941 i
TABLE 111 PARACHOR VALUESOF BRANCHED CHAINHYDROCARBONS Wane
2-Methylheptane 3-Methylheptane 4-Methylheptane 3-Ethylhexane 3-Methylpentane
P,n-isomer 351.0 351.0 351.0 351.0 271.0
P,exp. 349.4 347.7 347.6 345.0 267.9
I
I
Strain er
bran&
-1.8 -3.3 -3.4 -8.0 -3.1
Calculated from previously recorded data -6 8 304.2 311.0 3-Ethylpentane -1 9 3(19 1 311 0 2-Methylhexane 307.3 -3.7 311.0 3-Methylhexane -1.9 347.2 351.0 2,5-Dimethylhexane 344.9 -3.1 351.0 2.4-Dimethylhexane -3.5 351.0 344.1 2,3-Dimdhylhexane -4.2 351.0 342.6 3,4-Dimethylhexane 307.5 -1.8 2,4-Dimethylpentane 311.0 -3.3 304.3 2,3-Dimethylpentane 311.0 -3.1 384.9 2,5-Dimethylheptane 391 0 381 1 -5.0 2,4-Dimethylheptane 391.0 -9.0 373.1 2,3-Diinethylheptaiie 391.0 -2.3 426.4 431.0 2,7-Dimethyloctane -4.1 122.9 431 .O 3.4-Dimethyloctane I
the most compact structure would have the lowest parachor. The same effect may be noted in parachor values calculated from previously recorded densities and surface tensidns of hydrocarbons.lO These values are also included in Table 111. While certain regularities appear, sufficient data are not available to properly evaluate the variations in the effect of branching the chain.
Summary 1. The densities, surface tensions, and para(10) M.p. Dou, “Physical Constants of Principal Hydrocarbons,” Thud Edition, Texas Corp., 1942.
[CONTRIBUTION FROM
THE
~
L.
I
30 40 50 Temperature, OC. Fig. 3.-Parachors of normal hvdrocarbons. 30
chars of a series of hydrocarbons of high purity have been reported. 2. The parachor value of the CHI group is reported as 40.0. The atomic parachor of H is reported as 15.5, that of C as 9.0. 3. There is no apparent change in the CH, increment as the chain is increased up to duodecane. 4. The effect of branching the chain is not constant in the saturated hydrocarbons EMORY UNIVERSITY, GA. RECEIVED FEBRUARY 10,1944
CHARLES E. COATES CXEMICAL LABORATORY, LOUISIANA STATE UNIVERSITY]
A Spectrographic and Kinetic Study of the Alkaline Fading of Tetraiodophenolsulfonphthalein BY EDWARD S. AMISAND RALPH THEODORE OVERMAN
The alkaline form of iodo phenol blue (tetraiodophenolsulfonphthalein) has a characteristic absorption curve the intensity of which is a function of the amount of the dye present in the blue form. If an excess of the alkaline hydroxide is added to a solution of the iodo phenol blue, the dye fades to a colorless condition. The rate of fading depends upon the concentration of hydroxide present; When the colorless solution is acidified, the characteristic yellow acid form of iodo phenol blue develops progressively with time. This regeneration reaction has been studied quantitatively in the case of the brom
phenol blue.’ It is possible to study the structure of the faded and unfaded form of the dyes both spectrographically and kinetically. In this investigation a spectrographic study was made of both the unfaded and regenerated tetraiodophenolsulfonphthalein to determine whether the two were identical. A kinetic study of the fading process in the presence of iodide salt also was made. By these methods it was hoped that definite conclusions could be reached as b the validity of proposed mechanisms for the fading and regeneration processes. (1)
AmL a d Rice J. Phyr. Chmm., M ,888 (1948).
