Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 78-82
78
Functionalization at the Double-Bond Region of Jojoba Wax. 4. a//-trans-Jojoba Wax and I t s Derivatives Arnon Shanl Deparlment of Chemistry, Ben-Gurion University of the Negev, Be 'er-Sheva 84 120, Israel
Anti halogen addition to the cis double bonds of liquid jojoba wax, followed by substitution and elimination, yielded solid all-trans-jojoba wax, with E configuration of the double bonds, in better than 95% purity, while raising the melting point of the solid wax to 52-54 OC. This product served as a starting material for preparation of many of the derivatives that had previously been synthesized from the liquid wax and from partially isomerized jojoba wax, thus completing three series of derivatives of jojoba wax based on cis, cis/trans mixture, and all-trans double-bond configurations.
Introduction The two isolated double bonds of natural liquid jojoba (Simmondsia chinensis) wax have the Z configuration (cis), typical of natural fatty acids and alcohols. Isomerization of the double bonds to the E configuration (trans) increases the melting point of the wax (Table I). This phenomenon has some importance in the preparation of various jojoba products suitable for cosmetic and other applications (Shani, 1983b). The E configuration might also give these substances better physical and chemical properties for special uses. Chemical reactions a t cis or trans double bonds yield products with various properties, depending on the starting configuration of the double bond. Some examples for jojoba wax are bromination-dehydrobromination to yield acetylenic or allenic products (Shani, 1981) or epoxidation of the double bonds and then hydrolysis to tetraols (Shani, 1983a). To obtain jojoba products that consist of only one of the two possible isomers one should start from a substrate that is chemically pure with respect to the cis or trans configuration. The methods employed so far yield no more than 75% trans double bonds a t equilibrium in the jojoba wax (Wisniak, 1977),thus making it impossible to prepare pure all-trans-jojoba wax. We therefore tried to purify the isomerized wax with a urea-inclusion compound (Fieser and Fieser, 1967) but could not enrich for the content of trans double bonds. Small-scale purification of the isomerized wax by AgN0,-silica gel column chromatography yielded pure all-trans-jojoba wax (>95% E double bonds), as determined by IR (Wisniak and Alfandary, 1975), AgN0,-TLC (thin layer chromatography), and repeated crystallization from petroleum ether (the melting point did not change). However column chromatography nor preparative TLC is useful for large-scale production of all-trans-jojoba wax. We thus looked for a simple, short, efficient procedure for large-scale synthesis of all-transjojoba. Such a procedure should meet several chemical conditions and industrial-economical constraints: (1)The reactions involved should be simple and easy to scale up from the laboratory to the industrial level. (2) The reagents involved should be inexpensive and easy to handle, with no problems of safety and/or supersensitivity. (3) The reaction conditions should spare the ester functional site; i.e., conditions that are too basic or strongly acidic should be avoided. (4)The total cost of the chemical transformation should not drastically increase the price of the all-trans-jojoba wax over that of the starting wax.
Table I. Melting Points of Several Samples of Isomerized Jojoba Wax Prepared by Different Catalysts E double catalyst bonds, % mp, "C ref clay 25 29-31 Brown and Olenberg, 1983 36-40 Wisniak, 1977 Se 40-50 38-42 Wisniak, 1977 65-75 NO2 NO, (purified >95 52-54 Shani, 1981 product) Scheme I" 0 ( Z. 2 ) -C H3 (C H2 )-& H=C
I/
H(C H 2 ),,,CO(CHz
),C H=C
H(C H2)7C H3
XP -
I 0
I/
C H 3 ( C H 2 ) 7 C H C H ( C H 2 ) n C O ( C H 2 ) n C H C H ( C H 2 17 C H 3
I I x x
No1 L
I I x x
I1 0 ( E. E ) C H 3 ( C H 2 ) 7C H=C ~
II
H ( C H 2 )mC 0 ( C H 2 ) n CH=C
H (C H 2 )nC H 3
III "Ha, X = C1, IIb, X = Br. m = 7, 9, 11, 13; n = 8, 10, 12, 14.
A careful survey (Sonnet, 1980) of many chemical procedures showed that very few can really meet these conditions. Those that involve thermodynamic equilibrium yield a mixture enriched in E isomer, but do not result in complete conversion. Photochemical and radical reactions give the same results. Among the addition-elimination procedures, two seem to meet our requirements: (i) cleavage of epoxides followed by elimination; (ii) anti halogen addition followed by substitution and elimination. We studied these sets of reactions and found that the second one, which employs C12 or Br2 addition followed by NaI-induced elimination (Sonnet, 1980) (Scheme I and eq I), is better. Experimental Section General. The crude product after each chemical trandformation was used in the next step without further purification. The usual workup consisted of pouring the reaction mixture into H20,extracting with petroleum ether (60-80 "C), washing with saturated NaCl solution, and drying over anhydrous Na2S04. IR and 'H NMR spectra were used to monitor the chemical change occurring in each reaction. Purity was determined by 'H NMR (Shani, 1979; Shani and Horowitz, 1980). All NMR spectra gave
0196-4321/86/1225-0078$01.50/00 1986 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 1, 1986 79 Scheme 11" 0
/I
(E,E)-CH3(CH2)7CH=CH(CH2),cO(CH2),CH=CH(CH~)7CH3
NBS
111 CIS-
0
-
Br
-Ix
CH3(CH2)6CHCH=CHCH(CH2
""y,,
IV (-75% E-, 25% I-)
H
1
LizCOi LiCl
\
trans-
0
X = CI. B r
the following: terminal CH, as triplet a t 6 0.92-0.94, an intense signal at 1.2-1.4 for all aliphatic hydrogens, a triplet a t 2.20-2.26 for -CH,COO, and a triplet at 3.96-4.00 for -CH20C0. All other signals are described later and given in 6 units. Integration curves were consistent with the assignment of the different hydrogens. The NMR spectra were determined on a Bruker WP-200-SY in CC14or CDC1, solution with Me4Si as internal reference. The IR spectra were determined with a Perkin-Elmer Model 377 spectrometer. The samples were run neat or in CHC13solution. Analytical thin-layer chromatography (TLC) plates were prepared with silica gel KGS-254. Microanalyses were performed in the microanalytical laboratory of the Institute for Applied Research, BGU, Israel. Solvents. Petroleum ether (60-80 "C) was dried over CaC1, and distilled. Ether was dried over CaC1, and then over Na and distilled. Dichloromethane, chloroform, carbon tetrachloride, benzene, toluene, methanol, and tBuOH all were CP grade and used without drying. Hexamethylphosphoric acid triamide (HMPT) and dimethyl sulfoxide (Me2SO)were dried over CaH,. Dimethylformamide (DMF) was dried over molecular sieve 4A. Pyridine was dried over KOH. Acetone and chlorobenzene were dried over CaC1,. Thionyl chloride was freshly distilled before use. Tetrachlorojojoba (IIa). Into a solution of 200 g of jojoba wax (I) (0.33 