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Author: Subject: Benzyl and Benzal chloride, Benzaldehyde and Benzoic Acid - Illustrated Practical Guide
microcosmicus
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[*] posted on 1-4-2008 at 21:57


Quote:

Still toluene is the best solvent for contact adhesive,
I'm sure its used that way in the US as well.


Not anymore --- while hardware stores here carry plenty of
contact adhesives. the overwhelming majority no longer
carry toluene here. Rather, Americans are expected to make
do with other solvents or perhaps cleaning fluids which contain
toluene mixed with other ingredients.

[Edited on 2-4-2008 by microcosmicus]
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MagicJigPipe
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[*] posted on 2-4-2008 at 23:02


From what I've read the average benzene content in gasoline in the US 1% or less.

Microcosmicus is right. Toluene is only available in the US at a handful of places. Most of the non-specialist/big chain stores no longer carry it. In my area it seems to be due to the meth scare hence my experience with attempting to obtain it.

The solvent supplier I go to gave me a brochure the last time I went. Next to toluene it says "Restricted". I need to ask them why when I get a chance. Something tells me I already know.




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[*] posted on 3-4-2008 at 06:40


tolurne is still out there you just have to find it.



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[*] posted on 3-4-2008 at 19:01


"tolurne is still out there you just have to find it."

Yes, I know. What I was saying is that it is getting harder and harder to find. I remember when I posted the thread "Chemicals to Stock Up On" I mentioned something about my experiences trying to obtain toluene.

I really think we need to get that thread going again. Many called me paranoid then but it seems as if people are starting to see what I was talking about.




"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think, free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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[*] posted on 19-5-2008 at 22:54


interesting read len1.
I had to read it several times to fully absorb it, i have some questions though and apologise in advance if they are silly.
You didn't quote a bp range for the distillation carried out on the mono/di/tri chlorides after the UV rxn step, is there a reason for this? It appears that you spent considerable effort to remove the unreacted monochloride after the hydrolysis and i understand this was tricky given its similar bp to that of benzaldehyde but i wonder why you wouldn't fractionate it out before the hydrolysis, i'm sure there is a sound reason.
Finally, given it took considerable effort, it would appear, to ensure that small amounts of benzaldehyde did not get carried out through the HCl vent gases during the acid hydrolysis did you perhaps consider using this instead as your method to remove the chloride, by instead fractionally steam distilling the benzaldehyde as it forms during the hydrolysis? You could collect the HCl gas/benzaldehyde water in a water trap. I'm sure there is reason why this is not done also.

Further to this i am interested in discussing the mechanism's for the chlorination, as i understand the initial step is formation of the chlorine radical by the UV photon, the chlorine radical then has to successfully collide with the toluene to begin the chain of transforms leading ultimately to the HCl elimination. It would appear to me that the half-life of the chlorine radical, at temperature, in toluene is the rate determining factor. Unless of course, the half-life is so small that it essentially requires the Cl2 molecule to be in the vicinity of, and have a favourable orientation to, the benzylic carbon at the time it absorbs the UV photon.
As expected attempting to find any data on the chlorine radical under these conditions led to nothing, however i feel i am quite internet unsavvy so it may be my ineptness in searching, not lack of data available.
This is the point where this discussion has too many unknowns for it to continue to be worthwhile. Any light you or anyone else could shed on this would be of interest as it would help in establishing the optimal position for the uv light source.

Your time spent collating your practical efforts are appreciated and enjoyed, thank-you very much for the write up.

mark

[Edited on 21-5-2008 by Panache]




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len1
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[*] posted on 2-6-2008 at 02:36


Quote:
You didn't quote a bp range for the distillation carried out on the mono/di/tri chlorides after the UV rxn step, is there a reason for this? It appears that you spent considerable effort to remove the unreacted monochloride after the hydrolysis and i understand this was tricky given its similar bp to that of benzaldehyde but i wonder why you wouldn't fractionate it out before the hydrolysis, i'm sure there is a sound reason.
Finally, given it took considerable effort, it would appear, to ensure that small amounts of benzaldehyde did not get carried out through the HCl vent gases during the acid hydrolysis did you perhaps consider using this instead as your method to remove the chloride, by instead fractionally steam distilling the benzaldehyde as it forms during the hydrolysis? You could collect the HCl gas/benzaldehyde water in a water trap. I'm sure there is reason why this is not done also.


