A 1:1 co-crystal of the herbicide triflusulfuron-methyl and its degradation product triazine amine

Kurt Mereiter

doi:10.1107/S1600536811031631

. 2011 Aug 11;67(Pt 9):o2321–o2322. doi: 10.1107/S1600536811031631

A 1:1 co-crystal of the herbicide triflusulfuron-methyl and its degradation product triazine amine

Kurt Mereiter ^a,^*

PMCID: PMC3200658 PMID: 22058947

Abstract

The herbicide triflusulfuron-methyl (systematic name: methyl 2-{[4-dimethylamino-6-(2,2,2-trifluoroethoxy)-1,3,5-triazin-2-yl]carbamoylsulfamoyl}-3-methylbenzoate) and its degradation product triazine amine [systematic name: 2-amino-4-dimethylamino-6-(2,2,2-trifluoroethoxy)-1,3,5-triazine] form a triclinic 1:1 co-crystal of the title compound, C₇H₁₀F₃N₅O·C₁₇H₁₉F₃N₆O₆S, in which its two components are connected via a pair of complementary N—H⋯N hydrogen bonds, similar to the monoclinic crystal structure of the parent compound triflusulfuron-methyl [Mereiter (2011 ▶). Acta Cryst. E67, o1778–o1779] in which a pair of molecules related by a twofold axis are linked by two N—H⋯N bonds. The triflusulfuron-methyl molecules of both crystal structures are similar in geometric parameters and conformation, which is due to stiffening by a short intramolecular N—H⋯N bond [N⋯N = 2.620 (4) Å] and an intramolecular dipole–dipole interaction between the sulfamide and the carboxyl moieties, with O_s⋯C_c = 2.802 (5) Å and O_c⋯N_s = 2.846 (4) Å. Intermolecular N—H⋯O hydrogen bonds and slipped π–π stacking interactions between the diaminotriazine moieties [perpendicular distances of 3.25 Å within hydrogen-bonded tetramers and 3.27 Å between adjacent tetramers] link the two constituents of the co-crystal into columns parallel to the a axis. An intramolecular C—H⋯O hydrogen bond occurs in the triflusulfuron-methyl molecule and intermolecular C—H⋯O interactions between triflusulfuron-methyl molecules occur in the crystal structure. In the triflusulfuron-methyl molecule the dihedral angle between the least-squares planes of the two rings is 75.8 (1)°. In the triazine molecule, the CF₃ group is partly orientationally disordered.

Related literature

For the crystal structure of the herbicide triflusulfuron-methyl, see: Mereiter (2011 ▶). For information on the synthesis and herbicidal properties of triflusulfuron-methyl, see: Moon (1989 ▶); Peeples et al. (1991 ▶); Wittenbach et al. (1994 ▶). For general information on the herbicidal properties of triflusulfuron-methyl and its degradation product triazine amine, see: EFSA (2008 ▶).

Experimental

Crystal data

C₇H₁₀F₃N₅O·C₁₇H₁₉F₃N₆O₆S
M _r = 729.64
Monoclinic,
a = 9.0388 (18) Å
b = 12.120 (2) Å
c = 27.820 (5) Å
β = 91.883 (3)°
V = 3046.0 (10) Å³
Z = 4
Mo Kα radiation
μ = 0.21 mm⁻¹
T = 100 K
0.42 × 0.03 × 0.03 mm

Data collection

Bruker KAPPA APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ▶) T _min = 0.87, T _max = 0.99
29573 measured reflections
5239 independent reflections
3575 reflections with I > 2σ(I)
R _int = 0.085

Refinement

R[F ² > 2σ(F ²)] = 0.059
wR(F ²) = 0.152
S = 1.04
5239 reflections
461 parameters
31 restraints
H-atom parameters constrained
Δρ_max = 0.36 e Å⁻³
Δρ_min = −0.45 e Å⁻³

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT (Bruker, 2008 ▶); data reduction: SAINT, SADABS and XPREP (Bruker, 2008 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: PLATON (Spek, 2009 ▶) and publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536811031631/pk2336sup1.cif

e-67-o2321-sup1.cif^{(40.1KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811031631/pk2336Isup2.hkl

e-67-o2321-Isup2.hkl^{(256.6KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811031631/pk2336Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N⋯N5	0.88	1.94	2.620 (4)	133
N2—H2N⋯N8	0.88	2.20	3.080 (4)	176
N7—H7NA⋯N3	0.88	2.11	2.989 (5)	174
N7—H7NB⋯O3ⁱ	0.88	2.13	2.996 (4)	167
C5—H5⋯O2ⁱⁱ	0.95	2.57	3.434 (5)	152
C8—H8A⋯O2ⁱⁱⁱ	0.98	2.43	3.398 (5)	170
C9—H9A⋯O5	0.98	2.40	3.210 (5)	140
C16—H16B⋯O5ⁱ	0.99	2.47	3.373 (5)	152

