2-Ethylhexyl Nitrate (2-EHN)

What it is

2-Ethylhexyl nitrate (2-EHN, also written as ethylhexyl nitrate, octyl nitrate, or EHN; CAS 27247-96-7) is an organic nitrate ester. The neat substance is a clear, pale-yellow liquid with a mild ester odor and a density near 0.96 g/mL. It is the dominant cetane number improver used in the diesel fuel market.

Typical treat rate in finished refinery or terminal-blended diesel sits between 300 and 2,000 ppm. Aftermarket in-tank diesel additives sold to consumers usually deliver an in-tank concentration of 200 to 500 ppm once mixed with a full tank.

How it works

EHN is a free-radical initiator. The nitrate ester bond has a low thermal-decomposition temperature, so as the fuel-air charge is compressed and heated in a diesel cylinder, the molecule breaks apart before the bulk fuel reaches its autoignition point. Decomposition yields nitrogen dioxide (NO2) and an alkyl radical, both of which seed the combustion chain reaction earlier in the compression stroke.

The practical result is a shorter ignition delay. Effects associated with shorter ignition delay in diesel engines include easier cold starting, reduced white smoke during warm-up, smoother idle on older direct-injection engines, and a measurable bump in cetane number from base diesel.

Where it appears in car care

The most common consumer encounter with EHN is inside diesel fuel additives: cetane boosters, winter-blend anti-gel and starting aids, and combination diesel fuel system cleaners that market a cetane claim. It also turns up in some racing or performance gasoline additives that advertise cetane equivalence, though gasoline engines do not benefit from cetane improvement in the same way diesels do.

In the CarCareTruth catalog, EHN shows up specifically on the ingredient list of diesel-targeted fuel additives and fuel system cleaners.

Thermal stability and shipping

EHN concentrates are sensitive to heat. Bulk neat EHN can self-decompose if stored at elevated temperatures, which is why aftermarket diesel additives blend it with stabilizers and dilute it well below concentrate strength. Bulk shipments of the neat substance move under DOT and UN transport rules as a Class 5.1 oxidizer, typically Packing Group II at concentrate.

Finished consumer additive bottles do not ship as Class 5.1 because the in-bottle concentration sits well below the cutoff thresholds.

SDS facts

Safety data sheets for neat 2-EHN typically carry the following CLP hazard statements:

• H272: may intensify fire; oxidizer
• H315: causes skin irritation
• H319: causes serious eye irritation
• H335: may cause respiratory irritation

The H302/H312/H332 acute toxicity classifications reported on this product page reflect the mixture-level SDS data used for the CarCareTruth scoring snapshot. Acute oral toxicity in rats is reported around LD50 500 mg/kg.

Organic nitrates can oxidize hemoglobin to methemoglobin, and methemoglobinemia is a recognized industrial-exposure hazard for workers handling bulk EHN. The published case literature is at occupational exposure levels, not at the dilute concentrations present in a consumer fuel additive once dosed into a diesel tank.

Environmental profile

At finished-fuel concentrations, EHN has low aquatic toxicity, is not classified as persistent, and is not bioaccumulative. The dominant environmental pathway is combustion in the engine, where the nitrate group contributes to engine-out NOx. NOx is a regulated air pollutant, and an increase in NOx is one of the trade-offs documented when cetane improvers are evaluated against base diesel.

Regulatory snapshot

2-EHN is not listed on California Proposition 65. It is a volatile organic compound by general definition but is not on the EPA's lists of specific regulated VOCs for finished-fuel additive use. Workplace exposure to the neat substance falls under the OSHA Hazard Communication Standard via the CLP hazard statements above.

Where to look on the SDS

For a quick read on a diesel additive that lists 2-EHN as an ingredient:

• Section 2: confirm the H272 oxidizer classification and any acute-tox H-codes.
• Section 3: composition and 2-EHN concentration range.
• Section 9: physical and chemical properties. Boiling point of the neat substance is roughly 260 °C and density is around 0.96 g/mL.
• Section 14: transport classification. Concentrate ships as UN3358 / Class 5.1 PG II; diluted consumer bottles usually do not.