4-Cyano-2-methoxybenzaldehyde, designated by CAS registry number 21962-45-8 and molecular formula C9H7NO2, is supplied as a pharmaceutical-grade aromatic aldehyde intermediate for downstream synthesis of active pharmaceutical ingredients intended for tableting, encapsulation, granulation, and injectable processing. The material is a pale-yellow to off-white crystalline solid with a molecular weight of 161.16 g/mol. The commercial document set typically identifies the material by manufacturer-specific batch number and the grade designation 4-Cyano-2-methoxybenzaldehyde Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable; no harmonized pharmacopoeial monograph currently exists for this compound, and release therefore follows a validated in-house specification aligned with ICH Q7 and the relevant residual solvent, elemental impurity, and microbiological chapters of Ph. Eur. and USP-NF. The aldehyde is not itself a finished dosage form active substance; the route-specific designation indicates that it is qualified to support the synthesis of APIs whose final oral solid or injectable formulations are prepared under the stated dosage forms after further chemical transformation and purification.

What distinguishes the 4-cyano-2-methoxy substitution pattern from unsubstituted and isomeric aldehydes?

The simultaneous presence of the electron-withdrawing nitrile at the 4-position and the electron-donating methoxy at the 2-position relative to the formyl group produces a dipolar aromatic system with altered electrophilicity at the carbonyl carbon. The methoxy substituent contributes lone-pair electron density into the ring and introduces steric hindrance adjacent to the aldehyde, while the cyano group withdraws electron density through both inductive and resonance pathways. This substitution pattern modifies the rate of base-catalysed side reactions relative to unsubstituted benzaldehyde, and it reduces the tendency for benzoin condensation under strongly basic conditions. The regiochemistry of the nitrile at the 4-position, rather than at the 3-position, affects both chromatographic retention on C18 stationary phases and the regioselectivity of subsequent palladium-catalysed coupling or reduction steps. In comparison with 4-cyano-2-hydroxybenzaldehyde, the methoxy-protected form avoids phenolic oxidation during storage and prevents formation of intramolecular hydrogen bonds that would alter solubility in aprotic granulation solvents.

Release specifications are established by high-performance liquid chromatography with ultraviolet detection at 254 nm, using a reversed-phase C18 column and a mobile phase of acetonitrile and 0.1% phosphoric acid. The representative acceptance limits in Table 1 are derived from supplier certificates of analysis and are not a substitute for a pharmacopoeial monograph. Published data for this specific configuration is limited; therefore, batch-specific method validation and impurity spiking studies should be performed by the receiving analytical unit.

How are residual aldehyde and nitrile functionalities controlled during wet granulation and terminal sterilization?

The free aldehyde group is sensitive to oxidation, amine addition, and bisulfite complex formation. In wet granulation of downstream intermediates, aqueous granulating fluid above pH 6.5 can accelerate aldol side reactions; therefore, granulation feed containing this aldehyde is typically prepared under low-moisture or non-aqueous conditions. The aldehyde should be stored under inert gas at 2–8 °C in sealed, light-resistant containers to limit air oxidation to the corresponding carboxylic acid and to suppress discoloration. Pre-drying at 40 °C under vacuum for at least 4 h is required when storage relative humidity exceeds 60%. For terminal sterilization of derived injectable APIs, the aldehyde itself is not autoclaved; thermal exposure above 120 °C may degrade the formyl group and promote nitrile hydrolysis. The compound is incompatible with strong bases, primary amines, and reducing agents such as lithium aluminium hydride unless the reaction is intentionally designed for reduction to the corresponding benzylamine or aminomethyl intermediate. These operational boundaries apply to the isolated aldehyde and not to the final formulated drug product.

In downstream synthesis, the formyl group is used for reductive amination with pharmaceutical amines under sodium triacetoxyborohydride or sodium cyanoborohydride conditions in solvents such as dichloromethane or tetrahydrofuran. The nitrile group can be reduced to the aminomethyl analogue under hydrogenation over Raney nickel or palladium on carbon, or hydrolysed to the carboxylic acid under acidic or basic conditions. The methoxy group may be retained as a lipophilic substituent or deprotected to a phenol using boron tribromide in dichloromethane at −78 °C to 0 °C. When the final API is intended for tablet or capsule dosage forms, the derived active is milled and blended with excipients meeting Ph. Eur. or USP-NF monographs. For granule dosage forms, wet or dry granulation is selected based on the particle size distribution of the final API; the aldehyde intermediate itself is not granulated. The pharma-grade designation supports oral and injectable routes by requiring low residual metals and controlled endotoxin when the downstream API is formulated for parenteral administration.

