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Heats of fusion of glycerides
~ e w d ~ r y grid/~ys;** of L ~ M , 2 ! ¢,~978) * " 113-129
~ A T $ OF FUSION OF GLYCE~DES
Umle~d R~.grdL: The ~ t h e , ~elwyn, Hens., Um~ed&fngdom P.eeeDed April 3td, 19~'*
accepted Septembe~ 13th, 1977
The previous work on ~ heats of f ~ n of g l y ~ s is reviewed. Additional data for ma~y a~d, tmtttraCed and unsat~ated trigb/cerides is ~eported and a s~t of best hea~s e4 fusioa values for the stable forms of tri-, di- and monoglyeefldes is give".. • The following equation is shown to r~es¢nt the data for the # polymol~phs of simple melee i
AHf 0 k ~ m o l e )
= 1.023 (Carbon Number) -- 7.79 + 2.03 (No. of Hydroxy Groups) ~
where the Carbon Number is: the chain length for saturated adds; 10.4 for oleic acid; 8.9 for kh'~o1¢i¢ acid; 13.9 for elaidie acid. U ~ this equation ~ h additional corrections for waxed acid riyal*aid stable # p o l y m ~ s , it is possible to calculate AHf for mo~ glycerides of commercial interest. Agzeement between calculated and avm'hble experimental values is good within the
experh-nentalerror. AHf and &$f ate also eaL.~alatcdfor the CH2 groups and for the end groups. The converge,ce tempfmt'a.-e (Le. the maximum melting point) ~f *xiglyeerides is calculated to be 128°C~ "[~e minimum in the M.pt. vs. C.No. plot for fatty a¢ iris is mterpreted in terra~ of greater entropy of th~ groups in the ~ 1 ~ than in the liquid phase and the increasing interaction of the end groups a~ the cha~ length shortens. For monoglycerifle~, h y d ~ n bonding effuses that the end groups are more orderlgl in the solid than in the liquid and there is no ~ i l a r mu~mum in the M.pL vso C~No.
plot.
I. Introduction and review of experimeatal heats of fusi~ B ~ e y [16] in 1950 reviewed the available heat of fusion data. Nowadays, this review is far from complete as there is so much more info~afion available. Now that feeble rraem-ealortmeters (e.g. the Perkin-Elmer DSC-IB and DSC II) are corn. mere/ally a~aflable, many more heats of fusion have been determined for a much wider range of glyeerides. Table I gives details of ~ the heats of fusion of the most stable polymorphic forms ~ have boon , r ~ 1 ~ d to date (December 1976). Several previously unpublished dc~rminations by Unflever auLllors arid our own e x p e ~ e n t a t r ~ t s are also included. There is tie,fly a very heart concentration on the ~ p l e , single acid, saturated trigly~fldes wtde~hwakes it ~ifficutl to decide on a best A~. value for these tnglycerides P ~ 8~d~*ess: ~ O , ~ion HigheVt, V i e t o ~ 3190, A u ~ l i a .
of F~
R~-~trch~ Dairy Re,earth L~boratory, P.O. I~ox 20,
113
1 ~-,
R.E. Timmx, l/eats o/Fusion ofglycerides
TAE Lli Pceviousl/determined heats of fusion (~"l/e) (Data refers to O f~rrn unless otherwise indicated).
Giy~eridea
Heats of Fusion b
Refs. in same older as heats of fueion
YYY CCC LL,L
34.1 (C) 40.2 (C) 45.8 (C), 46.2 (C), 48.7 (X) 47.8 (C), 45.8 (C), 43.2 (C) 49.8 (C), 50.3 (C), 51.8 (X), 48.7 (CJ 46.2 (C), 49.5 (C) 50.6 (C), 50.8 (C), 53.1 (C), 52.1 (C) 53.9 (X), ~9.2 (C), 53.1 (C), 50 (Z), 48.9 (C), 50.8 (C), 62.3 (Q), 49.8 (C) 49.0 (C) 52.0 (C), 52.0 (C), 54.5 (C), 54.6 (C) 557 (X), 50.0 (C), 50.7 (C), 55.0 (C) 50.6 (C), 61.6 (Q), 48.4 (C), 55.0 (¢) 54.5 (C), 50 (S),51.4 (C), 51.8 (C) 54.6 (C) 59.1 (C) 36,7 (C) 41.7 (C) 42.2 (C) 43.2 (C) 40.6 (C) 44,9 (C) 46.1 (C), 47.8 ((3, 48.7 (C), 47.3 ({2) 44.9 (C), 52.2 (CL 48.0 (C) 44.4 (C) 48.3 (C), 46.5 (C) 46.0 (C), 50.0 (C) 41.9 (C), 45 (C), 4.:.5 (S), 37.0 tO)
1 2 1, 3,4b 5,5,5 2, 3, 4b, 5 5,6
MM,t4 PPP
StStSt
A:.A
E;SB CLC ~') ELM MML PYP PCP PStM (~') PStP O') PPSt StCSt StPSt PStSt POP
27(Z), 42.4 (C) POSt StPO (/3) PStO (~') AOSt StOSt StStO (# D PPO (~') POO ( ~ StO0 (:': PlinP f:') OPO OOO PEP PPE StESt
40.6 (C) 34.9 (C) 30,8 (C) >41.1 (C) c 40.8 (C), 47 (C), 46.5 (S) 45 (S), 51.8 (S) 46.0 (C), 40.7 (X), 33. ' (C) 35 (C), 32.5 (S), 32.5 (~') 26.? (C) 29.5 (C) 28.6 (C) 30.2 (C), 34.9 (C) 33.0 (C), 30.5 (Z), 29 (D) 25..8 (C) 42.9 (C) 44.7 (C) 43.8 (C)
1, 2, 3, 4a 4b, 5, 6, 7 work, 8, 9, 10 20 1, 2, 3,4a 4b, 5, 5.6
8, 9, 10, 11 12, 13, 20, Thtt work 20 20 2 2 2 2 2 2 8, 10, 11, 12 2, 8, 10 2 8,10 2, 10 2, 4b, 4b, 28 7, 14 This work This work 1"hi. work This work
2, 4b, 4b 13, 15 4b, 4b, This work 4b, 4b, This work This work This work This work 14, This work 1, 7, 16, 20 28 2 2
R./_'.'. !un:a.., /-l~,ae,~ o/.:usion o f gly,"e,,~der.
! i ~"
Table 1 (continue.d) Glycertde a
~ a t s of Fusios b heats of f~sion
PEE EEE ErErEr LinLinLin trans-ErErEr P (OH) P St (OH) St P (OH) (OH) St (OH) (OH)
36.? (¢} 40.0 (X), 36 (D), 39.5 ~(~ 36.8 (X), 33.0 (C) 23.0 (C), 22.2 (C) 34.4 (C) 54 (S),46.9 (C) 51.3 (C) 50.7 :t3 (O, 43 (S) 54.4 ± 3 (C)
A (OH) (OH) ~,(OH) (OH) Tri-c~.4
51.6 +- 3 (C) 25.4 (C)
17, I~ 17 17 l? 29
30.2 (C)
2.0..
octadecenvi~ Tri-c/s-5octadecenoin Tri-c/s-6 -
53.2 ± 3 (C)
30.7 (C) octadecenoin Tris.cis- ?28.9 (C) octadecenoin Tri-cis-~ octadeccnoin
This wo:k 4b, 16, .~0 4b, 20 20, "'),is work 20 18, Th.s work This work
20 29
25.9 (C)
Z9
27.8 (C)
29
27.1 (C)
20
21.2 (C)
29
21.7 (C)
29
30.6 (C)
29
29.6 (C)
29
Tri-trant-4octadeeenoin Td.mms-5 octadecenoin
38.0 (C)
29
35.6 (C)
29
Trl-mmt-6octadecenoL-~ Tri-tmnz-7octadecenoin Tr/-tva~-8octadecenoin Tri-trans-I 0octadecenoin Tri-tra~- I loctadecenoin Tri-tra/~-I2octadecenoin
43.0 (C)
20
36.0 (C)
29
34.1 (C)
29
34.8 (C)
29
38.7 (C)
29
33.9 (C)
29
T-i.c/s-10octadecenoin Tri~/r-I loctadecenoin Tri-ch-I 2octadcc~noin Tri~/s-I 3 octadecenoin Tri-~-14octadecenoin Tri-cis-15octadecenoin
JC.E. T'unmr, Heats of fusion of giycerides
116 Table 1 (continued) Glyceridea
Heats of Fusion b
Refs. in same order ~L~ heats of fusion
Yri-trans-I3-
28.9 (C)
29
33.8 (C)
29
33.6 (C)
29
32.8 (C)
29
27.7 (C)
20
octa~ecenoin
Tri-tran~- 14octadecenoin Tn-rrans-15 octztdecenoin Tri-I 7oct~decenoin Tri~cis~he×adecenoin
asee Appendix 1 for abbreviations. b Code letters indicate the following methods of determination: C, by calorimetry; D, by cori~lalion with dilationsl Q, unknown, original reference not ~¢n; $, from solubility mcasu~ments; X, from solubilities at 15~C in :oluene adjusted to refer to |O°C below M. Ot. Roqui~ -,, +2.6 cal/g further adjustment to b~lg to M. pt.; Z, DTA on mixtures of glyczrklcs. c To be regarded as a minimum value as complete stabflisation in the ~ form was not aghieved.
