P-Naphthaldehyde

In a 2-1. three-necked round-bottomed flask, provided with a mechanical stirrer, a reflux condenser carrying a drying tube, and an inlet tube reaching nearly to the bottom of the flask, are placed 76 g. (0.4 mole) of anhydrous stannous chloride (Note 1) and 400 cc. of anhydrous ether. The mixture is then saturated with dry hydrogen chloride, while it is slowly stirred this requires two and one-half to three hours, during which time the stannous chloride forms a viscous lower layer. 

The inlet tube is replaced by a dropping funnel, and a solution of 30.6 g. (0.2 mole) of /3-naphthonitrile, m.p. 60-62° (Note 2), in 200 cc. of dry ether is added rapidly Hydrogen chloride is again passed into the mixture until it is saturated, and the mixture is then stirred rapidly for one hour and allowed to stand overnight while the yellow aldimine-stannichloride separates completely. 

The ethereal solution is decanted, and the solid is rinsed with two 100-cc. portions of ether. The solid is transferred to a 5-1. flask fitted for steam distillation and immersed in an oil bath, the temperature of which is maintained at 110-120° (Note 3). Dry 

The white solid is filtered and allowed to dry in the air it amounts tc 23-25 g. (73-80 per cent of the theoretical amount) and melts at 53-54°. For further purification, it is distilled under reduced pressure (Note 5) the water-clear distillate (b.p. 156— 158°/15 mm.) is poured into a mortar while hot and is.pulverized when cool. The recovery is 93-95 per cent, and the melting point is 57-58°. 

The success of this type of reaction depends on the quality of the catalyst. The most active and dependable form of anhydrous stannous chloride 1 is prepared as follows In a 600-cc. beaker is placed 204 g. (189 cc., 2 moles) of acetic anhydride (99-100 per cent) and, while the liquid is stirred by hand, 226 g. (1 mole) of commercial c.p. crystalline stannous chloride dihydrate is added. This operation should be performed in a hood, for the heat of the reaction is sufficient to cause the acetic anhydride to boil. After about one and a half hours, the anhydrous stannous chloride is filtered on a large Buchner funnel, rinsed with two 50-cc. portions of dry ether, and dried overnight in a vacuum desiccator. The yield is quantitative (189 g.). The product may be kept in a tightly closed bottle until it is wanted. The product secured by dehydrating crystalline stannous chloride in an oil bath at 195-200° is satisfactory in many instances but is not dependable. 

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Decant the ethereal solution from the yellow aldimine stannichloride which has separated, rinse the solid with two 50 ml. portions of ether, and transfer the solid to a 2-5 litre flask fitted for steam distillation and immersed in an oil bath at 110-120°. Pass steam through a trap (compare Fig. 11,40, 1,6) to remove condensed water, then through a superheater heated to 260° (Fig. I, 7, 2), and finally into the mixture (2). Continue the passage of y steam until the aldehyde is completely removed (4-5 litres 8-10 hours). Filter the white soUd at the pump, and dry in the air. The resulting p-naphthaldehyde, m.p. 53-54°, weighs 12 g. It may be further purified by distillation under diminished pressure (Fig. II, 19, ) -, pour the colourless distillate, b.p. 156-158°/15 mm., while hot into a mortar and powder it when cold. The m.p. is 57- 58°, and the recovery is over 90 per cent. 

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. 

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. 

Griesbeck, A. G., Mauder, H., Peters, K., Peters, E.-M., and von Schnering, H. G., Photocycloadditions with a- and P-naphthaldehyde complete inversion of diastereoselectivity as a consequence of differently configurated electronic states, Chem. Ber., 124,407,1991. 

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