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leu
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The direct alkylation of DPU has been published in:
A non-phosgene route for the synthesis of alkyl N-phenylcarbamate. From: Chemistry and Industry | Date: June 17,
1991| Author: Ayyangar, Nagaraj; Kalkote, Uttam R.
Recently, a non-phosgene route was reported' for the synthesis of N,N'-diethyldiphenylurea, commercially known as Centralite-I. This involves the
alkylation of sym-N,N'-diphenylurea (DPU), (Ia, R=H) with diethyl sulphate in the presence of sodium hydroxide/potassium carbonate and a phase
transfer catalyst. A detailed study of the alkylation of DPU by different alkylating agents has also been carried out.
The same basic chemical process was patented in:
Abstract of US5124451
Process for the N-alkylation of ureas by reacting a urea with an alkylating agent in the presence of a solid base and a phase transfer catalyst in a
diluent.
Attachment: US5124451A1.pdf (443kB)
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Chemistry is our Covalent Bond
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leu
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A nitrocellulose stabilization patent:
Attachment: FR369797A.pdf (72kB)
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leu
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Another nitrocellulose stabilization patent:
Attachment: FR410239A.pdf (76kB)
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leu
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And another gunpowder patent:
Attachment: US701591A1.pdf (106kB)
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Sauron
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Thanks, leu. The patent ought to be interesting. Chem & Ind is unfortunately unavailable online, so requires someone to trek down to a good
library.
Annoyingly the full text IS available online from some pay service called HighBeam, $200 a year. They have a phony 7 day "free trial" offer wherein
you have to cough up credit card data up front to activate your "free trial" - my mother didn't raise any stupid children so I declined.
I did obtain about half of the next paragraph of the article:
"The importance of methylene-diphenyl isocyanate (III)3 (MDI) in polymer chemistry prompted the development of a method for the preparation of
ethylphenyl carbamate (EPC), (IIa, R=H, R'=Et), a key intermediate in the synthesis of MDI. The known procedures for the ... "
which tells us what their sudden interest in diethyl diphenylurea is all about, and it isn't propellants.
That Austrian-owned US patent is indeed similar chemistry but only explicated the alkylation of urea and monoalkyl ureas, and only with alkyl bromides
(and one example of a chloride). No phenylureas are mentioned, possibly because of prior art. Most of the examples are of preps of unsymmetrical
dialkylureas from monoalkylureas.
Thus, the Chem & Ind paper appears to be the only one "on point" for the specific target compound and with comparative details for various
alkylating agents.
[Edited on 8-8-2008 by Sauron]
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Sauron
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And as it turns out, the above 1991 paper merely points to a 1988 paper in same journal, pp 599-600, by same principle authot A.Ayyangar, entitled "A
Non-Phosgene Route to N,N'-Diethyldiphenylurea" and this is our target.
This 1988 paper is cited in the EP patent corresponding to the US patent posted above.
That EP patent (in German) is attached.
[Edited on 8-8-2008 by Sauron]
Attachment: EP0471983A1.pdf (87kB)
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Sauron
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According to the introductory section of that US patent above, all prior art teaches that N-alkylation of ureas is impossible. Specifically, only
O-alkylation occurs with alkyl halides, or, with dialkyl sulfates, the products are the isouronium salts.
Only in the presence of a PTC (or DMSO) do alkyl halides react with ureas to form alkylureas.
We are only able to surmise (until the text becomes available) that N.Ayyangar's 1988 Chem.Ind. paper teaches that PTC also alters the path of the
alkylation of ureas with dialkyl sulfates to allow succesful N-alkylation without rearrangemnent to the isourea.
And meanwhile we can but speculate that iodoethane or bromoethane could be used instead of diethyl sulfate in the PTC assisted ethylation of
diphenylurea.
The EP version of the patent does include a CA citation of the 1988 paper, but all attempts to google the author's name, the title as given, or both
return only that patent, or the 1991 article, equally inaccessible, and which is on derivatives (carbamates and isocyanates) rather than our target
ethyl centralite proper.
N.Ayyangar turns up in Google Books as a contributor or editor of a text on Phase Transfer Catalysis. But otherwise, this chemist's publications
appear to be limited to the above and a paper on production of codeine from morphine. (And that may or not be actually the same author.)
The patent also cites a paper by another author in Synthesis, on N-alkylation of thioureas. I will retrieve this one. I have Synthesis here on CDs.
[Edited on 8-8-2008 by Sauron]
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Nicodem
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| Quote: | Originally posted by Sauron
@Nicodem, back to an idea I was kicking around upthread:
N,N'-diphenyl-N-ethylurea is readily made from ethyl isocyanate and N-ethylaniline.
Can't one alkylate this to ethyl centralite? Say, iodoethane?
The isocyanate is readily made from diethyl sulfate, potassium cyanate and sodium carbonate by heating with caution as per: |
Just a minor note since I did not read this carefully enough yesterday. Using EtNCO on PhNHEt would give you EtNH-CO-NEtPh of which N-ethylation would
give Et2N-CO-NEtPh and not the target compound. To use isocyanates you would have to react phenyl isocyanate with PhNHEt and then N-ethylate to obtain
the target urea PhEtN-CO-NEtPh.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Sauron
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Thanks. I was going too fast and transposed those.
Anyway the isocyanate route and the trisubstituted urea intermediate are basically out the window, replaced by diphenylurea alkylation with PTC,
Et2SO4, NaOH/sodium carbonate and a little PTC. Those are my best guesses at present till this article from Chem.Ind. turns up.
