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Acetamid
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  Acetamid
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« na: Lipanj 30, 2016, 09:45:25 »

Pozdrav.Da li netko poznanaje dobar nacin priprave acetamida posto  u zadnje vrijeme sam pronasao razne nacine dobivanja no ipak me zanima vase misljenje. wink1 wink1
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« Odgovor #1 na: Siječanj 20, 2017, 03:27:30 »


Reakcijom etil acetata i 25% otopine amonijaka (preuzeto sa nekadašnje frogfot.com stranice):

Citat:
   Introduction

Acetamide can be prepared easiest by reacting ethyl acetate with aqueous ammonia. For more detail look at general reaction mechanism of amidation.

Together the reactants will form a heterogeneous mixture, since ethyl acetate is poorly soluble in 25% ammonia. As a result, reaction in the beginning will go slowly, however, it will proceed noticeably. Forming acetamide will act as a solvent for the whole reaction mix. After a while, when enough acetamide forms, it will give a complete homogenization. At this point, reaction will go much faster.

To hurry up homogenization, a magnetic stirrer may be employed. However, it's not necessary. I found that occasional stirring will do, without any big difference.
Yield here will be basically quantitative. The only factor that'll decrease yield significantly, will be decomposition reaction of ethyl acetate:

CH3COOCH2CH3 + H2O <==> CH3COOH + HOCH2CH3

Fortunately this reaction proceeds slowly.


    Procedure

Materials:
Ethyl acetate (CH3COOCH2CH3)
Ammonia (NH3(aq, 25%))

Mix 40 ml of ethyl acetate and 60 ml of 25% ammonia in a flask and close container air-tightly with a rubber stopper. The stopper should be secured in place by a wire to avoid it popping off.
The contents is then stirred (at room temp) occasionally until mixture becomes homogenous, this should take less than 24 hours. (with magnetic stirrer this time may be decreased).
When reaction mix is homogenous, stop stirring and leave flask in room temperature for 2-3 days. Longer, if greater yield is required.

Distil reaction mix until fumes above it gets to 150oC (caution, ammonia gas is evolved) with a water cooled condenser. On cooling of remaining liquid, acetamide will precipitate as white crystals. Raw product is stored in airtight container.
After 3,5 day reaction time (after homogenization) yield is about 20 g (about 83 +/- 8% from theoretical). Excuse my crappy scale..
For purification refer to additional preparation procedure below.

Pure acetamide have mp of 81oC, bp of 222oC. Soluble in water (g/100 ml: 97,5@20oC; 178@60oC) and alcohol (g/100 ml: 25,0@20oC; 257,1@60oC).


    Additionally (other procedure)

One organic chemistry book1 suggested to bubble ammonia gas through cold (8-10oC) mixture of 50 g ethyl acetate and 75 g 25% ammonia until it becomes homogeneous, mixture is then leaved for 2 days in air tight container in fridge. This is then distilled first up to 150oC with water distiller and after, with air distiller. A fraction of 190-225oC is collected. Product is dried in excicator and redistilled or recrystallized from ether. Yield is 22 g (69% from theoretical)


    References

1. S.S.Gitis A.I.Glaz A.V.Ivanov Practicum of organic chemistry, 1991


Možeš ga dobiti i reakcijom amonijevog karbonata sa 100% octenom kiselinom, ali ja osobno ne bih išao tim putem. Mislim da je jednostavnije doći do etil acetata i amonijaka, nego do amonijevog karbonata i (pogotovo) 100% octene kiseline.

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« Odgovor #2 na: Siječanj 22, 2017, 08:05:12 »

Hvala na informaciji. Grin
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