U . S. Department of Commerce Research Paper RPl900 National Bureau of Standards Volume 41, July 1948 Part of the Journal of Research of the National Bureau of Standards Acid-Base Reactions in Organic Solvents. Behavior of Some Halogenated Derivatives of Phenolsulfone­ phthalein with Different Classes of Organic Bases in Benzene By Marion Maclean Davis, Priscilla J. Schuhmann, and Mary Ellen Lovelace This paper, the second in a series co ncerning the use of indicator dyes to st udy t he re­ actions of organic acids a nd bases in o rganic solvents, deals with halogen derivatives of phenol­ sulfonepht halein. Spectrophotom etric data arc given for mixt ures of bromocresol gree n, bromophenol blu e, iodophenol blue, a nd tetrabromophenol blue wit h prima ry, seconda ry, and tertia ry aliphatic amines in benzene; and qualita tive data a re tabulated fo r chlorophenol blue, b romochl orophenol bllle, chlorophenol red , b romophe nol red , bromocresol purple, and brom othymol blue. Comparisons a re m ade of the p henolsulfon eph t halein s a nd t he bromo­ pht halein magentas. The st ru ctura l changes that accompa ny t he color p henomena a re discussed. Sugges t ions a re m ade regard in g t he use of the indicators in in ert solvents. I. Introduction occ urs during the second stage of neu tralization depends upon the nature of the base that is add ed. A previous article [ljl described in detail the It is differen t for primary, secondary , and ter tiary , preparation of the acidic indicators, bromo­ aliphatic amines. The e differen tiating reactions phthalein magenta E and bromophthalein magen ta parallel those previously described for bromo­ B (respectively, thc ethyl ester and the n-butyl phtllalein magenta [1] . The reactions of the phenol­ ester of tetrabromophenolphthalein), and their sulfonephthaleins were inves tigated less thor­ reaction with various types of organic derivatives oughly than those of the bromophthalein ; of ammonia in benzene and in other organic soI­ magentas, because various a pects of their be­ l v ents. The obj ec tives of our work on the appli­ havior are predictable from their structural cation of indicator dyes to the measurement of relationship to the bromophthalein m agentas, and acidity and basicity in organic solvents were also because the sulfonephthaleins are in general I discussed, and a review of theoretical aspects of less suitable acid-base indicators for organic acid-base reactions in organic media and of experi­ solvents than the bromophthalein magentas. m ental contributions of several other inves tigators The structures and reactions of the two groups of to this field was also presen ted. indicator dyes are compared in sections to follow, This ar ticle deals with the reactions of 10 but reference to the first paper in this series is halogen derivatives of phenolsulfonephthalein essential for complete details of th e reactions of wi th~ different types of organic bases in benzene. the bromophthalein magentas and for a more The phenolsulfoneph thaleins are dibasic acids. extensive interpretation of the role of the solven t They are readily available commercially and are in acid-base reactions. widely used as acid-base indicators in aqueous m edi a, because they undergo vivid color changes II. Apparatus and Method at definite pH values. Their behavior in benzene The spectrophotometric data were obtained wi th is more complex. In par ticular, the change that a Beckman quar tz photoelectric spectrophoto­ meter [2, 3] in which a pair of stoppered cells and 1 Figures in brackets indicale lhe li terature references a t lhe end of lhis pa per. a spec ially designed cell compartment were sub- Acid-Base Reactions in Organic Solvents 27 ----------------~-~---------------------~------- stituted for the cells and cell holder supplied with H the commercial instrument. Each cell consisted o, of a pair of optically matched crystalline quartz X-r:l-Y endplates 2 mm in thickness and a st,oppered Z-~, quartz cylinder 3.8 cm in diameter and 1 em in C-G) length, open and polished at the ends. The con­ " , struction of the cell holder and the manner of B 'OSO 2 x-Z-0' -Y assembling the parts of the cell were described , previously [1]. o In most of the measurements, one cell contained H the pure solvent and the other cell contained the FIGURE 1. Stmctw'al formula for a phenolsulfonephthalein solution under investigation. Solutions were pre­ indicator pared in a room kept at 25° C, and measurements were made at 26° ± 2° C [1]. Volumetric flasks mula for phenolsulfonephthalein indicators is and pipettes calibrated at the Bureau were used given in figure l. The nature of the substituents throughout. Stock solutions of known concentra­ in positions X , Y, and Z of rings A and B is shown tions of the separate compounds were prepared in table 1. In tetrabromophenol blue, the four and