Bromides s. Halides Replacement

Si-Bridges, elimination 21, 970 Bromide ion 21, 879 Bromides s. Halides, Replacement... 

Bridges, formation, stereospecific 23, 276 S-Bridges 22, 607, 622 23, 601 Si-Bridges, elimination 21, 970 Bromide ion 21, 879 Bromides s. Halides, Replacement... 

Bridges s. Methylene bridg..., Steroids, bridged Bromides s. Halides Bromination s. Halogenation, Replacement of hydrogen by halogen... 

In the first systematic study on nucleophilic substitutions of chiral halides by Group IV metal anions, Jensen and Davis showed that (S )-2-bromobutane is converted to the (R)-2-triphenylmetal product with predominant inversion at the carbon center (Table 5)37. Replacement of the phenyl substituents by alkyl groups was possible through sequential brominolysis and reaction of the derived stannyl bromides with a Grignard reagent (equation 16). Subsequently, Pereyre and coworkers employed the foregoing Grignard sequence to prepare several trialkyl(s-butyl)stannanes (equation 17)38. They also developed an alternative synthesis of more hindered trialkyl derivatives (equation 18). 

I would like to bring up a couple of points here because I think Basolo and Baddley s experiment of blocking the fifth and sixth positions is a very good one. I would like to ask them if they would do the experiment, if they have not done it, in which chloride, bromide, and iodide are replaced as leaving groups to see if the order reverses to give the octahedral halide leaving order, rather than the planar one in which iodide is slower than chloride. This would help firm up this case. 

An intermediate in Hudson s synthesis4 of D-rhamnose (24) is methyl 2,3,4-tri-0-benzoyl-6-deoxy-a-D-mannoside (25). Frequently, direct replacement of the methoxyl group at C-l of O-acylated hexopyranosides by halide proceeds with difficulty (or not at all) however, treatment of (25) with hydrogen bromide in acetic acid resulted in the slow replacement of the methoxyl group by bromide ion, to give the desired 2,3,4-tri-O-... 

Cognate preparations. s-Butyl bromide (2-bromobutane). The quantities required are as for butyl bromide but with butan-2-ol (b.p. 99-100 °C) replacing the butan-l-ol. Two to three washings with concentrated hydrochloric acid are necessary, i.e. until the volume of the acid layer remains unchanged on shaking with halide. The yield of s-butyl bromide, b.p. 90.5-92.5 °C, is 150 g (92%). 

Crystallography revealed a bound chloride ion at the amino terminus of the helix containing the proximal His336 which can be replaced with bromide. Crystal structures of the human MPO-cyanide, MPO-cyanide-bromide, and MPO-cyanide-thiocyanate have also been determined by Fenna and coworkers to 1.9 A. These results support a model for a single common binding site for halides and thiocyanate as substrates or as inhibitors near the S-meso carbon of the porphyrin ring in myeloperoxidase. 

Vinyl halides. The method of Normant et al. (6, 270) for preparation of vinylcopper compounds can be used to obtain vinyl halides. Reaction of 1 with iodine gives vinyl iodides directly, but this reaction when extended to Bf2 or CI2 gives mainly dimers. The desired vinyl chlorides and bromides canTte obtained with NCS or NBS in fair to good yields. The replacement occurs with retention of initial stereochemistry. The American group also stresses the importance of the purity of the copper salt and uses House s cuprous bromide complex with dimethyl sulfide (6, 270). 

After Charles Richet had proved that acid secreted by the stomach is hydrochloric acid, he wondered whether the stomach can also secrete hydrobromic acid. He fed a dog some sodium bromide, but he could not find any bromide in the dog s gastric juice. Pavlov s collaborator, Shumova-Simanovskaya, reported in 1894 that she and Nencki had fed a dog increasing amounts of sodium bromide, for a total of 53 g in 9 days. They stated the halide concentrations in percentages to three decimal places. I have converted the values to millinormality to show the stochiometric relations between the ions that were not recognized by Shumova-Simanovskaya and Nencki. A control sample of gastric juice was 145 mN in HCl, and one of their experimental samples was 89 mN in Cr and 49 mN in Br. Bromide replaced chlo-ride. ... 

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