2- bromo-2-iodo-acetic acid

Pyridine and chloroacetic acid react normally to give the stable betaine derivative, but 2,5-dimethylpyrazine is quite different in its behavior. Chloroacetic acid is without action while both bromo- and iodo-acetic acid react smoothly, more rapidly in nitrobenzene than in... 

The limited knowledge of thermal behaviour of halogenated acids has been extended significantly by a pyrolysis (infrared laser-powered) and semiempirical study which has established that mono-, di- and tri-chloroacetic, trifluoroacetic, and bromoacetic acid eliminate HX and that both bromo- and iodo-acetic acid undergo C—X bond homolysis acetic acid undergoes decarboxylation and dehydration under the same conditions.46 The semiempirical calculations of corresponding activation energies are consistent with these conclusions. 

Bromo- bzw. iodo-acetic acid Cleavage Product after cleavage ... 

Benzene- 1,2-diacetonitriles e.g. 19, in the presence of hydrogen bromide in acetic acid, or in diethyl ether, cyclize to 4-bromo-l //-3-benzazepin-2-amines, e.g. 20a.41,42 l//-Naphtho[2,3-t/]azepines, e.g. 22a, are prepared in a similar manner from naphthalene-2,3-diacetonitriles, e.g. 21.41 Replacement of hydrogen bromide by hydrogen iodide yields the corresponding 4-iodo derivatives, e.g. 20b and 22b. 

More convenient for the formation of aryl fluorides 4 is the decomposition of triazenes with hydrogen fluoride/pyridine (70 30 w/w) mixture, easier to handle than pure hydrogen fluoride. In this case, decomposition is performed at a lower temperature (18-50°C) and acetic acid, for example, is a suitable solvent.299 However, radical side reactions can be more pronounced, especially with bromo-, iodo-, nitro- or 2-methoxy-subslituted substrates. 

Chloroindole has been prepared from indole and sulfuryl chloride (66JOC2627) and 3-bromo- and 3-iodo-indole have been obtained by direct halogenation in DMF (82S1096). 2-Methylindole reacts with sodium hypochlorite in carbon tetrachloride to give a 2 1 mixture of 1,3- and 3,3- dichloro derivatives (81JOC2054). 3-Substituted indoles are halogenated to yield 3-haloindolenium ions which react in a variety of ways, as illustrated by the reaction of 3-methylindole with NBS in aqueous acetic acid (Scheme 12). 

In contrast with the relatively facile nucleophilic substitution reactions at the 2-position of the indole system, only 3-iodoindole has been reported to react with silver acetate in acetic acid to yield 3-acetoxyindole (59JOC117). This reaction is of added interest as 3-iodo-2-methylindole fails to react with moist silver oxide (72HC(25-2)127). It is also noteworthy that the activated halogen of ethyl 3-bromo-4-ethyl-2-formylpyrrole-5-carboxylate is not displaced during the silver oxide oxidation of the formyl group to the carboxylic acid (57AC(R)167>. 

An important advance was made when it was observed that photolysis of the (3-enamido ketone 165, which was readily available from the indoline 163 by Birch reduction followed by N-aryloylation, delivered the lactam 168 as the only photoproduct (Scheme 17) (125). Reduction of 168 with LiAlH4 gave ( )-a-anhydrodihydrocaranine (143), which was then converted to ( )--y-lycorane (93) on hydrogenation over Adams catalyst in acetic acid. In a similar fashion, irradiation of the bromo or iodo enaminones 166 (Z = Br, I), which were obtained by alkylation of the intermediate imino ether formed on Birch reduction of 163, afforded a mixture (approximately 3 2) of the lactam 168 together with the photoreduction product 167 (126). 

Bromination of 67a in acetic acid gives first the 2-bromo, then the 2,3-dibromo derivative.290 The 2-iodo derivative is obtained by iodination of... 

Knoevenagel and Polack733 have given directions for the preparation of aromatic sulfinic anhydrides by the action of acetic anhydride on a suspension of the dry sulfinic acid in a little acetic acid. The reaction is catalysed by sulfuric acid or a 0.1% solution of iron(m) chloride in glacial acetic acid or acetic anhydride. Benzene-, / -toluene-, / -xylene-, pseudocumene-, mesitylene-, and / -bromo- and / -iodo-benzene-sulfinic anhydride have been obtained in this way. 

Bromination of (115) with bromine or iodination with iodine monochloride gave the respective 3-bromo (116) and 3-iodo (117) derivatives, while nitration with nitric and sulfuric acids in glacial acetic acid led to the formation of the corresponding 3-nitro (118) derivative <92BCJ3419>. Nitration of (98) with nitric and sulfuric acids gave a mixture of the nitroso (119, 85%) and nitro (120, 15%) derivatives. No nitration occurred on the imidazole ring <84JCR(S)28>. 

---