Magnesium, iodine-activated

Reaction (1) usually proceeds readily provided the magnesium is activated with iodine and the water content does not exceed one per cent. Subsequent interaction between the magnesium ethoxide and water gives the highly insoluble magnesium hydroxide only a slight excess of magnesium is therefore necessary. 

Iodine-activated magnesium - is used to initiate the reaction of magnesium and methyl chloride. About 0.5 g. of magnesium turnings and 0.1 g. of iodine are placed in a 10-ml. test tube and covered with about 2 ml. of anhydrous ethyl ether. After the reaction has proceeded for about 5 minutes, the excess liquid is decanted, and the test tube is heated carefully with a free flame to a dull redness. The test tube is allowed to cool somewhat. While it is still warm, about 5 ml. of tetraethylene glycol dimethyl ether, previously saturated with methyl chloride, is added. Additional gentle warming may be required if the reaction does not start immediately. 

The proposed mechanism to rationalize the enhanced reactivity of iodine-activated magnesium involves the formation of magnesium(I) iodide, which functions as the active agent in the formation of the Grignard reagent [12]. Magnesium(I) iodide is more soluble... 

The examples in Table 2 illustrate the scope of this addition reaction. The solvents of choice are the same ethers and hydrocarbons mentioned in Section III. A. In some cases the magnesium is activated with iodine, HgCl2, or amalgamated with Hg. 

Spirolactone moieties are important components of some biologically active steroids that possess antitumor activity. A prelude to formation of the spiro unit is the introduction of an allyl side chain into a steroidal ketone. This reaction can be accomplished in good yield by the Barbier reaction of allyl bromide, ketone, and iodine-activated magnesium in ether. With 5a-cholestan-3-one, 51 and 48% of the epimeric allyl alcohols are isolated. With 3(i-(tetrahydropyran-2-yloxy)-5a-androstan-17-one, 98% of the allyl alcohol is isolated [39]. 

One of the benefits of the Barbier reaction over the Grignard reaction is generally the production of products with little or no R-R dimer formation. However, because of the radical nature of the reaction Wurtz-type dimer formation can be the primary reaction in the absence of an electrophilic coreagent. Some Russian chemists have reported the dimerization of halogenated alkenes and alkanes using iodine-activated magnesium with silver bromide [Eqs. (27) and (28) 64]. 

BORON FLUORIDE (7637-07-2) Reacts with moist air, water, steam, producing hydrogen fluoride, boric acid, and fluoboric acid. Violent reaction with allyl chloride, alkyl nitrate, benzyl nitrate, calcium oxide, ethyl ether, iodine, magnesium tetrahydroaluminate, active metals (except magnesium). Used as a polymerization catalyst contact with monomers may cause explosions. Corrodes most metals in the presence of moisture. 

Equation (a) depicts the Grignardization of lO-methoxy-4 H-benzo [4, 5] cyclohepta [1, 2-b] thiophen-4-one (I) with iodine-activated magnesium shavings in a medium of tetrahydrofuran to give rise to the formation of the corresponding Grignard s derivative (II). 

With Iodine. As is the case with magnesium (see Sect. 5.3.1) iodine has been applied [58] in a Barbier-type reaction with propargyl bromide and cyclohexanone. More recently, in a Reformatsky reaction under sonication [59], use was made of iodine-activated zinc. In the absence of iodine the sonicated mixture of zinc, ethyl 2-bromo-ethanoate and acetophenone reacted slowly and gave no addition product recovery of the ester and the ketone were quantitative. 

K2C03 CaH2, CaO or sodium, then fractionally distd. Near-dry alcohol can be further dried by refluxing with magnesium activated with iodine, as described for ethanol. Further purification is possible using fractional crystn, zone refining or preparative gas chromatography. 

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