Reactive Extraction of Cyclic Polyhydroxy Carboxylic Acid Using

Article pubs.acs.org/jced

Reactive Extraction of Cyclic Polyhydroxy Carboxylic Acid Using Trioctylamine (TOA) in Different Diluents Amaç Fatih Tuyun* and Hasan Uslu Chemical Engineering Department, Engineering & Architecture Faculty, Beykent University, Ayazağa, Iṡ tanbul, Turkey ABSTRACT: Quinic acid is a cyclic polyhydroxy carboxylic acid compound that is implicated in the perceived acidity of raw materials. It is a constituent of the tannins. In this work, the extraction of quinic acid was studied by using trioctylamine (TOA) with respect to the functional groups. The quinic acid extraction experiments employed TOA + solvent mixtures or pure solvent. The solvents included two acetates, two alcohols, and two ketones. The obtained experimental results of the extraction experiments are reported as distribution coefficients, KD, loading factors, Z, and extraction efficiencies, E. The highest synergistic extraction efficiency was found to be 83.191 % for the TOA + 1-octanol extractant system, which had a KD value of 4.949 and a Z value of 0.258.

1. INTRODUCTION Quinic acid [(1R,3R,4R,5R)-(−)-1,3,4,5-tetrahydroxycyclohexane-1-carboxylic acid] is a cyclitol. It is a crystal obtained from cinchona bark, coffee, and other products and made synthetically by hydrolysis of acid. It is a constituent of the tara tannins. Quinic acid is a precursor of shikimic acid, which is involved in the synthesis of lots of natural compounds.1 It is a white crystal compound that is soluble in water, alcohols, and glacial acetic acid but unfortunately is insoluble in ether. The acid is very common in the plant kingdom in the free form or as esters,1 such as in leaves of tobacco, cinchona bark, coffee, and carrot. Also, the acid is predominant among the metabolites.2 The acid has five functional groups that can coordinate with metals.3 It can also yield versatile kinds of salts and is an important precursor for the asymmetric multistep synthesis of many natural and other compounds.4 Quinic acid is commonly used as a chiral strating material for the synthesis of active compounds. An example of a final product is the antiviral drug oseltamivir, a neuraminidase inhibitor used in treatment and prophylaxis. The ion−ion and ion−solvent interactions (i.e., the behavior of the electrolytes in solution) can be important depending on the transport properties (conductivity, transference number, diffusion coefficient, and ionic mobility) of these electrolytes in solutions.5−11 Because of the importance of quinic acid and in continuation of our research, the present study aimed to investigate the reactive extraction of quinic acid in different media through the determination of the distribution coefficients, KD, loading factors, Z, and extraction efficiencies, E, of quinic acid.12 Physical extraction with highly pure organic solvents has not been confirmed to be suitable for the recovery of some organic acids without amine and phosphorus compounds. Since organic acids have high affinity for water, they give low distribution coefficients. The pure diluents could not extract the solute, while the modifier influences the extracting power of the amine. When the salts of amines with carboxylic acids are slightly soluble in the aqueous medium, a critical role of the modifier is to improve the solubility of the salts in the extracted phase.13 Physical extraction of the acid by a suitable extractant has been © 2012 American Chemical Society

found to be an important alternative process. Some scientists14−16 have examined the recovery of carboxylic acids by liquid−liquid equilibria (LLE) with aliphatic tertiary amines dissolved in organic media. The behavior and base strength of versatile extractant types in the reactive extraction in toluene diluents has been reported.17 It is noteworthy that the base strength increased in the following order: tertiary > secondary. Extraction of carboxylic acids using some aliphatic amines and hydrogels has been successful, and some reports could be found in the literature hitherto.18−33

2. THEORY The extraction of an acid (HA) with a trialkylamine (R3N) can be described by the following reaction: HA (1) + *R3N (2) ⇄ *(HA) ·(R3N) (3)

