 0.2199 90 66.78 0.6678 0.3032 87 67.65 0.6765 0.3203 400 70 62.16 0.6216 0.2155 90 64.00 0.6400 0.2498 72 73.43 0.7343 0.4414 69 74.34 0.7434 0.4619 MB 100 91 50.65 0.5065 0.0112 112 55.20 0.5520 0.0996 120 55.71 0.5571 0.0996 112 58.36 0.5836 0.1465 200 82 55.65 0.5565 0.0985 103 58.80 0.5880 0.1455 113 58.30 0.5830 0.1455 106 60.59 0.6059 01867 300 80 56.75 0.5675 0.1179 97 61.20 0.6120 0.2890 92 66.05 0.6605 0.2890 90 66.54 0.6654 0.2985 400 78 57.83 0.5783 0.1371 91 63.60 0.6360 0.3777 80 70.47 0.7047 0.3777 76 71.74 0.7174 0.4045 log q q - log q q - log q q - log q q - Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(5), 29-35, Aug. (2011) Res.J.Chem.Sci. International Science Congress Association 32 temperature were observed at lower concentrations of HCl. The results indicate that reaction number decreases with increasing concentration of inhibitor as well as that of acid. Maximum efficiencies are lower as observed in thermometric method than in weight loss method. Corresponding variation of Reaction Number (RN) with concentration of inhibitor in 3N HCl are shown in figure 2. Table-2 Reaction Number (RN) and inhibition efficacy () for aluminum in HCl solution with given concentration of inhibitor Conc. of 1N HCl 2N HCl 3N HCl inhibitor (120 min.) (12 min.) (4 min.) (ppm) RN(Kmin-1) RN(Kmin-1) RN(Kmin-1) Uninhibited 0.085 _ 1.09 _ 3.75 _ MB 100 0.0383 54.17 0.0408 62.54 1.170 68.80 200 0.0341 59.88 0.3166 70.95 1.050 72.00 300 0.0316 62.82 0.2416 77.83 0.810 78.40 400 0.0283 66.70 0.1966 81.96 0.590 84.26 MB 100 0.0399 53.05 0.5083 53.36 1.320 64.80 200 0.0350 58.82 0.4890 55.13 1.130 69.86 300 0.0325 61.76 0.4057 62.77 0.952 74.61 400 0.0301 64.58 0.2010 81.55 0.620 83.46 MB 100 0.0410 51.76 0.6012 44.84 1.901 49.33 200 0.0361 57.52 0.4932 54.75 1.500 60.00 300 0.0340 60.00 0.4227 61.22 1.300 65.66 400 0.0320 62.35 0.3213 70.52 0.940 74.93 MB 100 0.0489 42.47 0.6212 43.00 2.050 45.33 200 0.0400 52.94 0.5225 52.06 1.601 57.33 300 0.0350 58.82 0.4321 60.35 1.450 61.33 400 0.0330 61.17 0.3987 63.42 1.152 69.33  \n    \r \n    \rFigure 2: Variation of reaction number with concentration of inhibitor for aluminium in 3N HCl \r \r \r \r Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(5), 29-35, Aug. (2011) Res.J.Chem.Sci. International Science Congress Association 33 Corrosion inhibition efficiency of Mannich bases is based on the phenomenon of adsorption. Mannich bases containing heteroatoms like N and in some cases O, S get adsorbed on the surface of metals according to Langmuir adsorption. Hetero atoms like N, O, S which have higher electron density get adsorbed more tightly on the surface of metal due to strong interactions with metallic molecules and thus blocking the active centers on the metallic surface for electrochemical reaction taking place during corrosion. More the surface coverage by mannich base less will be the availability of active sites on the surface and consequently less will be the corrosion rate. Presence of phenyl group on MB1 and MB further enhanced the electron density which ultimately decreases the active sites and thus increases the corrosion inhibition efficiency of MB and MB. That is why, MB1 and MB show higher percentage of inhibition efficacy in comparison to MB3 and MB. It has also been observed that efficiency of inhibitors increase on increasing concentration of HCl. Table-3 Weight loss () and inhibition efficacy (%) for aluminum in HCl solution with parent amine (DMA) Temperature: 25 + 0.1C, Area of specimen: 8cm2 Conc. of inhibitor 0.5 N HCl (72hrs.) 1N