Textbook Question
Show how you would add Grignard reagent to acid chloride or ester to synthesize the following alcohols.
a. Ph3C–OH
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Ch.10 - Structure and Synthesis of Alcohols
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 10, Problem 18b
A formate ester, such as ethyl formate, reacts with an excess of a Grignard reagent to give (after protonation) secondary alcohols with two identical alkyl groups.
(b) Show how you would use reactions of Grignard reagents with ethyl formate to synthesize the following secondary alcohols.
(i) pentan-3-ol
(ii) diphenylmethanol
(iii) trans,trans-nona-2,7-dien-5-ol
Verified step by step guidance1
Step 1: Understand the reaction mechanism. Grignard reagents (R-MgX) react with esters to form ketones as intermediates. When an excess of the Grignard reagent is used, the ketone reacts further to form a tertiary alcohol after protonation. In this case, ethyl formate (HCOOCH2CH3) reacts with the Grignard reagent to form a secondary alcohol with two identical alkyl groups.
Step 2: For (i) pentan-3-ol, identify the Grignard reagent needed. Pentan-3-ol has two identical ethyl groups attached to the central carbon. To synthesize this, use ethylmagnesium bromide (CH3CH2MgBr) as the Grignard reagent. React ethyl formate with two equivalents of ethylmagnesium bromide, followed by protonation, to obtain pentan-3-ol.
Step 3: For (ii) diphenylmethanol, identify the Grignard reagent needed. Diphenylmethanol has two phenyl groups attached to the central carbon. To synthesize this, use phenylmagnesium bromide (C6H5MgBr) as the Grignard reagent. React ethyl formate with two equivalents of phenylmagnesium bromide, followed by protonation, to obtain diphenylmethanol.
Step 4: For (iii) trans,trans-nona-2,7-dien-5-ol, identify the Grignard reagent needed. This compound has two identical trans,trans-butadienyl groups attached to the central carbon. To synthesize this, use trans,trans-butadienylmagnesium bromide (CH2=CH-CH=CHMgBr) as the Grignard reagent. React ethyl formate with two equivalents of trans,trans-butadienylmagnesium bromide, followed by protonation, to obtain trans,trans-nona-2,7-dien-5-ol.
Step 5: Generalize the process. For each target secondary alcohol, the key is to identify the Grignard reagent that corresponds to the desired alkyl group. React ethyl formate with two equivalents of the chosen Grignard reagent, then protonate the resulting product to obtain the desired secondary alcohol.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Grignard Reagents
Grignard reagents are organomagnesium compounds that act as nucleophiles in organic reactions. They are formed by reacting alkyl or aryl halides with magnesium metal in dry ether. Grignard reagents can react with carbonyl compounds, such as esters, to form alcohols after protonation. Understanding their reactivity is crucial for synthesizing various alcohols from carbonyl precursors.
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Carbonation of Grignard Reagents
Ester Reactions
Esters, like ethyl formate, can undergo nucleophilic addition reactions with Grignard reagents. When a Grignard reagent attacks the carbonyl carbon of an ester, it forms a tetrahedral intermediate, which can lead to the formation of a secondary alcohol after protonation. This reaction is essential for constructing complex alcohols from simpler ester starting materials.
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Synthesis of Secondary Alcohols
Secondary alcohols can be synthesized by the reaction of Grignard reagents with esters, where the resulting product has two identical alkyl groups. The choice of Grignard reagent determines the structure of the final alcohol. For example, using a specific Grignard reagent with ethyl formate can yield pentan-3-ol or diphenylmethanol, showcasing the versatility of this synthetic approach.
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Related Practice
Textbook Question
Show how you would synthesize the following alcohol by adding Grignard reagents to ethylene oxide.
(c)
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Textbook Question
A formate ester, such as ethyl formate, reacts with an excess of a Grignard reagent to give (after protonation) secondary alcohols with two identical alkyl groups.
(a) Propose a mechanism to show how the reaction of ethyl formate with an excess of allylmagnesium bromide gives, after protonation, hepta-1,6-dien-4-ol.
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Textbook Question
Show how you would add Grignard reagent to acid chloride or ester to synthesize the following alcohols.
c. dicyclohexylphenylmethanol
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Textbook Question
Acetylide ions also add to ethylene oxide much like Grignard and organolithium reagents. Predict the products obtained by adding the following acetylide ions to ethylene oxide, followed by a dilute acid workup.
(a) HC≡C:–
(b) CH3CH2–C≡C:–
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Textbook Question
Show how you would synthesize the following alcohol by adding Grignard reagents to ethylene oxide.
(a) 2-phenylethanol