Picric-A
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Phenylthiocarbamide
'70% of humans can taste this non-toxic compound and it tastes incredible bitter, 30% can not taste it all.'
http://en.wikipedia.org/wiki/Phenylthiocarbamide
I would love to make a sample of this compound to test whether me and my family can taste the compound. The compound looks very simple and so no doubt
it can be easily made.
One idea i had was reaction of 0.1 mole bromobenzene with an excess of thiourea in acetone wth K2CO3 present. Would this work?
Has anybody got any other ideas for the synthesis? I have tryed looking in google, vogel ect. but all i can find are patents showing genetics.
Any help appreciated.
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DJF90
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You can't do an Sn2 on an sp2 center. And thiourea is typically nucleophilic at the sulfur atom, anyhow. You'd likely have to go via the phenyl
isothiocyanate, which I'm sure isn't a pleasant compound.
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ScienceSquirrel
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I would suggest treating aniline hydrochloride with potassium thiocyanate, this is a modification of Wohlers synthesis of urea and works for thiourea.
You will want this paper or similar;
https://www.thieme-connect.com/ejournals/abstract/synthesis/...
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Picric-A
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Thanks for the reply. That makes sense. I will probably order the Phenyl Isothiocyanate in because it would betoo much of a hastle to make but just
out of curiosity, Phenyl Isothiocyate can be made from the reaction shown below. How would the final step (Pb(NO3)2 )be performed?
Also, would the Phenyl Isothiocarbamate be reacted with ammonia in a solvent (say Et2O?) to form the desired compound PTC?
Thanks,
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ScienceSquirrel
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The reaction of aniline hydrochloride with potassium thiocyanate uses cheaper, more readily available and easily handled reagents.
The preparation of phenyl isothiocyanate is in Organic Syntheses;
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...
Reaction of ammonia with PITC would be best carried out in aqueous ethanolic or ethanolic solution.
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smuv
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I always wanted to make this. What you do, is you make aniline and then you condense it with a thiocyanate salt to make the thiourea. Very otc.
"Titanium tetrachloride…You sly temptress." --Walter Bishop
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ScienceSquirrel
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Have a look at this paper, if you can get your mitts on aniline and ammonium thiocyanate, it is easy;
http://www.aensionline.com/jasr/jasr/2010/1014-1018.pdf
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Picric-A
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That does look incredibly easy! IM confused though because in the reaction i showed at the beggining ammonium thiocyante is essentially being made
in-situe form NH3 + CS2 but that reaction goes through two intrmediates before making the phenylthiocarbamide wheras this shows only amonium
thiocarbamide is needed. whats going on?
Does PITC not react with ethanol (alcohols)?
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DJF90
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| Quote: | | IM confused though because in the reaction i showed at the beggining ammonium thiocyante is essentially being made in-situe form NH3 + CS2
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Really? Cos to me, the product of ammonia with carbon disulfide is a dithiocarbamate. Maybe all the big words are scrambling your brains a little.
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smuv
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what happens with the CS2 reactions, is you first have the condensation w/ the CS2 to make the arylthiocyanate which is then condensed with ammonia to
make the thiourea. Essentially it is the opposite of making the phenylthiourea from aniline and thiocyanate.
Edit: or depending on the rxn conditions the dithiocarbamate may be the principle intermediate (as DJF90 Stated). Acidic condensations favor
arylthiocyanate.
[Edited on 5-17-2011 by smuv]
"Titanium tetrachloride…You sly temptress." --Walter Bishop
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ScienceSquirrel
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Really it is simple.
Ammonium thiocyanate is a structural isomer of thiourea.
I f you imagine ammonia NH3 and thiocyanic acid HNCS being in equilibrium with the ammonium thiocyanate NH4NCS.
The ammonia can attack the thiocyanic acid, switch a few protons around and you have thiourea.
A simple extension gives you an alkyl or aryl derivative.
This is the basis of Wohler's synthesis of urea from ammonium cyanate that destroyed the theory of vitalism and laid one of the the intellectual
foundations of modern synthetic organic chemistry.
PITC will react with alcohols but amines are a lot stronger nucleophiles by orders of magnitude so react preferentially. Also the alkyl
dithiocarbamate esters formed would react with the amine to form the urea anyway.
Bollocks, dithiocarbambamates, Flintstone fever
[Edited on 17-5-2011 by ScienceSquirrel]
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smuv
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Here is some stuff I have on thioureas/phenythiourea, including the paper ScienceSquirrel referenced.
Attachment: phenylthiocarbamide_tasting_in_a_sample_of_twins.pdf (366kB)
This file has been downloaded 429 times
Attachment: Phenylthioureas_NH4SCN_Aniline_deriv.pdf (33kB)
This file has been downloaded 572 times
[Edited on 5-17-2011 by smuv]
Edit: Also, you stated phenylthiocarbamide is non-toxic, this is not true, it is reasonably toxic. Not at the doses for genetic testing, but still,
it should not be treated as a non-toxic compound, especially during human trials.
[Edited on 5-17-2011 by smuv]
"Titanium tetrachloride…You sly temptress." --Walter Bishop
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Picric-A
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Thanks for all the great replys guys, it has been realy helpful. Im going to see if we have any ammonium thiocyanate in stock, if not i will order it
in and when i have it i will perform the reaction, taking photos to upload onto here.
Where i took the reaction product of NH3 + CS2 was wikipedia saying the following;
"Ammonium thiocyanate is made in the United States by the reaction of carbon disulfide with aqueous ammonia. Ammonium dithiocarbamate is formed as an
intermediate in this reaction, which upon heating, decomposes to ammonium thiocyanate and hydrogen sulfide:
CS2 + 2 NH3(aq) → NH2C(=S)SNH4 → NH4SCN + H2S
"
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ScienceSquirrel
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A few lines of write up will do for me.
A photo of the product, but one set of colourless needles looks like any other.
Get a melting point and any other evidence that it is what you claim it to be and it is pure.
A few photos of you and your friends sucking on a crystal! 
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