Xylene Cyanole FF, Redox Indicator HAZEL M. TOMLINSON, OTTO T. AEPLIl, AND HELEN M. EBEHT* Temple University, Philadelphia, Pa. In searching for a redox indicator giving a pronounced color change at the equivalence point in determinations of certain metallic ions with ferrocyanide, one of the dyes added to the conventional indicators was xylene cyanole FF. This dye was found to be a suitable redox indicator for titrations of arsenite, ferrocyanide, and ferrous ions with ceric sulfate. The values thus obtained were in excellent agreement w-ith those determined potentiometrically as well as with better known indicators. Attempts were then made to determine the transition and oxidation potentials over a range of acid concentrations.
x
TEcyanole FF, a dye of the triphenyl carbinol type, is hell LEA known through its use in modified methyl orange indicator (6). Weinberg ( 1 2 ) , who patented a method for its manufar t u r r , stated that reducing agents transformed the dyestuff into the leucoform. Brahmajirao ( 2 ) has reported that it is oxidized irreversibly by potassium dichromate and is unsuitable for the determination of ferrous ion by this okidant.
1.5 M in hydrochloric acid were found to yield almost identical values. In these titrations also, the blanks did not exceed 0.01 ml. of 0.05 X ceric sulfate.
__ Table 11. ~~~~~~i~~~ of x,lerle cyanole FF with Other Indicators in Mohr’s Salt Titrations with Ceric Sulfate Indicator Mohr’s Salt Solution, Y
EXPERlMENTAL
The authors ( 1 ) have found that xylene cyanole FF serves as well as does ferroin in the standardization of ceric sulfate with arsenious acid based on the method of Gleu (6). In four such analyses using ferroin indicator, the normality of a ceric sulfate solution was 0.05783 = 0.00001; in four similar titrations in which xylene cyanole FF indicator was used, the average value of the normality of this same ceric sulfate solution was 0.05782 * 0.00001. ,41so, the results obtained in titrations of ferrocyanide ions with ceric aulfate using either eriogreen or erioglaucine, of the same general type as xylene cyanole FF, as well as the more widely recognized redox indicators, diphenylamine and sodium diphenylamine sulfonate, are in excellent agreement with those in which this indicator was used. This is clearly shown in Table I, in which reported values are average values of two determinations; no deviation exceeded 0.6 part per thousand.
b
0.04831 0.04831 0.04831 0.04829
Table 111. Comparison of Analyses of Ferrocyanide and Rlohr’s Salt Solutions with Ceric Sulfate, Using Potentiometric Method and Xylene Cyanole FF Indicator Reagent, N Potassium ferrocyanide, soln. 1 Potassium ferrocyanide, s o h . 2 Mohr’s salt soln.
Method Xylene cyanole FF P o t e n t i o m e t G 0.04964 0,04954 0.05070 0.05069 0,04788 0.04788
Knopf (8) has reported that the transition potential of xylene cyanole FF is +0.71 volt. It was the authors’ plan to redetermine the transition potential and t o determine the formal oxidation potential according t o the method of Walden, Hammett, and Chapman ( 1 1 )in the case of 1,lO-phenanthroline-ferrous complex (10). The values which they obtained, as revised by Hume and Kolthoff ( 7 ) ,were duplicated by the authors (5). In the titrations in which xylene cyanole FF was used, potentials which drifted with time and with accompanying color changes were observed. Changes in indicator and in acid concentration were ineffective in eliminating these drifts. To produce a more pronounced differential curve without introducing a highly colored system, the ferrous-ferric sulfate system in 1 M sulfuric acid was replaced by the ferrocyanide-ferricyanide system in 0.01 M sulfuric acid. This system exhibits the lowest oxidation potential of those reductants readily available and convenient. Also a saturated calomel electrode replaced the quinhydrone electrode of Walden and his co-workers when the concentration of sulfuric acid was 0.01 -11,since the latter was found somewhat insensitive to changes in the potential of the accompanying half-cell. ,411 chemicals used except the xylene cyanole FF were of reagent grade. This dye had been found ( I ) unchanged after adsorption by activated alumina from an ethyl alcohol solution and consequent extraction with water, Five milliliters of 0.004 ,M aqueous solution of dye were present in 100 ml. of the solution used for the titration in each case. The 0.01 JP ceric sulfate solution used as oxidant was prepared by dilution of a portion of 0.05 JP stock solution; sufficient sulfuric acid was added in the process of dilution to give the desired acidity in each case. The 0.002 111 potassium ferrocyanide solution was passed through a Kalden reductor immediately before use.
