6152
Vol. 74
COMMUNIC.4TIONS TO TNR EDITOR
(D!d). Space group Pz21 does not permit a tetrahedral arrangement of atoms around the phosphorus atom. Since the structure appeared t o be isotypic with tetramethylammonium dichl~roiodide~ and since the Patterson projection could be explaiced on the basis of this structure, the structure based on P421m W ~ chosen. S Crystal Structure.-Using ( h k o ) data, a Pattersou pi ojection was made on (OOE) atid the approximate x- aiid yparameters determined. From these parameters the signs of the F(hkO),\,,d were calculated and used in a Fourier projection on (001). The x- and y-parameters were refined as much as possible by a repetition of this Fcurier projection. The z-parameters were obtained from a Patterson projection OII (110). In order to obtain better agreement between the calculated and observed F values, an empirical temperature correction factor of the form e-1.61 *ln*O was applied t o the calculated F values. I t was felt by the authors that the usual scheme of computing R1 does not make sufficient allowance for reflections, which, while not zero, are not sufficiently strong to record on film with ordinary exposures. Accordingly, a slightly modified method of calculating the l i ~values, consisting of assigning each absent or unobserved reflection an F value which was calculated as follows, was used. The minimum intensity observable was corrected by the angle factors corresponding to each of the unobserved reflections. Taking one-half of the square roots of the quantities thus obtained yielded F values which were arbitrarily assigned to the aboent reflections for the purpose of calculating R1. The KI calculated in this manner is defined as R:. Using the p.1rxnc~twschowail mi UT value of 0.27 was obtained.
The compound proved t o be isostructural with tetramethvlammonium dichloroiodide.' with the following atoms a t the following positions of space group D$d-Pq 2&: 2 P a t ( b ) ( 0 0 l / 2 ) , ( I / z I/z l/d; 2 I a t ( c ) (0 l / 2 z ) , (I/z 0 i) with z = 0.161; 4 C1 a t (e)-x, I/* 5 , z; 5, 1/2 x, z ; 1/2 i .2, 3 , 2; l / 2 - 2, x , z with x = 0.18n. z = 0.161; s c1 a t ( f 1 xyz; 1/2 - x , '/2 y, i; apz; 1/2 , x , l/2, - y , E; x , z wtth x = j x i ; 1 / ~ y. l / 2 f x , z; yi%; '/z - y, 11. 0.185, y = 0.079, z = 0.398.
+
-
+
+
This structure consists of regularly tetrahedral PC&+ions, and linear CIICI- ions with the interatomic distances in Sngstrorn units are P-8-fold C1 I-4-fold C1 5-fold C1-8-fold C1 (within Pel,+ tetrahedra) 8-fold C1-8-fold C1 (from one PCll+ to the next) 4-fold C1-5-fold c1
1.9s 3 36 3.23 3.50 3.86
Extensive calculations of intensities based on selected chlorine positions near those given above showed that the positions of chlorine atoms could be changed considerably without affecting the R: value. For example ?c
for 4 (e)
N I"
0.17 0.18 0.19 0.20 0.16 ,270 ,272 ,277 ,285 ,271
DEPARTMENT OF CHEMISTRY STATE UNIVERSITY O F IOWA IOWA CITY,IOWA
COMMUNICATIONS T O T H E EDITOR its protium analog. The alcoholysis of lithium aluminum hydride-t3 and of lithium borohydride-t4 Sir: did not give consistent values of k T / k H , possibly Recently, Gilman, Dunn and Hammond re- because of changes in the reacting species; the ported' that triphenylsilane-d was hydrolyzed in observed values fell between 1.2 and 0.8. In view of these results we have reinvestigated moist piperidine "almost six times faster than its protium analog." They attributed this unusual the hydrolysis of triphenylsilane in moist piperidine. isotope effect to the displacement of a hydride ion Tritium-labeled triphenylsilane was prepared5 by in such a manner that a hydrogen-hydrogen bond the reduction of triphenylchlorosilane with lithium of considerable strength is present in the transition aluminum h ~ d r i d e - t . ~The triphenyl-silane4 was