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evil_lurker
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Be careful with DCM... from what swim understands from reading patents, the reaction can go screwy fast resulting in a runaway explosion!
It must be moderated, preferably by putting in tubing or what not every .5 to 1cm or so to stop the radicals from going chain too fast.
I could be wrong, but better safe than sorry.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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Intergalactic_Captain
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So how much light is actually necessary to facilitate a chlorination? It seems like everyone here is using something around a 500watt lamp...I'm
assuming this is simply because those who are performing these reactions have the fume hood / venting system to perform them in a lab setting. What
about the sun, though? I've been doing some reading and it sounds like it's possible, though nobody here seems to have done it...unless I'm missing
something.
I'd like to attempt the chlorination of toluene tomorow...I can build the setup (nigger-rigged, of course), but the strongest artificial light I can
do is a 100watt (incandescent) bulb...It's supposed to be sunny with minimal cloud cover this weekend though, so I'm planning on using the sun
unassisted...Should it fail, I could always rig up a light bulb, though I'd really rather not - my dad took my good extension cord while I was at
school and I haven't seen it since.
So, if anyone's done up the toluene chlorination, did you do it in the sun? How well did it work? Also, just how bad is benzyl chloride - I know its
a nasty lachrymator and all that jazz, but will sitting a few meters away be too close?
One last question - I'm planning on making benzaldehyde anyway...Is it absolutely necessary to distill off the toluene before the water/bicarb boil?
Something about distilling tear gas without a respirator just doesn't sit too well with me. I'm thinking of rigging up a good magnetic stirrer and
trying to react it as an emulsion...On second thought, this probably won't work too well if at all, but has anyone ever tried it?
EDIT - I just realized this is the chlorine thread...I know Organikum started it with the intent to use it for benzaldehyde, so I guess it's not too
off topic...For relevance, though, I'm planning on dripping H2SO4 into a stoichiometric mix of KMnO4 and NaCl in water. I know there's a danger of
Mn2O7, but I'm thinking it'll go to HCl->Cl2 in situ...It's more expensive than HCl, but easier for me to get ahold of the reagents for some odd
reason.
[Edited on 5-18-07 by Intergalactic_Captain]
If you see me running, try to keep up.
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G.i.B.
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I used the glass tube from an old mariuana growing light as a reaction vessel to chlorinate toluene, and did it in direct sunlight. It worked quite
well. I only made about 20-30 ml just for the hell of it, and I am not sure about the purety of my end product. I used a 200 ml syringe to add the
acid, so I had no problems with the pressure build-up.
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Intergalactic_Captain
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How bad was the tear-gas effect though? Benzyl chloride is supposed to be quite potent, though not very volatile...Would you have been able to pick
up your tube and carry it a short distance without tearing up/etc.?
If you see me running, try to keep up.
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Magpie
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Garage chemist says:
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There is no need to remove HCl gas from the chlorine stream, as your reaction (chlorination of DCM) produces HCl anyway, like most organic
chlorinations do.
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Um...of, course. That's what I get for not writing out the reaction equations.
| Quote: |
your method of chlorination has to be improved. For instance, a reflux condenser is absolutely vital if you are chlorinating anything.
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Yes, I see your point. I wasn't sure how much heat chlorination of DCM would require. I know from experience that heat is necessary for aliphatic
bromination. Also, DCM is so volatile it would be difficult or impossible to contain it without a condenser.
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I doubt that you will be able to get more than one chlorine attached to the DCM
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I am sorry to hear this. My hope was to make CCl4. But CHCl3 would of value also.
Use of the syringe sounds like a clever way to get around the pressure problem. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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G.i.B.
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Intergalactic_Captain. I am sure that you can carry it a short distance, Getting the benzyl chloride out of your reaction vessel and into your
storage bottle, is another matter, you do not want to smell too much of it. Gasmask is advised ! And clean anything that comes in contact with it
outside, you want nothing in your sink, you can smell it for weeks.
[Edited on 19-5-2007 by G.i.B.]
[Edited on 19-5-2007 by G.i.B.]
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Magpie
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I finally got everything together for another attempt at the free radical chlorination of DCM. This time I had benefit of a pressure equalizing
dropping funnel, a gas mixing vessel, and a condenser. Also, instead of two H2SO4 water absorption bottles I used 1 bottle filled with BB size CaCl2
followed by 1 H2SO4 water absorption bottle.
