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Safe lab setup help required - carbon treatment under reflux

  1. Feb 15, 2013 #1
    I will be treating carbon in 3 steps under reflux and I would really appreciate some suggestions, tips and advice on getting a proper and SAFE setup in the lab. I have at my disposal a fume hood and standard laboratory glassware.

    Treatment 1: 20g carbon treated with 100mL 65% Nitric Acid under reflux for 24 hrs.

    This is what I came up with, a 250mL round bottomed flask connected to a standard Liebig condenser held in the vertical position with cold water entering the bottom and hot from the top. Would a different condenser be more appropriate? I am not sure whether or not I should stopper of my condenser?
    I might be able to get a round bottom flask heating mantle to use as the heat source if not then maybe an oil bath and a hot plate.

    Treatment 2: 0.8 g of the Nitric Acid treated carbon (Treatment 1) to be further treated with 5mL Thionyl Chloride (SOCl2) and 5mL Benzene for 24hrs

    The MSDS for Thionyl chloride says that upon contact with water or humid air, it releases HCl and SO2. This is a huge concern for me. What precautions should I take?

    Should I vary my setup than the round bottom flask, heating mantle/hot plate and condenser setup? Also should I cap the stopper the top of the condenser?

    Treatment 3: 0.8g of the carbon from Treatment 2 to be further treated with 2.60mL of Ethylene Diamine and 6mL of Chloroform under reflux for 48hrs.

    Ethylene Diamine has a low flash point of 34 degC

    Vary Setup ?

    If want to scale up the treatments, specifically treatment 2 and 3, by using 20g of carbon rather than 0.8g and increasing the quantity of the other chemicals. What precautions should I take into consideration?

    EDIT: After each treatment the carbon would be properly washed to remove any trace chemicals and dried to remove any moisture trapped.
  2. jcsd
  3. Feb 15, 2013 #2


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    That should work. I would use an Allihn if it were available but the Liebig will work.
    Never, never, never, never stopper a condenser while you are using it during reflux.
    Oil baths are dangerous when you are using water in the condenser or refluxing aqueous reaction mixtures. It's the last choice I would make for heating a vessel under any circumstance.

    Handle with gloves, measure by volume rather than weight, perform all operations in the hood. I use a syringe to handle it on small scale. It is a fairly oily liquid that only slowly reacts with moisture in the air so its not as bad as you might imagine. It will annihilate any rubber it comes into contact with. Not instantly but you can be sure that any rubber bulbs or hoses that come into contact with the vapors will develop cracks and deteriorate. Clean your glassware that comes in contact with it in the hood. I usually have a tub of warm soapy water available to soak everything in. If possible leave the cleanup tub in the hood for several hours or overnight. Remember that benzene is a carcinogen. It's expensive to get rid of so don't contaminate the rest of the lab's waste with it. Have a special bottle for benzene waste for this step. Write down what goes into the bottle. For example, if you filter the carbon through a buchner funnel, you will have a lot of thionyl chloride contaminating the benzene filtrate. If you transfer the filtrate directly to the waste bottle, you have a dangerous situation. You have a lot of leftover thionyl chloride that can react with moisture to produce HCl and SO2 AND you have a nasty carcinogen bouquet to go with it. You will probably want to quench the filtrate to decompose the thionyl chloride before disposal and that quench will need to be handled as if it were benzene. The volume of waste grows and grows, you see, and you will need to identify everything that goes into it so you can properly label your lab waste. Why not use cyclohexane or toluene instead?
    Don't stopper the top of the condenser. If you are concerned about moist air contaminating your setup, attach a drying tube charged with a dessicant like Drierite but DON'T STOPPER YOUR REACTION WHILE YOU ARE USING HEAT OR PRODUCING GASES LIKE HCl OR SO2! BOOM!

    You should be fine provided you are using explosion proof equipment and the operation is performed in the hood.

    When you scale up your risk is scaled as well. You are scaling up from a 10 mL volume to about 250 mL. While these volumes are not huge, you need to consider things like how fast you should add reagents and worry about bumping and the drying tube. In small vessels, you add reagents all at once and any heat generated is lost quickly because you are dealing with small volumes and comparatively large heat contact areas. ln larger scales, you must add reagents over time so that you don't get a runaway reaction and the reaction mixture has time to dissapate any evolved heat or gases in this case. Drying tubes don't like bumping when you are refluxing. It's worse the larger you go. You will need to use a much larger drying tube and don't let it dangle from or rest on top of the condenser. Do you intend to just vent the evolved HCl and SO2 or will you need to scrub the evolved gases first?

