Extraction Equilibria of Gibberellic Acid by Tridodecylamine Dissolved

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Extraction Equilibria of Gibberellic Acid by Tridodecylamine Dissolved in Alcohols Hasan Uslu,† Dipaloy Datta,*,‡ and Hisham Saeed Bamufleh§ Engineering and Architecture Faculty, Chemical Engineering Department, Beykent University, Ayazağa, Iṡ tanbul, 34433, Turkey Department of Chemical Engineering, Thapar University, Patiala, 147004, India § Department of Chemical Engineering and Materials Engineering, Faculty of Engineering, King Abdulaziz University, Jeddah, 22254, Saudi Arabia † ‡

ABSTRACT: Gibberellic acid (1.877·10−3 mol·kg−1) extraction from aqueous solution using tridodecylamine (TDA, 0.1 mol·kg−1 to 0.8 mol· kg−1) as extractant dissolved in three solvents (isoamyl alcohol, octane-1ol, and decane-1-ol) at 298 K has been studied. Extraction parameters such as loading factor Z, extraction efficiency E, and distribution coefficient D, have been found using experimental data. The highest removal of gibberellic acid is found to be 96.37 % (D = 26.602, TDA = 0.5 mol·kg−1) with isoamylalcohol, 87.74 % (D = 7.160, TDA = 0.4 mol· kg−1) with octane-1-ol, and 71.87 % (D = 2.554, TDA = 0.4 mol·kg−1) with decane-1-ol. As per the experimental values of Z (1.19 to 6.52 with isoamyl alcohol, 0.85 to 5.26 with octane-1-ol, and 0.71 to 4.18 with decane-1-ol) and Bizek’ approach, the equilibrium complexation constants for 1:1 and 1:2 acid−TDA complexes have been determined. The linear solvation energy relationship (LSER) model is used to represent the extraction equilibrium of acid by TDA. D values are predicted using the LSER model parameters which fit the experimental results.

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distribution coefficient.2−14 Keshav et al.11 tested the reactive extraction of propionic acid from aqueous media to investigate the effect of pH and also determined the optimum pH range. Another study performed by Zhong et al.12 on the reactive extraction of propionic acid used Alamine 304 as an extractant. The extractant was diluted in octane-2-ol and decane-1-ol to increase the efficiency of Alamine 304. Keshav et al.13 had investigated effect of binary extractants couple as a new extractant system for the recovery of carboxylic acids. The study by Uslu14,15 was focused on the extraction of gibberellic acid by trioctylamine and trioctylmethylammonium chloride in different diluents. In the work reported by Uslu et al.,16 the extraction of levulinic acid was described using different alcohols (isoamyl alcohol, hexane-1-ol, and decane-1-ol). Tuyun and Uslu17 had reported extraction equilibrium data for picolinic acid by using tridodecylamine (TDA). The aim of this study was to explore the reactive extraction of gibberellic acid from aqueous solutions using tertiary amine, and tridodecylamine (TDA) dissolved in three different solvents. The extraction of gibberellic acid (1.877·10 −3 mol.kg−1) from aqueous solutions by TDA extractant in a variety of diluents was examined in a wide range of amine concentration (0.1 mol.kg−1 to 0.8 mol.kg−1). Batch extraction experiments were performed with TDA dissolved in alcohols

INTRODUCTION Gibberellic acids are naturally occurring plant hormones. The acids are used in agriculture as plant regulators to stimulate both cell division and cell elongation that affects leaves as well as stems (eventually affecting fruit development and fruit set). Applications of this acid can also hasten plant maturation and seed germination. Gibberellic acid and its isomers (gibberellins) have been classified as biochemical pesticides as they are naturally occurring compounds and have a nontoxic mode of action in target plants.1 Although various alternative methods such as distillation, adsorption, and electrodialysis, etc. have been used for the recovery of carboxylic acids from aqueous solution, the method of solvent extraction was shown to be the most promising one.2 An appropriate liquid−liquid extraction can provide a high distribution coefficient, high selectivity, and thus high financial potentials.3,4 The improved results established this technology of reactive extraction for carboxylic acids recovery. Organophosphorous compounds and secondary, tertiary, and quaternary amines were widely used to extract carboxylic acids. Out of the above extractants, tertiary amines were most successful in the recovery of carboxylic acids from dilute aqueous solutions.5−9 Important studies on the influence of diluents on the amine extraction of carboxylic acids was performed by Tamada and King.10 The studies reported in literature on the reactive extraction of acids focused to analyzen the analysis of the effect of diluents, pH, initial acid concentration, and temperature on the © 2014 American Chemical Society

