Bromination s. a. Halogenation

Bromate s.a. Dichlorobromate Bromides s. Halides Bromination (s.a. Halogenation)... 

Rates of enolization can be measured in several wt s. One method involves determining the rate of halogenation of the ketone. In the presence of a sufficient concentration of bromine or iodine, halogenation is much faster than enolu ation or its reverse and can therefore serve to measure the rate of enolization ... 

Since bromination and chlorination result in a greater variety of di-substituted products of thieno[2,3-Zi]thiophene 1 than of thieno[3,2-6]-thiophene 2, the conclusion has been drawn that a halogen in position 2 in thienothiophene 1 deactivates position S to a lesser extent than in thienothiophene 2 and that the halogen deactivating effect in 1 is similar to that in thiophene. 

HOFMANN S REACTION. Reaclion used lor preparation of a primary amine from an amide by treatment with a halogen (usually bromine) and caustic soda. The resulting amine has one fewer carhon atom than the amide used. 

Acrylic acid derivatives with a heteroatom (N, O, S, Hal) at C-3 can be cleanly deprotonated at this position with BuLi or LDA at low temperatures [329, 333-338] (Scheme 5.37). Some of these anions rearrange to the a-metalated acrylates on warming [329], but can also decompose (see Section5.4.7). Non-heteroatom-substi-tuted lithium /3-lithioacrylate [329] or /3-magnesioacrylic acid derivatives [339, 340] have been prepared by bromine-lithium or halogen-magnesium exchange. 

Ley and Barton s observation that di-4-methoxyphenyltelluride could be used catalytically was the first entry into the use of in situ generated selenoxides or telluroxides as catalysts. As shown in Fig. 8, a variety of different nucleophiles can be introduced via the selenoxide or telluroxide followed by reductive elimination to generate oxidized product and reduced selenide or telluride. If the nucleophile is relatively inert to oxidation by hydrogen peroxide, then the reduced selenide or telluride can be reoxidized by hydrogen peroxide and the overall oxidation of the nucleophile becomes catalytic in the selenide or telluride. In the case of thiols, disulfides are the final product and the selenides or tellurides exhibit thiolperox-idase-like activity 60-62 64 82 83 If halide salts (chloride, bromide, iodide) are the nucleophiles, then positive halogen sources are the oxidized products and the selenides and tellurides exhibit haloperoxidase-like activity.84-88 The phenoxypro-pyltelluride 59 has been used as a catalyst for the iodination and bromination of a variety of organic substrates as shown in Fig. 24.87... 

OSHA PEL TW A 0.01 mg(A /m3 ACGIH TLV WA 0.01 mg(Ag)/m3 DOT CLASSIFICATION Forbidden SAFETY PROFILE Explodes when heated above 270°C or on impact. Pure silver azide explodes at 340°. An electric field or irradiation by electron pulses can explode the crystals. Shock-sensitive when dry and has detonated 250°C. Solutions in aqueous ammonia explode above 100°C. Reacts to form more explosive products with iodine (forms iodine azide) bromine and other halogens. The presence of metal oxides or metal sulfides increases the azide s sensitivity to explosion. Mixtures with sulfur dioxide are explosive. When heated to decomposition it emits toxic fumes of NO,. See also AZIDES and SILVER COMPOUNDS. 

HCl, HBr, and HI add to alkenes by a two-step electrophilic addition mechanism. Initial reaction of the nucleophilic double bond with H give.s a carbocation intermediate, which then reacts with halide ion. Bromine and chlorine add to alkenes via three-membered-ring bromonium ion or chloronium ion intermediates to give addition products ha%dng anti stereochemistry. If water is present during halogen addition reactions, a halohydrin is formed. 

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