Reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine derived from 4-phenylphenol cyanate ester and phenyl glycidyl ether were analyzed. In addition to an isocyanurate compound and an oxazolidone compound which were well known as reaction products of cyanate esters and epoxy resins, compounds with hybrid ring structure of cyanurate/isocyanurate were determined. Gibbs free energies of the compound having hybrid ring structure of cyanurate/isocyanurate with two isocyanurate moiety were found to be lower than that of the compound with cyanurate ring structure through calculations. Calculation data supported the existence of hybrid ring structure of cy-anurate/isocyanurate. It was revealed that isomerization from cyanurate to isocyanurate occurs via hybrid ring structure of cyanurate/isocyanurate in the reaction of aryl cyanurate and epoxy.
Cyanate ester resins have been investigated as high heat resistant thermosetting resins, with applications for various products such as structural composites, printed wiring boards, adhesives and coatings [
Scheme 1 shows reactions of cyanate ester and epoxy. Triazine rings, formed by trimerization of cyanate esters, react with epoxy resins [
In this study, we investigated the reaction products of a compound with a cyanurate ring and a compound with epoxy using 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine and phenyl glycidyl ether as model compounds. From this reaction, we find that partial isomerization occurs, resulting in the formation of a hybrid ring structure of cyanurate/isocyanurate.
Scheme 1. Reactions of cyanate ester and epoxy [
LC-MS identified three peaks whose molecular weight agreed with the reaction products of a and two or three molecules of b.
The compound with a molecular weight of 885 was equivalent to the molecular weight of the reaction product of a and two molecules of b. The compounds with molecular weights of 1035 were equivalent to the molecular weight of the reaction product of a and three molecules of b.
These three peaks were then separated by preparative HPLC and each chemical structure was analyzed by 1H NMR, 1H-13C HSQC-NMR, edited 1H-13C HSQC-NMR and FT-IR.
MW1035b had one kind of methine proton (
MW1035a had three kinds of methine protons (
The 1H NMR spectrum of MW885 showed four kinds of methine protons. The ratio of aromatic proton peak integrations with those of methine and methylene protons agreed with the reaction product of a and two molecules of b. The ratio of the four methine proton peak integrations was 0.54:0.92:0.37:0.17. This ratio does not agree with any compound among the four candidates of MW885 (
In the case of triallylcyanurate, Gillham and co-workers proposed the Claisen rearrangement as a possible reaction mechanism of the isomerization [
Regarding other reaction products, 4-phenylphenol was thought to be a product by hydrolysis of a with water in the air or elimination of phenyl phenol from reaction product of a and b [
a reaction product of phenyl phenol and b. Formation of oxazolidone was confirmed in the reaction of a and b (Scheme 1) [
We are conducting further investigation of unknown reaction products (UK1, UK2, and others).
To discuss the partial isomerization from cyanurate to isocyanurate, Gibbs free energies at 298.15 K and at 1 atm of the assumed reaction products of a and b (
Regarding isomers with molecular weight of 885, the Gibbs free energy of 885-2 was lower than that of the other isomers (885-0, 885-1 and 885-1’). Regarding isomers with molecular weight of 1035, the Gibbs free energies of 1035-2 and 1035-3 were lower than that of the other isomers (1035-0 and 1035-1). Free energy decreases sharply when hybrid ring with two isocyanuate moiety forms in both isomers with molecular weights of 885 and 1035. Scheme 2 shows the assumed reaction between a and b. According to the above discussion, the reaction route via 885-2 and 1035-2 is assumed to be the main route toward isocyanurate (1035-3) at 200˚C. These calculations result in the supported formation of hybrid ring structure in experiment.
In conclusion, we investigated the reaction products of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine (a) and phenyl glycidyl ether (b). We found that partial isomerization occurred in this reaction, forming a hybrid ring structure of cyanurate/isocyanurate. Calculations of Gibbs free energy supported the existence of hybrid ring structure.
4-Phenylphenol cyanate ester was synthesized from 4-phenylphenol by standard procedure [
To a 100 ml single-neck round bottomed flask with a magnetic stirring bar, 4-Phenylphenol cyanate ester (4.0 g, 6.83 mmol), toluene (1.0 g), and zinc 2-ethylhexanoate (20.0 mg) were added and vigorously stirred for 2 h at 100˚C. The resultant white precipitate was filtered and washed with methyl ethyl ketone and then dried for 8 h under vacuum at 80˚C. The chemical structure of 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine was determined by nuclear magnetic resonance (NMR) and liquid chromatography-mass spectroscopy (LC-MS).