Received: August 19, 2014 Accepted: October 15, 2014 Published: October 27, 2014 3882

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without further purification were isoamyl alcohol (Merck, > 99 %), octane-1-ol (Merck, > %99), and decane-1-ol (Merck, > 99 %). The experimental method and analysis of the extraction of gibberellic acid by amine-based extractant was done according to the procedure explained in a previous study by Uslu.14 The yield of gibberellic acid produced by the fermentation method with fungi Gibberella f ujikuroi was observed to be 0.65 g·kg−1. This was considered as the initial concentration of gibberellic acid in the extraction study, and the aqueous solution was prepared by dissolving it in distilled water (1.877·10−3 mol· kg−1). Eight different constant concentrations of TDA had been prepared by mixing diluents (isoamyl alcohol, octane-1-ol, and decane-1-ol). Prepared concentrations of TDA had been changed from 0.1 mol·kg−1 to 0.8 mol·kg−1 with an interval of 0.1. These (TDA + diluent systems) mixtures help to find the optimum concentration of amine. Equal volumes of an aqueous solution of gibberellic acid and an organic solution of TDA were mixed in Erlenmeyer flasks, and the thus prepared two-phase systems were shaken in a temperature controlled shaker at 50 rpm and at a temperature of 298 K for 2 h. After equilibration, both phases were separated. The concentration of acid in the aqueous phase after extraction was analyzed by UV spectrophotometer at 254 nm as explained by Holbrook et al.19 Determination of relative uncertainty in concentration measurement was found to be ± 1 %. The deviation of amount of acid in both phases was determined to be ± 1 %.

(isoamyl alcohol, octane-1-ol, and decane-1-ol). Distribution coefficients, loading factor, and extraction efficiency were calculated from the results of batch extraction experiments to analyze the extraction behavior. In addition to these, complexation constants were estimated and the LSER model was applied.

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THEORY The extraction of gibberellic acid (HA) with amine (R3N) can be described by eq 1 as18 pHA + qT̅ ↔ (HA)p (T)q

(1)

where HA represents the undissociated part of the acid present in the aqueous phase. p and q are the stoichiometric coefficients of the acid and extractant, respectively. The organic phase species are marked with an overbar. Equation 1 can be characterized by the overall thermodynamic extraction constant, eq 2:

[(HA)p (T)q ]

KE =

[HA]p [T]̅ q

(2)

where square brackets denote concentrations. It could be possible to study the extraction of acid by pure diluent in order to obtain the distribution coefficient, but there is no evidence of the real value of this coefficient in the presence of amine and its complexes formed with the acid. The change of the distribution coefficients with amine concentration can be caused by both the conditioned character of this constant and the stoichiometry of complex formation. Therefore, the loading factor must be taken into consideration. The loading of the extractant, Z, is defined as the ratio of total concentration of acid in the organic phase at equilibrium to the total concentration of amine in the organic phase. The expression for the loading Z is given by eq 3. Z=

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RESULTS AND DISCUSSION Physical extraction of gibberellic acid with pure diluents was taken from a previous study15 and results are presented in Table 1. All diluents used in this study gave very poor Table 1. Physical Extraction of Gibberellic Acid with Pure Diluents15 at a Temperature of 298 K and Pressure of 1 atm

Corg Ce,org

(3)

In eq3, Corg is the equilibrium concentration of gibberellic acid in the organic phase, Ce,org is the total TDA concentration in the organic phase. The distribution coefficient D for gibberellic acid extracted from water into organic phase is determined as D=

(4)

