382
COMMUNICATIONS TO THE EDITOR
VOl. 64
Since the crystalline aluminosilicate is a one- of the A zeolite, known as “molecular sieves,”5 component catalyst, as distinguished from multi- having “port” sizes of 4 to 5 A. Such observations, component or amorphous catalysts, an opportunity in addition to providing an unusual type of catis afforded for detailed study of the compositional alytic selectivity, support the concept of “intraand structural factors which impart catalytic crystalline catalysis,” in contrast to activity of the activity for this reaction. exterior surface of crystals. With the Ca++ form of the A crystal, we have SOCONY MOBILOIL COMPANY RESEARCH DEPARTMENT GEORGET. KERR carried out the selective dehydration of 1-butanol PAULSBORO, NEWJERSEY GEORGEC. JOHNSON in the presence of isobutyl alcohol. Conventional ~LECEIVED FEBRUARY 25, 1960 silica-alumina catalyst dehydrates both alcohols at comparable rates. In contrast to the Ca++form the “X” crystal, we observed cracking of only INTRACRYSTALLINE AND MOLECULAR- of n-paraffins over this solid to only straight chain SHAPE-SELECTIVECATALYSISBY ZEOLITE products, consistent with molecular sieve action SALTS which does not allow egress of isomeric products. As an example of imparted activity, molecularsir: shape-selective hydrogenation catalysts have been We have foulid unexpected intrinsic catalytic prepared by incorporation of platinum in the A activities on synthetic crystalline inorganic zeolite crystal. We have selectively hydrogenated 1salts. 1 . 2 butene in a mixture of 1-butene and 2-Me-propene. The sodium aluminosilicate isostructural with In a mixture of equal volumes of 1-butene, isofaujasite, known as “13X,”3 is more active for the butene and hydrogen, at 25O with a contact tune cracking of normal paraffins than conventional of ca. 0.1 sec., 50yoof only the 1-butene was consilica-alumina, cracking catalysts (10% ~ 1 1 2 0 3 , verted to butane. A platinum on alumina catalyst g2O m.*,/g.:iudace area). If one replaces most of converted approximately equal quantities of both the Na+ by (la++, the cracking activity is further olefins. increased (Table I). The products from the Cat+ Sot all catalytic activities exhibited by the form resemble those from silica-alumina. Wowever, the products from t,he S a + form n.re free of zeolites need be intracrystalline. For example. with a n X zeolite of 4k.port size we have observed branched-chain structures. Patdysis for the hydration of ethylene oxide to TARLE r ethylene glycol and polyglycols with no hindrance effect of port size in evidence. Herr the catalytic WDECANE (:R.4CKIXG. 3 HR. ~ P E H A T I O N , 470”, T = activity appears to be located at the euternsi surface 9 SEC., 1 ATM. of the crvstallites. IsoTsoOlefins in vo butane: pentane: crncketl !n conventional surface catalysis the termination Decane n-butane n-pentano products. Cntalytic S&I converted ratio rntio wt. Sr, ( t i a three-dimensional solid structure is considereci Silica-alumina 25 3.1 3 0 37 to he the locus of actimty. For these zeolites, the Na-aluminosilicate! X 32 0.0 0 0 62 concept of surface loses its conventional meaning Ca-aluminosilicate, S 39 1. 1 2 4 30 and the molecular participants can find themselves In contrast with its high catalytic activity for the exposed to unusual coulomb fields. W t t wish to acknowledge contributions made X C I cracking of paraffins, the Na+ form is inact,ive for the dealkylation of isopropylbenzene even at 510’; various phases of the above work by fl. W. Maathowever, the (:a++ form produces extensive conver- man, It. L. Golden, E. Mower, arid G ’f. Km-. $ion at 465‘. Alpha-pinene undergoes no reaction Socohiv ~ I O B OIL I L COUPANY, INC. P B. u EISZ when refluxed with the Na+ form, but is converted l’AUL5BORO LABORATORIES I’il’l \HORO, J. V J FRII,E~TF extensively to camphene by the Ca++salt. R r C L I V E D FEBRI‘ARY 25, 1qM) The observed cracking activities are unexpected _ _ _ _ _ because of the cwmmon view that acid it,^" is a (5) 1) W Brrch, rtl I 4 m Chpm Soc . 