Salicylic Acid CAS 69-72-7

What is Salicylic Acid?

Salicylic acid is 2-hydroxybenzoic acid — a benzoic acid carrying a hydroxyl group on the adjacent carbon, C₇H₆O₃. That ortho relationship between the acid and the phenol is the whole story: it allows an internal hydrogen bond, it makes the acid stronger than benzoic acid, and it is what lets the molecule be acetylated to aspirin.

It is a white crystalline powder or fine needles melting at 158–161 °C, with a faintly sweet then acrid taste and a characteristic odour. It is only slightly soluble in cold water, freely soluble in ethanol and in ether, and it sublimes readily when heated carefully — a property still used industrially for purification.

Two quite different markets buy it. One is synthesis: aspirin, methyl salicylate, salicylate salts, aminosalicylic acids and dye intermediates. The other is direct use as an active — the keratolytic in acne preparations, wart removers and anti-dandruff shampoos, and the beta hydroxy acid of the cosmetic exfoliation market.

Commercially it is a mature, high-volume product made by the Kolbe–Schmitt reaction, and grade is what separates one lot from another. Technical grade for rubber and dye work, pharmacopoeial grade for API and dermatology, and cosmetic grade with its own particle size and colour expectations are genuinely different products at genuinely different prices.

Why salicylic acid specifically

• The ortho hydroxyl is the active group. Its position next to the carboxylic acid is what gives salicylic acid both its keratolytic action and its acetylation chemistry. The meta and para isomers do neither.
• One step from aspirin. Acetylation of the phenolic hydroxyl with acetic anhydride gives acetylsalicylic acid directly, which is why it has never been displaced as the feedstock.
• A lipid-soluble exfoliant. Unlike the alpha hydroxy acids, it is oil-soluble enough to work inside the follicle, which is exactly why acne formulations use it rather than glycolic acid.
• Pharmacopoeial everywhere. IP, BP, Ph. Eur. and USP monographs all cover it, so a specification argument can usually be settled by naming a monograph rather than negotiating line by line.

How Salicylic Acid is Manufactured

Salicylic acid is made almost universally by the Kolbe–Schmitt carboxylation of sodium phenoxide. The route is over a century old and still the cheapest way to put a carboxyl group ortho to a phenol.

• Phenoxide preparation. Phenol is converted to dry sodium phenoxide with sodium hydroxide, and the water is removed carefully — residual moisture is the main yield killer in the next step.
• Carboxylation (Kolbe–Schmitt). The dry phenoxide is treated with carbon dioxide under pressure at elevated temperature. The carboxyl group enters ortho to the phenoxide oxygen, giving sodium salicylate.
• Acidification. The sodium salicylate solution is acidified, usually with sulphuric acid, precipitating crude salicylic acid, which is filtered and washed.
• Purification. Crude material is purified by recrystallisation or by sublimation. Sublimed grades carry very low ash and metal figures and command a premium; recrystallised grades are the commercial pharmaceutical norm.
• Drying and milling. Drying conditions and milling set the crystal habit and particle size, which matter enormously to formulators even though they say nothing about chemical purity.

Typical Commercial Specification

Figures below are representative of pharmacopoeial-grade material. Cosmetic and technical grades, and specific particle size distributions, are available — send us the specification or the monograph you work to.

Physical & Chemical Properties

Reactivity in practice

A carboxylic acid and a phenol on adjacent carbons. Both are addressable, and which one you touch decides the product:

• Acetylation of the phenol. Acetic anhydride acetylates the hydroxyl to give acetylsalicylic acid — aspirin — in a single step. Moisture in the feedstock consumes anhydride and costs yield.
• Esterification of the acid. Methanol gives methyl salicylate (oil of wintergreen); other alcohols give the wider salicylate ester family used in sunscreens and fragrances.
• Salt formation. Neutralisation gives sodium, magnesium and choline salicylates, used medicinally and as intermediates.
• Ferric complexation. The violet colour with ferric salts is both the standard identity test and the reason iron contact discolours the material in plant and in storage.
• Keratolysis. In topical use it dissolves the intercellular cement between corneocytes, loosening the stratum corneum — the action behind every acne, wart and dandruff claim.

Salicylic Acid vs its Derivatives and Related Acids

Salicylic acid sits at the centre of a family. Buyers often arrive asking for one member and need another, so it is worth being explicit about which does what.

Stated plainly: moving the hydroxyl from the ortho position to the para position gives you paraben chemistry instead of salicylate chemistry — a preservative family rather than an analgesic one. Acetylating it gives aspirin, esterifying it gives the wintergreen esters, and neutralising it gives the salicylate salts. The ortho hydroxyl is the design feature, and everything in the family is built by deciding what to do with it.

