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Author: Subject: Esters and their Synth
tongqiancao
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smile.gif posted on 7-6-2007 at 04:57
Thanks for the first reply I have recieved


I come from the China. I am a university student of the chemistry department. This is the first time for me to visit a foreign disscussion board, so your reply courage me so much.
Thank you indeed.
When I wanted to get a article for my experiment by google someday, I finded this board.Glad to become a member of this board.

"dip by tooth pick" ...........I see;)




ssdd
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[*] posted on 7-6-2007 at 05:20


It's no problem, I have found that most everyone on this forum is pretty nice and willing to share their knowledge with people.

Feel free to U2U me or use aim if you can...

(Is the china firewall we hear about really like that?)

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JohnWW
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[*] posted on 7-6-2007 at 10:16


Instead of using www.google.cn in China (to which attempting to log onto www.google.com automatically redirects to), you could either directly access the national Google sites of other countries, e.g. www.google.co.uk, www.google.com.au, www.google.fr, www.google.com.br, www.google.co.nz, www.google.ca, www.google.es, etc.; or else access these, according to their countries, through configuring a browser other than Internet Explorer with a proxy server located in some country outside China. Lists of the IP addresses, port numbers, and countries of proxy servers are given at www.samair.ru and www.proxy4free.com .
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LSD25
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[*] posted on 17-6-2008 at 06:59


This has some potential for making the ethyl ester of benzoic acid in good yields in a short time.

This article (actually taken from a textbook) describes the various routes to esters, such as from the anhydride of the acid and the heating of the acid in solution with the alcohol in the presence of an acid:

http://courses.chem.psu.edu/chem36/SynFa06Web/Expt84.pdf

The attached article deals with the existence of a mixed anhydride between benzoic acid and polyphosphoric acid in solution.

Now, if one added ethanol to the mixed anhydride what would be the product? Would it be reasonable to expect that the acid anhydride (even the mixed one) would rapidly combine with the alcohol to give the ester in quick time?

The only problem I foresee is that the strong acid (PPA) might cause saponification of the ester before it can be removed. Of course, the other possibility is that the phosphoric anhydride might itself form an ester with the alcohol to form the alkylating agent.

The sudden interest is derived from a pressing need for benzamide so as to attempt the Hoffman rearrangement of the same to aniline. No real reason.

Any ideas would be greatfully received, I would like to try this out soon as I can get my benzoates.:D

Attachment: PPA.Benzoic.Anhydride.pdf (354kB)
This file has been downloaded 5442 times





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[*] posted on 17-6-2008 at 07:28


Yes, you can use polyphosphoric or pyrophosphoric acid for esterifications, but since it is much more simple and economic to use H2SO4, I doubt you will find much examples in the literature (if at all). The intermediate formation of alkyl phosphates is generally irrelevant as long as you let the reaction reflux long enough since the ester with benzoic acid is the thermodynamic product (similarly as I think I explained at the beginning of the thread for alkyl sulfates). Rather than making esters, the use of polyphosphoric acid or P2O5 is more practical for preparing certain volatile acid anhydrides which are otherwise difficult to prepare. The formation of the mixed anhydride is of advantage since even thermodynamically less favorable acid anhydride products can be distiled out given the unvolatility of P2O5, polyphosphoric acid and the mixed anhydrides (for example even triflic anhydride, bp 82°C, can be prepared this way).

To prepare benzamide you can use benzoic acid directly with urea (there is a thread on this somewhere - some members experimented with this method).

[Edited on 17/6/2008 by Nicodem]




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LSD25
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[*] posted on 17-6-2008 at 07:51


Thanks, it is nice to be on the right track for a change:D



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Panache
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[*] posted on 17-6-2008 at 17:43


Quote:
Originally posted by Eclectic
Taste is only satly, sweet, bitter, sour, umami.

Taste

Everything else is smell.


Nice to see the world finally starting to acknowledge umani, i knew all those cheap japanese take-outs had an important role for society.

There is taste, there is smell and there is touch. For consuming foods, the palate, which is a less directly measurable, is a combination of these three senses in the mouth and nasal cavity. To a certain extent how an item looks also affects its 'palatability' but in any decent testing regime testing is done blindly.