In eq 4, Caq is the equilibrium concentration of gibberellic acid in the aqueous phase. The degree of extraction E is defined as the ratio of gibberellic acid concentration in the organic phase at equilibrium to the initial acid concentration in the aqueous phase and is defined in term of D as

E% =

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D·100 1+D

Caq

D

E

(mol·kg−1)·103

(mol·kg−1)·103

(−)

%

isoamyl alcohol octane-1-ol decane-1-ol

0.120 0.087 0.059

1.757 1.790 1.818

0.068 0.048 0.032

6.3 4.6 3.1

extraction efficiency (3.1 % to 6.3 %). The highest distribution coefficient was obtained by isoamyl alcohol as 0.068. Table 2 presents experimental results of the equilibrium data of the distribution of gibberellic acid (1.877·10−3 mol·kg−1) between water and TDA (0.1 mol·kg−1 to 0.8 mol·kg−1) dissolved in isoamyl alcohol, octane-1-ol, and decane-1-ol. Table 2 and Figure 1 demonstrate the influence of the concentration of organic solvent (TDA) on the distribution of gibberellic acid extraction between two phases. It can be seen that the extraction power of TDA−diluent mixture increases first and then decreases with an increase in the initial concentration of TDA in the organic phase with all the alcohols. The intake of acid by TDA, that is, the acid concentration in the organic phase after the extraction increases from 0.652 mol·kg−1 to 1.809 mol·kg−1 with isoamyl alcohol (TDA = 0.1 mol·kg−1 to 0.5 mol·kg−1), from 0.526 mol·kg−1 to 1.647 mol·kg−1 with octane-1-ol (TDA = 0.1 mol·kg−1 to 0.4 mol·kg−1), and from 0.418 mol·kg−1 to 1.349 mol·kg−1 with decane-1-ol (TDA = 0.1 mol·kg−1 to 0.4 mol·kg−1). The extraction power of the TDA− diluent mixture is increased to a maximum value when the amount of TDA in the organic phase is between 0.4 and 0.5

Corg Caq

Corg diluent

(5)

EXPERIMENTAL WORK Gibberellic acid, C19H22O6, (M = 346.37 kg·kmol−1; purity, > 99 %) and TDA (tridodecylamine, trilaurylamine), C36H75N, (M = 522.01 kg·kmol−1; purity, > 99 %) a commercial product, was purchased from Merck, USA. Other chemicals used 3883

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Table 2. Results for the Extraction of Gibberellic Acid with Individual Diluting Solvents at a Temperature of 298 K and Pressure of 1 atm Ce,org

Corg

D

Dcalc

Z

E

diluents

mol·kg−1

(mol·kg−1)·103

(−)

(−)

(−)

%

K11

K12

isoamyl alcohol

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.652 1.048 1.317 1.764 1.809 1.521 1.233 0.952 0.526 0.898 1.215 1.647 1.551 1.247 0.984 0.685 0.418 0.681 1.053 1.349 1.315 1.022 0.724 0.571

0.532 1.264 2.351 15.610 26.602 4.272 1.914 1.029 0.389 0.917 1.835 7.160 4.757 1.979 1.101 0.574 0.286 0.569 1.277 2.554 2.339 1.195 0.627 0.437

0.575 1.430 3.161 18.533 32.852 3.766 1.685 1.063 0.296 1.255 2.148 8.184 5.352 2.078 1.251 0.706 0.296 0.682 1.645 2.854 2.677 1.268 0.712 0.452

6.52 5.24 4.39 4.41 3.61 2.53 1.76 1.19 5.26 4.49 4.05 4.11 3.10 2.07 1.40 0.85 4.18 3.40 3.51 3.37 2.63 1.70 1.03 0.71

34.73 55.83 70.16 93.97 96.37 81.03 65.68 50.71 28.02 47.84 64.73 87.74 82.63 66.43 52.42 36.49 22.26 36.28 56.10 71.87 70.05 54.44 38.57 30.42

5.32 6.32 7.83 39.02 53.20 7.12 2.73 1.28 3.89 4.58 6.11 17.90 9.51 3.29 1.57 0.71 2.86 2.84 4.25 6.38 4.67 1.99 0.89 0.54

