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Author: Subject: toluene --> benzaldehyde
LoKi
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[*] posted on 14-3-2008 at 22:42


an interesting fantasy I had a few years ago..
styrofoam coffee cups are ground fine, heated to distill styrene
styrene is oxidized to benzoic acid and (hopefully) 30% benzaldehyde.
I find some references but I think the "benzal from coffee cups synth" is more comical than practical/ plausible
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not_important
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[*] posted on 15-3-2008 at 00:00


You want to look at this thread http://www.sciencemadness.org/talk/viewthread.php?tid=6914&a... and do some searching for 'styrene' in the posts.
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[*] posted on 20-3-2008 at 08:12


There was a method posted somewhere else that described a method of preparing benzaldehyde from toluene that used ammonium persulfate, toluene and an unknown (I forgot) compound but was easily acquired - I think it was a ceramic chemical that produced relatively pure and in high yield benzaldehyde. But I can't remember the third chemical or the quantities used.

I actually did a small scale (like 50ml of toluene) reaction following the instructions and the lab and surrounding area was overcome with the smell of bitter almonds.

Any ideas?
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[*] posted on 20-3-2008 at 08:42


Another rxn I found was to heat phenylalanine with a 5N NaOH solution for 5hrs at 110C and it decomposes yielding benzaldehyde.
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[*] posted on 26-3-2008 at 19:35


I am trying the synthesis for benzal chloride in Vogel's 3rd which uses toluene at reflux and chlorine. I am using TCCA to generate Cl2 and then drying it with CaCl2 and Rooto sulfuric acid (~93%). It is then sparged into the toluene through a sintered glass diffuser tube. I am also using a Hg vapor light (100w). When I ran out of Cl2 the boiling point had risen as far as 136C. Running out of Cl2 was expected and I plan to recharge the generator and continue the chlorination tommorrow.

Everything is going smoothly but there is significant charring as indicated by the brown/black color of the product. Materials used are: glass vessels & tubes, Tygon (PVC) tubing, and rubber stoppers. All ground glass joints were sealed with Dow Corning silicone grease. I can't see any deterioration of the rubber, Tygon, or grease.

Edit: I just measured the pH of the product: it is 1. I assume this is due to the HCl byproduct from the following reacton:

C6H5CH3 +Cl2 ---> C6H5CH2Cl + HCl

Is charring normal for this method? What might be causing it? Is there something I should change?



[Edited on 26-3-2008 by Magpie]
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[*] posted on 27-3-2008 at 07:42


The only time I got (insignificant) charring with this reaction was when I used the light source too close to the reaction vessel - which created a hot-spot on the glass. This source of charring however is obvious from a round black ring at the point of the hot spot. Other than that the reaction mixture should yellow but not char.

I also think you wont get an accurate measurement of HCl concentration with a standard pH meter in toluene, as its not an aqueous solvent. Len
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[*] posted on 27-3-2008 at 09:41


Although I can not visually detect this I'm wondering if a very fine aerosol of H2SO4 might be carrying over in the Cl2 stream from the H2SO4 water absorber. Could the presence of H2SO4 char the toluene/benzyl chloride at 136C?

My lamp is ~9cm from the reaction flask as shown in the picture below. When in operation I place a large sheet of aluminum foil loosely around the lamp/flask with the top and back sides open. The system is in standby waiting for a recharge of the Cl2 generator.

Len1, do you think I can continue chlorination and salvage this batch? Or do I need to solve the charring problem first?

Picture notes: The back bottle is a CaCl2 dryer, then the H2SO4 dryer bottle, then a safety bottle (Erlenmeyer flask) filled with Cl2 from yesterday. The sparge tube is being soaked in toluene in a a test tube.

[Edited on 27-3-2008 by Magpie]

benzal chloride.jpg - 61kB
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[*] posted on 27-3-2008 at 09:53


Magpie, I don't think the charring is too much cause for concern.
Did you distill the toluene beforehand to clean in from heavy metal traces? If yes, there should be no problems despite the darkening.

What is mor cause for concern with this synthesis is the fact that you will have to fractionally distill very carefully in order to get a pure compound.
I have made benzyl chloride from toluene this way and even with this lower chlorination stage, there was a lot of black high-boiling oil in the distilling flask. Not to mention the work it was to isolate reasonably pure benzyl chloride. With a 30cm vigreux column, I had to do three distillations in order to get a "benzyl chloride" material that distilled over a range of 10°C.
A lot of undefined intermediate-boiling byproducts seemed to form here, and the distillation is very time-intensive and the yields low.

I will certainly never again attempt to chlorinate toluene, whenever I need benzyl chloride I make it from benzyl alcohol and HCl.
Benzaldehyde is easily available here, but if I needed to make it, I would look for an oxidation method for benzyl alcohol, of which there are plenty that have been discussed here.




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[*] posted on 27-3-2008 at 10:08


Yes, the toluene was distilled and then placed over 3A mole sieves.

I had a feeling that this was not a preferred route as it is not discussed much on this forum. I will continue, however, just out of curiosity and because I have already made a significant investment in time and effort. Thanks for giving me the benefit of your experience, GC.

You say you were making benzyl chloride. Did you attempt to add the 2nd chlorine to get benzal chloride?
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[*] posted on 27-3-2008 at 10:16


My target product was benzyl chloride, and I stopped the chlorination at the temperature the Organikum gave if benzyl chloride is to be the main product.



