| Pages:
1
2 |
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by laekkerBoy  |
After posting this thread, I have learned that the easiest way to synthesize Phenol is by the following route:
Toluene --(Friedel-Crafts)-->
Benzene --(Chlorination)-->
Chlorobenzene --(Raschig-Hooker)-->
Phenol.
I hope that this can help you guys too! I'll promise to post some pictures or a video of my reaction when I am able to do it. |
That is supposed to be the easiest way to synthesize phenol? Are you trying to appear funny or make fun of us?
| Quote: | | Nicodem: I am sorry for that I didn't tell any pages or so with literature. I'll remember that for the next time. |
There already was a next time and you did not remember! What is the reference for the Friedel-Crafts disproportionation of toluene?
| Quote: | | I think that the salicylic acid way is too expensive when you think of the final product, but thanks anyways! |
This makes no sense. You would go investing money onto building an apparatus able to withstand the pressure required for transforming chlorobenzene
into phenol, but have troubles acquiring salicylic acid? You don't mind doing research into the transformation of toluene into benzene, but have
troubles doing a known decarboxylation of salicylic acid? If it is about the price, then why don't you just buy phenol? Or buy 2,4,6-trichlorophenol
for that mater? Maybe you should simply get serious, because at the moment it appears as if you were some teenager not knowing what to do with your
time and yourself.
|
|
|
bbartlog
International Hazard
Posts: 1139
Registered: 27-8-2009
Location: Unmoored in time
Member Is Offline
Mood: No Mood
|
|
There is a previous thread regarding phenol (probably multiple ones), including one I started when I wanted some advice on what sort of gunk I had
made by reacting sodium hypochlorite and aspirin. See http://www.sciencemadness.org/talk/viewthread.php?tid=13026#...
Dry pyrolysis of sodium salicylate will get you phenol. One of the members here (benzylchloride1) describes his procedure in the abovelinked thread.
Further, it appears to me that it is not necessary to proceed through phenol as such in order to obtain 2,4,6-chlorophenol. I notice (again in the
above thread) the following comment from Nicodem:
| Quote: | | The chlorination of salicylic acid proceeds in this order: 5-chlorosalicylic acid (and some 3-chloro regioisomer), 3,5-dichlorosalicylic acid,
2,4,6-trichlorophenol (via ipso electrophilic substitution) |
So rather than synthesize phenol it seems that you might be better off chlorinating salicylic acid directly, with the third chlorination providing
decarboxylation at the same time. Exactly what method of chlorination you would want to use is an interesting question, but a little research would
surely provide you an answer.
| Quote: | | I think that the salicylic acid way is too expensive when you think of the final product, but thanks anyways! |
I have no idea what country you are in, but here in the USA I can go to the drugstore and buy plain old aspirin at a price that comes out to about $7
per mole of (acetyl)salicylic acid. Which as organic reagents go is ridiculously cheap, and given that this is a pharmaceutical it's probably even
fairly pure once the binders/additives are removed.
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Indeed, purchase ordinary generic uncoated aspirin and you have a low cost source that requires little workup.
The main exception is in Japan, where in most places you have to buy little boxes with only a few tablets and highly market p, from little mom&pop
stores.
|
|
|
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by bbartlog | Further, it appears to me that it is not necessary to proceed through phenol as such in order to obtain 2,4,6-chlorophenol. I notice (again in the
above thread) the following comment from Nicodem:
| Quote: | | The chlorination of salicylic acid proceeds in this order: 5-chlorosalicylic acid (and some 3-chloro regioisomer), 3,5-dichlorosalicylic acid,
2,4,6-trichlorophenol (via ipso electrophilic substitution) |
|
I based that mostly on the analogy of nitration where nitration of salicylic acid with fuming HNO3 gives picric acid and the nitration of
3,5-dichlorosalicylic or 3,5-dibromosalicylic acids gives 2,4-dichloro-6-nitrophenol and 2,4-dibromo-6-nitrophenol correspondingly (see examples cited
in Chem. Rev., 40 (1947) 117–140). The ipso aromatic electrophilic substitution of the carboxylic group occurs quite commonly on
some substrates, so I thought it was a general phenomena for salicylic acid. Now that I searched for trichlorination of salicylic acid I can not find
any such reaction. In highly acidic the product is 3,5,6-trichlorosalicylic acid as described in the two references given upthread. I would expect
that under basic conditions (chlorination of the phenoxide) there should form 2,4,6-trichlorophenol, but I can not find any such example in the
literature. There are only three 19th century papers describing what appears a two step preparation 2,4-dichlorophenol by chlorinating salicylic acid
followed by treatment with lime for the retro-Kolbe-Schmitt reaction. Unfortunately, I can't get the original papers and this is all info I can get
out of Beilstein. On the other hand, the bromination of sulfosalicylic acid gives 2,4,6-tribromophenol (J. Am. Chem. Soc., 43 (1921)
303–315). The reaction can be performed one-pot from salicylic acid.
