Life Cycle of a Toxic Natural Product

Introduction Objectives Life Cycle of a Toxic Natural Product Summary Evaluation Further References
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Overview of Urushiols

This lesson introduces students to the natural product Urushiol. It includes a hands-on activity and a short lecture.

Materials

Mangoes
Cashews
Poison Ivy, oak, or sumac leaves (in a plastic baggie)

Activity

Pass the items around the class and ask the students to make observations about them. Make sure all of the students have the opportunity to see all of the items.

Q & A

Once the students have examined all of the items, use the following questions to help them share their observations.

• Hold up each item and ask the students to identify them. The cashews and mangoes should be easy, the ivy (oak or sumac) might prove a little more difficult.
• After identifying the items, ask the students to figure out what they have in common.
• Urushiol is an oil found in plants of the Family Anacardiaceae
• Urushiol is also found in the nut shell of cashew fruit (Anacardium occidentale)
• Mangoes, cashews, and pistachios are all drupes
• Some people get dermatitis from touching mango peel or sap
• Why do you think these plants contain urushiols

Chemistry

Use the following information to present the chemistry of urushiols.

• Urushiol is an oil found in plants of the Family Anacardiaceae, especially Toxicodendron spp. (e.g. poison oak, poison ivy, and poison sumac)
• The oxidation and polymerization of urushiol in the tree's sap in the presence of moisture allows it to form a hard lacquer, which is used to produce traditional Chinese and Japanese lacquerwares
• Urushiol is a yellow liquid with a boiling point of 200-210 °C
• It is soluble partially in alcohol and ether, but nearly insoluble in water.
• Chemically, urushiol is a mixture of several closely related organic compounds. Each consists of a catechol substituted with an alkyl chain that has 15 or 17 carbon atoms.
• The alkyl group may be saturated or unsaturated urushiol oil is a mixture of the saturated and unsaturated urushiol molecules.
• The exact mixture depends on the species of the plant. For example, poison oak urushiol contains mostly catechols with C17 side chains, but poison ivy and poison sumac contain mostly catechols with C15 side chains.
• The allergic reaction is dependent on the degree of unsaturation of the alkyl chain. Less than half of the general population reacts with the saturated urushiol alone, but over 90% react with urushiol containing at least two degrees of unsaturation (double bonds).

R = (CH2)14CH3 or R = (CH2)7CH=CH(CH2)5CH3 or R = (CH2)7CH=CHCH2CH=CH(CH2)2CH3 etc.