whether the hydrazone (I) is adsorbed in the dibasic aci-nitro-enol form (IIb). It seemed entirely possible that in alkaline milieu there is an equilibrium between the IIa and I I b forms, and that only the monobasic aci-nitro form participates in the chemical adsorption. To decide this question, a study was made of the beharior of S-methylisatin whose nitrophenylhydrazone (111) (IIIa) provides no possibility for enolization of the CO group, but does not prevent the development of the aci form through prototropic rearrangement. ~
o-,‘
111
C = N - S = O =__ NOOH
IIIa
I
I
CH3
In its isomeric aci-nitro form; this azo compound OH
v
co
CH.3
OGLO
0H
CH3 I t was found that .I’--methylisatin behaves like isatin-Le., a blue color lake results from the condensation with p-nitrophcnylhydrazone, followrl by addition of magnesium oxide. -kccordingly, it is evident that the group -C=S-S=o=SOOH ~
,C=O
is responsible for the color reaction of isatin-3-(p)-nitrophenylhydrazone with hlg (OH)2. The fact that this group participates in the formation of the color lake led to the expectation that it would also lead to the formation of blue magnesiuni color lakes with other compounds containing this group. Accordingly, p-cresol was treated n-ith diazotized p-nitroaniline; coupling in the position ortho to the OH group results:
CH,
contain- tlic same group as the nci forms IIa and IIIa of the p-nitrophenylhydrazones of isatin and S-niethylisatin, respectively, and in fact i t yields a blue ( olor lake n ith magnesium o\ide. Since thc coupling of phenol and of the iqonirric 0- and m-cresols rrith diazotized p-nitroaniline docs not result in the group essential t o the formation of the lake. and since the coupling and lake formation proceed rapidly even 17 ith small amounts, a characteristic tr-t for p-cresol could be worked out. PROCEDURE
The test is conducted in a micro test tube. Several centigrams of magnesium oxide are treated in succession n-it,h 1 drop of the test solution, and 1 drop of the nitrobenzene diazonium salt solution, and 1 drop of 5% potassium hydroxide solution. The magnesium oxide should be heated t o 300’ to 400” before use. If p-cresol is present, a blue color appears almost immediately. If the colored mixture is placed on filter paper, evpn minute amounts of the color lake can be readily seen. The limit of identification is 0.2 fig. of p-cresol. Preparation of Nitrobenzene Diazonium Salt Solution. T o prepare t h e rcyigcnt solution 0.1 grain of pnitroanilinc: antidiazotat’e is dissolved in 100 nil. of n-atc.r. Then 10 drops
of concentrated h>~clrocliloric acid are added. If potassium p-nitrophenyl antidiazotate is not olitainnble, t’he reagent solution may be prepared tiy dissolving 0.1 gram of p-nit’roaniline in a mixture of 5 nil. of nater and 10 drops of concentrated hydrochloric acid. About 0.1 gram of sodium nitrite is added, and after the solution beconies colorless it is diluted t o 100 nil. Any excess of nitrous acid iiiiiet be destroyed by adding several centigranic of sulfaniic acid. sodium azide, or urea. r .
1lie procedure is coinpletely reliable for distinguishing p-crcenl from its isomers and from phcnol. Cresylsulfuric acid, which splits off p-cresol readily on warming with dilute mineral acids, can also be rirtectecl in this manner. The following conq)oun(ls behave like p-cresol: resorcinol, 1-naphthol. clnomotropic acid, H-acid. iii:ilon:iniide, ant1 pyrrole. LITERATURE CITED
of Specific, Selective, and Sensitive Reactions,” Chap. S,Academic Pre-. S e n Yo&,
~ 1 Feiyl, ) F., “Cheniistrj 1040 .., - , .
( 2 ) Feiyl, F., Goldstein, I ) , , Z’aluriitr 4, ”00 l1060).
RECEIVEDfor review June 20, 1960. AcceptPd August 29, 1960.
