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Multiple Choice
During the dehydration of (ethanol) using concentrated , ethene () is formed as the main product. What other alkene is also formed as a minor product in this reaction?
A
(ethyne)
B
(propene)
C
(ethene)
D
(butene)
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1
Identify the starting material and the reaction conditions: ethanol (C\_2H\_5OH) is dehydrated using concentrated sulfuric acid (H\_2SO\_4), which typically promotes elimination reactions to form alkenes.
Understand the main reaction pathway: dehydration of ethanol primarily leads to the formation of ethene (C\_2H\_4) by elimination of water (H\_2O) from the ethanol molecule.
Consider the mechanism: the acid protonates the hydroxyl group, making it a better leaving group, followed by the loss of water and formation of a carbocation intermediate, which then loses a proton to form the alkene.
Recognize that minor products can form via rearrangements or alternative elimination pathways; in this case, since ethanol is a simple primary alcohol, rearrangements are unlikely, but oligomerization or polymerization of ethene can lead to higher alkenes such as butene (C\_4H\_8) as minor products.
Conclude that the minor alkene product formed alongside ethene during ethanol dehydration is butene (C\_4H\_8), due to possible dimerization or side reactions under the reaction conditions.