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Langmuir 1998, 14, 1940-1941
Cleavable Quaternary Hydrazinium Surfactants David A. Jaeger,* Jennifer Wettstein,1 and Abdullah Zafar Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071-3838 Received November 3, 1997. In Final Form: January 8, 1998
Introduction Cleavable surfactants2,3 can be converted into other compounds after their use for any one of a number of beneficial purposes, thereby eliminating potential problems resulting from the presence of an intact/aggregated surfactant during subsequent manipulations. Several types of cleavable surfactants have been reported,2-4 which are based on the stability/lability characteristics of a variety of functional groups. To our knowledge, there has been no report of the cleavable nature of surfactants based on a quaternary hydrazinium group. Herein we report the demonstration of quaternary hydrazinium surfactants 1 as cleavable surfactants. There have been a few previous reports of the syntheses of N-alkyl-N,N-dimethylhydrazinium surfactants,5 including that of 1a,5a but they have contained only limited characterization of their molecular and surfactant properties.
Results and Discussion Surfactants 1 were prepared in one step by the reaction of N,N-dimethylhydrazine with bromoalkanes 2 (eq 1). The characterization of surfactants 1 included the measurement of Krafft temperatures (Tk) and critical micelle concentrations (cmc’s). Aggregated 1 was characterized by 1H NMR spectroscopy and dynamic laser light scattering (DLLS). * To whom correspondence should be addressed: telephone 307766-4335; fax, 307-766-2807; e-mail,
[email protected]. (1) NSF Research Experiences for Undergraduates participant, Summer 1997. (2) Jaeger, D. A. Supramol. Chem. 1995, 5, 27. (3) Holmberg, K. Curr. Opin. Colloid Interface Sci. 1996, 1, 572. (4) For examples, see: (a) Cuomo, J.; Merrifield, J. H.; Keana, J. F. W. J. Org. Chem. 1980, 45, 4216. (b) Ono, D.; Masuyama, A.; Okahara, M. J. Org. Chem. 1990, 55, 4461. (c) Ringsdorf, H.; Schlarb, B.; Venzmer, J. Angew. Chem., Int. Ed. Engl. 1988, 27, 113. (d) Kida, T.; Masuyama, A.; Okahara, M. Tetrahedron Lett. 1990, 31, 5939. (e) West, C. A.; Sanchez, A. M.; Hanon-Aragon, K. A.; Salazar, I. C.; Menger, F. M. Tetrahedron Lett. 1996, 37, 9135. (f) Dunkin, I. R.; Gittinger, A.; Sherrington, D. C.; Whittaker, P. A. J. Chem. Soc., Chem. Commun. 1994, 2245. (g) Wang, G.-W.; Liu, Y.-C.; Yuan, X.-Y.; Lei, X.-G.; Guo, Q.-X. J. Colloid Interface Sci. 1995, 173, 49. (h) Hayashi, Y.; Shirai, F.; Shimizu, T.; Nagano, Y.; Teramura, K. J. Am. Oil Chem. Soc. 1985, 62, 555. (i) Yamamura, S.; Nakamura, M.; Takeda, T. J. Am. Oil Chem. Soc. 1989, 66, 1165. (j) Ono, D.; Masuyama, A.; Nakatsuji, Y.; Okahara, M.; Yamamura, S.; Takeda, T. J. Am. Oil Chem. Soc. 1993, 70, 29. (k) Wilk, K. A.; Bieniecki, A.; Burczyk, B.; Sokolowski, A. J. Am. Oil Chem. Soc. 1994, 71, 81 and references therein. (5) (a) Kameyama E.; Minegishi, Y.; Kuwamura, T. Kogyo Kagaku Zasshi 1968, 71, 1671. (b) Westphal, O. Chem. Ber. 1941, 74, 1365. (c) Ohio State University Research Foundation Br. Patent 824 357, 1959; Chem. Abstr. 1960, 54, 9964.
The Tk values of 1a and 1b in H2O are 99 vol %) for each surfactant with hydrodynamic diameters as follows: 1a, 3.2 ( 0.5 nm; 1b, 4.1 ( 0.5 nm. These sizes correspond to spherical micelles.8 The cleavable nature of surfactants 1 is represented by the conversion of 1a into dodecyldimethylamine (3). The cleavage of the nitrogen-nitrogen bond, required in the formation of 3, was effected in two ways. The first involved the reaction of 1a with nitrous acid (eq 2), which presumably proceeds by nitrosation of the primary amino group, followed by the loss of N2O to give 3. Under the acidic reaction conditions 3 is protonated to give dodecyldimethylammonium chloride, which itself is a surfactant with a cmc of 1.6 × 10-2 M in H2O at 25 °C.6,9 Basification of the reaction mixture then gives nonsurfactant 3. The reaction of 1a with nitrous acid at 0 °C for 2 h gave a 92% yield of 3, which increased to 97% when the reaction proceeded for an additional 16 h at 25 °C. The second method involved the reduction of 1a by sodium dithionite under basic conditions (eq 3), which gives amine 3 directly. The reaction gave an 89% yield of 3 after 12 h at ca. 95 °C. In a control under the same basic conditions but without sodium dithionite, 3 was not formed and 82% of 1a was recovered after 18 h at ca. 95 °C.
The conditions for the nitrous acid-mediated conversion of 1a into 3 are among the mildest reported to date for the cleavage of cleavable surfactants.2-4 On the other hand, the conditions for the sodium dithionite-mediated conversion of 1a into 3 are harsher than most cleavage conditions. (6) Mukerjee, P.; Mysels, K. J. Natl. Stand. Ref. Data Ser. (U. S. Natl. Bur. Stand.) 1971, NSRDS-NBS 36. (7) Browning, J. L. In Liposomes: From Physical Structure to Therapeutic Applications; Knight, C. G., Ed.; Elsevier/North-Holland: New York, 1981; Chapter 7. (8) Briggs, J.; Dorshow, R. B.; Bunton, C. A.; Nicoli, D. F. J. Chem. Phys. 1982, 76, 775. (9) Ralston, A. W.; Broome, F. K.; Harwood, H. J. J. Am. Chem. Soc. 1949, 71, 671.
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Note that the cmc of dodecyldimethylammonium chloride6,9 is greater than that of 1a. Without basification in the nitrous acid-mediated cleavage, it should be possible to go from a solution containing aggregated 1a to one containing unaggregated dodecyldimethylammonium chloride. Under these conditions 1a would function as a second generation cleavable surfactant,2 since it is cleaved to give another surfactant with a higher cmc. Summary Surfactants 1, prepared by the reaction of N,N-dimethylhydrazine with bromoalkanes 2, form micelles in H2O. Their cleavable nature was demonstrated by the conversion of 1a into nonsurfactant amine 3 by its reaction with nitrous acid (eq 2) or sodium dithionite (eq 3). Experimental Section General Procedures and Materials. 1H (400 MHz) and 13C (100.6 MHz) NMR spectra, unless noted otherwise, were recorded in CDCl3 with Me4Si and CDCl3 (center line at δ 77.00 relative to Me4Si) as internal standards, respectively. 1H NMR spectra of 1a and 1b recorded in D2O employed their methylene envelopes [(CH2)8 and (CH2)10, respectively] as internal standards at δ 1.26. The Tk values were determined according to a literature procedure.10 The cmc’s were obtained from plots of surface tension (du Nou¨y ring) vs [1] using a Fisher model 20 tensiometer; the reported values are averages of two determinations. Extracts were dried over MgSO4, and melting points are uncorrected. Elemental analyses were performed by Atlantic Mircolab, Atlanta, GA. N-Dodecyl-N,N-dimethylhydrazinium Bromide (1a).5a A solution of 20.7 g (83.1 mmol) of 1-bromododecane in 20 mL of absolute EtOH was added dropwise over 40 min to a stirred solution of 5.00 g (83.2 mmol) of N,N-dimethylhydrazine in 50 mL of absolute EtOH under N2. Then the reaction mixture was stirred at 25 °C for 16 h, refluxed for 24 h, and rotary evaporated. The resultant 25.2 g (98%) of crude product was recrystallized (5 °C) from EtOH-Et2O to give 23.1 g (90%) of 1a: mp 160-161 °C; 1H NMR δ 6.72 (s, 2 H, NH2), 3.67 (m, 2 H, CH2N), 3.56 (s, 6 H, (CH3)2N), 1.83 (m, 2 H, CH2CH2N), 1.36 (m, 2 H, CH2CH2CH2N), 1.26 (s, 16 H, (CH2)8), 0.88 (t, 3 H, CH3); 1H NMR (0.015 M in D2O) δ 3.50 (m, 2 H, CH2N), 3.30 (s, 6 H, (CH3)2N), 1.81 (m, 2 H, CH2CH2N), 1.34 (m, 2 H, CH2CH2CH2N), 1.26 (s, 16 H, (CH2)8), 0.86 (t, 3 H, CH3); 13C NMR δ 69.45, 55.52, 31.83, 29.52, 29.39, 29.31, 29.26, 29.14, 26.07, 23.40, 22.61, 14.06; IR (KBr) 3073 and 3185 cm-1 (NH2). Anal. Calcd for C14H33N2Br: C, 54.36; H, 10.75. Found: C, 54.35; H, 10.71. N-Tetradecyl-N,N-dimethylhydrazinium Bromide (1b). With the procedure for 1a, 1-bromotetradecane and N,Ndimethylhydrazine gave (90%) 1b: mp 167-169 °C; 1H NMR δ 6.74 (s, 2 H, NH2), 3.66 (m, 2 H, CH2N), 3.55 (s, 6 H, (CH3)2N), 1.82 (m, 2 H, CH2CH2N), 1.35 (m, 2 H, CH2CH2CH2N), 1.25 (s, 20 H, (CH2)10), 0.88 (t, 3 H, CH3); 1H NMR (0.005 M in D2O) δ 3.57 (m, 2 H, CH2N), 3.36 (s, 6 H, (CH3)2N), 1.86 (m, 2 H, CH2CH2N), 1.36 (m, 2 H, CH2CH2CH2N), 1.26 (s, 20 H, (CH2)10), 0.86 (t, 3 H, CH3); 13C NMR δ 69.45, 55.56, 31.86, 29.62, 29.59, (10) De´marcq, M.; Dervichian, D. Bull. Soc. Chim. Fr. 1945, 12, 939.