    I would definitely go with the Allihn with the large scale but you just might be able to get away with using the Liebig condenser. The minimum size vessel I would consider would be 500 mL but I would prefer a 1L, round-bottomed vessel, especially when working with thionyl chloride. Everything will grow in size. You won't be able to use a syringe to measure the thionyl chloride, for example. Your waste stream will increase by a factor of 20-30 as well. Any spills will become 'events'. Wiping up 5-10 mL of spilled thionyl chloride/benzene is pretty straightforward but cleaning up a 250 mL spill would require a spill kit, for example.
  4. Feb 15, 2013 #3
    So without a stopper this means that I will be allowing any vapors escape my system and at the same time my liquid quantities will reduce. How do I properly control the mixtures and make sure it will not dry out while it's left overnight?

    It's great that you brought up cleanup and waste disposal I forgot to mention them in the thread. Would regular household dish soap do or some Alconox glassware detergent? I was also doing some reading about disposal of thionyl chloride and in some sites it's been suggested to neutralize it in sodium hydroxide or sodium carbonate overnight.
    Can I use a plastic tub for soaking or should it be made of another material?

    The procedure involves adding both the thionyl chloride and benzene together with the carbon for treatment. So in this case they would both come out as the filtrate when I'm collecting the carbon.

    I'm not actually sure about the Chemistry involved when using benzene and what its role with thionyl chloride is, all I could find was that benzene is used as an inert solvent when thionyl chloride is involved. However using benzene is an issue for me because I'll be using the treated carbon after treatment 3 for adsorption studies of benzene, toluene and xylene from aqueous solutions. So the benzene (from treatment 2) will adsorb on the carbon surface and fill up the adsorption sites before I even use the carbon the adsorbtion study.

    After treatment 2, I'm supposed to dry the mixture in a rotary evaporator wash the carbon "extensively" with benzene to remove any traces of thionyl chloride. How much benzene should I use and how do I know that all the thionyl chloride is removed?

    Also after treatment 3, I am to wash the carbon extensively with chloroform to remove any of the ethylene diamine and separate out the carbon by centrifugation (not rotary evaporator is mentioned). Again how much chloroform is enough?

    The last treatment uses chloroform for the washing and benzene is soluble in chloroform. So any benzene adsorbed on the carbon should get removed and I can remove the chloroform by using water. So it should be okay right and it shouldn't effect my adsorbtion study?

    I can't say whether or not they would work but as far as toluene goes it's the same issue as with benzene since I'll be using the carbon for toluene adsorption studies.

    The fume hoods look like they have pretty good suction and the lab is always cold and controlled at 19 deg C. As for the drying agents all what I've seen available is Calcium Chloride.

    I have standard lab glassware and a fume hood, do they count as explosion proof?

    I was planning to just let the fume hoods' fan suck out any gases. If a scrubber is more safe I will do that but can you explain on how I can set that up (pictures would be great)?
  5. Feb 16, 2013 #4


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    Your condenser will handle that.

    You should only have traces of thionyl chloride on your glassware. Before placing anything in the plastic (yes, plastic is the way to go) tub, you should rinse the glassware with fairly dry hexanes. Straight out of the bottle should do. Use Alconox if you have it or something like Dawn. Add sodium carbonate to the wash tub. This tub will be at pH ~10 so even with sodium carbonate, it is considered hazardous to bare hands. You must use gloves... big thick dishwashing gloves not those wimpy nitrile one-use throwaways. Try not to stack glass on glass. Broken glass defeats PPO every time.

