Grignard reagents is reactive due to
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In a Grignard reaction, alkyl-, aryl-, vinyl organomagnesium halide compounds react with molecules that have polarized bonds, including ketones, esters, aldehydes, organic acids, nitriles, and amides. These organomagnesium halide compounds, known as Grignard reagents, are nucleophiles that attack the electrophilic carbon atom in, for example, carbonyl bonds. Grignard reactions are important due to their ability to form carbon-carbon bonds.
Grignard reagents are strong bases and will react with protic compounds which makes them exceedingly valuable tools for organic synthesis. As an example, organomagnesium halides will undergo addition to the carbonyl bond of a ketone or aldehyde forming an adduct which is then hydrolyzed to form an alcohol. Hundreds of different alcohols have been synthesized via the Grignard reaction.
Importance of Grignard Reactions
Importance of Grignard Reactions
Effective Production of C-C Bonds
The value of the Grignard reaction cannot be overstated. In general, Grignard reactions represent one of the best ways in organic chemistry to produce C-C bonds and enable the coupling of alkyl chains. For example, Grignard reagents are frequently used to alkylate aldehydes and ketones. There are few reagents available to the chemist that are as effective as Grignards for C-C bond formation.
Carbon is more electronegative than magnesium, and the metal-carbon bond in Grignard regents is quite ionic. These carbanions are quite nucleophilic and readily react with electrophilic groups such as carbonyl moieties. Thus, Grignard reagents react with formaldehyde to form primary alcohols, with aldehydes to form secondary alcohols and ketones, and esters and acid halides to form tertiary alcohols.
Reactions of various organic compounds with Grignard reagents yield amines, ketones, nitriles, thiols, aldehydes, etc. Grignard reagents can react with a variety of halides to form carbon-hetero atom bonds.
Safety Considerations in Grignard Reagent Synthesis
Minimizing Hazard with Inline Reaction Monitoring
Due to the exothermicity of Grignard formation, as well overall reactivity of Grignard reagents, synthesizing them can be particularly hazardous. Notwithstanding, the formation of Grignard reagents and subsequent Grignard reactions are widely used in the production of fine chemical and pharmaceutical compounds.
The synthesis of a Grignard reagent may have a variable induction period associated with an autocatalytic process that accelerates the formation of radicals on the magnesium metal. Although the reaction may be slow to initiate, as the number of magnesium radicals quickly increase, the reaction may advance rapidly with concurrent significant heat release. If not well controlled, this issue of induction period followed by rapid initiation may result in a runaway reaction. The variability and overly-lengthy induction period is often due to the presence of trace impurities in solution, or passivity caused by an oxide layer on the magnesium surface. Overdosing the organohalide during this period exacerbates the hazardous nature of the reaction when initiation occurs.
The issues associated with reagent and reactant purity, the type of Grignard reagent formed, and reaction variables need to be carefully understood and controlled. For this reason, chemists and engineers have turned to the RC1mx reaction calorimeter to measure the exothermicity of Grignard reactions, and ReactIR to monitor the organic halide concentration dosing and to track the formation of the Grignard reagent. The use of heat and mass balance online monitoring reveals the link between reaction variables and reaction performance, ensuring the safety of Grignard reagent synthesis.
Answer:
the presence of a halogen atom
the presence of magnesium atom
the polarity of the C-Mg bond
ALL OF THESE