Synthesis and Surface Properties of Glycerol ... - ACS Publications

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Synthesis and Surface Properties of Glycerol Based C8 Chain Monoethers Sandra Bigot,† Herv
e Bricout,‡ Isabelle Suisse,*,† Andr
e Mortreux,† and Yves Castanet*,† †

Universit
e de Lille Nord de France, ENSCL, Unit
e de Catalyse et Chimie du Solide, UMR 8181, BP 90108, 59652 Villeneuve d'Ascq Cedex, France ‡ Universit
e de Lille Nord de France, Facult
e Jean Perrin, Unit
e de Catalyse et Chimie du Solide, UMR 8181, Rue Jean Souvraz, SP 18, 62307 Lens Cedex, France ABSTRACT: The telomerization of butadiene with solketal (1,2-isopropylideneglycerol) in the presence of palladium complexes has been studied under aqueous biphasic conditions. This reaction followed by deprotection in acid medium leads to monooctadienyl ethers of glycerol (linear and branched) with a high selectivity into the linear isomer. The corresponding glyceryl monooctyl ethers are obtained by hydrogenation of the octadienyl ethers. The surface properties of these two classes of compounds have been appraised and compared showing the influence of the double bonds on these properties.

’ INTRODUCTION Oxygenated amphiphilic solvents are an important class of solvents which have found applications in many industries such as cleaning, pharmaceutical, medicine, inks, and perfumery.1 These solvents combine the advantages of solvents for solubilization of organic or inorganic compounds and of surfactants which help the solubilization in micellar systems or microemulsions. Among this class of solvents, ethers derived from ethylene glycol and propylene glycol have been extensively studied. For glycol ethers derived from ethylene oxide (the E series), five glycol ethers are classified “toxic for reproduction” and some of them are today forbidden in Europe.2 In the case of glycol ethers derived from propylene oxide (the P series), none, until now, has shown any effect on reproduction in experimental studies, with the exception of 1-propylene glycol 2-methyl ether (1PG2ME) and its acetate (1PG2MEA).3 They represent actually the main substitutes for the ethylene glycol ethers, but they also derive from petrochemistry and suffer from the label “glycol ether” as well. Thus the development of substitutes for glycol ethers is of interest. In this context, ethers derived from glycerol could play this role. Actually, in the context of green chemistry, the increased expansion of biodiesel has led to a large availability of glycerol as a byproduct in biodiesel manufacturing and new efficient transformations of glycerol into valuable chemicals are needed.4 Some publications described the direct synthesis of glycerol alkyl ethers. Behr5 and Mravec6 reported the etherification of glycerol with isobutylene in the presence of heterogeneous catalysts such as Amberlyst-15 or zeolites or over homogeneous catalysts such as p-toluenesulfonic acid in order to synthesize m-GTBE (monoglycerol tert-butyl ethers) and h-GTBE (higher glycerol tert-butyl ethers). Sulfonic acid functionalized mesostructured silicas have also demonstrated excellent catalytic behavior in the etherification of glycerol with isobutylene to yield tert-butylated derivatives.7 These products could also be obtained from glycerol and tert-butyl alcohol in the presence of similar catalysts.8 In every case, a mixture of the mono-, di-, and r 2011 American Chemical Society

triethers was obtained. To our knowledge, only a few publications described the direct selective monoetherification of glycerol. For instance, the synthesis of long alkyl chain ethers through etherification of biomass-based alcohols with 1-octene over heterogeneous acid catalysts was investigated by Weckhuysen.9 In the same way, Barrault10 described the synthesis of monoalkyl glyceryl ethers with alkyl alcohols, olefins, and dibenzyl ethers using an acid functionalized silica as catalyst. Moreover, selective synthesis of 1-O-alkyl glycerol has been recently performed by catalytic reductive alkylation of glycerol in the presence of 0.5 mol % Pd/ C under 10 bar of hydrogen using a Brønsted acid as cocatalyst.11 In order to obtain selectively the 1-monoalkyl ether of glycerol, protected glycerol as solketal (1,2-isopropylideneglycerol) was preferentially used. For example, Bachir-Lesage12 described the synthesis of glyceryl ethers by direct alkylation of solketal with various bromoalkanes (from C6 to C12) in the presence of potassium hydroxide. Rivaux proposed an easier and cleaner synthesis using phase transfer catalysis.13 In their procedure, short chain (C4
C6) glyceryl 1-monoethers derived from glycerol are obtained by reaction of solketal with 1-bromoalkanes in the presence of tetrabutylammonium bromide.14 As these products have the characteristics of solvents as well as surfactants, they can be entitled “green solvo-surfactants” and constitute a new class of compounds that should be considered for the replacement of glycol ethers. However, the main drawback of their synthesis lies in the formation of stoichiometric amounts of alkali bromide as byproduct. On the other hand, an atom-economical way15 to synthesize alkadienyl ethers is the telomerization of a conjugated diene (butadiene16 or isoprene17) with an alcohol in the presence of palladium catalysts.18 In this context, after the preliminary work of Gruber,19 who in 1993 was the first to describe the transition metal catalyzed telomerization of butadiene with glycerol to afford glyceryl unsaturated Received: April 12, 2011 Accepted: July 20, 2011 Revised: July 19, 2011 Published: July 20, 2011 9870