    Benzene is there as an inert solvent only. Your experiment is converting all the acidic (carboxylic acid) sites to basic sites with the difunctional amine. You will be converting those carboxylic sites into amides with an aliphatic primary amine tail. If you are trying to duplicate someone's result, you must perform the procedure as it was originally published. If you are copying a procedure for a different purpose, you may change whatever you wish. You are heating to reflux so you should understand that the primary consideration for the use of one solvent over another is the temperature control you have with the lowest boiling component or a low boiling azeotrope, in this case it is thionyl chloride at 75oC or its azeotrope with benzene (temp?). Cyclohexane boils at essentially the same temperature and toluene boils at 111oC. I'm not sure if cyclohexane azeotropes with thionyl chloride but it really shouldn't matter.

    I believe that BTEX compounds bind reversibly to carbon so you might be heat treating and purging the carbon before your experiment else you must change solvent systems. Everything you are describing should work with 100% thionyl chloride and no solvent. That's the safest way to go. For workup, co-distill with a non-reactive aliphatic solvent close to the boiling point of the thionyl chloride to remove the final traces. Remember that when you rotovap or vacuum distill thionyl chloride, you are pulling nasty stuff through your pumps unless you take precautions. If you are using a water aspirator to lower the pressure, you should place a drying tube between the apparatus and the aspirator. The only time I used an aspirator with thionyl chloride it filled the lab with vapors. Won't do that ever again unless the aspirator and the rotovap is in the hood.

    I would use a higher boiling aliphatic solvent instead. Maybe methylcyclohexane (BP 101oC). To determine how much is enough, you need to heat the dry carbon after washing 10X with volume equal to volume of carbon (estimate this) and insert a moist litmus paper into the headspace briefly. You are co-distilling the thionyl chloride in this step. Add solvent, evap to dryness, stop, repeat 9 more times. Test after the last wash.

    Ten times an equal volume based on volume of carbon plug at the bottom of the centrifuge tube. 0.8 g of carbon will be roughly 1 mL. 20 g will be roughly 20 mL.

    Remove chloroform (BP 61oC) from the carbon with water? Think through this step very carefully.

    That will work.

    How will you apply heat? Rotovap? In my experience, fume hoods are built to be explosion proof. YMMV.

    If the hood will handle it, then go with it. If you need to scrub the gas, here's how. You will need three side arm filter flasks. The first flask will be empty and placed between your reaction mixture and the wet scrubbers. It should be sized to contain the contents of both of the other wet scrubbers. Use either a cork or rubber stopper with a hole sized to accomodate a short piece of glass tubing that will attach to the hose leading from the reaction setup. The glass tubing should be inserted far enough into the flask so that it just below the level of the side arm nipple.
    Attach a hose from the side arm nipple to a glass tube inserted through the cork or rubber stopper of the second flask. The glass tubing should reach down to just above the bottom of the flask. Attach a rubber tube to the side arm nipple of the second flask to another glass tube inserted through the cork or rubber stopper of the third flask. Again, the glass tube should reach almost to the bottom of the flask.
    Fill the second and third flasks with the scrubbing solution. 5% NaOH should work fine. Note the total volume in both of the flasks to be sure that the first, empty flask can fully contain the contents of the second and third in the event of suckback. Now attach a 'y' or 't' connector to the top of your condenser and fit with a rubber tube of sufficient length to reach the first vessel's side arm nipple. Attach to the side arm nipple.
    The remaining arm from the 'y' or 't' is attached to a dry nitrogen source and dry nitrogen is introduced slowly. The nitrogen will carry away any HCl or SO2 evolved during the reaction, through the empty first flask into the remaining two flasks containing the NaOH solution. Adjust the flow so that bubbles are slowly seen in both of the scrubber flasks. Now wire everything tightly since everything will now be under a slight positive pressure. Be sure you don't run out of dry nitrogen. Don't use argon.

    Easy, right?
  6. Feb 16, 2013 #5
    My final purpose is to introduce basic sites into my carbon just as you said. I am more or less going to follow the exact procedure listed in the article (just scaling up) but the use of benzene (or toluene) as a solvent is an issue as I explained. You seem to have a vast amount of knowledge and experience in this sort of experiment, have you done this before?

    I was about to ask about the temperature control and you just pointed it out. So I should adjust my reaction mixture temperature to that of the lower boiling point compound, right?
    So for example with thionyl chlordie (BP 75C) and benzene (BP 80C) I should maintain the temp at 75 deg C and for the amine (BP 116C) and chloroform (61C) it should be at 61 deg C?

