ASPECTS OF
THE CONSTITUTION OF FATTY
OILS AND RELATED ESTERS
PROEFSCHRIFT
TER VERKRUGING VAN DE GRAAD VAN DOCTOR IN DE TECHNISCHE WETENSCHAP AAN DE TECHNISCHE HOGESCHOOL TE DELFT OP GEZAG VAN DE RECTOR MAG-NIFICUS DR. R. KRONlG, HOOGLERAAR IN DE AFDELING DER TECHNISCHE NATUUR-KUNDE, VOOR EEN COMMISSIE UIT DE SENAAT TE VERDEDIGEN OP WOENSDAG 28 FEBRUARI 1962 DES NAMIDDAGS TE 2 UUR
DOOR
GOUW
TAN
HOK
scheikundig ingenieur
geboren te Djakarta (Indonesië)
'
-~
DIT PROEFSCHRIFT IS GOEDGEKEURD DOOR DE PROMOTOR PROF. DR. IR. J. C. VLUGTER
CHAPTER CHAPTER CHAPTER 1 1.1 1.2 1.3 IA 1.5 1.6 1.7 1.8 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 2.15 CONTENTS Introduction Theoretical considerations
Additivity and correlations of physical constants Application of additivity to mixtures . . Homologous series . . . . Fatty acid methyl esters and triglycerides Alternative method . .
Choice of temperature Application to fatty oils Summary of CHAPTER 1
Preparation of model compounds Introduction. . . . Physical separation and purification methods . Description of preparative distillation column Low temperature crystallization
Chromatographic separation. . . . Urea complexes . . . . Chemical syntheses and purification methods . Acetone-permanganate oxidation. .
Esterification and trans-esterification Storage . . . . Prep:otration of model compounds Saturated fatty acid methyl esters. Unsaturated fatty acid methyl esters Triglycerides Mixed triglycerides . . Summary of CHAPTER 2 page 9 11 13 15 16 18 20 21 23 24 24 25 29 32 34 35 36 37 38 38 43 46 47 47 3 Gas-liquid chromatographic analysis of fatty acid methyl
esters
3.1.
3.2.
Introduction. Trace analysis
3.3 Preliminary investigations; negative peaks 3.4 Combustion analysis . . . .
3.5 Description of the utilized gas chromatographic unit 3.6 Columns . . .
3.7 Quantitative determinations . . . . 3.8 Retention volumes . . . . 3.9 Purity determinations of fatty acid methyl esters 3.10 Butterfat fractions . . . .
3.11 Summary and discussion of CHAPTER 3
49 49 52 53 54 58 60 61 62 62 66
CHAPTER 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 CHAPTER 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 CHAPTER 6 6.1 6.2 6.3 6.4 6.5 6.6 CHAPTER 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 CHAPTER 8 8.1 8.2
Density and molar volume Measurement of density . . . .
Density values of model compounds .
The SMITTENBERG relation. . . . .
Molar volume of saturated fatty acid methyl esters Triglycerides
Unsaturation
Summary of CHAPTER 4
Refractive index and molar refraction Introduction. . . .
Measurement of refractive index . . . .
The SMITTENBERG relation. . . .
Molar refraction of saturated fatty acid methyl esters
Triglycerides . . . . Unsaturation . . . .
Limiting value of refractive index.
Saponification and iodine value Three-dimensional diagram
Summary of CHAPTER 5. . . .
Dispersion and molar dispersivity
Introduction. . . .
Molar dispersion of saturated fatty acid methyl esters Triglycerides . . . . Unsaturation . . . . Limiting value and three-dimensional diagram
Summary of CI-IAPTER 6 . . .
Ultrasonic sound velocity Introduction. . . .
Sound velocity and compressibility
Measurement of sound velocity . . The SMITTENBERG relation. . . . Additive functions of the sound velocity Saturated fatty acid methyl esters.
Triglycerides
Unsaturation . . . . . . . . Correlation of physical constants
Summary of CHAPTER 7
Dielectric constant Introduction. . . . .
Measurement of dielectric constant
page 69 69 72 76 78 80 81 83 85 91 93 98 100 103 104 106 106 108 IlO 113 114 116 118 119 119 121 123 126 129 132 134 137 141 142 143
page
8.3 The SMITTENBERG relation . 147
8.4 Additive functions of the dielectric constant 149
8.5 Saturated fatty acid methyl esters. 150
8.6 Triglycerides 152
8.7 Unsaturation 154
8.8 Limiting value of the dielectric constant . 155
8.9 Correlation of physical constants 156
8.10 Summary of CHAPTER 8 . 157
CHAPTER 9 Graphical representation
9.1 Cross-sections of three-dimensional diagram 159 9.2 Nomographic solutions for rp = f (n, d, J. V.) 167
9.3 Summary of CHAPTER 9 167
CHAPTER 10 Fatty oils
10.1 Introduction. 168
10.2 Original fats and oils 168
10.3 Butterfat fractions 170
10.4 Hydrogenated linseed oil fractions 170
10.5 Molecu\ar distillation fractions . 170
10.6 Physica\ measurements 171
10.7 Correlation of physical constants 175
10.8 Summary of CHAPTER 10 179
Summary 180
Samenvatting 182
Glossary of investigated fatty acids 184
INTRODUCTION
An estimated 34.2 million tons of oils and fats were processed in 1960 [88]. This figure demonstrates the importance of lipids as raw material for an ever expanding industry processing a multiplicity of edible and inedible products. In the Department of Chemical Technology of the Technological University in Delft a great amount of research has been carried out on graphical-statistical analysis of mineral oils, and it was felt that the large experience gained in this area merits a concurrent application of these methods to the oleaginous field.
The essen ti al point in graphical-statistical or struclural group analysis has been the transition from the individual molecule or atom to average structural elements or characteristics of the mixture. A quantitative evaluation of these magnitudes results in an improved insight in the structure of the substance. This analytical method avails itself of various physical constants and functions to identify or characterize the complex mixtures usually observed in nature or modern technology. Mineral oils, fatty oils, coals, and their derivatives, such as gas oil, lubricating oils, asphaltic bitumen, drying oils, and cokes are but a few examples of products existing in a complexing variety of components.
Even with the high resolving power of modern analytical methods, separation of these products into individual components entails laborious methods. This has been the chief reason for the introduction of these analytical methods, which have successfully elucidated many aspects of the constitution of these products. Scope and applicability have been presented in several reviews [155, 115, 230].
Application of these methods to the analysis of fatty oils is a logical development of the cited investigations. In comparison to mineral oils and coals, however, the general characteristics of a fatty oil are much simpler. A fatty oi1 is principally composed of trig1ycerides, molecules of well-defined structures. But generally the jàtty acid is considered as the essential building stone of a fatty oi1, and in nature only a limited number of fatty acids are observed.
The qualitative determination and the quantitative evaluation of the fatty acid composition pose no particu1ar difficulty. Modern gas
chromato-graphic techniques are generally sufficient for this purpose. In the event of doubt, confirmation may be obtained by the conjunct application of infrared analysis.
