Which of the following product is formed in the reaction $\ce{CH3MgBr}$ in DryIce/acid?
A) $\ce{CH3COOH}$
B) $\ce{CH4}$
C) $\ce{CH3OH}$
D) $\ce{CH3CH2CHO}$

My answer is A, since dry ice is $\ce{CO2}$ and it has one carbon atom and reactant has one carbon, so in all the product should have two carbon atoms, which is option A.

Am I correct?


You are correct. Grignard reagents $\ce{RMgX}$ (where $\ce{R}$ stands for some hydrocarbon group and $\ce{X}$ is a halogen, usually $\ce{Cl}$, $\ce{Br}$, or $\ce{I}$) react with carbon dioxide to produce carboxylic acids after acidic workup:

$$\ce{RMgX ->[1)\ \ce{ CO2}][2)\ \ce{ H3O+}] RCO2H}$$

$$\ce{RMgX + CO2 -> RCO2- MgX+}$$ $$\ce{RCO2- + H3O+ -> RCO2H + H2O}$$

In general your reasoning when approaching this problem is a good one. If you are reacting two 1-carbon reagents, then you probably have a 2-carbon product.

| improve this answer | |
  • $\begingroup$ Just to confirm, acidic workup or adding water, would be fine right? $\endgroup$ – Mixcels May 26 '15 at 6:36
  • 2
    $\begingroup$ Acidic workup would be better, since we want our acidic product and not its conjugate base. $\endgroup$ – Ben Norris May 26 '15 at 10:17

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