Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
 Pages:  1  ..  4    6    8  ..  19
Author: Subject: Acetaldehyde synthesis
Aqua_Fortis_100%
National Hazard
****




Posts: 302
Registered: 24-12-2006
Location: Brazil
Member Is Offline

Mood:

[*] posted on 21-1-2007 at 05:50


guy ,this is a very nice pdf!!!

but i have a doubt : they discribes a catalyst made from CuCl ,phenanthroline(phen) , K2CO3 and some others substances @ 70 to 90°C...
about the CuCl: the oxigen in process oxodizes the copper in Cu II ? has this similar or same eficience as catalyst?
thanks




"The secret of freedom lies in educating people, whereas the secret of tyranny is in keeping them ignorant."
View user's profile View All Posts By User
guy
International Hazard
*****




Posts: 982
Registered: 14-4-2004
Location: California, USA
Member Is Offline

Mood: Catalytic!

[*] posted on 21-1-2007 at 13:51


This method is less complicated, provided you have pyridine and palladium acetate. Works with normal pressure. The reason it works with palladium is because it can make the alcohol do a beta-hydride elimination.

Attachment: palladium_catalyzed_alcohol_oxidation.pdf (62kB)
This file has been downloaded 1219 times





View user's profile View All Posts By User
Nerro
International Hazard
*****




Posts: 596
Registered: 29-9-2004
Location: Netherlands
Member Is Offline

Mood: Whatever...

[*] posted on 21-1-2007 at 14:46


pyridinium chlorochromate is an oxidizer which should oxidize only to the CHO (rather than proceed to the COOH).

I've used it in a practical and it worked quite well.




#261501 +(11351)- [X]

the \"bishop\" came to our church today
he was a fucken impostor
never once moved diagonally

courtesy of bash
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 24-1-2007 at 16:04


Oops. I thought this thread was "aldehyde synthesis." My apologies.

I have been oxidizing n-butanol to n-butyraldehyde using the classic and well known dichromate method:

3CH3(CH2)2CH2OH + Na2Cr2O7 +4H2SO4 --->
3CH3(CH2)2CHO +Na2SO4 +Cr2(SO4)3 + 7H2O

This reaction is a bit hard to control as it is exothermic. And one has to keep the pot hot enough so that the aldehyde will be immediately driven to the condenser before it has a chance to oxidize further to butyric acid. But you don't want the pot too hot or you will drive off too much water and butanol into the distillate. The apparatus I used is shown in the attached photo. As you can see the clear alcohol is being added via dropping funnel. Although I have not done final workup this procedure appears to have given me some nominal amount of aldehyde.

My procedure (Brewster, 1962) specifies something I don't understand. It calls for dichromate at a mole ratio to alcohol of 1:1 instead of the stoichiometric 1:3. The same text, however, in a 1977 edition, changes from n-butanol to n-propanol, and uses a stoichiometric ratio. It also reverses the dropping funnel reactant to dichromate/H2SO4/water, with the n-propanol in the pot. I tried this with the n-butannol and it was a complete failure (disaster), never getting hot enough to flash off the aldehyde and then giving me a runaway when 90% of the dichromate had been added.

So if you have any ideas about the mole ratios specified for this type of reaction I'd like to hear them.

[Edited on 25-1-2007 by Magpie]

n-butyraldehyde.jpg - 59kB




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
Rosco Bodine
Banned





Posts: 6370
Registered: 29-9-2004
Member Is Offline

Mood: analytical

[*] posted on 24-1-2007 at 17:23


Here's something that is relevant and perhaps directly
applicable to what you are doing , with the bonus of having
an easily regenerable reagent which reportedly has a good efficiency in both the oxidative reaction as well as the regeneration .

[Edited on 25-1-2007 by Rosco Bodine]

Attachment: US4297520 Aldehydes via Dichromate Oxidation with electrolysis regenerable reagent.pdf (326kB)
This file has been downloaded 1153 times

View user's profile View All Posts By User
bio2
National Hazard
****




Posts: 447
Registered: 15-1-2005
Member Is Offline

Mood: No Mood

[*] posted on 24-1-2007 at 18:16


Magpie, that's an interesting looking heating mantle
you've got there.