I have been working on making many of these esters and some aldehydes (cinnamonaldehyde, benaldehyde) palatable, without using sugar synergies for some time and its very difficult. We are wired to detect quickly fats. Fats are the only inherently palatable food even sugars are not and the taste must be acquired, although it is readily acquired. Anything bitter needs to be generally at 1000 times lower the concentration of sugars or fats in the mix to be pleasant. This is explained by the taste bud sensitivity, much much more sensitivity to anything bitter, because bitter=poision.

Apologies for the seeming off-topicness but i saw an opportunity to ask a question of members. Sometimes an off hand piece of knowledge can help immensely. If anyone has any interesting 'tips' on this kind of work (ie getting falvanoids palatable without using simple sugars, fats or sweetners) i'd love it if you could message me, posting here would be off topic.

Thanking you all in advance.




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[*] posted on 12-4-2009 at 16:55


I've recently tried making isopropyl benzoate by following an analogous reaction to that of methyl benzoate as that outlined in Williamson's Organic Experiments. Well, at least in principle, because when it comes to chemistry reagents and apparatus I'm nearly hopeless. Instead of using the typical roundbottom, condenser etc. I used test tubes instead and instead of highly pure sulfuric acid I had to content myself with drain cleaner (don't you wish you were as privileged as me!?). The isopropyl alcohol and benzoic acid I'm lucky enough to be in fairly pure form, sot that's not really my worry.

Now, here's the deal. I've tried this twice and twice I've failed. I take ~0.5g Benzoic acid with 7.5 times the moles amount of alcohol without any use of solvent, I let the stuff sit under "reflux" (with me next to it making sure to keep the stuff refluxing with an improvised test-tube condenser) for an hour, then I neutrilize it with bicarbonate, dry with anhydrous MgSO4 and then simply drive off the excess alcohol. Result? A big nice juicy precipitate of Benzoic acid.

I can't be sure what it's wrong with my synthesis or my procedure or why it would fail. I'm thinking that perhaps the reflux should be done for a longer time (what a hassle without the appropriate equipment) but also the otherwise gunky useless drain sulfuric acid may be the problem. I've noticed this in the color of the semi-oily solution that forms after reflux, and I know that the ester is supposed to be clear. This does not change after neutralizing and drying. I've tried to look for an official synthesis without much success (the ones I've found in the literature are all new fancy stuff--as usual--nothing practical to the mere household chemist). Does anyone know, or may suggest, what I'm doing wrong (except just about everything) or why it wouldn't work?
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DJF90
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[*] posted on 12-4-2009 at 20:00


You didnt mention ADDING your acid catalyst... So did you?
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[*] posted on 12-4-2009 at 20:32


Are you sure the drain cleaner was H2SO4? Also, maybe it was too dilute - dilute acid will hydrolyze esters.

I've made esters quite a few times and it has always worked. Though I did have a condenser and I used pure reagents.

Edit:
Also, in the future, if you want to make them on a large scale, reflux for longer. 1 hr isnt anywhere enough when trying to make something like 200 ml.

[Edited on 4/13/2009 by Saerynide]




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[*] posted on 12-4-2009 at 20:52


______, my best guess is not enough heating. Secondary alcohols like iPrOH react slower than primary ones. Other than that, I don't see anything particularly wrong with your procedure, test tubes can work for small scale. Also - Are you using 100% iPrOH (rather than the more easily available OTC 91% stuff?) You want to avoid any excess water.

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[*] posted on 13-4-2009 at 15:22


I dried my IPr before hand, so I know I must be using >99%. The acid is dilute though (not sure how much) so this may be a problem. I also think you are right, pantone159, the reflux may just need more time (2-3hours?). I think, if I have the time, I'll try this again and see if it works out.
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Panache
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[*] posted on 19-4-2009 at 14:54


Quote: Originally posted by __________  
I dried my IPr before hand, so I know I must be using >99%. The acid is dilute though (not sure how much) so this may be a problem. I also think you are right, pantone159, the reflux may just need more time (2-3hours?). I think, if I have the time, I'll try this again and see if it works out.


You are using a solvent, it just happens to be the same as one of your reagents in this case.
This will work if your acid catalyst concentration is around 3% of benzoic acid mass. So if you are using 10g BA use 3% of this mass added as H2SO4.

SOME DRAIN CLEANERS ARE CAUSTIC.

Reflux overnight.

Longer reaction times are needed with esterifications when the alcohol is in excess (as opposed to the acid in excess, benzoic acid that is in this case). If you have some mol. sieves lying around throw them in to reduce the reaction time.

[Edited on 19-4-2009 by Panache]




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