Synthesis, characterization, and thermal properties of new flavor compounds

Abstract

Synthesis, characterization, and thermal properties of new, flavor, long chain esters were presented. The new compounds were obtained in the catalytic esterification process of a stoichiometric ratio of trans-3,7-dimethyl-2,6-octadien-1-ol, succinic anhydride, and aliphatic chain diol. As diols ethylene glycol, 1,4-buthylene glycol, 1,5-pentylene glycol, and 1,6-hexylene glycol were applied. The spectroscopic analyses completely confirmed that the applied synthesis conditions allowed obtaining the new compounds with high yield and purity. Their thermal properties were studied in inert and oxidative atmospheres. The esters were less thermally stable in inert (IDT 186-195°C) than in oxidative (IDT 210-228°C) atmosphere. Two, non-completely divided decomposition steps were visible during their pyrolysis. In contrast, the new, long chain compounds decompose in three major steps in air. The analyses of the volatile products emitted during their pyrolysis indicated on the asymmetrical disrupt of their bonds. The formation of acyclic and alicyclic monoterpene hydrocarbons, succinic anhydride, diols, alcohols, alkenes, and water was observed. It indicated mainly on the b-elimination reactions during their pyrolysis. Also, belimination reactions of esters are mainly expected in air. Initially, it resulted in the formation of acyclic and alicyclic monoterpene hydrocarbons, hydroxyl compounds (diols, alcohols), and its b-elimination products: aldehydes, alkenes, and water. However, the presence of oxygen in the medium causes the partial decarboxylation and oxygenation of aldehydes and thus the formation of alkenes and carbon dioxide. In addition, the beginning of evaporation of succinic anhydride was detected at T max1 . At T max2 the evaporation of succinic anhydride, their partial decarboxylation to CO 2 , the small amounts of diols, alcohols, and aldehyde fragments were indicated. Finally, succinic anhydride, water, and carbon dioxide were only observed during decomposition of studied esters in air.

Thermal properties of neryl long-chain esters obtained under microwave irradiation

“…Also, in this decomposition stage, the evaporation of water vapor (3,600-3,740 cm -1 ) [26-30, 35, 36] and emission of carbon dioxide (670 cm -1 and 2,330-2,365 cm -1 ) [26-30, 34, 37] are indicated. At T max2 , besides the products observed at T max1 , the evaporation of an acid anhydride (signals at 900, 1,050, 1,811 and 1,870 cm -1 responsible for m C-O and C=O groups) is clearly indicated for neryl esters obtained using shorter acid chain length (succinic anhydride and glutaric anhydride) [26][27][28][29][30]. For neryl esters based on adipic acid and sebacic acid, the evaporation of an acid anhydride…”

“…[29,30] and microwave-assisted synthesis using butylstannoic acid as a catalyst. In a typical experiment, the reagents were used at the molar ratio of 2:2:1 (nerol/anhydride acid/diol).…”

“…The 7 and 11 membered anhydrides due to their low stability, decomposes in air losing CO 2 . In this reaction, as a main decomposition compounds, cyclic ketones are formed [26][27][28][29][30]. The formation of those compounds during decomposition of neryl esters based on adipic and sebacic acids was confirmed by the presence of absorption signals at 1,768-1,790 cm -1 (m C=O) and at 1,008-1,178 cm -1 (m C-O) on FTIR spectra [31].…”

“…Traditionally, chemically those esters are prepared in catalyzed esterification process of monoterpene alcohols with acid anhydrides or acid chlorides using large excess of terpene alcohol and often toxic solvents [13,25]. Recently, we have proposed the method of the preparation of geranyl, neryl and citronellyl diesters [26][27][28] and long-chain esters of geraniol [29,30] using butylstannoic acid as a catalyst under conventional conditions. The use of such catalyst allowed reducing the formation of by-products, using of stoichiometric amount of reagents and significantly increasing the yields of pure product which consequently reduced the production cost of flavor esters for cosmetic, laundry and perfume applications.…”

“…To compare the results, those esters were also obtained under conventional method described in Refs. [29,30]. Their thermal properties and the type of emitted gaseous products under oxidative conditions were studied by TG/FTIR-coupled method, and the obtained results were compared to the previously studied [29,30].…”