Preparation of Acetylferrocene

Experimental Principle

Ferrocene is a sandwich transition metal organic complex. It cannot undergo electrophilic addition reactions like cyclopentadiene, and it is easy to undergo electrophilic substitution reactions such as Friedel-Crafts acylation due to the aromatic properties of cyclopentadiene. Monoacetyl ferrocene or diacetylferrocene can be formed during acylation due to different catalysts and reaction conditions. The structure of diacetylferrocene has been confirmed, and the two acyl groups are not on the same ring. This is due to the inactivation of the acetyl group, which makes it difficult for the second electrophilic group to attack the ring. The structure shows that the crossed conformation of diacetylferrocene is the dominant conformation, but only one kind of diacetylferrocene has been found, indicating that cyclopentadiene can rotate around the axis of reconciliation with metal iron.

The acetylation reaction of ferrocene is as follows:

The reaction process of ferrocene acetylation can be traced by thin layer chromatography, and the separation between the product and the raw material can be carried out by column chromatography.

Reagents and Instruments

1. Reagents

Ferrocene, Acetyl Chloride, Zinc Oxide, Sodium Bicarbonate, Dichloromethane, Ethyl Acetate, Petroleum Ether, Calcium Chloride, Anhydrous Magnesium Sulfate.

2. Instruments

100 mL three-neck flask, drying tube, constant pressure dropping funnel, separatory funnel, magnetic stirrer.

Experimental Procedure

1. Ferrocene 0.93 g (0.005 mol) and zinc oxide 0.49 g (0.006 mol) were put into a 100 mL three-port flask equipped with calcium chloride drying tube, install a reflux condenser, and quickly add 10 mL of dry dichloromethane, turn on magnetic stirring.
2. Cool in an ice-water bath to 0 ^oC.
3. Slowly add 1 mL (0.015 mol) of acetyl chloride dropwise, and complete the addition in about 10 minutes.
4. The ice-water bath was removed, and the reaction was carried out at room temperature.
5. Take a sample every 5 minutes, spot the plate, and observe the reaction of the raw material ferrocene by thin layer chromatography. Once the raw material fades and disappears, stop the reaction immediately.
6. Pour the reaction solution into 30 mL of ice water with constant stirring, and separate the organic phase with a separatory funnel.
7. The aqueous phase was extracted three times with 30 mL of dichloromethane, and the organic phases were combined.
8. The organic phase was washed three times with saturated NaHCO₃ solution of 30 mL, and then washed three times with 30 mL deionized water.
9. The organic phase is dried with anhydrous magnesium sulfate and the solvent is removed by decompression.

The product was separated and purified by column chromatography with Al₂O₃. The eluent was ethyl acetate-petroleum ether mixed solvent (volume ratio 1:10).

Pure acetylferrocene is an orange needle-like crystal with a melting point of 85-86 ^oC.

Safety Tips and Precautions

1. Acetyl chloride has high activity and rapid reaction, so attention should be paid to safe operation.
2. Acetyl chloride is very easy to absorb water and deteriorate, so the instrument must be dry without water and feed quickly.
3. The reaction time should not be too long, in order to prevent the formation of by-product acetyl ferrocene, so it is necessary to use thin layer chromatography to track the reaction process.
4. If the reaction time is too long and diacetylferrocene is formed, it can be separated by column chromatography. The eluent is eluted with petroleum ether-ether mixed solution (volume ratio is 3:1) to elute orange acetylferrocene, then ether is used as eluent to elute diacetylferrocene, and two acetylated products can be obtained by removing the solvent.