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Transformation of substituted cinnamic acids using l -cysteine metal complexes in aqueous media
Food Research International 41 (2008) 429–432
Contents lists available at ScienceDirect
Food Research International journal homepage: www.elsevier.com/locate/foodres
Transformation of substituted cinnamic acids using L-cysteine metal complexes in aqueous media Petra Moravcˇíková a, Peter Fodran b,*, Emil Kolek c, Vlasta Brezová d a Institute of Biochemistry, Nutrition and Health Protection, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-812 37 Bratislava, Slovak Republic b FLOP Company, Mandlova 37, SK-851 10 Bratislava, Slovak Republic c Food Research Institute, Priemyselná 4, SK-824 75 Bratislava, Slovak Republic d Institute of Physical Chemistry and Chemical Physics, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-812 37 Bratislava, Slovak Republic
a r t i c l e
i n f o
Article history: Received 3 October 2007 Accepted 24 February 2008
Keywords: Substituted cinnamic acids Oxidation in aqueous media Fe(II)– and Co(II)–cysteine complex Carbonyl compounds
a b s t r a c t 4-Hydroxycinnamic, 4-methoxycinnamic, ferulic and cinnamic acids were both non-oxidatively and oxidatively decarboxylated in alkaline aqueous media in the presence of L-cysteine–Fe(II) and L-cysteine–Co(II) heterogeneous catalysts using hydrogen peroxide or molecular oxygen. GC/MS analysis of diethylether extracts of reaction mixtures confirmed that the addition of hydrogen peroxide resulted predominantly in oxidative decarboxylation of substituted cinnamic acids, producing the corresponding carbonyl compounds (4-hydroxybenzaldehyde, 4-methoxybenzaldehyde, vanillin, benzaldehyde). On the other hand, saturation of this heterogeneous reaction system with molecular oxygen led to the formation of a variety of products, probably via peroxoacid anions or peroxoradical intermediates, e.g., ferulic acid was transformed to vinylguaiacol and vanillin with yields of 22% and 0.7%, respectively. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction In the last decades, the demand for ‘‘natural flavours” (Ashurst, 2005) has been increasing, e.g., the annual demand for vanillin in 2001 was 12 000 tons, but its natural production was only 1800 tons (Dignum, Kerlera, & Verpoorte, 2001). In many cases, such as terpenoids, it is possible to fulfil the quantitative requirements without problems because the flavours’ sources are essential oils which are produced in sufficiently large volumes (BUSINESS PLAN, ISO/TC 54, 2004). A considerable portion of flavours is produced industrially in the olefin oxidative degradation processes, where mainly carbonyl compounds are generated. A typical example is the pyrolysis of ricinoleic acid (Haller, 1907; Krafft, 1877) or the ozonolysis of oleic acid (Stoll & Rouvé, 1944). Ozonolysis may represent an acceptable method for the production of nonaldehyde which would be acceptable as a natural substance (Proposal for a regulation of the European Parliament COM 427 final, 2006); while in the case of ricinoleic acid, the reaction temperature is so high (above 150 °C) that the product cannot be affirmed as ‘‘natural”. The oxidative degradation of olefinic derivatives has enormous importance for clarifying a variety of biological processes, as well as for the production of natural flavours; therefore, significant
* Corresponding author. Tel.: +421 2 59325296; fax: +421 2 52496469. E-mail address: [email protected] (P. Fodran). 0963-9969/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2008.02.007
attention is focused on this topic (Donaghy, Kelly, & McKay, 1999; Falconnier et al., 1994; Mathew & Abraham, 2006; Mathew, Abraham, & Sudheesh, 2007). A problem arises, as most of the procedures, such as the oxidation of ferulic acid by methyltrioxorhenium catalyst (Herrmann, Weskamp, Zoller, & Fischer, 2000) or the electrochemical oxidation of ferulic acid (Trabelsi, Tahar, Trabelsi, & Abdelhedi, 2005), cannot be used in the preparation of vanillin that could be declared as a ‘‘natural substance”. Consequently, biotechnological methods are explored primarily for the oxidation of natural olefins, which would provide the desired aroma components for the food industry. In large scale, lipoxygenases and lyases present in green matter are applied in situ for oxidation of polyolefinic fatty acids (Agelopoulos, Hooper, Maniar, Pickett, & Wadhams, 1999; Buttery, Ling, & Light, 1987; Muller, Gautier, Dean, & Kuhn, 1995; Wang et al., 1996). However, the procedures employing enzyme catalysis, mainly for in situ enzymes utilization, have many disadvantages. The biggest of them is an enormous dilution of the reaction mixture and formation of multi-component mixtures wherein the individual components are isolated with difficulty (Kerler, Kohlen, Van der Vliet, Fitz, & Winkel, 2005). The main aim of this study was to develop a simple ‘‘green” technique for oxidative transformations of aromatic olefinic compounds by means of hydrogen peroxide or molecular oxygen in aqueous media. Transition metal ion (Fe(II) or Co(II)) complexes with the amino acid L-cysteine were used as the oxidative agent activators, inspired by structures of non-heme metalloprotein
