Introduction
C24H25ClN2O is a molecular formula that corresponds to a small organochlorine heterocycle containing two nitrogen atoms and one oxygen atom. The compound is an aromatic amide derivative in which a chlorobenzene ring is fused to a secondary amide group bearing a secondary amine substituent. Because the formula allows for several possible structural isomers, the most common representation is the 4‑chloro‑N‑(p‑phenyl)‑N‑(methyl)benzamide, which features a chlorobenzyl moiety, a tertiary amide nitrogen, and an anilide nitrogen. The compound is encountered primarily as an intermediate in the synthesis of medicinal agents, dyes, and agrochemicals. Its physical and chemical characteristics are typical of aromatic amides: a moderate melting point, limited water solubility, and a strong UV absorption band near 280 nm.
Structural Features
Molecular Architecture
The molecular skeleton of C24H25ClN2O consists of a benzene ring bearing a chlorine atom at the para position, a tertiary amide linkage, and a secondary amine attached to a phenyl group. The amide carbonyl carbon is sp² hybridized and participates in conjugation with the aromatic system, which reduces its electrophilicity compared with aliphatic amides. The nitrogen atoms are sp³ hybridized; one nitrogen is tertiary and bonded to the carbonyl carbon, a methyl group, and a phenyl ring, while the other nitrogen is secondary and bound to the carbonyl carbon and a hydrogen atom. The oxygen atom is part of the amide carbonyl and is doubly bonded to the carbonyl carbon.
Electronic Distribution
The electron density of the molecule is delocalized over the aromatic ring and the amide group. The presence of the chlorine substituent introduces an electron-withdrawing inductive effect, which slightly lowers the electron density at the para position. The amide nitrogen atoms exhibit resonance structures that contribute to the stability of the carbonyl group. The conjugation between the aromatic system and the carbonyl extends the π‑electron cloud over the entire aromatic ring, enhancing the molecule’s UV absorbance. The electron‑rich tertiary amine nitrogen can act as a proton acceptor, which may influence the compound’s basicity (pK_a ≈ 5.4 for the secondary amide nitrogen, pK_b ≈ 8.9 for the tertiary amine nitrogen).
Isomeric Possibilities
Because the formula does not specify connectivity, several isomers can be conceived. In addition to the 4‑chloro‑N‑(p‑phenyl)‑N‑(methyl)benzamide, a 4‑chloro‑N,N‑dimethylbenzamide derivative with an aniline substituent on the nitrogen is possible. Another structural variant involves the chlorine attached to the phenyl ring of the secondary amine, yielding 4‑chloro‑N‑(3‑chloro‑p‑phenyl)benzamide. Each isomer differs in its spectroscopic signature, melting point, and reactivity, but the most frequently reported is the 4‑chloro‑N‑(p‑phenyl)‑N‑(methyl)benzamide due to its synthetic accessibility and applications in pharmacology.
Synthesis
General Synthetic Strategy
Typical laboratory preparation of C24H25ClN2O involves the condensation of a chlorobenzyl chloride with a secondary amine followed by amidation of the resulting amine. The overall sequence can be described in three steps: (1) nucleophilic aromatic substitution of 4‑chloroaniline with methyl iodide to form 4‑chloro‑N‑methylaniline; (2) acylation of the tertiary amine with benzoyl chloride to introduce the amide carbonyl; (3) purification by recrystallization or column chromatography. Each step employs standard reagents and conditions commonly used in organic synthesis laboratories.
Step‑by‑Step Procedure
- Formation of 4‑chloro‑N‑methylaniline: 4‑Chloroaniline (10 g) is dissolved in acetone (100 mL) and methyl iodide (12 mL) is added dropwise under stirring at 0 °C. The mixture is warmed to room temperature and refluxed for 4 h. After cooling, the solvent is removed under reduced pressure, and the crude product is washed with water to remove salts. The product is then purified by silica gel chromatography (hexane/ethyl acetate 8:1) to yield a pale yellow solid (yield ≈ 80 %).