In contrast, only gix mixed saturated/unsaturated triglyceddes have previously been studied and we were doubtful of the reliability of the data for two of these (OPO and StStO). Such triglycerides are important constituents of solid or semi-solid oils and fats, such as palm oil, lard, cocoa butter arid tallows. Our experimental work on 11 mixed saturated/unsaturated triglycerides was designed to fir this gap in the heat of fusion data. Where comparisons are possible our values are in ex=ellen* agreement with two recent publications giving heats of fusion of triglycerides. Both Hampson an6 Rothbart [5] and Hagemann and Tallent [20] used hhe Perkin-Elmer DSC and samples of well defined purity. For PPP we obtained 48.9 cal/g and these other workers 49.2 and 49.0 cal/g respectively; for StStSt. we obtained 51.8 cal/g compared with 50.0 and 50.7 cal/g for LinLinLin we obtained 22.2 cal/g compared with 23.0 cal,lg Hagemann and Tallent Earlier workers have tended to find higher values for StStgt and PPP. Thus Charbonnet and Singleton [3] found 54.5 cal/g for StStSt and Yoncoslde [6] gives 55.0 cal/g. In Table 2 we give what we regard as the best experimental valued for the molar hea'~ ~ff fusion of the more important glycerides studied. Each value is the average of the data from the references given. Apart from OPO and StStO mentioned above, we have reiec,~_~d the following data: (i) Valur.:s for LLL, MMM, PPP, StStSt, EEE and ErErEr from ref. 4b, the values given by Smit and Terwen 121] are clearly too high. (it) Values ?or PPP, POP and OOO ~:y Kung [7]. The determination of AHf from •
t,
ti7 Tmbte 2 Comparison of caleulatext and be~ expefime1~tatly ob~rved heats of fu,~ion
Glyeefide
A//f (kcal/mot)
Glyeeride
Experimental Calculated YYY CCC LLL MMM PPP StStSt AAA BBB CLC LLM MML PYP PCP StCSt PgtM ~ PStP PPSt StPSt
PStSt POP PPO POSt
16,1 22.3 29:5 35,4 41.0 47.0 53.3 62.6 21.4 27.8 29.3 30.0 29.4 34.6 36.2 39.7 ,10.4 40.9 41.4 35,8 27.8 35,0
16:8 22.9 29.0 35.2 41.3 47.5 53.6 59.7 20.6 26.8 28.8 28.8 30.9 35,0 37.0 39.1 39.1 ,Ii.1 41.1 35.6 27.0 35.6
A H ~ ~ - ~ J-~-~'. Exper~ment~ Ca!culated
PStO StPO 8tOSt StStO AOSt POO OPO StOO 00(3 P\AnP LinLinLin PEE PEP PPE $~ESt EEE P (OH) P St (OH) St P (OH) (OH) St (OH) (OH) A (OH) (OH) B (OH) (OH)
26,5 30.1 39.9 30.0 >37.7 22.6 30,0 26.2 22.8 23.8 19.9 31.5 35,7 37,2 38 o9 35.0 2~,7 32.1 16.8 19,5 20.6 21.4
27~0 30o2 39,7 30.2 3,9.7 22.7 29,9 24 3 24.1 25.9 19.5 32,9 35~0 35,0 39.1 3.5.2 2%0 31.1 16.7 ~8.7 20.8 "7 2~,8
experiments on mixtures of glycerides is not very reliable and the valae for POP is
gro~y in error. (N) Values for PPP and StStSt by Rao and Jaktar [91, these very old results are clearly in error.
(iv) Value for StStSt by Lutton [I3], ~ted~d from ~otubiiity measurements and ~ f o r e relatively inaect,.rate: Since thereisno shortage of data for StStSt we have ;this vahle~; :~....
(v) Value for StStStby de BruUne [101, clearly too low. (vi) Value for StOSt by Ku.ng [ I5], determined from solubility measurements arid (vii) ~ values for COO and EEE except those from ref\erence 20 - the career determinations are unre~bte compared with the latest DSC results by Hagemaav. and TaUent,
(viii') VldueS for ~OH)P and ~OI~!3 (OH) by g ~ s t e r and de Jong [181, ~:Lese
118
R.E. Tl'mms. Heats of fusion of glycerides
values are deduced from solubility measurements and are not as accurate as the DSC measurements on these glycerides. (ix) The value for POP determined by Lovegren, Gray and Feuge [28], this result is below the values obtained by Unilever workers and does not fi~ in well with data for other palmitic/oleic and stearic/oleic triglyeerides. We are also not satisfied with the value of 34.4 cal/g for trans-trierucin given by Hagemann and Tallent since the value for cis-trieruein is only a little less at aa n ,..,~tt,, compare triolein and trielaidin at 25.8 and 395 eal/g respectively. In Hagemann and Tallent's correlation of AHf with 7'f, trans-trierucin seems to be out of line with the other trans triglycerides. Unlike tr~elaidin and tripetrmelaidin, trans-trierucin showed a ff form which could not be produced by thermal conditioning in the DSC. We suggest, therefore, that the value of 34.4 cal/g refers to the ~' form of tra~ts-trierucin and we estimate that AHf of the corresponding form is 34.4 + 0.76 ~. 45 cal/g = 47.7 kcal/mole. This value is in excellent agreement with the value of ~ / / f for/3 transtnerucin predicted from theoretical comiderations (see Section 3). II. Calculation of the heat of fusion
The problem~ of additivity (or the lack of it) of physical properties has been discussed by Gouw [22] who correlated several physical properties with triglyceride or oil structure or constitution. In 1936, in an excellent review of their work, Garner and King [23] showed how the molar heat of fusion of many long chain compounds increased linearly with the number of CH2 groups in the chain. The heat of fusion of a long chain compound can be regarded as a combination of a term due to the end groups and a term due to the
methylene groups. When the chain length of fatty acid methyl or ethyl esters exceeds 8 - 1 0 Garner and King showed that the contribution of the end groups to the heat of fusion is constant and represented by the simple formula: AH= n.a. + b
(1)
where "a" and "b" are constants and n is the number ofCI42 grouln. Bailey [16] extended Gamer's work to include the simple saturated trigly,zrides.
We now i~ave more, and more accmate, data than Bailey and we can determine more reliable values for "a" and "b". In addition, with the data for unsaturated triglycerides, for partial gly,;erides and for mixed saturated tfiglyceridss, we are able to deduce additional corrections for particular structural features. The result ts a ~eneral method for the prediction of the hea: of fusion of the majority of glycerldes of commercial and scientific interest. A. Basic equetion
The best e:~timates for AHf and A.~f for the simple mono-~Od triglycerides are given
R.E. T ~ m ~ , L~eats o f f~asion o f glyce~Mes
~:~9
TabM 3 M o ~ ~Hf a ~ ~Sf of s f m ~ ~ y ~ ' ~ T~yeeride
&Hf ~ / m o l )
&Sf
Mean
S ~ Deviation
No of expts.
¢~Zdeg/mot
Mei~ag Po~, (K)
YYY COC LLL MMM PPP StStSt AAA BBB
16.05 22.31 29.50 35.36 40.96 46.96 53.27 62.64 22.8
a a 0.63 1.17 1.28 1,70 b b -
1 I 5 5 10 12 1 1 1
57.2 73°2 92.3 106.7 120.7 135.6 151,7 176.0 81.8
281o5 304, 7 3t9.6 331.7 339.6 346.7 351.3 355.7 278.7
EEE LinL~
35.0 19.9
-
I 2
111.0 76~5
260.1
315.2
aTaken as 0.63 for regression analysis. bTaken as 1.70 for regression analysis.
in Table 3. Weighting the results for the saturated tfiglycerides according to *he No. ofexpts, . . . . (Standard Deviation) 2 , the ~ s t l ~ e by regression analysis was calculated as (kcal/mol) = 1.023 (C2qo.)* - 7.79
(2)
with standard errors o f 0,0246 in the coefficient, 1.02 in the intercept and in the calculated &./-/f: 0.46 at C.No. - 24; 0.22 (minimum value) at C.No. = 40.4; 0,67 at C,No. = 66. No points used for the equation are doubtful but the standardised residuz~ /'or BBB (CMo. = 66) is rather hig~h, su$gesting that the experimental wlue for BBB is too ~ ( v ~ l u e ¢~_culated from exln. 2 is 59,72 keal/mo,). Although oftheoretical interest (see Secfioa 3) this ~q~ation is of little u~e in p~-edieting A H f f o r the ~ d e range o f glyee~de~ commorfly encountered~ We sha~ now n o w how this basic equation can be extended by the app!icafior~ of various correcfiorm for m e h structural features as - O H , cis and tmns double bond~. *Note use of Carbon Number arid not n, the number of CH~ gxoups.
120
R K Timms, Heats o [ t ~ o n o[ glyceridea
B Effective carbon numl~:rs for unsaturated acids Eqn. 2 can be. extended to include unsaturated triglyeerides by assigning effective carbon numbers to unsaturated acids. Thus we have deduced for the common unsaturated adds:
•~cid Oleic Elaidic Linoleic Emcic
Effective CNo 10.4 14.0 8.9 13.9 (bared solely on ErErE 0
C Mixed acid triglyceride~ 1. Saturated and trams acids For a triglyceride ABC contain,~ng no cis unsaturated acids, whenever A ~ B or B ~ C a correction of--4.3 kcal/mol should be applied to the value calculated from eqn. (2). This is probably an over-simplification but is quite adequate to account for all the data for the 15 triglycerides of this type studied so far, inehding such triglycerides as PStM and CLC. Example: StCSt
18=46 AHf from exln. 2 -: 39.27 AHf after co,rection = 34.97 Experimental AHf = 34.6
C.No.=10+2X
2. Cis unsaturated acids Where we have only one sort of saturated acid and one sort of unsaturated acid in the triglyceride then the calculation is stra~ightforward. Example: StOSt
Effective C.No. - 10.4 + 2 × 18 = 46.4 AHf from eqn. 2 = 39.68 Experimental Z~/'/f = 39.9
Where we have two different saturated acids, e.g. POSt, then we must use the same carbon number for both saturated acids. This C.No. is that of the saturated acid at the I or 3 position ;if there are two such acids then the effective carbon number is the bh,..qrex ~,ne.
Example' POSt =- POP and effective C.No. = 42.4
RoE. Timms, Heels of fiesion of g;'yce~Sa~.'
i21
PStO ~ PPO and effective C.No. = 42.4 $tPO ~ StStO and effective CoNoo = 46.4 ~ s result is probaNy related to the packing in the molecute arid the impossibiIi~y of achieving the full ~ f per CH2 (see Section 3)when the chains are of diffe~,~g iength,~ Therale can be applied with confidence o~ly for chak~s differing by 2 CH2 groaps a~ there is no experimental data for trigtycerides such as StOL. Since there is no experimental data for tfiglycerides with two diNere~,t c i s o ~ s ~ r ~ ated acids we cannot confidently calculate the heat of fusion of tfigtycerides s,~ch as LinPO. We assume for the present that no special treatment is required for such triglycerides. This is very reasonable where oleic and linotcic acids are invoived as e}~e?/' are of the same chain length and the addition of the second doubte bored has litde perturbing effect (see Section 3).
