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Salicylic Acid Anhydrous, also known as Anhydrous Salicylic Acid, 2-Hydroxybenzoic Acid Anhydrous and CAS No. 69-72-7, is an aromatic hydroxy acid with the formula C7H6O3 that contains no water of crystallization and is supplied as a white crystalline powder or needle-shaped crystals with a low moisture content. Salicylic Acid Anhydrous is used in particular as a starting material in the synthesis of acetylsalicylic acid (aspirin), in the production of methyl salicylate and other salicylate esters and salicylate salts, as an acid catalyst in the synthesis of novolac-type phenolic resins, in foundry resins, as a scorch retarder in the rubber industry, as a coupling component in azo dye production and as an analytical reagent.
Salicylic Acid Anhydrous is the same chemical as standard Salicylic Acid, with the same CAS and EC numbers; the term “anhydrous” indicates that the product is supplied in anhydrous form with a low moisture content. Thanks to the phenolic hydroxyl and carboxyl groups in its molecule, Salicylic Acid Anhydrous is a versatile synthesis building block that can undergo acetylation, esterification, salt formation and coupling reactions.
Salicylic Acid Anhydrous helps limit the water carried into the reaction with the raw material in aspirin synthesis, where acetic anhydride is decomposed by water, and in esterification processes where the water load matters. In the patent literature, Salicylic Acid Anhydrous is used as an acid catalyst in novolac resin synthesis, preferably at 0.5–2% of the weight of phenol, and it is also evaluated in foundry resins, rubber compounds and azo dye production.
Moisture content, purity, phenol and hydroxybenzoic acid impurities and quality grade are decisive in the selection of Salicylic Acid Anhydrous, and these values should be checked on the COA for each batch. Since Salicylic Acid Anhydrous is harmful if swallowed, can cause serious eye damage and is classified as toxic to reproduction Category 2, it should be stored in tightly closed packaging in a dry place protected from light to preserve its anhydrous property and handled on the basis of the current SDS.
WHAT IS SALICYLIC ACID ANHYDROUS?
Salicylic Acid Anhydrous is chemically the same substance as Salicylic Acid, with the same CAS number (69-72-7) and the same EC number (200-712-3). The word "Anhydrous" in the product name indicates that Salicylic Acid is supplied in anhydrous form and that its moisture content is kept low.
The difference between Salicylic Acid Anhydrous and Salicylic Acid therefore lies not in the molecular structure, but in the moisture content of the product and in the fields of use where this property is emphasized.
Chemically, Salicylic Acid Anhydrous is 2-hydroxybenzoic acid. This monohydroxybenzoic acid, formed by the attachment of a hydroxyl group to the ortho position of benzoic acid, also belongs to the phenolic acid and beta hydroxy acid classes.
Commercial Anhydrous Salicylic Acid is produced from phenol by the Kolbe-Schmitt process. In this process, dry sodium phenoxide is reacted in a stream of carbon dioxide at 150–160 °C and a pressure of 5 bar; the resulting sodium salicylate is acidified to give salicylic acid.
According to the literature, the yield of the Kolbe-Schmitt process carried out under pressure is about 90%; without pressure the yield does not exceed 50%. Technical grade Salicylic Acid Anhydrous obtained by this method is already of high purity: salicylic acid content about 99.5%, water content about 0.2% and ash below 0.1%.
Higher-purity, pharmaceutical grade Salicylic Acid can be obtained by crystallizing sodium salicylate from water at a temperature not exceeding 20 °C, or by subliming the acid at a pressure of 20 mbar and a temperature of 154 °C.
Salicylic Acid Anhydrous should not be confused with "salicylic anhydride". Salicylic anhydride is a separate chemical derived from two salicylic acid molecules and has different identifiers.
Not every Salicylic Acid Anhydrous product on the market has the same technical properties. Since moisture content, purity, impurity profile and quality standard may vary by manufacturer, product selection should be based on the TDS, SDS and COA documents.
COMMON PRODUCT AND CHEMICAL NAMES:
Salicylic Acid Anhydrous
Anhydrous Salicylic Acid
Susuz Salisilik Asit
Salisilik Asit (Susuz)
Salicylic Acid
Salisilik Asit
2-Hydroxybenzoic Acid
2-Hidroksibenzoik Asit
o-Hydroxybenzoic Acid
ortho-Hydroxybenzoic Acid
Benzoic Acid, 2-hydroxy-
2-Carboxyphenol
Phenol-2-carboxylic Acid
Acidum Salicylicum
C7H6O3
HOC6H4COOH
Salicylic Acid Technical Grade
Salicylic Acid Ph. Eur. / BP / USP
Salicylic Acid ACS Reagent
The terms "anhydrous" and "susuz" describe the moisture content of the product; the chemical names and identifiers used for Salicylic Acid Anhydrous are the same as those of Salicylic Acid.
Some of these names express the chemical name in the IUPAC and CAS systems, some the Latin pharmacopoeia name, and others the technical, pharmaceutical or reagent quality grade. The quality grade of a product referred to as Salicylic Acid Anhydrous should be verified separately from the product documents.
CAS NO, EC / EINECS NO AND CHEMICAL IDENTIFICATION
Product name: Salicylic Acid Anhydrous / Anhydrous Salicylic Acid
Chemical name (IUPAC): 2-Hydroxybenzoic acid
CAS No: 69-72-7
EC / EINECS No: 200-712-3
CLP index no: 607-732-00-5
Molecular formula: C7H6O3
Linear formula: 2-(HO)C6H4COOH
Molecular weight: 138.12 g/mol
MDL No: MFCD00002439
Chemical class: Monohydroxybenzoic acid / phenolic acid / aromatic carboxylic acid
Main functions: Synthesis starting material, acetylation and esterification substrate, novolac resin catalyst, scorch retarder, azo dye coupling component, analytical reagent
CAS No 69-72-7, EC No 200-712-3 and CLP index no 607-732-00-5 used for Salicylic Acid Anhydrous are the same as those used for standard Salicylic Acid. This shows that the term "anhydrous" does not describe a different chemical substance, but the moisture state of the product.