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[*] posted on 27-3-2008 at 14:09


Magpie, I thought about the aerosol possibility - generally toluene does not char with H2SO4 it is after all nitrated at 100C with oleum in the TNT reaction, but at 136C and benzyl chloride is another matter.

The chlorine generator I use has the great advantage that no H2SO4 is needed! I just use a single CaCl2/CaSO4 drying tube and it works great. When I had charring due to formation of hot-spots I continued the reaction, it had almost no effect on the yield - so I think you can continue - mind you standard texts are full of errors on this reaction - Ill post on thi shortly.

Stefan - did the benzyl chloride have any physiological effect on you? I find that I get a horrible taste in my mouth even when I can detect none of its smell?

PS Why do people call each other by these nick names? It feels artificial to me anyway. Do you prefer to be called by your first name?

[Edited on 27-3-2008 by len1]
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[*] posted on 27-3-2008 at 20:11


Sorry but I was not able to get to the lab today so as yet do not have anything to report on the continuation of this experiment.

I was perusing Vogel's 3rd when I found a procedure for the introduction of a large stream of Cl2 from a cylinder, dried with H2SO4. It said to use a bottle full of glass wool to prevent entrained H2SO4 from entering the reaction vessel.

Len, I used your method for the generation of Cl2. I dripped 15wt% HCl onto ground up swimming pool TCCA, no heat, no agitation. It gave a nice steady stream of Cl2. I controlled it between 1-4 bubbles/sec.

I have considered filling my Erlenmeyer flask safety bottle with glass wool. However, even though my wool is nice and white, it is from a house insulation batt. This might just introduce another impurity.

[Edited on 27-3-2008 by Magpie]
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[*] posted on 28-3-2008 at 06:12


I think you can dispense with the H2SO4 and wash bottles altogether, I got good results with just the U-tube. I also love the TCCA Cl2 generator (using TCCA was originally Organikums idea) its almost like having a bottle of Chlorine

[Edited on 28-3-2008 by len1]
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[*] posted on 28-3-2008 at 09:15


Quote:
Originally posted by chemninja
Another rxn I found was to heat phenylalanine with a 5N NaOH solution for 5hrs at 110C and it decomposes yielding benzaldehyde.


Do you have any references for this, or anyone for that matter? Phenylalanine is cheap and so is NaOH, but I worry about the OH attacking the carbonyl; I think yields would not be great. Off topic but I have a paper on taking phenylalanine to benzyl cyanide with TCCA and pyridine in 75% yields if anyone is interested? BzCN has interesting chemistry itself.


@Len, that chlorine generator is indeed very nice! Thanks to you and Organikum on that one.




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[*] posted on 28-3-2008 at 09:33


I suspect benzaldehyde is not the product of such NaOH treatment of phenylalanine, but rather one of the products. Besides, this annoying claim was reposted already several times and none ever provided the reference, so it pretty much looks like some self reproducing misinformation.

I don’t know if Organikum got the idea of using the oxidation of HCl with TCCA as a handy chlorine generator independently or not, however that method is surprisingly even patented: GB1401120 (surprisingly because chlorine is used in the production of TCCA)
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[*] posted on 30-3-2008 at 16:26


fleaker I would love that reference. could I please get it off you :)



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[*] posted on 31-3-2008 at 09:42


came across this


Conversion of Phenylalanine to Benzaldehyde Initiated by an Aminotransferase in Lactobacillus plantarum

http://aem.asm.org/cgi/reprint

but trying to go back ------this url would not past in.

so go to primary aem site and search




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[*] posted on 31-3-2008 at 09:44


Lactobacillus plantarum -- wouldn't that be a bacteria derived from milk? so maybe accesible?



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[*] posted on 31-3-2008 at 09:49


then this came forth so maybe this bacteria is available ala sour dough break conjourers !!!

Purification and Characterization of Novel Antifungal Compounds from the Sourdough Lactobacillus plantarum Strain 21B




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[*] posted on 31-3-2008 at 10:42


here's how (i think) to isolate and culture

http://www.google.com/patents?id=VC8YAAAAEBAJ&printsec=d...


i know kind of extreme but it should work right? i mean if one has the motivation and --- ???

[Edited on 31-3-2008 by jimwig]




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[*] posted on 9-4-2008 at 02:13
benzaldehyde from phenylalanine


I have read about the production of benzaldehyde from phenylalanine initiated by amino transferase in lactobacillus plantarum. If this is a viable method it could be an alternative way of producing benzaldehyde or at least looked at.
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[*] posted on 9-4-2008 at 08:21


That would be a pretty expensive way of obtaining benzaldehyde!
I would rather look towards toluene oxydation, benzyl alcohol oxidation, or even almond flavourings.
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[*] posted on 9-4-2008 at 10:37


Rosenmund reduction of benzoyl chloride.

Probably too expensive.

TCCA gives benzaldehyde from benzyl alcohol. Yield about 52%. Now that's cheap.




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[*] posted on 9-4-2008 at 12:17


I'm sure yields can be increased to the litterature-claimed >90% with TEMPO derivative catalysis. Using Ca hypochlorite/BnOH/DCM proved to be more efficient with plain benzyl alcohol IIRC.
The semi-electrolytic Mn alum oxidation seems pretty interesting for >50-100g quantities..
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[*] posted on 9-4-2008 at 13:44


Synthesis of benzaldehyde, heat phenylalanine with 5N NaOH solution for 5 hours, at 110 C, it then decomposes, yielding benzaldehyde........solo


..............source of information,


http://www.ajinomoto.co.jp/amino/e_aminoscience/bc/amino_13....




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