| Description | 1-methylnaphthalene is a methylnaphthalene carrying a methyl substituent at position. It is a polycyclic aromatic hydrocarbon (PAH). It is present in cigarette smoke, wood smoke, tar, asphalt, and at some hazardous waste sites. The main use of 1-methylnaphthalene is as a raw material for naphthoic acid, fluorescent whitening agents, and surfactants. It is also used as a raw material for dyestuff dispersants and heat transfer oils, and as a solvent for agricultural chemical. |
| Chemical Properties | 1-methylnaphthalene is a colorless, bluefluorescing liquid with an earthy, phenolic odor. It is insoluble in water but dissolves in alcohol and ether. With a density greater than water, this combustible substance is obtained from coal tar and used in organic synthesis. It has a role as a carcinogenic agent and a plant metabolite. |
| Occurrence | Methylnaphthalene was identified as a volatile component of cassava, roasted filberts and nectarines. Assorted types of lima, pinto, red kidney, black, navy and mung beans, soybeans, split peas and lentils were found to contain 1-methylnaphthalene at concentrations ranging from 2.8 to 49.2 ppb. |
| Uses | The main uses of methylnaphthalene are as a raw material for dyestuff dispersants and heat transfer oils, and as a solvent for agricultural chemical. It is used in insecticide manufacturing; manufacture of phthalic anhydride; solvent in organic synthesis; asphalt and naptha constituent. It is also used as a test substance for the determination of the cetane number of diesel fuels. Further, it is employed in the preparation of 1-methylnaphthalene-d10 using deuterium oxide, sodium deuteroxide. |
| Definition | ChEBI: 1-methylnaphthalene is a methylnaphthalene carrying a methyl substituent at position 1. It has a role as a carcinogenic agent and a plant metabolite. |
| Preparation | 1-Methylnaphthalene is primarily derived from coal tar and petroleum oils. It is present in high-temperature coal tar in a concentration of 0.5% and is produced industrially from the methylnaphthalene fraction, which boils between 240 and 245 °C, by redistillation of the 2-methylnaphthalene filtrate following crystallization and separation of 2-methylnaphthalene. |
| Aroma threshold values | Detection: 7.5 to 20 ppb. |
| Taste threshold values | Taste characteristics at 1 ppm: naphthyl-like with a medicinal nuance. |
| Synthesis Reference(s) | Journal of the American Chemical Society, 65, p. 295, 1943 DOI: 10.1021/ja01242a503
The Journal of Organic Chemistry, 53, p. 4466, 1988 DOI: 10.1021/jo00254a009
Tetrahedron Letters, 29, p. 97, 1988 DOI: 10.1016/0040-4039(88)80026-1 |
| General Description | 1-methylnaphthalene is a colorless liquid. Freezing point -22 °C (7.6 °F). Boiling point 240-243 °C (464-469 °F). Flash point 82 °C (180 °F). Denser than water. Derived from coal tar and used in organic synthesis. |
| Air & Water Reactions | Insoluble in water. |
| Reactivity Profile | 1-Methylnaphthalene is sensitive to heat. Reacts with strong oxidizing agents. Incompatible with oxygen and peroxides . |
| Hazard | Moderate fire risk. Lower respiratory tractirritant and lung damage. Questionable carcinogen. |
| Health Hazard | Harmful if inhaled. Liquid causes irritation of the eyes and skin and skin photosensitization. Harmful if swallowed. Chronic exposure may cause liver or kidney damage. |
| Fire Hazard | 1-Methylnaphthalene is combustible. |
| Carcinogenicity | The carcinogenic potential of
1- and 2-methyl was investigated in B6C3F1 mice. Female
and male mice were given methylnaphthalene in their diets
for 81 weeks. The results indicated that 1-methyl was a
possible weak carcinogen in the lung of male but not female
mice whereas 2-methyl did not possess unequivocal
carcinogenic potential in these mice. |
| Purification Methods | Dry 1-methylnaphthalene for several days with CaCl2 or by prolonged refluxing with BaO. Fractionally distil it through a glass helices-packed column from sodium. Purify it further by solution in MeOH and precipitation of its picrate complex by adding to a saturated solution of picric acid in MeOH. The picrate, after crystallisation to constant melting point (m 140-141o) from MeOH, is dissolved in *benzene and extracted with aqueous 10% LiOH until the extract is colourless. Evaporation of the *benzene solution under vacuum gives 1-methylnaphthalene [Kloetzel & Herzog J Am Chem Soc 72 1991 1950]. However, neither the picrate nor the styphnate complexes satisfactorily separate 1-and 2-methylnaphthalenes. To achieve this, 2-methylnaphthalene (10.7g) in 95% EtOH (50mL) has been precipitated with 1,3,5-trinitrobenzene (7.8g) and this complex has been crystallised from MeOH to m 153-153.5o (m of the 2-methyl isomer is 124o). [Alternatively, 2,4,7-trinitrofluorenone in hot glacial acetic acid could be used, and the derivative (m 163-164o) is recrystallised from glacial acetic acid]. The 1-methylnaphthalene is regenerated by passing a soution of the complex in dry *benzene through a 15-in column of activated alumina and washing with *benzene/pet ether (b 35-60o) until the coloured band of the nitro compound had moved down near the end of the column. The complex can also be decomposed using tin and acetic-hydrochloric acids, followed by extraction with diethyl ether and *benzene; the extracts are washed successively with dilute HCl, strongly alkaline sodium hypophosphite, water, dilute HCl and water. [Soffer & Stewart J Am Chem Soc 74 567 1952.] It can be freed from anthracene by zone melting [Beilstein 5 IV 1687.] |
