Sandmeyer反应的应用之一就是将芳香化重氮盐转化为芳香磺酸。这是一类很经典的反应。具体操作是将芳胺经重氮盐在二价金属离子催化下（一般是二价铜）用液态二氧化硫处理，就可以得到芳香磺酸。

2-Nitro-phenylamine (13.8 g) are dissolved in conc. H2SO4(75mL), H3PO4 (100 mL) and water (50 mL).  The solution of NaNO2 (8.3 g) in water (25 mL) was slowly addeddropwise under ice-water cooling.  The temperaturewas maintained at 10－15 oC. NH3-SO3H was added in batches to remove the extraformed HNO2.  The reaction wascooled down to -10 oC, liquid SO2 (50 mL) was addeddropwise.  The reaction mixture waspoured into another mixture of FeSO4.7H2O (55.7 g) and Cu (1 g).  Half anhour later, the reaction was filtered, the residue cake was washed with mixtureof ether (750 mL) and CH2Cl2  (750 mL). The combined filtrate and washings were washed with brine, dried andconcentrated.  The residue wasprecipitated in water (50 mL), then diluted ammonia was used to adjust pH equal9 under stirring.  Filtered, the filtratewas acidified with HCl (6 N), the precipitate was collected by filtration and driedto afford desired 2-Nitro-benzenesulfonic acid, (9.4 g, 65% yield.) 

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