Sciencemadness Discussion Board

Hazardous concerns

EvlRenne - 31-10-2018 at 00:50

Hello everyone!

Guys, in my upcoming synthesis, there is a one step, which I worry about quite a lot.

I'm about to do reaction between dimethyl benzyl carbinol + acetonitrile and conc. H2SO4.

I was searching the web and as usual found 2 opposite answers...

Question is, will be produce gaseous HCN during the reaction above?
I was reading few topics, which are saying that during nucleophilic substitution there is no HCN production, and at the same time some people are saying that H2SO4 + C2H3N will produce HCN.

I need your help for obvious reason, I don't want to die *_*

Swinfi2 - 31-10-2018 at 05:40

My recommendation is to (safely) test if you have the right genetics to smell HCN, it smells like almonds or absolutely nothing. I'd only do this if i know theirs no risk or I can smell it and be able to know if it's gone wrong and get away from it. As for the chemistry, I'm not the right person to ask with this one.

Atrum - 31-10-2018 at 06:09

Hazard to self is pretty damned accurate, Swinifi2

DavidJR - 31-10-2018 at 06:40

I can't find any references stating that acetonitrile + sulphuric acid can produce HCN. It doesn't seem very likely to me.

Pyrolysis and incomplete combustion of acetonitrile can, however, produce HCN.

I have also heard that technical grade acetonitrile may contain free HCN as an impurity.

[Edited on 31-10-2018 by DavidJR]

Swinfi2 - 31-10-2018 at 19:10

I didn't exactly tell him to gas himself with HCN to see if it was HCN *facepalm*, there are many ways to do the same thing. Ex: https://youtu.be/d1rUw21MIII

Not knowing if you are sensitive (or insensitive in a potentially non-ideal situation) to a potential hazard seems more reckless if you ask me.

AvBaeyer - 31-10-2018 at 19:29

The reaction described by OP is the "Ritter reaction." There is no chance of HCN evolution from this reaction. I do not know of any normal reaction conditions involving H2SO4 and acetonitrile that will produce HCN.

AvB

zed - 6-11-2018 at 14:29

Well, seems to me, the methyl radical is pretty rapacious.... Meaning not very stable... Meaning unlikely to allow significant hydrolysis of acetonitrile to methanol and HCN. But, that isn't the final word, and acetonitrile itself is quite toxic if you are exposed to a significant amount of it.

Your body can convert acetonitrile to HCN, internally. When acetonitrile use, migrated from closed industrial systems, into common lab use, there were a fair number of surprise deaths reported.

I would expect more HCN release during hydrolysis of Phenylacetonitrile, whereas the benzyl radical, being more stable, might be more easily shuck off HCN.

As always, proceed with caution. https://www.youtube.com/watch?v=Tc2UamEkRjk

DavidJR - 6-11-2018 at 16:00

Quote: Originally posted by zed  
But, that isn't the final word, and acetonitrile itself is quite toxic if you are exposed to a significant amount of it.

It is moderately toxic, but it's actually quite significantly less toxic than other small nitriles.

AvBaeyer - 6-11-2018 at 20:50

Zed,
I have never in many years heard of any deaths related to lab use of acetonitrile. Can you support your statement with references to some reports? We used to run benchtop HPLC using gallons of acetonitrile every week. No one died or became ill. All waste streams were dumped down the drain. Can you also document any experimental eveidence for HCN formation from phenylacetonitrile hydrolysis? Its hydrolysis does not involve any free radical formation that I have ever heard of.

AvB

DavidJR - 7-11-2018 at 03:40

Quote: Originally posted by AvBaeyer  
Zed,
I have never in many years heard of any deaths related to lab use of acetonitrile. Can you support your statement with references to some reports? We used to run benchtop HPLC using gallons of acetonitrile every week. No one died or became ill. All waste streams were dumped down the drain. Can you also document any experimental eveidence for HCN formation from phenylacetonitrile hydrolysis? Its hydrolysis does not involve any free radical formation that I have ever heard of.

