Description of the molecule structure and the monoclinic crystal structure in comparison to the reported hexagonal structure

The structural differences in the two structures compared thereafter are mainly given by their different space groups. Therefore the hexagonal structure 2−298 K can be described by an asymmetric unit which is only the third of the molecular structure (fig. 4). But in the monoclinic structure of 2−100 K the whole molecule is one asymmetric unit (fig. 5).

Discussion

Figure 4. An ORTEPIII[8] _{view of triazine 2, showing the atom-labeling scheme.}

Displacement ellipsoids are drawn at the 50 % probability level and H atoms are shown as small spheres of arbitrary radii. Measurement at 298 K.[6] (left) Measurement at 100 K (right).

Looking at the molecular structure of the 2−298K the C3-symmetry leads to a whole molecule that is planar, and the exocyclic groups are ordered in the same plane as the ring (fig.4). Also there are big thermal ellipsoids at the oxygen which is not uncommon for room temperature measurements. Comparing the molecular structure of the

2−100K with the 2−298K structure, it may be recognized that the exocyclic groups show little torsion shift (fig.5). That means the O3 and O5 atoms as well as the C9 and C12 are not in ring plane but turned out. This fixed, non-symmetric behavior is typical for the phase change as the molecules are not able to vibrate around the ground state at lower temperatures as much as at room temperature and the distortion of symmetry leads to a lower energy molecular structure. By rotation around the CH2-CH3 or the O- CH2 bond all degrees of freedom are considered that could minimize the molecular and crystal symmetry.

Figure 5. A view of 2 at 298 K showing the stacking of layers in the [001] direction.[5]

Discussion

Figure 6. A view of 2 at 100 K showing the stacking of layers in the [100] direction.

Comparing the crystal structures there can be seen in the 2−298 K structure - looking in the [001] direction (fig.6) - that the molecules are even stacked, which is another effect of the planar molecular structure. Else in the 2−100 K structure, there you find a wave-like packing looking in the [100] direction. The cell dimension is nearly doubled up as you can assume from the figures 6 and 7 or looking up the crystal data. The length of the c-axis of 2−100 K is 21.77 Å and in 2−298 K the corresponding b-axis is 10.98 Å.[7]

Hydrogen bonding in both of those molecules are not possible through classical concepts with nitrogen or oxygen as donor groups, but in this case the rare carbon hydrogen bonds takes the role as hydrogen donor. In the 2-298 K crystal structure the intermolecular bonding are covered by the connection C—H O=C of the C5 at (x, y, z) via H5A to O2 at (2y, x y, z) as does the O2 (x, y, z) act as acceptor of the H5A (2x + y, 2x, z). As there is a C3 symmetry in the molecular structure this bonding can be found three times each molecule, which makes a surrounding of six different molecules in the plane (001) for one molecule (fig. 8). This behavior can be found in a similar way in the plane (010) of the 2-100 K structure, where the you can see connections between the C11 and C12 at (x,y,z) via H12B and H11B to the acceptor bifurcated O1 at (−1+x, 0.5−y, −0.5+z) as does the O1 (x,y, z) to the C11 and C12 at ( 1+x, 0.5−y, 0.5+z). There is another connection from the C9 (x, y, z) via H9B to the acceptor O5 at (1+x, y, z) and the O5 (x, y, z) binds at the C9 at (−1+x, y ,z). The last bonding to mention is the interaction between the donor C6 at (x, y, z) via H6B to the O3 (x, 0.5−y, 0.5+z), which can be found at O3 at (x, y, z) connection to C6 at (x, 0.5−y, −0.5+z).

These hydrogen bonds form a network, where one molecule interacts with six other molecules as it does in the 2−298 K structure. The lengths of all bonds are shown in table 1.

Discussion

Table 1. Intermolecular hydrogen-bond parameters (d [Å]; < [°] ) of 2−298 K and 2−100 K. D—H∙∙∙A H∙∙∙A D∙∙∙A < D—H∙∙∙A Compound 2-298K C5—H5A∙∙∙O2i _{2.580(2) 3.286(4) 130.6(3)} Compound 2-100K C12—H12B∙∙∙O1ii C11—H11B∙∙∙O1ii C6—H6B∙∙∙O3iii C9—H9B∙∙∙O5iv 2.558(1) 2.661(1) 2.706(1) 2.652(1) 3.232(2) 3.094(1) 3.385(1) 3.331(1) 125.96(8) 106.74(4) 126.67(5) 126.60(6) Symmetry codes: (i) 2y; xy; z; (ii) −1+x, 0.5−y, −0.5+z; (iii) x, 0.5−y, 0.5+z; (iv) 1+x, y, z

Figure 7. Part of the crystal structure of 2−298 K, showing a hydrogen-bonded sheet in the (001) plane. Hydrogen bonds are shown as dashed lines[5]_.

Discussion

Figure 8. Part of the crystal structure of 2−100 K, showing a hydrogen-bonded sheet in the (010) plane. Hydrogen bonds are shown as dashed lines.

Discussion

Synthesis

2.2

Figure 9. Synthesis of NOX (Nitration with acetic anhydride/ nitric acid).

The synthesis starts with the cheap common bulk materials sodium cyanide and ethyl chloro formate. The sodium cyanide is solved in water and the ethyl chloro formate in dichloromethane. The solutions are stirred together rapidly under cooling and the addition of the phase transfer catalyst tetrabutylammonium bromide. The product could be easily separated from the organic phase by removing the solvent and subsequently distillation to remove residues of ethyl chloro formate. The yield was over 80 %. The formed ethyl cyano formate (1) was undergoes cyclization by adding

Discussion gaseous hydrogen chloride for half an hour. It was found that the product has not to be hundred percent free of chloroformate for this reaction. So for mass production the distillation could possibly be omitted. The reaction yields in over 90 % pure crystalline product tri-ethyl-1,3,5-triazine-2,4,6-tri-carboxylate(2, TECT). The TECT and TRIS were added to an ethanol containing flask. To the mixture little concentrated hydrogen chloride solution was added and afterwards refluxed for four hours. The product (3, TTHMM-TCA) was filtered at a temperature of 40°C and washed with cold ethanol. The product was recrystallized from water. The yield was 65 %. Nitration was done in acetic anhydride with 100% nitric acid under ice-cooling. The yield was about 84.5 % of 4 (NOX). Crystals were obtained by recrystallization from acetone.

Thermodynamical and Spectroscopic Characterization