Bromination selective

XfjT Conversion m-nitro toluene Conversion bromine Selectivity benzyl bromide Selectivity benzal bromide Selectivity side product... 

Since bromine addition to olefins leads to brominated compounds of synthetic interest, there are many studies of bromination products in the literature. Typical examples have been reviewed by Schmid and Garratt (1977). However, there are few systematic product analysis studies related to the role of the structure and the solvent in determining bromination selectivities. 

Boron trifluoride etherate, co-catalyst, 53, 30, 32 a-Bromination, selective of aralkyl ketone, 53, 111 Bromine, with 3-chlorocyclo-butanecarboxylic acid and mercuric oxide to give 1-bromo-3-chlorocyclobutane, 51, 106... 

Bromine selectively suhstitutes for a henzylic hydrogen in toluene in a radical suhstitution reaction to produce hromomethylhenzene or henzylhro-mide. A-hromosuccinimide is used to carry out henzylic hromination of toluene. 

The index of refraction of bromine gas at 0° and 760 mm. for the /Mine is 1 001132 according to E. Mascart. The atomic refraction of liquid bromine, according to J. H. Gladstone, is 15 3 and, according to J. W. Briihl, 8 455 by the /t2-formula. The specific refraction, according to A. Haagen, is 01918. The refractive indices of liquid bromine, selected from measurements by C. Riviere, for rays of different wave lengths, at different temp, as indicated in Table I. These data show that the... 

Table 9.12 compares partial rate factors for substitution by phenyl radical with those for electrophilic bromination. Selectivity is clearly much lower for the radical substitution furthermore, for attacking phenyl radical, nearly all positions in the substituted benzenes are more reactive than in benzene itself, a finding that reflects the tendency for most substituents to stabilize a radical, and thus to lower transition state energy for formation of the cyclohexadienyl intermediate, when compared with hydrogen. The strong polar effects, which cause the familiar pattern of activation and deactivation in the electrophilic substitutions, are absent. One factor that presumably contributes to the low selectivity in radical attack is an early transition state in the addition step, which is exothermic by roughly 20 kcal mole-1.178... 

Such high selectivity induced by bromine on zeolite 5 A may be explainable by the idea that bromine is first activated to form Br with a OH site on zeolite SA, and thus the most active and less hindered para position of the aniline nucleus has dominant access to the Br that is located near a pore window of the zeolite, as an aniline molecule is too large to enter the pores of zeolite SA. It is interesting that the presence of organic bases such as pyridine or 2,6-lutidine not only improved the conversion, owing to neutralization of the generated HBr, but also increased the para-bromination selectivity. 

Bromination. Selective bromination of alkylbenzenes using the NaBrOj-NaHSOj system is reported. In aqueous EtOAc, benzylic bromination occurs, but in aqueous MeCN nuclear bromination predominates. 

Particularly mild methods of bromination are often wanted for treatment of unsaturated alcohols and ethers. One such is the use of pyridine dibromide hydrobromide, which, for example, adds bromine selectively to the C=C bond in an unsaturated side chain of a phenyl ether such as safrole which is brominated in the benzene ring when treated with molecular bromine alone. This reagent may be prepared in situ, by adding the calculated amount of bromine to a solution of the substance to be brominated and a pyridine salt in glacial acetic acid. 

The 11,12-double bond of the taxoids is rather unreactive to most reagents, because it is buried within the tetracyclic skeleton and is also tetrasubstituted. As examples of its general unreactivity, cephaloman-nine (2.1.1) can be brominated selectively on its side chain to give the dibromide 2.1.2 (30), and catalytic hydrogenation of taxol hydrogenates the aromatic rings but does not reduce the C-11,12 double bond (57) ... 

Chemical Tests. Several tests can be mn to determine the presence of unsaturation, aromatic character, and the presence of bromine. Select the appropriate tests from Chapter 9. Do your results confirm the presence of these groups ... 

A practical synthesis of nojirimycin from D-glucose has been described, giving an overall yield of 50% from 1,2-0-isopropylidene-D-glucofuranose oxidation of this compound with tributyltin oxide/ bromine selectively gave the 5-keto sugar, which was then converted to the 5-amino-sugar and hence to nojirimycin. The isolation of... 

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