12. A. S. Davydov, Theory of the Absorption of Light in Molecular Crystals [in Russian], Kiev, p. 156, 1951; ZhETF, 18, 201, 1948.

13. K. R. Popov, in -Molecu la r Spectroscopy [in Russian], Leningrad University, p. 18q, 1960. 14. A. E. Lutskii, ZhOKh, 88, 1601, 1963.

15. K Watanabe, J. Chem. Phys., 26, 542, 1957. 16. V. I. Vedeneev et a l . , Chemical Bond Energies [in Russian], Izd-vo AN SSSR, 1962. 17. R. Berry, P. Brocklehurst, and A. Burawoy, Tetrahedron 10, 109, 1960.

164,

5 March 1965, revised 9 September 1965

Khar'kov Polytechnic Institute

AN E M P I R I C A L LAW IN O X I D A T I V E C A T A L Y S I S

V. Ya. Vol'fson

Teoreticheskaya i Eksperimental 'naya Khimiya, Vol. 2, No. 1, pp. 123-126, 1966

It was recently shown [1] that a definite relationship exists between the reducibility of oxides and their catalytic activity in bringing about the oxidation of a number of substances. It may be supposed that the reactivity of the oxygen in the surface oxides is associated in a definite way with the ease of valence transitions of the metal ion in the catalyst. On the other hand, in the same work [1] a dependence was found between the reducibility of the most suitable oxide of the catalyst used for the oxidation of any particular substance, and the donor capaci ty of this substance. As a measure of the donor capaci ty of the substance undergoing oxidation, its ionization potential U may be employed. It is therefore natural to suppose that a definite correlation will exist between U and the energy of the valence transitions of the metal ions in the catalyst, which may be post- ulated during stationary operation of the optimum catalyst (the so-called catalysis-determining valence transitions) if the ioni- zation potential of the gaseous metal ion U k is taken as a measure of this energy.

It is found that such a correlation is actuaIly observed in the oxidation of substances whose ionization potential lies in the range 8 -10 .8 eV. If a graph is constructed with ionization poten- tial (in all cases, unless specia!ly indicated, taken from [2]) for the catalysis-determining valence transitions* of the optimum catalyst metal ions for the oxidation of any particular substance** on the abscissa, while the ionization potentials of the correspond-

~eV

I0

9

8

19• ' oI5 I4 o/6

2 I I I

Io zo so do 50 U,,eV

Dependence of the ionization potentials of the optimal for oxidation, catalysis-determining valence transitions of the metal ions in the catalyst, on the ionization potential of the substance undergoing oxidation. Description of the points is given in the text.

ing substances undergoing oxidation is shown on the ordinate axis, then points corresponding to published data known to the author are satisfactorily grouped about a straight line (as shown in the figure). It is necessary to stress, however, that the dependence is only of an approximate nature, since the ionization potentials of gaseous metal ions are used as

parameters.

The optimum catalyst for the oxidation of naphthalene (ionization potential U = 8.1 eV) to phthalic anhydride is an oxidized vanadium catalyst i s ] (of which the catalysis-determining valence transition is V a+ -* V a+ , point 1). It is known [4] that on the same catalyst phenanthrene (U = 8 . 0 - 8 . 1 eV) is selectively oxidized to phthalic anhydride (catalysis-determining valence transition V 4+ --, V s +, point 2). Point 3 lies satisfactorily on the straight line, and corresponds to the gaseous oxidation of o-xylene (U = 8.56 eV) to acids and aldehydes on vanadium pentoxide [5] (catalysis-determining valence transition is also in this case V a+ -~ Vb+). p-Xylene (U = 8 .44 eV) is oxidized with high yield to terep+hthalic acid on manganese dioxide in sulfuric acid solution [6] (catalysis-determining valence transi- tion Mn 3+ ---* Mn 4 , point 4). Manganese dioxide is also the optimum catalyst for the heterogeneous liquid-phase oxida- tion of dibutyl sulfide to dibutyl sulfoxide [7 ] (catalysis-determining valence transition the same, point 5). [Since the

*For heterogeneous catalytic processes, the catalysis-determining valence transition represents the change X - 1 *-~ X where X is the valence of the metal ion of the initial catalyst.

**The criterion of optimum character for the catalyst is the relative yield of the final product.

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published information only gives the ionization potential of dimethyl sulfide (8.73 eV), diethyl sulfide (8.48 eV), and dipropyl sulfide (9.2 eV), the ionization potential of dibutyl sulfide is taken as the mean of the ionization potentials of these three sulfides, or 8.8 eV. It is necessary to observe that the ionization potential of dimethyl sulfide is some- what lower than that of dimethyl sulfoxide (8.85 ev). ]

The best catalyst for the liquid-phase oxidation of toluene (U = 8.82 eV) to carboxylic acids and benzaldehyde (U = 9.60 eV) is vanadium tetroxide [8 ]. The corresponding point 6 lies satisfactorily on the straight line (catalysis- determining valence transition V a+ ~ V 4+). Point 7 (corresponding to the gaseous oxidation of benzene, U = 9.24 eV) to maleic anhydride on vanadium-molybdenum catalyst (catalysis-determining transition V s ~- ~ V 4~) lies a little less satisfactorily on the line. To obtain a high stable concentration of V 4+ ions in the catalyst, molybdenum trioxide is added to vanadium pentoxide.