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reactive centers (Lerch, 1994; Moravcˇíková, Brezová, Fodran, & Kolek, 2006). 2. Experimental 2.1. Materials Sodium hydroxide, CoSO4 7H2O, FeSO4 7H2O of analytical grade were purchased from Lachema (Czech Republic). Hydrogen peroxide of analytical grade (28%) from Peroxides (Sokolov, Czech Republic) was used. L-cysteine was obtained from Sigma. 4-Hydroxy-3-methoxycinnamic acid (ferulic acid, natural substance from rice bran), 4-hydroxycinnamic acid (Merck), 4-methoxycinnamic acid (Aldrich) and cinnamic acid (natural product from Styrax gum) were used without further purification. The structures of the investigated cinnamic acids are summarized in Table 1. 2.2. Instruments and procedures GC/MS analysis of products was performed by HP 5890II (USA) gas chromatograph coupled with a mass selective detector 5971A, using the following temperature program: oven – 60 °C (1 min), 10 °C min1 to 220 °C (10 min); column: DB-Wax, 30 m 0.25 mm 0.25 lm; carrier gas – helium, 35 kPa; TEM voltage: 1550 V; full scan 29–350 amu; A/D samples: 3; injection: 0.5 lL, split 30:1, temperature 250 °C; search libraries databases NIST05.L and Wiley Nist05.L. The relative concentration of individual products was evaluated from the peak area of GC/MS records. 2.3. L-cysteine–Fe(II) and L-cysteine–Co(II) complexes preparation Metal complexes were synthesized by a modified method published by Massabni, Corbi, Melnikov, Zacharias, and Rechenberg (2005). Disodium salt of L-cysteine, prepared from 0.02 mol of Lcysteine and 0.04 mol of NaOH in 50 mL of distilled water, was mixed with an equimolar amount of FeSO4 7H2O or CoSO4 7H2O in 20 mL of distilled water. All operations were carried out under inert atmosphere. After blending both solutions, the aqueous heterogeneous suspension of the corresponding metal complex was produced, which revealed a pink colour for Co(II) and a green colour for Fe(II), respectively. The suspension was then transferred under inert gas into a 100 mL volumetric flask, and was doubly diluted with distilled water. Finally, the prepared aqueous suspensions containing L-cysteine–Fe(II) or L-cysteine–Co(II) complexes were used as the oxidative catalysts. 2.4. Transformation of cinnamic acids with H2O2 The 0.4 molar solution of the sodium salt of cinnamic acid prepared by stoichiometric neutralization of the acid (0.02 mol) with NaOH in 50 mL of distilled water was placed in a two-neck round bottom flask equipped with a magnetic stirrer and an addition funnel, and 10 mL of the corresponding Co(II)- or Fe(II)-catalyst suspension was added under air. The oxidizing agent, H2O2 (2.5 mL
Table 1 Structures of investigated cinnamic acids
O OH R2 R1
R1
R2
Name
OH OCH3 OH H
H H OCH3 H
4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid (4-hydroxy-3-methoxycinnamic acid) Cinnamic acid
of 28% H2O2 in 50 mL H2O) was slowly added dropwise under vigorous stirring. After adding the full volume of hydrogen peroxide solution, the reaction mixture was stirred overnight at room temperature. In the experiments with cinnamic acid, the reaction time was shortened to 5 h, due to the generation of benzaldehyde, which is easily oxidized to benzoic acid. The reaction mixture was extracted twice with 100 mL of diethylether, after drying with Na2SO4 the solvent was evaporated, and the weight of extracted products was determined. 2.5. Transformation of cinnamic acids by molecular oxygen A three-neck round bottom flask was equipped with a tube for O2 insertion, an addition funnel and a Claisen condenser was placed in a heating mantel. The sodium salt of the corresponding cinnamic acid derivative (0.02 mol) prepared by stoichiometric neutralization of the acid with NaOH in 50 mL of distilled water was placed into the apparatus. Then, 10 mL of the corresponding Co(II)- or Fe(II)-catalyst suspension was added under air. Simultaneously, heating and oxygen flow were started. The process of distillation was regulated by heating. Distilled water was continuously added to the reaction mixture from the addition funnel to maintain a constant volume of the reaction mixture. The heating was turned off after 4 h. The distillate was extracted twice with 100 mL of diethylether, the combined extract was dried with Na2SO4 and then the solvent was removed. The analogous extraction and drying procedure was applied for the reaction residue remained in the round bottom flask. The weights of extracted products in distillate and in the reaction mixture extracts were evaluated. 