TP - NISCAIRnopr.niscair.res.in/bitstream/123456789/53232/1/IJCA 15A(9) 827-82… · of NO;) as the...
2
of NO;) as the viscosity decrease due to the distor- tion of the solvent structure i.e. 'r. D is small and 1)E+'IJA +1)D. In the case of salts containing Br", 1)D increases (excepting at 35°) and hence the B coefficient decreases with the increase in tempe- rature. The lesser the value of t he B coefficient the greater is the structure breaking effect or ion- solvent interaction and solvation. Hence the struc- ture breaking effect or ion-solvent interaction follows the order Bc>NOil>CI-, and in agreement with that of Kay15,16 who distinguished between the structure breaking and structure making ions by plotting b.(AoY)o)jb.Tversus b.Bjb.T. Ions with greater crystal radii and small charge densities, would possibly have a weak orienting effect in th« first layer. Therefore, Y,E and 'fjA will be small. Also there exist a considerable amount of distortion in the vicinity of such ions due to the competition between the ionic field and bulk struc- ture and consequently TP will be larger. Thus B will be smaller for K+ salts than for Na+ salts. Further investigation are in progress with that of other monovalent cations. Md<ae 17 has suggested that the dioxane molecules has two nonadjacent dipolar groups whose moments cancel, so that the effective reaction is probably greater than is indicated by microscopic properties. Hence the frozen layer as suggested by Frank and Evans-s. around the cation is expected to be consti- tuted of both water and the dioxane molecules possibly consisting more of the former than of the latter. The diffused layer would consist of loosely oriented water and dioxane molecules, the extent of orientation decreasing with the distance from the ion till the outermost laver has the same struc- ture and composition as that of the solvent. When the dioxane content of the solvent increases, more dioxane molecules take part in constituting the diffused layer thereby promoting a sort of ordering effect in the solvation sphere leading to larger value of Y)E and 1).1. This will be reflected in increase in B values with increase in dioxane content- (Table 1). References 1. DAS, N. C. & DAS, P. B., Indian I Chem., 15A (1977), in press. 2. GURNEY, R. \'1., Ionic processes in solutions (McGra.w- Hill, New York), 1953, 159. 3. HARNED, H. S. & OWEN, B. B., Physical chemistry of electrolytic solutions (McGraw-Hill, New York), 1958, 117. 4. STOKES, R. H. & MILLS, R., Viscosity of electrolytes and related properties (Pergamon Press, New York), 1965, 39. 5. KAY, R. L., VITUCIO, T., ZAWOSHI, C. & EVANS, D. F., I phys. Chem., 70 (1970), 2336. . 6. KRICHKARD, K & SKINNER, J. F., I phys. Chem., 73 (1969), 2060. 7. YAO, N. P. & BENNION, D. N., I phys. Chern., 75 (1971), 1927. 8. BARE, J. P. & SKINNER, J. F.,I phys. ci-«, 76 (1972),434. 9. CHACKRAVARTY, A. S. & PRASAD, B., Trans. Faraday Soc., 35 (1939), 1466. 10. SRINIVASAN, M. K. & PRASAD, B., Trans. Faraday Soc., 35 (1939), 1442. 11. DAS, P. B., DAS, P. K. & PATNAIK, D., I Indian chem, Soc., 37 (1960), 683. 12. DAS, P. B., I Lnstn Chem., 48 (1976), 207. 13. FALKENHAGEN, H., Z. Phys., 32 (1931), 745. 14. AGGRAWAL, D. K & SINGH, K., I Indian chem. Soc., 53 (1975), 482. NOTES 15. KAY, R. L., In water, a comprehensive treatise, Vol. 3, edited by R. Frank (Plenum Press, New York), 1973, 194. 16. KAY, R. L., Advance chemical series, No. 73, edited by R. F. Gould (American Chemical Society, Washington DC), 1968, 1. 17. l\1CR.~E, E. G., Chem. Rev .• 18 (1936), 349. 