on going from henzyl alcohol to benzaldehyde indicites that benzaldehyde is a more complex molecule than is benzyl alcohol. This fact suggests that the benzaldehyde molecules may exist in some associated form, involving coordination of the electrophilic carbonyl carbon atom of one molecule with the nucleophilic oxygen atom of a second molecu1e.j On comparing lines 1, 3 and 4 of Table I1 we see that the addition of hydrogen atoms to the double honds of the benzene ring results in a lowering of AH* of the reaction by about 7.0 kcal. (passing f i m ~anisole or benzyl alcohol to cyclohexanol). Instead of a -I effect of the phenyl group we now hare n +I effect of a cyclohexyl group, resulting in :2 considerable increase in the effective negative charge on the hydroxyl oxygen atom. Another evample of this effect has been reported in a study of the relative basicities of aniline and cyclohexylamine.6 The large decrease in AS* on going from benzyl alcohol or anisole to cyclohexanol may be attributed to the larger extent of association of the alicyclic alcohol. Acknowledgments.-The support of this resclsrch by the Xational Science Foundation, Rashington, D. C., is gratefully acknowledged. ( 5 ) K. Huckel, "Theoretical Principles of Organic Chemistry," V31 11, Elsevirr Publishing Co , N e n York, N. Y., 1958, p. 322 et sep. (6) (a) N. I . Hall a n d hI. R. Sprinkle, J . Bm. Chem. Soc., 64, 3469 (1932), (b) E A Braude and F C Nachod, ' Determination of Organic s t r u c t u r i s b y Phjsical Means '' lcademic Press, Inc , New York, U T I955 p 581
THE PHOTOLYSIS OF L4MMOXIA (K"H3) IN THE PRESESCE OF NITRIC OXIDE' BYR.S R I X I ~ A S A ~ Department of hemnstry, Unzuersaty of Rochester, Rochester 20, S e w York Receaued November 1 3 , 1969
It was obserred by Seremicz and Koyes2 that the photolysis of ammonia in the presence of nitric oxide led to the formation of nitrogen, nitrous oxide, water, and small amounts of hydrogen. For moderate pressures of nitric oxide (1 to 8 nim.), they proposed the following sequence of rcnctioris to account for these product..
+ + + +
+ +
KHt hu +NH, H KH? NO +Tz H2O IT XO HXO 2HSO Hi0 ZiZO I€ H S O --+ H? S O
+ +
(1) (2) (3) (4) (5)
The present study was undertaken to obtain confirmatory evideiice for this mechanism by the use of nitrogeni6 to label the nitrogen atom in the ammonia molecule. Steps 1 to 4 would then he
+ hu + + S I 4 O --+ H + Xi40
K'lH? S15HH,
-
-
1\'I6H2
NW14
+H + H20
HXldO
2 ~ ~ 1+ 4 0 H?O
+~240
(la) (2a) (3a) (4a)
(1) This research mas supported in p a i t by Contract AF18(600) lb28 u i t h the United States I i r Force through the Air Force Office of Scientific Research of t h e Air Research a n d Development Command Reproduction in whole or in part is permitted foi a n y purpose b y t h r United States Goiernment (2) A Serewics and IT A Y o y r s , J r , THISJOURUAL,63, 843 (1 959)
I
Fig. 1.-Rate
2 4 6 8 10 12 Pressure of nitric oxide, mni. of nitrogen production VB. premirc of nitric oxide.
The mechanism predicts that the nitrogen molecules formed will be exclusively mass 29 aiid the nitrous oxide exclusively mass 44. Experimental P H 3was obtained from Isomet Corporation, S . J. It had a stated isotopic purity of 99.4%. Kitrir o\itic was piirified as drscribed by Serewicz and Soyes.2 Photolyses were carriecl out in ii qii:trta cell 20.0 X 3.9 cm. The gases were mixed prior to photolysis and in the middle of a run by repeated expansion into a large volume. While this was not a very satisfactory way to keep the reactants well mixed during a run, it was adopted in order t o keep the dead space small, and thus conserve material. The source of radiation was an unfiltered Hanovin 8-100 medium pressure mercury arc. Separation of the products and unreacted material n as achieved as described in the earlier n-ork.? Hydrogen and water were not determined. Mass spectrometric analysis of nitrogen and nitrous oxide mere made with a Consolidated Engineering Co. type 21-620 mass spectrometer. Standard cracking patterns and sensitivities for nitrogen, nitric oxide, nitrous oxide and ammonia on this instrument were determined by the use of pure samples of each gae. On the basis of this information, corrections for the small amount of nitric oxide found in the nitrogen fraction, and ammonia in the nitrous oxide could be made. The sensitivity of thr instrument to the parent peaks of Y a X " and 1:'' was assumed to he the same.