HCl (120min.) 1.5 N HCl (20min.) 2N HCl (12min.) (ppm)  \n   \n \n   \n  q \n         \n\n  \n\n          \n              \n  \n  \n      \n    \n       \n  \n  \n   \n   \n \n \n          \n   \n  \n  \n\n  log q q - log q q - log q q - log q q - \n   logogqqqq/(1-) ] Fig 3: Langmuir Adsorption Isotherm for aluminium in 2N HCl \r \r \r \r Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(5), 29-35, Aug. (2011) Res.J.Chem.Sci. International Science Congress Association 34 The probable reason of this may be due to the more ionization of Mannich bases in more acidic strength. Hoar and Holliday have used the Langmuir adsorption isotherm to study inhibition charteristics, assuming that inhibitors adsorbed on the metal surface decrease the surface area available for cathodic and anodic reaction using following equation16. log [ /(1-) ] = log A + log C –(Q /2.303 RT ) This equation should give a straight line of unit gradient for the plot of log [ /(1-) ] v/s log C, where A is the temperature independent constant, C is the bulk concentration of the inhibitor and Q is the heat evolved during the adsorption. The corresponding plots between log [ /(1-) ] and log Cshown in fig.3 for aluminium in 2N HCl. The plots are linear but gradients are not equal to unity as would be expected for the ideal Langmuir adsorption isotherm equation. This deviation from unity may be explained on the basis of the interaction among the adsorbed species on the metal surface. It has been postulated in the derivation of the Langmuir isotherm equation that the adsorbed molecule do not interact with one another and form a monolayer on the metal surface but practically this is not possible in the case of organic molecules having polar atoms or groups which are adsorbed on the anodic and cathodic sites of the metal. Such adsorbed species may interact by mutual repulsion or attraction. This phenomenon is also possible for present inhibitor molecules those are adsorbed on anodic and cathodic sites to interact with metallic surface as well as with each other so they may not form monolayer on the surface of metal which may be a possible cause of deviation from unit gradient. A comparison was made between the synthesized Mannich bases and their parent amine i.e. dimethyl amine. The results for the parent amine have been summarized in table 3 for HCl. It was found that maximum efficiency is 57.83% in 0.5N HCl. It can been observe from the table that inhibition efficiency of amine decreases with increasing concentration of acid. Corresponding variation of inhibition efficiency with the concentration of inhibitor in different concentrations of HCl are given in figure 4. ConclusionsA study of four newly synthesised Mannich bases i.e. MB, MB, MB3 and MB has shown them to be effective inhibitors for corrosion of aluminium in HCl solution. Both weight loss and thermometric determination have shown that the inhibition efficiency of Mannich bases increases with increasing concentration of acid and that of inhibitor. Among the synthesised inhibitors under investigation the highest inhibition efficacy was shown by MB1 and MB at the highest concentration of inhibitor i.e. at 400 ppm. A comparison between the inhibition efficiency of synthesized Mannich bases and their parent amine has shown that synthesized Mannich bases are better corrosion inhibitor than parent amine. It has also observed that Langmuir adsorption isotherm deviate somewhat from their ideal behavior. This is attributed to the fact that adsorbed molecules interact with each other causing deviation in the behavior of Langmuir adsorption isotherm. AcknowledgementOne of the authors Pooja Sharma is grateful to Department of Chemistry Government College, Ajmer for laboratory assistance.       