peak in normal carbon dioxide, samples enriched in oxygen-18 are relativdy leas enriched in oxygen-17 (8). and under thew circumstances the contribution of C1JO’QoL7 is nut significant. Table I shows that, before equilibration, the mass 47 peak was five times greater than the mass 48 peak, and that the mass ratio 48/44 increased tenfold during equilibration. These facts aione are sufficient evidence that the distribution of oxygen isotopes in the carbon dioxide formed in the Unterzaucher procedure is nonrandom. The agreement between the peak heights observed before and after equilibration and the values calculated for nonrandom and random distribution, respectively, is in all cases within experimental error, and thus lends fu!l support to this conclusion. The authors have found the following simple equation, derived from the probability expressions described above, useful in calculating the results of mass spectrometric analyses of Unterzaucher sampies. z = atom fraction 0 1 8 in the compouna R = ohsrlvrd rat-io, mass 46/mam 44 R‘ = R - 0.00204 then z = - R‘ l+R’ This equation takes into account the oxygen introduced by the iodine pent-
Table 1.
Mass NO. 44 45 46 47 48
Mass Distribution in Carbon Dioxide from the Unterzaucher Procedure
Obsd., before equil. 1OO.OOO
Relative Peak Heights Calcd., nonrandom dist.
1.59Bf0.008 9.59 f0.02 0.109 f 0.003 0.02 f O . O 1
oxide used in the Unterzaucher method, and is based on a nonrandom distribution of the oxygen-18 in the carbon dioxide. It is assumed that the only species contributing to the ma= 46 peak is C1201Q18.If the mass spectrometer used does not give the expected reading for standard (tank) carbon dioxide, R may be normalized by multiplying by 0.00409/Retd. If not all of the oxygens are labeled in the compound analyzed, multiplication of (z - 0.00‘204) by the appropriate factor gives the atom fraction excess in the labeied positions. I n cme the sample is enriched in oxygen17 to the point that the quantity a17($) becomes significant with respect to 1, the right side of the equation is multiplied by (1 - a,,(,,).
The authors are indebted to R. A. Alberty for use of an Unterzaucher appara-
Obsd., after
1.579 f 0.004 9 19 f 0 02 0.119 f 0.003 0.19 f O . 0 1
0.106 0.019
ACKNOWLEDGMENT
Standard Deviations Calcd., random equi!. dis: 1OO.ooc;
&
1.575 9 10 0 121 0.21!
tus and to Irving Shain for use of the mass spectrometer. LITERATURE CITED
(1) Bender, M. L., Kemp, K. C., J . A m . C h m . SOC.79, 1 1 1 , 116 (1957j. (2) Chem. Eng. Mews 36, KO. 21, 57; (1958). (3) Clark, S. J., “Quantitative hfethods of Organic Microanalysis,” p. 154, Butterworths, London, l95C. (4) Denney, D. H., Greenbnum, M. .%.) J.Am.,Chem. SOC.79,979 ( 1057 ;. ( 5 ) Doering, W. von E., Dorfman, E.. Ibid., 75, 5595 (1953). (6) Schaeffcr, 0. A., Owen, H. R., J . Chem. Phys. 23, 1305 (1955). (7) Schutze, M., 2. anal. Chem. 116, 245 (1939-40). (8) Unterzaucher, J., B w . 73, 391 (1940). ( 9 ) Urey, H. C., Grriff, L. J., 2 . AWL. Chem. SOC.57,321 (1935) and referencw
there cited.
RECEIVEDfor revirm October 2, 1958. Accepted June 1, 1950.
Tetrahydrofuran-Water Mixture as a PoIa rogra phic So Ivent Determination of the Lower Polyphenyls LOUIS SILVERMAN, WANDA G. BRADSHAW,’ and MARY E. SHIDELER Atomics International, A Division of North American Aviation, Inc., Canoga Park, Calif.
b Tetrahydrofuran-water mixture is a satisfactory medium for polarographic studies of certain organic compounds. it is particularly adaptable for routine analyses because it may be purchased in a relatively pure form and any small amounts of impurities present may be quickly and easily removed by passing it through a column of activated alumina. Tetrahydrofuran has good solvent action for supporting electrolytes such as tetrabutylammonium iodide and for many organic compounds. The diffusion currents obtained for organic compounds in this medium are higher than those obBitained in dioxane-water solvent. phenyl and the terphenyls can be
determined quantitatively using this medium and reduction waves also have been obtained for p-bromodiphenyl, nitrobenzene, naphthalene, triphenylene, 2-bromonaphthalene, anthracene, and pyrene.
