45 2
Ind. Eng. Chem. Prod. Res. Dev. 1904, 23,452-454
CHCfrom oligomerization = (total HC products) (HC produced by dehydration of DME) (HC formed by methylation of propene) amount of hydrocarbons formed by oligomerization = 0.376 - 0.0185 - 0.016 = 0.342 gg-l cat-h-' Registry No. Dimethyl ether, 115-10-6;propene, 115-07-1; l-butene, 106-98-9methanol, 67-56-1.
Cormerals, F. X.; Perot, G.; Chevalier, F.; Gulsnet, M. J . Chem. Res. ( S ) , 1080, 362. Derouane, E. G.; Nagy, J. B.; Dejaifre, P.; van Hooff, J. H. C.; Spekman, B. P.: Vedrlne, J. C.; Naccache. C. J . Catal. 1978, 53,40. Dessau, R. M.;Lapierre, R. 8. J . Catel. 1982, 78, 136. Esplnoza, R. L.; Sander, C. M.; Mandersloot, W. G. B. Appl. Catal. 1983, 6, 11-26. Kaeding, W. W.; Butter, S. A. J . Catal. 1980, 6 1 , 155. Perot, G.; Cormerais, F. X.; Gulsnet, M. J . Chem. Res. ( S ) , 1982, 58. Perot, G.; Cormerais, F. X.; Gulsnet, M. J . Mol. Catel. 1082, 17, 255. Van den Berg, J. P.; Wolthulzen. J. P.; van Hooff. J. H. C. I n "Proceedings, Vth Conference on Zeolites"; Naples, Italy, 1980 p 649.
L i t e r a t u r e Cited
Received for review August 15, 1983 Accepted January 11, 1984
Anderson. J. R.; Mole, T . ; Christov, V. J . Catat. 1980, 67, 477. Chang, C. D.; Chu, C. T. W.J . Catal. 1980, 7 4 , 203.
Preparation of Monoglycerides of Fatty Acids from Epichlorohydrin by Phase-Transfer Catalysis. Glycidyl Esters Abraham Aserln, Nloslm Garti,' and Yoel Sasson' Casali Institute of Applied Chemistty, School of Applled Science and Technolcgy, The Hebrew Unlvers@ of Jerusalem, 8 1804. Jerusalem, Israel
The exlsting lndustrlal reactions for the preparation of monoglycerides of fatty acids are based on acidic or basic catalysis at elevated temperatures and prolonged reaction times. The product is an equilibrium mixture of isomers which need further expensive and tedious molecular distillation. The following study presents a selective method for the preparation of pure monoglycerides of fatty acids. The reaction is based on treatment of epichlorohydrin with sodium stearate soap in the presence of various phase-transfer catalysts. Over 90% of pure monoglycerides are obtained in quantitative yields after short reaction time at relatively low temperatures. The effects of reactants ratio, catalyst type and concentration, temperature, and industrial aspects have been investigated.