Inhibition efficiency (  \n    \rFig 4: Variation of inhibition efficiency with concentration of inhibitor for aluminium in different concentrations of HCl     Research Journal of Chemical Sciences _______________________________________________________ ISSN 2231-606X Vol. 1(5), 29-35, Aug. (2011) Res.J.Chem.Sci. International Science Congress Association 35 References1. Sampat S.S. and Vogra J.C., Study of corrosion inhibition efficiency of some Schif’s bases on aluminium in trichloroacetic acid solution Corrosion Science, 14,591(1974) 2. Upadhyay R.K. and Mathur S.P., Effect of Schiff's Bases as Corrosion Inhibitors on Mild Steel in Sulphuric Acid E-Journal of Chem., 4(3), 408-414(2007) 3. Mahor D.K.,Upadhyay R.K. and Chaturvedi A.,Study of corrosion inhibition efficiency of some Schif’s bases on aluminium in trichloroacetic acid solution, Rev.Roum.Chim, 55, 227 (2010) 4. Sethi T. Chaturvedi A., Upadhyay R.K and Mathur S.P,Synergistic inhibition between Schiff’s bases and sulphate ion on corrosion of aluminium in sulphuric acid,Protectionof Metals and physical Chemistry ofSurfaces, 45, 466-471 (2009) 5. Sethi T.,Chaturvedi A., Upadhyay R.K. and Mathur S.P., Corrosion inhibitory effects of some schiff’s bases on mild steel in acid J.Chil.Chem.Soc, 52, 1206(2007) 6. Wang J. and Zhang W., Inhibitory behavior and corrosion inhibition mechanism of mannich base, fine Petrochemical Speciality Petrochemicals, 4,(2001) 7. Zhang j., zhang Q., Ren H., Zhao W. and Zhang H., Inhibition performance of 2-mercaptobenzothiazole derivatives in CO saturated solution and its adsorption behavior at Fe surface, App. surface sci2537416, (2007) 8. Village G.J., Li F., Yongji W and Li L.Synergistic effect of mannich bases corrosion inhibition, Xinjiang oil and gas, , (2007)9. Wang W.,Qing B. and Zhao F.L,A new imidazolineinhibitor compound of A steel in CO2 saturated aqueous solution of salt corrosion performance inhibition properties of a novel imidazoline complex for A steel in salt water saturated by CO, J.petroleum, 3 (2006) 10. Ziang W and Jing Y., Corrosion inhibition for carbon steel A3 in phosphoric acid by Mannich’s base inhibitor KA-01 and thiourea Oilfield Chemistry, (1999) 11. Zhang D.Q., Gao L.X. and Zhou G.D., Polyamine compound as a volatile corrosion inhibitor for atmospheric corrosion of mild steel,Materials and Corrosion, 58, 594 (2007) 12. Quraishi M.A., Ahmad I., Singh A.K., Shukla S.K., Lal B and Singh V., N-(piperidinomethyl)-3-[(pyridylidene)amino]isatin:A new and effective acid corrosion inhibitor for mild steel, Materials Chemistry and Physics, 112,1035 (2008) 13. Kumar S., Arora S., Sharma M., Arora P. and Mathur S.P., Synergistic effect of calotropis plant in controlling corrosion of mild steel in basic solution,J.Chil.Chem.Soc.54, 83-88 (2009) 14. Mohanty U.S., Tripathy B.C., Singh P and Das S.C.,Effect of pyridine and its derivatives on the electrodeposition of nickel from aqueous sulfate solutions part I: Current efficiency,surface morphology and crystal orientation,J.applied electrochem., 31, 579-583 (2001) 15. Shams A.M and Fakhr M.Y., A thermometric study of the reaction between Fe and HNO, Corrosion science, 14, 635-644 (1974) 16. Gomma G.K. and Wahdan M.H.,Schiff bases as corrosion inhibitors for aluminium in hydrochloric acid solution,Materials chemistry and physics, 39, 209-213 (1995)