toluene --> benzyl chloride --> benzaldehyde

[elfspice]

I've been utfseing around a bit about the subject of turning toluene into benzaldehyde, and it seems to me this is how you do it:

anhydrous toluene with dry bleaching powder cooked up at 105°C at a roughly molar 1:1 ratio... well, the reaction says 1:1 weight for weight, but that would be a 100:155 (tol to bleach) molar ratio... should it be equimolar or equal weight? (ie 100:155 bleach to tol ratio)

chemfinder says that benzyl chloride reacts with water, and someone said something about how the product of this reaction with water is benzaldehyde... so would one just cook up the dry bleach and toluene, then dump a load of distilled water in, and distill out the benzaldehyde?

the reaction of benzyl chloride with water would be (i have balanced the equation as well):

2x(Phe-CH-Cl + H₂O) --> 2x(Phe-CH=O) + Cl₂ + 2x(H₂)

(*whew* i thought i wasn't going to do that, dang it's been a while)

anyways, have i surmised this correctly?

if so, then making benzaldehyde is simple. just dry bleach dry toluene at 105°C then when the reaction completes, add distilled water slowly with swirling and lots of ventilation blowing the vapours away from any spark source or living creature. then presumably it will split into a two phase mixture and you separate and distill the upper phase, removing the residual toluene, then collecting the benzaldehyde... and what does the possible other reaction products become in water? would using the equimolar ratio as i have mentioned prevent any excess? i think it would be better to under-do this reaction than overdo it as the toluene can always be recovered and re-reacted.

nice way to make bulk flavouring for grandma's marzipam  

[elfspice]

oops pardon me, i hope nobody beats me to this

the reaction with water produces hydrochloric acid, so i'll try figure it again cos they don't say the other products in msds

Phe-CH2-Cl + H₂O --> HCl + 1/2x(H₂) + Phe-CH=O

ooh one thing, benzyl chloride is explosive, it would be much preferable if it were not dealt with for very long nor at much temperature... would it work to dump it into a large amount of cold (4°C) water after the reaction to chill it down and change it to what you want? ice cubes?

interesting... you could make it and pipe the vapours through an anhydrous nonpolar with freebase at the same time...

should the mixing of water be done slowly or fast, the water cold, should there be a lot of water all at once or just carefully adding little by little (my intuition says dump it into a 10x or greater volume of water to absorb the heat and stir the buggery out of it to keep the convection smooth or sit on ice with stirring or shaking, maybe put ice in the water as well to ensure all heat can be absorbed before temperatures get unpleasant)

[prerequisite]

Check out this outstanding site about the chlorination of toluene. All is answered, from the spectrum of light wwhich is ideal (blue) to temperatures to the amount of moles of chlorine. About 2.07 moles is optimal, which yields mostly benzalCl, and benzylCl.

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

If you don't have the capability to fractionally distill it's difficult to isolate benzaldehyde.

Benzoic acid can be basified to sodium benzoate, making it then soluble to wash out with water.

What I'm saying is, almost always you'll want several steps or reactions to reach a high yield from the origional feedstock-toluene. i.e The first reaction, then separation via distillation, and then a reaction for 2 or 3 of the fractions, whatever they may be.
BenzylCl, BenzylOH, BenzalCl, benzotrichloride, benzoic acid.

The benzal is easily converted, however you need to separate and work out what you'll be doing with the others. Benzyl OH is easy to. benzyl Cl just needs further chlorination.

>>ooh one thing, benzyl chloride is explosive, it would be much preferable if it were not dealt with for very long nor at much temperature...

Actually if you run the reaction at low temperatures it causes chlorination of the benzene ring so get over it, to put it bluntly. ~100C is a good temperature.
I've never read about much emphasis being placed on the explosiveness of benzyl chloride, it can't be too bad?

It isn't cheap or easy making benzaldehyde I found after investigation. But more easy than cheap...

