Bromides titration

Several crops of crystals are now taken by evaporating the aqueous solution to the saturation point on a hot plate with stirring, then cooling. Each crop is dried for 2 hours at 100° and analyzed for unsaturation by the bromate-bromide titration method (Note 10). The first two crops usually total about 380 g. (based on 300 g. of sulfur trioxide), 49% yield, and are about 95% pure by titration. They may be further purified by one recrystallization from water, with about 80% recovery of 99+% pure salt. 

Undecanoic acid, 32, 104 10-Undecynoic acid, 32, 104 Unsaturation, quantitative estimation by bromate-bromide titration method, 34, 86, 89 Urea, 30, 24 31, 11 Urea, I-(T -bromophenyl)-, 31, 8 1-(o-chlorophenyl)-2-thio-, 31, 21 1,1-dimethyl-, 32, 61 I-(P-phenetyl)-, 31,11... 

The methyl oleate was prepared by esterification1 of commercial u.s.p. grade oleic acid and fractionated through a Widmer column. The fractions used boiled at 140-144° (0.5 mm.), 175-179° (2 mm.), and had d 1.4500-1.4527 and an iodine number of 93-97 (calcd. 85.6) by iodine bromide titration.2... 

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). 

Ferrous Sulfdte Titration. For deterrnination of nitric acid in mixed acid or for nitrates that are free from interferences, ferrous sulfate titration, the nitrometer method, and Devarda s method give excellent results. The deterrnination of nitric acid and nitrates in mixed acid is based on the oxidation of ferrous sulfate [7720-78-7] by nitric acid and may be subject to interference by other materials that reduce nitric acid or oxidize ferrous sulfate. Small amounts of sodium chloride, potassium bromide, or potassium iodide may be tolerated without serious interference, as can nitrous acid up to 50% of the total amount of nitric acid present. Strong oxidizing agents, eg, chlorates, iodates, and bromates, interfere by oxidizing the standardized ferrous sulfate. 

Unsaturation value can be determined by the reaction of the akyl or propenyl end group with mercuric acetate ia a methanolic solution to give acetoxymercuric methoxy compounds and acetic acid (ASTM D4671-87). The amount of acetic acid released ia this equimolar reaction is determined by titration with standard alcohoHc potassium hydroxide. Sodium bromide is normally added to convert the iasoluble mercuric oxide (a titration iaterference) to mercuric bromide. The value is usually expressed as meg KOH/g polyol which can be converted to OH No. units usiag multiplication by 56.1 or to percentage of vinyl usiag multiplication by 2.7. 

Analysis. The abiUty of silver ion to form sparingly soluble precipitates with many anions has been appHed to their quantitative deterrnination. Bromide, chloride, iodide, thiocyanate, and borate are determined by the titration of solutions containing these anions using standardized silver nitrate solutions in the presence of a suitable indicator. These titrations use fluorescein, tartrazine, rhodamine 6-G, and phenosafranine as indicators (50). 

Chloride. Chloride is common in freshwater because almost all chloride salts are very soluble in water. Its concentration is generally lO " to 10 M. Chloride can be titrated with mercuric nitrate. Diphenylcarbazone, which forms a purple complex with the excess mercuric ions at pH 2.3—2.8, is used as the indicator. The pH should be controlled to 0.1 pH unit. Bromide and iodide are the principal interferences, whereas chromate, ferric, and sulfite ions interfere at levels greater than 10 mg/L. Chloride can also be deterrnined by a colorimetric method based on the displacement of thiocyanate ion from mercuric thiocyanate by chloride ion. The Hberated SCN reacts with ferric ion to form the colored complex of ferric thiocyanate. The method is suitable for chloride concentrations from 10 to 10 M. 

There is also evidence for stable 3,4-adducts from the X-ray analysis of 2-amino-4-ethoxy-3,4-dihydropteridinium bromide, the nucleophilic addition product of 2-aminopteridine hydrobromide and ethanol (69JCS(B)489). The pH values obtained by potentiometric titration of (16) with acid and back-titration with alkali produces a hysteresis loop, indicating an equilibrium between various molecular species such as the anhydrous neutral form and the predominantly hydrated cation. Table 1 illustrates more aspects of this anomaly. 2-Aminop-teridine, paradoxically, is a stronger base than any of its methyl derivatives each dimethyl derivative is a weaker base than either of its parent monomethyl derivatives. Thus the base strengths decrease in the order in which they are expected to increase, with only the 2-amino-4,6,7-trimethylpteridine out of order, being more basic than the 4,7-dimethyl derivative. 

Bases on the data of curve of the potentiometric titrations of [AuBr ] ions by thiourea (Thio), it consistently replaces bromide ions in [AuBr ] ion. They are formed mixed bromide-thiourea complexes of Au(III) AuBr Thio, AuBiyr/iio AuBrThio, AuBrThioJ. ... 

The preparation of cyclohexylmagnesium bromide is described on p. 22. The solution may be standardized by titrating against 0.5 N hydrochloric acid, and exactly one mole equivalent is used in the preparation. Five cubic centimeters of cyclohexylmagnesium bromide solution is slowly added to 20 cc. of water, an excess of the standard acid is added, and the excess acid titrated with sodium hydroxide. If 85 g. (3.5 moles) of magnesium, one liter of dry ether, and 571 g. of cyclohexyl bromide (3.5 moles) are used, a solution results which is about 2 molar. 

