Question
What is organo metallic compound? Explain grignard reagent.
✓
Answer
→ Most organic chlorides, bromides and iodides react with certain metals to give compounds containing canr bon-metal bonds. Such compounds are known as organo-metallic compounds.
→ An important class of organo-metallic compounds discovered by Victor Grignard in 1900 is alkyl magne sium halide, RMgX, referred as Grignard Reagents.
→ These reagents are obtained by the reaction of haloalkanes with magnesium metal in dry ether.
→ In the grignard reagent, the carbon-magnesium bond is covalent but highly polar, with carbon pulling electrons from electropositive magnesium; the magnesium halogen bond is essentially ionic.
$\begin{array}{l}\delta-\quad \delta+\delta- \\ R - Mg X \\\end{array}$
→ Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons.
RMgX + H2O → RH + Mg(OH)X
$\underset{\text{Ethyl magnesium bromide}}{CH _3 CH _2 MgBr} + H _2 O \rightarrow \underset{Ethane}{CH _3- CH _3}+ Mg ( OH ) Br$
It is therefore necessary to avoid even traces of moisture from a Grignard reagent. That is why reaction is carried out in dry ether. On the other hand, this could be considered as one of the methods of converting halides to hydrocarbons.
→ An important class of organo-metallic compounds discovered by Victor Grignard in 1900 is alkyl magne sium halide, RMgX, referred as Grignard Reagents.
→ These reagents are obtained by the reaction of haloalkanes with magnesium metal in dry ether.
→ In the grignard reagent, the carbon-magnesium bond is covalent but highly polar, with carbon pulling electrons from electropositive magnesium; the magnesium halogen bond is essentially ionic.
$\begin{array}{l}\delta-\quad \delta+\delta- \\ R - Mg X \\\end{array}$
→ Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons.
RMgX + H2O → RH + Mg(OH)X
$\underset{\text{Ethyl magnesium bromide}}{CH _3 CH _2 MgBr} + H _2 O \rightarrow \underset{Ethane}{CH _3- CH _3}+ Mg ( OH ) Br$
It is therefore necessary to avoid even traces of moisture from a Grignard reagent. That is why reaction is carried out in dry ether. On the other hand, this could be considered as one of the methods of converting halides to hydrocarbons.
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