namely, an additional step for ethane formation a t the high temperature. The disagreement between the intercept values may be due to strong absorption for trimethylamine (in comparison to acetone) and the consequent smaller effective volume. This also accounts for the small effects observed at low temperatures when the concentration of trimethylamine and the incident intensity were variqd. Trimethylamine begins to absorb a t about 2370 A.8 with an extinction c?efficient of about 0.13 X 106 mole a t 2500 A: which increases to 1 X lp6 cm.2/mole a t 2330 A. and 4 X lo6 a t 2000 A. These high extinction coefficients imply transinittancy values much less than 0.05% in agreement with the above conclusion. In the presence of cyclopeiitane, methane can also be formed by the reaction CH3 Cyclo-CsHio + CHI -t C > C I O - C & I(10) ~ It is possible to calculate4 a value of El0 (positive for the two highest temperatures only) of 14.3 kcal. This value is about 6 kcal. too high and signifies an incomplete mechanism. Ai reaction sequence utilizing an excited intermediate in the primary process can account for the results
querice is consistent with the results a t low tciiiperature where a decrease in coilcentration of triI.~ methylamine from 0.27 X lo1? ~ o ~ . / c ~toI 0.11 X lo1* mol./cm.3 is accoinpanied by a slight increase in RcH,. At low temperature, the results (Table 11) show that R c ~ H , / ( X C H ~ R H ~is) approximately equal to unity (0.97 O.OG), and that RH,IRcH,has an average value of 1.5 with a mean deviation of i 0.24. It is reasonable to assume that reactioii 9 does not occur at the low temperature. Hence if all methyl radicals react t o form ethane, then thc methane and hydrogen are formed by- the disI)roportionation of the dimethylamine radical. I t is therefore proposed that a t low temperatures, reactions 1I , 12, 13 and 7 are followed by the reaction
+
k, , +1 1 2 + s 3(C1I3)*S--~
+
+ +
(CH3)3?; IZV +(CEIJ,Xr (CH3)3N* hl --+ (CH3jjX RI (CH3)3S* --+ (CH3)2?; CH3
-
(11) (12) (13)
+
where M is a molecule or the wall. Such a se(8) E Tannenbauni E hl Coffin a n d 4 J Harrison J P h p , 21, 311 (1953)
I ,
,C(lX'l'RIBU'l'l(JS I X U M l'HE
Cheiiz
----+C€Jd
-1- Y
ki,
wlicre k , ' k b is 1.2and X and ' I arc the liquid 1)roclucts arid perhaps dimethylaniinc. I t is hoped that a detailed study of the reactions of the dimethylamine radical will further clarify the mcchanism. Acknowledgment.-The authors are indebted t o I l r . George Ensell of the National Research Council of Canada for the construction of the low temperature cell. WINNIPEG, CANADA
D E P A K ~ X E01'S ~CIIEhfIS~K\', ~ ' 0 I . Y T E C I L S I C
I
I N S ' I I l ' U l I< 01; ~ ~ l i O O K l . Y S
Photoreduction of Methylene Blue by Ethylenediaminetetraacetic
Acid'","
BY GERALD OSTERAND KEIL ~VOTHERSPOOI~ RECEIVED APRIL 1, 1957 hlcthyleiic blue ill tlic presciice of etli~~leiiccliaminetetra~~cetic acid (EDTA) is reduced to the leuco t l y ~O I I irrdiatiiiii n i t h red light. The rate of photoreduction depends upon PH in the same way a s does the b,tse titration of EDTA. E D T A is consumed in the reaction suggesting that it is osidized although i t does not normally fuiiction as a reducing agent. A number of nitrogen-containing chelating agents were tested but only those wth secondary or tertiary nitrogens 1 ) e I ~ : t v ~ d as electron donors in the photochemical reaction. T h e photoreduction involves a lo:ig-lived excited st:ite of the d y e ( IO5 times t h a t of the first electronically excited state) and is retnrded by srnzll amounts of p-phenylenediatnine. T!lc rate of reageneration of the dye by near ultraviolet irradiation of the leuco forin increases with increasing hydrogen ion coiiceritr:ititiil
Introduction Early workers in the development of photographic bleach-out processes noted that thiazine dyes are photoreduced readily in the presence of mild reducing agents such as allylthiourea, anethol, glyoxal2 and ferrous ~ u l f a t e etc. ,~ When a thiazine dye is photoreduced by ferrous ion t o give the leuco dye, the ferric ion thus produced oxidizes the leuco dye in the dark, and for intermediate illu(1) (a) T h i s paper represents a p a r t of t h e dissertation t o be submitted b y Xeil Wotherspnon t o t h e faciilty of t h e Gradirate School t h e Polytechnic I n s t i t n t e of n r o o k l , ~i ~ n ~partial fufillineiit o f t h e requirements for t h e degree of Doctor of Philosophy. ( b ) This researvh was supported b y t h e United Statr.s Air Force thriiiigh t h e Air Force office of Scientific Research o f tile Air Reiearcli auql 1 ) t : v i ~ l o p n l e n t Command under C o n t r a c t KO, AF 18(600) 1182. (2) hZ. Aludrovcic. Z.wiss. Photo., 26, 171 (1928). (3) IC. Weber, 2. p i i y s i k . Chei~z, B15, 18 (1931); G. IIolst, ;bid., B169 9 (19341. cjf
mination levels, a steady state is achieved.4 Stannaus chloride and ascorbic acid, on the other hand, do not allow the leuco dye to revert to its colorcd form, but under excitation with near ultraviolet light the dye is r ~ g e n e r a t e d . ~ Nickerson and Merke16 in their studies 011 the photochemistry of riboflavine noted that methylene blue is photoreduced with ethylenediarninetetraacetic acid (EDTA). This is an unexpected result since EDTA does not normally function as a reducing agent. It is the purpose of the present paper to investigate the role of EDTA as Ltn elcc(4) J. U'eiss, T r n i i i . i : n i o ~ / u r S o c . , 32, 1131 (l!l3(i): 35, 18 (19:3:)),, See also 1%;. l < a t ~ i n o w i t ~"hI ,' l ~ i t ~ r s y n t h r Interscience Publishers, I n c . , New I'ork, S . Y . , l!bG. p . 7ii. ( 5 ) 0 Oster a n d N. TVotherspnon, J . Chenz. Piirs., 22, 157 (1954). ( 6 ) J . I