942
EDWARD s. AMISAND RALPHTHEODORE OVERMAN
Vol. 66
molar using the same quality of dye I. The Spectrographic Study.-The fading is up to assumed to take place according to the reaction2sa and the same procedure employed by Amis and LaMer3 in studying the kinetics of the fading of 1 bromo phenol blue. The alkali for the fading was made up according to the specifications of the above authors. All measurements were made + OH- + I from cells with a column of absorbing medium sea- \ \ a z o which was 2 em. in length. The light source for the visible region was a Mazda filament lamp and -I I for the ultraviolet region was a hydrogen discharge tube. The setting for the visible spectra was --C--OH position 3 of the glass system covering a frequency of 450-700 fresnel units. For the ultraviolet W so*absorption of the faded dye, positions 5 and 9 of the quartz system covering a region of 450-1500 I fresnel units (2000-6000 .k.) were used. and hence the regeneration is simply the reThe procedure consisted of printing a millimeter forming of the colored quinoid form of the dye scale on the plate, exposing the plate as a blank from the colorless carbinol. According to Brode* with no absorption cells in the light beam, and the quinoid structure has a characteristic ab- then interposing the cells, one being filled with sorption band a t a more or less definite region of distilled water and the other containing the the spectrum depending on the other groups sample being studied and measuring the absorppresent. The product formed in reaction (1) tion. The respective cells for the water and for would show absorption due to the carbinol, phenol the sample were always the same. The blank and sulfonic acid groups which have no absorption was made necessiry by the fact that it was found in the range of the normal photographic plate.4 to be impossible to equate the light intensities of The regeneration reaction it is presumed (1) the two parts of the beam visually so that they takes place according to the following mechanisms gave identical readings on the densitometer. The blank mad; it possible to correct for the initial difference in intensity of the two beams. The times of exposure were three, four and five seconds. The final cume was plotted from the average of the three densitometer readings corresponding to a given frequency. The absorption as a function of the degree of fading was determined by setting the dye m)to fade a t room temperature in a known strength of alkali and at stated intervals of time measuring the absorption of the fading material. The fading was carried out in such concentrations of alkali that the short time used in taking absorption represented little change in the condiHz0 tion of the dye since the rate of fading was very slow. The densitometer used was an Amlied Thus the quinoid structure of the dye is re- Research Laboratories Instrument which ‘measgenerated and since this material is identical ures the density of the plate by use of a photowith the unfaded acid form of the dye, the ab- electric cell. In t h i s instrument the dark current sorption spectrum of the regenerated material is set to zero on the galvanometer scale and the should of necessity coincide with that of the acid reading of 100 as the transmission of a clear form of the unfaded iodo phenol blue when the portion of the plate. The densitometer readings two are at like PH. (D’s) then ranged from zero to one hundred. Apparatus and Procedure.-The spectroThe logarithm of the ratio of the galvanometer graphic data were obtained using a large Littrow deflection (D)for the beam which had passed spectrograph with spectrometric attachments. through the dye to that (Do) which had passed For these experiments dye solutions were made through the water can be related to the absorption (2) Thiel, MmaLh., 68/64, 1008 (1929). of the incident light by the dye solution when (3) Amis and LaMer, Tars JOUXNAL, 61, 905 (1939). proper corrections are made for the corresponding (4) Brode, “Chemical Spectroscopy,” J. Wiley and Sons, Inc., deflections (D’ and D6)obtained from t h i blank, New York, N. Y.,1939, PP. 127-142.
C-7-c/q0-
/q\&-
+
A STUDY OF
June, 1944
-
10.0
5.0 O’O JOO 70.0
-
I
943 FADING OF TETRAIODOPHENOLSULFONPHTHALEIN
THE ALKALINE
v
0
I
I
700
@W
I
I
I
CURVE 2
-
Q
1
I
f 1
” I
I
I500
1300
1’00
1
I
1
1
I
I
-
60.0
i
50.0 40.0
30.0 20.0
10.0
0
450
500
550
600
650
700
f (frequency in fresnel units). Fig. L-Specific extinction coefficient, k, versus frequency, f: Curve 1, monosodium salt of iodo phenol blue; Curve 2, iodo phenol blue faded in 0.009 molar sodium hydroxide; Curve 3, unfaded and regenerated iodo phenol blue in like strength of dilute hydrochloric acid.
