ANALYTICAL CHEMISTRY
1306 reactor the volume of the catalyst is the constant factor. However, when density variations are small, corrections for this variable ~vouldbe slight. Surprisingly, however, in the case just mentioned where the correlation was very poor, even making the density correction failed t o produce good agreement between observed and calculated cracking activities. This lack of agreement may be due t o diffusional effects in the cracking reaction or t o an actual change in the quality of the active centers caused by the n-ide variation in preparational procedures and the gel structures produced. The latter might, correspond to changes in the pK, of the gel acids due t o structural differences. Severtheless, even for those catalyst preparations which fail to follow the general pH-activity curve a specific correlation curve can, undoubtedly, be established which \ d l hold for that particular type of cat.alyst its activity changes owing t o aging. It is further true t h a t the presence of any ion in the catalyst which is capable of base exchange, whether added intentionally or as a contaminant in the cracking stock, upsets the pH-ammoniumuptake relationship and, therefore, the pH-activitJ- correlat,ion. For example, the indicat,ed gasoline production is different from the actual production by as much as 10% (bawd on charge) when the catalyst is impregnated with 500 p,p.ni. of nickel. However, it’ kvould be very unusual for catalysk to pick up such quantities of contaminant from the charge stock. In fact, this much nickel results in a severely metal-poisoned catalyst, so that the very lack of agreement serves as an indication of poisoning. I n general, the amount of metal added from most charge stocks is not sufficient to interfere viith the applicability of the test. -4s much aa lo00 p.p.ni. of iron or 500 p,p,ni. of vanadium added by impregnation had almost no effect on the pH-activity correlation. Soncalcined clays (including acid-activated montniorillonite) fall into the category of catalysts containing exchangeable ions other than hydrogen. Severtheless mnples of a specific calcined acid-activat,ed niontmorillonite clay have been shown t o give results falling on a displawd correlation curve. It is anticipated t h a t each type of clay will require it3 o m correlation curve, because of compositional diffcrencrs. Thus while the standard pH test described here, or a simple modification thereof, can be used niorr generally than previously described tests as a simp!e nieawre of caatalytir cracking activity
of silica-alumina compositions, the method is still limited. However, it should have definit’e applicabilitj- as a control test or a rapid screening test with catalj-st t j p e s knon-n to conform t,o t’he indicated pH-activity relationships. S o t only fresh catalysts but also catalysts aged in coniniercial use are amenable to the indicated correlation. KO attempt has been made to correlate the activities of catalysts other than silica-alumina by this test. Silica-zirconia, silica-thoria, and alumina-boria. for example, are of very little interest commercially at present, Silica-magnesia, however, has been used commercially and represents a class of catalysts of definite interest to the pet,roleum industry. It is known t,hat the test descrilml in this paper cannot be rcadily used t,o characterize thip c*l:issof catalysts; silica-magnesia composites hydrolyze in aqueouy media to give hydroxyl ions. The reLmltwould be, of course, an upset of the p H activity correlation. Some of the types mentioned, however, should prove capable of correlation those sucah a s dim-zirconia and by the “pH test”-namely, silica-thoria n.hich should not hj-drolyze. LITERATURE CITED
Alexaiider, Proc. Am. Petroleum Inst., 27 (III),51 i.lY4i). Alexander, J., and Shimp, H. G.. S a t l . Petroleum Sews. 36, R 537-8 (1944). (3) Bitegash, Yu. A . , J . Gen. Chem. (U.S.S.R.). 17, 199 (1917). (4) Brunauer, 8.. Emmett, P. H., and Teller. E., J . .4m.Chem. Soc., (1) 12)
6 0 .,3 0-9 (1938). ~ ~
~
I
(5) Drake, L. C., and Ritter, H. L., ISD. ESG. CHEM..-1x.4~.ED., 17,787-91 (1945).
( 6 ) Rlarisic, & M., I.U. (7)
S.Patent 2,384,217 (1945). Mills, G. A , , Boedeker, E. R.. and Oblad, A. G.. J . A m . Chem.
SOC.,72,1554-60 (1950). (8) Mills, I. TV., Oil Gas J . , 46, No. 28, 237-41 (1947). 19) Plank, C. J., Symposium on Colloid Chemistry of Catalysts, S e w Tork Diamond Jubilee Meeting, AMERJCANCHEMICAL SOCIETY, September 7, 1951 (submitted to J . Phys. Colloid Chem.). (10) Scheumann, W.W., and Rescorla, A. R.. Oil Gns J.. 46, To. 28, 231-2 (1947). (11)
Thomas, C. L., I d . Eny. Chevz., 4 1 , 2 5 6 5 (1949).
