Amine Oxides: a Review

Amine Oxides: A Review

＊ Sudhir Kumar SINGH, M. BAJPAI and V.K. TYAGI Department of Oil and Paint Technology, Harcourt Butler Technological Institute (Kanpur-208 002, INDIA)

Edited by M. Iwahashi, Kitasato Univ., and accepted September 20, 2005 (received for review August 29, 2005)

Abstract: Amine oxides are amine-based surfactants, represent one of the smaller classes of surfactants as compared to alcohol ethoxylates and sulfonated and sulfated anionic surfactants. However, the uniqueness of the hydrophile in such surfactants provides specific properties that are difficult, if not impossible, to replicate by the use of classic nonionic and anionic surfactants. The aim of the present paper is to survey the most important developments and understandings of the chemistry of amine oxide production, it’s physico-chemical studies, applications and environmental properties. Key words:amine oxide, amine-based surfactant, hydrophile, physico-chemical, environmental

dispersant, and in deodorant bars (anti-bacterial agent), 1 Introduction due to their compatible synergistic effect and environ- Although, amine oxides were known and studied ment friendly nature. Amine oxides are exothermic, before 1900, it was not until 1939, with the issuance of second order reaction products of tertiary amines and an I.G. Farbenindustrie patent that material such as hydrogen peroxide (3). The nature of tertiary amine in dimethyldodecyl amine oxide were recognized as sur- amine oxides may be aliphatic, aromatic, heterocyclic, factant. After a further 22 years their utility in liquid alicyclic or combination thereof. In current amine household formulations was disclosed and widespread oxides the surfactant precursor is generally a C12 - C18 interest was generated. The substitution for the tradi- alkyldimethyl amine (4). tional fatty alkanolamides as foam booster in dishwash- Amine oxides come under the special class of surfac- ing was the specific example which brought recognition tant known as amphoteric surfactant. The basic reason to the amine oxides. Their favourable weight/effect behind that is, amine oxide changes from net cationic ratio offsets the considerably higher cost in this applica- via zwitterionics to nonionics on going from low to tion (1). high pH; which confirms it’s amphoteric nature. Reaction of hydrogen peroxide with secondary or This paper presents a detailed review on amine primary amines does not result in commercially useful oxides, with special emphasis on the chemistry of oxi- materials (2), but with tertiary amines a variety of com- dation, physico-chemical studies, various applications mercial useful materials obtained which are used not and anti-microbial activity with variation in chain only in various types of cleaning formulations but also, length. The last part of this paper is briefly focused on proving their utilities in liquid bleach products (surfac- the safety of amine oxides. tant basis), textile industry (anti-static agent), rubber industry (foam stabilizer), polymer industry (polymer- ization catalyst), anti-corrosion compositions, lime soap

＊ Correspondence to: V.K. TYAGI, Department of Oil and Paint Technology, Harcourt Butler Technological Institute, Kanpur - 208002, INDIA E-mail: [email protected], [email protected]

Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online 99 http://jos.jstage.jst.go.jp/en/ S.K. Singh, M. Bajpai and V.K. Tyagi

During the synthesis of amine oxides information on 2 The Chemistry of Oxidation for Amine the amount of unreacted tertiary amine present is need- Oxide Formation ed in order to follow the reaction. A number of analyti- The generally accepted mechanism for oxidation of cal procedure including chromatographic procedures tertiary amines with hydrogen peroxide involves the have been devised to obtain this information. But all of ammonium peroxide as an intermediate followed by these procedures have some limitations. Wang and Met- splitting off water. Previous work (3) strongly suggests calfe (6) developed a simple, rapid, non aqueous titra- the reversibility of the formation of the ammonium per- tion procedure that makes use of the “anamalous salt” oxide. The proposed mechanism is as follows: behaviour of amine oxides. A modified solvent and

k1 ∗ k3 titrant is used to obtain two potential breaks in the titra- RN3223223+⇔ HO() RNHO. →+ RNO HO 2 k2 rxn.intermediate tion. The first break corresponds to half of the amine From the above proposed mechanism, the rate of for- oxide. The second break represents the second half of mation of amine oxide can be derived; using “steady- the amine oxide plus any unreacted amine. With this state approximation”. The rate of formation of amine information the amine oxide and unreacted amines can oxide can be written as, be calculated. γ = []∗ ()RNO3 kRNHO33. 22 ･･･････････････････（I） 3Synthesis of Amine Oxides Since, the concentration of intermediate is so small that it can’t be measured, so, it has to be replaced by the 3･1 Synthesis of Dimethylalkyl Amine concentrations that can be measured. Oxides and Cyclic Amine Oxides From proposed mechanism we have, Friedli et al. (3) prepared dimethyllauryl amine oxide, ∗ N-laurylmorpholine oxide, N-laurylpiperidine oxide γ ()RNHO. ∗= kRNHO13[][] 22− kRNHO23[]. 22 322 ･･(II) and N-lauryl-3- methyl piperidine oxide with their − ∗ kRNHO33[]. 22 respective amines by reacting with 51% aqueous hydro-

Now, because the concentration of (R3N. H2O2)* is gen peroxide at 75℃. Their rates of formation indicates always extremely small, one may assume that it’s rate that the reaction is of second order and two piperidine of change be zero {This is called “steady-state approxi- versions form slower than dimethyl-lauryl amine oxide, mation” (5)}. while lauryl morpholine reacts much faster. Hence, γ ()∗ = RN322.. HO 0 ･･･････････････････････････(III) 3･2 Synthesis of 2-alkoxy-N, N- From equations (I), (II) and (III) we get, dimethylethyl Amine N-oxides kk[][] RN HO Hayashi et al. (7) prepared 2-lauryloxy-N,N- γ = 13 3 2 2 RNO3 dimethylethyl amine N-oxide with it’s amine by react- kk23+ ing with 30% aq hydrogen peroxide at room tempera- or ture. The amine oxide was concentrated in a drying box γ = [][] RNO3 KRN322 HO ････････････････････(IV) under reduced pressure resulted into a crystalline solid where K is overall rate constant and amine oxide. Such amine oxides are stable up to 100℃,

K = k1k3 / (k2 + k3) but decomposes rapidly to vinyl ethers at 150℃. At low So, from equation (IV) it is evident that overall order temperature they deoxygenated to their tertiary amine. of reaction for amine oxide formation is 2, and is in Hygroscopic property decreases as length of the alkyl complete agreement with the experiment. chain increases. It has been observed that the degree of conversion of tertiary amines to its amine oxides is dependent on the 3･3Synthesis of Alkyl Benzene Derived purity of the tertiary amines. With commercially avail- Amine Oxides able undistilled tertiary amine yields in the range of Marmer and Linfield (8) prepared aromatic amine 85% to 87% are obtained. But with freshly redistilled oxides via a three step route from a variety of pure 1- tertiary amine and with 10% molar excess hydrogen phenylalkanes and also from a commercial detergent peroxide the yield may go upto 99% (1). alkylate mixture. The process includes (i) sulfonation of

100 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review the phenylalkane with chlorosulfonic acid in 1,2- dichloroethane. (ii) reaction of resulting alkarylsulfonyl chloride with H2N(CH2)3NMe2 (Me is for -CH3 group) or H2N(CH2)3N(CH2CH2OH)2 under anhydrous conditions at room temperature, and (iii) oxidation of resulting tertiary amines with 30% aqueous hydrogen peroxide at 65℃. Such aromatic amine oxides were found to be thermally stable below 125℃.

