For the first time since 1986, chemical synthesis reactions have been carried out in simple domestic microwave ovens. Since then, microwave chemical organic synthesis (MAOS) has become popular in the development of modern chemical synthesis.
Microwave applications: Microwaves for organic synthesis including esterification, Diels-Alder, rearrangement, Knoevenagel, Perkin, Witting, Reformatsky, Dveckman, Carboxaldehyde condensation, ring opening, alkylation, hydrolysis, olefin addition, elimination synthesis, Substitution, free radical, stereoselective, ring formation, ring conversion, transesterification, ester amination, catalytic hydrogenation, decarboxylation, and synthesis of sugars, organometallic compounds, radiopharmaceuticals, and the like.
In the early days, we used organic microwave ovens for organic chemistry experiments. Although there are still microwave advantages, the benefits of microwaves are not visible in some specific reactions. Therefore, the microwave oven can increase the reaction rate, reduce side reactions, increase productivity, improve efficiency, and the like, and cannot satisfy all organic chemical reactions.
The disadvantages are as follows:
1. Microwave chemical organic synthesis reaction in a closed system can make the reaction system instantaneously obtain high temperature and high pressure, the reaction speed is accelerated, and the reactor is easily deformed or even exploded. High pressure condition
2. The temperature reflected by the reaction cannot be measured;
3. The drying reaction is carried out on a carrier. Therefore, the amount of reactants participating in the reaction is limited. At the same time, there are certain difficulties in the selection of solid supports, which limits the application range of microwave drying organic synthesis;
4. The power density is relatively low. For some experiments, the high field strength requirement cannot be realized in the household microwave oven, and the microwave oven cannot measure the temperature of the reaction system, and the specific state of the reaction cannot be known.
5. Microwave heating of household microwave ovens is mainly concentrated on the tray at the bottom of the furnace chamber. Most organic synthesis requires stirring, reflux and dropping system, and reaction center. Usually in the middle of the furnace, the heating of the material is not uniform, resulting in more side reactions;
6. Household microwave ovens are intermittently heated, and the effective power of microwave ovens is greatly affected by grid voltage fluctuations.