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Industrial & Engineering Chemistry Research mono-, di-, and trioctyl ethers (Scheme 1), we and others more recently studied this reaction. For instance, Behr20 transposed the reaction into aqueous medium using the hydrosoluble ligand TPPTS (sodium salt of trisulfonated triphenylphosphine). The low solubility of butadiene and telomers in water led to a biphasic system, allowing an easy recycling of the catalyst and an improved selectivity into monotelomers due to its reactive extraction (product mixture containing more than 80% monooctadienyl ethers was obtained).21 With the use of the TOMPP (tris(o-methoxyphenyl)phosphine) ligand, higher activities compared to the TPPTS/Pd catalyst were reported but a mixture of the different telomers was always obtained.22 In our laboratory, we studied also this reaction under aqueous biphasic conditions in order to optimize the different selectivities into each telomer, but unfortunately, we were unable to produce the telomers with selectivity close to 100%.23 This paper describes the selective synthesis of the monooctadienyl and monooctyl ethers of glycerol in order to determine their different surfactant properties as, to our knowledge, no such study has been reported in the case of glyceryl C8 ethers.

’ RESULTS AND DISCUSSION As the direct telomerization applied to glycerol, even under optimized conditions, leads to a mixture of monotelomers, ditelomers, and even tritelomers that are difficult to separate, Scheme 1. Telomerization of Butadiene with Glycerol

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we envisioned using solketal as precursor because it can be easily obtained from glycerol by acetalization.24 The telomerization of butadiene with this compound followed by hydrolysis should furnish only monoethers (linear and branched). Then, catalytic hydrogenation of the two double bonds of the C8 chain should lead to the monooctyl ethers (see Scheme 2). In order to develop an environmentally friendly process, we have chosen to perform the telomerization reactions in water. First, the reaction was carried out under the conditions that we have previously used for the butadiene
glycerol telomerization,23 i.e., in the presence of Pd(acac)2/TPPTS (1/5) dissolved in an alkaline solution of sodium hydroxide at 80 °C. Excellent chemioselectivity was obtained with a 1/2 ratio of 98/2 (entry 1, Table 1), but surprisingly, the conversion of solketal after 3 h reached only 3% whereas, with glycerol, a conversion of 93% was obtained after only 2.5 h. Confronted with these disappointing results, we checked the influence of different experimental parameters in order to increase the conversion. The results are listed in Table 1. The change of the phosphine ligand from TPPTS to TPPMS (sodium salt of monosulfonated triphenylphosphine), keeping constant the other catalytic conditions, induced a high increase in the solketal conversion (81% conversion after 3 h) (entry 2, Table 1) with nevertheless a lower linear to branched ratio of 91/9. This result could be explained by the more amphiphilic character of TPPMS compared to TPPTS; in that case, a better solubility in the aqueous phase of the ketal is expected as well as a higher solubility of the catalyst in the organic phase, resulting in a higher conversion. This encouraging result prompted us to increase the reaction time, and after 5 h, a total solketal conversion was obtained with the same 1/2 ratio. As only 2 equiv of butadiene is needed to form the monotelomers, we decreased the butadiene/ solketal ratio to 2.5. In that latter case, the telomerization is almost as effective as with 7.5 equiv of butadiene with 78% conversion obtained after 3 h but more selective since a 1/2 ratio of 95/5 was

Scheme 2. Telomerization of Butadiene with Solketal Followed by Acid Hydrolysis and Hydrogenation

