Textbook Question
In each part, rank the compounds in order of increasing rate of nucleophilic attack at C=O by a strong nucleophile like methoxide.
(b)
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22. Carboxylic Acid Derivatives: NAS
Nucleophilic Acyl Substitution
7:43 minutesProblem 55c2
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.
Verified step by step guidance1
Understand the structure of diethyl carbonate (C5H10O3) and methyl isocyanate (CH3NCO). Diethyl carbonate contains two ethoxy groups (-OCH2CH3) attached to a central carbonyl group (C=O), while methyl isocyanate contains a methyl group (CH3) attached to an isocyanate functional group (-N=C=O).
Recall the structure of Sevin® insecticide, which is carbaryl (1-naphthyl N-methylcarbamate). It is synthesized by introducing a carbamate functional group (-NHCOO-) to a naphthol derivative. The goal is to replace methyl isocyanate with diethyl carbonate in this synthesis.
Propose a reaction mechanism where diethyl carbonate reacts with 1-naphthol (C10H7OH). The hydroxyl group (-OH) of 1-naphthol can act as a nucleophile, attacking the carbonyl carbon of diethyl carbonate, leading to the formation of an intermediate.
Account for the elimination of ethanol (C2H5OH) during the reaction. This occurs as the ethoxy group (-OCH2CH3) is displaced, leaving behind the desired carbamate functional group attached to the naphthol ring.
Verify the final product structure to ensure it matches the structure of Sevin® (1-naphthyl N-methylcarbamate). The reaction should yield the carbamate derivative of 1-naphthol, completing the synthesis using diethyl carbonate as a substitute for methyl isocyanate.
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Video duration:
7mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Diethyl Carbonate
Diethyl carbonate is an organic compound classified as a carbonate ester. It is a colorless, flammable liquid with a fruity odor, commonly used as a solvent and reagent in organic synthesis. Its structure allows it to participate in nucleophilic substitution reactions, making it a versatile building block in the synthesis of various organic compounds, including pharmaceuticals and agrochemicals.
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Carbonation of Grignard Reagents
Methyl Isocyanate
Methyl isocyanate (MIC) is a highly reactive organic compound known for its use in the production of pesticides, particularly carbamate insecticides like Sevin®. It is a toxic and volatile compound that can pose significant health risks. Understanding its reactivity and the mechanisms of its reactions is crucial for safely substituting it with less hazardous alternatives like diethyl carbonate in synthetic pathways.
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Carbamate Insecticides
Carbamate insecticides are a class of chemicals derived from carbamic acid, known for their effectiveness in pest control. They work by inhibiting the enzyme acetylcholinesterase, leading to the accumulation of acetylcholine and resulting in paralysis of the target pests. Understanding the synthesis and action of carbamates is essential for developing safer alternatives and improving the environmental profile of insecticides.
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