1). Stable [3' polymorphic forms Eqn. 2 gives the AHf for ~ potymorphs. Some glycerides have no ~ form, but a stable ~' form. Only if the triglyceride contains a cis unsaturated acid is a correctior~ required for a stable/3' polymorph. Thus, for trig!ycerides containing cisounsaturated a~ds only:AHf (lff) = 0.76 X AHf (~) This equation is only empirically derived for the situation where a ~ %,m does ~ot exist and AHf (~) is the result from eqn. 2, It is probably quite satisfactory also for calculating AHf ~ ' ) from AHf (9) ',~her~ the/3 form is stable and has also been used to estimate AHf for the sub.,3 form ~,b~ served for PLinP.
Example: P00
Effective C.No. = 16 + 2 × 10.4 = 36.8 AHf from eqn. 2 = 29.86 AHf from eqn. 3 = 22.69 Experimental A H f "=22.6
E. Partial glycerides Partial glycerides should obey eqn. 1 but with constant °%" different from the °'b ~' for trig~eerides b e c a ~ of the different end groups. Eqn. 2 can then be exte~;Icd ~o include partial glycerides:
AHf = 1.023 (C.No.) - 7.'19 + 2.03 (nh) 2
! 22
li.E. Timing, Heats offum~on ofglycertd~
where .qh is the number c,fhydroxy gruup=. In Table 2 observed mtd calculated values for AHf axe compared and the agreement is seen to be very satisfactory in most cases. The experimental standard deviations for the simple saturated triglycerides range from 0.63 kcal/mol for LLL to 1.70 kcal/mol for StStSt. The rootme~ut square error* between obsevced and calculated LLHf is 1.01 kcal/mol for all 44 glycerides in table 2. The maximum ~ between observed and calculated is 2.87 kc=J/mol for BBB; but this is still within 95% confidence limits assuming the same standerd deviation as :"or StStSt. Since we observe suc~, = ~,~,,, ,., to the basic equation for Ill the otter simple saturated triglyceddes it is probably the experimental value that h. in error.
m . Theoretical comidem flons Irt table 4 we give ~ e heat and en.:ropy of fusion per r~ethylen¢ group and per end group .for triglycefides, diglycefides, moncglycetides, fatty acids and methyl esters of even saturated fatE' acids carbon i umber 8 mt:l above. The entropy of fusion may be de= ribed by an equation sindlar to ..*qn. 1 e.g. ASf = n.c. + d. The comp:ting effects of the inter= ction:, between methylene groups and the end groups have been weU di=,cussed by G Inter ;rod King [23] and by Bailey [16]. For f~tty acids, methyl esters and g ycerides the roughly I kcal/CH2 increment in * Root
mean
~ u z r , , =. e r r o r
=
" No. of Obs.
Table 4 tteat and entropy of fmfionpcr methylene gt )up anti r.er end group for fatty acids a~d their esters Compound
asf (=a/ Jmot)
a/if (kcsl/mol) I~r Clt=
P,n aid gro~
Triglycerides 1,3-Diglycerides
1.02
.4)~;5 a
1.02
-0J:3 b
1-Monoglycerides Fatty acids d ~,~ethyl esters d
1.02 1.03 1.08
+2.38 c -1.~5 -1.99
~I/3b riG) b0.sb (1,313(3) Cb (I-MG) ~4 from ref. 23.
Per CH= 2.54
~,2.5 2.5 2.65 2.83
Per end group 4.S
", 3.,t 13 1.0 -
,nrns, l t e , rs o / f u s i o n o]'gl~,cerides
! ;'..-~
AHf and the 2.5 cal/degJCtl2 increment in ASf !cad "~o a ste: dily h'~creasin~. ~t~biiip:.' of the solid state, i.e. to a higher melting point, since lhe ena group co~ ~:rib~.~,::-, i:. constant. ]'he convergence temperature for triglycerides is calculated from our data ~o be 128°C which i~ in good accord with the 125°C suggested for the maxitnum melting point of an extended CH2 chain [16]. Because of*.he negative heats of fusion and almost zero entropies of fusion of '!ae end groups o f methyl es:ers aad fatty acids, there is a marked tendency !'or '..l:~se c::,.; groups to enter the liquid state. In Garner and King's words the end gro;~ps ate iv~ "more expanded state" in the solid than in the liquid. Hence, in the proce:-s ,.)f r.."~eiti~,.,.; energy is required only to separate the methylene groups, ener D is reh'a~;ed in co.,.we ~,. ing the end groups from the sclid to the liqu'2d state. The situation is very different for the monoglycendes. Here A H , of the end group is positive and A,gf is +13 suggesting that the end group is less expande,~, i e less mobile and more o:dered, in the solid than in the liquid. This effect, must be :elated to the hydroxy groups in the monoglyeeride and the possibility, of hydro:;en bonding increasing the order in the solid state. There are interesting consequ.;nce~ for the melting points (Tf) of monoglycerides compared with fatty acids. The melting point of a glyeeride may be written as: AHf
a.n + b
ASf
e.n + d
Table 5 Melting points (C) of fatty acids, rnonoglycerides and triglycerides (Refs. 16,24,23)
No. of CH2
Fatty acidg
Monoglycerides
rrif-lyc-e,,idcs
16.6 a -7.9 -3.4 16.7
Liquid b~i I.iq uid d 19.4 --
_~,8c -, -7 5 =25 8,3
I¢'oups 0 2 4 6
8
31.6
53.0
31.5
10 : 12 14 16
44.2 54.4 62.9 69.6
63.0 7~3.5 77.0 81.5
46.4 58.5 66.4 73 5
a Acetic add. b Monoacetin. eTdacettn. dNo melti~ point given: by DTA on sample of ~echnical grade monoacetin w~ ob~r.".:~ n~ .-.:~:!'ing but glass Uansition at -650C.
",24
R.E. Timing, tte,a~ o[ ,iafon oy glyc~fda
since AGf = 0. For very long chain compou l&~, n °. and Ff tends'to the convergence temperature a/c. For methyl esters and fatt r acids, b is negative for n > 6 and d is about zero. As the chain length shortens, tte end groups start to interact and b can, and does, char~ge sign to give the conventio ml situation g~ere the end groups are mote ordered in the solid than in the liquid. This is the explanation for the characteristic minimum in the melting point vs. Caqo. pl, ,t for fatty adds. For monoglycerideg, b is positive and d s positive, even for large C.No. As the chain shortens and the end groups start to intera, "t, this can restdtonly in grea~:ezorder in the solid state and there can be no tendenc y for b to change sign. Tf canaot then go through a minimum v~lue. Triglycerides seem to be intermediate ~etween monoglycerides and fatty acids. AHf of the e ld group is only slightly n e ~ fi~-¢-_.ndAS¢ is slightly positive suggesting that a rather s~;qht minimum would be ex! coted ha ~he M.pt.vs. C~lo. curve. These conclusions are in agreement wi: a the available :melting point data (Table 5) although the data is not as complete as we should like. The effect of inserting a double bond i Ro a methylen,.• chain is sho~vn in Table 6. Doubi~ b,Jnd,% like the end groups, introd uoe disorder int:o the structure o f the solid glyceP.de, as shown by the large negative AAHf and AASf'S. The variation of AHf
with double bond position has been discussed by Hagetmmn et al. [29]. There is very
Table 6 Change in AHf and ASf when two CH2 gwups are replaced by a c/s or tra~. double bond (zefs. 20, 29) Position from carbonyl group
4,5 5,6 6,7 7,8 6,7 8,9 9,10 ~3,14 10,1", 11,12 12,1~ 13,14 14,15 15,16
No. of CH2 groups in chain
No. of.~ ato,ns from m~.,.1wlgroup
AAHf (kcal/mol)a cl~ i~
16 16 16 16 14 16 16 20 16 16 16 i6 16 16
13 12 II 10 9 9 8 8 7 6 5 4 3 2
-8.'~ -6.8 -6.6 -7.1 -6..~ -8.0 -.8.1 -8.3 -7.$
a Estimated accuracy is ± 0.5 kcal/moL b Estimated accuracy is ± I e.al/deg/moL
-7.7
-9.4 -9.3 -6.6 -6.9
-4.5 -53 -3.0 -5.0 -5.6 -4.0 -7.8 --5.4 -4.2 -5.7 -7.1 -5.7 -5.7
AASf (calldeg/mol)b '
cl~'
tranl'
-20.8 -14.2 -15.1 -14.7 -14.6 -19.5 -17.9 -18.0 -17.9 -16.9 -24.7 -23.8 -16.7 -17.6
-10.9 -11.3 - 6.1 -11.1 -14.Q - 8.5 -19.4 -13.3 - 9.0 -14A -18.3 -15.1 -15.0
125
R ~ ~. fin,ms, Heat, effusion c,f :flycerMes
limited data available for other than fatty acid &a::~s cf c::rbo~ ::~mb~r ! ~ ((CH2)n wheren = I6),but th# data does suggest that the position of the double bond with restmct to the methyl end group is more important than its position with respect to the:carbonyl end group. Maximum disruption of the (CH2)n structure occars wi~h the insertion' o f a dc:..~Nc ~ond at 4 or 5 carbon ~.~oms from the met~hyt end group. &&H) and ~ S f becmne less negative away from these positions, indicating decreasing dis° raption to the structure. A&Hf and A&Sf vary within this overail pattern, bu~ these detailed variations are poorly understood. T~s:dout:le bonds fit in better than c~ bonds with the zig-zag structure 0 ' ~be moth,erie ch;dn, so that AAHf and AASf are k-ss negative for trans than for ci:: bo~dx maximum disruption to the structure occurs at 4 carbon ~toms group. It was not~.~d earlier that the AHf value reported for trans-triemcin [201 ~, probably wrong. This i:~ suggested in Table 6 by the fact that AAIIf and zS&Sf R)r the tmns 13, 14 bond are more characteristic of a cis than a trans bond in the same retatien to the methyl end group. Assuming that R is the position relative to the methyI end group that is impor:ant, we can calculate AHf for trans-tfierucin to be 47.9 kcal/m ~1. This value is m very good agreement with the figure of 47.7 kcal/mo! cal~ulated assuming that the reported AHf of 36.3 kcal/mol refers to the fl' form. The effect of inserting a second double bond in the chair, is rather small. ~nd the second bond introduces little extra disorder or mobility to t~e chNn. Thus w ~calculate the extra effect of adding a second cis double bond to the oleic acid in triol~ in at the 12, 13 potdtion (linoleic acid) is only AAB) = -0.9 kcal/mol and &&Sf = - ~ .8 cal/ deg/mol.
