I've conducted an extraction of ITCs from rocket using dichloromethane and have had to store samples in a freezer overnight. I'm hoping to detect sulforaphane and other ITCs but there is very little in the literature regarding compound stability. Does anyone have any experience with the stability of ITCs in DCM over short periods?
Dear Luke,
Generally, isothiocyanates undergo hydrolysis in aqueous media at different pHs. The presence of bacterial cells accelerates the degradation rate. Benzylic and allylic-type isothiocyanates are much more stable that the other derivatives.The t 1/2 for the degradation of isothiocyanates in PBS is about 4-5 hours.
Regarding the stability in DCM; if DCM is water free or moisture free, dried and stored with molecular sieves in dry conditions, it is expected that NO or negligible hydrolysis will occur since the presence of water is a necessity for such degradation. In addition, hydrolysis reactions are accelerated by increasing the temperature. Therefore, storage at -20 C will reduce the possibility of hydrolysis to occur in DCM (in case it has traces of water).
In summary, a storage in dry DCM at low temperatures (-20 C) for few days will be appropriate and the risk for hydrolysis to occur is minimal.
The following links describe stability of isothiocyanates in aqueous media:
http://rdo.psu.ac.th/sjstweb/journal/37-6/37-6-3.pdf
http://pubs.acs.org/doi/abs/10.1021/jf3041534
Hoping this will be helpful,
Rafik
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