Alcohols reaction with hydroxyl radical

Reaction pathway for substituted alcohols reacting with hydroxyl radicals. 

With the exception of a-haloalcohols, the atmospheric lifetime of halogen substituted saturated alcohols is determined by their reaction with hydroxyl radicals. In laboratory experiments to simulate the atmospheric oxidation of halogen substituted alcohols, it is often convenient to use chlorine atoms, rather than OH radicals to initiate the oxidation. To aid in the design and interpretation of such experiments, a knowledge of the kinetics of reactions with chlorine atoms is desirable. Rate constants for the reactions of organic compounds with chlorine atoms are also useful because they can be used to estimate the rate constants of reactions with OH radicals. 

Nelson, L., Rattigan, O., Neavyn, R., Sidebottom, H., Treacy, J., Nielsen, O. (1990) Absolute and relative rate constants for the reactions of hydroxyl radicals and chlorine atoms with a series of aliphatic alcohols and ethers at 298 K. Int. J. Chem. Kinet.22, 1111-1126. 

Wallington, T.J., Dagaut, R, Liu, R., Kuoylo, M.J. (1988c) Gas-phase reactions of hydroxyl radicals with the fnel additives methyl fert-butyl ether and fert-bntyl alcohol over the temperatnre range 240-440 K. Environ. Sci. Technol. 22, 842-844. 

Campbell, I.M., McLaughlin, D.F., Handy, B.J. (1976) Rate constants for reactions of hydroxyl radicals with alcohol vapours at 292 K. Chem. Phys. Lett. 38, 362-364. 

A similar degradation process could also occur by the reactions of hydroxyl radicals, which are generated by peroxidase enzymes, with the secondary alcohol groups in poly(vinyl alcohol) and with the ketone groups formed either by this type of chemical reaction or by the enzymatic reactions described above. The mechanisms of the chemical reactions are shown below ... 

Absolute rate constants have been determined for the reaction of the hydroxyl radical with a variety of aromatic compounds in aqueous solution. The rate constants obtained are significantly higher than values previously reported. Rate constants for the reaction of the hydroxyl radical with methyl alcohol and ethyl alcohol have also been determined by competition kinetics using three of these absolute rate constants as reference values. Comparison of our results with the published values from competition kinetics suggests that the rate constants for the reaction of hydroxyl radicals with iodide ion and thiocyanate ion are significantly higher than reported in earlier work. The ultraviolet absorption bands of the various substituted hydroxycyclohexadienyl radicals formed have been observed. 

Table III. Rate Constants for the Reaction of Hydroxyl Radicals with Methanol and Ethyl Alcohol Determined by Competition Kinetics...

We may note that the mechanisms of reactions included in the last two types are, in general, not the same for paraffins, on the one hand, and aromatic hydrocarbons, on the other hand, even if the products of these reactions are of the same type. For example, alcohols and phenols may be obtained from alkanes and arenes respectively by the reaction in air with hydroxyl radicals generated by the action of a metal complex. However, in the case of alkane, an alcohol can be formed by the reduction of alkyl peroxide, whereas hydroxyl is added to an arene with subsequent oxidation of a radical formed. Hence follows the possibility that arenes and alkanes may exhibit different reactivities in each specific reaction. 

However, the oxidized metal complex may be able to perform a second oxidative event at the deoxyribose radical ( 2-electron oxidation mechanism). This oxidative event may be an electron transfer or an oxygen rebound mechanism (direct hydroxylation by Mn -OH species). Alternatively, hydroxyl radical can combine with a carbon-centered radical. Oxygen rebound, reaction of hydroxyl radicals, or the attack of a molecule of water at a carbon cation, give rise to an alcohol at the oxidized carbon of the deoxyribose. 

The diffusion kinetic analysis of spur-decay processes requires a model of the initial distribution of reactive species produced by radiolysis. These reactants are able to diffuse from their original location and, if they encounter another reactant, reaction can occur. Most work on spur-decay processes has been with water as the solvent and with such solute species as N2O, HCOO as electron scavenging solutes, OH as a proton scavenger, and alcohols to scavenge hydroxyl radicals. Water is so polar that coulomb interactions may be disregarded and the reactants treated as uncharged radical species. Most of the reactions thought to be important were listed in Sect. 4.2. Many of these reactions occur at or close to the diffusion-limited rate and most of the rate coefficients have been measured. It should be recalled that a spur is a localised cluster of... 

The rate data for reaction of NO3 with aliphatic esters show that the presence of the ester group in an organic molecule has little influence on the reactivity compared to the parent alkane. The reactivity trends exhibited by the nitrate radical for reactions with alcohols, ethers and esters are similar to those shown for the analogous reactions of hydroxyl radicals. The major products identified from the NO3 radical-initiated oxidation of alcohols, ethers and esters under atmospheric conditions were esters, carbonyls and alkyl nitrates. Similar products arise from the reactions of OH radicals with these molecules under atmospheric conditions. 

Absolute and relative rate constants for the reaction of hydroxyl radicals and chlorine atoms with a series of aliphatic alcohols and ethers,... 

Wallington, T. J., P. Dagaut, R. Liu, and M. J. Kurylo. 1988. Gas-phase Reactions of Hydroxyl Radicals with the Fuel Additives Methyl tert-Butyl Ether and tert-Butyl Alcohol over the Temperature Range 240-44(fK, Environ. Sci. Technol., vol. 22, no. 7, pp. 842-844. 

Oh, S., and J.M. Andino (2001), Kinetics of the gas-phase reactions of hydroxyl radicals with Ci-Cg aliphatic alcohols in the presence of ammonium sulfate aerosols, Int. J. Chem. Kinet., 33, 422-430. 

WaUington, T.J., and M.J. Kurylo (1987h), The gas phase reactions of hydroxyl radicals with a series of ahphatic alcohols over the temperature range 240-440 K, Ini. J. Chem. Kinet., 19, 1015-1023. 

Ionizing radiations (a, ft and y) react unselectively with all molecules and hence in the case of solutions they react mainly with the solvent. The changes induced in the solute due to radiolysis are consequences of the reactions of the solute with the intermediates formed by the radiolysis of the solvent. Radiolysis of water leads to formation of stable molecules H2 and H2O2, which mostly do not take part in further reactions, and to very reactive radicals the hydrated electron eaq, hydrogen atom H" and the hydroxyl radical OH" (equation 2). The first two radicals are reductants while the third one is an oxidant. However there are some reactions in which H atom reacts similarly to OH radical rather than to eaq, as e.g. abstraction of an hydrogen atom from alcohols, addition to a benzene ring or to an olefinic double bond, etc. 

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