Did you make it yourself with that metal ring looking
heater?
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 24-1-2007 at 19:34


bio2, that is just a regular Glas-Col 500 mL mantle sitting in an iron ring with fiberglass fabric support straps sewn onto it in an "X" pattern. These rings are specially made for that purpose in different sizes and are available through the scientific supply houses. I have a 500mL and a 100 mL size as these are my mantle sizes. With these mantles I can heat all of my RBF's from 25mL to 500mL.



The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
chemrox
International Hazard
*****




Posts: 2953
Registered: 18-1-2007
Location: UTM
Member Is Offline

Mood: LaGrangian

[*] posted on 27-1-2007 at 16:41


So given a way to make acetaldehyde.. it doesn't last very long unless you polymerize it to paraldehyde a substance with certain virtues of its own not the least of which include its use in certain biological test reagents .. so extending the discussion, does anyone have a facile method for taking acetaldehyde to paraldehyde? I tried one published on Erowid and it was bogue...
View user's profile View All Posts By User
fractional
Hazard to Self
**




Posts: 74
Registered: 29-8-2006
Member Is Offline

Mood: No Mood

[*] posted on 28-1-2007 at 04:51


From Cohen, Practical Organic Chemistry, 1910:

" Add a drop or two of concentrated sulphuric acid to 1 c.c. of [acet]aldehyde. The mixture becomes hot in consequence of the aldehyde undergoing polymerisation to paraldehyde (C2H4O)3, b.p. 124deg, which separates as an oil on adding water."

The sulphuric acid serves as a catalyst here. This reaction can be used advantageously to transform acetaldehyde to paraldehyde immediately, rather than storing (or trying to store...) acetaldhyde. Acetaldehyde produced in whatever way is led into a suitably sized RBF with a few drops of sulphuric acid (typically "one drop per cc. of acetaldehyde"), yiedling paraldehyde.
The reverse reaction takes place when paraldehyde is heated again with a few drops of sulphuric acid. "Paraldehyde does not show the characteristic aldehyde reactions; on destillation with dilute sulphuric acid it is converted back to the ordinary variety" (Gattermann, Practical Methods of Organic Chemistry). The liberated acetaldehyde can be collected in a cold-trap (e.g. cooled with an ice/salt mixture, etc.).

[Edited on 28-1-2007 by fractional]
View user's profile View All Posts By User
Rosco Bodine
Banned





Posts: 6370
Registered: 29-9-2004
Member Is Offline

Mood: analytical

[*] posted on 28-1-2007 at 08:22


Paraldehyde is physiologically active IIRC , it is a hypnotic similar in action to chloral hydrate . So you might wish to be careful with this material , so as not to nod out unexpectedly .....and I don't recall what was the route of exposure ....contact , inhalation , or ingestion ....but
it is not a benign material .
View user's profile View All Posts By User
fractional
Hazard to Self
**




Posts: 74
Registered: 29-8-2006
Member Is Offline

Mood: No Mood

[*] posted on 29-1-2007 at 04:20


Rosco is absolutely right about paraldehyde: it is physiologically active and a controlled substance (at least here in Europe). One can avoid handling this substance by applying a minor modification to the procedure:

"If aldehyde is cooled and treated with sulphuric acid, or if at the ordinary temperature gaseous hydrochloric acid, sulphur dioxide, or other compounds are passed into it, a solid polymerisation product, metaldehyde, is formed; this can also be coverted back into the ordinary variety." (Gattermann).

As a solid, metaldehyde is easy to handle, but it is also toxic, especially by inhalation. Wikipedia claims that it used as camping fuel for small stoves. I don't know about this, though.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 1-2-2007 at 17:09


This is a followup to my post on making n-butyraldehyde from n-butanol using dichromate. I made 3 batches. The 2nd two were an effort to improve the control or efficiency of the 1st. The 1st was "by the book," only 1/3 scale because of the smaller size of my 19/22 glassware.

I didn't bother to calculate yields from each batch but just combined them for a final distillation to isolate the aldehyde. Upon review I think the book procedure is the best. The 2nd batch where I added the oxidant instead of the alcohol was pretty much a failure/disaster/runaway. For the 3rd batch I tried to conserve oxidant by using 2/3's of the specified alcohol and 1/2 of the specified oxidant. Near the end of the alcohol addition I ran out of oxidant as was evident from a lack of reaction as the alcohol was dripping into the pot.

I ended up with about ten mLs of aldehyde as a distillate from a fractional distillation using a 4 inch (10 cm) column packed with broken glass. Instead of coming over at the specified boiling point range of 72-76C (bp = 76C) it came over at 66C. I believe that this likely is an azeotrope with water which is 90.3% aldehyde and has a bp = 68C. I don't know what else to think.