Ae~owle~ements: I wish tot.hmtk Mr, C, Carlton-Smith for assistance ~ t h the experimental deter° minationofflte heats offusicm, Mr. J, Taylor for assistance with the re~e~ion analysis, Dr; J. Ward and staff for the synt.hesis of many triglyc ~,fides, Un~ever Ltd. for per° ~onm publish this article and to refer to previous] ¢ ur~puNished data°
AFFENIraX 1: A~reviatio m used for fatty acids Acid
Cap~lic
C~ori No. Double Bonds
8:0
I0 : 0 12:0 14:0 16:0
Abbre~4atkm
Y
C L M P
• 26
R.£: Timms, H¢.Tlsof fusion ofglyceKdes
Acid
C_~bon No. Double Bonds
Abbreviation
Stearic Arachidic behenic ?almitoleic Olcic Elaidic L,nolcic
lg:0 2,3:0 22:0 16 : 1 18:1 18:1 18 : 2 22:1 22 : 1
St A B Po O E Lin Er
Erucic
:rans-Frucic a
- 7e -9c -9t - 9c, 12e - 13c - 13t
trait, Er
a s o m e t i m e s called bra.ssidic a d d .
Examples Tricaprylin Trierucin 2-ole'>dipalmitin /,3 dis.earin I -monopaimltin
YYY ErErEr POP St (OH) St P (OH) (OH)
APPENDIX 2: Experimental details A. Method
Heat s of fusion were deterr.nned using a Perkin Elmer DSC-IB differential scanning c:dorimeter, gndium (#Hf = 6.79 cal/g) was usc,d tO calibrate the instrument. Each s~mple was weighed into an aluminium capsule to -+0.01 rag. The sample size varied between 4 and 16 mg. An empty aluminium capsule was used as the reference and the s~mple capsule was surrounded by nitrogen at a flow rate of 20 ml/min. The heating t~ te was 8°C/ram. Samples were stabilised for various lengths of time, see Table AI. The areas under the curves were measured with a planimeter and the reported ,'esult,, ate the average of 3 - 5 determinations on separate samples. The experimental standard deviation was about 0.5 cal/g. B Origin ,_..:.: ~,trity ofglycerides used
The or~#n and purity o,~the glycerides is given in Table AI .The purity of the mixed :v: id *.riglycerides is generally about 95%. i'ut-ity was determined by fatty acid methyl ester analysis, triglyceride analysis by high temperature GLC and tfiglyceride analysis by silver nitrate TIE, although all ~!~ree methods were not used in every case.
R.E.
Timms,
H e a t s of1~asion,
o1"gl.~'cerides
~~"
Teble AI
Glycerid¢
Source
Purity (%)
Stabilisatioa
P ~[ymot,oh
PPP StStSt
Applied .Science Applied Science
99 99
4 days 25°C None, used from Bottle
;.~-2 /~-2
PPO
Unilever Research, (~/laardingen) Unilever Research (Vh~fdingen)
91-95
7 days 26°C
~'-~
92-96
~ days 26°C 9 days 30°C
;~'-3
90-93
9 days 30°C
~-3
94-98
9 days 30°C
If-3
95-99
9 d~ys 30°C
~'-3
94-98
9 day:, 35°C
~-3
91-95
17 days I~°C
StStO POSt StPO PStO AOSt
OPO POO
StO0 PLinP LinLinLin PEE P (OH) P
St (OH) St
Un~v~r Research, ~ e n . ~ Unilever R~earch, ~ ~ m ) Unilever Research, (Vlaardinsen) Unilev~r Research, (Vlaatdt~en) Unilever Research, (Vlaardingen) Unilever Reseazch (Vlaardingen)
+6 days 7~C
~-3
4 days -5°C+ 26 days 10°C
~'-3
95-99
8 day~ 15°C
:J'-3
92 93-97
7 day~ 20°C a
~,ub~3-3 ~
92
IJlldlcv~[ Research, (Vhatdingen) Unilever Research (Vlam'dtngen) Hormel Imtitu~ Unilever Research, OVelwyn) Unileve= Research, (Welwyn)
..95
9 days 30°C
~3
94
None. used from Bottle
;3
Unilever Research, (Welwyn)
96
None, used from Bottle
aCooi~ to --?0°C at 4°C/rain, heated to -40°C a~:4*C/rain, -40°C for 10 min, -40°C to -20"C :t 8*C/rain, -20°C for 15 ruin, -20"C to -33°C at 4°C/m'm.
c. , ,tymo,#rUm The polymorphic form w u assigned b y reference to the M.pt., stabiIisation c.' v.di tion, attd comparison with the literatu~. In one or two cases X.ray evide-:. ,~.wa~ ~.ised for additional confirmation. The polymorpMsm of PI.~nP or oth~-r m<;noim, e,,.~ triglyceride it not reported in the literature. The X-ray long and short spaci, tg• (or
128
RE. ~mms, Beau of fusion of ~lycevide:
I'Linf (M.pt. 27.3°C) are given in Table A2 and compared with data for #'-3 PPO, tl-3 I?OP and sub ~-3 StOSt. The X-ray diffraction pattern of the stable form of PLinP shows features typical of both/3 and t~' forms. The diffraetiot~ pattern most closely resembles the pattern given for the intermediate form of StOSt [30] which Let'ton has described as a sub # form. Wille and Lutton [31 i I~ve also reported that the solid gtyeerides ofcottonseed oil stearine (chemically a mixture of POP and PLinP) elystallise in the sub ~-3 form. We h2ve therefore desi~,aated the observed stable polymorphie form of PLinP as sub ~-3.
X-ray Data (~) for the Stable Forms of PLinP (thit work), POPand PPO[26,27], and the "Intermediate'form ofS05130] P L,nP hkl 002 003 005 006 007 008 Averagect d
3a.2 22.3 13.3 11.1 9.58 8.36 66.8 5.2f, 4.74 453
vs m m w w v, w s m
4.00 vs 3.60 m
POP (8-3)
PPO (8'-3)
StOSt (sub O-3)
30.3 s 20.5 .,,w 12.1 m 10.15 w
33.0 vs 21.8 m 13.1 m 11.0 w 9.23 w 8.22 w 65.3 5.51 w÷ 4.65 m 4.42 w 4.20 w÷ 4.05 $÷ 3.77 s
36.6 vs 24.0 in+ 14.6 m+
60.9 5.42 w 4.56 vs 4.04 m 3.85 w 3.65 m
9.15 w 72.9 5.22 m4.74 s 4.55 m4.23 w 3.88 vs 3.60 m÷
References
[!1 121 131 141 151 161 I81 [91 [~01 112l :13t
.].H.M. Rek and M. Greep, Unilever internal communication, Vlurdingen (1964) D. Tress, r, Unilever ir,ternal communication, Welwyn (1969) G.H. Ch.'.rbonn':.t a:,d W.S. Singleton, J. Am. Oil Chem. Sot., 24 (1947) 140 (a) ~.W. Hendxikse and J. Stip, Unilever i~fternal communication, Vlaardingen (1962); (b) P.W. Hendrikse, Unilever internal communication, Vlaardingen (1962) J.W. Hampson and H.L. Rothbart, J. Am. Oil Chem. Soc., 46 (1969) 143 R.W. Yoncoskie, J. Am. Oit Chem. Soc., 44 (1967) 446 H.C Kung, Lever Bros. internal communication, Edgewater (1959) P.De Bruijne, Unilever internal communication, Vlaardingen (1967) M.~I.R. Rao and S.K.K. Jaktaz, J. Indian Chem. Soc. 12 (1935) 574 M. gnoester, P. De Bruijne and M. Van Den Tt,mpel, Chem, Phys. Lipids, 9 (1972) 309 P. De Btuijne, Unilever internal communication, Vlaazdingen (1966) P. De Bruijne, Unilever internal communication, Vlaaxdinlten (1966) E.S. Lutton, J. Am. Oil Chem. Sot., 32 (1955) 49
R.Eo Timms, He~ts o f ~aqon of g~ycer~dez
129
D.P3. Moran, J. AppL Chemo, (London) 13 (1963) 91
i15 H.C. Rung, Lever Bros. internal cogTm~:aggo~, ~ o g e w ~ ~ ~ 6 ~ [I6! A~E~ Batty, Melting and ~[~ifcSat~or~ ¢,f fats~ Interse~ence (1950) [t 7I E.S. Lutton, J. Am. Oil Chem. So~. 48 (1971) 778 M. Knoester and D J . de Jong, UnJlever imernal c<~mmum~:ation~V]~ard~en ~i973) J. Hannewijk and A:J. Haighton, Unilever internal communication, ~¢q~dL~ger~ (I 955) [20I H.W. Hagemann avM WoH. TaUenL J. Am. O~t Chem. Soc. 49 (1972) t18 E . Smith, Unilever intemat eommunica~iono ~qaardingen (1945) G o u w T~n Hok, ~ e t s of the constitution of fatty oii~ and reiated esters, Doctoga~ t?~es~:~, Technical Umversity o f Delft (1962); T,H, Gouw and J.C, Vlug~e~ J. Am. O~ Chem, 5oc,~ 4~1 0 9 6 4 ) , t42, 426,514, 524 and 675; T.H. Gouw and J.C. Vitig~e:, Fette 8eifea A~str{c~ mittel 68 (I966) 544 and 999 [23] AM. King and W.E. C~mer, J. Chem, Soc., 1368 (1936) [ 2 4 ] K.S. Ma,'~ley, Fatty acids Part 2. InterseJ¢nce (1961) 825 1251 Handbook of chemistry and physics: Ch~mieal Rubber p u b t i s h ~ Co. (45th edn.) [261 E.S. Lutton, L Am. Chem. So¢., 73 (1951) 5595 [271 E ~ . LuRon and F.L.Jackson, L Am. Chem. Soc., 72 (1950) 3254 12g! NoV. Lov~ren, M.S. Gray and R.O. Feugv, J. Am. Off Chem. Sot., 53 (1 ~76) 519 I291 LW. Hagemann, W.H. Tallent, J.A. Barve, I.A. Isrn~| and FD. G~stone~ J oA ~ O~ C~era° Soc., 52 (1975) 204 [301 R.L. Wflle and E.S, Lutton~ L Am. Oil Chem, Sot., 43 (1966) 491