Interesting questions. First the distillation was done to separate the benzylCl2 from the condensation tars rather than from the benzylCl. The bps are 205C/179C respectively and therein lies the answer why no fractional distillation was attempted. Its an interesting idea to let the BzO distill with the HCl as its formed so shifting the equilibrium. I might try this keeping in mind success is not guaranteed given that the chlorotoluenes might come along for the ride - their bps are similar to that of the benzaldehyde and it will have to be extra binding strength of BzO to water if this is to work - the distilate will have to be analyzed, and assuming its 90% or more percent free of reactant this could be a goer.

If you look at the section on the photocatalysis I did some investigations as to rate determining step. I found increase in light flux does not substantially increase chlorination rate, thus all Cl2 is essentially 'radicalised' and its the reaction of radical with toluene thats the rate determining step in my setup.
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[*] posted on 4-6-2008 at 18:27


Your hydrolysis product is Benzaldehyde and Benzyl Chloride?
Did you consider adding hyroxide (as salt) to convert to benzyl alcohol?
eg NaOH (in EtOH) + BzCl > NaCl + BzOH.
Then you have Benzaldehyde and Benzyl alcohol, either fractionally distil or even add persulfate to oxidise the alcohol to aldehyde. Excess of reagents will leave only very little Benzyl Chloride. Benzaldehyde should remain unchanged from stong base and persulfate.
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len1
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[*] posted on 4-6-2008 at 20:00


If you read carefuly my article you would know thats not possible.
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[*] posted on 29-10-2008 at 16:31


a big thanky goes out to mr lens for all his highly informative info.

thanks you, SIR




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Panache
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[*] posted on 31-10-2008 at 05:53


Quote:
Originally posted by len1
Quote:
You didn't quote a bp range for the distillation carried out on the mono/di/tri chlorides after the UV rxn step, is there a reason for this? It appears that you spent considerable effort to remove the unreacted monochloride after the hydrolysis and i understand this was tricky given its similar bp to that of benzaldehyde but i wonder why you wouldn't fractionate it out before the hydrolysis, i'm sure there is a sound reason.
Finally, given it took considerable effort, it would appear, to ensure that small amounts of benzaldehyde did not get carried out through the HCl vent gases during the acid hydrolysis did you perhaps consider using this instead as your method to remove the chloride, by instead fractionally steam distilling the benzaldehyde as it forms during the hydrolysis? You could collect the HCl gas/benzaldehyde water in a water trap. I'm sure there is reason why this is not done also.


Interesting questions. First the distillation was done to separate the benzylCl2 from the condensation tars rather than from the benzylCl. The bps are 205C/179C respectively and therein lies the answer why no fractional distillation was attempted. Its an interesting idea to let the BzO distill with the HCl as its formed so shifting the equilibrium. I might try this keeping in mind success is not guaranteed given that the chlorotoluenes might come along for the ride - their bps are similar to that of the benzaldehyde and it will have to be extra binding strength of BzO to water if this is to work - the distilate will have to be analyzed, and assuming its 90% or more percent free of reactant this could be a goer.

If you look at the section on the photocatalysis I did some investigations as to rate determining step. I found increase in light flux does not substantially increase chlorination rate, thus all Cl2 is essentially 'radicalised' and its the reaction of radical with toluene thats the rate determining step in my setup.


I have up until now had issue with this, however unable to frame my arguments coherently i have had to wait until i found someone else who could or until i understood what my issues were.

My main issue is that the photo initation step, namely the formation of the chlorine radical, occurs only in the vapour phase. Re-reading your response i see you now never said that rather you said that 'in my setup' it appears all chemistry occurs in the vapour phase. i believe Not important also mentions earlier a large column packed with broken glass that the cl2/hcl fractionated upwards through and this is the point his light source is positioned.

Well someone else described it for me, namely here

http://www.faizkaskar.8k.com/light1.html

For those unwilling to trawl through the various pages on photochlorination of toluene, the argument is quite basic, the Cl2 molecule has a bond energy that correesponds to the energy of a photon of light of wavelength of 488nm or obviously lower (more energy again). The 488 nm slightly below is blue light quickly descending into the UV range as the wavelength drops.
Once you have light of this wavelength or lower (and hence higher energy) the key parameter is the extinction coefficient of the wavelength of light being used. It determines how far into the solution the light will travel before being, well extinct. For blue light a simple calculation will give a penetration of roughly 11.5cm into toluene before 90% of the radiation is absorbed, whereas UV will only travel 0.3cm for 90% of radiation to be absorbed. In the gas phase obviously both penetrate much further.

Hence the reason the reaction appears not to occur in the liquid phase is that no uV is effectively getting to the reagants. The author advocates intense blue being used directly into the liquid phase.

The link explains it much better.

I might try this out this weekend, with a run using a blue light focused only on the solution and see if the reactions occurs more conveniently.