3･4 Synthesis of N, N-dimethylalkyl Amine N-oxide by Micellar-Autocatalysis Rathman and Kust (9) investigated the synthesis of N,N-dimethyldodecyl amine N-oxide in aqueous solutions by micellar autocatalysis. The lipophilic reactant, dimethyl dodecylamine was initially solubilized in micellar solutions of the amine oxide surfactant, resulting in substantially higher reaction rates. Amine con- versions of 90-100% were obtained within 2 h at 70℃. The effects of reactant concentrations, temperature, and initial surfactant concentration were studied. This method is important because of two main reasons: (I) Micellar auto catalysis provides a method for synthesiz- Fig. 1 Molecular Structures of Respective Amine Oxides ing surfactants without employing volatile organic sol- of Section 3. vents in the reaction medium, providing potential eco- nomic and environmental benefits and (II) studies of 5 Physico-Chemical Studies on micellar auto catalysis can refine and extend the under- Amine Oxides standing of the other types of reactions in aqueous surfactant solutions. It is well known that the dissociation constant K of weak electrolytes at the charged interface are different from those in their solutions. Funasaki (12) were meas- 4 Analysis of Amine Oxides ured the dissociation constant K of acid -base indicators Pinazo and Domingo (10) investigated turbidimetric in aqueous solutions of 20 mM dodecyldimethyl amine analysis of amine oxides and amine oxide - anionic sur- oxide (DDAO), 1% Brij 35 (C12H25-(O-CH2-CH2-)23- factant mixtures. This automatic analysis has been OH),and 20 mM cetyltrimethylammonium bromide shown to be a simple and accurate method to determine (CTAB) spectroscopically and also determined the K Ki the actives in anionic surfactants as well as the actives applicability of the equation p = p － (0.4343 e0y0/kT), in amine oxides. This technique has been applied to to the micelle-solubilizate systems. The surface poten- dilute solutions of these surfactants in the mM range. tial Y0 of mixed micelles of sodium dodecyl decaoxy Turney and Cannell (11) determined a method known ethylene sulfate and dodecyldimethylamine oxide in the as alkaline methylene blue method for determination of presence of 0.1 M sodium chloride at 25℃ have found anionic surfactants, also this method in conjunction by Tokiwa and Ohki is somewhat unreasonable. with the acid methylene blue titration may be used to Funasaki (13) evaluated more reasonably the surface determine the amount of amine oxides in formulated potential of these mixed micelles. products like detergents etc, based on the cationic It has been known that micelle of ionic surfactants nature of amine oxides at low pH and nonionic nature at grows with increasing concentration of added salt. The high pH. For concentrations of less than 100 PPM a electric repulsion between charged headgroups is a spectrophotometric method was used. main size - limiting factor in micelle formulation, and the effect of added salt on the micele size has been

101 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi attributed to the electrostatic shielding effect of counter- water soluble polymers poly (vinyl methyl ether) ions on the charged micelle. Ikeda et al. (14) studied (PVME), poly (propylene oxide) (PPO), and poly (ethy- the effects of ionization on micelle size of aqueous lene oxide) (PEO) on the aggregation behaviour of n- NaCl solution of dimethyldodecyl amine oxide, by dodecyldimethyl amine oxide (DDAO), at various using the light-scattering method for the determination stages of protonation. of molecular weight, from the Debye plot. Hoffman et al. (20) reported the phase diagram of the Imae and Ikeda (15) measured angular dependence of ternary surfactant system tetradecyldimethyl amine light-scattering from micellar solutions of dimethyl- oxide / heptanol / water for small surfactant concentra- oleyl amine oxide in water and 10-4 M NaCl at different tions. With increasing cosurfactant / surfactant ratio, the micelle concentrations from the critical micelle concen- generally observed sequence of the phases L1, La and -2 -3 tration (CMC) to 0.15 × 10 g cm . The intensity of L3 is found. These single phases are separated by nar- light scattered from the micellar solutions increases row two phase regions. In all these phases the L3 or so- with an increase in scattering angle, in contrast to the called sponge phase has drawn much attention. It is a usual behaviour. This is caused by the effect of external low viscous, slightly turbid, and optically isotropic interference which is stronger than that of internal interference. Dimethyldodecyl amine oxide and dimethyltetradecyl amine oxide are known to form spherical micelles in water and 0.20 M NaCl solutions; but, if the hydrocarbon part of nonionics with amine oxide head group is made longer for e.g. dimethyloleyl amine oxide, forms rod like micelles in dilute aqueous solutions determined from light-scattering measurements. Ritsu Kamiya et al. (16) presented electron micrographs of rod like micelles regenerated from aqueous solutions of dimethyloleyl amine oxide and gave support for the Fig. 2 The Phase Diagram under the Visual Inspection for results from the light scattering measurements. Aqueous Solutions of C16 DAO. I, Transparent and Imae and Ikeda (17) investigated the pH dependence Isotropic Solution; II, Turbid Solution; III, of upper and lower consolute phase boundaries for Iridescent Solution. aqueous NaCl solutions of dimethyloleyl amine oxide Reprinted from J. Colloid Interface Sci., Vol. 131, 601-602, at temperatures between 5 and 85℃ for pH less than 8 Copyright with permission from Elsevier. at different NaCl concentrations. The consolute phase boundary is also given as a function of surfactant concentration. Toyoko Imae et al. in their another investigation (18) found that aqueous solutions of dimethylalkyl amine oxides (CnDAO, n = 16,18) present the iri- descence at surface concentrations of 0.3 - 2 wt%, when the temperature of the solutions is lower than 23℃ for

C16 DAO and 46℃ for C18 DAO. The Colour changes from yellowish red to blue with an increase in surfac- Fig. 3 The Phase Diagram under the Visual Inspection and tant concentration, and disappears at pH below Ca. the Crossed Nicol for Aqueous Solutions of 6.5 for C16 DAO and below Ca. 4.5 for C18 DAO (see C18DAO.――, visual inspection; ―-―-―-―, Figs. 2 & 3). crossed nicol. I, transparent and isotropic solution; Polymer-micelle complexes have found applications II, turbid solution; III, iridescent solution; IV, in many industrial products, such as paints and coat- weakly birefringent solution; V, strongly ings, laundry detergent, and cosmetic products and they birefringent solution. also play a role in tertiary oil recovery. Brackman and Reprinted from J. Colloid Interface Sci., Vol. 131, 601-602, Engberts (19) studied the influence of the nonionic Copyright with permission from Elsevier.

