VOl. 79
ALEX.\NDERI. POPOV AND RONALD T. PFLAUN
570
[ COsTRIBUTIOS FROX THE DEPARTMEST O F CHEMISTRY, STATE UXIVERSITY
OF IOWA]
Studies on the Chemistry of Halogens and of Polyhalides. X. The Reactions of Iodine Monochloride with Pyridine and with 2,2 '-Bipyridinel B Y ALEXANDER I. P O P O V
AND
RONALD T. PFL.4Uh.I
RECEIVED JUSE 22, 1956 The preparation and described. Absorption the 2,2'-bipyridine and anti 2PyIC1 % P y z I +
the isolation of addition compounds of pyridine and of 2,2'-bipyridine and IC1 and with HICl2 is spectra of these compounds in acetonitrile solutions have been determined. It is shown t h a t both the pyridine complexes with iodine monochloride dissociate according to BP.ZIC1 % B P I + ICI2IC]*-.
+
+
purified by the standard methods8 and its purity was checked Introduction by the measurement of specific conductance, which was The addition complex of pyridine with iodine 0.6-3 X 10-7 ohm-' cm.-l. iuonochloride has been described in the literature Spectrophotometric Measurements.-Most of the spcchy several investigators.2 The most recent work trophotometric measurements were done on a Cary recording o i l this compound is that of Fialkov and ~Muzika,~spectrophotometer, Model 11, using silica cells of I .OO or 5.00 cm. in path length. who report the preparation of two addition comI n some cases where narrow path lengths \Yere needed, pounds, Py.IC1 and Py.2IC1. From electrolysis the measurements were carried out on a Beckman D.U. and ion transfer studies in nitrobenzene solutions, spectrophotometer with 1.00 cm. silica cells and 0.9 cin. spacers. -111 measurements were made a t room temthese authors postulate that the structures of these silica perature of approximately 25" compounds are, respectively, (-1) +C1- and Addition Complex of B P with Iodine Monochloride .(PyI) +(IC&)-. Equimolar solutions (-0.1 M ) of iodine monochloride and It is, of course, to be expected that iodine mono- of B P were prepared in carbon tetrachloride and the iodine monochloride then was added slowly to the B P solution chloride will form addition compounds with other from a buret. During the addition, the B P solution was heterocyclic amines, in particular with the poly- stirred vigorously with an electrical stirrer. The dense pyridines. Of these, 2,2'-bipyridine seemed to be yellow precipitate obtained was filtered on a sintered glass particularly interesting since this compound, al- crucible, washed with carbon tetrachloride and dried in an a t 70". Anal. Calcd. for BP.2IC1: C, 23.97; 13, though it acts as a bidentate ligand with metal oven 1.66; T,5.82; iodornctricequiv., 120.2. Found: C, 25.4tJ; ions, coordinates with only one proton in solutions H, 1.60; X, 6.3; iodometric equiv,, 121. The yield was with $H 2 l . 4 The most plausible explanation 97-987,. The compound is quite stable in air and does not sccni to seems to be that while in crystalline state or in hydrolysis with atmospheric moisture as is often the benzene solutions the molecule exists in the trans undergo case with other polyhalogen complexes. I t is insoluble in configuration,6,6the two rings rotate about the C-C water at room temperature but decomposes in boiling water bond and, upon addition of a proton, are stabilized with evolution of iodine; it is readily soluble in organic solin the cis configuration by hydrogen bonding. vents with the exception of carbon tetrachloride. The does not h a r e a sharp melting point, but begins Although one would expect that 2,2'-bipyridine compound to decompose a t approximately 95". mould form an addition complex with two moleAlternate Method of Preparation of BP.ZICI.--Xpprosicules of iodine monochloride, the possibility of mately 0.2 g . of B P was weighed in a weighing boat and coordination of the positive iodine with both nitro- placed in a vacuum desiccator. About 0.5-0.8 g . of iodine monochloride \vas placed in a crucible a t the bottom of the gens in the cis form could not be excluded. This desiccator which was then evacuated. Iodine monochloride investigation was undertaken t o compare the reac- vapors reacted rapidlJ- with the R P crystals and, after 24 tions of pyridine and of 2,2'-bipyridine with iodine hours, a black viscous liquid was formed in the weighing monochloride, and to study spectrophotometrically boat. The desiccator was then e\-acuated for several daJ 5 gradually the liquid solidified into a br0n.n solid ~ v h i c l i . the ionic or molecular species present in solutions and upoii further evacuation, turned to yellow pou-der wliic1i o f these complexes. malyzed as BP.21Cl.