- Amidation with benzoyl chloride: 4‑Chloro‑N‑methylaniline (5 g) is suspended in dichloromethane (50 mL) and cooled to 0 °C. Benzoyl chloride (5 mL) and pyridine (5 mL) are added sequentially. The reaction is allowed to reach room temperature and stirred for 2 h. The mixture is washed with 1 M HCl to remove pyridinium chloride, then with saturated NaHCO₃ to neutralize residual acid. After drying over Na₂SO₄ and filtration, the solvent is evaporated, and the crude amide is recrystallized from ethanol to give a white crystalline product (yield ≈ 70 %).
- Final purification: The crystalline amide is dissolved in methanol (10 mL) and passed through a silica plug containing 5 % diethyl ether in hexane to remove any unreacted aromatic amine. The filtrate is concentrated and the product is isolated by recrystallization from acetone, providing the final compound in high purity (≥ 99 %).
Alternative Routes
Other synthetic approaches exploit the use of Buchwald–Hartwig amination to form the C–N bond directly between 4‑chloroaniline and a phenylboronic acid, followed by oxidation to introduce the amide functionality. A third route involves the reaction of 4‑chloro‑benzoyl chloride with N,N‑dimethylaniline to yield a symmetrical bis‑amine that can be converted to the desired amide by selective N‑methylation and protonation. Each route presents advantages in terms of step count, reagent availability, and overall yield.
Physical and Chemical Properties
Basic Physical Data
The compound crystallizes as a white to off‑white solid with a melting point of 152–154 °C (decomposition 2 °C above). The density of the crystalline form is 1.35 g cm⁻³ at 20 °C. The substance has a faint chloro‑benzene odor and is practically insoluble in water. It is soluble in polar organic solvents such as ethanol, methanol, acetone, and dimethyl sulfoxide, with solubility values ranging from 10 mg mL⁻¹ (ethanol) to 30 mg mL⁻¹ (DMSO).
Spectroscopic Data
In the IR spectrum, the amide carbonyl stretch appears at 1676 cm⁻¹, while the N–H stretch is observed at 3362 cm⁻¹. The aromatic C–H stretches appear between 3030 and 3100 cm⁻¹, and the C–Cl vibration is noted at 698 cm⁻¹. The ^1H NMR spectrum (400 MHz, CDCl₃) shows multiplets for the aromatic protons between 7.02 and 7.81 ppm, a singlet at 3.84 ppm for the N‑CH₃ group, and a broad singlet at 8.34 ppm for the amide N–H. The ^13C NMR spectrum (100 MHz, CDCl₃) displays signals at 160.2, 138.9, 135.4, 129.6, 127.8, 126.5, 122.4, 121.3, 115.2, 112.6, 51.7, and 41.2 ppm. High‑resolution mass spectrometry confirms the molecular weight of 387.1542 Da (calculated for C₂₄H₂₅ClN₂O, [M+H]⁺ = 388.1615).
Reactivity
The compound displays typical reactivity of aromatic amides. It undergoes reduction to the corresponding amine under hydrogenation conditions (Pd/C, H₂, 1 atm, 20 °C). The amide can be converted to the corresponding acid chloride by thionyl chloride or oxalyl chloride. Nucleophilic substitution at the chlorinated aromatic ring is feasible with alkoxides or cyanide, leading to the formation of 4‑alkoxy or 4‑cyanophenyl derivatives. The tertiary amine nitrogen can be alkylated using alkyl halides to form quaternary ammonium salts, which are often more soluble in water.
Thermal Stability
Thermogravimetric analysis shows a single decomposition step beginning at 165 °C, with 100 % weight loss by 200 °C. The compound does not decompose under standard laboratory conditions and is stable in the solid state for several months when stored at 4 °C in a dry environment.
Applications
Pharmaceutical Intermediates
Due to its amide functionality and chlorine substituent, C24H25ClN2O serves as a versatile building block in the synthesis of various heterocyclic pharmaceuticals. It can undergo cyclization with β‑hydroxy ketones to generate substituted pyridazinones, which are core structures in antiviral and anticancer agents. Moreover, the molecule can be employed in the preparation of 4‑chloro-2‑(p‑phenyl)benzoate derivatives, which are precursors to selective serotonin reuptake inhibitors. The ease of functional group interconversion allows medicinal chemists to access libraries of analogues for structure‑activity relationship studies.
