The Synthesis of Benzoyl Chloride via The Sulfur Catalyzed Chlorination of Benzaldehyde

Good day all,

I have not had occasion to do any meaningful chemistry as of late, but I will post one of my more successful reactions circa January 2020.

Just from my own notes, extrapolated and explained a bit of course.

Few things before we touch off:

1. Benzaldehyde was purchased (not illegal where I am) from eBay, but it could've easily been made. I used up my home-made and vac distilled batch I made via Praxyis(sp) aka Doug from Dougs Lab & Tom from Tom's Lab thread on the Nitric acid oxidation of Benzyl Alcohol to Benzaldehyde doing test runs that failed, but in my opinion the failures had nothing to do with the quality of the benzaldehyde, just my poor temperature control.

http://www.sciencemadness.org/talk/viewthread.php?tid=72076


2. Chlorine was made from the TCCA and HCl dripped method, re: Nurdrage and many others here; I used a 2 molar excess but would use a bit more (2.25 - 2.5 mol excess) in the future as not all reacts even with heating and stirring.

https://www.youtube.com/watch?v=hLHfN7GvAyI


3. I used ordinary garden Sulfur as the catalyst, recrystallized from toluene so it was a shiny, sparkly pure yellow (what a waste of time but I didn't have another source and I wasn't waiting weeks for eBay).


4. You need a hood, great ventilation or a good 550 CFM fan and 6 inch tubing like I had with my temporary setup to suck out not only unreacted chlorine, but the HCl gas this generates. It fumes in air, damp night air much more vividly, for the neighbour conscious among us.

I use a 3M mask with Acid cartridges the entire time I do anything like this as backup, but it WILL NOT stop anything but blow-by or nuisance chlorine vapours so be warned. The chlorine generator, once started, can't be stopped easily in my experience.


Ok, onto the preamble:



Introduction
-----------------

Benzoyl Chloride was Synthesized via the Sulfur Catalyzed Reaction of Chlorine upon Benzaldehyde at Moderate Temperatures.

Read the attached MSDS for Benzoyl Chloride before diving into this one, as it can be pretty toxic and fumes in open air. It's also very lacrimatory. Spill some on a hot stove or hotplate? Bam you just made PHOSGENE gas.... Be warned!

US Patent 3894923 (Attached below), was used (but kind of not used) as a guide.

What I mean by this is their patent is all about UV light helping the chlorination along, but they give a comparative example at the very bottom using plain old Sulfur.


Materials & Reagents
--------------------------

312 grams TCCA (Tri-Chlorocyanuric Acid)
500 ml 31.45% Hydrochloric Acid
212 grams Benzaldehyde
0.5 grams Sulfur
CaCl2 for drying tube(s)

Hotplate
Stirbar
Silicone Tubing
1 x 2000 ml 3-neck flat bottom flask
1 x 500 ml 3-neck flat bottom flask
4 x screw-down type thermometer adapters (3 minimum)
1 x 500 ml pressure equalized dripping funnel (or smaller one and be able to add more to it as you go, which is bloody TERRIBLE with a reactor under pressure making Chlorine)
1 x drying tube
1 x reflux condenser
1 x small aquarium air pump (optional but recommended)
1 x wicked ventilation system or fume hood


Experimental
------------------

To a 3-neck, 500 ml flat bottomed flask was added 2 moles of Benzaldehyde (212 grams), 0.1% of this weight in elemental Sulfur (about 0.5 grams was used), and a small stir bar.

The flask was then placed on a hotplate, one neck affixed with a thermometer well attached to an electronic thermo-couple, the center neck attached to a reflux condenser, and the other side neck attached to a thermometer adapter that had a small hollow borosilicate glass tube running through it down into the stirred benzaldehyde for chlorination. To the top of the reflux condenser was attached a drying tube packed with CaCl2, to prevent water condensing down into the reaction flask.

The aforementioned glass tube was attached via silicone fish tank style tubing to the chlorine generator, which will now be described:

A 2000 ml flat bottom 3-neck flask was filled with 312 grams of powdered TCCA, the center neck rigged with a 500 ml pressure equalized dripping funnel. The dripping funnel was filled with a slight molar excess of 31.45% Hydrochloric acid, approximately 500 ml (or about 160 grams of HCl) worth. More HCl can be added to make swirling this flask easier to ensure all the TCCA reacts.