I ran some qualitative tests on this distillate. It gave a positive test for Tollen's reagent (silver mirror) but a negative test for Fehling's reagent (Cu2O ppt). It gave a positive test with 0.3% KMnO4. It produced a small amount of white crystals after mixing with a saturated solution of potassium metabisulfite and cooling.

In conclusion I feel that this is an interesting but touchy way to make an aldehyde, and that one shouldn't expect a high yield. I would be interested in hearing about anyone else's experiences with this method.

Edit: I also wanted to mention that my aldehyde had a smell reminiscent of squeezed orange peels. It was pungent and overwhelming if I smelled too much of it.

[Edited on 2-2-2007 by Magpie]




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
fractional
Hazard to Self
**




Posts: 74
Registered: 29-8-2006
Member Is Offline

Mood: No Mood

[*] posted on 3-2-2007 at 04:13


Butyraldehyde forms an azeotrope with water:

b.p. 68,0 degC, with 90.3% butyraldehyde and 9.7% H2O in the azeotrope. (My source, a table of azeotropes from an old edition of the HB of Chem and Physics, only says "butyraldehyde", so I can only assume that they mean n-butyraldehyde)

So this seems to explain the lower boiling point. However, the table also indicates that two phases should be formed (with 96.8% butyraldehyde and 3.2% H2O in the upper and 7.1% butyraldehyde and 92.9% H2O in the lower layer). Is this in line with your observations?
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 3-2-2007 at 10:19


@fractional: Interesting. No, I cannot see two phases. I am giving some thought to dewatering with 3A molecular sieves and then rechecking the boiling point.



The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
Nicodem
Super Moderator
*******




Posts: 4230
Registered: 28-12-2004
Member Is Offline

Mood: No Mood

[*] posted on 4-2-2007 at 13:15


Magpie, you might want to try out the method from the attached paper. It is ridiculously easy, but therefore also kind of suspicious (especially since it is from Tet. Letters and there is no experimental data). It would be nice if someone verify it and report back the results, since I might have a use for it on an aliphatic alcohol as well. n-Butanol is not one of the substrates tested, but the yield from n-pentanol to n-pentanal was 65% which sounds really good for an aliphatic alcohol.

PS: Molecular sieves on aliphatic aldehydes does not sound as a very good idea…

Attached is: Tetrahedron Letters, 43 (2002) 8843-8844. doi:10.1016/S0040-4039(02)02234-7

Attachment: Selective solvent-free oxidation of alcohols with K2Cr2O7.djv (170kB)
This file has been downloaded 1042 times





…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!
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 4-2-2007 at 15:56


@Nicodem: Thanks for that reference. It seems like a simple method for making aldehydes and I might give it a try.

Why do you say not to use molecular sieves to dry an aliphatic aldehyde?




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
not_important
International Hazard
*****




Posts: 3873
Registered: 21-7-2006
Member Is Offline

Mood: No Mood

[*] posted on 5-2-2007 at 00:57


Quote:
Originally posted by Magpie
Why do you say not to use molecular sieves to dry an aliphatic aldehyde?


The sieves can function as bases or acids, depending, and give condensation and/or cross-redox products.

Sodium sulfate for a first drying, polish with MgSO4.
View user's profile View All Posts By User
leu
National Hazard
****




Posts: 368
Registered: 13-10-2005
Member Is Offline

Mood: No Mood

[*] posted on 19-3-2007 at 13:37


Butyraldehyde is synthesized from butanol using manganese dioxide using a column in Proceedings of the Chemical Society 110 (1964) :D

[Edited on 20-3-2007 by leu]

Attachment: harrison.zip (20kB)
This file has been downloaded 824 times





Chemistry is our Covalent Bond
View user's profile View All Posts By User
Rosco Bodine
Banned





Posts: 6370
Registered: 29-9-2004
Member Is Offline

Mood: analytical

[*] posted on 21-12-2007 at 04:00
more interesting info about V2O5:H2O2


This should have many possible uses .

Attachment: Synthesis of Vanadium Oxide Gels from Peroxovanadic Acid Solutions A 51V NMR Study.pdf (119kB)
This file has been downloaded 3228 times

View user's profile View All Posts By User
Siddy
Hazard to Self
**




Posts: 81
Registered: 8-10-2007
Member Is Offline

Mood: No Mood

[*] posted on 23-12-2007 at 21:17


^ I cant work that link?

