Thursday, April 23, 2009

47) Simplest Organic Redox Cycle

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Harold J. Morowitz mentions a simple system of redox cycles of CO2 +H2O yielding formaldehyde and O2 and back again catalyzed by Fe2+/3+ under sunlight/shade, can we do that lab? how would we detect it's working? I suppose the BZ reaction is already more complex and it has a visual indicator!

If I have a vat of water (with CO2 dissolved in it ) over some catalyst, such as Fe++ ions, spread on the bottom, and I let high energy light (like ultraviolet) strike the catalyst on one side and leave the other side in the dark, we get something like Benard convection. On the lit side we get CO2 + H2O yielding higher energy molecules: CH2O + O2, these will diffuse to the dark side and oxidize back to CO2 and H2O, and as the catalyst on the light side use up all the CO2 there, the CO2 from the dark side will diffuse back to the light side, forming a cycle. This is theoretical, I haven't done it, or seen a physical description of it. The BZ reaction, however, under similar non equilibrium conditions does produce spiral wave patterns. These patterns from above might look stationary but they are made out of migrating molecules, so they are a different sort than patterns in crystals and snowflakes.

Notice that we need a hot side AND a cold side. If i we shone the UV light on the whole vat of water, and insulated the vat so that no heat was able to escape, the molecules would just build up more and more complicated gunk as the temperature rose, and then as the temperature rises even higher they would eventually come apart until the whole setup would be as hot as the UV source and it would consist of a random plasma of atomic ions. NO PATTERN, gotta have the hot and cold.

can I do a reaction like this?

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