Methylnaphthalenes

Both methylnaphthalene isomers are present in coal tar, at levels of 0.7% (1-methylnaphthalene) and 1.5% (2-methylnaphthalene). 

Methylnaphthalenes are also found in petroleum-derived feedstocks, such as pyrolysis tar from ethylene production and cat-cracker residues (see Chapter 9.2.2). The l-/2-methylnaphthalene isomer ratio, which is around 1 2.5 for methyl-naphthalenes in coal tar, is higher in this case, because of the lower temperature exposition of the raw material, and is close to 1 1. Recovery of methylnaphthalenes from these sources is generally only carried out on a small scale, since it can be extremely intricate to separate co-boiling compounds petroleum-derived methylnaphthalenes has served as a feedstock for naphthalene production by dealkylation, especially in the USA in the 1960 s and 70 s. 

Worldwide production of 2-methylnaphthalene is around 1,500 tpa. In addition, l-/2-methylnaphthalene mixtures are used in roughly the same amount as solvents and heat transfer oils. 

Applications for 1-methylnaphthalene are relatively sparse it is primarily used as a feedstock for production of 1-naphthylacetic acid (NAA), one of the first plant growth regulators produced in 1936 by ICI, which is obtained by side-chain chlorination, followed by reaction of the naphthyl chloride with potassium cyanide and subsequent hydrolysis. 

2-Methylnaphthalene is commonly used as a feedstock in the production of vitamia K3 (menadione). Methylnaphthalene is oxidized to menadione with chromic or nitric acid, in a similar method to anthracene oxidation. Menadione is used as an intermediate in the production of vitamin Ki.To produce vitamin Ki, menadione is reduced with hydrogen on Pd/activated-carbon catalysts to mena-diol. Esterification of the two hydroxyl groups with acetic anhydride yields mena-diol diacetate, which is converted into the 1-monoacetate with ammonia. Vitamin Ki (phytomenadione) is produced by the reaction of 1-menadiol monoacetate with phytol, using a BF3/ether complex as catalyst, followed by hydrolysis and dehydrogenation. 

---

A diesel fuel has a cetane number X, if it behaves like a binary mixture of X% (by volume) n-cetane and of (100 - A) % a-methylnaphthalene. 

In practice, the reference base is usually taken not as a-methylnaphthalene but as heptamethyinonane (HMN), a branched isomer of n-cetane. The HMN has a cetane number of 15. In a binary system containing Y% of n-cetane, the cetane number CN vyOl be, by definition (./ - V ... 

In a 500 ml. flask, fitted with a reflux condenser, place 53 g. of 1-chloro-methylnaphthalene (Section IV.23), 84 g, of hexamethylenetetramine and 250 ml. of 1 1 acetic acid [CAUTION 1-Chloromethylnaphtha-lene and, to a lesser degree, a-naphthaldehyde have lachrymatory and vesicant properties adequate precautions should therefore be taken to avoid contact with these substances.] Heat the mixture under reflux for 2 hours it becomes homogeneous after about 15 minutes and then an oil commences to separate. Add 100 ml. of concentrated hydrochloric acid and reflux for a further 15 minutes this will hydrolyse any SchifiF s bases which may be formed from amine and aldehyde present and will also convert any amines into the ether-insoluble hydrochlorides. Cool, and extract the mixture with 150 ml. of ether. Wash the ether layer with three 50 ml. portions of water, then cautiously with 50 ml. of 10 per cent, sodium carbonate solution, followed by 50 ml. of water. Dry the ethereal solution with anhydrous magnesium sulphate, remove the ether by distillation on a steam bath, and distil the residue under reduced pressure. Collect the a-naphthaldehyde at 160-162718 mm. the yield is 38 g. 

P-Naphthaldehyde. This preparation illustrates the use of -bromo-succinimide (Section VI.26) in the conversion of the readily available P-methylnaphthalene into 2-bromomethylnaphthalene and of the latter into p-naphthaldehyde by the Sommelet reaction. 

Under the conditions mentioned, i-methylnaphthalene was nitrated appreciably faster than was mesitylene, and the nitration was strongly catalysed by nitrous acid. The mere fact of reaction at a rate greater than the encounter rate demonstrates the incursion of a new mechanism of nitration, and its characteristics identify it as nitration via nitrosation. 

Polynuclear Aromatics. The alkylation of polynuclear aromatics with olefins and olefin-producing reagents is effected by acid catalysts. The alkylated products are more compHcated than are those produced by the alkylation of benzene because polynuclear aromatics have more than one position for substitution. For instance, the alkylation of naphthalene [91-20-3] with methanol over mordenite and Y-type zeoHtes at 400—450°C produces 1-methylnaphthalene [90-12-0] and 2-methylnaphthalene at a 2-/1- ratio of about 1.8. The selectivity to 2-methylnaphthalene [91-57-6] is increased by applying a ZSM-5 catalyst to give a 2-/1- ratio of about 8 (102). 

---