(1)

where HA represents the nondissociated portion of the acid present in the aqueous phase and species in the organic phase are marked with asterisks (*). Reaction 1 can be characterized by the overall thermodynamic extraction constant, K. The loading factor for the extractant, Z, is defined as the total concentration of the acid in the organic phase (CHA * ) divided by the total concentration of the amine in the organic phase (CR*3N):

* /C R* N Z = C HA 3

(2)

The distribution coefficient, KD, for extraction of the acid from the aqueous phase into the organic phase is given by * /C HA KD = C HA

(3)

in which CHA is the concentration of the acid in the aqueous phase after the extraction. Finally, the extraction efficiency, E, is expressed as Received: December 13, 2011 Accepted: June 20, 2012 Published: July 5, 2012 2143

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Journal of Chemical & Engineering Data E = [1 − (C HA /C HA,0)] × 100 %

Article

Table 1. Results of Physical Extraction of Quinic Acid Using Pure Solventsa

(4)

where CHA,0 is the initial concentration of acid in the aqueous phase.

CQA *

3. MATERIALS AND EXPERIMENTAL PROCEDURE 3.1. Materials. Trioctylamine (TOA) (M = 353.67 g·mol−1, mass-fraction purity > 0.99) and quinic acid (QA) (mass fraction purity > 0.98) were purchased from Merck (Darmstadt, Germany). Alcohols (octan-1-ol and decan-1-ol), ketones (heptan-2-one and octan-2-one), and esters (ethyl acetate and hexyl acetate) (mass-fraction purity > 0.99) were supplied from Merck and Fluka. All of the chemicals were used without further purification. 3.2. Experimental Procedure. Quinic acid was dissolved in distilled water to prepare solutions with initial acid concentrations of 0.357 mol·kg−1. The initial organic phases were prepared by dissolving TOA in the diluents to produce solutions with approximately constant concentrations. The LLE experiments were conducted in Erlenmeyer flasks. Each extraction was done in a closed 50 mL Erlenmeyer flask into which both the aqueous quinic acid solution and the organic phase (pure solvent or solvent enriched with TOA) were introduced. The concentration of TOA in the diluent as an organic solvent was varied between 0 (pure solvent) and 1.148 mol·kg−1. After the introduction of the two phases into the Erlenmeyer flasks, the flasks were agitated at 100 rpm in an orbital shaking incubator (GFL) for 2.5 h at 25 ± 0.1 °C to ensure equilibrium. After agitation, the Erlenmeyer flasks were transferred into trays, and a settling time of at least 6 h was allowed and shown to be sufficient. After the settling period, samples of the aqueous phase were taken. The accuracy of the analytical method was determined to be ± 3 %. The concentration of quinic acid in the aqueous phase was determined by titration with aqueous 0.1 mol·kg−1 sodium hydroxide (relative uncertainty 1 %) in the presence of phenolphthalein as the indicator. In most cases, the relative uncertainty of the aqueous phase determination did not exceed 3 %. The pH of the aqueous phase was determined with a pH meter (Mettler Toledo) with an uncertainty of 1 %.

E

solvent

pHaq

mol·kg−1

KD

%

ethyl acetate hexyl acetate heptan-2-one octan-2-one octan-1-ol decan-1-ol

2.40 2.34 2.35 2.34 2.32 2.32

0.001 0.001 0.001 0.000 0.007 0.004

0.003 0.002 0.003 0.000 0.020 0.010

0.333 0.167 0.333 0.000 1.995 0.982

Symbols: pHaq is the pH of the aqueous phase after extraction; C*QA is the total concentration of quinic acid in the organic phase; KD is the distribution coefficient; E is the extraction efficiency.

a

Table 2. Results of Extraction of Quinic Acid Using TOA/ Solvent Systemsa CTOA *

E

mol·kg−1

pHaq

mol·kg−1

KD

Z

%

ethyl acetate

0.230 0.460 0.690 0.920 1.148 0.230 0.460 0.690 0.920 1.148 0.230 0.460 0.690 0.920 1.148 0.230 0.460 0.690 0.920 1.148 0.230 0.460 0.690 0.920 1.148 0.230 0.460 0.690 0.920 1.148

