Unlocking a variable for electrochemistry

Recently, much of my work has been focussed on using the Vapourtec Ion electrochemical reactor; one of the key features I’ve been investigating is control of temperature. The Ion can be heated well above ambient and cooled to below zero (as we’re still before the official release, I can’t tell you the absolute values), which opens up a vast chemical reaction space to explore. A quick search of the literature, which is already pretty light on electrochemical syntheses, shows that the vast majority of electrochemical reactions are carried out at room temperature; and there are very few examples of cooling an electrochemical reaction.

I suppose the most immediate question is “does temperature have any effect on an electrochemical reaction?” to which I can direct you to a couple of very interesting publications: A group at Pfizer published in 2017 that by incorporating electrochemistry into a nickel-catalysed cross-coupling, they were able to optimise the reaction with much greater control and achieve better conversions and selectivities than with the analogous activated metal powder reactions. The key point here is that the reaction is a thermally mediated coupling, taking place at 65 degrees, but the electrochemistry is used to help control and direct the outcome. A second paper earlier this year from Keio University, Japan, describes a palladium-catalysed iodination performed at 90 degrees. Addition of electrochemical oxidation improved the rate of iodination at hindered positions, and enabled the researchers to direct the reaction to one product over another. Exciting stuff, and both need the ability to heat the electrochemical reactor.

I think there are a number of other phenomena that are temperature dependent to consider: molecules adsorbing to electrode surfaces, followed by ions desorbing; changes in viscosity affecting rates of ion diffusion; the potential for non-electrochemical side reactions – all are worth considering and most probably influenced by the reaction temperature. Certainly in light of the recent literature, combining electrochemistry with thermal processes offers fascinating potential for directing the outcome of reactions.

Below are some HPLC traces for my model reaction – the methylation of 4-t-butyl toluene that I’ve written about before. The key point with these experiments is that methanol (reagent and solvent) is taken well beyond its boiling point in the high temperature example. This is only possible because the Ion has been designed to operate at pressure, specifically to allow super-heating of the solvent.

Looking at the results below (I’ve discussed elsewhere that the largest peak, due to an aldehyde, has a much stronger chromophore than the other materials – I have adjusted for this in my integration which is why the apparent peak areas don’t quite much the percentages), the influence of temperature is marginal for this reaction under these conditions.

The model reaction at low temperature – 79% conversion,  with 16% reacted over to the aldehyde
The model reaction at low temperature – 84% conversion,  and 10% of the products have reacted on to the aldehyde
The reaction at high temperature – full conversion, but 25% of the aldehyde

What I think is most exciting is the limited information in the literature regarding the effect of temperature on these reactions.

Pass me my pith helmet – there’s some exploring to do!

For more information about Vapourtec, click here.

Return on the 12th of September for the next blog about measuring the electrical behaviour inside the Ion

YouTube, You learn

With every R-Series purchased, Vapourtec provides training on-site after the installation. I quite often carry out training and I am always careful to be thorough, even laying traps for the users between experiments to see if they have learned or not. It’s always well received, but then I leave and after a few months, things can be forgotten or new users join the group and aside from the manual, that experience can be lost.

Enter YouTube. It’s the ideal platform to show some videos of an experienced user (which I humbly have to tell you, is me) going through the process of preparing and running a reaction, so that our users have something to refer to if they can’t quite remember. It’s a great idea and has been really well received, but recording the videos can be quite the experience. A professional video maker, Jim – from Green Spark Productions, arrives with a car load of cameras, lights, microphones, and my lab becomes a film studio. I always make an outline of the video, with key points that I need to cover at each stage, and I keep it nearby to refer to. But, to be honest, there are a lot of bloopers. In one particular video in which I am carrying a nanoparticle synthesis I have to say “iron tetrafluoroborate hexahydrate and 1,2,4-triazole” (which are the reagents for this particular synthesis). Needless to say, it took quite a few goes, and when I finally did say it, I had totally forgotten what I was supposed to say next. Not to mention dropping things…

Overall, it’s a great experience though. I’ve really enjoyed making the series so far and the benefits to our customers and distributors around the world are clear. Already (at the time of writing) one of the videos, a Suzuki coupling, has had just over 1000 views! People at conferences have even started mentioning them to me; it’s not easy being a super star, but I manage.

Autographs available on request.

For more information about Vapourtec, click here.

Return on August the 29th for the next blog about temperature control in the Vapourtec Ion


Carbon is carbon, right?

Electrochemistry at Vapourtec has come a long way in just a few short months! Our electrochemical reactor, now known as the Ion, can now operate under a wide range of temperatures, pressures, and using a variety of different electrode materials.

I’ve admitted before that my experience with electrochemistry is limited, and looking through the literature I feel I would be forgiven if I thought that electrode choice didn’t make a difference; especially when using materials such as carbon – I don’t mean electrode pairs, which of course will make a difference as different metals/conductors have different surface potentials.

Throughout the literature, graphite is often called upon to act as an electrode and, more recently, carbon-loaded polymers such as PVDF. The Ion has been designed to take a wide range of electrodes, and as carbon is available in so many different incarnations I thought it would be interesting to trial a bunch of different carbon electrodes under the same electrochemical conditions to see if it makes any difference.

It does.

Take a look below; the chemistry is a very commonly studied model reaction, oxidising 4-tertbutyl toluene with methanol to the methyl ether, then the acetal (the aldehyde can crop up as well (see the peak at around 6.4 mins?), but after extensive investigation I found that the aldehyde chromophore is 10 x more strongly absorbing than the toluene, so it’s never quite as bad as it looks).

Carbon electrode material 1
Carbon electrode material 2
Carbon electrode material 3
Carbon electrode material 4
Carbon electrode material 5

What I see right away is a big difference between each of the different materials. Carbon-loaded PVDF (material number 4) has resulted in a rather poor conversion with a significant amount of the aldehyde (even accounting for the stronger chromophore), whereas some of the other materials have quite high conversions, and some show the start of interesting selectivities. The baseline noise changes considerably between electrodes as well. Each measurement is preceded by a blank solvent run for comparison, and they always come through clean.

It just goes to show – not all carbon is equal…

For more information about Vapourtec, click here.