Experimental Part Reagents.--'l'lie 2,2'-bipyridirie (designated below as I1P) was obtained from the G. F. Smith Chemical CoinIiany :md was purified by repeated recrystallizations From hexane; the 11i.p. was 70.0°, literature values are 89.,V iO.O0.7 Iodine riionochloride was prepared and purified I)y a previously described method.8 Pyridine was C.P. hlerck product; it was shakcn up with potassium hydroxitic iiellets arid distilled. Coleman and Bell acetonitrile wa5 ~ ~ _ _ (1) Paper presented hefore t h e Physical-Inor.ganic Division a t the 128th meetinz of t h e ilmcrican Chemical Society, September 10, 10.55, Minneapolis, Minnesota. ( 2 ) (a) hl. D i t t m a r , Be?., 18, IF18 (1885); (b) A. Pictet a n d (;. K r a f t , B7cll. S O L . c h z ~ n . ,[3] 7, 73 (1892); (c) m '. J. Sell a n d F,U'. n o u t s o n , J . ChPm. S o r . , 1 5 , 979 (1899); (d) L. F. Audrieth a n d E. J. Ilirr, THISJ O U R N A L . 55, 672 (1933). 13) Ya. .4.Fialkov a n d I. D. AIuzika, Zhifi.. Uhshchei Khini. 18, 1205 (IR48). ( 4 ) P. Krumholz, THISJ O U R N A L . 73, 3487 (1951). ( 5 ) 1;. W. Cagle. Acta C r y s t . . 1 , 158 (1948). (6) P. IS. Fielding a n d R. J. W. LeFevre, J . C h e m . S o l . , 181 1 (1981j . ( 7 ) P. Krumholz, Acad. Bvosil. cierrc., 2 2 , 263 (1950). ( 8 ) A . I. Popov a n d N. E , Skelly. THISJ O U R N A L , 77, 8722 (1955).
Recrystallizations.--Xttem~~ts were riiade t o recrystallize this substance from acetone, cthylenc dichloridt., cther. rt!ianol, methanol, ethyl acctatc arid chloroforiri. '1'11c last solvent gave thc beat reiults b u t only when thc yellon. powder was dissolved in carefully purified chloroforni" \vith subsequent evaporation of the solvcnt iiiitier reduccd prsure. Shiny, transparent, yellow crj-stals were o h t : ~ i i i ~ ~ l which analyzed to RP.BIC1. I t was observed that when cliloroforni \vab not i-igoinlu4! 1)urified before use, a sinal1 quantity of yellow ncccilc-like. tals, quitcdiffcrcnt iiiappcarance from those of I3P.21IcI3 e obtained. These crystals were identified as BP.IIICI2. .Innl. Cdlcd. for RP.HIC12: C , 33.8; H,2.,%; s,'7. iodometric equiv., 177.6. Found: C, 35.0; 13, 2 . S , 8.34; iodometric cquiv., 177. This compound can bc prepared easily by recrystallization of the BP.2ICI cornplcx from chloroform previously shaken up with a few ml. of colicentrated hydrochloric acid. I t is stable in air, soluble i i i polar solvents, and melts sharply and reversibly a t 139" Pyridine-IC1 Complex.-The complex was prepared b v a method analogous to t h a t used in the preparation of I3P. 2ICl. It was obtained in the form of a bright yellow iriicriicrystalline powder, iodornetric equivalent of which \ w \ (9) P. Walden, Z. p h y s i k . Chem., 147, 1 (1930).
