Ethylmagnesium bromide, reactivity with

The rate of reaction shows first order dependence on the concentration of iron and ethyl bromide, but is independent of the concentration of ethylmagnesium bromide. The rate, however, varies with the structure of the Grignard reagent, and disproportionation usually results except when the alkyl group is methyl, neopentyl or benzyl which possess no g-hydrogens. The reactivities of the alkyl bromides (t-butyl >i-propyl >n-propyl) as well as the kinetics are the same as the silver-catalyzed coupling described above and suggest a similar mechanism ... 

Triethyl amine has no effect on the rate of reaction of diethylmagnesium with 1-hexyne, but it has a significant effect on this reaction of ethylmagnesium bromide (relative rate increased from 100 to 493). It was suggested that the amine influenced the bridging between two magnesium species in complexes formed in solution and, by so doing, influenced the reactivity. 

One year later, in 1934, Vavon and co-workers [5] determined the relative reactivities of Grignard reagents with a different type of substrates benzoic acid esters. Steric requirements played a role when the alcohol component of the ester was changed from primary, to secondary, to tertiary the relative rates of reactions of ethylmagnesium bromide were 400 40 1, respectively. The relative rates of reaction of ethyl-, isopropyl-, n-butyl-, and phenylmagnesium bromide with ethyl benzoate decreased in this order. The reaction with rert-butylmagnesium chloride was reported to be extremely slow."... 

Changes in the steric requirements of the benzoic acid component of the ester did suggest a strong influence on the reactivity the reactions of ethylmagnesium bromide with the ethylesters of benzoic acid, o-methylbenzoic acid, and 2,4,6-trimethylbenzoic acid had relative rates of 1000 30 1. An interesting series studied in the same paper consisted of the... 

Solvent effects were studied in the fate 1950s for reactions of alkylmagnesium compounds with 1-hexyne in diethyl ether. These reactions have already been discussed several times in this and in Chapter 11 (see Scheme 10) [22a], When 1.0 molEq triethylamine was added to the reaction mixture, the relative reactivity of methylmagnesium iodide toward 1-hexyne, which is 7 (the reactivity of ethylmagnesium bromide was arbitrarily set... 

It has been reported that the adduct of N-sulfinylaniline and 2,3-di-methylbutadiene is stable to ethylmagnesium bromide.23 However, Weinreb and co-workers36-38,52 have recently found that a number of N-acyldihydrothiazine oxides are susceptible to ring opening by a variety of reactive carbon nucleophiles. For example, when dihydrothiazine oxide 44 was treated with phenylmagnesium bromide, followed by trimethyl phosphite, (EJ)-threo-hydroxycarbamate 45 was produced exclusively [Eq. (24)].36... 

Explain the difference in reactivity for the reaction of this ketone with ethylmagnesium bromide, with ethyllithium, and with methylmagnesium bromide, as shown. 

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