Neryl acetate synthesis from nerol esterification with acetic anhydride by heterogeneous catalysis using ion exchange resin
Graphical abstract
Introduction
Esters play an important role in the fine chemical industry as they are widely used in solvents, lubricating oils, medicines and essences [1]. They can be obtained by different methods such as natural source extraction, chemical synthesis and biotransformation [2]. Chemical synthesis by solvolytic esterification includes the direct conversion of carboxylic compounds through a reaction with hydroxylic compounds, such as the direct esterification of acids, the alkylation of carboxylic salts, the alcoholysis – of acyl halides, anhydrides, nitriles, amides or ketones – and transesterification [3]. The acylation of alcohols is often performed by treatment with anhydride acids because they are more reactive than carboxylic acids and acid catalysis is one of the most common methods for this type of esterification [3].
Heterogeneous catalysts have been used in ester synthesis by the esterification process [4], especially solid acids, ion exchange resins, metal oxides, zeolites, treated clays and enzymatic catalysis [2], [5], [6], [7]. Among a wide variety of ion exchange resins commercially available [8], cationic resins are commonly used as heterogeneous catalysts for esterification reactions [4], [9], [10]. These resins have their surface functionalized with extremely strong acid groups (Brønsted), essentially with sulfonic groups [11], they are non-corrosive and easy to be separated from the reaction mixture [12], [13].
Ion exchange resins composed of sulfonic acid groups as an active site, linked to the carrier polymer, can offer better selectivity for the desired product and better reuse compared to homogeneous acid catalysts [4], [13]. Generally the reuse is made for several cycles with relatively low loss of catalytic activity and good thermal stability [12], which are important characteristics for large-scale application [14]. When acidic anhydrides are used, despite being more electrophilic than carboxylic acids, sulfonic resins are still frequently recommended to catalyze the esterification reaction [12].
Lewatit® GF 101 resin is a solid ion exchange resin, polymer-based, spherical in shape, opaque in appearance, strongly acidic and with the presence of sulfonic groups (sulfonic acid). It has a porous structure, a high degree of crosslinking, good mechanical stability and can be used in polar or nonpolar media [15]. The use of Lewatit® GF 101 resin as a catalyst for esterification reactions was reported by Zeferino et al. [16], for the geranyl acetate synthesis from the esterification of geraniol with acetic anhydride, and by Tischer et al. [17] for the eugenyl acetate synthesis from the esterification of eugenol with acetic anhydride. In both studies the resin showed good catalytic performance.
Nerol (3,7-dimethyl-2,6-octadiene-1-ol) is an acyclic, liquid and volatile monoterpene alcohol, an important component of essential oils, extracted from spices such as neroli (Citrus aurantium), rose (Rosa damascena) and lavender (Lavandula dentata, Lavandula stoechas and Lavandula multifida) [18], [19], [20], [21]. It has a pleasant sweet floral odor and is used in flavors in food products, cosmetics, fine fragrances, personal care products and cleaning products [18], [19], [21]. Nerol can be used in esterification reactions with different acyl donors for the production of neryl acetate [22], [23]. Neryl acetate (3,7-dimethylocta-2,6-dienyl ethanoate) is found in essential oils from several plants such as different species of salvia, Citrus lemon, Helichrysum italicum, grapefruit mint, among others [24], [25], [26], [27]. It presents a pleasant floral and fruity aroma emphasizing the orange and rose aromas, a characteristic that makes it widely applicable as a flavoring agent in food, cosmetics, perfumes and hygiene products [28], [29].
There are few studies on neryl acetate synthesis reported in the literature by esterification reaction using heterogeneous catalysis. Lozano et al. [23] used enzymatic catalysis for the esterification of nerol with acetic acid and Jiang and Cheng [22] used enzymatic catalysis for the transesterification of nerol with ethyl acetate. However, there are no studies reported using ion exchange resin as a catalyst despite the technological importance of this ester and the advantages of using ion exchange resins to catalyze this class of reaction, especially the Lewatit® GF 101 resin that provided high conversions and yields with good reusability in the catalysis of similar reactions [16], [17], making it competitive when compared to enzymatic catalysis.
As there are few studies reporting the neryl acetate synthesis from nerol esterification, it is necessary to carry out further research with other catalysts, so it will be possible to compare the results with those obtained by enzymatic catalysis and enable new production routes, especially those that can provide better results for the reaction or similar results at a lower cost. Therefore, the need and opportunity for studies on the topic are imminent, especially for potential industrial applications. In this context, the present work has investigated the synthesis of neryl acetate from nerol and acetic anhydride by heterogeneous catalysis with commercial ion exchange resin Lewatit® GF 101.
Section snippets
Materials
Nerol (≥97%) from Sigma-Aldrich (Brazil) and acetic anhydride (≥97%) from Vetec (Brazil) were used as reagents. Lewatit® GF 101 resin (total capacity dry min. 4.7 eq/kg, uniformity coefficient max. 1.6, bead size 0.4–1.25 mm, effective size 0.5–0.62 mm, bulk density 760 g/L, density 1.15 g/mL, water retention 60% wt, stability −20 to 130 °C) provided by LanXess Energizing Chemistry (Germany) was used as a catalyst for the esterification reaction. N-hexane (≥95%) from Dinâmica (Brazil) and
Synthesis of neryl acetate
The esterification reaction for the catalytic neryl acetate synthesis from nerol and acetic anhydride is shown in Fig. 1.
For identical experimental conditions the conversion of the esterification reaction between nerol and acetic anhydride using the proposed catalyst (Lewatit® GF 101 resin) was approximately 83% greater than without a catalyst (Table 1). The esterification reaction without catalyst was 100% selective for neryl acetate and using the proposed catalyst demonstrated a reduction of
Conclusion
In this work, neryl acetate was synthesized by heterogeneous catalysis in an organic solvent-free system from an esterification reaction between nerol and acetic anhydride using the ion exchange resin Lewatit® GF 101 as a catalyst. The influence of temperature, catalyst content and molar ratio between nerol and acetic anhydride in the reaction was studied. The catalyst content showed a more significant effect in the nerol conversion and neryl acetate yield than the other variables. The neryl
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Government of Santa Catarina State, the Community University of Chapecó Region (Unochapecó) and Federal University of Santa Catarina (UFSC).
The authors acknowledge the Coordination for the Improvement of Higher Education Personnel (CAPES), the Community University of Chapecó Region (Unochapecó), the Federal University of Santa Catarina (UFSC) and the Caxias do Sul University (UCS) for technical and scientific support. The authors are deeply grateful to Professor
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