y Radiolysis of lsobutyrate Salts
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y Radiolysis of lsobutyrate Salts R. S. Marshall, B. M. Tolbert, and W. C. Goltschall, Jr: Chemistry Department, University of Colorado,BouMer, Colorado 80302 and Chemistry Department, university of Denver, Denver, Colorado 802 10 (Received January 30, 1975) Publication costs assisted by the University of Denver
I ~ o b u t y r i c - l - ~acid ~ C was prepared from Ba14C03 via a Grignard reaction. Eight i ~ o b u t y r a t e - l - ' ~salts C were prepared by treating hydroxides or carbonates with isobutyric-1-14C acid. The salts were irradiated in vacuo with y radiation from a 137Cs source. 14C02from the salts was quantitatively measured by an ionization chamber method and G (14COz)values were calculated. Initial G(l4CO2)values for sodium, potassium, calcium, strontium, barium, nickel(IJ), copper(II), and zinc isobutyrate-l-l4C are 0.34, 1.2, 1.5, 1.1, 1.9, 0.48,0.48, and 1.3, respectively.
Introduction A moderate amount of information has been published on the y radiolysis of salts and ~ h e l a t e s , l -with ~ Johnson's book4 representing the outstanding compilation to date. Although one might expect a correlation between cation electronic properties and rates of decomposition for a given ligand or anion, this does not appear to be the case. Thus, for example, cation ionization potential, radius, charge density, and polarizability do not correlate with observed stabilities nor do macroscopic properties of the crystals such as density, melting point, temperature of thermal decomposition, or free volume. This study was undertaken to obtain additional facts concerning cation effects on radiation stability. We felt that combining known cation properties and macroscopic properties from an organic moiety would furnish a fresh look a t the stability question. Despite considerable interest in the solid state reactions, mechanisms have been poorly understood and theories or postulates have not endured. Ultimately it was hoped that by finding known parameters that would correlate with G(C02) values, a better understanding of radiation stability or a t least radiation-induced decarboxylation mechanisms could be obtained. 14C02 evolution is studied in this series because the carboxyl position is readily labeled with 14C, the acidic nature of COz simplifies analytical techniques, and because CO:! has been shown to be the major product in the parent a ~ i dand ~ , in~ these salts in the course of this study. Experimental Section Syntheses. I ~ o b u t y r i c - l - ~acid ~ C was prepared by a Grignard8 reaction using J. T. Baker reagent grade magnesium powder, Eastman Kodak White Label isopropyl iodide, Mallinkrodt analytical reagent absolute ethyl ether, barium carbonate-14C from New England Nuclear, and Baker and Adamson reagent grade sulfuric acid. Eastman Kodak White Label isobutyric acid was added to the distillation flask and the isobutyric-l-14C acid was distilled twice before use. A specific activity of 6.85 f 0.09 &i/mmol was determined for this acid. Sodium isobutyrate-1-14C was prepared by titration of the acid with Baker reagent grade sodium hydroxide.
* Address correspondence to this author at the Department of Chemistry, University of Denver, Denver, Colo. 80210.
Potassium isobutyrate-1- 14C was prepared by titration of the acid with Baker reagent grade potassium hydroxide. Calcium isobutyrate-1-14C was prepared by allowing the acid to react with Baker and Adamson reagent grade calcium oxide. Strontium i ~ o b u t y r a t e - l - ~was ~ C prepared by allowing the acid to react with Merck technical grade strontium oxide. Barium isobutyrate-1- 14C was prepared by allowing the acid to react with Baker and Adamson reagent grade barium hydroxide monohydrate. Nickel(I1) isobutyrate-1-14C was prepared by allowing the acid to react with Merck reagent grade NiCOy2Ni(OH)2. 4H&. The nickel(I1) isobutyrate-I-14C was extracted with hot distilled water and filtered twice through fritted glass funnels. Copper(I1) isobutyrate-1-14C was prepared by allowing the acid to react with J. T. Baker reagent grade copper(I1) carbonate. The copper(I1) isobutyrate-1-14C was extracted with USP 95% ethanol and filtered twice through fritted glass funnels. Zinc(I1) isobutyrate-1 -14C was prepared by allowing the acid to react with J. T. Baker reagent grade zinc carbonate. The zinc(I1) isobutyrate was extracted with a 50/50 mixture of distilled water and USP 95% ethanol and filtered twice through fritted glass funnels. Irradiation. All salts were dried on a vacuum line a t less than 30 p of mercury for 12 hr or more before use. All samples were weighed into Pyrex tubing capillaries of 1.75 f 0.5 mm i.d. with a wall thickness of 0.2 f 0.1 mm and length of 10 f 2 cm. Drybox techniques were required for the hygroscopic salts and all salts were redried in a vacuum desiccator for a t least 12 hr, at 30 p of mercury or less before sealing under a vacuum of 20 f 10 of mercury. Replicate samples were irradiated in the University of Colorado cesium-137 y source calibrated a t 2.77 X 1019 eV g-' hr-l with a Fricke Dosimeter for doses ranging from 1.3 to 6.7 X loz1eV g-l. Analytical Procedure. Samples were analyzed via basically the same procedure discussed previously5 using the same type of set up. The ionization chambers used with the Cary vibrating reed electrometer were calibrated frequently and the specific activities of the salts determined by combustion with this set up yielded values within 2% of those calculated. Experimental points from the measured CO:! yields were plotted and generally gave good straight The Journal of Physical Chemistry, Vol. 79, No. 15, 1975