The salts and esters of Salicylic Acid, on the other hand, have separate identifiers. For example, the CAS number of sodium salicylate is 54-21-7.
The main impurities in Salicylic Acid Anhydrous products originating from the Kolbe-Schmitt production process are phenol, 4-hydroxybenzoic acid and 4-hydroxyisophthalic acid. These impurities are also defined in the European Pharmacopoeia.
In technical grade Anhydrous Salicylic Acid these impurities may be present at a total level of about 0.05–0.1%; in pharmaceutical grade, separate and stricter limits apply to each of them.
CHEMICAL STRUCTURE AND MOLECULAR PROPERTIES OF SALICYLIC ACID ANHYDROUS
The Salicylic Acid Anhydrous molecule contains a benzene ring, a carboxyl group (–COOH) attached to this ring, and a phenolic hydroxyl group (–OH) in the immediately adjacent (ortho) position. The proximity of the two functional groups is the basic feature that determines the chemical behaviour of Anhydrous Salicylic Acid.
The SMILES notation for Salicylic Acid Anhydrous is C1=CC=C(C(=C1)C(=O)O)O and its InChIKey is YGSDEFSMJLZEOE-UHFFFAOYSA-N.
Salicylic Acid Anhydrous is an acid with a pKa of about 3.0 and is markedly stronger than unsubstituted benzoic acid (pKa about 4.2). This difference arises because the hydroxyl group in the ortho position facilitates dissociation of the carboxyl group.
The pH of a saturated aqueous solution of Anhydrous Salicylic Acid is 2.4 at 20 °C. This acidity is the basis for the use of Salicylic Acid Anhydrous in acid-catalysed processes such as novolac resin synthesis.
The Salicylic Acid Anhydrous molecule has 2 hydrogen bond donors, 3 hydrogen bond acceptors and 1 rotatable bond. Its calculated topological polar surface area is 57.5 Ų.
The octanol/water partition coefficient of Anhydrous Salicylic Acid has been reported as log Pow 2.25 (25 °C). This value explains the molecule's affinity for organic phases and its good solubility in organic solvents.
The importance of Salicylic Acid Anhydrous in synthesis comes from its two different reactive centres. The phenolic hydroxyl group is acetylated with acetic anhydride or acetyl chloride to give aspirin.
The carboxyl group, on the other hand, esterifies with alcohols to form esters such as methyl salicylate and reacts with bases to form salts such as sodium, potassium and magnesium salicylate. The aromatic ring can also take part in coupling reactions in azo dye production.
PHYSICAL AND CHEMICAL PROPERTIES OF SALICYLIC ACID ANHYDROUS
Salicylic Acid Anhydrous is a white, odourless solid; it occurs as crystalline powder or fine needle-shaped crystals. Some sources describe a colour ranging from white to pale yellow and a faint nutty odour.
The colour and crystalline appearance of Anhydrous Salicylic Acid may vary depending on the production method, purification process and storage conditions.
General technical properties:
Physical appearance: White crystalline powder or needle-shaped crystals
Odour: Odourless
Molecular formula: C7H6O3
Molecular weight: 138.12 g/mol
CAS No: 69-72-7
EC / EINECS No: 200-712-3
Melting point: 158–161 °C
Boiling point: 211 °C (20 mmHg)
Flash point: 157 °C (closed cup)
Density: 1.44 g/cm³ (20 °C)
pH: 2.4 (20 °C, saturated aqueous solution)
pKa: About 3.0
Vapour pressure: 1 hPa (114 °C)
Lower explosion limit: 1.1% (V) (200 °C)
Partition coefficient (log Pow): 2.25 (25 °C)
Loss on drying (example pharmacopoeia specification): ≤ 0.5%
Solubility in water: 1.24 g/L (0 °C); 2.48 g/L (25 °C); 4.14 g/L (40 °C); 17.41 g/L (75 °C); 77.79 g/L (100 °C)
Solubility in organic solvents: 62.48 g/100 g in methanol (21 °C), 39.6 g/100 g in acetone (23 °C), 34.87% by weight in absolute ethanol (21 °C), 27.36% in propanol (21 °C), 2.22 g/100 mL in chloroform (25 °C), 0.775 g/100 g in benzene (25 °C)
Stability: Stable under normal conditions; light-sensitive
Materials to avoid: Oxidizing agents, strong bases, iodine, fluorine, iron salts, lead acetate
The high solubility of Salicylic Acid Anhydrous in methanol allows salicylic acid to be dissolved directly in methanol and reacted in methyl salicylate synthesis. Its high solubility in acetone and ethanol is also an advantage in solvent selection and crystallization operations.
The water solubility of Anhydrous Salicylic Acid increases markedly with temperature: it is 2.48 g/L at 25 °C and reaches 77.79 g/L at 100 °C. This property allows purification by crystallization from hot water.
Salicylic Acid Anhydrous is light-sensitive and can cause discolouration with iron salts. The material of the packaging and process equipment is therefore important.
The values above are general information compiled from the literature and safety data sheets and are not binding specifications. The moisture content and other exact values of the Salicylic Acid Anhydrous product to be used should be checked against the TDS and COA documents.
HOW DOES SALICYLIC ACID ANHYDROUS WORK AT THE MOLECULAR LEVEL?
The industrial functions of Salicylic Acid Anhydrous are based on reactions proceeding via the phenolic hydroxyl group, the carboxyl group and the aromatic ring of its molecule.
Acetylation:
The phenolic hydroxyl group of Salicylic Acid Anhydrous reacts with acetic anhydride to form acetylsalicylic acid (aspirin) and acetic acid as a by-product. On a laboratory scale this reaction is generally carried out with sulphuric acid as a catalyst.
Acetic anhydride is decomposed by water into acetic acid. Water entering the reaction medium with the raw material can therefore consume part of the acetic anhydride needed for acetylation; the use of Anhydrous Salicylic Acid is evaluated from this standpoint.
Esterification:
The carboxyl group of Salicylic Acid Anhydrous esterifies with alcohols in the presence of an acid catalyst. Its reaction with methanol gives methyl salicylate, and its reactions with other alcohols give esters such as butyl, hexyl, benzyl and isoamyl salicylate.
Water is also formed as a by-product in the esterification reaction. In esterification processes, water coming from the raw material should therefore also be considered as part of the total water load.
Salt formation:
Salicylic Acid Anhydrous reacts with bases to form the salicylate salts of metals such as sodium, potassium, calcium, magnesium and bismuth. These salts are used in pharmaceutical and personal care products.
Acid catalysis:
Thanks to its acidic character, Salicylic Acid Anhydrous can act as an acid catalyst in the condensation reaction in which phenol and formaldehyde are converted into novolac resin.
Coupling:
Salicylic Acid Anhydrous is used as the coupling component that couples with diazonium salts in the production of azo dyes.
Main functions of Salicylic Acid Anhydrous:
Acetylation substrate (aspirin production)
Esterification substrate (methyl salicylate and other salicylate esters)
Starting material for salicylate salts
Acid catalyst in novolac resin synthesis
Scorch retarder in rubber compounds
Coupling component in azo dyes
Analytical reagent
IN WHICH INDUSTRIES IS SALICYLIC ACID ANHYDROUS USED?
Salicylic Acid Anhydrous is used mainly in industries engaged in synthetic chemistry and intermediate production. According to the industrial literature, about 55% of salicylic acid is consumed in acetylsalicylic acid production, 18% in salicylate esters and salts, 10% in resins and 10% in dyes and colourants.
According to older market data, salicylic acid consumption was distributed as 65% aspirin, 20% salicylate esters and salts, 7% foundry resins and 8% other uses such as rubber retarders and dye intermediates.
Main industries of use:
Pharmaceutical raw material production
Flavour and fragrance chemistry
Organic chemicals production
Phenolic and foundry resin production
Foundry industry
Rubber industry
Dye and colourant production
Agrochemicals production
Plastic raw material and plastic product manufacturing
Paint and coating manufacturing
Primary metal manufacturing
Analytical chemistry and laboratories
Cosmetic and dermocosmetic products
The main properties expected from Salicylic Acid Anhydrous in industries engaged in synthesis are low moisture content, high purity, low phenol and hydroxybenzoic acid impurities, and consistent quality from batch to batch.
In the resin, rubber and dye industries, technical grade Anhydrous Salicylic Acid is evaluated for its balance of process-appropriate purity and price. In pharmaceutical raw material production, compliance with the relevant pharmacopoeia requirements is expected.
USE OF SALICYLIC ACID ANHYDROUS IN THE SYNTHESIS OF ASPIRIN AND SALICYLATE ESTERS
The largest field of use of Salicylic Acid Anhydrous is the production of acetylsalicylic acid, i.e. aspirin. About 60% of the salicylic acid produced in the USA in the late 1980s and early 1990s was consumed in aspirin production.
Aspirin is obtained by acetylation of the phenolic hydroxyl group of Salicylic Acid Anhydrous with acetic anhydride or acetyl chloride.
Methods reported in the literature for aspirin production:
In the current industrial method described in the patent literature, salicylic acid is reacted with excess acetic anhydride in a pressure reactor at about 98 °C for 2–3 hours. This is followed by filtration, cooling to 0 °C, centrifugation, crystallization and washing; the reported yield is about 90%.
Older methods include refluxing salicylic acid and acetic anhydride at 150 °C for about 2 hours, using sulphuric acid as a condensing agent, and working at 40–95 °C with about a 20% molar excess of acetic anhydride.
Moisture control in aspirin production:
Acetic anhydride reacts with water to form acetic acid. The use of Salicylic Acid Anhydrous is evaluated from the standpoint of limiting the amount of water carried into the reaction with the raw material.
The patent literature states that water in the reaction medium and water-forming components can increase the decomposition of aspirin and the amount of free salicylic acid in the product. The moisture content of the Anhydrous Salicylic Acid to be used in aspirin synthesis should therefore be checked on the COA.
Methyl salicylate production:
Methyl salicylate is produced by esterifying Salicylic Acid Anhydrous with methanol using sulphuric acid as a catalyst. In the typical process reported in the literature, salicylic acid is dissolved in methanol, sulphuric acid is added, and the mixture is heated with stirring at 90–100 °C for about 3 hours.
After the reaction, the mixture is cooled below 30 °C, the oil phase is separated and washed with sodium carbonate solution until the pH exceeds 8, then with water. The product is purified by vacuum distillation, collecting the fraction at 95–110 °C under a pressure of 1.33–2.0 kPa.
According to the same source, the yield of this process is above 80% and the product purity is about 99.5%. About 950 kg of salicylic acid and 400 kg of methanol are reported to be consumed per tonne of methyl salicylate.
Methyl salicylate is used as a flavouring substance, a fragrance component, an ingredient in oral care products and an active ingredient in topical products for muscle and joint pain.
Other derivatives:
Salicylic Acid Anhydrous is also the starting material for the production of pharmaceutical salts such as sodium salicylate, bismuth subsalicylate and choline salicylate, and of fragrance components such as benzyl salicylate and isoamyl salicylate. Anhydrous Salicylic Acid is also used in the synthesis of other active pharmaceutical ingredients via ester, amide and salt derivatives.
RESIN, RUBBER, DYE AND ANALYTICAL APPLICATIONS OF SALICYLIC ACID ANHYDROUS
Novolac resin synthesis:
In the patent literature, Salicylic Acid Anhydrous is given as an example of hydroxy-substituted benzoic acid catalysts in the production of novolac resin from phenol and formaldehyde. In this use, salicylic acid is used at 0.1–10%, preferably 0.5–2%, of the weight of phenol.
The same source defines the reaction conditions as pH 1.5–4.0, a temperature of 100–270 °C and 0.5–0.8 mol of formaldehyde per mol of phenol.
According to the same patent, the thermal stability of novolac resins catalysed with salicylic acid is lower than that of those catalysed with benzoic acid. Resins catalysed with Salicylic Acid Anhydrous are therefore considered suitable for applications with lower thermal stability requirements.
Foundry resins:
Salicylic Acid Anhydrous is evaluated in the production of resins used in the foundry industry. In patent examples relating to novolac resins developed for shell moulding, salicylic acid is added to the resin at about 2% by weight.
According to older market data, about 7% of salicylic acid consumption is accounted for by foundry resins.
Rubber industry:
Salicylic Acid Anhydrous is used as a scorch retarder in rubber compounds. In the patent literature, salicylic acid is listed together with benzoic acid and PVI among the well-known scorch retarders.
Scorch retarders help prevent the rubber compound from curing prematurely during processing. The use level should be determined by trials according to the rubber type and the vulcanization system.
Dyes and colourants:
Salicylic Acid Anhydrous is used as a coupling component in the production of azo dyes. About 10% of salicylic acid consumption is directed to dye and colourant applications.
Agrochemicals:
Technical grade Salicylic Acid Anhydrous is used as an intermediate in the production of agrochemicals.
Analytical chemistry:
Salicylic Acid Anhydrous is used in laboratories as an analytical reagent. ACS reagent grade is preferred for analytical work.
Other industrial uses:
According to US Environmental Protection Agency (EPA) data, salicylic acid is used in insulating materials, as a polymerization promoter, as a processing aid and as an intermediate.
IS SALICYLIC ACID ANHYDROUS USED IN COSMETIC, FOOD AND PHARMACEUTICAL APPLICATIONS?
Since Salicylic Acid Anhydrous is the same substance as Salicylic Acid, all provisions of cosmetic, food and pharmaceutical legislation apply equally to this product.
Pharmaceuticals:
Salicylic Acid Anhydrous is the starting material for pharmaceutical raw material synthesis in the production of aspirin and other salicylate derivatives. Salicylic acid itself is also a topical active pharmaceutical ingredient with keratolytic, antifungal and anti-inflammatory effects.
Salicylic acid is described in the European, British, United States and Japanese pharmacopoeias and is included in the World Health Organization Model List of Essential Medicines as a 5% topical solution. Salicylic Acid Anhydrous to be used in pharmaceutical applications must comply with the relevant pharmacopoeia monograph.
Cosmetics:
Under the EU Cosmetics Regulation (EC) No 1223/2009, salicylic acid is a restricted ingredient. The limits in the ready-for-use product for non-preservative use are as follows:
Rinse-off hair products: Maximum 3.0%
Body lotion, eye shadow, mascara, eyeliner, lipstick and roll-on deodorant: Maximum 0.5%
Other products: Maximum 2.0%
For use as a preservative, the limit is a maximum of 0.5% as acid. Salicylic Acid Anhydrous must not be used in products for children under 3 (except shampoos for preservative use), in oral products or in applications that may lead to lung exposure by inhalation.
For cosmetic products in Türkiye, the current annexes of the Turkish Cosmetics Regulation should be taken as the basis.
Food:
Salicylic Acid Anhydrous is not among the permitted additives in the Turkish Food Codex Regulation on Food Additives and cannot be used as a preservative in foods. In 1961, JECFA did not allocate an ADI for salicylic acid and stated that it is unsuitable as a food additive.
Salicylic acid is included as a flavouring substance in the EU list of flavouring substances (Regulation (EU) No 872/2012); in 2001 JECFA also found no safety concern at current levels of intake for its use as a flavouring agent. In the USA, salicylic acid is among the substances in food-contact materials under 21 CFR 175.105, 175.300 and 177.2600.
INDUSTRIAL APPLICATIONS OF SALICYLIC ACID ANHYDROUS
The industrial importance of Salicylic Acid Anhydrous stems from its role as a basic building block in large-volume synthesis processes. In these processes, the moisture content, purity and batch-to-batch consistency of the raw material directly affect production yield.
Pharmaceutical raw material production plants:
In plants producing aspirin and salicylate salts, Salicylic Acid Anhydrous is used in large quantities as the main raw material. Low moisture content, low impurities and pharmacopoeia compliance are key in these plants.
Flavour and fragrance chemistry plants:
In the production of esters such as methyl salicylate, benzyl salicylate and isoamyl salicylate, Anhydrous Salicylic Acid is the starting material of the esterification reaction. Since water is also formed in esterification, keeping water from the raw material limited is evaluated in terms of process control.
Resin production plants:
In novolac and foundry resin production, Salicylic Acid Anhydrous can be used as an acid catalyst and resin component.
Rubber compounding plants:
In plants preparing rubber compounds, Salicylic Acid Anhydrous is evaluated as a scorch retarder to increase the processing safety of the compound.
Dye intermediate production:
Azo dye manufacturers use Salicylic Acid Anhydrous as a coupling component.
Industrial sectors:
According to EPA data, the sectors in which salicylic acid is processed include plastic material and resin manufacturing, plastic product manufacturing, paint and coating manufacturing, basic organic chemical manufacturing, other chemical product manufacturing and primary metal manufacturing.
The quality grade, moisture content and impurity profile of Salicylic Acid Anhydrous to be used in industrial applications should be determined according to the requirements of the process.
WHICH PROBLEMS CAN SALICYLIC ACID ANHYDROUS HELP SOLVE?
Reagent loss in acetylation reactions:
By limiting the water carried into the reaction with the raw material, Salicylic Acid Anhydrous can help reduce the unwanted consumption of acetic anhydride, which is decomposed by water.
Increase of free salicylic acid in aspirin production:
The patent literature states that water can increase the decomposition of aspirin and the amount of free salicylic acid. The use of low-moisture Anhydrous Salicylic Acid can help control this risk on the raw material side.
Water load in esterification processes:
Water is formed as a by-product in esterification reactions. The use of Salicylic Acid Anhydrous helps reduce the additional water load coming from the raw material.
Need for a catalyst in novolac resin synthesis:
Salicylic Acid Anhydrous can be used as an acid catalyst in phenol-formaldehyde condensation.
Scorch in rubber processing:
As a scorch retarder, Salicylic Acid Anhydrous helps prevent rubber compounds from curing prematurely during processing.
Need for a coupling component in dye production:
Salicylic Acid Anhydrous is used as a coupling component in azo dye synthesis.
Batch-to-batch quality variation:
The use of Salicylic Acid Anhydrous whose moisture content and impurity profile are checked with a COA supports consistent results from batch to batch in synthesis processes.
POINTS TO CONSIDER WHEN USING SALICYLIC ACID ANHYDROUS
Moisture uptake:
The anhydrous property of Salicylic Acid Anhydrous can only be preserved through proper storage. Packaging should be kept tightly closed when not in use and the product should not be left open in humid environments.
In processes where moisture content is critical, the moisture content of Anhydrous Salicylic Acid should be compared with the COA values before use and checked if necessary.
Working with acetic anhydride:
Acetic anhydride, used in aspirin synthesis, reacts with water. Therefore, in addition to Salicylic Acid Anhydrous, the dryness of the equipment and other raw materials should also be considered.
Process conditions:
The temperature, time and ratio values given in this text are example conditions reported in the literature. The conditions of each synthesis to be carried out with Salicylic Acid Anhydrous should be determined through laboratory and pilot-scale trials.
Incompatible materials:
Salicylic Acid Anhydrous is incompatible with oxidizing agents, strong bases, iodine, fluorine, iron salts and lead acetate. Since contact with iron can cause discolouration, care should be taken in selecting equipment materials.
Dust and ignition:
Salicylic Acid Anhydrous dust is combustible; a lower explosion limit of 1.1% (V) has been reported for the dust. Dust formation and ignition sources should be kept under control during operations such as milling, sieving and pouring.
Eyes and respiratory tract:
Salicylic Acid Anhydrous can cause serious eye damage; its dust can irritate the nose and throat. Suitable eye and face protection should be used during handling and dust formation should be avoided.
Reproductive toxicity:
Salicylic Acid Anhydrous is classified as toxic to reproduction Category 2 because it is suspected of damaging the unborn child (H361d). Special instructions should be obtained before use.
Regulation:
If Salicylic Acid Anhydrous is to be used in cosmetic or pharmaceutical products, the cosmetic limits and pharmacopoeia requirements applicable to standard salicylic acid apply equally. The product must not be used as a preservative in foods.
STARTING FORMULATION APPROACHES FOR SALICYLIC ACID ANHYDROUS
The following examples are starting approaches prepared to show how Salicylic Acid Anhydrous can be evaluated in synthesis and process development work. They are not validated production instructions.
The conditions given are based on example values reported in the literature. Since the grade of Anhydrous Salicylic Acid used, the other raw materials and the equipment can significantly change the results, final conditions should be determined through laboratory trials, safety assessment and analyses.
EXAMPLE 1: EVALUATION OF THE EFFECT OF SALICYLIC ACID ANHYDROUS MOISTURE CONTENT IN ASPIRIN SYNTHESIS
Objective: To compare the effect of raw material moisture content on acetylation yield and the amount of free salicylic acid in the product.
Starting approach:
Salicylic Acid Anhydrous: Two or three samples with different moisture contents (determined from the COA or by loss on drying measurement)
Acetic anhydride: Same molar excess relative to salicylic acid in all trials; kept constant
Reaction temperature and time: Kept constant, using the industrial conditions reported in the literature (about 98 °C, 2–3 hours) as a reference
Crystallization and washing conditions: Kept constant
Application approach:
The moisture content of each sample is measured and recorded before the trial.
The Salicylic Acid Anhydrous samples are acetylated under the same conditions.
Product yield and the amount of free salicylic acid in the product are determined by suitable analytical methods.
The results are compared according to raw material moisture content.
Based on the data obtained, an acceptable moisture limit is defined for Anhydrous Salicylic Acid.
