With the current trend of increasing efforts to develop non-isocyanate-based polyurethanes (NIPUs), this study aimed to check the feasibility of the development of a method using cyclic carbonate modified catechin and amine to synthesis non-isocyanate urethane with the objective to further extend these results to polyurethane synthesis. The methods used in this study consist of four steps: glycidilation of catechin, hydrolysis of epoxide, cyclic carbonate synthesis, and carbamate synthesis through condensation of butylamine. The resulting products were analyzed using FTIR (Fourier transform infrared) spectroscopy and NMR (nuclear magnetic resonance) spectroscopy. The results showed that carbamate could be successfully obtained through this four-steps synthesis, opening the possibility to further developments for the synthesis of polyurethanes starting from catechin and condensed tannins.
Polyurethanes are organic polymers linked by carbamate junctions. They are primarily used in the manufacture of seals, foams, high-performance adhesives, and coatings, as well as in a multitude of other fields [
In this context, numerous studies have been conducted to develop isocyanate-free polyurethane from natural compounds. Some of the chemical compounds used in these studies are polyphenols, which can be found naturally in wood and bark [
(+)-Catechin hydrate, epichlorohydrin (99.0%), benzyltriethylammonium chloride (≥98.0%), sodium hydroxide (≥98.0%), potassium carbonate, cesium carbonate and butylamine were obtained from Sigma-Aldrich Chimie, France.
A 100-mL two-necked flask equipped with a condenser, a septum cap, and a magnetic stirring bar was charged with 1 g of catechin (3.445 mmol). Catechin was mixed with epichlorohydrin (5 mEq./OH) and heated under reflux at 100°C, after which benzyltriethylammonium chloride (0.05 mEq./catechin) was added. After one hour, the resulting solution was cooled down to 30°C and an aqueous solution of NaOH 20 wt% (2 mEq./OH) was added dropwise with additional amount of benzyltriethylammonium chloride (0.05 mEq./catechin). The mixture was stirred vigorously to prevent precipitation of the reaction mixture for 90 min. The organic layer was separated, dried over MgSO4, and concentrated under vacuum.
In a 100-mL round-bottom flask equipped with a condenser, glycidyl catechin (1.03 g, 2 mmol) was added to 12 mL of distilled water; then, 6 mL of tetrahydrofuran (THF) was added. The solution was stirred at 80°C and monitored using thin-layer chromatography (TLC). Increase of the temperature to 80°C allowed reaction of water with epoxide and homogenization of the mixture. The reaction monitored by TLC was completed after 4 to 5 h. After completion, the mixture was concentrated under vacuum to remove THF. The remaining water was then removed using a freeze dryer.
In a 100-mL three-neck flask fitted with a condenser and a CaCl2 guard tube, the diol was stirred with 24 eq. of dimethyl carbonate (3.64 mL, 43.18 mmol) and 0.03 eq. of K2CO3 (0.07 g, 0.054 mmol). The mixture was refluxed at 80°C for 24 h. The excess of dimethyl carbonate was then evaporated under reduced pressure.
In a 100-mL three-neck flask fitted with a condenser and a CaCl2 guard tube, butyl amine and cyclic carbonate catechin derivative were stirred, and then 5 to 10 mL of methanol was added to lower the viscosity of the reaction mixture. The reaction medium was subsequently, vigorously stirred using magnetic stirrer and heated at 80°C for 8 h. The progress of the reaction was monitored by Fourier transform infrared (FTIR) analysis. After completion, methanol was removed under vacuum using a rotary evaporator. The reaction mixture was then extracted using 150 mL of ethyl acetate. The organic phase was washed with 2 × 35 mL of 1 N HCl and 35 mL of a saturated NaCl solution, dried over MgSO4, filtered and then concentrated under reduced pressure.
The products were identified by NMR performed on a Bruker Avance DRX 400 (Bruker, Germany) at 400 MHz. Samples were dissolved either in methanol-d4, or in chloroform-d, or in DMSO-d6 for 1H NMR analysis. Chemical shifts were expressed in parts per million (ppm).
