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Ch. 21 - Amino Acids, Peptides, and Proteins
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
Chapter 22, Problem 23b

What alkyl halide is used in the acetamidomalonic ester synthesis to prepare
b. phenylalanine?

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1
Understand the acetamidomalonic ester synthesis: This is a method used to synthesize α-amino acids. It involves the alkylation of the acetamidomalonic ester, followed by hydrolysis and decarboxylation.
Identify the target amino acid: Phenylalanine is an α-amino acid with a benzyl side chain (C6H5-CH2-). This means the alkyl halide used must introduce this benzyl group.
Determine the structure of the required alkyl halide: To introduce the benzyl group, the alkyl halide should be benzyl bromide (C6H5-CH2-Br) or benzyl chloride (C6H5-CH2-Cl). These are common alkyl halides used for this purpose.
Outline the reaction mechanism: The acetamidomalonic ester undergoes deprotonation at the α-carbon (between the two ester groups) using a strong base, forming a carbanion. This carbanion then performs an SN2 nucleophilic substitution on the alkyl halide, replacing the halide group with the benzyl group.
Conclude the synthesis: After the alkylation step, the product undergoes hydrolysis to remove the ester groups and the amide group, followed by decarboxylation to yield phenylalanine.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acetamidomalonic Ester Synthesis

Acetamidomalonic ester synthesis is a method used to create amino acids, particularly phenylalanine. This reaction involves the use of acetamidomalonic ester, which undergoes alkylation to introduce an alkyl group, followed by hydrolysis and decarboxylation to yield the desired amino acid. Understanding this synthesis is crucial for identifying the specific alkyl halide needed for the reaction.
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Alkyl Halides

Alkyl halides are organic compounds containing a carbon atom bonded to a halogen atom (such as chlorine, bromine, or iodine). They serve as key reactants in various organic reactions, including nucleophilic substitutions. In the context of acetamidomalonic ester synthesis, the choice of alkyl halide affects the structure of the resulting amino acid, making it essential to select the correct one for phenylalanine production.
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Nucleophilic Substitution Reactions

Nucleophilic substitution reactions are fundamental processes in organic chemistry where a nucleophile replaces a leaving group in a molecule. In the synthesis of phenylalanine, the nucleophile (the acetamidomalonic ester) attacks the carbon atom of the alkyl halide, leading to the formation of a new carbon-carbon bond. Understanding the mechanisms and types of nucleophilic substitutions is vital for predicting the outcomes of the synthesis.
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