1) Explain why a significant excess of sodium borohydride, NaBH 4 is used to red
ID: 818886 • Letter: 1
Question
1) Explain why a significant excess of sodium borohydride, NaBH4 is used to reduce aldehyde compounds containing additional acidic functional groups (e.g. phenols, carboxylic acids). Provide a balanced chemical reaction for one mole of a carboxylic acid (R-COOH) reacting with one mole of NaBH4.
2) Lithium aluminum hydride, LiAlH4 is a much more powerful reducing agent than sodium borohydride,
NaBH4; however, both reagents readily reduce ketones or aldehydes. Provide brief justification for why it may be more desirable to use NaBH4 over LiAlH4 to reduce an aldehyde.
3)If the reduction of an ester is required, which is a better choice of reagent: lithium aluminum hydride, LiAlH4, or sodium borohydride, NaBH4? Please briefly explain your choice.
Having trouble with these questions regarding a chem lab, 2nd yr orgo chem. Please help, thanks!
Explanation / Answer
1)sodium borohydride is basic in nature, so when we treat it with acidic compound like phenol or carboxylic acid, it will first react with acidic hydrogen ( acid base reaction is much faster than reduction). RCOOH + NaBH4 ------->>>>>>>> RCOO- + NaOH Further reduction of of above compound will not take place by NaBH4.
2) it is more desirable to reduce the ketone and aldehyde by NaBH4 selectivily. since LiAlH4 has more reducing capacity and it will reduce ester and amide also. therefore when we take the organic compound containing both ester or amide and aldehyde(or ketone) group and we want to reduce only ketone or aldehyde group then we have to use only NaBH4.
3) for reduction of ester LiAlH4 has is better choice since it will reduce the ester faster. although NaBH4 can also reduce the ester but the reaction is very slow. therefore it is more desirable to use LiAlH4 over NaBH4 in ester reduction. best reducing agent for ester is LiBH4.
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