    If by bind reversibly you mean I can desorb the BTEX compounds then you are correct but I don't have the setup for it. I collect the "spent" carbon after my experiments in a waste container.

    I still don't understand what is the purpose of a solvent with thionyl chloride. And using benzene as a solvent seems worse because it is a carcinogen. Handling the SO2 and HCl gases given off by thionyl chloride would be much easier than handling benzene.

    In case I only use thionyl chloride without any solvent, how would I adjust the experiment? With 0.80g of carbon its a 1:1 ratio or 5mL:5mL of thionyl chloride and benzene, should I just use 10mL of thionyl chloride with 0.8g of carbon?

    I have a feeling that scaling up the experiment is going to be an issue :/

    The rotovap setup is actually just outside the fume hoods and getting it setup inside is not an option, unfortunately.

    The final step after all the treatments would be to use chloroform to wash the carbon to remove any of the amine. So I was thinking of using a Buchner funnel and vacuum filtration setup and wash the carbon with water to remove the chloroform since chloroform is highly soluble in water. And at the same time benzene is soluble in chloroform. So I was hoping that in the end I'd have wet carbon (with no benzene, thionyl chloride, chloroform or amine) which I can simply dry in an oven.

    I'm planning on using a round bottom flask heating mantle as my heat source, I'll just have to check if there any larger ones that can handle a 250mL+ round flask.

    I had to read it a couple of times to get the picture but it does sound easy. Except I don't have any nitrogen gas or any gases except for the fume hoods air supply. Can I work without it and just have the series of scrubbers?
    The nipple of the third side-arm flask is basically not connected to anything, yes?

    One more thing about the rotary evaporator, as far as I can tell no one cleans any of its glassware except for the sample and waste collection flasks. So there's probably some things stuck on the inside of the condenser and around the coils. Since I'll be evaporating thionyl chloride, it should be cleaned?
    I'll need to have a better look at the rotovap setup and check whether I can install the drying tubes.

    It's actually the weekend over here and I'll be in the lab tomorrow, Sunday. I'll have to check all the glassware and prepare a preliminary setup first to get the entire thing clear in my head and make sure I don't miss out on anything.
    Last edited: Feb 16, 2013
  7. Feb 17, 2013 #6
    Based on the glassware I could find this is the setup I came up with:

    1L 3-necked round bottomed flask (I couldn't find a regular 1L round bottomed flask) connected to an Allihn condenser, water in the bottom and out the top. Drying tube attached to one of the necks of the flask since you advised not to connect it to the top of the condenser.

    Since I don't have any N2 I'll be using an aspirator to draw the gases through my scrubbers, here's how:
    Just above the condenser opening I'll have an inverted funnel connected to 3 scrubbers just as you described, with the first one empty and the other two containing my NaOH scrubbing solution. I've added a fourth filter flask to be attached to the third scrubber and that would be connected to the vaccuum. The purpose of the fourth filter flask is to avoid any moisture entering the asiprator and in case of back-suction it will collect the liquid.

    Edit: After some thought, maybe 4 filter flasks is overkill. Can I have 3 and place them in reverse, i.e. scrubber, scrubber, empty, aspirator/vacuum ?

    I have an issue with my heat source, the largest round bottomed heating mantle I could find has a 250mL capacity. Can I still manage with it? If not, what other alternative can I use?

    Please let me know what you think.
    Last edited: Feb 17, 2013
  8. Feb 17, 2013 #7


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    Ha, ha... I've done a few thionyl chloride reactions. I've done them on scales larger than you are contemplating. Solvents are used to control temperature, to limit reaction rate and to ensure that the reagent and products are soluble. The temperature in the pot (not what you supply) is generally limited to the boiling point of the lowest boiling component. So, reactions done in diethyl ether (BP 35oC) happen at a different temperature than those that happen in refluxing toluene (BP 111oC). This has implications for reaction rate, solubility, removal of volatile reaction products and the stability of products formed. There are also issues due to a solvent's coordination ability, polarity and so forth but they aren't that critical to your experiment. Switching from benzene to toluene will mean that the thionyl chloride will be the lowest boiling component. If you don't use enough excess, it will fill the headspace, depleting somewhat the concentration of it in the reaction pot. It may not be a problem but you think about that kind of thing when changing solvents. Cyclohexane has roughly the same boiling point as benzene and might work for you better than no solvent at all but you might also find that you don't need a solvent. You're always going to have a two phase reaction so you don't worry about solubilities. There isn't any magic about 10 mL per 0.8 g carbon. It's just handy to have a little volume to pour with your solid.