What about thought Ethyl Chloride (Chloroethane)?

EtOH + HCl > EtCl
(ZnCl2 catalyst)

EtCl + H2O2 > EtO
(catalyst?)
View user's profile View All Posts By User
carbonic
Harmless
*




Posts: 17
Registered: 22-2-2008
Member Is Offline

Mood: No Mood

[*] posted on 22-2-2008 at 15:03


I have a paraldehyde synth that's up for discussion or debunking. I was not trying to make paraldehyde, just to test some oxidizers so I wasn't taking notes or anything but it's easy to repeat if someone would like to check it against a Tollin's test or something.

I used two routes, percarbonate alone and percarbonate with ferric chloride. It seemed to me that percarbonate was a nice way to get a gently basic H2O2 oxider so I used ethanol as a test platform. H2O2 solution plus iron is called Fenton's reagent and is commonly used to oxidize contaminants all the way to carbon dioxide. It seems the ferrous (not ferric) ion busts the H2O2 into hydroxyl radicals, which are vicious oxidizers. From my tests, the ferric chloride just precipitates iron which makes all the H2O2 fizz out of solution. So although I got similar results using each method, I doubt the ferric was helping.

At any rate, the synth was simple: Add oxiclean (basically pure percarbonate with some borate stabilizers) to vodka and heat. About a scoop of percarbonate to 100ml 50% EtoH was what I used but I did not try to optimize. After heating for about 10 minutes, what I found was upon cooling, the solution split into two layers. One test was to pipette some of the lower layer into a test tube run under cold water - it solidified. Run under hot water it melted again, and would be kind of sludgy if left at room temp.

The second test was to filter the whole shebang (to get out the insoluble carbonates) and drop in an ice cube and stick it in the fridge. Almost the whole hundred ml turned to sludge which was then filtered and subjected to the same melting/freezing tests.

At first I was a bit puzzled, as I had expected acetaldehyde as a water-soluble product, but then it occurred to me that peroxide was a very efficient polymerization initiator so the acetaldehyde was probably polymerizing as soon as it was formed, creating a less-soluble product that eventually dropped out of solution. The data on peraldehyde seemed to match the liquid that I had, so I called it a day and dumped it out.


Well that's it: oxiclean as an oxidizer, who knew? I may try again soon to see if the mystery liquid haloforms, but I think Tollen's would be a better test. I might get some useful data from haloforming it, because ethanol gives a really weak haloform, whereas real ketones/aldehydes haloform almost violently.

My results are easy to duplicate, so if anyone out there has the capability to better analyze this product, please let us all know!

Edited to add another question: Why the hell would anyone want paraldehyde or acetaldehyde anyway? What's it good for?

[Edited on 22-2-2008 by carbonic]
View user's profile View All Posts By User
Filemon
Hazard to Others
***




Posts: 126
Registered: 26-4-2006
Member Is Offline

Mood: No Mood

[*] posted on 24-2-2008 at 13:54


I read in Organic Sintheses, it may reduce to aldehyde from carboxilyc acid with formic acid. Making the pyrolysis of the calcic double salt. I have looked for the reference but I don't find it.
View user's profile View All Posts By User
Nicodem
Super Moderator
*******




Posts: 4230
Registered: 28-12-2004
Member Is Offline

Mood: No Mood

[*] posted on 24-2-2008 at 23:06


You forgot to look for those references on this forum as well:
https://sciencemadness.org/talk/viewthread.php?tid=2223&...
View user's profile View All Posts By User
carbonic
Harmless
*




Posts: 17
Registered: 22-2-2008
Member Is Offline

Mood: No Mood

[*] posted on 25-2-2008 at 09:48


but really, what is acetaldehyde good for?
View user's profile View All Posts By User
Sobrero
Harmless
*




Posts: 21
Registered: 20-5-2006
Location: Belgium
Member Is Offline

Mood: Lifting my skinny fists like antennas to heaven

[*] posted on 26-2-2008 at 05:08


Pentaerythritol synthesis ;).



"There exists a world. In terms of probability, this borders on the impossible." (Jostein Gaarder)
View user's profile Visit user's homepage View All Posts By User
 Pages:  1  ..  4    6    8  ..  19

  Go To Top