…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!
|
|
|
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
I'm wandering if someone can help me out. I understand ipso substitution very well, or at least I though I did. In an attempt to write a response to
this thread I found myself unable to explain why the ipso substitution of trinitrobenzoic acid takes place - a very well known textbook reaction - as
in the formation of the wheland intermediate this requires the formation of the arenium ion directly adjacent to the electron withdrawing nitro group!
Now this should be massively disfavoured, so the reaction is either kinetically controlled, or thermodynamically driven (although I cannot see how
so).
Salicylic acid however does not suffer from such problems, as the phenolic group stabilises the wheland intermediate and all is above board from
there. Bromination should be analogous, but details may be scarce in the literature because nitration is the main reaction that was studied regarding
Ipso substitution.
EDIT: Sussed it. Former occurs via different mechanism (SE1) compared to SEAr. o-nitro substituents aid this mechanism, as the sp2 anion is
in the plane of the ring and so oblivious to mesomeric effects: the NO2 groups provide good inductive withrdrawal to stabilise the anion, and as the
inductive effect decreases with distance, it explains why ortho EWGs work very well.
A corrolary of this appears thusly: Both o- and m-nitrobenzoic acids could possibly yield nitrobenzene by refluxing in acid (via the
two different mechanistic pathways). This would be a nice amatueristic route, especially as nitration of toluene and subsequent oxidation would yeild
the former, and nitration of methyl benzoate and hydrolysis would lead to the latter. Interestingly the hydrolysis step with methyl
m-nitrobenzoate may even be done in situ using acid to effect hydrolysis and decarboxylation in one step
[Edited on 22-4-2010 by DJF90]
|
|
|
White Yeti
National Hazard
Posts: 816
Registered: 20-7-2011
Location: Asperger's spectrum
Member Is Offline
Mood: delocalized
|
|
How about making phenol from benzene and Fenton's reagent? It's an obscure way to make phenol, but it seems to work.
|
|
|
UnintentionalChaos
International Hazard
Posts: 1454
Registered: 9-12-2006
Location: Mars
Member Is Offline
Mood: Nucleophilic
|
|
| Quote: Originally posted by White Yeti | | How about making phenol from benzene and Fenton's reagent? It's an obscure way to make phenol, but it seems to work. |
To avoid destruction of the phenol, the reactants need to be extremely dilute and you need a very large excess of benzene, from what I remember
reading.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
|
|
|
White Yeti
National Hazard
Posts: 816
Registered: 20-7-2011
Location: Asperger's spectrum
Member Is Offline
Mood: delocalized
|
|
"To avoid destruction of the phenol, the reactants need to be extremely dilute and you need a very large excess of benzene, from what I remember
reading."
That makes sense.
What concentration would you recommend?
|
|
|
UnintentionalChaos
International Hazard
Posts: 1454
Registered: 9-12-2006
Location: Mars
Member Is Offline
Mood: Nucleophilic
|
|
| Quote: Originally posted by White Yeti | "To avoid destruction of the phenol, the reactants need to be extremely dilute and you need a very large excess of benzene, from what I remember
reading."
That makes sense.
What concentration would you recommend? |
That makes recovery of the phenol from the reaction mixture very difficult, and I am suggesting that you don't bother pursuing it as a preparative
technique unless you can find some literature on it.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
|
|
|
White Yeti
National Hazard
Posts: 816
Registered: 20-7-2011
Location: Asperger's spectrum
Member Is Offline
Mood: delocalized
|
|
"That makes recovery of the phenol from the reaction mixture very difficult, and I am suggesting that you don't bother pursuing it as a preparative
technique unless you can find some literature on it."
I wasn't even planning on making it, for the simple fact that benzene and phenol are about the same price. Any reaction pathway that would yield
phenol from benzene is not worth trying out. Both substances are dangerous/ flammable/ carcinogenic, I'd rather buy phenol than make it.
I was just suggesting Fenton's reagent as an unexplored possibility that none of the other users have mentioned (probably for a good reason).
|
|
|
bfesser
|
Threads Merged
14-11-2013 at 19:33 |
bfesser
|
Thread Pruned
14-11-2013 at 19:34 |
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
