Grignard reagents bromide

This preparation illustrates the preparation of a liquid hydrocarbon from a Grignard reagent. The Grignard reagent from n-hexyl bromide may be decomposed either with dilute sulphuric acid or with solid ammonium chloride the latter gives a somewhat better 3neld. 

A general method for the synthesis of l -alkenes is provided by the action of a Grignard reagent upon allyl bromide, for example ... 

If reaction does not occur when a little allyl bromide is first introduced, further addition must be discontinued until the reaction has commenced. Remove 2-3 ml. of the Grignard solution with a dropper pipette, add about 0-5 ml. of allyl bromide and warm gently to start the reaction after this has reacted well, add the solution to the main portion of the Grignard reagent. 

Prepare a Grignard reagent from 24 -5 g. of magnesium turnings, 179 g. (157 ml.) of n-heptyl bromide (Section 111,37), and 300 ml. of di-n-butyl ether (1). Cool the solution to 0° and, with vigorous stirring, add an excess of ethylene oxide. Maintain the temperature at 0° for 1 hour after the ethylene oxide has been introduced, then allow the temperature to rise to 40° and maintain the mixture at this temperature for 1 hour. Finally heat the mixture on a water bath for 2 hours. Decompose the addition product and isolate the alcohol according to the procedure for n-hexyl alcohol (Section 111,18) the addition of benzene is unnecessary. Collect the n-nonyl alcohol at 95-100°/12 mm. The yield is 95 g. 

Anilides or p-toluidides of acids from esters. Esters are converted into the corresponding anilides or p-toluidides by treatment with anilino- or with p-toluidino-magnesium bromide, which are readily obtained from any simple Grignard reagent and aniline or p-toluidine ... 

After the air in the flask had been replaced completely with nitrogen, 100 ml of dry diethyl ether, 0.20 mol of the cumulenic ether (see Chapter V, Exps. 7, 8 and 11) and 1 g (note 1) of copper(l) bromide were placed in it. A solution of the Grignard-reagent, prepared from 0.50 mol of the chloride (see Chapter II,... 

Vote 2. A large excess of R MgCl is required, as the subsequent metallation of the enyne is rapid. In the case of C2H5 the Grignard reagent was prepared from ethyl bromide. 

Another feature of the Pd—C bonds is the excellent functional group tolerance. They are inert to many functional groups, except alkenes and alkynes and iodides and bromides attached to sp carbons, and not sensitive to H2O, ROH, and even RCO H. In this sense, they are very different from Grignard reagents, which react with carbonyl groups and are easily protonated. 

It should be noted that Grignard reagents obtained from 2-methylthiazole do not yield acetyl derivatives (31). Ketones can also be obtained from cyanothiazoles and Grignard reagents (87). Thus phenyl magnesium bromide and 5-cyanothiazole give phenyl 5-thiazolyl ketone (Scheme 35). 

Solvent Preparation. The most critical aspect of the solvent is that it must be dry (less than 0.02 wt % of H2O) and free of O2. If the H2O content is above 0.02 wt %, then the reaction of Mg and RX does not initiate, except for an extremely reactive RX species, such as benzyl bromide. Although adventitious O2 does not retard the initiation process, the O2 reacts with the Grignard reagent to form a RMg02X species. Furthermore, upon hydrolysis, the oxidized Grignard reagent forms a ROH species that may cause purification problems. 

There are five components to the cost of using a Grignard reagent (/) magnesium metal, (2) the haUde, (J) the solvent, (4) the substrate, and (5) disposal of the by-products. The price of magnesium in mid-1992 was 3.20/kg, having risen from 1.20/kg in 1966 to 1.36/kg in 1970 and 2.90/kg in 1979. Prices for tetrahydrofuran and diethyl ether, the two most commonly used solvents, have also increased (Table 3) in the same period. The cost of the hahde depends on its stmcture, but as a general rule the order of cost is chloride < bromide < iodide. 

Acetylene Grignard reagents, which are useful for further synthesis, are formed by the reaction of acetylene with an alkyhnagnesium bromide. 

Metalation. Benzene reacts with alkaH metal derivatives such as methyl or ethyUithium ia hydrocarbon solvents to produce phenyUithium [591 -51 -5], CgH Li, and methane or ethane. Chloro-, bromo-, or iodobenzene will react with magnesium metal ia ethereal solvents to produce phenyHnagnesium chloride [100-59-4], C H MgCl, bromide, oriodide (Grignard reagents) (32). 

The halogen influences the rate of reaction, and, in general, the order of reactivity is HI > HBi > HCl. Impoitant uses of etfiyl chloiide include the manufacture of tetraethyllead and ethylceUulose. Ethyl bromide can be used to produce ethyl Grignard reagent and various ethyl amines. 

Reaction of pyridazine 1-oxide with phenylmagnesium bromide gives 1,4-diphenyl-butadiene as the main product and l-phenylbut-l-en-3-yne and 3,6-diphenylpyridazine as by-products, while alkyl Grignard reagents lead to the corresponding 1,3-dienes exclusively (79JCS(P1)2136>. 

Reaction of quaternized isoxazolin-5-ones with phenylmagnesium bromide produced a chalcone and dibenzoylethane. Those 5-ones with a 4,4-disubstituent undergo addition of the Grignard reagent to give a 5-ol (Scheme 63) (73BSF3079). 

---