Hydrochloric Acid → Diethyl 5-nitro-2-[2'-hydroxy-6'-sulphonaphthylazo]-phenylphosphonate

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Reaction Steps

27 parts of sodium 1-(2'-bromo-4'-nitrophenylazo)-2-hydroxy-6-naphthylsulphonate are stirred with 130 ml of water, and 20 parts of copper sulphate 5-hydrate in 70 parts of water are added. The pH value is adjusted to 7-8 and the mixture is stirred for one hour. Thereafter, 35 parts of phosphorous acid diethyl ester are added dropwise at pH 8. The mixture is subsequently stirred at room temperature for 4 hours and acidified with hydrochloric acid. The precipitate is filtered off, washed and dried and gives 23 parts of diethyl 5-nitro-2-[2'-hydroxy-6'-sulphonaphthylazo]-phenylphosphonate almost free from starting compounds and by-products.

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