untitled ISSN 2 Kinetic s cobalt(II Farah Sam 1 Chemistry Depa 2 Laboratory of M 3 Faculty of Pharm * Corresponding Tel.: +961.5.4126 ARTICLE INF DOI: 10.5155/eu Received: 05 July Received in revis Accepted: 12 Au Published online Printed: 30 Sept KEYWORDS Ion‐pair Aquation tert‐Butanol Solvent effect Dicarboxylic acid Cobalt(III) comp 1. Introducti Cobalt(III tion, notably complexes w also member axial ligands agent [1]. Als form of its tr the reduction bio‐reductive Carboxyli sedimentary water at mg/ 8% of the dis concentration complexes wi their roles in ment, trace formation an toxicity. By fo surface or by acids are cap 2153‐2249 (Prin studies of II) comple mih Zeitouni artment, Faculty of Material, Catalysis, macy, Lebanese Un author at: Chemist 654. Fax: +961.5.21 FORMATION urjchem.8.3.273-2 y 2017 sed form: 11 Augu gust 2017 e: 30 September 20 tember 2017   d plex ion I) complexes h y because of th ith tetradentat rs of the vitam have been sy o, the electroch ris(methylpipyr n potential of t ely activated at ic acids are fo basin fluids, bu /L concentration ssolved organic ns in natural ith metal cation mineral dissolu element mob nd migration, t orming comple y decreasing th able of increas Eu t) / ISSN 2153‐2 ht Europ f ion‐pairi ex in diffe 1,*, Jinane K f Science, Beirut Ara Environmental and niversity, Hadath, B try Department, Fa 10528. E‐mail addre 278.1609 ust 2017 017 have attracted heir biological e aliphatic Schi min B series or ynthesized as p hemical studies ridyl) amine co he complex is hypoxic tumor ound at mg/L ut are typically ns where they c carbon. In sp waters, their ns have led to n ution, secondar bility, ore dep trace element xes with metal he pH of soil s ing dissolution uropean Journal Europe 2257 (Online)  2 ttp://dx.doi.org/10 pean Jo Journal web ing effects erent dica Kamal Chaab ab University, Riad d Analytical Metho Beirut, Lebanon aculty of Science, Be ess: farahzeitouni@ ABSTRACT The study of th different types mixed solvent metrically at d reaction rates with respect of butanol is intr mentioned con ΔG*ip is more indicating the p Cite this: Eur. J considerable a activity. Cobal iff bases, conta their analogue potential antitu s of cobalt(III) i omplex showed suitable for it sites [2]. L concentration y present in su can account for ite of their var r abilities to numerous studi ry porosity enha position, petro bioavailability l cations on mi solutions, carbo of aluminosilic of Chemistry 8 ( ean Journal of Ch 2017 Atlanta Pub 0.5155/eurjchem ournal bpage: www. s on the a arboxylate ban 2 and Ra El‐Solh, Beirut, Leb ds, Faculty of Scien eirut Arab Universi @yahoo.com (F.S. Z he kinetic aquat s of dicarboxyla media of wate different temper and mechanism f different buffe roduced. Examin nditions will lea or less linearly presence of com J. Chem. 2017, 8( atten‐ lt(III) aining es, as umor n the d that to be ns in urface r 5 to riable form ies of ance‐ oleum y and neral oxylic cates, carb form asso S halo know aqua inter sepa depe any T aqua malo 0.04 cont an a dyna to ob 2. Ex 2.1. (3) (2017) 273‐2 hemistry lishing House LLC m.8.3.273-278.16 of Che eurjchem.com aquation o e media a mzi Kassem banon nces, Section I, Leba ty, Riad El‐Solh, Be Zeitouni). tion of chlorope ate solutions (M r with tert‐buta atures (30‐60 ° m. Comparison o rs (Malonate, m nation of the li ad to diagnoseth varied among pensation effect (3), 273‐278 bonates, quartz ming fluids, wh ociated as a resu Several works opentaammine wn that the ated by an esse ractions result arates the ion‐p endent on the specific chemic The purpose ation of chlor onate, succinat 4 mol/L of dicar taining 30% (v: ttempt to deter amic parameter btain informati xperimental Reagents 278 C ‐ All rights rese 09 emistry m of chlorop at 30% of m Hamed 3 anese University, Ha eirut, Lebanon. entaammine cob Malonate, malate anol (30%, v:v) C) in the light o of the kip (Rate c malate, tartarate inear free energ he mechanism. the studied dic t between ΔH*ip a z and barite po ere metal‐orga ult of high temp investigated cobalt(III) in d halopentaamm entially dissoci t in contact ion pair. The streng charge to size cal interactions of the introdu ropentaammine te, malate and rboxylic acid ne :v) tert‐butanol rmine the therm rs of activation on about the so rved ‐ Printed in y pentaamm tert‐buta adath, Beirut, Leba balt(III) ion in t e, tartarate and is investigated of the effects of constant of ion‐ and succinate) gy relationship The free energ carboxylate ion‐ and ΔS*ip. ort in high‐tem anic complexes perature [3‐5]. the kinetics o different media mine cobalt(II ative process. S n‐pairing, whe gth of ion‐pairin ratio of the ion [13]. uced work is e cobalt(III) p d tartarate solu eutralized by 80 l at different te modynamic and where the data olute‐solvent in the USA mine anol anon the presence of d succinate), in d spectrophoto‐ f ion‐pairing on pairing) values at 30% of tert‐ (LFER) at the gy of activation pairing ligands mperature ore‐ can be highly of aquation of a [6‐12]. It is I) complexes Stronger ionic ere no solvent ng is primarily ns and not on to study the perchlorate in utions (0.008‐ 0% of Na2CO3) mperatures in d extrathermo‐ a can be linked teraction. 274 Zeitouni et al. / European Journal of Chemistry 8 (3) (2017) 273‐278 Table 1. Values of rate constants (ko×106) for the aquation of [Co(NH3)5Cl]2+ in the absence of dicarboxylate ion‐pairing tert‐butanol (30%) at different temperatures. T (°C) 30 35 40 50 60 ko×106 (1/sec) 0.51 1.80 3.56 30.40 37.80 Table 2. Values of rate constants (kobs×106 (1/sec)) for the aquation of [Co(NH3)5Cl]2+ in malate media (m1) containing tert‐butanol (30%) at different temperatures. m1 (mol/L) T (°C) 30 35 40 50 60 0.008 0.78 3.39 14.47 39.95 61.20 0.016 0.74 3.43 13.83 38.32 57.61 0.024 0.76 3.71 11.35 21.46 55.97 0.032 0.78 3.59 6.86 11.38 54.80 0.040 0.65 3.90 7.31 10.43 32.89 Table 3. Values of rate constants (kobs×106 (1/sec)) for the aquation of [Co(NH3)5Cl]2+ in malonate media (m1) containing tert‐butanol (30%) at different temperatures. m1 (mol/L) T (°C) 30 35 40 50 60 0.008 2.65 5.02 6.82 31.36 50.24 0.016 2.83 4.27 7.51 29.67 55.52 0.024 1.69 2.20 7.24 32.49 53.84 0.032 0.87 5.83 7.42 29.68 51.65 0.040 1.26 5.09 5.26 40.33 56.27 Table 4. Values of rate constants (kobs×106 (1/sec)) for the aquation of [Co(NH3)5Cl]2+ in tartrate media (m1) containing tert‐butanol (30%) at different temperatures. m1 (mol/L) T (°C) 30 35 40 50 60 0.008 0.57 4.13 5.84 18.60 47.23 0.016 2.24 3.25 6.52 17.58 45.90 0.024 2.45 2.95 4.22 16.14 44.42 0.032 0.74 2.79 20.74 35.29 67.13 0.040 0.83 3.33 12.06 26.70 60.80 Table 5. Values of rate constants (kobs×106 (1/sec)) for the aquation of [Co(NH3)5Cl]2+ in succinate media (m1) containing tert‐butanol (30%) at different temperatures. m1 (mol/L) T (°C) 30 35 40 0.008 1.51 2.01 5.34 0.016 1.05 1.51 2.31 0.024 0.85 2.20 3.20 0.032 1.27 3.09 3.02 0.040 1.35 2.31 3.93 Cobalt(II) carbonate, ammonia, malonic acid, succinic acid, tartaric acid, malic acid, sodium carbonate and tert‐butanol were purchased from Fluka Chemika. Hydrogen peroxide was purchased from Riedel‐de Haën. Hydrochloric acid was purchased from Chemical Management Consulting. Perchloric acid was purchased from Merck. The chloropentaammine cobalt(III) perchlorate complex was prepared by using the method of Hynes [14]. 