Benzothiadiazole 1,1-Dioxide

2-Nitrobenzenesuljinic acid (Note 1). Caution1 This reaction should be done in a good hood because noxious fumes are released. 

2-Nitroaniline (13.8 g., 0.10 mole) (Note 2) is dissolved in a hot solution of 75 ml. of 96% sulfuric acid, 100 ml. of phosphoric acid (density 1.7), and 50 ml. of water in a 1-1. beaker. A stirrer and a thermometer are introduced into the mixture, and the beaker is immersed in an ice bath. A solution of 8.3 g. (0.12 mole) of sodium nitrite in 25 ml. of water is added dropwise to the well-stirred solution at such a rate that the temperature is maintained at 10-15°. Excess nitrite is destroyed by adding sulfamic acid in small portions (Note 3). The mixture is cooled to —10° in an ice-salt bath, and about 50 ml. of liquid sulfur dioxide 

After 30 minutes the solid sulfinic acid is separated on a fritted-glass filter. The sulfinic acid is dissolved from the filter by a mixture of 750 ml. of ether and 750 ml, of methylene chloride. The solution is dried over calcium chloride and evaporated to dryness under reduced pressure (bath temperature 25°) (Note 5). The residue is suspended in 50 ml. of water, and small portions of dilute ammonia are added to the well-stirred suspension until it has a pH of 9 (Note 6). Insoluble impurities are separated by filtration, and 2-nitrobenzenesulfinic acid is precipitated from the filtrate by adding 5-ml. portions of 6N hydrochloric acid with cooling the sulfinic acid precipitated by each portion of acid is separately collected on a Buchner funnel (Note 7). The acid, a pale yellow solid, is dried on a clay plate in a vacuum desiccator over potassium hydroxide pellets, m.p. 120-125° (dec.), weight 9.4-14.9 g. (50-80%). If the 2-nitrobenzenesulfinic acid is to be used for the hydrogenation of the next step high purity is required, and it is generally advisable to reprecipitate the acid once more in the same way (Note 8). 

Sodium 2-aminobenzenesulfinate. 2-Nitrobenzenesulfinic acid (3.74 g., 0.020 mole) is suspended in 10 ml. of water, and sufficient 1AT NaOH (about 20 ml.) is added to the well-stirred mixture to dissolve the acid and bring the pH to 9. Palladium oxide (0.2-1.0 g., Note 9) is suspended in 20 ml. of water in a 200-ml. glass hydrogenation bottle. The bottle is attached to a hydrogenation apparatus such as that of Adams and Voorhees,2 and the suspension is shaken with hydrogen under a pressure of 

2- nitrobenzenesulfinic acid is added, and the mixture is shaken under a hydrogen pressure of 1-3 atm. The solution becomes completely decolorized in 2-6 hours, during which time about 95% of the calculated amount of hydrogen is absorbed. The catalyst is separated by filtration and washed with two 20-ml. portions of water, which are added to the filtrate. The filtrate, 

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C. 1,2,3-Benzothiadiazole 1,1-dioxide. Caution 1,2,3-Benzo-thiadiazole 1,1-dioxide in the solid slate can explode spontaneously, particularly on being warmed, jolted, or scratched. For most purposes it need not be isolated, but can be used in solutions, which are relatively safe. Any operations involving the solid material should be done very carefully, using good shielding. 

Benzothiadiazole 1,1-dioxide slowly decomposes even at 0°, hence it should always be used on the day on which it is made. For most purposes it is not necessary to isolate the dioxide the ether solution can be used, or solutions in other solvents can be prepared by adding the other solvent and distilling off the ether under reduced pressure (bath temperature 0°). In this way larger amounts of the dioxide than are described in this procedure can be handled without danger. 

