Textbook Question
The acid-catalyzed hydration we learned here in Chapter 8 is reversible.
(a) Propose a mechanism for the formation of an alkene from an alcohol.
9. Alkenes and Alkynes
Dehydration Reaction
4:37 minutesProblem 37c
Textbook Question
Starting from bromobenzene and any other reagents and solvents you need, show how you would synthesize the following compounds. Any of these products may be used as starting materials in subsequent parts of this problem.
c. 1-phenylpropan-2-ol
Verified step by step guidance1
Step 1: Begin with bromobenzene as the starting material. Perform a Grignard reaction by reacting bromobenzene with magnesium in anhydrous ether to form phenylmagnesium bromide (a Grignard reagent).
Step 2: React phenylmagnesium bromide with propanal (CH3CH2CHO) to form 1-phenylpropan-2-ol. This reaction involves nucleophilic addition of the Grignard reagent to the carbonyl group of propanal, followed by protonation during workup.
Step 3: To synthesize the target compound (1-phenylpropan-2-ol), ensure the reaction conditions are controlled to avoid side reactions. Use an acidic workup (e.g., HCl or H2O) to protonate the alkoxide intermediate formed during the Grignard reaction.
Step 4: Purify the product using techniques such as distillation or recrystallization, depending on the physical properties of 1-phenylpropan-2-ol.
Step 5: Verify the structure of the synthesized compound using spectroscopic methods such as NMR or IR to confirm the presence of the hydroxyl group and the phenyl-propane backbone.
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4mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile attacks an electrophilic carbon atom, replacing a leaving group. In the case of bromobenzene, the bromine atom acts as a leaving group, allowing the nucleophile to form a new bond with the carbon. This reaction is crucial for synthesizing alcohols like 1-phenylpropan-2-ol from bromobenzene.
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Grignard Reagents
Grignard reagents are organomagnesium compounds that act as strong nucleophiles in organic synthesis. They are formed by reacting alkyl or aryl halides with magnesium in dry ether. In the synthesis of 1-phenylpropan-2-ol, a Grignard reagent can be generated from bromobenzene and then reacted with a suitable carbonyl compound to introduce the propanol group.
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Alcohol Synthesis
The synthesis of alcohols is a key transformation in organic chemistry, often involving the reduction of carbonyl compounds or the substitution of halides. In this case, the target compound, 1-phenylpropan-2-ol, can be synthesized by first forming a Grignard reagent and then reacting it with a ketone or aldehyde. Understanding the mechanisms and conditions for these reactions is essential for successful synthesis.
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