Identification of Adsorbed Species by infrared Spectroscopy Thiophene-Cobalt Molybdate Systems SIN: Infrared absorption bands have been observed recently for thiophene adsorbed on the surface of solids which :trr catalytically active for hydrogemtion. ,4 Perkin-Elmer Model 112 spectrometer was employed, with thr light source mounted vertically above a specially constructed cell (4) equipped with connections to a vacuum line ant3 appurtenanees. Several possibilities for the structure of adsorbed thiophene are: one-point adsorption, in which the catalyst functions as a Lewis acid, and where the sulfur atom is attached to the surface; two-point adsorption involving an associative reaction in which two carbon atoms are united with the solid; four- or five-point adsorption whereby the adsorbed species consists of a thiophene molecule with four carbon atoms affixed to the surface. It would be anticipated a priori that the infrared spectrum of thiophene united with a solid in the one-point form should cxhihit carbon-hydrogen stretching modes in the vicinity of 3000 to 3100 cm.-' that are characteristic of unsaturation. The two-point form could be expected to have these same hydrogen vibrations a t lower frequencies--i.e., 2900 to 2950 cm.-' I n addition. the two-point form could be predicted to show bands attributable to the residual ethylenic double bond, which is noF unconjugated, a t some frcquency intermediate between the spectral position of absorption maxima for t h c oneand four-point structures. The first portion of Figure 1 contains the infrared spectrum of gaseous thiophene in the carbon-hydrogen stretching region using calcium fluoride optics, a path length of 23 cm., 37-mm. pressure, and 0.100-mm. slit width The esscntial features of the spectrum are threc, bands located a t 2998, 3071. and 3111 cm.-l ascribable (3) to vibrational modes numbers 7 and 16, resonancc' of modes 8 and 17, and the third harmonic of mode number 2. The second portion of the figure shons the absorption spectrum of thiophene adsorbed on a commercially available cobalt molybdate hydrogenation catalyst, Harshaw 0301-T (85% y-alumina, 15% cobalt molybdate). The catalyst \\as pretreated for 16 hours a t 450" C. in :tn atmosphere of hydrogen containing 2% hydrogen sulfide. These gases were irmoved by pumping for 2 hours a t 450' C. The surface area of the catalyst was 190 sq. meters per gram. Gravimet-
Figure 1.
Infrared spectra of adsorbed species
left. Gaseous thiophene Right. Thiophene-cobalt molybdate system
ric measurenients taken simultaneouslx with the spectroscopic data upon an identical sample of the catalyst indicated that approximately 1.5% (weight) of thiophene was absorbed a t a nonequilibrium pressure of 4 mm. The gas pressure in the infrared cell was maintained near 25 mm. for 3 hours preceding the start of the infrared scans: immediately following rapid reduction of the pressure to about 4 mm., spectra were obtained between 3400 and 2500 cm.-l. Blank experiments were made with y-alumina. The infrared spectra are consistent primarily with a surface species formed by attachment of the sulfur grouping in the thiophene molecule to the solidLe., the case cited above describing onepoint adsorption, near room temperature. When thiophene reacts with the cobalt molybdate surface a t temperatures exceeding 250' C. , small increases in band intensity in the carbon-hydrogen stretching region between 2960 and 2850 cm.-' are observed. The appearance of this single new band is indicative that some of the thiophene exists on the catalyst surface in the four-point form. If the two-point structure were created, on a hydrogen free surface, txT-0 new absorption modes would be detectable under
the conditions of high resolution employed in the current investigation; these bands would be, as outlined above, associated with the saturated or tertiary hydrogen stretching vibrations and with the olefinic hydrogen motion. It is the two- or four-point forms of absorbed thiophene which are active intermediates in catalytic processing (1). Similar results were obtained in an infrared investigation of the adsorption of thiophene on molybdenum sulfide catalysts. except that in certain instances absorption bands assignable to the two-point structure could be identified in addition to the four-point structure. I n every system studied it was possible to desorb the surface species and recover pure thiophene from the special infrared cell. Evidently an equilibrium exists between gaseous thiophene and/or physically held or one-point thiophene and the multipoint species; reduction in the pressure of thiophene in the vapor phase produces a corresponding diminishing of the latter forms. The results cited above may be contrasted with earlier spectroscopic data from which it was deduced (2) that thiophene reacts with platinum and rhodium surfaces supported on Alon-C a t 175' C. and higher temperatures to VOL. 32, NO. 10, SEPTEMBER 1960
1365
yield principally the four-point species. Spproximately one half of the surface compounds could be removed by extended evacuation followed by hydrogenation a t even higher temperatures. The fact that an apprcciablc portion of the surface species could not be desorbed from the platinum and rhodium surfaces is indicative of a distribution of active sites of very widely differing energies.
man, H. M.,J . din. Chem. Soc. 71, 797 (1949). (4) Yang, A. C., Garland, C. W., J. Phys. Chem. 61, 1504 (1957).