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[*] posted on 31-10-2008 at 06:53


Len1 has not posted for some time. I thinknthe prch light is on but nobody's home.

The radical chlorination of toluene in liquid phase with SO2Cl2 and benzoyl peroxide or AIBN initiation works quite well. In fact it will proceed to banzaldichloride is 2 mols SO2Cl2 are used. This reaction of course has nothing to do with photochemistry and proceeds just fine in the dark and well below the reflux temperature of toluene.




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[*] posted on 27-12-2008 at 03:05


I am still here, but have gotten a bit tired writing these articles since I dont see where this is leading to. To be honest a number of the preparations I posted I had to do at work a while back and in what I posted here I adapted them for the amateur since I thought it a way to make these known and I couldnt publish them in the literature as they do not represent the synthesis of anything 'new'. Now Im thinking of releasing them as a compilation soon.
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[*] posted on 27-12-2008 at 12:54


Quote:
Originally posted by len1
Now Im thinking of releasing them as a compilation soon.


That would be very cool! I'd love to see that :)
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[*] posted on 27-12-2008 at 15:06


Quote:
Originally posted by len1
I am still here, but have gotten a bit tired writing these articles since I dont see where this is leading to. To be honest a number of the preparations I posted I had to do at work a while back and in what I posted here I adapted them for the amateur since I thought it a way to make these known and I couldnt publish them in the literature as they do not represent the synthesis of anything 'new'. Now Im thinking of releasing them as a compilation soon.


Len IMHO your "illustrated guides" pretty much set the standard on this board.I hope you can continue to find time and motivation to prepare them.Whilst,perhaps,they represent nothing 'new' and hence perhaps somewhat tedious for you.For me and I'm sure many others find them clear,concise, workable instructions that fill in the gaps of preparatory manuals like Vogels.
Perhaps it not professional publication,but it is certainly inspiring to non academic researchers such as myself.
Please keep up the good work!
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[*] posted on 27-12-2008 at 20:16


Nice to see you back Len!

To be honest, I think if you collated all of your various syntheses together and did a few more, you could make quite the book(let) for the advanced amateur chemist.

Your illustrated syntheses are always a pleasure to read.




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[*] posted on 10-2-2009 at 03:03


its a very big help for my pre-laboratory discussions. thank you. I just wonder if you could supply me the NET EQUATION for the pathway of benzal chloride to benzaldehyde. thanks
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[*] posted on 10-2-2009 at 06:24


I suggest you send a PM (private message) to len1

Use the U2U (User to User) buttom just below one of his posts.




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[*] posted on 18-3-2009 at 20:38


I am currently preparing benzaldehyde using Len's method, but running the reaction on a 1 mole scale. I currently have about 118g of benzal chloride that I prepared last weekend. The reaction is very slow using a 60 W light bulb. The reaction took me about 12 hours. I ended up distilling the product at 8 hours, but it still had a density of 1.18. I chlornated for another 4 hours and ended up with a product that has a density of 1.23. The CRC Handbook of Organic Compound Identification states that benzal chloride has a density of 1.295.



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[*] posted on 8-10-2010 at 20:28


Very nice writeup. I did NOT find it "too wordy." I would suggest being more 'academic' and listing at least the key refs. I missed one detail: I don't see where you identified the light source you used. Light sources are much on my mind these days and I want all the information and suggestions I can find on uv sources for free radical reax. Thanks for the post. CRX



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[*] posted on 9-10-2010 at 13:19


If anyone's still after benzyl alcohol to go backwards, I've got it cheap from here (UK, but I think they'll ship worldwide): www.thesoapkitchen.co.uk
£7.75 a litre. well I could barely get toluene for that price.
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[*] posted on 15-4-2011 at 10:25


I haven't seen any mention of this, so I thought I'd ask.
Wouldn't a "black light" be well suited for catalyzing radical chlorination? The main emission peak is around 400nm, which seems pretty ideal for this purpose. Is this really the case?
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[*] posted on 9-5-2013 at 05:46


Have you ever tried Blanc chloromethylation?


Quote:



The Blanc chloromethylation is the chemical reaction of aromatic rings with formaldehyde and hydrogen chloride catalyzed by zinc chloride to form chloromethyl arenes. The reaction should be performed with care, as (like most chloromethylation reactions) it produces highly carcinogenic bis(chloromethyl) ether as a by-product.

http://en.wikipedia.org/wiki/Blanc_chloromethylation


http://www.scielo.cl/scielo.php?pid=S0717-97072010000100023&...

http://universitypublishingonline.org/foundation/chapter.jsf...
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[*] posted on 25-5-2013 at 16:18


No questions. Spam reported.
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