Synthesis of Chemiluminescent Esters

“The one sitting on the throne was as brilliant as gemstones – jasper
and carnelian. And the glow of an emerald circled his throne like a rainbow. “– Revelation 4:3, Holy Bible

An ester is formed when an acid and an alcohol unite. Because of this, they can be used as solvents, as you will see in this experiment. Many types of esters, such as ethyl acetate, are used in household cleaners, polishes, and finishing sprays. Esters have also been known to give a fruity aroma, like what you might smell from a ripe banana. [L.G. Wade, Jr. – Chapter 21- 12]
Chemiluminescence is the production of light through a chemical reaction which ends up producing very little heat. In the specific reaction of this experiment, esters become oxidized by hydrogen peroxide in the presence of a suitable acceptor molecule (9,10-diphenylanthracene, chlorophyll). The energy from this catapults an electron to an excited state. The light is then emitted when the acceptor finds its way back to a relaxed state.

The television show CSI: Crime Scene Investigators is a good example of how chemiluminescence is used in real world situations. The CSIs use luminol (5-amino-2,3-dihydro-1,4-phthalazinedione/ C8H7N3O2) which is a yellowish solid and is soluble in water and most polar solvents. Luminol is used to detect trace amounts of blood. To create this luminol solution, it is first mixed with a solution of hydrogen peroxide (the oxidant) and a hydroxide salt (the activator). When the luminol solution is introduced to iron, which is found in the hemoglobin of blood, it reacts and becomes unstable. As the “excited” electrons relax, excess energy is released as photons of blue light. The blue glow lasts for about 30 seconds and can be photographed.

Another popular way to see chemiluminescence in action is through the use of glowsticks. In order to activate the “glowing” action of the glowstick, a person has to bend the stick. Inside the stick is a casing which holds two chemicals and when this casing is broken, the two chemicals are able to mix and therefore start the chemical reaction. Voila!

Part I: Making the Ester

You will be working with many dangerous phenols and other chemicals. Make sure proper safety attire, including gloves and goggles, remain on throughout the duration of the experiment.

You will be assigned only one of the four phenols listed here:

Name Grams (step 2)

2,3,6-trifluorophenol 1.44
4-nitrophenol 1.32
2,4-dinitrophenol 1.80
2,4,6-trichlorophenol 1.88

In a hood, measure out the listed amount of your phenol and observe its smell and appearance.

Place the phenol into a clean, dry 100mL round-bottom flask using a funnel. (If magnetic stirrers are available then add a stirring bar)

Add 16mL of acetone to your round-bottom.

Add 1.4mL of triethylamine to the flask.

Place the mixture in an ice bath and obtain .4mL of oxalyl chloride in a syringe.

Using the syringe, add the .4mL dropwise to the mixture in the ice bath. Stir vigorously for a while after each drop is added. Wait for the smoke to clear before adding the next drop.

Add a single drop of triethylamine to the solution.

Remove from the ice bath and stir for 20-30 minutes at room temperature.

The color of the solution should be either white or pale yellow. If the color of the solution becomes dark, add one or more drops of oxalyl chloride until the color of the reaction mixture turns pale yellow.

When finished, evaporate the solution on a rotary evaporator. (If there is a stir bar in the solution, remove it before evaporating.) If the rotary evaporator is unavailable, then blow air into the solution to evaporate it.

IMPORTANT NOTE: If you were assigned 2,4-dinitrophenol you must make certain the product is very dry.

Part II: Testing the Ester

Prepare two dry 100mL beakers.

To the first beaker, mark it A and add 10mL of 0.002M solution of rubrene.

To the first beaker, mark it B and add 10mL of 0.002M solution of 9,10-diphenylanthracene.Add half of the crystals from Part I to each beaker.

Mix well and watch it glow.