Introduction
Glycerol esters of fatty acids have been available for many years and are produced by many companies. Several patents and papers have been published describing methods of manufacturing, properties, and applications. Glycerol esters of fatty acids are generally prepared in two different methods: esterification and transesterification. The esterification (Grummit et al., 1945; Hatman, 1962; Gros et al., 1964) is carried out between glycerol (2-3 mol) and fatty acids (1-1.3 mol) at elevated temperatures (170-240 "C) in the presence of acids or bases (0.5-1.5 wt %). The transesterification (Hilditch et al., 1937; Franzke et al., 1963; Zwiezykowski et al., 1972) is accomplished by treating glycerol (2-3 mol) and triglycerides (1-1.5 mol) a t similar conditions. The product in both methods contains 40-60% monoglycerides, 30-45% diglycerides, &15% triglycerides, 1-5% free fatty acids and/or their salts, and 2-10% glycerol. Since the required product is the monoglyceride, the mixture is molecular distilled to obtain 90-95 % of monoglycerides. Therefore, any method leading to the formation of pure monoglycerides in a one-step reaction from relatively low cost raw materials will have significant industrial advantage. As potential raw materials, one can consider the use of epichlorohydrin or glycidol for the preparation of pure monoglycerides. The direct reaction between epichlorohydrin and sodium stearate has been studied previously in the presence (Kester et al., 1948; Malkemus, 1959; Maerker et al., 1961; Carreau 1970; Martinez et al., 1973) and in the absence (Dalby, 1966) of catalysts. It was observed that the main difficulty in the process is the low solubility of the acid 0196-4321l84l1223-0452$01.50/0
salt in epichlorohydrin and in other apolar solvents. To overcome this problem a very large excess of epichlorohydrin (up to 16:l on a molar basis) has been used. The common catalyst which was applied is benzyltrimmetylammonium chloride. No explanation was given to the function of the catalyst in the reaction mechanism although it was proved that its presence is essential (Maerker et al., 1961). Based on the modern theories of phase transfer catalysis (Starks et al., 1978; Dehmlow et al., 1980) we believe that the quaternary ammonium salt assists in extracting the stearate anion into the organic phase via a liquid anionexchange mechanism (see Discussion). Since benzyltrimethylammonium chloride and even benzyltriethylammonium chloride are very poor extracting agents in phase transfer reactions due to low lipophilicity (Starks, 1971), we have examined the activity of an efficient phase-transfer catalyst in order to develop a practical procedure for the synthesis of glycidyl esters and monoglycerides. Experimental Section A. Materials. Epichlorohydrin (99%) was obtained
from Aldrich Chemical Co., Inc.; sodium stearate (98%), from Riedel-de-Haen. Tetramethylammonium chloride (TMAC), tetraethylammonium bromide (TEAB), tetrabutylammonium bromide (TBAB), and tetrahexylammonium bromide (THAB) were all pure grade (>98%) from Fluka AG. Pyridine (99%), hexamethyldisilazane, and trimethylchlorosilane were purchased from Sigma Chemical Co. B. Kinetics Runs. Experiments were carried out in a 500-mL glass reactor equipped with a mechanical stirrer, 0 1984 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 3, 1984
453
100 THAB
ap 80 C
.g 60 E > 40 0
20
IO
20
X,
Figure 1. Effect of catalyst structure on the reaction rate. Molar ratio of epichlorohydrin:sodium stearate = 2:l;temperature = 110 O C ; 5% of the catalysts.
a condenser, and a heating mantle through which heating oil was circulated by means of a thermostatic bath. Dried toluene was used as a solvent in all of the runs. Samples were taken from the liquid phase of the reaction mixtures every 5 min and analyzed by GLC. For complete mass balance both the disappearance of the epichlorohydrin as well as the appearance of the glycidic ester were followed with an internal standard. C. GLC Analyses. The GLC analyses were performed on two different gas chromatographs: (I) a Gow-Mac gas chromatograph series 150 equipped with thermal conductivity detector and 10% Carbowax on Chromosorb (6 f t X l/s in.; 100/120 mesh) stainless steel column; temperature of the column, 90 "C; follow-up of the epichlorohydrin consumed by the reaction was achieved using this method (0-xylene was used as internal standard); (11) Packard model 420 equipped with a flame ionization detector and 3% OV-17 on GCQ (3 f t X l/sin.; 100/120 mesh) glass column. The appearance of glycidyl ester was detected by programming of temperature from 140 to 325 "C. The samples containing ca. 20 mg of monoglyceride, were diluted in 1mL of reagent composed of 9 mL of dry and fresh pyridine, 3 mL of hexamethyldisilazane, and 1 mL of trimethylchlorosilane, before injection into the gas chromatograph. D. Procedure for Glycerol Monostearate. Epichlorohydrin (55.5 g, 0.6 mol), solid sodium stearate (92 g, 0.3 mol), and 140 mL of toluene were heated in the reaction vessel described above to 110 OC while mixing. TBAB (4.83 g, 0.015 mol) was added and the mixture was refluxed with vigorous stirring (400 rpm) for 1 h. After cooling, the organic phase was washed three times with 200-mL portions of water. The washed organic phase was evaporated to remove the toluene (110 "C at atmospheric pressure) and the excess of epichlorohydrin (116 "C at atmospheric pressure) (20 g recovered). Alkalinic aqueous solution (100 mL, 0.1 M NaOH) were added and the mixture was heated to 80 "C while mixing for 2 h. The organic phase was separated and analyzed to contain glycerol monostearate (97% pure). The crude product was analyzed by periodic tests to determine monoglyceride content, hydroxyl value, and GLC analysis. In addition, confirmation of its purity was obtained by elemental analysis together with its typical infrared spectrum. The yield was 97 g (90%). Extraction of the aqueous phase of the first washes with 500 mL of chloroform followed by evaporation yielded 3.9 g of the tetrabutylammonium catalyst, most of it in chloride form. Results and Discussion Solid-liquid reactions of sodium stearate with epichlorohydrin (reaction 1)in the presence of toluene as a solvent and quaternary ammonium salts as catalysts were carried out at 110 "C with efficient mechanical stirring.