Results ;It room temperature, and a t a pressure of ammonia of 40 + 1 mm., the initial rate of production of N 1 5 1 4and X2I4are plotted a< a function of nitric oxide pressure, in Fig. 1. In all these experiments there was no evidence for more than a trace of ? J 2 1 6 , while the nitrous oxide was found to be wholly 52140.The ratio of nitrous oxide to nitrogen vas obcerved to vary from 0.21 at 4.0 mm. of nitric oxide to 0.27 a t 12.3 nim. This may be compared with the values of 0.36 to 0.26 for the same pressure range found by Serewicz and NoyesS2 Since they obserred that a change in the surface to volume ratio of the cell changed the ratio of the products, a better agreement between the relative rates of production of nitrous oxide and nitrogen may not be expected. In one experiment, the cell was filled with 11.5 mm. of nitric oxide alone. The light beam passed through a 4.4 cm. long filter cell filled with ammonia (K15H3) at 198 mm. pressure, 1,efore it entered the nitric oxide cell. After irradiation for 60 minutes, the nitric oxide waq found t o contain a mere trace of nitrogen.
680
Discussion The 1.esi11ts indicate that a t pressnreq of nitric oxide of 4 mm. 01: less, the nitrogen coiltailled 95% or more of Nl5xl4 and the nitrous oxide was l&olly x2110. 111 this narrOr$r range of conditioi1s1 the mechanLsnl of sere\l-icy. and Eoyesz may be said to be confirnled. Theie rvorkel:s hasre obserircd that with at1 illcrease in the pressure of nitric oxide, the btoichiometrp of the products is illincreasingly unsatisfactory. The preqent study points out why this is so. As indicated in Fig. 1, up to 4 mm. of nitric oxide, the rate of formation of X2I4is 110 more than the uncertainty in the results. But a t higher pressures of nitric oxide this is no lorlger It found Serewice and NOYes3 :Lnd crlllfirmed in the Preserlt instance, that at room tcniperatnre, ~ n d e rotherwi-ise constant conditions, tlie rate of production of i3itroge.n xvith an increase ill the nitric oxide pressure If the light abqorhi12g species is Only ammonia, and the reactions 1-6 are the only important steps, this trend cannot be explained. On the other hand, the rate of production of h~15~14 alone is seen to be constant with nitric oxide pressure within experimental error. QThile it is clear that in addition to step 2a, nitric oxide gir;es rise to llitrogellin a second Tvaysince this i i the only way W214 may be formedit is not obvious by what reaction this takes place. Both nitric oxide and ammonia absorb in the same general m\-e length region3 but most of the light is absorbed hy the ammonia since its extinctioll coefficierltis Mla173r times greater than that of nitric oxide. since the absorption s p e c t r y of ammonia is discrete down to a t least 2175 A., it is possible that some particular mercury line or lines may be absorbed bp nitric oxide even in the presence of ~ ~to lead ~ to ~ very ~ ammonia. H ~ )this~appears little del-omposition in View Of the meager yield of K,I4 in the photolysis of nitric oxide with light filtered bv ammonia. The trjnsferof ellcrgy from an excited ammonia mol~culeto a nitric oxide through a collision 3Ppears to be exuc~liitledby the fact that in its excited state, the ammonia molecule has a very short lifetime. On the mode Of formation Furth”r of nitrogen from nitric oxide in this system must await a more detailed analysis of the products of the photolysis a t high nitric ovide pressures. Acknowledgment.-The author wishes to thank Professor W. Albert NOYPS, Jr., for his advice and ei7couragemenl.
’”‘
( 3 ) For r r f v e n c e s and a summary see R. A. Noyes, Jr., and P. A. Leiehton, “The Photochemistry of Gases ” Reinhold Publ. Corp., Wew York, Y. T , 1311, p ~ 135 . 370.