3. Results and discussion The mechanisms of metabolic oxidative transformations of cinnamic acids were published previously by Gasson et al. (1998). Under the experimental conditions used in our study, the reaction is most probably initiated by the generation of oxygen-centred radical species via transition metal cations (Eq. (1)), as described previously for Fe(II) complexes (Halliwell & Gutteridge, 1999) cysteine—FeðIIÞ þ O2 $ fcysteine—FeðIIÞ—O2 $ cysteine—FeðIIIÞ—O 2 g
ð1Þ
Additionally, the simultaneous presence of Fe(II) species and hydrogen peroxide can result in the formation of reactive hydroxyl radicals via the Fenton mechanism (Halliwell & Gutteridge, 1999). Alternatively, reactive oxygen species (ROS) are produced by the decomposition of hydrogen peroxide in alkaline media, as was confirmed previously by EPR spectroscopy (Polovka, Brezová, & Staško, 2003). We proposed that generated superoxide anion-radicals, O 2 , play a significant role in the oxidative processes via nucleophilic attack on the carbonyl carbon (Braun, Maurette, & Oliveiros, 1986; Panda & Patnaik, 2001; Webster & Bond, 1997) producing the corresponding peroxoacid anions. The alternative reaction pathway in which olefinic double bond oxidation in the presence of O 2 /O2 resulting in the generation of peroxoradical intermediates is in agreement with aldehydes formation via decarboxylation process with side-chain oxidation (Ren et al., 2004). Table 2 summarizes reaction yields of products generated by oxidative and non-oxidative decarboxylation of substituted cinnamic acids in the oxygen-saturated systems activated by L-cysteine-metal complexes, as found by GC/MS analysis. The variety of reaction products identified demonstrates a multifaceted process, in which the different reaction pathways occur simultaneously as is summarized in Scheme 1. The formation of vinylguaiacol (4-hydroxy-3-methoxy-styrene) or 4-vinylanisol
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Table 2 Products of cinnamic acids transformation by molecular oxygen in the presence of cysteine–Fe(II) or cysteine–Co(II) complexes Reactant
Products
Cysteine–Fe(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid Cysteine–Co(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid *
Products yield (%) Distillate extract
Reaction mixture extract
Total
4-Hydroxybenzofuran* 4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde 4-Vinylanisol Vinylguaiacol Vanillin Benzaldehyde
5.9 0.2 4.5 0.1 12.6 – –
20.0 3.2 3.0 – 9.4 0.7 0.1
25.9 3.4 7.5 0.1 22.0 0.7 0.1
4-Hydroxybenzofuran 4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde 4-Vinylanisol Vinylguaiacol Vanillin Benzaldehyde
5.0 0.6 – 7.6 4.1 0.5 0.6
32.0 4.0 7.5 – 4.9 – 0.3
37.0 4.6 7.5 7.6 9.0 0.5 0.9
Main products are underlined.
Application of molecular oxygen in the presence of cysteine– Fe(II) or cysteine–Co(II) under the given experimental conditions resulted in the formation of reaction products in accordance with non-oxidative decarboxylation and cyclisation processes via radical mechanisms. The oxidative decarboxylation of cinnamic acids via peroxoradical intermediates may be also proposed, producing the corresponding aldehydes (Scheme 1). However, the results of GC/MS analysis demonstrated that in oxygen-saturated systems the non-oxidative decarboxylation reaction pathway predominated for 4-hydroxycinnamic, ferulic and cinnamic acids (Table 2).
(1-methoxy-4-vinyl-benzene) may be explained by the formation of intermediates with resonance structures resulting from the disrupted aromaticity of the benzene ring, which are decomposed in aqueous media forming carbon dioxide. It should be noted that in the case of 4-hydroxycinnamate anion, a further, competitive cyclization reaction leading to a benzofuran structure may also be observed (Scheme 1). However, for ferulic acid this reaction was not observed due to the strong positive inductive effect and resonance from the methoxy group.
O
O
CH2
oxygen O
OO
cysteine-Fe(II) or cysteine-Co(II) complex
R2
R2
R2
R1
R1
R1 O
R2
R1 OH OCH3 OH H
R2 H H OCH3 H
– 4-vinylanisol vinylguaiacol –
R1 R1 OH OCH3 OH H
H
O O R2 R1
R2 H H OCH3 H
4-hydroxybenzofuran – – –
O
hydrogen peroxide cysteine-Fe(II) or cysteine-Co(II) complex
R2 R1 R1 OH OCH3 OH H
R2 H H OCH3 H
4-hydroxybenzaldehyde 4-methoxybenzaldehyde vanillin benzaldehyde
Scheme 1. Alternative mechanisms of substituted cinnamic acids transformation with molecular oxygen or hydrogen peroxide in the presence of cysteine–Fe(II) and cysteine–Co(II) complex.