Table I. Comparison of Xylene Cyanole FF with Other Indicators in Potassium Ferrocyanide Titrations with Ceric Sulfate Indicator Xylene cyanole FF Eriogreen Erioglaucine Diphenylamine Sodium diphenylamine sulfonate
Xylene cyanole F F a Enogreen“ Erioglaucinea Ferroinb 5 drops of indicator-O.l%. 3 drops of indicator-0 025 X.
Pota.sium Ferrocyanide, -V 0,04943 0.04940 0.04942 0 04949 0.01913
The comparison of xylene cyanole FF with three other redox indicators used in the titrations of blohr’s salt with ceric sulfate according t o the method of Furman and Wallace ( 4 ) was made. Table I1 shows that the indicator gives values in agreement with the other indicators the authors employed; duplicate determinations agreed within 0.2 part per thousand. Table I11 likewise shows that the deviation in the results obtairirtl by the potentiometric method and those involving the visual end point using sylene cyanole FF are within the limits of experimental error. Titrations of approximately 0.05 N potassium ferrocyanide containing 2 ml. of concentrated sulfuric acid and 1 t o 50 drops of indicator, and with final volumes of 95 to 100 ml., required blanks of less than 0.01 nil. of ceric sulfate. In titrations involving the same reagents, concentrations up to 4 111 in sulfuric acid and up to P r e e n t address, Pennsylvania Salt .\If& Co., Philadelphia, Pa. Present addreso, Franklin 1n;titiite Laboratories for Research and Develoiiirienr, Philadelphia, Pa. 1
2
286
V O L U M E 2 3 , NO. 2, F E B R U A R Y 1 9 5 1 The electronietric- apparatus included a student potentiometer, standarcl \Yeston cell, and galvanonieter of moderately high semitivity. .4wferenre electrode vas prepared for each titration correspontliiig to the acid coneentration of the solution containing the indicator. The half-cells v,-ere immersed in a bath held a t 2.5" * 0.1' C. Calibrated burets and a universal p H indirator aswml)ly were used. Inasmuch as continued atidition of ceric sulfate, acid by prepariit ion, should progressively increase the hydrogen concentration of tht. solution being titrated, the p H of t,his half-cell was nieasutwl :it the several critical potentials being determined. This was dotira by co-nipleting a separate titration only to the desired potential, removing a portion of the solution in the half-cell, and then niwxuring its pH instrumentally. The solution for titration xhich contained potassium ferroryaiiidc~.x y l ~ n ec*yanoleFF, and water had a deep blue color with chcri'>.tints. ;is ceric sulfatb solution was added, the cherry color I ) t ~ a m predoniinnnt e just past the equivalence point of the ositia.ium ferrocyanide to potassium ferricyanide. Rlue tintr, xlway? present, in the cherry, turned t o olive, t>hento gold n w r the oxidation potential of xylene cyanole FF. Ho~vever,the reti color masked this visual end point. The mixture of rcd and gold theit blcndcd into a bright orange nhich persisted until, near the rnd of the titration, the solution hecame clouded with a finegrained, Jvhite prccipitatr. This cornpourid has been identified iuni cL>i'ou*E I ~ I or~yanitlc.. ~I Immediately after the predoniinancne of t h v red color i n the solution, constant, voltages could not ht>obtained. JVith the appearance of the orange c ~ ~ l o r , ho\vrver, the voltages again berame constant. ill1 color c1i;inges wcw gradual : there was iio sharp visual end point. In order to establish the range for possible study of the effect of rhanges in acid concentration upon the oxidation potential of the indicator, titrations xere first carried out in solutions 1 .lI and 2 .lf with rwpcJct to sulfuric acid. I n the former, suggestions of a differential w r v e were indicated but, in the latter, curves with only one point of inHertiori iwre obtained. .4ccortlingly, dc>terminatione \ v i > r ~attcmptetl in 0.2,i, 0..50, 0.7.5, and 1.00 .II arid. The
287
transition potentials obtained at these acidities were 1.02, 0.!)6, 0.97, and 0.98 volt, respectively, while the indicated irreversible oxidation potentials of the indicator were 1.08, 1.11, 1.10, and 1.11 volts. Potentials mere measured using both platinum and gold elect,rodes according t o the standard of reproducibility of Mic:haelis ( 9 ) . Values agreed within 10 to 20 mv. co\~:L~l~loY8
Sylenr, cyanole FF has been found to compare favoral)ly with the more widely used organic, redox indicators in the titrations of 1Iohr's salt and arsenious acid with 0.05 .lf ceric sulfate as well as i n tit,rations of ferrocyanide in solutions up to 4 -11in sulfuric ac4d or 1.5 -1!f in hydrochloric acid with the same oxidant. An attempt was made to determine hoth transition and formal oxidation pottantials of the indicator i i t sulfuric wid solutions.