102 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review phase which shows flow birefringence under shear. It is very interesting to investigate the behaviour of The interactions between water and nonionic surfac- surfactant mixtures, which have different head groups tants are important in both fundamental and applied with synergistic interactions but also different chains surface chemistry. Mol et al. (21) determined the struc- with antagonistic interactions. Hoffman and Possnecker tural parameters of the hexagonal and lamellar phase of (23) investigated the mixing behaviour of surfactants by the dimethyldodecyl amine oxide (DDAO)- water sys- using the phase separation model. In their investigation tems using X-ray diffraction. The result obtained are they used pairs of nonionic hydrocarbon surfactants and discussed in the light of the on going debates about (i). perfluorinated anionic surfactants; in one example they The relative importance of steric / protrusion forces and took the tetradecyldimethyl amine oxide as nonionic hydration forces between surfactant bilayers and (ii) the surfactant with the mentioned anionic surfactants. With molecular origin of the temperature dependence of the this anionic surfactant it was possible to reach nearly interactions displayed in several nonionic water sys- identical CMC values of the nonionic and the anionic tems. surfactant. To create special starting conditions, they The electrostatic potential is one of the important used a hydrophobic tetraethyl ammonium counterion of factors for the stabilization of dispersed colloidal parti- the anionic surfactant (see Figs. 8 & 9). cles in aqueous medium. The electrokinetic phe- Desnoyers et al. (24) studied the thermodynamic nomenon such as electrophoresis, which may be evalu- micellar properties of n-octyldimethyl amine oxide ated by mobility, is in close connection with electrostat- hydrochloride (OAO.HCl) in water. The apparent molar ic potential. Imae and Hayashi (22) performed elec- volumes and heat capacities of OAO. HCl were meas- trophoretic light scattering measurements for aqueous NaCl solutions of dodecyl-, tetradecyl-, and oleyldimethyl amine oxides (C12DAO, C14DAO & ODAO). It was observed that Electrophoretic mobility changed with the degree of protonation (see Figs. 4 to 7).

Fig. 5 Electrophoretic Mobility as a Function of Degree of

Protonation for 0.1 M NaCl Solutions of C14DAO at Surfactant Concentration of 0.5×10-2 g cm-3. Reprinted from Langmuir, Vol. I, 3385-3388, Copyright with permission from Am. Chem. Soc.

Fig. 4 Electrophoretic Light Scattering Power Spectra for

0.1 M NaCl Solutions of C14DAO at Surfactant Fig. 6 Electrophoretic Mobility as a Function of Degree of Concentration of 0.5×10-2 g cm-3 with Various Protonation for 0.03 M NaCl Solutions of ODAO at Degrees of Protonation. Surfactant Concentration of 0.1×10-2 g cm-3. Reprinted from Langmuir, Vol. I, 3385-3388, Copyright with Reprinted from Langmuir, Vol. I, 3385-3388, Copyright with permission from Am. Chem. Soc. permission from Am. Chem. Soc.

103 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi

Fig. 8 Plot of the Surface Tension vs the Logarithm of the Fig. 7 Electrophoretic Mobility as a Function of Degree of Total Surfactant Concentration of the System (I) Protonation for 0.05 M NaCl Solutions of C DAO 12 C DMAO/NEt -PFOS in 10 mM NEt OH Solution at Surfactant Concentration of 10-2 g cm-3. Square 14 4 4 at Different Mixing Ratios C DMAO/NEt signs are data for 0.1 M NaCl solutions of C DAO. 14 4 12 PFOS: a, 9:1; b,7:3; c, 3.5:6.5; d, 2:8. Reprinted from Langmuir, Vol. I, 3385-3388, Copyright with Reprinted from Langmuir, Vol. 10, 381-389, Copyright with permission from Am. Chem. Soc. permission from Am. Chem. Soc. ured in water as a function of concentration between 2 and 55℃ and the apparent molar relative enthalpies of the same system at 25℃. Also, the apparent molar expansibilities were calculated from the temperature dependence of the volumes (see Figs. 10 to 14). Okamura et al. (25) investigated supramolecular assemblies in ternary systems of alkyldimethyl amine oxide (C DAO, n=12, 16)/Cinnamic acid/ water by n Fig. 9 cmc as a Function of the Mole Fraction a of small angle neutron scattering(SANS). The fine struc- NEt PFOS for the Mixtures (I) C DMAO/NEt tures of molecular assemblies were quantitatively 4 14 4 PFOS in 10 mM NEt4OH Solution. examined for solutions with different mixing ratios. Reprinted from Langmuir, Vol. 10, 381-389, Copyright with Since SANS is operated at the neutron radiation of 1- permission from Am. Chem. Soc. 16 Å wavelength, it results in distances of nanometer scale such as the shape of small micelles, the crossec- tion of rod like micelles, and the lamellar thickness and the dependence on concentration and temperature (26), distance. Such data have never been obtained from and pressure (27) of the mean aggregation number (N) TEM and light scattering experiment. The molecular of rodlike tetradecyldimethyl amine oxide micelles in arrangement in supramolecular assemblies is discussed D2O. Small angle scattering with neutrons (SANS) or in relation to the structure geometry (see Figs. 15 to with X-rays (SAXS) is one of the most direct methods 20). for obtaining information about structural details and The influence of thermodynamic parameters on the their changes and also may help to clarify the results mechanism of self-organization of surfactants in aque- obtained by other experimental techniques. The combi- ous solutions are of deep interest giving a deep insight nation of pressure, temperature and SANS or SAXS in into the “new science of complex fluids”. The rich phase the study of physical properties of micellar systems behaviours of complex fluid systems is associated with opens up new prospects for examining amphiphilic the fact that particles are molecular aggregates rather solutions on a microscopic level. than simple molecules. The aggregates are thermody- Zimmerman and Schnaare (28) extended the method namically stable structures, which change their size and of Rathman and Christian for determining the micellar shape in response to changes in concentration, compo- activities of dimethyldodecyl amine oxide by pH titra- sition, counterion species, temperature, pressure and tion in the presence of swamping electrolyte to accom- other conditions. Garski et al. (26,27) studied by means modate non swamping electrolyte conditions. of small angle neutron scattering (SANS) experiments, Dimethyltetradecyl amine oxide was used as a model

104 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review

Fig. 12 Apparent Molar Expansibilities of OAOHCl and OAO at 25℃; Full Lines are from the Mass-Action Fig. 10 Apparent Molar Volumes of OAOHCl at Various Model. Temperatures; Full Lines are from the Mass-Action Reprinted from Langmuir, Vol. 11, 1905-1911, Copyright with permission from Am. Chem. Soc. Model. Reprinted from Langmuir, Vol. 11, 1905-1911, Copyright with permission from Am. Chem. Soc.

