The kinetics of the title reduction studied in aqueous ethanolic
media spectrophotometrically. The effect of hydrogen ion concentration on the reduction rate was investigated in buffer solutions at constant ionic strength of 1.0. The reaction was found to be of the first order in both reactants and inverse first order with respect to the hydrogen ion. The rate of the reaction decreased with increasing ethanol as well as hydrogen ion concentrations. Pseudo-first-order rate constant, kob was obtained by monitoring the disappearance of the [dye]. Activation parameters have been evaluated and a tentative reaction mechanism was discussed

M. M. Girgis

R. M. Hassan

Z. H. Khalil

English

Hrčak - Portal of scientific journals of Croatia

CROATICA CHEMICA ACTA CCACAA 60 (4) 687-695 (1987)CCA-1765YU ISSN 0011-1643UDe 547.775Original Scientific PaperKinetics and Mechanism of Reduction of 4(p-Dimethylamino)--Benzylidene-3 -Methy 1-1-Pheny 1-2-Pyrazolin -5-one byBisulphite Ions in Aqueous Ethanolic MediaM. M. Girqis, R. M. Hassan, and Z. H. KhalilChemistry Department, Faculty of Science, Assiut University, Assiut, EgyptReceived October lO, 1986The kinetics of the title reduction studied in aqueous ethanolicmedia spectrophotometrically. The effect of hydrogen ion concen-'tration on the reduction rate was investigated in buffer solutionsat constant ionic strength of 1.0. The reaction was found to be ofthe first order in both reactants and inverse first order withrespect to the hydrogen ion. The rate of the reaction decreasedwith increasing ethanol as well as hydrogen ion concentrations.The experimental data give a good fit to- d [dye]/dt = kob, [dye] = [dye] [bisulphite](!:a + kb Kd [H+r1)1 + x, [HT1Pseudo-first-order rate constant, kob" was obtained by monitoringthe disappearance of the [dye]. Activation parameters have beenevaluated and atentative reaction mechanism was discussed.INTRODUCTIONKinetics of the reduction of inorganic compounds by sodium bisulphitehas been reported earlier.v" However, much less attention has been focusedon its application to organic compounds.š-" Pyrazolone dyes are of specialinterest because they have a wide application in different fields, particularlyphotographic industry.v" electrophotography,? and in dyeing processes.w-!'Kinetics of the reduction of the carbonyl group in pyrazolones has not beenmentioned before. Therefore, we were prompted to undertake the presentinvestigation on the title reduction using bisulphite ion in aqueous ethanolicmedia with a view of getting an insight into the reaction mechanism.MATERIALS AND METHODSodium bisulphite, ethyl alcohol and piperidine were of Analar (BDH) grade,whereas p-dimethylaminobenzaldehyde was of GR (E. Merck) grade. 4-(p-Dimethyl-amino)benzylidene-3-methyl-l-phenyl-2-pyrazolin-5-one was prepared by refluxingequimolar ratios of 3-methyl-l-phenyl-2-pyrazolin-5-oneI2 and p-dimethylamino-benzaldehyde in ethanol containing piperidine as catalyst'". The obtained separatedsolid product was recrystallized from ethanol. The structure of the prepared dyeis represented by the formr688 M. M. GIRGIS ET AL.rn i p . z; 165°(;\ ,= 460 nm, t = 70200 in pure ethanol.mJ~ maxThe results of elemental analyses of this derivative were in accordance with itsstructure, Table I.TABLE IThe ELementaL AnaLysis Data of the Dye(I) and its Reduction Product (II)Found (Calc.) %Compound FormulaC H NI C19H19N30 74.64 6.18 13.71(74.73) (6.27) (13.76)II C19H21N30 74.01 6.76 13.54(74.24) (6.89) (13.67)Stock solution of the dye was prepared by dissolving an accurate arnountof the dye in the appropriate volume of ethanol. Stock solution of sadi um bisulphitewas prepared by dissolving an apprapriate weight of the recrystallized salt indoubly distilled conductivity water and standardized against iodinc'".Kinetic MeasurementsKinetic experiments were carried out in a temperature-controlled (± 0.1 aC)water bath. The reaction was initiated by adding the requisite quantity of pre--equilibrated dye solution to an equilibrated mixture of sodium bisulphite, waterand ethanol. The course of the reaction was followed by measuring the absorbanceof the remaining dye at known interval s at the corresponding maximum absorptionwavelength of the dye. The Am" values were measured by rapid recording of thedye spectrum in the presenee of the same percentage of EtOH-H20 mixture andthe same amount of NaHSOs as in the kinetic solutions. Absorption measurernentswere followed on a Shimadzu UV-200 S. double beam spectrophotometer, usingthe cell of 1 cm path length. The spectral change of the reaction is shown inFigure 1. It was verified that there is no interferenee due to other reagents 01'reduction product at J.ma< of the dye. The reactions were usually followed up tonot less than three half-lives. The pH measurements were carried out at 200Con WG PYE model 290 pH-meter accurate to ± 0.005 pH units.The kinetics of the present work were conducted under pseudo-first-orderconditions where [bisulphitej z- [dye]. Under these conditions, the rate equationcan be written as follows,d [dye]dt = kobs [dye] (1)where kob, is the observed pseudo-first-order rate constant, which may be expressedby the equation:kobs = k2 [bisulphite] (2)and k2 is the second-order rate constant.tQ)U'~ 0-4..oL..ou'l..oc:::rORGANIC REDUCTION BT BISULPHITE 6890·8 rr---------------------.....,1,'''..' \I:!0·6IjIi(\.i\i\\I 2. iI ."', \I .I i \ ~i, .\ iI! I iI! i ': ! ' \I I 3 \ '.: i •....... '\!I. r \ ':, I \'\ \I· I \ .,: I I I \!,.I \ -:\ \ ~..I.i,' 4 \ '1 \ttl: ....\i\'. \ ..;' i ;' ./ ':..\I.i: i / .... ".\\:/ . / : . \/ ./ I .... :.Ii:/ ./ I .... 5 '.1'1: / / .' : 1\:.I ./ // •..•..• ':\\\;' ./ / ". '..\\\.-...--:~<~;~~.~:~~~~~------~---"<)~\- <, -'::.;:;"\.0-20·0220 460 540300 380>--- ,,n m ---+-Figure 1. Spectra change as a function of time of the reduction reaction: [dye] == 2.77 X 10-5 M; [HS03-] = 1.0 X 10-3 M; (EtOH-H20) mixture = 34.60/0 (wjw); tem-perature = 28°C. Time (min.): 1) 2.25; 2) 5.25; 3) 8.30; 4) 11.00; 5) 17.00; 6) 25.30;7) after completion of the reaction.RESULTSa) Stoichiometry and Product Ana!ysisThe stoichiometry of the overall reaction of bisulphite ions with excessof the dye was determined spectrophotometrically in terms of the consumptionratio ([dye]consumed/[bisulphite]o).The reaction mixture was placed in a ther-6.90318On f1lr+~cl)uc'u -on<-cl) oul IfJ('I'nf1lO0\X .sIfJn +o~0·2 07'050·10-300 01M. M. GIRGIS ET AL.322 326 3301 5 o -1 dT x10 r K ---+10 20 30 (EtOH-H20)% wt/wt-cutb-5025·1O 2d a 247125'\ 24-3'\ C+,<,<,--+- - -- --- (}O 23·94 6 8 Time,min -a8 12 [ HSO; ] X 103, M -+bo 4Figure 2. a. Dye dependency. {Plot of 1 + log (absorbance) versus time: [dye] == 2.24 XlO-5 M; [HS03-] = 1.0 X 10-3 M; (EtOH-H20) mixture = 34.6%(w/w); tem-perature = 25 =cj.b. Bisulphite dependency: {Plot of kob, versus [bisulphite]: [dye] = 4.4 X 10-5 M;(EtOH-H20) mixture = 34.60/0 (w/w); temperature = 25 CC}.c. Effect of ethanol content on the reduction rate at 25°C: [dye] = 2.24 X 10-5 M;[HS03-] 1.0 X 10-3 M.d. The Eyring plot of -In h/kT k2 versus I/T.mostated water bath at 25 CC. The unreacted [dye] was estimated periodicallytill it attained a constant value. A stoichiometric ratio of 1 with in experimentalerror was obtained in ten different initial concentrations of the dye.The reduction product was isolated from the reaction mixture containinga large excess of bisulphite ions after completion of the reaction. A successiveextraction with ether followed by drying over anhydrous sodium sulphateunder N2 gas gave a solid product confirmed by elemental (Table I) and i. r.ORGANIC REDUCTION BYBISULPHITE 691spectral analysis as 4 (p-dimethylamino)-benzylidene-3-methyl-1-phenyl-2-py-razolin-č-ol.From the above results, the stoichiometry of the overall reaction can berepresented by equation (3).(3)b) Rate Dependenee on [Dye]The order with respect to the dye was determined by studying thereaction at different initial concentrations of the dye with fixed [bisulphite].The [dye] was varied in the range (0.5-5.0) X 10-5 M, whereas [bisulphite]suitable for kinetic measurements was 1.0 X 10-3 M, the ethanol-water mixturewas 34.6% (w/w) at 25 "c. Under thess conditions where [bisulphite] » [dye],the plots of log (absorbance) versus time were linear, indicating the first-orderdependence of rate on [dye], Figure 2 (a). The average value of kobs was foundto be (1.64 ± 0.05) X 10-- sec'.e) Rate Dependence on [Bisulphite]The order with respect to HS03- ion was deduced from the measurementof the reaction rates at several bisulphite and fixed dye concentrations. The[bisulphite] was varied in the range (0.5-19.5) X 10-3 M, [dye] = 4.4 X 10-5 M,ethanol-water mixture = 34.6010 (w/w) at 25 aC. The plot of kob., versus [bi-sulphitel was found to be linear passing through the origin, Figure 2 (b).This indicates that the reaction is also first-order with respect to [HS03-] ion.Thus, the reduction of the dye using bisulphite ion follows over all second--order kinetics.d) Rate Dependenee on Ethanol- Water Mixture CompositionThe effect of the medium content of ethanol on the dye reduction rateswas investigated at 25 aC. The ethanol was varied in the range (8.1-76.0)%(w/w), [dye] = 4.4 X 10-5 M, [bisulphite] = 1.0 X 10-3 M. The reduction rateswere found to decrease sharply with increasing the medium content of ethanol,Figure 2 (c).e) Rate Dependenee on [Hydrogen ion]To clarify the influence of [H+] on the reduction rates and to elucidatethe reduction mechanism, the reaction of 2.02 X 10-5 M dye with 4.86 X 10-4M NaHS03 in 34.6010 (w/w) ethanol-water mixture at 22 "c was investigatedin a series of citric acid-Na2HP04 buffer solutions of different pH's andconstant ionic strength of 1.0. The dependence of kobs on [H+] is presentedin Table II. An increase in hydrogen ion concentration leads to· inhibition ofTABLE IIEffect of Varying [H+] on the Rate of Reduction: [dye] = 2.02 X 10-5 M;[HSOn = 4.86 X 10-4 M; (EtOH-H20) Mixture = 34.6% (w/w), Temperature = 22 =c0.11 0.20 0.40 1.38 3.70 6.592.56 1.45 0.81 0.25 0.09 0.05692 M. M. GIRGIS ET AL.the reactioil rate. The power dependence of [H+] on k2 was determined fromthe empirical equation:(4)The value of n was found to he inverse first-order. The integer value suggeststhat the reaction involves only one hydrogen ion path. A plot of k2 versus[H+r1 gives a good straight line passing through the origin, Figure 3 (a)..o rtl,...,..t t'lo 1(])ul o(])1-' ulo 1-,E OQ) EL"-' OJL,.L..,J.