Halogenation Bromination Chlorination

A different synthetic route involves halogenation (bromination, chlorination) of pyrene 77, which is thus converted to the tetrahalogen derivative. Oxidation with sulfuric acid to form a diperinaphthindandione with subsequent oxidation, once again in a sodium hydroxide solution [7], yields the tetra sodium salt of naphthalene tetracarboxylic acid 78 ... 

Monohalogenated products are obtained by treatment of this heterocycle (20) with elemental halogens (bromine, chlorine, or iodine) in concentrated sulfuric acid containing silver sulfate. This acidic reaction medium aids electrophilic attack by the positive halogen species on a protonated thienopyridine. Subsequently, nonacidic conditions have been identified for the monobromination reaction <74JHC205>. Monobromination of the isomers (21) and (23) has also been reported <70AK(32)249>. 

OH — X. Pi. carbohydrate hydroxyl group can be replaced by halogen (bromine, chlorine, iodine) by treatment in DMF with 2 eq. each of triphenylphosphine and an N-halosuccinimidc. The by-products are succinimide and triphenylphosphine oxide. Yields are generally high. Primary hydroxyl groups can be selectively replaced in the presence of secondary hydroxyl groups. 

Electrophilic addition of hydrohalic acids (hydrogen fluoride, hydrogen bromide, hydrogen chloride), carboxylic acids (e.g. acetic acid) and halogens (bromine, chlorine, iodine) to bicy-cloheptadiene gave a homoallyl cation which underwent rearrangement to nortricyclyl derivatives, i.e. 5-substituted tricyclo[2.2.1.0 ]heptanes. ... 

Incompatibilities and Reactivities Halogens (bromine, chlorine, carbonyl chloride, antimony pentachloride, tin(IV) chloride), water ... 

Air, copper, halogens (chlorine, bromine, iodine), alkali metals Acids, water, hydroxy compounds, polychlorinated hydrocarbons (for example, CCI, halogens, carbon dioxide, oxidants, terminal alkynes Halogens (bromine, chlorine. Iodine), hydrofluoric acid, liquid oxygen, calcium or sodium hypochlorite, heavy metals (silver, gold, mercury), nitric acid... 

Halogens - Bromine, chlorine and fluorine can all attack PARK as would be expected from their ability to halogenate aromatic... 

To determine which halogen is present, take 1-2 ml. of the filtrate from the sodium fusion, and add dilute sulphuric acid until just acid to litmus. Add about 1 ml. of benzene and then about 1 ml. of chlorine water and shake. A yellowish-brown colour in the benzene indicates bromine, and a violet colour iodine. If neither colour appears, the halogen is chlorine. The result may be confirmed by testing the solubility of the silver halide (free from cyanide) in dilute ammonia solution silver chloride is readily soluble, whereas the bromide dissolves with difficulty, and the iodide not at all. 

Another teat, which indicates the reactivity of the halogen atom (chlorine and bromine), is based upon the fact that sodium chloride and sodium bromide are sparingly soluble in pure acetone ... 

It IS convenient m equations such as this to represent generic alcohols and alkyl halides as ROH and RX respectively where R stands for an alkyl group In addition to con venience this notation lets us focus more clearly on the functional group transformation that occurs the OH functional group of an alcohol is replaced as a substituent on car bon by a halogen usually chlorine (X = Cl) or bromine (X = Br)... 

The reaction of an alcohol with a hydrogen halide is a substitution A halogen usually chlorine or bromine replaces a hydroxyl group as a substituent on carbon Calling the reaction a substitution tells us the relationship between the organic reactant and its prod uct but does not reveal the mechanism In developing a mechanistic picture for a par ticular reaction we combine some basic principles of chemical reactivity with experi mental observations to deduce the most likely sequence of steps... 

Halogenation Bromine reacts with benzene in the presence of iron(lll) bro mide as a catalyst to give bromobenzene Chlorine reacts similarly in the presence of iron(lll) chloride to give chlorobenzene... 

Halogenation Bromination and chlorination of phenols occur readily even in the absence of a cata lyst Substitution occurs primarily at the position para to the hydroxyl group When the para position IS blocked ortho substitution is observed... 

The halogen fluorides are binary compounds of bromine, chlorine, and iodine with fluorine. Of the eight known compounds, only bromine trifluoride, chlorine trifluoride, and iodine pentafluoride have been of commercial importance. Properties and appHcations have been reviewed (1 7) as have the reactions with organic compounds (8). Reviews covering the methods of preparation, properties, and analytical chemistry of the halogen fluorides are also available (9). 

Halogenation The commercially important halogens are chlorine, bromine, fluorine, iodine. Refer to Table 5.19 for properties All are highly toxic Reactions are highly exothermic and chain reactions can occur, which may result in detonation... 

The Halogens Fluorine, Chlorine, Bromine, Iodine and Astatine... 

---