Fig. 13 Apparent Molar Relative Enthalpies of OAOHCl, OAO, and OABr at 25℃; Broken Lines are from the Mass-Action Model. Reprinted from Langmuir, Vol. 11, 1905-1911, Copyright with permission from Am. Chem. Soc.

Fig. 11 Apparent Molar Heat Capacities of OAOHCl at Various Temperatures; Full Lines are from the Mass-Action Model. Reprinted from Langmuir, Vol. 11, 1905-1911, Copyright with permission from Am. Chem. Soc. surfactant in this study. Amine oxide surfactants exist in solution either as the unprotonated, electrically neutral Zwitterionic form (AO±) or as the protonated, cationic Fig. 14 Temperature Dependence of Volume Parameters of form (HAO+). OAOHCl and OAO from the Mass-Action Model; Myrzakozha et al. (29) reported the molecular orien- ＋’s are from the Second Series of Measurements. tation and structure in one and multilayer Langmuir - Reprinted from Langmuir, Vol. 11, 1905-1911, Copyright Blodgett (LB) films of octadecyldimethyl amine oxide with permission from Am. Chem. Soc. (C18 DAO) and dioctadecyldimethyl ammonium chloride (2C18DAO) on gold and silver-evaporated glass slides. It was found that the structures of LB films show entation and order of alkyl chains in the first layers are clear dependence upon the number of monolayers and changed largely upon the deposition of the second lay- substrates. The most important finding was that the ori- ers. In their another investigation (30), they reported the

105 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi

Fig. 15 SANS Data for the C12DAO/Cinnamic Acid/D2O System. Mixing Ratio: ○, X=0; ●, X=0.2; △, X=0.4; ▲, X=0.6. Reprinted from J. Colloid Interface Sci., Vol. 180, 98-105, Fig. 17 Replots of SANS Data for the C DAO/Cinnamic Copyright with permission from Elsevier. 12 X (“Q” is Bragg wave number and “I” is SANS intensity) Acid/D2O System at Mixing Ratios =0.45. 0.6 and 1. Reprinted from J. Colloid Interface Sci., Vol. 180, 98-105, Copyright with permission from Elsevier. (“Q” is Bragg wave number and “I” is SANS intensity)

Fig. 16 Replots of SANS Data for the C12DAO/Cinnamic

Acid/D2O System at Mixing Ratios X=0 and 0.2. Reprinted from J. Colloid Interface Sci., Vol. 180, 98-105, Fig. 18 SANS Data for the C16DAO/Cinnamic Acid/D2O Copyright with permission from Elsevier. System. Mixing Ratio: ●, X=0; ○, X=0.2; ▲, (“Q” is Bragg wave number and “I” is SANS intensity) X=0.4; □, X=0.6. Reprinted from J. Colloid Interface Sci., Vol. 180, 98-105, Copyright with permission from Elsevier. thermal behaviour of the one - and five - monolayer LB (“Q” is Bragg wave number and “I” is SANS intensity) films of C18DAO and 2C18 DAC on the gold and silver evaporated glass slides. It has been generally recog- ization has been made for LB films of various com- nized that the interaction between a head group and a pounds from simple fatty acids to complicated organic substrate and the longitudinal interaction between dyes by use of IR, UV-Vis, and Raman spectroscopies monolayers are two important factors which control the and atomic force microscopy (AFM). Structural thermal stability of LB films. LB films have been a changes in the films induced by aging, doping and matter of keen interest because of their fundamental variations in pH and temperature have also been importance in surface science as well as their potential explored extensively. Myrzakozha et al. (31) presented application in optoelectronics. an IR study of structure and aging -behaviour of one-

Because the elucidation of the relationship between layer LB films of C18DAO and 2C18DAC. The IR meas- the structure and function of the films is essential for urements suggests that the alkyl chains of one-layer both basic studies and applications, structural character- LB film of C18DAO on a gold-evaporated glass slides

106 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review

amine oxide (C16DAO) solutions at different surfactant concentrations and upon addition of cinnamic acid or HCl. The variation of surface forces depending on the conditions is discussed, concerning the adsorption

structure of C16 DAO on glass surfaces. Also, the inter- surface interaction forces are compared with the forces which act in molecular assemblies in solutions. Fukada et al. (33) investigated the lyotropic phase behaviours of the nonionic and cationic (protonated) forms of dodecyldimethyl amine oxide (DDAO). Phase diagrams for DDAO + water, hydrochlric acid salt of DDAO (DDAOHCL) + water and an equimolar mixture of DDAO and DDAO HCl, (DDAO (1/2) HCl) + water systems were determined on the basis of polarized light Fig. 19 Replots of SANS Data for the C16DAO/Cinnamic microscopy, small angle x-ray diffraction, and differen- Acid/D2O System at Mixing Ratios X=0 and 0.2. tial scanning calorimetry. Also, water activity was meas- Reprinted from J. Colloid Interface Sci., Vol. 180, 98-105, ured to see the non ideality of water in lyotropic liquid Copyright with permission from Elsevier. crystaline phases. (“Q” is Bragg wave number and “I” is SANS intensity) Kiraly and Findenegg (34) determined the material and enthalpy balances of adsorption of the N,N-

dimethyldecyl amine N-oxide (C10DAO) and n-octyl b-

D-monoglucoside (C8G1) from dilute aqueous solutions onto hydrophilic silica glass and hydrophobic graphite (graphitized carbon black) at 298.15 K up to the critical micelle concentration. An automated flow sorption/ microcalorimeter system was used for simultaneous measurements of the adsorption isotherm and the enthalpy isotherm of displacement. Barlow et al. (35) studied the internal structure of oil -in-water microemulsion dropletes by SANS using contrast variation. The single chain surfactant used was N, N-dimethyldodecyl amine N-oxide, and the oil phase was one of two semipolar ethyl esters, ethylhexade- Fig. 20 Replots of SANS Data for the C16DAO/Cinnamic canoate or ethyl octanoate. Acid/D2O System at Mixing Ratios X=0.4, 0.6, and Clays are added to many emulsions designed for 1. industrial applications. During the emulsification sur- Reprinted from J. Colloid Interface Sci., Vol. 180, 98-105, face active agents adsorb onto clay and produce Copyright with permission from Elsevier. hydrophobic colloids. Adsorption of surfactant onto (“Q” is Bragg wave number and “I” is SANS intensity) clays is also of interest for environmental issues and enhanced oil recovery. Studies of clay - surfactant inter- have some gauche conformers i.e., less ordered than actions deal with ionic and neutral compounds. Gevers 7 23 that of 2C18 DAC. It was also noted that the molecular and Grandjean (36) studied that Li and Na NMR orientation and structure in the film showed strong pH spectrum of clay suspension in water have shown how dependence, presumably because of the strong interac- the smectite structure and nature of alkali counterions tion between the headgroups and the substrates (see modulate the quadrupolar interaction. These probes, Figs. 21 to 26). together with 13C and 2H nuclei, have been also used to Kato and Imae (32) investigated the surface forces study the interaction of dodecyldimethyl amine oxide between glass surfaces in aqueous hexadecyldimethyl with laponite and differently charged saponites dis-