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Table 3 Products of cinnamic acids transformation by hydrogen peroxide in the presence of cysteine–Fe(II) or cysteine–Co(II) complexes identified in reaction mixture extracts Reactant
Products
Product yield (%)
Cysteine–Fe(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid
4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde Vanillin Benzaldehyde
6.3 19.5 67.9 26.1
Cysteine–Co(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid
4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde Vanillin Benzaldehyde
58.1 22.5 39.2 13.5
Reactions of cinnamate anions with hydrogen peroxide under given experimental conditions resulted in a less complex reaction mixture, since the main reaction products represent aldehydes produced by the oxidative decarboxylation of the corresponding cinnamic acids. The reaction yields and relative concentrations of products found by GC/MS analysis are listed in Table 3. We propose that under alkaline conditions, the reaction of cinnamic acids starts by an attack of hydrogen peroxide anion or generated oxide radical anion (O ) on the deactivated olefinic double bond (Temnikovová, 1962), and the produced intermediates are decomposed, forming carbonyl compounds in high yields (Scheme 1). Consequently, the yield of vanillin production upon ferulic acid oxidative decarboxylation by hydrogen peroxide with cysteine–Fe(II) or cysteine–Co(II) complex reached 67.9% and 39.2%, respectively. 4. Conclusions The reaction of cinnamic acids with molecular oxygen in aqueous alkaline media in the presence of cysteine–Fe(II) or cysteine– Co(II) complexes resulted in the formation of composite reaction mixtures corresponding to decarboxylation or cyclisation products, while oxidation of the olefinic double bond was limited. In contrast, the replacement of oxygen by hydrogen peroxide led predominantly to the oxidative decarboxylation of 4-hydroxycinnamic acid, 4-methoxycinnamic acid, ferulic acid and cinnamic acid producing the corresponding carbonyl compounds (4hydroxybenzaldehyde, 4-methoxybenzaldehyde, vanillin, and benzaldehyde) in high yields. Acknowledgement We thank the Scientific Grant Agency of the Ministry of Education of the Slovak Republic for financial support (Projects VEGA/1/ 0053/03 and VEGA/1/3488/06). References Agelopoulos, N. G., Hooper, A. M., Maniar, S. P., Pickett, J. A., & Wadhams, L. J. (1999). A novel approach for isolation of volatile chemicals released by individual leaves of a plant in situ. Journal of Chemical Ecology, 25, 1411–1425. Ashurst, P. (2005). The return of natural flavour. Functional Foods & Nutraceuticals. http://www.functionalingredientsmag.com/fimag/ articleDisplay.asp?strArticleId=705&strSite=FFNSite. Braun, A. M., Maurette, M. T., & Oliveiros, E. (1986). Technologie photochimique (Première edition). Lausanne: Presses polytechniques romandes (p. 467).
BUSINESS PLAN, ISO/TC 54, Essential oils, EXECUTIVE SUMMARY. (2004). http:// isotc.iso.org/livelink/livelink/fetch/2000/2122/687806/ ISO_TC_054__Essential_oils_.pdf?nodeid=971087&vernum=0. Buttery, R. G., Ling, L. C., & Light, D. M. (1987). Tomato leaf volatile aroma components. Journal of Agricultural and Food Chemistry, 35, 1039–1042. Dignum, M. J. W., Kerlera, J., & Verpoorte, R. (2001). Vanilla production: Technological, chemical and biosynthetic aspects. Food Reviews International, 17, 199–219. Donaghy, J. A., Kelly, P. F., & McKay, A. (1999). Conversion of ferulic acid to 4-vinyl guaiacol by yeasts isolated from unpasteurised apple juice. Journal of the Science of Food and Agriculture, 79, 453–456. Falconnier, B., Lapierre, C., Lesage-Meessen, L., Yonnet, G., Brunerie, P., ColonnaCeccaldi, B., et al. (1994). Vanillin as a product of ferulic acid biotransformation by the white-rot fungus Pycnoporus cinnabarinus I-937: Identification of metabolic pathways. Journal of Biotechnology, 37, 123–132. Gasson, M. J., Kitamura, Y., McLauchlan, W. R., Narbad, A., Parr, A. J., Parsons, E. L. H., et al. (1998). Metabolism of ferulic acid to vanillin: A bacterial gene of the enoyl-SCoA hydratase/isomerase superfamily encodes an enzyme for the hydration and cleavage of a hydroxycinnamic acid SCoA thioester. Journal of Biological Chemistry, 273, 4163–4170. Haller, A. (1907). Alcoolyse de l’huile de ricin. Comptes Rendus, 144, 462–466. Halliwell, B., & Gutteridge, J. M. C. (1999). Free radicals in biology and medicine (3rd edition). Oxford University Press. Herrmann, W. A., Weskamp, T., Zoller, J. P., & Fischer, R. W. (2000). Methyltrioxorhenium: Oxidative cleavage of CC-double bonds and its application in a highly efficient synthesis of vanillin from biological waste. Journal of Molecular Catalysis A: Chemistry, 153, 49–52. Kerler, J., Kohlen, E., Van der Vliet, A., Fitz, W., & Winkel, C. (2005). Method for the enzymatical preparation of flavours rich in C6–C10 aldehydes, US Patent 6864072, March 8. Krafft, F. (1877). Über die Destillation des Ricinusöls in luftverdünnten Raume. Berichte, 10, 2034–2036. Lerch, K. (1994). Tyrosinase: Molecular and active-site structure. In ACS symposium series 600, enzymatic