~,......1 (\j-r-1 10+::r: x b'--' (\j"'d ..x2::c+..--'-"" 5·0(\j.x;ro 2-50-0 0·0OO214 62 3Figure 3. Effect of [H+] on the reduction rate at 22°C: a. Plot of k2 versus [H+r1;b. Plot of k2 (1 + Kd [H+rl) versus [H+r1: [dye] = 2.02 X 10'5 M; [HS03-] = 4.86 X 10-'M; (EtOH-H20) mixture = 34.6~/o (w/w).ORGANIC REDUCTION BY BISULPHITE 693tJ Rate Dependence on TemperatureThe reaction was studied at 20; 23.5 30.5, 35 and 40 DC at [dye] = 4.4 X 10-5M, [bisulphite] = 1.0 X 10-3 M, and 34.6% (w/w) ethanol-water mixture. Thesecond-order rate constants (k2) were calculated from rate expressions. Theplot of - In h/kT k2 against l/T of Eyring Equation!", gave a good straight line,Figure 2 (d). The values of the enthalpy and entropy of activations weredetermined from the slope and the intercept of the obtained straight line,respectively. These values are summarized in Table III.TABLE IIIParameterActivation Parameters of the ReactionValue~ G =F (kJ mol-I)(I, H =F (kJ mol-I)(I, S =F (kJ mol? deg'")71.54 ± 3.5941.64 ± 2.23-100.32 ± 4.56DISCUSSIONThe first-order dependence on both bisulphite and dye reactants lead usto formulate the following simple rate equationd [dye]dtd [bisulphite]dtd [product]dt= k2 [dye] [bisulphite] (5)Retardation of the reduction rate on increasing the ethanol content maybe interpreted by the formation of a solvent cage between the dye andethanol molecules via hydrogen bonding which retards the attack of HS03-ions. On the other hand, increasing the amount of water may facilitate thereductant attack owing to the formation of hydrogen bonding as a bridgebetween the dye molecule and the solubilized reductant. This can be expressedas follows:)= O ... HO"- ./ -,~ O··· H HThe large negative value of the entropy of activation obtained, c. f.Table III, can be explained in part by the necessity of the reductant ions topenetrate those cages in order to bring the pyrozolone dye into the reductantform.1YIechanismFrom the inverse dependence of the second-order rate constant on [H+]at moderately pH's used and from the linearity plot shown in Figure 3 (a),the mechanism can be visualized by a fast dissociation-" of HS03- prior tothe rate determining step694 M. M. GIRGIS ET AL.KdHS03-;.:= H++ SO/- (6)Introducing the dissociation constant (Kd), definedby Eq. (6), and the analy-tical concentration of bisulphite ions,(7)the concentrations of HS03- and SOl- species may be expressed by theequations:1[HS03-] = ~ [HSO -]1 + Kd [H"]"! ~ 3 Total (8)and(9)When the following competitive reactions are considered for the rate deter-mining stepkadye + HS03- -7 [#] ;.:= productslow fast(10)kbdye + SO/- -7 [#];.:= productslow fast(11)the variation of the second-order rate constant with the change of hydrogenion concentration would be expressed by the formka + kb Kd [H+t'1 + Kd [H+t' (12)From the experimental results, the value of ka is nearly zero as shown inFigure 3 (a). Consequently, Eq. (12) can be recast in the form[H+] 1(13)Eq. (13) indicates that the plot of (k2tl versus [H+] should be linear with theslope