mol) in 500 mL of CHCl,, chlorine gas was bubbled until 48 g were added and the solution became yellowish-green. Excess chlorine was removed, and the solution was washed with aqueous NaHS0, and dried over anhydrous Na2S04. The solvent was evaporated to yield 246 g of IIa, semisolid, which solidified at around 20 "C: IR (neat) 2950-2850,1720,1500,1170,780,720,640,590, 540 cm-l; lH NMR 3.90-4.15 (6 H, -CH,OC(O), -CHCl, m), 2.20 (2 H, CHzCOO, t, J = 7 Hz), 2.00-1.15 (all aliphatic hydrogens), 0.9 (6 H, 2 CH,, t, J = 7 Hz). Some small peaks a t 6 5.2-5.4 indicated that starting material and probably allylic chlorination products contaminated the product (less than 10%). Anal. Calcd for C1: 19.3. Found: 18.01 (Scheme I). all-trans-Jojoba Wax (111). 1. From TetrachloroIIa. A suspension of 6 g of tetrachloro(I1a) (8 mmol) and 30 g of NaI (0.2 mol) in 60 mL of HMPT was heated at 170 "C for 24 h. The reaction mixture was then poured into water and extracted with petroleum ether (60-80 "C) (3 x 100 mL). After regular workup, the product left after solvent evaporation (3.6 g, 76%) solidified and melted a t 45-50 "C. Column chromatography of the product on 100 g of silica gel, eluted with 1%ether in petroleum ether, yielded 2.5 g of purified all-trans-jojoba: mp 52-54 "C; IR (KBr) 2900, 2830, 1720, 1170, 965, 720, 590 cm-l; 'H NMR 5.3 (3.6 H, -CH=CH, m), 3.98 (2 H,-CH,OC(O), t, J = 7 Hz), 2.20 (2 H, -CH,COO, t, J = 7 Hz), 1.95 (7.3 H, allylic H, m), 0.9 (6 H, 2CH,, t, J = 7 Hz). An iodine
It
0r )~-ICO(CH~),,CHCH=CHCH(CH~)~CH~
C y ( C H z ) CH=CHCH=CH(C ~
II
H2I1 CO(CHz), CH=CHCH=CH(C
H2 1, C H3
V ( E € ) - major (I€)-minor =In V, x = 5 , y = 7, 9, 11, 13;x = 5 , z = 8, 10, 12, 14;x = 7, y = 5, 7, 9, 11; x = 7, z = 6,8, 10, 12.
value (Wijs) of 77.7 indicated ca. 93% double-bond equivalence. Analysis of C1 showed 1.3% left in the product, which is ca. 7% of the original chlorine content of IIa. TLC on 20% AgN0,-impregnated plates, eluted with 2% ether in petroleum ether, gave Rf values of 0.5 for all-trans-jojoba, 0.45 for purified NO2-isomerizedjojoba wax, and 0.3 for jojoba wax (cis double bonds). Elution with 5% ether in petroleum ether gave Rf values of 0.9, 0.9, and 0.7, respectively. IR measurement of the trans double bond content according to a known procedure (Wisniak and Alfandry, 1975) showed at least 95% E double bond absorption in the 965-cm-l region. 2. From Tetrabromo-IIb (Shani, 1981). (a) A suspension of 3 g of tetrabromo-(IIb) (3.3 mmol) and 10 g of NaI (0.067 mol) in 30 mL of HMPT was heated at 150 "C for 3 h. The crude product (0.9 g, 46%) was purified on 10 g of silica gel: mp 48-50 "C. (b) The same reaction as above in DMF at 170 "C for 3 h yielded 1.5 g of I11 (67%), and after column chromatography the product melted at 43-45 "C (Scheme I). Jojobatetraene (V). Allylic bromination of 3.6 g of all-trans-jojoba (111) (6 mmol) with 2.52 g of NBS (14 mmol) yielded 4.7 g of IV, identical in NMR and IR to the product that was obtained from jojoba wax or the isomerized wax (Shani, 1981). This product, upon reaction with 4 g of Li,C03 and 4 g of LiCl in 20 mL of dry chlorobenzene at 120 "C for 24 h, yielded 2.2 g of V, which was identical with the product obtained from jojoba wax or isomerized wax under the same reaction conditions (Shani, 1981). The UV spectrum of the product showed some 10-15% of hexaene (Shani, unpublished results), with the following UV absorption peaks: (XmaxCeH1z 257 (8300), 268 (10050), 278 (8520), 301 (8801, 314 (660) (Scheme 11). Bis(ma1eic anhydride) Adduct (VI). A solution of 0.3 g of V (0.5 mmol) and 0.11 g of maleic anhydride (1.1 mmol) in 10 mL of toluene was refluxed for 15 h to yield 0.3 g of product identical with that obtained previously (Shani, 1982) (Scheme 111). Bis(N-methylmaleimide) adduct (VII) was obtained as above and was identical with that obtained previously (Shani, 1982). Anal. Calcd for N: 3.6. Found: 3.0 (Scheme 111). Bis(cyc1ic peroxide) (VIII) was obtained from 0.3 g of V and 20 mg of Rose Bengal in 6 mL of t-BuOH after 10 h in sunlight (Scheme 111). E , E Dibromo Ester (X). To a solution of 5.9 g of all-trans-jojoba (111)(0.01 mol) in 30 mL of CC1, a solution of 3.2 g of Brz (0.02 mol) in 10 mL of CC1, was added
80
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 1, 1986
Scheme I11
/
Br
XIV
Br
Br
Br
LX
/ J
xv 0
dropwise, keeping the inside temperature at 5-15 "C, to yield 9.1 g of IX. Anal. Calcd for Br: 35.2. Found: 36.3. This product was treated with 2.8 g of t-BuOK (0.025 mol) in 50 mL of dry MezSO a t 100-120 "C for 6 h to yield 5.5 g of X: 'H NMR 5.70 (2 H, -CH=CBr-, H, Br cis, t, J = 7 Hz), 4.02 (2 H, -CH,OC(O), t, J = 7 CPS), 2.40 (4 H, -CH,CBr=C-, t, J = 7 cps), 2.00 (4 H, -CH,CH=C(Br)-, m). The corresponding bromoolefinic acid (XII) and alcohol (XIII) were obtained by hydrolysis of X in dilute basic aqueous isopropyl alcohol solution. These two products exhibited the same NMR spectra as did X except for the peaks due to -CH,OC(O), which were replaced by two triplets at 6 3.50 for the alcohol and at 2.20 for the acid (Scheme IV). Jojoba Diepoxide (XIV). A solution of 2 g of I11 (3.4 mmol) and 1.5 g of m-chloroperbenzoic acid (nCPBA) (85% pure, 7.4 mmol) in 15 mL of CHC1, was kept at room temperature for 24 h to yield 1.7 g of diepoxide XIV: mp 50-52 "C. 'H NMR of the product showed the trans oxirane protons at 6 2.62 (1.7 H) and the cis oxirane protons at 2.87 (0.3 H) (Scheme IV). Jojobatetraol (XV). A solution of 1.7 g of XIV (2.7 mmol) in 10 mL of petroleum ether and 5 mL of 20% HCl was refluxed for 5 h to yield 1.3 g of XV as a very viscous and slow-moving liquid. 'H NMR showed broad singlets in 1:l ratio a t 3.78 and 3.58 for the erythro and threo stereoisomers (Scheme IV). Hydrolysis of I11 to (E)-Jojoboic Acid (XVIa) and (E)-Jojobyl Alcohol (XVII). Basic hydrolysis of 3 g of I11 (5 mmol) in aqueous isopropyl alcohol solution yielded 1 g of purified XVIa, mp 44-46 "C and 1 g of XVII, mp 50-52 "C (Scheme V). @)-Methyl Jojoboate (XVIb). Two hundred milli-
