Tetra-n-butylammonium tribromide

Subsequent kinetic and product distribution data on the reactions of 1,3-butadiene with molecular bromine, pyridine-bromine complex and tetra-n-butylammonium tribromide in chlorinated solvents have shown that pyridine-Br2 and tribromide ion act as independent electrophiles, rather than as sources of molecular bromine75. 

Halogens are frequently used as oxidation agents and, under two-phase conditions, they can either be employed as ammonium complex halide salts [3], or in the molecular state with or without an added quaternary ammonium catalyst [4]. Stoichiometric amounts of tetra-n-butylammonium tribromide under pH controlled conditions oxidize primary alcohols and low-molecular-weight alkyl ethers to esters, a,cyclic ethers produce lactones [3], and secondary alcohols yield ketones. Benzoins are oxidized to the corresponding benzils (80-90%) by the tribromide salts in acetonitrile in the presence of benzoyl peroxide [5]. 

C16H22011 b-D-galactose pentaacetate 4163-60-4 25.00 1.3200 2 29814 C16H36Br3N tetra-n-butylammonium tribromide 38932-80-8 25.00 1.3364 2... 

Somewhat less clear is the nature of catalysis by halogens and positive halogen compounds, such as I2 [176, 177], NBS [178], tetra-N-butylammonium tribromide [179], and hexamethylenetetramine-bromine complex [180]. These compounds would be expected to react with indoles by halogenations, generating the hydrogen halide as a by-product. Another halogenated catalyst, 2,4,6-trichlorotriazine, is believed to function by generation of HCl in the presence of moisture [181]. 

There was a solvent kinetic isotope effect on the tribromide reaction in CHCla/CDCla, with ku/kx) = 1.175, but there was no solvent isotope effect for the addition of Bra. Reaction with Bra (the third-order reaction, equation 9.7) gave a AH value of -8.4 kcal/mol, while the reaction with tribromide (equation 9.8) gave a AH value of -t- 6.0 kcal/mol. For reactions exhibiting third-order kinetics, the rate-limiting step appears to involve formation of a bromonium ion-tribromide ion pair from a complex of one alkene and two bromine molecules. With tetra-n-butylammonium tribromide as the source of bromine, the rate-limiting step is thought to be a backside nucleophilic attack at an olefin-Bra charge transfer complex (in equilibrium with Brs" and the olefin) by the ammonium bromide ion pair that has become detached from Bra at the moment of formation of the CT complex or that is present as added salt. ... 

CAUTION The brominating agent is a rruld lachrymator. It should be dispensed in the hood. An alternative solid brominating agent is tetra-N-butylammonium tribromide. 

As an alternative to the use of quaternary ammonium tribromide, A -bromosuccin-imide tetra-n-butylammonium bromide converts alkenes into the dibromoalkanes generally in high yield (>90%) [8]. It is probable that the ammonium tribromide is formed in situ. 

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