I charged the 500 mL RBF with 55 g of coarsely ground TCCA and the dropping funnel with about 200 mL of 20% HCl. The dip tube in the H2SO4 was about
3cm submerged and I placed about 75 mL of DCM in the gas mixing vessel. The sparge tube in the DCM was also about 3cm submerged. Once chlorine
generation was steadily underway I placed a 100w mercury vapor light next to the gas mixing vessel.
I wasn't sure what products I would get from this experiment (if any) but I was hoping for some nominal amount of CCl4. Most importantly, however, I
wanted to verify that my new setup could generate dry chlorine in a controlled fashion.
At first things were disapointing. Chlorine generation was irregular and my safety relief (glass stopper in dropping funnel) kept popping out. Then
once I had about half of the HCl added things settled down and Cl2 generation was a nice steady 1-2 bubbles/sec as seen in the H2SO4 water absorption
bottle. I never did apply any heat to the RBF but did turn up the mag stirrer as the gas generation rate dropped off. After about an hour of steady
chlorination I terminated the run without adding the rest of the HCl.
My hood was very useful here, steadily removing the Cl2 as it left the top of the condenser. I can't envision working with Cl2 without a hood. It
doesn't take much in your breathing space to really make you uncomfortable. Outside I could barely smell it just under the vent. 25 feet away I
couldn't smell it - of course it didn't hurt to have a windy day. 
Here's a picture of my setup. I built a small ss wire cage for the outlet of the gas tube in the CaCl2 bottle before covering it with the CaCl2 BB's.
I don't know if that was necessary but I tried to do everything I could to reduce backpressure in the system.
Any questions, comments or critique of this setup and/or the halogenation, is welcomed.
[Edited on by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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12AX7
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Hmm, you should have more shielding on that light, UV isn't great stuff.
Tim
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Magpie
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That's a good comment Tim. I was wondering just how much of a hazard that light is when unshielded. The lamp is unfrosted and is a relacement lamp
for the shielded outside garage security lights.
The single most important condition for a successful synthesis is good mixing - Nicodem
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evil_lurker
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Most mercury vapor lamps have UV shielding in the bulb themselves... if the outer jacket gets broken, then yes there is a problem wiht UV radiation...
this is a safety precaution by the manufacturers.
Likewise for most chemical reactions, UV radiation isn't an effective catalyst because pyrex type glassware absorbs quite a bit of UV rays.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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Magpie
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Yes, lurker, I see what you mean. I thought that somehow I was protected but had forgotten why. The lamp I have is a Caster type R. The packaging
has this warning:
"WARNING: THIS LAMP CAN CAUSE SERIOUS SKIN BURN AND EYE INFLAMATION FROM SHORTWAVE ULTRAVIOLET RADIATION IF OUTER ENVELOPE OF THE LAMP IS BROKEN OR
PUNCTURED. DO NOT USE WHERE PEOPLE WILL REMAIN FOR MORE THAN A FEW MINUTES UNLESS ADEQUATE SHIELDING OR OTHER SAFETY PRECAUTIONS ARE USED. LAMPS
THAT WILL AUTOMATICALLY EXTINGUISH WHEN THE OUTER ENVELOPE IS BROKEN OR PUNCTURED ARE COMMERCIALLY AVAILABLE."
When we did free radical brominations in organic chemistry class we used an ordinary but unfrosted incandescent lamp, ~75w. We also just used
ordinary test tubes (I assume borosilicate) IIRC. We also increased the temperature from 25C to 50C. Now I'm wondering if the added "hv" actually
had any effect?
The single most important condition for a successful synthesis is good mixing - Nicodem
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The_Davster
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The few UV light sources I have used contained the bulb in quartz(?) and was intended for direct imersion into the reaction vessel.
However I think some UV must get through pyrex. I have prepared compounds that fluoresce under UV, and illuminating them through standard pyrex glass
with a broad spectrum UV source did cause fluoresence.
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12AX7
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As I recall, pyrex will transmit low UV, but not high UV, which only quartz will transmit. Soda-lime glass transmits neither to an appreciable
degree.
Tim
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Magpie
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It seems like to make my uv light system effective and safe I will need to:
1. Break off the outer glass envelope on my mercury vapor lamp.
2. Use a quartz reaction vessel.
3. Place a safety shield around the lamp/vessel.
Perhaps if I just made sure that my hood sash was down when the lamp was on I would be protected. My sash is double-pane tempered glass.