One side neck of the above mentioned flask was fitted with a hollow 200 mm 24/29 borosilicate glass tube, packed with CaCl2 and cotton-balled at both ends. This is to ensure the generated chlorine gas is dry. This 200 mm packed drying tube was attached to yet another thermometer screw-down type adapter and silicone hosing to the reaction flask glass tube to provide the chlorine.

The other and final neck of the flask was fitted with a thermometer adapter, silicone tubing, and that tubing was attached to a VERY tiny aquarium style pump. This was to keep mild but consistent positive pressure in the chlorine generator to prevent suck-back issues. I tend to do this on every gas generator reaction I do, especially HCl gas generators, to avoid suck-back. As long as that drying tube is well packed with a suitable drying agent, it has always worked well.

The 500 ml pressure equalized dripping funnel was filled with 500 ml of 31.45% HCl, and the small aquarium air pump turned on to check the flow, bubble size and depth into the benzaldehyde from the chlorine generator (at this point it was all just regular room air).

Cold water was now run through the reflux condenser, and the hotplate and magnetic stirring was turned on and a temperature of approx (+/- 5 C) 120 Degrees C was reached. Ventilation was begun (ideally should be on before now as a rule).

The 500 ml HCl was now slowly at first dripped onto the TCCA powder. Immediately a yellow-green chlorine gas haze was seen in the chlorine generator flask, and chlorine was starting to be piped into the benzaldehyde.

The chlorine generator flask was lifted and swirled occasionally, and as the reaction continued the drip rate was adjusted to provide a steady (as can be) stream of gas into the reaction flask.

At approximately T + 10 minutes the reaction flask temperature was approximately 135 Degrees C, and the hotplate heating was turned off and passive air cooling was started. HCl gas was steadily evolving from the top of the reflux condenser, out the drying tube and being sucked out of the lab space. Litmus paper held above this drying tube turned bright red very quickly.

After approximately T + 1 hour the reaction flask cooled to the point where I stopped the cooling fan, but did not re-start the hotplate.

Around T + 1.5 hours the reaction was approximately 110 Degrees C and the hotplate was cautiously restarted. Litmus paper at the exit drying tube atop the reflux condenser was still bright red with HCl gas evolution.

Around T + 2.25 hours the chlorine generation began to slack considerably, and the flask was swirled. I placed in on a small pan and used a gas range to briefly heat the flask, but this was discontinued as it really was not doing much in the way of gas generation. Litmus paper at the exit drying tube atop the reflux condenser was still bright red with HCl gas evolution.

Around T + 2.5 hours, the entirety of the 500 ml HCl was finished dripping into the chlorine generator. Litmus paper at the exit drying tube atop the reflux condenser was still bright red with HCl gas evolution.

At T + 3 hours, the reaction flask was approaching 95 Degrees C, the entirety of the HCl was long since added, and litmus paper at the exit drying tube atop the reflux condenser was no longer instantly turning bright red, indicating the HCl gas evolution from the reaction was slowing and the reaction was close to completion.

At T + 3.25 hours, I turned off the hotplate, stirring, cooling water, and CAREFULLY disconnected the glass tube feeding the reaction flask with chlorine (aquarium air pump still on as to avoid any suck-back). I then quickly stoppered the reaction flask and turned off the aquarium air pump to avoid filling the room with even more HCL and Chlorine gas vapours. The Chlorine generator flask was quenched carefully with water several times and its contents disposed of.

The contents of the reaction flask were poured into a 250 ml round bottom, affixed with a vigereux column, and set up for vacuum distillation.

Everything was collected until there was a brown tar and what remained of the Sulfur catalyst in the distillation flask. In the collecting flask was 204.4 grams of a clear, slightly syrupy liquid that fumed upon exposure to air. Temperature was approx 210 - 220 Degrees C at the still-head when it was shut down.

This flask was then setup for fractional distillation at atmospheric pressure. Everything below 197 degrees was discarded (Benzoyl Chloride bp = 197.2 C), and 199.9 grams of clear, colourless liquid was collected. This liquid was slightly viscous and fumed upon exposure to air.

