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P. Yang, Y. Gu / Chinese Chemical Letters 21 (2010) 558–562
diamine-based benzoxazine containing benzoxazole structure (Boz-BOA). By incorporating benzoxazole structure
as a rigid structure into the benzoxazine, we expected to form a polybenzoxazine with better thermal stability. High-
purity Boz-BOA was synthesized successfully using 2-(4-aminophenyl)-1H-benzoxazole-5-amine (BOA) and
ortho-hydroxybenzaldehyde.
1. Experimental
Ortho-hydroxybenzaldehyde (24.4 g, 0.2 mol), BOA (24.4 g, 0.1 mol) and N,N-dimethylacetamide (DMAc)
(120 mL) were introduced into a 250 mL three-neck flask under a nitrogen atmosphere. The mixture was stirred at
50 8C for 4 h. After the mixture cooling to room temperature, the precipitate was filtered and dried in a vacuum oven at
150 8C for 2 h. Brick red powder (42.4 g, 98% yield) with a melting of 267 8C (DSC) and a melting enthalpy of 108 J/
g. FTIR (KBr): 1616 cmÀ1 (C N stretch), 3404 cmÀ1 (OH stretch).
Boz-1 (21.7 g, 0.05 mol) and ethanol (120 mL) were introduced into a 250 mL three-neck flask with a nitrogen inlet
and a magnetic stirrer. 5.7 g (0.15 mol) of sodium borohydride (NaBH4) was added portions while the mixture was
stirred. After 12 h, the mixture was poured into de-ionized water (500 mL) and the precipitate was filtered and dried in
a vacuum oven at 105 8C for 2 h. 21.6 g (99% yield) of chrysoidine powder with a melting peak of 208 8C (DSC) was
obtained. 1H NMR (400 MHz, DMSO-d6): d 4.22 (d, 2H, –NH–CH2–Ar–), 4.27 (d, 2H, –NH–CH2–Ar–), 5.89 (t, 2H,
Ar–NH–CH2–), 6.03 (t, 2H, Ar–NH–CH2–), 9.57 (d, 2H, –Ar–OH), 6.61–7.81 (15H, Aromatic H). FTIR (KBr):
1272 cmÀ1 (C–N stretch), 1522 cmÀ1 (N–H bending), 3409 cmÀ1 (N–H stretch), 3200–3500 cmÀ1 (OH stretch).
Boz-2 (16.4 g, 0.04 mol), paraformaldehyde (2.64 g, 0.088 mol), 1,4-dioxine (100 mL) and N,N-dimethylforma-
mide (DMF) (10 mL) were introduced into a 250 mL three-neck flask. The mixture was stirred at 85 8C for 8 h. After
the mixture was cooled to room temperature, the precipitate was filtered and dried in a vacuum oven at 140 8C for 2 h.
15.6 g (86% yield) of saffron powder with a melting of 204–206 8C (micro-melting point apparatus) and a curing peak
temperature of 267 8C was obtained. 1H NMR (400 MHz, DMSO-d6): d 4.69 (s, 2H, –N–CH2–Ar–), 4.78 (s, 2H, –N–
CH2–Ar–), 5.48 (s, 2H, –N–CH2–O–), 5.55 (s, 2H, –N–CH2–O–), 6.71–8.01 (15H, Aromatic H). FTIR (KBr): 927 and
943 cmÀ1 (oxazine), 1034 cmÀ1 (Ar–O–C symmetric stretch), 1225 cmÀ1 (Ar–O–C asymmetric stretch), 1373 cmÀ1
(C–N stretch).
2. Results and discussion
Because of the poor solubility of BOA and the formation of gelation between BOA and paraformaldehyde, high-
purity Boz-BOA was not synthesized by traditional method. In this work, both of them were well solved and high-
purity Boz-BOAwas successfully synthesized by three-step synthetic method (Scheme 1). In the first step, Boz-1 was
synthesized by ortho-hydroxybenzaldehyde and BOA. The 1H NMR spectra of Boz-1 was not showed because Boz-1
could dissolve in neither CHCl3 nor DMSO well.
Fig. 1. 1H NMR spectra (DMSO-d6) of Boz-2 (a) and Boz-BOA (b).