~ A T $ OF FUSION OF GLYCE~DES
Umle~d R~.grdL: The ~ t h e , ~elwyn, Hens., Um~ed&fngdom P.eeeDed April 3td, 19~'*
accepted Septembe~ 13th, 1977
The previous work on ~ heats of f ~ n of g l y ~ s is reviewed. Additional data for ma~y a~d, tmtttraCed and unsat~ated trigb/cerides is ~eported and a s~t of best hea~s e4 fusioa values for the stable forms of tri-, di- and monoglyeefldes is give".. • The following equation is shown to r~es¢nt the data for the # polymol~phs of simple melee i
AHf 0 k ~ m o l e )
= 1.023 (Carbon Number) -- 7.79 + 2.03 (No. of Hydroxy Groups) ~
where the Carbon Number is: the chain length for saturated adds; 10.4 for oleic acid; 8.9 for kh'~o1¢i¢ acid; 13.9 for elaidie acid. U ~ this equation ~ h additional corrections for waxed acid riyal*aid stable # p o l y m ~ s , it is possible to calculate AHf for mo~ glycerides of commercial interest. Agzeement between calculated and avm'hble experimental values is good within the
experh-nentalerror. AHf and &$f ate also eaL.~alatcdfor the CH2 groups and for the end groups. The converge,ce tempfmt'a.-e (Le. the maximum melting point) ~f *xiglyeerides is calculated to be 128°C~ "[~e minimum in the M.pt. vs. C.No. plot for fatty a¢ iris is mterpreted in terra~ of greater entropy of th~ groups in the ~ 1 ~ than in the liquid phase and the increasing interaction of the end groups a~ the cha~ length shortens. For monoglycerifle~, h y d ~ n bonding effuses that the end groups are more orderlgl in the solid than in the liquid and there is no ~ i l a r mu~mum in the M.pL vso C~No.
plot.
I. Introduction and review of experimeatal heats of fusi~ B ~ e y [16] in 1950 reviewed the available heat of fusion data. Nowadays, this review is far from complete as there is so much more info~afion available. Now that feeble rraem-ealortmeters (e.g. the Perkin-Elmer DSC-IB and DSC II) are corn. mere/ally a~aflable, many more heats of fusion have been determined for a much wider range of glyeerides. Table I gives details of ~ the heats of fusion of the most stable polymorphic forms ~ have boon , r ~ 1 ~ d to date (December 1976). Several previously unpublished dc~rminations by Unflever auLllors arid our own e x p e ~ e n t a t r ~ t s are also included. There is tie,fly a very heart concentration on the ~ p l e , single acid, saturated trigly~fldes wtde~hwakes it ~ifficutl to decide on a best A~. value for these tnglycerides P ~ 8~d~*ess: ~ O , ~ion HigheVt, V i e t o ~ 3190, A u ~ l i a .
of F~
R~-~trch~ Dairy Re,earth L~boratory, P.O. I~ox 20,
113
1 ~-,
R.E. Timmx, l/eats o/Fusion ofglycerides
TAE Lli Pceviousl/determined heats of fusion (~"l/e) (Data refers to O f~rrn unless otherwise indicated).
Giy~eridea
Heats of Fusion b
Refs. in same older as heats of fueion
YYY CCC LL,L
34.1 (C) 40.2 (C) 45.8 (C), 46.2 (C), 48.7 (X) 47.8 (C), 45.8 (C), 43.2 (C) 49.8 (C), 50.3 (C), 51.8 (X), 48.7 (CJ 46.2 (C), 49.5 (C) 50.6 (C), 50.8 (C), 53.1 (C), 52.1 (C) 53.9 (X), ~9.2 (C), 53.1 (C), 50 (Z), 48.9 (C), 50.8 (C), 62.3 (Q), 49.8 (C) 49.0 (C) 52.0 (C), 52.0 (C), 54.5 (C), 54.6 (C) 557 (X), 50.0 (C), 50.7 (C), 55.0 (C) 50.6 (C), 61.6 (Q), 48.4 (C), 55.0 (¢) 54.5 (C), 50 (S),51.4 (C), 51.8 (C) 54.6 (C) 59.1 (C) 36,7 (C) 41.7 (C) 42.2 (C) 43.2 (C) 40.6 (C) 44,9 (C) 46.1 (C), 47.8 ((3, 48.7 (C), 47.3 ({2) 44.9 (C), 52.2 (CL 48.0 (C) 44.4 (C) 48.3 (C), 46.5 (C) 46.0 (C), 50.0 (C) 41.9 (C), 45 (C), 4.:.5 (S), 37.0 tO)
1 2 1, 3,4b 5,5,5 2, 3, 4b, 5 5,6
MM,t4 PPP
StStSt
A:.A
E;SB CLC ~') ELM MML PYP PCP PStM (~') PStP O') PPSt StCSt StPSt PStSt POP
27(Z), 42.4 (C) POSt StPO (/3) PStO (~') AOSt StOSt StStO (# D PPO (~') POO ( ~ StO0 (:': PlinP f:') OPO OOO PEP PPE StESt
40.6 (C) 34.9 (C) 30,8 (C) >41.1 (C) c 40.8 (C), 47 (C), 46.5 (S) 45 (S), 51.8 (S) 46.0 (C), 40.7 (X), 33. ' (C) 35 (C), 32.5 (S), 32.5 (~') 26.? (C) 29.5 (C) 28.6 (C) 30.2 (C), 34.9 (C) 33.0 (C), 30.5 (Z), 29 (D) 25..8 (C) 42.9 (C) 44.7 (C) 43.8 (C)
1, 2, 3, 4a 4b, 5, 6, 7 work, 8, 9, 10 20 1, 2, 3,4a 4b, 5, 5.6
8, 9, 10, 11 12, 13, 20, Thtt work 20 20 2 2 2 2 2 2 8, 10, 11, 12 2, 8, 10 2 8,10 2, 10 2, 4b, 4b, 28 7, 14 This work This work 1"hi. work This work
2, 4b, 4b 13, 15 4b, 4b, This work 4b, 4b, This work This work This work This work 14, This work 1, 7, 16, 20 28 2 2
R./_'.'. !un:a.., /-l~,ae,~ o/.:usion o f gly,"e,,~der.
! i ~"
Table 1 (continue.d) Glycertde a
~ a t s of Fusios b heats of f~sion
PEE EEE ErErEr LinLinLin trans-ErErEr P (OH) P St (OH) St P (OH) (OH) St (OH) (OH)
36.? (¢} 40.0 (X), 36 (D), 39.5 ~(~ 36.8 (X), 33.0 (C) 23.0 (C), 22.2 (C) 34.4 (C) 54 (S),46.9 (C) 51.3 (C) 50.7 :t3 (O, 43 (S) 54.4 ± 3 (C)
A (OH) (OH) ~,(OH) (OH) Tri-c~.4
51.6 +- 3 (C) 25.4 (C)
17, I~ 17 17 l? 29
30.2 (C)
2.0..
octadecenvi~ Tri-c/s-5octadecenoin Tri-c/s-6 -
53.2 ± 3 (C)
30.7 (C) octadecenoin Tris.cis- ?28.9 (C) octadecenoin Tri-cis-~ octadeccnoin
This wo:k 4b, 16, .~0 4b, 20 20, "'),is work 20 18, Th.s work This work
20 29
25.9 (C)
Z9
27.8 (C)
29
27.1 (C)
20
21.2 (C)
29
21.7 (C)
29
30.6 (C)
29
29.6 (C)
29
Tri-trant-4octadeeenoin Td.mms-5 octadecenoin
38.0 (C)
29
35.6 (C)
29
Trl-mmt-6octadecenoL-~ Tri-tmnz-7octadecenoin Tr/-tva~-8octadecenoin Tri-trans-I 0octadecenoin Tri-tra~- I loctadecenoin Tri-tra/~-I2octadecenoin
43.0 (C)
20
36.0 (C)
29
34.1 (C)
29
34.8 (C)
29
38.7 (C)
29
33.9 (C)
29
T-i.c/s-10octadecenoin Tri~/r-I loctadecenoin Tri-ch-I 2octadcc~noin Tri~/s-I 3 octadecenoin Tri-~-14octadecenoin Tri-cis-15octadecenoin
JC.E. T'unmr, Heats of fusion of giycerides
116 Table 1 (continued) Glyceridea
Heats of Fusion b
Refs. in same order ~L~ heats of fusion
Yri-trans-I3-
28.9 (C)
29
33.8 (C)
29
33.6 (C)
29
32.8 (C)
29
27.7 (C)
20
octa~ecenoin
Tri-tran~- 14octadecenoin Tn-rrans-15 octztdecenoin Tri-I 7oct~decenoin Tri~cis~he×adecenoin
asee Appendix 1 for abbreviations. b Code letters indicate the following methods of determination: C, by calorimetry; D, by cori~lalion with dilationsl Q, unknown, original reference not ~¢n; $, from solubility mcasu~ments; X, from solubilities at 15~C in :oluene adjusted to refer to |O°C below M. Ot. Roqui~ -,, +2.6 cal/g further adjustment to b~lg to M. pt.; Z, DTA on mixtures of glyczrklcs. c To be regarded as a minimum value as complete stabflisation in the ~ form was not aghieved.
