Hi,

Hydrazones are quite unstable (they undergo hydrolysis) in acidic medium. If you used during your synthesis or workup some acid (for example acetic acid)  there is a strong possibility, that some part of vestigial acid remains within your compound. Pure carboxylic acids are in practice undissociated but also very hygroscopic. They absop water from air, dissociate and provide smooth hydrolysis or other reactions catalyzed via acidic envirioment (especially in case of rich-electron aromatic compounds like your's).

I strongly suggest you to dry this compound (after crystalization) in vacuo at 60oC for a few hours. It should remove any volatile carboxylic acids and other solvents, resulting in pure and dry compound.

Best regards,

Arkadiusz

I only can help you with some basic principles. Please, evaluate some manuscipts. All the best.

Thanks Prof. Vladimir A. Kulchitsky:

Yes Sir, I am also having the same paper from molecules that you have provided me, as one of my references. The procedure that I have followed to synthesize the acetophenone phenylhydrazone is well established and there is no problem with the method, but the problem is that, the formed product is not stable at least for 5 hrs, first I had obtained light yellow crystals, then started changing to brown, next dark brown and finally reddish brown color and getting liquefied finally.

I would be really happy to hear some suggestions or guidance further from you regarding the stability of the acetophenone phenylhydrazone.

Let me think for one day. I will answer.

Thank you very much Sir.....

The literature is saying that acetophenone phenylhydrazone will not be stable after few days, but for me it was 15-16 hrs.

Before complete drying of the crystals itself the product had started decomposition.

http://www.orgsyn.org/demo.aspx?prep=cv3p0725

Pls Check the above link.

Hi,

Hydrazones are quite unstable (they undergo hydrolysis) in acidic medium. If you used during your synthesis or workup some acid (for example acetic acid)  there is a strong possibility, that some part of vestigial acid remains within your compound. Pure carboxylic acids are in practice undissociated but also very hygroscopic. They absop water from air, dissociate and provide smooth hydrolysis or other reactions catalyzed via acidic envirioment (especially in case of rich-electron aromatic compounds like your's).

I strongly suggest you to dry this compound (after crystalization) in vacuo at 60oC for a few hours. It should remove any volatile carboxylic acids and other solvents, resulting in pure and dry compound.

Best regards,

Arkadiusz

Thanks Mr. Arkadiusz:

Your guess is correct, I had utilized catalytic amount of glacial acetic acid as a catalyst to carry out the synthesis of acetophenone phenylhydrazone.......

Thanks & Regards,

Nagendra Babu M.

Let me send you an explanation of Professor Potkin.

The reaction of simple forms hydrazone. Explanation of the observed effect may be several. The first one is - the substance itself is unstable. The second one is - the compound is unstable in air and oxidized through the stages of education

Azines (they are usually red or red-brown). This is most likely.

The third one.  It is possible that the initial reagents and the dirty solvent that promotes the decomposition of the product.

Most likely the second explanation. Output is as follows: after the preparation of the compound quickly identify (filter), washed with solvent, drying (preferably in vacuo), and stored in an argon atmosphere (available under nitrogen but argon is heavier and better in practice). All manipulations with the compound is also better in an argon atmosphere.

All the best, Vladimir

Professor Vladimir A. Kulchitsky:

I would be thankful for the explanation, with this I would start the root cause analysis for this issue based on the given explanation from your side.

Thanks & Regards,

Nagendra Babu M.

Try out for crystallization use of isopropyl alcohol (+ activated charcoal), rapid separation of crystals and dried in vacuo without heating (= RT). If that fails, attempt to find a less polar solvent e.g. toluene, tert -butyl methyl ether, cyclohexane, mixture chloroform-hexane, etc. (+ silica gel),  rapid separation of crystals and dried in vacuo without heating (= RT). The product should be stable against oxidation due to a different packing in the crystal.

