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# 19 /3-0/7 EPA-560/11-79-012 August 1979

STRUCTURE REACTIVITY CORRELATIONS FOR ENVIRONMENTAL REACTIONS

by Theodore Mil l Physical Organic Chemistry Department Physical Sciences Division 7

Contract 68-01-41-09

Project Officer
Asa Leifer

OFFICE OF TECHNICAL EVALUATION OFFICE OF TOXIC SUBSTANCES U .S . ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D . C. 20460

Q lln ttematior

63980000352p. 2

The review of Mabey and Mill (1978) is a useful point of departure for summarizing the SRC for hydrolysis in pure or natural water where only H20HOand H+ are important catalytic agents . Organic chemicals can hydrolyze by a variety of processes including both solvolytic and substitution mechanisms catalyzed by H30+ and OH- . We can narrow the scope of the enquiry by restricting our interests to reactions proceeding at pH 7 and 25*C . ' General and detailed effects of structure on hydrolytic reactivity, as measured by the half-life at pH 7, are summarized in Tables 4 through 11 . In some cases half-lives are expressed only as > or < 1 year or some multiple thereof .* By this classification, one can quickly differentiate the reactive from the unreactive chemical structures . For some classes, the information on LFER can be use d to make detailed estimates of reactivity based on structure . Table 12 provides an summary of hydrolyzable chemical structures that will be expected to persist in water for significantly more than a year at pH 7 and 25*C . These classes of chemicals probably need not be screened in the laboratory for hydrolysis using the current screening tests because these tests are designed to estimate reliably only those half-lives of a few hours to a few months ; longer half-lives are not well-defined by the test method (Federal Reg ., 1979) and, indeed, current assessment procedures generally focus onl y on chemicals that exhibit loss rates of days to weeks . Photochemistry Measurement Methods The cutoff for the solar spectrum by the upper atmosphere is at about 290 nm; only absorptTon of photons-b~ Kemcailat this or longer wavelengths can result in direct photochemical transformations . Direct absorption of sunlight may result in cleavage of bonds, dimerization, oxidation, hydrolysis , or rearrangement . No simple selection rules are available to predict the specific chemical process that may occur, although some .useful generalizations have been found (Calvert and Pitts, 1967 ; Turro, 1978) .

Quantitative aspects of direct photolysis in water, on soil surfaces, or in the atmosphere have the same general kinetic relationships . The rat e of absorption of light, IA (rate constant ka), by a chemical at one wavelength is determined by eX, the molar absorbance ; IX, the intensity of the incident light at wavelength X ; and [C], the concentration of chemical . At low concentrations of C where only a small percentage of the light is absorbed IA(X) ' ' I X [C] = ka(X)ICI (17) The rate of direct photolysis of a chemical at wavelength X is obtained by multiplying ka(X) by the quantum yield ~X, which is the efficiency for
This time limit is somewhat arbitrary but corresponds to the limits on estimation of rate constants using EPA screening test protocols . 15 C),p. 3

TABLE 13. APPROXIMATE ABSORPTION REGIONS FO R ORGANIC MOLECULES Region Clas~__ Example nm Reference Aliphatics c hydrocarbons n-C4H10 120-170 a fluorides, chlorides CHBr3, CHC13 180-260 a, b bromide s -"~Iodides C3H,I 180-320 b ethers, alcohols C,H,OH, C2H1OC2H5 150-200 a aldehydes CH3CHO 240-340 a . %o ketones C2HsC(O)CH3 240-320 a, b acids CH'C(0)O 200-230 a, b esters CH,C(O)OCH, 200-240 a amides C2H,C(O)NHt2 180-220 a, b amines (C2H!1)3N 180-240 a, b azines (CH3)2C=N-N=C(CH3)2 200-29G b
azo CH3-N=N-CH3 200-230, 320-400 a nitro CH3NO2 200-220, 260-320 a, b nitroso (CH3)3CNO 200-300, 540-740, a nitrite (CH3)3CONO 200-240, 320-400 a, b nitrate C2H,ON02 200-300 a sulfide C2H5SC2Hs 200-220 a, b disulfide CH3SSCH3 200-240 a, b Non-conjugated c Olefinics and Acetylene s hydrocarbons (CH3)2C=C(CH3)2 170-240 a, b aldehydes CH2=CHCHO 200-250, 290-400 b ketones CH,CH=CH-C(O)CH3 200-240, 260-330 b nitro CH,C(N02)=C(CH3)2 180-380 b

a Calvert and Pitts (1967) . bPerkampus (1971) . c From Hendry and Kenley (1979) .

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