June 20, 1957
COMMUNICATIONS TO THE EDITOR
32S5
also seem to be r e q ~ i r e d to ~ ~explain ,~ gas phase processes and to recoil labelling by the halogens,2 halogen atom recoil reactions. Reactions such as which appear to involve ion-molecule steps.2 CH4T+ f CH4 + CzH8T+ Hz which may not be Typical distributions of tritiated products which observable a t mass spectrometer pressures may be we have obtained by gas chromatographic analamong those which contribute to chain lengthening. ysis2 of mixtures of hydrocarbons with TZor HT, The absence of a scavenger effect on the yield of activated by self irradiation with about 2 X lo' tritiated parent indicates that the neutral stable roentgens of tritium beta radiation or by doses of molecule is formed by a single step such as T + about 5 x 106 roentgens of CoGogamma rays are shown in Table I. Both chain lengthening and CHI + CH3T H+, or T f CH4 CH3T H , or that its formation from a species such as TABLE I CH4T+ is not altered by halogen. Although i t usually is not possible to differentiate RELATIVE AMOUNTS O F TRITIATED PRODUCTS FROM THE hot radical reactions from ion-molecule reactions OF \.AR~OUS ~ I I X T U R CONTAINIXG ES CHI, IRRADIATION in condensed phases, i t seems plausible that ionCzH8, H T , H P AND molecule steps such as seem to be required above Sample C H ~ C ~ H : C ~ Hc4Erlo ~ c ~ H ~ ~ may also be involved in tritium labelling in conCI&-HT-I&* h 2 5 1 2.8 2.7 4.1 densed phases2 and in a number of other unique CHI-HT-IW (i.i 1 2.8 11.5 15.8 processes recently reported. These include the CHa-HT-H2-12d 5 ,4 1. 4 1 2.7 1 .:I 0 -I reactions of tritonslO and C14 ions" accelerated by CII~-HT-H?-IT' 1 ii 1 ,4 1 9 . 2 GO. 0 0 cu. 0 . 0 CHr-T?' 3.5 l ( 1 2 . 6 ) r3.9 1.9 electric fields, and the tritium labelling method of h h CaHa-T?" 1.2 0.4 1 that such steps also i V . T r i l z b a ~ h .It ~ ~is~ ~probable ~ a CHa, C4H6, CaHs, C4Hlo characterized with knowii accountg for part, but not all, of the products of samples: CaHip and C6"a identity assumed from position on halogen recoil reactions in solution. gas chromatogram. ca. 5 X lo6 r. Co@ garnma radiation,
+
+
+
+
ii
PRODUCTS OF THE
'l'ritiatedb product
I-IT CHsT C~HLT CsH7T GHpT GHsT CsHiiT CaHilT
TABLE I He3in,p)H3REACTION IN GASEOUS CH4, CpHe, ASD CsHs"
Allcane reactantCHI or CZH6 C3Hs CH4 Brz) C2H6 (Brz) CaHs (12) Per cent. of total T in each product 46 40 43 42 43 4% 31 5 0 5 2 4 4 ti.8 Trace 28 37 2.5 1.5 5 Trace 9 0 3tj 47 1.5 0 7 0 3 1 l.i 0 0 0 2 1 1.2 o 4 0 5 1.5 1.9 0 0 0 0 0 1.9 0 d 0 4 1 1 0 0 0 0 1 (12
CaHa (Brd
ca. 6 X l o 6 r. 2.5 pc. tritium, 7 mm. Hp, 60.7 cm. CHI. Corn gamma radiation, 2.5 pc. tritium, 57 mxn. Hp, 52.4 cm. CHa. ca. 3.5 X 10' r. CoB0gamma radiation, 2.5 pc. tritium, 5 mm. Hp, 64.5 cxn. CHI, solid 1 2 . e ca. 3.0 X l o 6 r. Coco gamma radiation, 2.5 pc. tritium, ti xnm. Hp, 61.0 cin. CHI, solid I?. f ca. 5 mc. TP, 50 cm. CH4, 7 2 days standing. 0 ca. 5 mc. Tp,48 cm. C3Hs, 49 days standing. * Relative abundance of this species not determined in this experiment.
