Die chemie des ninhydrins und anderer cyclischer 1,2,3-tricarbonylverbindungen

Pseudo-oxocarbons. Synthesis of 2,1,3-bis-, and 1,2,3-tris (dicyanomethylene) croconate salts. New bond-delocalized dianions, croconate violet and croconate blue

“…NC -CH2 -COOC2 Hs), and found that they all react at the more polarized, central carbonyl group to give aldols in good yield. The authors [18] also confirmed the report [19] that the uncatalyzed reaction of malononitrile with indanetrione in benzene yields an aldol product, e.g., 2-(dicyanomethylene)-1,3-indandione. As ob served in this laboratory 74 [20], direct fusion of ninhydrin with an excess of malononitrile (1-2 min at 100-110 0c), followed by methanol treatment of the cold reaction mixture, produced 2-(dicyanomethylene)-1,3-indandione in over 85 percent yield.…”

“…In acyclic polycarbonyl compounds, the reactivity is due to the destabilization of polyketones, as a result of flexibility of the adjacent dipolar carbonyl groups. Cyclic triketones, however, in which the unfavorable dipolar interaction between adjacent carbonyl groups is maximal and the carbonyl groups are eclipsed (S-cis-conformation) are more reactive in regard to the formation of hydrates, aldols, half-acetals, and other addition compounds, as compared to the openchain triones [S-trans (staggered) conformation] [16][17][18]. Schonberg and Singer [18] studied the uncatalyzed reaction of a variety of cyclic triketones, e.g., 1,2,3,-indantrione and ninhydrin (1,2,3-indantrione monohydrate) with enolizable ~-diketones and other active methylene compounds (e.g.…”

Intramolecular Reversible Addition Reactions to the C=O Group

“…The condensation of ninhydrin with 2-amino-phenol and -thiophenol gives the ring structure (124, X = 0, S) as shown by [425,426] means of IR, IH-NMR, and 13C-NMR spectroscopy, thus correcting incorrect structure assignments [427]. The introduction of substituents R 1 and R4 into molecules of ninhydrin condensation products with polyphenols shifts the equilibrium (125A) ~ (125B) in favor of the cyclic isomer [428].…”

Changes During Cheese Curing

“…The extent of cheese proteolysis has been related to the ammonium content, which can be measured by different methods. These include ninhydrin (Schonberg and Singer 1978), trinitrobenzenesulfonic acid (TNBS) (Clegg et al 1982), Nessler's reagent (Mrowetz 1979), Carrez reagent (Behringer and Klostermeyer 1981), or by direct titration with HC1 (Clegg etal. 1982).…”