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Organic Chemistry II

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n-Butyllithium Titration

Обзор

Source: Vy M. Dong and Diane Le, Department of Chemistry, University of California, Irvine, CA

This experiment will demonstrate a simple technique to titrate and obtain an accurate concentration of the organolithium reagent, n-butyllithium (n-BuLi). Organolithium reagents are extremely air- and moisture-sensitive and proper care must be taken to maintain the quality of the reagent so that it may be used successfully in a reaction. The n-BuLi titration experiments should be performed regularly to obtain accurate concentrations prior to use in a chemical reaction. Subsequently, we will demonstrate the addition of the titrated n-BuLi to benzaldehyde.

Процедура

1. Preparation of Titrant

  1. To a flame-dried round bottom flask equipped with a stir bar under N2, add diphenylacetic acid (250 mg, 1.18 mmol) and anhydrous THF (5 mL).

2. Titration of n-BuLi

  1. Calculate the approximate amount of n-BuLi solution (in hexanes) needed to consume the diphenylacetic acid. Using a syringe, slowly adda solution of n-BuLi dropwise. The reaction mixture will turn temporarily yellow and back to a colorless

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Результаты

Representative results for the titration of n-BuLi for Procedures 1-3

Procedure Step Color of reaction mixture
1.1 Colorless
2.1 Yellow, then colorless
2.2 Deep yellow
3.1 1.18 mmol diphenylacetic acid/1 mL n-BuLi

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Заявка и Краткое содержание

In this experiment, we have demonstrated how to determine the concentration of an n-BuLi solution by using diphenylacetic acid. We have also performed a reaction by adding n-BuLi to benzaldehyde.

Accurate concentrations of n-BuLi are important for its successful application in a number of reactions. n-BuLi is commonly used in lithium-halogen exchange reactions to prepare aryllithium or vinyllithium reagents, which can be subsequently used in C-C bond forming

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