The crystal structure of 4-dimethylaminoantipyrine hydrochloride, C₁₃H₁₈N₃OCl

1 Source of materials

To synthesize the title compound, 0.10 g (0.435 mmol) of 4-dimethylaminoantipyrine (DMAAP, M = 231.29 g mol⁻¹ was weighed into a glass vial. To this was added 1 mL of 4-heptanone (reagent) and 3 mL of methanol (solvent). The mixture was sonicated for 5 min to promote dissolution. A single drop of concentrated hydrochloric acid (33 %, catalyst) was added to initiate the reaction. The solution was allowed to stand at ambient temperature. A colourless crystal salt formed within 2 days via slow evaporation of the solvent (Table 1).

2 Experimental details

First the non-hydrogen atoms were refined isotropically, then anisotropically by full matix least-squares calculations based on F². Carbon-bound hydrogen atoms were located in the difference map then positioned geometrically and were allowed to ride on their respective parent atoms with thermal displacement parameters 1.2 times of the parent C atom. The coordinates and isotropic displacement parameters of the nitrogen bound H atom was allowed to refine freely. Diagrams and publication material were generated using Ortep-3, ⁴ Wingx ⁵ and Platon. ⁶

3 Discussion

4-Dimethylaminoantipyrine (DMAAP) is a synthetic pyrazolone derivative structurally related to phenazone-based nonsteroidal anti-inflammatory drugs. It has been widely studied for its antipyretic and analgesic properties, but also demonstrates potential as a redox-active scaffold in coordination chemistry and sensor applications. ^{7 , 8 , 9} Recent pharmaceutical investigations have explored its quantification in drug formulations ⁷ and its antioxidant reactivity towards reactive oxygen species such as hydroxyl radicals. ⁸ Furthermore, 4-dimethylaminoantipyrine has gained attention as a useful component in the fabrication of electrochemical sensors due to its broad redox response and compatibility with conductive platforms. ^{9 , 10}

This work forms part of our ongoing investigation into the synthesis and structural characterization of salt and hydrogen-bonded assemblies of bioactive pyrazolone analogues.

The asymmetric unit of the salt contains one organic cation and one chloride anion with the systematic name: (N,N,1,5-tetramethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-aminium chloride and crystallizes in the monoclinic P2₁/c space group. A strong N-H···Cl hydrogen bond connects the chloride anions and organic cation. With regard to packing, DMAAP cations interact via π–π stacking of the phenyl rings with a distance of 3.4 Å between them.