Titanium Tetrachloride-Assisted Direct Esterification of Carboxylic Acids

Ester compounds, widely found in pharmaceutical and natural products, play a crucial role in organic synthesis, prompting the development of numerous methods for their synthesis. An important chemical approach in synthesizing esters from carboxylic acids involves the activation of the carboxyl function, requiring the conversion of the hydroxyl group into a suitable leaving group. This paper presents the findings of our investigations into an efficient method for producing esters from carboxylic acids and alcohols, using the Lewis acid titanium tetrachloride. Titanium tetrachloride has proven highly effective as a coupling reagent for the one-pot formation of esters from carboxylic acids and alcohols operating under mild and neutral conditions. Notably, the reaction eliminates the need for bases, yielding carboxylic esters in high purity and yields. The method is efficient, even with long-chain carboxylic acids, and operates well with primary alcohols in dichloromethane. Steric hindrance, potentially present in carboxylic acids, has a moderate effect on the reaction. Alcohol substrates that easily form stable carbocations require, instead, the use of non-polar solvents like hexane for the reaction.

Strategic Design and Synthesis of Ferrocene Linked Porous Organic Frameworks toward Tunable CO2 Capture and Energy Storage

This work focuses on porous organic polymers (POPs), which have gained significant global attention for their potential in energy storage and carbon dioxide (CO2) capture. The study introduces the development of two novel porous organic polymers, namely FEC-Mel and FEC-PBDT POPs, constructed using a simple method based on the ferrocene unit (FEC) combined with melamine (Mel) and 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) (PBDT). The synthesis involved the condensation reaction between ferrocenecarboxaldehyde monomer (FEC-CHO) and the respective aryl amines. Several analytical methods were employed to investigate the physical characteristics, chemical structure, morphology, and potential applications of these porous materials. Through thermogravimetric analysis (TGA), it was observed that both FEC-Mel and FEC-PBDT POPs exhibited exceptional thermal stability. FEC-Mel POP displayed a higher surface area and porosity, measuring 556 m2 g-1 and 1.26 cm3 g-1, respectively. These FEC-POPs possess large surface areas, making them promising materials for applications such as supercapacitor (SC) electrodes and gas adsorption. With 82 F g-1 of specific capacitance at 0.5 A g-1, the FEC-PBDT POP electrode has exceptional electrochemical characteristics. In addition, the FEC-Mel POP showed remarkable CO2 absorption capabilities, with 1.34 and 1.75 mmol g-1 (determined at 298 and 273 K; respectively). The potential of the FEC-POPs created in this work for CO2 capacity and electrical testing are highlighted by these results.

Low-Temperature Thermal Formation of the Cyclic Methylphosphonic Acid Trimer [c-(CH3 PO2 )3 ]

We report the formation of the cyclic methylphosphonic acid trimer [c-(CH₃ PO₂ )₃ ] through condensation reactions during thermal processing of low-temperature methylphosphonic acid samples exploiting photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) along with electronic structure calculations. Cyclic methylphosphonic acid trimers are formed in the solid state and detected together with its protonated species in the gas phase upon single photon ionization. Our studies provide an understanding of the preparation of phosphorus-bearing potentially prebiotic molecules and the fundamental knowledge of low-temperature phosphorus chemistry in extraterrestrial environments.

Direct anabolic metabolism of three carbon propionate to a six carbon metabolite occurs in vivo across tissues and species

Anabolic metabolism of carbon in mammals is mediated via the one- and two-carbon carriers S-adenosyl methionine and acetyl-coenzyme A. In contrast, anabolic metabolism of three-carbon units via propionate has not been shown to extensively occur. Mammals are primarily thought to oxidize the three-carbon short chain fatty acid propionate by shunting propionyl-CoA to succinyl-CoA for entry into the TCA cycle. Here, we found that this may not be absolute as, in mammals, one nonoxidative fate of propionyl-CoA is to condense to two three-carbon units into a six-carbon trans-2-methyl-2-pentenoyl-CoA (2M2PE-CoA). We confirmed this reaction pathway using purified protein extracts provided limited substrates and verified the product via LC-MS using a synthetic standard. In whole-body in vivo stable isotope tracing following infusion of ¹³C-labeled valine at steady state, 2M2PE-CoA was found to form via propionyl-CoA in multiple murine tissues, including heart, kidney, and to a lesser degree, in brown adipose tissue, liver, and tibialis anterior muscle. Using ex vivo isotope tracing, we found that 2M2PE-CoA also formed in human myocardial tissue incubated with propionate to a limited extent. While the complete enzymology of this pathway remains to be elucidated, these results confirm the in vivo existence of at least one anabolic three- to six-carbon reaction conserved in humans and mice that utilizes propionate.

