2- Bromomethyl-3-methylnaphthalene

Dissolve 71 g. of P-methylnaphthalene in 460 g. (283 ml.) of A.B. carbon tetrachloride and place the solution in a 1 -litre three-necked flask equipped with a mechanical stirrer and reflux condenser. Introduce 89 g. of JV-bromosuccinimide through the third neck, close the latter with a stopper, and reflux the mixture with stirring for 16 hours. Filter ofiT the succinimide and remove the solvent under reduced pressure on a water bath. Dissolve the residual brown oil (largely 2-bromomethyl naphthalene) in 300 ml. of A.R. chloroform, and add it to a rapidly stirred solution of 84 g. of hexamine in 150 ml. of A.R. chloroform contained in a 2-litre three-necked flask, fitted with a reflux condenser, mechanical stirrer and dropping funnel maintain the rate of addition so that the mixture refluxes vigorously. A white solid separates almost immediately. Heat the mixture to reflux for 30 minutes, cool and filter. Wash the crystalline hexaminium bromide with two 100 ml. portions of light petroleum, b.p. 40-60°, and dry the yield of solid, m.p. 175-176°, is 147 g. Reflux the hexaminium salt for 2 hours with 760 ml. of 60 per cent, acetic acid, add 160 ml. of concentrated hydrochloric acid, continue the refluxing for 5 minutes more, and cool. Extract the aldehyde from the solution with ether, evaporate the ether, and recrystallise the residue from hot -hexane. The yield of p-naphthaldehyde, m.p. 69-60°, is 60 g. 

A typical procedure is that described in Expt 6.119 for the synthesis of 1-naphthaldehyde. The synthesis of p-nitrobenzaldehyde provides an example in which the intermediate crystalline hexamine salt is isolated prior to hydrolysis. 2-Naphthaldehyde is prepared from the bromomethyl compound, the preparation of which illustrates the use of Af-bromosuccinimide for effecting benzylic bromination of 2-methylnaphthalene. 

For example, benzyl bromide is thus obtained from toluene,361,385 and the corresponding bromomethyl compounds from 1- and 2-methylnaphthalene 387,388 numerous other examples are given by Homer and Winkelmann.354... 

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