Fructone: Flavor Material & Catalytic Synthesis Approaches

Fructone is an aromatic compound with a strong fruity odor. The olfactory factor is described as pineapple-, strawberry- and apple-like. It is primarily utilized as a fragrance and flavoring material in cosmetics, food and beverages, manufacture of drugs and detergents, and perfume industries. Fructone is grouped within the fruity family. On a blotter it opens with a bright medley of pineapple, strawberry and apple, all wrapped in a gently woody sweetness that evokes freshly cut pine. The fruit impression feels ripe rather than candied giving it a natural juicy vibe that lifts almost any accord it touches. In the classic perfume pyramid top notes are the first to rise and disappear while heart notes give body and base notes offer lasting depth. Fructone starts in the top where its tropical sparkle is most vivid yet it lingers well into the heart, smoothly bridging the transition to florals, musks or woods. It does not sit in the true base but leaves behind a faint woody echo that can complement cedar or sandalwood facets.

Preparation of fructone catalyzed by water-soluble Brønsted acid ionic liquids

Fructone (2-methyl-2-ethylacetoacetate-1, 3-dioxolane) is a flavoring material with apple scent, and its synthesis usually involves the condensation reaction of ethyl acetoacetate with glycol in the presence of acid catalysts, such as H2SO4, HAc, Lewis acids (zinc chloride), alumina, zeolites, etc. However, many of the methods mentioned above present limitations due to the use of toxic or corrosive catalyst, the tedious work-up procedure, and the necessity of neutralization of the strong acid media producing undesired wastes. For economic and ecological reasons, organic synthetic chemists face an increasing obligation to optimize their synthetic methods in order to produce the desired product in high yield through a safe and environmentally acceptable process. Hence, to develop an environmentally benign method for the synthesis of fructone is needed. Ionic liquids (ILs) have recently gained recognition as green “designer solvents and/or catalysts” and have been successfully applied in many areas of chemistry. In continuation of our efforts to explore novel ILs and the application of acidic ILs in organic synthesis, we further reported here the preparation of fructone, using five water-soluble Brønsted acid ILs as catalysts for the first time.[1]

The catalytic activity of the obtained Brønsted acid ILs was tested in the synthesis of fructone from ethyl acetoacetate and glycol (Shanghai Chem. Reagent Co., AR) in a three-necked flask equipped with a magnetic stirrer, a water knockout vessel and a condenser. The typical reaction conditions were as follows: 70 °C of reaction temperature; 2 h of reaction time; 1.5 mol/mol of the molar ratio of glycol to ethyl acetoacetate; and 1.5% of the mass fraction of catalyst in the reaction medium. After reaction, the fructone could be isolated from the reaction system automatically, followed by a GC analysis and the IL could be directly reused without dehydration. In summary, we first reported the preparation of fructone catalyzed by several water-soluble Brønsted acid ILs. And [Hmim]BF4 shows the highest catalytic activity for the preparation of fructone among the five Brønsted acid ILs. After reaction, the fructone could be isolated from the reaction system automatically, and the IL could be directly reused without dehydration. Further investigation on the application of water-soluble Brønsted acid ILs in organic synthesis is in progress.

Highly efficient heterogeneous procedure for the synthesis of fructone

The synthesis of fructone (ethyl 3,3-ethylendioxybu- tyrate), a flavouring material with apple scent, involves the acetalization of ethyl acetoacetate with ethylene glycol. This process is catalyzed by strong acids, such as p-toluenesulfonic acid. It is known that in homoge neous media a strong acid and the water formed during the acetalization can cause the hydrolysis of the ester, producing the corresponding 3,3-ethylenedioxy-butanoic acid. The formation of this product not only can reduce the yield of fructone, but also, when it is present in amounts 3%, can alter the organoleptic characteristic of the final product. Here, we present a simple procedure for preparation of the novel heterogeneous acid catalyst. The novel catalyst was synthesized through the copolymerization of p-toluenesulfonic acid (PTSA) and paraformaldehyde in the catalyst amount of sulfuric acid (Scheme 1). The PTSA molecules were attached together by covalent bonds with methylene groups as the linkages.[2]

A novel heterogeneous strong acid catalyst has been synthesized through a simple procedure and has been found to be highly efficient for the synthesis of fructone. After optimizing the reaction condition, a comparative study and the reuse of the catalyst were taken. The re sults showed that the novel catalyst owned great advan tages over the commonly used catalysts, such as H2SO4, PTSA, Hβ, and Nafion. The operational simplicity, low cost of the catalyst used, high activity, applicability to large-scale reactions, and reusability made the catalyst one of the best choices for the reaction.

References

[1] Yuan Yuan Wang . (2007). Preparation of fructone catalyzed by water-soluble Brønsted acid ionic liquids. Chinese Chemical Letters, 18 1, Pages 24-26.

[2] Shan Gao. (2008). Highly efficient heterogeneous procedure for the synthesis of fructone fragrancy. Science China Chemistry, 51 7.