ABSTRACT: Sodium, lithium, and calcium soaps obtainedby saponification of high-oleic sunflower oil were studied byFourier-transform infrared spectroscopy. Spectra of crudemixtures containing soap, glycerin, residual alkali, and triacyl-glycerols were compared to those of pure soaps obtainedfrom fatty acids. The infrared spectra of crude soaps showedthe same characteristic bands as pure ones. The absorptionbands of asymmetric (ω2) and symmetric (ω1) stretching vibra-tions of the carboxylate group indicated that the metal–oxy-gen bonds of these soaps had an ionic character whosestrength differed from one cationic counterion to another.Once the characteristic absorption bands of the soaps wereassigned, a kinetics study of saponification was performed.Saponification by sodium, anhydrous lithium, and calcium hy-droxides was an autocatalytic reaction, characterized by an S-shaped kinetics curve, whereas saponification by aqueouslithium hydroxide was stoichiometric. The structure of themetal–oxygen bond played a role in the kinetic mechanisms.

Paper no. S1345 in JSD 6, 305–310 (October 2003).

KEY WORDS: Alkaline-earth soaps, alkaline soaps, high-oleic sunflower oil, infrared spectroscopy, kinetics of saponifi-cation, saponification.

Among all the oleaginous plants having a high-oleic acidcontent, only sunflower is grown on a large scale in openfields throughout the world. The high-oleic sunflower oil(HOSO) obtained from these plants is available for fooduses as well as for industrial ones. The properties of HOSOare linked to their high content of oleic acid (18:1): stabil-ity vs. oxidation, fluidity, and a monounsaturated substrate.Its vegetable origin is a commercial asset for many applica-tions, commercial as well as technical.

Soap manufacture from vegetable oils is quite wellknown and used, but few quantitative studies have beendone on the saponification reaction itself. Soaps with ahigh-oleic acid content once were manufactured from tal-

low, but because of the spread of the bovine spongiform en-cephalopathy and the importance of oleaginous plant farm-ing in the northern hemisphere, e.g., sunflower cultivation,a more accurate study of saponification is now needed toproduce alkaline or alkaline-earth soaps easily from veg-etable oils.

Study of the infrared spectra of soaps allows us to com-pare crude soaps, obtained from the saponification of tri-acylglycerols (TAG) of vegetable oils, with those obtainedby more traditional means [the neutralization of fatty acids(1,2), a double decomposition reaction between an alkalinesoap and a metallic salt (3), or the fusion of fatty acids (3)].The choice of metallic counterion in the soap is essential;physiochemical properties of the final product, and thus itsuses, depend on it. Moreover, Fourier-transform infrared(FTIR) spectroscopy enables one to compare the kineticsof saponification of HOSO based on the metallic hydroxideused: sodium, lithium, or calcium hydroxide. The aim ofthis study was thus to characterize crude soaps and then toevaluate the kinetics of the saponification reactions.

EXPERIMENTAL PROCEDURES

Materials. The vegetable oil used for saponifications was acrude HOSO obtained from high-oleic sunflower seeds(Toulousaine des Céréales, Toulouse, France) by a twin-screw extruder in our laboratory (4,5). The fatty acid com-position of the crude oil was determined by gas chromatog-raphy after methylation (column: CP-FFAP CB, film thick-ness = 0.25 µm, 25 m × 0.15 mm; injector: split, 280°C; oven:1 min at 160°C, 160 to 200°C at 2°C/min, 10 min at 200°C,200 to 220°C at 5°C/min, 25 min at 220°C; detector: FID,300°C) as follows: palmitic acid 16:0, 3.9%; stearic acid 18:0,3.8%; oleic acid 18:1, 83.1%; linoleic acid 18:2, 8.2%; andbehenic acid 22:0, 1.0%. Moreover, the oil had the follow-ing characteristic values, as calculated from standards (6):acid value = 1.84 mg KOH/g fat (NF T60-204); saponifica-tion value = 190 mg KOH/g fat (NF T60-206), iodine value= 95–96 mg/g fat (NF T60-203); peroxide value = 157–158µg active oxygen/g fat (NF T60-220); unsaponifiable con-tent: 0.58 g unsaponifiable/g fat (NF T60-205).

