Bromocresol-green

Other Names Bromocresol green Phenol, 4,4 -(3H-2,l-benzoxathiol-3-yUdene)fcM[2,6-dibromo-3-methyl-, S,S-dioxide m-Cresol, 4,4 -(3H-2,l-benzoxathiol-3-ylidene)fcw[2,6-dibiomo-, S,S-dioxide o-Toluenesulfonic acid, a,a-fci5 (3,5-dibromo-4-hydroxy-(3-tolyl)-a- hydroxy-, y-sultone 3H-2,l-Benzoxathiole, phenol deriv. 3, 3 ,5, 5 -Tetrabromo-m-cresolsulfonephthalem BCG Bromcresol green NSC 7817 Tetrabromo-m-cresolphthalein sulfone CA Index Name Phenol, 4,4 -(l,l-dioxido-3H-2,l-benzoxathiol-3-ylidene)to[2,6-dihromo-3-methyl-CAS Registry Number 76-60-8 Merck Index Number 1386 Chemical Structure 

Chemical/Dye Class Sulfonephthalein Molecular Formula C2iHi4Br405S Molecular Weight 698.01 pH Range 3.8-S.4 

Physical Form Slightly yellowish-brownish crystals 

Solubility Sparingly soluble in water soluble in ethanol, ether, ethyl acetate 

Boiling Point (Calcd.) 626.0 55.0°C Pressure 760 Torr Synthesis Synthetic methodsi-  

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Heat reagent-grade material for 1 hr at 255-265°C. Cool in an efficient desiccator. Titrate sample with acid to pH 4-5 (first green tint of bromocresol green), boil the solution to eliminate the carbon dioxide, cool, and again titrate to pH 4-5. Equivalent weight is one-half the formula weight. 

In this experiment the equilibrium constant for the dissociation of bromocresol green is measured at several ionic strengths. Results are extrapolated to zero ionic strength to find the thermodynamic equilibrium constant. Equilibrium Constants for Calcium lodate Solubility and Iodic Acid Dissociation. In J. A. Bell, ed. Chemical Principles in Practice. Addison-Wesley Reading, MA, 1967. 

Eor each of the following, determine the forms of alkalinity (OH , HC03, C03 ) that are present, and their respective concentrations in parts per million. In each case, a 25.00-mL sample is titrated with 0.1198 M HCl to the bromocresol green and phenolphthalein end points. 

Dissolve the sample in about 100 mL of H2O, and then dilute to the mark. Using a pipet, transfer a 25-mL aliquot of this solution to a 125-mL Erlenmeyer flask, and add 25-mL of H2O and 2 drops of bromocresol green indicator. Titrate the sample with 0.1 M HCl to the indicator s end point. 

Apparent equivalent weight can be deterrnined by titration with hydrochloric acid using a bromocresol green indicator. Calculations give the equivalent weight of total amines and are not specific for the mono-, di- or tri alkan olamines. 

Bromocresol Green (3, 3",5, 5"-tetrabromo-m-cresolsulfonephthalein) [76-60-8] M 698.0, m 218-219 (dec), 225 (dec), pK 4.51. Crystd from glacial acetic acid or dissolved in aqueous 5% NaHC03 soln and ppted from hot soln by dropwise addition of aqueous HCl. Repeated until the extinction did not increase (X ,ax 423nm). Indicator at pH 3.81 (yellow) and pH 5.4 (blue-green). 

Bromocresol green (3.8...5.4) aliphatic carboxylic acids[103,187 — 204] triiodobenzoic acid [205], derivatives of barbituric acid [206] amphetamine derivatives [207, 208] phenazones, morazone [209] alkaloids [91, 209] nephopam [210] phenyramidol metabolites [211] diethylalkylacetamide derivatives [212] zipeprol (Mirsol) [213] thalidomide and hydrolysis products [214] cyclohexylamine derivatives [215] herbicide residues [216]... 

Bromocresol Green — Bromophenol Blue — Potassium Permanganate Reagent... 

Dissolve 40 mg bromocresol green and 15 mg bromophenol blue in 100 ml ethanol. 

The detection of acids takes place on the basis of the pH-dependent color change of the two indicators bromocresol green (pH range 3.8 —5.4) and bromophenol blue (pH range 3.0—4.6) from yellow to blue. 

Bromocresol green Tetrabromo-m-cresolsulphonphthalein 3.6-5.2 Yellow Blue 4.7... 

Sulphonphthaleins. These indicators are usually supplied in the acid form. They are rendered water-soluble by adding sufficient sodium hydroxide to neutralise the sulphonic acid group. One gram of the indicator is triturated in a clean glass mortar with the appropriate quantity of 0.1 M sodium hydroxide solution, and then diluted with water to 1 L. The following volumes of 0.1 M sodium hydroxide are required for 1 g of the indicators bromophenol blue, 15.0 mL bromocresol green, 14.4 mL bromocresol purple, 18.6 mL chlorophenol red, 23.6 mL bromothymol blue, 16.0 mL phenol red, 28.4 mL thymol blue, 21.5 mL cresol red, 26.2 mL metacresol purple, 26.2 mL. 