Industries We Supply Salicylic Acid To

The same white powder goes to an API plant, a shampoo line and a rubber compounder. What changes between them is the grade, the particle size and the documentation each sector expects.

Where Salicylic Acid is Used

Salicylic acid is unusual in being both a major synthesis feedstock and a finished active in its own right. These are the end uses our customers buy it for.

In aspirin manufacture

Salicylic acid is acetylated with acetic anhydride, usually with an acid catalyst, and the acetylsalicylic acid is crystallised out. The step is sensitive to moisture, because water consumes anhydride and because residual free salicylic acid in the finished aspirin is itself a monograph-limited impurity. Loss on drying on the incoming feedstock is therefore not a formality — it directly affects both your yield and your downstream impurity profile.

In dermatology and topicals

Here salicylic acid is the active, not an intermediate. Concentration sets the claim: around 0.5–2% in daily acne and cleansing products, substantially higher in wart and callus preparations. Formulators care about particle size and dissolution behaviour, because an undissolved crystal in a lotion is a complaint waiting to happen, and about pharmacopoeial compliance because the finished product is a regulated medicine in most markets.

In cosmetics and haircare

The cosmetic market buys it as BHA, and its selling point against glycolic and lactic acid is lipid solubility — it penetrates sebum and works inside the pore rather than only on the surface. Permitted concentrations are regulated by territory, and cosmetic buyers usually have their own colour, odour and heavy metal expectations on top of the monograph.

In synthesis and industrial use

Esterification gives methyl salicylate for analgesic rubs and wintergreen flavour; neutralisation gives the salicylate salts; further substitution feeds aminosalicylic acids and dye intermediates. Industrial users also buy it as a rubber vulcanisation retarder, where the specification is loose and the price sensitivity is high.

Quality Control & Testing

Every lot is released against a batch-specific Certificate of Analysis written against the monograph you nominate. The methods are the pharmacopoeial ones, and we are happy to work to your own in-house protocol alongside them.

• Assay — titration or HPLC on the dried basis, reported against the monograph range rather than as a bare percentage.
• Related substances — 4-hydroxybenzoic acid, 4-hydroxyisophthalic acid and free phenol, the three figures that distinguish a compliant lot from a technical one.
• Melting range — a fast check that catches moisture and impurity carry-over before anything else does.
• Appearance of solution and colour — the figure cosmetic and topical formulators react to first.
• Loss on drying and residue on ignition — moisture and inorganic residue, both of which affect aspirin yield calculations.
• Heavy metals and iron — iron especially, because it both fails the monograph and visibly discolours the product.
• Particle size — by sieve or laser diffraction where a distribution has been agreed.

Common Process Problems & Likely Causes

When salicylic acid causes trouble in a plant, the cause is usually one of a short list of things. This table is the shortcut our technical desk works through before anyone opens a complaint file.

Packaging, Storage & Shipping

• Standard packing. 25 kg net in HDPE laminated bags with inner liners, or in fibre drums where the customer prefers them, palletised and shrink-wrapped.
• Storage. Cool, dry and well-ventilated, protected from light, away from iron salts, strong alkalis and oxidising agents.
• Iron contact. Avoid unlined mild steel in handling and transfer equipment. Iron contact produces the violet ferric complex, which fails the monograph and is visible long before it is measurable.
• Dust control. The powder is a nuisance dust and an irritant. Charge under local exhaust ventilation and avoid free-fall transfers that aerosolise it.
• Sublimation. The material sublimes on heating. Do not store near steam lines or in hot warehouses, and keep drying temperatures controlled in your own process.
• Materials of construction. Stainless steel, lined vessels or suitable plastics. Avoid iron, copper and lead-bearing alloys.
• Shelf life. Typically 36 months in unopened original packing under those conditions. Beyond that, re-test assay and related substances rather than assume.
• Transport classification. Generally shipped as a non-dangerous good for most modes; where a classification applies it is handled as a harmful solid. Confirm against the current SDS and the shipper's declaration for your destination and mode.

Hazards & Safe Handling

Salicylic acid is harmful if swallowed and causes serious eye damage, and the dust irritates the respiratory tract. In several jurisdictions it also carries a reproductive-toxicity classification. It must be handled by trained personnel under a proper risk assessment — the current SDS supplied with your consignment is the governing document.

