1014
NOTES
Experimental Preparation of Materials. p-Methylmercaptobenzoic Acid.-p-Aminobensoic acid (17 g.) was diazotized with sodium nitrite (15 9.)aiid hydrochloric acid (50 ml.) under the usual conditions. The resulting diazonium salt solution was poured into a hot (70") freshly prepared solution of potassium ethyl xanthate (20 g. in 200 ml. of water) containing sodium carbonate (50 g.) to neutralize the acid in the diazonium salt solution. After the brisk evolution of gases had subsided, the mixture was treated with sodium hydroxide solution (5 g. in 50 ml. of water) and dimethyl sulfate (15.8 g.) and refluxed for 5 hr. On cooling and acidifying with hydrochloric acid, the crude p-methylmercaptobenzoic acid separated; yield 16.8 g. (80%). This on recrystallization from ethanol melted a t 189-190". Gattermann6 who prepared this acid by oxidizing p-methylmercaptobenzaldehyde reports the same melting point. p-Ethylmercaptobenzoic Acid.-Thie was prepared by the method of Donleavy and English.6 p-Isopropylmercaptobenzoic Acid.-The method used for its preparation was the same as that for p-methylmercaptobenzoic acid, except isopropyl bromide was substituted for dimethyl sulfate. The yield was almost quantitative. After a number of recrystallizations from methanol, the acid melted a t 155-156'. Anal. Calcd. for CIOHIZOZS: C, 61.2; H, 6.1. Found: C, 61.4; H, 5.8. Determination of Acidity Constants of the Acids.-0.001 Af solutions of the acids were prepared in 1: 1 ethanol-water, free from carbon dioxide. In each case a known volume of the solution was neutralized to the extent of 20, 40, 50 and 60% by using carbonate-free sodium hydroxide solution (0.001 M ) . The mixture was made up to 100 ml. The pH of the solution a t 32' was determined by means of a Cambridge pH meter using the Morton glass electrode. The ~ K values A were caIculated from the Henderson equation' and are the average of four determinations a t 20, 40, 50 and 60% neutralization; the spread in ~ K for A any acid did not exceed by 0.04.
Vol. 61
correlate the stability of metal salicylaldehyde only with the shift of the C=O stretching frequency. It is anticipated that, as the metal-ligand bond becomes stronger, all the fundamentals of the ligand should be shifted progressively to higher or lower frequencies depending upon their modes of vibration. Therefore we studied the infrared spectra of metallic oxalates since the structure of the oxalate ion is simple, and the assignment of the oxalate ion fundamentals based on the F.G method* is available. I n the present paper, we will discuss the relation between the strength of the M-0 bond and the direction and magnitude of the shift of each fundamental of the metallic oxalates. Although the infrared spectra of many oxalates already have been measured by Douville, et u Z . , ~ their experimental results are different from ours, and, moreover, no discussion was given on the relation between the stability and the band shift. Experimental The oxalates of Ala+, Cos+, Crsf, Fe8f,8 CuZf,loCoZ+,*l and Ni2+,I2 were prepared according to the literature. Measurements of infrared spectra were made by a PerkinElmer Model 21 double beam infrared spectrophotometer using NaCl and KBr prisms. The Nujol mull technique was employed.
Discussion The X-ray analysis of sodium oxalateI3 indicates that the oxalate ion is planar and the interatomic distances and angles are
(5) von L. Gattermann, Ann., 393, 226 (1912). (6) J. J. Donleavy and J. English, J . A m . Chem. SOL, 62, 220 (1940). (7) S. Glasstone, "Textbook of Physical Chemistry," 2nd ed., D. Van Nostrand Co., Inc., New York. N. Y . , 1947, p. 1003.
