m-Nitrophenol synthesis
Gubby
Here is the procedure that i've followed, its basically from "Textbook
of Practical Organic Chemistry" By Vogel.
3.5g of m-NA was dissolved in 5.5 ml of conc. sulphuric acid and 7.5ml
of water. The mixture was stirred till a thick paste was formed. To
this about 10g of crushed ice was added and the mixture was kept in an
ice bath.
In a separate beaker NaNO2 solution was prepared using 1.8g NaNO2 and
4ml water. This solution was cooled and added dropwise, with constant
stirring to the acid amine mixture. The temperature,while addition,
was maintained in the range 0-5 degrees Celcius.
For hydroxylation 16.5ml of conc sulphuric acid was added to 15ml
water and heated. The addition of the diazonium salt was begun after
the temperature of the acid reached 110. The entire diazonium salt
solution was added over a period of 20-25 mins.The temperature at the
end of the addition was around 150 degrees Celcius. After the addition
was over the solution was allowed to boil for another 5 mins. It was
then poured in a beaker set in an ice bath. When cold enough it was
filtered and the resulting product was recrystallized using 1:1 HCl.
Now the problem is i've not managed to get yields in excess of 20%.
The literature gives the expected yield to be around 70%. Also when
the addition is in progress the frothing occurs till a certain time,
and then there is no frothing, even after more diazonium salt is
added. Doesn't the frothing indicate the loss of Nitrogen? And so does
it mean that the reaction is not taking place, as there is no
evolution of nitrogen?
Also i tried to do the diazotisation at room temperature, but was
unable to get any solid product, my question is, if we are gonna
finally hydrolyse the diazonium salt, why take that extra care to
stabilize the salt, and then hydrolyse it. Coupling of the formed
phenol with the un-hydrolysed diazonium salt can be a probable side
reaction, but will the phenol couple at that acidity?
It would be very kind of you to please point out any mistakes in the
procedure and look forward to any valuable suggestions from your end.
Appreciate your reading this.
Gubby
Ron Jones
Have a read of http://www.orgsyn.org/orgsyn/pdfs/CV1P0404.pdf
--
Ron Jones
Process Safety & Development Specialist
Don't repeat history, unreported chemical lab/plant near misses at
http://www.crhf.org.uk Only two things are certain: The universe and
human stupidity; and I'm not certain about the universe. ~ Albert
Einstein