In contrast, only gix mixed saturated/unsaturated triglyceddes have previously been studied and we were doubtful of the reliability of the data for two of these (OPO and StStO). Such triglycerides are important constituents of solid or semi-solid oils and fats, such as palm oil, lard, cocoa butter arid tallows. Our experimental work on 11 mixed saturated/unsaturated triglycerides was designed to fir this gap in the heat of fusion data. Where comparisons are possible our values are in ex=ellen* agreement with two recent publications giving heats of fusion of triglycerides. Both Hampson an6 Rothbart [5] and Hagemann and Tallent [20] used hhe Perkin-Elmer DSC and samples of well defined purity. For PPP we obtained 48.9 cal/g and these other workers 49.2 and 49.0 cal/g respectively; for StStSt. we obtained 51.8 cal/g compared with 50.0 and 50.7 cal/g for LinLinLin we obtained 22.2 cal/g compared with 23.0 cal,lg Hagemann and Tallent Earlier workers have tended to find higher values for StStgt and PPP. Thus Charbonnet and Singleton [3] found 54.5 cal/g for StStSt and Yoncoslde [6] gives 55.0 cal/g. In Table 2 we give what we regard as the best experimental valued for the molar hea'~ ~ff fusion of the more important glycerides studied. Each value is the average of the data from the references given. Apart from OPO and StStO mentioned above, we have reiec,~_~d the following data: (i) Valur.:s for LLL, MMM, PPP, StStSt, EEE and ErErEr from ref. 4b, the values given by Smit and Terwen 121] are clearly too high. (it) Values ?or PPP, POP and OOO ~:y Kung [7]. The determination of AHf from •
t,
ti7 Tmbte 2 Comparison of caleulatext and be~ expefime1~tatly ob~rved heats of fu,~ion
Glyeefide
A//f (kcal/mot)
Glyeeride
Experimental Calculated YYY CCC LLL MMM PPP StStSt AAA BBB CLC LLM MML PYP PCP StCSt PgtM ~ PStP PPSt StPSt
PStSt POP PPO POSt
16,1 22.3 29:5 35,4 41.0 47.0 53.3 62.6 21.4 27.8 29.3 30.0 29.4 34.6 36.2 39.7 ,10.4 40.9 41.4 35,8 27.8 35,0
16:8 22.9 29.0 35.2 41.3 47.5 53.6 59.7 20.6 26.8 28.8 28.8 30.9 35,0 37.0 39.1 39.1 ,Ii.1 41.1 35.6 27.0 35.6
A H ~ ~ - ~ J-~-~'. Exper~ment~ Ca!culated
PStO StPO 8tOSt StStO AOSt POO OPO StOO 00(3 P\AnP LinLinLin PEE PEP PPE $~ESt EEE P (OH) P St (OH) St P (OH) (OH) St (OH) (OH) A (OH) (OH) B (OH) (OH)
26,5 30.1 39.9 30.0 >37.7 22.6 30,0 26.2 22.8 23.8 19.9 31.5 35,7 37,2 38 o9 35.0 2~,7 32.1 16.8 19,5 20.6 21.4
27~0 30o2 39,7 30.2 3,9.7 22.7 29,9 24 3 24.1 25.9 19.5 32,9 35~0 35,0 39.1 3.5.2 2%0 31.1 16.7 ~8.7 20.8 "7 2~,8
experiments on mixtures of glycerides is not very reliable and the valae for POP is
gro~y in error. (N) Values for PPP and StStSt by Rao and Jaktar [91, these very old results are clearly in error.
(iv) Value for StStSt by Lutton [I3], ~ted~d from ~otubiiity measurements and ~ f o r e relatively inaect,.rate: Since thereisno shortage of data for StStSt we have ;this vahle~; :~....
(v) Value for StStStby de BruUne [101, clearly too low. (vi) Value for StOSt by Ku.ng [ I5], determined from solubility measurements arid (vii) ~ values for COO and EEE except those from ref\erence 20 - the career determinations are unre~bte compared with the latest DSC results by Hagemaav. and TaUent,
(viii') VldueS for ~OH)P and ~OI~!3 (OH) by g ~ s t e r and de Jong [181, ~:Lese
118
R.E. Tl'mms. Heats of fusion of glycerides
values are deduced from solubility measurements and are not as accurate as the DSC measurements on these glycerides. (ix) The value for POP determined by Lovegren, Gray and Feuge [28], this result is below the values obtained by Unilever workers and does not fi~ in well with data for other palmitic/oleic and stearic/oleic triglyeerides. We are also not satisfied with the value of 34.4 cal/g for trans-trierucin given by Hagemann and Tallent since the value for cis-trieruein is only a little less at aa n ,..,~tt,, compare triolein and trielaidin at 25.8 and 395 eal/g respectively. In Hagemann and Tallent's correlation of AHf with 7'f, trans-trierucin seems to be out of line with the other trans triglycerides. Unlike tr~elaidin and tripetrmelaidin, trans-trierucin showed a ff form which could not be produced by thermal conditioning in the DSC. We suggest, therefore, that the value of 34.4 cal/g refers to the ~' form of tra~ts-trierucin and we estimate that AHf of the corresponding form is 34.4 + 0.76 ~. 45 cal/g = 47.7 kcal/mole. This value is in excellent agreement with the value of ~ / / f for/3 transtnerucin predicted from theoretical comiderations (see Section 3). II. Calculation of the heat of fusion
The problem~ of additivity (or the lack of it) of physical properties has been discussed by Gouw [22] who correlated several physical properties with triglyceride or oil structure or constitution. In 1936, in an excellent review of their work, Garner and King [23] showed how the molar heat of fusion of many long chain compounds increased linearly with the number of CH2 groups in the chain. The heat of fusion of a long chain compound can be regarded as a combination of a term due to the end groups and a term due to the
methylene groups. When the chain length of fatty acid methyl or ethyl esters exceeds 8 - 1 0 Garner and King showed that the contribution of the end groups to the heat of fusion is constant and represented by the simple formula: AH= n.a. + b
(1)
where "a" and "b" are constants and n is the number ofCI42 grouln. Bailey [16] extended Gamer's work to include the simple saturated trigly,zrides.
We now i~ave more, and more accmate, data than Bailey and we can determine more reliable values for "a" and "b". In addition, with the data for unsaturated triglycerides, for partial gly,;erides and for mixed saturated tfiglyceridss, we are able to deduce additional corrections for particular structural features. The result ts a ~eneral method for the prediction of the hea: of fusion of the majority of glycerldes of commercial and scientific interest. A. Basic equetion
The best e:~timates for AHf and A.~f for the simple mono-~Od triglycerides are given
R.E. T ~ m ~ , L~eats o f f~asion o f glyce~Mes
~:~9
TabM 3 M o ~ ~Hf a ~ ~Sf of s f m ~ ~ y ~ ' ~ T~yeeride
&Hf ~ / m o l )
&Sf
Mean
S ~ Deviation
No of expts.
¢~Zdeg/mot
Mei~ag Po~, (K)
YYY COC LLL MMM PPP StStSt AAA BBB
16.05 22.31 29.50 35.36 40.96 46.96 53.27 62.64 22.8
a a 0.63 1.17 1.28 1,70 b b -
1 I 5 5 10 12 1 1 1
57.2 73°2 92.3 106.7 120.7 135.6 151,7 176.0 81.8
281o5 304, 7 3t9.6 331.7 339.6 346.7 351.3 355.7 278.7
EEE LinL~
35.0 19.9
-
I 2
111.0 76~5
260.1
315.2
aTaken as 0.63 for regression analysis. bTaken as 1.70 for regression analysis.
in Table 3. Weighting the results for the saturated tfiglycerides according to *he No. ofexpts, . . . . (Standard Deviation) 2 , the ~ s t l ~ e by regression analysis was calculated as (kcal/mol) = 1.023 (C2qo.)* - 7.79
(2)
with standard errors o f 0,0246 in the coefficient, 1.02 in the intercept and in the calculated &./-/f: 0.46 at C.No. - 24; 0.22 (minimum value) at C.No. = 40.4; 0,67 at C,No. = 66. No points used for the equation are doubtful but the standardised residuz~ /'or BBB (CMo. = 66) is rather hig~h, su$gesting that the experimental wlue for BBB is too ~ ( v ~ l u e ¢~_culated from exln. 2 is 59,72 keal/mo,). Although oftheoretical interest (see Secfioa 3) this ~q~ation is of little u~e in p~-edieting A H f f o r the ~ d e range o f glyee~de~ commorfly encountered~ We sha~ now n o w how this basic equation can be extended by the app!icafior~ of various correcfiorm for m e h structural features as - O H , cis and tmns double bond~. *Note use of Carbon Number arid not n, the number of CH~ gxoups.
120
R K Timms, Heats o [ t ~ o n o[ glyceridea
B Effective carbon numl~:rs for unsaturated acids Eqn. 2 can be. extended to include unsaturated triglyeerides by assigning effective carbon numbers to unsaturated acids. Thus we have deduced for the common unsaturated adds:
•~cid Oleic Elaidic Linoleic Emcic
Effective CNo 10.4 14.0 8.9 13.9 (bared solely on ErErE 0
C Mixed acid triglyceride~ 1. Saturated and trams acids For a triglyceride ABC contain,~ng no cis unsaturated acids, whenever A ~ B or B ~ C a correction of--4.3 kcal/mol should be applied to the value calculated from eqn. (2). This is probably an over-simplification but is quite adequate to account for all the data for the 15 triglycerides of this type studied so far, inehding such triglycerides as PStM and CLC. Example: StCSt
18=46 AHf from exln. 2 -: 39.27 AHf after co,rection = 34.97 Experimental AHf = 34.6
C.No.=10+2X
2. Cis unsaturated acids Where we have only one sort of saturated acid and one sort of unsaturated acid in the triglyceride then the calculation is stra~ightforward. Example: StOSt
Effective C.No. - 10.4 + 2 × 18 = 46.4 AHf from eqn. 2 = 39.68 Experimental Z~/'/f = 39.9
Where we have two different saturated acids, e.g. POSt, then we must use the same carbon number for both saturated acids. This C.No. is that of the saturated acid at the I or 3 position ;if there are two such acids then the effective carbon number is the bh,..qrex ~,ne.
