11/5/2017 Refractive Indices and Densities of Normal Saturated Fatty Acids in the Liquid State - Journal of the American Chemical Society (ACS Publicati…
`Refractive Indices and Densities of Normal Saturated Fatty Acids in the
`Liquid State
`
`A. Dorinson, M. R. McCorkle, A. W. Ralston
`
`J. Am. Chem. Soc., 1942, 64 (12), pp 2739–2741
`DOI: 10.1021/ja01264a004
`Publication Date: December 1942
`
`http://pubs.acs.org/doi/abs/10.1021/ja01264a004
`
`Reactive Surfaces Ltd. LLP
`Ex. 1048 (Ray Attachment N)
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`

`Dec., 1942
`
`INDICES AND DENSITIES OF NORMAL SATURATED FATTY ACIDS
`REFRACTIVE
`
`2739
`
`[CONTRIBUTION FROM THE RESEARCFI LABORATORY OF ARMOUR AND COMPANY]
`
`Refractive Indices and Densities of Normal Saturated Fatty Acids in the Liquid State
`BY A. DORINSON, M. R. MCCORKLE AND A. W. RALSTON
`
`tion from this Laborat01-y.~ Refractive indices
`were measured with an Abbe type refractometer,
`the temperature of whose prisms could be held
`constant to *0.05. A calibrated thermometer
`was used. Densities were determined in a modi-
`fied Ostwald pycnometer a t 80 * 0.05". Weigh-
`ings were corrected for the buoyancy of air.
`
`18
`17
`16
`
`B
`11 2
`
`id
`
`\
`
`Few systematic studies of the refractive indices
`of the saturated fatty acids are found in the litera-
`ture; there is the classical work of Eijkdan,' the
`investigation of Scheij2 on the naturally occurring
`fatty acids, and the more modern work of Water-
`man and Bertram.3 Determinations were made
`at arbitrary and scattered temperatures ; only the
`work of Falk4 on butyric acid embraces a large
`number of determinations over a wide range of
`temperature. We have measured the refractive
`indices of the normal saturated fatty acids in the
`liquid state, from caproic to stearic inclusive, at a
`sufficient number of temperatures between 20 and
`SO" to enable us to plot the variation of refractive
`index with temperature for each acid, as shown in
`Fig. 1. In addition, the densities of these acids
`were determined at 80" and these data were used
`to calculate the molar volume and the molar re-
`fractivity of each acid at that temperature. The
`refractive indices are listed in Table I and the den-
`sities in Table 11. The values listed in Table I
`have not been corrected for the effect of tempera-
`ture on the refractometer prism, since we feel that
`less confusion will arise among investigators using
`these figures if they are left uncorrected. When-
`ever we shall have occasion here to treat the re-
`fractive indices as functions of the homologous
`series, a correction given by
`0.00006 (t - 20)
`(1)
`where t is the temperature at which the refractive
`index was determined, will be added. This is the
`correction for the refractometer prism only. A
`correction should also be applied for the effect of
`temperature on the compensating prisms in the
`refractometer, but since their temperature could
`be estimated only crudely, this correction will be
`omitted. Since the compensating prisms do not
`deviate the sodium D line, the correction is prob-
`ably very small.
`
`Experimental
`The acids used were carefully purified; their
`preparation is described in another communica-
`(1) Eijkman, Rec. Woo. chitn., 1'2, 157 (1893).
`(2) Scheij, ibid., 18, 182 (1899).
`(3) Waterman and Bertram, tbid., 46, 699 (1927).
`( 4 ) Falk, THIS JOURNAL, 31, 9G (1909).
`
`70
`
`80
`
`3
`
`30
`
`50
`60
`40
`Temperature, "C.
`variation of refractive index with tem-
`Fig. 1.-The
`perature. Change of slope is shown by comparison with
`the extrapolation from the curve a t higher temperatures.
`Extrapolation is represented by a dotted line.
`Discussion
`Molar Volumes.-The
`molar volumes at
`80' of the acids from caproic through stearic were
`calculated from the densities determined in this
`work. By taking advantage of the fact that the
`densities of the straight chain saturated acids are
`linear functions of temperature, we were able to
`(5) Hoerr, Pool and Ralston, Oil and Soap, 19, 126 (1942).
`Reactive Surfaces Ltd. LLP
`Ex. 1048 (Ray Attachment N)
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`