E.g to produce 1 mole of Cl will require 4 moles/400-500ml of HCl 31.4% solution if the MnO2 route to Cl is used. This will give you ~100ml of benzyl chloride (like wow...) if yields are 100%.
Benzyl chloride isn't even what you want; it isn't enough to kill the stress even if it was magically benzal chloride, etc etc.

Hypochlorite might be a much better option, if you can fractionally distill. otherwise it's likely to be another gay day.
Watching TV and not stressing is the best bet, no evil thoughts of making chemicals etc, until tomorrow- then it's okay.

[Rhodium]

Benzyl chloride is not explosive. It is a lachrymator though.

[stratosphere]

elfspice i noticed a mistake
PhCH2Cl+H20-->PhCH20H+HCl
not PhCH2Cl+H20-->PhCH20+HCl+1/2H2

and as rhodium stated, benzyl chloride is not any more flammable/explosive then a similiar molecular wieght hydrocarbon, but the shit is like tear gas, open the stopper for about 5sec outside a fume hood with no gas mask and youll be cryin for a half hour.

however there are some explosive possibilities when heating any organic with a pure hypochlorite.

an alternative pathway is air oxidation of toluene by passing toluene vapor and air over a catalyst.
for instance

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

claims that a V2O5/K2SO4 catalyst is the most selective for this transformation giving yield of 60%.
it uses air at 1atm and temps of 400C.
other information on that site seems to indicate benzaldehyde formation is favored by a low conversion rate per pass, indicating that using a less then stochiometric 02 to PhCH3 feed rate is optimal, it also states that a contact time of 0.1-1.0 sec between the vapour and catalyst is optimal.

in many ways this procedure should not be any more difficult to setup and aquire needed materials then the hypochlorite synth.

[zero_nrg]

don´t forget about the extremely easy benzyl alcohol + aqueous HCl --> benzyl chloride. utfse.  Have done this several times.  Procedure can be done at room temp and the HCl ratio can be decreased as well (think I posted something about this but not sure as TFSE is not available now).  Can honestly say that benzyl chloride is the nastiest chemical I´ve worked with thus far - the presence of it in the air (low concentrations) immediately turns my skin red and irritated.  Fume hood recommended.

[amalgum]

SWIM suggests using lithium hypochlorate.  LiOCl is very cheap and easy to pick up at hardware store by the pound.  Look in pol section.  SWIM has tried both LiOCl and Cl2 gas for chlorination, and Cl2 sucks ass.  Never tried NaOCl or Ca(OCl)2, but should work about the same.  Remember, HCl is a byproduct of chlorination, which is not very soluable in toluene or the chloride so pipe those fumes somewhere safe or into NaOH trap.

[BOS]

THis is an interesting titbit of info I found whilst surfing google.Dont know how serious it is but.

I recall Dwarfer mentioning using ttt as a chlorinating agent a while back.

Organikum has posted a patent of late, which claims the addition of hexamine avoids ring chlorination.
He also describes a process in which mixtures of benzyl and benzal chloride are treated with aqueous hexamine sollution to yield benzaldehyde.
Once the fucking serch engine is fixed you can look it up for your own.

For those of you that have chlorinated toluene with Cl2, you know how messy
it is. The endpoint is coneviently determined by bp of the solution, but the
HCl that's given off makes for a mess. The fume hood rots, rubber tubing
that conducts the HCl to a trap rots, and the trap has to be carefully
constructed or water will back up into your reaction (shut down and run
time!)!!!! Throughout the reaction, the HCL is pulling benzyl chloride over
into the trap, and hey, it's a mess!

Trichloro triazine trione (TTT) is a cholrinating agent used for swimming
pools and powerful cleansers, the pool type being pressed into 5-7 cm dia
tablets, and available at most US hardware stores. You put a tablet into a
plastic bag and crush it into a powder with a hammer (or squeeze it in a
vise). Put about 300ml of toluene and a large stribar in a 1 liter Erlenmyer
flask on a stir/hotplate. Fit the flask with a short, wide bore, straight,
water cooled condenser and bring the toluene to reflux under stir. Aim a
powerful (150 watt) lamp at the reaction, and add spoonfuls of TTT
cautiously, down through the condenser, watching for a vigorous reaction,
most notably by observing the level where vapors condense in the condenser.
DO NOT OVERFEED THE REACTION. Add a few drops of water (if necessary) to
begin the reaction.

