Grignard Reagent Grignard Reagent The Grignard reaction (pronounced /ﾉ｡riﾉｲar/) is an organometallic chemical reaction in which alkyl- or aryl-magnesium halides (Grignard reagents) add to a carbonyl group in an aldehyde or ketone. This reaction is an important tool for the formation of carbon窶田arbon bonds. The reaction of an organic halide with magnesium is not a Grignard reaction, but provides a Grignard reagent. Grignard reactions and reagents were discovered by and are named after the French chemist Franﾃｧois Auguste Victor Grignard (University of Nancy, France), who was awarded the 1912 Nobel Prize in Chemistry for this work. Grignard reagents are similar to organolithium reagents because both are strong nucleophiles that can form new carbon-carbon bonds. Organolithium :- Organolithium compounds are extremely important owing to their use as reagents in preparative chemistry. They are readily prepared, exhibit high chemical reactivity and are soluble in hydrocarbons. The organolithium compounds are of the type LiR. Despite the apparent simplicity of this formula special problems of structure and bonding are inherent.
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Organolithium is one of the important organo metallic reagent used in many organic syntheses because of the smaller metal ion. It is prepared by reacting the alkyl,aryl or vinyl halide with metallic lithium. R—X + 2Li → R— Li + LiX where R = alkyl, aryl or vinyl group and X = Halogen Among the alkali metals Lithium is most preferred because Lithium is the most electropositive alkali metal. Among the halogens the order of preference is I > Br > Cl. The reason is that iodine gets reduced easier than the other halogens by the strong reducing agent lithium. The smaller size of the lithium ion makes it easy to bond with even larger and branched organic halide. This makes it a convenient reagent. Organolithium reagents are very reactive, they even react with the gases in the air. So, the reactions need to be carried out under a nonreactive atmosphere usually argon. Although they are less bulky than Grignard reagents, the structure of organolithium compounds is not simple and can involve the formation of dimers and trimers, etc. Nomenclature of Organometallic Compounds :They are generally named as substituted metals since the alkyl group shares the electron of the metal, e.g., methyl lithium, ethyl sodium etc. When a halogen is also there with the organometallic compound, they are generally referred as grignards reagents. Alkyl magnesium halide is the common name for such compounds, e.g., propyl magnesium iodide, methyl magnesium bromide etc. <<--- RC≡C-Cd type of compounds are called metal acetylides which are again very reactive reagents. With water they produce alkynes.
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<<--- R2CuLi is another organometallic compound and is called organolithium cuprate. <<--- When two metals are there, the univalent metal takes the first preference in the name. There are many organometallic compounds other than reagents. To name a few, Chlorophyll contains Mg, haemoglobin has Fe. Ni, Co, Fe, forms their carbonyl compounds, while Tetra ethyl lead is an anti knocking agent and has Pb. Organo aluminium compounds are highly basic and reactive used in polymer industry. Trimethyl gallium, trimethyl indium are used as semiconductors. EDTA is a chelating agent which forms many metallic complex compounds.
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