    You misunderstand, the temperature is limited to the boiling point for the most part. Apply more heat and you get faster boiling but not a serious increase of pot temperature.

    Agreed. I wouldn't use a solvent at all. Of course I'd start small before I committed to a larger reaction to get a feel for the reaction rate, offgas rate and so forth.

    If you can suspend all of the carbon in 5 mL, I'd use that volume. In your reaction, handling considerations will dominate how much reagent to use. Easier to pour out a thin slurry than a mudpie.

    Not so.

    Solvent washing may not remove all of the benzene that is adsorbed onto the carbon. That takes heat and airflow.

    My point was that you need to use power sources that are explosion proof. If you are plugging the mantle into a VariAC, make sure that the VariAC is not inside the hood with the fumes to be absolutely safe. I would mount the VariAC to the outside of the hood to avoid corrosive or flammable fumes from this procedure and lead the extension cord from the outside of the hood to the mantle.

    You could use lab air if you want to. I always have dry nitrogen available so I use it for everything. Just don't sweep the top of the condenser with the air supply. I would install a hose adapter to the top of the condenser and lead a long tube away from it to the 'y' or 't' and from there to the scrubbers. You might install a drying tube between the 'y' or 't' and the top of the condenser just to be sure.


    When you use thionyl chloride in the rotovap you might need to replace the main gasket before you begin. Most that I have used have main gaskets that are in bad shape and if you need to keep moist air out of the vessel it probably needs to be replaced. Chasing or codistilling the trace amounts of thionyl chloride with a high boiling solvent like heptane will help. Most rotary evaporators use water in the bath and you don't want any moisture to contaminate your sample. If you are distilling a reactive material through a rotovap, it will need to be clean and dry. You will need to clean and dry it after every use to maintain harmony in the lab with your coworkers. Use gloves when you work with the old gasket and whenever you disassemble the rotovap. No telling what that rubber gasket has absorbed.

    Thionyl chloride produces HCl gas which attacks most metals. Search it out and kill it before it screws up everything electrical or metallic in the lab.
  9. Feb 17, 2013 #8


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    Whoa there! I just meant that you don't want a heavy 3-4lb dryer tube hanging from the top of your apparatus. Attach a hose to the top of the Allihn and lead it away from the the condenser to the drying tube lying on the floor of the hood or suspended by a clamp. Stopper the other two joints unless you want to add reagents slowly. In that case, attach a supported addition funnel with its own drying tube and add reagent (thionyl chloride in a large scale reaction) through it. If the addition funnel is a pressure equalizing type, just stopper it. If the addition funnel doesn't have a ground glass joint that matches the 1L flask where it attaches, it probably isn't worth the trouble to use one.

    I would not use an aspirator to sweep a reaction free of evolved, reactive gases in a scrubber setup. Forget it would be my advice.
  10. Feb 18, 2013 #9
    The setup will be condenser - tubing - drying tube - y or t connector - air supply in one connection - other connection with tubing to scrubbers.
    Wouldn't an air flow into my system, cause the gases to return backwards through the drying tube and into the condenser and reaction flask avoiding them to pass through the scrubbers?
  11. Feb 20, 2013 #10
    I've done the first treatment with concentrated nitric acid but I only let it reflux for about 2 hours rather than the planned 24 hours.

    There was too much NO2 gas and even with two scrubbers containing 5% NaOH it was pretty difficult to control.
    I kept trying to adjust the heat to my reaction flask and air flow but I ended up building up too much pressure in my empty filter flask causing the cork to pop out, that's when I decided to stop.
    It is possible that one problem/mistake in my setup is that I had too many pieces of tubing with different sizes, so the flow of gases from my reaction vessel was restricted.
  12. Feb 20, 2013 #11


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    You only need to use the complicated scrubber setup when using water-sensitive reagents and only use the scrubber train IF your lab policy requires that you don't vent corrosives. You should not have needed if for the aqueous HNO3 treatment.
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