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COMMUNICATIONS TO THE EDITOR
Vol. 85
TABLE I11 Accordingly, zinc electrodes were electrolyzed in 3y0 potassium chloride and in 37" potassium sulfate a t 2.5' DEVIATIONSO F A T O M S IS COPPER TETRAPHESYLPORPHINE The FROM THE PLASEPARALLEL TO THE 001 PLASEAND PASSING employing a current density of 60 ma. cm.-*. results confirm the studies of Sorenson, et al.,that THROUGH THE ORIGIN Atom
cu N C1
cz
C1
C4
cs cs Cl
Deviation in
A.
0.00 04 .26 .24 - .09 - .24 - .42 - .76 - 1.42
The bond distances in the copper tetraphenylporphine and nickel etioporphyrin I agree to within the experimental errors. Both molecules have a nonplanar configuration of the porphyrin ring although the details of the non-planarity are different for the two molecules. The X-ray analysis of palladium tetraphenylporphine, which is isomorphous with copper tetraphenylporphine, is in progress, and both structures will be published in detail a t a future time. Acknowledgments.-The author wishes to thank W. Busing, K. Xartin, A. Levy and A. Zalkin for making available their computer programs. The author also wishes to thank A. Tulinsky for his initial encouragement in the determination of porphyrin structures.
anodic dissolution in non-oxidizing electrolytes involves only the formation of bipositive ions. Anodic dissolution of zinc in 3% potassium nitrate a t 25 and 38' results in valences of less than two (1.82-1.87 a t 23') considerably outside of experimental errors. This is in harmony with results obtained by Sorenson, et al., for zinc dissolving in sodium nitrate. However, when zinc amalgam is electrolyzed a t GO ma. ern.-* in nitrate solution, there is no evidence of univalent ions; the agreement between the faradaic equivalent obtained from the current based on bipositive ions compares excellently with the amount of zinc dissolved as determined by titration with EDTA, and confirmed by weight measurements of the electrode (Table I). TABLE I W t . zinc (calcd.), g.
W t . zinc (exptl.), g.
0.1262 ,1939 ,2851 ,2864 ,0892
0.1269 ,1951 ,2817 2734 ,0903
Temp., 'C.
25 3~ 0 . 2 25 25 58 58
Apparent valence
1.99 1.99 2.02 2.09 1.98
No mercury was detected in solution. A loosely adhering black film was observed on the zinc anode DEPARTMENT OF CHEMISTRY during electrolysis in potassium nitrate but was not UNIVERSITY OF CHICAGO present on the amalgam or on zinc in other electrolytes CHICAGO 37, ILLINOIS EVERLY B. FLEISCHER (sulfate and chloride). RECEIVED FEBRUARY 20, 1963 The value of 2.09 is higher than normal experimental error can account for and suggests the possibility of a competing electrolytic anode reaction which might VALENCE EXHIBITED BY ZINC AMALGAM ANODICALLY DISSOLVING IN NITRATE SOLUTIONS' conceivably compensate for a decrease in apparent Sir: valence arising from non-electrolytic oxidation of unipositive zinc ion by the electrolyte. However, the Sorenson, Davidson and Kleinberg* have proposed only possible competing electrolytic oxidation would that zinc and cadmium dissolve anodically in certain require oxygen evolution and no evolution was oboxidizing agents (chlorates and nitrates) with an initial served a t the anode. Furthermore, no nitrite ion was mean valence between one and two. Other investigadetectable in the anolyte after prolonged electrolysis. t o r ~ have ~ - ~ reported the anodic disintegration of such The results clearly show, inasmuch as the concept metals as Be, Mg, AI and Fe in salt solutions. In the of uncommon valence states is inadequate to explain case of Be and Mg "chunks" of metal have been obthe anodic dissolution of zinc in oxidizing electrolytes, tained as a residue and shown to have originated from that mechanisms involving breakdown of the anode into