2-Phenylbenzimidazole-5-sulfonic acid (CAS 27503-81-7)

2-Phenylbenzimidazole-5-sulfonic acid

  A formulator in a South Korean cosmetics R&D lab spent two seasons working on a broad-spectrum sunscreen that would hold its UV-B efficacy through sweat and seawater without leaving white cast on deeper skin tones. The benchmark ingredient she kept returning to was ♦2-Phenylbenzimidazole-5-sulfonic acid. What made it useful in that context was not merely its absorption profile — it was the compound’s water solubility, which set it apart from most organic UV filters that require oily phases to stay dispersed. She dissolved it directly in the water phase at pH 7.2, combined it with a lipophilic UVA blocker in the emulsion’s oil droplets, and within three prototype batches had a formulation that passed both in vitro spectrophotometry and panel wear tests. The sulfonic acid group that gives the molecule its water compatibility also keeps it stable in slightly alkaline aqueous environments, which is exactly what that formulation needed.

  The chemistry behind that stability is worth understanding for anyone placing this compound in a process. The benzimidazole ring system provides a rigid aromatic scaffold with significant UV absorbance, and the phenyl substituent at position 2 extends the conjugated system to shift absorption toward the 300–320 nm range that defines UV-B. The sulfonic acid group at position 5 contributes both water solubility and a degree of ionic character that reduces photoreactivity — a property that matters when the molecule will remain in contact with skin or fabric for extended periods under sunlight. The combination of these structural features explains why this compound appears in regulated sunscreen active ingredient lists across the EU Cosmetics Regulation and several Asian national frameworks, typically at maximum concentrations between 4% and 8% by weight of the finished product.
  Beyond sunscreens, industrial dye chemists have used the compound as a building block in azo dye synthesis. The amino group generated after reduction of a related intermediate can be diazotized and coupled to form water-soluble azo colorants with good light fastness. A textile dyehouse in Ahmedabad that dyes nylon yarn for activewear fabrics had switched to a dye class incorporating this sulfonated benzimidazole core because the resulting colors showed markedly better resistance to repeated machine washing at 60°C compared to simpler sulfonated azo dyes — a difference the lab head attributed to the rigidity of the benzimidazole ring reducing photodegradation pathways. The same rigidity that makes it a good UV absorber in sunscreens is what makes dyes built on this scaffold retain their hue under prolonged light exposure.
Pharmaceutical and analytical chemistry laboratories use 2-Phenylbenzimidazole-5-sulfonic acid as a reference standard and as an intermediate in heterocyclic synthesis research. Its defined structure and water solubility make it convenient for aqueous calibration standards, and its benzimidazole core appears in a significant number of pharmacophores, so it serves as a starting material in exploratory synthesis campaigns. A research group at a Taiwanese institute studying kinase inhibitor scaffolds used this compound to explore how sulfonation of the benzimidazole ring affected cell membrane permeability — the answer, as expected, was that the sulfonic acid group sharply reduced passive membrane crossing, which shifted the target profile toward extracellular enzymes rather than intracellular ones, a finding that helped redirect their SAR effort toward less polar analogs.
2-Phenylbenzimidazole-5-sulfonic acid
Shandong zhishangchem Co., Ltd. supplies 2-Phenylbenzimidazole-5-sulfonic acid (CAS 27503-81-7) in purity grades suited to cosmetic formulation and fine chemical synthesis. Each production lot is analyzed by HPLC against an authenticated reference standard, and the released certificate of analysis covers purity, water content, and appearance. Standard export quantities ship within 5 to 12 business days; sample quantities are available for qualification testing. Technical questions on specification or application fit can be directed to the chemistry team at sales001@sdzschem.com or through zhishangchem.com.
 

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