It is clear that neither thymolphthalein nor phenolphthalein can be employed in the titration of 0.1 M aqueous ammonia. The equivalence point is at pH 5.3, and it is necessary to use an indicator with a pH range on the slightly acid side (3-6.5), such as methyl orange, methyl red, bromophenol blue, or bromocresol green. The last-named indicators may be utilised for the titration of all weak bases (Kb> 5 x 10-6) with strong acids. 

For the weak base (Kb = 1 x 10 7), bromophenol blue or methyl orange may be used no sharp colour change will be obtained with bromocresol green or with methyl red, and the titration error will be considerable. 

For the primary stage (phosphoric) V) acid as a monoprotic acid), methyl orange, bromocresol green, or Congo red may be used as indicators. The secondary stage of phosphoric) V) acid is very weak (see acid Ka = 1 x 10 7 in Fig. 10.4) and the only suitable simple indicator is thymolphthalein (see Section 10.14) with phenolphthalein the error may be several per cent. A mixed indicator composed of phenolphthalein (3 parts) and 1-naphtholphthalein (1 part) is very satisfactory for the determination of the end point of phosphoric(V) acid as a diprotic acid (see Section 10.9). The experimental neutralisation curve of 50 mL of 0.1M phosphoric(V) acid with 0.1M potassium hydroxide, determined by potentiometric titration, is shown in Fig. 10.6. 

Boric acid behaves as a weak monoprotic acid with a dissociation constant of 6.4 x 10-10. The pH at the equivalence point in the titration of 0.2M sodium tetraborate with 0.2 M hydrochloric acid is that due to 0.1 M boric acid, i.e. 5.6. Further addition of hydrochloric acid will cause a sharp decrease of pH and any indicator covering the pH range 3.7-5.1 (and slightly beyond this) may be used suitable indicators are bromocresol green, methyl orange, bromophenol blue, and methyl red. 

The pH range for bases with Kb> 10 5 is 3-7, and for weaker bases (Kb > 10 6) 3-5. Suitable indicators will be methyl red, methyl orange, methyl yellow, bromocresol green, and bromophenol blue. 

The mixed indicator, bromocresol green-dimethyl yellow, may be used with advantage. The indicator consists of 4 parts of a 0.2 per cent ethanolic solution of bromocresol green and 1 part of a 0.2 per cent ethanolic solution of dimethyl yellow about 8 drops are used for 100 mL of solution. The colour change is from blue to greenish yellow at pH = 4.0 — 4.1 the colour is yellow at pH = 3.9. 

In the direct method, a solution of the ammonium salt is treated with a solution of a strong base (e.g. sodium hydroxide) and the mixture distilled. Ammonia is quantitatively expelled, and is absorbed in an excess of standard acid. The excess of acid is back-titrated in the presence of methyl red (or methyl orange, methyl orange-indigo carmine, bromophenol blue, or bromocresol green). Each millilitre of 1M monoprotic acid consumed in the reaction is equivalent to 0.017032 g NH3 ... 

A sharper colour change is obtained with the mixed indicator methyl red-bromocresol green (prepared from 1 part of 0.2 per cent methyl red in ethanol and 3 parts of 0.1 per cent bromocresol green in ethanol). 

Procedure. The test solution should contain between 0.001 and 0.02 mg of cobalt. Evaporate almost to dryness, add 1 mL of concentrated nitric acid, and continue the evaporation just to dryness to oxidise any iron(II) which may be present. Dissolve the residue in 10 mL of water containing 0.5 mL each of 1 1 hydrochloric acid and 1 10 nitric acid. Boil for a few minutes to dissolve any solid material. Add 2.0 mL of a 0.2 per cent aqueous solution of nitroso-R-salt and also 2.0 g of hydrated sodium acetate. The pH of the solution should be close to 5.5 check with bromocresol green indicator or with a pH meter. Boil for 1 minute, add 1.0 mL of concentrated hydrochloric acid, and boil again for... 

Chromatography on thin layers of Avicel C (microcrystalline cellulose from American Viscose Division, F.M.C. Corp., Newark, Del.), in 1-butanol-water-acetic acid (4 5 1) with bromocresol green as indicator. Countercurrent distribution in same solvent by single withdrawal procedure with 299 transfers and 100 elements... 

Testing is undertaken by several methods, including chloroform extraction and use of a sulfonphthalein dye (absorbance of yellow-colored complex using bromophenol blue and bromocresol green) or the use of eosin (sodium tetrabromofluorescein) solution in acetone and tetrachloroethane solvent. After shaking with a citric acid buffer and eosin addition, upon standing the lower layer turns pink if filmer is present. Subsequent titration with Manoxol OT (sodium dioctyl sulfosuccinate) quantifies the filmer, with loss of the pink color indicating the end point. 

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