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Properties of substance:

ninhydrin



skc-file

Synonyms:

2,2-dihydroxy-1,3-indanedione

Group of substances:

organic

Physical appearance:

prismatic crystals

Empirical formula (Hill's system for organic substances):

C9H6O4

Molar/atomic mass: 178.14

Boiling point (°C):

242

Solubility (g/100 g of solvent):

diethyl ether: sparingly soluble [Ref.]
ethanol: sparingly soluble [Ref.]
water: very soluble [Ref.]

Synthesis 1:

Reference: Heffner, R. J., & Joullie, M. M. Synthetic Routes to Ninhydrins. Preparation of Ninhydrin, 5-Methoxyninhydrin, and 5-(Methylthio)Ninhydrin / Synthetic Communications. - 1991. - Vol. 21, No. 21 pp. 2254 [doi: 10.1080/00397919108055457]

To a solution of 3-bromo-1-indenone (0.50 g, 2.8 mmol) in benzene (10 mL) was added dimethylsulfoxide (10 mL), followed by the addition of bromine (0.23 g, 1.4 mmol). The solution was heated at reflux, and after six hours was cooled to 25 °C. The reaction was then diluted with water (20 mL). The aqueous phase was then extracted with ethyl acetate (4 x 10 mL) and organic extracts were combined, washed with water (5 mL), dried over Na2SO4, filtered, and concentrated under reduced pressure to yield a solid. This material was recrystallized from water to provide ninhydrin (0.25 g, 60% yield): mp 240 °C, lit. mp 241 °C.

Rf 0.61 methylene chloride : methanol (90 : 10).

IR (KBr): 3530-2900 (broad), 1745 (strong), 1750 (strong), 1715 (strong), 1590 (medium), 1385 (medium), 1290 (weak), 1255 (weak), 1185 (strong), 1150 (medium), 1080 (medium), 1060 (medium), 1010 (medium), 1000 (medium), 940 (strong), 880 (weak), 740 (strong) cm-1.

1H NMR (DMSO-d6): δ 7.58 (2H, s), 8.04-8.10 (4H, m); 1H NMR (DMSO-d6, D2O): 8.04-8.12 (4H, m).

Dissociation:

pKa (1) = 8.6 (25°C, water)

References:

  1. CRC Handbook of Chemistry and Physics. - 95ed. - CRC Press, 2014. - pp. 3-320
  2. Dictionary of organic compounds. - Vol. 3, naphthacarbazole - zygadenine. - М.: ИИЛ, 1949. - pp. 947
  3. Рабинович В.А., Хавин З.Я. Краткий химический справочник. - Л.: Химия, 1977. - pp. 165 [Russian]
  4. Химический энциклопедический словарь. - Под ред. Кнунянц И.Л. - М.: Советская энциклопедия, 1983. - pp. 379 [Russian]

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    © Collected Ruslan Anatolievich Kiper, burewestnik@mail.ru