Polarography in Liquid Ammonia above Its Critical Temperature WLODZIMIERZ HUBlCKl and MlCHALlNA DABKOWSKA Department o f Inorganic Chemistry, Universify Mariae Curie Sklodowska, Lublin, Poland
b The preparation and physical properties of the anhydrous liquid amrnoniate of LiC104 are described. Polarographic measurements are used to show that in this medium it is possible to carry out investigations in liquid ammonia above its critical temperature. 90
ANALYTICAL CHEMISTRY
S
knon n suhtances, in the anhydrouq stage, absorb gaseous anhydrous ammonia and form a liquid as a rebult of abqorption. To this group belong, among others, SH&Oa, LiXOa, XHdSCS. and SHJ. For them the molar ratio -alt-SHa is dependent on ET ERAL
temperature and XH3 prei5urc; thcrefore, unle- the exact compo-ition- of the products of abqorption are given, these product3 are generally called liquid ammoniates and referred to h y formulas of the type: -1B.nSH3. Liquid ammoniates arc aii qolvent3
many and various substances. From tlic point of view of dissolution ability. only one has been invertigatid so far and that, only qualitatircly: S H 4 S 0 3nSH3. discovercd by Dinm (4) an(\ called by liis nanics. 'Ylit, ,soluljilitirb of several salts in various liquid ammoniates have been measured quantitatively in our laboratory. and thv rcwlts \rill be published later. A\nimoiiia is the dissolving agent in liquid :immoniateb. Liquid amnioniatcbs :IT(' ortm superior in laboratory use to pur(' liquid amnionin, as they ran be fi:iritllctl :it rooni or even highcr t m i p(wtures without special preybure arr:ingmi(~iib. For instance, the liquid of tlie above-mentionctl :inimoniat salt- unit1t.r p.?-Ha = TGO mni. of mercury rcmi:iin liquid zit the follon-ing aliproxim:ttc' t ( w p ( m t u r i ~ s ;a h o w these temper:itwc. they liecome unsolvated salts: for
(1s
c. +25 +7Ci
+78 +60 +2:c
Liquid aninioniatcs are good contluctors of electricity. The salts diisolved in them dissociate into ions. I1.l i c w proiwrties enable liquid :immoni: t t e to Iw used as solvent3 in polarogruphic rwearc'h. "4x03. n S H 3 was usecl by Vecrhi (1.9) and Hubirki and 1Iatysik (6.11-13.16); LixO3.7ZxH3by IIubivki a n d Zychiexicz (6, 14, 15, PO); S H , F C S . n 9 H 3 by Hubicki and Stasiewicz (6. I c j ' ) n n d C'urti and Locchi ( 1 , 2 ) ; S a S C S . uSH3 liy Hubicki (6, 7 ) : and S H 4 1 . n S H 3b y Hubicki and .Jusiak (9. I O ) . K H , S 0 3 . n S H 3 Tvas used in potentiomt~tric~ dettwiinat~ionsby Hubicki iind Gro*zek (8). In our research on t h r neiv liquid :ininioniatp., n.liicli could h a r e a wider rnnpci of :~l>plication! re u-ere interested in t'hv :ininioniate of LiClO,. Thc fact that LiC10, tlelique fluenct. of gxbeour nmnionia was denionstratetl 1,) Ilphraim ( 5 ) . He stated that during the saturation of LiC104 with ommoni:i :i liquid is formed n-hicli corrc>poii(l$in conipobit'ion t,o tlie forniiila Li('l0, 4SH3. Smeets ( 1 7 ) . who follon-cvl F;plir:iiiii's invrstigations, completed tlir tlata roncerning ammoniates of LiClO, a n d -lion-et1 that LiCIOI.2SH3. LiC1o4.3SH3, arid LiClO,. 5 S H 3 c111 :iIso exist under Tarious conditions. €I(%slioirecl that a t room tenipcwture t lit' ammoniate of LiClO4 beconies liquid a t tlic ratio 1 LiC101-3.5 9H3. but on further ;nturatioii solid LiClO,. 4.3?;H3 is formctl. ScJitlicr Ephraim nor Smeets has inrcstigatecl the other physical properties CJf LiCIOj. nSH3. EXPERIMENTAL
Lithium perchlorate was prepared by the action of stoichiometrically propor-