2.2. Procedure The rate of aquation of [Co(NH3)5Cl](ClO4)2 complex was followed spectrophotometrically by using Unicam Helios Alpha and Beta spectrophotometer at λ = 240 nm, in 30% (v:v) tert‐butanol in different dicarboxylate media (Malonate, succinate, malate and tartarate) (0.008‐0.040 mol/L at 30‐60 °C). Knowing that, the buffer solution was prepared from 0.1 M of the dicarboxylic acid and 0.08 M of sodium carbonate. The spectrophotometer was fitted with thermostated cell holders, heated by water circulating from a Heto HMT 200 thermostat. 3. Results and discussion The observed first order rate constant in the presence of dicarboxylate buffers for different temperatures in 30% (v:v) tert‐butanol were computed from the slopes of the good linear least squared first order plots of log (At‐A∞) against time depending on the first order Equation (1) [15]. Where At is the absorbance at different time and A∞ is the absorbance at the infinite time. Ln (a0/a0‐x) = k×t (1) The observed rate constants (kobs) are collected in Tables 1‐5. The ion‐pair rate coefficient (kip) was calculated according to the following Wyatt and Davis equation [16]. kobs.m3 = k0 ×[CpX2+] + kip × [CpXL] (2) where k0, the observed rate constant in the absence of dicarboxylate ion; kobs, the observed rate constant in the presence of dicarboxylate ion; m3, the stoichiometric concentration of the complex salt; [CpX2+], the free complex ion concentration and [CpXL], the ion‐pair concentration. [CpXL] was calculated with the aid of the following Equations: CpXL ⇌ CpX2+ + L2‐KD (3) NaL‐ ⇌ Na+ + L2‐KNaL‐ (4) H2L ⇌ HL‐ + H+K1 (5) HL‐ ⇌ L2‐ + H+K2 (6) Zeitouni et al. / European Journal of Chemistry 8 (3) (2017) 273‐278 275 Table 6. Calculated values of rate constants (kip×105, 1/sec) for the aquation of [Co(NH3)5Cl]2+in dicarboxylate buffer containing 30% of tert‐butanol at different temperatures. T (°C) Malate Malonate Tartrate Succinate 30 0.38 0.835 0.30 0.21 35 1.95 1.23 0.42 0.22 40 6.02 1.32 0.925 0.33 50 8.49 3.14 2.30 60 21.10 7.68 4.95 Table 7. Values of the thermodynamic parameters: Enthalpy of activation Δ ∗ , entropy of activation Δ ∗ and Gibbs of free energy of activation Δ ∗ of the ion‐ pairing aquation of [Co(NH3)5Cl]2+in different buffers containing 30% of tert‐butanol at40 °C. T (°C) Buffer ∗ (kJ/mole) ∗ (J/K.mole) ∗ (kJ/mole) 40 malate 98.25 ‐18.74 104.11 40 malonate 52.49 ‐168.50 105.22 40 tartrate 72.48 ‐112.11 107.57 40 succinate 22.18 ‐280.11 109.86 Where; KD = [CpX2+][L2‐] /[CpXL] (7) (L2‐ represents the dicarboxylate anion) K1 = [H+][HL‐] /[H2L] (8) K2 = [H+] [L2‐] γ2 / [HL‐] (9) KNaL‐= [Na+] [L2‐] γ2 / [NaL‐] (10) Log γi = ‐A×(I1/2 / (1+1.3×I1/2)‐0.3×I) (11) (Debye‐Hückel equation) (Log γ2 = 4 Log γ1) I is the ionic strength γ1 and γ2 are the activity coefficients of the univalent and divalent ions, respectively. I = 0.5×([H+] + [HL‐] + 4×[L2‐] + 4×[CpX2+] + 2×m3 + [Na+] + [NaL2‐]) (12) m1 = [H2L] + [HL‐] + [CpXL] + [NaL‐] (13) m3 = [CpX2+] + [CpXL] (14) The principle of calculations performed by computer programs can be summarized as: for the first cycle [H+] = 0, [CpXL] = 0, [NaL‐] = 0, [CpX2+] = m3 – [CpXL], [HL‐] = 0.5×m2, [H2L] = 0.3×m1, [L2‐] = m1 – [HL‐] – [CpXL] – [NaL‐] – [H2L] and [Na+] = 2×m2 – [ NaL‐]. Where, m2 is the concentration of sodium carbonate. Then the ionic strength takes its first approximated value and then γ1 and γ2 after which the following terms take their new value [H+] = K2 [HL‐] / [L2‐] γ2 (15) [H2L] = [HL‐][H+] / K1 (16) [HL‐] = 2×m1 ‐2×m2 – 2×[H2L] – [H+] (17) [L2‐] = m1 – [HL‐] – [H2L] – [CpXL] – [NaL‐] (18) [NaL‐] = [Na+] [L2‐] γ2 / KNaL‐ (19) [CpXL] = m3/[(KD/ [L2‐]) +1] (20) [CpX2+] = m3 – [CpXL] (21) then I, γ1 and γ2 recalculated again. These steps of calculations were repeated many times until the difference between two successive values of [CpXL] becomes equal to or less than 1×10‐7. The calculated average values of kip in dicarboxylate buffer containing 30% of tert‐butanol at different temperatures are collected in Table 6. 