The TTT releases HOCL on contact with water, along with some free Cl2. The
Cl2 reacts at the methyl of the toluene and releases HCl. The HCl goes back
to the TTT and realeases CL2. The beauty of this is that you don't need to
mess with gaseous CL2, and the HCl is recycled! It's cheap, quick, and the
TTT reaction product (cyanuric acid) is easily filtered off from the
finished reaction mixture. Workup consists of simple distillation, after a
quick filtering and water/carbonate wash.

I've only tried this with toluene, but my suspicion is that the in-situ
generation of chlorine will be effective with many substrates. Small scale
experiments, with a few mL in a test tube very conveniently demonstrate the
effect of actinic light on the free radical generation aspect of the
reaction: heat the mixture over a small flame until just at the boiling
point, and expose the test tube to a powerful light. While in the light, the
reaction is vigorous; when the light is turned off, the reaction subsides. A
great demo for the classroom!

http://list.pengus.net/pipermail/chemfan/2002/000031.html

[amalgum]

I recall Dwarfer mentioning using ttt as a chlorinating agent a while back.

Yeah SWIM was just about to suggest that, as he just remembered reading that thread.  SWIM hasn't tried it but it probably is the best route to take.

And BOS, you are damn right about the Cl2 chlorination.  I wouldn't try it again in a million years.  The only reason why SWIM did it the first time was because money was tight, and it was out of pool season for the LiOCl.  So it was easy enough to use bleach and muriatic SWIM had laying around to make the Cl2 gas.  Two kneck rb flask equipped with one hole stopper and pressure equalized add. funnel charged with bleach was used, and the muriatic was dripped in.  The gas was led via tube to another two kneck rb with one hole stoppers in each kneck, for suckback trap.  That was led via tubing into a third larger 2 kneck that held the stones and some toluene, topped off with friedrichs condensor.  The top of the freidrichs was sealed off with a straight vacuum adaptor (not angled like those for distilling), that was sealed with a glass stopper.  The hose barb on the vacuum adaptor had some tubing attatched that SWIM ran out a window (he was in a secluded area).

SWIM used the same setup for LiOCl chlorination, minus the gassing apparatus.  The second kneck on the still flask was stoppered with glass stopper, and periodically removed for placement of large powder funnel for LiOCl addition.  It was quite easy.  Yeilds were average (SWIM also got horrible yeilds when using Cl2).  Sunlight was used as light source.

[amalgum]

SWIM laso made a little benzyl bromide one time also.  He used almost the same setup, except H2O2 was dripped into KBr and H2SO4 solution and gently heated to distill off Br2.  Liebig was used to condense the Br2.  This dripped straight into app. mentioned above filled with toluene.  When all Br2 distilled over, the toluene flask was heated in sunlight to reflux for a few hours.  This gave pretty high yeilds of benzyl bromide, but if you think the chloride will make you cry, man oh man!  All it takes is some benzyl bromide residue to be rinsed off of the glass to send you hauling ass clawing at tearing eyes and stinging nostrils toward the door.  If you try this make sure you have excellent fumehood and gas mask.  You'll regret it if you don't.

[Organikum]

I tried the chlorination of toluene with TTT - trichloroisocyanuric acid - several times and had never ANY success with it. The procedure as described looks also very sketchy to me for the simple reason that - as told - benzylchloride is a strong lachrymator and the "great demo for the classroom" would end with crying teacher and pupils so it would work. The fact that the lachrymatoric properties of BzCl have been never mentioned in the writeup makes me believe it is a piece of shit out of somebodys ass.
If somebody can prove me wrong - great! I would love to have such a simple pathway to BzCl.
Rhodium has also an article on the reactions of TTT available on his page - the authors mention there that no BzCl is formed from TTT and toluene.