tioned quantities of dilute perchloric acid (British Drug Houses, 60 to 62%, specific gravity 1.54) on Li2C03(Chemical Laboratory Toxa, Warsan ). The solution obtained was evaporated in quartz flasks dipped in a temperatureregulated oil bath. Part of the nater evaporated, and LiC104 3H20 was formed. It melted at 95" C. and, a t a slightly higher temperature, became the monohydrate. The latter is completely dehj-drated a t a temperature above 150" C. I n any case, at 150" C. dried LiClO, still contains tratrls of n-ater. To avoid thil presence of n ater. a stream of dried SH3 naq passed through the melted LIC104. HzO, from 120" to 160" C. by gradually raising the temperaturc of the oil bath. The turbid, melted LiCIOl H29, combined nit11 gaseous ammonia, quic*l\l> produces a mobile clear anhydrous liquid. The KH3 outlet of the flask nas provided n i t h a mercury valve, giving ail overpressure of 10 mm. of mercury. The ammonia had been dried for several rveeks in steel bottles which also (mitained flakes of metallic sodium. If the temperature of heated I,iC104 nSH3 in the flask rose to 150" to 160" C. the heating element of the oil bath n a c siritched off and ?;H3 nas p a s 4 through until the liquid reached tlie temperature of 25" C. Glass vesscls n ere unsuitable; the aqueous solutionof LiClO,, and particularly of its melted hydrates, attacked the glass to a great degree. (Quartz is attacked also. but does not contaminate the liquid ammoniate of LiClO, 13 ith undesired polarographic active ions.) This procedure gave anhydrous LiCl0, nSH3. which reactcd n ith the metallic. sodium very slonly, but did not dissolvix it. The ratio of LiCIOl to S H 3 nas I to 4 a t 25" C. The density nic:iiurid pycnomctrically a t 25" C. n a s 1.21 grams per nil. and the electric conductivity. determined by a Kagncr briclgcx kilo-ohm per cm. was 50 X Heyrorskf's micropolarograph 11102 and oscillograph RFT 1 KO $12. nith an attachment containing an amplifying and differentiating system ellabling the curves d E / d t L S . I? to be registered. were used for the polarographic meaurements. The dropping m t w u r j cathode had a rate of flow of 5.7 mg. per second and a drop time of 1.7 seconds a t $26" C. (The drop time changed to 0.42 second nlirn the temperature was increased t o 140" C.) All the nieasurements !$ere referred t o a
Table I.
mercury pool anode. The polarographic cell, fitted with a thermometer, was maintained a constant distance between the outlet of the capillary and the surface of the anodic mercury. The cell was immersed in a thermostated oil bath. During the measurements, ITH3 was passed over the surface of the liquid ammoniate solutions through a T-pipe with cocks, mountetl a t the top of the cell. Preliminary nicasivements indicaated that LiC104.n S H 3 giws n.cll defined and reproducible current-voltage curves. The slope of the rrsidual current was negligible. Decomgorition started a t - 1.7 volts, a t a niorc negative potential than all the other liquid ammoniates already invcstigatrd. It is imposrible, as n-e have shown in our laboratory, t o obtain, for instance. a polarographic zinc wave in the liquid ammoniatrb of such salts as SHdSO3. L i s & S a C S S , and S H J . Thcy d l decompose a t -1.1 to - 1.3 x - o h , the same range in which the %n+? wave appears. Curti and Locchi obtained the zinc ~ a v c ' in S H I S C S .n S H 3 mtdium, xhich decoinpohe a t - 1 . 5 5 volts a t 0" C. (e). 11-e have dcnionstratrd that ~ ~ de1 1 fined and distinct polarographic TWVES are givim in liquid LiC104.nSH3 b y the folloji-ing ions: TIC1,Cu+?, Pb-b2) Cd+?. s i + ? . CoT?. CrL3. Zn+', IOg-', TOi-'. CrOaP2.aiid I M ) 3 - 1 . The quantitative results of these investigations have hccn rcyortcd (3). This papcr givw only the result's of polarographic mea$urcments obtained using I , i C 1 0 ~ , n S H 3as a sol~-entat some tenipcratures higher than room temperature. and for three example:: only: Cd+*. Zn+?. and Pby' salt solution?. The salts PljSO,, ZnCOa. and CdCO3, i\-hich are insoluble in n-ater hut t o some extent soluble in the liquid ammoniatc of LiC'104. n'rre chosen. From t1ic.e salt>we prcparctl. hy Ireighing, solutions approximately 10-3Jf for i w h ion in LiClOl.nSH3. The nieasurenirmts ww made at tcmperatiires from 25" t o 200" C . The results of one serks arr given in Table I, and the polarographic curves obtained are reproduced in Figure 1. The polarograms from 25" t o 104" C. are accurately t r a c d from polarographic photorecords
Results of One Series of Measurements
Pb Temp., O
e.