A SPFC’I‘ROPHOTONETRIC STUDY OF THE HY1)ROLYSTS OF PLUTOSIUM(1V) BY S. K. RABIIIEAU AKD R. J. KLIXE Universzty 01 C c l t f o r i i n , Los Blamos Scientafic LaLoratoiy, Lo8 Alamos, New ilf extco Rereiiifd Soiember 19, 1959
The hJrdrolysis quotients Of Some Of the tetravalent actinides have hren determined both Tvith
electromotive force method&3 and with spectrophotometric procedure^.^-^ Also, from kinetic btudies of the reactioii betweeu I’u(V1) and PU(111) a value has been adduced for the hydrolysis quotient of Pu(IV) in DzO which is larger than that in HzO.’ Since with a spectrophotometric method the K K / K Dratios were found to be greater than unity for U(IV) arid Kp(1T’) in perchlorate solution,6 this method mas employed in a similar study ?f the effect of sollrent 11~011the hydrolytic v i l h u m for pu(ITT). The temperature coefficients of the equilibria both in and in n20 have heen measured. Experimental The Cary Model 14 recording spectrophotometer was used together with a &uble-chambered 10 cm. spectrophotometric absorption cell described previously.* The Pu(IV) stocsk solutions, prepared as described below, were added from a weight buret to one leg of the mixing cell. To the other leg, a pipetted volume of filtered sodium perchlorate solution of known concentration was added. Thp sodium perchlorate solution was used to maintain the ionic strength a t a constant value of two. After the solutions had attained temperature equilibrium in a water thermostat, they were mixed quickly, and the cell was placed in a temperaturecontrolled mater thermostat in the cell compartment of the spectrophotometer. First readings of optical densities were made within 20 sec. of the time of mixing. In general, the diminution of the optical densities with time as a result of the disproportionation of Pu(1V) was small, and extrapolatioIls were made to time with little difficulty. Spectrophotometoricmeasurements were made a t the Pu(IV) peak of 4692 A. and also on the shoulder at 3?00A. In D20solutions, the Pu(1V) peak shifted to 4684 A . Better precision in the valucs computed for the Pu(1V) hydrolysis quotieat was achieved in the use of the measurements at 3300 A. At this wave length, the observed molar absorptivities increased with decreasing acidity. Thus, the hydrolyzed form, p u o ~ + 3has , a molar absorptivity greater than that of PU7 4 a t this wave length. Stock solutions of Pu(1V) were prepared fresh daily by,the ,dissolution of purified Plutonium metal in the aPPrOPrlate weight of standardized 71yoperchloric acid, followed by dilution and by the oxidation of pu(111) to pu(1v) with a we‘ hed aliquot of a standard potassium dichromate solution. %nly enough oxidant was added t o convert 90% of the Pu(111) to Pu(IV) to avoid both the formation of higher oxidation states and the presence of excess dichromate. Although no slowness has been reported previously9 in the oxidation of Pu(II1) to Pu(1V) by dichromate, it has been found in the present study that in solutions of Pu(II1) in which the perchloric acid concentration was 0.1 hi’ or less, the yellow color of the dichromate disappefred gradually, and the maximum optical density a t 4692 A. was reached only after about a minute at 2.40. Accordingly, the stock solutions of Pu(1V) were made either 2.000 or 4.000 ,tf in perchloric acid, since under these conditions no slowness is observed and also the rate of disproportionation of Pu(1V) is negligibly small. The final acidity of the Pu(1V) solutions in the spectrophotometer cell was calculated from the weight of the combined solutions in the cell together with the measured solution density and the volume and acidity of the pu(IV) stock (1) This work was done under the aiispicer of the C. S. Atomic Energy Commission. (2) S. TV. Rabideau and J. F. Lemons, J. Am. Chem Soc., 73, 2895 (1951). (3) S. ’T Rabideau, ibid., 79, 3875 (1957). ( 4 ) K. A. Kraus and F. Kefson, abid., 72, 3901 (1950). ( 5 ) R. H.Betts, Can. J. Chem., 3 3 , 1775 (1955). (6) J. C. Suili\an and J. C. Hmdman, Tms JOTRNAL,63, 1332 (1959). (7) S.W.Rabideau and R. J. Kline, iLtd , 62, 617 (1958). (8) S. W. Rabideau, ?bid., 62,414 (1958). (9) R. E. Connich. “ T h e Actinide Elements,” Natl. Kuclear Energy Ser., AlcGraw-II111 Dooh Co., Inc.. Nea Yoih. X. P I Div. I V , I ~ - A IDN, [). ztx.