18. FRANK, H. S. & EVANS, M. W., I chon. Phys., 13 (1945), 507. Kinetic Evidence for Fast Protonation Pre- equilibrium in the Acid Hydrolysis of Acetamide: Evaluation of Protonation Constant (Mrs) SHANTI :MITTAL, K S. GUPTA & Y. K GUPTA Department of Chemistry, University of Rajasthan, Jaipur Received 29 January 1977; accepted 17 March 1977 Over an extended acetamide concentration range (1-6M), the acid hydrolysis obeys the rate law, Rate =kK[H+][Amide]j(l+K[Amide]), which provides a direct kinetic evidence for the step CH 3 CONH 2 +H+ ""CH3CONH~. The values of protonation constant, K, determined kinetically are in good agreement with those obtained by other methods. T HE hydrolysis of acetamide has been the subject of several studies- from various points of view, e.u, effect of different acids l ,2 and acidity", solvent effects 4 • 5 , activation parameters 2 ,5.6 and corre- lation of rate using Taft equation? have been investi- gated. Surprisingly the most important aspect of hydrolysis, the variation of amide over an extended concentration range, has not been studied so far. The accepted A- 2 mechanism (Eqs. 1 and 2) K Amide-j-H" -===;:[Amide HJ+1 ... (1) K [Amide HJ+ +H 2 0--i>-products ... (2) should lead to the familiar Michaelis-Mention rate law (3) or (4) when [amideJ[~ H+J Rate = kK[H+ J[AmideJj(I+K[AmideJ) (3) kobs = kK[AmideJj(1+K[AmideJ) (4) kobs is the first-order rate constant. We studied the hydrolysis of acetamide in the concentration range 1-6M at 55°, 60° and 65°. The kinetics were followed by estimating ammonia by formal titration method", The results were reproducible to ± 5~jo' In all kinetic runs acetamide was in excess over hydrochloric acid such that the reaction followed a pseudo first order kinetics. The maxi- mum concentration of acetamide employed, was limited by its solubility in water. The results are shown in Table 1. The plots of I! kobs versus 1! [Acetamide J were linear, the intercepts and slopes of which gave the values of k and K respectively. k (litre mol- l see l ) and K (litre mol:") were found to be (7·1 ± 0'1)xlO- 4 and (0·31±0·03) at 55°, (1l·0±0·5)x 10- 4 and (0·33±0·02) at 60°, and (18·5 ± 0·5) X 10- 4 and (0·36 ± 0·03) at 65°. K appears to be indepen- dent of temperature. The value of K is in good agreement with the reported values from other sources, i.e. 0.33 9 (60°), 0.42 10 (25°), 0.37 11 (25°) and 0.311 2 (25°). The energy of activation was found to be 18·7 kcal mol- l which also was in good 827
Transcript of TP - NISCAIRnopr.niscair.res.in/bitstream/123456789/53232/1/IJCA 15A(9) 827-82… · of NO;) as the...
of NO;) as the viscosity decrease due to the distor-tion of the solvent structure i.e. 'r.D is small and1)E+'IJA +1)D. In the case of salts containing Br",1)D increases (excepting at 35°) and hence the Bcoefficient decreases with the increase in tempe-rature. The lesser the value of the B coefficientthe greater is the structure breaking effect or ion-solvent interaction and solvation. Hence the struc-ture breaking effect or ion-solvent interaction followsthe order Bc>NOil>CI-, and in agreement withthat of Kay15,16 who distinguished between thestructure breaking and structure making ions byplotting b.(AoY)o)jb.Tversus b.Bjb.T.
Ions with greater crystal radii and small chargedensities, would possibly have a weak orientingeffect in th« first layer. Therefore, Y,E and 'fjA willbe small. Also there exist a considerable amountof distortion in the vicinity of such ions due to thecompetition between the ionic field and bulk struc-ture and consequently TP will be larger. ThusB will be smaller for K+ salts than for Na+ salts.Further investigation are in progress with that ofother monovalent cations.
Md<ae17 has suggested that the dioxane moleculeshas two nonadjacent dipolar groups whose momentscancel, so that the effective reaction is probablygreater than is indicated by microscopic properties.Hence the frozen layer as suggested by Frank andEvans-s. around the cation is expected to be consti-tuted of both water and the dioxane moleculespossibly consisting more of the former than of thelatter. The diffused layer would consist of looselyoriented water and dioxane molecules, the extentof orientation decreasing with the distance fromthe ion till the outermost laver has the same struc-ture and composition as that of the solvent. Whenthe dioxane content of the solvent increases, moredioxane molecules take part in constituting thediffused layer thereby promoting a sort of orderingeffect in the solvation sphere leading to larger valueof Y)E and 1).1. This will be reflected in increasein B values with increase in dioxane content-(Table 1).