The bill of materials, to borrow a term from another discipline, thus looks like:
Urea and aniline -> DPU
ethanol and H2SO4 -> diethyl sulfate
NaOH and sodium carbonate
Your favorite PTC
[Edited on 8-8-2008 by Sauron]
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Sauron
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The Synthesis article cited in EP above wasfrom 1984 and concerned N-alkylation of cyclic thioureas, specifically crown ethers containing thiourea
moiety.
In an earlier paper in same series the authors found that such cyclic thioureas could be S-alkylated, then N-alkylated as the isothiouronium salts and
hydrolyzed to the N-alkylated cyclic ureas.
In the subsequent paper nonaqueous conditions were employed and the isothiouronium salts were main products, these readily thermolyzed to the cyclic
N,N'-dialkylthioureas.
PTC was used in both instances, but alkylation initially proceeded via the usual S-attack and isomerization.
The papers are nonetheless instructive. I have combined them into a single pdf for posting here.
[Edited on 8-8-2008 by Sauron]
Attachment: s-1982-29837.pdf (187kB)
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Sauron
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Here is the CA abstract for the 1988 Chem Ind article.
"A non-phosgene route for the synthesis of sym-N,N'-diethyldiphenylurea. Ayyangar, Nagaraj R.; Chowdhary, Anil R.; Kalkote, Uttam R.; Natu, Arvind A.
Natl. Chem. Lab., Pune, India. Chemistry & Industry (London, United Kingdom) (1988), (18), 599-600. CODEN: CHINAG ISSN: 0009-3068. Journal written
in English. CAN 110:134854 AN 1989:134854 CAPLUS
Abstract
Condensation of PhNH2 with H2NCONH2 in alc. or excess PhNH2 gave 88% and 98% PhNHCONHPh (I) resp. Phase transfer-catalyzed alkylation of I with
Et2SO4, powd. NaOH and K2CO3 in xylene in the presence Et3BuN+Br- gave PhEtNCONEtPh in 93% yield."
>90% from aniline and urea in two steps. Now that's a prep!
So now I really want the full text.
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Sauron
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Here's the take from PATR 2700 Volume 3: useful or at least interesting perspective on the technological applications of the centralites, and a precis
on the phosgenation of N-ethylaniline on a lab scale.
I did not consult this earlier simply because I anticipated that no non-phosgene methods for manufacture would be mentioned. Michler's original prep
(1876) is referenced but he employed a carbamyl chloride, itself made of course from phosgene.
Still, this might be helpful in case anyone wants to go the long way round using triphosgene as a safe substitute.
[Edited on 9-8-2008 by Sauron]
Attachment: Pages from Encyclopedia of Explosives and Reated Items 2 by B. Fedoroff.pdf (483kB)
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vulture
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Sauron, could you please condense your posts into a small number as possible, unless you are using attachments? Your posting sequence is usually well
within the edit function time window.
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Sauron
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Thanks, vulture, I will endeavor to do so at all times.
[Edited on 11-8-2008 by Sauron]
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Sauron
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Thanks to gsd, here is the long awaited full text of the Chem & Ind paper from 1988 (attached.)
The aniline and urea were reacted in alcohol or excess aniline under reflux, giving 88% (in alcohol) or 98% (in aniline) of sym-diphenylurea. Aniline
was recycled without reduction in yield. Further details of this step were not given, but are very adequately covered in the literature.
The alkylation step is elucidated on a half molar basis as follows:
0.5 mol sym-siphenylurea in 800 ml xylene is stirred at 200 rpm and 80 C for 1 hour with 2.5 mol powdered NaOH, 0.5 mol powdered potassium carbonate
(anhydrous), and 100 mmol triethylbutylammonium chloride. Then 1.1 mol freshly distilled diethyl sulfate was added and stirring and heating continued
for two more hours. The sym-diethyldiphenylurea was worked up and recrystallized from ethanol, 93% yield.
sym-N,N'dimethyldiphenylurea was prepared in 91% yield by same method. It is known commercially as methyl centralite or centralite-2.
Other PTCs besides Et3BuN+Cl- were used with equal success including Bu4N+Br- and BnEt3N+Br-.
There are some interesting references in this paper. I am digging up two of them.
[Edited on 12-8-2008 by Sauron]
Attachment: A Non-phosgene Route for the Synthesis of Diethyldiphenylurea.pdf (822kB)
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Klute
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Oh I'm jealous of those 3 DVDs 
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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Sauron
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The paper references a 1985 Polish patent 126,634 but I found the Polish Patent Office databases to be wholly useless. Anyway it is probably in
Polish.
By the way, I misspoke above. The source of the paper was Axt not gsd. Thanks, Axt!
[Edited on 14-8-2008 by Sauron]
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Klute
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This following article might be helpfull for anyone interested in preparing diphenylurea:
A rapid microwave assisted synthesis of N, N'-diarylureas under solvent-free condition
S Sarveswari & T K Raja
Indian Journal of Chemistry, Section B; (2)45, 546-547 (2006)
IPC: Int.Cl.7 C 07 C
Abstract:
A novel microwave assisted phosgene-free synthesis of N,N¢-diaryl ureas under solvent free conditions has been described.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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Sauron
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Diphenylurea is prepared under solvent free conditions anyway, from aniline and urea, so I do not see the utility of substituting ethyl acetoacetate
for urea or of having to employ a MW which will restrict the scale.
At most, diphenylurea prep is only solvated with excess aniline which is recyclable to next batch, or with ethanol. Excess aniline gives essentially
quant. yields.
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