EXAMPLE 2: SALICYLIC ACID ANHYDROUS CATALYST LEVEL SCREENING IN NOVOLAC RESIN SYNTHESIS
Objective: To determine the effect of the Salicylic Acid Anhydrous level on reaction time, resin properties and thermal stability in phenol-formaldehyde novolac synthesis.
Starting approach:
Salicylic Acid Anhydrous: 0.5%, 1.0%, 1.5% and 2.0% of the weight of phenol (range preferred in the literature)
Formaldehyde: A single value chosen in the range of 0.5–0.8 mol per mol of phenol; kept constant
Reaction pH: Monitored in the range of 1.5–4.0
Reaction temperature: A profile chosen within the 100–270 °C range defined in the literature; kept constant
Application approach:
Phenol and Salicylic Acid Anhydrous are charged to the reactor and formaldehyde is added according to the chosen ratio.
pH, reaction time and temperature profile are recorded for each catalyst level.
Cure time, melting behaviour and free phenol content of the resulting resins are measured.
Thermal stability tests are carried out and the results are compared.
For applications with high thermal stability requirements, a comparative trial with alternative catalysts such as benzoic acid is planned.
EXAMPLE 3: PRELIMINARY TRIAL OF METHYL SALICYLATE ESTERIFICATION
Objective: To evaluate the effect of reaction time and raw material quality on yield and purity in methyl salicylate synthesis with Salicylic Acid Anhydrous.
Starting approach:
Salicylic Acid Anhydrous and methanol: A weight ratio close to the consumption ratio reported in the literature (about 950 kg of salicylic acid and 400 kg of methanol per tonne of product)
Catalyst: Sulphuric acid; fixed amount
Reaction temperature: 90–100 °C
Reaction time: 2, 3 and 4 hours (time reported in the literature: about 3 hours)
Application approach:
Salicylic Acid Anhydrous is dissolved in methanol and sulphuric acid is added.
The mixture is heated with stirring at the target temperature for the defined time.
The mixture is cooled below 30 °C and the oil phase is separated.
The oil phase is washed with sodium carbonate solution until the pH exceeds 8, then with water.
The product is purified by vacuum distillation and yield and purity are compared for each reaction time.
PRODUCTS SIMILAR TO SALICYLIC ACID ANHYDROUS AND ALTERNATIVES
When selecting an alternative to Salicylic Acid Anhydrous, the target reaction, the functional group required, solubility, moisture tolerance and the quality requirements of the final product should be evaluated together.
SALICYLIC ACID ANHYDROUS AND STANDARD SALICYLIC ACID
Standard Salicylic Acid and Salicylic Acid Anhydrous are the same chemical with the same CAS and EC numbers. The choice between the two products is made according to the moisture content of the product and the sensitivity of the process in this respect.
In water-based systems such as cosmetic and dermatological formulations, moisture content is generally not decisive. In moisture-sensitive syntheses such as acetylation, however, the moisture value of the product should be evaluated separately on the COA.
SALICYLIC ACID ANHYDROUS AND SODIUM SALICYLATE
Sodium salicylate (CAS No 54-21-7) is the sodium salt of salicylic acid and is more soluble in water than salicylic acid. It can be evaluated instead of Salicylic Acid Anhydrous in applications requiring dissolved salicylate ions in aqueous media.
However, since the carboxyl group in sodium salicylate is in salt form, it cannot directly replace Anhydrous Salicylic Acid in esterification or acid-catalysed processes that require the free acid.
SALICYLIC ACID ANHYDROUS AND METHYL SALICYLATE
Methyl salicylate is an ester obtained from Salicylic Acid Anhydrous. While it is used as a final product in flavour, fragrance and topical analgesic applications, it also serves as an intermediate in the synthesis of certain derivatives such as salicylamide.
In the literature, methyl salicylate is mentioned as a starting material for the production of certain derivatives in place of salicylic acid; however, it does not replace Salicylic Acid Anhydrous in reactions requiring a free carboxyl group.
SALICYLIC ACID ANHYDROUS AND BENZOIC ACID
Benzoic acid can be used as a non-hydroxy-substituted benzoic acid catalyst in novolac resin synthesis. According to the patent literature, novolac resins catalysed with benzoic acid show higher thermal stability than those catalysed with salicylic acid.
In the rubber industry, benzoic acid is also listed, like salicylic acid, among scorch retarders.
SALICYLIC ACID ANHYDROUS AND OTHER SCORCH RETARDERS
In the rubber industry, PVI and phthalic anhydride are also used as scorch retarders. In the patent literature, phthalic anhydride is described as a conventional retarder that delays crosslinking in rubber.
The choice between Salicylic Acid Anhydrous and these retarders should be made by trials according to the rubber type, the vulcanization system and the targeted processing safety.
SALICYLIC ACID ANHYDROUS AND DIFFERENT QUALITY GRADES
Technical grade Salicylic Acid Anhydrous may be sufficient for applications such as resins, rubber, dyes and agrochemicals. In pharmaceutical raw material synthesis, pharmaceutical grade meeting Ph. Eur., BP or USP requirements is preferred, and ACS reagent grade is preferred for analytical work.
QUALITY CONTROL AND PURCHASING CRITERIA FOR SALICYLIC ACID ANHYDROUS
When purchasing Salicylic Acid Anhydrous, the most critical parameter is the moisture content emphasized by the product name. Describing the product as "anhydrous" is not sufficient on its own; the moisture or loss on drying value should appear numerically in the specification and on the COA.