Example' POSt =- POP and effective C.No. = 42.4
RoE. Timms, Heels of fiesion of g;'yce~Sa~.'
i21
PStO ~ PPO and effective C.No. = 42.4 $tPO ~ StStO and effective CoNoo = 46.4 ~ s result is probaNy related to the packing in the molecute arid the impossibiIi~y of achieving the full ~ f per CH2 (see Section 3)when the chains are of diffe~,~g iength,~ Therale can be applied with confidence o~ly for chak~s differing by 2 CH2 groaps a~ there is no experimental data for trigtycerides such as StOL. Since there is no experimental data for tfiglycerides with two diNere~,t c i s o ~ s ~ r ~ ated acids we cannot confidently calculate the heat of fusion of tfigtycerides s,~ch as LinPO. We assume for the present that no special treatment is required for such triglycerides. This is very reasonable where oleic and linotcic acids are invoived as e}~e?/' are of the same chain length and the addition of the second doubte bored has litde perturbing effect (see Section 3).
1). Stable [3' polymorphic forms Eqn. 2 gives the AHf for ~ potymorphs. Some glycerides have no ~ form, but a stable ~' form. Only if the triglyceride contains a cis unsaturated acid is a correctior~ required for a stable/3' polymorph. Thus, for trig!ycerides containing cisounsaturated a~ds only:AHf (lff) = 0.76 X AHf (~) This equation is only empirically derived for the situation where a ~ %,m does ~ot exist and AHf (~) is the result from eqn. 2, It is probably quite satisfactory also for calculating AHf ~ ' ) from AHf (9) ',~her~ the/3 form is stable and has also been used to estimate AHf for the sub.,3 form ~,b~ served for PLinP.
Example: P00
Effective C.No. = 16 + 2 × 10.4 = 36.8 AHf from eqn. 2 = 29.86 AHf from eqn. 3 = 22.69 Experimental A H f "=22.6
E. Partial glycerides Partial glycerides should obey eqn. 1 but with constant °%" different from the °'b ~' for trig~eerides b e c a ~ of the different end groups. Eqn. 2 can then be exte~;Icd ~o include partial glycerides:
AHf = 1.023 (C.No.) - 7.'19 + 2.03 (nh) 2
! 22
li.E. Timing, Heats offum~on ofglycertd~
where .qh is the number c,fhydroxy gruup=. In Table 2 observed mtd calculated values for AHf axe compared and the agreement is seen to be very satisfactory in most cases. The experimental standard deviations for the simple saturated triglycerides range from 0.63 kcal/mol for LLL to 1.70 kcal/mol for StStSt. The rootme~ut square error* between obsevced and calculated LLHf is 1.01 kcal/mol for all 44 glycerides in table 2. The maximum ~ between observed and calculated is 2.87 kc=J/mol for BBB; but this is still within 95% confidence limits assuming the same standerd deviation as :"or StStSt. Since we observe suc~, = ~,~,,, ,., to the basic equation for Ill the otter simple saturated triglyceddes it is probably the experimental value that h. in error.
m . Theoretical comidem flons Irt table 4 we give ~ e heat and en.:ropy of fusion per r~ethylen¢ group and per end group .for triglycefides, diglycefides, moncglycetides, fatty acids and methyl esters of even saturated fatE' acids carbon i umber 8 mt:l above. The entropy of fusion may be de= ribed by an equation sindlar to ..*qn. 1 e.g. ASf = n.c. + d. The comp:ting effects of the inter= ction:, between methylene groups and the end groups have been weU di=,cussed by G Inter ;rod King [23] and by Bailey [16]. For f~tty acids, methyl esters and g ycerides the roughly I kcal/CH2 increment in * Root
mean
~ u z r , , =. e r r o r
=
" No. of Obs.
Table 4 tteat and entropy of fmfionpcr methylene gt )up anti r.er end group for fatty acids a~d their esters Compound
asf (=a/ Jmot)
a/if (kcsl/mol) I~r Clt=
P,n aid gro~
Triglycerides 1,3-Diglycerides
1.02
.4)~;5 a
1.02
-0J:3 b
1-Monoglycerides Fatty acids d ~,~ethyl esters d
1.02 1.03 1.08
+2.38 c -1.~5 -1.99
~I/3b riG) b0.sb (1,313(3) Cb (I-MG) ~4 from ref. 23.
Per CH= 2.54
~,2.5 2.5 2.65 2.83
Per end group 4.S
", 3.,t 13 1.0 -
,nrns, l t e , rs o / f u s i o n o]'gl~,cerides
! ;'..-~
AHf and the 2.5 cal/degJCtl2 increment in ASf !cad "~o a ste: dily h'~creasin~. ~t~biiip:.' of the solid state, i.e. to a higher melting point, since lhe ena group co~ ~:rib~.~,::-, i:. constant. ]'he convergence temperature for triglycerides is calculated from our data ~o be 128°C which i~ in good accord with the 125°C suggested for the maxitnum melting point of an extended CH2 chain [16]. Because of*.he negative heats of fusion and almost zero entropies of fusion of '!ae end groups o f methyl es:ers aad fatty acids, there is a marked tendency !'or '..l:~se c::,.; groups to enter the liquid state. In Garner and King's words the end gro;~ps ate iv~ "more expanded state" in the solid than in the liquid. Hence, in the proce:-s ,.)f r.."~eiti~,.,.; energy is required only to separate the methylene groups, ener D is reh'a~;ed in co.,.we ~,. ing the end groups from the sclid to the liqu'2d state. The situation is very different for the monoglycendes. Here A H , of the end group is positive and A,gf is +13 suggesting that the end group is less expande,~, i e less mobile and more o:dered, in the solid than in the liquid. This effect, must be :elated to the hydroxy groups in the monoglyeeride and the possibility, of hydro:;en bonding increasing the order in the solid state. There are interesting consequ.;nce~ for the melting points (Tf) of monoglycerides compared with fatty acids. The melting point of a glyeeride may be written as: AHf
a.n + b
ASf
e.n + d
Table 5 Melting points (C) of fatty acids, rnonoglycerides and triglycerides (Refs. 16,24,23)
No. of CH2
Fatty acidg
Monoglycerides
rrif-lyc-e,,idcs
16.6 a -7.9 -3.4 16.7
Liquid b~i I.iq uid d 19.4 --
_~,8c -, -7 5 =25 8,3
I¢'oups 0 2 4 6
8
31.6
53.0
31.5
10 : 12 14 16
44.2 54.4 62.9 69.6
63.0 7~3.5 77.0 81.5
46.4 58.5 66.4 73 5
a Acetic add. b Monoacetin. eTdacettn. dNo melti~ point given: by DTA on sample of ~echnical grade monoacetin w~ ob~r.".:~ n~ .-.:~:!'ing but glass Uansition at -650C.
",24
R.E. Timing, tte,a~ o[ ,iafon oy glyc~fda
since AGf = 0. For very long chain compou l&~, n °. and Ff tends'to the convergence temperature a/c. For methyl esters and fatt r acids, b is negative for n > 6 and d is about zero. As the chain length shortens, tte end groups start to interact and b can, and does, char~ge sign to give the conventio ml situation g~ere the end groups are mote ordered in the solid than in the liquid. This is the explanation for the characteristic minimum in the melting point vs. Caqo. pl, ,t for fatty adds. For monoglycerideg, b is positive and d s positive, even for large C.No. As the chain shortens and the end groups start to intera, "t, this can restdtonly in grea~:ezorder in the solid state and there can be no tendenc y for b to change sign. Tf canaot then go through a minimum v~lue. Triglycerides seem to be intermediate ~etween monoglycerides and fatty acids. AHf of the e ld group is only slightly n e ~ fi~-¢-_.ndAS¢ is slightly positive suggesting that a rather s~;qht minimum would be ex! coted ha ~he M.pt.vs. C~lo. curve. These conclusions are in agreement wi: a the available :melting point data (Table 5) although the data is not as complete as we should like. The effect of inserting a double bond i Ro a methylen,.• chain is sho~vn in Table 6. Doubi~ b,Jnd,% like the end groups, introd uoe disorder int:o the structure o f the solid glyceP.de, as shown by the large negative AAHf and AASf'S. The variation of AHf
with double bond position has been discussed by Hagetmmn et al. [29]. There is very
Table 6 Change in AHf and ASf when two CH2 gwups are replaced by a c/s or tra~. double bond (zefs. 20, 29) Position from carbonyl group
4,5 5,6 6,7 7,8 6,7 8,9 9,10 ~3,14 10,1", 11,12 12,1~ 13,14 14,15 15,16
No. of CH2 groups in chain
No. of.~ ato,ns from m~.,.1wlgroup
AAHf (kcal/mol)a cl~ i~
16 16 16 16 14 16 16 20 16 16 16 i6 16 16
13 12 II 10 9 9 8 8 7 6 5 4 3 2
-8.'~ -6.8 -6.6 -7.1 -6..~ -8.0 -.8.1 -8.3 -7.$
a Estimated accuracy is ± 0.5 kcal/moL b Estimated accuracy is ± I e.al/deg/moL
-7.7
-9.4 -9.3 -6.6 -6.9
-4.5 -53 -3.0 -5.0 -5.6 -4.0 -7.8 --5.4 -4.2 -5.7 -7.1 -5.7 -5.7
AASf (calldeg/mol)b '
cl~'
tranl'
-20.8 -14.2 -15.1 -14.7 -14.6 -19.5 -17.9 -18.0 -17.9 -16.9 -24.7 -23.8 -16.7 -17.6
-10.9 -11.3 - 6.1 -11.1 -14.Q - 8.5 -19.4 -13.3 - 9.0 -14A -18.3 -15.1 -15.0
125
R ~ ~. fin,ms, Heat, effusion c,f :flycerMes
limited data available for other than fatty acid &a::~s cf c::rbo~ ::~mb~r ! ~ ((CH2)n wheren = I6),but th# data does suggest that the position of the double bond with restmct to the methyl end group is more important than its position with respect to the:carbonyl end group. Maximum disruption of the (CH2)n structure occars wi~h the insertion' o f a dc:..~Nc ~ond at 4 or 5 carbon ~.~oms from the met~hyt end group. &&H) and ~ S f becmne less negative away from these positions, indicating decreasing dis° raption to the structure. A&Hf and A&Sf vary within this overail pattern, bu~ these detailed variations are poorly understood. T~s:dout:le bonds fit in better than c~ bonds with the zig-zag structure 0 ' ~be moth,erie ch;dn, so that AAHf and AASf are k-ss negative for trans than for ci:: bo~dx maximum disruption to the structure occurs at 4 carbon ~toms group. It was not~.~d earlier that the AHf value reported for trans-triemcin [201 ~, probably wrong. This i:~ suggested in Table 6 by the fact that AAIIf and zS&Sf R)r the tmns 13, 14 bond are more characteristic of a cis than a trans bond in the same retatien to the methyl end group. Assuming that R is the position relative to the methyI end group that is impor:ant, we can calculate AHf for trans-tfierucin to be 47.9 kcal/m ~1. This value is m very good agreement with the figure of 47.7 kcal/mo! cal~ulated assuming that the reported AHf of 36.3 kcal/mol refers to the fl' form. The effect of inserting a second double bond in the chair, is rather small. ~nd the second bond introduces little extra disorder or mobility to t~e chNn. Thus w ~calculate the extra effect of adding a second cis double bond to the oleic acid in triol~ in at the 12, 13 potdtion (linoleic acid) is only AAB) = -0.9 kcal/mol and &&Sf = - ~ .8 cal/ deg/mol.
