Organolithium compounds, titration

No carboxylic acid functionality was detected either by thin-layer chromatographic analyses or by end-group titration. Therefore, procedures are now available to control the carbonation of polymeric organolithium compounds to efficiently produce either the carbox-ylated chain ends or the corresponding ketone dimer. 

A sample of organolithium compound solution is added to an excess of standardized iodine solution in Et20 the excess iodine is extracted with aqueous KI and titrated with standard thiosulfate solution. Evaluation of the organometallic compound is made according to equation. A possible interference can be expected from the couphng reaction in equation 20. This was shown to be neghgible, as demonstrated spectrofluorometrically for phenyllithium , whereas a low titer was found for n-BuLi, attributable to this side... 

Analytical aspects of organolithium compounds 5. Nuclear magnetic resonance spectroscopy and magnetic titrations... 

Many of the titration methods for organomagnesium compounds are similar to those for organolithium compounds, which have been reviewed elsewhere ... 

The following procedure is representative of the preparation of almost all organolithium compounds with lithium metal and their titration. 

Scheme 9.17). The macrocycle (A) of Scheme 9.1 is the dpp-incorporating 30-membered ring 8 used earlier for making catenanes (see Protocol 5) it is sufficiently small to prevent release of the bis-porphyrin dumbbell. The preparation of 22+ takes place in seven steps.1819 One of the starting materials is 4-lithiotoluene 13, which may be obtained by direct interaction of an excess of freshly cut lithium with 4-bromotoluene 12 in ether under argon at reflux (Scheme 9.10).12 The resulting organolithium compound is titrated by the double titration method described by Gilman et alP The experimental procedure is very similar to that described in Protocol 1.

Organolithium compounds are highly sensitive to air and humidity. The commercial RLi usually contains varying amounts of alkoxides as impurities. The concentration of the organoUthium solution can be easily checked by several methods, which can be divided into two categories (i) direct titration methods, based usually on a color change of self-indicators, and (ii) double titration methods. Such different methods have been reviewed in detail [12, 151], The traditional double titration method provides the content of active organohthium and of lithium alkoxides/hydroxide (Fig. 26.9). 

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