362 Address all correspondence to Melisa Lalikoglu at firstname.lastname@example.org. J. Cosmet. Sci., 72, 362–378 (July/August 2021) The Synthesis of Benzyl Acetate as a Fragrance and Flavoring Agent with Green Solvents MELISA LALIKOGLU AND EROL İNCE Istanbul University-Cerrahpasa, ¸ Engineering Faculty, Chemical Engineering Department, 34320, Istanbul/TURKEY Accepted for publication May 2, 2021. Synopsis Benzyl acetate, which has a crucial role in the industry as a flavor and fragrance component, is important for human health to be obtained with a green and clean process. For this purpose, the esterification reac- tion of acetic acid (AA) and benzyl alcohol (BA) was investigated using five different ionic liquids (ILs) as catalysts. 1-Ethyl-3-methylimidazolium hydrogen sulfate, [EMIM] [HSO 4 ], 1-Ethyl-3-methylimidazolium tetrafluoroborate [EMIM] [BF 4 ], 1-methyl-3-octylimidazolium tetrafluoroborate [OMIM] [BF 4 ], 1-ethyl-3- methylimidazolium bis [(trifluoromethyl)sulfonyl] imide [EMIM] [NTf 2 ], and 1,3-diethylimidazolium bis [(trifluoromethyl)sulfonyl] imide [DEIM] [NTf 2 ] were used as catalysts. The best catalytic performance was obtained with 1-Ethyl-3-methylimidazolium hydrogen sulfate, [EMIM] [HSO 4 ]. The influence of different anions and cations in the IL’s structure, the reaction conditions such as initial acid/alcohol ratio, the catalyst amount, the reaction temperature, and the time on conversion were observed. The Box–Behnken experimen- tal design of response surface methodology was applied to estimate the relationship between acid conversion (%) and reaction parameters. According to the model, in all esterification experiments carried out at 110°C, the optimum conditions for maximum conversion were AA:BA molar ratio of 1:1, IL molar ratio of 0.66, and reaction time 4 hours. Under these conditions, 90.34% acid conversion was achieved. [EMIM] [HSO 4 ] can be used for up to three cycles with minimal loss in activity. INTRODUCTION Organic esters are valuable products in the chemical industry. One of the short-chain carboxylic acid esters, benzyl acetate, is used as a flavor and fragrance component in the food and cosmetics industry. The Council of Europe approved the use of benzyl acetate in foodstuffs in 2000 and included in the list of substances granted-A. In addition, it is considered safe as a flavor ingredient by the Flavor and Extract Manufacturers Association (FEMA). Although benzyl acetate is found naturally in cloves, chamomile, jasmine, and hyacinth, extracts obtained from these plants are not sufficient to meet the worldwide usage volume (about 10,000 tons per year). Therefore, it is obtained by many different chemical methods. Most commonly used method is the esterification reaction of acetic acid (AA) and benzyl alcohol (BA) (1–2).
363 SYNTHESIS OF BENZYL ACETATE The esterification reaction is an equilibrium reaction. It is carried out without or with catalyst. Because of the low rate of the carboxylic acid’s autoprotolysis, the reaction proceeds very slowly without catalyst in the medium and takes a long time to equili- brate. Therefore, by adding an acid catalyst to be used as a proton donor, the reaction occurs faster (3). Esterification reactions are generally carried out in the presence of homogeneous or heterogeneous catalysts. Various mineral acids such as H 2 SO 4 , HCl, H 3 PO 4 , HF, p-toluene sulfonic acid are used as homogeneous catalysts in different studies (4–8). Although these acids have high catalytic activity and selectivity, they have significant disadvantages. It causes corrosion of the equipment, excessive side reaction, and severe environmental pollution, and it must be neutralized at the end of the reaction. Besides, it is very difficult to remove the mineral acid from the reaction medium and reuse them as a catalyst (9). In order to eliminate these problems, het- erogeneous catalyst systems have been developed. Zeolites, ion-exchange resins such as Amberlyst 15 and heteropolyacids are used as catalysts in the esterification reactions of carboxylic acids. However, over time, heterogeneous catalysts also have problems that will affect the esterification reaction, such as a low number of active groups, high mass transfer resistance, long reaction times, low thermal stability, and catalyst residue control (10–21). Since the esterification reactions are reversible reactions, according to the Le Chatelier principle, the yield can be increased by shifting the excess of one of the reactants into the medium or removing the water formed at the end of the reaction by shifting the balance to the direction of the product. One of the techniques used to remove water is to add azeotrope with water by adding a water-trapping solvent such as hexane, benzene, toluene (22). However, in these processes, considerable energy is needed to recover the solvent or remove excess reactant. Besides, the loss of volatile organic solvents to the atmosphere increases the cost of production and causes environmental pollution (23). Esterification reaction systems need to be developed to reduce environmental pollution and production costs, easy separation of the product from the reaction medium, and reuse of cat- alysts with high selectivity and reactivity. For this purpose, the importance of ionic liquids (ILs) has been increasing in recent years due to their polarity and hydrophobic structure, and it has been used in many fields such as polymerization (24,25), alkylation (26,27), dehydration (28,29), oxidation (30,31), and acetalization (32,33). Since 2002, ILs have been proposed to be used as catalysts to improve esterification reactions (34). These substances stand out as an environmentally acceptable reaction medium due to their low vapor pres- sure, high thermal stability, adjustable acidity, recoverability, and low toxic effects (35–42). ILs, depending on their solubility, ensure that the reaction medium is homogeneous in the first steps of esterification reactions and heterogeneous toward the end of the reaction. Thus, they are easily separated from the product and reused many times (43). ILs act as catalysts in the esterification reaction of carboxylic acids and alcohols. At the end of the reaction, the water in the medium must be removed to obtain high ester conversion. Water passes into the IL phase and does not react. The ester is separated by decantation at the end of the reaction (44–47). Response surface methodology was developed in 1951 by Box and Wilson as an experi- mental design method (48). This method is a combination of statistical and mathematical techniques used for modeling and analysis of engineering problems. The experimental design establishes a relationship between the parameters that affect the system and the process outputs in processes. With this technique, savings (reduction) can be mentioned in
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