3.1. Variation of ion‐pair coefficients (kip) with different buffers Various studies [17] found that the rate of aquation of chloropentaammine chromium(III) ion is accelerated by nitrate, sulphate, malonate, tartrate and phthalate ions. These effects were attributed to the more reactive ion‐pairs. These studies clearly show the ion‐pairs formed between some bivalent anions and halopentaammine cobalt(III) or chromium(III) cations undergo aquation at a faster rate as compared to the free cations. Thus, by comparing kobs of all buffers with respect to ko (in the absence of buffer) at 30% of tert‐butanol (see Tables 1‐5), it was seen that kobs values are greater than the ko values. The rate of the acid hydrolysis of chloropentaammine cobalt(III) ion had been shown to be independent of hydrogen ion concentration below pH = 7 [18]. For that reason, the values of ion‐pair rate constant kip are approximately the same at different concentration of buffers. Table 6 shows the average values of kip for the different buffers at different temperatures containing 30% of tert‐butanol. By comparing the kip values with respect to different buffers, it was seen that the values of kip are of decreasing order: kip malonate > kip malate > kip tartrate > kip succinate at different temperature. Knowing that pK1 succinate > pK1 tartrate > pK1 malate > pK1 malonate. This means that malonate will disso‐ ciate more than the other buffers causing more anions of malonate in solution, thus helping in the formation of ion‐pair. Furthermore, the solute‐solvent and the solvent‐solvent interactions must be considered resulting from the presence of hydroxyl groups in both solvent components (water and tert‐ butanol) and the carbonyl oxygens group in the malate, malonate, tartrate and succinate buffers besides the hydroxyl groups in tartrate and malate in the formed ion‐pairs. So, tert‐ butanol has special effect on the formation of ion‐pair. This fact was also proven in previous studies [19‐21]. 3.2. Thermodynamic parameters of the ion‐pair aquation reaction The thermodynamic parameters of the activated complex at 40 °C were collected in Table 7. A useful comparison can be made with Δ ∗ values among the studied dicarboxylates. The most positive values of Δ ∗ were found for succinic buffer as shown in Table 7. The trend of stability of ion‐pairs is based on the ring size formed between the complex cation and dicarboxylate anion in which the stability increases with decreasing ring size [22]. Accordingly, malonate is the most stable one. The stability of tartrate and malate ion‐pairs is higher than succinate (same chain length) due to the presence 276 of hydroxyl complex cati more, the el molecules (f interactions a anions (HL‐, L ding solvent m of the alkyl ch Any expl changes on th in some way of a chemical of similar effe are thermod entropies. Th quantities are are called ex thermodynam mechanisms, modynamic r microscopic energy relati series (Δ ∗ ‐ [23] by deter in the transiti The plot plot is linear d Δ ∗ = a × Δ Figure 1. Δ ∗ v butanol for [Co( This per Knowing tha interaction. B attempts are The plot of Δ at 30% of ter But the plot o Figure 3. Thi selective solv complex patte Figure 2. Δ ∗ v butanol for [Co( groups which on increases t lectrostatic act field effect) al and their therm L2‐) of these aci molecules, whic