AvB



I was thinking this too. I found a few reports of deaths/poisonings with MeCN but none were lab workers. There have been a few children who have died as a result of ingesting acetonitrile based nail polish remover, including one case in the UK where this was misidentified as acetone and no cyanide antidote was given.

Also, I find it interesting that when I ordered solvents for my HPLC recently the delivery box had big warning stickers re the toxicity of methanol, but not about acetonitrile.

P.S. routinely disposing of large quantities of either MeCN or MeOH down the drain seems environmentally irresponsible, if not outright illegal (depending on location).

zed - 7-11-2018 at 16:57

There was a minor epidemic of Acetonitrile deaths, about 40 years ago.

Enough of them, that alerts were circulated.

Apparently, Acetonitrile proved less dangerous than initially feared.

That is not to say, it is non-toxic. It is toxic, if you get enough exposure, or if you happen to inhabit the wrong end of the bell curve.

So, as Clint Eastwood would say: "Are you feeling lucky?"

https://pmj.bmj.com/content/postgradmedj/73/859/299.full.pdf

AvBaeyer - 7-11-2018 at 20:14

Zed,

Thanks for the reference. The paper refers to an attempted suicide by acetonitrile ingestion and may not be entirely relevant to normal lab exposures. Nonetheless, I was unaware of P450 oxidative metabolism of acetonitrile in such a manner that cyanide was produced. I learn something new every day!

DavidJR,

I should have put my acetonitrile disposal comment in context. That happened back in the late 1970's when I was employed by a major pharma in New Jersey. Water miscible solvents just went down the drain, sometimes in fairly large quantities. We collected non-water miscible solvents and highly contaminated solvents (eg, acetone, ethanol, etc) in waste containers for off site disposal. No effort was required to separate chlorinated, hydrocarbon or other solvents into separate streams - it cost too much. That's all changed now.

At that time, I also worked in a 6-person lab with two shared 5-foot hoods. Needless to say, almost all chemistry but that which was malodorous was carried out on the bench. Roto-vaps, vacuum pumps, and solvent stills were also set up outside hoods. All chromatography, preparative and analytical, was run on the bench top. I ran butyl lithium reactions (and worse) at my bench. I should point out that we ran most reactions on relatively small scale - 100 ml flasks and smaller, mostly 14/20 glassware. There were a couple of old-timers in the lab that on Friday before going home would clean the droppings on there bench tops with benzene or chloroform or whatever else might be handy and evaporate quickly. Of the 6 of us that worked in that lab, 4 of us are still going strong (70+ years old) and the other two died well into their 80's. The point of all this is that toxicity of most chemicals in a laboratory setting is in my opinion quite overblown. Hell, we even used Magic Methyl before it was banned and survived. Enough about the old days. Things have changed with the advent of easy admission to law schools. Got to keep the lawyers busy peering under every rock looking for monetizable risks.

AvB

Panache - 7-11-2018 at 22:02

A recent NIH longitudinal study into the cause of cancers in humans, setup to understand whether the ad hoc explanation that50% of cancers were environment based (ie chemicals etc) and the remainder just genetic showed, that actually only 7% were environment based, meaning of course our fascination with labelling anything and everything a carcinogen is just plain wrong.

DavidJR - 8-11-2018 at 04:19

Quote: Originally posted by AvBaeyer  

I should have put my acetonitrile disposal comment in context. That happened back in the late 1970's when I was employed by a major pharma in New Jersey. Water miscible solvents just went down the drain, sometimes in fairly large quantities. We collected non-water miscible solvents and highly contaminated solvents (eg, acetone, ethanol, etc) in waste containers for off site disposal. No effort was required to separate chlorinated, hydrocarbon or other solvents into separate streams - it cost too much. That's all changed now.

