From: antonio regla (areglac$##$yahoo.com)
Date: Mon May 29 2000 - 12:33:35 EDT
Dear List Members,
I would like to ask someone who has prepared thiosemicarbazones in small scale in lab about any possible toxicity. We prepared the thiosemicarbazone of benzaldehyde in a teaching lab, being careful not to spill it on the skin, and noone did. However, we had to warm up the reaction mixture to speed up dissolution of thiosemicarbazide. The solvent was ethanol and the catalyst was a couple of drops of sulfuric acid. There were no noticeable smells in the lab during the experiment. A few students complained of irritation in the face and throat, a minor one, but noticeable nonetheless. I am aware of the reported toxicity of the reagent, but had no idea how the contact with the skin was made. One of my students mentioned to me that she had noticed a bitter taste in her thumb after the experiment, after washing her hands. When I got home that evening I washed my hands well and tasted my thumb out of curiosity, and it was very bitter. I was really puzzled by this, as I didn't touch the reagent myself. I checked Aldr
ich's Safety book and found information about thiosemicarbazide in a very summarized manner. Apparently it is able to form sulfur and nitrogen oxides by decomposition, I suppose acid catalyzed. What I would like to ask anyone who has handled this reagent is what is the source of the bitter taste in the hands, is it sulfur dioxide? I washed my hands several times and the bitterness still remained. Even the next morning I noticed the bitterness in my thumb. I would appreciate any information anyone could give me regarding this reagent. I have the MSDS for this reagent, I would like to hear about someone who has used it and experienced "bitter thumbs". Next time we use this reagent we will certainly take precautions not to leave hands exposed. Thanks for your attention to this.
Sincerely,
A. Regla
School of Pharmacy
Universidad Autonoma de Morelos
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