To obtain oleic soaps, sodium hydroxide (NaOH, 98%,40 g/mol; Fluka, Buchs, Germany), lithium hydroxide

Copyright © 2003 by AOCS Press Journal of Surfactants and Detergents, Vol. 6, No. 4 (October 2003) 305

*To whom correspondence should be addressed at Laboratoire deChimie Agro-Industrielle, UMR 1010 INRA/INP-ENSIACET, 118 routede Narbonne, 31077 Toulouse Cedex 4, France.E-mail: zéphirin.mouloungui@ensiacet.fr Abbreviations: ω1, carboxylate ion symmetric stretching vibration; ω2,carboxylate ion asymmetric stretching vibration; ω3, carboxylate bend-ing vibration; FTIR, Fourier-transform infrared; HOSO, high-oleic sun-flower oil; TAG, triacylglycerol.

Fourier-Transform Infrared Spectra of Fatty Acid Salts—Kinetics of High-Oleic Sunflower Oil Saponification

Gaëlle Poulenat, Sabine Sentenac, and Zéphirin Mouloungui*Laboratoire de Chimie Agro-Industrielle UMR 1010 Institut National de la Recherche Agronomique (INRA)/IInstitut

National Polytechnique de Toulouse (INPT)-Ecole Nationale Superieure des Ingenieurs en Arts Chimique et Technologiques (ENSIACET), 31077 Toulouse Cedex 4, France

monohydrate (LiOH·H2O, 99%, 41.96 g/mol; Fluka), andcalcium hydroxide [Ca(OH)2, 96%, 74.09 g/mol; Fluka]were used in either anhydrous form or in aqueous solution.Aqueous alkali solutions were prepared in distilled water.

Synthesis. Saponification reactions of HOSO were carriedin a 1-L reactor, under nitrogen, and stirred at about 700rpm. Reactions were carried out at 100°C for NaOH andLiOH and at 115°C for Ca(OH)2. Four runs of saponifica-tion reactions were completed: saponification by (i) aque-ous NaOH (20 wt%), (ii) aqueous LiOH (14 wt%), (iii) an-hydrous LiOH, and (iv) Ca(OH)2 catalyzed by aqueousNaOH (0.6 wt%). The reactions were carried out at a 1:3molar ratio of TAG/OH−. Experimental conditions aregiven in Table 1.

To follow the kinetics of the saponification reactions,samples were taken every half hour for quantitative analysis.All reactions were carried out until completion. The result-ing soaps consisted of a white solid for the Na fatty acid salt,a soft, yellowish soap for the Li salt, and a hard, brown solidfor the Ca salt. No purification was performed on soaps. Re-sults are given for crude soaps that contain the fatty acidsalt, glycerin, traces of TAG, traces of metallic hydroxide,and impurities from the crude oil.

FTIR analysis. Infrared absorption spectra of alkaline andalkaline-earth soaps were determined with a PerkinElmerSpectrum BX II spectrophotometer at 20°C. The data werecomputed with Spectrum 3v software. Soap samples wereanalyzed as KBr pellets in the sodium chloride (4000–700cm−1) and potassium bromide (900–400 cm−1) regions.

Qualitative analysis of soaps by FTIR spectroscopy. Saponifica-tion reactions were followed by the disappearance of thecarbonyl group stretching vibration at 1745 cm−1 of TAGand by the appearance of three characteristic soap bands:(i) the carboxylate ion symmetric stretching vibration, ω1(1426, 1403, and 1422 cm−1 for Na, Li, and Ca soaps, re-spectively); (ii) the carboxylate ion asymmetric stretchingvibration, ω2 (1561, 1580, and 1577 cm−1 for Na, Li, and Casoaps, respectively); and (iii) the metal–oxygen bond vibra-tion (538, 484, and 665 cm−1 for Na, Li, and Ca soaps, re-spectively).