state of the reaction. This picture of the reaction dissolved in a 1.0 M solution of water in piperidine, in a previously evacuated system, and permitted to path might be formulated as react a t 25'. At intervals, the reaction was O H - + PhsSiH +- IINCsIIIo -+ stopped by cooling to -SO0, and the evolved 013: hydrogen was collected. The volume of each I PhJSi---H---H---NCaHlo -+ PhaSiOH 4-1-12 + CJIIOS- fraction was measured manometrically and its tritium content was determined in an ion chamber Because of the unusual effect reported for this with a vibrating reed electrometer. The total reaction, we have examined several similar reactions volume and tritium content of the fractions agreed which involve the formation of hydrogen, presum- with those expected from analysisKof the triphenylably by abstraction of a hydride ion. To enhance silane-t by hydrolysis with moist piperidine and any isotope effects, tritium, rather than deuterium, potassium hydroxide. The experimental results was used in competitive measurements of k T / k H , are given in Table I. The ratio of the rate conthe ratio of the isotopic reaction rates. stants is calculated for each gas fraction from the The alkaline alcoholic hydrolysis2 of tripropyl- expression silane-t was found to be about 0.7 as fast as that of (3) K . E. Wilzbach and L. Kaplan, ibrd , 72, 5795 (1950). HYDROGEN ISOTOPE EFFECT IN THE HYDROLYSIS OF TRIPHENYLSILANE
(1) H Gilman, C 1: I)unn and t; S Harniriond, 79, 4499 (1951). ( 2 ) F. 1) Prii e , t b d , 69, :!COO (10471
T H I S lorrKv21
(4)
W
1CI5-2). (5) II
C,
Brown. I, Kaplan and K. E Wilzbach. i t i d , 74, 17-13
Ci1tii.m
and C I':
Ilunn, rbid., 7S, 3401 (1951).
COMMUNICATIONS TO THE EDITOR
Dec. 5, 1952
where ( H T ) t refers to the amount of tritium and (H& to the volume of gas collected up to time t. The average value of IZT/KH, over the course of more than 40% reaction is 0.796 i 0.004. This result is in good agreement with a theo~*~ only retical value of 0.8 c a l c ~ l a t e d considering the stretching frequencies of the Si-H and H-H bonds in the proposed model. The corresponding theoretical value of KD/IZH is 0.9. TABLEI
61 53
shift toward the dithiol form is the direct result of the light action and ‘that a biradical formed by dissociation of the disulfide bond in a strained fivemembered disulfide containing ring (as in 6,8thioctic acid and trimethylenedisulfide) is the species in which the quantum absorbed by the plant pigments and stored as electronic excitation in ~hlorophyll’~ appears first as chemical bond potential energy; ie., that a possible primary quantum conversion act of photosynthesis is represented hy the equation
Chl*
HYDROLYSIS OF TRIPHENYLSILANE-t
+ SI - IS +
Chl(ground)
I 1
-tS. S.
(I)
Subsequent abstraction of H a t o i n ~from ~ ~ a! ~ suit~ able donor by the thiyl free radicals would lead to Fraction yo kTkH the dithiol which would be reoxidized ultimately 1 16.2 0.286 20.9 73.1 0.803 by COZ. The residual oxidation product of the H 2 24.8 0.151 11.2 74.2 0.792 donor would lead in the end to molecular oxygen. 3 40.6 0.279 21.5 77.1 0.794 It is obvious that on both the reductant and oxidant 4 100.0 1.046 104.0 99.4 sides the chemical products of the conversion of Total 1.762 157.6 89.4 several quanta will be required to accomplish the reduction of each COz molecule and the generation (6) J. Bigeleisen, J. Chcm. Phys., 17, 675 (1949). (7) H. Eyring and F. W. Cagle, J . Phys. Chcm., 66,889 (1952). of each OZmolecule. These subsequent reactions, being strictly chemiARGONNENATIONALLABORATORY LOUIS KAPLAN P. 0. Box 299 KENNETH E. WILZBACHcal, may lead to diverse energy rearrangements. LEMONT, ILL. For example, the chemical potential of reduced RECEIVED OCTOBER1, 1952 carbon might be converted by oxidative phosphorylation reactions into the energy of phosphoric anA