Sodium Borohydride, NaBH

The tetrahydridoborate ion, as "sodium borohydride" NaBH is soluble in water and is similarly an excellent reducing agent in this solvent. (Lithium tetrahydridoaluminate cannot be used in water, with which it reacts violently to give hydrogen.)... 

Recent papers by a manufacturer of sodium borohydride, NaBH (145,146), have demonstrated that excellent removal of metals and color of acid, direct, and reactive dyes for textiles and paper can be achieved with bisulfite-catalyzed borohydride reduction in combination with polymer flocculation. 

Ketones undergo a reduction when treated with sodium borohydride, NaBH What is the structure of the compound produced by reaction of 2-butanone with NaBH4 if it has an IR absorption at 3400 cm-1 and M+ = 74 in the mass spectrum ... 

Very recently, ball milling was also nsed to synthesize sodium borohydride, NaBH, by mechano-chemical reaction of dehydrated borax (Na B O,), MgH and Na COj (at room temperature) according to the following reaction [176]... 

R.A. Varin, Ch. Chiu, Structural stability of sodium borohydride (NaBH ) during controlled mechanical milling , J. Alloys Compd. 397 (2005) 276-281. 

Reduction of a ketose yields a secondary alcohol, and reduction of an aldose yields a primary alcohol (ccilled an alditol). A possible reducing agent is hydrogenation in the presence of a catalyst, such as platinum another reducing agent is sodium borohydride (NaBH ) followed by hydrolysis. Figure 16-14 illustrates the formation of an alditol. 

Excellent results are obtained with LiAIH4 (see Section 16-4E), which is fairly selective and normally does not reduce C=C. Sodium borohydride, NaBH , is more selective and does not reduce carbonyl groups of acids and derivatives it also may be used in aqueous and alcoholic solution, whereas LiAIH4 may not. Borane (BH3) in oxacyclopentane readily reduces aldehydes and acids to primary alcohols (Section 16-4E). 

Carboxylic acids and acid derivatives are not reduced by the milder reducing agent such as sodium borohydride (NaBH). This reagent can, therefore, be used to reduce aldehydes and ketones without affecting any carboxylic acids or acid derivatives which might be present. 

In this section, details of an easily controllable, safe method for producing high-purity H2 gas are described. This method of generating H2 gas is particularly suitable for providing a clean source of H2 gas for use as an anodic fuel in fuel cells or as a fuel for internal combustion engines in transportation applications. This compact, portable H2 generator is based on a non-pressurized, aqueous solution of alkaline sodium borohydride (NaBH, tetrahydroborate). As found by Schlesinger et al.,1 when aqueous NaBH... 

The most important of these compounds is sodium borohydride, NaBH. This is a water-soluble salt containing the tetrahedral BH4 anion, which is isoelectronic with methane but has a negative charge since boron has one less proton in the nucleus than does carbon. 

Chemists at Glaxo exploited this reactivity sequence in their synthesis of the anti-asthma drug, salmefamol (sister of the best seller salbutamol, which will be discussed in Chapter 25). Three reducing agents are used in the sequence sodium borohydride (NaBH lithium aluminium hydride (LiAlH4) and hydrogen gas over a palladium catalyst. 

Sodium borohydride, NaBHorganomercury compounds, prepared by oxymerc-uration of alkenes, to convert the C-Hg bond to C-H (Section 7.4). 

Reduction of a variety of compounds that contain the carbonyl group provides s)mthetic methods to produce primary and secondary alcohols. A common, very powerful reducing agent is lithium aluminum hydride, LiAlH other reducing agents include sodium in alcohol and sodium borohydride, NaBH. ... 

Sodium borohydride (NaBH ) was obtained in 100-g samples (>97%) from Fluka Feinchemikalien GmbH, Neu-Ulm, Germany. 

This group of reagents is commercially available in large quantities some of its members-notably lithium aluminium hydride (LiAlH ), calcium hydride (CaH2), sodium borohydride (NaBH ) and potassium borohydride (KBH4)-have found widespread use in the purification of chemicals. 

Ketones undergo a reduction when treated with sodium borohydride, NaBH,. What... 

Even more common, reductions of ketones are done by the use of lithium aluminum hydride (LiAlHi ) or sodium borohydride (NaBH ), then treating the compound with HaSOi or HCl. The alcohol produced from ketones is a secondary alcohol after reduction and may be illustrated as follows ... 