Whereas the number of fatty acids is quite limited, the number of possible triglyceride isomers is a geometrical function of the molecular weight. And although many natural lipids exhibit a tendency to consist of only a few major triglycerides, the number of minor components can still be exceedingly large. This phenomenon is observed in an intensified form in the interesterified fats.
Successful separation and identification of a limited number of compo-nent triglycerides on a gas chromatographic column have recently been reported by severa1 authors [67, 164J. The procedure available at present, however, is only useful for purity control and for the analysis of relatively simple mixtures of triglycerides. The possibility of qualitative and quantitative ascertainment of complex lipid mixtures in the ne ar future is subject to doubt.
Therefore, development of a graphical-statistical method for assaying the general characteristics of a fatty oil offers interesting possibilities. This is particularly attractive as on1y a limited number of structural elements suffices for general characterization.
By employing the principles of additivity and by introduction of struc-tura1 parameters, a number of relations may be derived between physical constants and characteristics of a fatty oil. Two structural parameters, viz, one connected to the average chain length of the component fatty acid and the other to the degree of unsaturation, are sufficient to char-acterize the majority of fatty oils. To include other structural char-acteristics such as conjugation, average number of ramifications or average number of hydroxyl groups per molecule, more parameters and concurrently more physical constants are necessary.
In this investigation only the first two structural parameters have been considered, and the derived relations are therefore only strictly va1id for mixtures of triglycerides with non-conjugated, non-polymerized, straight-chain component fatty acids.
Investigations may expediently be commenced on the fatty acid methyl ester level. There is only a limited number offatty acids to be considered and the large resemblance between a triglyceride molecule and the three component fatty acid methyl esters is obvious. The transition from the latter compounds to the corresponding triglyceride is therefore not too difficult.
This thesis describes the preparation and purification of the model compounds, the physical measurements on these products to obtain the prime data necessary for quantification of the derived relationships, and the tentative checks of these relations to a nu mb er of fatty oils.
CHAPTER 1
THEORETICAL CONSIDERATIONS
1.1 Additivity and correlations of physical constants 1.1.1
For a given system an additive property is a quantity which is equal
to the sum of the corresponding properties of the constituents. A con-stitutive property, however, depends predominantly on the configuration of the atoms in the molecule and to alesser extent on the number and
nature of these constituents.
Mass is strictly additive; the mass of a molecule equals the sum of the constituent atoms and similarly the mass of a mixture is equal to the sum of the separate masses of the components. Other properties are
usually approximatively additive and are to an ex tent more or less dependant on the configural arrangement.
With varying accuracy many molecular properties such as the molar
refraction, the molar volume, the parachor, and several thermodynamic functions obey additivity rules and for a pure compound these quantities may therefore be calculated from the increments of the constitutive atoms or bonds. It is, ho wever, of importance to note that although application of the ruie of atomie increments generally results in fair approximation of properties such as the molar volume, refraction, parachor, and the magnetic susceptibility, for quantities such as the
enthaipy and intern al energy significant deviations are sometimes ob-served.
An improvement in the accuracy is attained by applying one of the several systems of corrections availabie. Thus, PAULING [163] utilized electronegativities to correct the rule of additivity of bond energies. The
ru Ie of bond properties is a modified form of the additivity of atomie
properties for which more prime data are needed. Another method is to
correct for the influence of constitutive effects, in which case we may
write
(1.1 ) Am
=
molar additive propertyai = increment of contributing element i
Pi
= number of these contributing elements ibj = constitutive corrections for a certain configurative arrangement j Zj
=
the number of these arrangementsGenerally the first term dominates. 1.1.2
For the application of group instead of atomic contributions more prime data are needed and applicability is more restricted; results, however, indicate an improved concurrence with experimental findings. These groups should be made as large as possible and in this manner the influence of the second term can of ten be reduced to a negligible level. In the calculation of the properties of a homologous series the CH2-increment is therefore expediently employed.
Investigations on binary and multi-component mixtures have indicated the feasibility of applying this additivity law not solelyon pure com-pounds, but also on mixtures of compounds. For an ideal binary mix-ture the following relation has been propounded and experimentally confirmed:
( 1.2)
Xl and X2 are moles of Al and A2 respectively in the mixture.
This is an easily understandable extension of the principle of additivity. For compounds of totally different composition non-ideal mixtures may result leading to appreciable deviations from the propounded equations, which must therefore be corrected, e.g.,
( 1.3) !5 is generally negligible for mixtures of organic compounds possessing analogous characteristics, such as members of a homologous series.
Applied to multi-component systems behaving ideally, equation (1.2)
evolves into
(1.4)
Ai
=
additive magnitude of component iMolar additive properties generally include the molecular weight and
the density to counteract contraction that may ensue through mixing. ,M
Am = AspM =F
-d
Asp
=
specific property = mass additive property M = molecular weightd
=
density(1.5 )
F' = combinatiQn of physical constants = volume additive property Thus, Asp = ~YiAi . . . . . (1.6)
yi = weight percentage of component i and F' = ~ ZtFi'. . . . . Zt = volume percentage of component i
(1. 7)
Equation (1.7) is only valid provided no contraction occurs.
1.2 Application of additivity to Dlixtures
A mixture in which the components possess large structural similarities
may be represented by an "average molecule" possessing the average
characteristics of the mixture. The molecular structure of this compound
may be represented as:
B+~ CiPi. . . . . . (1.8) B = basic structure all molecules have in common
P = structural parameter
C = number of structural parameter P
The molecular weight of this mixture is therefore: M
=
MB+~ ct}i(Pt ) • • • • • • . . .f
=
functionA molar additive property can therefore be represented as
( 1.9)
Am = RB+~ ciRpi . . . (1.10) R = increment of the additive function or a constitutive
The deduced specific magnitude is therefore RB+~ciRpi Asp = -M correction (l.lI) ( l.l2)
For another specific magnitude we may analogously compute
A2sv = ,B2+~ ajRp ; j
Combination and elimination results in
An+lsv = C' +i'(AIsv' A2sv ... Ansv)
= C" +i"(AIsv' A2sv ... Am, Pn- m+l ,
... Pn) . . . . . (1.13)
m< n
This general formulation can also be applied to adynamic event, where one may wish to pursue a certain reaction. In this case only those parameters undergoing a change have to be considered. Equation (1.13) may therefore be rewritten as
~An+lsv = C" +i"(~AIsv' ~A2sv ... ~Amsv'
~Pn-m+l ... ~Pn) . . . (1.14)
Sometimes several dependant parameters have been included in the choice of the parameters. If
PI
=
i'" (P2, P3, • • • • • • • Po) . . . (1.15)0
<
m<
nthen
An+lsv = C"+i"(Am+lsv··· Ansv' PI, Po+l'" Pm) (1.16)
and an analogous equation can be described for the dynamic event. The specific quantities are volume-additive, and generally therefore the density is present in the denominator of the proposed equations. Therefore, one can sometimes derive the following equation:
ep(F) = C'" +ep'(FI, F2 .... Fm, Pm+l, .... Pn, d) • . . (1.17) F = physical constant
ep = function
The ascertainment of a structural characteristic which is not depicted as a parameter, but which is directly correlated to the parameters by
G
=
ep"(PI, P2 ... Pp) • • • • • • • • • • • • (1.18) can be computed fromG = K+cp"'(Fp+I, . .... Fm, Pm+l ... Pn, d) . . . (1.19) K = constant
The following conclusions have been derived:
If a mixture of compounds with strongly resembling structures is described by a basic structure Band n parameters, then either n specific quantities or
n
+
1 physical constants are necessary for characterization of the mixture.Characterization of a reaction sequence involving variation in n in-dependant parameters can be carried out by application of either n specific quantities or
n+
1 physical constants.1.3 Homologous series
For a homologous series of organic compounds an additive property of any member may be expressed as
Am
=
RB+ nRcH2 . . . • . . . (1.20) RB=
increment of the basic structure B=
constantRCH2
=
increment of the methylene groupn
=
the number of additional methylene groupsIt has been noted, however, th at for the lower members appreciable deviations may occur if the coefficients of the eq uation have been derived from data on the higher members. Some investigators have therefore proposed two sets of data, one for the lower and one for the higher homologs [52]. Even then large deviations from linearity are of ten observed.