Benzothiadiazole 1,1-dioxide can be conveniently assayed and characterized without isolation by forming its adduct with cyclopentadiene.5 The following procedure illustrates characterization, for assay the same procedure can be applied to an aliquot, with all amounts scaled down in proportion. The dried ether extract of 1,2,3-benzothiadiazole 1,1-dioxide prepared from 1.43 g (0.0080 mole) of sodium 2-aminobenzene-sulfinate is concentrated to about 20 ml at 0°, and 20 ml. of acetonitrile at —20° is added. Twenty milliliters of cold, freshly prepared cyclopentadiene6 is added The mixture is kept overnight at —10° to 0°. Solvent and excess cyclopentadiene are removed by evaporation at 0° under reduced pressure to leave 1.20-1.28 g. (64-68% based on sodium 2-aminobenzenesulfinate) of crude 1-1 adduct, mp. 87° (dec.). For purification it is dissolved in 20 ml. of methylene chloride, 70 ml. of ether is added, and the solution is kept at —70°. Adduct decomposing at 90° crystallizes recovery is about 75%. From pure, crystalline 1, 2, 3-benzothiadiazole 1,1-dioxide the yield of adduct is 92-98%. 

Purer product can be obtained by reducing 1,2,3-benzothiadiazole 1,1-dioxide with zinc and acetic acid to 1,2,3-benzo-thiadiazoline 1,1-dioxide, which is oxidized back with lead tetraacetate.5... 

Benzothiadiazole 1,1-dioxide has been prepared only by the present method.5... 

Benzothiadiazole 1,1-dioxide decomposes smoothly in solution at 10° to give dehydrobenzene ( benzyne ), nitrogen, and sulfur dioxide.5,7 In this way, as well as by the thermal... 

Addition, acetic acid to bicyclo[2.2.1]-hepta-2,5-diene to give nortri-cyclyl acetate, 46, 74 1,2,3-benzothiadiazole 1,1-dioxide to cyclopentadiene, 47, 8 benzyne to tetraphenylcyclopentadie-none, 46,107 Br, F to 1-heptene, 46,10 carbon tetrachloride to olefins, 46, 106... 

Benzophenone 46, 36 solvent for Diels Alder reactions at elevated temperatures, 46, 44 1,2,3 Benzothiadiazole 1,1 dioxide, 47,4... 

Compounds of special interest whose preparation is described include 1,2,3-benzothiadiazole 1,1-dioxide (a benzyne precursor under exceptionally mild conditions), bis(l,3-diphenylimida-zolidinylidene-2) (whose chemistry is quite remarkable), 6- di-melhylamino)julvene (a useful intermediate for fused-ring non-benzenoid aromatic compounds), dipkenylcyclopropenone (the synthesis of which is a milestone in theoretical organic chemistry), ketene di(2-melhoxyethyl) acetal (the easiest ketene acetal to prepare), 2-methylcyclopenlane-l,3-dione (a useful intermediate in steroid synthesis), and 2-phenyl-5-oxazolone (an important intermediate in amino acid chemistry). 

Cyclopentadiene, adduct formation with 1,2,3-benzothiadiazole 1,1-dioxide, 47, 8... 

Photochemical generation has proved particularly important for the characterization of benzyne by spectroscopic methods (Section I), but it is not much used to study the reactions of benzyne on a preparative scale. Benzyne is generated in an argon matrix at 8 K by photolysis of either 13 or 14.6 Flash photolysis of 4 was employed by Berry et al. to obtain UV and mass spectral evidence of benzyne4,5 and photolysis of 1,2,3-benzothiadiazole 1,1-dioxide (8),15 o-iodophenylmercury derivatives,19 and other compounds in solution also serves to generate benzyne. 

In experiments aimed at the preparation of stable benzyne complexes of platinum of type (51), 1,2,3-benzothiadiazole 1,1-dioxides (52 R=H or Me), which are known to fragment under mild conditions, were used as a potential source of benzyne. However, their interaction with tetrakis-(triphenylphosphine)platinum in benzene did not giye the required benzyne complexes, but resulted in excellent yields of yellow crystalline azocomplexes of structure (53) or possibly (54 R = H or Me). ... 

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