You are correct, use sodium sulfide and add elemental sulfur into it and stir, the sulfur will go into solution in aqueous medium.  Alternately you may take NaOH solution make it two halves. In one half pass hydrogen sulfide  to get NaHS and then into it add the rest half of NaOH solution to create fresh Na2S . Into it you add elemental sulfur and stir. You will get polysulfide solution.  Normally in  Na2Sx , x varies from 2 to 5.

You are correct, use sodium sulfide and add elemental sulfur into it and stir, the sulfur will go into solution in aqueous medium.  Alternately you may take NaOH solution make it two halves. In one half pass hydrogen sulfide  to get NaHS and then into it add the rest half of NaOH solution to create fresh Na2S . Into it you add elemental sulfur and stir. You will get polysulfide solution.  Normally in  Na2Sx , x varies from 2 to 5.

Which kind of sodium polysulfide you want to prepare? I can send you exact procedure to prepre Na2S2, Na2S3, Na2S4 and Na2S5.   These are available in Brauer: Handbuch der preparativen anorganischen chemie, p. 281-285,. If you cannot reach it, I will send you a copy about these pages.

In aqueous solution the identity of different polysulfide will be lost  and one can get only mixture . One can get these individually  only by solid state reaction  as described in that hand book 

In aq. solutiuon generally mixture is formed, it is true, however, the question was "preferebly in aq. soln.", furthermore, e.g. alcoholic solution of Na2S4 can be prepared, and this solution of Na2S4 can be transformed into Na2S2.

Yes, I need just the water mixture of polysulfides, probably better with greater sulphur ratio, than lower; however, the solid state reaction could be also interesting. Thank you both gentlemen for your advices and dear László, please, if you can send me the copies of the Handbuch pages, that would be great, the book is unfortunately not available to me in the moment.

Dear Jan,

Here it is. I hope you can use it.

Dear László,

Thank you very much.

Not at all. If you need any help do not hesitate to contact with me.

can any one suggest me how to make Ammonium Polysulfide?

If you take ammonium hydroxide solution ( in water  of your required concentration , you can start also with liquor ammonia but then the reaction between this solution and H2S will be very much exothermic, required proper chilling of the solution and passage of H2S should be slow ) ) and pass hydrogen sulfide in cold ( use ice pot ) at the saturation point of the absorbed gas the color of the solution will be pale yellow due to decomposition of a part of hydrogen sulfide to elemental sulfur ( several reasons for such decomposition and the causes are well studied) . Now if you want a specific concentration of polysulfide to prepare  just add known amount of  elemental sulfur in powdered form into such solution  and continue the passage of H2S gas into it till the solid sulfur goes into solution. It is recommended that you add time to time a bit of liquor ammonia into the solution to keep the solution ammoniacal as  rapid bubbling of H2S may drive off some ammonia from the solution. Keep the clear orange yellow polysulfide solution properly closed and in cold condition. This is a practical recipe and I used it for more than 30 years in my research

Thanks Mr. Sarkar

Is there a fixed ratio of Na2S and sulfur? I tried making a polysulfide solution, but the sulfur wasn't soluble.

How  much NaOH you had taken to get Na2S and that amount says how much Na2S you have . You can calculate gram equivalent of this and may add 5 times of that your elemental sulfur and stir. It will dissolve and if there is a trace of elemental sulfur remained in the solution either filter that or add few mL of fresh Na2S to dissolve that. There are several equilbria exist with Na2Sx ( x = 2,3,4,5,6 ) solution and so based on your reaction the polysulfide you wish to get  will react.  Some metals like tetrasulfide some metals pentasulfide or disulfide . if you  add polar solvent like DMSO into a little of this polysulfide then you can see the dominant formation of  green S2- ( radical ) or blue S3- radical . So the hidden presence of these polysulfide radicals ( analogue of superoxide as one gets from oxygen)  should not be overlooked. If you have any  specific  query then you can directly write to me ( e-mail : [email protected] or [email protected]) for a solution of your query. Finally do not write that elemental sulfur is not soluble in Na2S

Prof. Sarkar Sir

can you pls tell me the procedure to prepare  only Na2S2 or from where it to buy.

In aqueous  or in methanol solution : X gm of NaOH to be dissolved in water or methanol. The solution to be made in two halves.  In one half , H2S gas is to be passed till it is saturated . This will generate NaHS . To this solution rest of the half NaOH solution to be mixed to get  Na2S. Into  this solution equivalent amount  ( one in this case per sulfide) of elemental sulfur to be added. and the sulfur will go into solution imparting a pale yellow color. The mixture is to be evaporated under vacuum to get Na2S2

Alternate: Sodium cut in small sizes  to be taken in DMF and into it equivalent amount of elemental sulfur to be added with stirring to get the dissolution of sodium  resulting the generation of Na2S2.