Ae~owle~ements: I wish tot.hmtk Mr, C, Carlton-Smith for assistance ~ t h the experimental deter° minationofflte heats offusicm, Mr. J, Taylor for assistance with the re~e~ion analysis, Dr; J. Ward and staff for the synt.hesis of many triglyc ~,fides, Un~ever Ltd. for per° ~onm publish this article and to refer to previous] ¢ ur~puNished data°
AFFENIraX 1: A~reviatio m used for fatty acids Acid
Cap~lic
C~ori No. Double Bonds
8:0
I0 : 0 12:0 14:0 16:0
Abbre~4atkm
Y
C L M P
• 26
R.£: Timms, H¢.Tlsof fusion ofglyceKdes
Acid
C_~bon No. Double Bonds
Abbreviation
Stearic Arachidic behenic ?almitoleic Olcic Elaidic L,nolcic
lg:0 2,3:0 22:0 16 : 1 18:1 18:1 18 : 2 22:1 22 : 1
St A B Po O E Lin Er
Erucic
:rans-Frucic a
- 7e -9c -9t - 9c, 12e - 13c - 13t
trait, Er
a s o m e t i m e s called bra.ssidic a d d .
Examples Tricaprylin Trierucin 2-ole'>dipalmitin /,3 dis.earin I -monopaimltin
YYY ErErEr POP St (OH) St P (OH) (OH)
APPENDIX 2: Experimental details A. Method
Heat s of fusion were deterr.nned using a Perkin Elmer DSC-IB differential scanning c:dorimeter, gndium (#Hf = 6.79 cal/g) was usc,d tO calibrate the instrument. Each s~mple was weighed into an aluminium capsule to -+0.01 rag. The sample size varied between 4 and 16 mg. An empty aluminium capsule was used as the reference and the s~mple capsule was surrounded by nitrogen at a flow rate of 20 ml/min. The heating t~ te was 8°C/ram. Samples were stabilised for various lengths of time, see Table AI. The areas under the curves were measured with a planimeter and the reported ,'esult,, ate the average of 3 - 5 determinations on separate samples. The experimental standard deviation was about 0.5 cal/g. B Origin ,_..:.: ~,trity ofglycerides used
The or~#n and purity o,~the glycerides is given in Table AI .The purity of the mixed :v: id *.riglycerides is generally about 95%. i'ut-ity was determined by fatty acid methyl ester analysis, triglyceride analysis by high temperature GLC and tfiglyceride analysis by silver nitrate TIE, although all ~!~ree methods were not used in every case.
R.E.
Timms,
H e a t s of1~asion,
o1"gl.~'cerides
~~"
Teble AI
Glycerid¢
Source
Purity (%)
Stabilisatioa
P ~[ymot,oh
PPP StStSt
Applied .Science Applied Science
99 99
4 days 25°C None, used from Bottle
;.~-2 /~-2
PPO
Unilever Research, (~/laardingen) Unilever Research (Vh~fdingen)
91-95
7 days 26°C
~'-~
92-96
~ days 26°C 9 days 30°C
;~'-3
90-93
9 days 30°C
~-3
94-98
9 days 30°C
If-3
95-99
9 d~ys 30°C
~'-3
94-98
9 day:, 35°C
~-3
91-95
17 days I~°C
StStO POSt StPO PStO AOSt
OPO POO
StO0 PLinP LinLinLin PEE P (OH) P
St (OH) St
Un~v~r Research, ~ e n . ~ Unilever R~earch, ~ ~ m ) Unilever Research, (Vlaardinsen) Unilev~r Research, (Vlaatdt~en) Unilever Research, (Vlaardingen) Unilever Reseazch (Vlaardingen)
+6 days 7~C
~-3
4 days -5°C+ 26 days 10°C
~'-3
95-99
8 day~ 15°C
:J'-3
92 93-97
7 day~ 20°C a
~,ub~3-3 ~
92
IJlldlcv~[ Research, (Vhatdingen) Unilever Research (Vlam'dtngen) Hormel Imtitu~ Unilever Research, OVelwyn) Unileve= Research, (Welwyn)
..95
9 days 30°C
~3
94
None. used from Bottle
;3
Unilever Research, (Welwyn)
96
None, used from Bottle
aCooi~ to --?0°C at 4°C/rain, heated to -40°C a~:4*C/rain, -40°C for 10 min, -40°C to -20"C :t 8*C/rain, -20°C for 15 ruin, -20"C to -33°C at 4°C/m'm.
c. , ,tymo,#rUm The polymorphic form w u assigned b y reference to the M.pt., stabiIisation c.' v.di tion, attd comparison with the literatu~. In one or two cases X.ray evide-:. ,~.wa~ ~.ised for additional confirmation. The polymorpMsm of PI.~nP or oth~-r m<;noim, e,,.~ triglyceride it not reported in the literature. The X-ray long and short spaci, tg• (or
128
RE. ~mms, Beau of fusion of ~lycevide:
I'Linf (M.pt. 27.3°C) are given in Table A2 and compared with data for #'-3 PPO, tl-3 I?OP and sub ~-3 StOSt. The X-ray diffraction pattern of the stable form of PLinP shows features typical of both/3 and t~' forms. The diffraetiot~ pattern most closely resembles the pattern given for the intermediate form of StOSt [30] which Let'ton has described as a sub # form. Wille and Lutton [31 i I~ve also reported that the solid gtyeerides ofcottonseed oil stearine (chemically a mixture of POP and PLinP) elystallise in the sub ~-3 form. We h2ve therefore desi~,aated the observed stable polymorphie form of PLinP as sub ~-3.
X-ray Data (~) for the Stable Forms of PLinP (thit work), POPand PPO[26,27], and the "Intermediate'form ofS05130] P L,nP hkl 002 003 005 006 007 008 Averagect d
3a.2 22.3 13.3 11.1 9.58 8.36 66.8 5.2f, 4.74 453
vs m m w w v, w s m
4.00 vs 3.60 m
POP (8-3)
PPO (8'-3)
StOSt (sub O-3)
30.3 s 20.5 .,,w 12.1 m 10.15 w
33.0 vs 21.8 m 13.1 m 11.0 w 9.23 w 8.22 w 65.3 5.51 w÷ 4.65 m 4.42 w 4.20 w÷ 4.05 $÷ 3.77 s
36.6 vs 24.0 in+ 14.6 m+
60.9 5.42 w 4.56 vs 4.04 m 3.85 w 3.65 m
9.15 w 72.9 5.22 m4.74 s 4.55 m4.23 w 3.88 vs 3.60 m÷
References
[!1 121 131 141 151 161 I81 [91 [~01 112l :13t
.].H.M. Rek and M. Greep, Unilever internal communication, Vlurdingen (1964) D. Tress, r, Unilever ir,ternal communication, Welwyn (1969) G.H. Ch.'.rbonn':.t a:,d W.S. Singleton, J. Am. Oil Chem. Sot., 24 (1947) 140 (a) ~.W. Hendxikse and J. Stip, Unilever i~fternal communication, Vlaardingen (1962); (b) P.W. Hendrikse, Unilever internal communication, Vlaardingen (1962) J.W. Hampson and H.L. Rothbart, J. Am. Oil Chem. Soc., 46 (1969) 143 R.W. Yoncoskie, J. Am. Oit Chem. Soc., 44 (1967) 446 H.C Kung, Lever Bros. internal communication, Edgewater (1959) P.De Bruijne, Unilever internal communication, Vlaardingen (1967) M.~I.R. Rao and S.K.K. Jaktaz, J. Indian Chem. Soc. 12 (1935) 574 M. gnoester, P. De Bruijne and M. Van Den Tt,mpel, Chem, Phys. Lipids, 9 (1972) 309 P. De Btuijne, Unilever internal communication, Vlaazdingen (1966) P. De Bruijne, Unilever internal communication, Vlaaxdinlten (1966) E.S. Lutton, J. Am. Oil Chem. Sot., 32 (1955) 49
R.Eo Timms, He~ts o f ~aqon of g~ycer~dez
129
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