Information recommended for review before purchase:
Product name and manufacturer
Quality grade (technical, Ph. Eur., BP, USP or ACS reagent)
CAS number (69-72-7) and EC number (200-712-3)
Moisture content or loss on drying
Purity (assay)
Melting point
Phenol content
4-Hydroxybenzoic acid and 4-hydroxyisophthalic acid content
Ash or sulphated ash
Iron and heavy metal content
Chloride and sulphate content
Product form and particle structure
Shelf life or retest period
Example specification values for Ph. Eur. / BP / USP grade salicylic acid:
Assay (on the dried substance): 99.5–100.5%
Loss on drying: ≤ 0.5%
4-Hydroxybenzoic acid: ≤ 0.1%
4-Hydroxyisophthalic acid: ≤ 0.05%
Phenol: ≤ 0.02%
Other impurities: ≤ 0.05%
Total impurities: ≤ 0.2%
Chloride (Cl): ≤ 0.01%
Sulphate (SO₄): ≤ 0.02%
Heavy metals (as Pb): ≤ 0.002%
Sulphated ash: ≤ 0.01%
Residual solvents: Passes test
Typical values reported in the literature for technical grade salicylic acid:
Salicylic acid content: About 99.5%
Phenol, 4-hydroxybenzoic acid or 4-hydroxyisophthalic acid: 0.05–0.1%
Ash: < 0.1%
Water: About 0.2%
These values are example values. The exact specification of the Salicylic Acid Anhydrous product to be used, especially its moisture content, should be checked against the manufacturer's TDS and COA documents.
TDS, SDS and COA:
The TDS defines the quality grade and specification limits of Salicylic Acid Anhydrous. The SDS contains the hazards of Anhydrous Salicylic Acid and information on safe handling, storage, transport and disposal.
The COA shows the actual values measured in a specific batch. In moisture-sensitive processes, the moisture value on the COA of each batch should be compared with the acceptance limit of the process.
STORAGE AND TRANSPORT OF SALICYLIC ACID ANHYDROUS
To preserve its anhydrous property, Salicylic Acid Anhydrous should be stored in its original, tightly closed packaging in a dry place. Opened packaging should be closed immediately after use, and the product should not be exposed to humid air for long periods.
Since Salicylic Acid Anhydrous is light-sensitive, it should be protected from direct light.
Salicylic Acid Anhydrous should be kept away from oxidizing agents, strong bases, iodine, fluorine, iron salts and lead acetate. The product falls under class 11 (combustible solids) of the German storage classification.
Dust accumulation should be avoided in storage and handling areas and ignition sources should be kept away.
The shelf life and retest period of Salicylic Acid Anhydrous vary by manufacturer and quality grade. For an example reagent grade, the recommended retest period is 4 years; the period for the product to be used should be checked against the TDS.
Salicylic Acid Anhydrous is not regulated as a dangerous good under ADR (road), IMDG (sea) and IATA (air) rules.
SALICYLIC ACID ANHYDROUS SAFETY INFORMATION
Salicylic Acid Anhydrous is classified as follows under the CLP Regulation (EC) No 1272/2008:
Acute toxicity (oral), Category 4 – H302: Harmful if swallowed
Serious eye damage, Category 1 – H318: Causes serious eye damage
Reproductive toxicity, Category 2 – H361d: Suspected of damaging the unborn child
Signal word: Danger
Main precautionary statements: P201 Obtain special instructions before use; P202 Do not handle until all safety precautions have been read and understood; P264 Wash skin thoroughly after handling; P280 Wear protective gloves/protective clothing/eye protection/face protection.
Toxicological data: For salicylic acid, the oral LD50 (rat, male) is reported as 891 mg/kg and the dermal LD50 (rat) as > 2,000 mg/kg.
NFPA classification: Health 1, flammability 1, instability 0. Salicylic Acid Anhydrous is a material that requires preheating before ignition can occur and normally remains stable even under fire conditions.
When working with Salicylic Acid Anhydrous, dust formation should be avoided, adequate ventilation provided, and suitable gloves and eye and face protection used. The product must not be allowed to enter the drains.
Waste should be disposed of in accordance with Directive 2008/98/EC, the Turkish Waste Management Regulation and other national and local regulations. Salicylic Acid Anhydrous is not on the REACH SVHC Candidate List.
The hazards of other substances used in synthesis processes, such as acetic anhydride, methanol, sulphuric acid, phenol and formaldehyde, differ from those of Salicylic Acid Anhydrous; the separate SDS of each should be taken as the basis.
WHAT SHOULD BE CONSIDERED WHEN PURCHASING SALICYLIC ACID ANHYDROUS?
When purchasing Salicylic Acid Anhydrous, it should be checked that the CAS number in the product documents is 69-72-7. A different CAS number may indicate that the product is a different substance, such as salicylic anhydride or a salicylate derivative.
In addition to the product being described as "anhydrous", the moisture or loss on drying value should be requested numerically in the specification. In moisture-sensitive processes, this value should be compared with the acceptance limit of the process.
A quality grade suitable for the field of use should be selected. Pharmacopoeia grade should be evaluated for pharmaceutical raw material synthesis, technical grade for resin, rubber and dye applications, and reagent grade Salicylic Acid Anhydrous for analytical work.
The levels of impurities such as phenol, 4-hydroxybenzoic acid and 4-hydroxyisophthalic acid should be checked on the COA, as they can affect final product quality, particularly in pharmaceutical and flavour syntheses.
Iron content and product colour should be checked. Marked deviations from a white colour may be a sign of impurity or degradation in Salicylic Acid Anhydrous.
Moisture-proof and tightly closable packaging should be considered to preserve the anhydrous property of the product during storage and transport.
It is important to obtain the COA, current SDS and TDS for each batch.