liters of methanol in a flask were cooled to 5 "C, 10 mL of acetyl chloride were added slowly, and then 20 g of all-trans-jojoba wax (111) in 20 mL of benzene were added. After reflux for 4 h and workup, a mixture of 20 g of XVIb and XVII was obtained in 1:l ratio. The mixture (0.2 g) was separated on TLC plates to yield XVIb and the alcohol XVII, mp 40-42 "C. (E)-Jojobamide (XIX). The procedure described before (Shani et d.,1980b)was repeated with 3 g of the above 1:lmixture of XVIb and XVII to yield 1.3 g of amide XIX, which was crystallized from petroleum ether: mp 85-86 "C (Scheme V). (E)-Jojobyl Alcohol (XVIIa). To a suspension of 0.2 g of LiAlH, in 15 mL of dry ether a solution of 1.5 g of I11 in 5 mL of dry ether was added dropwise. The product, 1.3 g of alcohol XVIIa, was crystallized from petroleum ether: mp 38-40 "C. The acetate (XVIII) was obtained as a liquid by the usual procedure with (CH,CO),O and pyridine (Scheme V). (E)-Jojobyl chloride (XX) was prepared from XVIIa, SOC1, and pyridine as a base in 1,2-dichloroethane as solvent. Anal. Calcd for C1: 10.7. Found: 11.1(Scheme VI). (E)-Jojobyl bromide (XXI) was prepared from XVIIa and PBr, in CC1,. Anal. Calcd for Br: 21.0. Found: 21.9 (Scheme VI). (E)-Jojobyl mesylate (XXII) was prepared from XVIIa and CH3S02C1and (C2H5l3N as a base in CH,Cl,
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 1, 1986
Scheme V
81
Scheme VI (E)-CH3(CHz )7CH=CH(CH2
)pOH
(E)-CHs(CHz )7CH=CH(CH2
XVIIa
IpBr
XXI \Par3
( E 1- CH 3 ( CH 2 )7C H=C
H( CH z 1P 0H
XVIIa SOClz
cn3s02ci
/ \ (C&
13N
( E)-CH~(CHZ)~CH=CH(CH~)~CI
xx
( E J - C H ~ ( C H ~ ) ~ C H = C H ( C H ~ ) ~ O S O Z% CH~
XXII
0
I1
(E)-CH~(CH~)TCH=CH(CHZ)PI
R3N
XXIXI ( E ) -C H 3 ( CH 2 ) 7 CH=C
'R,+ H ( CH 2 ) p N
-R 'I-
'RZ
XXIV a. R'. F?= C2Hs
b, R'* CH, R 2 =CH2C6Hs: c .
R',
R2=
Q
sorption peak a t 980-960 cm-' in IR and show different and crystallized from ethanol: mp 34-36 "C. Anal. Calcd for S: 8.4. Found: 9.7 (Scheme VI). (E)-Jojobyl iodide (XXIII) was prepared from XXII and NaI in acetone. Anal. Calcd for I 30.0. Found: 30.6 (Scheme VI). (E)-Quaternary ammonium salts (XXIVa,b,c) were prepared from XXIII and several amines. XXIVa was prepared from triethylamine, semisolid. Anal. Calcd: N, 2.74; I, 24.9. Found: N, 3.1; I, 23.7 (Scheme VI). XXIVb was prepared from dimethylbenzylamine, crystallized from ether: mp 183-187 "C. Anal. Calcd: N, 2.4; I, 21.7. Found N, 3.1; I, 22.2. XXIVc was prepared from pyridine, crystallized from ether: mp 200-210 "C. Anal. Calcd: N, 2.9; I, 26.0. Found: N, 2.3; I, 24.8.