Toluene Chlorination:
After the Ullmann the addition of some hexamine - 0,5% to 1% w/w - suppresses ring chlorination. Oxygen hinders the chlorination, so your chlorine source should produce chlorine free from oxygen (and free from water - drying is done by conc. H2SO4 in a washbottle). Hexamine also makes the reaction more tolerant aginst traces of oxygen.
The real fun is though that after chlorinating about 30% to 50% of thew toluene what will yield utmost only benzyl and benzalchloride one can add a good amount of hexamine in water and boil the whole soup for some time and all benzyl and benzalchloride will be changed to benzaldehyde. One pot, no crying. Steamdistillation and a simple (better: vacuum) distillation under exclusion of air as far as possible - done.

The benzyl/benzalchloride plus hexamine to benzaldehyde process is a wastestream process - shit to gold so to say - one can beleive it is a VERY robust reaction which is hard to fuck up.
So before somebody whines "how much hexamine in water do I have to add? buhuhu..",
- the answer is: ENOUGH.
"how do I know when the reaction is over? buhuhu...."
- when you dont start crying anymore whilst taking a sniff from the fumes. Then all BzCl has reacted.
(please recognize the high pedagogical value of this method - show patience or cry!   )

[ADDkid]

[Organikum]

Not to everybody benzylalcohol is easily available, at least not in pure form. Also bromine containing compounds are often not OTC in many countries.
ADDkid, you post making benzylbromide from benzylalcohol was for sure made with the best intentions but it is in a thread which is about benzaldehyde via chlorination of toluene so off topic as it can get.  

[elfspice]

ok, i don't quite understand how you can't find *any* form of bromide salt, organikum, i don't doubt that you've tried to find it locally however.

So what about iodination? I mean, of all things, it is the one halogen that is both available, and not likely to be taken out of circulation because of it's need in feed supplements or dietary supplements, as well as for sterilising things like milking equipment and so forth.

I have posted a link to a reference to a means of using microwaves and kaolin substrate, combined with sulphuric acid and iodine and the desired iodisable benzylic alcohol... right, i realise that this means, in this case, starting with benzyl alcohol... so that's not entirely helpful.

a means to synthesising benzyl alcohol would also be quite helpful, i imagine that there must be some way to oxidise toluene, dichromate, permanganate, hypochlorite, peroxide... something, under some particular conditions, should be able to add an oxygen to the methyl group.

[Organikum]

The by me posted procedure of using hexamine for preventing ringchlorination and for transforming benzalX and benzylX to benzaldehyde works for bromine compounds too as far as I know - i dont know though if it works with iodine compounds.

After my opinion the use of dry oxygen-free chlorine gas is the key to success in toluene chlorinations. The hexamine addition suppresses ringchlorination and makes the product pure enough for use in biosynthetic pathways. The transformation of benzyl and benzalchloride by hexamine makes the procedure "one pot" what is very important as everybody will understand who has worked with benzyl-X compounds.

I have spoken
ORG

[Mendeleev]

Amalgan stated that SWIM used tubing to bubble Cl2 through the toluene.  I am wondering what kind of tubing this was as toluene dissolves most plastics and polymers.  Was it glass or teflon or is there a widely available plastic that is resistant to toluene.  Concerning TTT method to benzyl chloride, I think it does work, but benzoyl peroxide is necessary as a radical initiator.  I quote from

https://www.thevespiary.org/rhodium/Rhodium/pdf/trichloroisocyanuric.pdf

:

"Toluene gave the 2- and 4-chlorotoluenes under acidic conditions (66%).  The main regioisomer was the 4-chlorotoluene.  With phenol and aniline the yield was lower giving mainly the para isomer.  With electron withdrawing groups no reaction occurred (Scheme 12).  Alternatively when benzoyl peroxide was used as radical initiator, benzylchloride was obtained in 44% from toluene."

This is straight from the journal of Organic Process Research and Development, so I think its fairly reliable.  Perhaps in Organikum's experiment he neglected to use benzoyl peroxide.