4.34 7.62 13.99 345.36 782.43 20.00 4.24 1.39 2.88 4.68 9.24 77.83 29.18 5.23 1.76 0.60 1.96 2.38 5.16 12.09 8.32 2.33 0.77 0.41

octane-1-ol

decane-1-ol

Figure 1. Plots of organic phase acid concentration against concentration of TDA in different alcohols at a temperature of 298 K and pressure of 1 atm. Symbols: ⧫, isoamyl alcohol; ■, octane-1-ol; ▲, decane-1-ol.

mol·kg−1, that is, an intermediate amine concentration. The highest removal efficiency is found to be 96.37 % (D = 26.602, TDA = 0.5 mol·kg−1) with isoamyl alcohol, 87.74 % (D = 7.160, TDA = 0.4 mol·kg−1) with octane-1-ol, and 71.87 % (D = 2.554, TDA = 0.4 mol·kg−1) with decane-1-ol. Therefore, isoamyl alcohol is found to be an effective diluting agent for TDA. The reason for equilibrium thermodynamic of this behavior was explained in a previous article.14 According to results shown in Table 2 and Figure 1, the capability of diluents in TDA follows the order for the gibberellic acid extraction as isoamyl alcohol > octane-1-ol > decane-1-ol.

Polarity of the solvent is the most effective factor which helps to dissolve the amine and to provide proper media to extract the acid from the aqueous solution. The polar nature of solvent is found to be decreased with an increase in carbon number. Also, the trend in the distribution coefficient is according to the carbon number of these solvents, that is, with an increase in carbon number D values are found to decrease. Solvation of the acid−amine complex by the diluent is a critical factor in the extraction of acid. The interactions between the complex and diluent generally take place by general solvation and specific interactions. Alkanes being nonpolar provide very low solvation 3884

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Figure 2. Comparison of organic phase concentration of gibberellic acid in pure individual solvents and TDA + solvents at a temperature 298 K and a pressure 1 atm.

of the polar complexes and hence give a very low distribution of the acid into the solvent phase. Aromatic diluents give higher distribution due to the interaction of the aromatic π-electrons with the complex. Alcohols being polar in nature can promote extraction by providing a good solvation media for the acid− amine ion pair. The polarity (or polarizability) of isoamyl alcohol accounts for the better solubility of acid molecules in the organic phase and confirms higher distribution coefficient and removal efficiency. In Figure 2, the comparison of distribution coefficients of gibberellic acid in pure individual solvents and TDA + diluents are presented. It is seen that the use of TDA dissolved in respective alcohols increased the distribution coefficient by about 15 times with isoamyl alcohol, about 19 times with octane-1-ol, and about 23 times with decane-1-ol as compared to pure solvents as extractant. The effect of TDA concentration on loading (Z) factor is presented and shown in Figure 3 and Table 2. The loading curve is a plot (Figure 3) of Z versus

amine concentration. Overloading has been generally observed at low amine concentration especially between 0.1 mol·kg−1 and 0.5 mol·kg−1. Generally, in the systems with only one amine per complex, total concentration of amine has no effect on the loading of amine by acid. But in the case of more than one amine per complex, the acid loading increases with an increase in the amine concentration in the organic phase. The values of loading are found in the range of 1.19 to 6.52 with isoamyl alcohol, 0.85 to 5.26 with octane-1-ol and 0.71 to 4.18 with decane-1-ol. These numerical values indicate that complexes include a large numbers of acid and amine molecules, and exhibit aggregation or formation of complexes with a large numbers of acid and amine molecules. In Figure 4, the variation of extraction efficiency with concentration of TDA (0.1 mol·kg−1 to 0.8 mol·kg−1) is shown. It can be seen that an increase in the amine concentration causes gradual increase in extraction efficiency up to a certain value of TDA concetration and after that it decreases. Extraction efficiency increase from

Figure 3. Plots of loading factor (Z) against concentration of TDA in different alcohols at a temperature 298 K and a pressure 1 atm. Symbols: ⧫, isoamyl alcohol; ■, octane-1-ol; ▲, decane-1-ol.

