Radical half-life

In ambient air, the primary removal mechanism for acrolein is predicted to be reaction with photochemically generated hydroxyl radicals (half-life 15-20 hours). Products of this reaction include carbon monoxide, formaldehyde, and glycolaldehyde. In the presence of nitrogen oxides, peroxynitrate and nitric acid are also formed. Small amounts of acrolein may also be removed from the atmosphere in precipitation. Insufficient data are available to predict the fate of acrolein in indoor air. In water, small amounts of acrolein may be removed by volatilization (half-life 23 hours from a model river 1 m deep), aerobic biodegradation, or reversible hydration to 0-hydroxypropionaldehyde, which subsequently biodegrades. Half-lives less than 1-3 days for small amounts of acrolein in surface water have been observed. When highly concentrated amounts of acrolein are released or spilled into water, this compound may polymerize by oxidation or hydration processes. In soil, acrolein is expected to be subject to the same removal processes as in water. 

To measure the enhancement factor for initial polarization, we must be able to estimate Sq. Ideally, as the initial polarization relaxes with the Ti of the radical ( 10 ys) when the light is switched off, and as the radical half-life is between 1 and 3 ms in our photochemical systems, q should be measured directly off the computer trace. However, the spectrometer has a response time of only 500 ys, and as a result of this the computer traces are distorted for this period of time after the light-off point. 

The greatest disadvantage of this mode of CIDEP experiment is that the enhancement factor measured is for the "steady-state" spectrum. To calculate the true enhancement factor of the process, both the radical Tj and the radical half-life t /2 have to be taken into account ... 

Radical Half-life with Typicai Substrate, 10 M, 37°C Ave. rx Rate, k (L mol sec" Reference... 

RDX is a widely used military explosive. It is a synthetic compound and is not known to exist in nature. Effluents and emissions from Army ammunition plants are responsible for the release of RDX into the environment. When released to the atmosphere, RDX may be removed by reaction with photochemically generated hydroxyl radicals (half-life =1.5 hours). When released to water, RDX is subject to photolysis (half-life = 9-13 hours). Photoproducts include formaldehyde and nitrosamines. 

Trichloroethane will enter the atmosphere from its use in the manufacture of vinylidene chloride and its use as a solvent. Once in the atmosphere, 1,1,2-trichloroethane will photodegrade slowly by reaction with hydroxyl radicals (half-life 24 to 50 days in unpolluted atmospheres and within a few days in polluted atmospheres). The soil partition coefficient of 1,2-trichloroethane is low and it will readily leach in the case of eventual, very slow biodegradation. Bioconcentration is not a significant process. It will also be discharged in wastewater associated with these uses and in... 

PROBABLE FATE photolysis-, the dissolved portion could undergo rapid photolysis, but very little compound is present in the dissolved form vapor phase reaction with photochemi-cally produced hydroxyl radicals (half-life 2 hr) may be an important fate process, may undergo direct photolysis in the atmosphere, photolytic half-lives adsorbed onto silica gel, alumina, fly ash, and carbon black 7,22,29,>1000 hrs respectively oxidation-, oxidation by chlorine and/or ozone could occur if enough chlorine or ozone is present, but is relatively unimportant hydrolysis-. not expected to hydrolyze volatilization probably too slow to compete with adsorption as a... 

PROBABLE FATE photolysis-, direct photolysis is not significant, photodissociation in stratosphere to chloroacetyl chloride oxidation photooxidation in water expected to be slow primarily removed in air by photooxidation degraded in atmosphere by reaction with hydroxyl radicals, half-life of 1 month and 1.9% loss/12 hr sunlit day products of photooxidation CO and HCl oxidation half-life 1.5 weeks-4 months hydrolysis not significant first-order hydrolytic half-life 1.1 yr volatilization high vapor pressure causes rapid volatilization, major transport process, half-life 30 min 25°C evaporation primary removal from water half-life from 1 ppm solution 25°C, still air, and an avg. depth of 6.5 cm 28 min., evaporation from water 25 °C of 1 ppm solution 50% after 29 min. and 90% after 96 min. 

PROBABLE FATE photolysis can occur in atmosphere, in air reacts with photochemi-cally generated hydroxyl radicals, half-life >23 days oxidation photooxidation in troposphere is probably important hydrolysis not expected to compete with volatilization, first-order hydrolytic half-life 15.8 yr volatilization probable important transport process, if injected to soil, primarily lost by volatilization, volatilization from surface water half-life 6hr and 10 days for a river and a lake respectively biological processes compound can be used as a carbon source by several soil bacteria washed out of air by rain... 

PROBABLE FATE photolysis photoisomeraization occurs, rate undetermined, photooxidation half-life in air 59 minutes-9.8 hrs, vapor phase hepatchlor in air will react with photo-chemically produced hydroxy radicals, half-life 36 min., direct photolysis may occur oxidation information is not available hydrolysis rapid hydrolysis for heptachlor in solution, first-order hydrolytic half-life 23.1 hrs or 129.4 hrs, significant in moist soils volatilization expected to be an important process, evaporates slowly, release to soil will result in volatilization from the surface, especially in moist soils sorption probably an important process, but no reliable data is available, sticks strongly to soil particles biological processes will bioaccumulate if not hydrolyzed, biodegradation is significant... 

PROBABLE FATE photolysis-, no data for rate of photolysis in aquatic environment oxidation-, in aquatic systems not expected to be important fate, photooxidation in troposphere is probably the predominant fate hydrolysis expected to be slow, neutral aqueous hydrolysis half-life 25 °C >50 years, first-order hydrolysis half-life 37 years pH 7 volatUiz/ttion primary transport process, volatilization from soil will occur biological processes NA evaporation from water 25 °C of 1 ppm solution is 50% after 21 min and 90% after 102 min release to water primarily through evaporation (half-life days to weeks) rate of evaporation half-life from water 21 min photodegrades slowly by reaction with hydroxyl radicals, half-life 24-50 days in polluted atmosphere to a few days in unpolluted atmospheres will be removed in rain... 

Stable free-radical. Half-life ca. 1 year at 20°. 

These temperature properties determine the polymerization initiation temperature and the length of time the free-radical initiation process is active. For example, low-temperature peroxides possess a relatively short free-radical half-life and offer a low-temperature initiation but also a lower peak temperature, while a high-temperature peroxide with a relatively long... 

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