were diluted quantitatively immediately unlabeled positions in ring C are occupied by before use, to give the desired mixtures. The bromine atoms; in all of the other sulfone­ microbalance used for weighing the indicator dyes phthaleins listed, by hydrogen atoms. gave a precision of 0.5 to l.0 percent. The indicators were obtained from several Readings were usually made at intervals of 5 commercial sources. Bromophenol blue, chloro­ or 10 mJ.L. In a few cases additional readings were phenol blue, iodophenol blue, and tetrabromo­ made at intervals of 1 mJ.L. Measurements of the phenol blue were dried in a vacuum oven or percentage transmittancy [4] were usually repro­ Abderhalden apparatus before use. The remain­ ducible within ± 0.2 percent. In the figures to ing indicators were taken from freshly opened follow the transmittancies in percentages and containers. wavelengths in millimicrons are plotted as ordi­ Microanalyses for the various indicators are nates. and abscissas, respectively. Values for the presented in table 2. The sample of bromo­ molar absol'bancy index, au, were calculated by chlorophenol blue appeared to contain an acidic , means of the equation impurity and was therefore not analyzed. Two samples of chlorophenol red, from different com­ mercial sources, were analyzed. Both samples showed a lower carbon content and higher chlorine in which T s= T so!n/ T so!v= the transmittancy of the content than the calculated values. Iodophenol solute, b is the depth of ·the cell in centimeters, blue showed too low carbon and too low iodine and ]vl is the molar concentration of the solution. content, and tetrabromophenol blue, high carbon The absorbancy, often referred to as the "optical and hydrogen and low bromine. The percentage density," is the negative IQgarithm of the trans­ compositions found for the other six indicators mittancy [4]. are in satisfactory agreement with the theoretical values. III. Materials IV. Color Transform a tions of The benzene used as the solvent and the organic Phenolsulfonephthaleins bases were the same materials as those used in the preceding investigation [1]. An understanding of the relation between the In table 1 the indicators are listed under both color and the environment of phenolsulfone­ common and chemical names, together with de­ phthaleins is necessary to interpret experimental \ scriptive comments. The general structural for- observations of their behavior in benzene. 28 Journal of Research TABLE 1. List and description of indicators Substituents pH I'ange and co loI' change in Common name a Chemiralname ColoI' of s01 id aqueous solution x y Bromophenoll>lue ____________ T etrabrollJophenolsu Ifonephtbalein _____________ Br Br Pale cream. _____ 3.0 (yellow) to 4.6 (purple)b Cblorophenol blue ____________ T etracil 101'0pbenolsu Ifon ephtbalei n ______________ CI CI Light orange ____ Do.b Iodophenol blu e _______________ T etraiodophenolsulfonephthalein ________________ Orange __________ 3 (yell ow) to 5 (blue)' Brom ochl ol'ophenol blue ______ Dibromodichiorophcnolsllifonephtbalein ________ Br CI Dark red ________ 3.0 (yell ow) to 4.6 (blue)d 'l'etrabromophenol blue _______ T etrabromophenol tetrabromosu Ifonephthalein __ Br Br Light brown ____ Do.e Bromocresol green ... __ _____ ._._ Tetrabromo-m-cl'esolsulfonephthalein ___________ Br Br CH, Pale cream ______ 3.8 (yell ow) to 5.4 (blue)d Chlorophenol red _____________ Dich lorophenolsulfonephtilalein _________________ CI ------- -- --- --- --- R ed-brown ______ 4.8 (yell ow) to 6.4 (red)d Bromophenol red _____________ Dibromophenolsulfonephthalein ________________ Br ------------ ------ Dark red _____ __ _ 5.2 (ycll ow) to 6.8 (red)d Bromocresol purple ____ _______ Di bromo-o-cl'esolsuifonepb thalein ________________ Br Cll, Pale cream ______ 5.2 (yellow) to 6.8 (purple)b BrollJothymol blue ____________ Di bromothYllJolsulfonephthalein ________________ Br (Cll,hCll Cll, Light pink ______ 6.0 (yell ow) to 7.6 (blue)b • The spelling used is that preferred by editors of publications of the American Chemical Society. b ll. A. Lllbs and W. M . Clark, J . Washington Acad. Scicncc G, 481 (191 6) . The range 2.8 to 4.6 is given for bromophenol blue and for cblorophenol blue instead of the values 3.0 to 4.6, now accepted. , Eastman Organic Chemicals List No. 35, Eastman Kodak Co., Rochester, N. Y. d B . Cohen, Heprint No. 1131 from the Public llealth Reports (Governmcnt Printing Office, Washington, D. C., 1927) . • W . C. llarden and N. L . Drake, J. Am. Chem. Soc. 51, 562 (1929). M. M. Haring and ll. A. Ueller, J. Am. Chern . Soc. 63, 1024 (194 1), give the pH range as 2.6 to 4.4. TABLE 2. Analyses of i ndicatoTs o o 0 11 " I Calculated Found 8 Name 8 11 8 8 11 I C H Xb S C H Xb s c-0 c-0 (--.4 c- 0 _._-------------- -------- I 1 I I "I % % % % % % % % 8 503- 8 503- 8 50;- Bromophenol blue , _______ 34.06 1.