Bromination bromo

Brom-. of or combined with bromine bromo- (as Brombenzoeadure, bromobenzoic acid) bromide of (as Brombaryum, barium bromide). -ammoD, tn., ammonium, n. ammonium bromide, -antimon, n. antimony bromide, -arsen, n., -arsem k, tn. arsem c bromide. ather, tn. ethyl bromide, -athyl, n. ethyl bromide. athylen, n. ethylene bromide, athyiformin, n. Pharm.) bromalin. -atom, n. bromine atom, -baryum, n. barium bromide. beere, /. blackberry, brombeerrot, a. blackberry ed. 

ALKYL BROMIDES Bromine. Bromo-triniethylsilane. Chlorotrimethylsilane-Lithium bromide. 

Benzene ring system Peroxybenzoic acid Succinic acid Pumice Lead Boron Boric acid Boron trioxide Pyruvic acid Bromine Bromo-... 

Certain phenols give white bromo derivatives with bromine water. 

On adding i drop of bromine water to catechol, a deep red coloration is produced immediately. On gradually adding bromine water to a solution of hydroquinone, a deep red coloration is produced, followed by the separation of deep green crystals which then dissolve giving a yellow solution, i- and 2-Naphthol will decolorise hromine water, but usually no precipitate of the bromo compound can be obtained. 

The conversion of an aliphatic carboxylic acid into the a-bromo- (or a-chloro ) acid by treatment with bromine (or chlorine) in the presence of a catal3rtic amount of phosphorus tribromide (or trichloride) or of red phosphorus is known as the Hell-Volhard-Zelinsky reaction. The procedure probably involves the intermediate formation of the acyl halide, since it is known that halogens react more rapidly with acyl haUdes than with the acids themselves ... 

The bromine adds on at the ethylenic linkage to form thedibromo compound (I), which easily loses hydrogen bromide to give the mono-bromo keto ester (II) ... 

An alternative procedure, more suitable for the preparation of somewhat larger quantities of the bromo derivative, is the following. Dissolve 10 g, of the compovmd in 10-15 ml. of glacial acetic acid, cautiously add 3-4 ml. of hquid bromine, and allow the mixture to stand for 15-20 minutes. Pour into 50-100 ml. of water, filter off the bromo compound at the pump, and wash with a httle cold water. Recrystallise from dilute alcohol. 

Fluorescein is obtained by condensing phthahc anhydride (1 mol) with resorcinol (2 mols) in the presence of anhydrous zinc chloride. The tetra-bromo derivative, readily prepared by the addition of the calculated quantity of bromine, is eosin. 

MO-Valeric acid is converted by phosphorus and bromine into a-bromo-tso-valeryl bromide the latter upon beating with urea gives bromural ... 

Equip a 1 litre bolt-head flask with dropi)ing fuuncl and a double surface reflux condenser to the top of the latter attach a device (e.g.. Fig. II, 8, 1. c) for the absorption of the hydrogen bromide evolved. Place 100 g. (108 ml.) of dry iso-valeric acid (Section 111,80) and 12 g. of pmified red phosphorus (Section 11,50,5) in the flask. Add 255 g. (82 ml.) of dry bromine (Section 11,49,5) slowly through the dropping funnel at such a rate that little or no bromine is lost with the hydrogen bromide evolved the addition occupies 2-3 hours. Warm the reaction mixture on a water bath until the evolution of hydrogen bromide is complete and the colour of the bromine has disappeared. Pour off the liquid reaction product into a Claisen flask and distil mider the reduced pressure of a water pump. Collect the a-bromo-wo-valeryl bromide at 117-122°/25-30 mm. The yield is 150 g. 

METHOD 2 This method is a backup use for all that bromo-safrole or phenylisopropyl-bromide that the chemist made. It is the simplest method in the entire book, uses the cheapest most basic ingredients and happens to be the first method that Strike ever studied [59]. Strike does not have many fond reminiscences about this method because it kind of sucks but the chemistry is so basic that it may well serve the most pathetic chemist. The reaction proceeds as follows which uses ammonia to replace the bromine giving MDA or amphetamine directly ... 

All this business of swapping out bromine would be a lot easier if that bromine were at the end of that aliphatic chain which would make it a primary bromine (don t ask). As it so happens, the bromine in bromo-safrole is at a secondary position which means that... 

The high nucleophilicity of sulfur atoms is preserved, even if it is bound to electron withdrawing carbonyl groups. Thiocarboxylales, for example, substitute bromine, e.g. of a-bromo ketones. In the presence of bases the or-acylthio ketones deprotonate and rearrange to episulfides. After desulfurization with triphenylphosphine, 1,3-diketones are formed in good yield. Thiolactams react in the same way, and A. Eschenmoser (1970) has used this sequence in his vitamin B]2 synthesis (p. 261). 

A classical reaction leading to 1,4-difunctional compounds is the nucleophilic substitution of the bromine of cf-bromo carbonyl compounds (a -synthons) with enolate type anions (d -synthons). Regio- and stereoselectivities, which can be achieved by an appropiate choice of the enol component, are similar to those described in the previous section. Just one example of a highly functionalized product (W.L. Meyer, 1963) is given. 

Acetamidothiazole (203) gives, according to the brominating agent, either 4-bromo- (204) or 2,4-dibromo-5-acetamidothiazole (205) (Scheme 129) (388). 

Bromination occurs on the 5-positton of the ring the bromo compound... 

As a further electrophilic substitution the bromination of selenazoles has been investigated. This is not as complicated as nitration. Bromination was carried out in several solvents and with various amounts of bromine. In spite of the great variation in conditions, monobromo derivatives containing the bromine atom in the 5-position are always formed. This could be established, for example, by the bromination of the 2-amino-4-p-nitrophenylselenazole (Scheme 34) and its 2-benzamino compound (98). The 2-benzamido bromo compound gives the same bromo... 

The 2-anilinoselenazoles follow an analogous reaction path. The entry of bromine into the 5-position is in agreement as seen in Scheme 35. The 2-anilino-4-phenylselenazole gives a 5-bromo derivative by bromination. It is not identical with either of the bromo derivatives prepared by direct synthesis (Scheme 35) (99). 

Bromination of 2,4-dimethylselenazole with cold bromine gives an unstable monobrominated derivative initially (m.p. 168°C). which is easily converted to a product [m.p. 205°C (decomp.)] considered by Haginiwa to be 5-bromO-2,4-dimethylselenazole hydrobromide (19). 

Unlike nitration. 2-amino-4-methylselenazole can be directly bromi-nated, using bromine in carbon tetrachloride solution, to give 2-amino-5-bromo-4-methylselenazole hydrobromide [m.p. 180°C (decomp.)] (19). The free base cannot be isolated. Use of excess of bromine can lead to destruction of the molecule. 

Replacement of the proton on nitrogen in succinimide by bromine gives N bromo succinimide a reagent used for allylic and benzylic brominations (Sections 10 4 and 1112)... 

X0 group present in hecogenin (79) is transferred to C-11 (84). Bromination of hecogenin in ben2ene yields the lla,23a-dibromo derivative (80). The latter is treated with sodium hydroxide in aqueous /-butanol to yield the crystalline 23-bromo-ketal (81) which is acetylated and then debrominated with... 

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