To determine the relative quantity of soap vs. the remain-ing TAG of HOSO, absorbances of the characteristic bandsof the components were calculated using the method of Pu-tinier (7), which was adapted for this study. The carbonylband of TAG appeared at 1745 cm−1. When there was a

majority of soap in the crude mixture, this band was a shoul-der at the base of the carboxylate soap band. When TAGwere the principal component, the opposite was observed.For a crude soap with a majority of soap and traces of TAG,the baseline of the TAG band was obtained by drawing a line connecting the two minimum points located on each side of the 1745 cm−1 band. The baseline absorbancewas read at the intersection of the baseline with a line drawnperpendicular to the zero line of the recorded spectrumand passing through the maximum point of the peak at 1745 cm−1. The baseline absorbance was subtracted from the maximum absorbance to obtain the absorbance ofTAG.

Once the absorbance was calculated for each compo-nent, the relative quantity of soap formed vs. remainingTAG could be calculated with Equation 1:

[1]

Quantitative analysis of crude oleic soaps. Crude Li and Casoaps were insoluble in the majority of organic solvents; thus,a quantitative analysis of soaps by FTIR spectroscopy in solu-tion was not workable. Therefore, saponification reactionswere quantified by use of a standard (NF T60-308) (6),which gives the total free alkali in the soap. It must be em-phasized that this standard was made for Na and K soaps butnot for Li and Ca soaps, so obtaining results for Ca soaps wasdifficult. Saponification reactions were thus quantified withanother standard (NF T60-309) to determine the unsaponi-fied and unsaponifiable contents in the soap. As for the totalfree alkali content standard, the unsaponified and un-saponifiable contents in soap were determined for Na and Ksoaps. Li and Ca soaps were not soluble but dispersed in thesolvents used in the standard, which made the analysis diffi-cult. In fact, Ca soap was dispersed well in the solvents, sotraces of soaps remained in the unsaponified and un-saponifiable matter, which lowered the yield of the saponifi-cation reaction. Thus, the yield of saponification reactionswas not determined by the unsaponified and unsaponifiablecontents but by the total free alkali in the soaps.

RESULTS AND DISCUSSION

FTIR spectra of alkaline and alkaline-earth oleic soaps. The char-acteristic bands of oleic soaps are given in Table 2. On theinfrared spectra, three regions were studied in the sodiumchloride domain: part 1 at 4000–2800 cm−1; part 2 at1800–1350 cm−1; and part 3 at 1350–1180 cm−1 and near720 cm−1. One region was studied in the potassium bromidedomain: part 4 at 670–440 cm−1 (8).

(i) Part 1. The region between 4000 and 3000 cm−1 wasassociated with the O–H stretching vibration of hydratedwater. Soaps have a broad absorption around 3400 cm−1,which is characteristic of the existence of different types ofhydrogen bonding attributable to the presence of manyoxygen atoms in the polar head of the soap molecule in acrystal lattice (8,9).

% soap =

soap absorbancesoap absorbance + TAG absorbance

306 G. POULENAT ET AL.

Journal of Surfactants and Detergents, Vol. 6, No. 4 (October 2003)

TABLE 1Experimental Conditions for the Saponification of High-OleicSunflower Oil (HOSO) by Alkaline and Alkaline-Earth Hydroxides

Anhydrous AqueousNa soap Li soap Li soap Ca soap

T (°C) 100 100 100 115Sampling 1⁄2 h 1⁄2 h 1⁄2 h 1⁄2 hHOSO (wt%) 59% 87% 50% 74.7%Base (wt%) 8% 13% 7% 9.8%Catalyst (wt%) 0% 0% 0% 0.6% (NaOH)Water (wt%) 33% 0% 43% 14.9%

The absorption band at 3400 cm−1 was stronger for Caand Na soaps (relative intensity vs. 2922 cm−1 peak: 50 and35%, respectively) than for Li soaps (relative intensity vs.2922 cm−1 peak: 17% for anhydrous soap and 30% for aque-ous soap). This indicates that the Ca soap was hydrated,generally monohydrated (8), and that the Na soap con-tained water because of its strong affinity for it.

