Textbook Question
Write the mechanism for the reaction of an amino acid with di-tert-butyl dicarbonate.
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Ch. 21 - Amino Acids, Peptides, and Proteins
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
Chapter 22, Problem 75a
Show how valine can be prepared by
a. a Hell–Volhard–Zelinski reaction.
Verified step by step guidance1
Step 1: Begin by identifying the starting material for the synthesis of valine. Valine is an α-amino acid with a branched alkyl side chain. To prepare valine using the Hell–Volhard–Zelinski (HVZ) reaction, start with a carboxylic acid that has the appropriate carbon skeleton, such as isobutyric acid (CH₃CH(CH₃)COOH).
Step 2: Apply the Hell–Volhard–Zelinski reaction to the carboxylic acid. This reaction involves treating the carboxylic acid with bromine (Br₂) in the presence of phosphorus tribromide (PBr₃). This step selectively brominates the α-carbon of the carboxylic acid, forming an α-bromo acid. The reaction mechanism includes the formation of an acyl bromide intermediate, which facilitates α-bromination.
Step 3: Convert the α-bromo acid into an α-amino acid. This is achieved by nucleophilic substitution, where ammonia (NH₃) is used to replace the bromine atom with an amino group (-NH₂). The reaction proceeds via an SN2 mechanism, resulting in the formation of valine.
Step 4: Purify the product. After the substitution reaction, the crude mixture may contain unreacted starting materials and byproducts. Use techniques such as recrystallization or chromatography to isolate and purify valine.
Step 5: Verify the structure and purity of valine. Use spectroscopic methods such as NMR (nuclear magnetic resonance) and IR (infrared spectroscopy) to confirm the presence of the amino group and the carboxylic acid functional group, as well as the correct branching in the side chain.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hell–Volhard–Zelinski Reaction
The Hell–Volhard–Zelinski (HVZ) reaction is a method for the halogenation of carboxylic acids at the alpha position. This reaction involves the formation of an acyl halide from the carboxylic acid, followed by halogenation at the alpha carbon using a halogen and a base. It is particularly useful for synthesizing alpha-halo acids, which can be further transformed into amino acids like valine.
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05:09
Heck Reaction
Alpha-Amino Acids
Alpha-amino acids are organic compounds that contain both an amino group (-NH2) and a carboxyl group (-COOH) attached to the same carbon atom, known as the alpha carbon. Valine, an essential branched-chain amino acid, is one such compound. Understanding the structure and properties of alpha-amino acids is crucial for grasping how they can be synthesized and modified in organic chemistry.
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09:36Standard Amino Acids
Synthesis of Valine
Valine can be synthesized through various methods, including the HVZ reaction, which allows for the introduction of a halogen at the alpha position of a carboxylic acid. Following the halogenation, further reactions such as hydrolysis and amination can convert the halogenated compound into valine. Familiarity with these synthetic pathways is essential for understanding how to prepare specific amino acids in organic chemistry.
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1:16Synthesis of Amino Acids: Strecker Synthesis Example 1
Related Practice
Textbook Question
Propose a mechanism for the rearrangement of the thiazoline obtained from the reaction of Edman's reagent with a peptide to a PTH-amino acid. (Hint: Thioesters are very reactive toward nucleophiles.)
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Textbook Question
Glycine has pKa values of 2.3 and 9.6. Do you expect the pKa values of glycylglycine to be higher or lower than these values?
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Textbook Question
Show how valine can be prepared by
d. a N-phthalimidomalonic ester synthesis.
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Textbook Question
Show how valine can be prepared by
c. a reductive amination.
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Textbook Question
Dithiothreitol reacts with disulfide bridges in the same way that 2-mercaptoethanol does. With dithiothreitol, however, the equilibrium lies much more to the right. Explain.
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