Synthesis of High Purity Nonsymmetric Dialkylphosphinic Acid Extractants

The overall goal of this protocol, is to introduce a universal synthetic method for nonsymmetric dialkylphosphinic acid extractants to a free radical addition reaction using sodium hypophosphite as a phosphorus source. The method can for a potential in the hydrometallurgy to develop a new dialkylphosphinic acid extractants. And novel potential extraction and separation with class of extractants.

Compared to the traditional method, which use phosphate as a phosphorus source, this method had the advantages of low toxicity, reaction conditions, easy purification, and potential for larger-scale production. The video takes two, three-dimethylbutyl-two, four, four-trimethylpentylphosphinic acid as an example, to demonstrate the synthesis of high-purity NSDAPA extractants. First, sodium hypophosphite reacted with two-three dimethyl-one-butene, mono-DMBPA.

Amantadine was adopted to remove the byproduct di-DMBPA, since only the mono-DMBPA can react with amantadine to form an amantadine mono-DMBPA salt, while the di-DMBPA cannot due to its large steric hindrance. The purified mono-DMBPA was then reacted with di-isobutylene to yield two, three-dimethylbutyl-two, four, four-trimethylpentylphosphinic acid. The unreacted mono-DMBPA can be easily removed by a simple base-acid post treatment, and other organic impurities can be separated out through the precipitation of the cobalt salt.

First, weigh the appropriate reagents into a 100 milliliter teflon-lined stainless steel autoclave. Place a magnetic stirrer into the autoclave and seal it. Place the autoclave in a vertical tube furnace placed on a magnetic stirring apparatus.

Start the magnetic stirring apparatus, and set the speed to 800 RPM. Then, start the heating program of the temperature controller connected to the autoclave. After the reaction is complete, transfer the mixture containing the product to a 250 milliliter one neck round bottom flask.

Remove the solvent and unreacted oliphants using a rotary evaporator. Following this, transfer the residues to a 250 milliliter separating funnel. Add 50 milliliters of four percent sodium hydroxide solution to the separating funnel, and shake vigorously.

After the phases have separated, transfer the bottom aqueous phase into a 500 milliliter separating funnel. Wash the organic phase three times with 20 milliliters of four percent sodium hydroxide solution to ensure that the aqueous phase exceeds pH 10. Then transfer the aqueous phases into the 500 milliliter separating funnel containing the first aqueous phase.

Add 90 milliliters of 10%sulfuric acid solution and 50 milliliters of ethyl ether to the separating funnel containing the combined aqueous phases, and shake vigorously. After the phases have separated, transfer the top organic phase into another 500 milliliter separating funnel. Extract the aqueous phase three times with 30 milliliters of ethyl ether.

Then transfer the organic phase into the 500 milliliter separating funnel containing the first organic phase. Wash the combined ethyl ether solution four times with 100 milliliters of saturated sodium chloride solution. After transferring the ethyl ether solution to a round bottom flask, add four grams of anhydrous magnesium sulfate to remove any soluble water.

Filter it to remove the solid, and collect the liquid in a clean 250 milliliter one neck round bottom flask. Then remove the ethyl ether using the rotary evaporator to obtain the crude product. Add the crude product dropwise to a previously prepared amantadine solution.

After allowing the solution to sit overnight, filter it under reduced pressure. Then wash the filter cake with 200 milliliters of ethyl ether. Transfer the filter cake to a 500 milliliter beaker.

Add 80 milliliters of one molar hydrochloric acid, and stir the mixture for five minutes. Then add 70 milliliters of ethyl acetate, and stir the mixture for another five minutes. Now add the mixture to a 250 milliliter separating funnel, and transfer the bottom aqueous phase into a 250 milliliter separating funnel.

