Study on products and reaction paths for synthesis of 3,4-dihydro-2H-3-phenyl-1,3-benzoxazine from phenol, aniline and formaldehyde

Synthesis of Benzoxazine-Based N-Doped Mesoporous Carbons as High-Performance Electrode Materials

In this work, nitrogen-doped carbon materials (NCMs) were prepared using aniline-phenol benzoxazine (BOZ) or aniline-cardanol benzoxazine as the carbon precursor and SBA-15 as the hard template. The effects of the carbonization temperature (700, 800, and 900 °C) and different nitrogen contents on the electrochemical properties of carbon materials were investigated. The samples synthesized using aniline-phenol benzoxazine as precursors and treated at 900 °C (NCM-900) exhibited an excellent electrochemical performance. The specific capacitance was 460 F/g at a current density of 0.25 A/g and the cycle stability was excellent (96.1% retention rate of the initial capacitance after 2000 cycles) in a 0.5 M H2SO4 electrolyte with a three-electrode system. Furthermore, NCM-900 also exhibited a high specific capacitance, comparable energy/power densities, and excellent cycling stability using a symmetrical electrode system. The characterization of the morphology and structure of the materials suggests it possessed an ordered mesoporous structure and a large specific surface area. NCM-900 could thus be considered a promising electrode material for supercapacitors.

Benzoxazine Formation Mechanism Evaluation by Direct Observation of Reaction Intermediates

Benzoxazine formation is a fundamental step in the preparation of polybenzoxazine resins, and a detailed description of the mechanism governing the formation of benzoxazine and side products is vital for improving the properties and performance of these resins. Determination of the nature and properties of reaction intermediates is not trivial. Therefore, a Mannich-type condensation of aniline, formaldehyde, and phenol was evaluated as a potential method to form benzoxazine. Coupling positive mode electrospray ionization mass spectrometry (ESI(+)-MS) with infrared multiple photon dissociation (IRMPD) spectroscopy allowed unambiguous determination of an iminium-based mechanism and the direct observation of iminium intermediates. The benzoxazine formation mechanism was indirectly confirmed by the observation of side products that are relevant to the polymerization step, and directly confirmed by the identification of four distinct reaction intermediates that were completely characterized by IRMPD spectroscopy. The benzoxazine monomer was also shown to undergo isomerization under standard ESI-MS analysis conditions, suggesting the presence of a mixture of three isomers during their usual ESI-MS analysis.

Effect of phenol on the synthesis of benzoxazine

The kinetic parameters of benzoxazine synthesis approximately equaled those of phenol consumption revealing that phenol was the key starting material.