The correct formulation should therefore re ad
. (1.21) as al ready noted by KARAPAT'YANTS [100], but more prime data are needed to evaluate the numerical solution of this equation.
With areasonabie degree of accuracy, however, a large number of additive relations is adequately represented by the linear relation (1.20), especially if the lower members are deleted.
For an alternative additive property Pm one may write the analogous expression :
Pm = R'B+nR'cH 2
and combination with relation (1.20) Am = C1Pm+C2 • • • • • wh ere and Cl
=
RCH2 / R' CH 2 C2 = RB- R'B·RcH2/R'CH2 results inBoth Cl and C2 are therefore constants.
. . . (1.22)
Values for Cl and C2 have been calculated for several homologous series and for several different physical constants by LAGEMANN and DUNBAR [119]. TATEVSKU'S third method [207] is analogous to the delin-eated procedure. Values for Cl and C2 have been reported by him and coworkers for several homologous series of paraffinic hydrocarbons.
1.4 Fatty acid lDethyl esters and triglycerides 1.4.1
The formula of a methyl ester of a saturated straight-chain fatty acid may be written as
CH3(CH2)n-2COOCH3
n - 2 = the number of additional CH2-groups; th is number may therefore
assume a negative value
n
=
the number of CH2-groups corresponding to the term number ofthe ester. This is equivalent to the number of C-atoms in the fatty acid chain
If q = the number of double bonds per molecule, the molecular weight (M) may be denoted as
M
=
46.026+ 14.026 n - 2.016q. . . . (1.24) In lipid chemistry the terms saponification and iodine value are colloquially employed to denote the ave rage molecular weight and the degree of unsaturation. The saponification value (S. V.) is defined as the amount of mg of KOH necessary to neutralize all fatty acids present as free fatty acid, ester or lactone in 1 gram of the product. The iodine value (1. V.) is defined as the amount of halogen, calculated as grams iodine, which can be added to 100 grams of the product. The relation between these quantities, the molecular weight M, and the unsaturation is therefore denoted by M = 56,104 S.V. (1.25 ) 6.631·1. V. q = . . . (1.26) S.V.For unconjugated straight-chain fatty acid methyl esters equation (1.11) may be rewritten as
RF = increment of double bond
_ RB M-46.026+ 2.016 q R L R - M + 14.026 CH 2 + M F
and substitution of the S. V. and the 1. V. in the Mand the q by application of equations (1.25) and (1.26) leads to
Asp = 7.13.10-2 R
CH2+ (1. 782 R B- 20.108 RCH2) . 10-5 S. V.+ + (5.66 RCH2+39.39 RF) .10-61. V. . . . . . . (1.28)
To obviate the effect of the primary terms this equation is therefore only valid for higher values of n, e.g., n ;;> 6.
1.4.2
Analogous lines can also be applied to triglycerides. A saturated triglyceride molecule with straight-chain component fatty acids may be
written as
o
CH20-C~
I
""-~H2
)
n
-
2
CR3 CHO-C( I ~H2) 111-2 CR3CH
2
0
-
C
~
""-(CH2)o-2 CR3For a triglyceride the relations between 1. V., S. V., M, and unsaturation are M = 168,312 . S.V. 6.6311. V. q= S.V.
where q is the average number of double bonds per molecule. The molecular weight may be calculated as
( 1.29)
( 1.30)
M = 124.046+ 14.026 (n+ m+o)-2.016q . . . (1.31)
Analogous to the derivation of relation (1.28) combination of equations (1.11), (1.29), (1.30), and (1.31) results in
Asp = 7.13.10-2RcH2+(5.94RB- 199.37 RcH2 )·10-6S.V.+
For n, m, and 0
<
6 deviations may be expected to occur.Equations (1.28) and (1.32) have been derived for a simple member of the series. They may, however, be extended to mixtures of these compounds. In the latter case one must consider the average charac -teristics of the mixture.
1.5 AIternative lDethod
The delineated procedure in the last sub-paragraph has the weak detail of having only one compound as a basic term. This compound, e.g., tricaprylin should therefore be available in a very high degree of purity and the physical constants unambiguously recognized as correct.
As will be noted in the subsequent chapters, we had at our disposal a number of high purity fatty acid methyl esters and some triglycerides of a lower purity. From the former members the CH2-increment is obtained with a high degree of precision as a statistical average. Given accurate values of the physical constants of the basic term, application of equation (1.32) will yield a relation which may be assumed to predict the desired values in a more than adequate manner. In the absence of comparative reliability the applicability of the obtained relation will depend on the accuracy of the data of this basic term.
Although unequivocality is unattainable from the value of one triglyceride of unknown absolute purity, results are greatly improved by considering a number oftriglycerides and the application of (statistical) averages. Given the data of the products at our disposal the best use of these values is described in the following method which is applied in the subsequent chapters:
For the higher members of a homologous series, where the observed CH2-increment is approximately a constant value the well-known relation reads
Am = A+n RCH~
for the saturated fatty acid methyl esters. Am = molar additive property
A
=
constant. . . (1.33)
n = the term number or the number of C-atoms in the fatty acid chain For advocates of atomic increments the value of A is equal to the contributions of one carbon, two oxygen, and two hydrogen atoms. A in these investigations is, however, an extrapolated value from the higher members of the series and is therefore only comparable to the increment of the CH200 group if RCH2 is invariant over the whole range of terms.
