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Wikipedia

Non-nucleophilic base

January 17, 2023

As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile. Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions. Typical non-nucleophilic bases are bulky, such that protons can attach to the basic center but alkylation and complexation is inhibited.

Non-nucleophilic bases

A variety of amines and nitrogen heterocycles are useful bases of moderate strength (pKa of conjugate acid

Non-nucleophilic bases of high strength are usually anions. For these species, the pKas of the conjugate acids are around 35–40.

Other strong non-nucleophilic bases are sodium hydride and potassium hydride. These compounds are dense, salt-like materials that are insoluble and operate by surface reactions.

Some reagents are of high basicity (pKa of conjugate acid around 17) but of modest but not negligible nucleophilicity. Examples include sodium tert-butoxide and potassium tert-butoxide.

Example

The following diagram shows how the hindered base, lithium diisopropylamide, is used to deprotonate an ester to give the enolate in the Claisen ester condensation, instead of undergoing a nucleophilic substitution.

 

This reaction (deprotonation with LDA) is commonly used to generate enolates.

References

  1. ^ K. L. Sorgi, "Diisopropylethylamine," Encyclopedia of Reagents for Organic Synthesis, 2001. doi:10.1002/047084289X.rd254
  2. ^ Rafael R. Kostikov, Sánchez-Sancho Francisco, María Garranzo and M. Carmen Murcia "2,6-Di-t-butylpyridine" Encyclopedia of Reagents for Organic Synthesis 2010. doi:10.1002/047084289X.rd068.pub2
  3. ^ Activation in anionic polymerization: Why phosphazene bases are very exciting promoters S. Boileau, N. Illy Prog. Polym. Sci., 2011, 36, 1132-1151, doi:10.1016/j.progpolymsci.2011.05.005

January 17, 2023
nucleophilic, base, name, suggests, nucleophilic, base, sterically, hindered, organic, base, that, poor, nucleophile, normal, bases, also, nucleophiles, often, chemists, seek, proton, removing, ability, base, without, other, functions, typical, nucleophilic, b. As the name suggests a non nucleophilic base is a sterically hindered organic base that is a poor nucleophile Normal bases are also nucleophiles but often chemists seek the proton removing ability of a base without any other functions Typical non nucleophilic bases are bulky such that protons can attach to the basic center but alkylation and complexation is inhibited Non nucleophilic bases EditA variety of amines and nitrogen heterocycles are useful bases of moderate strength pKa of conjugate acid N N Diisopropylethylamine DIPEA also called Hunig s Base 1 p 1 8 Diazabicycloundec 7 ene DBU useful for E2 elimination reactions pKa 13 5 1 5 Diazabicyclo 4 3 0 non 5 ene DBN comparable to DBU 2 6 Di tert butylpyridine a weak non nucleophilic base 2 pKa 3 58 Phosphazene bases such as t Bu P4 3 Non nucleophilic bases of high strength are usually anions For these species the pKas of the conjugate acids are around 35 40 Lithium diisopropylamide LDA pKa 36 Silicon based amides such as sodium and potassium bis trimethylsilyl amide NaHMDS and KHMDS respectively Lithium tetramethylpiperidide LiTMP or harpoon base Other strong non nucleophilic bases are sodium hydride and potassium hydride These compounds are dense salt like materials that are insoluble and operate by surface reactions Some reagents are of high basicity pKa of conjugate acid around 17 but of modest but not negligible nucleophilicity Examples include sodium tert butoxide and potassium tert butoxide Example EditThe following diagram shows how the hindered base lithium diisopropylamide is used to deprotonate an ester to give the enolate in the Claisen ester condensation instead of undergoing a nucleophilic substitution This reaction deprotonation with LDA is commonly used to generate enolates References Edit K L Sorgi Diisopropylethylamine Encyclopedia of Reagents for Organic Synthesis 2001 doi 10 1002 047084289X rd254 Rafael R Kostikov Sanchez Sancho Francisco Maria Garranzo and M Carmen Murcia 2 6 Di t butylpyridine Encyclopedia of Reagents for Organic Synthesis 2010 doi 10 1002 047084289X rd068 pub2 Activation in anionic polymerization Why phosphazene bases are very exciting promoters S Boileau N Illy Prog Polym Sci 2011 36 1132 1151 doi 10 1016 j progpolymsci 2011 05 005 Retrieved from https en wikipedia org w index php title Non nucleophilic base amp oldid 1118573408, wikipedia, wiki, book, books, library,

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