and from this relationship we calculate the specific regenerated iodo phenol blue is likewise plotted extinctidn coefficient, k, which according to Beer’s in Curve 3 of Fig. 1, the measurements being taken in dilute hydrochloric acid solution of like law is given by concentration (pH 3) in both cases. The two I D D; log - = - k d log $ - l 0 g . b spectra are identical and hence the regenerated la dye corresponds exactly to the unfaded material. or Thus the regeneration process is merely a change 1 OD: k =log frpm the colorless carbinol to the yellow acid cd D, d quinoid structure of the iodo phenol blue. This is plotted against frequency according to the These spectrographic data would support the su gestion of B r ~ d e . ~ mechanism of the fading to be the formation of bata and Discussion.-The specific extinction the colorless carhinol from the quinoid form of coefficients and the corresponding wave lengths the dye as accepted by ThieL2Biddle and Porter,6 of the unfaded monosodium salt of iodo phenol Kober and Marshall,s Kolthoff,’ and Amis and blue molar) in solution containing no LaMera rather than the mechanism proposed by excess alkali are plotted in Curve 1 of Fig. 1 Kilpatrick and c o - w o r k e r ~ . ~These ~ ~ ~ ~investi~ using frequency in fresnel units as abscissas and gators thought that the fading was due to the subspecific extinction coefficients as ordinates. This stitution of one of the four iodine atoms in the method of plotting corresponds to decreasing dye molecule by the hydroxide ion yielding iodide wave lengths of light from left to right. The ion. dye is seen to have a sharp absorption maximum Now if the fading mechanism were one of subat a frequency of 510 fresnel units or 5808 A. stitution of a heavier iodide atom by a lighter The specific extinction coefficient as a function of hydroxyl radical there should be only a shifting frequency for the alkaline faded iodo phenol blue of the absorption band to correspond to the differin 0.009 molar sodium hydroxide is plotted in (5) Biddle and Porter,THIS JOURNAL, 87, 1571 (1915). Curve 2 of Fig. 1. This absorption spectrum fs (6) Kober and Mushall, ibid., 88, 59 (1911). (7) Kolthoff, “Acid Base Indicators,” The Macmillan Co., New typical of non-chromophoric molecules, i. e., molecules containing linkages similar to those York, N. Y..1937, translated bqRosenblum from the fourth, 1931, German edition; aee pages 111, 116 and 218-227. found in alcohols, acids, etc. (8) Chose and Kilpatrick,THIS JOURNAL, 54,2284 (1932). The specific extinction Coefficient as a function (9) Kilpatrick, C h m . Rm.,16, 57 (1935). (10) Panepinto and Kilpatrick, THIS JOURNAL, 69, 1871 (1937). of frequency of both the unfaded and of acid
944
EDWARD s. AMISAND RALPHTHEODORE OVERMAN i
I
I
I
I
I
I
I
1'01. 66 I
I
1
pH z 11.05
Fig. 2.-Specific
extinctioii coelticieiit, k,
f (frequency in fresnel units). versus frequency, j , of fadiiig iodo pheliol bluc i n 0.009 molar sodium hydrouide.
ence in resonance of the molecule. The absorption, however, would still be in the visible. Curve 2 of Fig. 1 shows that the faded form of the dye is non-chromophoric and has, therefore, lost its quinoid structure. Further, the regenerated acid form of the dye is identical in absorption with the.acid form of the unfaded dye as shown by Curve .3 of Fig. 1. It appears that the acid regeneration is the removal of the hydroxyl radical from the carbinol and the reforming of the quinoid structure of the dye, rather than the reentering by acidification of the iodine atom into the benzene nucleus. Figure 2 represents the absorption of the iodo phenol blue as a function of the degree of fading in 0.009 molar sodium hydroxide. These curves strongly resemble the absorption of the phthalein dyes as a function of the PH of the solution.11 And as in the case of change of pH, the absorption band does not shift greatly in wave length but simply changes in intensity, with the increased fading of thedye. II. The Kinetic Study.-The fading of brom phenol blue as a function of hydroxid; ion concentration has been carefully studied.' In helping to prove the mechanism of the reaction it would be pertinent to study the salt effect upon the reaction velocity. Especially would it help if the rate were run in the presence of an iodide salt, since if the mechanism proposed by Kilpatrick, et al., is correct the hdide ion should exert a mass effect whereas if the fading is due to the formation of carbinol the iodide salt should exert a primary salt effect and increase the reaction rate since the reactants are both negatively charged. Panepinto and Kilpatrick'O found a (11) Brodc. THISJWJKNAL. 46, 3.51 (IULA).