SUPPLY OF SALICYLIC ACID ANHYDROUS FROM ATAMAN KİMYA
Salicylic Acid Anhydrous is a raw material used for different technical functions, such as starting material, catalyst and retarder, in aspirin and salicylate ester synthesis, novolac and foundry resins, rubber, dye and analytical applications.
You can obtain Salicylic Acid Anhydrous from Ataman Kimya as follows: by sharing your field of use and the technical requirements of your process, you can contact Ataman Kimya regarding product suitability, current supply status and a quotation.
The current stock status, origin, quality grade, moisture content, technical properties, packaging and specifications of the product should be confirmed with Ataman Kimya before ordering.
Sharing the following information in a quotation request makes it easier to evaluate the right Salicylic Acid Anhydrous product:
Industry and type of process
Requested quality grade
Maximum acceptable moisture content
Requested minimum purity
Impurity, iron and heavy metal limits
Estimated order quantity and frequency of use
Requested packaging type
Requested technical documents (TDS, SDS, COA)
TDS or COA information of the current product, if available
FREQUENTLY ASKED QUESTIONS ABOUT SALICYLIC ACID ANHYDROUS
What is Salicylic Acid Anhydrous?
Salicylic Acid Anhydrous is salicylic acid supplied in anhydrous form with a low moisture content. Its chemical name is 2-hydroxybenzoic acid and its formula is C7H6O3; it is used especially in the production of aspirin, salicylate esters, resins and dyes.
What does "anhydrous" mean?
"Anhydrous" means without water. In the name Salicylic Acid Anhydrous, this term indicates that the product contains no water of crystallization and that its moisture content is kept low.
What is the difference between Salicylic Acid Anhydrous and Salicylic Acid?
There is no chemical difference; both products are the same substance identified by CAS No 69-72-7 and EC No 200-712-3. The difference is that the moisture content of Salicylic Acid Anhydrous is kept low and this property is emphasized.
Are Salicylic Acid Anhydrous and salicylic anhydride the same thing?
No. Salicylic anhydride is a different chemical derived from two salicylic acid molecules. Salicylic Acid Anhydrous is salicylic acid itself.
Why is Salicylic Acid Anhydrous preferred in aspirin production?
Acetic anhydride, used in aspirin synthesis, is decomposed by water into acetic acid. Low-moisture Salicylic Acid Anhydrous is evaluated from the standpoint of limiting the amount of water carried into the reaction with the raw material.
Why should Salicylic Acid Anhydrous be stored dry?
The anhydrous property of Salicylic Acid Anhydrous is preserved only when it is stored in tightly closed packaging in a dry place. The moisture content of product left open in a humid environment may increase.
What is the CAS number of Salicylic Acid Anhydrous?
The CAS number of Salicylic Acid Anhydrous is 69-72-7, its EC number is 200-712-3 and its CLP index number is 607-732-00-5.
In which solvents is Salicylic Acid Anhydrous soluble?
Salicylic Acid Anhydrous dissolves readily in methanol, acetone, ethanol and propanol; it is sparingly soluble in cold water. Its water solubility is 2.48 g/L at 25 °C and 77.79 g/L at 100 °C.
How is Salicylic Acid Anhydrous used in resin production?
In the patent literature, Salicylic Acid Anhydrous is used as an acid catalyst in novolac resin synthesis, preferably at 0.5–2% of the weight of phenol. It is also evaluated in the production of foundry resins.
Can Salicylic Acid Anhydrous be used in cosmetics?
Yes. Since Salicylic Acid Anhydrous is the same substance as salicylic acid, it is subject to the same cosmetic regulatory limits. In the EU these limits are 0.5%, 2.0% and 3.0% depending on product type, and 0.5% for preservative use.
Is Salicylic Acid Anhydrous a hazardous substance?
Salicylic Acid Anhydrous is harmful if swallowed, can cause serious eye damage and is suspected of damaging the unborn child. For transport, however, it is not regulated as a dangerous good under ADR, IMDG and IATA rules.
SALICYLIC ACID ANHYDROUS – TECHNICAL SUMMARY
Salicylic Acid Anhydrous, known in Turkish as Susuz Salisilik Asit, is salicylic acid with the formula C7H6O3, a white crystalline structure and a low moisture content. Identified by CAS No 69-72-7, EC No 200-712-3 and CLP index no 607-732-00-5, Salicylic Acid Anhydrous is chemically the same substance as standard salicylic acid.
The feature that distinguishes Salicylic Acid Anhydrous is its suitability for synthesis processes in which moisture matters. Thanks to the phenolic hydroxyl and carboxyl groups in its molecule, it undergoes acetylation, esterification, salt formation and coupling reactions.
Salicylic Acid Anhydrous is mainly used in the production of aspirin, methyl salicylate and other salicylate esters and salts, as an acid catalyst in novolac resin synthesis, in foundry resins, as a scorch retarder in rubber compounds and in azo dye production.
In the selection of Salicylic Acid Anhydrous, moisture content, purity, phenol and hydroxybenzoic acid impurities and quality grade are decisive; these values should be checked on the COA for each batch. To preserve its anhydrous property, the product should be stored in tightly closed packaging in a dry place protected from light.
Since Salicylic Acid Anhydrous is harmful if swallowed, can cause serious eye damage and is classified as toxic to reproduction Category 2, appropriate occupational safety measures must be taken during handling and the current SDS must be taken as the basis.
Companies planning to source Salicylic Acid Anhydrous from Ataman Kimya are advised to confirm product suitability with Ataman Kimya by sharing their field of use, process type, quality grade, acceptable moisture content, minimum purity, impurity limits, quantity and technical documentation needs.