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Table 1. Influence of Various Experimental Parameters on the Telomerization of Butadiene with Solketala

a b

1b

2b

3

98

2

81

91

9

100

91

9

3

78

95

5

17

100

95

5

entry

phosphine

molar ratio butadiene/solketal

t (h)

1

TPPTS

7.5

3

2

TPPMS

7.5

3

3

TPPMS

7.5

5

4

TPPMS

2.5

5

TPPMS

2.5

solketal conversion (%)

Conditions: solketal = 29 mmol (3.9 g); Pd(acac)2 = 1.8  10
2 mmol; TPPTS = 0.087 mmol; aqueous NaOH solution (1 M) = 0.9 mL; T = 80 °C. Under these conditions butadiene dimers (linear and cyclic) were also formed but in very low amounts (the sum does not exceed 1
2%).

Figure 1. Determination of solubility of the glyceryl monooctadienyl ether fraction by light diffusion.

observed. Increasing the reaction time to 17 h allowed the reaction to go to completion with the same 1/2 ratio. After reaction, the palladium complex was eliminated by filtration. For the NMR analysis, the protected monotelomers could be easily separated from the reaction mixture by extraction with diethyl ether. After evaporation of the solvent, a separation on a silica column was carried out with a petroleum ether/diethyl ether (3/1) eluent mixture allowing the obtaining of a sample of each isomer 1 and 2 with high purity which could be characterized by NMR. After characterization of the isomers 1 and 2, their deprotection by acid hydrolysis in the presence of aqueous hydrochloric acid led to samples of pure glyceryl ethers 3 and 4.21,23 Nevertheless, for the evaluation of the detergence properties, the crude 1/2 mixture with a ratio of 95/5 was used directly without further purification. The solketal ethers were first deprotected by acid hydrolysis to afford the monoctadienyl ethers of glycerol 3/4. Hydrogenation on Pd/C at 50 bar of H2 of the mixture led to the monooctyl ethers 5/6 with a total conversion and the same linear to branched ratio of 95/5. The linear 511 and the branched 625 monooctyl ethers could be separated over a silica column, and NMR analyses have been performed and are described in the Experimental Section. However, such separation is rather tedious and, for an industrial point of view, the physical characteristics have been evaluated using the mixture of deprotected monotelomers 3/4 issued from the telomerization as well as those of their hydrogenated homologues 5/6 in order to appreciate their potential properties as detergents. The water solubility at 25 °C was first determined by the progressive addition of distilled and deionized water in a previously weighed amount of the ethers. Solubility values of the octadienyl and octyl compounds were found respectively at 40 and 5.7 mM. This latter value is the same as the one reported

Figure 2. Variation of the surface tension of aqueous solutions of monooctadienyl or monooctyl ethers (95/5 linear/branched) as function of the concentration C at 25 °C.

by Bachir-Lesage26 for the linear glyceryl monooctyl ether. This shows that the presence of 5% branched ether in the crude mixture has little influence on the solubility. The solubility of the octadienyl ethers, which has not been previously reported, was also determined more precisely by light diffusion with an optic fiber probe coupled to a spectrophotometer. Figure 1 presents the results obtained. The break in the curve corresponds to a solubility limit concentration of about 42 mM. This value, close to the one previously found by addition of water to the ethers, is more than 7 times higher than the one of the saturated counterpart octyl ethers at the same temperature. It appears that, as expected, the presence of the two double bonds strongly influences the water solubility of the ether. Then, the surface activities of a mixture of octadienyl ethers of glycerol and one of their hydrogenated homologues were evaluated by measuring the surface tension at different concentrations (see Figure 2). Upon increasing the concentrations of the two classes of glyceryl ethers, a continuous decrease of the surface tension down to values around 30
25 mN 3 m
1 was observed over a long range of concentrations. However, for the same concentration, the saturated ethers exhibit a lower surface tension (about 8 mN 3 m
1). At higher concentrations, from the break of the curves, the critical micellar concentration (cmc) can be estimated. Moreover, from the curves and using the Gibbs equation which for a nonionic surfactant 9872

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Table 2. The cmc's, Surface Tensions, and Areas of Glyceryl Ethers surface tension compound

cmc

γ at cmc

area

(mM)

(mN 3 m
1)

a (Å2)

monooctadienyl ethers of glycerol

8.3

30

45

monooctyl ethers of glycerol

7a

24

45

Concentration corresponding to the break of the curve γ = f(concentration) (see text).

a

takes the form indicated below, the surface excess concentration Γ (mol 3 m
2) can be calculated. Gibbs equation:
1 dγ Γ¼ 2:303RT d log C

!