RECEIVED for review January 14, 1952. Accepted June 7, 1952. Presented in part before the Division of Colloid Chemistry a t the 120th Meeting of the .kVERIClS C H E M I C A L SOCIETY, Ne\\, P o r k , N. I’.
Investigation and Application of the Zinc-1,lOPhenanthroline Complexes J . .\I. K K l S E 4YD W i K K E N W. BRANDT, Purdue I‘niuersity, Lafayette, Znd.
T
HE investigation of the reaction of zinc and 1,lO-phenan-
throline was undertaken in order t o determine whether the system could be of value analytically. Its similarity t o the ferrous system suggested a spectrophotometric investigation of the colorless reaction in the ultraviolet region, and indicated t h a t useful applications might be found in the field of anion precipitation. The existence and stabilities of three complexes of zinc with 1,lO-phenanthroline have been demonstrated by Kolthoff, Leussing, and Lee ( 3 ) . Their invrstigations, however, did not, consider the possible analytical utility of the system in the categories mentioned. Ih-STRUMENTS
The instruments used in the investi ation were the Beckman Model D U quartz spectrophotometer, t f e Beckman Model G p H meter, the Fisher Elecdropode, and a test-tube centrifuge running a t 1700 r.p.m. SPECTROPHOTOMETRIC STUDY
I n order to determine the possible spectrophotometric application, a preliminary survey was made of the absorption curve and
of the effect of pH upon absorption. Initial tests showed that even the best commercially available zinc, containing less than 0.002% iron, had to be purified further, as the small amount of iron interfered; iron from the atmosphere reacted with the solution. T o overcome this interference by iron, a stock solution of zinc vias prepared by dissolving shot zinc in hydrochloric acid and extracting the iron with isopropyl ether, using the method of Dodson, Forney, and Swift ( 2 ) . The solution was then standardized gravimetrically and kept in a stoppered bottle. -411 subsequent solutions were prepared from this standard solution. The preliminary survey showed t h a t the zinc-1,lO-phenanthroline complex did not absorb radiation a t wave lengths greater than 350 mp. I n the ultraviolet spectral region, between 200 and 320 mp, the complex showed an absorption curve very similar to that of ferroin or of 1,lO-phenanthroline itself (Figure 1). For this reason a blank containing a n equal amount of 1,lO-phenanthroline was used for all tests. Zinc ion showed no absorption in the range studied, T h e concentration of the complex was about 1 X 10-6 di for these teats. Over most of the range between 200 and
V O L U M E 2 4 , N O . 8, A U G U S T 1 9 5 2
1307
The reaction of zinc and 1,lO-phenanthroline was investigated i n order to determine possible analytical applications in spectrophotometry and as a n anion precipitant. .i detailed spectrophotometric studs of the absorbing species and 1,lO-phenan throline itself was rarried out in the spectral region of 220 to 320 mp. The abilit? to relate concentration to absorption was shown. The constitution of the absorbing species was determined by means of the method of continuous variations. The sensitivits of the sjsteni as a precipitant for vanadate, molybdate, and ferricyanide was demonstrated. 4 procedure for the microiolumetric determination of banadate w a s tested and shown to be applicable in
the range of 20 to 400 p.p.m. of vanadate ion. In the course of the work the polarographic curves for 1,lO-phenanthroline were determined and their relation to concentration was shown. The spectrophotometric study demonstrates a sensitive system for the determination of zinc by means of the absorption in the ultraviolet region of the bis-1,lOphenanthroline zinc(I1) ion. The polarographic curves of 1,lO-phenanthroline have been shown to be similar to a number of other monobasic amines. The applicability of the zinc-phenanthroline system in the field of qualitative and quantitative determination of vanadate, mol) bdate, and ferricyanide ions has been demonstrated.