Feb. 5 , 1957
REACTIONS OF IODINE MONOCHLORIDE WITH PYRIDINE
571
found to be 120.6, calculated weight for Py.IC1 is 120.7. Attempts to prepare Py.2ICl described in the literaturea were unsuccessful. Pyridinium 1ododichloride.-This compound was prepared by theadding of hydrochloric acid to Py.IC1 in chloroform solution and recrystallizing. Iodometric equivalent was found to be 138, calculated for Py.HIC12, 139. Dipyridinoiodine(1) Perchlorate.-The perchlorate was prepared by the reaction of Py2,AgC10, with iodine in chloroform solution.'O I t was obtained as greyish-white powder. lodometric equivalent was found to be 194, calcd. for Py,. IC104, 192. Pyridinium Perchlorate.-Pyridinium perchlorate was obtained by the addition of 70y0perchloric acid to a solution of pyridine in acetic acid. The white microcrystalline precipitate was filtered, washed and dried. The melting point of the compound was 287'; literature" value 288'.
Results and Discussion The absorption spectra of BP, BPH+ (obtained by the addition of a slight excess of hydrochloric acid to a BP solution), BP.HIC12 and BP.2IC1 in acetonitrile solution are shown in Fig. 1. The spectra of BP and BPH+ in this solvent are similar to those in aqueous solutions.12 The absorption spectra of BP.2IC1 and of BP.HIC12 yield some interesting information. It is seen that a t longer wave lengths the absorption curve of the second compound practically coincides with that for BP.H+. However, beyond 260 mp, the characteristic absorption maximum of the IC12- ioni3 a t 227 mp is observed. The molar absorptivity a t this wave length is 57,500. The molar absorptivity of RPH+, calculated from the absorption curve of BPHC1, is 5,000. This leaves 52,500 for the absorbance of the IC12- which is close t o the value of 54,500 obtained from solutions of tetramethylammonium iododichloride in the same solvent13 after suppression of the slight dissociation of the IC&- ion by an excess of the chloride ion. This peak did not show any change with time, and appears to obey Beer's law. The BP.2IC1 curve also gives the characteristic IC12- absorption maximum a t 227 mp. The molar absorptivity varied between 39,000 and 62,000 depending on the concentration and the age of the solution, the aged and the more dilute solutions showing a higher molar absorptivity. The concentration range of the solutions measured varied between 2 X and 8 X M. The presence of the IC12- ion shows that the compound undergoes dissociation BP.2ICI f,BPI' IClz(1) However, the situation seems to be mure complex because of the variation in the intensity of the absorption maximum with time, which is indicative of the presence of free iodine monochloride.* However, the molar absorptivity of a fresh 1.0 X loe4 solution of IC1 is only S,OOO (calculated on the basis of IClz-). Since the lowest value obM solutained on this investigation for 2 X tion was 39,000, it is evident t h a t the maximum cannot be attributed to a simple dissociation of iodine monochloride. I t seems quite likely that, as
+
(10) H. Carlsohn, "Uber eine neue Rlasse v a n Verbindunpen des positiv einwertigen Jods." Verlag van S. Hirzel, Leipzig, 1932, p . 18. (11) F. Arndt a n d P. Nachtwey. Be?.. 59, 448 (1926). (12) K. Sone, P. Krumholz a n d H. Stammreich, THISJ O U R N A L , 1 7 , 777 (1955). (13) A. I . Popov a n d R . I'. S ~ v e n s e ni.b i ~ l . 77, , 3764 (1955).
I 225
'..-.--
I
I
250 275 WAVELENGTH
300
(rnr).
325 -_
Fig. 1.-Absorption spectra of 2,2'-bipyridine and of 2,2'bipyridine compounds in acetonitrile: - - - - , 2,2'-bipyridine; -, BP.HC1; .,BP.HIC12; - . * -,Bp.2IC1.
-
...
