Description
2-Methylnaphthalene is a polycyclic aromatic hydrocarbon (PAH), consisting of two-fused aromatic rings with a methyl group attached on one of the rings at the number two carbon.
2-Methylnaphthalene is a natural component of crude oil and coal, and is found in pyrolysis and combustion products such as cigarette and wood smoke, emissions from combustion engines, asphalt, coal tar residues, and used oils (ATSDR, 1995; HSDB, 2002; Warshawsky, 2001).
In the United States, 2-methylnaphthalene is used for making detergents, dyes, solvents, as well as vitamin K. 2-methylnapthalene is also used to make some pesticides, or as an additional ingredient in some pesticides. 2- methylnaphthalene is released into the environment when wood or fossil fuels are burned or when there are spills of products containing fossil fuels. 2-methylnaphthalene can evaporate or break down quickly in soils exposed to air or containing certain microorganisms, but it could stay a year or more under other conditions in certain sediments or soils.
Chemical Properties
1-Methylnaphthalene and 2-methylnaphthalene are naphthalenerelated compounds. 1-Methylnaphthalene is a clear liquid and 2- methylnaphthalene is a solid. Insoluble inwater; soluble in alcohol and ether. Combustible. both can be smelled in air and in water at very low concentrations. The taste and odor of 2-methylnaphthalene have not been described. Its presence can be detected at a concentration of 10 ppb in air and 10 ppb in water.
Uses
2-methylnaphthalene are used to make other chemicals such as dyes, insecticides, Organic synthesis and resins. Pure 2-methylnaphthalene is a component used in the manufacture of vitamin K and the insecticide carbaryl (1-naphthyl-N-methylcarbamate) (HSDB, 2002).
Methylnaphthalene (CASRN 1321-94-4) refers to a mixture of approximately two-thirds 2-methylnaphthalene and one-third 1-methylnaphthalene (CASRN 90-12-0). Methylnaphthalene is manufactured from coal tar through the extraction of heteroaromatics and phenols. Distillation of methylnaphthalene removes 1-methylnaphthalene, leaving 2-methylnaphthalene. Mixtures containing 2-methylnaphthalene are used in the formulation of alkyl-naphthalenesulfonates (used for detergents and textile wetting agents), chlorinated naphthalenes, and hydronaphthalenes (used as solvents).
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 has been used as an indicator of smoke exposure in food and packaging materials.
Production Methods
Alkylnaphthalenes are formed as pyrolysis products in cigarette
smoke. Some have been identified in commercial
carbon paper. They are also the major components of the
C10–C13 alkylnaphthalene concentrate fraction, which distills
at 400–500F. A C11–C12 petroleum mixture of reformates
that contained about 23% alkylnaphthalenes caused
skin and eye effects. The toxicity of the alkylnaphthalenes
to marine species is greater than that of the alkylbenzenes
(85). The toxicity and the bioaccumulation increase
with molecular weight. Nocardia cultures, isolated from
soil, preferentially oxidized alkylnaphthalenes when methylated
in the two positions. Methylnaphthalene can
occur as the 1- or 2-, the alpha or the beta isomer.
1-Naphthalene, a flammable solid, has also been identified
in the wastewater of coking operations, and in textile
processing plants. Methylnaphthalene is used as a component
in slow-release insecticides and in mole repellents.
Workplace exposures to 18–32 mg/m3 for 2-methylnaphthalene
have been reported.
Definition
ChEBI: A methylnaphthalene carrying a methyl substituent at position 2.
General Description
White crystalline solid.
Air & Water Reactions
Insoluble in water.
Reactivity Profile
2-Methylnaphthalene is incompatible with strong oxidizing agents. 2-Methylnaphthalene is also incompatible with peroxides and oxygen.
Hazard
Lower respiratory tract irritant and lungdamage. Questionable carcinogen.
Fire Hazard
2-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.
Source
Detected in distilled water-soluble fractions of No. 2 fuel oil (0.42 mg/L), jet fuel A (0.17
mg/L), diesel fuel (0.27 mg/L), military jet fuel JP-4 (0.07 mg/L) (Potter, 1996), new motor oil
(0.42 to 0.66 μg/L), and used motor oil (46 to 54 μg/L) (Chen et al., 1994). Present in diesel fuel
and corresponding aqueous phase (distilled water) at concentrations of 3.5 to 9.0 g/L and 180 to
340 μg/L, respectively (Lee et al., 1992). Schauer et al. (1999) reported 2-methylnaphthalene in
diesel fuel at a concentration of 980 μg/g and in a diesel-powered medium-duty truck exhaust at
an emission rate of 511 μg/km.
