Lithium diisopropylamide

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Lithium diisopropylamide
Lithium diisopropylamide
Lithium diisopropylamide
Names
Preferred IUPAC name
Lithium N-(propan-2-yl)propan-2-aminide
Other names
LDA
Identifiers
3D model (
JSmol
)
ChemSpider
ECHA InfoCard
 100.021.721 Edit this at Wikidata
UNII
  • InChI=1S/C6H14N.Li/c1-5(2)7-6(3)4;/h5-6H,1-4H3;/q-1;+1 checkY
    Key: ZCSHNCUQKCANBX-UHFFFAOYSA-N checkY
  • InChI=1/C6H14N.Li/c1-5(2)7-6(3)4;/h5-6H,1-4H3;/q-1;+1
    Key: ZCSHNCUQKCANBX-UHFFFAOYAP
SMILES
  • ionic form: [Li+].CC(C)[N-]C(C)C
  • covalent form: CC(C)N([Li])C(C)C
  • dimer with THF: C1CCC[O+]1[Li-2]0[N+](C(C)C)(C(C)C)[Li-2]([O+]1CCCC1)[N+]0(C(C)C)C(C)C
Properties
LiN(CH(CH3)2)2
Molar mass 107.1233 g/mol
Appearance colourless solid
Density 0.79 g/cm3
Reacts with water
Acidity (pKa) 36 (THF)[1]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 corrosive
Related compounds
Related compounds
 Superbases
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Lithium diisopropylamide (commonly abbreviated LDA) is a

molecular formula LiN(CH(CH3)2)2. It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature. It is a colorless solid, but is usually generated and observed only in solution. It was first prepared by Hamell and Levine in 1950 along with several other hindered lithium diorganylamides to effect the deprotonation of esters at the α position without attack of the carbonyl group.[2]

Preparation and structure

LDA dimer with THF coordinated to Li centers

LDA is commonly formed by treating a cooled (0 to −78 °C) mixture of tetrahydrofuran and diisopropylamine with n-butyllithium.[3]

When dissociated, the diisopropylamide anion can become

conjugate base
is suitable for the deprotonation of compounds with greater acidity, importantly, such weakly acidic compounds (carbon acids) of the type HC(Z)R2, where Z = C(O)R', C(O)OR' or CN. Conventional protic functional groups such as alcohols and carboxylic acids are readily deprotonated.

Like most

dimer.[4][5] In nonpolar solvents such as toluene, it forms a temperature-dependent oligomer equilibrium. At room temperature trimers and tetramers are the most likely structures. With decreasing temperature the aggregation extends to pentameric and higher oligomeric structures.[6]

Solid LDA is pyrophoric,[7] but its solutions are generally not. As such it is commercially available as a solution in polar aprotic solvents such as THF and ether; however, for small scale use (less than 50 mmol), it is common and more cost effective to prepare LDA in situ.

Deprotonation using LDA.[8]

Kinetic vs thermodynamic bases

The deprotonation of carbon acids can proceed with either

aprotic solvent
which does not contain hydronium ions.

LDA can, however, act as a nucleophile under certain conditions.

See also

References

  1. ^ Evans pKa Table
  2. doi:10.1021/jo01147a026
    .
  3. ^ Smith, A. P.; Lamba, J. J. S.; Fraser, C. L. (2004). "Efficient Synthesis of Halomethyl-2,2'-Bipyridines: 4,4'-Bis(chloromethyl)-2,2'-Bipyridine". Organic Syntheses; Collected Volumes, vol. 10, p. 107.
  4. doi:10.1021/jo00053a001
    .
  5. doi:10.1021/ja00021a066
    .
  6. PMID 26014367
    .
  7. ^ SDS at Sigma-Aldrich
  8. doi:10.15227/orgsyn.087.0137
    .
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