At that time, I also worked in a 6-person lab with two shared 5-foot hoods. Needless to say, almost all chemistry but that which was malodorous was carried out on the bench. Roto-vaps, vacuum pumps, and solvent stills were also set up outside hoods. All chromatography, preparative and analytical, was run on the bench top. I ran butyl lithium reactions (and worse) at my bench. I should point out that we ran most reactions on relatively small scale - 100 ml flasks and smaller, mostly 14/20 glassware. There were a couple of old-timers in the lab that on Friday before going home would clean the droppings on there bench tops with benzene or chloroform or whatever else might be handy and evaporate quickly. Of the 6 of us that worked in that lab, 4 of us are still going strong (70+ years old) and the other two died well into their 80's. The point of all this is that toxicity of most chemicals in a laboratory setting is in my opinion quite overblown. Hell, we even used Magic Methyl before it was banned and survived. Enough about the old days. Things have changed with the advent of easy admission to law schools. Got to keep the lawyers busy peering under every rock looking for monetizable risks.


Interesting - times have certainly changed.

Regarding waste solvents: if you practice strict segregation then recovery of the solvents becomes economical, either yourself or by selling the waste to a solvent recovery company. Seems such a waste to dispose of countless litres of mildly-contaminated MeOH/H2O or MeCN/H2O waste from an HPLC. The more you mix waste of different types the more difficult/expensive it becomes to separate and recover the valuable resources it may contain.

Dr.Bob - 8-11-2018 at 06:47

Ritter reaction should be fine, no real risk of HCN generation, but the amount of sulfuric used does make the reaction a joy to work up, so be careful when quenching it. Good luck with the reaction, it works pretty well, but is not real clean due to side reactions.

I can second AvBaeyers that things have changed dramatically since I started. I ran benzene flash columns, worked in labs without much ventilation (I taught organic labs (with 2 others) in a 50 person lab with 4 small fume hoods), most rotovaps were on the bench and hooked to aspirators for vacuum, taking much solvent down the drain, and much more. But again, many people I worked with are still doing well in their 80s and 90's, including my friend Ed, who worked with fluorine, HF, and even the dreaded ClF3 a few times, and is going strong in his 90's, so even substantial chemical exposure did not seem to harm them, compared to others.

DavidJR - 8-11-2018 at 14:37

Quote: Originally posted by AvBaeyer  

Of the 6 of us that worked in that lab, 4 of us are still going strong (70+ years old) and the other two died well into their 80's. The point of all this is that toxicity of most chemicals in a laboratory setting is in my opinion quite overblown. Hell, we even used Magic Methyl before it was banned and survived.
Quote: Originally posted by Panache  
A recent NIH longitudinal study into the cause of cancers in humans, setup to understand whether the ad hoc explanation that 50% of cancers were environment based (ie chemicals etc) and the remainder just genetic showed, that actually only 7% were environment based, meaning of course our fascination with labelling anything and everything a carcinogen is just plain wrong.
Quote: Originally posted by Dr.Bob  

But again, many people I worked with are still doing well in their 80s and 90's, including my friend Ed, who worked with fluorine, HF, and even the dreaded ClF3 a few times, and is going strong in his 90's, so even substantial chemical exposure did not seem to harm them, compared to others.


Recently I was given a [patronising] telling off by my step aunt (who has a undergrad chemistry degree but works in software) for handling a vial of copper phthalocyanine (a remarkably inert blue pigment) without gloves on. Later, I mentioned this to my 76 year old grandfather, whose career in the dyestuffs industry doesn't seem to have done him much harm - despite being known to come home covered in green/blue. Specifically, he chlorobrominated copper phthalocyanine (marketed as Monastral Fast Blue) to produce Monastral Fast Green, at ICI Grangemouth, where the phthalocyanines were discovered.

I certainly agree that there's a lot of risk exaggeration that goes on re the health effects of all sorts of chemicals. It does seem that nowadays everything is considered a potential carcinogen to be avoided. But then again, when it comes to chronic toxicity, perhaps caution is not a bad thing.

However: it is clear that us humans have become a plague on earth. We've done an excellent job of royally fucking up this planet which no other species can come close to. So frankly we all have a responsibility to work in sustainable and ecologically-friendly ways - such as by recycling waste solvents into useful products, rather than pouring them down the drain.