hain of the acid lanation of the he rate or equil reflect the inhe reaction. When ects in a model dynamic, usual he simple relat e not part of th xtrathermodyn mics do not giv however, the relationship giv mechanism. T onship (LFER) Δ ), it will rmining the ext ion state. of Δ ∗ agains due to the follo + b versus ∆ for the NH3)5Cl]2+ at 40 °C rmits a suitab at, a and b are Besides the cor made for corre ∗ against Δ rt‐butanol is als of Δ ∗ against is non‐linear c vation of the fre ern of solute‐so versus ∆ for the NH3)5Cl]2+ at 40 °C Zeit h through inte the stability of tion transmitte lso governs th modynamics re ids impose ord ch interferes w [22]. e effect of stru librium of chem erent complexit n the explanati l reaction, the q lly free energ tionships often e formal therm namic relations ve identified d mathematical ves valuable inf Thus, examinin among the stu lead to diagno ent of bond for t Δ is show wing correlatio e different buffers C. ble medium fo e variables for rrelation of Δ ∗ elating Δ ∗ wit among the stu so linear as it is Δ is nonline correlation aris ee dicarboxylat olvent interactio different buffers C. touni et al. / Eur eractions with f ion‐pair. Fur ed through so hese solute‐so esults. The cha er on the surro with internal rot uctural or me mical reactions ty of the mecha on is given in t quantities comp gies, enthalpies found among modynamics but ships. Although detailed micros form of extra formation abou ng the linear udied dicarbox ose the mecha rmation or brea wn in Figure 1 on of Equation ( containing 30% o or ion associa r the solute‐so ∗ and Δ , sim th either Δ or udied dicarboxy s shown in Figu ear as it is show ses from the h te anion leading on. containing 30% o opean Journal of h the rther‐ olvent olvent arged ound‐ tation dium must anism terms pared s, or such t they h the copic ather‐ ut the free xylate anism akage . The (22): (22) of tert‐ ation. olvent milar r Δ . ylates ure 2. wn in igher g to a of tert‐ Figur butan S follo Δ ∗ O whe A ligan form Δ ∗ T activ rolle the solv the h posi linea pair anot dica the h 3.3. P activ texts tatio time satio from Enth inter dom solu buta entr chan Δ ∗ rent T 293 in m term lead solv restr solv f Chemistry 8 (3) re 3. Δ ∗ versus ∆ nol for [Co(NH3)5C Similar to (LFE owing Equation = c Δ + d Other correlat ere they are foun Also, the plot nd series is fou m of Equation (2 = e Δ + f The obtained vation Δ ∗ and ed. Moreover, t different dica ation, where th hydration shell tion taken by ar correlations, formation w ther primarily rboxylate grou hydroxyl group Isokinetic rela Plots of entha vation often for s [25,26] treat on of an extrath es called the is on effect. The m the slope ×1 halpy‐entropy rpreted by assu minant importa te and one of anol, is particu ropy will both nges in Δ ∗ be versus Δ ∗ fo t dicarboxylate Thus the comp K. This means mind. The true ms of solvent‐s s to stronger b ent molecules ricting the fre ent molecules, (2017) 273‐278 ∆ for the differe l]2+ at 40 ° C. R) , Δ ∗ is corr (23): d ions are done nd to obey Equ of Δ ∗ versus und to be linear 24): link suggest d association Δ the parallelism arboxylates is he controlled f l for the free co every dicarbo , depends on it which differs f because of the ups transmitted ps [24]. ationship alpies of activ rm straight line these linear p hermodynamic sokinetic effect isokinetic temp 000 of the line diagrams for uming that solv ance where th f the solvent ularly strong. T tend to Δ ∗ linear function or the ion‐pair media at fixed c puted value of t that the comp explanation of olute interactio binding betwee will lower th edom of vibra lower the entro 8 ent buffers contain