50 3 1.5 39 0 0 0 0 0 0
chain degradation occur, as with activation by the He3(n,p)H3 process. Methane-HT mixtures irradiated with gamma radiation appear to show higher yields of tritiated pentanes and hexanes than of propane. The ratio of yields is changed by a change in the methane-Ha ratio. Iodine C6Hi.T scavenger causes a drop in the tritiated and CsHiaT Iodides or C6H14 components relative to the other compobromides 0 10 0 18 0 ? ti nents. In view of the chain lengthening observed, The reaction mixtures contailled about 1 c t t t r i . of alkatie, the conclusion seems nearly inescapable that these G rnm. of He3 and either 6 mm. of Hp, 0.2 nim. of Is or 200 reactions are ion-molecule processes.2 Quantinim. of Brp. Duplicate formulas indicate isomers. tative studies on such systems should be rewarding by revealing the most probable stage of the chain (9) S . Aditya and J. E. Willard, THISJ O U R N A L , 79, 2680 (1957). (10) R. n'olfgang. 1'. Pratt and F. S. Kowland, ihid., 78, 5132 lengthening process for reaction of the chain carry(1956). ing species with hydrogen and with halogens. (11) R. A I . Lernrnon, F. Mazzetti, F. L. Reynolds and M. Calvin, Three possibilities must be considered for the ihid., 78, 6414 (195G). primary step in these tritiation reactions : ( I ) the (12) K. E. Wilzbach, ibid., 79, 1013 (1057). (13) R. W. Ahrens, M. C. Sauer, Jr., a n d J. E. Willard. ihid., step T-T -+ T + He3 (or, say, He3T+); (2) ioni79, 3285 (1957). zation of TZor H T by beta or gamma radiation; DEPARTXENT O F CHEMISTRY ADONA. GORDUS (3) ionization of the organic compound by beta or UNIVERSITY OF i V x s c o s s ~ l r MYRAN C. SAUER, J R . gamma radiation. The fact that reaction occurs MADISON 6, \VISCONSIN J O H N E. ~VILLARD in HT-CHI mixtures indicates that the moleculc RECEIVED APRIL 8, 1957 T 2 is not essential. If reaction were initiated solely by ionization of H2 and H T a G value of about 100 would be required to account for the yields of tritiated prodHYDROGEN LABELLING OF HYDROCARBONS USING IONIZING RADIATION ucts obtained in Table I, assuming no isotope effect. Consequently it seems probable that Sir : much, if not all, of the reaction is due to ionization m'ilzbach has demonstrated that exposure to of the methane. tritium gas is an effective method of labelling comThe ratios of tritiated C4H10. C5H12and CeH14 to plex organic compounds.1 It seems possible that tritiated C3Hs produced from CH4 are significantly such reactions are similar in mechanism to tritium higher when tritiation is induced by radiation recoil labelling by the He3(n,p)H3* and Li6 (n, a)H3
+
(1) I; I3 W r l ~ L . ~ r hT, H E J O W K X A I , 79, 1013 (1937)
(2) A. A. C.nrrliis, M. C. Sauer, Jr., and J. E. U'illnrd, :bid., 79, 3784 (1937).
(Table I) than when it is induced by the He3(n,p)H3 process. This seems to indicate that the mechanisms are different. I n the He3(n,p)H3case the formation of each carbon chain presumably is initiated by attack of a tritium ion on a CH4molecule. The many products formed in these reactions offer a valuable source of high specific activity labelled compounds when these non-parent “byproducts” can be separated in carrier-free form by gas chromatography or otherwise. This work was supported in part by the Atomic Energy Commission and in part by the Wisconsin Alumni Research Foundation.