References
1. DAS, N. C. & DAS, P. B., Indian I Chem., 15A (1977),in press.
2. GURNEY, R. \'1., Ionic processes in solutions (McGra.w-Hill, New York), 1953, 159.
3. HARNED, H. S. & OWEN, B. B., Physical chemistry ofelectrolytic solutions (McGraw-Hill, New York), 1958, 117.
4. STOKES, R. H. & MILLS, R., Viscosity of electrolytes andrelated properties (Pergamon Press, New York), 1965, 39.
5. KAY, R. L., VITUCIO, T., ZAWOSHI, C. & EVANS, D. F.,I phys. Chem., 70 (1970), 2336. .
6. KRICHKARD, K & SKINNER, J. F., I phys. Chem., 73(1969), 2060.
7. YAO, N. P. & BENNION, D. N., I phys. Chern., 75 (1971),1927.
8. BARE, J. P. & SKINNER, J. F.,I phys. ci-«, 76 (1972),434.9. CHACKRAVARTY, A. S. & PRASAD, B., Trans. Faraday
Soc., 35 (1939), 1466.10. SRINIVASAN, M. K. & PRASAD, B., Trans. Faraday Soc.,
35 (1939), 1442.11. DAS, P. B., DAS, P. K. & PATNAIK, D., I Indian chem,
Soc., 37 (1960), 683.12. DAS, P. B., I Lnstn Chem., 48 (1976), 207.13. FALKENHAGEN, H., Z. Phys., 32 (1931), 745.14. AGGRAWAL, D. K & SINGH, K., I Indian chem. Soc.,
53 (1975), 482.
NOTES
15. KAY, R. L., In water, a comprehensive treatise, Vol. 3,edited by R. Frank (Plenum Press, New York), 1973, 194.
16. KAY, R. L., Advance chemical series, No. 73, edited byR. F. Gould (American Chemical Society, WashingtonDC), 1968, 1.
17. l\1CR.~E, E. G., Chem. Rev .• 18 (1936), 349.18. FRANK, H. S. & EVANS, M. W., I chon. Phys., 13
(1945), 507.
Kinetic Evidence for Fast Protonation Pre-equilibrium in the Acid Hydrolysis of
Acetamide: Evaluation of Protonation Constant
(Mrs) SHANTI :MITTAL, K S. GUPTA & Y. K GUPTADepartment of Chemistry, University of Rajasthan, Jaipur
Received 29 January 1977; accepted 17 March 1977
Over an extended acetamide concentration range(1-6M), the acid hydrolysis obeys the rate law, Rate=kK[H+][Amide]j(l+K[Amide]), which provides adirect kinetic evidence for the step CH3CONH2+H+""CH3CONH~. The values of protonation constant, K,determined kinetically are in good agreement withthose obtained by other methods.
THE hydrolysis of acetamide has been the subjectof several studies- from various points of view,
e.u, effect of different acidsl,2 and acidity", solventeffects4•5, activation parameters2,5.6 and corre-lation of rate using Taft equation? have been investi-gated. Surprisingly the most important aspectof hydrolysis, the variation of amide over an extendedconcentration range, has not been studied so far.The accepted A - 2 mechanism (Eqs. 1 and 2)
KAmide-j-H" -===;:[Amide HJ+1 ... (1)
K[Amide HJ+ +H20--i>-products ... (2)should lead to the familiar Michaelis-Mention ratelaw (3) or (4) when [amideJ[~ H+JRate = kK[H+ J[AmideJj(I+K[AmideJ) (3)kobs = kK[AmideJj(1+K[AmideJ) (4)kobs is the first-order rate constant. We studiedthe hydrolysis of acetamide in the concentrationrange 1-6M at 55°, 60° and 65°. The kineticswere followed by estimating ammonia by formaltitration method", The results were reproducibleto ± 5~jo' In all kinetic runs acetamide was inexcess over hydrochloric acid such that the reactionfollowed a pseudo first order kinetics. The maxi-mum concentration of acetamide employed, waslimited by its solubility in water. The resultsare shown in Table 1.
The plots of I! kobs versus 1
INDIAN J. CHEM., VOL. 15A, SEPTEMBER 1977
TABLE 1 -' RATE CONSTANTS(kobs) AT DIFFERENT [AMIDE]AND TEMPERATURESIN THE HYDROLYSISOF ACETAMIDE
(Amide]111
(HCI conc.=O·lM)10'kobs [Amide]see'? M
10'kohssec!
TEMP. 55" TEMP. 60°1·0 1'73 3·0 5-182·0 2'69 4·0 6·144·0 3·84 6·0 6'905·00 4·61
TEMP. 60° TEMP. 65°0·80 2'23 1·0 4·421·0 2·57 2·0 7·961·5 3'46 3·0 9·602·0 4·22 4·0 11'52'5 4·99 5·0 12·3
agreement with the values cited" for lower [H+J.The rate law (3) thus provides a strong kineticevidence for the rapid proto nation pre-equilibriumin the hydrolysis of acetamide.