Strict comparability is the exception rather than the rule, A therefore being generally unequal to these contributions. One of the exceptions is noted in the molecular weight where A
=
RCH200=
46.026.For saturated and unsaturated straight-chain fatty acid methyl esters
the relation reads
Am = A+n R cH2+q RF' • . . . • . • • • (1.34) q = the number of unconjugated double bonds in the molecule RF = the increment of the double bond
Considering three moles of fatty acid methyl esters one obtains
~A~e = 3A+(n+m+o) R cH2+(q+q'+q") RF • • • • (1.35)
n, m, and 0 being the term numbers and q, q', and q" the nu mb er of
double bond in the three fatty acid methyl esters respectively. Comparison of the structure of a triglyceride molecule
,,1
0
o
H 2C-0- C"II
~
(
CH2)n
-
2CH3
CH3( CH2) m_2-C-0- CHI
/
0
H 2C- 0- C" "(CH2)o-2CH3with the 3 component fatty acids in the methyl ester form
demonstrates the small difference between the triglyceride and the com-ponent fatty acid methyl esters. This difference will subsequently be termed the glyceride increment Glyc.
A;,;i = ~A~e-Gryc . . . (1.36)
= 3A+(n+m+o) RCH2+ (q+q' +q") RF- GryC
and the molecular weight of this triglyceride is therefore
M = 3 ·46.026+ 14.026· (n+m+o) - 2.016 (q+q' +q") - 4·1.008 . . . (1.37) In terms of atomie increments the glyceride increment is equal to the contribution of 4 hydrogen atoms. In the subsequcnt chapters it wiU
be observed that Gryc is not computed from the hydrogen increment but rather as the average of the differences in the molar quantities of the triglycerides and the sum of the corresponding fatty acids in the methyl
ester form; Gryc is therefore calculated according to (1.36).
If now a mixture of triglycerides is considered as described in the preceding paragraphs, one may write:
A~~i = C+n RCH2+ij RF-GryC . . . (1.38)
C = constant = 3A
n
= average number ofC-atoms in the fatty acid chains ofthe triglyceridemolecule
ij = average number of double bonds per molecule
and the average molecular weight of this mixture is
M = 134.046+ 14.026 n- 2.016 ij . . (1.39)
Combination of these two last equations with relations (1.29) and
(1.30) yields
Asp = 7.13.10-2 R
cH2+{5.941 (C-Gryc) -56.78 RcH2}10-6
s.
v.++(5.66 RCH2+39.39 RF) .10-61. V. . . . . (1.40)
This equation is of course only a slight modification of (1.32). In the
event of accurate prime data both relations should yield equivalent
results. The latter relation, however, makes better use of the available data to approximate the correct numerical values.
1.6 Choice of teDlperature
Many additive properties are independant of temperature, but for accurate measurements and predictions the use of a standard temperature is mandatory.
In many fields of chemistry, especiaUy petroleum technology, 20 °C is the accepted standard temperature for the measurements of physical
constants. For comparable investigations in lipid chemistry the choice of the same temperature possesses salient advantages, as with the modern
development of industrial technology an intensified interaction is noted
between chemical fields which have hitherto been accepted as
independ-ant areas. The disadvantages are, however, more marked.
1. At 20 °C a large percentage of the natural lipids are semi-solid.
2. A preponderant amount of all saturated acids present in nature and
their methyl esters are solid at th at temperature.
3. In many tropical countries with an important oil and oil seed
industry the ambient temperature is higher than 20°C and this
tempera tu re is therefore not easily maintained for routine physical
measurements.
Many authors have suggested 40 °C as reference temperature and the
following advantages have been adduced:
1. At this temperature almast all natural lipids are liquid.
2. This temperature is generally higher than the ambient temperature,
but not so high as to entail particular precautions.
The disadvantage lies mainly in the lack of co-ordination with other
classes of organic compounds.
Although other reference temperatures have been proposed by many
authors, they have not been widely accepted as standards.
The measurements described in this thesis were usually executed at
40 °C. In the majority of cases measurements have also been carried out at 20 °C.
1. 7 Application to fatty oils
1. 7.1
As the additivity rules hold for mixtures as well as for pure compounds,
data on triglycerides can gene rally be applied to refined fats and oils.
Applicability to unrefined lipids is dependant on the amount and the
influence of the non-triglyceride components present. Concordant
ap-plication of these graphical-statistical methods will therefore have to
concern itself first on the isolation, purification, and determination of the
additivity contributions of these ancillary compounds.
1.7.2
Rifractive index and density are the acknowledged physical quantItIes
designation of these two constants as basic properties is therefore
partic-ularly suitable, as these two quantities have always been utilized in the
development of comparative analytical research in the mineral oil field.
A representation of lipids as mixtures of polymerized,
non-conjugated, straight-chain fatty acid triglycerides indicates the need of
two parameters for characterization and therefore at least 3 physical
constants.
The iodine value has been selected as the third physical constant for the following reasons :
1. The iodine value is directly related to the unsaturation and the
parameter q.
2. The iodine value possesses a large commercial importance.
3. Ascertainment of the iodine value is not difficult.
4. In the equations for specific magnitudes, the coefficient belonging
to the 1. V. is of ten relatively small. This indicates a small dependancy of the specific quantities of the iodine value. Mathematically it follows that a small error in a specific magnitude will result in a
large error in the derived iodine value and conversely a very large
error in the measured iodine value will only result in a small error
in the predicted specific property.
l.7.3
Equation (1.32) may be app1ied to the molar refraction according to
LORENTZ-LoRENZ [128, 129]; then,
n2- 1 1
- - - = Cl +C2 S. V.+C3 J. V. . . . . (1.41)
n2
+
2 d
Cl, C2 , and C3 are constants.
The specific magnetic susceptibility may be written as
x
d =
C4+C5 S. V.+Csl. V. . . . . (l.42)C4 , C5 , and C6 are constants.
Combination of the last two equations results in
x =
l'
(n, d, 1. V.) . . . (1.43)The same line of thought is applicable to other physica1 constants which are found in other additive quantities, such as the parachor, the
This results in
cp
=
f
(n, d, 1. V.) • . . • . • • . . . (1.44) cp = physical constantIn a three-dimensional diagram with the density, the rifractive index
and the iodine value on the three mutually perpendicular axes, planes of constant values for particular physical constants may be constructed.
Thus, the sound velocity, the molecular weight, magnetic susceptibility,
and other physical constants are quantities depictable in this diagram.
1.8 SUlDlDary of chapter 1
The additivity laws are reviewed and extended to cover the static
and dynamic aspects of mixtures of components possessing large
struc-tural similarities.
The results are applied to the homologous series of the fatty acid
methyl esters and to the triglycerides, and the applicability to fatty
oils is considered.
The rifractive index, density, and iodine value have been selected as the
CHAPTER
2
PREPARATION OF MODEL COMPOUNDS
*
2.1 Introduction
As indicated in CHAPTER 1, investigations on fatty oils can expediently be commenced at the methyl ester level. Reliable physical constants of pure compounds are very scarce and there is perhaps just as many conflicting as concurrent data. We therefore deemed it necessary to prepare these compounds ourselves in light of the paucity of the required data.