2,4,6-Tris(4-phenyl-phenoxy)-1,3,5-triazine (a) (20.1 mg, 0.0343 mmol) and phenyl glycidyl ether (b) (29.4 mg, 0.196 mmol) were placed in a vial. The reaction mixture was then heated at 200˚C for 1.5 h or 11 h with a heating block. a can react with 6 molecules of b theoretically (Scheme 1) [
Compound | Number of icocyanatemoiety | G (a.u.) | ΔG (kJ/mol) | |
---|---|---|---|---|
885-0 | 0 | −2890.46141 | 0 | |
885-1 | 1 | −2890.46812 | −17.61448 | |
885-1’ | 1 | −2890.45247 | 23.47197 | |
885-2 | 2 | −2890.48973 | −74.35679 |
Compound | Number of icocyanatemoiety | G (a.u.) | ΔG (kJ/mol) | |
---|---|---|---|---|
1035-0 | 0 | −3389.72979 | 0 | |
1035-1 | 1 | −3389.73289 | −8.14955 | |
1035-2 | 2 | −3389.75728 | −72.17499 | |
1035-3 | 3 | −3389.78551 | −146.29023 |
After heating, acetonitrile (10.1 g) was added to the test tube, and the reaction mixture was dissolved. The solution was then analyzed by high performance LC (HPLC), LC-MS, FD-MS, NMR, and Fourier transform infrared spectroscopy (FT-IR).
HPLC analyses were performed using Waters HP-1100 system with TOSOH ODS-120T column. UV detection was conducted at an absorbance of 274 nm. A mobile phase was a gradient of water and acetonitrile (50% to 100% over 30 min). The flow rate was 0.5 mL/min. Mass spectra were recorded on JEOL JMS-LCmate (LC- MS) or JEOL MS-700 (FD-MS). IR spectra were recorded on a Jasco FT/IR-410 spectrometer (KBr). NMR spectra were measured on Buruker spectrometer at 600MHz.
MW885: 1H NMR (600 MHz, CD3CN): δ (ppm) 4.15 - 4.59 (m, 8H, CH2), 5.01, 5.09, 5.12, 5.85 (s, 2H, CH), 6.88 - 7.65 (m, 37H, ArH). HRMS (APCI): m/z calcd for C57H48N3O7: 886.3492 [M + H]+; found: 886.3463.
MW1035a: 1H NMR (600 MHz, CD3CN): δ (ppm) 4.12 - 4.47 (m, 12H, CH2), 4.99 (s, 1H, CH), 5.03 (s, 1H, CH), 5.85 (s, 1H, CH), 6.83 - 7.56 (m, 42H, ArH). LC-MS (APCI): m/z [M + H]+; found: 1036.1.
MW1035b: 1H NMR (600 MHz, CD3CN): δ (ppm) 4.13 - 4.40 (m, 4H, CH2), 4.95 (s, 1H, CH), 6.89 - 7.50 (m, 14H, ArH). LC-MS (APCI): m/z [M + H]+; found: 1036.2.
Scheme 2. Assumed reaction between 2,4,6-tris(4-phenyl-phenoxy)-1,3,5-triazine (a) andphenyl glycidyl ether (b).
Oxazolidone: 1H NMR (600 MHz, CD3CN): δ (ppm) 3.58 - 3.86 (m, 4H, CH2), 3.97 (m, 1H, CH2), 4.07 (m, 1H, CH2), 4.28 (m, 2H, CH2), 4.79 (m, 1H, CH), 4.98 (m, 1H, CH), 6.82 (m, 2H, ArH), 6.97 (m, 4H, ArH), 7.14 (m, 2H, ArH), 7.22 (m, 2H, ArH), 7.32 (m, 3H, ArH), 7.45 (m, 2H, ArH), 7.59 (m, 4H, ArH). LC-MS (APCI): m/z [M + H]+; found: 496.0.
4-Phenylphenol + b: 1H NMR (600 MHz, CD3CN): δ (ppm) 4.09 - 4.21 (m, 4H, CH2),4.29 (m, 1H, CH), 6.98 (m, 3H, ArH), 7.06 (m, 2H, ArH), 7.32 (m, 3H, ArH), 7.45 (m, 2H, ArH), 7.61 (m, 4H, ArH) (m, 14H, ArH). MS (FD): m/z [M]+; found: 320.1.
4-Phenylphenol was identified by using a commercial product (Tokyo Chemical Industry Co., Ltd.).
The computations were performed using Research Center for Computational Science, Okazaki, Japan.
Daisuke Ohno,Kazuya Zenyoji,Youji Kurihara,Kazuyoshi Ueda,Hitoshi Habuka, (2016) Formation of Hybrid Ring Structure of Cyanurate/Isocyanurate in the Reaction be-tween 2,4,6-Tris(4-Phenyl-Phenoxy)-1, 3,5-Triazine and Phenyl Glycidyl Ether. International Journal of Organic Chemistry,06,117-125. doi: 10.4236/ijoc.2016.62013