KOTES
980
TETRANITROMETHANE AS h RADICAL SCAVENGER IN RADIATION CHEMICAL STUDIES BY A. HENGLEIN,~ J. LAMGHOFF AND G. SCHMIDT Inslitutefor Physical Chemistry, University o f Cologne, Cologne, Germanv Received December B Y , 1968
Previous studies of the radiation chemistry of tetranitromethane (TNM) in aqueous solution have shown that this substance is an effective radical scavenger when present a t concentrations above mole/L2 Hydrogen atoms reduce this solute to give nitroform which in aqueous solutions ionizes to form the intensely colored anion TC(NO&](extinction coefficient a t 350 mp; 15,000 mole-’ 1. cm.-’). Since a colored material is formed from H.
+ C(NO,),
+H + + [C(NOz)aJ- + NO2
(1)
the uncolored T N M extremely small changes in the concentration of this radical scavenger can be determined. The hydroxyl radicals formed in the radiolysis of water do not directly form nitroform from TNM. However, in the presence of an additianal solute, such as hydrogen peroxide or an organic substance, OH radicals are converted by hydrogen abstraction to give Hoe. or organic radicals which in turn reduce tetranitromethane
+ C(N0,)a + H + + [C(NOz)r]- + NOz + RtnH. + C(h’0z)I + H + + lC(NO2)31- + 11,” + NO, or RmH. + C(N02)a + K O + H + + LC(NOzh1- + RmHOH + NO, HOz.
0 2
(2) (3)
(4)
Thus in aqueous systems containing reducible solutes in addition to T N M total radical yields can be measured directly. I n neutral water the value of G for radical production was found to be 5.852in agreement with other measurements of this quaiitit^.^,^ Nitroform is also formed as the only product of the reactions of T N M in alcoholic solutions. Therefore the value of G for the formation of nitroform in the oxygen-free alcohols listed in Table I gives the 100 e.v. yields for the formation of free radicals in these compounds. TABLE I F O R M A T I O N O F NITROFORMI N ALCUHOLIC SOLIJTIONS T N M (10-2 R~oLE/L.) BY Co-60 ?-RAYS) Alcoliol
Methanol Ethanol 1-Propanol 2-Propanol %Butanol
C(nitroforni)
OL free s o h . li.6
7.0 6.8 (5.8 6.2
found for methanol is in fairly good agreement with the values of 6.15and 6.36found by using ferric ions as the radical detector. Dissolved oxygen has only a small influence on the yield of nitroform in methanol and ethanol and a negligible effect in the higher alcohols. It seems therefore that most of the free organic peroxy radicals also react with T N M to give aitroform RmHOO.
Oa natd. s o h .
5.4
6.6 6.8 6.8 6.2
( 1 ) Radiation Research Laboratories. Mellon Institute, Pittsburgh‘ Pa. (2) A. Henglein and J. Jaspert, Z . physzk. Chem. Neue Folge, 12, 324 (1957). (3) E. J. Hart, J . A m . Chem. Soc., 7 6 , 4198 (1954). (4) J. H . Baxendale and D. H. Smithies, Z. physik. Chem. Neue Folge,
+ ‘c(NOp)a+ H+
+ [C(NOP)SI-+ R, + NO? +
0 2
(5)
In hydrocarbons the yield for formation of nitroform is quite low since other products are formed simultaneously by the reduction of NO, groups in TKM. In benzene G(nitroform) is equal to 0.5; a brown polymer (C4H402X) precipitates during the irradiation. In aliphatic hydrocarbons G(nitroformj is equal to 1. Here a product is formed which can be extracted with water. It has a strong absorption a t 315 mp. The dependence of this absorption on the pH shows that the product is a weak acid. The compound can be extracted from its aqueous solution using ether. Attempts to concentrate these solutions result in decomposition of the solute to nitrous gases. The same cbmpound is formed in the radiolysis of aqueous solutions of nitroform and in the thermal reaction of dinitromethane with nitrous acid in aqueous solution. The preliminary formula of dinitroformaldoxime C(N02jzNOH is assigned to this compound. These results show that TNM is a useful radical scavenger for studies of the radiolysis of water and alcohols. Furthermore, T N M also may find some application in other fields of the chemistry of free radicals. It may even be used for scavenging of free radicale formed in the gas phase because of its rather high vapor pressure. ( 5 ) G . E. A d a n ~ sand .J. H. Baxendale, J . A m . Ckom. Soc., 80, 4215 (1958). (6) E. A. Clierniak, E. Chllinson, P’. S. Daintonand G . M. Meaburn, I ’ m . Chem. Soc., 54 (1058).
R E ~ ~ C T I O N SOF GASEOUS IONS. AMMONIUM ION FORMATION I N IONIZED AMMONIA US L E O N M.
1)ORL”MA.U‘ A N I )
1’.
c. NOBI&
General Electric &Zesear.ch Laboratory, SoAenecladU, N . Y . Received February I S , 1969
OF
Apparently the free radical yield in alcohols is somewhat higher than in water. The radical yield
1 , 242 (195G).
Vol. 63
The coiisiderable wriety of ioii-molecule reiictions which have now beell observed and whose rates have beeii determined2-5 consists largely of systems of organic molecules, principally the simple hydrocarbons. In the case of ionized ammonia it seemed likely, by analogy with the hydrocarbon reactions, that a hydrogen atom or proton transfer reaction would occur, forming ammonium ion in (1) Chemistry Division, Argonne National Laboratory, Lernont, Illinois. (2) D. P. Stevenson and D. 0. Schissler, J . Chem. Phys., 23, 1353 (1955). (3) V. 0. Schissler and D . P. Stevenson, i t i d . , 2 4 , 926 (1956). (4)
F. H. Field, J. L. Franklin and F. W. Lampe, J . A m . Chem.
Soc., 79, 2410 (1957). ( 5 ) G. G . Meisels, W. H. Hainill and
Phya., 2 5 , 790 (1956).
R. R. Williams, J . Cham.