7 8 , i W t 3 tICLiF) requirement arid the common experience o i poisoning by alkali and alkaline earth metals on conventional si1ic:ious cracking catalyst~s. We believe that the locus of catalytic activities THE NATURE OF THE SPECIES RESPONresides in the extensively developed interstkes of SIBLE FOR THE LONG WAVE LENGTH the X crystai. These interstices are accessible to ABSORPTION BANJ IN ACIDIC all molecules with critical diameters less than ea. SOLUTIONS OF OLEFINS 9A., Le., to ztll of t>hereactant and product molerules described above. Sir: We have heen able to demonstrate molecularDistinc.tly different electronic spectra are obshape-selective catalysis by utilizing intrinsic, t,ained from solutions of arylalkenes in .rmngly catalytic activities described above. or artificially acaidic. and weakly acidic media. ‘rhus, while inrorporat,ec.lc:Ltalytic materials within salt forms solutions of 1.1-diphenylcthylene (I)PE) in con: l i D. $4’. Brock, el d., J . ilm. Chem. Soc., 78, XM3 ( I D X ) . rcntrated sulfuric acid exhihit only the spectrum “2) R. X.Barrer. er ai., 7’rnn.v. Faraday Yor.. 63, 1 1 I 1 (1957). (Amax. = 423 mp; e = 4.7 X IO4 pm.-I mole-’ ‘3) Lindi, Air Prudiicts Co.. Tonawanda. New York. liter) due to the expected methyldiphenylcarbonium ‘ 4 ) E.@.. A . G. Ohlad, at al.. “.4dvances in (’atnlysis.” Vol. 1x1, ion,’ solutions in weakly acid media. e.g., sulfuric4cadernic I’rew New T o r k . N. Y . , 1951, PIX.199-L’&7.
COMMUNICATIONS TO THE EDITOR
March, 1960
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acetic acid mixtures, shows an additional intense absorption at 600 mp, (t lo4cm.-' mole-' liter). Similar spectra are obtained when DPE is chemisorbed on the acidic surface of a silica-alumina cracking catalyst.' It has been suggestedzb that this long wave length peak corresponds to a nonclassical carbonium ion (Pi Complex). However, recent British Work14as well as some of our own, has indicated that this probably is not the case. It is the object of this communication to offer evidence leading to the conclusion that this anomalous absorption band is due to the formation of an oxidation product whose properties closely resemble those of aromatilc radical i o m S (1) Khetic Evidence.-Reproducible kinetic measurements were made on the rate of formation of the species corresponding to the 600 mp absorption peak from IIPE in a solvent system composed of sulfuric acid, acetic acid and monochloroacetic acid. The over-all kinetic behavior showed that the formation of this species involved an induction period, autocatalysis and a competing decomposition process. VVhile the experimental data have not, so far, yielded to detailed kinetic analysis, the data are suggestive of a free radical chain mechanism. M'oreover, the observed rates could be increased by over 100-fold by addition of trace amounts of oxidizing agents such as HzSe04, H&Os and l&Fe(CN)a. ( 2 ) Spectrophotometric Evidence.-It was found that DPE could be reduced by Li, Na, K or Ca in tetrahydrofuran in the absence of air to produce either a blue (excess olefin) or red (excess metal) solution. These solutions were interconvertible. Similar behavior was observed with C&IsC== CHCJ&,, C & I r ~ ~ C C i € & ,C&&=CH-CH =CC&€s and has been reported previously6 with C&CH=CHC&. Furthermore, the blue solution produced a virtually identical spectrum having a single absorption maximum within 5 mp of that produced (600 mp) in the acid solution. As has been noted previously,6athis symmetry in behavior is predicted from the simple MO theory of Hiickel.:' (3) Magnetic Evidence.