corresponding to (kb Kdtl and intercept corresponding to (kb)-l. Thevalues of kb and kd were calculated and found to be 13.89 L mol-1 sec' and5.1 X lO-s M, respectively. The obtained value of the dissociation constant,Kd, is in good agreement with that reported in the Iiterature.v'-" On the otherhand, on using the reported'" value for Kd, 5.6 X lO-s M, a plot of k: (1 ++ Kd [H''[ ") against [H+] gives a good straight line passing through the origin,Figure 3 (b), which in turn confirms the kinetic analysis of the presentinvestigation.REl<'ERENCES1. T. Ta n a k a, M. K o i z u m i, T. Y o k o y ama, and Y. I s h i ha r a, Prepr.,Div. Pet. Chem., Am. Chem -. Soe. 24. (1979) 593.2. S. B. Ob 1a t h, S. S. Mar k ow i t z, T. N ova k o v, and S. G. C han g,J. Phys. Chem. 86 (1982) 4853.ORGANIC REDUCTION BY BISULPHITE 6953. C. R. Den n i s, S. S. B a s s o n, and J. G. Lei p old t, Polyhedl'on 2 (1983)1357.4. R. M. Ha s s a n and M. M. Kir g i s, Indian J. Chem. in press.5. M. M. G i r g i s, A. S. El - S h a h a w y, and Z. H. K h a l i 1, Croat. Chem.Aeta, in press.6. D. H. O. J o h n and G. T. J. F i e 1d, Photographie Chemistry, ReinhaldPublishing Corporation, New York, 1963, p. 69.7. Konishiroku Photo Industry Co., Ltd., .Jpn. Kokai Tokkyo JP. Pat. 58, 143, 342,25 Rug. 1983; Chem. Abstr. 99 (1983) 2033551.8. T. Ham a oka, IVI. IVIo r i g a k i, S. Sa w ada, N. Oh k i, and K. Nek a-m ura, Fuji Photo Film Co., Ltd., Ger. Offen. Pat. 2, 952, 420, 17 July 1980;Chem Abstr. 94 (1981) 93556.9. K. K. Can o n, Copyer Co. Ltd., Jpn. Kokai Tokkyo Koho JP. Pat. 58, 70, 231,26 Apr, 1983; Chem. Abstr. S9 (1983) 131335.10. Theraehemie Chemish Therapeutisehe G.m.b. Neth. Pat. 6, 609, 633 6 Feb., 1967;Chem. Abstr. 67 (1967) 44851.11. Sandoz Ltd. (by H. E g 1i and R. K e r n). Ger. Pat; 1, 112, 965, 21 Dee. 1957;Chem. Abstr. 56 (1962) 4995.12. A. 1. Vo g e 1, Praetieal Organie Chemistry 3rd Edn., Longmans, London,1961, p. 998.13. R. C. El der f i e 1d, Heteroeyclie Compounds, Vol. 5 New York. John Wiley& Sons., Inc. London, Chapman & Hall, Ltd., 1957, p. 132.14. A. 1. Vo g e 1, A Text-Book of Quantitative Inorganie Analysis, 3rd End.,Longmans, London, 1961. p. 370.15. S. G 1a s s t o n e, K. J. La i d l e r, and H. E y r i n g, The Theory of RateProcesses. IVIcGraw-Hill Book Company, Inc., New York, 1941, p. 417.16. IVI. J. S i e n k o and R. A. PIa n e, Chemistry. 3rd Edn., IVIcGraw-Hill, Inc.Tokyo Japan, 1966, p. 542.SAŽETAKKinetika i mehanizam redukcije 4(p-dimetilamido)-ben:riIidene-3-metil-l-fenil-2--pirazolin-5-ona pomoću bisulfitnih iona u vođenoj otopini etanolaM. M. Girgis, R. M. Hassan i Z. H. KhalilKinetika redukcija pirazolonskih boja bisulfitom proučavana je u vodeno]otopini etanola, Nađeno je da je brzina redukeije upravo proporcionaIna koncen-traciji reaktanata, a obrnuto proporcionalna koncentraciji vodikovih iona i etanola.Predložen je zakon brzine kemijske reakcije i mogući mehanizam redukeije.

Kinetics and Mechanism of Reduction of 4(p-Dimethylamino)-Benzylidene-3-Methyl-1-Phenyl-2-Pyrazolin-5-one by Bisulphite Ions in Aqueous Ethanolic Media

Kinetics and Mechanism of Reduction of 4(p-Dimethylamino)-Benzylidene-3-Methyl-1-Phenyl-2-Pyrazolin-5-one by Bisulphite Ions in Aqueous Ethanolic Media

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia

HRČAK - Portal of Croatian Scientific and Professional Journals