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

Abstract

Thermal properties of novel, neryl long-chain esters obtained through the esterification process of nerol, different chain lengths acidic components such as succinic anhydride, glutaric anhydride, adipic acid or sebacic acid and diol components such as ethylene glycol or diethylene glycol in solvent-free conditions under microwave irradiation were studied by TG/FTIR-coupled method. The studies confirmed that the use of microwave irradiation allowed obtaining flavor esters in absolutely shorter reaction time (only minutes) with high purity and yield compared to conventional method. The prepared novel, neryl long-chain esters were high thermal stable compounds and decomposed at three stages under air conditions including the breaking of ester bonds, oxidation and decarboxylation processes of formed intermediate products in a gaseous phase and thus the emission of various gaseous products. It was indicated on the same, complex and parallel decomposition mechanism under oxidative conditions for the present and previously studied long-chain esters of primary order terpene alcohols showing it independence on the type of alcohol used for their synthesis.

Microwave-Assisted Synthesis of Cinnamyl Long Chain Aroma Esters

“…Reaction yields higher than 90% was obtained under conventional conditions after 30–65 h, whereas microwave irradiation allows reducing the synthesis time significantly, as only between 10 and 20 min are needed to prepare the final products with high purity. The results obtained are in accordance with our previous studies, where the influence of microwave irradiation on the synthesis of neryl long chain esters was evaluated [28]. As is clearly visible, the synthesis of esters 1a – 1d requires less time to obtain a high reaction yield than that of esters 1e – 1h .…”

“…In addition, as the aliphatic chain length of acidic substrate is increased, the synthesis needs more irradiation time to be finished. It can be suspected that the differences are directly connected with the polarity of substrates used for the preparation of cinnamyl long chain esters [28,29,30,31].…”

TG/DSC/FTIR/QMS studies on the oxidative decomposition of terpene acrylate homopolymers

“…2 and 3, one can see that under oxidative decomposition process, firstly and mainly the emission of acyclic or cyclic terpene hydrocarbons is observed [29][30][31][32][33][34][35]. It is Absorbance/a.u.…”

“…Wavenumber/cm -1 Absorbance/a.u. confirmed by the presence of the characteristic bands for -CH 3 and -CH 2 -at 1378-1446 cm -1 (the deformation vibrations) and at 2870-2974 cm -1 (the stretching vibrations) and the presence of absorption bands for carboncarbon double bonds at 895-985 cm -1 (the out-of-plane deformation vibrations of =C-H groups), at 1590-1640 cm -1 (the stretching vibrations of C=C), and the bands centered at 3090 cm -1 (the stretching vibrations of =C-H) [29][30][31][32][33][34][35]. In addition, the creation of other terpene derivatives containing oxygen functional groups at the first decomposition stage was expected due to the presence of the bands at 1700-1790 cm -1 (the stretching vibrations of carbonyl groups), the bands from 1050 up to 1210 cm -1 (the stretching vibrations of C-O), the band at 2720 cm -1 (the stretching vibrations of C-H in aldehyde groups) and the bands above 3500 cm -1 (the stretching vibrations of -OH) on the FTIR spectra.…”

“…It indicates the formation of acids and aldehydes under oxidative decomposition of poly(geranyl acrylate) and poly(neryl acrylate) homopolymers. In addition, the presence of the bands at 1050-1210 cm -1 and the signals above 3500 cm -1 may indicate also the creation of terpene alcohols at T max1 [29][30][31][32][33][34][35]. However, it might be suspected that the formed alcohols and aldehydes can undergo the partial oxidation process to the corresponding acids under the presence of air.…”