Lv Jinge,Lu Chunbin,Yuan Cuili,Han Jianwei,Wang Limin

Shanghai Key Laboratory of Functional Materials Chemistry and Institute of Fine Chemicals,School of Chemistry and Molecular Engineering,East China University of Science and Technology,China

Abstract

A series of novel branched sodium carboxylate surfactants were synthesized from cyanuric chloride,behera amine,alcohol amine and 1,4-Bis (3-aminopropyl) piperazine through seven steps,and the total yield is about 25%.The chemical structures of target products were confirmed by 1H NMR,13C NMR,FT-IR and ESI-MS.Their critical micelle concentrations (CMC) were also determined by surface tension tests in the aqueous solutions at 22 ℃.The results showed that the CMC value of multi-carboxylate anionic surfactants decreased with the increase of hydroxyl.Additionally,the branched structure of end group can reduce surface tension more than straight-chain type,which was determined by γCMC.The decomposition temperature of the target compound was 250 ℃,which was also tested by TG/DTA curve.

Key words

cyanuric chloride;surfactant;branched compounds;surface tension

Introduction

Cyanuric chloride is an organic molecular with special chemical properties.Three chlorines in the s-triazine can be replaced efficiently by amine,hydroxyl or hydrosulfuryl group.[1]Cyanuric chloride can be substituted with the control of reaction temperature.It is obvious that cyanuric chloride can be easily single substituted at 0-5 ℃,the second one at 30-50 ℃,and further substitution reaction can be held above 80 ℃.[2]Besides,cyanuric chloride has different reaction activity with different amine and this character can be used in selective synthesis of cores,inner and outer groups of branched compounds.[3-4]

Cyanuric chloride derivatives are widely used in the field of dyes,catalysts and pharmaceuticals,especially the synthesis of branched compounds.[4-6]Dilly et al.have synthesized a series of triazine branched compounds by grafting cyanuric chloride to the different materials,like resin and silica gel.[7]Cyanuric chloride was also used in the synthesis of small molecule surfactants.Wang et al.have synthesized a series of symmetric surfactants based on cyanuric chlorides,which showed excellent surface activity with low CMC (5.3×10-6mol/L).[8]Qiao et al.have also synthesized a series of both single and double long-chain 1,3,5-triazine amphoteric surfactants.[9]Double long-chain sodium carboxylate compounds exhibit lower CMC than single long-chain surfactants.

Branched compounds have some advantages such as stable structure and low viscosity.The end group of it can be extended by the introduction of reactive or functional groups.Thus,the branched surfactants has been applied to coatings,water treatment and other related fields.[10-11]Grinstaff et al.have synthesized dendrimer molecular with controlled ratio of hydrophilic-hydrophobic group by the number of carboxyl and alkyl chains on the molecular surface.[12]Champan et al.have also reported branched compounds with good surface activity and foaming property.[13]However,it is uncommon that cyanuric chloride was used in the synthesis of branched surfactants.

In this paper,we synthesized a series of branched sodium carboxylate surfactants by cyanuric chloride,alcohol amine and behera amine,and studied the physicochemical properties of prepared compounds such as thermal stability,CMC and γCMC.

Experiment

Materials and methods

Nitromethane,diethylamine,ethanolamine and 2,2’-iminodiethanol were purchased from YONGHUA Chemical Technology Co.,Ltd.Tert-butyl acrylate,triton-B (40% in methanol) and cyanuric chloride were purchased from Energy Chemical.Potassium carbonate,Ni-Al alloy and sodium methanolate were purchased from Sinopharm Chemical Reagent Co.,Ltd.1,4-Bis (3-aminopropyl) piperazine was purchased from TCI Co.,Ltd.The solvents were purified according to the Purification of Laboratory Chemicals book.Melting points were determined by the open capillary method.The infrared spectra were recorded using KBr on FT-IR spectrophotometer and the results are expressed in wave number (cm-1).1H NMR and13C NMR spectra were recorded at 400 MHz and 100 MHz,respectively using tetramethylsilane as an internal reference.High Resolution Mass spectra (HRMS) were performed on an ESI-TOF spectrometer.

Synthesis of dendrimer compounds

Synthsis of compound 1

Triton B (1.0 mL) was dropped into nitromethane (6.1 g,0.10 mol) in 1,4-dioxane (20 mL) while the temperature was maintained at 70-75 ℃.Tert-butyl acrylate (38.5 g,0.30 mol) was dropped into the solution.Another Triton B (2.0 mL) was dropped while the temperature declined.After that,tert-butyl acrylate was continually added into the solution.Then the solution was heated to 80 ℃ for 3 h.

The solution was concentrated under vacuum to obtain a yellow solid.The solid was dissolved in ethyl acetate,and then washed with 10%HCl and saturated NaCl,and dried over anhydrous Na2SO4.The organic solution was concentrated under vacuum and purified by recrystallization in ethanol to obtain the white solid.The yield of compound 1 was 85%.Melt point (M.p.): 98-100 ℃.1H NMR (CDCl3,400 MHz): δ 2.20 (s,12 H),1.44 (s,27 H).13C NMR (CDCl3,100 MHz): δ 171.09,92.19,81.17,30.34,29.80,28.03.

Synthesis of behera amine (compound 2)

Compound 10 (22.3 g,0.05 mol),Raney Ni (10 g) and ethanol (300 mL) was added into a 500 mL round bottom flask.Hydrogen was filled after taking out the air.The mixture was then heated to 60 ℃ for 2 days.The filtrate was evaporated under vacuum.The behera amine was isolated by silica gel column chromatography,affording the product as a white solid.The yield of behera amine was 80%.M.p.: 50-52 ℃.1H NMR (CDCl3,400 MHz): δ 1.78 (s,12 H),1.44 (s,27 H).13C NMR (CDCl3,100 MHz): δ 171.35,80.17,51.07,30.05,29.66,28.05.

Scheme 1.The synthesis of dendrimer compounds

Synthesis of cyanuric chloride (TCT) mono substituted compounds (3)

Cyanuric chloride (3.68 g,0.02 mol) and potassium carbonate (2.07 g,0.015 mol) with acetonitrile (20 mL) was added into round bottom flask.The acetonitrile of compound 2 (4.17 g,0.01 mol) was added drop wise into the solution.The reaction was protected with N2and cooled to 0 ℃ for 3 h.The filtrate was evaporated under vacuum.The white solid was obtained by silica gel column chromatography.The yield of 3 was 80%.M.p.: 128-130 ℃.1H NMR (CDCl3,400 MHz): δ 6.24 (s,1 H),2.24-2.16 (m,6 H),2.11-2.05 (m,6 H),1.44 (s,27 H).13C NMR (CDCl3,100 MHz): δ 172.21,170.42,169.72,165.06,81.07,59.22,29.66,29.62,28.05.HRMS (ESI): m/z [M+H]+calculated for C25H40N4O6Cl2: 563.2403;Found: 563.2410.

Synthesis of 2,4-disubstituted cyanuric chloride (TCT) compounds (4)

Compound 3 (5.65 g,0.01 mol) was dissolved in acetonitrile (20 mL),followed by addition of diethyl amine (0.73 g,0.01 mol) and N,NDiisopropylethylamine (DIPEA,1.90 g,0.015 mol).The mixture was heated to 40 ℃ for 3 h.The solution was evaporated under vacuum,followed by the addition of ethyl acetate (100 mL).The filtrate was evaporated under vacuum.The product was then isolated by silica gel column chromatography.The yield of 4a,4b,4c were 88%,85%,90%,respectively.

4a: white solid.M.p.: 135-137 ℃.1H NMR (CDCl3,400 MHz): δ 4.97 (s,1 H),3.58-3.49 (m,4 H),2.24-2.18 (m,6 H),2.05-2.00 (m,6 H),1.42 (s,27 H),1.20-1.13 (m,6 H).13C NMR (CDCl3,100 MHz): δ 172.35,168.63,164.24,163.90,80.58,57.32,42.07,41.84,29.90,29.61,28.05,13.22,12.91.HRMS (ESI): m/z [M+H]+calculated for C29H50N5O6Cl: 600.3528;Found: 600.3550.

4b: white solid.M.p.: 130-131 ℃.1H NMR (CDCl3,400 MHz): δ 3.76 (d,J=10.6,2 H),3.60 (d,J=2.8Hz,2 H),2.24-2.18 (m,6 H),2.05-2.00 (m,6 H),1.43 (s,27 H).13C NMR (CDCl3,100 MHz): δ 172.57,168.27,165.85,164.69,80.93,60.94,57.85,43.36,29.98,29.59,28.05.HRMS (ESI): m/z [M+H]+calculated for C27H46N5O7Cl: 588.3164;Found: 588.3164.

4c: white solid.M.p.: 132-135℃.1H NMR (CDCl3,400 MHz): δ 5.18 (s,1 H),3.94-3.75 (m,8 H),2.23-2.19 (m,6 H),2.05-2.01 (m,6 H),1.43 (s,27 H).13C NMR (CDCl3,100 MHz): δ 172.63,168.37,165.42,164.17,81.04,61.89,59.73,57.62,51.91,51.75,29.91,29.55,28.05.HRMS (ESI): m/z [M+H]+calculated for C29H50N5O8Cl: 632.3426;Found: 632.3434.

Synthesis of TCT gemini compounds (5)

Compound 4a (6.00g,0.01 mol) and potassium carbonate (2.07 g,0.015 mol) was dissolved in 1,4-dioxane (20 mL),1,4-bis(3-aminopropyl)piperazine (1.00 g,0.005 mol) was added drop wise,followed by N2protection.The mixture was then heated to reflux for 48 h.The product 5a was isolated by silica gel column chromatography.The yield of 5a,5b and 5c were 58%,60%,60%,respectively.

5a: yellow oil.1H NMR (CDCl3,400 MHz): δ .51 (s,8 H),3.40 (s,4 H),2.77-2.37 (m,12 H),2.23-2.19 (m,12 H),2.05-2.00 (m,12 H),1.77 (t,J=6.4 Hz,4 H),1.42 (s,54 H),1.13 (t,J= 6.4 Hz,12 H).13C NMR (CDCl3,100 MHz): δ 172.86,168.53,164.29,163.79,80.53,57.91,56.97,49.96,42.07,41.84,40.17,29.90,29.61,28.05,27.55,13.22,12.91.HRMS (ESI): m/z [M+H]+calculated for C68H122N14O12: 1327.9445;Found: 1327.9443.

5b: yellow solid.1H NMR (CDCl3,400 MHz): δ 4.86 (s,2 H),3.66 (s,4 H),3.50-3.23 (m,8 H),2.89-2.42 (m,12 H),2.15-2.11 (m,12 H),2.04-1.95 (m,12 H),1.78 (s,4 H),1.36 (s,54 H).13C NMR (CDCl3,100 MHz): δ 172.83,168.49,165.81,164.49,81.03,60.94,58.12,50.91,43.36,40.17,29.98,29.55,28.07,27.59.HRMS (ESI): m/z [M+H]+calculated for C64H114N14O14: 1303.8717;Found: 1303.8714.

5c: yellow solid.1H NMR (CDCl3,400 MHz): δ 3.78-3.65 (m,16 H),3.41 (s,4 H),2.96-2.53 (m,12 H),2.21 (s,12 H),2.03 (d,J=3.8 Hz,12 H),1.85 (s,4 H),1.43 (s,54 H).13C NMR (CDCl3,100 MHz): δ 172.89,168.67,165.52,164.27,81.04,61.83,59.77,58.06,57.52,52.05,51.75,50.03,40.21,29.93,29.57,28.05,27.63.HRMS (ESI): m/z [M+H]+calculated for C68H122N14O16: 1391.9241;Found: 1391.9248.

Synthesis of carboxylic acid compounds (6)

Compound 5 was added into the anhydrous formic acid (20 mL).The mixture was stirred at room temperature for 24 h.The solvent was evaporated under vacuum.The yellow oil was obtained after dried.The yield of 6a,6b and 6c were 85%,88%,90%,respectively.

6a: yellow oil.IR (KBr): νmax3280,2973,2875,1719,1622,1545,1445,1357,1210,1089,1046,785 cm-1.1H NMR (D2O,400 MHz): δ 3.46-3.21 (m,12 H),3.03 -2.19 (m,12 H),2.05-2.01 (m,12 H),1.93-1.90 (m,12 H),1.70 (s,4 H),0.98 (t,J=6.8 Hz,12 H).HRMS (ESI): m/z [M+H]+calculated for C44H74N14O12: 991.5689;Found: 991.5696.

6b: yellow oil.IR (KBr): νmax3388,2971,1718,1630,1574,1450,1345,1184,1093,1049,785 cm-1.1H NMR (D2O,400 MHz): δ 3.56 (t,J=6.4 Hz,4 H),3.35-3.20 (m,8 H),3.08 -2.15 (m,12 H),2.06-2.02 (m,12 H),1.98-1.91 (m,12 H),1.73 (s,4 H).HRMS (ESI): m/z [M+H]+calculated for C40H66N14O14: 967.4961;Found: 967.4961.

6c: yellow oil.IR (KBr): νmax3296,2951,1721,1651,1572,1531,1355,1169,1093,1046,785 cm-1.1H NMR (DMSO-d6,400 MHz): δ 3.78-3.69 (m,16 H),3.45-3.25 (m,4 H),2.63-2.51 (m,12 H),2.30-2.13 (m,12 H),2.10-1.91 (m,12 H),1.75 (s,4 H).HRMS (ESI): m/z [M+H]+calculated for C44H74N14O16: 1055.5485;Found: 1055.5490.

Synthesis of carboxylic acid compounds (7)

Compound 6a (0.49 g,0.5 mmol) and sodium methanolate (0.16 g,3.0 mmol) was added into the methanol (20 mL).The mixture was stirred at room temperature for 24 h.The solvent was evaporated under vacuum.The yellow solid 7a was obtained after dried.The yield of 6a,6b,6c were 86%,89%,89%,respectively.

7a: yellow oil.IR (KBr): νmax3426,2931,2830,2361,1593,1510,1406,1361,1096,774 cm-1.HRMS (ESI): m/z [M+Na]+calculated for C44H68N14O12Na6: 1145.4425;Found: 1145.4434.

7b: yellow oil.IR (KBr): νmax3312,2956,2831,1628,1591,1399,1360,811,773 cm-1.HRMS (ESI): m/z [M+Na]+calculated for C40H62N14O14Na6: 1121.3697;Found:1121.3694.

7c: yellow oil.IR (KBr): νmax3418,2930,1596,1509,1400,1360,1048,771 cm-1.HRMS (ESI): m/z [M+Na]+calculated for C44H68N14O16Na6: 1209.4222;Found: 1209.4218.

Results and discussion

Synthesis and characterization of dendrimer surfactant

The branched compounds were synthesized through seven steps.First is the synthesis of Behera amine (2),and then used the different reaction activity of three chlorine atoms in cyanuric chloride to obtain the tertiary butyrate compounds 5.After hydrolysis and salt forming reaction,symmetric branched surfactants were obtained.1H NMR,13C NMR,HRMS and FT-IR were used to determine the structure of all products.Because of the large amount of nitrogen atoms in the molecular structure,it's not easy to observe the cracking of nuclear magnetic resonance (NMR) spectrum.Especially,the target molecules were sodium carboxylates with surface activity,and these compounds had poor solubility in organic solvents and could form micelle in water easily.So NMR was not suitable to characterize the compounds.Therefore,fourier-transform infrared spectroscopy (FT-IR) and high resolution mass spectrometry (HRMS) were used to determine the structure of final products as main basis.Figure 1 showed the FT-IR spectrum of compound 6a and 7a.We can conclude that the disappearance of characteristic peak of carboxylic acid (νC=O= 1719 cm-1) and appearance of characteristic peaks of carboxylate (νas(CO2-) = 1593 cm-1,νs(CO2-) = 1406 cm-1).This obvious change of FTIR spectrum proved the formation of sodium carboxylate.

Figure 1.FT-IR spectrum of compound 6a and 7a

Thermal stability test

Thermal stability of branched compounds was tested using thermogravimetry / differential thermal analysis (TG/DTA).The test was carried out under a dry nitrogen atmosphere,and the gas flow rate was 100 mL/min.The temperature was heated from 40 ℃ to 1000 ℃ at the rate of 10 ℃/min.

Figure 2 shows the thermal stability of branched surfactant.It can be observed that the initial decomposition temperature of branched surfactant 7a was about 250 ℃,and stopped at about 450 ℃.The weight loss at this temperature is mainly due to the decomposition of nitrogen heterocyclic ring.The high decomposition temperature indicated the good thermal stability of synthesized compounds.

Figure 2.The TG and DTA curve of 7a

Surface tension and critical micelle concentration (CMC)

The surface tension of aqueous solutions of TCTbranched surfactants (7a,7b and 7c) was measured with JK99B automatic tension meter by using the Wilhelmy plate method.The experiment was carried on at 22±0.1 ℃,and the surface tension of deionized water was 73 mN/m.

The concentration of tested compounds was prepared at 0.02 mol/L,0.01 mol/L and 0.003 mol/L,respectively.The solution was added into deionized water step by step to change the testing concentration.The surface tensions (γ) are a plotted function of the surfactant concentration (C) (Figure 3).It showed that the surface tension of compound 7a was declined with the increase of compound concentration in overall trend.A similar trend was also found in compound 7b and 7c (Figure 3).The value of CMC was determined from the break point of γ- lgC curve.The CMC values of three compounds (7a,7b and 7c) were 4.44×10-3,1.48×10-3,0.41×10-3mol/L,respectively.The surface tension at CMC (γCMC) of 7a,7b and 7c was 51,30,49 mN/m,respectively.

It is obvious that the addition of TCT-branched surfactants has greatly reduced the surface tension of aqueous solution from 73 to 30-50 mN/m.Their CMC values are decreased with the increase of hydroxyl number,especially when the end group is diethanol amine,the CMC has reached the minimum value 0.41×10-3mol/L.Similar to those observed in the conventional surfactants,in comparison to γCMCof 7a and 7b (51 and 30 mN/m),the increase of hydroxyl number was greatly contribute to the formation of hydrogen bonds,which was general favorable for the property of surfactivity.These factors resulted in that 7b exhibited the lowest surface tension at CMC (γCMC) among these three branched surfactants.However,the compound 7c,bearing the most hydroxyl,exhibited relatively higher γCMC(49 mN/m).The unusual behavior of these surfactants can be explained by the structure of end group.[14]Generally,in compound solution,to adsorb on the interface,the nonadsorbed molecules have to pass through an energetic barrier induced by the adsorbed molecular film.[15]Thus the steric hindrance caused by the large end group size,resulted in higher energies needed to pass the barrier.[16]These factors prevented the compound 7c from further reducing its dynamic surface tension.

Conclusion

Three novel branched surfactants were synthesized and characterized by NMR,HRMS and FT-IR spectroscopic techniques.It is found that the reaction conditions are more moderate by using cyanuric chloride.The results of thermal stability tests showed that the compounds decomposed at 250 ℃ which indicates high stability of the structure.The results of surface tension tests showed that all the branched surfactants could reduce the surface tension of water with low CMC values.The surface active properties of these compounds were strongly related to the end group of the structure.The branched surfactants with hydroxyl groups introduced had greater efficiency in reducing surface tension.

Figure 3.Surface tension as a function of surfactant concentration

Acknowledgements

This research was financially supported by the National Nature Science Foundation of China (21772039,21272069),and the Fundamental Research Funds for the Central Universities and Key Laboratory of Organofluorine Chemistry,Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences,and we thank the Chinese Scholarship Council for financial support.