Alkynes chlorinated/brominated

BRONZE POWDER (7440-50-8) The powder forms the friction-, heat-, or shock-sensitive explosive detonator, copper acetylide, with acetylene, acetylene compounds. Potentially violent reaction when finely dispersed powder comes into contact with strong oxidizers, ammonium nitrate, alkynes, azides, bromine vapor, bromates, calcium carbide, chlorates, chlorine, ethylene oxide, iodates, hydrazine mononitrate, hydrogen peroxide, hydrogen sulfide, iodates, finely divided iodine, lead azide, potassium peroxide, sodium peroxide, sulfuric acid. Incompatible with acids, anhydrous ammonia. 

Alkene/alkyne pair Bromination, Chlorination, Acid-catalyzed... 

The procedure for chlorination, bromination, and iodination of acetylenes in alkaline hypohalite solution432 is applicable to alkynes, alkynols, and acetylenemonocarboxylic acids with at least one hydrogen on the C=C group. 

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... 

Chlorine, bromine, and iodine react with alkenes to give the three-membered ring halonium ion, which reacts with the halide nucleophile to give trans dichlorides, dibromides, or diiodides. Alkynes react to give vinylhalonium ions that lead to vinyl dihalides 14,15,16,17,18,19, 20, 21, 22, 64, 73, 74, 75, 82, 83, 98,108. HOCl and HOBr react with alkenes to give halohydrins 23, 24, 75, 82, 83. 

Because vicinal dihalides are prepared by addition of chlorine or bromine to alkenes (Section 6 14) alkenes especially terminal alkenes can serve as starting mate rials for the preparation of alkynes as shown m the following example... 

Alkynes react with chlorine and bromine to yield tetrahaloalkanes Two molecules of the halogen add to the triple bond... 

Halogenation (Section 9 13) Addition of 1 mole of chlorine or bromine to an alkyne yields a trans dihaloalkene Atetrahalide is formed on addition of a second equivalent of the halogen... 

The iodination reaction can also be conducted with iodine monochloride in the presence of sodium acetate (240) or iodine in the presence of water or methanolic sodium acetate (241). Under these mild conditions functionalized alkenes can be transformed into the corresponding iodides. AppHcation of B-alkyl-9-BBN derivatives in the chlorination and dark bromination reactions allows better utilization of alkyl groups (235,242). An indirect stereoselective procedure for the conversion of alkynes into (H)-1-ha1o-1-alkenes is based on the mercuration reaction of boronic acids followed by in situ bromination or iodination of the intermediate mercuric salts (243). 

Bromine and chlorine also add to alkynes to give addition products, and trans stereochemistry again results. 

Alkynes show the same kind of reactions toward chlorine and bromine that alkenes do They react by addition. 

Most additions of chlorine and bromine to alkynes are anti additions and yield lrans-d haloalkenes. 

The isomerization of the smallest alkynes 80 with halogens in a propargylic position has been described for chlorine [151, 152], bromine [153] and iodine [154] (Scheme 1.35), but often might proceed by an SN2 -type substitution rather than a prototropic rearrangement [155-159]. On the other hand, transformations such as 82 —> 83 [160] or 84 —> 85 [161] are clearly prototropic (Scheme 1.36). This is also true for propargylic halides such as 86 with its additional ester group assisting the prototropic isomerization [162,163] (Scheme 1.37). 

Allenylcobaloximes, e.g. 26, react with bromotrichloromethane, carbon tetrachloride, trichloroacetonitrile, methyl trichloroacetate and bromoform to afford functionalized terminal alkynes in synthetically useful yields (Scheme 11.10). The nature of the products formed in this transformation points to a y-specific attack of polyhaloethyl radicals to the allenyl group, with either a concerted or a stepwise formation of coba-loxime(II) 27 and the substituted alkyne [62, 63]. Cobalt(II) radical 27 abstracts a bromine atom (from BrCCl3) or a chlorine atom (e.g. from C13CCN), which leads to a regeneration of the chain-carrying radical. It is worth mentioning that the reverse reaction, i.e. the addition of alkyl radicals to stannylmethyl-substituted alkynes, has been applied in the synthesis of, e.g., allenyl-substituted thymidine derivatives [64],... 

Alkene and alkyne Bromination, acetic acid Chlorination, acetic acid Acid-catalyzed hydration, water... 

Room-temperature ionic liquids may be used as green recyclable alternatives to chlorinated solvents for stereoselective halogenation.577 The bromination of alkenes and alkynes in [bmim][Br] is a/m -stereospecific, whereas that of 1,3-dienes gives selectively the 1,4-addition products. The reactions of arylacetylenes, however, are not selective when carried out in [bmim][PF6]. Tetraethylammonium trichloride, a stable crystalline solid may be used in the chlorination of alkenes and alkynes to afford the products with exclusive anti stereoselectivity.578 It has... 

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