Pyridine (CAS 110-86-1): Properties and Uses in Pharmaceutical and Agrochemical Synthesis

Pyridine is an aromatic nitrogen heterocycle with the formula C₅H₅N. Its six-membered ring contains five carbon atoms and one nitrogen atom, whose lone pair is available for protonation and reaction with electrophiles. Industrially, pyridine is used as a chemical intermediate, solvent, and reagent. Its chemistry depends on two distinct features: a basic nitrogen atom and an electron-deficient aromatic ring.

Core Chemical & Physical Profile

Typical reference properties are:

• CAS number: 110-86-1
• Molecular formula: C₅H₅N
• Molecular weight: 79.10 g/mol
• Density: approximately 0.978 g/mL at 25 °C
• Boiling point: approximately 115 °C at atmospheric pressure
• pKa: approximately 5.2 for the conjugate acid, pyridinium, in water
• Physical state: clear, colorless liquid at room temperature
• Solubility: miscible with water

These values describe the compound’s general properties. Batch acceptance requires a separate specification with defined analytical methods and limits.

The nitrogen lone pair occupies an sp² orbital outside the aromatic π system. Protonation leaves the ring aromatic, while nitrogen’s electron-withdrawing effect makes electrophilic substitution more difficult than in benzene. Suitable leaving groups at the 2- and 4-positions are more readily displaced by nucleophiles because the ring nitrogen stabilizes the addition intermediate.

The pKa value describes pyridinium dissociation, not the acidity of neutral pyridine. It also explains why pyridine is a weaker base than most aliphatic amines. A reaction that needs strong deprotonation may require a different base, even when pyridine works well as a solvent or nucleophilic reagent.

Downstream Industrial Applications

Agrochemical Intermediates

Substituted pyridines are used in the manufacture of herbicide, insecticide, and fungicide intermediates. The substitution pattern matters: changing the position of a functional group changes the available reactions and the downstream compound.

2-Chloropyridine is one example. Its chlorine substituent provides a site for further functionalization in agrochemical and pharmaceutical synthesis. Under suitable conditions, nucleophilic substitution at this position can introduce oxygen- or nitrogen-containing groups.

For route selection, compare the cost of buying the functionalized intermediate with the yield and purification burden of making it in-house. Positional impurities deserve particular attention if they can pass through subsequent steps and remain difficult to separate.

Pharmaceutical Synthesis

Pyridine is used in esterification and amidation chemistry, where it can act as an acid acceptor or participate in acyl transfer through N-acylpyridinium intermediates. Its role depends on the substrate and acylating reagent.

Pyridine also provides a route to Piperidine by catalytic hydrogenation. Hydrogenation saturates the aromatic ring and produces a secondary amine with different basicity and reactivity. Piperidine is then used as a reagent or building block in downstream synthesis.

In API process development, assess pyridine removal during workup and isolation. Incoming assay is only part of the qualification: water content and individual impurities may affect reaction performance, while residual pyridine requires control in the downstream material.

Fine Chemical Reaction Media

Pyridine is used as a solvent and reagent in specialty chemical and heterocyclic synthesis. Anhydrous grades are suitable for processes that require low water content, provided their moisture specification meets the reaction’s requirements.

The practical question is how much pyridine the reaction needs and where it goes afterward. When used in large quantities as a solvent, recovery and aqueous waste treatment become significant process considerations. Water miscibility affects its distribution during workup; an aqueous wash alone should not be assumed to remove it adequately.

Recovered pyridine needs its own release specification. Check water and accumulated impurities before reuse, particularly when the next batch contains moisture-sensitive reagents.

Industrial Handling, Storage & Quality Standards

Pyridine’s closed-cup flash point is approximately 20 °C, so flammable vapor can be present at ordinary working temperatures. Exposure can occur through inhalation, skin absorption, ingestion, and eye or skin contact. Strong acids and strong oxidizers require segregation.

Use closed transfer equipment and suitable ventilation. Bond and ground transfer systems, control ignition sources, and select gloves from chemical permeation data. Eye protection and accessible emergency washing facilities are necessary where splashes are possible.

Store tightly closed containers in a cool, ventilated area suitable for flammable liquids. Keep incompatible chemicals segregated and protect low-moisture grades from water ingress. Follow the current SDS for the supplied grade.

Hongda lists Pyridine in 200 kg steel drums. Confirm the container specification and closure condition as part of shipment acceptance.

Quality checks normally include assay by an agreed chromatographic method and water by Karl Fischer titration. Set limits for individual organic impurities where they affect the process. Color and nonvolatile residue may also need control, depending on the application.

Sourcing & Supply Specifications

Hongda Group is an integrated manufacturing partner supplying pyridine and related chemical intermediates. A purchasing specification should state the required grade, analytical methods, impurity limits, and packaging.

Review representative COAs before approving a supplier. For recurring supply, agree on batch traceability, retest periods, and notification of changes to manufacturing or specifications. Qualification should include material testing in the intended process.

Contact Our Technical Sales Team to request the TDS, SDS, and batch-specific COA, or to discuss moisture limits, packaging, and supply requirements for your application.