MCQ Detailed View

Grignard reagents (RMgX) are highly reactive organometallic compounds where R is an alkyl or aryl group and X is a halogen. They are strong nucleophiles and also strong bases, which means they react readily with even weak proton donors. One of the simplest and most fundamental reactions of Grignard reagents is with water (H₂O).

When a Grignard reagent is exposed to water, the nucleophilic carbon atom attached to magnesium extracts a proton (H⁺) from water. This reaction destroys the Grignard reagent but produces the corresponding hydrocarbon (RH) along with magnesium hydroxide halide (MgXOH).

The reaction can be written as:

RMgX + H₂O → RH + MgXOH

For example:

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  If the Grignard reagent is CH₃MgBr, the reaction with water produces CH₄ (methane).

  
  


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  If the reagent is C₂H₅MgCl, the product is C₂H₆ (ethane).

  
  


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  An aryl Grignard reagent like C₆H₅MgBr gives benzene (C₆H₆).

  
  

This property makes Grignard reagents extremely moisture-sensitive. They must always be prepared and handled under anhydrous (dry) conditions, usually in an inert atmosphere (nitrogen or argon), because even small traces of water can completely deactivate them.

It is important to note that while alcohols like CH₃OH can also protonate Grignard reagents, in laboratory practice the reaction with water is typically highlighted as the standard method leading to hydrocarbons. Therefore, in multiple-choice questions, the most correct and accepted answer is H₂O.

This simple yet important reaction is not just theoretical. It is often used as a test to confirm the presence of a Grignard reagent and demonstrates their high reactivity with protic substances.