2-Amino-5-nitrobenzenesulfonamide.
A mixture of 5 g. of nitrochlorobenzenesulfonamide, 5 g. of ammonium carbonate, 25 ml. of ammonium hydroxide (28%) and 1 g.of cupric sulfate was
heated in a sealed glass tube for
four hours at 120". The contents of the tube were
evaporated slowly to remove excess ammonia. The
solution, on saturation with sulfur dioxide, gave a yellow
precipitate. The product was filtered and recrystallized
from aqueous alcohol. The yield was 86%, m. p. 208"
I want to know the answer of the following question please
1-what is the difference between ammonium carbonate and ammonia in role????
2-what is the balanced equation of this reaction???and what is the expected vapour pressure of the reaction
3-what is the role of copper sulfate
I know I should search for the answer but I am in bad need to know the balanced equation and the vapor pressure as it is critical to know the diameter
of the sealed tube and max endured pressure
Attachment: goldfarb et al.pdf (213kB) This file has been downloaded 752 times
amrhamed2 - 22-4-2008 at 10:29
plz can anyone estimate the pressure resulting from this reaction ? .......Nicodem - 22-4-2008 at 11:14
The pressure should be in the range of 3-6 bar. Any autoclave can hold that easily.
The reaction is most probably a nucleophilic aromatic addition/elimination (S<sub>N</sub>Ar), though the authors believe it to be an S<sub>RN</sub>1 reaction. Therefore they added CuSO4. It could even really be an S<sub>RN</sub>1, but this substrate is
more than enough electron poor to proceed trough addition/elimination, hence the copper catalyst is probably obsolete (but only an experiment without
catalyst can confirm this).
The ammonium carbonate is there only to increase the concentration of NH3 above what can be achieved with concentrated aqueous ammonia (ammonium
carbonate is in equilibrium with NH3, H2O and CO2).not_important - 23-4-2008 at 06:20
Quote:
The ammonium carbonate is there only to increase the concentration of NH3 above what can be achieved with concentrated aqueous ammonia (ammonium
carbonate is in equilibrium with NH3, H2O and CO2).
Note that ammonium carbonate is well above it's standard pressure decomposition point at the reaction temperature, so it's contributing to the
pressure in the sealed tube as well as the aqueous ammonia and solvent water.
Nicodem's estimate of the pressure sounds reasonable to me.amrhamed2 - 23-4-2008 at 06:26
I know but actually I have no access to autoclave right now but I have a kimble kontes pressure vessel with PTFE stopper which can withstand approx
10-15 bar
I was reluctant to use it and I was about to calculate the vapor pressure of the resulting reaction but I have no clue up till now to find it
accurately
I would like to know how u estimated such pressure if u please ?amrhamed2 - 27-4-2008 at 15:14
Look I really need help :
This is the scenario
I have heavy wall pressure tube of capacity 100 ml and pressure rating of 10-15 bar
I need to know the amount of substances which should be added to give the pressure required for this reaction .
[Edited on 28-4-2008 by amrhamed2]Nicodem - 28-4-2008 at 05:58
The pressure has no influence on the reaction. You do not need the information on the pressure during the reaction, what you need is to maintain the
temperature required and that can easily be done by immersing your screw-cap vessel in an oil bath and heat it to 120°C. In short, just follow the
procedure from the paper which is nicely described.
I don't know exactly what kind of problem you are having. Please describe in more detail what exactly you do not understand about this procedure.amrhamed2 - 28-4-2008 at 08:09
The heating of ammonia solution in confined tube along with the ammonium carbonate decomposition will result in pressure which is necessary for the
reaction .
This pressure will vary of course from sealed tube to another according to its volume (for example 100 ml vessel will differ from 200 ml vessel for
the same quantities of reactant)
The questions are...
1-Is the pressure resulting from heating reaction mixture expected to exceed 10-15 bar limit ??I am asking because if so the tube is likely to
explode.
2-using the amounts mentioned the volume of space above the reactant mixture is likely to be 60 ml or little more
Is this ideal for this reaction ....(I am asking as of course if the volume is very big ,no high pressure will be exerted and the sealed tube will be
of no use ..)
3-There is general rule filling the tube half the volume .......I am filling it with approx 30 ml and the tube is 100 ml ....shall I multiply the
quantities by a factor to get 50 ml ...or it is ok using the mentioned quantities
I don't know if my approach in tackling this problem is not logical
[Edited on 28-4-2008 by amrhamed2]Nicodem - 28-4-2008 at 08:47
The amount of the ammonia and other components residing in the vapor phase at such relatively low pressures is nearly negligible to the amount
residing in the liquid phase. Therefore the volume of the "empty" space in the screw-cap vessel is not going to influence much the concentrations of
the components. Consequently not even the equilibrium pressure as long as this volume is comparable to the volume of the liquid phase. In other words,
it does not matter if you fill your vessel with 30 or 60 ml, the equilibrium pressure will not vary more than few percents utmost (and even this
difference will be mostly result due to the partial pressure of entrapped air). Read some book about basic physical chemistry, the chapters about
liquid/gas phase equilibriums and related stuff if you want to understand this in more detail. I forgot most of what we were thought in school so I
can't really give you as good a lesson as you could found in books.
As for the question of about the suitability of a screw-cap vessel for such an operation, I already gave you my estimate of the final pressure. I
can't see why a vessel rated for 15 bar could not resist the reaction conditions. Even if for some reasons (like rapid exothermic reaction or similar)
the pressure increased to 15 bar, your vessel should survive without problem since the rated pressure for glassware is generally the safe minimum,
while the unsafe maximum is usually double that. Just make sure there are no star cracks on it!
I often used screw-cap vessels at job, even for reaction at 150°C with solvents that boil at 80-100°C or even methanol at 120°C or any such system.
None ever blew up – that's what they are designed for.
But why don't you just try it out? It would surely take you less time than waiting for someone to vouch for something that can not be vouched for. The
vessel might blow up for any reason, not just because I estimated the equilibrium pressure wrongly, so there is no rational reason to ask for an
impossible assurance that only faith or insurance companies can give.
