2-Methylfuran (CAS 534-22-5): Properties, Handling and Its Role in the 2-MeTHF Route

2-Methylfuran (CAS 534-22-5) occupies a specific and increasingly important place in the chemical map: it is the intermediate between biomass-derived furfural and 2-methyltetrahydrofuran, one of the few genuinely bio-based solvents to have broken into mainstream pharmaceutical and fine-chemical use. That position explains both its commercial importance and why the material is specified so tightly – a precursor to a catalyst-sensitive hydrogenation step cannot afford to arrive wet, oxidised or contaminated.

1. The molecule

Property	Value
CAS	534-22-5
Formula / MW	C₅H₆O / 82.10 g/mol
Appearance	Colourless liquid, ethereal odour
Boiling point	About 63-64 °C
Density	About 0.913 g/cm³ (25 °C)
Refractive index (n_D²⁰)	About 1.434
Flash point	About -22 °C – highly flammable
Commercial specification	99% min assay, 0.05% max water

A furan ring with a methyl group at the 2-position: small, volatile, aromatic in the heterocyclic sense, and unusually reactive for a molecule this simple. The low boiling point and the very low flash point dominate everything about how it is stored, shipped and handled.

2. The route that gives it its value

Stage	Chemistry	What it produces
1. Biomass to furfural	Acid-catalysed dehydration of C5 sugars (xylose) from agricultural residues	Furfural – a mature, large-volume platform molecule
2. Furfural to furfuryl alcohol	Catalytic hydrogenation of the aldehyde	Furfuryl alcohol, the main industrial furan alcohol
3. Furfuryl alcohol to 2-methylfuran	Hydrogenolysis – removal of the hydroxyl group	2-Methylfuran – this product
4. 2-Methylfuran to 2-MeTHF	Ring hydrogenation	2-Methyltetrahydrofuran (CAS 96-47-9), the bio-based solvent

Each stage matters commercially. The reason 2-methylfuran is a defined commercial product rather than an intermediate that is always consumed on site is that the hydrogenation to 2-MeTHF is often run by a different company, in a different place, sometimes years later. That separation is what creates a merchant market – and what makes the specification critical, because a batch that degraded in storage between stage 3 and stage 4 fails at stage 4.

3. Why 2-MeTHF matters

2-Methyltetrahydrofuran is the reason the 2-methylfuran market exists at the scale it does. It is a saturated ether with a boiling point around 80 °C, and it competes with THF in exactly the applications where THF is most awkward:

Property	THF	2-MeTHF	Why it matters in practice
Water miscibility	Fully miscible	Only slightly soluble (about 14 g/100 mL)	Reaction work-up separates into two phases, so the solvent can be recovered by decantation rather than distillation
Origin	Petrochemical	Bio-based (from furfural)	Supports bio-content claims in pharmaceutical and consumer products
Stability to base and to organometallics	Good	Good, and the phase separation helps	Grignard and organolithium chemistry runs cleanly and the work-up is easier
Peroxide formation	Well known problem	Lower tendency, but not zero	Storage still requires the same precautions
Boiling point	About 66 °C	About 80 °C	Higher boiling point means slower evaporation and a wider process window

The commercial consequence: 2-MeTHF has moved from a curiosity to a standard solvent in process chemistry, and every tonne of it consumed traces back to 2-methylfuran.

4. The specification, and why each line is there

Item	Typical requirement	What it protects
Assay	99% min	Reaction stoichiometry and the purity of the downstream 2-MeTHF
Water	0.05% max	Catalyst life in the hydrogenation; suppression of acid-catalysed ring opening and resinification
Refractive index	1.434	Identity and dryness in a one-minute test
Appearance	Colourless	Oxidation products are coloured; a yellow tint means ageing has begun

The water limit is the line that distinguishes a real specification from a catalogue entry. At 0.05%, the material is safe for a catalyst-sensitive hydrogenation; at 0.5%, it is a different product with a different failure mode, and the price difference will not tell you which one you are buying.

5. Handling: three hazards, in order

Flammability. Flash point around -22 °C means the liquid gives off an ignitable vapour at any normal ambient temperature, including in winter. Grounding, bonding, explosion-proof equipment and vapour control are not optional.
Volatility. Boiling at 63-64 °C, it develops significant vapour pressure in a sealed drum. Summer storage and transport need headspace and venting discipline; opening a warm drum in a confined space is a genuine exposure risk.
Chemical instability. The furan ring is sensitive to oxygen (leading to coloured, higher-boiling oxidation products) and to acid (leading to exothermic resinification). Store under nitrogen, keep away from acids and rust, protect from light.

These three interact: a warm, half-empty, air-filled drum is the worst case for all of them at once. That is why pack size should match consumption.

6. What to put on the purchase order

Assay and moisture, with the moisture limit stated explicitly – not inherited from a generic catalogue sheet.
Refractive index as an incoming-goods check you can perform yourself.
Nitrogen padding and container type.
Transport classification and packing group, confirmed for your route.
Pack size matched to consumption, because a partially used drum of a volatile, oxidation-sensitive liquid is a liability.

7. Packaging and supply

Supplied in steel drums with nitrogen padding on request, and in smaller sealed containers for development work. Store cool, dry, dark and segregated from acids and oxidisers. Every lot ships with a COA and SDS, FOB or CIF against destination, with the flammable-liquid classification declared on the documents. Where the material is destined for a hydrogenation step, say so at enquiry stage: the moisture specification and the packaging are then agreed together rather than discovered as a problem on the second order.

8. The honest summary

2-Methylfuran is a straightforward molecule with an unforgiving specification. Buyers who treat it as a commodity solvent and compare on price per kilogram will eventually receive a lot at 0.3% water, discover that the hydrogenation catalyst lasts half as long, and spend more on catalyst than they saved on the drum. Buyers who treat the moisture figure as the specification get a precursor that behaves the same way every time – which, for a material feeding a catalytic step, is the only thing that matters.