Complex formation of lactic acid by atmospheric pressure chemical ionization

Oligomers and polymers of lactic acid are generally synthesized through condensation reactions by dehydration at high emperature under catalysis. In the present work, ionization behaviors of lactic acid produced by atmospheric pressure chemical ionization were investigated. Influence of the sample concentration, the heating zone temperature, and the source fragmentor voltage on kinds and abundances of the product ions was examined. Complex formation of the product ions with neutral species was also investigated. Not only lactate, [M-H]^- and its complexes but also ions of condended species, [nM-(n-1)H₂ O-H]^- with n = 2-5, and their complexes were observed. The condensation reactions occurred in an aerosol state generated in the heating zone for evaporation. By increasing the concentration of lactic acid, abundances of the product ions were increased and the increase of larger ones was noticeable. By increasing the heating zone temperature, abundances of the product ions were decreased and the decrease of larger ones was remarkable. By increasing the source fragmentor voltage, abundances of small product ions were increased and those of the complexes, [nM-(n-2)H₂ O-H]^- with n = 2-5, were significantly decreased. Complex formation of lactate with the neutral condensed species was more favorable than that of the condensed oligomer ions with a neutral lactic acid. The experimental results were explained by energies and structures of the product ions and neutral species obtained by theoretical calculations.

Benzothiazoles from Condensation of o-Aminothiophenoles with Carboxylic Acids and Their Derivatives: A Review

Nowadays, organic chemists are interested in the field of heterocyclic chemistry due to its use in the synthesis of a great variety of biologically active compounds. Heterocyclic compounds are widely found in nature and are essential for life. Among these, some natural nitrogen containing heterocyclic compounds have been used as chemotherapeutic agents. Their attachment to sugar molecules either as thioglycosides or as nucleosides analogues plays an important role in vital biological processes as well as in synthetic organic chemistry. Molecules containing benzothiazole (BT) nuclei are of this interesting class of compounds because some of them have been found to have a wide variety of biological activities. In this sense, we selected this topic to review and to then summarize the procedures related to the condensation reactions of o-aminothiophenoles (ATPs) as well as their disulfides with carboxylic acids, esters, orthoesters, acyl chlorides, amides, and nitriles. The condensation reactions with carbon dioxide (CO₂) are included. Conventional methods with the use of acid and metal catalysts as well as recent green techniques, such as microwave irradiation, the use of ionic liquids, and ultrasound (US) chemistry, which have proven to have many advantages, were found in the review.

Poly(N-vinylimidazole): A biocompatible and biodegradable functional polymer, metal-free, and highly recyclable heterogeneous catalyst for the mechanochemical synthesis of oximes

The catalytic activity of poly(N-vinylimidazole), a biocompatible and biodegradable synthetic functional polymer, was investigated for the synthesis of oximes as an efficient, halogen-free, and reusable heterogeneous catalyst. The corresponding oximes were afforded in high to excellent yields at room temperature and in short times using the planetary ball mill technique. Some merits, such as the short reaction times and good yields for poorly active carbonyl compounds, and avoiding toxic, expensive, metal-containing catalysts, and hazardous and flammable solvents, can be mentioned for the current catalytic synthesis of the oximes. Furthermore, the heterogeneous organocatalyst could be easily separated after the reaction, and the regenerated catalyst was reused several times with no significant loss of its catalytic activity.

Optical Fiber Based Mach-Zehnder Interferometer for APES Detection

A 3-aminopropyl-triethoxysilane (APES) fiber-optic sensor based on a Mach–Zehnder interferometer (MZI) was demonstrated. The MZI was constructed with a core-offset fusion single mode fiber (SMF) structure with a length of 3.0 cm. As APES gradually attaches to the MZI, the external environment of the MZI changes, which in turn causes change in the MZI’s interference. That is the reason why we can obtain the relationships between the APES amount and resonance dip wavelength by measuring the transmission variations of the resonant dip wavelength of the MZI. The optimized amount of 1% APES for 3.0 cm MZI biosensors was 3 mL, whereas the optimized amount of 2% APES was 1.5 mL.