related with Δ e to Δ ∗ with ation (23). s Δ of the r. This relation ts that both are largely m between Δ ∗ s probably re factor is the re omplex ion and oxylate buffer ts reactivity to from one dica e electrostatic d through (‐CH2 vation versus e. Several stand plots as authen relationship, w t, enthalpy‐entr perature can b ear plots of Δ mixed solven vent‐solute inter he interaction components, w Then, the enth and Δ ∗ led t ns. Figure 4 sho aquation react composition. the isokinetic t ensation effect f compensation ons. Any effect en a solute mol he enthalpy; it ation and of ro opy. ning 30% of tert‐ to give the (23) Δ and Δ , dicarboxylate ship takes the (24) entropies of y charge‐cont‐ and Δ for elated to ion eorientation of d ion‐pair. The in the above oward the ion‐ arboxylate to action on the 2‐) groups and entropies of dard chemistry ntic represent‐ which is some‐ ropy compen‐ be determined ∗ versus Δ ∗ . nts are often ractions are of between the which is tert‐ halpy and the to only small ows the plot of tions in differ‐ temperature is must be born n effect lies in t for example, lecule and the will also, by otation of the Table 8. Values tert‐butanol at 4 m1 0.008 0.016 0.024 0.032 0.040 Applicatio the result tha compensation very small e investigation. Figure 4. Δ ∗ v butanol for [Co( 3.4. Correlati All the a temperature the above co each dicarbox at different te of Δ , log K2 examples are is evident fro obtained resu pair of therm temperatures composition mechanism temperatures Figure 5. Log ki buffer for [Co(N 3.5. Empirica concentratio The aim o new empirica which are i of ligand concentr 40 °C. Mal 0.00 0.00 0.01 0.01 0.02 on of more exa at they will ge n between Δ ∗ effect on Δ ∗ w . versus Δ ∗ for the NH3)5Cl]2+ at 40 °C ion of log kip w above correlat which is 313 K orrelations amo xylate buffers a emperature is u 2 instead of Δ e chosen to sho m the plots tha ults indicate th modynamic func s for each support that t and same LF s. ip versus log Kass of H3)5Cl]2+ at differe al correlation o on of this part is t al correlation b influencing the Zeitouni et al. ration CL (mol/L) f late 0474529 0946801 1416970 1885338 2351778 ct theories to th enerally give ri ∗ and T Δ ∗ , which is the c e different buffers C. with log Kass, log tions are perf K. It is now ne ong the studie at fixed solvent used instead of and log Kass ins w such correla at these correlat hat the paralle ctions among th dicarboxylate these reactions FER behaviour f malonate contain ent temperatures. of kobs with dica to pay an effort between the d e rate of aqu . / European Jour for the aquation o Malona 0.00464 0.0092 0.0139 0.0184 0.0230 hese effects lea ise to a fairly and therefore case of the pre containing 30% o g K1 and log K2 formed at con ecessary to exa d temperature composition. Lo f Δ ∗ , log K1 ins stead of Δ . S ations Figures 5 tions are linear elism between he different stu buffer at s sharing the r also at diff ning 30% of tert‐bu arboxylate ani t in order to fo ifferent param uation in aqu rnal of Chemistry f [Co(NH3)5Cl]2+ in ate 4804 9403 0796 9560 5878 ads to exact e to a esent of tert‐ nstant amine es for og kip stead Some 5‐7. It r. The each udied fixed same ferent utanol ion orm a meters ueous dica Garr Kobs whe k0 it CL is (coll that and ligan appr Rate Figur butan Figur butan I the solu corr med cons Figu N cons attem the p posi show plots y 8 (3) (2017) 27 n different concent Tartrate 0.0048085 0.0096496 0.0144819 0.0193029 0.0241101 rboxylate solu rick [27] expres = k0 + kc×CL ere kobs is the ob s value is the ab s the stoichiom lected in Table the plots of kob extrapolated to nds the plots ar ropriate rate