Objective: To synthesize the aromatic organotransition metal compound ferrocene. To compare purification by recrystallization and sublimation.
Reference: "Chemistry 57 Lab Manual" Dartmouth College. pp. 95-8.
Macroscale and Microscale Organic Experiments, 4th ed. By K.L. Williamson. pp. 606-8.
Theory: .
The product of the reaction is an aromatic compound which exhibits the thermodynamic and kinetic stability expected for the delocalized pi electron systems. Like other aromatic compounds ferrocene will undergo substitution reactions in preference to addition reactions.
The aromicity of ferrocene is formed when the 6 outer shell electrons of the ferrous ion combine with the 12 pi electrons of the two cyclopentadiene anion. This combination satisfies Huckel's rule for N=4, thus 4N + 2 = 18.
The crude product will be purified by a new method in this lab, sublimation. Initial heating removes volatile impurities and water. A funnel is then placed over the sample. As the crude product sublimates it leaves behind nonvolatile impurities then solidifies on the cool surface of the funnel.
Table of Properties:.
Cyclopentadiene bp 42 C.
Iron (II) chloride tetrahydrate mw 126.8 - corrosive material.
Ferrocene mp 173-4 C.
Dimethoxyethane bp 85 C.
Dimethyl sulfoxide bp 189 C.
KOH - corrosive material.
HCl(aq) - corrosive material.
source: www.sigmaaldrich.com and "Chem 57 Lab Manual".
Equations and Mechanisms.
Prelab:.
p.613 - 1,2.
1) While the reagents and products are resistant to air the intermediates in the formation of ferrocene are air sensitive. Care must be taken to keep air out of the reaction mixture to obtain the desired product.
2) Diethyl ether has very strong non polar tendencies and will not solvate the polar compounds needed to carry out the reaction. DMSO and dimethoxymethane both contain polar oxygen groups which can solvate these compounds and are thus well suited as solvents for this reaction.
Procedure:.
Rapidly weigh 12 g of KOH into 100-ml rb flask, add 30 ml dimethoxyethane, immediately cool in ice bath.
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