Organic chemists like myself spend a lot of time searching for cheap sources of starting materials. An organic chemist is primarily interested in synthesis. That’s our training, our focus. Synthesis is the art of transforming one organic molecule into another. We begin with a simple molecule made up of carbon atoms, and we transform it into a different molecule using a chemical reaction. One part of the starting material molecule gets tweaked and we end up with something else. Once we have the product purified and we’ve positively identified it as the correct material, we may then use another reaction to take it a step further. The sequence continues until we reach the desired molecule. While the correct choice of reaction is obviously important, another critical choice is the nature of the starting material.
Theoretically, any organic molecule can be made from acetylene gas, which has a very simple structure and is very cheap. However, in practice, we try to select a starting material that already has a somewhat complicated structure. Ideally the structure would only need one or two steps of synthesis to reach the desired product. Choosing a starting material that already has a complicated structure can be very expensive, as they can be difficult to make. That is why there has been a movement towards “green” chemistry. Many chemists are now trying to minimize the impact of synthetic chemistry on the environment. More importantly, we try to obtain chemical starting materials from natural sources which are cheap and easily renewable. One such source is rice husks. The husks are inedible, which means that about 20 percent of the weight of harvested rice goes to waste. It’s a shame, because the discarded husks have some glorious molecular structures, from a chemists point of view, and over a hundred million tons of rice husks are thrown away every year.
That’s why I was happy to read a recent article published in the American Chemical Society’s Journal of Agricultural and Food Chemistry. The researchers, a group from Korea, took a sample of rice hulls and pyrolyzed them. Organic (carbon-containing) materials such as rice usually burn very well in air to produce carbon dioxide and carbon monoxide gas. To avoid losing the important carbon atoms to the atmosphere, the researchers heated the rice hulls to high temperatures (>400 degrees) in the absence of oxygen. With no oxygen gas to produce the carbon dioxide / monoxide, the materials instead decomposed. Organic materials are linked by covalent bonds, which are strong enough to withstand normal wear and tear but they’re nowhere near as strong as the ionic bonds found in table salt. After the rice hulls underwent this controlled thermal decomposition (called pyrolysis), the resulting powder was rich in a wide variety of carbon-rich molecules – over 160 different compounds. When this was dissolved in water, the resulting black liquid had a pleasant smoke aroma and taste and analysis of it’s composition showed it to be safe for eating.
The researchers suggest in their article that this material could be used as a smoke flavoring to be sold to consumers. However, there are already “liquid smoke” formulas on the market that are made from wood pyrolysis, and so there would have to be an additional incentive for companies to produce this rice product. With that in mind, the Korean researchers tested the liquid extract in Petri dishes and also in live mice. They discovered that the extract acted as a powerful antioxidant, protecting cells against harmful free radicals. The material was also found to be an anti-allergic and an anti-inflammatory. Skin application of a 1% concentration liquid significantly reduced inflammation in mice. The researchers suggest that these results show the potential value of rice hull smoke extract. I have to agree with them. I’ve developed numerous patent pending technologies that transform “waste products” from agriculture into valuable products, and so I have an appreciation for what the researchers have been able to accomplish here. It’s exciting because there will be less waste being burned or dumped, and there will be potential new medicinal treatments emerging in the near future.
The source of this article can be found at:
Kim, S.P., et al. “Composition of liquid rice hull smoke and anti-inflammatory effects in mice”. Journal of Agricultural and Food Chemistry 2011, 59, 4570-4581.