ExothermicReaction
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Nitrous Dioxide (NO2) - How Dangerous?
The trickiest aspect of the Sandmeyer reaction (GABA to GBL) is that is generates Nitrous Dioxide, which is toxic. I'm trying to get a good handle on
just how toxic this gas is. I've seen the stats for toxicity in parts per million but want to better understand how they translate into a real-world
situation.
The reaction involves dropwise addition of HCl to a mixture of GABA and Sodium Nitrite. Depending on the speed of addition, some brown fumes (NO2) are
generated which must be vented to the outside. What would you conder to be adequate precautions for a responsible execution of the procedure? Of
course, a organic fume/pesticide/paint respirator will be worn along with eye protection.
Consider the worst-case scenario of an instant spill of all the HCl into the GABA/NaNO2. I imagine the result would be an extremely vigorous reaction
producing a big cloud of brown vapor. In such a case, is the toxicity such that a single breath (without a respirator) would be fatal? Or how about a
less extreme scnario where there is some generation of gas in the flask, and the flask shatters. Is this a fatal situation as well or is Nitrous
Dioxide not quite this toxic?
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bilcksneatff
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Actually, it's nitrogen dioxide, not nitrous dioxide. It is very toxic because it will dissolve in water to form nitric and nitrous acids. Since you
body in 70% water, nitrogen dioxide is very dangerous. I don't think one breath without a respirator will kill you. Sure makes you cough a lot,
though.
I wouldn't vent the gases to the outdoors. I would do one of two things:
1. Bubble the gasses through water to form HNO3 and HNO2. This is nice because you can use HNO3 to form more sodium nitrite.
HNO3 + NaOH --> NaNO3 + H2O
NaNO3 + Pb --> PbO + NaNO2 (NaNO3 must be in liquid state)
2. Bubble the gasses through NaOH solution.
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ExothermicReaction
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re Nitrogen Dioxide vs Nitrous Dioxide : Hmm, I thought the two terms were interchangeable, as I see in some sites which talk about the gas. I'll stick with Nitrogen Dioxide from now on. Thanks.
re Bubbling: Very interesting. This is the first time I've seen this mentioned as an alternative. To make sure I understand, you are suggesting that,
rather then vent the gas outside, pass it through a volume of water of NaOH solution. Doing so, will convert the gas into Nitric and Nitrous acid.
A few questions :
1. How would this be set up? The current workup calls for a 2L Flask fitted with a Claisen adapter which is fitted with an addition funnel for
dropping the acid and also a reflux condenser to help cool the whole thing and to help the vapors up and out. So rather then suck the vapors outside
with an (improvised) fume hood, I would attach a hose to the top of the reflux condenser and run the hose into a tub of water or NaOH solution. Am I
understanding you properly?
2. How much water should I use? Could I fill a 5L drinking water container and run the hose to the bottom? Are you suggesting that I can be confident
that, if the N02 is bubbled through water, whatever gasses bubble out the top are not toxic?
3. What does bubbling through NaOH produce? Is this more desirable than plain water if my only concern is quelling the toxic gas? (Although thats very
nice to know that there is a route here to more NaNO2.)
Thanks a lot for the help.
[Edited on 21-11-2007 by ExothermicReaction]
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BromicAcid
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Nitrogen dioxide is fairly toxic, as stated previously it reacts with water forming a mixture of oxoacids of nitrogen. If this happens in your lungs
the damage can result in pulmonary edema (fluid in the lungs) which can be fatal. Additionally the body uses simple nitrogen oxides as chemical
messengers and as such this can have dramatic effects on your heart and other vital processes for living.
That being said a lung full will likely not be fatal as I am typing this now. I had the displeasure of distilling NO<sub>2</sub> from a
mixture of concentrated sulfuric acid and sodium nitrate, thinking that it was nitric acid. I got a couple lung fulls, not something to brag about,
just personal experience.
As for getting rid of it, bilcksneatff had the right idea about bubbling through a basic solution. Bubbling just into water will give you your mix of
acids however you will be surprised at how much NO<sub>2</sub> will make it out unreacted unless you have a decent bubbler so I would
recommend a basic solution instead which will react with those acids and gasses and more efficiently soak them up. Your product though will not be
the free acids but instead sodium nitrate and nitrite.
You will need another flask inline to prevent suck-back instead of just connecting to the top of your reflux. Otherwise when the gasses hit your
scrubbing solution they will react and dissolve into the water which means that there is less gas taking up the area that was just occupied by gasses,
meaning that the pressure is reduced in that area which will draw your solution up through your tubing.
You shouldn't need too much of a scrubbing solution so long as it is sufficiently concentrated, you mention a 2L flask but I still don't know how much
gas you are expecting to off gas. Unless you have an efficient glass frit bubbler you will likely not absorb all of your gas into the solution (i.e.,
your scrubbing efficiently will be <100%) so I still wouldn't breath the gasses coming out the other end.
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S.C. Wack
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I happen to know exactly how much NO2 is required to produce self-evident edema: not much. It's a pretty freaky feeling.
NaOH should be used for absorbtion.
I get the uncomfortable feeling more and more often as I get older that you shouldn't be fucking with it if you have to ask these kind of questions,
whereas I used to be more OK with "trial by fire". What is happening to me?
It's not like there aren't a lot of books out there that school you for basic things like this.
NO2 is also quite corrosive.
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ExothermicReaction
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Bromic : Thanks. This is really helpful.
Wack : re. your uncomfortable feeling. Consider that I am asking these questions well before I start the actual operation. That day will only come
when I am confident that I am ready. This info may be out there in books, and ten years ago, that's where I would have to find it, but now that forums
such as this exist, I consider responses from reputable members to be first-rate sources of knowledge. Text books might give me raw data, but the
first-hand experiences of people like you and Bromic are just as important, if not more so. Today, for instance, based on blicksneatff's post, I was
able to open up Vogel and read his section of the various setups for filtering a gas through a liquid. I might have been able to find it anyware, but
this forum is so key in helping me use my textbook time efficiently.
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