| Abstract
| - Ninhydrin (the fingerprint developing agent) spontaneously dehydrates in liquid ammonia and inhexamethylphosphoramide (HMPA) to form indantrione, which has a sufficiently large solutionelectron affinity to extract an electron from the solvent (HMPA) to produce the indantrione anionradical. In liquid NH3, the presence of trace amounts of amide ion causes the spontaneous formationof an anion radical condensation product, wherein the no. 2 carbon (originally a carbonyl carbon)becomes substituted with −NH2 and −OH groups. In HMPA, the indantrione anion radicalspontaneously forms condensation products with the HMPA to produce a variety of zwitterionicradicals, wherein the no. 2 carbon becomes directly attached to a nitrogen of the HMPA. Themechanisms for the formation of the zwitterionic paramagnetic condensation products are analogousto that observed in the reaction of ninhydrin with amino acids to yield Ruhemann's Purple, thecontrast product in fingerprint development. The formation of anion and zwitterionic radicalcondensation products from ninhydrin and nitrogen-containing solvents may represent an exampleof a host of analogous polyketone−solvent reactions.
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