Radical chain oxidation of hydrocarbons in solution has a zero order with respect to dioxygen concentration. This is a classical text book example.

Hi Yuri,

how do you reconcile the zero order with the increase of oxidation rate with the oxygen concentration?

regards

See the classical work 

LOW TEMPERATURE AUTOXIDATION OF HYDROCARBONS - THE KINETICS OF TETRALIN OXIDATION

By: WOODWARD, AE; MESROBIAN, RB

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Volume: 75 Issue: 24 Pages: 6189-6195 Published: 1953

okay

I guess that knowledge on oxidation has improved for 60 years ;) If you are interested, I can send you some more recent papers dealing with that.

just for being sure: do you feel that the oxidation rate equal if [O2] =0 or [O2] = 1 or 10 mol l-1 ?

regards

Thanks, Emmanuel. I know this area very well. Each reaction rate low is valid in a certain range of concentrations. Surely that at [O2] = 0,the rate is = 0. With an increase of [O2]. the rate increases and then reaches a plateau.  I gave a ref on old paper in order to show that a zero order with respect to O2 is known from 50s. The parameter (kp)^2/(2xkt) ( kp is for the reaction RO2 + RH, kt is for RO2 + RO2 --> keton(aldehyde) + alcohol + O2.) is commonly called the "oxidizability" of hydrocarbons. 

Hi Yuri,

now we agree: rOX = kp²/kt*RH²* [O2] / (1 + b[O2])

and, it can be simplified to apparent 0 or 1st order in well chosen ranges of O2 concentration. but, very formerly, its not a "true zero order".

(it was my phD research work ;) )

regards

Emmanuel,

the concept of the reaction rate order has been introduced a very long time ago. Later on, "the reaction rate law"  has been commonly used.  However, in numerous cases and even for a rather simple reaction mechanism you can't derive the formula for the reaction rate law. In some pretty rare cases under certain experimental conditions the reaction rate law simplifies to a classical equation: rate = k([A]^m)([B]^n) and you can determine the apparent reaction rate orders. In modern chemical kinetics the main goal is to write the reaction mechanism with reaction rate constants assigned to each elementary step. The fitting (simulation) of experimental curves can be performed using digital integration. The problem is considered to be solved, if experimental data/curves are consistent with calculated. From this point of view, the question on the apparent reaction rate order  is not important. Elementary chemical reactions could be only uni- or bimolecular (you can't call them the first or the second orders). In this context the term "true zero order" does not make any sense. 

I feel we agree. my answer dealt with the zero order of oxidation.

however, just for sharing, there are some zero order reactions regarding the reacant concentration in biochemistry field:

ethanol --> acetaldehyde catalyzed by some liver enzymes