Microwave chemistry

The microwave chemistry is concerned with the use of microwaves in the chemical industry and in the laboratory for synthesis or analysis .

The main advantage of microwaves for heating is that the chemicals are heated directly and at all points at the same time - and not via the vessel walls and convection with the disadvantage of uneven heating with the formation of cold and overheated areas. This optimal energy input and energy absorption leads to shorter reaction times and reduced energy consumption. In addition, higher yields with fewer by-products are also possible, as well as high purity of the reaction products. Since the energy supply can be regulated and also stopped very quickly, there are also safety advantages.

Household microwave ovens designed for heating water can only be used for aqueous solutions or reactions with water due to the wavelength of the microwaves used. If devices with different wavelengths are required for heating other substances, these are much more demanding and require correspondingly high costs.

With microwave pressure digestion, a sample is heated evenly in a closed system, temperature and time can be varied. This information can be used to determine the total metal content in dust samples in occupational safety . For this purpose, a new microwave pressure digestion process was developed and validated at the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA): The metal-containing dusts to be examined are separated on filters, the metals contained are broken down and quantitatively analyzed. Low-metal nitric acid (65%) serves as a disintegrant. This digestion can be used as an alternative to open conventional digestion, but it is not suitable for all metals, such as antimony , tin and tungsten .

Web links

Investigation of chemical reactions with long reaction times in the microwave field ( Memento from July 15, 2006 in the Internet Archive ), Innovationsforum May 5, 2004 in Zittau

literature

Doris Dallinger: Some like it hot - microwaves in organic synthesis . In: Chemistry in Our Time . tape 47 , no. 6 , 2013, doi : 10.1002 / ciuz.201300610 ( PDF ).

Individual evidence

↑ Raymond J. Giguere, Terry L. Bray, Scott M. Duncan, George Majetich: Application of commercial microwave ovens to organic synthesis. In: Tetrahedron Letters. 27, 1986, pp. 4945-4948, doi: 10.1016 / S0040-4039 (00) 85103-5 .
↑ K. Pitzke, K. Gusbeth, D. Breuer, R. Hebisch, M. Kirchner, C. Schuh, T. Schwank, R. Sonnenburg, K. Timm: Project study: Comparison of digestion methods for determining the total metal content in dust samples - Part 2: Round-robin test Part 1, DFG working group “Air Analysis”. In: Hazardous substances - keeping the air clean, 78 (2018) No. 4 - April. Retrieved October 22, 2018 .

[1] Raymond J. Giguere, Terry L. Bray, Scott M. Duncan, George Majetich: Application of commercial microwave ovens to organic synthesis. In: Tetrahedron Letters. 27, 1986, pp. 4945-4948, doi: 10.1016 / S0040-4039 (00) 85103-5 .

[2] K. Pitzke, K. Gusbeth, D. Breuer, R. Hebisch, M. Kirchner, C. Schuh, T. Schwank, R. Sonnenburg, K. Timm: Project study: Comparison of digestion methods for determining the total metal content in dust samples - Part 2: Round-robin test Part 1, DFG working group “Air Analysis”. In: Hazardous substances - keeping the air clean, 78 (2018) No. 4 - April. Retrieved October 22, 2018 .