In the region 3000–2800 cm−1, four absorption bands, lo-cated at 3004, 2955, 2922, and 2851 cm−1, represent the fre-quencies of the aliphatic chains of the soaps. These fre-quencies were the same as the aliphatic chain in the initialHOSO without modification of the chain during saponifi-cation.

(ii) Part 2. In this part of the spectra, the total disappear-ance of the stretching vibration at 1745 cm−1, attributed tothe frequency of the ester bond in TAG, was observed.Three modes of vibration, attributed to the carboxylategroup of the fatty acid metallic salt, were expected: the sym-metric stretching vibration, ω1, between 1400 and 1300 cm−1; the asymmetric stretching vibration, ω2, between 1610and 1550 cm−1; and a bending vibration, ω3, between 950

and 800 cm−1. The stretching vibrations are represented byone or more vibrational peaks (8).

The appearance of two absorption bands, an asymmetric(ω2) and a symmetric (ω1) stretching vibration, of the car-boxylate group instead of a single band at 1745 cm−1 showsthat Na, Li, and Ca soaps possess an ionized structure andthat metal–oxygen bonds in the soaps have an ionic charac-ter (2,3). In the case of Ca and Li soaps, these two stretchingvibrations were split into two or three bands: ω2, 1580 and1557 cm−1, and ω1, 1465, 1448, and 1403 cm−1 for Li soaps;ω2, 1577 and 1541 cm−1, and ω1, 1468, 1435, and 1422 cm−1

for Ca soaps. A single asymmetric stretching vibration and atriple symmetric vibration were observed for Na soaps: ω2,1561 cm−1, and ω1, 1462, 1446, and 1426 cm−1.

Thus, the structure of soap molecules would be more liketype I than type II (Fig. 1). The internal modes of vibrationof an ionized carboxyl group were similar to the normalmodes of a nonlinear XY2-type molecule. Moreover, the twoC–O bonds of the carboxylic group became equivalent andhad an identical strength, having an intermediate value be-tween those of single and double C–O bonds (2,3,8).

SAPONIFICATION FOLLOWED BY FTIR SPECTROSCOPY 307

Journal of Surfactants and Detergents, Vol. 6, No. 4 (October 2003)

TABLE 2Comparison Between Crude Soaps Obtained by Saponification of Triacylglycerols (TAG) of HOSO and Pure Soaps Obtained by Neutralization of Fatty Acids, Precipitation from Potassium Soaps, or Fusion of Fatty Acidsa

Frequencies (cm−1)

Na oleate Crude Na Li palmitate Li stearate Crude Li Ca palmitate (3), Crude CaHOSO (1) soap (2) (9) soap Ca laurate (13) soap Assignments

3472 (b) 3436 (b) 3446 (b) 3436 (b) 3436 (b) Broad absorption of stretching vibration O–H3005 (w) 3004 (w) 3004 (w) 3004 (w) Stretching =CH–H

2957 (ms) 2950 (ms) 2960 (ms) 2955 (ms) 2950 (ms) Asymmetric stretching CH3, C–H2922 (vs) 2922 (s) 2922 (vs) 2910 (vs) 2914 (vs) 2920 (vs) 2922 (vs) Asymmetric stretching CH2, C–H2853 (vs) 2853 (ms) 2852 (vs) 2850 (s) 2848 (vs) 2851 (vs) 2851 (vs) Symmetric stretching CH2, C–H1745 (vs) Stretching C=O (ester)

1690 (w) Stretching C=C1562 (vs) 1561 (vs) 1540 (vs) 1580 (vs) 1580 (vs) 1530 1577 (vs) Asymmetric stretching COO−, C–O (ω2)

1556 (s) 1557 (s) 1541 (vs)1462 (ms) 1465 (ms) 1468 (s)

