At work I learned about paraldehyde, a polymer made of three acetaldehyde molecules. It’s an undesirable product for the process I am working on, so considerable time this week was spent  looking up if it can be broken up back into acetaldehyde.

Reversible paraldehyde reaction from H. Kawasaki et al. Applied Thermal Engineering 19 (1999) 133-143

That led me to “Proposal of a chemical heat pump with paraldehyde depolymerization for cooling system” where researchers at the Tokyo Institute of Technology propose a heat pump that utilizes this reversible reaction. The formation of paraldehyde is exothermic, which would form the hot side of the pump releasing the stored energy, and the depolymerization is endothermic making up the cold side. They refer to two papers regarding materials to catalyze the reaction.

The first paper “Kinetics of the depolymerisation of paraldehyde in aqueous solution” (DOI:10.1039/JR9540000774) tested strong and weak aqueous acids. The strong acids included hydrochloric, sulphuric, and nitric acids. The weak acids were dichloroacetic, trichloroacetic acid, and potassium bisulfate. Bell and Brown find that the reaction rate is first order for strong acid, but for the weak acid some sort of catalysis occurs with the acid anions and the reaction rate is much faster than any of the strong acids. An interesting takeaway from the article is the proposed mechanism. Bell and Brown propose that without the catalyst, the depolymerization of paraldehyde is a single step through an electron rearrangement initiated by a hydrogen from the acid.

paraldehyde rearrangement
Electronic rearrangement mechanism of paraldehyde to acetaldehyde, Bell and Brown, DOI:10.1039/JR9540000774

When in the presence of an weak acid, the mechanism is a two step reaction. It could be the weak acids provide a support to stabilize the intermediate fragment. By requiring each part to line up so conveniently, the rearrangement is probably less likely to occur successfully. paraldehyde 2 step

Two step decomposition reaction, Bell and Brown, DOI:10.1039/JR9540000774

The other article is “The mechanism of depolymerization of paraldehyde catalyzed by solid acid” (pdf link here) which tested nickel sulfate and silica alumina catalysts. They further improved Bell and Brown’s homogeneous phase mechanism with a rate equation, but also worked on a heterogeneous catalyst mechanism and rate equation. The found the reaction follows the Michaelis-Menten law for nickel sulfate, and that the nickel sulfate resulted in a faster reaction than the stronger acid of silica alumina.

For the heat pump above, Bell and Browns work was probably of interest for the potassium bisulfate, and in Tanabe and Aramata’s work the nickel sulfate since the heat pump must have a solid catalyst, a liquid catalyst would not be easily trapped and could quickly ruin the heat pump. They end up using Amberlyst15E, which they don’t cite literature for. I’m going to guess it’s something they tested themselves. They say the coefficient of performance is the same as R-134a, so does that mean it can be used wherever R-134a is currently used? Or are there other limitations? It’s interesting though, from working with it I was told that acetaldehyde is very quick to react with itself to form side products. Kawasaki et al. mention crotonaldehyde as the sole side product, which occurs in the presence of a basic catalyst. Seems like aldol condensations should be a concern for the longevity of such a system. Additionally, I would think that acetaldehyde deviates significantly from the ideal gas assumption, so I would imagine a real system will behave differently.  Anyways, I thought the premise was really neat. Here, someone took a side product I want to get rid of into a useful application.

On a fun note, is the “Things I Won’t Work With” blog on Science magazine’s website. Derek Lowe humorously writes about all the chemicals he won’t touch and all of the (rightful) reasons why. In the piece on dimethylcadmium, he writes on purifying the material as “the rare experience of being bored silly by something that’s trying to kill you.” A personal favorite, currently working in the fragrance industry is “its odor is variously described as “foul”, “unpleasant”, “metallic”, “disagreeable”, and (wait for it) “characteristic”, which is an adjective that shows up often in the literature with regard to smells, and almost always makes a person want to punch whoever thought it was useful.” The one on dioxygen difluoride (FOOF) was how I was introduced. I’ll quote two sentences from it and let you read the rest of it, because if this doesn’t get your interest nothing will.

The paper goes on to react FOOF with everything else you wouldn’t react it with: ammonia (“vigorous”, this at 100K), water ice (explosion, natch), chlorine (“violent explosion”, so he added it more slowly the second time), red phosphorus (not good), bromine fluoride, chlorine trifluoride (say what?), perchloryl fluoride (!), tetrafluorohydrazine (how on Earth. . .), and on, and on. If the paper weren’t laid out in complete grammatical sentences and published in JACS, you’d swear it was the work of a violent lunatic.

To finish off, I would like to refer to the late Toys ‘R’ Us. Jeff Spross writing for The Week (some sort of internet publication) wrote how the collapse of what was once the cornerstone of the toy industry failed not because people weren’t buying toys. On the contrary, Toys ‘R’ Us was on the up and up when it went bankrupt. The real reason is that investment firms bought up all of the shares for the company using borrowed money  back in the 90s, and then charged that debt to Toys ‘R’ Us. On top of the debt, the firms Vornado, KKR, and Bain Capital charged the company fees for the management services. The debt was so massive that there was simply never a chance to pay off these debts. For the investment firms, it didn’t matter since they made their money back and then some, so despite Toys ‘R’ Us going bankrupt, they made out in the black. It’s an interesting read.