Alkyl ketene dimer

Alkyl ketene dimers (AKDs) are a family of organic compounds that are used in papermaking. In terms of their chemical structure, they are derivatives of diketene.

AKD's feature hydrophobic alkyl groups extending from a propiolactone ring. A specific example is derived from the dimerizaation of the ketene of stearic acid. This ketene is generated by pyrolysis of stearoyl chloride. AKD's react with the hydroxyl groups on the celluose via esterification reaction. The esterification is competitive with hydrolysis of the AKD. Prior to the development of AKD's, hydrophobicity was imparted by incorporating rosin into the paper.

Related to AKDs, is alkenylsuccinic anhydride (ASA). As for AKDs, ASA reacts with hydroxy groups of the cellulose to form an ester, anchoring the hydrophobic group to the surface. ASA is prepared by the ene reaction of unsaturated hydrocarbons with maleic anhydride.

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