Although contemplation of only even-membered fatty acids would suffice in the first approximation for the consideration of technicallipids, the investigations were also extended to the uneven members. The sp here of synthetic fats is therefore also partially covered; the presentation of physical data is more complete as all consecutive members are included in the envisaged range.
The methyl esters of the saturated fatty acids from C2 to C20 inclusive
and the unsaturated members methyl oleate, methyllinolate, methyl linolenate, and methyl erucate have therefore been prepared in high purity. Triglycerides have also been synthesized, although their purity is not comparable to that of the methyl esters. A number of these model compounds have been acquired by gift, loan, or purchase.
The preparation of these compounds entails a variety of syntheses and purification procedures, which may differ from compound to compound.
2.2 Physical separation and purification tnethods
2.2.1 Precise ester distillation
Distillation of methyl esters have always been extensively applied to the separation of fatty acid mixtures or for the purification of single components. Efficient columns have been developed which applied to fatty acid methyl ester analysis achieve almost complete separation in one through-put. There is an affiuence of literature on this subject
*
The au thor is indebted to Ir. TJOA GroK HOEN for the co-operation in a substan-tial part of the investigations described in this chapter.[26, 34, 113, 222]. A review on the application oflow pressure fractional
distillation to the investigations of lipids has been presented by
MUR-RAY [152].
2.2.2
We had at our disposal a spinning band distillation column, which
was developed and already described by SIE [189, 190]. Some pertinent
data of the column are presented in TABLE 2.1.
T ABLE 2.1 Characteristics of spinning band column
Separating power in theoretical plates at infinite reflux. 50 28 20 Distillation speed 120 ml/h 280 ml/h 0.4-2 mi Pressure atm atm 1.0 mm Test mixture n-heptane-methylcyclohexane n-heptane -methylcyclohexane di-n-butylphthalate-di-n-butylazeleate Hold-up
Pressure drop 0.007-0.29 mm Hg at atmospheric pressure
2.3 Description of preparative distillation column
2.3.1
As the spinning band column had a relatively small capacity and
utilization of th is apparatus was not solely confined to the investigations
described in this thesis, another preparative column with a larger
capacity was deemed necessary.
Special attention has been expended during the design of this new
apparatus to versatility to meet the varying demands of the products
as weIl as possible. Thus, columns and packings we re interchangeably
constructed, so a large choice of separating power and capacities is
available. The construction allowed for easy changing of the columns, and generally not more than half an hour's work is entailed per change.
To ensure pseudo-adiabatic distillation conditions an auxiliary heating mantle was installed, consisting of two concentrically mounted silvered glass tubes of about 80 cm length with internal diameters of 60 and
90 mm respectively. Resistance wires were fitted in the space between
propor-tc • thermocouple hot water cold \'Vater cqmpressed al( 2 3, : electronfc hmlng device solenoid
0
trF~==~~=~=;""""e==1300 Volt product ref{u,x
iron co re .~ .~ •• glass woof auxiliary heating L'_',-' _ _ _ :.'-.:-l 220 Voil
"""d:'l
. cartes/on manostatm9:111
0-25mV to com pensator and galvano-meter teflon chromium -plated- -reflector screen 220 Volt Ic 375 Watt infrared lamp 4 receiving fJasks pure nitrogen \..mJmercury manometer 0-800 rrrrHgOl
buffer vessel 20 liters 'tfJcuum pumptionally heavier wound than the upper part. A circular metal reflector screen covered with aluminum foil is concentrically mounted outside these tubes. The whole system is mounted on pressed asbestos and lined with asbestos thread to minimize upward drafts. Temperature readings at three different points in the mande during the on-stream periods of the apparatus indicated an excellent consistent temperature control within a few degrees over the whole column.
Vacuum jacketed columns we re applied throughout, and covered on
the outside with aluminum foil. Internal silvering generally resulted in collapse of the tube during annealing. The columns had the same extern al diameter which fitted closely in the asbestos-lined holes in the supports of the auxiliary heating mande. The intern al diameters we re 30, 20, and 8 mmo Whereas the two first-named columns were smooth tubes, the last column was a modified Vigreux with perpendicular protu -berances of an external diameter of 2 mm placed approximately 8 mm above each other and consecutively rotated in respect to each other over an angle of 90 degrees.
In the first two columns the Helipak column packing by Messrs. Podbielniak of Chicago, 111. was utilized. Two types were available, viz, type 6001 and type 6002 [167].
A vapour-phase reflux head piloted by an iron co re in a solenoid was
utilized. The intermittent magnetic field is generated and controlled by an electronic timing device. The draw-off can be varied in steps from 0-6 seconds and the reflux can be independandy adjusted in steps from 1 to 40 seconds.
The reflux head was provided with an internally silvered vacuum jacket. It was packed in glass wool kept approximately at the distillation temperature by auxiliary heating coils and totally encased by a circular metal screen covered with aluminum foil.
The product in the still pot is subjected to infrared healing which possesses many advantages above other conventional heating methods. As glass absorbs the infrared rays to a small extent only, heating is direct and high wall temperatures are avoided. With conventional external heating methods the heat is conducted through the glass and a significant heat gradient may ensue between the glass and the evaporating surface. Especially at the end of the distillation when the liquid level is low, many parts of the ketde tend to become dry and overheated, resulting in an increased tendency. of the product to decompose. Control of distillation flow is very sensitive, response being almost immediate to change of input. Equilibrium is speedily attained, heating is safe, and during the whole distillation the charge is clearly visible.
Temperature readings were effected by double copper-constantan ther-mocouples placed in the still pot, in the reflux, at three different points in the auxiliary heating mantle and in the coolant of the condensors. The temperature of melting ice was utilized as the reference point. By a pushbutton selector the desired thermocouples are either connected to a crude m V -meter, or to a compensator connected to a galvanometer. Temperature oscillations of 0.02-0.03 °C and larger are easily detected on the galvanometer.
By a simple switch compressed air, cold water from the tap, or warm water from a boiler can be utilized as coolant in the condensors of the
system.
The manostat employed was a mercury manostat of the cartesian diver type. It was a slightly modified apparatus as described by GILMONT [71], and the dimensions have been calculated for optimum conditions in the
50-200 mm pressure range.
Experience with this manostat indicates a constant pressure in the
system with oscillations of less than 0.1 mm in the optimum range af ter
stabilization has been achieved.
Through a system of valves nitrogen can be introduced in the kettle, in the system, or in the product receptacles. Provisions have been made for changing the receiving flasks without disturbing the vacuum of the
column.
Control of the column was facilitated by mounting as many controls as possible upon one panel.