The oxidation of benzaldehyde (U = 9.6 eV) to benzoic acid proceeds best when a manganese resinate is used as catalyst [10] (point 8). The catalysis is evidently determined by the valence transition M n 2 + ~ Mn a+. Oxidation of acetophenone (U = 9.65 eV) to benzoic acid is also best carried out on this catalyst [11] (Point 9). The position of points 10 and 11 on the straight line makes it possible to understand why the oxidation of isovaleric aldehyde (U = 9.92 eV) [12] into isovaleric acid takes place satisfactorily when manganese isovalerate and cobalt isovalerate as used as catalysts (valence transitions Mn 2+ ~ Mn a+, and Co 2+ ~ Co 3+ respectively [13]). The oxidation of butyraldehyde (U = 9.96 eV [12]) to butyric anhydride takes place satisfactorily using copper butyrate and cobalt butyrate as catalysts [14] (points 12 and 13; valence transitions Cu I§ ~ Cu 2+, and Co s+ ~ Co s+ respectively).

The liquid-phase heterogeneous oxidation of n-pentane (U = 10.06 eV) to acids and aldehydes, from a number of catalysts investigated, takes place best on the catalysts (WT204 + MOs), [A12Os and V204 + WTOa)], A1203 [8]. The addition of oxides of higher valence is necessary, presumably, to regenerate the V 3+ ions in the catalyst. The catalysis-determining valence transition is here apparently V 2+ ~ V 3+ (point 14).

In the oxidation of ammonia (U = 10.35 eV) to nitric oxide, the best catalyst is bismuth trioxide [15] (catalysis- determining valence transition Bi 2+ ~ Bi a+, point 15). In carrying out the oxidation of acetaldehyde (U = 10.22 eV) to acet ic acid (U = 10.35 eV) on a commercia l scale, it is known [16] that the best catalyst is cobalt acetate (catalysis- determining valence transition Co 2+ ~ Co s+, point 16).

The procedure here developed provides a natural explanation for the fact that from a whole range of compounds investigated vinyl chloride (U = 9.95 eV) and ethylene (U = 10. 516 eV) under the mildest conditions, for the shortest t ime, and with maximum yield, may be oxidized into acetaldehyde (U = 10.22 eV) in both phases, using palladium chloride as catalyst [17, 18] (catalysis-determining valence transition Pd i + 4 pd 2+, points 17 and 18 respectively).

Finally, points 19 and 20 lie satisfactorily on the straight line, corresponding to the oxidation of hydrogen sulfide (U = 10.47 eV) to sulfur dioxide (U = 12.4 eV) on cobalt and nickel sulfides [19] (catalysis-determining valence transi- tion Co 1+ ~ Co 2+, and Ni 1+ ~ Ni 2+ respectively).

Exceptions to the relationship under consideration are provided by substances whose ionization potentials lie out- side the limits 8 -10 .5 eV. In addition it should be observed that the dependence relates only to the ions of the ca ta - lyst, but not to the metal .

We have thus shown the existence of a definite connection between the ionization potential of the substance being oxidized (provided that its value lies between 8 and 10.5 eV) and the optimum catalysis-determining valence transi- tion of the metal ion of the catalyst. The ionization potential of the optimum catalysis-determining valence transition increases regularly with decrease in the ionization potential of the substance being oxidized. It can be seen that the more difficult it is to remove an electron from the substance being oxidized, the lower the ionization potential of the optimum catalyst should be. That is, the more readily should the oxygen take up electrons.

The presence of an optimum relation between the ionization potential of the substance being oxidized and the ionization potential of the catalysis-determining valence transition is comprehensible from the point of view of the Balandin energy correspondence principle [20] as applied to oxidation reactions [21, 22]. According to this principle, on the optimum catalysis the heat q of a hypothetical intermediate oxidation stage representing the interaction of the substance being oxidized with the catalyst, and the interaction of the reduced catalyst with the oxidizing agent, should be approximately equal, and be represented by half the heat of the overall process Q, while the values U and U k are associated with q and Q.

From an analysis of the regularity obtained it is possible to postulate that a decisive factor for the oxide catalyst is the interaction of the reacting substance with the metal ion of the catalyst. This is particularly clearly revealed in the fact that the straight line well represents points corresponding both to homogeneous and to heterogenerous catalytic reactions.