Agrochemical Precursors
The chloro substitution on the aromatic ring can be exploited to generate organophosphate insecticides through diazotization followed by substitution with phosphorous trichloride. In addition, the tertiary amine nitrogen can be protonated to create water‑soluble salts that function as herbicide adjuvants, improving the uptake of active ingredients in plants.
Materials Science
The compound is utilized in the fabrication of polymeric materials with high dielectric constants. When incorporated into a polyimide matrix through polycondensation with diamines, it yields copolymers that exhibit enhanced thermal resistance and mechanical strength. In photovoltaic research, the molecule’s conjugated amide system can be integrated into small‑molecule donor materials for organic solar cells, where it improves charge‑transport properties.
Analytical Standards
Because of its distinctive UV absorption and stable crystalline form, C24H25ClN2O is employed as a calibration standard for spectrophotometric assays that measure aromatic amides. The compound’s mass spectral profile serves as a reference in the analysis of complex mixtures containing amide‑containing contaminants.
Biological Activity
In Vitro Activity
When evaluated against a panel of cancer cell lines (HeLa, MCF‑7, A549), the compound shows moderate cytotoxicity with IC₅₀ values ranging from 35 µM to 58 µM. The chloro‑substituted amide appears to inhibit the proliferation of cells via disruption of microtubule dynamics. In antiviral screening, the molecule inhibits replication of influenza A virus in MDCK cells by acting as a precursor to a fused triazine scaffold, leading to a reduction in viral titers (IC₅₀ ≈ 12 µM).
In Vivo Activity
Preliminary studies in murine models demonstrate that the compound possesses an oral bioavailability of 32 % at a dose of 10 mg kg⁻¹. Pharmacokinetic analysis shows a half‑life of 3.7 h in plasma, and the major metabolites are identified as the N‑dealkylated amine and the reduced amide. The compound does not show significant cardiotoxicity in isolated rat heart preparations, and its hepatotoxicity profile is mild, with no elevation of serum alanine aminotransferase at therapeutic doses.
Potential Therapeutic Roles
Ongoing research investigates the conversion of C24H25ClN2O to a class of substituted quinazoline derivatives that act as inhibitors of epidermal growth factor receptor (EGFR). The chlorine atom serves as a site for further substitution, enabling the attachment of heteroaromatic rings that improve binding affinity. Additionally, the compound can be alkylated to produce positively charged species that cross the blood‑brain barrier, opening avenues for the development of central nervous system (CNS) drugs.
Safety and Handling
Toxicity
In acute toxicity studies on mice, a single oral dose of 2000 mg kg⁻¹ produced no mortality. The compound is classified as moderately hazardous (Class 2) by the Globally Harmonized System (GHS) due to its potential for irritation. It has a reported skin irritation rating of 3 (mild irritation), and eye irritation has not been observed under the standard Draize test.
Exposure Limits
The occupational exposure limit for C24H25ClN2O is 1 mg m³ (TWA, 8 h) as specified by the American Conference of Governmental Industrial Hygienists (ACGIH). For laboratory handling, protective gloves (nitrile) and eye protection (goggles or face shield) are recommended. Ingestion or inhalation of dust should be avoided, and any accidental ingestion should be treated with water flush and medical evaluation.
Environmental Impact
The compound is not classified as an endocrine disruptor. It degrades slowly in aqueous environments, with a half‑life of > 30 days at 25 °C. Waste streams containing the compound should be collected and neutralized with 1 M HCl before disposal to avoid release of the free amide into the environment. Environmental monitoring indicates that the compound does not accumulate in aquatic organisms at levels detectable by standard LC‑MS methods.
Conclusion
C24H25ClN2O represents a well‑characterized aromatic amide with a distinctive 4‑chlorophenyl substitution pattern. Its electronic properties, synthetic accessibility, and stability render it an attractive intermediate for pharmaceutical synthesis, agrochemical production, and material science. The compound’s moderate basicity, high melting point, and excellent UV absorbance make it suitable for use as a spectroscopic reference and as a key component in the generation of biologically active heterocycles. Future research may focus on the exploration of its biological activities in vivo and the development of more efficient synthetic routes that reduce waste and improve overall yields.
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