Dear Dr. Melanie Pilkington,

As cyanide is a strong nucleophile, it readily reacts in nucleophilic substitution reactions. I suggest you to carry out the same (preferably SN1) with a lipophilic alkyl halide. This will lead to the exchange of nucleophiles and lipophilic alkyl nitrile could be extracted in the organic solvent. Other component NaCl which is also the biproduct of the above reaction could be easily removed by desalinating the water for which many methods are reported. You can find one of these methods in the link below.

http://pubs.rsc.org/en/Content/ArticleLanding/2011/EE/c1ee01027a#!divAbstract

Dear Lady,

how stable is your complex? how much is dissolved into the only water or methanol? Is it extractable in a solvent, which is immiscible with water?

Removal of CN-: 4 CN- + 2Cu2+ = (CN)2 + (Cu+CN-)2 ; first is gaseous - very toxic, second insoluble.

Cl- and counterion to Cu2+ (as well as CN-, finally) can be removed by use of weakly basic  anion exchanger resin in neutral form (= amine quality, not quaternary ammonium).

Good luck

P.

For removal of CN long time bubbling by CO2, HCN gets out and NaHCO3 is very bad soluble into MeOH-H2O mix. For all examples, basic it is good stability of your CN-complex.

Thanks I would like to avoid HCN if possible but I appreciate your suggestions, best wishes Melanie

Melania,

O. K. Use of weakly basic anion exchanger resin will be the best because universal.

Pavel

Thank you all so much for the ideas trimethylsilyl cyanide sounds interesting, I might think about that, that's a great suggestion.

How about crystallization?

Hi there,

I think the Cu2+ suggestion above is quite viable, but what you also could try is simply adding AgNO3 to precipitate AgCN and AgCl, than filter them off. You need to watch out for the redox chemistry though, as Ag+ has got a quite high redox potential (0.8 V). Regardless you might get away with the precipitates before your Fe(II) is oxidized, as redox potential change quite substantially depending on the potential ligands / counterions in the mixture.

Thanks for the suggestions, believe me I have tried crystallization but coming out of water is impossible as the Fe(II) complex is so soluble in water, I could try salting it out with something like NaCl but so far no sign of any crystals or ppt. I wondered about additing AgNO3, might be worth a try.

Dear  Melanie,

You could try with solid phase extraction. There are for a lot of different compounds. I removed excess of dopamine from a iron dopamine complex with a specific solid phase. you can buy it from Perkin Elmer and oasis (waters).

greetings

Thanks David I was thinking about that I wondered if something would be specific for the excess NaCN, I will think about that some more thank you for your time.

If the Ag(I) salts oxidize your Fe(II) complex and the complex is only solvable in very polar solvens you can try to use KCN instead of NaCN and add a stochiometric amount of 18-crown-6. The resulting K[18crown6]CN will be soluable in less polar solvens e.g. acetone with which you could wash your product.

Fenton we have obviously tried those things, replacement of the counter ion does not give us clean products and we have tried with a range of counter ions including the ones you have suggested. Yes we have tried to make the Fe(CN)2 in situ but the macrocycle we are making does not template around this. We have also tried varying the number of equvalences of the cyanide and again without the excess of Na or KCN the templation reaction does not go very well. I am the research director of this project so thank you for your concern and no I don't need any supervision from you.  I was curious to see if the academic community had some ideas that are less obvious to the ones that you are suggesting.

Dear Melanie,

It would be helpful to know the type of ligand you are working with. Is it possible to demetallate your complex without destroying the ligand? If your macrocycle is stable in the absence of the coordinated metal ion and the metal ion can be removed, you could try, before adding NaCN, to remove Fe(II), for instance by addition of sulfide (Na2S) or by electrochemical reduction, and then to extract the ligand (solvent-solvent extraction) or to isolate it by another method. It would be something similar to the preparation of cyclam by Ni(II) template reaction. In that case, cyanide is used to remove Ni(II) from the template complex. Once you have got the free ligand, it should be easy to prepare the complex you like.

