Compounds · Other compounds · Heat (Maillard reaction and pyrolysis)
Naphthalene
Also known as Naphthalin — an analysis may use any of these names
Mothballs, asphalt, dry and dusty. Very particular and impossible to confuse.
- CAS
- 91-20-3
- Formula
- C10H8
- Molar mass
- 128.17
- Odour threshold
- 21 ppbin water
- Boiling point
- ≈ 218 °C at atmospheric pressure
For this compound the two axes sit close together. Volatility tells you whether it leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices.
Where it comes from
Biosynthetic pathway: Heat (Maillard reaction and pyrolysis) — fire breaks large molecules into ones you can smell.
Naphthalene is the only exception in the library with no present-day biological origin. It comes from petroleum and coal, that is, from organisms that died hundreds of millions of years ago and were transformed by geological heat and pressure. Classing it under heat is right in mechanism, only different in timescale.
About the threshold figure
Moderate. That is why the smell of mothballs spreads so clearly in a closed wardrobe.
Published thresholds differ by several orders of magnitude, because of differences in measuring method, sample purity and panel. The figure here is an order of magnitude for relative comparison, not a measurement. We give it only for compounds where the literature broadly agrees — 52 of the 106 compounds in the library. The rest are left blank rather than guessed.
Why it sits where it does
Two fused aromatic rings, flat and stable; it sublimes at room temperature — which is rare.
Where else you meet it
Asphalt, coal, mothballs, and vehicle exhaust.
Dictionary entries that mention this compound
Regulatory note
Not used in cosmetics. It is here because it is the reference point for an urban smell. This is a labelling requirement, not a warning about the product.