Reducing agents sodium borohydride

Fructose bisphosphate aldolase of animal muscle is a Class I aldolase, which forms a Schiff base or imme intermediate between the substrate (fructose-1,6-bisP or dihydroxyacetone-P) and a lysine amino group at the enzyme active site. The chemical evidence for this intermediate comes from studies with the aldolase and the reducing agent sodium borohydride, NaBH4. Incubation of fructose bisphosphate aldolase with dihydroxyacetone-P and NaBH4 inactivates the enzyme. Interestingly, no inactivation is observed if NaBH4 is added to the enzyme in the absence of substrate. 

An analogous series of reactions is involved when sodium borohydride is used as the reducing agent. Sodium borohydride is considerably less reactive than LAH, and reactions proceed much more slowly. This reagent may be used in alcoholic or even aqueous solution, so there are no particular hazards associated with its use. 

Application in reductive aminition Aniline can be used in reductive aminition reactions. For example, aniline can be converted to A-isopropy-laniline by the reaction with acetone (CH3COCH3) in the presence of the reducing agent sodium borohydride (NaBH4). 

A solution of appropriate salts can also be reduced in the liquid phase by the addition of an appropriate reducing agent. Sodium borohydride has been used but care must be taken to remove the boron from the catalyst, particularly for the mixed noble metals. This has been accomplished by adding a dilute borohydride solution to the mixed metal salt solution under rapid agitation followed by a thorough washing of the precipitated metal black with warm water.The use of hydrazine, formaldehyde or formic acid is preferred to borohydride since the byproducts of the reduction do not contaminate the catalyst. Another procedure is to use a ternary alloy and to leach out one component as in the preparation of Raney nickel and similar catalysts. 

In 1956 Herbert C. Brown (b. 1912) discovered that in ethereal solution diborane (B2H5) dissociates into borane (BH3), which can add to an alkene. The organoborane formed can be converted to an alcohol by treatment with hydrogen peroxide, and the overall result of this hydroboration reaction is the anti-Markovnikoff addition to the double bond. Brown was also responsible for the introduction into organic chemistry of the reducing agents sodium borohydride (sodium tetrahydridoborate(lll)) and lithium aluminium hydride (lithium tetrahydridoaluminate(lll)). 

There are two common hydride reducing agents sodium borohydride (7 NaBH4) and lithium aluminum hydride (8 LiAlH4). Borohydride is an ate complex (see Chapter 6, Section 6.5.4, for definition of an ate complex) of BHg (7 is a tetrahydridoborate) and aluminum hydride is an ate complex of AlHg (8 is a tetrahydridoaluminate their respective lUPAC names are sodium tetrahydridoborate and lithium tetrahydridoaluminate. The borate anion is the Lewis acid-Lewis base complex of BHg (borane) and a hydride, whereas the alumi-nate anion is the Lewis acid-Lewis base complex of AlHg (aluminum hydride) and a hydride. Examination of the periodic table reveals that hydrogen is more... 

The second, used for arsenic and antimoiy uses an extremely powerful reducing agent, sodium borohydride, which converts arsenic and antimoi in solution into arsine and stibine gas respectively. This is then swept into a heated sihca tnbe where it decomposes to neutral atoms of arsenic (or antimoi ) in the hght beam. 

The metal precursor silver nitrate (Reanal, purity 99.9%), palla-dium(II) chloride, rhodium(III) chloride hydrate (purity 98 /o), and the reducing agent sodium borohydride (purity 99%) were obtained from Aldrich. A polymer was used to stabilize the Pd and Rh nanoparticles poly(A-vinyl-2-pyrrolidone) (PVP, K-30, average molecular weight 4x10" g, Fluka). 

Since this method involved the use of a reducing agent, sodium borohydride, Zhu developed several methods in which amines, such as 7, were covalently linked to solid supports and water solution containing OPA was passed through the support. OPA was scavenged by forming a Schiff s base, 9, with the amines on solid supports. Silica was a common choice for this solid... 

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