In the oxymercuration process, the electrophilic addition of the mercuric species occurs resulting in a mercurinium ion which is a three-membered ring. This is followed by the nucleophilic attack of water and as the proton leaves, an organomercuric alcohol (addition product) is formed. The next step, demercuration, occurs when sodium borohydride (NaBH ) substitutes the mercuric acetate substituent with hydrogen. If an alkene is unsymmetric, Oxymercuration-demercuration results in Markovnikov addition. The addition of mercuric species and water follows an anti (opposite side) addition pattern. This reaction has good yield, since there is no possibility of rearrangement unlike acid-catalyzed hydration of alkenes. 

Sodium borohydride (NaBH ) can reduce aldehydes and ketones when reacted in aqueous or alcohol solutions. Carboxylic acids and esters are not reactive to sodium borohydride reduction. Lithium aluminum hydride (LiAlH ), a more powerful reducing agent, can reduce aldehydes, ketones, esters, and carboxylic acids. 

With a conventional desktop ink-jet printer an aqueous palladium(II) solution is sprayed onto a surface-treated PI film. The palladium(II) is then reduced by treatment with sodium borohydride (NaBH ). Finally, a copper layer is deposited by electroless copper plating. The surface treatment of the PI, in order to accept the palladium(II) consists either of oxidation with alkaline KMNO4 at 80°C for 60 min or simply with NaOH at room temperature for 72 h. The latter treatment gives better results. Structures with dimensions down to 100 jum with good copper adhesion can be built. 

The hydrogen in lignin is increased by a spectrum of reactions ranging fiom catalytic reaction with hydrogen gas, (g), to reaction with sodium borohydride, NaBH.,. 

Pileni and co-workers [411] also used normal micelles with Cu(DS)2 and with or without NaDS solubilized in an aqueous solution. Sodium borohydride, NaBH Cu(DS)2 = 2, was added to the solution after deaeration the reactions took place in a glove box. At [Cu(DS)2] = 1.2 x 10 M, pure Cu particles formed below this, absorption spectra indicated copper oxide as the major phase. Above the concentration of Cu(DS)2 = 1.2 x 10" M, both spherical and elongated particles were obtained. The peak size, as a function of the relative concentrations of the two surfactants, changed from 2 nm to -6 nm. 

The hydration of an alkene can be accomplished by treating it with mercury(II) acetate (mercuric acetate) in water followed by reduction of the resulting organomer-cury compound with sodium borohydride, NaBH. In the following structural formulas for mercury(II) acetate, the acetate group is written in full in the first formula and abbreviated as AcO in the other formulas. 

Reduction of the organomercury compound by sodium borohydride, NaBH, replaces HgOAc by H. 

Finally, treatment with LiAlH, reduces an epoxide to an alcohol. Lithium aluminum hydride is similar to sodium borohydride, NaBH, in that it is a donor of hydride ion, H , which is both a strong base and a good nucleophile. In the reduction of a substituted epoxide by LiAlH,, attack of the hydride ion occurs preferentially at the less hindered carbon of the epoxide, an observation consistent with reactivity. 

Similarly, reduction of both aromatic and aliphatic aldehydes and ketones where there is a chlorine (Cl) or bromine (Br) present elsewhere in the carbonyl-containing compound succeeds with sodium borohydride (NaBH,) and, occasionally, with lithium aluminum hydride (LiAIH,) at low temperatures. Catalytic reduction frequently leads to hydrogenolysis of the halogen, producing the halogen-free alcohol. 

The Schiff base is reduced to the amine bond by mild reduction with sodium borohydride (NaBH ). Immediately after formation of the Schiff base in the above reaction, the reaction mixture is cooled to 4° in ice and 15 mg of NaBHi in 1.0 ml of KHCO3 at pH 7.9 is added. The reduction is allowed to occur in a cold-room at 4° for 12 hr. Since the reaction liberates hydrogen gas, reaction tubes are loosely capped to avoid a buildup of pressure. Unreacted [ S]MMPR-OP and NaBH are removed by dialyzing the reaction mixture against excess KHCO3 at pH. 7.9 until the radioactivity in the buffer drops to background levels. 

---