This afternoon I attempted to decarboxylate nicotinic acid (niacin) via CuCl2 to produce pyridine. This synthesis has been done successfully before by
others on this board (Magpie, ubungy, and others) using various sources of Cu(II) including copper chromite, copper carbonate, and copper hydroxide.
My reaction was unsuccessful, most likely due to insufficient heating.
Materials:
Niacin (1kg), phil-outlet on ebay
CuCl2, provided from an old science teacher, origin unknown.
Procedure:
50.0g of niacin and 5.5g of CuCl2 were massed and mixed thoroughly on a piece of craft paper using the "diaper method" to reduce dust production (10%
by mass CuCl2). A 500mL round bottom flask was charged with the niacin/CuCl2 mix and set up for distillation with a 3 way adapter, 150 degree
thermometer, 600mm liebig condenser, 105 degree adapter, and 250mL receiving flask. The 500mL flask was partially submerged into a hot corn oil bath,
heated by a 1000W hot plate. The hot plate was turned on and the oil bath was heated to its smoking point.
When the temperature in the stillhead reached 64 degrees (approx. 20 mins), condensation was visible. For the next hour the still head temperature
hovered between 72 and 74 degrees. After a total of one hour and twenty minutes, only one drop of distillate was recovered.
The reaction failed to work most likely because of the oil temperature. Typical corn oil has a smoking point of 232 degrees which was close to
ubungy's reported reaction oil temperature of 235 degrees. However, unrefined corn oil has a much lower smoking point of 178 degrees. I believe my
corn oil was unrefined, producing an insufficient temperature to start the reaction. For those looking for an oil bath oil, beware that some grocery
store oils may not thoroughly processed to yield the highest possible smoking points. I will be re-attempting this reaction in the coming months,
either using a higher smoking oil or with some type of flame based heat source (alcohol lamp, propane torch, etc).
Thanks for the write-up Alkoxide, unsuccessful experiments are often just as important as successful ones.
I would recommend using a flame source the next time you try the experiment. I know that the dangers of heat stress and flammable gasses are often
cited as reasons for using an electric heat source, but I find that a good setup can eliminate these problems.
I myself use a gas cooker hooked up to a barbecue propane tank that I operate outside. I place my round bottom flask above the cooker inside of an
empty saucepan isolating it from the flame and providing extremely even heating. This method has the advantage of having a very low thermal mass (so
it's quick to get going) and not leaving any oily mess behind.
The setup can also reach pretty high temperatures - I don't think I've ever used it at above half it's output power.UC235 - 11-10-2015 at 16:36
I'm not sure why you used an oil bath. It is not necessary to do so (in this case) and significantly lowers the possible temps your hotplate can
reach. Just use an air bath and tent with aluminum foil if necessary. If you look further down on Magpie's thread I have a writeup using this
technique and a very small catalyst loading of copper chromite.morsagh - 16-10-2015 at 08:28
Why not just decarboxylation in calcium or sodium hydroxide? For benzoic it worksUC235 - 16-10-2015 at 14:20
Why not just decarboxylation in calcium or sodium hydroxide? For benzoic it works
Probably because copper-catalyzed decarboxylation of pyridine has been shown to be effective and high yielding. It uses less reagents and can be
performed in ordinary glassware at hotplate temperatures. There is a thread in prepublication on the subject started by magpie. I provide a writeup
using drastically less catalyst.
As for the thread starter, did the niacin melt at the oil bath temperature? While copper chloride may be effective, I imagine that copper carbonate
might work better and doesn't introduce HCl into the reaction.
