Chemical structure/property relationships in surfactants. 17. N‐substituted‐N‐acyl glycinates in pure and synthetic hard river water

Abstract

AbstractThe surface properties [effectiveness of surface tension reduction (γCMC), critical micelle concentration (CMC), efficiency of surface tension reduction (pC20), maximum surface excess concentration (ΓCMC), minimum area/molecule at the interface (Amin), and the CMC/C20) ratio] of well‐purified N‐substituted glycine derivatives, having the structural formula RC(O)N(R′)CH2COONa, where RC(O)=lauroyl, myristoyl, or oleoyl, and R′=Et, Pr, Bu, CH2CH2OH or CH2CH2CH2OCH3, were investigated at 25°C in hard river water and distilled water. These surfactants show greater surface activity in hard river water than in distilled water. The effect of both the main alkyl chain R and the N‐substituent R′ on surface properties was elucidated, the oleoyl group showing properties equivalent to that of a C16 saturated acyl group. A linear relationship was observed between the pC20 or CMC values and the number of carbon atoms in the alkyl chain R or in R′ when it was alkyl. With increase in the number of carbon atoms in either R or the N‐substituent R′ when it is alkyl, both pC20 and micelle‐forming ability increase, although the effect of R′ on the foregoing two surface properties is lower than that of R. When R′ is (CH2)3OCH3, however, the results suggest that R′ is only partly removed from contact with the aqueous phase either upon adsorption at the water/air interface or upon micellization. It increases Amin, is equivalent only to an ethyl group in its effect on pC20 and to a methyl group in its effect on CMC, and, in contrast to the effect of R′ when it is alkyl, produces no increase in the CMC/C20 ratio. As a result, γCMC increases with R when R′ is alkyl and decreases with R when R′ is (CH2)3OCH3.