320 nip the addition of zinc to the 1,lO-phenanthroline solution had the effect of increasing the transmittaricy of the solution even after accounting for any dilution. The effect of acidity on the a\)sorption by the ?oiiiples was studied. Solutions varying in acidity from pH 2.3 to 6.8 and with the Concentration of the complex a t 6.0 X 10-6 Jf were tested. The pH ot these solutions vias adjusted by diluting solutions of known concentration to 99 ml. in a 100-ml. volumetric flask, and adding sodium hydroside and hydrochloric acid from a dropper until the desired pH was attained. The total volume n-as then adjusted to 100 nil. T h e point of masimum difference i n absorbancy between the comples and the ],IO-phenanthroline shifted from 290 to 293 nip nhen the pH was varied from 2.8 t o 6.8. A gradual ovrr-all change in the absorbancy of both the 1,lO-phenanthroliiie and the comples ion with changes in pH Tvas observed over the entire ultraviolet range (Figure 2). For this reason the acidity \vas c*ontrolled to = t O . 1 pH unit. I t was demonstrated that the increase in absorbancy due to complex formation was proportional to the concent,ration of zinc in the wave-length regions of 268 to 273 and 290 to 295 mp. At a pH of 4.5 the molar absorptivity of zinc a t 270 mp n-as calculated to be 9800 and a t 292 nip it \vas 2100. The 292-mp peak provides a rewonable eensitivitJ- for zinc, while t,he one a t 270 n i p gives a very sensit,ive measure of zinc concentration. In order to a x e r t a i n the formula of the absorbing Epecies, the
I
-\
I
I
I
n,
‘t
0.8
a 0
c 0 n
0.6
L
5:
n U
0.4
,\- --
I 220
240
260
280
300
Wavelength (mp) Figure
2. Ultraviolet Absorption Spectra of Phenanthroline in Various Acidities
---
pH 6 . 6 .
....
pFI 4.9.
1,lO-
- pH 2.8
method of continuous variations was used ( 7 ) . I t was decided to use those wave lengths in the ultraviolet a t w-hich the comples had a higher absorbancy than the equal amount of 1,lC-phenanthroline. The wave-length regions of 268 t o 273 and 290 t o 295 mp were best suited for this purpose. Continuous variations were run at pH 4.2 and 7.3 without buffers, and a t pH 4.80 with a sodium acetate-acetic acid buffer. The ratio of zinc t o 1 , l O phenanthroline was varied from 1 : 9 t o 9 : l using 1 X 10-4 J I solutions. The continuous variation curves (Figure 3) obtained from the above solutions showed definite evidence for a complex of a 1t o 2 ratio of zinc to 1,Dphenanthroline as the most abundant absorbing species at these wave lengths in the p H and concentration range used. There is also evidence of smaller amounts of a 1 to 3 species having greater absorptivity. Such results are in agreement with the results of Kolthoff, Leussing, and Lee ( 3 ) in their study of the zinc-1,lO-phenanthrolinesystem. POLAROGRAPHlC STUDY
0.2
24 0
260
280
300
Wavelength (mv) Figure 1. Ultraviolet Absorption Spectra - 1,lO-Phenanthroline
---
Bis-1.10-phenanthroline-zinc(I1)
The polarographic behavior of the complex wvas studied. This method proved to be unsuccessful because the wave8 for the comples overlapped the waves for 1,lO-phenanthroline. However, data on 1,lO-phenanthroline itself m-ere obtained. The reduction proceeded in two steps (Figure 4). The reduction waves were dependent on pH, shifting to move more negative values with increasing pH. At p H 6 in a n 0.05 M acetate buffer, the first wave had a half-wave potential of -1.23 volts (os. S.C.E.) and the second nave a value of -1.47 volts (2s. S.C.E.). The t w o
1308
ANALYTICAL CHEMISTRY
I
Table I. Salt of Anion
0.012
Reaction of .inions with Bis-1.10-phenanthroline-Zinc(I1) Concentration of Anion, Salt of Ma Anion dnions F h i c h Form Precipitates
Concentration of Anion, Ma
0 4 KSCN 0 0025 0 4 ~fg(ClO4)z 0 00025 4 0 1 KsFe (CN)s 0 4 K4Fe (C N h 0 4 0 1 K.hfnO4 0 1 0 0001 SHiVOs 0 0001 0 1 Anions Which Do i i o t Form Precipitates NH4CzHs02 Sa.4102 XaNOz 3anSOa NaiHAsOs KCIOI NaNOs hazSO4 SazHAs01 NaF (NHI)HZPOI NazSzOs KBr KIOI NaHzPO4 (NH4)zSiOs KBrOi KIOi HiPtCla NaSiOa a Concentration of anion t o give precipitate with 0.0023 M complex uhen mixed in a 1 to 1 ratio. b 0.5 M anion mixed with 0.0023 M coinplex in 1 to 1 ratio.