As the products we re also designed for measurements on magnetic
susceptibility, care was taken to prevent the presence of ferromagnetic particles in the distillate. This was achieved by mounting 4 Ticonal magnetic bars of 8 mm diameter and 20 mm length in the top of the column. Ticonal is one of the few magnetic sub stances demonstrating only a slight decrease oftheir magnetic properties at higher temperatures. Particular care was taken in the construction of the receiving part of the column to ensure that no contact of the distillate was possible with stopcock grease. This was accomplished by funneling the distillate through the ground glass joints and by dropping the liquid exactly through the center of wide bore stopcocks. Drip tips were installed to
divert the flow of the distillate.
Efficient fractionation is counteracted by uneven boiling and local superheating of the charge [26]. HICKMAN and TREVOY [87] recognized
evaporation as being governed by surface conditions and that a torpid area may be formed on the surface of the distilland resulting in a dimuni-tion of the active section with concomitant higher temperature gradients
and explosive "bumpings". This is especially true with even heating of the still pot and quiet surface conditions. To counteract this
phenom-enon, stirring of the charge is essen ti al and the resultant improvements
are generally quite significant.
Mixing of the charge was promoted by sin tering small glass particles to the bottom of the still flasks to induce vigorous boiling. For work
under low pressure a controlled leak of nitrogen is introduced in the bottom of the flask to ensure turbulence and even evaporation.
2.3.2
Determination of the separating power is achieved by utilization of
a mixture of n-heptane and methylcyclohexane. Stearic acid in benzene
was applied to the determination of the column hold-up. The pressure drop
was measured by two independant manometers connected to the kettle
and to the top of the column; a small nitrogen stream was introduced in the tube between the manometer and the kettle to obviate
condensa-tion of the product in the leads.
The well-known equation of FENSKE [59], relating kettle composition,
overhead composition, and theoretical plates has been graphically
depicted in a nomogram by BROOKS [27] for a n-heptane-methylcyclo
-hexane mixture, utilizing a = 1.07. We made use of this nomogram for our measurements.
The distillation characteristics are depicted in the graphs on the following pages. TABLE 2.2 Column 2 3 4 5 7 Internal diameter mmm 20 20 30 30 8
2.4 Low telllperature crystallization
2.4.1 Packing 6001 6002 6001 6002 modified Vigreux
Crystallization at low temperatures has developed into a powerfu1 preparative tooI for the separation of glycerides, fatty acids, esters, and other classes of compounds.
.
.
0 Q. 0 i g ~ E ·s }~
!
t
CUfumn 70 50 7 la ' -100 250 500 1000 1500 2000 2500 ---<0_ through -put role ml/nFIG. 2.2 Column efficiencies at different through-put rates
column re flux 70 IJ IJ 50 JO
HJ~
.---.--.-
-la ~7-~ ---." 7 -IJ 100 250 500 1500 2000 2500 - t h r o u g h - p u t rale /000 mIlt 70 50 JO laFIG. 2.3 Comparison of column efficiencies at different refiux ratios. Test mixture: n-heptane-methylcyclohexane
/ 100 , / / / / / column 4 / ~--COIUmnJ column 'I 250 500 1000 1500 2000 2500
---<
._
through -put rale miJ hFIG. 2.4 Liquid hold-up in mI as a function ofthe through-put rate. Test mixture: stearic acid in benzene
-.
~ E E column] - - - - t .. _ through-put rat~ ml/hFIG. 2.5' Pressure drop through a packed column as function
of the through-put rate
applied to the separation of compounds highly soluble in organic solvents at room temperatures but which become sparingly soluble at low tem-peratures down to - 80 °C. This procedure has aptly demonstrated its applicability by superseding the now almost obsolete separation by difference of the solubilities of metal soaps. Reviews on the application
of these methods have been published by BROWN [29], BROWN and KOLB [30], and supplementary data are available from other authors in
the field [169, 10].
Separation of mixtures of fatty acids and their esters from solvents
depends in the first place on solubility differences between the
com-ponents at the temperature of crystallization. Exceptional results may be attained if the solubilities of the components in a mixture approximate
the solubility data of the pure compounds. In practice one is confronted
with the problem of intersolubilization and mixed crystal formation, depending on the solvents applied.
Crystallization at low temperatures is especially adapted to the separation of unsaturated fatty acid mixtures. However, for mixtures of fatty acids with four or more double bonds this procedure has not been very successful, due to the very high solubilities even at very low tem
-peratures. 2.4.2
The crystallization apparatus used in these investigations consisted
of a rectangular tank in which a cylindrical glass vessel of 10 liters capacity is placed on cork tablets and isolated with glass wool. In this
crystallizing vessel of 3 liters capacity is mounted. This metal structure
is necessary as it facilitates alignment of the paddie and prevents the
cylinder from capsizing during the latter stages of filtration.
The solution to be fractionated is introduced in the crystallizing vessel and a brass stirring paddie is inserted in the liquid. Slow stirring is
accomplished by a motor with gear box, resulting in an average of 6 revolutions per minute.
Cooling is accomplished by slowly adding finely crushed portions of solid carbon dioxide to the methylated spirit bath, and the resultant temperatures are checked by low temperature thermometers in the bath
and in the solution. To counteract excessive foaming, air is blown at a slight angle on the surface of the coolant.
Filtration is carried out by inverted suction through a fritted glass filter connected to a three-liter suction fiasko The stirrer is removed, the
adhering crystals scraped off by a long nickel spatuia and the crystals are allowed to settle down. Filter paper is slightly moistened and placed
on the glass filter and suction is applied which holds the filter paper in
place. Filtration is commenced on the supernatant liquid and proceeds quite rapidly.
The crystals are sometimes very voluminous, and removal of all mother liquor is therefore very difficult, even when the crystals are strongly pressed. Subsequent recrystallizations are therefore necessary, but this difficulty may be obviated by washing the crystals once or
twice with solvent which is precooled to about 15 to 20 °C below the temperature of crystallization. This expediently washes out the mother liquor from the crystals.
2.5 Chrotnatographic separation 2.5.1
Chromatographic columns packed with solid powdery absorbents are of ten applied in the solid-liquid chromatographic separation of fatty
acids or triglycerides. As absorbents alumina or silicic acid intimately mixed with filter-aid is generally employed. By the use of appropriate
. solvents separation may be achieved according to chain length or to the degree of unsaturation.
Chromatography has been successfully applied to the preparative separation ofhighly unsaturated fatty acids such as linoleic, linolenic, and arachidonic acid from natural sources [84, 89, 173], without having to resort to chemical bromination-debromination procedures which would
tomv..meter
1
ï rJrying to~' _arjusted helght .fuent -,~ ____ -,----,,-m column. elven I. 220 V. tv mercuryhave resulted in cis-trans modifications of the natural product. The very small quantities involved in chromatographic separations is the greatest disadvantage of this method.
2.5.2
Silicic acid is acidified by first washing with aqueous hydrochloric acid and then with water until free from acid. The product is dried at 180°C for several hours in a nitrogen atmosphere and subsequently 1eft to cool to room temperature. The absorbent is prepared by thor-oughly mixing 4 parts of silicic acid with 1 part of Celite filter-aid. Mter filling, the column is activated by heating to about 70°C for three hours in a current of nitrogen. Mensurability of the temperature in the heart of the column is achieved by the utilization of a double copper-constantan thermocouple mounted in a glass tube, which could be inserted through a metal tube extending through the column.
Nitrogen is purified by bubbling through a solution of bivalent vanadium, ama1gamated zinc and aqueous hydrochloric acid [148]. By adjusting the pressure valves the pressure difference between top and bottom of the column can be maintained at any desired level. Adjustment of the height of the solvent in the column is automatically accomplished by the connections as schematically depicted. The speed of elution can be adjusted by the pressure difference between top and bottom and by the teflon stopcock below the column. The receiving vessel is connected by a ground glass connection.
2.6 Urea cOJI1plexes
Although of quite recent ongm, urea complexes have irrefragab1y demonstrated their indispensability in the separation of fatty acids. An extensive literature has been published on this subject. Excellent reviews are available [rom TRUTER [218], SCHLENK [185], and from RIGAMONTI and RICCIO [174].
U rea, and to alesser ex tent thiourea, desoxycholic acid and other substances form relatively stabie crystalline inclusion compounds with straight-chain compounds containing at least 4-6 C-atoms in a ratio of approximately 3 : 1 by weight. Branched-chain and cyclic compounds do not form adducts.
In a mixture of fatty acids there is preferential crystal formation for saturated compounds in comparison to unsaturated compounds. Un-saturated conjugation is favoured above the non-conjugated iso mer [186], and the cis above the trans-configuration [62, 194].
Methanol is the general accepted solvent for small scale preparations ; for large scale work no solvent is usually present. The fatty acids can be recovered by decomposing the adduct with hot water or dilute acid and by subsequent separation of the oily layer.
Procedures include fractional precipitation of acids by adding in-sufficient amounts of urea for complete adduct formation ; by passing solutions offatty acids through columns containing mixtures of crystalline urea and silica [137], and by applying a liquid-solid counter-current distribution technique [200].
2.7 Chemica} syntheses and purmcation methods 2.7.1 Esterijication
Methyl esters we re not always available, but gene rally the free acids could be purchased or we re kindly put at our disposal. To transform these acids into their corresponding methyl esters two standard esterification procedures have been applied.
2.7.2
The saturated members of the homologous fatty acids are expediently converted into their corresponding methyl esters by esterification with methanol in the presence of sulphuric acid. To one mole of acid and 10-15 moles of methanol which had been purified by distillation, 5% by volume of concentrated sulphuric acid s.g. 1.84 is carefully added with stirring. This mixture is refluxed for 3-4 hours and cooled. Water is added and the ester layer is taken off in aseparatory funnel. The watery solution is extracted twice with n-hexane and the extracts added to the ester layer. The solution of esters in hexane is consecutively washed with water, a dilute solution of Na2C03 in water, a 10% solution of
NaOH-Na2C03, dilute hydrochloric acid, and twice again with distilled water.
The product is dried above solid Na2S04 or MgS04 overnight or longer.
Hexane is subsequently stripped off, and the product is ready for further purification.
2.7.3
For the more expensive acids which were only available in smaller quantities and for the unsaturated acids which could undergo structural modifications during prolonged heating, esterijication with diazomethane in
ethereal solution is especially adapted for the conversion of these products . into their corresponding methyl esters.
Diazomethane IS prepared according to the following reaction se-quence:
°
11 1. CH3NH2HCl+ K- C= N-+O -+ CH3N- C- NH2+ KCl H 2. CH3NHCONH2+ HN02 -+ CH3N(NO)CONH2+ H20 N-nitrosomethylurea 3. CH3N(NO)CONH2+KOH -+ CH2N2+KCNO+ 2 H20Diazomethane is distilled off and collected in cold ether.
Esterification is accomplished by addition of the yellow ethereal solu-tion of diazomethane in porsolu-tions to the solusolu-tion or suspension of the acid in ether. The yellow colour is discharged and nitrogen is simultane-ously evolved in the instantaneous reaction
RCOOH+ CH2N2 -+ RCOOCH3+ N2
Excess diazomethane is added to allow the yellow colour to persist even af ter shaking for several minutes. This excess is destroyed by adding small portions of formic acid or by heating the solution gently on a water bath.
2.8 Acetone-perll1anganate oxidation
Saturated products may be contaminated with small amounts of unsaturated material with the same chain length. Purification of these compounds entails tedious refractionation as there is usually only a sm all difference in boiling point. In those cases where the unsaturated compounds are only of ancillary interest removal is expediently carried out by oxidation and subsequent removal of the oxidation products. Commercial acetone is dried over MgS04, and af ter filtration purified by refluxing with an excess of KMn04 until the purple colour persists for at least 15 minutes. The acetone is subsequently distilled through a 60 cm Vigreux and the heart-cut utilized as solvent for the oxidation. Glacial acetic acid is purified by freezing twice and subsequently refluxing with excess KMn04. The purified product is distilled through a 60 cm
Vigreux.
The ester is dissolved in an excess of purified acetone and enough glacial acetic acid is added to obtain a concentration of 3-6% in the solution. This mixture is introduced in a four-necked round-bottomed flask, equipped with reflux condensor, gas-tight mechanical stirrer, ther-mometer, and a free neck for the addition of powdered KMn04.
Small portions of pure KMn04 crystals are added and the mixture
stirred until the colour persists for some time. It may be necessary to heat the mixture gently as the reaction proceeds, and at the end of the reaction it is boiled under reRux. Af ter each 16 gr of KMn04 added, 6 mI of ace tic acid is added to keep the concentration of the acid at approximately the same level [101]. The reaction is considered
com-pleted if af ter the addition of one gram of KMn04 the solution is not decolorized on boiling for approximately 20 minutes.
A short Vigreux distillation head is fitted, and the acetone is distilled off, the last traces at the reduced pressure of a water pump. Water is
added and the mixture is heated with the stirrer running until the mass breaks in a suspension. The Mn02 is dissolved by alternate addition of sodium bisulphite and dilute sulphuric acid.
The ester layer is extracted with n-hexane, washed consecutively with water, Na2C03 solution, and another two times with water. It is then
dried overnight above Na2S04 or MgS04. Af ter filtration the solvent
is Rashed off at low pressure, or the product is crystallized out at low
temperature.
2.9 Esterification and trans-esterification
The standard method for the preparation of mono-acid triglycerides
has been the conversion of the acid into the corresponding acid chloride, and reacting an excess of this compound with purified glycerol in the presence of quinoline or pyridine [44,223]. Simp Ie triglycerides are also conveniently prepared by heating a small excess of the theoretical
amount of fatty acid with glycerol at 140-150 °c for a few hours in the presence of 1-2% p-toluenesulphonic acid [233]. Mono-acid triglycerides are also obtained by inter-esterification of the methyl or ethyl ester of
the fatty acid with glycerol in the presence of alkaline catalysts, or with triacetin in the presence of sodium alkoxide [40, 112, 131].