the electrode and not through n ~ c l e a t i o n . ~There~~ atoms and/or atomic aggregates cannot be rejected. fore, any material dissolving in the electrolyte and not a part of the electrical circuit would not contribute to DEPARTMENT O F CHEMICAL ENGISEERING AND CHEMISTRY WILLIAMJ , JAMES SCHOOLOFMIXES AND METALLURGY the faradaic current, and could account for apparent GLESNE. STONER UNIVERSITY OF MISSOURI valencies of less than two. The presence of atomic ROLLA, MISSOURI aggregates of colloidal and sub-colloidal size also could RECEIVED FEBRUARY 16, 1963 account for the reducing properties of the anolyte. In July, 1962, Dr. T. P. Hoar (Cambridge, England) suggested that the mechanism of anodic dissolution of SOME CHARGE-TRANSFER SALTS OF lI2,3,4,5-PENTACARBOMETHOXYCYCLOPENTADIENYL zinc be studied by the use of a zinc amalgam electrode. ANION The amalgamation would prevent the disintegration of Sir : the electrode and the formation of films such as are obIn the cuurse of studving the chemistry of 1,2.3,4,3served on pure zinc (99.99%) electrodes in nitrate pentacarbomethoxycyclopentadiene' we found that its solutions. As the diffusion of zinc ions of any valence anion, I , will function as a planar donor in a series of would not be prevented by the amalgamation, one would organic charge-transfer salts, in which the isoelectronic expect the behavior of zinc amalgam to correspond planar cations tropylium, 2,4,G-trirnethylpprylium, to that of zinc in the same electrolyte as regards the pentaphenylpyrylium, N-methylpyridinium and Xinitial mean valence. methylquinolinium serve as acceptors. Good yields ( 1 ) This work supported by a research grant from O S K . of these stable salts? are obtained by stirring a suspen(2) 1). 1'.Sorenson, A . W. Ilavidson and J. Kleinberg, J . I n o v g . . Y t d C h e m . , lS, 64 (1960). ( 3 ) &I. E. Straumanis and 1). C. Mathis, J . Eleclrochem. Soc., 109, 434 (1902); J . Less-Common .Melds, 4, 213 (19G2). (1) W, J. James, M. E. Straumanis, B. K. Bhatia and J. W. Johnson, J . Elecfrochem. SOC.,109, 199C (1902). 67) B. Roald and M. A. Streicher, ibid., 97, 283 (1950). (6) G . A . Marsh and E . Schaschl, ibid., 107, 960 (1960) 17) h1. E. Straumanis and B. K . Bhatia, ibid., 110 (1903).
11) 0. Uiels, B e r , 7 6 , 14.52 19-12). .?) Salt formation ncr doubt is a result of the low nucleophilicity of I.
Less substituted cyclopentadienyl anions (thus, less delocalization of the negative charge) have been shown t o form covalent compounds with tropyliurn.3 pyryliuml and pyridium.' 3 ) 13' von E Doering and H. Krauch. A i r a m C h p m . , 68, 661 '1956); \ I B \.ol'pin. I . S. hkhrem and D. S . Kursanov, %h Obshch K h i i i i . , 28, ,4.30 19.58 , K Hafner. .-I?ZKPL Chrnf. 76, 43 '1903)
May Sj 1963
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COMMUNICATIONS TO THE EDITOR
sion of potassium 1,2,3,4,5-pentacarbomethoxycy~lopentadienylide, 11,6with an "yliurn'' salt in an appropriate solvent (e.g., I1 and tropylium tetrafluoroborate in acetone), separating the inorganic potassium salt (quantitative in all cases), then isolating and recrystallizing the organic salt. Physical properties of
R
Rm R
I1
I
R
composed of the absorptions of the individual ions plus a new long wave length absorption. That this long wave length arises from a charge-transfer transition is shown by a plot of the long wave length absorption frequencies of the cyclopentadienylide salts 111, IV, V, VI and VI1 against the charge-transfer absorptions of the corresponding iodides8 A nearly linear plot is obtained with a slope of approximately unity. Yellow acetonitrile solutions of triphenylcyclopropenyl salt, VIII, (identified by n.m.r. and ultravioletvisible spectra) are readily obtained; however, this salt could not be induced to crystallize. VI11 also appears to be of the charge-transfer type (long tailing of broad absorptions from 300 mb to 500 m ~ ) . ~
