Fluorescein is an organic fluorescent dye used in several areas, ranging from medicine to research applications. Structurally, fluorescein is similar to phenolphthalein, a well known dye indicator used in acid-base titrations. Fluorescein is fluorescent whereas phenolphthalein is not.

Fluorescence occurs due to the emission of light from the relaxation of the molecule from the excited state to the ground state. The electronic transition to the excited state occurs when the excitation wavelength corresponds to the energy difference between the ground state and the excited state. In the excited state, some energy is lost to vibrational relaxation. As a result, fluorescence energy is less than the absorption energy and the emitted light is observed at a longer wavelength than the excitation wavelength.

An organometallic compound is one that contains a carbon-metal bond. The key feature of many of these compounds is that the carbon on the carbon-metal bond carries a partial negative charge. The partial negative charge on carbon makes it basic and nucleophilic; this latter property can be exploited in organic synthesis to help construct carbon-carbon bonds. Organomagnesium compounds are referred to as Grignard reagents.

Crystal violet is a triarylmethane dye which is commonly used in general chemistry classrooms to study spectrophotometry and basic chemical kinetics. Here, you will synthesize crystal violet by preparing a Grignard reagent from the bromine-containing compound 4-bromo-N,N-dimethylaniline. Addition of this Grignard to diethyl carbonate followed by acid hydrolysis ultimately leads to the triarylmethane dye.

Friedel-Crafts reactions are examples of electrophilic aromatic substitution reactions. The reaction involves the substitution of hydrogen on the aromatic ring system by an electrophilic carbon species forming a new carbon-carbon bond. Friedel-Crafts reactions may be used to introduce either an alkyl or acyl group.

Ferrocene does not undergo addition reactions typical of cyclopentadiene, but undergoes electrophilic aromatic substitution. The Friedel-Crafts acylation reaction of ferrocene involves the addition of the acylium cation to one of the carbon atoms on the ring, followed by loss of a proton (to solvent). The acylium cation is produced from acetic anhydride, which also serves as a solvent for this reaction. If only one ring reacts, then the product is the orange acetylferrocene. If both rings react, then the product is the red 1,1-diacetylferrocene. The reaction time of this experiment is reduced to limit the formation of 1,1-diacetylferrocene.

Your objectives in this experiment will be to synthesize, isolate, and characterize acetylferrocene. In this experiment you will also become familiar with a technique called column chromatography, which can be used to separate the desired product from unreacted starting material and side products. The compounds are colored which will make it easy to see the separation. Melting temperature analysis will be used to characterize the synthesized product.