Atmospheric Chemistry of Titan Options

[Juramike]

Here is a "Benzene-O-Vision" graphic showing the amount of benzene and phenyl radicals at high altitudes on Titan. This is based on detections of benzene and phenyl radical (which recombined in the sample chamber to make benzene) using the INMS instrument during closest approach. The numbers are normalized to constant pressure altitude, roughly 1000 km.



The data was taken from Table 1 in: Vuitton et al, Journal of Geophysical Research 113 (2008) E05007. "Formation and distribution of benzene on Titan". doi: 10.1029/2007JE002997 [EDIT 5/24/10: Article freely available here] and overlaid on a map of Titan.

The authors mentioned that the errors in these measurements are 20%.

These detections are well above the detached haze layer. Most are at the same sun azimuth angle. (T23 observation had the lowest angle.) Assuming that the temporal difference is minimal (each dot is from a different flyby), there doesn't appear to be an obvious correlation with latitude.

This graphic does show that benzene is present even waaaay up in the thermosphere and ionosphere.

[Juramike]

Whoops. You are right, it is allene not cumene. "Cumulene" (different spelling) is a generic term for compounds with two or more consecultive double bonds. Allene is the simplest of these.

Both allene and methylacetylene can exist in equilibrium. (equilibrium data here: http://en.wikipedia.org/wiki/Methylacetylene)

When I whipped this mechanism out, I woulda thought that the ring strain of the cyclopropene ring would be such that it would love to open up. However, now looking at "Carbenes, Nitrenes and Arenes" by T.L. Gilchrist and C.W. Rees, Appleton Century and Crofts, New York, 1969, I see that 1,1-dihalocyclopropenes are stable intermediates, and can be hydrolyzed to the corresponding cyclopropenone, at least if there are alkyl substituents on the cyclopropane double bond. (This results from a low yeild reaction of dihalocarbenes on a disubsituted acetylene).

Now with that little piece of information, I'd redo my proposed mechanism to have the radical carbene doing a C-H insertion, followed by radical jumping in and H. kicking out to initially form allene. Which then could equilibrates to methyl acetylene. Either way, you've got C3H4 - three carbon building block for further use....