PRACTICE ONLY CHE 202 Sp 2011 7. 2017 PRACTICE Pre-lab quiz : Exp 30 (5 points;
ID: 1042595 • Letter: P
Question
PRACTICE ONLY CHE 202 Sp 2011 7. 2017 PRACTICE Pre-lab quiz : Exp 30 (5 points; 10 min max) week of Dec 22 me: 1. Why are anhydrous THF or anhydrous diethyl ether commonly used as solvents for a Grignard reaction? 1 point A) Ethers are generally unreactive with Grignard reagents. B) Ethers stabilize the product by coordinating with the alcohol C) Ethers are very reactive with Grignard reagents. D) Ethers stabilize the reaction by dissolving the adduct. 2. Why is it important to keep your apparatus dry what reaction will occur between the Grignard reagent and water 1 pointExplanation / Answer
1. D) Ethers stabilize the reaction by dissolving the adduct
Ether is crucial to the Grignard Reaction. Many catalysts are known for increasing the yields of Grignard reactions through various concepts, ranging from increasing the reactivity of magnesium, to providing inert reaction conditions, thus inhibiting side reactions that lower yield. Ethers are needed to stabilize RMgX species. It's obvious that the greater the ability to stabilize a grignard adduct that an ether has, the better the yield will be.
2. The Grignard reagent is a strong base and a nucleophile as there is carbon connected to a metal (RMgBr) which puts a lot of electron density on it. This carbon will immediately attack any proton whether from water which will react with a Grignard reagent and any other compound that is a proton donor. Ether solvents are aprotic solvents. Also ethers are particularly good solvents for Grignard reagents. In practice diethyl ether and THF are mainly used.
R-X+Mg ???dry etherX???R-MgX
The R-Mg bond is highly polar: ??Rl??+MgX
The Grignard carbon is highly basic and reacts with the acidic protons of polar solvents like water to form an alkane.
??Rl-?+MgX+H-OH?R-H+HO-MgX
Ether has no acidic protons, so Grignard reagents are stable in ether.
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