Knowing Γ, it is easy to evaluate the effective area a occupied by each adsorbed surfactant molecule, which is done by the following equation: a¼

1 NA Γ

in which NA is the Avogadro number. The different values of the critical micellar concentration (cmc), the surface tension γ at the cmc, and the calculated areas a for the monooctadienyl and octyl ethers of glycerol are reported in Table 2. The break of the curves γ = f(concentration) for both the octyl and octadienyl ethers arises for similar values of about 7
8 mM; these values are related to the presence of two hydroxyl groups and a carbon chain with a length of eight atoms. Moreover, the minimum surface tension values of the two classes of ethers are close to those generally found for glucidoamphiphilic compounds. However, it must be noticed that, in the case of the mixture of octyl ethers, the break of the curve occurs at a concentration slightly higher than the limit of solubility (7 mM versus 5.7 mM); thus it is more characteristic of the limit of solubility than of the cmc. Thus, with octyl ethers, a cmc value cannot be define although a cmc value of 7.1 mM (higher than the limit of solubility) has been reported for pure linear monooctyl ether of glycerol.26 This value, as well as the solubility limit and surface tensions γ, was similar for the pure linear glyceryl octyl ether and the mixture 95/5 linear/branched octyl ethers. The same remark can probably be made for the octadienyl ethers. Thus, the direct use of the crude product led to similar results in terms of surfactant activity as the pure linear ether. Finally, as for the two classes of glyceryl ethers (saturated and unsaturated), the slopes of the curves γ = f(log C) were almost the same; thus the calculated a values are identical. This fact seems to indicate that the area at the water
air interface of the glyceryl ethers is determined by the hydrophilic glyceryl moiety and not by the nature (saturated or unsaturated) of the bending C8 chain.27

’ EXPERIMENTAL SECTION Solketal was purchased from Aldrich, and butadiene was purchased from Linde Gas France. TPPTS and TPPMS were synthesized using previously reported procedures.28 Pd(acac)2

and Pd/C (5% Pd on activated carbon, reduced, dry powder) were purchased from Strem Chemicals. Instrumentation. Gas chromatographic (GC) analyses were carried out on a Varian 430-GC apparatus equipped with a flame ionization detector and a CP-Sil 5 CB column (30 m  0.32 mm i.d.). The different NMR spectra were recorded on a Bruker AC 300 spectrometer (1H, 300 MHz; 13C, 75.5 MHz) and referenced to TMS. Solubility determination of octadienyl ethers was obtained by using a UV
visible USB-2000+ spectrometer (Ocean Optics) equipped with a fiber optic probe. The surface tensions were determined using a Sigma 40 tensiometer (Instruments KSV) at 25 °C by the Wilhelmy plate method. They were measured until constant values were obtained. Equilibrium was reached after 15 min. The accuracy of the measurement was 0.1 mN 3 m
1. All solutions were prepared using bidistilled water. General Procedures. Catalysis. All experiments were performed under a nitrogen atmosphere using standard Schlenk techniques. Telomerization and hydrogenation reactions were carried out in a 60 mL stainless steel autoclave equipped with a thermocouple and a jacketed vessel allowing the cooling or heating of the autoclave by means of a cryostat or a thermostat. In a typical telomerization experiment, the catalyst Pd(acac)2 (5.4 mg; 0.018 mmol) and the phosphine ligand (0.089 mmol) were introduced in the autoclave, which was bolted and flushed with nitrogen. Solketal (3.9 g; 29 mmol) was dissolved in soda aqueous solution (1 M; 0.9 mL) and degassed under nitrogen flow. Then the solketal solution was transferred into the autoclave. The latter was cooled to
20 °C. A precise volume of butadiene (20 mL; 0.222 mol) was condensed in a Schlenk tube with an acetone
dry ice mixture and transferred into the autoclave. Finally, the reactor was heated to 80 °C and vigorously stirred (at a rate of about 1000 rpm) with a magnetic stirrer during the chosen reaction time. After the reaction, the system was cooled and excess gaseous butadiene was vented. The crude was homogenized by methanol addition. Conversions and selectivities were calculated from the GC analysis of the homogeneous mixture. To obtain a sample of pure compounds 1 and 2 for NMR analysis, water (20 mL) was added to the crude (without addition of methanol) and the mixture was extracted by diethyl ether. Then chromatography on a silica column was carried out using a mixture of petroleum ether/diethyl ether (3/1) as eluent. Deprotection of the Solketal Ethers. After evaporation of methanol, the palladium complex was first eliminated from the crude mixture by filtration over silica. Then 20% HCl (10 mL) was added and the solution was mixed for 4 h at ambient temperature. Neutralization with sodium hydroxide and extraction with cyclohexane afforded the monooctadienyl ethers. Linear Monotelomer 1. 1H NMR (300 MHz, CDCl3): 1.36 (3H, CH3); 1.42 (3H, CH3); 1.45 (2H, CH2
CH2
CH2, J = 7.4 Hz); 2.05 (4H, CH2—CHdCH(2), J = 6.6 Hz); 3.39
3.53 (2H, CH2 glycerol protons); 3.72
3.75 (1H, CH2 glycerol proton); 3.98 (2H, O—CH2—CHdCH, J = 6.1 Hz); 4.03
4.09 (1H, CH2 glycerol proton); 4.25
4.29 (1H, CH glycerol proton); 4.93
5.04 (2H, CHdCH2, J = 10.5 Hz: Hcis, J = 18 Hz: Htrans); 5.52
5.81 (3H, CH=). 13 C NMR DEPT 135 (300 MHz, CDCl3): 25.5 (CH3); 26.9 (CH3); 28.3 (CH2, CH2
CH2
CH2); 31.7 (CH2, CHdCH— CH2); 33.2 (CH2, CH2
CHdCH2); 67.0 (CH2, CH2
O
C); 9873