1518
R. W.
TABLE I: Sodium Isobutyrate
TABLE VI: Nickel(I1) Isobutyrate eV/g x
1.43 1.43 2.76 3.98 3.98
0.086 0.094 0.16 0.24 0.26
Marshall, B. M. Tolbert, and W. C.Gottschall
0.33 0.36 0.33 0.33 0.33
%‘Ic‘4c02
G(C02)
0.38 0.37 0.48 0.55 0.76 0.63 0.65 0.73
0.48 0.47 0.37 0.42 0.47 0.39 0.27 0.31
2.04 2.04 3.34 3.34 4.20 4.20 6.19 6.19
TABLE 11: Potassium Isobutyrate eV/g x 1.32 1.32 4.20 4.20 5.36 5.36
0.33 0.30 0.86 0.90 1.1 1.2
1.2 1.1 0.98 1.0 0.94 1.0
TABLE VII: Copper(I1) Isobutyrate eV/g x 1.34 1.34 3.32 3.32 4.64 4.64 5.83 5.83
TABLE 111: Calcium Isobutyrate
1.56 1.56 3.37 4.70 6.04 6.04
0.85 0.81 1.5 1.8 2.2 2.4
1.5 1.5 1.3 1.1 1.0 1.1
0.63 0.65 1.1 1.1 1.0 1.4
1.1 1.1 0.91 0.94 0.60 0,74
TABLE V: Barium Isobutyrate
1.77 3.12 3.12 4.50 4.50
1.4 2.2 2.2 2.8 2.8
eV/g x
Results and Discussion Tables I-VI11 present the data for the eight isobutyrate salts investigated. Table IX is a compilation of initial G(C02) values for the isobutyrates with acetate values included for comparison. Except for the sodium salt, all the isobutyrate salt The Journal of Physical Chemistry, Vol. 79, No. 15, 1975
G(C02)
0.87 0.99 1.6 1.7 2.2 2.2 3.1 3.1
1.2 1.4 1.2 1.3 1.2 1.2 1.2 1.2
TABLE IX: G Values for Irradiated Isobutyrate a n d Acetate Salts
Na K Ca Sr Ba Ni (11)
Cu(I1) Zn
lines from the slope of which the initial G(C02) values listed were determined. In all cases blanks were run in identical fashion and gave COz yields less than 1% of those determined for irradiated samples.
0.58 0.49 0.48 0.48 0.36 0.49 0.47 0.47
VCO~
1.82 1.82 3.26 3.26 4.58 4.58 6.55 6.55
Cation
1.9 1.4 1.4 1.2 1.2
0.30 0.26 0.61 0.61 0.64 0.88 1.1 1.1
TABLE VIII: Zinc Isobutyrate
TABLE IV: Strontium Isobutyrate
1.35 1.35 2.72 2.58 3.97 4.36
%%02
Isobu tyrate G ( C 0 , )
Acetate G(C02)
0.34 1.2 1.5 1.1 1.9 0.48 0.48 1.3
0.48 0.56 1.3 0.91 1.5 0.10 0.17 0.36
G (COz) values are higher than the corresponding acetate salt values. This fact is in accord with observations that secondary carboxylic acids have higher G(C02) values than primary carboxylic acids of similar molecular eight.^ The acetate values were included because one might anticipate similarity with this more studied, more simple aliphatic acid and in fact similar decomposition mechanisms for the parent acids have been shown.lOJ1 The mechanism consistent with these findings and as-
1519
Triboluminescence of Solid Methanol
sumed operable in the radiation decomposition of isobutyrate salts, despite their decreased radiation sensitivity compared to parent acid, is that postulated for the acid.'l The cation G(CO2) trends within periodic groups for isobutyrate and acetate salts are consistent and can be summarized as K > Na, Ba > Ca > Sr, and Zn > Cu > Ni and it should be noted that G(N02-) for the nitrates follows the same trend.lJ2 An all inclusive listing of cations according to decreasing G values, however, reveals no consistent correlation in accord with previous result^.^ From these observations, it appears that y radiation stability of salts depends to some extent upon electronic properties of the cation but that the predominant factor is some property of the salt as a whole.