For both the operation oxygen or air to be avoided. There could be a solid state reaction between elemental sodium and sulfur  in proper ratio but caution this could be very exothermic causing fire.

I

Could someone please estimate the molecular dimension of one Na2Sx molecule? E.g. if I want to dialyze them out of the aqueous solution, which membrane I should use? 

May I also ask, how stable the Na2Sx will be?

After a year, my Na2Sx has probably precipitated back to Na2S solution and solid sulfur. 

Polysulfide ( Na2Sx)  is definitely not very stable and on aging specially under light exposure reverted back to simple sulfide throwing excess of sulfur . Further traces of air or oxygen will set a series of redox reactions catalyzed by ppm or ppb level of transition metal ions present in the soup to several oxo-sulfur species like sulifite, thiosulfate or even sulfate.  

For your earlier question which I did not see earlier , I can only comment that  It is difficult to  preferentially dialyze one species through a membrane under aqueous medium as they   ( all those polysulfides )remain in dynamic equlibrium.

Thank you very much, that is an important answer. 

In the end, I preferred membrane centrifugation instead of dialysis, my point is not to isolate different Na2Sx species, but to wash all of the residues of Na2Sx from a reaction product (which will not go trough the membrane anyway) away; e.g. how big the molar mass of Na2Sx can be, but I suppose, that the "x " will lie between 2–5, as you wrote vide supra, so the M (Na2Sx) will not be greater than 200–300 g.mol–1, right?

Yes that is true and these will not be big. Hope your centrifugation works to your satisfaction

You can find procedures to prepare and isolate each Na2Sx polysulfides (S=2-5) in the book:  Brauer: Handbuch der Preparativen Anorganichen Chemie, p.279-285.

Thank you Mr. Sarkar,

if the centrifugation worked, I need to determine first.  And it seems now, that for this I need a differend analytical assay as ICP-OES.

__________

Are there any possibilities to determine sulfides (preferrably in the form of Na2S, Na2Sx, or H2S) from an aqueous solution, where MilliQ-water and 25 mg/L or 125 mg/L of trisodium citrate will be present?

The worst detection limit will be about 300-400 µg/L, but ideally like 2-4 µg/L.

It´s complicated by means of the ICP-OES as total sulfur, since even the MilliQ water and citrate can disturb.

We have ICP-MS, but unfortunately not VaporGenerator-ICP-MS or VG-AAS.

Does anyone have any suggestions? UV-VIS, Ion-Selective electrodes, polarography, isotachophoresis?

It should also be easily handable established method.

Thanks in advance.

It will be  difficult but I guess one can try to do this. It may work but some controlled experiments may be done to get it standardized. One can analyze the total sulfides and total sulfur present as polysulfide.   The exact analysis of different concentration of polysulfide present there requires good analytical skill but doable at least  from the training from good old analytical chemistry. The principle is as follows. : From known volume of the sulfide mixture  one can add either lead or cadmium salt solution in cold. All sulfides in the form of lead or cadmium will be precipitated along with free sulfur formed from the decomposition of  all  polysulfides present in the mixture. The mixture should be filtered  , washed with few times with water to free the precipitate from excess metal salt used to precipitate ( I mean either lead or cadmium) .  The precipitate should then be leached with toluene to dissolve free sulfur  and on evaporation the weight of the free sulfur would state the presence of polysulfide ( here in which form would be difficult. to make but there are ways). The residue will be only lead sulfide or cadmium sulfide. One can get this precipitate soluble in standard acid mixtures  and from this solution if one performs any standard analytical technique like AAS or  ICP to identify the amount of the metal  which will be equivalent to sulfide present there. The predominant polysulfides are with sulfur = 4 or  sulfur = 6  and using a little of the aqueous solution adding DMSO into that will lead to the formation of  the corresponding  S2 radical ( green) and S3 radical (blue)  one can have also red in color  ( for another sulfur radical). Electronic spectroscopy  may be used to find out the peak position and using standard concentration dependent Lambert-Beers law one can deconvolute to find out the relative concentration of S4 and S6 polysulfides . EPR would be another method to identify which polysulfide does exist as the corresponding dissociated radical has selective and specific EPR signal. Once this is identified the amount of sulfur may be used to fix the corresponding polysulfide present. By difference the free sulfide may be estimated. This analysis is based on classical analytical chemistry and it will work if one has patience and confidence. If there is further query kindly let me know.  