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Industrial & Engineering Chemistry Research 70.8 (CH2
O
CH2
CH); 72.4 (CH2, CH2
O
CH2); 74.7 (CH, CH
O); 109.4 (C(CH3)2); 114.8 (CH2, CHdCH2); 126.3 (CH, O—CH2—CHdCH); 134.8 (CH, O—CH2— CHdCH); 138.7 (CH, CHdCH2). Branched Monotelomer 2. 1H NMR (300 MHz, CDCl3): 1.36 (3H, CH3); 1.42 (3H, CH3); 1.4
1.65 (2H, CH2
CH2
CH2, J = 7.3 Hz); 1.98
2.08 (4H, CH2—CH2—CH2— CHdCH2, J = 6.5 Hz); 3.22 (1H, CH2
O); 3.28
3.40 (1H, O—CH—CHdCH2); 3.6 (1H, CH2
O); 4.05 (2H, O
CH
CH2
O); 4.25 (1H, CH
O); 4.9
5.2 (4H, CHdCH2); 5.50
5.82 (2H, CH2dCH). 13 C NMR DEPT 135 (300 MHz, CDCl3): 24.5 (CH2, CH2
CH2
CH2); 25.4 and 26.8 (2 CH3); 33.6 (CH2,); 34.9 (CH2, CH2
CH
O); 67.1 (CH, CH
OH); 69.7 (CH2, CH2
OH); 74.9 (CH2, CH2
O
CH); 82.3 (O—CH—CHdCH2); 114.5 (CH2, CHdCH2); 117.1 (CH, O—CH—CHdCH2); 134.4 (CH, O—CH—CHdCH); 138.8 (CH, CHdCH2). Linear Octadienyl Ether 321,23. 1H NMR (300 MHz, CDCl3): 1.45 (t, 2H, CH2
CH2
CH2, J = 7.4 Hz); 2.04 (q, 4H, CH2— CHdCH(2), J = 6.6 Hz); 3.41
3.82 (m, 5H, glycerol protons); 4.03 (d, 2H, O—CH2—CHdCH, J = 6.1 Hz); 4.93 (dd, 2H, CHdCH2, J = 10.4 Hz: Hcis, J = 17.8 Hz: Htrans); 5.52 (m, 1H, O—CH2—CHdCH, J = 15.5 Hz: Htrans); 5.63 (m, 1H, O— CH2—CHdCH); 5.76 (m, 1H, CH2—CHdCH2). 13 C NMR DEPT 135 (300 MHz, CDCl3): 28.5 (CH2, CH2
CH2
CH2); 31.8 (CH2, CHdCH—CH2); 33.1 (CH2, CH2—CHdCH2); 64.5 (CH2, CH2
OH); 70.0 (CH, CH
OH); 70.7 (CH2, CH2
O
CH2); 72.3 (CH2, CH2
O
CH2
CH); 114.5 (CH2, CHdCH2); 126.1 (CH, O— CH2—CHdCH); 134.9 (CH, O—CH2—CHdCH); 138.5 (CH, CHdCH2). Branched Octadienyl Ether 423. 1H NMR (300 MHz, CDCl3): 1.45 (q, 2H, CH2
CH2
CH2, J = 7.3 Hz); 2.06 (q, 4H, CH2—CH2—CH2—CHdCH2, J = 6.6 Hz); 3.26
3.66 (m, 5H, glycerol protons); 3.96 (d, 1H, O
CH
CH2, J = 5,2 Hz); 4.97 ppm (dd, 2H, CH2—CHdCH2, J = 10.2 Hz: Hcis, J = 18.6 Hz: Htrans); 5.20 (dd, 2H, CH2dCH—CH, J = 14.1 Hz: Htrans); 5.57 (m, 1H, CH2dCH—CH); 5.78 (m, 1H, CH2— CHdCH2). 13 C NMR DEPT 135 (300 MHz, CDCl3): 28.5 (CH2, CH2
CH2
CH2); 31.7 (CH2, O
CH
CH2); 34.0 (CH2, CH2—CHdCH2); 69.7 (CH, CH
OH); 71.0 (CH2, CH2
OH); 72.6 (CH2, CH2
O
CH); 81.8 (CH2, CH2
O
CH
CH2); 114.7 (CH2, CHdCH2); 117.3 (CH, O —CH—CHdCH2); 134.7 (CH, O—CH—CHdCH); 138.8 (CH, CHdCH2). Hydrogenation of the Monooctadienyl Ethers of Glycerol. the hydrogenation was performed in an autoclave at 50 bar of hydrogen and at 80 °C during 24 h in the presence of Pd/C. Total conversion was obtained and filtration of the catalyst over Celite afforded the pure monooctyl telomer fraction. Linear Octyl Ether 511. 1H NMR (300 MHz, CDCl3): 0.8 (3H, CH3); 1.21 (8H, CH2); 1.43
1.51 (4H, CH2); 3.36 (2H, O
CH2
CH2); 3.35
3.94 (5H, glycerol protons). 13 C NMR DEPT 135 (300 MHz, CDCl3): 14.1 (CH3); 22.7; 26.9; 29.4; 29.6; 30.1; 31.2 (6 CH2); 63.4 (CH2, CH2
OH); 70.9 (CH2, CH2
O
CH2); 71.7 (CH, CH
OH); 71.6 (CH2, CH2
O
CH2). Branched Octyl Ether 625. 1H NMR (300 MHz, CDCl3): 0.85
0.90 (6H, CH3); 1.21
1.31 (6H, CH2); 1.43
1.51 (4H, O
CH(CH2)2
); 2.90 (1H, O
CH(CH2)2
); 3.35
3.94 (5H, glycerol protons).

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C NMR DEPT 135 (300 MHz, CDCl3): 10.5 and 14.1 (2 CH3); 22.7 ; 26.9 ; 30.1; 31.2 (4 CH2); 30.7 (CH2, CH3
CH2
CH
O); 35.7 (CH2, CH2
CH
O); 67.5 (CH, CH
OH); 69.8 (CH2, CH2
OH); 72.9 (CH2, CH2
O
CH).

’ CONCLUSION Palladium catalyzed telomerization of butadiene with solketal under aqueous biphasic conditions constitutes a straightforward route to synthesizing monooctadienyl and after hydrogenation monooctyl glyceryl ethers provided that the appropriate ligand was used. In spite of the two hydroxyl functions, the octyl ethers exhibit a relatively low solubility in water at room temperature. In contrast, the solubilities of their unsaturated counterparts, the octadienyl ethers, are much higher, showing the influence of the double bonds. When added to water, both ethers induced an important decrease of the surface tension up to about 30 mN 3 m
1 for the glyceryl octadienyl ethers and 25 mN 3 m
1 for the octyl ethers. From the variation of the surface tension with the concentration, a cmc value of 8.3 mM was found for the former ethers; on the other hand, in the case of octyl ethers the cmc cannot be found, with an insoluble phase of octyl ethers in the aqueous medium appearing before the micellar formation. ’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (I.S.); [email protected] (Y.C.). Fax: (+33) 3 20 43 65 85.

’ ACKNOWLEDGMENT We are grateful to the CNRS, the R
egion Nord-Pas-de-Calais (grant to S.B.), and the Ministere de l'Enseignement Sup
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