(1943 ) .
J., I b d , 46, 263 (I!J241. (9) Michaelis. L.. "Oxidatio~i-l~cductioll Potentials." Philadell~hia and London. .J. H. Lippitic-ott ro.. 19:30. (10) Smith, G. F., and Richtei.. I'.I'., "Phenanthroline and Sul~stituted Phenanthivliiie liicliixtotw" C'olumbus, Ohio, G. 1:red( 8 ) Knopf,
erick Smith ('heniical
c'o.
( I 1 ) \Yaldeii, G . H., Hamniett, 1,. I'.. niitl r'hapman. R. P., .I. .41ri. Chem. SOC.,5 5 , 2649 ( l W 3 ) . (12) \Veinberg, .I.,U. S. Patent 472,091 and Brit. Patent 15.143 (1891); Germail Patent 7 3 . 7 1 7 ; French Patent 215,8:15.
RECEIVED XIaroh 7,
1!15U.
Distribution and Type of Sulfur Compounds in Straight-Run Naphthas .J. H. IIALE, C. J . TIIOMPSON, 11. G. H i R K K K , H. 11. SMITH, 4 \ J~. S. B 4 L L Petrolerim E x p e r i m e n t S t a t i o n , B u r e a u of AWines,Burtlescille, Okla., and P e t r o l e w m & Oil-Shale Kxperimen t Station, L a r a m i e , IVyo.
T
HIS riJport, vihich is the first caoncerning the work of Aniri.ican Prtroleum Institute Research Project 1 8 A 011 t h e separation and identification of sulfur compounds in crude oil, is in the nature of a survey to clrtrrmine the t,ypes of sulfur compounds that niay tw especated to be found i i i naphthas from high-sulfur crude oils. The distribution of free sulfur, hydi,ogen sulfide, nirrcaptans (thiols), disulfides, two types of sulfides having different activities, and residual (less reactive) sulfur vonipounds has been determined for naphthas, 482" F. (250" ('.) end point, from 17 typical high-sulfur crude oils of the United Statea and lliddle East. The naphthas included straight-run distillates produced in the laboratory from a number of crude oils by distillation both a t atniospherio pressure and a t very loiv pressures (0.5 t o 2.0 mm. of mercury), so that, comparative data were obtained showing the effect, of heating to the temperatures attained in the ordinary distillat.ion of naphtha. T h r results indicate a \vide range in the proportion of the different types of sulfur compounds. Honever, many of the oils or naphthas contain predominantly sulfides and mercap-
tans, lvhile relatively felv contain appreciable quantities of clisulfides. Two are characterized by large quantities of free sulfur. -4lthough many changes i n the sulfur compounds present may occur during distillation, the most olwious and interesting on(' is the almost universal decrease in t h r routrnt of that unreac+ive sulfur group called "residual sulfur." i i i thr naphthas producetl a t atmospheric pressure a? cvmpared to thore ohtained at rrducaed pressure. I n general, this rrducvtion i n residual sulfur sho~vsul) aR sulfide sulfur in the clistillatcx iiiailc~a t :ltmoPpheric pressure. A PI' A H A TU S
The apparatus usrtl in thv stud). is shown in Figure 1. Its operation and construction arc convrntional. Light distillates and hydrogen sulfide wrre c~ollrt~tcd in the liquid air trap, from whence, a t the completion of t h c rxperiment,, the hydrogen sulfide was vaporized by marming to room temperature. The libcrated hydrogen sulfide was preripitated as cadmium sulfide and the quantity of sulfur was deterniined t)j- direct weighing in some rases, but iodometrically in most of the experiments.