KCN KCSO KzCrO4 KzCriO7 "41 iiazM004 KaiWOd
0.009
Y
0.006
PRECIPITATION 4NA LYSIS
1 0.6
0.5
Figure 3.
0.7
0.8
0.9
Continuous Variations Study
Zinc-1,lO-phenanthroline eystem
-1.1
-1.3
-145
-
1.7
Volts (vs. S.C.E.) Figure 4. Polarogram of 1,lO-Phenanthroline in 0.5 M Sodium Chloride pH 6.0
eteps were proportional to the concentration of 1,lO-phenanthroline in the concentration range of 1 X 10-8 M . Using the diffusion coefficient of acridine ( f ) as an approximation, and also from the theoretical mobility of 1,lo-phenanthroline, it was calculated t h a t the first wave was a 1-electron reduction and the second wave a 2-electron reduction. The calculated diffusion coefficient for 1,lO-phenanthroline in 0.5 S sodium chloride and a 0.05 Jf acetate buffer of p H 6 w a ~3.65 X 10-6. The reduction mechanism appears to be similar to that postulated for quinoline ( 6 ) . It was not definitely established, however, t h a t the currents are diffusion-controlled. As in the cases of acridine ( f ) , pyridine (6),and quinoline ( 6 ) , catalytic hydrogen waves were observed. At p H values smaller than 3, the hydrogen wave cut off the second 1 , l O phenanthroline wave. The supporting electrolyte in this work wae 0.5 iV sodium chloride, and 0.001% gelatin was used for maximum supprespion. m2'Y16' = 2.07.
One of the purposes of the study of the zinc-1,lO-phenanthroline complex was the investigation of it's analytical applications as an anion precipitant. The insolubility of 34 different anions with the complex was tested (Table I). Tn-o drops of the reagent and 1 \YO drops of an anion were mixed on a spot plate and the liquid \vas watched for the formation of a precipit'ate or formation of volor. The concentration of the complex was kept at 2.4 X 10-3 JI complex and anions; the concentration of both were reduced until no more precipitate was formed. The complex was found to he a very sensitive precipitant for small concentrations of vsnadate, molybdate, and ferriryanide ions. As ferricyanide forms a far more insoluble precipitate than ferrocyanide, the comples can be used to detect ferricyanide in the presence of ferrocyanide. In this difference of solubility and sensitivity the zinc-1,lO-phenanthroline complex far surpasses the tris-2,2'-bipyridine-iron(II) complex mentioned by Polvekt'ov and Sazarenko (4). The det,ermination of vanadate ion with the complex was found to be unfeasible, as the complex decomposed on drying at room temperature. However, the volumetric determination of vanadate by centrifuging the precipitat'e of the complex with vanadate gave a straight-line calihration for 1 t o 20 mg. of vanadate per 50 ml. The precipitation can be carried out a t p H 3.5 to 7.0, and the time of centrifuging must be roughly proportional t o the amount of vanadate present. The concentration of reagent is unimportant in the analysis as long as a t least a stoichiometric amount is present. The lower hf vanadate (50 limit of this method was found to be 2.5 X p.p.m,) when 9 x 10-3 M complex was used ae precipitat,ing agent. Only molybdate and ferricyanide ion interfere. The qualitative detection of vanadate ion even in the presence of molybdate and ferricyanide is possible because of the yellow color of the vanadate precipit,ate. The limit of detection is 20 p.p.m. LITERATURE CITED
( 1 ) Breyer, B., Buchanan, G.
S.,and Duewell, H., J . Chem. Soc.,
1944, 360. (2) Dodson, R. W., Forney, G. S., and Swift, E. H.. J . A m . Chem. SOC.,25, 2573 (1936). (3) Kolthoff, I. M., Leussing, D. L., and Lee, T. S.. Ibid., 73, 390 (1951). (4) Polvektov, N. S., and Sazarenko, V. A , , J . Applzed Chem. ( C . S . S.R.), IO, 2105 (1937). (5) Shikata, M.,and Tachi, I . , Bull. - 4 g r . Chem. SOC.J a p a n , 3, 5 3 (1927). ( 6 ) Tachi, I., and Eiabai, H.. J . EEectrochem. Assoc. J a p a n , 3 , 250 (1937). ( 7 ) Vosburg, JV. C., and Cooper, G. R., J . Am. Chem. SOC.,63, 439 (1941 1. RECEIVED for review October 30, 1951. .4ccepted May 28, 1952. From a thesis submitted by Jurgen XI. Kruse in partial fulfillment of the requirements for the degree of master of science a t Purdue University.
