Butyl bromide intermediate

Neopentyl (2,2-dimethylpropyl) systems are resistant to nucleo diilic substitution reactions. They are primary and do not form caibocation intermediates, but the /-butyl substituent efiTectively hinders back-side attack. The rate of reaction of neopent>i bromide with iodide ion is 470 times slower than that of n-butyl bromide. Usually, tiie ner rentyl system reacts with rearrangement to the /-pentyl system, aldiough use of good nucleophiles in polar aprotic solvents permits direct displacement to occur. Entry 2 shows that such a reaction with azide ion as the nucleophile proceeds with complete inversion of configuration. The primary beiuyl system in entry 3 exhibits high, but not complete, inversiotL This is attributed to racemization of the reactant by ionization and internal return. 

If the intermediate reacts with Y (which may be the solvent) to give product much faster than it does with X to revert to reactant, then Eq. (8-65) will tend to the simple first-order form, v = A i[R-X]. In aqueous solvents /m-butyl bromide exhibits this kinetic behavior. 

The driving force behind this remarkable reaction in which the sulphone participates intramolecularly in a 5-exo-tet ring closure process96 is that the geometry of the intermediate bromonium ion is nicely set up for the attack by the sulphone oxygen. Probably, the process is assisted by the ready cleavage of the sulphur to the t-butyl bond, with the concomitant formation of t-butyl bromide. 

The first example of chemically induced multiplet polarization was observed on treatment of a solution of n-butyl bromide and n-butyl lithium in hexane with a little ether to initiate reaction by depolymerizing the organometallic compound (Ward and Lawler, 1967). Polarization (E/A) of the protons on carbon atoms 1 and 2 in the 1-butene produced was observed and taken as evidence of the correctness of an earlier suggestion (Bryce-Smith, 1956) that radical intermediates are involved in this elimination. Similar observations were made in the reaction of t-butyl lithium with n-butyl bromide when both 1-butene and isobutene were found to be polarized. The observations were particularly significant because multiplet polarization could not be explained by the electron-nuclear cross-relaxation theory of CIDNP then being advanced to explain net polarization (Lawler, 1967 Bargon and Fischer, 1967). 

Co(TPP) has been demonstrated to act as a catalyst for the electrocarboxylation of benzyl chloride and butyl bromide with CO - to give PhCHiCfOiOCH Ph and Bu0C(0)C(0)0Bu, respectively. The propo.sed mechanism involved Co(TPP)R and [Co(TPP-N-R) as intermediates (the latter detected by spectroscopy) in the catalytic production of free R or R-, which then reacted directly with Co(TPP) precipitated on graphite foil has been successfully used for the determination of organic halides, including DDT and 1,2,3,4,5,6-hexachlorocyclohexane (lindane), to sub-ppm level in aqueous solution. Deoxygenation of the solutions is not required, and the technique is moderately insensitive to the ionic composition of the solution. ... 

The [4+1] annulation of 1-azadienes to pyrroles can also be achieved through their carbonyl iron complexes (Scheme 6). Novel complex (1,4-diphenyl-2-methyl-l-azabutadiene)tricarbonyliron (0) 24 was obtained in 40% yield from the corresponding azadiene 23 and Fe2(CO)9 then nucleophilic attack by methyl lithium and quenching with tert-butyl bromide, as the proton source, gave 2,5-dimethyl-l,3-diphenylpyrrole 26 in 70% yield, probably through the anionic intermediate complex 25 [88TL1425 90JCS(P1)761]. 

Addition of HBr to 2-methylpropene gives mainly tert-butyl bromide, because the product with the more stable carbocation intermediate always predominates in this type of reaction. 

The El reaction involves the formation of a planar carbocation intermediate. Therefore, both syn and anti elimination can occur. If an elimination reaction removes two substituents from the same side of the C—C bond, the reaction is called a syn elimination. When the substituents are removed from opposite sides of the C—C bond, the reaction is called an anti elimination. Thus, depending on the substrates El reaction forms a mixture of cis (Z) and trans (E) products. For example, tert-hutyl bromide (3° alkyl halide) reacts with water to form 2-methylpropene, following an El mechanism. The reaction requires a good ionizing solvent and a weak base. When the carbocation is formed, SnI and El processes compete with each other, and often mixtures of elimination and substitution products occur. The reaction of t-butyl bromide and ethanol gives major product via El and minor product via SnI-... 

