Isopropylamine extraction from glyphosate herbicide

Isopropylamine, or 2-aminopropane, is an organic amine used mainly in herbicides and as a chemical intermediate. It is a colourless, highly volatile liquid with the strong rotten-fish smell typical of many amines. There are several reactions I plan to try out with isopropylamine in the future.

Isopropylamine can be fairly easily extracted from glyphosate herbicides. The herbicides contain the amine in the form of the glyphosate salt. The glyphosate is precipitated by adding hydrochloric acid, which leaves the isopropylamine in solution as the hydrochloride salt. Sodium hydroxide is then added to the solution to freebase the amine, which is distilled out of the mixture in fairly pure form.

To a 1000ml beaker, I added 500ml of Number 8 Ready To Go Glyphosate 360 Weedkiller (0.789 moles of isopropylamine glyphosate). With stirring, I poured in 88ml of 33% hydrochloric acid (0.789 moles of hydrogen chloride) and left the mixture to stand for 10 minutes. With addition of the hydrochloric acid, the mixture rapidly became cloudy as a dense white precipitate began to form. After 1 minute, a dense mass of crystals had precipitated. The crystals should in theory consist of N-(phosphonomethyl)glycine (glyphosate), however it's possible that the hydrochloric acid may cause the surfactants in the herbicide to precipitate as well. Anyway, I filtered the heavy white precipitate off, collecting the filtrate in a 1000ml conical flask. 40g (1.00 moles) of sodium hydroxide were then added to the mixture in small portions, with swirling of the flask between additions. A fairly violent reaction was observed with each addition and immediately an intense aroma of rotten fish was noticed. Once the addition was complete, I stoppered the flask and allowed it to cool to room temperature. I then poured the contents of the flask into a 1000ml flat-bottom boiling flask. Thankfully isopropylamine does not form an azeotrope with water, so distillation can be used to extract the amine. A stillhead, condenser, vacuum adapter and receiving flask were attached and a distillation was performed. Boiling water was used as the heat source. The isopropylamine gradually came over at 40-50 C as a colourless liquid.

After a while, I decided that just hot water was not a satisfactory heating source, so I placed a hotplate below the water bath to maintain a temperature of around 90 C. The heat was occasionally adjusted so the vapour temperature stayed at 40-52 C. When no more isopropylamine came over at this temperature, the distillation was ended. I dried the isopropylamine over sodium hydroxide, then redistilled it, collecting the fraction boiling at 30-41 C. Finally, I transferred the product to an amber vial for storage. I got 18ml (0.209 moles) of isopropylamine as the dry freebase. This represents a 26% yield. The density of the product was 0.601g/cm³ which is pretty close to the 0.988/cm³ of pure isopropylamine.

The distasteful smell of isopropylamine wasn't quite as bad as I was expecting. However, the foul odour was still quite unpleasant whenever I was working directly with the compound. Fishy ammoniacal, with a slight rancid note is how I would personally describe it.

The addition of hydrochloric acid at the beginning of the procedure is probably not necessary. I only added this step because I wanted to recover the glyphosate in solid form for easy disposal.


C3H9N.C3H8NO5P + HCl ==> C3H8NO5P + C3H9N.HCl

C3H9N.HCl + NaOH ==> NaCl + H2O + C3H9N