--
00
69
80 9$1 101 142 190
Semi-
tivity
El/?, Wave Height E,,,, volt l I m . pa. volt
Cd + 2 _ _ _ _Zn_-2 _ _ ~ ~ _ Wave Height E,,,, K a v e Height ~~
lIm. . .
1:50 1:50 1:50 1:50
1:50 1:50 1:150
0.40 0.39 0.38 0.38 0.37 0.38 0.37
6.5 7.3 8.0 10.2 11.5 14.0 7.0
pa.
~
volts _
.
lfm.
pa.
_ _
0.8. 9 . 0 2 . 7 0 1.:;: 19.0 5.80 0.79 li3.6 4 . 2 2 1.32 23.7 7.35 0.75 14.5 4.50 1.31 2 4 . 0 7.44 0.75 21.5 6 67 1.28 32.5 10.08 0.72 23.0 7 . 1 3 1 . 2 6 33.5 10.39 4 . 3 4 0.72 35.5 11.01 1.26 (72.0) (22.3) 6 81 0.il 11.0 l X 6 2 1 . 2 6 51.5 15.96
2.02 2.26 2.48 i3.16 i3.57
VOL. 33, NO. 1, JANUARY 1961
91
a
obtained a t 1 to 50 sensitivity; the polarograms a t 142” and 195” C., obtained a t 1 t o 150 sensitivity, are calculated to the same scale as the former and are plotted in dotted lines. DISCUSSION AND CONCLUSIONS
Figure 1 shows the increase in the wave height for each ion with increase of temperature. The cause of this increase can be attributed to many factors, such as increase of ion concentration as a consequence of the decrease of ammonia in the medium used (at 200” C. and under p ~ = ” 760 ~ mm. of mercury, LiC104 n 5 H 3 has n < l), increase of diffusion coefficients, and increase of the capillary efficiency and decrease of viscosity of the medium. I n calculating the relative values of diffusion coefficients (for each of the three ions studied) on the basis of wave heights, the possibility of association which probably takes place in the case of PbS04 must be remembered. The height of the P h f 2 wave is linearly proportional to the temperature. I n the case of Zn+2, the values of the diffusion current suddenly increase a t 120” C.; similar increase occurs lvith Cd+2 but in lesser degree. These differences of diffusion current values a t various temperatures can be interpreted in terms of the different desolvation temperatures of Zn+2, Cd+2, and Pb’2 ions. The decomposition of the solid ammoniates and hydrates of the salts of Zn, Cd, and P b usually increases with increase in the molecular weight of the salt. Water should have no effect, because precautions were taken to exclude i t from the LiC104.nNH3-for example, the preparation of solutions, the filling up of cells, etc., were carried out in an atmosphere of NH3 in a specially constructed hermetic box. Moreover, ammonia is generally a stronger solvating agent than water. The temperature coefficient of El/, in a n aqueous solution, for a reversible wave, depends upon the nature of the electrode reaction. It may be positive or negative, but is rarely greater than 1 mv. per degree. For an irreversible wave, the temperature coefficient is almost always positive and on the order of several millivolts per degree. Similar changes can be expected in the
92
e
ANALYTICAL CHEMISTRY
50
00 IOO‘C.
45 40
35 30 ’
At greater concentrations of Zn+Zthan have been used by us a second anodic notch appears. It is symmetric to the cathodic one, but much smaller. We have reason to believe that this notch is but an echo and does not indicate the Zn process. reversibility of the Zn t 2 The liquid ammoniate of LiC104 is a very interesting compound, which makes possible work with liquid ammonia under normal pressure a t temperatures far above the critical temperature of the ammonia. Research 011 this topic will be continued.
