[barcrphd]

i was trying to N-alkylate nitroimidazole with 1,2-dibromo ethane in acetonitrile in presence of potassium carbonate base. 1,2-dibromoethane was taken in excess to avoid nitroimidazole reacting at both the ends of 1,2-dibromoethane. initially i did overnight reaction under reflux condition and i got a product in excellent yield. but to my surprise the NMR spectra suggested that the compound was not the one i wanted. solving the NMR spectra i found out that an alkene derivative of nitroimidazole has been formed.

i feel that initially 1,2-dibromoethane must have reacted with nitroimidazole and then it must have undergone dehydrobromination. but still i am surprised how a weak base could do this.

i repeated the reaction this time at room temperature. same result.

i again repeated the reaction using potassium bicarbontate. this time i got the product i wanted but the formation is very slow. after 48 hours i found that the alkene derivative is also getting formed.

has anybody come across such a problem? how could i avoid dehydrobromination? will the use of triethyl amine solve the problem?

any suggestions?

[AWK]

K2CO3 is a quite strong base contrary to KHCO3. Try to explain this.