• Eye protection first. Serious eye damage is the headline classification. Chemical goggles are not optional during charging, screening or bag emptying, and an eyewash station must be within reach.
• Dust control. The main exposure route in a plant is airborne dust. Handle under local exhaust ventilation, avoid free-fall transfers, and use respiratory protection where dust is generated.
• Skin contact. It is keratolytic by design, which is exactly why repeated skin contact is a problem for workers rather than a benefit. Chemical-resistant gloves and covering clothing.
• Systemic exposure. Significant absorption — through broken skin, large treated areas or ingestion — can produce salicylate toxicity. This matters most to topical manufacturers handling concentrated material.
• Reproductive classification. Several territories classify salicylic acid as a suspected reproductive hazard, which brings specific workplace obligations. Check your own regulatory position and risk assessment.
• Incompatibilities. Iron salts, strong oxidising agents, strong alkalis, lead acetate and iodides. Iron contact is a quality failure as well as a chemistry one.
• Spill response. Avoid raising dust. Sweep or vacuum into a labelled closed container, ventilate the area, and wash down afterwards. Do not wash to drain.
• First aid. Flush eyes for at least 15 minutes and seek medical attention with the SDS to hand. Wash skin with plenty of water and soap, and remove contaminated clothing promptly.

Regulatory & Compliance Notes

Salicylic acid is an established pharmaceutical, cosmetic and industrial chemical, covered by monographs in the major pharmacopoeias and listed on the principal chemical inventories. Because obligations differ by territory, volume and use, the notes below are orientation rather than legal advice — confirm your own position with your regulatory adviser before importing.

• Pharmacopoeial status. Monographs exist in IP, BP, Ph. Eur. and USP. We supply against the monograph you nominate, with a compliance statement on the COA.
• Inventory status. Listed on the principal chemical inventories in the major importing regions. Ask us for the inventory confirmation relevant to your destination country.
• Cosmetic concentration limits. Use in cosmetics is restricted by concentration and by product type in several territories, including under the EU Cosmetics Regulation. Confirm the permitted level for your market and formulation before you specify.
• Topical medicine status. Above cosmetic concentrations, salicylic acid preparations are regulated as medicines in most markets, which changes both the grade and the documentation you need.
• Reproductive hazard classification. The classification applied in several jurisdictions triggers specific labelling and workplace exposure obligations. Factor it into your own risk assessment.
• Hazard communication. Supplied with an SDS compliant with the format applicable to your region, and labelled in line with the GHS classification for the product.
• Dangerous goods. Generally not restricted for transport. Confirm against the current SDS; declarations prepared for IMDG (sea) or IATA (air) where a destination requires them.

We Supply Salicylic Acid Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Salicylic Acid from India to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, pharmacopoeial documentation and freight so the material arrives ready to use.

• Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
• Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other Indian ports arranged where it suits the routing.
• Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and the monograph compliance statement issued as a complete set.
• Flexible volumes. A single bag for laboratory qualification, through LCL consolidations, up to repeat full container loads on a supply contract.
• Supply continuity. Because we are independent of any one producer, a plant turnaround or a shipping disruption at one source does not have to become your stock-out.

Buying Salicylic Acid from Chelora

We are an independent sourcing and supply partner. For salicylic acid that means settling two things at enquiry: which pharmacopoeia your filing references, and whether the material is going into synthesis, a topical medicine or a cosmetic — because the grade, the particle size and the paperwork differ between them.

• Documentation on every lot. Batch-specific COA written against the nominated monograph, current SDS and TDS.
• Samples before commitment. Trial quantities for formulation or process qualification ahead of a commercial order.
• Quantities. From a single 25 kg bag through to full container loads on contract supply.
• Grade and particle size matching. Pharmaceutical, cosmetic and technical grades, with agreed particle size distributions where your formulation needs one.
• Export experience. Packing, labelling and export documentation handled for sea and air freight.
• Related products. 4-Aminophenol, guaiacol and the wider pharmaceutical intermediate and excipient range from one supplier.

How ordering works

• Send the enquiry. Product, grade or pharmacopoeia standard, quantity, destination port and the Incoterm you buy on. If you have a spec sheet, attach it — it saves a round trip.
• We quote. Price, lead time, packing and a sample COA, normally within one working day.
• Sample and qualify. For first orders or critical applications, we send a trial quantity so your lab can sign off before you commit.
• Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
• Production and QC. Material allocated and released against a batch-specific COA, with a pre-shipment sample where the application calls for it.
• Ship and document. Packed, labelled and loaded with the full export document set, and tracked through to arrival.

Related Pharmaceutical Intermediates & Excipients

Buyers of salicylic acid usually source several of these alongside it. Consolidating them on one order cuts freight cost and gives you a single point of contact for documentation.