Sodium borohydride-bismuth chloride

Sodium borohydride-bismuth(III) chlorid Reduction of double bonds. This red bonds in such compounds as styrene and o.p... 

Chemical vaporisation. Some elements (such as arsenic, bismuth, tin and selenium) are difficult to reduce in a flame when they are in higher oxidation states. For these atoms, the sample is reacted with a reducing agent prior to analysis (sodium borohydride or tin chloride in acidic media) in a separate vessel. The volatile hydride formed is carried by a make-up gas into a quartz cell placed in the flame (Fig. 14.10). 

Mercury and those elements (antimony, arsenic, bismuth, germanium, lead, selenium, tellurium and tin) which form volatile covalent hydrides may be separated from the matrix by vapour generation. The use of tin(II) chloride to generate elemental mercury and its subsequent aeration into a long-path absorption cell with silica windows has been described elsewhere in this book, as has the use of sodium borohydride to produce hydrides which are swept to a flame or heated tube for atomisation. This approach is far more successful for mercury than for the other elements, as the hydride generation technique is subject to interference from a large number of transition metals and oxyanions. 

The Step 2 product (7.36 g) dissolved in 100 ml ethyl alcohol at 0°C was treated with bismuth chloride (2.84 g) followed by three 0.9 g additions of sodium borohydride and the mixture stirred 3 hours at ambient temperature. Ice water was added to the mixture and the crystallized inorganic deposits filtered out through celite. The filtrate was extracted with EtOAc, washed with water and brine, purified as in Step 1, and 7.40 g product isolated as a colorless oil. 

A combination of metallic bismuth or bismuth chloride and a reducing agent has been employed for the reduction of the nitro group and C-C/C-N double bonds, as shown in Schemes 5.21 and 5.22. The reducing ability and/or selectivity of sodium borohydride is improved considerably in the presenee of bismuth powder or bismuth chloride. 

Reduction of nitrobenzenes to aniiines with bismuth chloride-sodium borohydride typical procedure... 

Bismuth chloride (0.630 g, 2 mmol) was suspended in THF (25 ml), and sodium borohydride (0.076 g, 2 mmol) was added with stirring at ambient temperature. To the resulting black suspension was added 4-chloronitrobenzene (0.314 g, 2 mmol), followed by an additional amount of sodium borohydride (0.076 g, 2 mmol) in several portions at 60°C. The reaction mixture was stirred at 60°C for 1-2 h. After cooling, the solvent was removed under reduced... 

---