-The solutions of the negative ion were found to be paramagnetic and it was demonstrated that spin concentration followed the spectral intensity of the blue color. A single strong, sharp resonance line was obtained having a width of less than 10 gauss centered a t (1) (a) A. G . Evans and S. D. Hamann. Proc. Roy. Dublin Soc.. %6, 1939 (1950); A. G . E8vaas. J . A p p l . Chem., London, 1, 240 (1951); (b) V. Cmld and F. I.,. Tye. J . Chem. Soc., 2172 (10521; V. Gold, B. W. V. H a w w and F. L. Tye. ibid., 21G7 (1952). (2) (a) V. 1:. Lavrtlshin, B u r . O k b h e i Khim.. 36, 2697 (1956); (b) A. G.Evans, N. Janes, P . M. S. Jones and J. H. Thomas, J . Chem. SOC.,2757 (19.56);A . G . Evans, P. M. S. Jones and J. H. Thomas, did., 104 (i9.w). (3) (e) H. P. Leftin and W. K. Hall, Abstracts of Papers, 135th National Meeting, A.C.S.. Chicago, September, 1958, p. 345; (b) A. N . Webb, Preprinti. Div. of Pet. Chem., 4, C171, 135th National Meeting. A.C.S.. Boston, April (1959) (4) J. A. Gnace and M. C. R. Symons. J . Chem. SOC., 958 (1959). (5) (a) S. 1. Weissm;m, E. de Boer and J. J. Conradi. J . Chem. Phhs., 16,96311958) : (b) A. Carrington. F. Dravnieks and M. C. R. Symons. 1.Chem. Soc., 947 (19159). (6) D. E. Paul, D. Lipkin and S . 1. Weissman, J . Am. Chem. Soc.. 78, 116 (1956). 0 ) E. Hilck.el, Z . Physik. TO, 204 (1931).
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g = 2.00. An essentially identical e.p.r. signal
was obtained from a solution of DPE and SbCls in CH2C12(positive ion), whose optical spectrum was observed to be identical to that of the mixed that acid solution. It has been noted previo~ly14 paramagnetism cannot be observed in sulfuric acidacetic acid solutions containing the blue species formed from DPE. In the present work this was confirmed, although failure to observe a signal here might be attributed to the high conductivity and dielectric loss of the solvent system employed. Nevertheless, e.p.r. spectra have been obtained from polynuclear aromatic systemss in 98% H2So4. Furthermore, no e.p.r. resonance was observed when DPE was adsorbed on the surface of a silicaalumina catalyst, even when the latter was colored an intense blue. From the above discussion it appears evident that the species responsible for the 600 mp absorption peak, formed when DPE is adsorbed on a silica-alumina cracking catalyst, is an oxidation product of the olefin. It is tempting to suggest that this species is a positive radical ion, but on this basis the absence of paramagnetism remains to be explained. Work on this problem is continuing and a more detailed report will be made later. Thanks are due to Drs. A. J. Saracen0 and D. E. O'ReiUy of Gulf Research and Development Company for helpful discussions and to the former for the e.p.r. determinations. This work was sponsored by the Gulf Research and Development Company as a part of the research program of the Multiple Fellowship on Petroleum. MELLONINSTITUTE HARRYP. LEFTIN PITTSBURGH 13, PENNSYLVANIA W. KEITHHALL RECEIVED JANUARY 26, 1960
SEPARATION OF HYDROGEN, HYDROGEN DEUTERIDE, AND DEUTERIUM BY GAS CHROMATOGRAPHY
sir : A great deal of interest has been shown in the last few years in attempts to separate the isotopes of hydrogen by the methods of gas chromatography. Glueckauf and Kitt' separated pure deuterium from hydrogen by displacement chromatography in a column containing palladium black, but indicated that separation by gas-elution chromatography would not be possible. Thomas and Smith2 did obtain partial resolution of hydrogen and deuterium mixtures by gas-elutionchromatography on such a column; however, the palladium catalyzed the equilibrium between hydrogen, deuterium and hydrogen deuteride, so that only the pure isotopes can be obtained. Moore and Ward3 reported t,he separation of orthohydrogen from parahydrogen, and partial separation of (1) E. Glueckauf and G. P. Kitt, in D. H. Desty, "Vapor Phase Chromatography." Butterworths Scientific Publication. London. 1957. pp. 422-427; E. Glueckauf and G. P. Kitt, in the "Proceedings of the International Symposium on Isotope Separation." Interscience Publishers, Inc.. New York. N . Y., 1958,pp. 210-22(i. (2) C.0.Thomas and H. A. Smith, J . P h y s . Chrm., 65,427(1959). (31 W. R. Moore and H. R. Ward. J . A m . Chem. Soc., 80, 2909 (1958).