A Golgi Apparatus-Targeting, Naphthalimide-Based Fluorescent Molecular Probe for the Selective Sensing of Formaldehyde

Formaldehyde (FA) is a colorless, flammable, foul-smelling chemical used in building materials and in the production of numerous household chemical goods. Herein, a fluorescent chemosensor for FA is designed and prepared using a selective organ-targeting probe containing naphthalimide as a fluorophore and hydrazine as a FA-binding site. The amine group of the hydrazine reacts with FA to form a double bond and this condensation reaction is accompanied by a shift in the absorption band of the probe from 438 nm to 443 nm upon the addition of FA. Further, the addition of FA is shown to enhance the emission band at 532 nm relative to the very weak fluorescent emission of the probe itself. Moreover, a high specificity is demonstrated towards FA over other competing analytes such as the calcium ion (Ca²⁺), magnesium ion (Mg²⁺), acetaldehyde, benzaldehyde, salicylaldehyde, glucose, glutathione, sodium sulfide (Na₂S), sodium hydrosulfide (NaHS), hydrogen peroxide (H₂O₂), and the tert-butylhydroperoxide radical. A typical two-photon dye incorporated into the probe provides intense fluorescence upon excitation at 800 nm, thus demonstrating potential application as a two-photon fluorescent probe for FA sensing. Furthermore, the probe is shown to exhibit a fast response time for the sensing of FA at room temperature and to facilitate intense fluorescence imaging of breast cancer cells upon exposure to FA, thus demonstrating its potential application for the monitoring of FA in living cells. Moreover, the presence of the phenylsulfonamide group allows the probe to visualize dynamic changes in the targeted Golgi apparatus. Hence, the as-designed probe is expected to open up new possibilities for unique interactions with organ-specific biological molecules with potential application in early cancer cell diagnosis.

Kraft Process-Formation of Secoisolariciresinol Structures and Incorporation of Fatty Acids in Kraft Lignin

The complex chemical structure and the fact that many areas in pulping and lignin chemistry still remain unresolved are challenges associated with exploiting lignin. In this study, we address questions regarding the formation and chemical nature of the insoluble residual lignin, the presence of fatty acids in kraft lignin, and the origin of secoisolariciresinol structures. A mild thermal treatment of lignin at maximum kraft-cooking temperatures (∼170 °C) with tall oil fatty acids (TOFA) or in an inert solvent (decane) produced highly insoluble products. However, acetylation of these samples enabled detailed chemical characterization by nuclear magnetic resonance (NMR) spectroscopy. The results show that the secoisolariciresinol (β-β) structure in kraft lignin is formed by rearrangement of the β-aryl ether structure. Furthermore, fatty acids bind covalently to kraft lignin by reacting with the stilbene structures present. It is highly probable that these reactions also occur during kraft pulping, and this phenomenon has an impact on controlling the present kraft pulping process along with the development of new products from kraft lignin.

The Possible Side Reaction in the Annealing Process of Perovskite Layers

The high purity of light harvesting layers is one of the core issues for highly efficient perovskite solar cells. The perovskite precursor solution and the crystallization growth of thin films have been extensively studied in the past few years. Herein, we have unveiled some side reactions that occur during the evaporation of the residual solvent in the spin-coated films at elevated temperature, forming N-methyl formamidium iodide and N,N'-dimethyl formamidium iodide. Such side reactions will consume the precursor materials and then produce a secondary phase in the perovskite films, which is detrimental for the performance improvement. We have also found that a combination of room temperature aging and vacuum treatment of the spin-coated wet film is conducive to eliminate the side reactions and improve the perovskite phase purity, reaching an efficiency of 20.98%.

The Influence of β-Ammonium Substitution on the Reaction Kinetics of Aminooxy Condensations with Aldehydes and Ketones

The click-chemistry capture of volatile aldehydes and ketones by ammonium aminooxy compounds has proven to be an efficient means of analyzing the carbonyl subset in complex mixtures, such as exhaled breath or environmental air. In this work, we examine the carbonyl condensation reaction kinetics of three aminooxy compounds with varying β-ammonium ion substitution using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). We determined the activation energies for the reactions of the aminooxy compounds ATM, ADMH and AMAH with a panel of ketones and aldehydes that included acrolein and crotonaldehyde. The measurements indicate that the activation energies for the oximation reactions are quite low, less than 75 kJ mol^-1 . ADMH is observed to react the fastest with the carbonyls studied. We postulate this result may be attributed to the ADMH ammonium proton effecting a Brønsted-Lowry acid-catalyzed elimination of water during the rate-determining step of oxime ether formation. A theoretical study of oxime ether formation is presented to explain the enhanced reactivity of ADMH relative to the tetraalkylammonium analog ATM.

