Naphthalene
Properties
| State | Solid (crystalline, sublimes readily) |
| Color | White |
| Solubility | Insoluble in water (0.031 g/L at 25°C); soluble in ethanol, ether, benzene |
| Melting Point | 80.2°C |
| Boiling Point | 218°C |
About Naphthalene
Naphthalene (C10H8, 128.171 g/mol) is the simplest fused bicyclic aromatic — two benzene rings sharing an edge — and the textbook entry point for understanding how aromaticity behaves in polycyclic systems. The crystal is white and waxy with a melting point of 80.2 °C, but the more striking property is its substantial vapor pressure at room temperature (about 11 Pa at 25 °C). That sublimation is the reason mothballs visibly shrink over months sitting in a closet, and why the vapor builds up to concentrations that repel keratin-eating moth larvae. Industrially, naphthalene is the largest single component of coal tar (about 10% by weight) and gets recovered by fractional distillation of the 200-260 °C tar fraction. The biggest use by volume is air oxidation over a V2O5 catalyst at 380 °C to phthalic anhydride — the precursor to dioctyl phthalate plasticizer for PVC, alkyd paint resins, and unsaturated polyester for fiberglass boats. In organic chemistry teaching, naphthalene is the standard example for explaining why electrophilic aromatic substitution prefers the alpha (1) position over the beta (2): the arenium intermediate from alpha attack has more resonance structures that preserve aromaticity in the unsubstituted ring. Use as a moth repellent has declined sharply in the last two decades, replaced by paradichlorobenzene and ultimately by sealed storage and natural alternatives like cedar.
Where you'll encounter it
If you've ever opened a wardrobe at your grandparents' house and gotten that sharp, slightly tarry smell, you've smelled naphthalene at maybe 1 ppm in air. Most people recognize it instantly even if they can't name it. In an organic chem teaching lab, naphthalene is the standard sublimation demo: warm a watch glass of the flakes on a hot plate at 60 °C with a cool surface above and crystals grow visibly on the cool side within minutes — no melting in between. Industrially, anyone who has worked at a coke plant or coal-tar refinery has seen the pale flake naphthalene that drops out of the wash-oil distillation column. And in fragrance chemistry, it shows up unwelcome as a contaminant in some petroleum-derived solvents that have to be cleaned up before use in perfumery.
Common Uses
- Air-oxidation feedstock for phthalic anhydride at 380 °C over V2O5
- Mothball and clothes-storage moth repellent (declining domestic use)
- Sulfonated to naphthalenesulfonate dispersants for concrete admixtures
- Teaching example for electrophilic aromatic substitution regioselectivity
- Standard sublimation demo in undergraduate organic chemistry labs
- Intermediate for synthetic tanning agents and azo-dye couplers
- Reference compound for PAH analytical method development by GC-MS
Safety Information
GHS classifications: H302 (harmful if swallowed), H351 (suspected carcinogen, IARC Group 2B), H410 (very toxic to aquatic life with long-lasting effects). Acute oral toxicity in humans causes hemolytic anemia, particularly severe in patients with G6PD deficiency — there are well-documented cases of infant hemolysis from clothing stored with mothballs. Occupational exposure limits sit in the low-ppm range and carry a skin notation — vapor and dermal uptake both count. The IARC Group 2B classification is based on rodent inhalation studies showing nasal tumors at chronic high doses. Use a fume hood for any sublimation or melting work, nitrile gloves, and safety glasses. Store away from oxidizers — the flash point is 79 °C closed cup.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.