F-Butyl bromide

Table 6 Non-adiabaticity calculations for the homogeneous electron transfer to di-tert-butylperoxide, di-cumylperoxide and f-butyl bromide (t-BuBr).

Use a very strong base as the nucleophile. When we use a relatively weak base, such as ethyl alcohol, only about 20% of f-butyl bromide undergoes elimination. 

A good way to work this problem is to start by writing structures for all compounds with the molecular formula C4H4Br. There are only four. The first compound must have nine equivalent hydrogens. The only possible structure is f-butyl bromide ... 

Evidence for an intermediate stannyl radical implication in such SET processes was obtained directly by a stopped flow technique in the reaction of tributylstannyl anion with s- and f-butyl bromides and iodides (Scheme 34, Figure 14)192. 

The elimination reaction of f-butyl bromide happens because the nucleophile is basic You will recall from Chapter 12 that there is some correlation between basicity and nucleophilicity strong bases are usually good nucleophiles. But being a good nucleophile doesn t get hydroxide anywhere in the substitution reaction, because it doesn t appear in the first-order rate equation. But being a good base does get it somewhere in the elimination reaction, because hydroxide is involved in the rate-determining step of the elimination, and so it appears in the rate equation. This is the mechanism. 

It has been argued that insight into catalytic mechanisms can most readily be obtained by choosing reactions whose rate-determining step is unimolecular. The reactions best known to be unimolecular in homogeneous media are undoubtedly the solvolyses of tertiary butyl halides [161-163]. Their SN1 mechanisms are typified by the solvolysis of f-butyl bromide in an ethanol + water medium... 

Compton et al. (1990a) examined the mediated reduction of f-butyl bromide ( BuBr) by the photochemically excited radical anion of tetrachlorobenzo-quinone (TCBQ) in acetonitrile solution using a channel electrode. Under dark conditions, the reduction of TCBQ proceeded via a simple reversible one-electron transfer process in the presence of BuBr. On photo-excitation of the radical anion of TCBQ, the limiting current associated with its formation was enhanced suggestive of the EC mechanism (88). 

The reagent reacts with organic halides or acid chlorides to give acid amides, generally in good yield.1 Alkyl iodides and f-butyl bromide do not undergo dimethylcarbamoyla-tion. However, Arl and alkenyl halides (RCH=CHX) react readily. 

Trimethyl- i-pentene, t-butyl chloride, f-butyl bromide, n-nonane, isobutylene, methyl chloride, ethyl chloride, methyl bromide, methylene chloride and n-hexane were obtained in high purity and further purified by standard methods before use. 

The monopotassium salt (103) and the dipotassium salt (105) can be prepared in quantitative yield from (101) and potassium hydroxide. Reaction of (105) in DMF with alkyl halides gives dialkylation products (106a) from benzyl bromide, (106b) from methyl iodide, (106c) from allyl bromide, and (106d) from f-butyl bromide in low yield. 

Yields are low when only catalytic amounts of the resin are used. Yields are high ( 90%) with primary alkyl halides, but lower with secondary alkyl halides. Only traces of esters are obtained from f-butyl bromide. 

Sludge catalyst (2, 20 3, 7). Details of the Princeton sludge catalyst have been published. It is a heavy yellow oil that can be stored for some time under cyclohexane. Activity can be augmented or restored by addition of AlBra. The catalyst probably consists of polymerized isobutene, formed by dehydrobromina-tion of f-butyl bromide. It has been used to rearrange hydrogenated Bisnor-S to diadamantane in 70% yield. 

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