Study On Microwave-assisted One-pot Synthesis Of Dibenzo-diazepines And The Microwave "Nonthermal Effects"

As the microwave is used for heating in the organic chemistry more and morewidely, microwave-assisted-organic synthesis has become a focus of research anddebate. Compare with common heating （CH）, microwave irradiation （MW） can not onlyimprove speed of reactions, but also increase reactions yield, even make them have adifferent chemo selectivity. These phenomena, which can’t be explained byconventional theories of heat conduction, were named microwave "nonthermal effects"or "specific effects" by researchers. But debates about whether these effects exist or notcontinued until now. Dibenzo-diazepines is an important type of heterocycliccompounds. They have special structure and electronic states of seven-memberedheterocyclic ring, physiological activities of mitigation, antianxiety, antidepressant andso on, and few side effects. So, research about methods of their synthesis is becominghotter and hotter. In this paper, Dibenzo-diazepines were synthesized by one-potreactions of2-chlorobenzoic acids and o-phenylenediamine. Effects of microwave onreactions can be researched through the comparison of reactions results of CH and MW.And then, different powders of media were added to the reactions mixture to find outevidence of the existent of microwave "nonthermal effects".This paper is mainly consisting of two parts.In the first part, Dibenzo-diazepines were synthesized under microwaveirradiation by one-pot reactions of2-chlorobenzoic acids and o-phenylenediamine.Compare MW reactions results with the CH ones, microwave irradiation can not onlyshorten the reaction time, but also improve the yield of2-chlorobenzoic acid’s and2-chloronicotinic acid’s reactions. This illustrated there are obvious microwave"nonthermal effects" in these MW reactions. But, as molecular sieve was added, yieldof2-chlorobenzoic acid’s MW reaction was reduced. Initially, reason of this reductionwas attributed to the molecular sieve’s absorption of microwave irradiation.In the second part, media powders including SiC, molecular sieve, porcelain,Al₂O₃and glass were respectively added to the2-chlorobenzoic acid’s reaction mixtures.Yield of all these reactions declined in different degree. From these reaction results, itcan be inferred that some "inhibitory effects" were the main reason of the reduction ofthese MW reactions. Because these "inhibitory effects" were aroused only whenpowders were irradiated under microwave, they can be another type of microwave "nonthermal effects". Further research showed these "inhibitory effects" will enhance,as size of powders got smaller. And MW reactions were "accelerated" to reach theterminal or equilibrium point earlier when their yield was still low. This is themechanism how the "inhibitory effects" make the yield of MW reactions decline. In theresearch of2-chloronicotinic acid’s reactions, similar results were obtained.