1446 (s) 1446 (s) 1448 (s) 1448 (s) 1435 (ms) Deformation CH21464 (s) 1400 (s) 1426 (ms) 1460 (ms) 1403 (s) 1403 (s) 1410 1422 (ms) Symmetric stretching COO−, C–O (ω1)1377 (ms) 1380 (ms) 1375 (ms) 1377 (w) Symmetric deformation CH3

1400 (s) 1346 (w) 1350 (s) 1348 (w) Deformation CH2 adjacent to COO−

1322 (ms)1278 (ms) 1325–1100 1298 (ms) Twist and wag CH2

(vw) 1261 (w) Progressive bands1238 (ms) 1240 (w)

1110 (w) 1223 (w) Rocking CH31203 (w)

1164 (s) Deformation COOR1186 (w)

1111 (w) 1111 (w) 1111 (w) Glycerin1097 (ms) 1105 (w)

1042 (w) 1042 (w) 1042 (w) Glycerin993 (w) 993 (w) 993 (w) Glycerin924 (ms) 950 (w) 930 930 (vw) Deformation COO− (ω3) or glycerin854 (vw) 854 (vw) 854 (vw) Glycerin823 (ms) 814 (w) 828 (ms) 861 (vw)

764 (vw)730 (s)

722 (s) 721 (vw) 722 (ms) 710 (ms) 719 (s) 722 (ms) 722 (w) Rocking (CH2)n, n > 4 540 (ms) 538 (ms) 440 (ms) 484 (ms) 665 (ms) Metal–O bond

aAbbreviations: s, strong; vs, very strong; ms, medium strong; w, weak; vw, very weak; b, broad; for other abbreviation see Table 1.

(iii) Part 3. The spectral regions of the aliphatic chains,1350–1180 cm−1, were not modified when HOSO wassaponified, as seen in the 3000–2800 cm−1 region. The pro-gressive bands of the aliphatic chains (1350–1180 cm−1)were sensitive to the manner of hydrocarbon chain packing,that is to say, to the crystallization of soap. Many absorptionbands approximately equally spaced and with weak ormedium intensities, were observed in this region. They wereassigned to wagging and twisting vibrations of successivemethylene groups of the soap molecules (8,9).

Moreover, in this region, because the soap was crude andcontained glycerin, absorption bands characteristic of glyc-erin appeared and stacked on the progressive bands of thealiphatic chains between 1150 and 850 cm−1 (1111, 1042,993, 924, and 854 cm−1). This was the only difference in theinfrared spectra between the crude soaps obtained bysaponification of TAG of HOSO and the pure soaps ob-tained from fatty acids.

Between 950 and 916 cm−1, the absorption maxima wereassociated with a bending vibration, ω3, of the ionized car-boxylate group. In the vicinity of 720 cm−1 of the soap spec-tra, absorption bands with medium intensity were observedas a singlet (Ca soap at 722 cm−1), a doublet (Na soap at 722and 699 cm−1), or a triplet (Li soap at 737, 722, and 702 cm−1). These absorption bands were associated with a rock-ing vibration of successive methylene groups, –(CH2)–, ofthe soaps and depended on their mode of crystallization.The splitting into a doublet or a triplet was attributed to in-terchain interactions with neighboring hydrocarbon chainsof the soap molecules (8,9).

(iv) Part 4. The intensity of the metal–oxygen absorptionbands between 670 and 400 cm−1 was linked to the strengthof this bond. The more intense the band, the stronger thebond (1). Thus, the Li–O bond (absorption at 485 cm−1, rel-ative intensity vs. 2922 cm−1 peak is 25%) seemed to bestronger than the Na–O bond (absorption at 538 cm−1, rel-ative intensity vs. 2922 cm−1 peak is 10%), which wasstronger than the Ca–O bond (at 665 cm−1, relative inten-sity vs. 2922 cm−1 peak is 7%). The Li–O–C bond was con-sidered as a quasi-covalent bond, whereas the Na–O–C andCa–O–C bonds were delocalized.