Hi Antonio the ligand is a Schiff-base N3O2 macrocycle that as far as  I know does not demetallate like a cyclam. We have tried over he years to demetallate it  without any success and I have not come across any reports of successful demetallation reactions in the literature.. The ligand does not form in the absence of the metal salt and once the metal is in there the complex is very stable. I really was looking for a method for removing excess NaCN from aq solution. I think the crown ether suggestion with KCN might be a really good solution. As I explained to Fenton we thought that templating around Fe(CN)2 would be the solution but the macrpcycle doesn't template well around this but we havent givem up this route either. Our reaction conditions may just need optimizing. Thanks for your time in thinking about the problem. Best wishes Melanie

Dear Melanie,

but I still think that the deionization of your solution using a weakly basic anion exchange is the least laborious :-)

I will give that a go too :-)

Dear Melanie,

You could try an electrochemical demetallatioon. Another way to eliminate excess CN- might be to react it with NaClO. If you know the exact amount of the excess cyanide, you could try to add a stoichiometric amount of NaClO and keep the solution at room temperature for a few minutes. At the end you should have an increased amount of chloride in solution while CN- will be transformed into nitrogen and carbonate. Coordinated cyanide should resist the oxidation.

Best,

Antonio

Probably a completely 'off the wall' suggestion, but could you not use propanone to mop up the CN- via a cyanohydrin reaction?

Dear Melanie, 

Is your complex soluble in some other organic solvents? Could you simply evaporate MeOH/H20 mixture and treat the residue with some organic solvent (CH2Cl2, EtOAc, Toluene, Et2O...whatever solvent your complex is soluble) and simply do filtration to remove salts. Evaporate solvent and get pure complex.

If as you said, the NaCN had similar solubility to that of your complex in MeOH/H2O, the removal of NaCN is quite difficult. Did you try to isolate them in diferent temperature? For my experience, NaCl (whose solubility is 36) in room temperature, but it decrease largely with the temperature's decline. I often use this method to isolate my complexes from the solution with salt(NH4Cl or NaCl). I think you can try this method.

One tips, you need wait sometime when the temperature  declined for super-cooling solution often formed. 

Fenton,You're right. Probably Fe (II) oxidizes to Fe (III). Another possibility would be to add AgNO3 or Ag2SO4 and precipitate both chloride that cianiuro. Your idea to remove CN as HCN is good. HCN is dangerous, but it can be stopped simply by simply bubbling it into an alkaline solution of hypochlorite.

Why not simply crystallise the mixture carefully? NaCl (cubic) will probably not co-crystallise with your complex (for which I would expect far lower symmetry). NaCN crystallises monoclinic and might thus co-crystallise with a low symmetry complex. But It is worth a try. As Maolong Chen pointed out, the temperature might help you.

We have tried cooling the solution down to try and precipitate either the sodium cyanide/sodium chloride or the complex and this hasn't worked the macrocyclic complex seems to have a similar solubility to the NaCN in MeOH/H2O. We have tried removing the solvent and then doing a Soxhlet extraction with various solvents but to no avail.,

Thank you to everyone for some really useful suggestions, I like the titration idea but I am always nervous as the thought of generating HCN where students are concerned.

Is your compound stable enough to be loaded into reverse phase column?Meaning loaded in water or with few % of MeOH/MeCN, few CV of water and then use gradient to get your complex..

You can try it on HPLC analytical/praparational column or directly flash columnAdd your answer. Then your compound will be definitely purified and without unwanted salts.

Cyanid and chloride forms stable complexes with Ag+ in slightly (!) acidic solution!?

use other cynide instead of NaCN

Dear Dr. Melanie Pilkington,

may i suggest the use Fe(ClO4)2 instead of chloride salt?and then u can use a stichiometric  amount of cyanide salt instead of excess amount?