Results and Discussion The preferred procedure of addition-substitution-elimination in two steps involves simple anti addition of chlorine or bromine to the double bonds of jojoba liquid wax (I) in CC1, or CHC1, solution. The tetrachloro-(Ha) or tetrabromo-(IIb) derivative is then heated with NaI in HMPT or DMF solution. One SN2displacement and one anti elimination occur, to yield all-trans-jojoba of a purity better than 95% in the E configuration (Scheme I and eq 1). The product is identical with the purified NO,-isomerized product, as determined by melting point, mixed melting point, IR, AgN03-thin layer chromatography, and nuclear magnetic resonance. HMPT was found to be a better solvent for the reaction with the tetrachloro derivative while DMF was better for the tetrabromojojoba compound. Me,SO could not induce complete elimination to yield all-trans-jojoba wax. A series of products similar to those obtained from the natural liquid jojoba wax have been prepared from the solid all-trans-jojoba under the same conditions as those employed for the liquid wax and its derivatives. The E products exhibit essentially the same 'H NMR and IR spectra as those of the liquid jojoba wax products, except for the trans-olefinic hydrogens which exhibit a new ab-
J values for trans-H-H coupling in NMR. Products Derived from the Intact all-trans-Jojoba Ester. For Diels-Alder cycloaddition of a conjugated diene system to occur, it should acquire the s-cis conformation, which is best obtained from an E,E configuration m d is much less sterically crowded than that which cocld be obtained from a Z,E or an E,Z configuration. As we found earlier (Shani, 1981),the isomerized jojoba gives 65-70% of the E,E isomer. We thus repeated the reaction with all-trans-jojoba wax, which might yield, upon allylic bromination by NBS followed by HBr elimination, alltrans-jojobatetraene, Le., two conjugated diene units, one on each side of the chain, which constitutes an E,E structure. But we have found that the product was, in fact, a mixture of 70-75% E configuration and 25-30% Z configuration, similar to the mixture obtained earlier (Shani, 1981), as shown in Scheme 11. This is consistent with our previous finding that upon NBS reaction equilibrium between the E and Z configurations yields a mixture of E / Z of 65-75:35-25 (see V in Scheme 11). Diels-Alder adducts (VI)-(VIII) (Scheme III), which were obtained with maleic anhydride, N-methylmaleimide, and singlet oxygen, respectively, were found identical with those obtained previously (Shani, 1982). Indirect proof for the all-trans configuration was obtained by partial HBr elimination from tetrabromojojoba (IX, see Scheme IV) [by addition of 2 mol of Br, to 1 mol of I11 and subsequent reaction with 2.5 mol of t-BuOK in Me,SO (Shani, 198l)l. The bromoolefinic ester X exhibits only one triplet in NMR at 6 5.70 and none of the triplet of the other isomer (XI) that is derived from jojoba wax (Shani, 1981) (see Scheme IV). In previous studies we showed that NMR measurements of known mixtures can detect impurities above a limit of 2 4 % . We thus can conclude that the purity of the E configuration of alltrans-jojoba wax is better than 95%. The corresponding bromo acid (XII) and bromo alcohol (XIII) could be isolated, too, by hydrolysis of the ester X. They also comprised only one bromoolefinic product and none of the
Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 82-87
82
other isomer derived from liquid jojoba wax. The tetraol XV could be obtained from I11 via the diepoxide XIV (Scheme IV). The expoxidation reaction with m-chloroperbenzoic acid causes some isomerization, since up to 15% &-epoxide is detected in the NMR spectrum (see Experimental Section). Hydrolysis of XIV to the tetraol XV brings about the same results, which we noticed earlier in the reaction of partly isomerized jojoba wax (Shani, 1983a). The ratio of threo to erythro tetraols is ca. 1:1, as determined by NMR (2 H at 3.58 for threo and 2 H at 3.78 for erythro). This indicates an SN1type oxirane opening, allowing for isomerization of the trans-epoxide to both diastereoisomers (Shani, 1983a). In contrast, an SN2type reaction of a trans-epoxide, with one-step oxirane opening, should lead to the erythro isomer only. Products Derived from the Acidic (Jojoboyl) and Alcoholic (Jojobyl) Components of the Ester. Several products that are derived from either the acidic component [(E)-jojoboicacid (XVIa)] or the alcoholic one [(E)-jojobyl alcohol (XVII)] have also been prepared. The procedures for their preparation were identical with those