Novel reaction of N,N'-bisarylmethanediamines with formaldehyde. Synthesis of some new 1,3,5-triaryl-1,3,5-hexahydrotriazines.
The acid-catalyzed cyclocondensation of N,N'-bisaryl (aryl = 2-pyrimidinyl, 2-pyrazinyl and 4-nitrophenyl) methanediamines 5a-c with aqueous formaldehyde in refluxing acetonitrile leads to the formation of the corresponding 1,3,5-triaryl-1,3,5-hexa-hydrotriazines 6a-c. The stoichiometric reactions of 2-aminopyrimidine and 2-amino-pyrazine with aqueous formaldehyde in acetonitrile under reflux conditions also afforded 6a and 6b, respectively. Treatment of 2-aminopyrimidine with aqueous formaldehyde in a 3:2 ratio yielded N,N',N"-tris(2-pyrimidinyl)dimethylenetriamine (7a) as a sole product, which upon subsequent reaction with formaldehyde also afforded 6a. The reaction of N,N'-biphenylmethanediamine with formaldehyde was also investigated.
Recyclable, Strong Thermosets and Organogels via Paraformaldehyde Condensation with Diamines
Recyclable Thermoset Polymers The high mechanical strength and durability of thermoset polymers are exploited in applications such as composite materials, where they form the matrix surrounding carbon fibers. The thermally driven polymerization reaction is usually irreversible, so it is difficult to recycle the constituent monomers and to remove and repair portions of a composite part. García et al. (p. 732; see the Perspective by Long) now describe a family of polymers formed by condensation of paraformaldehyde with bisanilines that could form hard thermoset polymers or, when more oxygenated, produce self-healing gels. Strong acid digestion allowed recovery of the bisaniline monomers. A strong polymer formed by heating can be digested with strong acid to recover and recycle its bisaniline monomers. [Also see Perspective by Long] Nitrogen-based thermoset polymers have many industrial applications (for example, in composites), but are difficult to recycle or rework. We report a simple one-pot, low-temperature polycondensation between paraformaldehyde and 4,4ʹ-oxydianiline (ODA) that forms hemiaminal dynamic covalent networks (HDCNs), which can further cyclize at high temperatures, producing poly(hexahydrotriazine)s (PHTs). Both materials are strong thermosetting polymers, and the PHTs exhibited very high Young’s moduli (up to ~14.0 gigapascals and up to 20 gigapascals when reinforced with surface-treated carbon nanotubes), excellent solvent resistance, and resistance to environmental stress cracking. However, both HDCNs and PHTs could be digested at low pH (<2) to recover the bisaniline monomers. By simply using different diamine monomers, the HDCN- and PHT-forming reactions afford extremely versatile materials platforms. For example, when poly(ethylene glycol) (PEG) diamine monomers were used to form HDCNs, elastic organogels formed that exhibited self-healing properties.
The vapour-phase infrared spectrum and large-amplitude vibrations of N-methylaniline
Abstract Vapour phase IR spectra of N-methylaniline and its analogue deuterated on the nitrogen atom are presented between 30 and 425 cm−1. The absorptions associated with the three large amplitude vibrations of this molecule are identified, and potential energy barriers are calculated. The barrier to methyl torsion is found to be 12.9 ± 0.2 kJ mol−1, to HNCH3 torsion 14.5 ± 2.0 kJ mol−1, and to inversion at nitrogen approximately 2 kJ mol−1. These results are consistent with an earlier microwave study [1] but the error limits have been greatly improved. The most surprising result is the confirmation that N-methylaniline is more planar than aniline itself. The barriers to torsion around the NC (ring) bond are compared to those in similar molecules.