The infrared spectra of crude soaps obtained by saponi-fication of HOSO by alkaline and alkaline-earth hydroxideshad the same characteristic bands as those obtained by neu-tralization of fatty acids [Na oleate (1), Li palmitate (2)], byprecipitation of Ca soap from K palmitate (3), or by fusionof palmitic acid and LiOH·H2O (3). A comparison betweencrude soaps and pure soaps obtained by neutralization, pre-

cipitation, or fusion is given in Table 2. The difference be-tween the infrared spectra of crude and pure soaps was inthe presence of absorption bands between 1300 and 900cm−1, attributed to crude glycerin.

Kinetics of saponification reactions. To follow the kinetics ofthe saponification reactions of HOSO by various metallichydroxides, the behavior of the metallic carboxylate groupwas studied. The evolution of saponification of HOSO by al-kaline and alkaline-earth hydroxides was determined byplotting the relative quantity of soap vs. time for a charac-teristic vibration of the soap corresponding to the carboxy-late ion asymmetric stretching vibration, ω2 (Fig. 2). Amongthe three characteristic bands of soaps (the carboxylate ionsymmetric stretching vibration, ω1, the carboxylate ionasymmetric stretching vibration, ω2, and the metal–oxygenbond vibration), the asymmetric stretching vibration, ω2,was the strongest. Thus, this band was the most accurate andits height was consequently used to calculate the relativequantity of soap.

For saponification reactions carried out in the presenceof NaOH and Ca(OH)2 (Fig. 2A), the kinetic curves had avery marked S shape. They could be divided into three parts(10,11).

(i) Part 1—Slow emulsification stage or induction period. Theaqueous solutions of alkaline or alkaline-earth hydroxideswere not miscible with HOSO, which is why the reaction didnot begin readily. This slow first stage was carried out in aheterogeneous system, and the saponification reaction ratewas promoted by a vigorous stirring and by the formation

308 G. POULENAT ET AL.

Journal of Surfactants and Detergents, Vol. 6, No. 4 (October 2003)

FIG. 1. Structure of the ionized carboxyl group of soap molecules (8).

FIG. 2. Kinetics of high-oleic sunflower oil (HOSO) saponification by(A) (◆) NaOH and (■■) Ca(OH)2 or (B) (▲▲) anhydrous LiOH and (●)aqueous LiOH followed by Fourier-transform infrared spectroscopy.The relative quantity of soap was calculated from the asymmetricstretching vibration (COO−, C–O), ω2, of soap and the ester absorp-tion band of HOSO at 1745 cm−1.

of an emulsion stabilized by the soap generated. Theoil/water interface was a limiting factor to control.

(ii) Part 2—Fast autocatalytic stage or constant rate period.The product of the reaction was the soap. It created a largeinterfacial area between the reactants and catalyzed thesaponification reaction. The reaction rate acceleratedgreatly until a large amount of HOSO was reacted. Themain part of the reaction was pseudo-homogeneous, withHOSO probably “dissolved” in the soap micelles (11).

(iii) Part 3—Slow final saponification stage or falling rate pe-riod. The saponification rate slowed and the concentrationof residual HOSO fell. At this stage the rate depended onphysical conditions and on the overall mixing efficiency toensure that the last traces of HOSO had undergone a reac-tion. Thus, it seemed important to keep the reaction goingto have a sufficient residence time and to maximize thesaponification yield.

Because of their S-shaped curves (Fig. 2A), saponifica-tion reactions in the presence of NaOH and Ca(OH)2 canbe considered autocatalytic reactions (10,11). The saponifi-cation reaction in the presence of Ca(OH)2 was carried outat 115°C instead of 100°C. These thermal conditions shouldhave accelerated the reaction by raising the mobility ofionic species and organic compounds. However, the ther-mal effect did not promote the autocatalytic process as wellas expected: The first stage was slightly slower than the oneobserved during the saponification reaction in the presenceof NaOH. The saponification reaction in the presence ofCa(OH)2 continued until completion at about 6 h, com-pared to 3 h for the reaction with NaOH. This can be ex-plained by the presence of a small quantity of water in themixture during the TAG saponification reaction in the pres-ence Ca(OH)2. The mixture was heterogeneous and con-tact between the reactants was difficult.

