1,10-Phenanthrolines titration indicators

Ethereal methyl1ithiurn (as the lithium bromide complex) was obtained by the submitters from Aldrich Chemical Company Inc. The checkers used 1.19 M methyl1ithiurn-lithium bromide complex in ether supplied by Alfa Products, Morton/Thiokol, Inc. The concentration of the methyllithium was determined by titration with 1.0 M tert-butyl alcohol in benzene using 1,10-phenanthroline as indicator. The submitters report that ethereal methyllithium of low halide content purchased from Alfa Products, Morton/Thiokol, Inc., gave similar results. 

Butyl lithium in hexane was obtained from Vcntron Corporation and stored in a refrigerator under argon. The solution was titrated with 2-butanol in xylene, using 1,10-phenanthroline as indicator. 

Butyllithium was obtained from Aldrich Chemical Company, Inc., and methyl iodide from Merck S Company, Inc. Butyllithium was titrated with phenanthroline as indicator prior to use according to the method of Watson and Eastham. Fresh alkoxide-free butyllithium should be used to ensure pure product. 

Hesse, Org. Syn., 50, 66 (1970)]. The checkers standardized the solution immediately before use by diluting a 2.5-ml. aliquot with 10 ml. of benzene and titrating with alM solution of 2-butanol in xylene according to the procedure of Watson and Eastham3 [see M. Gall and H. O. House, Org. Syn., 52, 39 (1972)], with 1,10-phenanthroline as indicator. The submitters report that the yield of arylcyclopropane is lower if a commercially available solution of butyllithium in hydrocarbon solvents is used. 

Ce4+ is yellow and Ce3+ is colorless, but the color change is not distinct enough for cerium to be its own indicator. Ferroin and other substituted phenanthroline redox indicators (Table 16-2) are well suited to titrations with Ce4+. 

The n-butyllithium in hexane solution was purchased from Foote Mineral Company. The checkers obtained their material from Wako Pure Chemical Industries Ltd. (Japan) and titrated it with 0.80IU 2-butanol in xylene using 1,10-phenanthroline as indicator.2 Care should be exercised in handling w-butylhthium solutions. 

Butyllithium in hexanes (2.5 M) is purchased from the Aldrich Chemical Company, Inc. and titrated with 2-pentanol in ether, using 1,10-phenanthroline as indicator before use.2 Use of lower concentrations of butyllithium for the metalation of thiophene under these conditions results in incomplete lithiation. 

Cerium sulfate Potentiometric titration, using Fe2+ 1,10-phenanthroline as indicator Cioroi449... 

A THF solution of methylmagnesium bromide was purchased from Tokyo Kasei Kogyo Co., Ltd., Japan and titrated with sec-butyl alcohol using 1,10-phenanthroline as indicator. Rapid addition might raise the internal temperature and use of excess methylmagnesium bromide would cause undesired methylation of the A-ring enone. 

The mixture is most conveniently filtered by gravity filtration through an oven-dried coarse (15 pM) sintered glass frit (Notes 8, 9). The concentration of 1,4-dilithiobutane (2) in ether is determined by titration with sec-butyl alcohol using 1,10-phenanthroline as indicator. The molarity of the solution obtained under these optimized conditions is approximately 1.7 M In RLi", i.e., 0.9 M in 1,4-dilithiobutane (2) (Note 10). This solution is stable for several months when stored at -10°C under nitrogen. 

ButylKthium was obtained from Foote Mineral Co. The molarity was checked by titration of 2.00 mL of the butyllithium solution in 10 mL of diethyl ether with dry 2-butanol using 1,10-phenanthroline as indicator. 

Although gravimetric methods have been used traditionally for the determination of large amounts of tellurium, more accurate and convenient volumetric methods are favored. The oxidation of teUurium(IV) by ceric sulfate in hot sulfuric acid solution in the presence of chromic ion as catalyst affords a convenient volumetric method for the determination of tellurium (32). Selenium(IV) does not interfere if the sulfuric acid is less than 2 N in concentration. Excess ceric sulfate is added, the excess being titrated with ferrous ammonium sulfate using o-phenanthroline ferrous—sulfate as indicator. The ceric sulfate method is best appHed in tellurium-rich materials such as refined tellurium or tellurium compounds. 

Wet-Chemical Determinations. Both water-soluble and prepared insoluble samples must be treated to ensure that all the chromium is present as Cr(VI). For water-soluble Cr(III) compounds, the oxidation is easily accompHshed using dilute sodium hydroxide, dilute hydrogen peroxide, and heat. Any excess peroxide can be destroyed by adding a catalyst and boiling the alkaline solution for a short time (101). Appropriate ahquot portions of the samples are acidified and chromium is found by titration either using a standard ferrous solution or a standard thiosulfate solution after addition of potassium iodide to generate an iodine equivalent. The ferrous endpoint is found either potentiometricaHy or by visual indicators, such as ferroin, a complex of iron(II) and o-phenanthroline, and the thiosulfate endpoint is ascertained using starch as an indicator. 

To determine the cadmium content, add 20-25 mL of the 1,10-phenanthroline solution and titrate the liberated EDTA with the 0.05M lead nitrate solution until the colour change from yellow to red-violet occurs — a little practice is required to discern the end point precisely. Introduce further 2-5 mL portions of the 1,10-phenanthroline solution and note whether the indicator colour changes if so, continue the titration with the lead nitrate solution. The consumption of lead nitrate solution corresponds to the cadmium content. 

The standard redox potential is 1.14 volts the formal potential is 1.06 volts in 1M hydrochloric acid solution. The colour change, however, occurs at about 1.12 volts, because the colour of the reduced form (deep red) is so much more intense than that of the oxidised form (pale blue). The indicator is of great value in the titration of iron(II) salts and other substances with cerium(IV) sulphate solutions. It is prepared by dissolving 1,10-phenanthroline hydrate (relative molecular mass= 198.1) in the calculated quantity of 0.02M acid-free iron(II) sulphate, and is therefore l,10-phenanthroline-iron(II) complex sulphate (known as ferroin). One drop is usually sufficient in a titration this is equivalent to less than 0.01 mL of 0.05 M oxidising agent, and hence the indicator blank is negligible at this or higher concentrations. 

Butyllithium was purchased from Aldrich Chemical Company, Inc. and titrated using a solution of 2-butanol (1.0 M in p-xylene) with 1,10-phenanthroline as the end-point indicator. 

An indirect oxidimetric titration method for alkylhthium compounds may be carried out, taking advantage of the fact that vanadium pentoxide causes fast and complete oxidation of alkyllithiums in solution. After the end of this reaction the reduced vanadium compounds are dissolved in sulfuric acid and titrated with Ce(IV) sulfate, using as indicator Ee(II) and 1,10-phenanthroline (64) sulfate. This method is inadequate for aryllithium compounds because the lithium phenoxide impurities reduce vanadium pentoxide. ... 

Determination of Azide as NaNt. Pipette a 25 ml portion of the sample into a 500 ml Erin flask and dil with w to 150-200 ml. Titrate with 40% sulfuric acid to just fo the phpht end-point, not overrunning it. Add N/10 ceric sulfate soln in 5 ml portions until the soln becomes deep yel, indicating an excess of ceric sulfate. Record the exact amt used. Add 10 ml of 40% sulfuric acid and 2 drops of o-phenanthroline indicator (prepd by dissolving 14.85 g of o-phenanthroline monohydrate, CiaHsNa HaO in 1 1 of 0.025 M freshly prepd ferrous sulfate... 

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