2.43 2.54 2.55 2.57 2.59 2.36 2.39 2.40 2.42 2.44 2.37 2.40 2.42 2.43 2.45 2.37 2.40 2.47 2.48 2.49 2.44 2.57 2.67 2.68 2.70 2.41 2.62 2.67 2.68 2.69

0.041 0.182 0.215 0.218 0.238 0.005 0.009 0.017 0.028 0.038 0.005 0.054 0.106 0.119 0.125 0.001 0.002 0.022 0.037 0.040 0.103 0.234 0.284 0.294 0.297 0.069 0.221 0.263 0.266 0.270

0.131 1.036 1.511 1.560 2.008 0.013 0.026 0.049 0.084 0.118 0.015 0.179 0.423 0.498 0.542 0.003 0.007 0.065 0.116 0.125 0.407 1.901 3.867 4.648 4.949 0.238 1.622 2.807 2.920 3.115

0.180 0.395 0.311 0.236 0.207 0.021 0.019 0.024 0.030 0.033 0.023 0.118 0.154 0.129 0.109 0.005 0.005 0.032 0.040 0.034 0.449 0.509 0.411 0.319 0.258 0.299 0.480 0.381 0.289 0.235

11.565 50.880 60.168 60.936 66.754 1.331 2.493 4.647 7.784 10.581 1.497 15.165 29.716 33.232 35.142 0.333 0.666 6.135 10.417 11.073 28.915 65.533 79.453 82.296 83.191 19.234 61.858 73.735 74.490 75.696

hexyl acetate

heptan-2-one

octan-2-one

octan-1-ol

4. RESULTS AND DISCUSSION Since most of extractants used for reactive extraction are toxic for bacteria in the bioreactor, it was preferable to use a low concentration (around 10 %) of these in the present study. The results of the reactive extractions of quinic acid using TOA in different diluents are presented in Tables 1 and 2. It can be seen that increasing the extractant concentration increases the distribution coefficient. The physical extraction of quinic acid was studied first to obtain a better understanding of the effect of the amine on the extraction of quinic acid (reactive extraction). Table 1 and Figure 1 present the results for extraction of quinic acid by pure solvents without TOA. 1-Octanol exhibited the highest extraction efficiency (E = 1.995 %) among the pure solvents. In the diluent categories, alcohols were more effective than the others since they have higher polarities. The reactive extraction of quinic acid by TOA dissolved in alcohols (1-octanol and 1decanol), ketones (2-heptanone and 2-octanone), and esters (ethyl acetate and hexyl acetate) was studied next. Equilibrium data for the reactive extraction are presented in Table 2. The prepared constant concentrations of TOA in various solvents

CQA *

solvent

decan-1-ol

Symbols: CTOA * is the total concentration of trioctylamine in the organic phase; pHaq is the pH of the aqueous phase after the * is the total concentration of quinic acid in the organic extraction; CQA phase; KD is the distribution coefficient; Z is the loading factor; E is the extraction efficiency. a

were between 0.230 mol·kg−1 and 1.148 mol·kg−1. The quinic acid concentration in the initial aqueous phase was 0.357 mol·kg−1. According to Table 2 and Figure 2, the distribution coefficients for quinic acid extraction by TOA in the various solvents were obviously ordered as follows: In esters: ethyl acetate ≫ hexyl acetate In ketones: 2-heptanone ≫2-octanone 2144

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Figure 4 displays the changes in the extraction efficiency of TOA/diluent mixtures with increasing initial concentration of

Figure 1. Distribution coefficients of quinic acid between water and each of the solvents used in this study.

Figure 4. Variation of extraction efficiency with concentration of TOA in different individual diluting solvents: ◇, ethyl acetate; ◆, hexyl acetate; ○, heptan-2-one; ●, octan-2-one; □, octan-1-ol; ■, decan-1ol.