POSSIBLE PRIMARY QUANTUM CONVERSION hydrides which, in turn, could raise the potential ACT OF PHOTO SYNTHESIS'^* energy of intermediates in the reaction sequences Sir : leading to the evolution of molecular oxygen and To account for the 0bservation~*~,6 that illumina- to the reduction of COZ.’6“7 tion prevents the appearance of newly assimilated A value of the dissociation energy for this parcarbon in the compounds of the tricarboxylic acid ticular disulfide link lying in the region of 30-40 cycle, it was suggested6 that the light shifts the kcal. would constitute not only permissive evidence steady-state condition of the thioctic acid-con- for reaction (I) but positive evidence in its suptaining coenzymeaJ (protogen, lipoic acid, thioctic port, since hitherto it has been difficult to suggest acid, P.O.F.) toward the reduced (dithiol) form, any likely primary chemical step capable of usefully in which condition i t is incapable of oxidatively absorbing the greater part of the 30-40 kcal. decarboxylating pyruvic a ~ i d ,newly ~ , ~ formed from quantum of electronic excitation available for COZ, to give rise to the acetyl-CoA10.11B12 required photosynthesis. Estimates of D(RS-SR) from to bring this carbon into the compounds of the simple open chain compounds range from 50’8 Krebs cycle. We are here reporting some observa- t o 7019 kcal. However, the fact that 5,8-thioctic tions leading to the further suggestion that this acid is colorless, while 6,g-thioctic acid is yellow,?O suggested that the incorporation of the S-S bond (1) The work described in this paper was sponsored by the U. S. into a 5-membered ring might indeed introduce Atomic Energy Commission. (2) J. A. Barltrop, Rockefeller Fellow, 1952-1953, while on leave sufficient strain into it so as to reduce the S-S from Brasenose College and the Dyson Perrins Laboratory, Oxford dissociation energy by as much as 25-30 kcal., thus University, England. bringing i t down into the required range. A num(3) A. A. Benson and M. Calvin, J . Exfill. Bot., 1, 63 (1950). (4) J. W. Weigl, P . M. Warrington and M. Calvin, THIS JOURNAL, ber of experiments have been performed using the 73, 5058 (1951). product of the reaction of Na2S2 with (CH2)3Br2 (5) M. Calvin and Peter hlassini, Expcricntia, in press. (trimethylenedisulfide) as a model substance. Its (6) G.W. Kidder and V. C. Dewey, Acad. Press, New York, N . Y., Reaction cumulative
HI, mmole
HT, pcuries
HT/H.r, pcuries/ mmole
Prolosoo, Vol. I, 388, 1951. (7) E. L. Patterson, J. A. Brockman, Jr., P. P. Day, J. V. Pierce, M. E . Macchi, C. E. Hoffman, C. T. 0. Long, E. I,. R. Stokstad and T. H . Jukes. THISJOURNAL, 1 3 , 5919 (1951). (8) L. J. Reed, B. G. DeBusk, I. C. Gunsalus and G. H. F. Schnakenberg, ibid., 73, 5920 (1951). (9) I. C. Gunsalus, L. Struglia and D. J. O’Kane, J . B i d . Chcm., 194, 859 (1952).
(IO) J. R. Stern, “Phosphorus Metabolism,” Vol. I , Johns Hopkins Press, 1951. (11) S. Korkes, ‘!Phosphorus Metabolism,” Vol. I, Johns Hopkins Press, 1951. (12) R . S. Schweet, M Fuld. K.Cheslock and M. H. Paul, “Phosphorus Metabolism,” Vul. I, Johns Hopkius Press, 1951.
(13) (14) (15) (16)
L. N. M. Duysens, Nature, 168, 548 (1951). A. F. Bickel and E. C. Kooijman, ibid., 170, 211 (1952). E. F. P. Harris and W. A. Waters, {bid.. 170, 212 (1952). Phosphorus Metabolism, Vol. I, Johns Hopkins Press, 1951,
Sec. V. (17) M. Calvin, J. A. Bassham, A. A. Benson and P. Massini, Ann. Reo. Phys. Chcm., 3 , 215 (1952). 74, 4723 (1952). (18) A. H. Sehon, THISJOURNAL, (19) J. L. Franklin and H . E. Lumpkia, ibid., 14, 1024 (1952). (20) Several milligrams of each of these synthetic21 products were obtained through the courtesy of Dr. T.H . Jukes of Lederle Laboratories. (21) M . W. Bullock, J. A. Brockman, E. L. Patterson, J. V. Pierce and E . L. R. Stokstad, THISJOURNAL, 74, 3455 (1952).