111
(R = C02CH3)
each salt are shown in Table I. PHYSICAL PROPERTIES OF
TABLEI SALTS
THE
OF
1,2,3,4,5-PENTACARBO-
METHOXY CYCLOPENTADIENE
Charge-transfer absorptions h x mr(e)b [color]
Cation (m.p. of salt)"
@ CH3
N.m.r. spectra r(multiplicity)c assignmentd
470 (1870)
1.76 (S) C7+ protons 6 . 4 1 ( S ) 0-CHs
418 (758) [yellow]
3.05 (S) =C-H 6.37 ( s ) O-CHI 7 . 5 1 (S) 2,6-CHa 7 . 7 2 (S) 4-CH3
+
154-155" IV
I
r- 'R
R
VI11 I1 (R = C02CHa) The potassium salt I1 also forms charge-transfer salts with neutral acceptors. Thus, I1 and 1,3,5-trinitrobenzene afford the yellow crystalline salt, IX, m.p. 200-201°, I1 and trinitrofluorenone give a red crystalline salt, m.p. 199-200°, while I1 and tetracyanoethylene yield an unstable (in solution) blue complex (X";:i 590 mp). R
-. €Jh* Ph
0
+
Ph
-120 (17,000) [yellow]
I
2.25-3.10 ( M ) =C-H 6.41 (S) 0-CHs
250-251"
V
0, N I CH3 104-105"
350 (768) [pale y e l l o 1~
I
1.9-2.8 ( M ) =C-H 6.06 (S) S-CHJ 6 34 (S) 0-CHs
VI
q+ CH3
106-107"
402 (1020) [yellow ]
I
1.3-2.8 (M)=C-H 5 , 8 2 ( S ) N-CH, 6 . 4 1 (s)O-cH3
VI1 Melting points are corrected. e values were found to be somewhat concentration dependent. S = singlet, M = complex multiplet. Integrations consistent with assignments. a
The structure of each salt is established by its analysis, infrared and proton magnetic resonance spectrum.' The ultraviolet-visible spectra appear to be K . Hafner, Angeu?. Chem., 69, 393 (1957). K. Hafner, A n n . , 606, 79 (1957). T h e preparation and properties of this compound are described in P submitted t o J . O i g , Ckem. by the authors, (7) Satisfactory analyses were obtained from various commercial laboratories; infrared spectra were taken in solution (HCCla); n.m.r. spectra were recorded with a Varian A-GO spectrometer using chloroform-d a s solvent and tetramethylsilane as internal standard; ultraviolet-visible spectra were taken with dichloromethane solutions. (4) (.5) (6) paper
NO2
IX
(8) M. Feldman and S. Winstein, Tetvahedron Letters, 853 (1962). (9) We have found t h a t triphenylcyclopropenyl iodide, a yellow salt, has an absorption band a t 301 mp (CHsCW, a n absorption n o t found in the bromide. We believe this absorption is caused by a charge-transfer transition. This would place t h e charge-transfer absorption of VI11 in the vicinity of 300 mp, a portion of the spectrum where both triphenylcyclopropenyl cation (307, 320 mp) 10 a n d pentacarbomethoxycyclopentadienyl anion (294 mp)*l absorb strongly. (10) R. Breslow and C. Yuan, J . A m . Chem. Soc., 80, 5991 (1958). (11) R. C. Cookson, J. Hudec and B. Whitear, PYOC.Chem. Sac., 117 (1961).
MELLOSINSTITUTE EUGENE LE GOFF PITTSBURGH 13, PA. R. B. LACOUST RECEIVED FEBRUARY 28, 1963 MECHANISM OF THE PHOTOCHEMICAL FORMATION OF PHENANTHRENE FROM cis-STILBENE IN THE VAPOR PHASE
Sir: In an attempt to study the mechanism of the iormation of phenanthrene from the photolysis oi cis-stilbene, we have investigated this system in the vapor phase at lit)' a t a pressure of about 5 mm. Cnder these conditions, at both 3130 -4.and shorter wave lengths, photolysis of cis-stilbene led to the formation of phenanthrene and hydrogen in equivalent amounts (within experimental error) and trans-stilbene. This is in sharp contrast to the recent report' that in cyclohexane solution photolysis of cis-stilbene leads to phenanthrene only in the presence of oxygen. To reconcile the data in the two phases we have carried out a number of control experiments with the following results. 111 F B. J l a l l o r y C S. IVnod, J 'I Gordon, I. C. Lindquiat and 11. 1.. Savitz J A m Chem Ssr , 8 4 , 4 R G ! 19C2i.
