Cleavable surfactants

The review covers the development within the field of cleavable surfactants since 2003. Cleavable surfactants are amphiphiles in which a weak linkage has been deliberately inserted, normally, but not always, between the hydrophobic tail and the polar headgroup. Alkali labile linkages that have been used for the purpose include normal ester bonds, betaine esters, and carbonates. Ketals and ortho esters are example of bonds that are susceptible to acid hydrolysis. Several investigations deal with cationic ester-containing surfactants, both monomeric and dimeric species, the latter being gemini surfactants. Ester, amide and carbonate containing surfactants have been investigated with respect to enzyme catalyzed hydrolysis. The main incentive for the development of novel cleavable surfactants is to improve the biodegradation characteristics and the rate of biodegradation has consequently been studied for several of the surfactants. One interesting observation is that there is often very little correlation between rate of chemical and enzymatic hydrolysis on the one hand and rate of biodegradation on the other hand. A completely new type of cleavable surfactant is based on a Diels-Alder reaction between a maleimide derivative and a substituted furan. The product formed undergoes a retro-Diels-Alder reaction at a temperature of around 60 degrees C. This is an example of a thermally cleavable surfactant. (c) 2007 Elsevier Ltd. All rights reserved.