Synthesis, mol-ecular and crystal structure of 1-(1,2-di-hydro-phthalazin-1-yl-idene)-2-[1-(thio-phen-2-yl)ethyl-idene]hydrazine

The title compound, C14H12N4S, was synthesized by the condensation reaction of hydralazine and 2-acetyl-thio-phene and during the reaction, a proton transfer from the imino nitro-gen atom to one of the endocylic nitro-gen atoms occurred. The compound crystallizes in the monoclinic crystal system with two independent mol-ecules (mol-ecules 1 and 2) in the asymmetric unit. In each mol-ecule, there is a slight difference in the orientation of the thio-phene ring with respect to phthalazine ring system, mol-ecule 1 showing a dihedral angle of 42.51 (1)° compared to 8.48 (1)° in mol-ecule 2. This implies an r.m.s deviation of 0.428 (1) Å between the two mol-ecules for the 19 non-H atoms. The two independent mol-ecules are connected via two N-H⋯N hydrogen bonds, forming dimers which inter-act by two bifurcated π-π stacking inter-actions to build tetra-meric motifs. The latter are packed in the ac plane via weak C-H⋯π inter-actions and along the b axis via C-H ⋯N and C-H⋯π inter-actions. This results a three-dimensional architecture with a tilted herringbone packing mode.

Drosophila melanogaster nonribosomal peptide synthetase Ebony encodes an atypical condensation domain

The protein Ebony from Drosophila melanogaster plays a central role in the regulation of histamine and dopamine in various tissues through condensation of these amines with β-alanine. Ebony is a rare example of a nonribosomal peptide synthetase (NRPS) from a higher eukaryote and contains a C-terminal sequence that does not correspond to any previously characterized NRPS domain. We have structurally characterized this C-terminal domain and have discovered that it adopts the aryl-alkylamine-N-acetyl transferase (AANAT) fold, which is unprecedented in NRPS biology. Through analysis of ligand-bound structures, activity assays, and binding measurements, we have determined how this atypical condensation domain is able to provide selectivity for both the carrier protein-bound amino acid and the amine substrates, a situation that remains unclear for standard condensation domains identified to date from NRPS assembly lines. These results demonstrate that the C terminus of Ebony encodes a eukaryotic example of an alternative type of NRPS condensation domain; they also illustrate how the catalytic components of such assembly lines are significantly more diverse than a minimal set of conserved functional domains.

Formaldehyde-aminoguanidine condensation and aminoguanidine self-condensation products: syntheses, crystal structures and characterization

Guanidine is the functional group on the side chain of arginine, one of the fundamental building blocks of life. In recent years, a number of compounds based on the aminoguanidine (AG) moiety have been described as presenting high anticancer activities. The product of condensation between two molecules of AG and one molecule of formaldehyde was isolated in the protonated form as the dinitrate salt (systematic name: 2,8-diamino-1,3,4,6,7,9-hexaazanona-1,8-diene-1,9-diium dinitrate), C₃H₁₄N₈²⁺·2NO₃^-, (I). The cation lacks crystallographically imposed symmetry and comprises two terminal planar guanidinium groups, which share an N-C-N unit. Each cation in (I) builds 14 N-H...O hydrogen bonds and is separated from adjacent cations by seven nitrate anions. The AG self-condensation reaction in the presence of copper(II) chloride and chloride anions led to the formation of the organic-inorganic hybrid 1,2-bis(diaminomethylidene)hydrazine-1,2-diium tetrachloridocuprate(II), (C₂H₁₀N₆)[CuCl₄], (II). Its asymmetric unit is composed of half a diprotonated 1,2-bis(diaminomethylidene)hydrazine-1,2-diium dication and half a tetrachloridocuprate(II) dianion, with the Cu^II atom situated on a twofold rotation axis. The planar guanidinium fragments in (II) have their planes twisted by approximately 77.64 (5)° with respect to each other. The tetrahedral [CuCl₄]^2- anion is severely distorted and its pronounced `planarity' must originate from its involvement in multiple N-H...Cl hydrogen bonds. It was reported that [CuCl₄]^2- anions, with a trans-Cl-Cu-Cl angle (Θ) of ∼140°, are yellow-green at room temperature, with the colour shifting to a deeper green as Θ increases and toward orange as Θ decreases. Brown salt (II), with a Θ value of 142.059 (8)°, does not fit the trend, which emphasizes the need to take other structural factors into consideration. In the crystal of salt (II), layers of cations and anions alternate along the b axis, with the minimum Cu...Cu distance being 7.5408 (3) Å inside a layer. The structures of salts (I) and (II) were substantiated via spectroscopic data. The endothermic reaction involved in the thermal decomposition of (I) requires additional oxygen. The title salts may be useful for the screening of new substances with biological activity.

