Grignard reagent

Grignard reagent is an abbreviation for Grignard reagent, named after the discoverer VAGrginard. It is very active and easily reacts with water, carbon dioxide, alcohols, aldehydes, ketones, esters, amines and epoxy compounds to form various types of organic compounds. The yield is generally high, from halogenated alkane to magnesium metal in anhydrous ether. It is prepared by the action of a solvent. The formula is RMgX, R is an alkyl group, an aryl group or another organic group, and X is chlorine, bromine or iodine. For example, an ether solution of CH3MgI, C2H5MgBr, and C6H5MgCl (Br). Grignard reagent is an important reagent in organic synthetic chemistry and is widely used in the synthesis of elemental organic compounds. Keep in strict contact with wet air and pay attention to the danger of fire. [Related Chemical Reactions] 1. Grignard reagent can react with various unsaturated bonds to form different types of products. During the reaction, the C-Mg bond in the Grignard reagent is broken, and the hydrocarbon group is added to the atom having a small density of electron clouds in the unsaturated bond, and the magnesium atom is added to the atom having a high electron cloud density. 2. The Grignard reagent reacts with lead dichloride, and according to the amount of the Grignard reagent and the lead dichloride, a dihydrocarbyl lead or a tetrahydrocarbyl lead can be produced. 3. The Grignard reagent reacts with the cuprous halide to form a hydrocarbyl cuprous. The cuprous halide may be cuprous iodide, cuprous bromide or cuprous chloride. 4. The Grignard reagent reacts with the mercury dihalide to form a hydrocarbon-based mercury. The commonly used mercury dihalide is mercury dibromide and mercury dichloride. The reaction is carried out in an inert solvent such as diethyl ether. 5. The Grignard reagent reacts with an equimolar amount of zinc halide to form a hydrocarbyl zinc halide, and an excess of Grignard reagent produces a dihydrocarbyl zinc. A commonly used zinc halide is zinc chloride, and a commonly used Grignard reagent is C2H5MgXCH2=CHMgX, (CH3)3CMgX and the like. 6. The Grignard reagent reacts with boron trihalide to form an alkyl boron. The halogen in the Grignard reagent may be F, Cl, Br, I. The boron trihalide is generally BF3, BCl3. The yield is 50% to 90%. This reaction cannot be used to prepare tri-tert-butyl boron. Because of the action of the tertiary butyl magnesium halide with boron trichloride or boron trifluoride, the rearranged product - tert-butyl is obtained. The mechanism of diisobutylboron or triisobutylboron is unknown. 7. Grignard reagents can be used in combination with other halogenated hydrocarbons to form higher hydrocarbons. The commonly used halogenated hydrocarbons are brominated or iodohydrocarbons, and chlorinated hydrocarbons are not active. Reaction formula: R-MgX+X-R1===R-R1+MgX2. In this reaction, metal halides are effective catalysts. When R=R1, a silver catalyst is often used, and when R≠R1, a copper catalyst is effective. A high iron catalyst can be used in the presence of vinyl bromide. If the inactive vinyl halide or aromatic halide is catalyzed by a divalent nickel dichlorobis(triphenylphosphine) complex or cobalt dichloride. The reaction process catalyzed by cobalt dichloride is as follows: Figure 1 shows the reaction history of cobalt dichloride catalysis. [Preparation method] The magnesium metal is usually reacted with an organic halogenated product in anhydrous diethyl ether to prepare a Grignard reagent. RX+Mg=RMgX The raw materials and solvents used must be sufficiently dry. The organic halogenated substance may be aliphatic or aromatic, and may differ depending on the kind of the halogen, whether the reaction is easy, and the yield of the Grignard reagent. The difficulty of the reaction mainly depends on the structure of the hydrocarbon in the halogenated hydrocarbon and the type of the halogen. If the hydrocarbon group is the same, the iodine is most easily reacted, and the chlorine is most difficult to react. However, when iodine is used, the Wutz side reaction is likely to occur to lower the yield. If the halogen is the same, the larger the hydrocarbon group, the more difficult the reaction. Sometimes, in order to increase the yield, it is possible to react at a low halogen concentration and at a low temperature as much as possible. In order to increase the reaction rate, a small amount of iodine is added at the beginning to initiate the reaction. Once the reaction starts, since the reaction is exothermic, it should be cooled rapidly. It is also possible to use a small amount of 1,2-dibromoethane in place of iodine, especially when a small amount of water is present in the ether, which is preferred because the resulting magnesium bromide has a dehydrating action. As the solvent, diethyl ether, butyl ether, tetrahydrofuran, anisole or the like can be used. The solvent is different, which directly affects the difficulty of the reaction and the level of the yield. According to the H. Normant, it is easy to use a tetrahydrofuran to make it difficult to prepare a Grignard reagent from vinyl chloride or chlorobenzene. This is because vinyl chloride and chlorine bound to the olefinic carbon cannot react with magnesium in diethyl ether, but can be reacted in tetrahydrofuran, and the thus obtained chloroethylmagnesium reagent, also known as Norman's reagent. In addition to tetrahydrofuran, 2-methyltetrahydrofuran can also be used as a solvent. In the preparation of the Grignard reagent, if it is carried out in xylene, the reaction rate is very slow, and after a small amount of diethyl ether is added dropwise, the reaction rate is greatly accelerated, so that diethyl ether can be considered as a catalytic action. It has also been confirmed that the action of chloroalkane and magnesium under pressure can directly synthesize a Grignard reagent without a solvent. It can also be obtained by an indirect method, for example, by reacting bromoethylmagnesium with an active hydrogen compound such as acetylene to produce a metal-hydrogen displacement reaction, thereby producing bromoethynyl magnesium. Or react with magnesium bromide to replace the metal, as shown in Figure 2 below: Figure 2 is an indirect method for preparing Grignard reagent.