MANUFACTURING PROCESS OF 1-METHYLNAPHTHALENE

1-Hydroxy-1-methyl-1,2,3,4-tetrahydronaphthalene. 

• Prepare an ethereal solution of ethylmagnesium iodide from 1.8g (0.075 mol) of magnesium, 10.6g (4.7 ml, 0.075 mol) of methyl iodide and 30 ml of ether in a 100-ml two-necked flask fitted with a dropping funnel and a reflux condenser protected by a calcium chloride guard-tube. 

• Slowly add a solution of 7.3g (0.05 mol) of a-tetralone in 10 ml of ether, swirling the contents of the flask from time to time, and finally heat under reflux on a steam bath for 1 hour to complete the reaction. 

• Cool in ice, and decompose the reaction mixture with a cold saturated aqueous solution of ammonium chloride. 

• Separate the ether layer, and extract the aqueous phase with 10 ml of ether. 

• Wash the combined ethereal solutions with aqueous ammonium chloride solution, dry over anhydrous sodium sulphate and evaporate off the ether. 

• A solid residue of 1 -hydroxy-1-methyl-1,2,3,4-tetrahydronaphthalene of sufficient purity for use in the next stage is obtained; the yield is 7.5g (92%), m.p. 77-79 °C. 

• Recrystallise a sample from light petroleum (b.p. 60-80 °C); the purified material has m.p. 86-87 °C.

 

Figure 1

1-Methylnaphthalene:

• This preparation illustrates the general procedure for catalytic dehydrogenation.

•  The apparatus used is shown in Figure 1.

• Heat a mixture of 3.2g (0.02 mol) of the above hydroaromatic compound with 0.3g of palladised charcoal at 250-270 °C in a slow current of dry carbon dioxide in a Silicone oil or fusible metal bath for 3 hours (1). 

• Cool, dissolve the residue in ether and filter off the catalyst. 

• Wash the extract with dilute aqueous sodium hydroxide and dry it over anhydrous sodium sulphate. 

• Remove the ether and distil the residual oil under reduced pressure; use a small-scale distillation apparatus. 

• Collect the 1-methylnaphthalene, b.p. 121-123 °C/20 mmHg. The yield is 2.5g (89%).

Notes to Keep in Mind:

1. If it is desired to follow the progress of the dehydrogenation, attach the side-tube through a U-tube packed with self-indicating soda-lime to a nitrometer filled with potassium hydroxide solution: almost the theoretical quantity of hydrogen will be collected.