law e = C1 (k0+kc KA re 6. Log kip vers nol for [Co(NH3)5C re 7. Log kip vers nol buffer for [Co(N In the present i possible emp tions containin relations rathe dium where the stant and hen ures 8 and 9 sho Now, it is ne stant (kobs) with mpts were test plots of 1/(kobs tive slope and wn on Figures 1 s leads to the fo 73‐278 trations m1 of dica 57 62 90 97 15 utions and th ssed his results bserved pseudo bsence of L, kc i metric concentra e 8). Jones, Har bs against CL of o a common k0 re nonlinear. Th w is: CL)/ (1+KACL) us log K1 of tartra l]2+ at different tem sus log K2 of mala NH3)5Cl]2+ at differ investigation it pirical correlat ng 30% of ter r than the pu e added tert‐bu nce assisted t ow such plots w ecessary to co h the free ligan ted and one of t s‐k0)versus 1/ d positive inte 10 and 11. The l ollowing empiri rboxylate buffer c Succinate 0.00475858 0.00962388 0.01448540 0.01933650 0.02417636 hat containing in terms of Equ o‐unimolecular s the catalytic c ation of the un rris and Walla f univalent ligan 0 at CL = 0 whil hus, it was conc ate buffer contain mperatures. ate buffer contain rent temperatures. is now necessa tions in the rt‐butanol whic ure aqueous d utanol lowered he ion‐associa which appear sm orrelate the o nd concentratio them was only CL give a straig ercept. Some linearity obtain ical correlation 277 ontaining 30% of tert‐butanol. uation (25): (25) rate constant, coefficient and nivalent ligand ace [28] found nd were linear le for divalent cluded that the (26) ning 30% of tert‐ ning 30% of tert‐ ary to examine dicarboxylate ch assist such dicarboxylates the dielectric ation process. mooth. observed rate n CL. Different valid in which ght line with a examples are ned from these : 278 a Where a and take another kobs = Figure 8. kobs ve buffer for [Co(N Figure 9. kobs v buffer for [Co(N Figure 10. 1/ ko butanol buffer fo Figure 11. 1/ko butanol buffer fo b are empirica form: ersus CL of malon H3)5Cl]2+ at 40 °C. ersus CL of tartara H3)5Cl]2+ at 40 °C. obs‐k0 versus 1/CL o or [Co(NH3)5Cl]2+ a bs‐ k0 versus 1/CL or [Co(NH3)5Cl]2+ a Zeit al constants and ate buffer contain ate buffer contain of malonate buffer at 40 °C. of tartarate buffer at 40 °C. touni et al. / Eur d Equation (27 ning 30% of tert‐bu ing 30% of tert‐bu r containing 30% o r containing 30% o opean Journal of (27) 7) can (28) utanol utanol of tert‐ of tert‐ 4. Co W [Co( dica the c stab the stab extra both ion‐p notic activ fract satio Ackn T of S Leba All t Geha and Refe [1]. [2]. [3]. [4]. [5]. [6]. [7]. [8]. [9]. [10]. [11]. [12]. [13]. [14]. [15]. [16]. [17]. [18]. [19]. [20]. [21]. [22]. [23]. [24]. [25]. [26]. [27]. [28]. f Chemistry 8 (3) onclusions We have not (NH3)5Cl]2+ com rboxylate buffe complex cation ility of ion‐pair complex catio ility increases athermodynam h solute‐solven pair formation ced at differ vation ∆ ∗ is m tion of tert‐but on effect betwe nowledgemen The authors ar Science, Chem anon for permi the thanks and an Subruiti and help. erences Osinsky, S. P.; Le I. T.; Campanell 2639. Failes, T. W.; Ham Prapaipong, P.; 1999, 63(17), 25 Ismail, A.; Chaab Namor, A. F. D 110(31), 9575‐9 Naik, N. C.; Nand Naik, N. C.; Nand Jones, T. P.; Phill Amira, M. F.; Ab Soc. India 1982, El‐Naggar, G. A. Chem. 2002, 216 El‐Subruiti, G. M Chem. Kinet. 200 El‐Subruiti, G. M Chem. Kinet. 200 Hunt, H. R.; Taub Hynes, A.; Yano 3053‐3054. Atkins, P.; Paula and Company, 2 Wyatt, P. A. H.; D Walker, J. B.; Mo Laurie, S. H.; Mo Elgy, C. N.; Well 2376. Zeitouni, F. S.; E Chem. 2011, 2(4 Ismail, A. M.; Se 2012, 3(2), 196‐ Younes, G. O. J. C Amira, M. F.; Ca 1980, 1726‐173 Zeitouni, F. 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