history
founding by French chemist Grignard year of 1901. An organic halogen compound (halogenated alkyl, halogenated aromatic active) with magnesium metal to form an organomagnesium reagent of absolute ethyl ether, known as "Grignard reagent", referred to as "the Grignard reagent." In the French chemist Normand 1953 tetrahydrofurfuryl (THF) as solvent to give a Grignard reagent. The improvement called "Grignard - Normand reaction."
is now commonly used in a halogenated hydrocarbon with magnesium anhydrous diethyl ether or tetrahydrofuran (THF) in the reaction of preparation process must be carried out in absolute ethanol without water without carbon dioxide, a substance having active hydrogen conditions. Generally represented by the formula R-Mg-X. Grignard reagent is a reactive reagents in organic synthesis, can occur: conjugated, addition, substitution and other types of reaction, it has a high value in organic synthesis.
There are two general Grignard reagent, 1: chlorobenzene (benzyl chloride) in diethyl ether (tetrahydrofuran) and the reaction of magnesium, 2: Bromocyclopentane under ether (tetrahydrofuran) and magnesium (zinc) reaction.
properties
referred to as a Grignard reagent. A class of the general formula R-Mg-X reagent, wherein R is an aliphatic or aromatic hydrocarbyl group, X is a halogen (Cl, Br, or I). Preparation usually in dry diethyl ether or tetrahydrofuran, a halogenated hydrocarbon with magnesium metal. Extremely lively nature, with compounds having active hydrogen (e.g., H 2 O, ROH, RC≡CH ...) an aldehyde, ketone, ester, acid halide, nitrile, oxirane, alkyl halide, carbon dioxide , phosphorous trichloride, boron trichloride, silicon tetrachloride and other reactions. Important reagents in organic synthesis.
structure
Grignard reagent is a covalent compound, a magnesium atom directly attached to the carbon polar covalent bonds, carbon electronegative end, the Grignard reagent is therefore extremely Lewis base, from water and other protic Lewis acids captured, it is not a Grignard reagent, carbon dioxide in contact with water, the Grignard reagent prepared by the reaction for an initiator and needs in anhydrous conditions under an air isolation.
prepared
Grignard reagent is generally composed of a halogenated hydrocarbon with magnesium in diethyl ether or anhydrous tetrahydrofuran (THF) in a reaction. (Halobenzene must respond in THF) Grignard reagent may form a complex with an ether oxygen atom or tetrahydrofuran, in the manufacturing process must be of absolute ethanol, carbon dioxide-free substance having an active hydrogen (such as: water, alcohol performed ammonia, hydrogen halides, terminal alkynes, etc.) conditions.
in the active hydrogen material or of THF: R-Br + Mg → R-Mg-X
Due to the high price of an alkyl iodide, alkyl bromide using the general synthesis. Halogenated alkyl bromide is most commonly used in the preparation of the Grignard reagent, but chlorine, methyl bromide gas are inconvenient to use, typically using methyl magnesium iodide, methyl iodide synthesis. Chlorobenzene in the preparation of the Grignard reagent must control the temperature and pressure. Allylic type and benzyl Grignard reagents, coupling occurs not reacted with the halogenated hydrocarbon after synthesis, thus requiring strict control of temperature.
prepared
in 250mL three-neck flask, fitted with stirrer, constant pressure dropping funnel and with CaCl reflux condenser 2 drying tube. Placed 2.9g (0.12mol) of magnesium turnings in a three-necked flask, 20mL of anhydrous diethyl ether with immersion. Under stirring, added dropwise to a solution of 5mL 25% halogenated ether (prepared from the halogenated hydrocarbons and 0.12mol anhydrous ethyl ether formed). If the reaction was rendered turbid and the temperature rise, indicating that the reaction has begun. If this phenomenon is not generated, it is necessary to add 1 to 2 fine iodine crystals, and slightly heated. Moment, iodine color started to fade, the solution became cloudy, the reaction began, the heating was stopped. The remaining solution was added dropwise to the reaction flask halogenated hydrocarbon, steady drip rate to maintain the reaction solution boils appropriate. Addition was complete, with a warm water bath heated at reflux for about half an hour to complete the reaction, i.e., diethyl ether solution of Grignard reagent.
Notes
(1) whenever not want diethyl ether was evaporated to dryness.
(2) drying the instruments required. Reagents and solvents must be dried.
(3) heating in hot water bath, must not heated by flame.
(4) that oxygen in the air with a Grignard reagent oxidation occurs slowly, a diethyl ether solution of the Grignard reagent in a dark room beautiful emits light, is for this reason. Accordingly, the Grignard reagent can not be set long, usually with the use with the system.
Grignard reaction
Grignard reagent and certain active hydrogen compound (water, alcohols, acids, etc.), CO 2 , carbonyl compound, or metal the reaction becomes a non-metal halide and the like Grignard reaction. Common to the preparation of hydrocarbons, alcohols, ketones, acids and the like. For example: