ZWITTERIONIC (AMMONIOMETHYL)TETRAFLUOROSILICATES OF THE FORMULA TYPESF4SICH2NH2(CH2)(N)ME (N = 5-11) AND F4SICH2NME2(CH2)(5)ME - A NEW CLASS OF HIGHLY EFFICIENT SURFACE-ACTIVE COMPOUNDS

The zwitterionic (ammoniomethyl)tetrafluorosilicates F4SiCH2NH2(CH2)(n )Me (n = 5-11; compounds 4-10) were synthesized by reaction of the cor responding (aminomethyl)-triethoxysilanes (EtO)(3)SiCH2NH(CH2)(n)Me (n = 5-11; compounds 13-19) with HF. The silanes 13-19 were obtained by reaction of (EtO)(3)SiCH2Cl with the corresponding n-alkylamines H2N(C H2)(n)Me (n = 5-11). The zwitterionic (ammoniomethyl)tetrafluorosilica te F4SiCH2NMe2(CH2)(5)Me (11), the N,N-dimethyl derivative of 4, was s ynthesized by reaction of (MeO)(3)SiCH2NMe2 with n-C6H13Br, followed b y reaction of the resulting quaternary ammonium salt [(MeO)(3)SiCH2NMe 2(CH2)(5)Me]Br with HF. Compounds 4-11 are characterized by the presen ce of a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom. F4SiCH 2NH2(CH2)(9)Me (8) was structurally characterized by single-crystal X- ray diffraction. The coordination polyhedron around the silicon atom o f 8 in the crystal is a slightly distorted trigonal bipyramid, with fl uorine atoms in the axial positions (Berry distortion 8%). Intermolecu lar N-H ... F hydrogen bonds influence the packing of the zwitterions in the crystal. Surface tension measurements with solutions of 4-11 in 0.01 M hydrochloric acid demonstrated that these compounds are highly efficient surfactants, Increase of the n-alkyl chain length (4 --> 10 ) was found to result in an increase of surface activity. The equilibr ium surface tension vs concentration isotherms for 4 and 11 (solutions of ''surface-chemically pure'' samples in 0.01 M hydrochloric acid) w ere analyzed quantitatively and the surface thermodynamics of these su rfactants interpreted an the molecular level. Preliminary studies demo nstrated that aqueous solutions of 4-11 led to a hydrophobizing of gla ss surfaces.