29.54, 29.42, 29.34, 29.30, 29.17, 26.09, 23.41, 22.63, 14.07; IR (KBr) 3077 and 3188 cm-1 (NH2). Anal. Calcd for C16H37N2Br: C, 56.96; H, 11.05. Found: C, 56.72; H, 10.95. Cleavage of 1a with Nitrous Acid. The following procedure is adapted from a procedure for the conversion of nonsurfactant quaternary hydrazinium halides into tertiary amines.11 A solution of 0.33 g (4.8 mmol) of NaNO2 in 8.0 mL of H2O was added dropwise during 10 min to a stirred solution of 0.50 g (1.6 mmol) of 1a in 9.5 mL of 4.0 M hydrochloric acid at 0 °C under N2. The resultant mixture, containing 2.2 M HCl, was stirred at 0 °C for 2 h and then at 25 °C for 16 h. Thereafter, the reaction mixture was added to 10 mL of aqueous 10% NaOH and extracted with 50 mL of Et2O. The extract was dried and rotary evaporated to give 0.33 g (97%) of amine 3, whose 1H NMR spectrum [δ 2.24 (m, 2 H, CH2N), 2.21 (s, 6 H, (CH3)2N), 1.45 (m, 2 H, CH2CH2N), 1.26 (m, 18 H, (CH2)9), 0.88 (t, 3 H, CH3)] was identical to that of authentic 3 (Aldrich). A 92% yield of 3 was obtained from a comparable reaction that was worked up after 2 h at 0 °C. Cleavage of 1a with Sodium Dithionite. The following procedure is adapted from a procedure for the reduction of an azo compound to an amine.12 To a solution of 0.50 g (1.6 mmol) of 1a in 15 mL of 1.7 M NaOH at 50 °C was added 0.50 g (2.4 mmol) of Na2S2O4 (technical grade, 85%) in small portions over 10 min, followed by the addition of 2.81 g (13.7 mmol) of Na2S2O4. The resultant mixture was refluxed for 12 h and then extracted with two 25-mL portions of Et2O. The combined extracts were dried and rotary evaporated to give 0.31 g (89%) of 3, whose 1H NMR spectrum was identical to that of authentic 3. Control on the Stability of 1a in 1.7 M NaOH. A solution of 0.50 g (1.6 mmol) of 1a in 15 mL of 1.7 M NaOH was refluxed for 18 h and then extracted with two 25-mL portions of Et2O. The combined extracts were dried and rotary evaporated to give 3 mg of an unknown oil that did not contain 3. The aqueous solution was evaporated to give a solid residue that was extracted with four 25-mL portions of CH2Cl2. The combined extracts were dried and rotary evaporated to give 0.41 g (82%) of solid that was identified as 1a by 1H NMR. DLLS. Measurements were made for 1a and 1b at 25 and 35 °C, respectively, on the instrumentation described previously.13 The DLLS samples were prepared as follows. A solution of 1 in H2O (1a, 15 × 10-3 M; 1b, 5.9 × 10-3 M) was filtered through a 0.45-µm filter (Millipore SJHV004NS) into a 6-mm × 50-mm culture tube (Kimble 73500-650). The tube was capped (5-mm NMR tube cap) immediately and inserted into the particle sizer and the run begun with a photopulse rate of 300-400 kHz. Data were analyzed by Nicomp distribution analysis software (version 12.3), which gave histograms of relative volume vs diameter. The reported hydrodynamic diameters are averages of two runs.
Acknowledgment is made to the National Science Foundation (CHE-9526188) for the support of this research. We thank Professor Hiraku Shinozaki for a translation of ref 5a. LA971202K (11) Smith, R. F.; Coffman, K. J. Synth. Commun. 1982, 12, 801. (12) Fieser, L. F. Organic Syntheses; Wiley: New York, 1943; Collect. Vol. II, p 35. (13) Jaeger, D. A.; Sayed, Y. M. J. Org. Chem. 1993, 58, 2619.
