Titration methods double

Quantitative Analysis of All llithium Initiator Solutions. Solutions of alkyUithium compounds frequentiy show turbidity associated with the formation of lithium alkoxides by oxidation reactions or lithium hydroxide by reaction with moisture. Although these species contribute to the total basicity of the solution as determined by simple acid titration, they do not react with allyhc and henzylic chlorides or ethylene dibromide rapidly in ether solvents. This difference is the basis for the double titration method of determining the amount of active carbon-bound lithium reagent in a given sample (55,56). Thus the amount of carbon-bound lithium is calculated from the difference between the total amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, allyl chloride, or ethylene dibromide. 

The double titration method, which involves the use of ben2ylchloride, 1,2-dibromoethane, or aUyl bromide, determines carbon-bound lithium indirectly (101,102). One sample of the //-butyUithium is hydroly2ed directly, and the resulting alkalinity is determined. A second sample is treated with ben2ylchloride and is then hydroly2ed and titrated with acid. The second value (free base) is subtracted from the first (total base) to give a measure of the actual carbon-bound lithium present (active base). 

Phosphoms content usually is measured by a double end point titration method in which a 1.0-g sample is dissolved in a hot HNO —H2SO4—HCIO4 mixture. The pH is adjusted to 2.5 with NaOH, and the resulting H PO is titrated with 0.5-A[ NaOH, using an automatic titrator. The titer between the first and second end points is used to quantify the phosphoms as H PO. ... 

In contrast to aspirin itself, the U.S.P. monograph for aspirin tablets has undergone considerable changes. For some reason, U.S.P. does not use the ferric salt test for free salicylic acid, as does the British Pharmacopeia of 1973. Apparently, certain excipients such as citric and tartaric acid interfere with this reaction.77 Already in 1913, a double titration method was developed78 which was made an official method in 1926.79 This method was used as the assay method when the aspirin tablets monograph was introduced into U.S.P. XII in 1942. 

Double-cell system, in soil and ground water treatment, 25 835 Double crucible technique, 11 135-136 Double-deck kiln, 15 530 Double-drum dryers, 9 134 Double-drum separator, 15 446 Double-effect distillation, 10 153 Double end point titration method,... 

Double-stranded RNA (dsRNA) in yeast, 26 451—452 Double-stranded RNA viruses, 3 135 Double-suction pumps, 21 60, 63 Double tipping pan vacuum filter, 11 352 Double titration method, 15 145 Double vacuum-arc remelting (VAR), in titanium sponge consolidation, 24 854 Double wall nanotubes (DWNT), 26 737 Double-wall tanks, 24 296 Doubly smart block copolymers,... 

In this work, halogens were added across the double bonds of unsaturated fatty acids (commercial available sunflower oil) to form addition compounds and the degree of uptake was measured. A measured excess of iodine monobrontide (IBr) was allowed to react with the oil in the dark. At the end of a timed period, an excess of K1 was added to convert the remaining IBr to The 1 formed was then titrated with standard thiosulfate. This was a back-titration method. A back-titration blank was also required, where the sample was omitted. The uptake of iodine was calculated... 

The reproducibility of the reaction was examined by performing the parallel anionic polymerization of St. The polymerizations were performed in cyclohexane and initiated by x-BuLi. The obtained polymers were analyzed by SEC and the difference between the results was less than 3%. This corresponds to less than 5% deviation after calculating the real concentration of the initiator in the reactors by a double titration method [56]. 

It is also possible with sulphurous acid solutions, using methyl orange as indicator, to titrate with a standard solution of an alkali to the halfway bisulphite stage.6 If necessary the alkali hydrogen sulphite may then be estimated by the addition of mercuric chloride and further titration with alkali, as already described. By this double titration method it is possible to estimate sulphurous aeid in the presence of other sulphur acids.7... 

The amount of oil in a sample is determined by Scott oil analysis (AOAC, 1990e). This is a bromination reaction previously used to determine the number of fatty acid double bonds. This titration method quantifies the recoverable oil in fruits and fruit products based on the release of Br2 and the formation of limonene tetrabromide (Braddock, 1999). Figure Gl.5.3 illustrates the chemical reaction for the bromination of limonene. Other monoterpenes (a-pinene and citral) also react however, the method is accurate to within 10 ppm limonene (Scott and Valdhuis, 1966). For this procedure, limonene is co-distilled with isopropanol and titrated with a potassium bromide/bromate solution. 

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.

Accordng to the method of Hodnett [11], the average valence of vanadium was determined by the double titration method using KMn04. 

Iodine and acid values obtained by standard titration methods (17.18) are given In Table I, along with approximate values of epoxy equivalent weights and oxlrane and double bond contents, for the epoxldlzed crambe and lunarla oils, and for a typical epoxldlzed commercial linseed oil. 

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). 

The classical double titration method has certainly the advantage that it can also be employed to titrate organomagnesium intermediates, metal dialkylamides, and even radical anions. Moreover, self-indicators and anhydrous and oxygen-free conditions are not required. 

In acidic medium, potassium bromide and potassium bromate produce bromine stoichiometrically, and this is the basis of a titration method [82], which has been used to determine double bonds in polymethylacrylate. After bromination, excess bromine is estimated by the addition of potassium iodide and the iodine produced by the reaction is titrated with standard sodium thiosulfate to the starch end-point. 

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