Thank you to everyone for your responses.

As it turns out, the colleague that tested this lab before incorporating it into the curriculum only had 4 students in a lab designed for 24 that is double wide as it has a front section for lectures.  This did not transfer well to the true experience of our labs of 20 in a room less than half the size.  Following the instructions in the book had them using a TON of sulfuric acid AND phosphoric acid causing immediate reaction even before heating.  I believe that a significant amount of the sulfuric acid had reacted with the alcohol right away as my students were concerned that their reactions turned brown immediately, then eventually became black.  This would have given off sulfur dioxide.  The sulfur dioxide would have been escaping through the vent on the vacuum adapter placed before the receiving flask.  It must have been in quantities too high for my hoods to handle (also keep in mind how dense the gas is) and escaped into the room.  I suffered a massive asthma attack that caused me to vomit.  All hoods being turned to emergency exhaust could not clear the room fast enough.

The next class to do the lab was half an hour later and thanks to your responses I had them eliminate the sulfuric acid from the reaction and things went much smoother.  I will be writing the authors about my experience and concern over their procedure.  It seems that most people have been using exchange resins in place of either of the acids recommended by the authors.

 

 

We don't do this particular one. Instead, we dehydrate a pentanol (I think it's 4-methyl-2-pentanol?) using sulfuric and (I think?) glacial acetic acid. No phosphoric acid whatsoever. We also do this on a microscale level. I'm pretty sure we do this in a conical vial with a condenser on the top. The students analyze the products by GC, which we autosample.

Does it stink? Oh yes. Those pentenes are truly offensive. We minimize this by having them perform the workup in a test tube that is immersed in an ice bath, and they immediately rinse all glassware that came into contact with them with acetone into the waste bottle. At the most, you get a quick whiff of it and then it's gone.

 

 

 

Hi Monique - I can't help answer your question, but we do do this experiment.  Lots of waste as well.  We disperse chemicals in a reagent hood and all our students work in hoods, so I guess we are fortunate in that way.

Looking forward to the answers.
Sammye

Hi everyone,

I am reaching out to see if anyone has experience with the dehydration of 4-methylcyclohexanol to 4-methylcyclohexene lab in the Pavia et al lab textbook. The reaction seems to call for an awful lot of H2SO4 in addition to H3PO4 and is giving off several noxious odors.  I would like to recommend getting rid of the H2SO4 but am concerned about whether this may cause unwanted organophosphates to be produced.  I am concerned as I cannot figure out what kind of byproduct or decomp products we may be getting.  

Does anyone have any thoughts on this?  I am not an organic chemist, so maybe I am just overthinking this one too much.

Monique

_________________________________________________________

Monique Wilhelm, M.S., NRCC Certified CHO

ACS CHAS Secretary|2017 CERM E. Ann Nalley Award Recipient

Laboratory Manager|Adjunct Lecturer|Chemistry Club Advisor

Department of Chemistry & Biochemistry|University of Michigan-Flint