amount of HT. ‘The addition of 0.2 mm. of iodine as a radical scavenger has little effect on the yield of CH3T but virtually eliminates the yield of higher labeled hydrocarbons and reduces the yield of HT. Studies on the slowing of charged particles passing through matter3 indicate that the tritium is uncharged on reaching its final reaction site. Taking this into account, our observations suggest two distinct modes of reaction of the tritium atom: (A) Most tritium combines by direct hot replacement reaction. For methane
+ CHI +CHaT -+ H T* + CHI +HT + CH3
T*
DEPARTMEST O F CHEMISTRY ROLLAND W. AHRENS UVIVERSITV OF WISCONSIN MYRANC. SAUER, JR. MADISON, WISCONSIN JOHS E. WILLARD Radical intermediates are definitely ruled out and RECEIVED APRIL8. 1957 Mralden inversion probably is involved. (B) Some
tritium escapes incorporation in stable molecules by hot reaction and becomes thermalized. Its reactions CHEMICAL REACTION OF RECOIL TRITIUM WITH then become sensitive to radical scavengers, such as 12. In their absence the tritium can react comGASEOUS ALKANES’ petitively to (1) abstract H to form part of the HT Sir: observed, or ( 2 ) combine with radiation produced lye have studied the reaction of high energy radicals or ions to form the higher labeled hydrotritium, as produced by nuclear reaction, with carbons. (Production of the latter probably ingaseous methane and ethane. The reactions volves hydrocarbon chains lengthened by ion moleHe3(n,p)H3 (0.78 Mev.) and Li6 (n,a)H3 (4.7 cule reaction^.^) Mev.) were used to supply the “hot” tritium. I n The results observed with ethane are consistent the He3 runs about 0.1 cm. He3 was sealed with 10- with this picture. Most of the activity appears in GO cm. CH4 in a 7 ml. quartz ampoule. In the H T and CzHjT with smaller amounts in CH3T and Li6runs a film of normal lithium nitrate formed the higher hydrocarbons. Only C3 and higher hydroinside coating of similar vessels. After irradiation carbons are eliminated by Iz. This means that in the Brookhaven reactor, carriers were added and degradation products such as CHIT from ethane the various tritium labeled species separated and are largely formed by direct hot replacement recounted, largely as described elsewhere.2 actions (type A). A summary of some of our results on the chemical I t has been demonstrated that neither radical state of the tritium following interaction with intermediates nor a solvent cage, the central conmethane is shown in Table I. This distribution of cepts of earlier theories of hot-atom reactions,6are necessary for hot reaction of hydrogen. lyhether TABLE I the reaction model postulated here holds also for recoil tritium reactions in the condensed phase reCHEMICAL STATEOF RECOILTRITIUM STOPPED IN METHASE mains to be seen. The similar product distribuExpressed as 70of total gaseous activity in absence of IZ tions in gaseous and liquid2 alkanes are suggestive. -Irradiation conditions1012.6 109.8 109.3 But the retention of configuration observed in the neutrons neutrons neutrons solid phase6would require further explanation. cm. --I sec. -1, cm. -2 sec. - 1 , cm. - 2 sec. -*,
-
Chemical state
I3T CHBT C2HsT C~HIT C3fT) hydrocarbons Higher tritiated hydrocarbons and iodides
+
no I2 present
no 1% present
11 pres-
50.6 30.9 8 2 5.0
61.9 29.1 2.9 2.4
29.8 26 0 0.1 0.2
5.3
3 7
43 9
en t
activity is independent of the source of the tritium, the pressure and the temperature (range 30200”). However, a drastic reduction of neutron flux, with accompanying decrease in radiation density, although having little effect on the production of CHBT,seems to reduce significantly tlie yields of labeled higher hydrocarbons while increasing the (1) Research supported $y t h e Atomic Energy Commission. See also accompanying communication by Cordus, Sauer and Willard, 1, 3284. ( 2 ) \Volf:nng, Erp-nel and Rowland, J Phys C k i , m . , 6 0 , 1137 (1956)
(3) S. K. Allison and S. D. Warshaw, Rev. M o d . P h s , 25, 779 (1953). ( 4 ) hleisels, Hamill and Williams, J. Chem. P h y s . , 25, 790 ( l ( J 5 7 ) . ( 5 ) J. Willard, Apin. Rev. X ‘ I L CSci., . 3, 193 (1953). ( 6 ) Rowland, T u r t o n and Wolfgang, TEIISJ O U R N A L , 78, 2351 (1958); F. S. Kowland, prioate communication.
CHEMISTRY D E P A R T X E N T S BROOKHAVES NATIONSL LABOR.4TORV YORK ~ T O S T A F A FAHMIAMR EL SAVED FLORIDA STATEUNIVERSITY TALLAHASSEE, FLORIDA RICHARD WOLFGANG YALEUSIVERSITY KEW HAVEN,CONSECTICUT RECEIVED APRIL 22, 1957 U P T O N , NEW
DEGRADATION OF BRAIN GANGLIOSIDE TO GLUC 0CEREBROSIDE Sir :
Since Klenk first described the brain gangliosides,‘ evidence has been presented that they arc (1) lT Klenk,
I: ph3szol L h e i n , 273, 76 (lYd?)