Practical Synthesis of Chalcone Derivatives and Their Biological Activities

Practical synthesis and biological activities of 4-hydroxy-3-methoxy-2-propene derivatives are described. The novel chalcone derivatives were prepared by acid catalysed one-step condensation of 1,3- or 1,4-diacetylbenzene and 1,3,5-triacetylbenzene with 4-hydroxy-3-methoxybenzaldehyde. They were then evaluated for free radical scavenging activity, suppression of lipopolysaccharides (LPS)-induced NO generation, and anti-excitotoxicity in vitro. It was found that all compounds showed good effects for 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging, LPS-induced NO generation, and anti-neurotoxicity. Compounds 6 and 7 were potent suppressor of NO generation with the concentration range 10 µM and especially compound 8 showed very potent anti-inflammatory activity with 1 µM. In addition, the di- and tri-acetylbenzyl derivatives 6, 7, and 8 showed enhanced anti-neurotoxicity activity in cultured cortical neurons. Molecular modelling studies to investigate the chemical structural characteristics required for the enhanced biological activities interestingly revealed that compound 8 has the smallest highest occupied molecular orbital-lowest energy unoccupied molecular orbital (HOMO-LUMO) gap, which signifies easy electron and radical transfer between HOMO and LUMO in model studies.

Engineering a Promiscuous Tautomerase into a More Efficient Aldolase for Self-Condensations of Linear Aliphatic Aldehydes

The enzyme 4-oxalocrotonate tautomerase (4-OT) from Pseudomonas putida mt-2 takes part in a catabolic pathway for aromatic hydrocarbons, where it catalyzes the conversion of 2hydroxyhexa-2,4-dienedioate into 2-oxohexa-3-enedioate. This tautomerase can also promiscuously catalyze carbon-carbon bond-forming reactions, including various types of aldol reactions, by using its amino-terminal proline as a key catalytic residue. Here, we used systematic mutagenesis to identify two hotspots in 4-OT (Met45 and Phe50) at which single mutations give marked improvements in aldolase activity for the self-condensation of propanal. Activity screening of a focused library in which these two hotspots were varied led to the discovery of a 4-OT variant (M45Y/F50V) with strongly enhanced aldolase activity in the self-condensation of linear aliphatic aldehydes, such as acetaldehyde, propanal, and butanal, to yield α,β-unsaturated aldehydes. With both propanal and benzaldehyde, this double mutant, unlike the previously constructed single mutant F50A, mainly catalyzes the self-condensation of propanal rather than the cross-condensation of propanal and benzaldehyde, thus indicating that it indeed has altered substrate specificity. This variant could serve as a template to create new biocatalysts that lack dehydration activity and possess further enhanced aldolase activity, thus enabling the efficient enzymatic self-coupling of aliphatic aldehydes.

Crystal structure of N,N'-bis-(pyridin-3-ylmeth-yl)cyclo-hexane-1,4-di-ammonium dichloride

The title salt, C18H26N42+·2Cl-, was obtained by the protonation of N,N-bis-(pyridin-4-ylmeth-yl)cyclo-hexane-1,4-di-amine with hydro-chloric acid in ethanol. The asymmetric unit consists of one half of an N,N-bis-(pyridin-3-ylmeth-yl)cyclo-hexane-1,4-di-ammonium dication, with a crystallographic inversion centre located at the centre of the cyclo-hexyl ring, and a chloride anion. The central cyclo-hexyl ring in the dication adopts a chair conformation. The two trans-(4-pyridine)-CH2-NH2- moieties at the 1- and 4-positions of the central cyclo-hexyl ring occupy equatorial sites. The terminal pyridine ring is tilted by 53.72 (6)° with respect to the mean plane of the central cyclo-hexyl ring (r.m.s. deviation = 0.2413 Å). In the crystal, N+-H⋯Cl- hydrogen bonds between the dications and the chloride anions, and π-π stacking inter-actions between the pyridine rings of the dications afford a two-dimensional sheet extending parallel to the ab plane. These sheets are further connected through weak C-H⋯Cl- hydrogen bonds, resulting in the formation of a three-dimensional supra-molecular network.