`

`274.0
`
`Acid
`Caproic
`Enanthic
`Caprylic
`Pelargonic
`Capric
`Hendecanoic
`Lauric
`'Tridecanoic
`Myristic
`Pentadecanoic
`Palmitic
`hrargaric
`Stearic
`
`Vol. 64
`
`G5 0'
`
`TABLE I
`I<hFRACTI\E INDICES (dD) OF NORMAL SATURATED FATTY ACIDS
`10 0'
`50 0'
`0'
`60 0'
`5 5 0'
`30 0'
`2 5 0'
`211 0'
`L j
`
`70.0'
`80.0'
`I 4170 1 1150 1 4132 1 4095
`1 4054
`1 4012
`d ,3972
`1.3931
`1 4230
`I 4209 1 4192
`1 4155
`1 4114
`1 4073
`1.4037
`1.3993
`1 1.167
`I 1280 1 4260 14243 1 4206
`1 4125
`1.4049
`1 ,4089
`1 4322 1 4301
`1 4287 1 4250
`1 4210
`1 1171
`1.4092
`1.4132
`1 4288
`1 4248
`1 4210
`1.4130
`1.4169
`1 43 19
`1 4279
`1 4240
`1.4202
`1.4164
`1 4323 1 1304 1 4288 1 4267
`1.4250 1.4230
`1.4191
`1 4328 1 4310 1 4290 1 4272 1 4252 1 4215
`1 4310 14291 14273 142363
`1 4329
`1 1348 1 1329 14310 14292 14254
`1 4328 14308 14272
`1 131.0 1 1.321 1 4287
`I w37 1 42w
`
`'1'.4HI.E 11
`1)emrnris OF NORMAL SATURATED FATTY ACIDS AT 80'
`Acid
`Acid
`<!'.,
`Caproic
`Tridecanoic
`0.87'51
`Enanthic
`.8670 Myristic
`Caprylic
`,8615
`Pentadecanoic
`Pelargonic
`8570
`Palmitic
`Capric
`,8531 Margaric
`Hendecanoic
`,8505
`Stearic
`Lauric
`,8377'
`
`' I ' d
`0,8458
`8439
`8423
`w11
`8396
`,8390
`
`convert data already in the l i t e r a t ~ r e ~ i ~ , ~ - - I ' to the
`
`proper temperature and to extend this series of
`calculations a t 80" down to acetic acid, and also
`to make a series of calculations from formic acid
`to pelargonic acid a t 20'
`(see Table 111). At
`20" the molar volumes from acetic acid to pelar-
`gonic acid are adequately expressed by
`1'"' = l6.89n + 23.62
`(2)
`where n is the number of carbon atoms in the
`chain. At 80" the equation
`= 17.25n + 28.88
`l;,
`i:i)
`holds for butyric and higher acids. The deviation
`of the first three members of the series from line-
`arity is quite sharp and the addition of a term of
`the form k/n does not extend thevalidity of the
`equation to include these three members. The
`molar volumes of the normal saturated acids, ar-
`ranged serially, do not show as much deviation
`from a linear relation as noticed by Huggins12 for
`the normal saturated hydrocarbons, nor does this
`deviation extend as far up the series for thr acids
`as for the hydrocarbons.
`(6) Timmermana and Hennaut-Roland, J. clrini. piis. , a7, 420,
`422, 425 (1930); 29, 650 (1932).
`(7) Merry and Turner, J . Chem. Soc., 105, 758 (1:JHI.
`(8) Eijkman, Chem. Zc+Ik., '78, 11, 1210 (1907).
`(9) Dunstan, J . Chem. Soc., 101, 667 (1915).
`(10) Deffet, Bull. SOL. chim. Be&., 40, 386 (1931).
`(11) Garner and Ryder, J. Chcnt. Soc., 12'7, 728 (19251
`(11') Huggins, T ~ r s JOUKYAL. 6S, 110 i l O 4 l )
`
`TABLE I11
`x f O L 4 R \ OLUhfES OF NORMAL SATURATED FATTY ACIDS
`V,n at 80'
`1'- at Z O O
`Ca1cd.b
`Exptl , fi
`Exptl.
`Ca1cd.c
`A C l d
`Formic
`37.71
`40.51
`. . . .
`Acetic
`57.40
`57.21
`61.11"
`63.38
`Propionic
`74.29
`74.55
`79.68"
`80.63
`Butyric
`91.18
`91.93
`97.95"
`97.88
`Valeric
`108.69
`108.07
`115.33"
`115.13
`Caproic
`125.04
`124.96
`132. 6'id
`132.38
`Enanthic
`141.89
`141.85
`150.07
`149.63
`Caprylic
`158.74
`158.57
`167.30
`166,88
`174.53
`Pelargonic
`175.63
`184.50
`184,13
`Capric
`201.80
`201.38
`Hendecanoic
`218.90
`218.63
`Lauric
`235.88
`236.29
`'Tridecanoic
`253.13
`253.27
`Myristic
`270.38
`270.41
`Pentadecanoic
`287.63
`287.61
`Palmitic
`304.56
`304.88
`Margaric
`322.13
`321.90
`Stearic
`338.85
`339.38
`Calculated from densities obtained from references 2,
`4, ij-11
`Calculated from equation (2). Calculated
`' This figure and subsequent figures
`from equation (3).
`in this column were computed from densities in Table I1
`
`Fig. 1 we have plotted the
`Refractivities.-In
`refractive indices of the acids, corrected accord-
`ing to equation (l), against temperature. The
`refractive indices for each acid fall upon a straight
`line between 40 and 80'. Below this temperature
`change of direction is observed.
`X plausible
`explanation of this phenomenon can be found in
`the theory of molecular refractivity and in current
`viewpoints on the structure of liquids consisting
`of polar molecules. To begin with, the molar re-
`fraction for visible light, calculated by the Lo-
`rentz-Lorenz equation, is equal to the electron
`polarization. -1 collection of molecules which are
`inherent dipoles, such as the molecules of a fatty
`acid, act on each other to cause more or less orien-
`
`