INFRARED SPECTRA OF METALLIC COMPLEXES. 111. T H E INFRARED SPECTRA OF METALLIC OXALATES BY JUNNOSUKE FUJITA, KAZUONAKAMOTO AND MASAHISA KOBAYASHI Department of Chemistry, Osaka University, Osaka, Japan Received December 8 , 1966
I n the first paper of this series,l we have studied the effect of coordination on the infrared spectra of typical metallic complexes of non-chelated ligands such as ammine, rhodanato and azido complexes. Some work has been reported on complexes with chelated ligands2-'; however, most of the bands observed are difficult to assign because of the complicated structures of the molecules. As a consequence, discussions have been limited to a few bands which are relatively sensitive to the kinds of metals. For example, Bellamy and Branch4 could (1) J. Fujita, K. Nakamoto and M. Kobayashi, J . A m . Chem. SOC., 78, 3295 (1956). (2) F. Douville, C. Duval and J. Lecomte, Compt. rend., 212, 697 (1941). (3) J. Leaomte, Disc. Faraday Soc., 9, 125 (1950). (4) L.J. Bellamy and R. F. Branch, J . Chem. Soc., 4487 (1954). (5) K. Ueno and A. E. Martell, THIS JOURNAL, 69, 998 (1955).
(6) T. R. Harkins, J. L. Walter, 0. E. Harris and H. Freiser, J . A m . Chem. SOC.,7 8 , 260 (1956). (7) R. G. Charles, H. Freiser, R. Friedel, L. E. Hilliard and W. D. Johnston, Spectrochim. Acto, 8, 1 (1956).
Although the angles of C-(2-01 and C-(2-011 are not equal, this might be due to the error of the Xray analysis. Thus we assume that the ion has V h symmetry, On the other hand, the X-ray data of K[Cr O X ~ ( H ~ O ) ~ ]give . ~ Hthe ~O dimensions ~~ TABLE I CLASSIFICATION OF THE 12 FUNDAMENTALS IN OXALATE ION Vb' 3 ag (R)
CPVO
Assignmentb in C P ,
3 al (R, I R )
u(C-O), v(C-C), sym S(0c-0) 1 a, (inactive) 1 a2 (R) Out-of-plane 2 bl (R, I R ) v(C-O), asym. S(C-C-0) 2 b1g (R) 1 b2 (R, I R ) Out-of-plane 1 bl, (IR) 1 a2 (R) Out-of-plane 1 bzg ( R ) 2 al (R, I R ) v(C-0), sym. S(C-C-0) 2 bZU(IR) 0 bz (R, I R ) 0 bsg (R) 2 b3" (IR) 2 bl (R, I R ) v(C-O), asym. S(0-C-0) G. Hereber!; a R, Raman active; I R , infrared active. "Infrared and Raman Spectra of Polyatomic Molecules, D. Van Nostrand Co., Inc., New York, N.Y., 1049, p. 331. (8) H. Murata and K. Kawai, J . Chem. Phys., 26, 589 (1956); H. Murata, K. Kawai and J. Fujita, $bid., 86, 796 (1956). (9) "Inorganic Syntheses," Vol. I, 1939, pp. 36, 37. (10) M. SchBfer, 2.anorg. Chem., 4 6 , 301 (1905). (11) C. Winkelhlech, Ann., 18, 167 (1835). (12) W. Deakin, Z . physil. Chsm., 69, 129 (1909). (13) G. A. Jeffrey and G. S. Parry, J . A m . Chem. Soc., 7 6 , 5283 (1954). (14) J. N. van Nikerk and F. (1951).
R. L. Schoening, Acta Cryat., 4, 36
4
1015
NOTES
July, 1957
TABLE I1 INFRARED SPECTRA OF METALLIC OXALATES A N D FREE OXALATE ION ( C M . - ~ ) asym.
Coinpd. (CZV)
bat
u(C-0)
a1
a1
KSAIOXS
1718,1695,1656
1404
&COO13
1710,
1658
K3Crox3
v(C-0)
bi
S(0-c-0)
905
822 806 824 810 817 807 804 795 804 790 772 768
545b
bau asym. S(0-c-0)
bl. asvm. S(C-c-0)
ai
1389
1290 1270 1257
900
1714,1684,1650
1390
1259
894
K,Feoxl
1712,1675,1641
1389
886
KLCIIOXI
1675
1272 1255 1280 1306 1316 1335 1316
KQNioxZ 0x2-
1637
1415 (1450)
1630
1485b 1450b
1625 1620
K~COOX~
1664b
..
b2u
b1g
(VI]) a
$!E%)
as
sym. u(C-0)
The assignment of these bands is not clear.
b
asyrn. a(c-c-0) bi
v(C-C)
897
.. ..