A Convenient Synthesis of 3,7'-Bisindole Derivatives

An efficient and convenient method to synthesize highly functionalized 3,7'-bisindole derivatives has been developed via a Michael addition and cyclic condensation reaction of heterocyclic ketene aminals (HKAs) with 2-(1H-indol-3-yl)cyclohexa-2,5-diene-1,4-dione derivatives in ethanol-based solvents at room temperature. This strategy provides an efficient, environmentally friendly approach for easy access to various novel 3,7'-bisindole derivatives in moderate to good yields.

Microwave-Assisted Condensation Reactions of Acetophenone Derivatives and Activated Methylene Compounds with Aldehydes Catalyzed by Boric Acid under Solvent-Free Conditions

We here disclosed a new protocol for the condensation of acetophenone derivatives and active methylene compounds with aldehydes in the presence of boric acid under microwave conditions. Implementation of the reaction is simple, healthy and environmentally friendly owing to the use of a non-toxic catalyst coupled to a solvent-free procedure. A large variety of known or novel compounds have thus been prepared, including with substrates bearing acid or base-sensitive functional groups.

Two different products from the reaction of 1-aryl-5-chloro-3-methyl-1H-pyrazole-4-carbaldehyde with cyclohexylamine when the aryl substituent is phenyl or pyridin-2-yl: hydrogen-bonded sheets versus dimers

Cyclohexylamine reacts with 5-chloro-3-methyl-1-(pyridin-2-yl)-1H-pyrazole-4-carbaldehyde to give 5-cyclohexylamino-3-methyl-1-(pyridin-2-yl)-1H-pyrazole-4-carbaldehyde, C16H20N4O, (I), formed by nucleophilic substitution, but with 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde the product is (Z)-4-[(cyclohexylamino)methylidene]-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one, C17H21N3O, (II), formed by condensation followed by hydrolysis. Compound (II) crystallizes with Z' = 2, and in one of the two independent molecular types the cyclohexylamine unit is disordered over two sets of atomic sites having occupancies of 0.65 (3) and 0.35 (3). The vinylogous amide portion in each compound shows evidence of electronic polarization, such that in each the O atom carries a partial negative charge and the N atom of the cyclohexylamine portion carries a partial positive charge. The molecules of (I) contain an intramolecular N-H...N hydrogen bond, and they are linked by C-H...O hydrogen bonds to form sheets. Each of the two independent molecules of (II) contains an intramolecular N-H...O hydrogen bond and each molecular type forms a centrosymmetric dimer containing one R2(2)(4) ring and two inversion-related S(6) rings.

Crystal structure of N'-[(E)-(4-chloro-phen-yl)(phen-yl)methyl-idene]-4-methyl-benzene-sulfono-hydrazide

The title compound, C20H17ClN2O2S, was obtained by a condensation reaction between 4-chloro-benzo-phenone and tosyl hydrazide. The plane of the methyl-substituted benzene ring forms dihedral angles of 20.12 (12) and 78.43 (13)° with those of the chlorine-substituted benzene ring and the benzene ring, respectively, with the last two rings forming a dihedral angle of 67.81 (13)°. The chlorine substituent was also found to be 0.868 (2):0.132 (2) disordered over these two rings. In the crystal, mol-ecules are linked through pairs of N-H⋯O hydrogen bonds, giving centrosymmetric cyclic dimers [graph set R 2 (2)(8)], which are linked by weak C-H⋯O and C-H⋯Cl inter-actions into a chain structure which extends along the a-axis direction.

(E)-1-[(5-chloro-3-methyl-1-phenyl-1H-pyrazol-4-yl)methylidene]-2-phenylhydrazine: sheets built from π-stacked hydrogen-bonded chains

The reaction between 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde and phenylhydrazine proceeds via condensation to provide the title compound, C17H15ClN4, (I), rather than via the alternative routes of simple nucleophilic substitution or cyclocondensation. With the exception of the phenyl group bonded directly to the pyrazole ring, the non-H atoms of (I) are nearly coplanar, with an r.m.s. deviation of 0.058 Å. The molecules are linked into C(7) chains by a single N-H···N hydrogen bond, and the chains are linked by π-π stacking interactions to form sheets.