Aniline-2-sulfonic acid, 95%, stands as a widely recognized chemical raw material with a vital role in multiple industrial syntheses. Its origins trace back to the sulfonation of aniline, a method resulting in a crystalline compound often used by dye, pigment, and pharmaceutical manufacturers. The common description for this product centers around its clear physical traits—it usually presents as a light brown solid that can form as flakes, powder, pearls, or stick together into small clumps, depending on storage and temperature conditions. This flexibility in form helps during weighing and mixing when preparing solutions in laboratory or production settings. Chemically, it shares a close relationship to aniline with an added sulfonic acid group, giving the molecule increased reactivity and solubility in water compared to straight aniline. The systematic name, 2-aminobenzenesulfonic acid, reflects the position of the amino and sulfonic acid groups on the benzene ring, underlining its utility as a building block.
On a molecular level, aniline-2-sulfonic acid carries the formula C6H7NO3S and a molecular weight of about 173.19 g/mol. Visualizing its structure, the sulfonic acid group (–SO3H) attaches at the second position on the benzene ring, opposite the amino (–NH2) group, which introduces both polar and hydrogen-bonding properties. Looking at its format, most people will find it as a crystalline powder, yet it can show up in flakes or even compact pearls, ready to dissolve into aqueous solutions. The density usually lands around 1.5 g/cm³ at room temperature, and its melting point hovers close to 290°C, providing a material that withstands moderate heat during processing yet readily dissolves for most applications. The substance does not mix well with non-polar solvents, but it easily forms a clear solution in water or in dilute acid.
Consistency in the chemical industry comes down to well-defined specifications. With aniline-2-sulfonic acid, 95% purity has become the practical standard, balancing cost and chemical performance for manufacturing intermediates and additives. That 5% impurity margin typically results from unreacted aniline or minor organic byproducts left during synthesis, but for most dye work, that margin passes muster. The standard product should show minimal caking and flow freely, with a bright crystal appearance instead of clumped or damp material. A proper certificate of analysis details the assay (not less than 95%), moisture content, melting point range, and heavy metal traces, keeping everyone downstream informed—especially those overseeing quality control in pharmaceuticals or electronics applications where higher purity may mean the difference between a smooth process and costly downtime. The product often holds an HS Code of 29214200 under international trade systems, marking it for easy identification and customs passage as an organic sulfonic acid of aniline derivatives.
In my own work with dyes and pigments, aniline-2-sulfonic acid forms the backbone for constructing Azo dyes, which brings vibrant colors to fabrics, inks, and plastics. Chemists lean on its reactivity to produce reactive intermediates, coupling it with diazonium salts or using it to introduce sulfonic acid groups, which improve color fastness and water solubility. Its water-friendly nature also shows up in formulating dispersants and corrosion inhibitors. Other groups reach for it in synthesis labs to act as a nucleophile under gentle conditions. With its reliable performance as a raw material, aniline-2-sulfonic acid bridges basic organic chemistry and specialized end-use markets from display technology to agricultural chemicals. The wide adoption directly traces to its chemical features: water solubility, moderate reactivity, and compatibility with large-scale processes.
Working around aniline-2-sulfonic acid requires respect for its reactivity and potential hazards. Direct contact can cause irritation to skin and eyes, and the dust becomes a respiratory hazard if handled without proper ventilation or respiratory protection. From my lab time, gloves, goggles, and a dust mask form the first defense. Workers should wash hands and exposed skin right after handling, especially before meals or breaks. The chemical does not burn easily, but under heating may release noxious gases like nitrogen oxides and sulfur oxides. For storage, keep the container sealed, dry, and out of direct sunlight to avoid picking up moisture from the air, which causes clumping and possible reaction. Though aniline-2-sulfonic acid does not rate as acutely toxic as pure aniline, chronic exposure or large spills still threaten both health and the environment, especially water systems. Most safety data sheets flag it as an irritant with the potential for chronic harm upon long-term exposure, so workplace monitoring for air and surface contamination makes real sense.
Better safeguards often start with worker training and clear standard operating procedures about storage, spill management, and first aid measures. Material transfers using sealed systems, ventilation hoods, and good labeling stop most accidents. Responsible manufacturers now look at waste handling and effluent treatment since sulfonated compounds persist in the environment. Modern plants often invest in closed-loop systems for process water, backed by regular environmental testing. Switching to higher-purity forms can help when trace metals or byproducts could compromise performance, especially in pharmaceutical synthesis, where compliance with regulatory bodies such as the FDA or EMA requires a spotless record. Research keeps moving, with efforts underway to develop less hazardous substitutes or greener production methods, but as of now, the established industry remains reliant on clear protocols and accountability. Each batch produced and shipped carries an obligation, not only under regulatory frameworks but as part of a bigger push toward personal and environmental responsibility.