As the esters are purified much more easily than the acids,
trans-esterification methods possess certain advantages from the stand point
of time and simplicity [79]. Esterification and trans-esterification we re
conducted in the following lay-out (FIG. 2.7).
Nitrogen was purified by bubbling through an acid vanadium-zinc-amalgam solution [148] and dried through CaCb· Oaq before
in-troduction in the reaction vessel. This is a round-bottomed vessel equipped with variabie heating, thermometer, gas-tight stirrer, and a reRux condensor cooled by a thermostat at 60°C. The evolved methanol
mercury
oxygen
removal
220 V
FIG. 2.7 Esterification and trans-esterification unit
manometer
ice and CaCh, and liquid air respectively and weighed af ter completion of the reaction. The pressure of the whole system is maintained at a controlled level by a cartesian mercury manostat coupled to water suction.
Three moles of a fatty acid or a fatty acid methyl ester and 0.9 mole of purified glycerol or triacetin are heated together in the presence of small amounts of catalyst. For lrans-esterification with glycerol LiOH· laq is utilized, and for triacetin NaOCH3 is present as a catalyst.
Af ter completion of the reaction the products are neutralized with dilute ace tic acid and extracted with hexane. The solution is washed several times with water and dried above MgS04· 3aq.
2.10 Storage
The products which are liquid at room temperature are stored under dried and purified nitrogen in a refrigerator at -20 °C. Solid products are stored in dessicators in a purified and dried nitrogen atmosphere above CaCh· Oaq at 0 °C. The unsaturated products are stored under nitrogen in sealed glass ampoules at -20 °C. Storage as urea adducts would, as a matter of fact, have been preferabie.
2.11 Preparation of Dlodel cODlpounds Saturated fatty acid Dlethyl esters 2.11.1 Methyl acelale
and three times distilled from P205 to remove the last traces of methanol. The product was subsequently distilled through column 4, and the he art-cut carefully redistilled through the same column.
2.11.2 Methyl propionate
Methyl propionate purum (Fluka) was distilled through column 4 and a constant boiling middle fraction isolated. This was twice distilled from P205 and then carefully through column 4.
2.11.3 Methyl butyrate
Methyl butyrate (Fluka and British Drug Houses Ltd.) was purified by distilling through column 2 and carefully redistilling the heart-cut through the same column.
2.11.4 Methyl valerate
N-valeric acid puriss. (Fluka) was esterified with distilled methanol in the pres en ce of sulphuric acid. The crude product was fractionated on column 2 and the middle fraction further purified by redistilling through column 2.
2.11.5 Methyl caproate
N-caproic acid (Riedel & de Haën) was esterified with methanol ac-cording to 2.7.2. The cru de product was distilled through column 2 and the heart-cut redistilled through the same column.
2.11.6 Methyl oenanthate
Oenanthic acid (Maschmeyer Jr.)
*
was esterified with distilled meth-anol and sulphuric acid. The crude product was distilled through column 3, and the heart-cut redistilled through the same column. Gas-liquid chromatography indicated about 0.5% impurities in the product, and the product was therefore subjected to an acetone-permanganate oxida-tion. The crude products were distilled through column 2 and the middle fraction subsequently redistilled through the spinning band column.2.11. 7 Methyl caprylate
Caprylic acid 99-100% (Amsterdamsche Kininefabriek) was esterified
*
Oenanthic acid, pelargonic acid, undecylic acid, and lauryl alcohol have been kindly put at our disposal by Messrs. A. Maschmeyer Jr., Amsterdam.with distilled methanol and sulphuric acid and the crude product distilled through column 4. The constant boiling middle fraction was further purified by redistilling through column 2.
2.11.8 Methyl pelargonate
Pelargonic acid (Maschmeyer Jr.) was esterified with methanol in the presence of concentrated sulphuric acid. The crude product was carefully distilled through column 2 and the heart-cut redistilled through the spinning band column.
2.11.9 Methyl caprate
Capric acid (British Drug Houses Ltd.) was esterified with methanol, and the crude product distilled through column 4. An intermediate fraction was redistilled through column 2, and the heart-cut of this last distillation once more distilled through column
2.
2.11.10 Methyl undecylate
Undecylic acid (Maschmeyer Jr.) was esterified with distilled methanol
(2.7.2). The crude product was distilled through column 4 and the middle fraction redistilled through column 3. Gas-liquid chromatography indicated about 0.6% methyl undecylenate, and th is product was there-fore subjected to an acetone-permanganate oxidation (2.8.1). The prod-ucts we re subsequently distilled through column 5 and a heart-cut finally purified through the spinning band column.
2.11.11 Methyl laurate
Methyllaurate was obtained by distilling the methyl esters of coconut fatty acids through a short packed column. It was further purified by distilling through column 2 and redistilling through the spinning band column.
2.11.12 Methyl tridecylate
Lauryl alcohol (Maschmeyer Jr.) was purified by distillation and treated with red phosphorus and bromine at 200 °C. The resultant bromide was distilled three times through a 60 cm Vigreux and subsequently
converted into the corresponding Grignard compound.
12
Treatment with CO2 and subsequent hydrolysis yields tridecanoic acid
o
CH3(CH2)l1MgBr+ C02 --l>-CH3
(
CH2
)
l1C
~
"'-0 MgBro
CH3(CH2)l1Ü,f --l>- CH3(CH2)l1 COOH+ Mg(OH)Br "'OMgBr+ H 20Esterification was carried out with methanol and sulphuric acid (2.7.2).
The crude product was purified by distillation through column 4 and carefully redistilling an intermediate fraction through the spinning band
column.
2.11.13 Methyl myristate
Methyl myristate (Eastman Kodak) was purified by careful distillation through the spinning band column and subjecting the heart-cut to 6
consecutive recrystallizations from acetone-water.
2.11.14 Methyl pentadecanoate
Purified methyl myristate was saponified with alcoholic KOH.
Thionyl-chloride was purified by distillation from chinoline (to re move HCl and S02) and subsequently from linseed oil (to re move Ch), and the colourless
product refluxed with myristic acid to form myristoylchloride. This was added to diazomethane in ether and allowed to stand for 24 hours after which it was further cooled to - 20 °C. Yellow flakes of
l-diazopen-tadecanon-2 were precipitated,
CH3(CH2)r2COCl+ CH2N2 --l>- CH3(CH2)r2COCHN2+HCl
and this product was subsequently subjected to the ARNDT-ErsTERT
reaction [5,237]
CH3(CH2)r2COCHN2+ CH30H
A-;O
CH3(CH2)I2CH2COOCH3+ N2by the addition of a large excess of purified methanol and small portions of Ag20 powder during 30 hours at 57-60 °C. The crude product was
purified by careful distillation through the spinning band column and
repeated recrystallizations from acetone and from methanol.
2.11.15 Methyl palmitate
Methyl palmitate (Eastman Kodak) was subjected to an acetone-permanganate oxidation to re move traces of palmitoleate. Purification of the product was effected by distillation through column 5,