But the addition product is 99+% tert-butyl bromide so the reaction clearly is kinetically controlled, tert-butyl bromide being formed considerably faster than isobutyl bromide. The slow, or rate-determining, step in this reaction is the formation of the intermediate cation rather than the reaction of the cation with bromide ion. So to account for the formation of tert-butyl bromide we have to consider why the tert-butyl cation is formed more rapidly than the isobutyl cation ... 

The residue from which no more alcohol can be distilled is treated with about 2 1. of water and shaken thoroughly. The upper layer of M-butylmalonic ester is separated (Note 4) and distilled under diminished pressure from a 2- or a 3-I. Claisen flask. First a low-boiling portion is collected, consisting of alcohol, water, and butyl bromide then a small intermediate fraction of unchanged malonic ester comes over and finally tt-butylmalonic ester boiling at i40-i45°/40 mm., i3o-i3S°/2o mm., and 235 240°/76o mm. The first fractions amount to less than 100 cc., while the main fraction amounts to 860-970 g. (80-90 per cent of the theoretical amount). 

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. 

Another important factor to deduce the involvement of radicals in a transition metal-catalyzed process is the integrity of stereocenters. In oxidative addition or Sr 2-type processes the stereochemical information - retention or inversion, respectively - is preserved for optically active substrates like sec-butyl bromide (Sect. 2.2), while racemic products are observed when radical intermediates are generated. On the other hand, stereochemical convergence is observed for strongly biased diastereomeric substrates, such as exo- and endo-norbomyl substrates 25 (Fig 9) The reactions occur almost exclusively at the exo-face of the norbomyl... 

We have proposed that, under the conditions we have described, methyl bromide reacts with hydroxide ion by the Sn2 mechanism, and that ferf-butyl bromide reacts by the SnI mechanism. Since 5ec-alkyl bromides are intermediate in structure between these two halides, it is not surprising to find that they can react by either or both mechanisms. 

The UV spectra of the radicals R3S11 have been observed in the non-chain reaction of Bu3SnK with s- and t-butyl bromides 48 A CIDNP effect in the 119Sn NMR spectra of the Bu3SnSnBu3 and Bu4Sn which are formed from the reaction of Bu3SnK with n-butyl bromide and iodide, similarly confirms the formation of intermediate R3Sn" radicals.49... 

In contrast, the hydrolysis of tm-butyl bromide (2-bromo-2-methylpropane) occurs in a stepwise manner (reaction 1.1b). In the first slow step, the C-Br bond breaks, with the bromine atom taking both electrons from the bond and leaving as a negatively charged bromide ion. The remainder of the molecule is the positively charged tert-butyl cation (2-methylprop-2-yl cation). This is a highly reactive intermediate, which reacts rapidly with the hydroxide ion to form the corresponding alcohol. 

A new and little understood technique that is worthy of attention is chemically induced dynamic nuclear polarization (CIDNP). A hexane-ether solution containing w-butyl-lithium, n-butyl bromide and diphenylacetylene, gives a transient spectrum resembling that of but-l-ene in which some of the lines are inverted. The authors ascribe the phenomena to the presence of free-radical intermediates, although the lines show no evidence of broadening due to paramagnetic induced relaxation. See also ref. 7a. 

Neopentyl (2,2-dimethylpropyl) systems are resistant to nucleophilic substitution reactions. They are primary and do not form carbocation intermediates moreover the r-butyl substituent hinders back-side displacement. The rate of reaction of neopentyl bromide with iodide ion is 470 times less than that of n-butyl bromide. Under solvolysis conditions the neopentyl system usually reacts with rearrangement to the... 

Table 1. Reactivity of polar organometallic intermediates towards butyl bromide in 1 1 mixtures of THF and hexane temperature ranges for butylation with n-C4H9Br in preparative experiments...

Both 1-methylpyrrole and 1-methylindole can be easily lithiated and the resulting intermediates have been used extensively in synthesis. The range of electrophiles which can be used with lithiated pyrroles and indoles is quite broad. Aldehydes and ketones give carbinols. A,A-Disubstituted formamides give aldehydes. Carbon dioxide and alkyl chloroformates have been used to make carboxylic acid derivatives. Alkyl halides, sulfates and sulfonates can be used to introduce alkyl groups. Interestingly, even t-butyl bromide has been used successfully for alkylation (see entry 3, Table 7). Some examples are given in Table 7. 

---