Identification of an Aldehyde or Ketone Raymond Oldham, Michael Lester, Audrey Paulzak CH-238 QZ
Introduction: When determining if there is an aldehyde or ketone functional group, chemical test are the easiest way to detect them. A reaction with 2,4-dinitrophenylhydraznie to form a cooled solid product is a strong indication of a ketone or aldehyde. Because aldehydes are easily oxidized, Tollen’s , Fehling’s or Benedict’s solution will give positive tests for aldehydes but not ketones. Once the function group has been determined, solid derivatives are produced to identify the compound by examing the melting point. Melting points can not identify a single compound alone, but the chances of two compounds having derivatives with the same melting point is very small. Mechanism: Iodoform Test R O H + O H-R CH 2-CH 2 + I I x3 R O I R O I I I + O H-R CH 3 O + C-I I I I I I H Semicarbazone R 1 O R + N H 2 R 2 O-R R 1 NH 2 + R 2 R NH R 1 O H 2 + R 2 R N + R 1 R 2 H + O H 2 R N R 1 R 2
Table of Reagents: Amt. Used Molecular Wt. (g/mol) MP °C Density (g/mL) NaOH 3.5 mL 39.9971 318 2.1 AgNO 3 1 mL 169.87 212 NH 4 OH 2 M 35.0456 CH 3 OH 32.04-97 0.791 Iodine 0.5 g 126.904 113.7 Potassium iodide 1 g 166 681 2,4-Dinitrophenyhydrazine 2 g 1.84 H 2 SO 4 10 mL 98.087 10 0.799 C 2 H 4 OH 2 mL 46-116.3 Hydroxylamine hydrochloride 0.5 g 33.02 33 Semicarbazide hydrocholoride 0.2 g 75.08 Safety Information: 1) 2,4-Dinitrophenylhydrazine, semicarbazide and hydroxylamine are toxic. Silver nitrate can stain your skin and clothing blak. Sulfiric acid is corrosive. Sodium hydroxide is caustic. Wear gloves and avoid contact with your skin or clothing when using any of these reagents or the 2,4-Dinitrophenylhydrazine derivatives, and wash spills with water. 2) Petroleum ether is flammable.
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