40
50
60
70
Time, min
Time, min
Figure 2. Effect of catalyst concentration. Molar ratio of epich1orohydrin:sodium stearate = 2:l; temperature = 110 "C; catalyst = TBAB. 100
ap 80 C
;.
60
P 40 V
20
Time, min
Figure 3. Influence of reactants ratio (epich1orohydrin:sodium stearate); temperature = 110 O C ; 5 % TBAB. Table I. The Dependence of Initial Rate of Reaction 1 on the Catalyst Concentration cat. concn, mOl/L 0.0150 0.0375 0.0750 0.1500
init rate, mol/L h
0.90 1.62 2.16 3.78
Table 11. The Dependence of Initial Rate on the Epichlorohydrin Concentration epichlorohydrin concn, mol/L init rate, mol/L h
1.77 3.00 4.00 4.78
~~
0.80 2.16 3.27 4.57
We have initially studied the effect of catalyst structure on the reaction rate for four symmetrical ammonium salts-tetramethylammonium chloride (TMAC), tetraethylammonium bromide (TEAB), tetrabutylammonium bromide (TBAB), and tetrahexylammonium bromide (THAB) each with 5 mol % ' ratio to the sodium stearate. The reaction profiles for each of these catalysts is presented in Figure 1. It is clear that catalysts with a larger number of carbons (which are more lipophylic) are more efficient in the catalytic process. This should be expected from phase-transfer extraction mechanisms (Starks et al., 1973; Herriott et al., 1975). Further evidence for mechanism can be found in Figure 2, where the effect of catalyst quantity on the rate of reaction 1in the presence of TBAB is presented. It can be seen that the rate depends almost linearly on the concentration of the catalyst. In Table I the initial rate of these experiments is presented as a function of TBAB concentration. The concentration of epichlorohydrin also has a strong effect on the reaction rate. This is shown in Figure 3, where the reaction profiles with various epichlorohydrin:sodium stearate ratios are presented. Table I1 summarizes the initial reaction rate as a function of initial epichloro-
454
:-80p 1
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 3, 1984
100
m
t
I? 60
C
2%
0 40
20
20
IO
30
40
50
60
70
T i m e , min
Figure 4. Influence of the temperature. Molar ratio of epichlorohydrin:sodium stearate = 2:l;5 % TBAB.
