The reaction of ozone with thiophene in the gas phase

Abstract

The reaction between ozone and thiophene was studied from 30 to 125°C over a pressure range of 0.005-0.3 torr ozone and 0.1-1 torr thiophene. The most abundant product was 0 2 with smaller amounts of CO, and SOZ. The mass balance was 100% for oxygen and approached 100yo for sulfur a t the higher values of [O&. The carbon balance, however, was only 25% and no H-containing products were found, suggesting that the missing product is a hydrocarbon which may be a polymer. The rate law found waswhere 1,og kl(M-l.sec-l) = 7.8 f 0.5 -(8400 =t 700)/2.3RT, and log k,(M-z-sec-l) = 12.4 f 0.4 -(4700 f 400)/2.3RT. Added O2 had no effect on kl but reduced kz to a limiting value.It is thus not possible to measure the primary rate constant in this system by measuring the overall rate in the presence of oxygen, and this restriction may also apply to other ozone systems. A mechanism is postulated involving two chain sequences, one of which is inhibited by added lo2. A comparison with other ozone systems is made, and the chain lengths are far greater for ozone + thiophene than other systems, under the conditions employed. Possible intermediates in the mechanism are discussed.

The gas-phase oxidation of organic sulfur compounds

“…Likewise, Atkinson et al [18] reported that the rate coefficient of 03 with thiophene was slower than they could measure, the upper limit being 6 x 10 -20 cm3/molec-/s. This is consistent with the value found by Kaduk and Toby [16] at 298K, and is also in concordance with the finding of Becker et al Ill] that the 03 + H2S reaction is also slow, with a rate coefficient ~ 2 x 10 -20 cm3/molec./s. Thus, the reaction of 03 with sulfides and mercaptans probably proceeds through a free-radical chain.…”

“…In all cases the chemiluminescence resembled that from the SO + 03 reaction, and the investigators concluded that the reactions produced SO as a precursor to the chemiluminescence. Kaduk and Toby [16] found a complex rate law for the reaction of 03 with thiophene between 30 and 125°C over a pressure range of 0.005-0.3 Torr 03 and O.l-I Torr thiophene. The rate law was first order in thiophene but had two components, one of which was first order in 03 (ka) and one of which was second order in 031(kb) The Arrhenius expressions for these rate coefficients are: log (k a, M_-sec -i) = 7.8 ± 0.5 -(8400 ± 700)/2.3RT and log (k b, M_-2sec "I) = 12.4 ± 0.4 -(4700 ± 400)/2.3RT.…”

Kinetics of the reactions of O3 and OH radicals with furan and thiophene at 298 ± 2 K

“…The present upper limit of <6 X 10-20 cm3/molec-s for the rate constant for the reaction of O3 with thiophene is only just lower than the value of 7.3 X cm3/molec.s calculated at 298 K from the Arrhenius expression of Kaduk and Toby [6]. Although the rate constant data of Kaduk and Toby 161 were subject to significant uncertainties due to secondary reactions involving long chains [6], this may indicate that Kaduk and Toby [6] overestimated the primary rate constant from their observed ozone decay rates.…”

The evaluation of rate constants in rate laws containing two terms

“…IJnder such conditions it obviously would not be possible to measure the primary rate constant from measurements of the overall rate. Typical chain lengths, however, are much shorter, and a recent compilation [13] for some reactions of ozone gives values from unity to 50, and with normal experimental precision such systems are amenable to the method we have described. The method has been checked with data from three different kinetic systems, and it is about an order of magnitude faster than graphical [9] or differential I151 methods previously used.…”