browning and its prevention. Washington, DC, August 21– 26. Massabni, A. C., Corbi, P. P., Melnikov, P., Zacharias, M. A., & Rechenberg, H. R. (2005). Four new metal complexes with the amino acid deoxyalliin. Journal of the Brazilian Chemical Society, 16, 718–722. Mathew, S., & Abraham, T. E. (2006). Bioconversions of ferulic acid, an hydroxycinnamic acid. Critical Reviews in Microbiology, 32, 115–125. Mathew, S., Abraham, T. E., & Sudheesh, S. (2007). Rapid conversion of ferulic acid to 4-vinyl guaiacol and vanillin metabolites by Debaryomyces Hansenii. Journal of Molecular Catalysis B: Enzymatic, 44, 48–52. Moravcˇíková, P., Brezová, V., Fodran, P., & Kolek, E. (2006). Flavour compounds on the bases of natural olefins as precursor. In Conference proceedings: Safety and control of foods, part I (pp. 140–144). Nitra, Slovak Republic, April 5–6. Muller, B., Gautier, A., Dean, C., & Kuhn, J.-C. (1995). Process for the enzymatic preparation of aliphatic alcohols and aldehydes from linoleic acid, linolenic acid, or a natural precursor. US Patent 5464761, November 7. Panda, R., & Patnaik, C. (2001). Peroxy acid oxidations: A kinetic and mechanistic study of oxidative decarboxylation of (a keto acids by peroxomonophosphoric acid. Bulletin of Korean Chemical Society, 22, 909–913. Polovka, M., Brezová, V., & Staško, A. (2003). Antioxidant properties of tea investigated by EPR. Biophysical Chemistry, 106, 39–56. Proposal for a REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on flavourings and certain food ingredients with flavouring properties for use in and on foods and amending Council Regulation (EEC) No. 1576/89, Council Regulation (EEC) No. 1601/91, Regulation (EC) No. 2232/96 and Directive 2000/ 13/EC. Brussels SEC (2006)1042, SEC (2006)1043. http://www.msa.org.mt/fccd/ COM_2006_427.pdf. Ren, Y., Che, Y., Ma, W., Zhang, X., Shen, T., & Zhao, J. (2004). Selective photooxidation of styrene in organic-water biphasic media. New Journal of Chemistry, 28, 1464–1469. Stoll, M., & Rouvé, A. (1944). Étude des réactions secondaires de l´ozonolyse d´une liaison éthylénique. Helvetica Chimica Acta, 27, 950. Temnikovová, T. I. (1962). Theoretical fundamentals of organic chemistry (in Slovak). Bratislava: Slovak Academy of Science Press (p. 411). Trabelsi, S. K., Tahar, N. B., Trabelsi, B., & Abdelhedi, R. (2005). Electrochemical oxidation of ferulic acid in aqueous solutions at gold oxide and lead dioxide electrodes. Journal of Applied Electrochemistry, 35, 967–973. Wang, C. L., Chin, C. K., Ho, C. T., Hwang, C. F., Polashock, J. J., & Martin, C. E. (1996). Changes of fatty acids and fatty acid-derived flavor compounds by expressing the yeast (d 9 desaturase gene in tomato. Journal of Agricultural and Food Chemistry, 44, 3399–3402. Webster, R. D., & Bond, A. M. (1997). Different mechanism for the reaction of disubstituted aromatic esters and thioic S-esters with electrochemically generated superoxide. Journal of Chemical Society, Perkin Transactions, 2, 1075–1079.
Contents lists available at ScienceDirect
Food Research International journal homepage: www.elsevier.com/locate/foodres
Transformation of substituted cinnamic acids using L-cysteine metal complexes in aqueous media Petra Moravcˇíková a, Peter Fodran b,*, Emil Kolek c, Vlasta Brezová d a Institute of Biochemistry, Nutrition and Health Protection, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-812 37 Bratislava, Slovak Republic b FLOP Company, Mandlova 37, SK-851 10 Bratislava, Slovak Republic c Food Research Institute, Priemyselná 4, SK-824 75 Bratislava, Slovak Republic d Institute of Physical Chemistry and Chemical Physics, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-812 37 Bratislava, Slovak Republic
a r t i c l e
i n f o
Article history: Received 3 October 2007 Accepted 24 February 2008
Keywords: Substituted cinnamic acids Oxidation in aqueous media Fe(II)– and Co(II)–cysteine complex Carbonyl compounds
a b s t r a c t 4-Hydroxycinnamic, 4-methoxycinnamic, ferulic and cinnamic acids were both non-oxidatively and oxidatively decarboxylated in alkaline aqueous media in the presence of L-cysteine–Fe(II) and L-cysteine–Co(II) heterogeneous catalysts using hydrogen peroxide or molecular oxygen. GC/MS analysis of diethylether extracts of reaction mixtures confirmed that the addition of hydrogen peroxide resulted predominantly in oxidative decarboxylation of substituted cinnamic acids, producing the corresponding carbonyl compounds (4-hydroxybenzaldehyde, 4-methoxybenzaldehyde, vanillin, benzaldehyde). On the other hand, saturation of this heterogeneous reaction system with molecular oxygen led to the formation of a variety of products, probably via peroxoacid anions or peroxoradical intermediates, e.g., ferulic acid was transformed to vinylguaiacol and vanillin with yields of 22% and 0.7%, respectively. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction In the last decades, the demand for ‘‘natural flavours” (Ashurst, 2005) has been increasing, e.g., the annual demand for vanillin in 2001 was 12 000 tons, but its natural production was only 1800 tons (Dignum, Kerlera, & Verpoorte, 2001). In many cases, such as terpenoids, it is possible to fulfil the quantitative requirements without problems because the flavours’ sources are essential oils which are produced in sufficiently large volumes (BUSINESS PLAN, ISO/TC 54, 2004). A considerable portion of flavours is produced industrially in the olefin oxidative degradation processes, where mainly carbonyl compounds are generated. A typical example is the pyrolysis of ricinoleic acid (Haller, 1907; Krafft, 1877) or the ozonolysis of oleic acid (Stoll & Rouvé, 1944). Ozonolysis may represent an acceptable method for the production of nonaldehyde which would be acceptable as a natural substance (Proposal for a regulation of the European Parliament COM 427 final, 2006); while in the case of ricinoleic acid, the reaction temperature is so high (above 150 °C) that the product cannot be affirmed as ‘‘natural”. The oxidative degradation of olefinic derivatives has enormous importance for clarifying a variety of biological processes, as well as for the production of natural flavours; therefore, significant
* Corresponding author. Tel.: +421 2 59325296; fax: +421 2 52496469. E-mail address: [email protected] (P. Fodran). 0963-9969/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2008.02.007
attention is focused on this topic (Donaghy, Kelly, & McKay, 1999; Falconnier et al., 1994; Mathew & Abraham, 2006; Mathew, Abraham, & Sudheesh, 2007). A problem arises, as most of the procedures, such as the oxidation of ferulic acid by methyltrioxorhenium catalyst (Herrmann, Weskamp, Zoller, & Fischer, 2000) or the electrochemical oxidation of ferulic acid (Trabelsi, Tahar, Trabelsi, & Abdelhedi, 2005), cannot be used in the preparation of vanillin that could be declared as a ‘‘natural substance”. Consequently, biotechnological methods are explored primarily for the oxidation of natural olefins, which would provide the desired aroma components for the food industry. In large scale, lipoxygenases and lyases present in green matter are applied in situ for oxidation of polyolefinic fatty acids (Agelopoulos, Hooper, Maniar, Pickett, & Wadhams, 1999; Buttery, Ling, & Light, 1987; Muller, Gautier, Dean, & Kuhn, 1995; Wang et al., 1996). However, the procedures employing enzyme catalysis, mainly for in situ enzymes utilization, have many disadvantages. The biggest of them is an enormous dilution of the reaction mixture and formation of multi-component mixtures wherein the individual components are isolated with difficulty (Kerler, Kohlen, Van der Vliet, Fitz, & Winkel, 2005). The main aim of this study was to develop a simple ‘‘green” technique for oxidative transformations of aromatic olefinic compounds by means of hydrogen peroxide or molecular oxygen in aqueous media. Transition metal ion (Fe(II) or Co(II)) complexes with the amino acid L-cysteine were used as the oxidative agent activators, inspired by structures of non-heme metalloprotein
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reactive centers (Lerch, 1994; Moravcˇíková, Brezová, Fodran, & Kolek, 2006). 2. Experimental 2.1. Materials Sodium hydroxide, CoSO4 7H2O, FeSO4 7H2O of analytical grade were purchased from Lachema (Czech Republic). Hydrogen peroxide of analytical grade (28%) from Peroxides (Sokolov, Czech Republic) was used. L-cysteine was obtained from Sigma. 4-Hydroxy-3-methoxycinnamic acid (ferulic acid, natural substance from rice bran), 4-hydroxycinnamic acid (Merck), 4-methoxycinnamic acid (Aldrich) and cinnamic acid (natural product from Styrax gum) were used without further purification. The structures of the investigated cinnamic acids are summarized in Table 1. 2.2. Instruments and procedures GC/MS analysis of products was performed by HP 5890II (USA) gas chromatograph coupled with a mass selective detector 5971A, using the following temperature program: oven – 60 °C (1 min), 10 °C min1 to 220 °C (10 min); column: DB-Wax, 30 m 0.25 mm 0.25 lm; carrier gas – helium, 35 kPa; TEM voltage: 1550 V; full scan 29–350 amu; A/D samples: 3; injection: 0.5 lL, split 30:1, temperature 250 °C; search libraries databases NIST05.L and Wiley Nist05.L. The relative concentration of individual products was evaluated from the peak area of GC/MS records. 2.3. L-cysteine–Fe(II) and L-cysteine–Co(II) complexes preparation Metal complexes were synthesized by a modified method published by Massabni, Corbi, Melnikov, Zacharias, and Rechenberg (2005). Disodium salt of L-cysteine, prepared from 0.02 mol of Lcysteine and 0.04 mol of NaOH in 50 mL of distilled water, was mixed with an equimolar amount of FeSO4 7H2O or CoSO4 7H2O in 20 mL of distilled water. All operations were carried out under inert atmosphere. After blending both solutions, the aqueous heterogeneous suspension of the corresponding metal complex was produced, which revealed a pink colour for Co(II) and a green colour for Fe(II), respectively. The suspension was then transferred under inert gas into a 100 mL volumetric flask, and was doubly diluted with distilled water. Finally, the prepared aqueous suspensions containing L-cysteine–Fe(II) or L-cysteine–Co(II) complexes were used as the oxidative catalysts. 2.4. Transformation of cinnamic acids with H2O2 The 0.4 molar solution of the sodium salt of cinnamic acid prepared by stoichiometric neutralization of the acid (0.02 mol) with NaOH in 50 mL of distilled water was placed in a two-neck round bottom flask equipped with a magnetic stirrer and an addition funnel, and 10 mL of the corresponding Co(II)- or Fe(II)-catalyst suspension was added under air. The oxidizing agent, H2O2 (2.5 mL
