CO2 generation from hydroxyl radicals is a very ordinary reaction that occurs permanently around us, in troposphere (from ground level up to ca. 12 km altitude) due to sun radiation. The mechanism is radicalic, via the intermediate HOCO that goes to CO2 and H*. Hydroxyl radical is generated in the air from oxygen radical and water vapors, it is very reactive (its life time is less than 1 sec.), it reacts majorly with CO generating CO2, also with organic compunds (hydrocarbons) generating alkyl radicals, carboxyl radicals and finally CO2. Such reactions are common as many other radicalic reactions in the atmosphere and also much necessary, to remove organic compounds, carbon monoxide and clean the air. I don't know which kind of scientific papers you are looking for, I send you a paper/course that explains this mechanism. Based on this info you can further search some papers focused on your concern.

https://courses.seas.harvard.edu/climate/eli/Courses/EPS281r/Sources/OH-reactivity/www.atmosphere.mpg.de-oxidation-and-OH-radicals.pdf

At the end of the chain of radical reactions, the intermediate tend to release to the environment a stable molecules like CO2. This is the final stage of oxidation reactions. But often it is not reached nad reactions can end forming ketones or carboxylic acids.

Check this papers:

Article Wastewater treatment by means of advanced oxidation processe...

Article Method for the determination of carboxylic acids in industri...

Article Wastewater treatment by means of Advanced Oxidation Processe...

regards,

G

Dear Dr. Boczkaj, I'm skeptic that often CO2 is not reached but process ends to ketones and carboxylic acids, as you stated. A new radical of OH* will instantly attack the carboxylic acid, going to CO2 and H2O: RCOOH + OH* -> R* + CO2 + H2O, alkyl radicals combines and so on. This is the mechanism of cleaning the air naturally, otherwise we would have such organic pollutants in the air (acids, ketones). I personally didn't hear about this, if it occurs this is extremely rare. I didn't find in the indicated papers the radicalic oxidation start from OH*, the papers are related to other combined processes.

Dear Dr Mateescu,

I'm referring to aqueous conditions (and I think that

Dhurba Raj Pandey also asked about that).

best regards,

GB

I still tend to believe that this mechanism is the same, for air and waters as well. Mr. Pandey could be more explicit. But it is clear that radicals generate new radicals, in my opinion going to CO2 preferentially and alkyl radicals. I cant see any batch reactor for such processes, OH* can be generated by passing air with water through an electric arch before the reactor. Nevertheless OH* follows the multiple radicalic reactions in air or in liquids, generating various new radicals and simple, stable molecules. I would read some papers which might deny my answer... Regards.

Hi Dr Boczkaj and Carmen

Thank you for your suggestions.

I am concerned with aqueous phase reactions, and in my system (batch system) the contaminants (chlorinated hydrocarbon) undergo degradation but I do not see any CO2 evolving.

But, I have read couple of field based papers saying OH* might be responsible for release of CO2 from organic compounds and contribute to climate change.

Thank you Mr. Pandey for these details. I send you a paper (and some other references enclosed) about efficiency of OH in removing chlorinated hydrocarbons from waste waters. The authors stated that "The transformation of TCE (trichlorethylene) to CO2, Cl− and H+ was suggested by others researchers after observing complete dechlorination of aqueous-phase TCE with hydroxyl radical (Chen et al., 2001; Hirvonen et al., 1996; Li et al., 2007). From these results it can be suggested that the advanced biooxidation of chlorinated hydrocarbons is a clean process because: (i) the chance of having chlorinated byproducts is low (as demonstrated by the absence of byproducts in GC analysis and the almost complete dechlorination of TCE and 1,2,4-TCB) and (ii) the ability of 📷OH to convert TCE to CO2 was demonstrated and it may be also extended to the other hydrocarbons tested."

Article Induction of hydroxyl radical production in Trametes versico...