Cannizzaro Reaction: Industrial Importance
The combination of crossed-Cannizaro reaction and aldol condensation is used in industry to prepare polyols. In this process, advantage is being taken of the fact that all α-hydrogen atoms of the aldehyde react with formaldehyde in an aldol condensation. In a subsequent crossed-Cannizaro reaction, the aldehyde group is then reduced to alcohol with excess formaldehyde .
For example, neopentylglycol (2,2-dimethyl-1,.3-propanediol) is synthesized from isobutyraldehyde (isobutanal) and formaldehyde. In the first step, the α-hydrogen atom is removed by base followed by aldol condensation with formaldehyde.
The reaction is carried out with an excess of formaldehyde. The crossed-Cannizaro reaction yields neopentylglycol which is being used in polyesters (for resins used in airplane or boat manufacturing), varnish coatings, synthetic lubricants, and plasticizers. The neopentyl structure provides excellent resistance to light, heat and hydrolysis.
The polyols pentaerythrit (2,2-bis(hydroxymethyl)-1,3-propanediol) and trimethylolpropane (2-ethyl-2-hydroxymethyl-1,3-propanediol) are prepared in similar fashion. Of the three polyols mentioned and synthesized using the above procedure, pentaerythrit is produced in largest quantities. Its main use is as raw material in the varnish industry. Its tetranitrate is an explosive. Some esters of pentaerythrit with higher fatty acids are being used as oil additives, plasticizers and emulsifiers. Because of its low-cost synthesis, trimethylolpropane has been used in many applications as a glycerin substitute, for example in alkyd resins. Similar to other polyols, it is being used for the preparation ofand