References1. O'CONNOR, C., Quart, Rev., 24 (1970), 553.2. RABINOV'ITCH,B. S. & '\TINKLER, C. A., Can. J. Res.,
20B (1942), 73.3. BOLTEN, P. D. & JACKSON,L., Aust. J. cu«, 24 (1971),
969.4. ELSEMONGY,M. M., ABU ELAMAYEM,M. S. & MOUSSA,
M. N. H., J. Indian chem. Soc., 52 (1975), 321.5. AZUl, M. A. & ILAHI, M. B., J. nat. Sci. Matll.s Pakistan,
4 (1964). 193.6. BOLTON, P. D. & WILSON, 1. R., Aust . J. Chem., 18
(1965), 795.7. BOLTON, P. D., FRIER, R. D. & NAXCARROW,P. C.,
Aust. J. Chem., 25 (1972), 303.8. HAWK,P. B.,Practical physiological chemistry (P. B1akiston,
Philadelphia), 1920, 525.9. YAMANA, T., MrzuKAMI, Y., TSUJI, A., YASUDA, Y. &
MASUDA,K., Chern. Pharm. seu., 20 (1972), 881.10. GOLDFARB, A. R., MELE, A. & GUTSTEIN, N., J. Am.
chem, Soc., 77 (1955), 6194.11. KEZDY, F. & BRUYLANTS, A., Bull. Soc. ciu«, Fr.,
(1959), 947 (cited in ref. 9).12. HALL, N. F., J. Am. chem. Soc., 52 (1930), 5115.
Nitration of Some Mixed Ligand Cu(II) Com-plexes of Acetylacetone, Benzoylacetone,
Dibenzoylmethane & Schiff Bases
U~fA DORASWAMY& P. K. BHATTACHARYADepartment of Chemistry, M.S. University of Baroda
Baroda 390002
Received 18 September 1976; revised 21 April 1977 ;accepted 13 May 1977
Nitration of the coordinated ligands in the complexesof the type [CuLLl where L= salicylaldimine or 2-hy-droxyacetophenonimine or 2-hydroxy-3-methylaceto-phenonimtne and L' = acetylacetone or benzoylacetoneor dibenzoylmethane have been carried out. Trinitrocompounds have been obtained in all the cases, exceptin the case of 3-methyl derivative of acetophenone wherea dinitro compound is obtained. The substitution pro-ducts have been characterized by elemental analysis,magnetic moments, conductance measurements andIR spectral studies.
828
THE ~-diketonates of metal ions are reported=?to undergo electrophilic substitution reactions.
Tetra-substituted compounds have been obtainedwith divalent metal complexes of salicylaldehydeunder electrophilic substitution reaction condition-".We have earlier reported-! the nitration of mixedligand imine complexes [CuLL'] where L'H =-~ sali-cylaldimine, L'H = 2-hydroxyacetophenoniminc or2-hydrox y-3-meth ylacetophenonimine.
In the present study nitration reactions havebeen carried out on Cu(II) mixed ligand iminecomplexes of the type [CuLL'] where LH = sali-cyladimine or 2-hydroxyacetophenonimine or 2-hydroxy-3-methylacetophenonimine and L'H =acetylacetone (acac) or benzoylacetone (bzac) ordibenzoylmethane (dbm).
The reagent used were of AR grade. The mixedligand imine complexes were prepared as describedin a previous publication-".
Nitration of imine complexes _. Mixed ligand iminecomplex (0·0016 mole) and acetic anhydride (10 ml)were taken and cooled, and to this was added pow-dered Cu(_ 03)2·3H20 (0·0024 mole) in small portionswith stirring during 30 ruin under ice-bath cooling.The ice-bath was removed after 5-6 hr. In thecases of bzac, dbm anc 2-hydroxy-3-methylaceto-phenonimine mixed complexes, a longer time periodwas allowed for stirring at .--.0°. The resultinggreen-coloured slurry was decomposed by pouringinto ice-cold water (100 nil) containing sufficientamount of sodium acetate and stirring for 1 hr.The precipitate obtained was filtered under suction,washed with water and finally with ethanol. Thecompounds were analysed for metal and nitrogencontents. The characterization data" of the mixedligand complexes are given in Table l.
As the complexes under study are unstable inthe presence of nitric acid, a mild nitrating agent,acetyl nitrate-" prepared in situ was employed.Nitronium ions produced from this reagent actas electrophile to form the resonance stabilizede-complex intermediates.
In the present mixed ligand complexes (I) thesubstitution of a nitro group leads to a trinitrocompound (II).
In the ~-diketone moiety only one group canenter as the hydrogen atom on the Y-carbon atomis labile and susceptible to electrophilic substitu-tions. On the other hand the nitrosubstitutioncan take place at 3- and 5-positions on the salicvl-ideneimine moiety. Positions 4 and 6 in the benzenering of aldehyde or acetophenone are not attackedby the electrophile as that would tend to placea positive charge at a carbon adjacent to an atomalready carrying a positive charge in the e-cornplexintermediate creating an energetically unfavourablesituation.