Thomas and Delfino (1991) equilibrated contaminant-free groundwater collected from
Gainesville, FL with individual fractions of three individual petroleum products at 24–25 °C for
24 h. The aqueous phase was analyzed for organic compounds via U.S. EPA approved test method
625. Average 2-methylnaphthalene concentrations reported in water-soluble fractions of unleaded
gasoline, kerosene, and diesel fuel were 256, 354, and 267 μg/L, respectively.
California Phase II reformulated gasoline contained 2-methylnaphthalene at a concentration of
1.33 g/kg. Gas-phase tailpipe emission rates from gasoline-powered automobiles with and without
catalytic converters were approximately 1.00 and 50.0 mg/km, respectively (Schauer et al., 2002).
Based on laboratory analysis of 7 coal tar samples, 2-methylnaphthalene concentrations ranged
from 680 to 42,000 ppm (EPRI, 1990). Detected in 1-yr aged coal tar film and bulk coal tar at
concentrations of 25,000 and 26,000 mg/kg, respectively (Nelson et al., 1996). A high-temperature
coal tar contained 2-methylnaphthalene at an average concentration of 1.23 wt % (McNeil, 1983).
Lee et al. (1992a) equilibrated eight coal tars with distilled water at 25 °C. The maximum
concentration of 2-methylnaphthalene observed in the aqueous phase is 1.4 mg/L.
Detected in wood-preserving creosotes at a concentration of 3.0 wt % (Nestler, 1974).
Typical concentration of 2-methylnaphthalene in a heavy pyrolysis oil is 7.4 wt % (Chevron
Phillips, May 2003).
An impurity identified in commercially available acenaphthene (Marciniak, 2002).
Schauer et al. (2001) measured organic compound emission rates for volatile organic
compounds, gas-phase semi-volatile organic compounds, and particle-phase organic compounds
from the residential (fireplace) combustion of pine, oak, and eucalyptus. The gas-phase emission
rates of 2-methylnaphthalene were 15.0 mg/kg of pine burned, 9.61 mg/kg of oak burned, and 5.69
mg/kg of eucalyptus burned.
Environmental Fate
Biological. 2-Naphthoic acid was reported as the biooxidation product of 2-methylnaphthalene
by Nocardia sp. in soil using n-hexadecane as the substrate (Keck et al., 1989). Dutta et al. (1998)
investigated the degradation of 2-methylnaphthalene using a bacterial strain of Sphingomonas
paucimobilis grown on phenanthrene. Degradation products identified using GC-MS were 4-
methylsalicylate, 2-methylnaphthoate, and 1-hydroxy-2-methylnaphthoate.
Estimated half-lives of 2-methylnaphthalene (0.6 μg/L) from an experimental marine mesocosm
during the spring (8–16 °C), summer (20–22 °C), and winter (3–7 °C) were 11, 1.0, and 13
d, respectively (Wakeham et al., 1983).
Photolytic. Fukuda et al. (1988) studied the photodegradation of 2-methylnaphthalene and other
alkylated naphthalenes in distilled water and artificial seawater using a high-pressure mercury
lamp. Based upon an experimentally rate constant of 0.042/h, the photolytic half-life of 2-
methylnaphthalene in water is 16.4 h.
Phousongphouang and Arey (2002) investigated gas-phase reaction of naphthalene with OH
radicals in a 7-L Teflon chamber at 25 °C and 740 mmHg containing 5% humidity. The rate
constant for this reaction was 4.86 x 10
-11 cm
3/molecule?sec.
Chemical/Physical. An aqueous solution containing chlorine dioxide in the dark for 3.5 d at
room temperature oxidized 2-methylnaphthalene into the following: 1-chloro-2-methylnaphthalene,
3-chloro-2-methylnaphthalene, 1,3-dichloro-2-methylnaphthalene, 3-hydroxymethylnaphthalene,
2-naphthaldehyde, 2-naphthoic acid, and 2-methyl-1,4-naphthoquinone (Taymaz et al.,
1979).
Purification Methods
Fractionally crystallise repeatedly from its melt, then fractionally distil under reduced pressure. It has been crystallised from *benzene and dried under vacuum in an Abderhalden pistol. It can be purified via its picrate (m 114-115o) or better via the 1,3,5-trinitrobenzene complex as for 1-methylnaphthalene (above). [Beilstein 5 IV 1693.]