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. 

A solution of methyl ithium in ether is prepared from lithium wire and methyl bromide according to the literature procedure, and titrated by the same method as Note 6. The checkers used 1.1 M methyl ithium from Aldrich. 

Although ethereal solutions of methyl lithium may be prepared by the reaction of lithium wire with either methyl iodide or methyl bromide in ether solution, the molar equivalent of lithium iodide or lithium bromide formed in these reactions remains in solution and forms, in part, a complex with the methyllithium. Certain of the ethereal solutions of methyl 1ithium currently marketed by several suppliers including Alfa Products, Morton/Thiokol, Inc., Aldrich Chemical Company, and Lithium Corporation of America, Inc., have been prepared from methyl bromide and contain a full molar equivalent of lithium bromide. In several applications such as the use of methyllithium to prepare lithium dimethyl cuprate or the use of methyllithium in 1,2-dimethyoxyethane to prepare lithium enolates from enol acetates or triraethyl silyl enol ethers, the presence of this lithium salt interferes with the titration and use of methyllithium. There is also evidence which indicates that the stereochemistry observed during addition of methyllithium to carbonyl compounds may be influenced significantly by the presence of a lithium salt in the reaction solution. For these reasons it is often desirable to have ethereal solutions... 

A) Preparation of 3-Bromopropyltriphenylphosphonium Bromide Triphenylphosphine, 1.0 kg, and 770 grams of 1,3-dibromopropane are dissolved In 2.0 liters of xylene and the solution is stirred under a nitrogen atmosphere at 130°C. After 20 hours the mixture is cooled, and the crystalline product, which precipitates, is collected and washed with 20 liters of benzene. After drying in vacuo the product weighs 1,578 grams, MP 229°-230°C titration for bromide ion Found, T7.1% calculated, 17.2%. 

Chlorinity When a sample of sea water is titrated with silver nitrate, bromides and iodides, as well as chlorides are precipitated. In calculating the chlorinity (Cl), the entire halogen content is taken as chloride, and chlorinity is defined as the weight in grams of silver required for precipitation of total halogen content per kilogram of sea water, multiplied by 0-328 533. (Chlorinity is always expressed as parts per thousand, using the symbol %o.)... 

Theory. The anion exchange resin, originally in the chloride form, is converted into the nitrate form by washing with sodium nitrate solution. A concentrated solution of the chloride and bromide mixture is introduced at the top of the column. The halide ions exchange rapidly with the nitrate ions in the resin, forming a band at the top of the column. Chloride ion is more rapidly eluted from this band than bromide ion by sodium nitrate solution, so that a separation is possible. The progress of elution of the halides is followed by titrating fractions of the effluents with standard silver nitrate solution. 

Weigh out accurately about 0.10 g of analytical grade sodium chloride and about 0.20 g of potassium bromide, dissolve the mixture in about 2.0 mL of water and transfer quantitatively to the top of the column with the aid of 0.3 M sodium nitrate. Pass 0.3 M sodium nitrate through the column at a flow rate of about 1 mL per minute and collect the effluent in 10 mL fractions. Transfer each fraction in turn to a conical flask, dilute with an equal volume of water, add 2 drops of 0.2M potassium chromate solution and titrate with standard 0.02M silver nitrate. 

Before commencing the elution titrate 10.0 mL of the 0.3 M sodium nitrate with the standard silver nitrate solution, and retain the product of this blank titration for comparing with the colour in the titrations of the eluates. When the titre of the eluate falls almost to zero (i.e. nearly equal to the blank titration) — ca 150 mL of effluent — elute the column with 0.6M sodium nitrate. Titrate as before until no more bromide is detected (titre almost zero). A new blank titration must be made with 10.0 mL of the 0.6M sodium nitrate. 

Plot a graph of the total effluent collected against the concentration of halide in each fraction (millimoles per litre). The sum of the titres using 0.3 M sodium nitrate eluant (less blank for each titration) corresponds to the chloride, and the parallel figure with 0.6M sodium nitrate corresponds to the bromide recovery. 

Pipette 25.0 mL of the bromide ion solution (0.01-0.02M) into a 400 mL beaker, add excess of dilute silver nitrate solution, filter off the precipitated silver bromide on a sintered glass filtering crucible, and wash it with cold water. Dissolve the precipitate in a warm solution prepared from 15 mL of concentrated ammonia solution, 15 mL of 1M ammonium chloride, and 0.3 g of potassium tetracyanonickelate. Dilute to 100-200 mL, add three drops of murexide indicator, and titrate with standard EDTA (0.01 M) (slowly near the end point) until the colour changes from yellow to violet. 

Similar remarks apply to the determination of bromides the Mohr titration can be used, and the most suitable adsorption indicator is eosin which can be used in dilute solutions and even in the presence of 0.1 M nitric acid, but in general, acetic (ethanoic) acid solutions are preferred. Fluorescein may be used but is subject to the same limitations as experienced with chlorides [Section 10.77(b)], With eosin indicator, the silver bromide flocculates approximately 1 per cent before the equivalence point and the local development of a red colour becomes more and more pronounced with the addition of silver nitrate solution at the end point the precipitate assumes a magenta colour. 

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