After extracting the aqueous phase with ethyl acetate, wash the ethyl acetate solution twice with 30 milliliters of one molar hydrochloric acid and three times with 80 milliliters of saturated sodium chloride. After transferring the ethyl acetate solution to a round bottom flask, add four grams of anhydrous magnesium sulfate to remove any soluble water. Filter to remove the solid, and collect the liquid in a clean 250 milliliter one neck round bottom flask.

Then remove the ethyl acetate using a rotary evaporator to obtain the pure product. Transfer the purified product to a 100 milliliter teflon-lined stainless steel autoclave. Add the appropriate reagents and a magnetic stirrer to the autoclave, and seal it.

Place the autoclave in a vertical tube furnace placed on a magnetic stirring apparatus. Start the magnetic stirring apparatus and set the speed to 800 RPM. Start the heating program of the temperature controller connected to the autoclave.

When the reaction system cools down to room temperature, add another 0.3 grams of DTBP to the autoclave and restart the heating program. After the reaction is complete, dilute the product with 100 milliliters of ethyl ether, and transfer the solution to a 250 milliliter separating funnel. Wash the ethyl ether solution three times with 30 milliliters of four percent sodium hydroxide solution to ensure that the aqueous phase exceeds pH 10.

After removing the bottom aqueous phase, add 70 milliliters of 10%sulfuric acid solution to acidify the product. Wash the acidified ethyl ether solution several times with 80 milliliters of saturated sodium chloride solution until the aqueous phase pH is six to seven. After transferring the ethyl ether solution to a round bottom flask, add four grams of anhydrous magnesium sulfate to remove any soluble water.

Filter to remove the solid, and collect the liquid in a clean 250 milliliter one neck round bottom flask. Then remove the ethyl ether and unreacted oliphants using the rotary evaporator to obtain the crude product. Dissolve 2.3 grams of sodium hydroxide in 40 milliliters of deionized water.

Add the previously prepared sodium hydroxide solution to the flask containing the crude product, and shake vigorously for five minutes. Following this, add 0.5 molar cobalt chloride solution dropwise while shaking until no more blue precipitate is generated and the solution is pink. Filter the pink solution, and wash the blue precipitate with deionized water until the filtrate is colorless.

Then transfer the filter cake back to the flask, and add 100 milliliters of acetone. On the following day, pulverize the blue filter cake using a stainless steel spoon to release any impurities trapped in the bulk. Filter the solid and wash it with 100 milliliters of acetone.

After drying the filter cake at room temperature, add 120 milliliters of ethyl ether and 80 milliliters of 10%sulfuric acid solution to the filter cake. Transfer the resulting solution into a 250 milliliter separating funnel, and shake vigorously until the blue precipitate disappears. After removing the bottom aqueous phase, wash the ethyl ether solution several times with 30 milliliters of 10%sulfuric acid solution until the aqueous phase is colorless.

Then wash with 80 milliliters of saturated sodium chloride solution until the aqueous phase pH is six to seven. After transferring the ethyl ether solution to a round bottom flask, add four grams of anhydrous magnesium sulfate to remove any soluble water. Filter to remove the solid, and collect the liquid in a clean 250-milliliter one neck round bottom flask.

Finally, remove the ethyl ether using the rotary evaporator to obtain the pure product. Phosphorus NMR spectra were collected for the intermediate monoalkylphosphinic acid before and after purification by the amantadine method. During the monoalkylphosphinic acid synthesis, it is difficult to avoid the generation of the dialkylphosphinic acid byproduct, which is the reason for the peak at 62.507 PPM in the spectra.

Phosphorus NMR spectra, proton NMR spectra, MS spectra, and FTIR spectra, were collected for the acid product after purification by the cobalt salt precipitation method. Potentiometric titration curves of the acid product indicate that the purity of the product can exceed 96%High-purity nonsymmetric dialkylphosphinic acid can be obtained through this method, which allows exploration of new extractants. This class of extractants can be used to aid the extraction and the separation of rare earth irons, nonferrous metals, rare metals, et cetera.

The separation and extraction performance can be fine-tuned by modifying the alkyl chains.