`

`Dec., 1942
`
`REFRACTIVE INDICES AND DENSITIES OF NORMAL SATURATED FATTY ACIDS
`
`2741
`
`tation, even in the liquid state, and consequently
`produce an electric field within the body of the
`liquid. Onsager13 has published a theoretical
`treatment of this effect on the determination of
`dipole moments of polar substances by means of
`an external electrical field. It is beyond the
`scope of this paper to attempt a quantitative
`treatment of the effect of the internal electric
`field on the bonding electrons in the relatively
`non-polar part of the fatty acid chain, and hence
`on the refractivity, but qualitatively we would
`expect the electron polarization of a substance
`such as a fatty acid to depend on the statistical
`orientation of the individual molecules within the
`body of the liquid. On the other hand, the ther-
`mal motions of these molecules will tend to pro-
`duce disorder, and at some temperature they
`should be vigorous enough to completely over-
`come the restraints caused by dipole interaction.
`The molecules within the liquid will then exhibit
`a perfectly random configuration and the net
`field there will be zero. On these grounds we
`would expect to find a temperature for each acid
`above which the molar refractivity will be con-
`stant and below which it will depend on tempera-
`ture. We have taken the data of Falk4 for bu-
`tyric acid and instead of smoothing out the values
`of the refractive index, we have calculated the
`molar refractivities from the data as they stand.
`This examination shows that the molar refrac-
`tivity is practically constant above 42' and a
`linear function of
`the temperature below this
`point. This is the only fatty acid reported for
`which a sufficient number of molecular refrac-
`tivities could be calculated from the original
`data over a wide temperature range.
`To eliminate the possibility that the discon-
`tinuities in the plot of the refractive indices of the
`acids might be due to some systematic defect in
`the refractometer or in the calibration of the ther-
`mometer, the refractive index of n-heptane was
`determined between 20 and 50'. The data so ob-
`tained lie on a straight line and the data of
`Shepard, Henne and Midgleyl* also lie on this
`line in full agreement with ours.
`If a plot of the molar refractivity of a normal
`fatty acid shows discontinuity with temperature,
`it can be shown that a plot of the refractive in-
`dices will also exhibit discontinuity. The den-
`sities of
`the fatty acids are continuous linear
`(13) Onsag-er, THIS JOURNAL, 58, 1486 (1936).
`(14) Shepard. Henne and Midgley. ibid., 68, 1948 (1931).
`
`functions of the temperature from zero to at least
`80'. The density factor, then, will produce no
`discontinuity in the molar refractivity as calcu-
`lated from the Lorentz-Lorenz formula
`n 2 - - 1 M
`- 7
`but any discontinuity in the temperature varia-
`tion of n will show up in the molar refractivity
`and vice versa, since it is impossible to eliminate
`n from the ratio n2 - l/n? + 2.
`
`The molar refractivities of the normal saturated
`fatty acids, from caproic to stearic inclusive, can
`be expressed as a function of the number of carbon
`atoms in the chain by
`R, = 4.654n + 3.83
`(4)
`The observed values and those calculated from
`this formula are listed in Table IV.
`TABLE IV
`MOLAR REFRACTIVITIES OF NORMAL SATURATED
`FATTY
`ACIDS AT 80"
`R, (calcd.)b
`R m (exptl.)a
`Acid
`31.70
`Caproic
`31.75
`Enanthic
`36.34
`36.40
`Caprylic
`41.08
`41.06
`Pelargonic
`45.66
`45.71
`Capric
`50.36
`5 0 . 3 i
`Hendecanoic
`55.02
`55.02
`Lauric
`59.73
`59.68
`Tridecanoic
`64.35
`64.33
`Myristic
`69.00
`68.99
`Pentadecanoic
`73.65
`73.64
`78 30
`Palmitic
`78.30
`Margaric
`83.01
`82.95
`Stearic
`8 i . 59
`87.61
`n2 - 1 J4
`n2 + 2 d '
`Computed from the formula R, =
`- refrac-
`* Calcd. from equation (4).
`tive indices corrected
`Summary
`The refractive indices of the normal satu-
`1.
`rated fatty acids from caproic to stearic inclusive
`have been determined at a number of tempera-
`tures between 20 and 80". For each acid the re-
`fractive indices are straight line functions of the
`temperature with an abrupt change of a slope a t
`40'.
`2. An explanation of this change of slope has
`been presented.
`3. The densities of these acids at 80' have
`also been determined. Molar volumes and molar
`refractivities for the homologous series have been
`computed and shown to be linear with respect to
`the number of carbon atoms in the chain.
`CHICAGO, ILLINOIS
`RECEIVED JUNE 24, 1942
`
`~
`
`