TAG saponification reactions in the presence of LiOHwere quite different (Fig. 2B). With anhydrous LiOH, thesaponification reaction was autocatalytic (showing an S-shaped curve), but was very slow because of the heterogene-ity of the mixture and the poor contact between reactants.Moreover, the saponification of TAG stopped quickly: After3 h of reaction, the media became too viscous to allow fur-ther stirring. In contrast, the saponification reaction in thepresence of aqueous LiOH was stoichiometric. The conver-sion of TAG into fatty acid lithium salt started quickly, andpractically the same rate was maintained until completion.

It is reasonable to assume that there is a relationship be-tween the reactivity of NaOH, LiOH, and Ca(OH)2 and thestrength of the metal–oxygen bond. From infrared data, weobserved that the Li–O–C bond was quasi-covalent and thatthe Na–O–C and Ca–O–C bonds were particularly delocal-ized. Through electrostatic binding, the smaller cations(e.g., Li+, Na+) and the larger cation (e.g., Ca2+) reachedspecific binding sites. Thus, the TAG saponification reac-tion followed a catalytic mechanism in the presence of an-hydrous metallic hydroxides.

Moreover, water played an important role in the mecha-nism of TAG saponification reactions. Two mechanisms are

proposed to explain the two different kinetics of TAGsaponification in the presence of anhydrous LiOH or aque-ous LiOH: autocatalytic and stoichiometric. Water im-proved contact between the reactants and enhanced the re-action, causing the aqueous LiOH saponification rate to beconstant: The kinetics curve followed a first-order reaction.In the presence of water, contact between the reactants wascreated easily, so the saponification reaction was enhancedin the presence of aqueous LiOH by the emulsion created.Owing to the effect of ionic species (e.g., Li+, OH−) on theself-diffusion of water and the ionic self-diffusion concen-tration, water helped to put the reactants in contact and en-hanced the kinetics of TAG saponification in aqueous LiOH(12). The velocity of the reaction probably depended onthese parameters. The hydration numbers of Li+ and OH−,around 10 and 12, respectively, indicated that water in-creased the self-diffusion rate in aqueous LiOH (12). More-over, the molar ratio of TAG/LiOH supported a stoichio-metric reaction.

Infrared data on the soaps enabled us to characterize thestructures of the metal–oxygen bonds, to determine the ve-locity of transformation of an ester bond to a carboxylatebond, and to establish the relationship between reactivityand the saponification mechanism. Thus, FTIR spec-troscopy seemed to be well adapted to the direct study ofTAG saponification reactions.

Moreover, the relative quantity of soaps vs. the remain-ing TAG of HOSO could be linked to the reaction yieldsowing to standards analyses. Thus, the reaction yields canbe predicted all along the saponification. The results ofstandards analyses are given in Table 3. As the kinetics studyfollowed by FTIR showed, saponification by NaOH was prac-tically complete (about 99% of saponification). Those byLiOH (anhydrous and aqueous) were practically total (al-most 98 and 97%, respectively). However, the saponificationyield by Ca(OH)2 was lower (95%). This can be explainedby the difficulty of putting the reactants in contact duringthe reaction (due to the small quantity of water) or by thefact that this standard was not adapted to Ca soaps.

ACKNOWLEDGMENTS

This work was financially supported by the French Research De-partment under contract number 01P0408 and by the sous-réseauLipotechnie. We are grateful to the ENSIACET Control Labora-tory (Toulouse, France) for the use of their infrared spectrometer.We also thank the French Institute on Fats and Oils (ITERG) Li-brary (Pessac, France) for its bibliographic assistance.

SAPONIFICATION FOLLOWED BY FTIR SPECTROSCOPY 309

Journal of Surfactants and Detergents, Vol. 6, No. 4 (October 2003)

TABLE 3Saponification Yield (%) Based on Standards Analyses

Yields Na Anhydrous Aqueous Cabased on soap Li soap Li soap soap

Free alkalia 99 98 97 95Unsaponified and

unsaponifiable contentsb 99 95 98 52aNF T60-308.bNF T60-309 (6).

