Acid-Base Indicator Properties of Synthesized Phenylhydrazones: 4-(2-(2,4-Dinitrophenyl) Hydrazono) Methyl)-2 Methoxy Phenol and 4-(2-(2,4-Dinitrophenylhydrazono) Methyl) Benzene-1,3-diol

4-(2-(2,4-Dinitrophenyl) hydrazone) methyl)-2 methoxy phenol (IND-X) and 4-(2-(2, 4-dinitrophenylhydrazono) methyl) benzene-1,3-diol (IND-Y) were synthesised by condensation reactions with 2,4-dinitrinophenylhydrazine and were observed to possess acid-base indicator properties. The study was conducted to explore and verify their use in different analytical situations and, consequently, validate them. Analysis of their use in acid-base titrations between strong acids/strong bases and weak acids/strong bases as well as pharmaceutical applications in the assay of ibuprofen pure powder and batch of ibuprofen tablets (400 mg) using standard methods in the British Pharmacopoeia (2020) was all considered. The validations were performed by the International Conference on Harmonisation of Technical Requirements for the registration of Pharmaceuticals for Humans Q2 (R1) guidelines. The outcomes were statistically compared with existing conventional analytical approaches. Titrimetric data obtained were analyzed statistically by Student’s t-test and one-way ANOVA at a 95% confidence level. IND-X and IND-Y were shown to be similar in behaviour to phenolphthalein, methyl orange, and methyl red as visual indicators after preliminary evidence of sharp colour changes in acid, alkaline, and neutral pH solutions. The use of the two indicators in the assay of ibuprofen powder and tablets has also been established. The validation parameters considered were found to be consistent with respective acceptance criteria for analytical purposes. IND-X and IND-Y are therefore proposed as alternative acid-base indicators to methyl red, methyl orange, and phenolphthalein for routine volumetric analysis in students’ laboratory experiments. They also serve as alternative indicators to phenolphthalein for the titrimetric analysis of ibuprofen-based samples and products.

1-(2-Chlorobenzylidene)-2-(2,4-dinitrophenyl)hydrazine

In the title compound, C₁₃H₉ClN₄O₄, there are two crystallographically independent mol­ecules in the asymmetric unit, which have very similar conformations. The C=N—N angles in each independent mol­ecule are 115.0 (2) and 116.6 (2)°, which are significantly smaller than the ideal value of 120° expected for sp²-hybridized N atoms. This is probably a consequence of repulsion between the nitro­gen lone pairs and the adjacent N—N bonds. Two bifurcated intra­molecular N—H⋯O hydrogen bonds help to establish the mol­ecular conformation and consolidate the crystal packing.

1-Cyclopentylidene-2-(2,4-dinitrophenyl)hydrazine

The title compound, C₁₁H₁₂N₄O₄, was synthesized by the reaction of (2,4-dinitro­phen­yl)hydrazine with cyclo­penta­none. The cyclo­pentyl fragment is disordered over two sites with occupancies of 0.63 (1) and 0.37 (1). An intra­molecular N—H⋯O hydrogen bond helps to establish the conformation. Pairs of mol­ecules are held together by π–π inter­actions between adjacent benzene rings [centroid-to-centroid distance 3.589 (2) Å].