an example of this. Alternatively, higher yields of one product (usually the alcohol) can be achieved in the crossed Cannizzaro reaction, in which a sacrificial aldehyde is used in combination with a more valuable chemical. In this variation, the reductant is formaldehyde, which is oxidized to sodium formate and the other aldehyde chemical is reduced to the alcohol. Thus, the yield of the valuable chemical is high, although the atom economy can be low. The final stage in the synthesis of pentaerythritol is an example. A solvent-free reaction has been reported involving grinding liquid 2-chlorobenzaldehyde with potassium hydroxide in a mortar and pestle: Variations In the Tishchenko reaction, the base used is an alkoxide rather than hydroxide, and the product is an ester rather than the separate alcohol and carboxylate groups. After the nucleophilic base attacks an aldehyde, the resulting new oxygen anion attacks another aldehyde to give a hemiacetal linkage between two of the formerly aldehyde-containing reactants rather than undergoing tetrahedral collapse. Eventually tetrahedral collapse does occur, giving the stable ester product. Certain ketones can undergo a Cannizzaro-type reaction, transferring one of their two carbon groups rather than the hydride that would be present on an aldehyde. See also Meerwein–Ponndorf–Verley reduction Oppenauer oxidation References Organic redox reactions Name reactions