The temperature at collection was very sharp and steady, and the space between fractions very large. Inside the distillation flask was a small amount of a slightly yellowish clear fluid, which crystallized upon cooling. This was most likely benzoic acid from the atmospheric distillation of whatever remaining benzaldehyde came over during the vacuum distillation.

The Benzoyl Chloride was poured into a dark glass bottle and stored in the fridge. Depending on what you are using it for, some desiccant may be advisable for storage.

See attached paper, Cahiez 2001, for a broad overview on storage and handling.


Yield
--------

2 moles Benzaldehyde 212.28 grams = 2 moles Benzoyl Chloride 281.14 grams theoretical yield.

199.9 grams actual yield of Benzoyl Chloride / 281.14 grams theoretical yield = 71.1%

Ergo, the final molar yield was 71.1% on starting Benzaldehyde.


Comments
---------------

As mentioned, without risking di and/or tri-chlorinating the Benzaldehyde, a bit more chlorine could be used. This might get the yield up a bit.

The yield tracks decently from the example in the patent (Their yield was listed as 82%).

Overall I think this worked pretty damn well all things considered. Working with chlorine or any gas really always kind of sucks, especially in an amateur setting, so I feel this was a great success.

Questions, critiques and comments always welcome!

Cheers~!





Attachment: US3894923 - Sulfur Catalyzed Winner - Copy.pdf (119kB)
This file has been downloaded 492 times

Attachment: cv3p0112 - Benzoyl Chloride Purification Ref - Copy.pdf (313kB)
This file has been downloaded 452 times

Attachment: BENZOYL-CHLORIDE MSDS - Copy.pdf (57kB)
This file has been downloaded 624 times

*EDIT: Typos, attachments, and flask sizes corrected*


Attachment: cahiez2001 - Benzoyl Chloride Facts - Copy.pdf (77kB)
This file has been downloaded 577 times

[Edited on 1-9-2020 by Johnny Windchimes]



[Edited on 2-9-2020 by Johnny Windchimes]

Quote: Originally posted by S.C. Wack

Have you tried it without S2Cl2 or UV?

Quote: Originally posted by clearly_not_atara

Quote: Originally posted by S.C. Wack   Have you tried it without S2Cl2 or UV? The reaction works with just BzH + TCCA in CH2Cl2 as in e.g.: http://doi.org/10.1002/adsc.201500912 http://doi.org/10.1021/acs.orglett.5b01579 (free Supporting Information) Also reported to work with BnOH but may give some BzOBn.

Quote: Originally posted by clearly_not_atara

Quote: Originally posted by S.C. Wack   Have you tried it without S2Cl2 or UV? The reaction works with just BzH + TCCA in CH2Cl2 as in e.g.: http://doi.org/10.1002/adsc.201500912 http://doi.org/10.1021/acs.orglett.5b01579 (free Supporting Information) Also reported to work with BnOH but may give some BzOBn.

Quote: Originally posted by Johnny Windchimes

*EDIT* No, never tried UV, or anything like S2Cl2

Quote: Originally posted by clearly_not_atara

Well, the good news is you didn't make phosgene. You had already distilled off the DCM when the explosion occurred; if there was any phosgene, you'd be dead.

Quote: Originally posted by S.C. Wack

Quote: Originally posted by Johnny Windchimes   *EDIT* No, never tried UV, or anything like S2Cl2 Well, I'd think that would be the point of hot S + Cl, although the older directions call for cold no-S.

Quote: Originally posted by Johnny Windchimes

Quote: Originally posted by clearly_not_atara   Well, the good news is you didn't make phosgene. You had already distilled off the DCM when the explosion occurred; if there was any phosgene, you'd be dead. Yes indeed. I wasn't intending on posting that 'failure', (if such a brush with the afterlife can be such ascribed to...), but when that Gaspa article was posted I felt hurriedly compelled to do so.

Can't be overstated. For myriad reasons, not just the scaling.

Solubility in DCM aside, I should point out I did vac filter off the very insoluble unreacted TCCA / reaction mixture to be left with a crystal clear yellow liquid before distilling it.

Definitely helped it go down from ultra lethal hand grenade type explosion to just a garden variety horrifyingly scary accident I would wager....


@Tsjerk, I started experimenting with the simplest method(s) I could find, and could not for all my 'skill' get the catalyst free reaction(s) to run properly. 10.... 20 percent yields tops. Very frustrating at the time, so I looked into alternatives like Gaspa.