For a related discussion, also dealing with sodium polysulfide: https://www.researchgate.net/post/Is_there_a_method_available_for_preparing_a_stable_polysulfide_electrolyte_redox_system

I would like to have a one more question regarding on Na2Sx stability. Generally, the literature suggests to ultrasound and vortex Na2S and S in aqueous dispersion, both for 10 min, and then react the mixture at 80 °C for 12 hours. I have, by one replicate of the synthesis, obtained from the dispersion a clear bright yellow solution after about 4 hours, and when I left the reaction run further to the prescribed 12 hours, the mixture went back to clear Na2S probably and the S precipitated on the magnetic stirrer.

- Is there some dynamic equlibrium in between the Na2S and Na2Sx states?

- How can I avoid this in the future? Should I just stop the reaction after I get the yellow bright solution?

The reaction runned in MilliQ-water in a well cleaned glass roundbottom flask with a reduction and Dimroth-cooler in an oil bath set at 80 °C. 

The entire operation should have been done under oxygen free condition. One can preserve the yellow colored solution for days if it is stored under oxygen free condition.. Further light can catalyze the decomposition and if traces of metal ion (ppm or ppb) is present the reaction will be fast. Kindly adopt these precautions.

Thank you :) . 

After about 15 h of reaction, when trying to protect the reaction mixture from air (under Ar atmosphere from balloon) and from sunlight (Al foil), I am getting something like this. Clear bright yellow solution, but the sulfur seems not to be dissolved completely. Should I react further or try to filter the solution (the sulfur particles wir disturb inf further reaction of direct sulfidation of Ag0 nanoparticles). 

I understand your problem.  The concentration you are using for Na2S is not actually what you are using but less. This might happen if you use solid Na2S procured from the market as it may not be very pure or got decomposed on standing.. Best thing you should start with Known amount of NaOH dissolved in a fixed volume of water, using half of this volume to pass H2S to saturate, chase out the excess of H2S from the solution by Argon for a few minutes and then add the rest half volume of the NaOH solution to get pure Na2S of desired strength. Here you add the elemental sulfur and stir under inert atmosphere and this will go into solution to provide you pale yellow Na2S2 solution.

In the present case , you decant the Na2S2 solution for your use, be careful to handle it in the absence of oxygen as more oxygen more it will get oxidized to more complex mixture of thiosulfate, sulfites etc You will succeed  after couple of attempts. Go ahead and if anything more you require do ask me. Thanks

Thank you.

I have filtered it through 0,45 um syringe filter, and let stay in a vial under Ar (but it vas a normal vial and Ar dosed from a balloon), after two days the product is still yellow, but S is precipitating. 

Yes, I am usind solid Na2S, but I have not much further possibilities. I can try to dissolve the Na2S (and use it in surplus) in NaOH solution (which concentration?) and then add the S, everything under Ar, but that´s probably the best we can do here. 

Should I store the Na2Sx better in a refrigerator?

Funny thing is, that for the first time it completely worked without Ar-atmosphere and the product seemed to be stable (clear and yellow) for months. So, it really might be that reason, that my bought Na2S is not so pure anymore?

You are absolutely correct as sealed bottle of Na2S  is relatively pure but once opened then it starts decomposing  under exposure with air.. Keeping it under cold condition(fridge) will enhance its stability. The dissolution of  more Na2S into NaOH will not help . Had it been NaHS then addition of NaOH would have created fresh Na2S. Next time when you get a new pack of Na2S and when you first time opening it, you can distribute required amount of Na2S in several small vials for future use and the operation should be done in the absence of air and moisture and tightly closed vials to be stored in desiccator . The problem you face here is the basic chemistry of Na2S and in water it hydrolyses to produce  NaHS and NaOH so the extra NaOH is not good for polysulfide generation.

Dear Prof. Sarkar,

thank you very much. If I see the problem correctly, it lies in the quality of Na2S, which is not stored under Ar or N2 and is going hydrated in time to NaHS, which is not able to sequestrate the sulfur?

It will be a bit challenging in my conditions (environmental chemistry lab, not a synthetic one), but I can obtain a new Na2S and plastic bag-glovebox and work with it.

Precisely such thing is happening. Use new and freshly open bottle then the problem can be minimized several folds. I wished that you had a small cylinder of H2S gas and some NaOH and good water to avoid such a problem permanently but with new bottle you will get your work.Best wishes,

SS