Greener Nylon Synth? Just Add UV and Ozone!

"Any sufficiently-developed technology is indistinguishable from magic" - Arthur C. Clarke

Looks like we'll soon have a more straightforward way to make stockings, zip-ties, and tire belts. 

Adipic acid, a six-carbon diacid representing one of the "sixes" in Nylon 6-6, apparently takes quite a bit of industrial "elbow grease" to make. The current process, starting from cyclohexane, requires cobalt, manganese, copper, and vanadate salts, high pressures of oxygen gas, and hot nitric acid. Out the other side, its responsible for 5-8% of the nitrous oxide we humans spew into the atmosphere each year.

From Science 2014, Hwang and Sagadevan

Now, researchers Hwang and Sagadevan (National Tsing Hua University, Taiwan) believe they have a better method. Reporting in this week's Science, the two disclose a method that sounds so much simpler: flush a sample of cyclohexane with ozone and UV light, and, presto! Solid adipic acid at the bottom of your reactor. No metal salts, no nitrous oxide, no high pressures or temperatures.

Wow, that looks a lot simpler.

The researchers note that zapping ozone produces both singlet oxygen, ¹O₂, and a single singlet oxygen atom O(¹D). The highly reactive single singlet (say that three times fast!) can easily insert into C-H bonds, and, since it seems to prefer insertion next to an already-oxidized carbon, the diol, diketone, and finally diacid products are formed preferentially.

Applause, please: Look at this beautiful pictorial SI!
Twice, in two days.

Just for fun, Hwang and Sagadevan crack open some larger hydrocarbons, and check the selectivity of alkyl-functionalized rings and aromatics. There are tantalizing possibilities here that I'm sure, given the ease of this reaction setup, most organic chemists will already be trying: how do complex natural products* react under these conditions? If anyone tries it this weekend, please drop me a line.

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*For that matter, I wonder if this pathway is operative in human tissues under physiological conditions? Sunlight does have some 300 nm band, and we certainly come into contact with ozone out in the wide world. Hmm.

More Car Talk "Chemistry"

Regular readers know my fascination for all things NPR, and Car Talk in particular. This week's broadcast had me rolling in the aisles for a different reason: some cover-your-eyes-awful chemistry.

A "white residue" in the engine?
Get the peanut butter!

Let's set the scene: Tom and Ray had taken a call from Ann, who begged that they were her "last hope" for an aging, ailing Subaru wagon. Ann's son apparently noted a funny white "mist" coming out of the car a few months ago. After several expensive repairs (heater core, radiator), a white, powdery substance was still forming in the engine block.

The guys considered that a single engine part had failed, perhaps something plastic or rubber, but discarded that theory since previous repairs had not fixed the problem. Then Tom suggested that the car might be continuously producing the white residue, perhaps through combustion gases which found their way into the radiator fluid through a leaky gasket.

Tom short-listed some potential combustion "bad actors" - carbon, carbon dioxide, carbon monoxide, nitrous oxide. Aha! The nitrous oxide must be forming nitric acid, thus corroding the engine block. "It's Chemistry 101!" he exclaimed.

Except...not. I know that nitrogen dioxide or NO_x emissions from cars generate nitric acid in the presence of water, but last I checked, whipped cream cans and dental offices everywhere remained safe from acidic corrosion.

Undaunted, through admitting "I have no idea, I'm just making it up," Tom pressed on: perhaps a salt, such as copper nitrate (a blue solid) or, even better, copper carbonate ("It just sounds more white, like sodium bicarbonate") gummed up the works. Maybe, since the heater core was made from aluminum, that was the culprit?

Tom: "What about aluminum carbonate, A-L two C-O three!"
...or, maybe Al₂(CO₃)₃?

Finally, Ray chimed in: "MIT's on Line 1, they want their diploma back."

Happy Saturday,
SAO

Note: I paraphrased this conversation as best I could, since the recording hasn't yet appeared online. When it does, you can hear the full 3/30/13 episode at cartalk.com.