89gb
b3u
ag
v(C-C)
bi
sym.
aym. S(C-c-0)
S(0-c-0) ai
a1
581
43 1
483"
559
44F
476"
543
488
413"
532
503
538
485 507 524 518
.. ..
9
.
.. ..
..
bau syrn. 6(C-C-O)
443b aym. 6(O-C-O)
Raman data by Murata and Kawai.8
It is clear that the formation of the Cr-0 bond lengthens the C-01 bonds and shortens the C-011 bonds. Although the two C-Or and C-011 bond lengths are not equal in each pair, it is reasonable to suspect that this is due to poor resolution of the carbons as suggested by van Niekerk and Schoening.14 Therefore we assume Cz, symmetry for the oxalate ion coordinated to the metal. Thus, it is anticipated that, as the M-0 bond becomes stronger, lowering of symmetry will be more distinct, and the shifts of the fundamentals of the oxalates relative to that of the free ion will increase. Table I shows the classification of the 12 fundamentals of the oxalate ion in v h and CL"symmetries. Among those 12 fundamentals, 9 are in-plane and 3 are out-of-plane vibrations. The number of infrared active in-plane modes are only 4 for v h , but increases to 9 in Czv. Of these 9 fundamentals, we could observe 8 bands in the range between 1700 and 400 cm.-'. Their locations in various metallic oxalates are given in Table 11. Table I1 indicates that, as the metal is changed in the order of Ni2+, Co2+, Cu2+, Fe3+, Cra+, Coa+ and Ala+, 2v(C-O), asym. S(0-C-0), and asym. S(0-C-0) are shifted progressively to higher frequencies whereas 24C-0) and sym. S(C-C-0) are shifted to lower frequencies. Although some irregularity is seen in the AI complex, this might be due to the difference of A1 from the other metals in atomic weight and electronic configuration. As discussed above, it is reasonable to expect that, as the M-0 bond becomes stronger, the C-01 bond is more lengthened and the C-011 bond is more shortened, resulting in the shifts of v(C-01) and v(C-011) to lower and higher frequencies, respectively. The relation between the strength of the M-0 bond and the shifts of the bending modes
is not simple. It may be anticipated, however, that, as the two C-0 bonds become more uneven, asym. S(0-C-0) and asym. S(C-C-0) are shifted to higher frequencies and sym. S(C-C-0) and sym. S(0-C-0) are shifted to lower frequencies. Therefore, we conclude that the M-O bond becomes stronger in the order of the metals, Ni2+, Co2+, Cu2+,Fe3+, Cr3+,Co3+and A13+. This spectroscopic result is in good accord with the order of stability constant (pK1K2)l6for the divalent ions. Although the data of stability constants for trivalent ion are not available, the order obtained in this study, A1 > Co > Cr > Fe, is consistent with that of other metallic complexes which are coordinated by oxygen. Acknowledgment.-The authors wish to express their sincere thanks to Mr. S. Tanaka of the SunStar Tooth Paste Company for aid in obtaining the spectra in the KBr region. (15) For example, see A. E. Martell and M. Calvin, "Chemistry of the Metal Chelate Compounds," Prentice-Hall, Inc., New York, N. Y., 1952. p. 516.
HIGH-ENERGY ELECTRON IRRADIATION OF NEOPENTANE BY F. W. LAMPE Research and Development Division, Humble Oil and Refining Company Baytown, Teras Received Fsbmary $8, 1067
The author recently carried out studies of the high-energy electron irradiation of methanel which, in conjunction with the results of studies of secondary reactions in the methane mass ~ p e c t r u m , ~ - ~ suggest that the reactions of hydrocarbon ions with methane molecules are not only important but, indeed, may account for the majority of the over(1) F. W. Lampe, J . Am. Chem. Soc., 79, 1055 (1957).
(2) D. P. Stevenson and D. 0. Schissler, J..Chem. Phys., 88, 1858 (1955). (3) D. 0. Schissler and D. P. Stevenson, ibid., 84, 926 (1956). (4) F. H. Field, J. L. Franklin and F. W. Larnpe, J. Am. Chem. SOC.,79, 2419 (1967).
