SCAVENGING OF HYDROCARBON RADICALS FROM FLAMES WITH DIMETHYL DISULFIDE .1. CHARACTERIZATION AND DISCUSSION OF THE METHOD AND THE SCAVENGINGPROCESS

The method of scavenging free radicals sampled through a rarefied free -jet from stationary low-pressure high-temperature reaction systems (f lames, pyrolysis) in the condensed phase of dimethyl disulfide (DMDS) has been studied systematically. For this purpose the flat open conden sing device originally used has been replaced by a condensation trap c onsisting of two stainless-steel hemispheres cooled with liquid nitrog en. The scavenging products were separated and identified by GC/MS. Th e condensing efficiencies of the scavenger DMDS and condensable substa nces from the reaction system were so determined as to make the scaven ging R+CH3SSCH3-->RSCH(3) + CH3S a quantitative method of radical anal ysis. It is shown that with a sufficient excess of DMDS the scavenging reaction takes place to 90-100% for hydrocarbon radicals with two or more C atoms, with a slight interference from addition reaction of rad icals to condensable unsaturated products from the reaction system. Th e type of reactions with mono- and divalent radicals and carbenes in t he solid DMDS matrix are investigated. Consecutive reactions during wa rming-up are also studied and discussed. It is stated that this scaven ging method is well suited for the analysis of all hydrocarbon radical s heavier than ethyl, provided that the scavenging products can be sep arated and identified, which might become a problem with heavy polycyc lic aromatic radicals.