priniary salt effect upon the rate constants for the fading of the chloro, bromo, and iodo phenol blue dyes in the presence of potassium chloride and bromide but found the values for the internal energy were not of sufficient accuracy to test the primary salt effect upon this function. Materials and Procedure.-The materials and methods in these studies were essentially those used by Amis and LaMer.a The stock solution of iodo phenol blue was 1 x 10-4 molar. The sodium iodide (J. T. Baker analyzed) was made up before each run by weighing on an analytical balance and diluted to a suitable volume. The temperature was held constant to t0.01'. Ten milliliters of the 1 X lo-' molar dye solution was placed in a volumetric flask and sufficient sodium iodide solution, sodium hydroxide solution and water were added to make a total volume of 100 milliliters of solution which was 1 X 10-6 molar with respect to the dye, 0.006 molar with respect to the sodium hydroxide and with such concentrations of sodium iodide as to give the various ionic strengths used in the studies. The time of addition of sodiuni hydroxide was noted and used as the initial time in the runs. A standard neutral solution of the dye (1 X 10-6 molar) was also made up and placed in the thermostat. To make a reading five milliliters of the fading dye solution was pipetted into one colorimeter cup and five milliliters of the standard unfading dye into the other colorimeter cup. Using a Klett top-reading colorimeter the amount of fading was determined as a function of time The illumination used was a Mazda lamp with a blue filter. The rate constants were calculated using the pseudounimolecular rate equation. The bimolecular rate COIIstant was obtained by dividing the pseudounimolecular rate constant by the molarity of the sodium hydroxide which remained sensibly constant throughout a given run. The concentration was expressed in moles per liter and the time in days. In Table I are tabulated the bimolecular rate constants at various ionic strengths and for the temperatures 25, 35 and 45"; also the energies of activation and the Arrhenius frequency factors are recorded in this table. The quantitative agreement of the data on the rate constants with the requirements of Bronsted's theory of primary salt effect can Le illustrated by plotting log k us. 6 (see Fig. 3).
June, 1944
A
STUDY OF THE
ALKALINEFADINGOF TETRAIODOPHENOLSULFONPHTHALEIN 945 TABLEI
DATAFOR WATERWITH ALKALIHYDROXIDE AND ALKALI SALT ADDED: DYE
0.000 .006 .008
.O l C
,012 ,016
0.OOOb
.0775 .OS95 ,1000 .lo96 .1265
k, 25'
k, 35"
k, 45'
(14.3) 19.7 20.5 21.6 22.6 24.0
(27.7) 38.5 40.6 42.2 44.2 47.0
(50.2) 69.9 73.9 76.9 80.6 86.0
AE*, 25-35'
12,070 ia,i80 12,190 12,210 12,230 12,250
M,NaOH 0.006 N
WITR
ADDEDNaI
B, 25-35'
AE*, 35-45'
B, 85-4Lo
10 * 00 10.24 10.28 10.32 10.34 10.37
11,520 11,640 11,660 11,680 11,700 11,730
9.61 9.84 9.87 9.91 9.96 10.01
Log k obeys the limiting law to a higher ionic strength than would ordinarily be expected as was found for the alkalilie fading of brom phenol blue by Amis and LaMer.' Plots can be made of the energies and Arrhenius frequency factors, respectively, as a function of ionic strength. The slopes of these curves agree well with the limiting values of the slopes given by the equationsll AE* AE* AS*/2.3R AS*/2.3R
= 1569 4; (temperature 30") 1605