AvBaeyer - 8-11-2018 at 20:37

DavidJR,

I do not want to drag this out too far but I need to comment on the idea of recycling solvents in an industrial research lab environment. I gather from your comments, hopefully correctly, that you have no industry experience. First, many solvents are mixed as a result of running reactions and workup. These solvents may not be easily separable or chemically compatible for recycling. Second, having collection vessels spread throughout a lab space for each solvent type or class is just not practical. Most importantly, recycling solvents is not cost effective, at least it was not several years ago, especially if you want to recover highly pure lab useful solvents. Take, for example, HPLC effluent based on acetonitrile. This contains not only acetonitrile but also water, trifluoroacetic acid and/or various buffers some of which may be volatile. Recovering HPLC grade acetonitrile from this mix is not trivial nor cheap. Similar situations exist with other solvent mixtures, for example, ethyl acetate-hexane mixtures. When I was heading up a sizable discovery chemistry department I was berated by my CEO (a sarcastic but loveable Brit accountant) regarding our solvent purchase and disposal expenses. I was tasked with looking into recycling our waste stream for either internal use or getting some value from it. After spending more time than it was worth it turned out that we could not find anyone to deal with our "low" output of waste for recycling. We were told the economics did not make sense. Moreover, our waste stream had no residual value for other uses after accounting for costs of hauling it away. It just came down to the basic economics of running a research operation (time is money, do not waste it.) Perhaps things are different now but I cannot say.

The foregoing is dealing with waste solvents in a research lab situation. My experience when running a process development lab is quite different. Processes were developed to minimize solvent use and if possible reuse recovered solvents in a process. It's an entirely different world with regard to economics (and environmental concerns) when compared to a basic research lab environment. Solvent use can be enormous as are disposal costs if you cannot reuse.

AvB

EvlRenne - 9-11-2018 at 03:23

Thanks to all of you guys, regarding the answers about my topic, I was searching information myself and found, that it could be dangerous when your exposed to it for a long time within huge concentration in the air or when you absorb it via skin / eyes it metabolize into CN and you start to suffer CN poisoning symptoms.

DavidJR - 9-11-2018 at 05:45

Quote: Originally posted by AvBaeyer  

I do not want to drag this out too far but I need to comment on the idea of recycling solvents in an industrial research lab environment. I gather from your comments, hopefully correctly, that you have no industry experience. First, many solvents are mixed as a result of running reactions and workup. These solvents may not be easily separable or chemically compatible for recycling. Second, having collection vessels spread throughout a lab space for each solvent type or class is just not practical.

You're correct that I have no industry experience. I get that sometimes solvents will be mixed in reactions etc, and if using smallish quantities of large numbers of different solvents it may be impractical to recycle in any way other than combining the lot and sending off for disposal, e.g. incineration for energy recovery.
Quote: Originally posted by AvBaeyer  

Most importantly, recycling solvents is not cost effective, at least it was not several years ago, especially if you want to recover highly pure lab useful solvents. Take, for example, HPLC effluent based on acetonitrile. This contains not only acetonitrile but also water, trifluoroacetic acid and/or various buffers some of which may be volatile. Recovering HPLC grade acetonitrile from this mix is not trivial nor cheap.

I'm sure you are aware that producing HPLC-grade solvents is non-trivial in the first place, even starting from virgin reagent grade material. I don't think it's necessarily particularly practical to recycle HPLC eluent waste into HPLC-grade solvents.

But that doesn't mean the waste is worthless. It's relatively easy to segregate solvent systems by switching out the waste container as appropriate. The contamination from buffers, additives, and the samples themselves, are going to be <1%. HPLC waste is probably one of the easiest sources of waste solvent to recycle into a useful product, because you started with very pure solvents and added only very small concentrations of contaminants. Fractional distillation would be necessary to remove most of the water, of course, which would probably go a fair way to removing buffer salts too. At that point you then have mostly pure methanol or acetonitrile (azeotrope w/ water unfortunately) which could well be used for many non-critical applications.

unionised - 9-11-2018 at 16:23

Concentrated sulphuric acid will catalyse the condensation of acetonitrile to cyclic trimers

This reaction can become violent.

It's not HCN I'd worry about.