Product Identity and Physical Properties
Methyl acetate (CAS 79-20-9) is the methyl ester of acetic acid, with the formula CH3COOCH3 and a molar mass of 74.08 g/mol. It is a clear, colourless, volatile liquid with a mild fruity odour, and it is one of the least expensive ester solvents available in bulk. Its low boiling point and low flash point dominate the way it is stored, transferred and used.
| Property | Value |
|---|---|
| Molecular formula | CH3COOCH3 |
| CAS number | 79-20-9 |
| Molar mass | 74.08 g/mol |
| Boiling point | 56.9 C |
| Flash point, closed cup | about minus 10 C |
| Density at 20 C | about 0.93 g/cm3 |
| Solubility in water | about 24 g per 100 mL |
| Miscibility | alcohols, esters, ketones, aromatic solvents |
The combination of a flash point near minus 10 C and a boiling point below 60 C means that vapour is generated quickly at ordinary workshop temperatures, and that vapour is heavier than air and can travel to a distant ignition source.
Hazard Classification Explained
Under the harmonised European classification, methyl acetate carries three statements: H225, highly flammable liquid and vapour; H319, causes serious eye irritation; and H336, may cause drowsiness or dizziness. The label therefore shows the flame pictogram together with the exclamation mark for health effects. Acute oral toxicity is low, which is a common source of misunderstanding: a solvent can be only slightly toxic by ingestion and still present a serious fire and inhalation risk. Methyl acetate is also a volatile organic compound, and its emissions fall under solvent emission rules in coating and printing installations.
Exposure Control and Workplace Practice
Effective control starts with engineering rather than with personal protection. Closed transfer from drums or intermediate bulk containers, local exhaust ventilation at mixing and printing stations, bonding and earthing of all conductive equipment, and flammable gas detection in enclosed areas together keep vapour concentrations low. Where exposure cannot be eliminated, the applicable national occupational exposure limit sets the target for air monitoring. Nitrile or laminated gloves, chemical goggles and, in confined spaces, supplied-air respiratory protection are standard measures. Because the vapour is heavier than air, low-lying areas, pits and sumps require particular attention.
Industrial Uses and Solvent Recovery
Methyl acetate is used as a fast-evaporating solvent in nitrocellulose and cellulose ester coatings, in printing inks, in adhesives and in some cosmetic formulations. It is also a chemical intermediate: hydrolysis gives acetic acid and methanol, and it is used in the manufacture of acetic anhydride and in several acetylation steps. In plants where the solvent is used in large volumes, recovery by distillation is common practice, because the ester forms a low-boiling azeotrope with methanol and the recovered fraction must be analysed before it is returned to the process.
Quality Control, Packaging and Storage
Purchase specifications normally state ester content, acidity expressed as acetic acid, water content and colour. Water is determined by Karl Fischer titration and purity by gas chromatography. Methyl acetate hydrolyses slowly in the presence of water and acid, so storage in dry, closed vessels is important; mild steel, stainless steel and lined drums are all used, and contact with strong oxidising agents must be avoided. The material is shipped in 180 kg drums, in 1000 litre intermediate bulk containers and in tankers, always with flammable liquid labelling, and storage tanks should be bonded and earthed with provision for vapour recovery. Suppliers should issue a batch certificate of analysis and a current safety data sheet with each delivery, because transport and classification requirements are updated from time to time.
Frequently Asked Questions
Q: Is methyl acetate hazardous?
A: Yes, mainly because it is highly flammable, with a closed cup flash point near minus 10 C, and because its vapour can cause drowsiness. It is also an eye irritant, although its acute oral toxicity is low.
Q: What do the hazard codes H225, H319 and H336 mean?
A: H225 means highly flammable liquid and vapour, H319 means serious eye irritation, and H336 means the vapour may cause drowsiness or dizziness.
Q: How should the solvent be stored?
A: In closed, dry vessels in a cool, ventilated area free of ignition sources, with bonding and earthing of transfer equipment and separation from strong oxidising agents.
Q: Is methyl acetate miscible with water?
A: It dissolves readily, at roughly 24 g per 100 mL, and it also mixes freely with alcohols, ketones, esters and aromatic solvents.
Q: How is the purity of the delivered material verified?
A: By gas chromatography for ester content and by Karl Fischer titration for water, together with titration of acidity and a colour check against the agreed specification.
Q: Can recovered methyl acetate be reused?
A: Yes, recovery by distillation is common, but the recovered fraction must be re-analysed for water, acidity and methanol content before it is returned to production.