Table 1 Structures of investigated cinnamic acids
O OH R2 R1
R1
R2
Name
OH OCH3 OH H
H H OCH3 H
4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid (4-hydroxy-3-methoxycinnamic acid) Cinnamic acid
of 28% H2O2 in 50 mL H2O) was slowly added dropwise under vigorous stirring. After adding the full volume of hydrogen peroxide solution, the reaction mixture was stirred overnight at room temperature. In the experiments with cinnamic acid, the reaction time was shortened to 5 h, due to the generation of benzaldehyde, which is easily oxidized to benzoic acid. The reaction mixture was extracted twice with 100 mL of diethylether, after drying with Na2SO4 the solvent was evaporated, and the weight of extracted products was determined. 2.5. Transformation of cinnamic acids by molecular oxygen A three-neck round bottom flask was equipped with a tube for O2 insertion, an addition funnel and a Claisen condenser was placed in a heating mantel. The sodium salt of the corresponding cinnamic acid derivative (0.02 mol) prepared by stoichiometric neutralization of the acid with NaOH in 50 mL of distilled water was placed into the apparatus. Then, 10 mL of the corresponding Co(II)- or Fe(II)-catalyst suspension was added under air. Simultaneously, heating and oxygen flow were started. The process of distillation was regulated by heating. Distilled water was continuously added to the reaction mixture from the addition funnel to maintain a constant volume of the reaction mixture. The heating was turned off after 4 h. The distillate was extracted twice with 100 mL of diethylether, the combined extract was dried with Na2SO4 and then the solvent was removed. The analogous extraction and drying procedure was applied for the reaction residue remained in the round bottom flask. The weights of extracted products in distillate and in the reaction mixture extracts were evaluated. 3. Results and discussion The mechanisms of metabolic oxidative transformations of cinnamic acids were published previously by Gasson et al. (1998). Under the experimental conditions used in our study, the reaction is most probably initiated by the generation of oxygen-centred radical species via transition metal cations (Eq. (1)), as described previously for Fe(II) complexes (Halliwell & Gutteridge, 1999) cysteine—FeðIIÞ þ O2 $ fcysteine—FeðIIÞ—O2 $ cysteine—FeðIIIÞ—O 2 g
ð1Þ
Additionally, the simultaneous presence of Fe(II) species and hydrogen peroxide can result in the formation of reactive hydroxyl radicals via the Fenton mechanism (Halliwell & Gutteridge, 1999). Alternatively, reactive oxygen species (ROS) are produced by the decomposition of hydrogen peroxide in alkaline media, as was confirmed previously by EPR spectroscopy (Polovka, Brezová, & Staško, 2003). We proposed that generated superoxide anion-radicals, O 2 , play a significant role in the oxidative processes via nucleophilic attack on the carbonyl carbon (Braun, Maurette, & Oliveiros, 1986; Panda & Patnaik, 2001; Webster & Bond, 1997) producing the corresponding peroxoacid anions. The alternative reaction pathway in which olefinic double bond oxidation in the presence of O 2 /O2 resulting in the generation of peroxoradical intermediates is in agreement with aldehydes formation via decarboxylation process with side-chain oxidation (Ren et al., 2004). Table 2 summarizes reaction yields of products generated by oxidative and non-oxidative decarboxylation of substituted cinnamic acids in the oxygen-saturated systems activated by L-cysteine-metal complexes, as found by GC/MS analysis. The variety of reaction products identified demonstrates a multifaceted process, in which the different reaction pathways occur simultaneously as is summarized in Scheme 1. The formation of vinylguaiacol (4-hydroxy-3-methoxy-styrene) or 4-vinylanisol
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Table 2 Products of cinnamic acids transformation by molecular oxygen in the presence of cysteine–Fe(II) or cysteine–Co(II) complexes Reactant
Products
Cysteine–Fe(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid Cysteine–Co(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid *
Products yield (%) Distillate extract
Reaction mixture extract
Total
4-Hydroxybenzofuran* 4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde 4-Vinylanisol Vinylguaiacol Vanillin Benzaldehyde
5.9 0.2 4.5 0.1 12.6 – –
20.0 3.2 3.0 – 9.4 0.7 0.1
25.9 3.4 7.5 0.1 22.0 0.7 0.1
4-Hydroxybenzofuran 4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde 4-Vinylanisol Vinylguaiacol Vanillin Benzaldehyde
5.0 0.6 – 7.6 4.1 0.5 0.6
32.0 4.0 7.5 – 4.9 – 0.3
37.0 4.6 7.5 7.6 9.0 0.5 0.9
Main products are underlined.