If the downstream API is intended for injectable dosage forms

Additional controls are applied at the intermediate stage to reduce the risk of particulate contamination and endotoxin carryover. The material is supplied in double polyethylene bags inside a fibre drum, with the inner bag purged under nitrogen. Particle size is controlled by jet milling or pin milling when the aldehyde is used in a step where dissolution rate affects reaction yield; however, because the material is not present in the final injectable solution, particle size is not a release criterion for the final dosage form. Bioburden is typically specified as total aerobic microbial count ≤ 100 CFU/g, total combined yeasts and moulds ≤ 10 CFU/g, and bacterial endotoxins < 0.25 EU/mg for parenteral-grade supply. These limits are applied even though the aldehyde will be consumed in a subsequent synthesis, because microbial metabolites and endotoxins may survive downstream processing if not controlled at the registered starting material level. Solvent residues are limited to ICH Q3C Class 3 solvents with a total residual solvent limit of 0.5% unless the manufacturing route specifically includes a Class 2 solvent, in which case the compound is dried until the relevant Ph. Eur. or USP limit is met.

Comparative positioning against other benzaldehyde derivatives is determined by regioisomeric purity, residual palladium, and the absence of the free phenol. 4-Cyano-2-methoxybenzaldehyde differs from 4-cyano-2-hydroxybenzaldehyde in that the methoxy-protected material avoids O-alkylation side reactions with alkyl halides and does not require protection during Grignard or hydride addition steps. Compared with 4-cyano-3-methoxybenzaldehyde, the position of the methoxy group relative to the formyl carbon alters the ortho substitution pattern and the resulting steric environment in reductive amination; the 2-methoxy isomer imposes greater steric hindrance at the carbonyl and can slow imine formation with bulky primary amines. Compared with 4-formylbenzonitrile, the additional methoxy group improves crystallinity of the isolated aldehyde and provides a synthetic handle for subsequent deprotection to a phenol or conversion to a triflate for cross-coupling. Technical-grade material may contain higher levels of the corresponding carboxylic acid and 4-cyano-2-methoxybenzyl alcohol; pharma-grade material is controlled for these process-related impurities by HPLC area% limits.

On production scale, the powder is charged through a nitrogen-purged glovebox or split-valve system into glass-lined reactors because the aldehyde is incompatible with iron and copper surfaces under acidic aqueous conditions. Glass-lined reactors and polytetrafluoroethylene gaskets are recommended. Stainless steel 316L may be used for short contact periods, but prolonged storage in unlined carbon steel containers is not recommended because residual moisture can initiate surface corrosion and discolouration. Centrifugal filtration of the isolated material is performed under nitrogen blanket; drying is carried out in a double-cone or agitated vacuum dryer with a jacket temperature of 40–45 °C and a vacuum level below 10 kPa absolute. Over-drying above 60 °C is avoided because it can cause partial sublimation and loss of yield. These processing limits are drawn from standard fine-chemical isolation practice for low-molecular-weight aromatic aldehydes.

Regioisomeric impurities such as 3-cyano-2-methoxybenzaldehyde and 4-cyano-3-methoxybenzaldehyde are separated using a C18 column with a mobile phase containing acetonitrile and phosphate buffer at pH 3.0; detection is at 230 nm and 254 nm. The resolution between the 4-cyano-2-methoxy and 3-cyano-2-methoxy peaks is typically not less than 2.0. If the receiving site uses LC-MS, the molecular ion [M+H]⁺ at m/z 162.1 and the sodium adduct at m/z 184.0 are used for identity confirmation in positive ion electrospray mode. Headspace GC-MS is used for residual solvent quantification with a DB-624 column and a column flow of 1.2 mL/min helium. These method parameters are representative and must be validated for the specific batch matrix.

The product designation Pharma Grade API for Tablet / Capsule / Granule / Injection, Oral & Injectable indicates that the lot has been manufactured under current good manufacturing practice conditions for registered starting materials. For oral solid dosage forms, the critical quality attributes of the final API derived from this intermediate include particle size distribution, bulk density, and polymorphic form, which are controlled after the final API crystallization rather than at the aldehyde stage. For injectable dosage forms, the derived API must meet bacterial endotoxin, bioburden, and particulate matter limits; the intermediate is controlled for these attributes because endotoxin introduced at the registered starting material stage may persist through synthesis and purification. Therefore, the product is supplied with a reduced-endotoxin certificate when requested for parenteral routes.

Because no monograph exists, the receiving manufacturer is responsible for establishing API starting material suitability under ICH Q7, including closed-system handling and dedicated or validated multipurpose equipment. The aldehyde is stable for 24 months when stored at 2–8 °C under nitrogen from the date of manufacture; after opening, the material should be used within 30 days if stored under nitrogen at 2–8 °C. Residual water is controlled at release because the formyl group can form hydrates that alter the effective assay and complicate stoichiometric charging in later synthesis steps. Residual solvents from the typical synthetic route include methanol, tetrahydrofuran, and ethyl acetate; these are controlled to ICH Q3C Class 2 and Class 3 limits. Elemental impurities are controlled according to ICH Q3D Criteria 1 and 2, with particular attention to palladium, nickel, and copper when catalytic reductions are used to convert the nitrile to the aminomethyl intermediate.