Question

Explain how a microwave synthesis is different than a conventional synthesis. Give at least two reasons why a microwave synthesis requires less time than a conventional synthesis. Discuss why using a microwave synthesis is considered a greener alternative.  

In investigating [Co(salen)], (FW 325.12) as an oxygen carrier, 0.250 g was reacted with 5.00 mL DMSO in an oxygen rich environment, initially with 100.00 kPa O₂ pressure, flask volume of 136.7 mL, and 23.1^oC. The final oxygen pressure was determined to be 93.08 kPa. Calculate the moles of O₂ absorbed and the ratio of O₂ / [Co(salen)] (R = 0.08206 l•atm/mol•K; 1 atm = 101.325 kPa).

Answer 1

process time is limited by the rate of the heat flow into the body of the material from the surface as determined by its specific heat, thermal conductivity, density and viscosity. Surface heat is not only slow, but also non-uniform with the surfaces, edges and corners being much hotter than the inside of the material. Consequently, the quality of conventionally heated materials is variable and frequently inferior to the desired result.

Microwaves are not forms of heat, but rather forms of energy that are manifested as heat through their interaction with materials. Microwaves initially excite the outer layers of molecules. The inner part of the material is warmed as heat travels from the outer layers inward. Most of the moisture is vaporized before leaving the material.

Microwave energy does not heat the room — only the desired material — without harmful greenhouse gas emissions from the heat source. The energy is mainly absorbed by a wet material placed in the cavity. Water, fat and sugar molecules in food materials absorb energy from the microwave in a process called electromagnetism, a phenomena associated with electric and magnetic fields, and their interactions with each other, and with electric charges and currents.