6334
Vol. s1
~ O M l r l U N I C A T I O h ' STO THE E D I T O R
From the slope of the plot of 1/@ us. 1/'[BH*],the value of k d / k r is found to be 0.050. Consideration of this number compels the conclusion that the triplet state is responsible f o r the chemical reaction. The largest value that kr can be imagined to have is lo9 liter mole-' set.-', the diffusion controlled rate.4 This gives an upper limit of 5 X lo7 set.-' for k d . Fluorescence rate constants for singlet statese are believed to be of the order of l o 8 set.-' (11) (a) S. Englard, F e d . PYOC., 18, 222 (1059) (b) S. Englard, Since benzophenone solutions have no visible fluoperaunal communication. W e wish t o t h a n k Dr. Englard for sending us his manuscript prior t o publication. rescence, the actual rate of non-radiative quenching (12) T h e other results, Ref. 11, are also consistent with t h e scheme of the lowest singlet state must be a t least 10IOsec.-'. presented in Fig. 1. I t is clear that some longer lived state must be in(13) S a t i o n a l Science Foundation Cooperative Graduate Fellow. volved in the measured competition. DEPARTMEKT O F CHEMISTRY DUQCESNE UNIVERSITY OSCARGAWRON Reaction (5) actually must be much slower than PITTSBURGH, PA. THOMAS P.FOSDYI3 diffusion-controlled since a substantial isotope effect is observed when a-deuteriobenzhydrol is used RECEIVED SEPTEMBER 25, 1959 as the hydrogen donor. The value of k d / k r ( D ) is 0.133, which indicates that k r ( H ) / k r ( D ) is 2.7. THE ROLE OF A TRIPLET STATE IN THE In summary, the results indicate t h a t intersystem PHOTOREDUCTION OF BENZOPHENONE crossing to a triplet state must be complete, and Sir: that the triplet is responsible for chemical reaction. Irradiation of benzene solutions of benzopheAcknowledgments.-This work was supported by none and benzhydrol with near ultraviolet light pro- grants from the Film Department of the du Pont duces benzpinacol stoichiometrically according to Company and from the National Science Foundaequation (1). tion. keeping with the truns nature3 of the cis-aconitase system. The stereochemistry of the Krebs cycle from fumaric acid to isocitric acid may now be that the 3traced (Fig. 1) utilizing the finding11~12 monodeuterio-L-malic acid (from the fumarase rereaction) gives, biochemically, isocitric acid lacking deuterium and utilizing our previously suggested3 scheme for the &-aconitase system.
(C6&)2CO
+ (C6Hs)gCHOH
-
(C&)X-C(
I
1
C6HS)Z
OH OH
(1)
Experiments were carried out using a collimated beam from a Westinghouse SAH800-C Mercury arc Gltered to give a band having a maximum a t 3660 A. and a band pass of 500 A. Photolysis rates were measured by spectrophotometric determination of residual benzophenone and by titration of the pinacol with lead tetraacetate.' Quantum yields were based upon uranyl oxalate actinometry although the reaction of benzophenone with 2-propanol2 was used as a secondary standard. Solutions were degassed to mm. A series of experiments was run using 0.1 M benzophenone and varying concentrations of benzhydrol. Graphical analysis showed the l/@ was a linear function of 1/[BH2]. This relationship indicates a simple competition between deactivation of the chemically active state and its reaction with benzhydrol. Since the intercept of the plot is one, physical quenching by benzhydro1 must be negligible. The mechanism shown accounts for these facts. B
-+n + Izu -n+ B 1(singlet) B'
-
--+
B3 (triplet)
(2) (3)
kd
B
+
B3 ----f B (all deactivation steps) (4) kr BHs 2( CBHJ)ZCOH ----f Benzpinacol ( 3 )
Application of steady state kinetics to the concentrations of excited states gives the rate law.
(1) R. Criegee, Ber., 64B,264 (1931). (2) J. N. P i t t s , R . L. Letsinger, R. P. T a y l o r , J. M. Patterson, G. Rechtenwald a n d R. B. M a r t i n , THISJOURNAL,81, 1068 (1959). (3) Light absorption was essentially complete. O t h e r experiments show t h a t t h e q u a n t u m yields are independent of both light intensity a n d ketone concentration.
(4) Calculated by t h e method of Schultzs using a diffusion coef ficient of 10-6 cm.2 see.-' for benzophenone a n d benzh)drul in ben zene. ( 5 ) G . V . Schultr, Z . p h y s i k . Chem., 8, 284 (195ti). (GI M. K a s h a , Disc. F a r a d a y SOL, 9, 11 (19:O). However, see J. W. Sidman. Chem. Ret's., 68, 689 (1958), for a possible lower estimate.
COSTRIBL-TION Fo. 2505
GEORGE S. HAMMOND
G A T E S A S D C R E L L I S LABORATORIES CALIFORNIA ISSTITUTE O F TECHNOLOGY PASADENA, CALIFORXIA WILLIAMAI. MOORE
RECEIVED SEPTEMBER 8, 1059
T H E ADDITION OF NITRONES TO OLEFINS. A NEW ROUTE TO ISOXAZOLIDINES
Sir: The isolation of cis-N-methyl-3-oxa-"-azabicyclo [3.3.0]octane (111) from the pyrolysis o f FI mixture of the isomeric N-methyl-a-pipecoIiI'e oxides' suggests that the unsaturated nitrone I may be an intermediate. We have therefore itivestigated the cyclization of I and a homolog. Monofunctional aliphatic nitrones have iiot been reported, since their preparations generall!r lead to aldol-type dimers. * Nevertheless, tlic reactive nitrone linkage of I, generated in s i t u might well undergo intramolecular addition to the terminal olefin group. Oxidation of an ether solution of N-methyl-N-3hexenylhydroxylamine (V) with excess mercuric oxide afforded 111, characterized as its hydroger! oxalate (m.p. and m.m.p. 82-82.5') and by comparison of the infrared spectra,' in 24% yield. (1) A. C. Cope a n d N. A. LeBel, Abstracts of Papers, 133rd h l e e t ing, American Chemical Society, S a n Francisco, California, April 1318, 1958, p . 6 2 - N : THISJOURNAL, in press. (2) R . B o n n e t t , R . F. C. Brown, V. M. Clark, I . 0. Sutherland and A. T o d d . J . C h e m Sac.. 2094 (1959), present a s u m m a r y of t h e various dimeric structures f o r nitrones including aldolization structures, and report t h e syntheses of several monomeric alicyclic nitrunes. C/. also R. F. C. Brown, V. 31. Clark, I. 0 . Sutherland a n d A . T o d d , ibid , 2109 (l
