Crystallization
of the nonsteroidal anti-inflammatory drug (NSAID)
flunixin in acetone and in acetone–hexane produced two conformational
polymorphs, as predicted by hydrogen-bond propensity analyses, which
are similar to three of the polymorphs of the related NSAID clonixin.
The two polymorphs of flunixin display an intramolecular hydrogen
bond between the amine N–H and the carbonyl oxygen of the carboxylic
group. However, the intermolecular hydrogen-bond pattern of Form I
(crystallized from acetone) is characterized by the acid–pyridine
heterosynthon, while Form II (from acetone-hexane) displays the acid–acid
homosynthon. Form I of flunixin is similar to form I of clonixin,
while form II of flunixin is related to forms III and IV of clonixin.
Hirshfeld surface maps were used to show the differences in the interactions
present in the two flunixin polymorphs and the similarities with the
polymorphs of the related compound clonixin. Energy framework calculations
corroborate the similarity between Form I of flunixin and clonixin
and indicate that Form II of flunixin is more closely related to Form
IV of clonixin than to Form III.
In the title compound, C10H7FN2OS, the mean plane of the central amide fragment (r.m.s. deviation = 0.048 Å) makes dihedral angles of 35.28 (8) and 10.14 (12)° with those of the fluorobenzene and thiazole rings, respectively. The thiazole S and amide O atoms lie to the same side of the molecule. In the crystal, pairs of N—H⋯N hydrogen bonds connect the molecules into inversion dimers with R
2
2(8) motifs, and weak C—H⋯O interactions connect the molecules into C(6) [001] chains. Together, the N—H⋯N and C—H⋯O hydrogen bonds generate (100) sheets.
The 1-[N-(methyl)-(3,5-dimethylphenylamino)]methylnaphthalene (chemical formula C20H21N) was prepared by means of a condensation between alpha-naphthylaldehyde and 3,5-dimethylaniline in anhydrous ethanol to obtain the aldimine (1) which was reduced with NaBH4 to afford the 1-[N-(3,5-dimethylphenylamino)]methylnaphtalene (2), and finally, the compound (3) was obtained by N-alkylation reaction of (2) with methyl iodine (CH3I) and potassium carbonate (K2CO3) in acetone. Final compound (3) was purified by chromatographic column. The XRPD pattern for the new compound, 1-[N-(methyl)-(3,5-dimethylphenylamino)]methylnaphthalene, was obtained. This compound crystallizes in monoclinic system with space group P21/a (No. 14) and refined unit-cell parameters a=13.260(4) Å, b=15.495(5) Å, c=7.719(5) Å, β=90.19(6), and V=1586(1) Å3.
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