107 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi

Fig. 23 (a) An IR RA Spectrum of an Aged One-Layer LB

Film of C18DAO on a Gold-Evaporated Glass Slide. (b) An IR Transmission Spectrum of an Fig. 21 (a) An IR RA Spectrum of One-Layer LB Film of Aged One-Layer LB Film of C18DAO on a CaF2 C DAO on a Gold-Evaporated Glass Slide. (b) An 18 Plate. (c) An IR/ATR Spectrum of an Aged One- IR Transmission Spectrum of a One-Layer LB Layer LB Film of C18DAO on a Ge Prism. All of Film of C DAO on a CaF Plate. (c) An IR/ATR 18 2 the spectra in this figure were measured after the Spectrum of a One-Layer LB film of C DAO on a 18 films were kept in a Desiccator for 24 h. Ge Prism. Reprinted from Langmuir, Vol. 15, 6890-6896, Copyright Reprinted from Langmuir, Vol. 15, 6890-6896, Copyright with permission from Am. Chem. Soc. with permission from Am. Chem. Soc. (Aqueous subphase at pH 5.8)

Fig. 24 (a) An IR RA Spectrum of an Aged One-Layer LB

Film of 2C18DAC on a Gold-Evaporated Glass Slide. (b) An IR Transmission Spectrum of an

Fig. 22 (a) An IR RA Spectrum of One-Layer LB Film of Aged One-Layer LB Film of 2C18DAC on a CaF2

2C18DAC on a Gold-Evaporated Glass Slide. (b) Plate. (c) An IR/ATR Spectrum of an Aged One- An IR Transmission Spectrum of a One-Layer LB Layer LB Film of 2C18DAC on a Ge prism. All of

Film of 2C18DAC on a CaF2 Plate. (c) An IR/ATR the spectra in this figure were measured after the

Spectrum of a One-Layer LB Film of 2C18DAC on films were kept in a desiccator for 24 h. a Ge prism. Reprinted from Langmuir, Vol. 15, 6890-6896, Copyright Reprinted from Langmuir, Vol. 15, 6890-6896, Copyright with permission from Am. Chem. Soc. with permission from Am. Chem. Soc. (Aqueous subphase at pH 5.8)

108 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review

Fig. 27 7Li Double-Quantum Filtered Spectra of Lithium- Fig. 25 (a) An IR RA Spectrum of a One-Layer LB Film Exchanged Laponite Suspended in Water (Clay of C DAO on a Gold-Evaporated Glass Slide + 18 Content, 17.8 g/L; Li Concentration, 13.0 mM) Prepared from the Aqueous Subphase at pH 3.0. (Top, q = 90°; Bottom, q = 54.7°). (b) An IR Transmission Spectrum of a One-Layer Reprinted from J. Colloid Interface Sci., Vol. 236, 290-294, LB Film of C18DAO on a CaF2 Plate Prepared from Copyright with permission from Elsevier. the Aqueous Subphase at pH 3.0. Reprinted from Langmuir, Vol. 15, 6890-6896, Copyright with permission from Am. Chem. Soc.

Fig. 28 7Li Double-Quantum Filtered Spectrum (q = 54.7°) of Lithium-Exchanged Saponite (Charge 0.35)(Clay Content, 40.0 g/L; Li+ Concentration, 37.1 mM) Suspended in Surfactant Solution (0.1 Fig. 26 (a) An IR RA Spectrum of a One-Layer LB Film M).

of 2C18DAC on a Gold-Evaporated Glass Slide Reprinted from J. Colloid Interface Sci., Vol. 236, 290-294, Prepared from the Aqueous Subphase at pH3.0. (b) Copyright with permission from Elsevier. An IR Transmission Spectrum of a One-Layer LB tion, the surface electric potentials were estimated. Film of 2C18DAC on a CaF2 Plate Prepared from the Aqueous Subphase at pH 3.0. Kawasaki and Maeda (38) used Fourier-transform Reprinted from Langmuir, Vol. 15, 6890-6896, Copyright infrared spectroscopy (FT-IR) coupled with attenuated with permission from Am. Chem. Soc. total reflection (ATR) to investigate the proposed H-

bond between the head groups of C12 DAO (a = 0.5) in persed in surfactant solutions (see Figs. 27 & 28). both an aqueous medium and the solid state. To clarify Kakehashi et al. (37) examined the effects of the this hydrogen bond (H-bond), they focused on the OH hydrocarbon chain length, the bulkiness of the polar band of the headgroup of C12 DAO (a = 0.5 and 1) in head group, the added salt concentration, the surfactant this study (see Figs. 29 to 32). concentration, and temperature on the hydrogen ion Dielectric relaxation spectroscopy is a very powerful titrations of amine oxides. The surfactants studied are method to investigate the motion of molecules possess- alkyldimethyl amine oxides (CnDAO) with hydrocarbon ing electric dipole moments. Itatani and Shikata (39) Chain lengths of 10-16, and N,N-bis(2-hydroxy ethyl) examined the dielectric relaxation behaviour of aque- alkyl amine oxide (CnDHEAO) with hydrocarbon chain ous dodecyldimethyl amine oxide (DDAO) solutions by lengths of 10-14. From the results of hydrogen ion titra- changing the concentrations of DDAO, NaBr and the

109 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi

Fig. 31 Dependence of a Continuous Absorption Band (1300-800cm-1) of the Solid C12DAO on the

Degree of Ionization, a. The peak intensity IN is Fig. 29 (A) FT-IR Spectra of Solid C12DAO with normalized by that of the symmetric CH2 Different Degrees of Protonation, a (a = 0, 0.5, stretching band. Reprinted from Langmuir, Vol. 17, 2278-2281, Copyright and 1), at 25℃. (B) Comparison of the IR Spectra with permission from Am. Chem. Soc. of C12DAOHCl with that of C12DAOHNO3. Reprinted from Langmuir, Vol. 17, 2278-2281, Copyright with permission from Am. Chem. Soc.

Fig. 32 FT-IR-ATR Spectra of C12DAO with Different Degrees of Protonation, a (a = 0, 0.5, and 1), in Aqueous Solutions at 25℃. The weight percent of the surfactants is 55. Reprinted from Langmuir, Vol. 17, 2278-2281, Copyright with permission from Am. Chem. Soc.

Fig. 30 (A)FT-IR-ATR Spectra of C12DAO with Different Degrees of Protonation, a (a = 0, 0.5, and 1), in the Aqueous Liquid Crystalline Phase (Hexagonal) pH value to elucidate dynamic features in micelles of at 25℃. DDAO in aqueous solutions. The Weight Percent of the Surfactants is 55.(B)FT- Adsorption and self assembly are central characteris- IR-ATR Spectra of C1DAOHCl in Aqueous tics features of surfactant molecules. The adsorption of Solutions of Various Concentrations at 25℃.The surfactants from solutions onto solid surfaces has been weight percent of C1DAOHCl(from top to bottom) investigated over many years in relation to numerous was 40, 30, 20, and 5. For comparison, the FT-IR- practical applications, as well as the scientific interest. ATR spectrum of the C12DAOHCl (55 wt%) is Hideya Kawasaki et al. (40) investigated the effect of also shown (a). The spectral subtraction of water protonation on the aggregate structures of tetradecyl- from the IR spectra was performed on only adimethyl amine oxide (C14DAO) surfactants at mica- C1DAOHCl spectra of 5 wt%. solution and graphite - solution interfaces by atomic Reprinted from Langmuir, Vol. 17, 2278-2281, Copyright force microscopy (AFM). C DAO solutions are mix- with permission from Am. Chem. Soc. 14 tures of the nonionic (C14H25(CH3)2N → 0) and the ion-

ized (protonated) cationic species (C14H25(CH3)2N-

110 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review

OH). The composition aM (the degree of ionization) in the micelle is determined by pH under a given ionic strength. The mixture of the protonated and unprotonated species show an extreme synergism due to the short range attractive interaction between the headgroups. Pettersson and Rosenholm (41) reported on microcalorimetric studies of the adsorption of alkyldimethyl amine oxides (CnDAO with n = 8, 10 and 12) on mesoporous and slightly negatively charged silica gel from aqueous solutions at 298.15 K. Since the pH was natural, the study of CnDAO concerns adsorp- Fig. 33 Dependence of pH on x’HCl for C12AO-NaDS-HCl- tion from mixed nonionic-cationic surfactant solutions. H2O and C12AO-Mg(DS)2-HCl-H2O Solutions at Due to increase in pH, the proportion of cationic surfac- xAO = xMeDS = 0.0005 and t = 50℃. tant decreases at increasing surfactant content. The Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright adsorption from dilute solution of all surfactants studied with permission from Am. Chem. Soc. was exothermic and enthalpically driven due to formation of H-bonding between nonionic headgroups and surface silanol groups, and due to electrostatic interactions between ionic adsorbates and oppositely charged dissociated surface silanol groups. Pettersson and Rosenholm (42) also studied the x-potential of granular silica gel interacting with aqueous solutions of

CnDAO(with n = 8, 10 and 12). The x-potential was determined by measuring the streaming potential across the capillary of the plug of sample. Aqueous mixtures of alkyl amine oxides and dodecyl sulfates draw much attention owing to their peculiar physico-chemical behaviour and miscellaneous applica- Fig. 34 The Dissolution Temperature versus x’ in the tions. Smirnova et al. (43) examined that strong syner- AO C12-AO-NaDS-HCl-H2O System at xtotal = 0.001. gistic effects are responsible for the specific phase Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright behaviour of amine oxide-sodium (magnesium) dodecyl with permission from Am. Chem. Soc. sulfate micellar solutions. The dissolution temperature and the CMC value are greatly dependent on relative surfactant concentration and pH. The phase diagrams in scanning calorimetry. Effects of alkyl chain-length on the two studied systems C12 AO- Me DS- H2O are quite the dissolution temperature for a homologous series of similar at low pH and differ at the natural acidity. At octadecyl-, hexadecyl-, and tetradecyldimethyl amine low pH, the complex AOH+DS- is crystallized over a oxide were also examined. It was observed that the wide range of surfactant based concentrations (see Figs. transition temperature and associated thermodynamic 33 to 40). quantities DH and DS increased systematically with the Solid-solution phase behaviour of surfactant mix- chain length. tures is important both in theoretical and applied aspects and has been studied extensively. The dissolu- 6 Applications of Amine Oxides tion temperature of binary mixed surfactants has been reported to show a temperature maximum where the The application of these compounds varies with the complex between the two components is formed. size of the main alkyl chain and the substituents on the Kawasaki et al. (44) studied the effects of protonation nitrogen atom of amine oxide. For example, the coco (ionization) of alkyldimethyl amine oxides on the disso- range alkyldimethyl amine oxide serve as very effective lution temperature in aqueous media by differential foam boosters in light duty detergents and shampoos

111 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi

Fig. 35 The Dependence of the pH Value on x’AO in the C -AO-NaDS-HCl-H O Solutions at x = 0.001. 12 2 total Fig. 38 The Dissolution Temperature versus x’ in the Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright AO with permission from Am. Chem. Soc. C12-AO-Mg(DS)2-HCl-H2O System at Various pHs; the Total Surfactant Content is 0.1 mol% (0.1 mol%, 10 wt% at Natural pH). Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright with permission from Am. Chem. Soc.

Fig. 36 The Dissolution Temperature as a Function of x’HCl

in the C12AO-NaDS-HCl-H2O System at xAO =

xNaDS = 0.0005.

Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright Fig. 39 The Dependence of the pH Value on x’AO in the

with permission from Am. Chem. Soc. C12-AO-Mg(DS)2-HCl-H2O Solutions of Various

Acidity, xtotal = 0.001. Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright with permission from Am. Chem. Soc.

(45), while the higher stearyl amine oxides can be used as hair conditioners (46). Tomah company of Milton, WI developed a series of amine oxide namely Tomah AO-728 special, AO-14-2, AO-405 and AO-455 having property of high foaming, moderate foaming , low foaming and extremely low foaming respectively, get- ting application in various types of cleaners. Tomah Fig. 37 The Dissolution Temperatures as a Function of AO-728 special is an economical replacement for lauryl dimethyl amine oxide and many alkanolamides. Tomah x’NaOH in the C12AO-NaDS-NaOH-H2O System at AO-14-2 is considered a more environmentally safe x’AO = 0.8 and xtotal = 0.001; x’NaOH = xNaOH/(xAO +

xNaOH). alternative to solvent coating systems. In particular, Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright AO-14-2 can replace the use of glycol ethers in clean- with permission from Am. Chem. Soc. ing compounds. AO-405 and AO-455 are especially

112 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review

Guest and guest-guest interactions. Recently photo- physical and photochemical properties of intercalation compounds have attracted increasing interest. By use of dodecyldimethyl amine N-oxide. Ogawa (49) prepared smectite / dodecyldimethyl amine N-oxide intercalation compounds a specific type of surfactant - modified clays. Intercalation compounds with two different arrangement of the intercalated dodecyldimethyl amine N-oxide were obtained, depending on the adsorbed amounts.