TOA in the organic phase. The highest extraction efficiency of quinic acid was found to be E = 83.191 % using 1-octanol at 1.148 mol·kg−1 initial concentration of TOA. The acid concentration in the organic phase at equilibrium, CQA * , increased from 0.103 mol·kg−1 to 0.297 mol·kg−1 with increasing concentration of TOA from 0.230 mol·kg−1 to 1.148 mol·kg−1. The distribution coefficient increased from 0.407 to 4.949 with increasing initial TOA concentration among the all diluents used in this study (Figure 2). Obviously, it can be seen from Table 2 that increasing the amine concentration brings about gradual increase in the extraction efficiency. At 1.148 mol·kg−1, the maximum E values of 83.191 % and 75.696 % were obtained using 1-octanol and 1-decanol, respectively. The equilibrium data on the distribution of quinic acid between water and TOA dissolved in 2-heptanone and 2octanone (Table 2) show that the extraction power of TOA is more effective in the presence of 2-heptanone than 2-octanone. The extraction of quinic acid using tridodecylamine (TDA) in the presence of esters, ketones, and alcohols was studied previously.23 Different parameters such as the distribution coefficient, degree of extraction, and loading ratio were determined. The highest synergistic distribution coefficient was found for the TDA + octan-1-ol extractant system (KD = 2.022), while the highest value of KD in this study is 4.949 for TOA + octan-1-ol at 1.148 mol·kg−1. The high affinity of the acids for water increases the difficulty of product recovery and purification. In previous work, malic acid (a hydroxydicarboxylic acid) was extracted from aqueous solution by different solvents with and without TOA.34 The TOA was dissolved in five different esters, five different alcohols, and two different ketones. The most effective solvent was determined to be isoamyl alcohol with an extraction efficiency of 94.5 %, while the highest extraction efficiency in this study was 83.19 % for TOA + octan-1-ol. This shows that if there is a OH group or a COOH group in the extractant, TOA gives a high distribution coefficient and extraction efficiency in the reactive extraction. Reactive extraction of carboxylic acids increases in going from mono- to di- to tricarboxylic acids because TOA and the COOH groups give complexes by means of hydrogen bonds.

Figure 2. Variation of distribution coefficients with concentration of TOA in different individual diluting solvents: ◇, ethyl acetate; ◆, hexyl acetate; ○, heptan-2-one; ●, octan-2-one; □, octan-1-ol; ■, decan-1-ol.

In alcohols: 1-octanol >1-decanol In contrast to the variation of the KD values, Figure 3 obviously shows that the loading factors gradually decreased with increasing TOA concentration in the organic phase. At low concentrations, overloadings (Z > 1) have been observed in the literature.19

Figure 3. Variation of the loading factor with the concentration of TOA in different individual diluting solvents: ◇, ethyl acetate; ◆, hexyl acetate; ○, heptan-2-one; ●, octan-2-one; □, octan-1-ol; ■, decan-1-ol. 2145

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Therefore, the chemical structures of the acid and amine are very important.

5. CONCLUSION The reactive extraction of quinic acid using trioctylamine dissolved in six diluents was investigated. The distribution coefficients, loading factors, and extraction efficiencies were obtained for these extraction systems. The highest synergistic extraction efficiency, E = 83.19 %, was found for TOA + 1octanol extractant system, with a distribution coefficient of KD = 4.949. Polar diluents have been found to be more convenient diluents than inert (nonpolar) ones, as shown by their higher distribution coefficients. However, active polar diluents or diluents containing proton-donating groups such as alcohols have been shown to be the most suitable diluents for extraction because they give the highest distribution coefficients, resulting from the formation of solvates through specific hydrogen bonding between the proton of the diluent and the acid−amine complex. The use of polar diluents with trioctylamine for the extraction of quinic acid is efficient.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +90 212 4441997. Fax: +90 212 8675066. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Board of Trustees of Beykent University for supplying the equipment and materials.

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REFERENCES

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dx.doi.org/10.1021/je201311n | J. Chem. Eng. Data 2012, 57, 2143−2146