I
search for polarographic solvents for biphenyl and the terphenyls, tee rahydrofuran was found t o have certain advantages as a solvent in polarographic work. Abrahamson and Reynolds ( 1 ) tried tetrahydrofuran as a solvent for the organohalosilanes, but no reduction was obtained. No other use of tetrahydrofuran in the polarcgraphic field has been mentioned in the literature. E; A
Of the several solvents studied i n this investigation tetrahydrofuran dissolves both a suitable supporting elcctrolyte and the organic biphenyl and terphenyis, and also permits the attainment of very negative potentials (-2 t o - 3 volts). When used with tetr3butS13mnioniurn iodide as the supporting electrolyte, it offers a polarographic medium for organic compounds in Lvhich the samples are easily and quickly prepared. EXPERIMENTAL
Apparatus.
The
current-voltage
1 Present address, Lockheed hircraft Corp., Sunnyvale, Calif.
VOL. 31, NO. 10, OCTOBER 1959
1669
auives were obtained with a Eargent Xodel XXI visible recording polarograph. A two-piece cylindrical electrolysis vessel provided with side arms ior anode conneuion (mercury pool xode) and for admission of helium was used. The characteristics of the dropFing mercury electrode in the tetrahydrofuran-water medium are given in Table i. The m vaiue was determined in the tetrahydrofuran-water solvent and the might of the mercury column was 47 cm. The accuracy of the recorded potentials, corrected for I R drop, was checked by a wide range Sargent potentiometer vith a limit of error of i 1 mv.
Reagents. Tetrahydrofuran (Matheson Coleman & Bell). This can be purified by passing 100 to 200 ml. 7,hrough a column (10 x 1.8 cm.) containing 1 part of Celite to 3 parts of freshly activated aiumina. The purified solvent is immediately stored over aiumina. Tetrabutylammonium Iodide (Matheson Coleman & Bell). This is best purchased in small bottles of 25 grams or less. It is transferred to a small weighing bottle and weighed quantities ire dispensed as required. After opena g , the bottle should be kept tightly realed and refrigerated. This grade is of sufficient purity for polarographic work, if a blank polarogram is subxacted from the sample polarogram. For critical work, or if the tetraiutyiammonium iodide is not of sufficient purity, it can be purified by a modification of the method of Pickard and Neptune (4). I n the modified method, the salt is dissolved in 1 to 3 methanol in acetone, Lhe filtrate is partially evaporated a t room temperature, and water is added to precipitate pure crystals of the tetrabutyl salt (6). n-Terhenyl (Eastman and Matheson Coleman & Bell). Separate samples were fractionallv distilled and recrystallized. Nitrobenzene (Eastmanj. The sampie was uistilled. Ilelium. This contained about 4 i1.p.m. of oxygen and was not further ,?arified. Frocedure. The medium used Lhroughout was 10 ml. of tetrahydro5iran-water mixture in a 3 to 1 ratio. (Water must be present to dissolve the supporting dectrolyte.) Each soluhion contained 0.20 gram of tetrabutylwnmonium iodide as the supporting dectrolyte. The dissolved oxygen was removed by purging the solutions for 2 to 3 minutes with helium which was presaturated with water. All diffusion zurrent values reported were obtained b y subtracting the blank polarogram ‘Tom the .;ample polarograms. RESULTS A N D DISCUSSION
C d c a t i o n of Tetrahydrofuran. Ts?trahydrofuran can be suitably purified €or polarographic use by passing the ether through a column of alumina-Celite mixture {3 t o 1) in 9 1670
ANALYTICAL CHEMISTRY
Table 1. Characteristics of Dropping Mercury Electrode in TetrahydrofuranWater m2/st”6
Volts -2.0 -2.2 -2.4 -2.6
t,
Sec.
