Sulfanuric acid

As Hantzsch and Stuer (62) suggested, trimeric sulfimide (LXXVa) should have an isomer (LXXVb), to which the name sulfanuric acid has been given. However, this acid, like sulfimide, cannot be isolated as the hydrogen compound itself, though the acid chloride (LXXVI) is readily accessible. It can be made by the reaction of amidosulfonic acid with PCI5 and thermal decomposition of the product (73, 74)-... 

Sulfanuric acid (LXXVb) should be the first product of the hydrolysis of sulfanuryl chloride (LXXVI), but this substance is clearly very unstable. Even on careful acid hydrolysis, imidosulfamide (LXXVIII) and sulfuric acid are formed immediately. 

It is striking that compound (LXXVa) is clearly much more stable than the isomer (LXXVb) and that hydrolysis leads to different products. Whereas sulfimide in an acid medium gives sulfuryl amide, amidosulfonic acid and sulfuric acid, the hydrolysis of sulfanuric acid leads to imidosulfamide (86). 

Sulfanuric chloride may also be obtained as a mixture of a and P isomers in a two-stage reaction from sulfamic acid or, preferably, sulfamoyl chloride. The P isomer is stable in the solid state or in nonpolar solvents but changes to the a isomer in ca. 1 h in acetonitrile ... 

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