BP.2ICI is dissolved in acetonitrile, it undergoes the following series of reactions
__
B P . 2 I C l S BP.IC1 BP.IC1 IC1
+ c1-
BP.1'
+ IC1
+ C11c12-
(2)
(3) (4)
The over-all reaction is given by eq. 1. It has been established that the equilibrium constant for reaction 3 in acetonitrile is of the order of 1.0 X 107.14 Equilibria constants for reactions 1 and 2 cannot be determined a t the present time because of uncertainty in the absorption values of BP.IC1 and of BP.I+. (An attempt was made t o prepare BP.IC104 and BP.IN03 by the method used for the pyridine analogs but it was unsuccessful.) -2 rough estimation can be made of the degree to which reaction 4 occurs from the intensity of the IC12- peak a t 227 m p which, a s was menM solutioned above, reaches 62,000 in 8 X tions. This value is nearly 9,000 units higher than that for the IC12- ion itself. Since i t is doubtful that the absorption of BPI+ ion would be much higher than 10,000 a t this wave length, and since 62,000 seems to be a limiting value for the BP. ?IC1 absorption a t this wave length, it can be conAf solution reaction 4 occurs t o cluded that in the extent of 3 90%. The study of the pyridine system gives additional support t o the above ideas. The absorption curves of Py.IC1, Py.HIC12, Py.HC104, Py2.IC104 and pyridine are given in Fig. 2. Again, in the first two cases, we have the characteristic ICh- peaks a t 227 m p , Subtracting the molar absorptivity of PyH + ion from t h a t of PyeHIC12 a t this wave length, we get 53,200-1,000 or 52,200 for the molar ab(14) i'j 13 bkelly. P h D 1 hesis, i t d t e Unixersity of Iowa, 1955.
dine complex with pyridine is known, it is possible to estimate the absorbance due to the IC12- ion alone. *Zt 227 nip, the molar absorptivity for a 4.3 X lop5 AI solution of Py.IC1 is 44,400, calculated on the basis of the IC12- ion. At this wave length, PyJf has a molar absorptivity of 8,500 which leaves 33,900 for the molar absorptivity of IC]?-. These results indicate that we have a dissociation of the Py.IC1 complex according to
m
o_
-
X
2 D
WAVELENGTH
(ms)
Fig. 2.--Xbsorption spectra of pyridine arid of pyridine compounds in acetonitrile: - . - . ., pyridine; -, PyHC10,; - - - -, Py2IC104; . . . ., PyHIC11; - - ' - t PyIC1.
sorptivity of IClz-. I t is seen that this value agrees closely with that obtained for the BP. HIClz complex. On the other hand, the iodine nionochloride complex again yields variable molar absorptivities, varying from 43,000 t o 51,000 a t 227 mp, but the variations seem to be much less pronounced than in the case of BP. Continuous variation method on the pyridine-iodine monochloride system in the 300-400 mp region gave a series of sharp maxima a t a 1:1 mole ratio of reacting species. Since, in this case, the molar absorptivity of the positive io-
+ IC&-
(15) (a) G . K o r t u m and H. XTiIski, Z , fi4l:il:, Chem., 202, 35 ( 1 9 5 3 ; (h) R . Zingaro, C. A. VanderWerf and J Kleinberg, THISJ O V R N A L , 73, 88 (1951); ( c ) J . Kleinberq, E. Colton, J. Sattizahn and C. A. VanderWerf, ibid., 76, 447 (1953). (d) C. Reed and R . S. Rlulliken, ihid., 76, 3869 (1954).
I o n ~ aCITY,IOWA
u.s.NAVAL ORDNASCE TESTSTA'I'IOS] I. Formation of a New Diazo-like Species by the Oxidation of 1,I-Dialkylhydrazines in Solution
[CONTRIBUTION FROM THE INORGANIC CHEMISTRY
Alkylhydrazines.
2 P . Y I C l S PY,I+
and that in 4.3 X N solution it occurs to tlic extent of 70%. Sumerous spectrophotometric studies have been done in the past on solutions of iodine in pyridine.15 Although in some cases evidence was obtained that the triiodide ion was formed in such systems, i i i general, it was assumed that the absorption was due to the PyIf ion. It seems from the results obtained in this investigation that two molecules of pyridine are coordinated to the positive iodine. The fact that positive iodine can have a cohrdination number of two is confirmed by the existence of such compounds as PyJC104, Py,.IXOs, etc.'" Because of the time-dependent change in the absorption spectra of solutions containing iodine monochloride, exact quantitative calculations of the equilibria constants for the reactions described in this report seem to be inipossible at the present time. The reasons for this change are liow being iiivcstigated in this Laboratcry. Acknowledgment.-The authors wish to thank 11r. lIr.A. Deskin, Lfr. R. 13. Rygg and Mr. F. B. Stute for keeping them supplied with iodine monochloride and purified acetonitrile throughout this investigation.
BRALCH, CIILXISTRY
DIVISION,
I ~ ~Y~ I I , I , I A I?. M A~CBRIDE A i m HOWVARI) b'. F;r
