Experiment 1- Synthesis of Co (acac)3
Date of experiment performed: 03 August 2011
Date of hand in: 10 August 2011
To prepare cobalt (III) acetylacetonate in the laboratory using cobalt (II) carbonate and acetylacetone at room temperature and pressure. Introduction
The anion acetylacetone (acac) used in this practical functions as a ligand which forms a complex with the cobalt metal cation in an octahedral array where there is electrostatic bonds between the cobalt metal and both the oxygen’s of the acetylacetone to form a six membered ring1.
Figure1: The 3-D molecular structure of cobalt (III) acetylacetonate 2 Figure2(a): Water formed as a by-product2 Figure2(b): Carbon dioxide formed as a by-product2
The hydrogen peroxide used in this practical as an oxidizing agent to produce the cobalt (III) acetylacetonate from cobalt (II) carbonate and a stoichiometrically calculated amount of acetylacetone3. 2CoCO3 + 6CH 3COCH 2COCH3 + H2O2 2Co(CH3COCHCOCH3 ) + 2CO2 + 4H2O 4 (1)
Equation (1) shows stoichiometrically the reaction that occurs between the reagents. The transition of Co2+ to Co3+ is apparent by the colour change of the new complex formed which is a shiny greenish black colour from a dull brown colour.
A slurry of cobalt (II) carbonate and acetylacetone was made using (2.53g, 0.021 mole) of cobalt (II) carbonate and approximately (20ml, 0.2mole) of acetylacetone, these were added to an 100ml Erlenmeyer flask and were stirred with a glass stirring rod to produce the slurry. The mixture was then heated to 100°C on a hot plate the temperature was measured using a thermometer placed directly into the slurry. The mixture was removed from the heat and hydrogen peroxide was added directly to the mixture at a rate of 2ml/min ensuring that the solution did not bubble over from the hydrogen peroxide being added in too...