Figure 4. Plot of extraction efficiency against concentration of TDA in different alcohols at a temperature 298 K and a pressure 1 atm. Symbols: ⧫, isoamyl alcohol; ■, octane-1-ol; ▲, decane-1-ol. 3885

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34.673 % to 96.37 % with isoamyl alcohol (TDA = 0.1 mol·kg−1 to 0.5 mol·kg−1), from 28.02 % to 87.74 % with octane-1-ol (TDA = 0.1 mol·kg−1 to 0.4 mol·kg−1), and from 22.26 % to 71.87 % with decane-1-ol (TDA = 0.1 mol·kg−1 to 0.4 mol· kg−1). At the vicinity of 0.5 mol·kg−1 of TDA, almost all the amount of gibberellic acid (96 % w/w) is extracted by using isoamyl alcohol as solvent for this extraction. The interaction of acid molecules with the TDA−alcohol systems can be explained by the formation of different types of acid−amine complexes which are affected by the nature of the diluents in different ways. Using the Bizek approach two types of acid−amine complexes such as (acid)·(amine) and (acid)· (amine)2 are assumed to exist in the organic phase.18 Therefore, only K11 and K12 complexation constants are considered for the alcohols according to the theory proposed by Bizek. The values of the individual extraction constants (K11 and K12) are estimated and presented in Table 2. Therefore, the reactive extraction mechanism as per the Bizek approach18 for a proton-donating diluent (such as alcohol) can be described by the following reactions for the (acid)·(amine) and (acid)· (amine)2 solvates. K11

HA + R3N ↔ (HA)(R3N)

K11 =

[(HA)(R3N)] [HA][R3N]

LSER Model Results. The mechanism of an acid−amine system where separation takes place by H-bond formation can be presented by theoretical-based models of the mass action law including the physical interaction terms, or by using the concept of multiscale association, as well as by applying a generalized solvatochromic approach with linear solvation energy relationship (LSER).22 A modified version of LSER for predicting the extraction equilibria of an amine/diluent/acid system is given by Bizek et al.19 The prediction of the distribution coefficients of the acid by amine dissolved in solvents can be obtained by the LSER model equation and were described in Uslu’s earlier works.23 Briefly, the following equation can be used to describe the effect of diluents on the values of distribution coefficient (D). log10 D = log10 D0 + s(π * + dδ) + bβ + aα

(8)

where, π*, δ, β, and α are the solvatochromic parameters of the solvent. s, d, b, and a are regression coefficients dependent on the properties of solute. D0 represents the distribution coefficient for an ideal pure solvent. The values of the distribution coefficients can be correlated according to eq 8 with the solvatochromic parameters of the solvents24 as shown in Table 3. An error function known as the

(6)

Table 3. Solvatochromic Parameters for Alcohols24 K12

HA + 2R3N ← → (HA)(R3N)2

K12 =

[(HA)(R3N)2 ] [HA][R3N]2 (7)

[(HA)(R3N)] and [(HA)(R3N)2 ] are the concentrations of the 1:1 and 1:2 acid−TDA complex in the organic phase. [HA] is the undissociated acid concentration in the aqueous phase at equilibrium. [R3N] is the free TDA concentration in the organic phase.The resulting acid−amine complexes are supposed to be stabilized due to H-bonding with the solvent in the organic phase.20,21 The structure of acid−TDA complexes formed in the solvent phase can be explained by the principles described by Barrow and Yerger.21 According to them, the first acid molecule interacts directly with the amine to form an ion pair, and the −OH of the carboxyl of the second acid forms a Hbond with the conjugated CO of the carboxylate of the first acid to form a complex. Figure5 shows the complex formation of gibberellic acid and TDA in the presence of alcohol as solvating media.

solvents

π*

δ

β

α

isoamyl alcohol octane-1-ol decane-1-ol

0.40 0.40 0.40

0 0 0

0.84 0.81 0.81

0.84 0.77 0.72

root-mean-square deviation, rmsd, is defined from the difference between the experimental data and the predictions of the LSER model to estimate model parameters using following equation: 1 N

rmsd =

N

∑ (Dexp − Dcalc)2 (9)

i=1

where, Dexp and Dcalc are the experimental and calculated distribution coefficient. N is the number of experimental data points. The estimated values of LSER model parameters are presented in Table 4. Using the values of these parameters, Table 4. Values of LSER Model Parameters with Coefficient of Linear Regression R2 and Standard Error SE at a Temperature 298 K and a Pressure 1 atm log11D0

