Wednesday, July 10, 2013


The most bizarre term in all of polymer chemistry, and probably organic chemistry as well is that awful word from polyurethane chemistry that sticks to your tongue and leaves your mouth with all the ungainliness of a 3-legged horse wearing a cast and using crutches - "allophanate". Pronounced as "al-LOFF-a-nate", the term describes the product of a reaction between a urethane and an isocyanate.
That -N-(C=O)-N-COO- entity is what the fuss is all about.

Take a course in polyurethane chemistry and you will encounter the term from anyone trying to impart a "complete" knowledge of urethane chemistry upon your brain. Although a common reaction for isocyanates is to form urethanes upon addition of an alcohol, formation of allophanates from the excess isocyanate is rather uncommon as the reaction is much slower than the primary with alcohols is.

I did some digging to find origin of this putrid term and was surprised that it has actually been part of the chemical literature for almost 170 years. It turns out that a certain J. Liebig and F. Wöhler [*] described the formation of allophanic acid in the March 1, 1847 edition of the Chemical Gazette. Allophanic acid was the product of a reaction between cyanic acid and alcohol. Being the good chemists that they were, they immediately starting making esters of it - hence allophanates. The Merriam-Webster online dictionary gives the etymology of the word as coming from the Greek allophanes, meaning "appearing otherwise".

Since isocyanates also react with amines to make ureas, you shouldn't be surprised to find that there is an amine analog to the allophanate called a biuret, a term that is just another ho-hum chemistry term, but it sort of makes sense as the grouping is 2 ureas sharing a common nitrogen atom. What is rather strange however, is that there are mentions from long ago of a biuret also being called a allophanamide. After about 5 tries at pronouncing this and in most cases giving up halfway through because things were just falling completely to pieces, I think it would likely be pronounced as al-lo-PHAN-a-mide.

So answer me this: Somehow the allophanamide was able to cast aside it's horrible birthname - how come we can't do the same for the allophanate?

[*] Oh great! Now I'm picking a battle with the founders of organic chemistry!

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