hydrin concentration. It seems that the rate is practically first order with epichlorohydrin. Finally, the effect of temperature on the behavior of reaction 1was studied. The reactions were carried at 80, 95, and 110 “C; the profiles at these temperatures are presented in Figure 4. In general, it can be concluded that at 110 “C the reaction is very efficient and is completed within 50 min. Based on the above results, we propose the following two-stage mechanism for the esterification reaction 1 in the presence of phase-transfer catalysts (e.g., with TBAB): extraction of the stearate anion from the solid phase (S) by anion exchange with the quaternary ammonium salt C1,H3,C00-Na+(S) + Bu4N+C1-(org) C1,H,,CO0-Bu4N+(org) + NaCl(S) (1)
-
nucleophilic substitution of chloride in the epichlorohydrin by the extracted stearate anion in the organic phase
0
I
-
-
[ C ~ ~ H ~ ~ C O O C H ~ L H C H & I ] N + B UB~u ~ N + C I -
+
I7
H~sCOOCH~CHCH~ (2)
c17
It should be noted that although the catalyst is introduced as bromide salt it is converted to chloride or stearate salt after a few catalytic cycles. Since the extraction coefficient (Brandstrom, 1974) of the stearate anion is probably much larger than that of either chloride or bromide anion, we can expect that the
catalyst is practically in the form of stearate ion pair through the reaction. If step 2 was rate-determining, as in most phase transfer catalyzed displacement reactions, we would expect to observe first-order kinetics (Gordon et al., 1977). Our experimental kinetic profiles suggest fractional order as a result of shifting order mechanism. In addition, the activation energy estimated from Figure 4 (assuming elementary mechanism) is less than 10 kcal/mol. These results indicate that resistance to solidliquid mass transfer plays an important role in the overall reaction rate and under certain conditions setp 1 is apparently the rate-determining one. Based on these results, an efficient and economical procedure for synthesis of glycerol monostearate was developed by base hydrolysis of the glycidic ester (see Experimental Section). This procedure includes recycle of the solvent and the excess of epichlorohydrin as well as recovery of 80% of the catalyst. In spite of the fact that monoglycerides prepared by this method are not food-grade, it is clear that commercial monoglycerides for non-food applications can be synthesized via this improved procedure. Registry No. TMAC, 75-57-0;TEAB, 71-91-0; TBAB, 164319-2;THAB, 4328-13-6;sodium stemate, 822-16-2;epichlorohydrin, 106-89-8; glycerol monostearate, 31566-31-1.
Literature Cited Brandstrom, A. “Preparative Ion Pair Extraction”; Apotekarsocieleten, Hassle-Lakemedei, 1974. Carreau. J.P. Bull. Soc. Chlm. Fr. 1970, 4104. Dalby, G. U.S. Patent 3351 870, 1988. Dehmlow, E. V.; Dehmlow, S. S.“Phase Transfer Catalysis”; VerlagChemie: Weinhein, 1980. Franzke, C.; Kretzchmann, F. Fefte, Selfen, Anstrlchm. 1963, 65, 275. Gordon, J. E.; Kutula. R. E. J . Am. Chem. SOC. 1977, 99, 3903. Gros, A. T.; Fenge, R. 0. J . Am. OliChem. SOC. 1964, 41, 727. Grumml, 0.;Fleming, H. Ind. Eng. Chem. 1945, 37, 485. Hatman, L. Name (London) 1962, 795, 701. Herriott, A. W.; Picker, D. J . Am. Chem. SOC. 1975, 97, 2345. HiMitch, T. P.; Rigg. J. G. U.S. Patent 2073797, 1937. Kester, E. 6.;Preusser. H. M. U S . Patent 2448602, 1948. Maerker, G.; Carmichael, J. F.; Port, W. S.J . Org. Chem. 1961, 26, 2881. Malkemus, D. U.S. Patent 2 910 490, 1959. Martinez, R.; Olano, A. &asas Aceites (Sevllle) 1973, 2 4 , 13. Meade, E. M.; WaMer, D. H. J . Am. 011 Chem. SOC.1962, 39, 1. Starks, C. M. J . Am. Chem. SOC. 1971, 93, 195. Starks, C. M.; Owens, R. M. J . Am. Chem. SOC. 1973, 95, 3613. Starks, C. M.; Liotta, C. ”Phase Transfer Catalysis”: Academic Press: New York, 1978. Zwiezykowski, W.; Ledonchavska, E. R o c z . Techno/. Chem. Zywn. 1972, 22. 215.
Received for review August 22, 1983 Accepted D e c e m b e r 5, 1983
