Oxalyl bromide

In the acylation of enamines derived from 3-substituted cyclohexanones, 6-acylated products were favored over 2-acylated products (398), thus revealing another selective enamine reaction sequence. The use of oxalyl bromide for the acylation of enamines has also been described (399). 

Surface-mediated addition of HC1 or HBr can be carried out in the presence of silica or alumina.150 The hydrogen halides can be generated from thionyl chloride, oxalyl chloride, oxalyl bromide, phosphorus tribromide, or acetyl bromide. The kinetic products from HC1 and 1-phenylpropyne result from syn addition, but isomerization to the more stable Z-isomer occurs upon continued exposure to the acidic conditions. 

Experimental support for the above analysis of 2,3-disubstituted 1,3-dienes is available. For example, 2,3-dichlorobutadiene has been shown to exist preferentially in a planar tram geometry 20S A more interesting case is the conformational isomerism exhibited by oxalyl bromide and chloride. It is found that in the gas phase, these molecules exist in an equilibrium mixture of tram and gauche isomers but no detectable concentration of the cis conformation was observed206, 207 ... 

The existence of a large concentration of the gauche conformation implies that pi nonbonded interactions of the type discussed previously play some role in the conformational isomerism of oxalyl bromide and chloride. 

Interchange of halogen is a means of synthesis of certain acyl halides which cannot be conveniently prepared by other methods. Acetyl fluoride is made from acetyl chloride and sodium hydrogen fluoride in acetic anhydride solution." By passing a stream of hydrogen bromide through oxalyl chloride an 85% yield of oxalyl bromide, (COBr), is obtained. The bromide cannot be made by the action of phosphorus pentabromide on oxalic acid. The method has also been applied to the preparation of acetyl bromide and iodide and other acyl iodides. ... 

Oxalyl chloride, (COCl), and oxalyl bromide are similarly used to make acyl chlorides and bromides in excellent yield. The only other products of these reactions are the gases hydrogen halide, carbon monoxide, and carbon dioxide. For the preparation of acyl bromides, sodium salts rather than the free acids have been treated with oxalyl bromide. This procedure requires a smaller excess of reagent. 

Finally, among the various acyl halogen compounds, formyl fluoride, oxalyl chloride, oxalyl bromide, etc., are interesting possibilities as war gases. 

Oxalyl bromide, (COBr), has been obtained by the action of hydrobromic acid on oxalyl chloride. Heat decomposes it with production of carbon monoxide and carbonyl bromide. It reacts easily with water forming carbon monoxide, carbon dioxide and hydrobromic acid. 

Oxalyl bromide photolysis (mercury arc) to carbon monoxide and bromine has also been studied by Rollefson et Both in the gas phase and in carbon... 

A mild, and often superior reagent is oxalyl chloride (113) and oxalyl bromide, since oxalic acid decomposes to CO and CO2, and the equihbrium is thus driven to the side of the other acyl hahde. These reagents are commonly the reagent of choice, particularly when sensitive functionahty is present elsewhere in the molecule. 

Similarly, oxalyl bromide leads to 3-bromo-l,2-dithiolium bromides. Thiophosgene or Af-trichloromethyldichloromethanimine may also be used for converting either l,2-dithiol-3-ones or l,2-dithiole-3-thiones into the... 

Figure 2 Energy profiles along the torsional angle of oxalyl fluoride (- -), oxalyl chloride (—) and oxalyl bromide ( )...

Figure 2 displays the energy profiles of the trans cis rotational isomerization of oxalyl fluoride, oxalyl chloride, and oxalyl bromide. 

For all molecules the cis conformation is the absolute minimum, whereas the trans conformation is either a secondary minimum (oxalyl fluoride) or a maximum (oxalyl chloride and oxalyl bromide). Oxalyl bromide presents a shallow minimum corresponding to a gauche conformer. Substituting F by Cl yields a cusp catastrophe which changes the two maxima at tt/2 and the minimum at 0 into a maximum at 0. The substitution of Cl by Br is responsible for a dual-fold catastrophe in which two wandering points near 27t/3 give rise to a new minimum (gauche conformation) and a new maximum. 

Acetylthio-l,2-dithioIylium salts have been described.116 A variety of methods are available for the preparation of 3-halides. The reaction of oxalyl chloride with l,2-dithiol-3-ones gives 3-chloro-l,2-dithiolylium salts (66)116 (Scheme 6). In some cases the reaction can be realized with 1,2-dithiole-3-thiones too. Phosgene can be used instead of oxalyl chloride. Oxalyl bromide gives the corresponding 3-bromo-l,2-dithiolylium salts.117 3-Chloro-l,2-dithiolylium dichlorophosphates have been prepared from 1,2-dithiol-3-ones and phosphorus oxychloride.118 The corresponding... 

Oxalic acid, 15-16, 80, 764-767,1013 Oxalyl bromide, 767 Oxalyl chloride, 28, 29, 286, 767-772 Oxanthrone acetate, 543, 545 Oxasteroids, 201 Oxaziranes, 788 OxaioUdlnei, 379 Ouwlidonn, 748... 

Kuhlberg, Ann. 163, 123 (1872) von Miller, Ann. 188, 196 0877). Synthesis (Perkin reaction) Irom benzaldehyde, aoe-tic anhydride, and potassium acetate Org. Reactions 1, 248 (1942) from oxalyl bromide + styrene Treibs et aL, NatUr-wiss. 45, 85 (1958) from acetylene + benzaldehyde Her-betz, Her. 92, 541 (1959). Prepn of cis- and traui-isomers Comte et at. Compt. Rend. 245, 1144 (1957). lsoln from wood-rotting fungus, Stereum subpileatum Berk. St Curt. Birkinshaw et at, Biochem. J. 66, 188 (1957). 

Acid bromides can be obtained analogously from carboxylic acids or their Na salts by means of oxalyl bromide.1118... 

Oxalyl bromide, b.p. 102-103°/720 mm, is obtained in 85% yield by passing HBr [8 moles per mole of (COCl)2] into pure oxalyl chloride (100 g) for about 12 h and, after a further 6 h, fractionating the mixture. Discoloration due to bromine is removed by shaking with mercury.1109... 

Diketones can be obtained by use of dicarbonyl dichlorides, e.g., 1,6-di-phenyl- 1,6-hexanedione in 81% yield from adipoyl dichloride.549 For the use of oxalyl bromide see page 980. 

Further, oxalyl bromide (or the chloride), at low temperature in the absence of a catalyst, gives very good yields of the very reactive oc-oxo carbonyl bromides ... 

DBN (2) is prepared in 92% yield by treatment of A-(3-azidopropyl)-y-lactam with oxalyl bromide after quenching with anisole (run 3). A trace of the reaction by IR spectrum suggests the formation of a bromoiminium intermediate, which spontaneously cyclizes to the bicyclic system through either 1,2-addition (path A) or [3 + 2]cycloaddition (path B) (Scheme 3.12). 

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