THE JOURNAL OF
PHYSICAL CHEMISTRY (Registered in U.S. Patent 0f;‘ice) (@ Copyright, 1963, by the American Chemical Society)
VOLUME67, KUMBER1
JANUARY 22, 1963
URANYL SENSITIZED PHOTOIIECOMPOSITIQY OF ORGANIC ACIDS I N SOLUTION1 BY G. E. HECKLER, A. E. TAYLOR, C. JENSEN, D. PERCIVAL, R. JENSEN, ASD P. FUNG Department of Chemistry, Idaho State College, Pocalello, Idaho Received February 9, 1969 Uranyl senuitized photodecomposition products of various organic acids are presented. Sensitized photodecomposition rates for malonic, succinic, and glutaric acids were determined in the pH range 0.5 to 3.0 by measuring the gas produced in a Warburg micromanometric apparatus. Theoretical analysis of these results shows that the photosensitive species is a 1:1 complex of diionized acid with uranyl ion for malonic acid and a mixture of 1:1 complex and 2: 1 complex of monoionized acid with uranyl ion for succinic and glutaric acids.
Photodecomposition of oxalic acid in solution sensitized by uranyl ion has been used extensively :for actinometry.2 Uranyl sensitized photodecomposition stud.ies of other organic acids have been rnade.3 Pafit studies of such systems have involved iiitlernal analysis of the organic acid and residual by stand.ard analytical techniques. In this Laboratory, Taylor and Jarvis4s6used a Warburg apparakus with high intensity ultraviolet lamps and quartz flasks for external micromanometric measurement of the amount of gaseous prod.uct. This technique permits continuous measurement of the extent of reaction without disturbing the reacting system.. HOWever, the nature of the gas evolved must be known to apply theoretical analysis to the experimental measurements. This paper presents results of investigation for photodecomposition products from a variety of acids; it also discusses the results and makes a theoretical analysis of the nature of the reacting system for photodecomposition of a group of three organic acids. Experimental
as well as Baker and Adamson A.C.S. acetic acid, were used as received. Eastman White Label glutaric acid was repurified by crystallization from benzene t o give a product of m.p. 97-!>8’. Tests of Eastman malonic acid indicated hi.;h purity, but micro amounts of a photosensitive impurity were revealed during this investigation. These were removed by crystallization from acetone. Eastman White Label valeric anhydride was hydrolyzed to obtain a solution of valeric acid. Uranyl chloride solutions were prepared as described in ref. 5. Apparatus.--A rectangular Warburg apparatus-modified by introduction of high intensity ultraviolet lamps (G.E. G36T6)was used for micromanometric determination of the production of gas. According t o the manufactyrer’s specifications, 90% of the output of these lamps is 2537 A. Hg radiation. For reaction vessels, quartz single side-arm flasks of approximately 25-ml. capacity were used. Absorbancy measurements were obtained with a Beckman DU spectrophotometer; pH measurements, with a Beckman Model G pH meter; gaseous infrared analysis with a Beckman IR-E;. Method.-A. Photodecomposition Products.- Solutions containing U02Cl2 and one of the acids were placed under an argon atomosphere in a 250-ml. quartz flask and irradiated by a bsnk of six 18-in., 15 w. Sylvania germicidal lamps for periods ranging from 3 to 16 hr., depending upon the organic acid being examined. The gas was transferred to a 10-em. infrared gas cell by a gas handling apparatus which permitted measurement of the approximate partial pressure of the decomposition product. All solutions were 0.05 M in U02Cl2 and 0.5 M in acid except the following: valeric acid, 0.038 M iri UO2C12 and 0.154 M in arid; malonic, 0.062Min U02Cl~and 0.398M in acid; succinic, 0.288 A! in avid. The non-gaseous photodecomposition products were identified by a paper chromatographic method described by Kennedy and Barker .e B. Micromanometric.-Of the 14 manometers in the rectangular Warburg apparatus, two were used for barometric corrections and two were used to assure a constant intensity of light produced by the fluorescent lamps. These latter two flasks contained 0.1 M oxalic acid and 3.75 X 10-4 2cZ UOd212 at a pH of 1.30 Z!C 0.02 during all measurements. To correct for physical variations between flasks, “premmre ronstarits” were experimentally determined for the other ten flasks. These “pressure constants” were measured by irradiating
Chemicals.-The melting points of Baker Analyzed Reagent formic, oxalic, succinic, and tartaric acidrr and of Eastnnan White Label propionic acid indicated a high degree of purity. These, (1) This paper iu based on work performed under contract with the United States Atomic Energy Commission, contract no. AT(10-1)-310 with Idaho State College. (2) C. R. Masaon, V. Bookelheide, a n d W. A. Noyes, Jr., “Techniquea of Organic Chemistry,” Vol. 11, 2nd Ed., Ed. b y A. Weissberger, Interscience Publishers, Inc., New York, N. Y.,1956, pp. 292-298. (3) G. K. Rollefson a n d M. Burton, “Photochemistry a n d the Mechanism of Chemical Reactions,” Prmtice-Hall, Inc., E~iglewoodCliffs, N. J., 1934, pp. 241-244. (4) A. E. Taylor a n d F. 0. Jarvis, Presented a t t h e Northwest Regional Meeting of the American Chemical Society, J u n e 16, 1958, i.n Portland, Oregon. ( 5 ) A. E, Taylor, G. E. Heckler, a n d D. R . Percival, Talanta, 7, 232 (1961).
(6) E. P. Kennedy a n d FI. A. Barker, Anal Ciiem., 23, 1033 (1951).
1
2
Vol. 67 TABLE I Gascous photo-
Acid
Acid
UOz bz pI1 of concn.. iM conon., 31 systani
I7ormulu.
Formic HCOOH Acetic H;C--COOH Propionic HIC-CHz-COOH \~7:~loric H,C-( CH,),-COOII Oxalic IIOOC--COOH hIalonir HOOC-CI-Iz-COO1:I Tartnrict HOOC--CH( OH)--CH( OII)-COOIT Succinic HOOC---( CH2)z-COOH Gliitarie IIOOC-(CHZ)~--COOII a Moles of COS > moles of CO. * n-Butaric.
0.5 .ci .R .I5 .5
.04 .05
.o(i
5
,03 .05
. :1 .A
,
Ha0
1.5 COP,CO,” (HP) COP,CHa 1.8 1 .8 COP, C P H ~ I .!-ICOz, C4HiC1, 0.6 CO?, CO 0.9 co:! coz 1. 1 CO? 1 .fi coz 1 .ci
0.05 .04 ,05
. .1
Kon-gaseous deconiponition products
decomposition products
o,;
None None None 1120 I-I~C-COOI~ (€I&( O€I)CJI(OFT)COOI I ) II,C-CI-I2~--COOH &C-( C112)*-C001I
16
I
8
I
I
I
40
I 2
6
4
8
I
I
80
1
,
I20
1
1
160
1
200
b
10
Alm.
E’ig. I .--Gas produced us. irradiation tirnr for oxalic acid ( ~ € 1 1.32), A ; rndonic acid ( p l l 1.9:1), 0;succinic acid ( p H 2,(i:3)l X ; glutaric acid (pII 3.00), 0 ; tartaric acid (PI€1.9!)), 0 . CoricenJI in riran>l for all trations were 0.1 .If in wid arid 3.75 x
*,.OS @ ’,
(’:BeS.
2
4
G
8
10
>[in.
Fig. 2.--Gas produced as a function of timc for 0 . I .If mnlonic acid at, pl-1 2.20, 0 ; pH 2.00, 0 ; plf 1.83, A ; PI1 1.:
