4-Methylpentan-2-ol

4-Methylpentan-2-ol (MIBC, methyl isobutyl carbinol, CAS 108-11-2) is a secondary alcohol co-solvent used in fuel-system and carburetor cleaners as a wetting agent and mild gum/lacquer remover. It appears in Ford's Motorcraft Carburetor Tune-Up Cleaner (PM-3) at 2-4% by weight.

This compound is chemically distinct from methyl isobutyl ketone (MIBK, 4-methylpentan-2-one, CAS 108-10-1), a ketone, not an alcohol, that shares the same carbon skeleton and a similar name but is a different substance with its own separate ingredient file (content/ingredients/methyl-isobutyl-ketone.md). MIBK carries genuine California Prop 65 carcinogen (listed 2011-11-04) and developmental toxin (listed 2014-03-28) designations. 4-Methylpentan-2-ol does not. A prior version of this file incorrectly asserted prop65_listed: true for 4-methylpentan-2-ol on the basis of MIBK's listing, describing MIBK as a "close chemical relative": that reasoning conflates two distinct CAS numbers and is not how Prop 65 listings work. ACGIH, OSHA, and multiple state regulations assign skin-absorption designations to 4-methylpentan-2-ol, meaning dermal contact during use is a meaningful exposure route, independent of the Prop 65 question.

At typical formulation concentrations of 2-4%, it is a minor contributor to carb-cleaner chemistry. Where a finished product's SDS discloses actual MIBK (CAS 108-10-1) as a separate component, track and cite that under its own ingredient identity, not under this one.

Regulatory status

• Not California Prop 65 listed: no entry for 4-methylpentan-2-ol / methyl isobutyl carbinol, CAS 108-11-2, on the OEHHA list. The compound sometimes confused with it, methyl isobutyl ketone (MIBK, CAS 108-10-1), is separately Prop 65 listed as both a carcinogen and a developmental toxin, but that listing does not extend to this different CAS number.

Sources

• OEHHA Proposition 65 list cross-check: data/prop65/oehha-list.json (986 entries, published 2025-12-05) checked by CAS 108-11-2, no match. MIBK (CAS 108-10-1) confirmed present twice in the same file (cancer, listed 2011-11-04; developmental, listed 2014-03-28).
• Blast-radius check: the sole consuming product, content/products/motorcraft/motorcraft-pm3-carburetor-tune-up-cleaner/index.md, already cites its Prop 65 warning correctly against MIBK (prop65_ingredient: "4-methylpentan-2-one (CAS 108-10-1)", SDS §15), not against this alcohol, and the same product's structured ingredients[] array separately lists cumene (CAS 98-82-8, genuinely Prop 65 listed) at a concentration tier that already drives the product's warning independent of this ingredient. Correcting this flag does not change that product's published Prop 65 value.
• Hazard/health/environment data (H315/H319, skin-absorption designations, LD50) unchanged from the prior sourcing pass; not re-verified in this correction, which is scoped to the Prop 65 flag only.