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Betaine vs. Amphoteric
Posted: February 27, 2008
Industry expert Tony O'Lenick explains the difference between a betaine and an amphoteric...
Amphoteric surfactants are a class of compounds that have both a positive (+) and negative (-) charge in the same molecule. The amphoteric class of compounds has, within it, several additional types of compounds, depending on how the molecule’s charge changes as a function of pH. A betaine is simply one type of amphoteric.
One class of compounds within the amphoteric family is the betaine. Because of its structure, it can exist in only two ionic forms, zwitterionic and cationic. Betaines have the following structure:
The structure shown is a zwitterionic form, having both positive and negative charges present in the molecule. As the pH is lowered, the carboxyl group is protonated and a compound with a positive (+) charge develops. This structure is: