Urea as dye

[Tim_Lou]

my latin teacher told me that in acient Roman, people use urea as a purifying dye.

they use them to dye the color white.

 

thats pretty disgusting...

 

well, as people heat urea, they get ammonium, thats how it is able to dye white.

NH2--CO--NH2 --> NH4CNO

[TINNY]

what's the relation of ammonia with ability to dye white?

[Tormod]

what's the relation of ammonia with ability to dye white?

 

Yeah...doesn't ammonia simply remove colors?

[Tim_Lou]

well, its not really dye white... but remove colors on the wools so that it appears white.

(all Roman clothes are made out of wools... well, maybe silk, but its only for very rich peopple)

[TINNY]

so you've tested it?

[Tim_Lou]

lol...

i can just buy bleacher in store, no need to use urea ;) .

[TINNY]

of course. but i thought you should verify the accuracy it just for the sake of it. You obviously don't want to put your urea to practical use!

[Tim_Lou]

well, i cant do this experiment, but i find something on the internet:

 

http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Urease-e.htm

 

take a look at the chemical equation at the nearly bottom.

 

(er, cant find an online demo) ;)

[TINNY]

oh.... so you need the urease enzyme. i thought you just produce your own urea onto the cloth that you want to dye.

No wonder I thought it strange that water and urea can so easily produce ammonia...

[Tim_Lou]

edit: urease enzyme is required in the decomposition of urea in soil, but in the case of boiling it, it is not necessary to have enzyme.

[TINNY]

so you can't just pee on your clothes and turn it colorless

[Tim_Lou]

lol....i dont think so....well, you can heat it... ;)

[TINNY]

so 37 degrees C is not warm enough huh?

[Tim_Lou]

its an equilibrium problem,

37 degrees might not have a good yield of ammonia...

anyway, after many more research, i figured out that when urea is heated, the reation should be:

CO(NH2)2 --> NH4NCO, the reverse of Wöhler's famous synthesis of urea. (1st time of converting inorganic compounds to organic compounds), where NH4- ion converts to NH3 and escape, leaving the dangerous NCO- (cyanate) ion...

"In an open system, half the urea was destroyed after 5 hr @ 90 o C and pH 7, Half life estimated 25 years @ 25 o C "

from http://carewinnipeg.com/OriginofLifeStudies.htm...

in order to calculate the yield under certain temperature, or the reaction rate, an equilibrium constant or reaction rate constant in certain temperature is needed..... which i cant find them anywhere, sorry about that... :)