Fig. 40 The Dissolution Temperature as a Function of x’HCl Several instances of synergistic interaction have been

in the C12AO-Mg(DS)2-HCl-H2O System at xAO = identified between amine oxides and alcohol ethoxy- et al xMg1/2DS = 0.0005. lates in various surfactant formulations. Miller . Reprinted from Langmuir, Vol. 18, 3446-3453, Copyright (50) examined whether these benefits could be observed with permission from Am. Chem. Soc. within the framework of generic hard surface cleaning formulations. Comparative evaluations were also car- ried out to determine the performance characteristics of suited for hard surface applications where low or zero low- and zero-phosphate systems in which foam generation is required. alkyldimethyl amine oxides and linear alcohol ethoxy- Smith et al. (47) developed, high active alkyldimethyl lates are used. Best cleaning was observed with 1:1 amine oxide powder permits the use of this valuable mixtures of the subject surfactants, but substantial surfactant in water sensitive formulations such as bar improvements over alcohol ethoxylate alone also were soaps. Study of the various amine oxide homologs in noted with formulations that contained lower ratios of key performance properties of soap bars showed them amine oxide. These system displayed good cleaning to be effective foam modifiers, plasticizers and syner- performance when tested on vinyl floor tiles soiled gistic lime soap dispersants. The solid amine oxides with an oily/ particulate soil. were found to be a versatile additive which could readi- Mel’nikova and Lindman (51) investigated pH con- ly be formulated into a wide variety of personal care trolled DNA condensation in the presence of dode- bars. cyldimethyl amine oxide (DDAO). Interactions between Crutcher et al. (48) studied the interaction of solid DNA and amphiphilic systems have attracted much alkyldimethyl amine oxide (AX) and ditallowdimethyl attention from the pharmaceutical perspective: e.g, ammonium chloride (DTMAC) and ditallowdimethyl cationic lipid systems are found to be effective as a ammonium sulfate (DTMAS) quats in representative nonviral vehicle for controlled gene transfer. In the types of fabric softener systems with particular focus on investigation it was observed that positively charged synergistic behaviour. Softening, whiteness retention, DDAO ions in vesicular form behave as a more effi- wetting, static build up and detersiveness were evaluat- cient DNA-condensing agent than those in the micellar ed for laundry rinses, laundry detergents and dryer form. sheets. In laundry rinses, blends of amine oxide and Aqueous mixtures of the single - chain zwitterionic

DTMAC proved to be synergistic for improving the surfactant alkyldimethyl amine oxide (C14DMAO) with wetting of cotton towels. Although no synergism was other surfactants and cosurfactants are known to pro- observed in laundry detergents, formulations containing duce a very rich phase behaviour with different amine oxide (AX) gave better detersiveness than sys- microstructures when the amphiphilic composition is tems with DTMAC without the splotching associated varied. From all the phases, the vesicle (La) phase is of with the quaternary salt. In dryer sheets, it was discov- particular interest and has attracted a large number of ered that blends of amine oxide and DTMAS gave syn- investigations because of the potential for these equilib- ergistic softening of cotton towels and were unexpect- rium aggregates to serve as good biological model edly effective in preventing static charge build up on membranes as containers for encapsulation and eventu- polyester fabric (see Figs. 41 to 55). al release of drugs, flavors, and fragrances, and as

113 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi

Fig. 44 Laundry Rinse Synergy: Softness Rating. Fig. 41 Laundry Rinse: Softness Rating. Variability = ± Variability = ± 0.3 for 95% confidence level. 0.3 for 95% confidence level. Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Copyright with permission from Am. Oil Chem. Soc. Copyright with permission from Am. Oil Chem. Soc.

Fig. 42 Laundry Rinse: Whiteness Rating. Variability = ± Fig. 45 Laundry Rinse Synergy: Whiteness Rating. 0.5 for 95% confidence level. Variability = ± 0.5 for 95% confidence level. Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Copyright with permission from Am. Oil Chem. Soc. Copyright with permission from Am. Oil Chem. Soc.

Fig. 43 Laundry Rinse: Wetting Rating after Four Cycles. Fig. 46 Laundry Rinse Synergy: Wetting Rating after Four Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Cycles. Copyright with permission from Am. Oil Chem. Soc. Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Copyright with permission from Am. Oil Chem. Soc.

114 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review

Fig. 50 Laundry Detergent: Wetting Rating after Four Fig. 47 Laundry Rinse Synergy: Antistatic Activity after Cycles. One Cycle. Values for untreated fabrics are: Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, polyester, 2.63 kV; cotton/polyester, 1.01 kV; Copyright with permission from Am. Oil Chem. Soc. cotton, 4.09 kV. Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Copyright with permission from Am. Oil Chem. Soc.

Fig. 51 Laundry Detergent: Detersiveness Rating from Fig. 48 Laundry Detergent: Softness Rating. Variability = Tergotometer Evaluations of Dust-Sebum Cotton/ ± 0.3 for 95% confidence level. Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Polyester Test Fabric. Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Copyright with permission from Am. Oil Chem. Soc. Copyright with permission from Am. Oil Chem. Soc.

Fig. 49 Laundry Detergent: Whiteness Rating. Variability Fig. 52 Dryer Sheet Synergy. Softness rating. Variability = = ± 0.5 for 95% confidence level. ± 0.3 for 95% confidence level. Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, Copyright with permission from Am. Oil Chem. Soc. Copyright with permission from Am. Oil Chem. Soc.

115 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) S.K. Singh, M. Bajpai and V.K. Tyagi

microreactors for the formation of a range of inorganic nanoparticles. Hao et al.(52) investigated a cationic / anionic surfactant system that consists of the zwitteri-

onic alkyldimethyl amine oxide (C14 DMAO) and the

anionic dihydro-perfluorooctanoic acid (C6F13CH2 COOH, DHPFOA, pKa = 3.35). In the investigated system, the cationic surfactant is produced by the protonation of the amine oxide by the perfluorooctanoic acid. Fig. 53 Dryer Sheet Synergy: Whiteness Rating. As a result of this proton transfer reaction, the mixed Variability = ± 0.5 for 95% confidence level. system does not contain excess salt as do other studied Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, cationic / anionic surfactant systems. With increasing Copyright with permission from Am. Oil Chem. Soc. concentrations of DHPFOA; L1-phase, a viscous L1-

phase, a two phase L1/La-region, and slightly vis-

coelastic La-phase were observed. The main purpose of this investigation was to demonstrate that in many cases vesicles in aqueous mixtures of cationic and anionic surfactants do not form spontaneously but may be the result of the shear forces that are due to the mixing of the components.

7 Anti-Microbial Activity of Amine Oxides with Variation in Chain Length Alkyldimethyl amine oxides has been shown to have pronounced anti-microbial activity when used individu- Fig. 54 Dryer Sheet Synergy: Wetting Rating after Four ally or in combination with alkyl betaines. Although Cycles. several studies have been conducted with these com- Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, pounds in combinations, only equimolar concentrations Copyright with permission from Am. Oil Chem. Soc. of the C12/C12 and C16 /C14 chain lengths for the betaine and the amine oxide, respectively, have been investigated. Birnie et al. (53) investigated the anti-microbial

activity of a wide range of chain lengths (C8 to C18 ) for both the amine oxide and betaine and also attempted to correlate their micelle - forming capabilities with their biological activity. Anti-microbial activity was found to increase with increasing chain length for both homologous series up to a point, exhibiting a cut off effect at chain lengths of approximately 14 for amine oxide and

16 for betaine. Additionally, the C18 oleyl derviative of both compounds exhibited activity in the same range as Fig. 55 Dryer Sheet Synergy: Antistatic Activity after One the peak alkyl compounds. Although each of these Cycle. Values for untreated fabrics are: polyester, compounds have shown pronounced anti-microbial 10.9 kV; cotton/ polyester 2.2 kV; cotton, 2.9kV. activity alone against a variety of microorganisms, they Reprinted from J. Am. Oil Chem. Soc., Vol. 69, 682-689, have also been used in combination to exhibit a syner- Copyright with permission from Am. Oil Chem. Soc. gistic effect (54). The variation in length of the long-hydrocarbon tail is thought to influence the extent of anti-microbial

116 J. Oleo Sci., Vol. 55, No. 3, 99-119 (2006) Amine Oxides: A Review activity. Like most other surfactants, they are believed ence Series, Vol. 82, p. 40 (1999). to be membrane perturbants, disrupting the cell mem- 5. O. LEVENSPIEL, Chemical Reaction Engineering, 3rd edn., John Wiley & Sons, Inc, pp. 21-25 (1999). brane of the microorganism. It is believed that interac- 6. C.N. WANG and L.D. METCALFE, The Determination of tion with the surface of the microorganism is a function Unreacted Amines in Long Chain Amine Oxides by Potentio- of the polar head groups of the amine oxide, betaine or metric Titration, J. Am. Oil Chem. Soc., Vol. 62, 558-560 (1985). mixture of these molecules and that the hydrocarbon 7. Y. HAYASHI, F. SHIRAI, T. SHIMIZU, Y. NAGANO and K. tail subsequently becomes integrated with the lipid TERAMURA, Synthesis and Properties of 2-Alkoxy-N,N- bilayer of the cell membrane. This integration causes a Dimethylethylamine N-Oxides, J. Am. Oil Chem. Soc., Vol. 62, disruption in the membrane and inevitably causes leak- 555-557 (1985). age of the cell contents. The length of the alkyl chain of 8. W.N. MARMER and W.M. LINFIELD, Soap Based Detergent Formulations: XVII. Synthesis and Surface Active Properties of the surfactants is thought to contribute to the extent of Alkyl Benzene Derived Amine Oxides, J. Am. Oil Chem. Soc., this membrane disruption, because the higher chain Vol. 53, 73-76 (1976). lengths may be incorporated into the lipid bilayers of 9. P.R. KUST and J.F. RATHMAN, Synthesis of Surfactants by the plasma membrane. The increased hydrophobic Micellar Autocatalysis: N, N-Dimethyldodecylamine N-Oxide, effect of these longer chain tails may aid in this disrup- Langmuir, Vol. 11, 3007-3012 (1995). tion. 10. A. PINAZO and X. DOMINGO, Turbidimetric Analysis of Amine Oxides and Amine Oxide - Anionic Surfactant Mixtures, J. Am. Oil Chem. Soc., Vol. 73, 143-147 (1996). 8Safety of Amine Oxides 11. M.E. TURNEY and D.W. CANNELL, Alkaline Methylene Blue Method for Determination of Anionic Surfactants and for Amine Amine oxides have low potential for bioaccumula- Oxides in Detergents, J. Am. Oil Chem. Soc., Vol. 42, 544-546 tion in aquatic tissues, indicating low potential for bio (1965). concentration in terrestrial organisms, also this is highly 12. N. FUNASAKI, The Dissociation Constants of Acid-Base Indi- removed by conventional sewage treatment. Sansoni cators on the Micellar Surface of Dodecyldimethyl Amine (55) demonstrated that amine oxides surfactants are Oxide, J. Colloid and Interface Science, Vol. 60, 54-59 (1977). nonvolatile and readily biodegradable under aerobic and 13. N. FUNASAKI, A Consideration Concerning the Surface Poten- tial of Mixed Micelles of Sodium Dodecyldecaoxyethylene Sul- anaerobic conditions, according to SDA research. fate and Dodecyldimethylamine Oxide, J. Colloid and Interface All available information on amine oxides demon- Science, Vol. 62, 189-190 (1977). strates it has low-to-moderate level of toxicity. 14. S. IKEDA, M. TSUNODA and H. MAEDA, The Effects of Ion- ization on Micelle Size of Dimethyldodecylamine Oxide, J. Col- loid and Interface Science, Vol. 70, 448-455 (1979). Acknowledgment 15. T. IMAE and S. IKEDA, Intermicellar Correlation in Light Scat- The authors are grateful to late Prof. R.K. Khanna, tering from Dilute Micellar Solutions of Dimethyloleylamine Oxide, J. Colloid and Interface Science, Vol. 98, 363-372 Department of Oil and Paint Technology, H.B. Techno- (1984). logical Institute Kanpur, for his valuable guidance and 16. T. IMAE, R. KAMIYA and S. IKEDA, Electron Microscopic motivation. Observation of Rod - Like Micelles of Dimethyloleylamine Oxide Regenerated from Its Aqueous Solutions, J. Colloid and Interface Science, Vol. 99, 300-301 (1984). References 17. T. IMAE and S. IKEDA, The pH Dependence of Upper and 1. L.W. BURNETTE, Miscellaneous Nonionic Surfactants, in Non- Lower Consolute Phase Boundaries for Aqueous NaCl Solutions ionic Surfactants (M.J. SCHICK, ed.), Surfactant Science Series, of Dimethyloleylamine Oxide, J. Colloid and Interface Science, Vol. 1, pp. 403-410 (1966). Vol. 113, 449-455 (1986). 2. L. DAHLGREN, L. AVE, D. FERRY and D. STEICHEN, Nitro- 18. T. IMAE, M. SASAKI and S. IKEDA, Formation of Iridescent gen - Based Oleochemicals Production and Application, Inform, Solutions of Dimethylalkylamine Oxides, J. Colloid and Inter- Vol. 11, 508-512 (2000). face Science, Vol. 131, 601-602 (1989). 3. C.J. TONEY, F.E. FREDLI and P.J. FRANK, Kinetics and 19. J.C. BRACCKMAN and J.B.F.N. ENGBERTS, Effect of Surfac- Preparation of Amine Oxides, J. Am. Oil Chem. Soc., Vol. 71, tant Charge on Polymer Micelle Interaction: n-Dodecyldimethyl- 793-794 (1994). amine Oxides, Langmuir, Vol. 8, 424-428 (1992). 4. O.D. 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