2.6 2.2 1.7 1.2
~g.2~a~ec.’-1/2
1.279 1.220 1.152 1.097
much shorter time than the commonly used distillation method (1). The stability of the purified solvent was investigated by running polarograms on the tetrahydrofuran a t various time intervals after it had been passed through the alumina column. Polarograms were obtained from 0 to 7 hours after purification of the solvent (Figure 1). The base lines of these curves have been adjusted to a common value to facilitate the comparison. The solvent waa completely stable up to 1.5 hours after purification, after which time a gradual increase in diffusion current at voltages from -2.3 to -2.8 was apparent. From 2.5 to 4 hours, the polarogram was about the same as for the unpurified solvent, and after 4 hours, the tetrahydrofuran became unsatisfactory for polarographic use. Control of Peroxides. A correlation of the polarographic change in the solvent with time to the peroxide concentration was attrmpted. Peroxides could form in the tetrahydrofuran at a rate high enough to account for the increases in current at the more negative voltages. The peroxide content in the tetrahydrofuran was determined by adding an excess of ceric suifate solution to the sample and backtitrating with ferrous ammonium sulfate solution using ferroin as an indicator. The peroxide concentration (calculated as H201)was reduced by the purification procedure but the peroxide increased from 10 p.p.m. after 1.5 hours to 180 p.p.m. after 24 hours (Table 11). This would seem to correiate with the curves in Figure 1. However, the H202 content of the unpurified solvent was 500 p.p.m. and its polarogram COTresponds to a !ower peroxide content (about 15 p.p.m.). It cannot be concluded, then, that the peroxide titrated in this way is emirely responsible for the polarographic instability of the tetrahydrofuran with respect to time. ‘The peroxide formation in the purified tetrahydrofuran can be greatly reduced and maintained a t a low vaiue by immediately storing the freshly purified solvent over activated aiumina. Solvent which had Seen purified and stored over alumina for 24 hours increased to only 23 ?.p.m. peroxide and its polarogram was satisfactory (Figure 3). Solvent which had ‘seen purified hi; not stored over alumina contained
about 200 p.p.m. peroxide ;‘%de 11) and had a high polarogram. Tetrahydrofuran-WaLerRatio. The tetrahydrofuran was iraried From 60 to 90% by voluxne in water with tetrabutylammonium iodide present. The polarograms obtained on these mixtures showed very little dserence between 60 and 75y0 tetrahydrofuran. When the tetrahydrofuran concentration reached 90%, the blank polarogram WLLBhigh; furthermore, the supporting electrolyte is not soluble in this mixture. The 75% tetrahydrof ~ r a n - 2 5 7 ~water mixture was cnosen as the optimum solvent mixture. Use of Tetrahydrofuran for Biphenyl and Terphenyls. New interest in the application of the terphenyls as coolants in nuclear power reactors stimulated the investigation of the poiarographic analysis of the lower poiyphenyls. The reduction of m- and o-terphenyls at the dropping nierrury c+ctrode has not been reported. The half-wave potentials for biphenyl (6) and for p terphenyl (2) in dioxane-watc,r solution5 have been, and thc electrode process of the biphenyl reduction has been discussed by Hoijtink and Van Schooten (3) and Wawzonek and Laitinen (6). Tetrahydrofuran-mater (3 to 1) nuxture when used with tetrabutylammonium Iodide as the supporting electrolyte is a particularly suitatde medium for poiarogrnms of biphenyl and tht. terphenyls. Typical results are stlowi~ in Table 111. The diffusion currents or bipnenvl and the terphenyls are h e a r l y pr+ oortional tc the concentramns in the range from 0.05 to 0.5 mg. per mi. or slightly higher. Tn the early studies of biphenyl in this medium, the cyect of mercury pressure on the l:mitir,g current was measured and the limiting current was linearly proportional to the square root of the height of the mercur) :evel. This indicates that the reducation of biphenyi in tetrahydrofurnnwater medium 1s controlled by diffusioii The idjCm2’3tl’6 for biphenyl ’s considerably iargtbr than that reportecl s y Vawzonelc and Saltinen (6). who obtaineci a vslue of 7 in ciioxame-wacer as sompared to 20 in tetrahydrofuranwater (Tabie 111). poecause zhe half-wave rdentiais 01 biphenyl and the terphenyis occur close t u or a t the \%me potentiai, one can-lot be determined in the presence of any nf the others. Xowever 3ny one d chew compounds couid be quanata5veiy ciecerrnineti m the zbsence of more reaaily reducible substances. The standard deviation for biphenyi ’:I the Concentration range of 0.5 to I mg. is 0.1 =ne;., ana in tfie range 5 to 10 rng., the standard deviation s 0.4 mq. The standard deviation ?or v-ter-
ACKNOWLEDGMENT
30
The authors thank Barbara M. Jones, of this laboratory, who performed the peroxide analyses.
28 26
Figure 1. Change of purified tetrahydrofuran with time A.
Unpurified 0.5 hours after Purification 1.5 hours after purikation 2.5 hours after purification 4.0 hours after purification 5.0 hours after purification 7.0 hours after purification
ti. C
D.
E. F. G.
24
LITERATURE CITED
(1) Abrahamson, E. A., Jr., Reynolds. C. A., ASII.. CHEM.24, 1827 (1952) (2) Hoijtink, G. J., Van Schooten Y., Rec. trav. chmi. 72, 903 (1953). (3) Ibid., 73, 355 (1954). (4) Pickard, P. L., Neptune, W. E., AN.^,. CHEM.27, 1358 (1955). (5) Silverninn, Louis, Bradshaw, Wantlc.
22 20
w vi
a
w
16
Atomics inrernational Spec. Rept . NAA-SR-1660, (Oct. 15, lY56). (6) Wawzonek, S., Laitinen, H. A., J . An.
0 14
L 12
Chem. Sor 64. 2365 (1042).
RECEIVED for review November 17, 19% Accepted July 6 1059. Work based on studies conducwd for The Atomic E n e r y Commission under Contract AT-ll-,GEN-8. Pittsburgh Conference on hnalytical Chemistry and Applied Spcctroscopl-, Pittshurgh, Pa., March 39.5.3.
IO
8
6
4
2
, 1
0
- 1.6
-16
16 W
a
-26
-28
Table II.
Peroxide Formation in Purified Tetrahydrofuran Hours after &Ox,
"
I4
,y 12
5 IO
0
,re g 6
r
-22
vri-s
The id/Cni2%1/6values 'obtained for the organic compounds in the tetrahydrofuran-watcr nitYiium are somewhat larger (about 2 t o 3 times) than those reported in tlic literature for other solvents (6). No maxima nerc observed fur any of the organic coinpounds investiq tetl, using this medium.
20 I8 v)
.. -24
I
-20
Purification
P.P.M.
0 (ynpiirified) 0.3 1 .j 2.5 5.0 7.0 8.0 24,o
530 9 8 15
27 37 43 181
4
2
Table 111.
0 -16
-10
20
22
2 4
26
Diffusion Current Data of Various Compounds in Tetrahydrofuran-Water (0.20 gram of tetrabutylammonium iodide y r 10 mi.)
28
VOLTS
Figure 2. Change of purified tetrahydrofuran stored over alumina A 6. C D.
0.5 hour after purification, 5 2 hours after purification, 20 4 hours after purification, 14 24 hours after purification, 23
p.p.m. p.p.m. p.p.m. p.p.m.
HLO? HzOs
c,
Compound Biphenyl
HzO2
HzOz
phenyl is 0.4 mg. in the range between 1 to 5 mg. I n the range from 0.5 t o 10 mg., the 0- and m-terphenyls show a standard deviation of 0.4 mg. Use of Tetrahydrofuran for Other Organic Compounds. The tetrahydrofuran-water medium was used t o study a number of organic compounds and the d a t a are listed in Table 111. Benzene, chlorobenzene, aniline, and Tetralin were not reduced under these conditions; however, three reduction waves were obtained for nitrobenzene. Two waves were observed for pbromodiphcnyl, the first at -1.6 volts and the second at -2.4 t o -2.5 voits. The latter wave corresponds to the wave obtained for unsubstituted biphenyl. A series of fused-ring compounds was also investigated. Single waves were obtained for naphthalene and triphenylene, while double waves were noted for Zbromonaphthalene, anthracene, and pyrenc.
o-Terp henyl m-Terphenyl p-Terphenyl
Millimoles/ Liter 0 65 3 25 6.50 0 43 2 17 4 34 0 43 2 17 4 34
2 2 2 2 2 2 2 2 2
13 6: 144 8 58 120 10 51 144
17 21 16 24 26 20 21 32
(2 2 (2 2
4.30
2-Bromonaphthalene
4.83
Naphthalene Anthracene
3.91 2.81
Phenanthrene Triphenyleno Pyrene
2.80 2.20 2.48
d ._
Cm * ' 3 t 1
2.6C
p-Bromodiphenyl
L
pa.
(;
4.88
ad,
Volt.
0 43
4.34
Nitrobenzene
-Eli2. 20 37 50 30 34 46
20 35 46
); ;
04, 58 04)
66
0 48
0 % 2.70 1 6% 2 43 1 52 2 4;! 2 34 1 55 2 3s 2 3: 2.23 1 7.5 2 3P
(2) 15
17
(3) 30 (5' 29
(22) 144 15 96 84 17 73 20 72 60 8 22 90 66 18 51
VOL. 31, NO. 10, OCTOBER lo59
(5)
34 3 20
17
4 15 4 14 14 3 ? 2" 26 7
IF
1671
