Carbonyl Synthesis Lab Report

Identify an unknown carbonyl compound
© KCl http://hk.geocities.com/fatherofchemistry
Objective
To classify a carbonyl compound by a simple test and to identify it by the precipitation of a derivative.
Principle
In this experiment, the unknown compound is either an aldehyde or a ketone from Table 90. In the first part, on undergoing Tollen's & Fehling's tests, ketone will have no reaction. In the second part, by preparing a derivative of the compound with 2,4-dinitrophenylhydrazine, the sharp melting point can be used to identify the unknown carbonyl compound. Carbonyl compound can form a precipitate with 2,4-dinitrophenylhydrazine with high melting point: [pic]
[pic]
[pic]
Reason:
|1.> It forms a silver mirror with Tollen's reagent: |
| CH3CHO + 2Ag(NH3)2OH → RCOO-NH4+ + 2Ag(s)↓ + H2O + 3NH3 |
| |
|2.> It turns deep blue Fehling's solution to green:
[ANS] The solvent must not react with the solid. The solubility of the solid in the solvent should be high at high temperature & low at room temperature. If possible, the impurities should be insoluble in the solvent.

2.> How were soluble impurities removed from the derivative?
[ANS] By soaking the impure derivative in 1 cm3 of methanol and resume suction. Repeat this for about 2 times.

3.> In the recrystallization procedure, why were the crystals dissolved in only the minimum amount of