Explain how LDA is synthesized ?
Lithium di-iso-propyl-amide (commonly abbreviated LDA) is a chemical compound with the molecular formula [(CH3)2CH]2NLi. It is used as a strong base and has been widely utilized due to its very fine 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.
PREPRATION METHOD-
LDA dimer with THF coordinated to Li centers.
LDA is commonly formed by treating a cooled (0 to −78 °C) mixture of tetrahydrofuran and di-iso-propylamine with n-butyllithium.
When dissociated, the diisopropylamide anion can become protonated to form diisopropylamine. Diisopropylamine has a Pka value of 36. Therefore, its conjugate base is suitable for the deprotonation of compounds with greater acidity, importantly, such weakly acidic compounds (carbon acids) of the type R2CHZ, where Z = C(O)R', CO2R' or CN. Conventional protic functional groups such as alcohols and carboxylic acids are readily deprotonated.
Like most organolithium reagents , LDA is not a salt, but is highly polar. It forms aggregates in solution, with the extent of aggregation depending on the nature of the solvent. In THF its structure is primarily that of a solvated dimer.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.
Solid LDA is pyrohoric 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 m mole), it is common and more cost effective to prepare LDA
Deprotonation using LDA.
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