Musk xylene is a synthetic musk fragrance which mimics natural musk. It has been used as a perfume fixative in a wide variety of consumer products, and is still used in some cosmetics and fragrances. Musk xylene was once the most widely used of the "nitro-musks", but its use has declined sharply since the mid-1980s due to safety and environmental concerns. Its explosive and carcinogenic hazards are recognized to be borderline, and musk xylene is a useful example of the lowest level of such risks which need to be taken into account. However, it is a very persistent and very bioaccumulative pollutant in the aquatic environment (vPvB substance), and is the first substance to be proposed as a "substance of very high concern" (SVHC) for these reasons alone under the European Union REACH Regulation. Since no company has applied for authorisation, it is banned in the EU.
Synonyms Musk xylene is also known in english as musk xylol, 1-tert-butyl-3,5-dimethyl-2,4,6-trinitrobenzene, tert-butyl-trinitro-xylene, 5-tert-butyl-2,4,6-trinitroxylene, 1-(1,1-dimethylethyl)-3,5-dimethyl-2,4,6-trinitrobenzene, 2,4,6-trinitro-1,3-dimethyl-5-tert-butylbenzene, 2,4,6-trinitro-3,5-dimethyl-tert-butylbenzene, 5-tert-butyl-2,4,6-trinitro-m-xylene, 5-tert-butyl-2,4,6-trinitro-meta-xylene and xylene musk.
Production and use Musk xylene is produced from meta-xylene (1,3-dimethylbenzene), by a Friedel–Crafts alkylation with tert-butyl chloride and aluminium chloride followed by nitration with fuming nitric acid or with a 70:30 mixture of nitric acid and sulfuric acid. The crude product is recrystallized from 95% ethanol.
Musk xylene has been used in a wide variety of consumer products since the early 1900s, usually in very small quantities. World production of nitro musks in 1987 was about 2500 tonnes, but had fallen to about 1000 tonnes by the early 1990s: musk xylene made up roughly two-thirds of the production of nitro musks during this period. Production was concentrated in Western Europe, with the United Kingdom alone accounting for 28% of world production of nitro musks. Use of musk xylene continued to decline through the 1990s, as fragrance manufacturers voluntarily switched to alternative fragrance compounds. For example, musk xylene has not been used in Japanese products (on a voluntary basis) since 1982, and the Association of the German Toiletries and Detergents Industry (IKW) recommended the replacement of musk xylene by another compound in 1993. Production of musk xylene in the European Union came to a halt and, by 2000 (the last year for which full data are available), imports to Europe were only 67 tonnes, with China as the most important source. The estimated 2008 usage of musk xylene in the European Union was 25 tonnes. Musk xylene permitted until 2011 for use in cosmetics products (except oral care products) in the European Union under the Cosmetics Directive. The permitted quantities are: up to 1% in fine fragrances; up to 0.4% in eau de toilette; up to 0.03% in other products. European Union suppliers must inform their customers on request if a product contains more than 0.1% by weight of musk xylene. In 2011, it is listed as a product to "be banned within the next three to five years unless an authorisation has been granted to individual companies for their use".
Safety Musk xylene is an analogue of the explosive trinitrotoluene (TNT), so it is unsurprising that its safety characteristics have been studied in some detail. Indeed, the nitro musks were first discovered in an attempt to produce new high explosives. It has also been used – albeit in very small amounts – in mass-market consumer products for the last hundred years. The discovery of musk xylene residues in the environment prompted new concerns about its possible long-term toxicity, and led to the sharp decline in its use from the mid to late 1980s. The European Chemicals Agency has listed musk xylene as a "substance of very high concern" (SVHC) under the REACH Regulation, judging it to be "very persistent and very bioaccumulative" (vPvB) but not meeting the criteria for human or environmental toxicity to be of concern.
Explosive properties Musk xylene is used as an example case in the United Nations Manual of Test Methods and Criteria as a substance which shows some explosive properties but which does not have to be transported as Class 1 dangerous goods under the Model Regulations. It is transported as small flakes in plastic bags (maximum 50 kg net mass), which are themselves within cardboard drums to avoid tearing. This does not count as "confinement" in the meaning of explosives tests: indeed, the special packing is intended to prevent over-confinement during transport. It will explode when detonated under confinement (UN gap test) or when heated under confinement (Koenen test), but does not explode under the BAM fallhammer test (limiting impact energy 25 J) or the BAM friction test (limiting load >360 N). There is no ignition, explosion, self-heating or visible decomposition when musk xylene is heated (without confinement) to 75 °C for 48 hours. Nevertheless, musk xylene is classified in the European Union as an explosive under the Dangerous Substances Directive and as a category 1.1 explosive under the CLP Regulation. The European Union classification reflects the fact that hazardous heating under confinement cannot be excluded in the industrial use of musk xylene, as opposed to its transport, and so it is necessary to warn potential users of the risk.
… excerpt ends here. Continue reading the full article.
