SINTESIS DE MAGNESON, Apuntes de Química Orgánica

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Sintesis Magneson II

Sintesis Magneson Il Experiment 6.83 4(4-NITROBENZENEAZO)-1-NAPHTHOL (Mag- neson 11) eS O,N NJ + ES oH4—— 57 ON) anos > OH PRAGTICAL ORGANIC CHEMISTRY Dissolve 5.0 g (0.036 mol) of p-nitroaniline (Expt 6.68) in a warm mixture of 13 ml of concentrated hydrochloric acid and 13 ml of water contained in a 250-ml beaker, Place the beaker in an ice-salt bath and cool to 0-5"C whilst stirring vigorously; p-nitroaniline hydrochloride will separate in a finely divided crystalline form. Add a cold solution of 3.7 g (0.054 mol) of sodium nitrite in 8ml of water slowly and with stirring to an end-point with potassium iodide-starch paper: do not allow the temperature of the solution to rise above 8 *C. Dissolve 5.2 g (0.035 mol) of 1-naphthol in a solution of 7 g of sodium hydroxide in 25ml of water, cool in ice and add the diazotised solution slowly and with stirring. Then add concentrated hydrochloric acid slowly and with vigorous stirring to the cold mixture until it is strongly acid to Congo red paper, The colour will change from violet to dark red-brown. Filter with gentle suction, wash with water until free from acid and dry upon filter-paper in the air. The yield is 8 g (74%). 2,4-Dihydroxy-4'-nitroazobenzene ('Magneson 1”) may be similarly pre- pared by substituting resorcinol for 1-naphthol; it may be recrystallised from methanol and melts at 199-200”C.