The single most important condition for a successful synthesis is good mixing - Nicodem
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not_important
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Chlorine radical reactions are triggered by light in the 300 to 380 nm range, Pyrex and similar borosilicates transmit down 280 nm or so; there's no
need for quartz unless the reaction requires that extra energy in the radicals formed. BTW, bromine absorbs in the range 360 to 510 nm.
Some mercury vapour lamps include shunts within the outer bulb that will open if run in air. Also, if the design of the bulb places the phosphors on
the inner surface of the outer bulb; removing that bulb will given you lots of short wavr UV. But there were designs that had the phosphors coating
the inner bulb or on a separate envelope, which would not give nearly the increase in UV when the outer bulb was removed.
You can take the chlorination all the way to CCl4, the 4th C-Cl bond is about 10% lower in energy than the others and steric factors come into play,
but that just means taking additional time.
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evil_lurker
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| Quote: | Originally posted by not_important
Chlorine radical reactions are triggered by light in the 300 to 380 nm range, Pyrex and similar borosilicates transmit down 280 nm or so; there's no
need for quartz unless the reaction requires that extra energy in the radicals formed. BTW, bromine absorbs in the range 360 to 510 nm.
Some mercury vapour lamps include shunts within the outer bulb that will open if run in air. Also, if the design of the bulb places the phosphors on
the inner surface of the outer bulb; removing that bulb will given you lots of short wavr UV. But there were designs that had the phosphors coating
the inner bulb or on a separate envelope, which would not give nearly the increase in UV when the outer bulb was removed.
You can take the chlorination all the way to CCl4, the 4th C-Cl bond is about 10% lower in energy than the others and steric factors come into play,
but that just means taking additional time. |
Not_important is dead on.. deep blue light is what is needed to generate chlorine radicals, not UV light.
I noticed my yields went way up when chlorinating toluene when I switched over to a 20,000K metal halide vs 500w halogen.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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Magpie
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not_important your post is indeed good news. I'm glad I won't have to remove the outer envelope glass on my lamp, or find a quartz reaction vessel!
And also about the wavelength needed for brominations - I guess my instructor knew what he was doing after all.
Below is a picture of my mercury vapor lamp. It is a 100w Caster H38 model, type R, made in China. It is also marked "02 06" which I assume is a
date of manufacture. I couldn't find any specs on it but assume it is a "high pressure" lamp. I've been trying to find a spectrum for this type of
lamp but haven't really been successful yet.
It does have a shunt w/resistor as you can see but I believe this is just part of the starting circuit using a 3rd electrode.
Evil_lurker I believe you are likely correct in that you have the best OTC lamp for chlorinations. I'm just trying to get a setup that will do the
job at hopefully a lower cost. I'll just probably have to run my lamp longer than you would.
[Edited on by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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As described above I attempted to make CCl4 by free radical chlorination of CH2Cl2 (dichloromethane, or DCM). Tonight I did a fractional distillation
of the 60mL of product from that chlorination. I used a Hempel reflux column packed with ss scrub pad. Before the distillation I washed the product
once with 50mL of dilute aqueous Na2CO3 and then once with 50 mL of just water.
First condensate came over at 38.5C and was cloudy. After about 12 mL had collected the condensate had cleared up and T=39.5C. Then the remainder of
the distillate was collected (40 mL) in the range T=39.5 to 40.3C. I took this to be all DCM. (DCM literature bp = 40.2C.)
The few mL left in the pot was a little sour smelling and had a slight yellow tint. It didn't have any chloroform or carbon tet smell at all.
So I have to say that my attempt at producing CCl4 was a total failure. I would be interested in hearing of the experiences of any others who have
tried this.
The single most important condition for a successful synthesis is good mixing - Nicodem
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MagicJigPipe
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100w? I'm no expert in free radical chlorination or electromagnetic waves but... Why does it matter what kind of light source you use as long as it
produces enough light/UV in the appropriate wavelengths. And saying that, 100w doesn't seem to be near enough energy even if it was extremely
efficient. I mean instead of a 100w mercury vapor lamp, why not just go to home depot and buy a 1000w halogen lamp? It's cheap (except for the
energy cost, which still isn't much worse than running a large microwave for a while) I mean, light is light no matter what the source.
Or is this all about maximum efficiency?
Also, c'mon you guys you're talking about UV like its gamma radiation. I would imagine the main risk is to your eyes. So, why not just cover it up,
wear UVA/UVB sunglasses when you're working with it and don't let it shine on your skin for extended periods. I don't think that's too lax. Am I
wrong?
"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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not_important
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The chlorination runs as a radical chain, giving thousands of C-Cl bond formations per photon. Plus there's no sense pumping in more energy than is
convenient to remove, why overdo things?
If you have a lot of UV around it will be everywhere, not easy to avoid if you're working with it. I've had several chunks of skin cut out by
doctors. Friends have corneas shaved. All effects from UV, why add to the total dose you get - for some parts of the body free radical damage is
forever.
I've had success with this, but long ago. Starting with methane feed from the gas line and a slow electrolytic Cl2 feed; mercury vapour light. A 10
cm diameter borosilicate reaction tube 30 cm long at on focus of a buffed aluminium sheet elliptical reflector. Cooled collection flask for
halogenated products. Ran it continuous for many days, mostly ignoring it, then removing several 100 ml of product for fractionation.
Liquid phase may shorten the radical chains, reducing yield per photon.
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Magpie
lab constructor
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Thank you not_important for providing me the benefit of your experience with chlorinating methane. In trying to explain why my attempt failed, the
fact that it was in the liquid phase vs gas phase was one explanation I had thought about. In an old book this reaction was done in the gas phase.
But in one sense I had this condition in the gas phase over my liquid phase, i.e., evaporating DCM and escaping chlorine. In the end I rationalized
the lack of reaction as due to the low tendency of a zero degree alkyl group to participate in the free radical mechanism.
For MajicJigPipe: I had tried a 400w halogen light but it generated so much heat that that in itself became a problem for the low bp DCM. However,
that attempt was quickly aborted for that and other unrelated reasons.
The single most important condition for a successful synthesis is good mixing - Nicodem
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MagicJigPipe
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Ok, then why is everyone so obsessed with maximum light input, talking about that bright sunlight is best? more photons = more free radicals = faster
chlorination, right? Or is that an oversimplification?
And I could understand the heat issue (maybe an extremely effecient reflux condenser could compensate?). But say you could get a fluorescent light
that emmitted nearly as much light as a 300w Hg vapor lamp. Wouldn't that be just as good if not better than a 100w Hg vapor?
I guess my whole point is. Why is Hg vapor so great and why should I spend the extra time and effort to get one?
P.S. Nice fume hood magpie. I'm still in the process of purchasing materials for mine.... Some day though.... 
[Edited on 11-12-2007 by MagicJigPipe]
"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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not_important
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| Quote: | Originally posted by MagicJigPipe
...
I guess my whole point is. Why is Hg vapor so great and why should I spend the extra time and effort to get one?
... |
Because as I said earlier, Chlorine radical reactions are triggered by light in the 300 to 380 nm range, with some effectiveness on up to 430
nm or so. The phosphors in a fluorescent lamp convert most of the UV to wavelengths longer than 550 nm
http://commons.wikimedia.org/wiki/Image:Fluorescent_lighting...
mercury spectrum
http://www.lamptech.co.uk/Documents/M3%20Spectra.htm
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Magpie
lab constructor
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Here's some more spectra on the Hg vapor lamps:
http://crystec.com/lamp1.gif
and a transmission curve for borosilicate glass:
http://www.sinclairmfg.com/datasheets/borosilicatecurve.htm
Thanks for the note on the hood.
I think use of a regular reflux setup would have been better than what I used, i.e., keeping everything at a boil would increase any reaction rate.
Today I designed an elliptical reflector for my next use of the Hg vapor lamp. Now I just need to find a cheap source of sheet aluminum.
[Edited on by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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MagicJigPipe
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So, what about a tanning bed light since they are specifically designed to emit light in those wavelengths? And you wouldn't have to modify the bulb.
Ok, it's time to stop questions and start experimenting.
Arggggg!!! I forgot about my broken reflux condenser and all I have now is a 300mm jacket West condenser. I don't think that will do it.... I
wonder if I put a fractioning column between the pot and the condenser, if that would be sufficient. That's going to be really tall though... I'll
figure something out.
"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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