Ethylenes, ozonization rates

Ozone rate constants, 27 771 Ozone reactions activation of, 27 779 kinetics and mechanism of, 27 778-779 Ozone resistance, of ethylene-propylene polymers, 10 704, 717 Ozone synthesis, energy requirements for, 27 798... 

Slight improvements in sensitivity can be achieved by cooling the phototubes used to detect the emitted light or by increasing the ethylene flow rate. Chemiluminescence produced by the reaction of ozone with ethylene has been designated by the epa as the reference method for monitoring ozone. Several different commercially produced instru< ments are available. 

At atmospheric pressure, when the mixture was admitted through the aluminum tip, no ignition took place with hydrogen, cyanogen, and methane (ozone rate 6 cc. per second). Carbon monoxide and ethylene, however, ignited spontaneously and burned normally afterwards without initiating an explosion or detonation in the ozone line. 

The gas-phase reactivity of various terpenes has been measured. Stephens and Scott were the first to include two terpenes (pinene and a-phel-landrene) with their study of the relative reactivity of various hydrocar ns. Both monoterpenes showed the high reactivity predicted by their olefinic structure. Conversion of nitric oxide to nitrogen dioxide in e presence of isoprene is at a rate intermediate between those for ethylene and trans-2-butene, and Japar et al, reported rate constants for the a-pinene and terpinolene-ozone reactions. Grimsrud et a/. measured the rate con-... 

The effects contributed by alkyl groups to the relative rate constants, kreh for the reaction of ozone with cis- and trans-1,2-disubstituted ethylenes are adequately described by Taft s equation = k °reX -f pSo-, where So- is the sum of Taft s polar substituent constants. The positive p values (3.75 for trans- and 2.60 for cis-l,2-disubstituted ethylenes) indicate that for these olefins the rate-determining step is a nucleophilic process. The results are interpreted by assuming that the electrophilic attack of ozone on the carbon-carbon double bond can result either in a 1,3-dipolar cycloaddition (in which case the over-all process appears to be electrophilic) or in the reversible formation of a complex (for which the ring closure to give the 1,2,3-trioxolane is the nucleophilic rate-determining step). 

The trends in the ozonolysis rates of simple olefins require further examination. The object of the present work was to obtain kinetic data on the reaction of ozone with simple alkyl-substituted ethylenes. The results will allow a discussion of the substituent effects on the reaction rates and of the mode of ozone attack on the carbon-carbon double bond. 

These scattered observations indicate that ozonolysis of a halogen-ated double bond occurs at a much slower rate than that of a non-halogenated double bond, even if the former is part of the more strained ring system as in 6 or if the double is monohalogenated as in 8. This qualitative picture was substantially confirmed by the results of a quantitative study of the rate of ozone attack at variously chlorinated ethylenes (6). As shown in Table I, the rates of ozone attack decrease dramatically as chlorine is successively substituted for hydrogen in ethylene. 

The above data show that three pathways exist for the reaction of ozone with ethylene eoordinated and non-eoordinated addition in the singlet state and a reaction in the triplet state. The latter pathway is hardly possible for the thermal reaction the former two pathways exist in eompetition. To assess the effieieney of each pathway, we calculated the corresponding reaction rate eonstants. For this pmpose, a MOLTRAN program and results of the quantum ehemieal ealeulations were used to calculate the enthalpies (AH") and entropies (AS") of activation of the two reaction pathways. From the data obtained, the eorresponding rate constants k were ealeulated in terms of the standard transient state theoiy ... 

Figure 2. Visible emission spectrum from the chemiluminescent reaction of ozone with ethylene at room temperature (uncorrected for spectral sensitivity). Total pressure 0.4 torr flow rate of 0 /02 is 30 cc/min flow rate of ethylene 5 cc/min spectral slit width 10.6 nm.

---