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We may observe that the existence of correlation between the catalytic activity and the ionization potential of the corresponding valence transitions of the metal ion in the catalyst definitely does not indicate that these valence transitions actually take place on the catalyst surface. In addition, the correspondence between the catalytic activity and the heats of the hypothetical intermediate stages of the oxidation process [21] does not signify that catalysis actually occurs through these stages. During catalysis the metal ions of the catalyst may apparently be present in any of the catalysis-determining valences, depending on the determining stage of the process.

Restricting ourselves to the single question, it seems to us that the results have considerable importance. In [23] it was shown that a high yield of a product formed by incomplete conversion of the initial substance during catalytic oxidation occurs only when the ionization potential of this product is higher than that of the initial substance. The material presented in this paper is fundamentally in agreement with this conclusion.

REF ERENC ES

1. G. I. Golodets, TEKh [Theoretical and Experimental Chemistry], I, 755, 1965. 2. Handbook of Chemistry [in Russian ], Goskhimizdat, Leningrad-Moscow, rot. t , 325, 1962. 3. C. Conover and H. D. Gibbs, Ind. Engng. Chem., 14, 120, 1922. 4. N. N. Vorozhtsov and D. A. Gurevich, ZhPKh, 18, 10, 1945. 5. S. K. Bhattacharyya et al., J. Indian Chem. Soc., 38, 470, 1961. 6. Asanagi et al. , J. Chem. Soc. Japan, 59, 690, 1956. 7. A. V. Mashkina and L. B. Avdeeva, Summaries of Communications to the Conference on Processes of

Heterogeneous Catalytic Oxidation of Organic Compounds [in Russian], Leningrad, p . 9, 1965. 8. I. I. Ioffe and N. V. Klimova, Kinetika i kataliz, 4, 779, 1968. 9. S. K. Bhattacharyya et al. , I. Indian Chem. Soc., 88, 466, 1961.

10. Z. Csuros, J. G4czy, and J. Morg6s, Aeta Chim. Akad. Scient. Hung., 629, 99, 1961. 11. I. I. Ioffe, N. V. Klimova, and M. S. Brodskii, Khim. nauka i prom-st, 4, 799, 1959. 12. V. I. Vedeneev, L. V. Gurvich, V. N. Kondrat'ev, V. A. Medvedev, and E. L. Frankevich, The Breaking

Energy of Chemical Bonds; Ionization Potentials and Electron Affinity [in Russian], Izd-vo AN SSSR, Moscow, 1962. 13. S. V. Uvov, V. B. Fal'kovskii, N. G. Kostyuk, A. V. Starkov, I. B. Golenkova, N. B. Kuskova, and

T. A. Tyuricheva, ZhPKh, 35, 700, 1962. 14. N. G. Kostyuk, S. V. L'vov, V. B. Fal'kovskii, A. V. Starkov, and N. M. Levina, ZhPKh, 85, 2021, 1962.

15. 16. 17. 18. 19. 20. 21. 22. 23.

N. P. Kurin and M. S. Zakharov, Izv. VUZ, Khimiya i khimicheskaya tekhnologiya, 8, 141, 1960. B. N. Dolgov, Catalysis in Organic Chemistry [in Russian], Goskhimizdat, Leningrad, 206, 1959. J. Smidt, W. Hafner, R. lira, R. Sieber, J. Sedlmeier, and A. Sabel, Angew. Chem., 74, 98, 1962, M. Sirtig, Hydrocarbon Process and Petrol Refiner, 48, 175, 1962. G. Pannetier, J. Lefebvre, and P. Barret, Bull. Soc. chim. France, 2, 390, 1961. A. A. Balandin, The Multiplet Theory of Catalysis [in Russian], vol. II, Izd-vo MGU, Moscow, 1964. G. I. Golodets and V. A. Roiter, Ukr. khim. zhurnal, 29, 667, 1963. G. I. Golodets, Dissertation, IFKh AN UkrSSr, 1968. V. Ya. Vol'fson, Kinetika i kataliz, 6, 553, 1965.

13 May 1965 Pisarzhevskii Institute of Physical Chemistry, AS UkrSSR, Kiev

M~)SSBAUER EFFECT IN ORGANOTIN COMPOUNDS WITH

METAL-BEARING GROUPS

A. N. Karasev, N. E. Kolobova, L. S. polak, V. S. Shpinel, and K. N. Anisimov

Teoreticheskaya i EksperimeutaI'naya Khimiya, Vol. 2, No. i , pp. 126-180, 1966

There is much interest in organometallic compounds at the present time, and much valuable information on the nature of the bonds can be derived via the M6ssbauer effect. Here this method is applied to the bonds of tin with some transition metals in organometallic compounds: Sn - - Mn, Sn - - Re, Sn - - Co, Sn - - Mo. It has been shown [1, 2] that the bonds Sn-H, Sn-Li, and Sn-Sn in organotin compounds behave as covalent, their presence producing no appreciable field gradient at the tin nucleus. It is of interest to establish how far this applies to the bonds of tin with other electron donors and also to examine the effects of strong acceptors (e. g. , halogens) directly bonded

to the tin. This aspect is considered here.

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