Cyclopentyl bromide, reaction

Secondary alkyl bromides (e.g., isopropyl bromide) react less readily and higher temperatures are required. To avoid any decomposition of the lithiated thioacetal or its reaction with THF, the alkylations are usually carried out with the iodides [1]. Cyclopentyl bromide (reaction carried out at + 10°C) and LiCH(SCH3)2 gave the expected product in a moderate yield [3]. With cyclohexyl bromide the predominant reaction is dehydrobromination [1]. 

The reaction of cyclopentyl bromide with sodium cyanide to give cyclopentyl cyanide... 

The alternative combination cyclopentyl bromide and sodium ethoxide is not appropriate because elimination will be the major reaction... 

Cognate preparation. Nitrocycbpentane. Use cyclopentyl bromide (22.0 g, 0.15mol), sodium nitrite (18g, 0.26mol) and 100ml of dimethyl sulphoxide allow the reaction mixture to stir at 15 °C for 3 hours. The product (9.9 g, 58%), b.p. 62°C/8mmHg, no1 1.4538, was isolated as above. 

Iodide ion is both a better nucleophile than cyanide and a better leaving group than bromide. The two reactions shown are therefore faster than the reaction of cyclopentyl bromide with sodium cyanide alone. 

On the other hand, cyclopentyl bromide reacts almost quantitatively with Ph2P ions in the dark or under irradiation. Both reactions were partially inhibited by p-DNB. All these results suggest that 79 reacts with Ph2P ions by the S l mechanism, while the bromine derivative reacts by a polar and ET reaction151. 

Table 10 Relative Rates of Reaction of Cyclopentyl Bromide and Cyclopentyl Chloride with Magnesium in Several Solvents...

Further work [8IQ, which demonstrated that the rates of reaction of cyclopentyl bromide with magnesium fit the kinetic features of a transport-limited heterogeneous reaction, was based on two sets of experiments. First, the relative rates of reaction of cyclopentyl bromide and cyclopentyl chloride with magnesium in solvents of different viscosities [8If] were examined by applying the constant-surface kinetics technique. The results are summarized in Table 10. These demonstrate that the relative rates of reaction of cyclopentyl bromide with magnesium in a series of solvents were proportional to the inverse of the solvent shear viscosity whereas the reaction of cyclopentyi chloride... 

As a variation from the general procedure the reaction mixture may be poured into ice-water, and the crude bromide separated, extracted with light petroleum or ether, washed with water or 5% sodium carbonate solution, and dried over CaCl2. It may also be possible, e.g., with cyclopentyl bromide,936 to add water after completion of the reaction and to distil out the bromide in steam. 

In reactions in DEE with Mg turnings and ordinary stirring, the effect of [RX] on the product distribution is small to non-existent over a range down to 0.2 M, at least (Section 7.2.13), implying that the flux and rate of reaction remain constant as [RX] varies. Explicit zeroth-order in RX has been found for the reaction of cyclopentyl bromide in diethyl ether containing LiBr j 1.5] and for reactions of adamantyl bromide, where a thick deposit (largely biadamantyl) forms on the Mg early in the reaction (Section 7.2.17) 165. ... 

Reaction of cyclopentanol with hydrogen bromide gives cyclopentyl bromide. Then cyclopentyl bromide can be eonverted to cyclopentyl cyanide, as shown in part a). 

Cyclohexyl and cyclopentyl bromides underwent rapid reaction with SbCl, in CCl to give vicinal trans- bromochlorides in high yield. The insertion compound of SbClj in graphite, Cj SbClj, was also employed with the above substrates, where the major products were cyclohexyl and cyclopentyl chlorides ca. 60 %) and smaller amounts (18—35%) of vicinal trans-bromochlorides. Cyclohexyl chloride was obtained in 86% and 22% yield from the iodide and tosylate. 

Whitesides group provided a significant contribution on Grignard reagents and has continued its study on the mechanism of formation of these compounds. The rate of reaction of cyclopentyl bromide with magnesium in rotating disc experiments is mass-transfer controlled. 

Specifically in the reaction of cyclopentyl bromide (R Br) in EtgO it was established that (/) -d[R Bi]jdt is proportional not only to [R Br] and the surface area of magnesium, but also to the rate of stirring of the solution and inversely proportional to the viscosity and (i7) the activation energy is small, ca. 2—3 kcal mol. There appears to be an upper limit to the rate of reaction of alkyl halides with magnesium. For less reactive halides, e.g., MeaCCHaBr, the rates are also dependent on the dielectric constant. 

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