-
2s
LITERATURE CITED
20 15
(1) Curti, R., Locchi, S , “Actas do XV
Congress0 Internacional de Quimica Pura e Aplicada,” F’ol 1, p. 1, Lisbon, 1937.
IO 5
-0
QZ 0.4
46 O B 1.0 1,2 1.4 /,6
2.2 2+ 4 6 L‘
Figure 1. Polarogram and oscillopolarograms of Pb+?, Cd+2, and Zn+2 salt solution in liquid LiC104.nNH3 at different temperatures
case of salts used in the liquid ammoniate of LiC104. The El/, values of Pb+2, as the temperature increases, are shifted very little toward more positive values of potential; therefore the process of reduction for Pb+2 seems to be reversible. However, it appears to be irreversible for Cd+2 and Z n t 2 , because the shift is in the direction of positive values and is greater than for Pb+2. This conclusion is confirmed b y the oscillopolarograms. The oscillopolarogram obtained a t 25” C. (Figure I) has in the cathodic part three notches corresponding t o the reductions of Pb+2, Cd+2, and Zn+2; in the anodic part only one notch for Pb+2 is seen, whereas a t 100” C. the second one common for Cd+2 and Z n f Z appears. Thus, we can accept the reduction of Pb+2 as reversible. whereas that for is reversible only a t higher temperature and for Zn+2 not a t all. The anodic dissolving of Zn+2 and Cd+2 appears at the same potential because the second anodic notch is deeper than the former (Pb+2). The addition of KI did not reverse the Zn+2 reduction.
(2) Curti, R., Locchi, S.,ASAL. CHEM. 29, 534 (1957). (3) Dgbkowska, M., Ann. Cniv. Mariae Curie Sktodowska 13, Sec. .4A, 5 (1959). (4) Divers, E., Phil. Trans. 163, 359 (1873 (5) Ephraim, F., Be?. 5 2 , 236 (1919). (6) Hubicki, W.,Ann. liniv. Mariae Curie Sktodowska 10,Sec. AA, 5 (1955). (7) Hubicki, IT7., Dabkonska, PI., Communiqu6, VIth Congrecs Pol. Chem. SOC., Warsaw, 1959. “Chemia AnaIityczna,” p. 3‘19. ‘ (8) Hubicki, IT., Groszek, H., Ann. Univ. Mariae Curie Sktodowska 11, Sec. AA, 3 (1956). (9) Hubicki, W.,Jusiak, S., Ibid., 12, Sec. AA, 11 (1957). (10) Hubicki, W., Jueiak, S., CommuniquB, VIth Congress Pol. Chem. SOC., Warsaw, 1959, “Chemia Analityczna,” p. 319. (11) Hubicki, W.,Matysik, J., $nn. Cniv. Mariae Curie Sklodowska 9, Sec. AL4,1 (1954). (12) Ibid., 11, 5 (1956). (13) Hubicki, IT., Llatysik, J., Zychiewicz, Z., Ibid., 10,Sec. SA, 10 (1955). (14) Hubicki, W.,Zvchiewicz, Z., Ibid., 9, Sec. AA, 7 (1954). (15) Hubicki, W., Zychiewicz, Z., Communique, VIth Congress Pol. Chem. SOC., Warsaw, 1959, “Chemia Analityczna,” p. 320. (16) Matysik, J , Zbid., p. 319. (17) SmeetE, C., Natuurw. Tzjdschr. 17, 213 (1935). (18) Stasiemicz, A., Communiquk, VIth Congress Pol. Chem. SOC., Warsaw, 1959, “Chemia Analityczna,” p. 72. (19) Vecchi, E., Rend. accad. nazl. Lincei 14,( 8 )290 (1953). (20) Zychiem-icz, Z., Communique, VIth Congress Pol. Chem. SOC., Warsaw, 1959, “Chemia Analityczna,” p. 379. RECEIVEDfor review April 20, 1960. Accepted August 8, 1960.
