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Ch. 21 - Carboxylic Acid Derivatives
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 21 - Carboxylic Acid DerivativesProblem 55c1
Chapter 21, Problem 55c1

Grignard reagents add to carbonate esters as they add to other esters.
(c) Diethyl carbonate is a liquid reagent that is easy to handle. In contrast, phosgene is a highly toxic and corrosive gas. Show how you might use diethyl carbonate instead of phosgene to make Lexan®.

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1
Understand the context: Lexan® is a polycarbonate polymer, typically synthesized using bisphenol A (BPA) and phosgene. Phosgene acts as a carbonylating agent, introducing carbonate linkages (-O-C(=O)-O-) into the polymer backbone. In this problem, we aim to replace phosgene with diethyl carbonate, a safer alternative.
Identify the reactivity of diethyl carbonate: Diethyl carbonate (C2H5O)2CO contains a carbonate group and can act as a carbonylating agent. It can react with nucleophiles, such as the phenoxide ion derived from bisphenol A, to form carbonate linkages.
Propose the reaction mechanism: First, deprotonate bisphenol A using a strong base (e.g., NaOH or KOH) to generate the bisphenoxide ion. This ion is a strong nucleophile and can attack the electrophilic carbonyl carbon of diethyl carbonate, displacing one ethoxide group (C2H5O−) and forming a mono-carbonate intermediate.
Extend the reaction to polymerization: The mono-carbonate intermediate can undergo further reaction with another bisphenoxide ion, displacing the second ethoxide group and forming a di-carbonate linkage. Repeating this process leads to the formation of the polycarbonate polymer (Lexan®).
Consider reaction conditions: To optimize the reaction, use an aprotic solvent (e.g., dimethylformamide or tetrahydrofuran) and maintain a controlled temperature to facilitate the nucleophilic substitution reactions. Additionally, ensure the removal of ethanol (a byproduct) to drive the reaction forward.

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Key Concepts

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

Diethyl Carbonate

Diethyl carbonate is an organic compound used as a solvent and reagent in organic synthesis. It is a non-toxic, liquid ester that can participate in various chemical reactions, including carbonylation and alkylation. Its favorable handling properties make it a safer alternative to more hazardous reagents, such as phosgene.
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Carbonation of Grignard Reagents

Phosgene

Phosgene is a colorless gas with a musty odor, primarily used in the production of isocyanates and polycarbonate plastics. It is highly toxic and poses significant health risks, including respiratory damage. Understanding its reactivity and the risks associated with its use is crucial for developing safer synthetic routes in organic chemistry.
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Polycarbonate Synthesis

Polycarbonate synthesis typically involves the reaction of bisphenol A with phosgene to produce Lexan®, a durable thermoplastic. This process can be modified to utilize safer alternatives like diethyl carbonate, which can provide the necessary carbonyl groups for polymerization without the associated toxicity of phosgene, thus enhancing safety in industrial applications.
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Related Practice
Textbook Question

Grignard reagents add to carbonate esters as they add to other esters.

(a) Predict the major product of the following reaction.

(b) Show how you would synthesize 3-ethylpentan-3-ol using diethyl carbonate and ethyl bromide as your only organic reagents

1355
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Textbook Question

Show how you would accomplish the following syntheses. Some of these conversions may require more than one step.

(d) ethyl acetate → 3-methylpentan-3-ol

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Textbook Question

Show how you would accomplish the following multistep syntheses, using the indicated starting material and any necessary reagents.

(a) hept-6-en-1-ol → ε-caprolactone

(b) methoxybenzene → p-methoxybenzamide

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Textbook Question

Grignard reagents add to carbonate esters as they add to other esters.

(c) Diethyl carbonate is a liquid reagent that is easy to handle. Also show how you might use diethyl carbonate instead of methyl isocyanate to make Sevin® insecticide.

743
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Textbook Question

One mole of acetyl chloride is added to a liter of triethylamine, resulting in a vigorous exothermic reaction. Once the reaction mixture has cooled, 1 mole of ethanol is added. Another vigorous exothermic reaction results. The mixture is analyzed and found to contain triethylamine, ethyl acetate, and triethylammonium chloride. Propose mechanisms for the two exothermic reactions.

903
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Textbook Question

Show how you would accomplish the following syntheses. Some of these conversions may require more than one step.

(e) cyclohexylamine → N-cyclohexylacetamide

(f) bromocyclohexane → dicyclohexylmethanol

675
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