S

d

a

b

R2

SE

2.246

−4.024

7.183

18.221

−3.852

0.965

0.150

the D values are predicted and presented in Table 2 as Dcalc. The calculated values of D show a good correlation to the experimental data with R2 = 0.965 and SE = 0.15. The rmsd value of the LSER model is found to be 0.089. This value of rmsd shows that all predicted distribution coefficients agree well with each other, and also the agreements between predictions and measurements are acceptable, taking into consideration the experimental uncertainty. Therefore, it has been concluded that the distribution coefficients of gibberellic acid between water and amine + diluent system can be described by using the LSER model.

Figure 5. Complex formation of gibberellic acid and TDA: (a) acid; (b) complex. 3886

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(15) Uslu, H. Distribution of Gibberellic Acid from the Aqueous Phase to the Organic Phase. J. Chem. Eng. Data 2012, 57, 902−906. (16) Uslu, H.; Gob, A.; Kirbaslar, S. I. Phase Equilibria of (Water Plus Levunilic Acid Plus Alcohol) Ternary Systems. Fluid Phase Equilib. 2008, 273, 21−26. (17) Tuyun, A. F.; Uslu, H. Extraction Equilibria of Picolinic Acid from Aqueous Solution by Tridodecylamine (TDA). Desalination. 2011, 268, 134−140. (18) Bizek, V.; Horacek, J.; Kousova, M. Amine Extraction of Citric Acid: Effect of Diluent. Chem. Eng. Sci. 1993, 48, 1447−1457. (19) Holbrook, A.; Edge, W.; Bailey, F. Spectrophotometric Method for Determination of Gibberellic Acid. Adv. Chem. Ser. 1961, 28, 159− 167. (20) Yerger, E. A.; Barrow, G. M. Acid−Base Reactions in Nondissociating Solvents: n-Butylamine and Acetic Acid in Carbon Tetrachloride. J. Am. Chem. Soc. 1955, 77, 6206. (21) Yerger, E. A.; Barrow, G. M. Acid−Base Reactions in Nondissociating Solvents: Acetic Acid and Diethylamine in Carbon Tetrachloride and Chloroform. J. Am. Chem. Soc. 1955, 77, 4474− 4481. (22) Senol, A. Effect of Diluent on Amine Extraction of Acetic Acid: Modeling Considerations. Ind. Eng. Chem. Res. 2004, 43, 6496−6506. (23) Uslu, H. Linear Solvation Energy Relationship (LSER) Modeling and Kinetic Studies on Propionic Acid Reactive Extraction Using Alamine 336 in a Toluene Solution. Ind. Eng. Chem. Res. 2006, 45, 5788−5795. (24) Kamlet, M. J.; Abboud, J. L. M.; Abraham, M. H.; Taft, R. W. Linear Solvation Energy Relationships. 23. A Comprehensive Collection of the Solvatochromic Parameters, π*, β and α, and some Methods for Simplifying the Generalized Solvatochromic Equation. J. Org. Chem. 1983, 48, 2877−2887.

CONCLUSION Gibberellic acid extraction from aqueous solution has been studied by TDA in various diluents. Isoamyl alcohol shows a maximum extraction efficiency of about 96.37 %. The extraction equilibrium has been taken as a result of successive formation of two acid-amine species with stoichiometries of 1:1 and 1:2. The individual thermodynamic extraction constants K11 and K12 are also estimated from the regression of experimental data. The results show that the use of an amine with a polar diluent in the extraction is more efficient than physical extraction with diluent alone. Correlation of the results is suitable for the design of extractors. From the experimental results it can be concluded that the isoamyl alcohol is a suitable diluent and can be used with 0.5 mol·kg−1 of TDA concentration to extract gibberellic acid from dilute aqueous solution.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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