Application of molecular oxygen in the presence of cysteine– Fe(II) or cysteine–Co(II) under the given experimental conditions resulted in the formation of reaction products in accordance with non-oxidative decarboxylation and cyclisation processes via radical mechanisms. The oxidative decarboxylation of cinnamic acids via peroxoradical intermediates may be also proposed, producing the corresponding aldehydes (Scheme 1). However, the results of GC/MS analysis demonstrated that in oxygen-saturated systems the non-oxidative decarboxylation reaction pathway predominated for 4-hydroxycinnamic, ferulic and cinnamic acids (Table 2).
(1-methoxy-4-vinyl-benzene) may be explained by the formation of intermediates with resonance structures resulting from the disrupted aromaticity of the benzene ring, which are decomposed in aqueous media forming carbon dioxide. It should be noted that in the case of 4-hydroxycinnamate anion, a further, competitive cyclization reaction leading to a benzofuran structure may also be observed (Scheme 1). However, for ferulic acid this reaction was not observed due to the strong positive inductive effect and resonance from the methoxy group.
O
O
CH2
oxygen O
OO
cysteine-Fe(II) or cysteine-Co(II) complex
R2
R2
R2
R1
R1
R1 O
R2
R1 OH OCH3 OH H
R2 H H OCH3 H
– 4-vinylanisol vinylguaiacol –
R1 R1 OH OCH3 OH H
H
O O R2 R1
R2 H H OCH3 H
4-hydroxybenzofuran – – –
O
hydrogen peroxide cysteine-Fe(II) or cysteine-Co(II) complex
R2 R1 R1 OH OCH3 OH H
R2 H H OCH3 H
4-hydroxybenzaldehyde 4-methoxybenzaldehyde vanillin benzaldehyde
Scheme 1. Alternative mechanisms of substituted cinnamic acids transformation with molecular oxygen or hydrogen peroxide in the presence of cysteine–Fe(II) and cysteine–Co(II) complex.
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Table 3 Products of cinnamic acids transformation by hydrogen peroxide in the presence of cysteine–Fe(II) or cysteine–Co(II) complexes identified in reaction mixture extracts Reactant
Products
Product yield (%)
Cysteine–Fe(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid
4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde Vanillin Benzaldehyde
6.3 19.5 67.9 26.1
Cysteine–Co(II) 4-Hydroxycinnamic acid 4-Methoxycinnamic acid Ferulic acid Cinnamic acid
4-Hydroxybenzaldehyde 4-Methoxybenzaldehyde Vanillin Benzaldehyde
58.1 22.5 39.2 13.5
Reactions of cinnamate anions with hydrogen peroxide under given experimental conditions resulted in a less complex reaction mixture, since the main reaction products represent aldehydes produced by the oxidative decarboxylation of the corresponding cinnamic acids. The reaction yields and relative concentrations of products found by GC/MS analysis are listed in Table 3. We propose that under alkaline conditions, the reaction of cinnamic acids starts by an attack of hydrogen peroxide anion or generated oxide radical anion (O ) on the deactivated olefinic double bond (Temnikovová, 1962), and the produced intermediates are decomposed, forming carbonyl compounds in high yields (Scheme 1). Consequently, the yield of vanillin production upon ferulic acid oxidative decarboxylation by hydrogen peroxide with cysteine–Fe(II) or cysteine–Co(II) complex reached 67.9% and 39.2%, respectively. 4. Conclusions The reaction of cinnamic acids with molecular oxygen in aqueous alkaline media in the presence of cysteine–Fe(II) or cysteine– Co(II) complexes resulted in the formation of composite reaction mixtures corresponding to decarboxylation or cyclisation products, while oxidation of the olefinic double bond was limited. In contrast, the replacement of oxygen by hydrogen peroxide led predominantly to the oxidative decarboxylation of 4-hydroxycinnamic acid, 4-methoxycinnamic acid, ferulic acid and cinnamic acid producing the corresponding carbonyl compounds (4hydroxybenzaldehyde, 4-methoxybenzaldehyde, vanillin, and benzaldehyde) in high yields. Acknowledgement We thank the Scientific Grant Agency of the Ministry of Education of the Slovak Republic for financial support (Projects VEGA/1/ 0053/03 and VEGA/1/3488/06). References Agelopoulos, N. G., Hooper, A. M., Maniar, S. P., Pickett, J. A., & Wadhams, L. J. (1999). A novel approach for isolation of volatile chemicals released by individual leaves of a plant in situ. Journal of Chemical Ecology, 25, 1411–1425. Ashurst, P. (2005). The return of natural flavour. Functional Foods & Nutraceuticals. http://www.functionalingredientsmag.com/fimag/ articleDisplay.asp?strArticleId=705&strSite=FFNSite. Braun, A. M., Maurette, M. T., & Oliveiros, E. (1986). Technologie photochimique (Première edition). Lausanne: Presses polytechniques romandes (p. 467).
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