P-Toluenesulfonic acid methyl ester — more widely known as methyl tosylate, methyl p-toluenesulfonate, or MPTS — is a sulfonate ester that occupies a central role in modern organic synthesis. Assigned CAS number 80-48-8, this compound is prized industrially for its reliable performance as a methylating agent, esterification aid, and acylation reagent across pharmaceutical intermediates, dye chemistry, and resin production.

1. Chemical Identity and Quick Reference Data

2. Physical and Chemical Properties

Methyl tosylate typically presents as a colorless to light yellow liquid or low-melting crystalline solid, depending on ambient temperature and purity. It is hygroscopic and should be handled under controlled humidity conditions. Reported physical constants from multiple analytical sources are summarized below.

3. Manufacturer Specification Sheet

Commercial-grade methyl tosylate is generally supplied to the following technical specification, consistent with industrial esterification-agent grade material used in downstream synthesis:

Because residual PTSA and unreacted PTSC directly affect downstream reaction yield and impurity profiles in fine chemical and pharmaceutical synthesis, buyers should always request a batch-specific certificate of analysis (CoA) rather than relying on nominal specification ranges alone.

4. Production Process Overview

Methyl tosylate is manufactured industrially through the controlled esterification of p-toluenesulfonyl chloride with methanol under mildly alkaline conditions. In a typical process route, p-toluenesulfonyl chloride is combined with methanol while dilute sodium hydroxide solution is added gradually, keeping the reaction temperature below approximately 25 °C to suppress hydrolysis side reactions and control exotherm. Alkali addition is stopped once the mixture reaches a pH near 9, after which stirring continues to drive the reaction to completion. The crude product is then separated, washed to remove residual salts and unreacted starting material, dried, and purified — commonly through vacuum distillation — to reach commercial purity. Process control at each stage (temperature, pH, and reaction time) is what ultimately determines the residual PTSA/PTSC levels reflected in the specification table above.

5. Industrial and Laboratory Applications

The reactivity of the methyl-oxygen bond in the tosylate group makes this ester an effective methyl-group donor, and it is used across several distinct chemical process categories:

• Methylating agent in organic synthesis — transfers a methyl group to nucleophilic sites (amines, alcohols, heterocycles) under relatively mild conditions compared to more aggressive alkylating agents.
• Esterification and acylation processes — functions as an esterification agent and acylating reagent in multi-step fine chemical synthesis.
• Dehydrating agent — assists specific condensation reactions where controlled water removal is required.
• Selective heterocycle substitution — used in selective 1-substitution reactions of tetrazole rings, relevant to agrochemical and pharmaceutical intermediate synthesis.
• Dye and pigment manufacturing — serves as a methylation intermediate in several dye synthesis routes.
• Alkyd resin processing — used in resin modification chemistry within coatings and polymer applications.

6. Safety, Handling, and Regulatory Considerations

Methyl tosylate is classified as an alkylating agent and should be handled with the same rigor applied to other reactive sulfonate esters. Published hazard classifications include acute oral toxicity, eye damage, and skin sensitization potential, and the compound is recognized in pharmaceutical impurity literature as a sulfonate ester of concern under genotoxic impurity guidelines such as ICH M7, since alkyl sulfonate esters can form as trace by-products in processes using methanol with sulfonic acid catalysts. This makes controlled, low-residual manufacturing — as reflected in the PTSA/PTSC/water specification limits above — particularly important for pharmaceutical intermediate applications.

Recommended handling practices include:

• Use in a fume hood or adequately ventilated area to limit vapor and mist exposure.
• Wear chemical-resistant gloves, safety goggles, and standard laboratory or plant PPE.
• Avoid contact with skin, eyes, and mucous membranes; wash immediately with water if contact occurs.
• Store in tightly sealed containers away from moisture, strong bases, and oxidizing agents.
• Transport under UN 3261, Class 8 (corrosive), Packing Group II regulations, as applicable in your jurisdiction.

This section provides general handling guidance only and does not replace a current Safety Data Sheet (SDS). Always consult the SDS supplied with your specific batch before use.

7. Comparison with Related Sulfonate Esters

Methyl tosylate is one of several alkyl tosylate esters used in organic synthesis, each offering different reactivity and volatility profiles. The table below compares it with two closely related compounds available in our intermediates range.

8. Quality Control and Testing Methods

Reliable quality control for methyl tosylate batches typically involves a combination of the following analytical techniques:

• Gas Chromatography (GC) — for purity assay and detection of trace organic impurities.
• Karl Fischer Titration — for precise water content determination against the 0.3% maximum specification.
• Acid-Base Titration — to quantify residual PTSA content.
• Melting Point Determination — as a rapid indicator of overall purity and crystallinity.
• Gravimetric Ash Testing — to confirm inorganic residue remains within the 0.05% maximum limit.

9. Supplier Overview

This technical profile is maintained by Jiaxing Jinli Chemical Co., Ltd., a manufacturer specializing in sulfonate ester intermediates, blowing agents, and plasticizer-series chemicals for industrial buyers. The company's Intermediates Series includes methyl tosylate alongside related sulfonyl chloride and sulfinate salt products, supported by in-house process development documented on the Technology page. Buyers evaluating suppliers for regulated applications should request current batch CoAs, SDS documentation, and — where relevant to pharmaceutical use — genotoxic impurity data prior to procurement.

10. Related Intermediates

The following related products from the same intermediates line may be relevant to formulators sourcing complementary sulfonate chemistry:

• Sodium p-Toluenesulfinate (824-79-3)
• Benzenesulfinic Acid Sodium Salt
• P-Toluenesulfonyl Chloride (PTSC)
• Ethyl P-toluenesulfonate

11. Frequently Asked Questions

Is methyl tosylate the same as methyl tosylate ester or PTSME?
Yes. Methyl p-toluenesulfonate, methyl tosylate, PTSME, and p-toluenesulfonic acid methyl ester all refer to the same compound, CAS 80-48-8.

What is the shelf life of methyl tosylate?
When stored sealed at 2–8 °C away from moisture, typical shelf life is 12 months, though this should be confirmed against the specific supplier's CoA and retest date.

Can methyl tosylate be used in pharmaceutical manufacturing?
It can serve as a methylating intermediate, but because it is also monitored as a potential genotoxic impurity class member, pharmaceutical users should apply ICH M7-aligned control strategies and confirm residual-level compliance for their specific process.