Boron nitride

Boron nitride is an interesting compound used in ceramics and cosmetics. It's moderately heat resistant and can withstand temperatures up to 2,800 C in the absence of oxygen. Boron nitride occurs in several different forms, which are structurally very similar to the allotropes of carbon. Graphite, diamond and lonsdaleite each have boron nitride analogs.

There are several good ways to make boron nitride. I tried a couple of them out. The reaction of urea with boron trioxide I found to be by far the most reliable, so this is the one I decided to present in this post.

The first step is to convert boric acid to the required boron trioxide.

To a metal can, I added 16g of boric acid. I then strongly heated the can over a camping stove. The boric acid began to melt and give off steam. The mixture became a glassy bubbling syrup as the boric acid was converted to boron trioxide. After about 15 minutes, the bubbling had almost completely stopped and I allowed the mixture to cool. Upon cooling, the boron trioxide solidified into a brittle glass-like substance. I scraped the product out of the can and was left with 8.6g of boron trioxide.

With boron trioxide prepared, I moved on to making the boron nitride.

I ground up the 8.6g of boron trioxide (made above) with 20g of urea. I then poured this mixture into a metal can, which I heated over a camping stove for 30 minutes with gradually increasing heat and fairly constant stirring. The mixture formed a bubbling melt, which diminished after a few minutes to a solid mixture. If the heat is increased too rapidly, a significant amount of boron trioxide can fail to react. I made this mistake, so after the 30 minutes of heating, I added an additional 10g of urea and continued heating for 10 minutes. This probably wouldn't have been necessary had I not started heating so strongly at the beginning.

Anyway after this, I allowed the mixture to cool to room temperature. I then crushed the mixture up and added it to a 150ml beaker containing 75ml of dilute hydrochloric acid. I left this to soak overnight. The next morning most of the white boron nitride had settled to the bottom of the beaker. Above it there was a thin layer of brown material. I stirred the mixture up, waited until the most of the boron nitride had settled, then carefully decanted and discarded as much of the supernatant liquid-brown material suspension as I could. I then washed the residual boron nitride with 100ml of cold water. I filtered off the boron nitride, washed it on the filter with 20ml of ethanol, then dried it. I was left with 2.15g of white boron nitride which is a 35% yield.

The procedure I was following (here) called for boiling the product in water to purify it. However I've found in previous runs that this tends to completely destroy the product. It's well known that hot water reacts with boron nitride, so I'm not sure why they suggest this method of purification.

2 B(OH)3 ==> B2O3 + 3 H2O    /   B2O3 + (NH2)2CO ==> 2 BN + 2 H2O + CO2

B2O3 + 3 C2H5OH ==> (C2H5)3BO3 + B(OH)3

Myristic acid synthesis

Myristic acid, or tetradecanoic acid, is a fatty acid with very few common uses. It is however, a useful organic building block. Under standard conditions, myristic acid is a low melting white crystalline solid. I'm not sure if I'll use my myristic acid for anything, although maybe I'll make some myristyl alcohol or a myristate ester.

Myristic acid can be made by the alkaline hydrolysis of trimyristin. This is a fairly easy and straightforward synthesis.

To a 500ml round-bottom flask, I added 1.43g of trimyristin and a solution of 11.43g sodium hydroxide in 48ml of water. I then added in 45ml of ethanol and attached a Liebig condenser to the flask. I refluxed the mixture for 1 hour and 30 minutes on a medium heat, adding in an additional 10ml of ethanol after the first 45 minutes. The trimyristin dissolved quickly and the liquid turned red, but after this, there wasn't much visible change. Once the reflux was complete, I let everything cool to room temperature. I then poured the mixture into a 200ml conical flask. At this point, the mixture consists of mostly sodium myristate dissolved in water. To get the myristic acid, the sodium myristate must be acidified with a strong acid. So I added 27ml of 33% hydrochloric acid. The red colour lightened to a yellow and the mixture became cloudy. I did add in a little bit more hydrochloric acid by accident, which was completely unnecessary.

Anyway, after a few minutes, a white precipitate of myristic acid began to collect on the bottom of the flask. I chilled the mixture down to get as much myristic acid to crystallize out as possible. A bit of unreacted trimyristin floated on top of the liquid and this was carefully decanted off. I then filtered off the myristic acid, washed it with 50ml of water, then dried it. I got 0.36g of myristic acid, which is a 27% yield.

I'm honestly not sure why the yield was so low.

(C13H27COO)3C3H8 + 3 NaOH ==> 3 NaC13H27COO + C3H8(OH)3

NaC13H27COO + HCl ==> C13H27COOH + NaCl

Oxidation of toluene to benzoic acid

Benzoic acid is an aromatic carboxylic acid used as an organic building block. It occurs naturally in a wide range of plants, and is used as a food preservative. It's also an ingredient in many cosmetics. I plan to use benzoic acid to synthesize Benzamide and eventually aniline.

Benzoic acid can be made very easily from toluene. I did a test run to see if I could get this to work.

To a 250ml beaker I added 15g of potassium permanganate and 157ml of water. With a bit of stirring, most of the potassium permanganate dissolved giving a dark purple solution. I then added this solution (and the small amount of undissolved potassium permanganate) to a 500ml round-bottom flask. Next I added 35ml of technical grade toluene and attached a liebig condenser to the flask. I then strongly refluxed the mixture for 2.8 hours. The mixture gradually darkened as the potassium permanganate was converted to brown manganese dioxide. After 2.8 hours of reflux, I allowed the mixture to cool to room temperature. The purple colour of permanganate had completely gone, indicating all potassium permanganate had been consumed. I filtered the mixture to remove the manganese dioxide by-product. Manganese dioxide is a useful chemical to have, so I kept mine rather then discarding it.

 Anyway, I transferred the clear filtrate to a 250ml beaker, a small layer of excess toluene floated on top of the surrounding liquid. I removed the toluene with a syringe and saved it for future runs. After this, I was left with about 125ml of liquid in the beaker. This is a solution of potassium benzoate in water. I slowly added 33% hydrochloric acid to the solution and fluffy white crystals of benzoic acid precipitated. I kept adding hydrochloric acid until no more precipitate formed.

I then filtered off the benzoic acid and dried it. I got 2.45g of benzoic acid as fine fluffy white crystals.

The reason for the small amount of product obtained was my scales which were broken and gave a false reading.
Due to this I actually used a lot less than 15g of permanganate. I have no idea how much permanaganate I used so I can't calculate the real yield.

2 KMnO4 + C6H5CH3 ==> KC6H5COO + 2 MnO2 + KOH + H2O

KC6H5COO + HCl ==> C6H5COOH + KCl