LITERATURE CITED
( 1 ) Emmett, P. H., McKinley, J., “Ca-
talysis,” Vol. V, p. 431, Reinhold, Sew York, 1957. ( 2 ) hleites, L., Sicholson, D. E., “Handbook of Analytical Chemistry,” Chapter on Infrared Spectroscopy in the Sodium Chloride Region, NcGraw-Hill, Ken. York, in press. (3) Waddington, G., Knowlton, J. IT., Scott, I). R., Oliver, G. D., Todd, S. S., Hubbard, IT. X., Smith, J. C , Huff-
D a s E. NKCHOLS~S Research and Development Division Humble Oil &. Refining Co. Baytown, Tex.
RECEIYED for review April 32, 1960. cepted June 15, 1960.
.‘IC-
Radiochemical Evaluation of Solvent Extraction of Indium as the Bromide at High Concentrations SIB: ’l’lie production and analysis of high purity indium has niadt, it’ tiesirable to he able to separato trace, quantities of impurities from large quantities of indium. Many papers dealing with the solvent ext’raction of indiuin arc found in the literaturr, with tliosr hy Irving and Rossotti (I-4) heing perhaps the most complete and that’ by Sunderman and coworkcrs (6) tht. most rcwnt,. Of the, many articles seen hy the present author only that of Iiriox and Spiiiks ( 5 ) gave data on extractions on indium coiicentrations above 0.1.11, and tlicse data were not very complcte. The present paper reports the rewilt:: of extractions from solutions 0.1 to O.T.11 in indium.
solvent. anti the washing removed without mixing with the acid layer. The second extractiou. was then made with 5 nil. of fresh solvent. All extractions were made at room temperature. After the extraction a portion of the acid phase was removed for the radiation measurements. The exbraction srparations were evaluated by comparing the radioactivity of extracted and unextracted portions of the test 3olutions. The measuremt>nte of tlic gamma emit’ter? were made on 3 nil. of the solution in a glass via1 5 cm. high by 1.5 cm. in outside cliamctcr having :I 1-mm. wall thickness. ,111 of thv pwmma eniit’ters except lcad-210 \wre iiwssured with :I well-t~ye scintillation iounter. ?‘lie lead-210 solution \\-:IS measured n-itli :i sointillation spectronietrr with the ba*e
thc suppliers 11 ere diluted aiid ahquoted t o measure the required amount of the element using the data furnished by the suppliers for calculating the element concentrations The isotoppq uqcd are 3hon n in 1”lde I PROCEDURE
The extractiuiis were effected 111 1 6 1111. glass-stoppered centrifuge tube. by shaking vigorously by hand for 5 minutes 5 ml. of the hydrobromic acid solution containing the indium and the radioactive isotope with 5 ml. of the organic solvent. The phases were then beparateti in a centrifuge a t about 3300 r.p.m. for 5 minutes. When a second extraction wa5 to be done, the organic la? er from the firbt extraction n a s carefully removed with a pipet. the top of the tiilic \~sqhedwith 2 ml of fresh
REAGENTS A N D SOLUTIONS
A stock solution of indium was madc by , dissolving high purity nictallic indium in nitric acid, adding concentrated hydrobromic acid, and evaporating almost to dryness. Twice mort. the residue was dissolved in hydrobromic acid and evaporated almost to dryness. Finally, the nearly dry ma+ \\as put into solution and diluted to volume with 4.5N hydrobromic acid. For the experiments on the extractability of indium, portions of the indium stock solution were tagged with indium114 and diluted with water and hydrobromic. acid to the desired indium and acid concentrations. The solutions for the impurity separation experiments were prepared by adding to a portion of the indium stock solution a sufficient quantity of a radioactive element to obtain 10 y of inipurity element per gram of indium. The solutions were then diluted with water and hydrobromic acid to get thc desired indium and acid concentrations. A separate solution was made for each impurity element under study. Thv radioisotope solutions as received from 1366
ANALYTICAL CHEMISTRY
Table I.
Extraction Losses of Impurities with 2-Pentanone Extraction
Extracted _ _ _ _ _ _ c{ __ ______~~ 4.5N HBr 3.51%’ HBr l!!lenlc~Ilt
Isotope Usrd
Single extn
37.2 36.0 Y9 >99 74
Double extn. 79.c)