FTIR spectrums were recorded with an ATR cell on a Perkin Elmer Spectrum 2000 instrument in the range of 4000 to 600 cm−1 at a resolution of 4 cm−1.
The glycidylation of catechin was conducted in the presence of a phase transfer catalyst [
Chemical structure of the tetraglycidylcatechin was assigned by 1H NMR and FTIR analysis (
NMR spectrum of catechin after glycidylation indicated aliphatic signals arising from methyl oxirane groups. Signal of hydrogens of CH2 group of epoxide ring (2 × Ha), overlapping with hydrogens of benzylic group belonging to the flavonoid skeleton (2 × Hj), appeared as a massif between 2.75 and 2.95 ppm. A multiplet between 3.20 and 3.40 ppm corresponds to the hydrogen of CH of epoxide (Hb). The two massifs between 3.68 and 3.85 ppm and 4.05 and 4.35 ppm correspond each to one hydrogen of the methylene in α of the epoxide group (2 × Hc). H2 of catechin (Hh) appeared as a doublet at 4.5 ppm, while H3 (Hi) was masked under the signals of epoxide. H6 (He) and H8 (Hd) signals of catechin moiety appeared as a massif around 6.03 ppm, while those of H2′, H5′ and H6′ appeared as a massif between 6.75 and 7.25 ppm.
Comparison of the FTIR spectrum of catechin before and after glycidylation shows the presence epoxide ring at 908.5 cm−1 in the reaction product. Intensity of the stretching vibration bands of hydroxyl groups in the 3000 to 3500 cm−1 area also differ showing a decrease of hydroxyl band in the tertraglycidylated product ascribable to the substitution of phenolic groups.
Hydrolysis of epoxide was conducted by heating the crude product in hot water at a temperature comprised between 60 and 80°C for 16 h (
FTIR analysis (
To confirm the formation of diol, NMR analysis was conducted.
Carbonate synthesis was conducted to obtain cyclic carbonate, which afterwards can be reacted with amines to provide carbamate function. The reaction with dimethyl carbonate was carried out at 80°C for 24 h as shown in
Formation of cyclic carbonate was investigated by FTIR (
To confirm the chemical structure of the cyclic carbonate derivative, NMR analysis was conducted.
To evaluate the feasibility of carbamate formation, butylamine was used as an model amine to test reactivity of carbonate moiety. The reaction was carried out by heating the cyclic carbonate with 10 eq. of butylamine at 80°C for 16 h (
To confirm the formation of urethane bond, the product was then examined using FTIR (
Measurements on crude product using 1H NMR were difficult to interpret due to the presence of residual butyl amine masking partially signals of butyl moiety in the urethane (
.
The synthesis of carbamate starting from catechin carbonate derivative has successfully been achieved using butylamine chose as model amine. All the fourth steps of the synthesis involving glycidilation of catechin, hydrolysis of epoxyde, carbonatation with dimethylcarbonate and reaction of cyclic carbonate with amine have been completed and characterized using FTIR showing the formation of the carbamate at the end of the synthesis. Further works are under investigation to extend these preliminary results to the formation of polyurethanes using diamine instead of butylamine, but also to extend the procedure to tannins instead of catechin used in this study.
Febrina Boer would like to express her gratitude to the Ministry of Education and Culture of Indonesia (Kementerian Pendidikan dan Kebudayaan Indonesia) for their scholarship, “Beasiswa Unggulan”, which supports her double degree Master education both in Indonesia and France, and Campus France with French Ministry of Foreign Affairs for their social coverage scholarship. The authors gratefully acknowledge the “Ministère des Affaires étrangères et du développement international” (MAEDI)” and the “Ministère de l’Education nationale, de l’Enseignement supérieur et de la recherche (MENESR)” for the financial support through the Bio-Asie Program (2015–2016). LERMAB is supported by a grant overseen by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” Program (ANR-11-LABX-0002-01. Lab of Excellence ARBRE) and by the “Impact Biomolecules” Project of the “Lorraine Université d’Excellence” “Investissements d’avenir–ANR 15-004” and by the French Ministry of Agriculture and the Lorraine-FEDER for the support of “EXTRAFOREST” Project.