[Edited on 3-9-2020 by Johnny Windchimes]

Thanks for the response!

I guess I'll just have to use a conservative quantity of TCCA, and add more if necessary, dealing with the inevitable escape of chlorine from the flask when I have to open it to add new TCCA


Yes I can see the reaction of the o-chloro substituted aldehyde is a lot slower, I think when I first did this reaction using benzaldehyde, it only took around three hours.

How problematic is dissolved HCl in acyl halides?

Hi,

I have since attempted the chlorination of benzaldehyde to make benzoyl chloride, and it was quite successful, the chlorination itself was the most fun I've had in years!


However there is a problem, and I am wondering if anyone has a suggestion as to how I should progress;

My benzaldehyde was prepared by the oxidation of benzyl alcohol using nitric acid.
Unfortunately, it is likely that it contained some unreacted benzyl alcohol (I did not know this earlier).

I then carried out the chlorination, and distilled the product.

I collected benzoyl chloride from 194-202c, whereupon a fraction of benzyl alcohol began to distill over up to 206c.

After that, nothing more distilled, however a fairly large quantity of viscous, tarry liquid remained in the distilling flask.

During the distillation, a lot of hydrogen chloride gas was evolved.

"Wait a second", I hear you say, "How could benzyl alcohol and benzoyl chloride possibly coexist?"

I suspect that when the mixture of benzyl alcohol and benzaldehyde was chlorinated, the benzaldehyde reacted, forming benzoyl chloride, but the benzyl alcohol would remain unchanged.

Since the reaction between acyl halides and alcohols is quite slow, they would not have reacted straight away, but heating to distill the product would have resulted in a lot of the benzyl alcohol reacting with benzoyl chloride, forming benzyl benzoate, which is probably the viscous high-boiling liquid left in the distilling flask.


I attempted to vacuum-distill the viscous stuff, but it required too high a temperature, given my vacuum setup.

So anyway, the problem is, I have a clear distillate consisting mainly of benzoyl chloride, however it may contain some benzyl alcohol too.

Since the reaction between benzyl alcohol and benzoyl chloride is slow, it may not immediately esterify.

If I were to carry out a second distillation, I would be able to distil off the benzoyl chloride, however doing this might produce more hydrogen chloride by the reaction of benzyl alcohol with benzoyl chloride.

Alternatively, I could reflux my product, which would ensure that all of the benzyl alcohol reacts, however I am wary about doing this, because perhaps refluxing benzoyl chloride will result in some loss due to polymerization, etc?

In any case, it might be a good idea to pass dry air through the benzoyl chloride to remove dissolved hydrogen chloride.


Tl;Dr:

My benzoyl chloride might be contaminated with benzyl alcohol, and it might also contain some dissolved HCl.

How big of a problem is dissolved HCl in acid halides, is it even soluble in them?

I imagine that every time you open a bottle of an acid halide, some water will get in, resulting in the formation of hydrogen chloride, which would surely dissolve in the acid halide...

Quote: Originally posted by clearly_not_atara

I think that the solubility of HCl in BzCl is probably quite low. HCl is highly volatile and only dissolves in solvents by dissociation. But the basicity of BzCl is certainly low, probably lower than that of BzOH, so the pKa of HCl in BzCl is probably higher than 3. But if BnOH is present then it can react to BnCl, and if BzOBn is present then it can be protonated. Samples of acyl chlorides are rarely rigorously pure. If you distill it and the residue is not very much, it should be clean enough for most practical purposes. I don't think it polymerizes very easily.

Thanks for the reply!

It had never occurred to me that the solubility of HCl is due to dissociation, but it makes sense of course!

I tried converting some of my benzoyl chloride to acetyl chloride by distilling it with acetic acid, and I obtained a 60% yield, so I am quite pleased with this result...
The residue, consisting mainly of benzoic acid, contained some unreacted benzaldehyde, which must have been present in the benzoyl chloride due to incomplete chlorination; Still, it doesn't seem to have been a problem

As a side note: If anyone makes benzoyl chloride and thinks "oh this isn't too reactive", this behaviour isn't typical of acyl chlorides, as I discovered to my detriment after preparing acetyl chloride, whereupon I was met with clouds of hydrogen chloride gas upon merely opening the receiving flask!