[Memo. M]

Hello guys..

I faced a serious problem in chem lab.. after the cyclization by NaOH, during the acidification in order to obtain different derivatives of 1,2,4-triazole, a very large amount of the solid formed (around 25 gm) while the weight of the starting (thiosemicarbazide) = 0.7 gm 

the solid formed doesn't dissolve in most of the solvents ( chloroform, ethanol, DMF, acetonitrile, ethylacetate, DMSO....etc) even in water!!!! but with large volume of MeOH, small weight did, (which dissolve in water  like salts)

this large amount formed with different derivatives !!!!!!!

[TheUnassuming]

That does seem odd, but the key I think is in what you haven't said. 
Can you give a more detailed description on your procedure?

[Memo. M]

That does seem odd, but the key I think is in what you haven't said. 
Can you give a more detailed description on your procedure?

during the cyclization a part of precipitate doesn't dissolve even with adding excess amount of aq. NaOH. so, I filtrate the solid then i did hot filtration to the solution by water.

after approximately 2 hr in low temp. I started the acidification using PH papers. the solid formed and disappear until PH=3-2. that's the problem, a huge amount of white solid formed.

the solid doesn't dissolve even in water. I added 200-250 ml of methanol with stirring and heating then after filtration and evaporated the solution around 0.9gm of beautiful white crystals produced.. It dissolves in water only but not in any other solvents !!!!!
In TLC (eluent : petroleum ether only ) the spot moved from baseline to the center of the plate !!!

many thanks..

 

[TheUnassuming]

Well 900mg from 700mg sounds far more reasonable as far as an expected mass, though I have to admit I'm a bit confused at this point. 
 
You were able to get material to dissolve into MeOH well enough to filter it and evaporate the solvent, giving you white crystals.... but it won't redissolve in anything but water?
Also it can only dissolve in water but by TLC has an Rf of 0.5 in pure pet ether indicating it is extremely non polar. 

Do you have access to an NMR or Mass Spec so you can see what you have?  What other functional groups do you have on your molecule?  Have you confirmed that your starting material is clean and correct? 

[408]

Please post entire synthesis.  I have a suspicion but I need more info.

Did you happen to use sulfuric acid to neutralize the reaction?

[Memo. M]

Well 900mg from 700mg sounds far more reasonable as far as an expected mass, though I have to admit I'm a bit confused at this point. 
 
You were able to get material to dissolve into MeOH well enough to filter it and evaporate the solvent, giving you white crystals.... but it won't redissolve in anything but water?
Also it can only dissolve in water but by TLC has an Rf of 0.5 in pure pet ether indicating it is extremely non polar. 

Do you have access to an NMR or Mass Spec so you can see what you have?  What other functional groups do you have on your molecule?  Have you confirmed that your starting material is clean and correct?

I forgot to mention that also MeOH dissolves it.. currently I don't have access to an NMR or Mass Spec because of technical breakdowns. I have phenyl in the molecule beside 1,2,4-triazole..

the starting was pure according to TLC ( one spot ).. but the formation of large amount of solid during the acidification keep repeating in other two different schemes which differ completely in the substituted except for 1,2,4-triazole!!

[Memo. M]

Please post entire synthesis.  I have a suspicion but I need more info.

Did you happen to use sulfuric acid to neutralize the reaction?

the main synthesis is formation of substituted 1,2,4-triazole by thiosemicarbazide passing by hydrazide..
NaOH was used in cyclization then dil.HCl in acidification..!! sulfuric acid wasn't used..

thank you all..

[TheUnassuming]

Well I'm not sure exactly what the 25g of precipitate you get is (especially if you are working on less than a gram scale).  Agree that you need to post entire synthesis (Mols of materials used, amount of solvent, temps, time ect). 
My first instinct is that your product is being trapped/complexed in the salt when it crashes out.  When you dissolve the salt your compound is freed up and you don't see the salt by TLC so it just looks like your compound.  What happens when you do an extraction with water/DCM or EtoAc?