Grignard Reagent and Its Applications

Study Notes

Magnesium (Mg) is highly reactive with water, and other alkali metals.
A Grignard reagent is an organometallic compound, formula RMgX.
It is prepared by reacting an alkyl halide (R-X) with magnesium (Mg) in anhydrous ether.
The Grignard reagent is ionic.
Ionic compounds have complete positive and negative charges, while polar covalent compounds have slightly positive and negative charges.
Anhydrous ether must be used in the preparation of the reagent.
Magnesium must be fully consumed to form the reagent correctly.
Grignard reagents are water soluble, and all ionic compounds are water soluble.

Preparation of Alkanes (Corresponding): RMgX + HOH → RH + Mg(OH)X, RMgX + HX → RH + MgX₂
Preparation of Alkanes (Non-Corresponding): RMgX + RX → R₂R₁ + MgX₂, R₁MgX + R₂NH₂ → R₁R₂ + MgX₂NH₂

Diazonium salts are formed under specific conditions.
Pri-aromatic amines are used in the preparation and not secondary or tertiary amines.
They are prepared by reacting aromatic amines with NaNO₂ and 2HCl at 0-5°C.
The reaction mechanism involves the formation of a nitrosonium ion.

Benzene diazonium salts are resonance-stabilized and therefore stable.
They are only stable at low temperatures.
They are used in the analysis of PBA (primary aromatic amines) containing drugs (e.g., SEPTRON).

Diazonium salts can undergo various reactions, including coupling reactions and Sandmeyer reactions.
Coupling reactions involve reactions of diazonium compounds with nucleophiles to form azo compounds.
Sandmeyer reactions involve the replacement of the diazonium group with a halogen (Cl, Br, or I) using copper(I) chloride, bromide, or iodide.

Benzene diazonium salts can be used to prepare halobenzenes via Sandmeyer reactions.
Diazonium salts react with CuCl/HCl, CuBr/HBr, or CuI to yield chlorobenzene, bromobenzene, and iodobenzene respectively.

Other reactions can occur in the presence of strong bases or mild acids.
These reactions can involve the loss or gain of nucleophilic character depending on the conditions.

Heterocyclic compounds are those compounds where the ring structure contains an atom other than carbon.
Some examples of heterocyclic compounds include pyridine, pyrrole, furan, and thiophene.
These compounds have specific properties owing to ring structure.
Important consideration for aromaticity - cyclic, all members are sp² hybridized, Huckel's rule (4n+2π electrons)

These compounds can be prepared from 1,4-dicarbonyl compounds, using phosphorus pentoxide (P₂O₅) or phosphorus trisulfide (P₂S₃).
Other methods may be applicable depending on conditions.