employed for the jojoba liquid derivatives studies before. Thus, (E)-jojobamide (XIX) was prepared by high-temperature and high-pressure reaction of (E)-methyl jojoboate (XVIb) (prepared by transesterification of alltrans-jojoba wax with acidic methanol) with NH3 (Shani et al., 1980b) (See Scheme V). (E)-Jojobyl alcohol was obtained by LiAlH, reduction of all-trans-jojoba wax (Shani, 1979), which was then converted to the corresponding chloride, bromide, iodide, mesylate, and several quaternary ammonium salts (Shani and Horowitz, 1980a) (see Scheme VI). As stated in the Introduction, isomerization to the E configuration changes some of the physical properties of the wax and its derivatives. Thus, the wax itself acquires the highest melting point of the isomerized jojoba waxes. Several derivatives exhibit t,he same trend toward a more
crystalline structure, as is expected for the trans configuration and for hydrogenated polyethylene chains. Since jojoba wax is a mixture of homologous long-chain esters: the increase in crystallinity and the consequent higher melting points are remarkable effects. The (E)-diepoxide (XIV) melts at a high temperature (50-52 "C)relative to the viscous liquid products derived from jojoba wax and even from the partly isomerized wax (Shani, 1983a). The (E)-jojoboic acid (XVIa) and (E)-jojobyl alcohol (XVII) and the amide XIX, derived from the all-trans-jojoba wax, have essentially the same melting points as those of the 2 configuration (Shani, 1980b, 1981). It seems, therefore, that the polar groups play a more significant role than the geometrical configuration of the double bonds in determining the strength of packing forces of the molecules in the solid phase. The mesylate (XXII) again shows higher crystallinity since it melts at 34-36 "C, as compared to the liquid (2)-mesylate (Shani, 1979). The other products are either semisolids or viscous liquids. Studies of the technological properties of these many products and others that can be derived from all-transjojoba wax might allow better application in special uses. Literature Cited Brown, J. H.; Oienberg. H. U.S. Patent 4360387; Chem. Abstr. 1983, 9 8 , 364782. Fieser, L. F.; Fieser. M. M. "Reagents for Organic Synthesis"; Wiley: New York. 1967; Vol. 1, pp 1262-1265. Shani, A. J . Chem. Ecol. 1979, 5 , 557. Shani, A. J . Am. OiiChem. SOC.1981, 5 8 , 845. Shani, A. J . A m . OilChem. SOC.1982, 5 9 , 228. Shani, A. Ind. Eng. Chem. Prod. Res. Dev. 1983a, 2 2 , 121. Shani, A. Soap Cosmet. Chem. Spec. l983b, 59(7), 42. Shani, A,; Horowitz, E. J . Am. Oil Chem. SOC.1980a, 5 7 , 161. Shani, A,; Lurie, P.; Wisniak, J. J . A m . Oil Chem. SOC. 1980b, 5 7 , 112. Sonnet, P. E. Tetrahedron Report No. 77 Tetrahedron 1980, 36, 557. Wisniak, J.; Aifandary, P. Ind. Eng. Chem. Process Res. Dev. 1975, 14, 177. Wisniak. J. Proc. Chem. Fats Other Lipids 1977, 15, 167.
Received for review April 29, 1985 Accepted September 3, 1985
Polydisperse Suspensions of Spherical Colloidal Particles: Analogies with Multicomponent Molecular Liquid Mixtures Eric Dicklnson Procter Department of Food Science, University of Leeds, Leeds LS2 9JT, England
Polydispersity affects the equilibrium and dynamic properties of suspensions of spherical colloidal particles. Fluid-phase equilibria in polydisperse systems, colloidal or molecular, can be conveniently described by an extended theory of conformal solutions devised originally for binary liquid mixtures. For electrostatically stabilized polydisperse suspensions, the theory predicts the occurrence of gas-liquid and liquid-liquid phase transitions. There are, however, other important aspects of polydisperse colloidal behavior that do not have any obvious analogue with multicomponent molecular systems. The effects of polydispersity on the order-disorder transition and the settling of particles under gravity both come into this category.
Introduction Suspensions of colloidal particles occur widely in nature and are important industrially. In many colloids of practical interest-food emulsions, for example-the dispersed particles are close to spherical in shape, but their sizes show considerable variations. These colloidal systems
can be regarded as being truly polydisperse, in contrast to a molecular system, which, however complex, is necessarily paucidisperse (from the Latin "paucus" meaning "few"). As well as particle size, there may also be a continuous distribution of other single-particle properties such as density, refractive index, thermal conductivity, or sur-
0196-4321/86/1225-0082$01.50/00 1986 American Chemical Society