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

supplementary crystallographic information

Comment

The crystal structure of the triazinylsulfonylurea herbicide triflusulfuron-methyl, C₁₇H₁₉F₃N₆O₆S, marketed under the trade names UpBeet, Debut, and Safari (originator DuPont^TM; Moon, 1989; Peeples et al., 1991; Wittenbach et al., 1994) for crop protection of sugar beet and fodder beet, was recently reported (Mereiter, 2011). The compound crystallizes in a monoclinic lattice of space group C2/c with a = 16.7107 (11) Å, b = 15.6406 (11) Å, c = 17.1875 (12) Å, β = 107.035 (1)°, V = 4295.1 (5) Å³, and Z = 8 at T = 100 K. This crystal form is subsequently denoted CMTFS whereas the chemical entity triflusulfuron-methyl is denoted TFS. Triflusulfuron-methyl degrades in aqueous solutions by hydrolytic cleavage of the sulfonylurea bridge yielding CO₂, CH₃OH, methyl-saccharine [systematic name: 7-methyl-1,2-benzisothiazol-3(2H)-one-1,1-dioxide, C₈H₇NO₃S] and triazine amine [2-amino-4-(dimethylamino)-6-(2,2,2-trifluoroethoxy)-1,3,5-triazine, C₇H₁₀F₃N₅O], denoted TA, as the primary products (EFSA, 2008). TA is a relevant impurity of technical TFS and should not exceed 0.6% for crop protection purposes (EFSA, 2008). During crystallization experiments of TFS (Mereiter, 2011), a new crystal species of triclinic symmetry and space group P1 was obtained the crystal structure of which is reported here. The title compound, (I), is a 1:1 cocrystal of TFS and TA as shown in Scheme 1 and Fig. 1. In this crystal structure, the TFS molecule exhibits geometric features similar to those in CMTFS (Mereiter, 2011). These characteristics are: (i) an approximately planar system formed by the diaminotriazine moiety and the adjacent atoms N2, C10, O5, N1, S1, O1, O6, and C16 (r.m.s. deviation from planarity 0.139 Å); (ii) a flat 2-methylphenyl group inclined to (i) at an angle of 75.8 (1)°; (iii) a flat carboxymethyl group inclined to (ii) by 47.9 (2)°; (iv) a short intramolecular hydrogen bond N1—H1n···N5, N1···N5 = 2.620 (4) Å (Table 1); and (v) a striking intramolecular dipole-dipole interaction between the sulfamide and the carboxylate moiety with the short distances O1···C7 = 2.802 (5) Å and O3···N1 = 2.846 (4) Å, which are important for the conformation of the molecule and its chemical reactivity. The corresponding dimensions in CMTFS are 75.26 (2)° and 48.07 (6)° for the interplanar angles and 2.641 (1), 2.800 (1), and 2.835 (1) Å, respectively, for the distances (Mereiter, 2011). At variance with CMTFS the carbon atom C17 of the CF₃ group in (I) is not coplanar with the triazine ring but twisted from it and has a torsion angle of C12—O6—C16—C17 = 127.5 (4)°. The corresponding angle in CMTFS is 176.1 (1)°. The TA molecule in (I) has dimensions similar to the corresponding fragment in the TFS molecule. Here too, is the carbon atom C24 of the CF₃ group not coplanar with the rest of the molecule. This CF₃ group is disordered over two sets of sites (see section refinement), of which the dominant set has a torsion angle of C19—O7—C23—C24 = -110.7 (4)° and the subordinate set an angle of C19—O7—C23—C24' = -141.0 (8)°. The mutual arrangement of the two components of (I) in the asymmetric unit and their connection by a pair of complementary N—H···N hydrogen bonds, N2—H2n···N8 (N···N = 3.080 (4) Å) and N7—H7na···N3 (N···N = 2.989 (5) Å) is visualized in Fig. 1. The two triazine rings in Fig. 1 deviate only by 0.038 Å from a common l.s. plane. This pair of molecules is linked with another centrosymmetric pair via two hydrogen bonds N7—H7nb···O3ⁱ (N···O = 2.996 (4) Å, O3 is a carboxyl oxygen) to form a finite cyclically hydrogen bonded tetramer of two TFS and two TA molecules shown in Fig. 2. The tetramers are stacked one above the other along the a-axis to form infinite columns, as shown in Fig. 3. Coherence within and between the hydrogen-bonded tetramers along the a-axis is provided by slipped π-π-stacking interactions with perpendicular distances of 3.25 Å within hydrogen bonded tetramers and 3.27 Å between adjacent tetramers. These distances refer to the combined mean plane of the two triazine rings in TFS and TA mentioned above; the planes are approximately parallel to either (111) or to its symmetry equivalent (111). A view of the resulting crystal structure seen along the a-axis, i.e. along the π-π-stacked columns, is given in Fig. 4. Perpendicular to the a-axis the columns are held together by van der Waals forces and several unremarkable C—H···O interactions (Table 1). The a-axis is also the needle axis of the crystals. The hydrogen bonded dimer TFS and TA shown in Fig. 1 resembles closely the situation in CMTFS, where a pair of TFS molecules related by a twofold axis is linked via two complementary N—H···N bonds measuring N···N = 2.900 (1) Å (Mereiter, 2011). However, the further spatial arrangement of the molecules in CMTFS differs significantly from (I).

Concluding remark: Cocrystal formation of bioactive compounds is a field of research nowadays very actively pursued with the goal of achieving new solids with superior properties like crystallization propensity, improved chemical stability, solubility, dissolution rate, etc.. In case of the title compound the cocrystal formation is interesting, but is not desirable on following grounds: The triazine amine as one of the two components of the cocrystal of (I) has unwanted biocidal properties, and the cocrystal formation may probably impede the purification of triazine amine contaminated triflusulfuron-methyl by industrial batch crystallization.

Experimental

In search of new crystal polymorphs a sample of technical triflusulfuron-methyl contaminated by some triazine amine (2-amino-4-(dimethylamino)-6-(2,2,2-trifluoroethoxy)-1,3,5-triazine) was dissolved in hot ethanol and boiled under reflux for 10 minutes. The solution was then cooled to room temperature and the solvent slowly evaporated within two days. Thin colorless needles of the title compound accompanied by larger crystals of triflusulfuron-methyl were obtained.