Spontaneous Dehydration of Sucrose
A little bit of potassium chlorate is mixed with sucrose, saturated with ethanol, and heaped up in a large evaporating dish. When it is ignited, the ethanol burns, enveloping the mass in flame. The heat of the ethanol flame initiates the oxidation of sucrose by the potassium perchlorate, resulting in in brilliant violet bursts of light. The heat released by the oxidation of sucrose is sufficient to initiate the spontaneous, exothermic dehydration of sucrose, resulting in the growth of snake-like columns of graphene.
This demo can be used towards the end of a general chemistry course when the composition of biological molecules is being discussed. It can also be used in an organic chemistry course when the aromatic stabilization of benzene is being introduced. This demo takes about seven minutes to perform.
This demo is adapted from "The Dehydration of Sugar without Sulfuric Acid: No More Choking Fumes in the Classroom!" by Todd Siverstein and Yi Zhang.1 Please refer to that article for further details on this demonstration. The dehydration of sucrose is spontaneous and exothermic at high temperatures. It is posited that this is due to the extensive aromatic stabilization of the product, graphene. Graphene is "sheet" of sp2 hybridized carbons arranged hexagonally. 1Silverstein, T.P. and Zhang, Y. J.Chem.Ed. 1998, 75, 748-749.
- 10g KClO3
- 25g sucrose
- wash bottle containing ethanol
- 120 mL evaporating dish
- small terra cotta flower pot
- glass stir rod
- butane "fireplace" lighter
- Place the evaporating dish so that it is resting securely on top of the flower pot.
- Mix the sucrose and the KClO3 together in the evaporating dish.
- Moisten the mixture with a few mL of ethanol and heap into a mound in the center of the evaporating dish using a stir rod.
- Ignite the mixture. It will burst into flame.
- After a few seconds it will start to flash with violet light. After a minute or so, "tentacles" of grayish-black graphene will start to grow off of it.
- This demo emits some fumes and should only be performed in a well-ventilated room.
- Keep a fire extinguisher at hand and clear all flammable materials away. The demo can "sputter," ejecting hot or burning reactant.
- The evaporating dish gets quite hot. The flower pot should protect the surface, but be very careful breaking the demo down. The pot remains hot for quite a while.
- KClO3 is a strong oxidizer. Handle with care.
- Ethanol is flammable. Handle with care.
- Once the KClO3 and the sucrose are mixed, there is a possibility that it could spontaneously ignite. Mix the reactants during the demo.
Grind KClO3 to a fine powder to enhance reaction.