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Sodium borohydride is soluble in protic solvents such as water and lower alcohols. It also reacts with these protic solvents to produce H 2; however, these reactions are fairly slow. Complete decomposition of a methanol solution requires nearly 90 min at 20 °C. [11] It decomposes in neutral or acidic aqueous solutions, but is stable at pH 14. [9]
Since sodium cyanoborohydride is a mild reducing agent, it gives good chemoselectivity for reaction with certain functional groups in the presence of others. For example, sodium cyanoborohydride is generally incapable of reducing amides, ethers, esters and lactones, nitriles, or epoxides. [8]
At low pH values, it efficiently reduces aldehydes and ketones. [7] As the pH increases, the reduction rate slows and instead, the imine intermediate becomes preferential for reduction. [ 7 ] For this reason, NaBH 3 CN is an ideal reducing agent for one-pot direct reductive amination reactions that don't isolate the intermediate imine.
Since, aldehydes reduce more easily than ketones, they require milder reagents and milder conditions. At the other extreme, carboxylic acids, amides, and esters are poorly electrophilic and require strong reducing agents. [17] The idealized equation for the reduction of a ketone by sodium borohydride is: 4 RCOR' + NaBH 4 → NaB(OCHRR') 4
Ball-and-stick model of the tetrahydroborate anion, [BH 4] −. Borohydride refers to the anion [B H 4] −, which is also called tetrahydridoborate, and its salts. [1] Borohydride or hydroborate is also the term used for compounds containing [BH 4−n X n] −, where n is an integer from 0 to 3, for example cyanoborohydride or cyanotrihydroborate [BH 3 (CN)] − and triethylborohydride or ...
Sodium borohydride and lithium aluminium hydride are commonly used for the reduction of organic compounds. [ 3 ] [ 4 ] These two reagents are on the extremes of reactivity—whereas lithium aluminium hydride reacts with nearly all reducible functional groups, sodium borohydride reacts with a much more limited range of functional groups .
The mechanism for the reduction of a nitrile to an aldehyde with DIBAL-H. The hydride reagent Diisobutylaluminium hydride, or DIBAL-H, is commonly used to convert nitriles to the aldehyde. [14]
The table below shows a few reduction potentials, which can be changed to oxidation potentials by reversing the sign. Reducing agents can be ranked by increasing strength by ranking their reduction potentials. Reducers donate electrons to (that is, "reduce") oxidizing agents, which are said to "be reduced by" the reducer. The reducing agent is ...