Sciencemadness Discussion Board

Electrochemical alkoxide production

Swede - 5-12-2012 at 08:45

I read an interesting tidbit in Wikipedia:
Quote:

Many alkoxides can be prepared by anodic dissolution of the corresponding metals in water-free alcohols in the presence of electroconductive additive. The metals may be Co, Ga, Ge, Hf, Fe, Ni, Nb, Mo, La, Re, Sc, Si, Ti, Ta, W, Y, Zr, etc. The conductive additive may be lithium chloride, quaternary ammonium halogenide, or other. Some examples of metal alkoxides obtained by this technique: Ti(OC3H7-iso)4, Nb2(OCH3)10, Ta2(OCH3)10, [MoO(OCH3)4]2, Re2O3(OCH3)6, Re4O6(OCH3)12, and Re4O6(OC3H7-iso)


I decided to give it a try, with the goal being a solid alkoxide, Titanium (IV) methoxide, or tetramethyl titanate.

In a small beaker, I added ~50 ml of methanol. Conductivity, tested with a simple ohmmeter, was nil. I added small portions of lithium chloride until the solution was capable of conduction.

Two electrodes were prepared from CP titanium sheet. These were immersed into the beaker, and voltage gradually increased.

The cell conducted immediately, and vigorously. I noticed an interesting reaction taking place... high current would turn the solution black, opaque. Turning OFF the current, the solution cleared! I repeated this a couple of times to verify it, and I am attributing this to the lithium component.

I dialed the current back to a more reasonable 200 Ma, and let it run for 3 hours. The result was the evolution of milky white solids, which settled to the bottom of the beaker.

Tetramethyl titanate is sensitive to water, and hydrolyzes rapidly, so I suspect what I have is simply titanium dioxide. I'm going to set up my MP rig and see if a sample melts at 200 C, which is the published MP.

The reaction overall was quite interesting, and I'm tempted to try again with anhydrous methanol, and a little more care taken w/regards to the setup and procedure. I took a few pics and I'll get them up if people are interested.

smaerd - 5-12-2012 at 13:40

I'd love to read more. I'd also be interested in seeing what kind of set up you would use to be moisture sensitive.

I wonder if it would work for Ti(IOPr)4?

Swede - 5-12-2012 at 17:23

As expected, the white solids (there was a lot) was TiO2. The methanol I used was technical grade and undoubtedly loaded with water.

I am going to repeat the experiment on a larger scale with anhydrous methanol. I'd try it with ethanol, but all I have is denatured, and no source of anhydrous ethanol.

On second thought, the methoxy product is a solid at RT, while the ethoxy is liquid, so separation is easier with the methyl.

I have no experience and no idea on how to handle tetramethyl titanate, and how rapidly it might decompose in the presence of atmospheric water and O2. Nothing for it but to try.

Smaerd, AFAIK if the solvent is an alcohol, there is a chance, given that the anode is the desired metal (like titanium), it might work. Separation of a liquid product without decomposition might be a challenge. And I was unable to find solubility of lithium chloride in methanol, so I simply eye-balled it. A proper methodology, when the product is a solid, would be to saturate the electrolyte with LiCl, and filter or otherwise ensure that what goes into the cell is devoid of solids. Per the Wiki article, there are "others" that provide conductivity in an otherwise unconductive electrolyte, but I don't know what they are, nor do I have any experience with them.

killer_lapin - 25-12-2012 at 19:34

Sounds pretty interesting. You can dry your methanol with anhydrous MgSO4, aka epson salt that have been dried in over at broil.

Swede - 28-12-2012 at 07:15

I still plan on giving this a shot, but the pressing need to synthesize a titanate was solved by simply purchasing it. :D

The amount of Ti shed from the anode was impressive for such a small setup. Scaled up, with proper procedure, I think yields would be good.