Synthesis And Properties Of Acetamidinium Bicarbonate Switchable Surfactants

Surfactants are extensively employed in many industrial processes.Commonly for these applications,surfactants are useful during certain stages and then hinder the separation of components later in the process cycle.The development of surfactants that are more easily recovered and reused can help alleviate the environmental stresses created by their use.Switching surfactant is a surfactant with a"switch"that controls the surfactant's surface activity"on"and"off"to convert between active and inactive when the systems need their surface ativity or switch them“off”when the systems don't need their surface activity,so they can solve the problems caused during the use of traditional surfactants.Amidine switchable surfactants use CO₂/N₂ as the trigger and they have mild reaction conditions and good biocompatibility.In this dissertation,a series of acetamidinium bicarbonate surfactants were synthesized,using octylamine,decylamine and dodecylamine as raw materials.Amidines with long alkyl chain were formed firstly by alkylamino-de-oxo-bisubstituton,then amidines reacted with CO₂ to produce acetamidinium bicarbonate surfactants.A series of switchable surfactants with double hydrophobic chains and a single hydrophilic head N,N'-dialkylacetamidinium bicarbonate with an alkyl length between diC8 and diC12 were synthesized,including N,N'-dioctylacetamidinium bicarbonate,N,N'-didecylacetamidinium bicarbonate and N,N'-didodecylacetamidinium bicarbonate.The corresponding surfactant with one hydrophobic chain were also synthesized,including N'-octyl-N,N-dimethylacetamidinium bicarbonate,N'-decyl-N,N-dimethylacetamidinium bicarbonate and N'-dodecyl-N,N–dimethylacet-amidinium bicarbonate.The structures of acetamidinium bicarbonate were characterized by¹H NMR and ESI-MS spectroscopy and the results showed that the synthesized products were all target products.Besides,in the synthetic process of N,N'-didodecylacetamidine,the reaction conditions were optimized by changing the reaction time,temperature,feed molar ratio,and solvent.The better reaction conditions were confirmed:the reaction solvent was methanol,catalyst was tetrahydropyrrole,temperature was 80?,the time 4 h and n?amine?:n?1,1-Dimethoxy-N,N-dimethylethylamine?2.2:1.In the same way,in the synthetic process of N'-dodecyl-N,N-dimethylacetamidine,the better reaction conditions were confirmed by the method of single factor experiments:the reaction solvent was tetrahydrofuran,the temperature was 60?,the time 2 h and n?1,1-Dimethoxy-N,N-dimethylethylamine?:n?amine?1.2:1.The surface activity in aqueous solution of N,N'-dialkylacetamidinium bicarbonate and N'-alkyl-N,N-dimethylacetamidinium were investigated by surface tension methods and the switchability,foam activity and emulsification were tested and studied.The results indicated that the values of cmc,?_cmcmc and A_minin were decreased and cmc/C₂₀0 and?_maxax were increased with increasing hydrophobic chain length,because the overall hydrophobic interaction is strengthened with the increasing hydrophobic chain length.Taking N,N'-dialkyl-acetamidinium bicarbonate as an example,the switchability and repeatability of acetamidinium bicarbonate surfactants were confirmed well.The values of cmc and?_cmcmc of double-chain surfactant were smaller than corresponding single-chain surfactant with the same length hydrophobic chain and double-chain surfactants showed stronger surface activity than single-chain surfactant.In this paper,a series of acetamidinium bicarbonate surfactants with long-chain alkyl groups were synthesized and they have good switchability and repeatability.They have potential application value.