REFERENCES

1. Varma, R.P., U. Kumar, and P. Sangal, Characterisation ofSodium Soaps and Their Refractive Index Studies in Methanol,Asian J. Chem. 12:659 (2000).

2. Mehrotra, K.N., L. Rani, and A. Kumar, Physico-chemical Prop-erties of Lithium Soap, Rev. Roum. Chim. 39:517 (1994).

3. Mehrotra, K.N., and S.K. Upadhyaya, Physico-chemical Studieson Calcium Soaps, Recl. Trav. Pays-Bas 106:625 (1987).

4. Dufaure, C., J. Leyris, L. Rigal, and Z. Mouloungui, A Twin-Screw Extruder for Oil Extraction: I. Direct Expression ofOleic Sunflower Seeds, J. Am. Oil Chem. Soc. 76:1073 (1999).

5. Dufaure, C., Z. Mouloungui, and L. Rigal, A Twin-Screw Ex-truder for Oil Extraction: II. Alcohol Extraction of Oleic Sun-flower Seeds, J. Am. Oil Chem. Soc. 76:1081 (1999).

6. Association française de Normalisation (ed.), Corps Gras,Graines Oléagineuses, Produits Dérivés. Recueil des NormesFrançaises, AFNOR, 1993.

7. Putinier, R.A., The Quantitative Analysis of Components in Lu-bricating Greases by Differential Infrared Spectrophotometry,NGLI Spokes. 34:204 (1970).

8. Koga, Y., and R. Matuura, Studies on the Structure of MetalSoaps, Mem. Fac. Kyushu Univ., Series C 4:1 (1960).

9. Shoeb, Z.E., S.M. Hammad, and A.A Yousef, Oleochemicals I:Studies on the Preparation and the Structure of LithiumSoaps, Grasas Aceites 50 :426 (1999).

10. Spitz, L., (ed.), Soaps and Detergents: A Theoretical and Pratical Re-view, AOCS Press, Champaign, 1996.

11. Woollatt, E. (ed.), The Manufacture of Soaps, Other Detergents andGlycerine, John Wiley & Sons, New York, 1985.

12. McCall, D.W., and D.C. Douglass, The Effect of Ions on theSelf-Diffusion of Water. I. Concentration Dependence, J. Phys.Chem. 69 :2001 (1965).

13. Mehrotra, K.N, and S.K. Upadhyaya, Thermal, IR and X-RayAnalysis of Calcium Soaps, Tenside Surfactants Deterg. 24:90(1987).

[Received December 3, 2002; accepted June 6, 2003]

Gaëlle Poulenat is a Ph.D. student at the Agro-Industrial Labora-tory (ENSIACET-INPT, Toulouse, France). She is an ENSCT engi-neer (2000, ENSCT-INPT) in the chemistry of agro-industrial prod-ucts. She joined the Agro-Industrial Laboratory in 2000 to prepareher Ph.D. on the team of Dr. Mouloungui. Her main research fieldsare lipochemistry and the chemical reactivity of vegetable oils. She isthe author of three presentations.

Sabine Sentenac is a chemistry technician at the Agro-IndustrialLaboratory. She joined Dr. Mouloungui’s team in 2001 to work onobtaining soaps from raw vegetable materials.

Dr. Zéphirin Mouloungui graduated from USTL (Montpellier,France) and INPT. He obtained a Ph.D. in physical organic chem-istry in 1982 and a second Ph.D. in agroresource transformationsin 1987. He is now the head manager of strategy in lipochemistryresearch at INRA and at the Agro-Industrial Laboratory, UMR-1010 INRA/INPT. He is the author and co-author of more than70 papers and presentations and 26 patents.

310 G. POULENAT ET AL.

Journal of Surfactants and Detergents, Vol. 6, No. 4 (October 2003)