Sulphobenzoic anhydride

Hydrolysis of saccharin (o-sulphobenzoic imide) (Section IV, 209) with dilute hydrochloric acid yields acid ammonium 0 sulphobenzoate, w hich upon 

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By condensing o sulphobenzoic anhydride with phenol in the presence of anhydrous zinc chloride, phenolsulphonephthalein (phenol red) is formed. Tetrabromination of the latter afibrds tetrabromophenolsulphonephthalein (bromophenol blue) ... 

Similarly o-sulphobenzoic anhydride and o-cresol yields o-oresolsulphone-phthalein (o-cresol red) dibromination of the last-named gives dibromo-o-sulphonephthalein (bromocresol purple) ... 

The mass spectrum of o-sulphobenzoic anhydride furnishes evidence for three competing decomposition paths (Scheme (38) on page 51). 

To test this prediction, a solution of o-sulphobenzoic anhydride (0-02 mole) in benzene (0-4 mole) was pyrolyzed at 690°, with a contact time of 18 sec. The pyrolysate, after removal of benzene, weighed 2 2 g. The product mixture, determined by mass spectrometry, is shown in Table 14 together with the products from identical pyrolyses of benzene (35-5 ml) alone (0-3 g product) and of phthalic anhydride (2 96 g 002 mole) in benzene (35-5 ml) (2-6 g product) for comparison. Relative concentrations (vol. %) of the three components for which we have the requisite calibration data (naphthalene biphenyl 3,4-benzocoumarin = 71 100 21) match closely the relative intensities shown in Table 14,... 

The data strongly suggest the formation of benzyne from o-sulphobenzoic anhydride—from the products of its reaction with benzene by 1,2- and 1,4-addition (naphthalene, phenylnaphthalene) and insertion (biphenyl, about four times as much by weight as from benzene alone). The uncondensed gases from the reaction were a 1 1 mixture of sulphur dioxide and carbon dioxide. This, in addition to the other products, indicates that the first step of Path 2, loss of sulphur dioxide, is the dominant primary process. However, the resulting zwitterion, unlike its cationic counterpart in the mass spectrometer, does not go on to lose carbon monoxide it stabilizes itself more easily by losing carbon dioxide... 

Benzene Phthalic o-anhydride in benzene Relative intensities8 Sulphobenzoic anhydride in benzene, b... 

Products from o-Sulphobenzoic Anhydride and Phthalic Anhydride with Pyridine... 

In Path II of the mass spectral scheme for the decomposition of o-sulphobenzoic anhydride, successive loss of S02 and CO from the parent ion gives an ion of mass 92, which may be represented as 31. 

Additional evidence that the thermal decomposition of o-sulphobenzoic anhydride parallels the mass spectral paths is furnished by the formation of phenol in its reactions with benzene and pyridine (at relative concentrations of 4 and 2 on the scales of Tables 14 and 15, respectively). Further, the reaction with benzene gives dibenzofuran and that with pyridine a compound of molecular weight 169, almost certainly a pyridine-derived analog of dibenzofuran, in relative concentrations of 12 and 2, respectively. 

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