Dr. Pavel Pazdera:

Sure I will follow your instructions during the crystallization, thanks again.

Regards,

Nagendra Babu M.

Dear Nagendra,

I believe your hydrazone was simply oxidized in the air; this happens with several  phenylhydrazones.    I suggest that after drying the crystallized compound please keep it under inert atmosphere, such as under nitrogen or argon.

 Good luck and best wishes,

Katalin

Dr. Katalin Prokai-Tatrai:

Sure I will follow that in my next trial of synthesis of acetophenone phenylhydrazone. Thanks a lot......

Regards,

Nagendra Babu M.

pl.check your product purity.such things happen with impure compounds

Got the hydrazone successfully, but at controlled conditions. Kept away from light, atmospheric air and at cool and dry place after synthesis.

Acetylation is also successful, pending spectral analysis.

Thanks to all for your valuable inputs..........thanks a lot.

Regards,

Nagendra Babu M.

I presume that if pure phenylhydazone is kept under vacuum , decomposition will be stopped.

Dr. Vishnu Ram:

Yes Sir, your are 100% correct, provided that the phenylhydrazine and acetophenone should be freshly used or distilled reactants need to be used to achieve better stability of the acetophenone phenylhydrazone.

Mennuru,

So you have got it. However you wrote that "Acetophenone Phenylhydrazone was synthesized and obtained as good yellow crystals after re-crystallization from ethanol." while the reported one was "colourless crystals " as follow

Acetophenone phenylhydrazone (3aa) 1

 A solution of phenylhydrazine (5.495 g, 50.8 mmol) in glacial acetic acid (10 ml) and water (10 ml) was added to a solution of acetophenone (4.12 g, 34.3 mmol) in glacial acetic acid (20 ml) contained in a boiling tube.  The mixture was cooled in ice and shaken for 5 minutes, colourless crystals of hydrazone precipitated.  The product was filtered, washed with dilute acetic acid and water to yield the hydrazone 3aa as colourless crystals (3.45 g, 48 %); dH (250 MHz; CDCl3) 2.4 (3 H, s) 7.1 (1 H, m) 7.4-7.7 (7 H, m) 8.0 (1 H, m).

1.     F. E. Henoch, K. G. Hampton and C. R. Hauser, J. Am. Chem. Soc., 1969, 676.

I know that you have, so good luck

Dr. Adel Amer:

Thanks for the reference and the probe related to the color of the crystals....

What ever the earlier hydrazone that I have prepared was in Yellow color, but after referring again few of the research papers and Reference books, I had prepared the acetophenone phenylhydrazone again by freshly procured starting materials i.e., phenylhydrazine and acetophenone. The crystals obtained were nearly colorless.

As per the root cause analysis, I had found that the phenylhydrazine was started to decompose (change in color was observed due to contact with air), so the product what I had synthesized earlier was not stable and pure, so I got yellow colored crystals (I hope).

My references along with the reference what you have mentioned:

1. Practical Organic Chemistry, Mann F.G. & B.C. Saunders, 4th Edition, Pg.No.: 257-258 (resembles to that of the work carried out by F.E. Henoch et al. J. Am. Chem. Soc., 1969, 676).

2. Intermediates for Organic Synthesis, V.K. Ahluwalia, Pooja Bhagat, Renu Aggarwal, Ramesh Chandra, Pg.No.: 272-273.

3.  Practical Heterocyclic Chemistry, A. O. Fitton, R. K. Smalley, Pg. No. 14.

Dear Dr. Adel Amer, once again thanks for your follow-up of the results of my query and your valuable time.

Regards,

Nagendra Babu M.

 you can follow another synthesis procedure in which phenylhydrazine HCL salt is used and sodium acetate in amixiture of ( ethanol+ 3M HCL solution) as reaction medium and undergo the reaction for 30 min at 40C temperature , try this procedure and tell me the color of yeild

Thanks for another procedure Fatima Mohammed Hussen.