Fery
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benzoin oxime = Cupron indicator
The reactant benzoin was prepared here:
https://www.sciencemadness.org/whisper/viewthread.php?tid=68...
1,00g benzoin 4,71 mmol (M=212.24 g/mol) was put into 25 ml Erlenmayer flask and 2,5 g 85 wt% isopropanol added (volume was not measured, the solvent
was added on a scale and was thus only weighed).
0,80 g hydroxylamine hydrochloride 11,5 mmol (M=69.49 g/mol) (more than 2-fold excess) was dissolved in 1 ml of water in a beaker 1
0,44 g NaOH 11 mmol (M=39.997 g/mol) was dissolved in 0,6 ml H2O in a beaker 2 (!!! heat evolution !!!)
The hydroxylamine hydrochloride in beaker 1 was neutralized dropwise with NaOH from beaker 2 while stirring.
The free base of hydroxylamine from beaker 1 was added into benzoin in Erlenmayer flask.
Beaker 2 was washed with 4 drops of water which was transferred into beaker 1 and finally into Erlenmayer flask.
The neck of flask was closed with a piece of plastic sheet and rubber band.
The flask was put into 80 C water bath for 1 hour, occasionally swirling the flask. After 10 minutes everything dissolved but 2 immiscible layers
formed so the flask was further swirled occasionally (circa every 2-3 minutes). Probably the reaction already completed when everything dissolved as
such amount of benzoin couldn't be dissolved in such amount of alcohol. Anyway the reaction was heated and swirled for totally 1 hour. Maybe when
using ethanol the reaction would be homogeneous? Ethanol denatured with methylethylketone should be avoided as MEK contaminant would undergo reaction
into its oxime.
10 ml of cold water added while swirling the flask. The solid product was crushed with glass rod into small pieces and the flask was cooled in fridge
at 4 C for 1 hour.
Gravity filtered, washed 2x5 ml of cold water, air dried for 1 day.
Yield 1,05 g (M=227.26 g/mol) 4,62 mmol, 98%.
Crude product dissolved in 2,0 g of methanol on heating, added 1,0 g H2O while still heating (attempt to crystallize only from methanol previously
unsuccessful, no crystallization from pure methanol). Cooled down to room temperature and later in fridge for 1 hour.
Crystals filtered, remainder of mother liquor soaked into additional filter papers, product air dried.
Yield 0,74 g.
m.p. (148-150 C, lit. 151 C Vogel, 153-155 C Sigma Aldrich https://www.sigmaaldrich.com/EN/en/product/aldrich/b8908)
useful information:
Vogel
Attachment: vogel_oximes.pdf (374kB)
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https://www.chemicalbook.com/ChemicalProductProperty_EN_CB81...
Hydroxylamine hydrochloride
Its solubility at 20 C is 85% in H2O, 6% in EtOH and 12% in MeOH. [Hurd Inorg Synth I 87 1939, Semon in Org Synth Coll Vol I 318 1941.]
Attachment: CN102702023A.pdf (355kB)
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Attachment: EP0006254B1.pdf (956kB)
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Attachment: Green Synthesis of alpha;-Benzoin Oxime, and the Selective Control and Separation of Its Cis-Trans Isomers.pdf (1.2MB)
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Attachment: jresv9n1p1_a2b.pdf (584kB)
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Attachment: synthesis-characterization-and-antimicrobial-evaluation-of-benzoinoxime-transition-metal-complexes.pdf (90kB)
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Fery
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reactants, from the left:
benzoin, hydroxylamine hydrochloride, NaOH
NaOH added into hydroxylamine hydrochloride (beaker in the middle)
hydroxylamine added into benzoin (Erlenmayer flask)
heating on 80 C water bath
everything dissolved after 10 minutes of heating and occasional swirling, but 2 immiscible layers formed
after 1 hour of heating the reaction was done, still 2 layers visible, on cooling down the upper organic layer still liquid (no crystallization
visible even after putting for 1 hour into fridge at +4 C)
after addition of 10 ml of cold water the product finally solidified
 
the solid product was scraped from walls and crushed to smaller pieces using a glass rod
 
gravity filtered, washed, air dried
 
crude product to be recrystallized (1,05 g, yield 98%)
1,05 g of the product did not crystallize out from 2,0 g of methanol
but it did crystallize from 2,0 g methanol + 1,0 g water
Cu(NO3)2 in methanol, then addition of methanolic solution of the oxime
 
Co(SO4)2 in methanol, then addition of methanolic solution of the oxime (not too much color change)
 
NiCl2 in methanol (dissolved very unwillingly, only after boiling), then addition of methanolic solution of the oxime (not significant color change)
 
Cu(NO3)2 in methanol again, much more diluted
 
[Edited on 25-11-2021 by Fery]
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Bedlasky
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Nice work, Fery!
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Fery
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Thx Bedlasky, the benzoin was synthesized from the aldehyde you gave me :-)
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