References and Notes (1)J. Cunningham, J. Phys. Chem., 65, 628 (1961). (2)E. R. Johnson and J. Forten, Discuss. Faraday Soc., 31, 238 (1961). (3)C. J. Hochanadel, Radiat. Res., 15, 546 (1961). (4)E. R. Johnson, "Radiation Induced Decomposition of Inorganic Molecular Ions", Gordon & Breach. New York, N.Y., 1970. (5) W. C. Gottschall and B. M. Tolbert, Adv. Chem. Ser., No. 81, I 374 (1968). (6)S. V. Choi and J. E. Willard, J. Phys. Chem., 66, 1041 (1962). (7)M. A. Sweeney, UCRL No. 9983,1962. (8) H. Giiman, "Organic Syntheses", Vol. 1, Wiiey, London, 1941. (9)A. J. Swallow, "Radiation Chemistry of Organic Compounds", Pergamon Press, New York. N.Y., 1960. (IO)P. B. Ayscough and J. P. Oversby. Trans. Faraday SOC., 67, 1365 (1971). (11) H. Rush, Masters Thesis, University of Colorado, Boulder, Colo.. 1962. (12)J. Cunningham and H. G. Heal, Trans Faraday Soc., 67, 1365 (1971).
Triboluminescence and Associated Decomposition of Solid Methanol Graham J. Trout, Douglas E. Moore.' Department of Pharmacy, The University of Sydney, New South Wales 2006, Australia
and John G. Hawke School of Chemistry, Macquarie University,New South Wales 21 13, Australia (Received May 30, 1974; Revised Manuscript Received January 2, 1975)
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An investigation of the phase change induced decomposition of methanol has been carried out. The decomposition is initiated by the cooling of solid methanol through the /3 CY transition at 157.8 K, producing the gases hydrogen, carbon monoxide, and methane. The passage through this X transition causes the breakup of large crystals of @methanol into crystallites of a-methanol and is accompanied by light emission as well as decomposition. The emitted light exhibits the properties of gas discharge triboluminescence, being accompanied by, and apparently produced by, electrical discharges through methanol vapor in the vicinity of the solid. The light has a spectrum similar to that produced by an electrical discharge through methanol vapor at low pressure. The potential differences needed to produce the electrical breakdown of the methanol vapor apparently arise from the disruption of the long hydrogen bonded chains of methanol molecules present in crystalline methanol. Charge separation following crystal deformation is a characteristic of substances which exhibit gas discharge triboluminescence; solid methanol has been found to emit such luminescence when mechanically deformed in the absence of the 0 CY transition. As expected for an electrical discharge phenomenon it has been found that the characteristics of the discharges are affected by the nature and pressure of the gas above the methanol. The decomposition products are not produced directly by the breaking up of the solid methanol but from the vapor phase methanol by the electrical discharges. That gas phase decomposition does occur has been confirmed by observing that the vapors of C ~ H B O HCH30D, , and CD3OD decompose on being admitted to a vessel containing methanol undergoing the /3 CY phase transition. The composition of the gas evolved from methanol and deuterated methanols has been explained using reactions occurring on electron impact in mass spectrometry.
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Introduction The decomposition of methanol to the gases hydrogen, methane, and carbon monoxide has been found to accompany the freezing of large volumes of methanol with liquid air.2 During such treatment the methanol would undergo a liquid-solid phase transition (175.37 K) followed by a solid-solid phase transition (157.8K). Further work has revealed that the latter p a solid phase transition is intimately associated with the decomposition and that there is an accompanying emission of light.3
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The /3 a phase transition in methanol has been reported to produce crystal breakdown4 and the destruction of crystals both organic and inorganic is frequently accompanied by the emission of light known as tribolumines~ e n c eThe . ~ light appears as a series of flashes or pulses of varying intensity. These light pulses have long been known to be associated with electrical discharges in or around the crystal being strained, and the detection of such discharges may be used to distinguish triboluminescence and crystalloluminescence.6 The Journal of Physical Chemistry, Vol. 79, No. 15, 1975
