Sutherland, M. D. (Maurice Davis)

Wilson, S.J.

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VoLUME I.
University of Queensland 
PAPERS 
DEPARTMENT OF CHEMISTRY 
1950 NUMBER 38 
THE PHYSICAL PROPERTIES 
OF PURE TERPENES 
Part 1.-MYRCENE
BY 
MAURICE D. SUTHERLAND and Mrss S. J. WILSON
Price: One Shilling 
UNIVERSITY OF QUEENSLAND PRESS 
BRISBANE 
DATE OF PUBLICATION 
16th JUNE, 1950 
VoLUME I. 
DEPARTMENT· OF CHEMISTRY 
1950 NUMBER 38 
THE PHYSICAL PROPERTIES OF 
PURE TERPENES 
PART I.--MYRCENE 
BY 
MAURICE D. SUTHERLAN D AND Mrss S. J. WILSON
THE UNIVERSITY OF QUEENSLAND PRESS 
BRISBANE 
DATE OF PUBLICATION: 
16th JUNE, 1950 
The Physical Properties of Pure Terpenes 
PART I.-MYRCENE.
Bv 
MAURICE D. SUTHERLAN D AND Miss S. J. WILSON.
SUMMARY. 
Myrcene was purified to 99. 5-100% purity and was found to have the properties 
d24
5 0.784 7, n2D
5 1,4 679 and " = 1.84 x 104 aL\ = 22 4 . 5  mfL in alcohol. max
The full development of the nfd diagram method (1, 2, 3) for the analysis of 
essential oils demands a more precise knowledge of the density and refractive index 
of most of the terpenes than is at present contained in the literature, and this paper 
describes the preparation and properties of a sample of myrcene of 99. 5-100% purity 
as a contribution to this end. 
· 
The essential oil of Medicosma cunninghamii (4 ) was chosen as a suitable source
of myrcene for purification since no substance other than myrcene had been detected 
in the fractions boiling between a-pinene and limonene . In addition these substances 
are well separated from myrcene in boiling point, have much higher densities than 
the latter and were strongly optically active in this essential oil. 
The properties of the fractions from the final fractional distillation are set 
out in Table I. Fractions 6, 7, and 8 are the purest judged by the criterion of
density which in this case was the property most sensitive to impurity. 
Frac- Volume 25 d25 tion aD nD No. (ml) 4 
--
---
--
-
-
-
-
-
-
1 5.0 +0.fi8° 1.4678. 0.78565 
2 5.0 +0.20° 1.467!12 0. 78562 
:3 10.0 ±0
0 1.46787 0. 78490 
4 1.0 - - -
5 10.0 ±0
0 1.46790 0.78490 
6 5.0 ±0
0 1.46787 0.7847. 
7 0.5. - - -
8 10.0 ±0
0 1.46787 0 .78475 
9 4.5 ±0
0 1.4679 0.78522 
TABLE I. 
Ultra-violet 
absorption 
max1mum 
"max 
-
1.8il8x 10• 
-
1.835 X liJ4 
--
,\max 
mfL 
--
-
224.5 
--
224.5 
-
Purity 
by diene 
analysis 
(av.) 
--
-
99.8 % 100.3% 
-
-
-
a-pinene a-pinene 
(by rota- (by 
tion)* density)t 
1.6% 1.3 % 
0.5% 1. 3% 
0.0% 0.2% 
- -
0.0% 0.2% 
0.0% 0.0% 
-
-
0.0% 0.0% 
-
-
*Assuming a-pinene 
.
(a2� = +42.94°) to be the only source of optical rotation in the fraction. 
t Assuming a-pinene (d2i = . 0.8542) to be the only impurity and -fraction No. 6 to be pure 
myrcene. 
Calculation of the proportion of a-pinene in the early fractions from the optical 
rotation shows the elimination of a-pinene to be complete by the third fraction. 
The difference in pinene content as calculated frarn rotation and from density is 
attributed to the rapid autoxidation of part of the distillate which was in the 
receiver of the still overnight. The rise in density of fraction 9 without the 
appearance of a corresponding rotation suggests the presence of a trace of a previously 
unsuspected optically inactive constituent of lower boiling point than limonene. 
2 THE PHYSICAL PROPERTIES OF PURE TERPENES 
Conjugated diene analysis gave useful results in indicating the fractions 5 and 6 
to be virtually wholly composed of" conjugated terpenes, but it was not sufficiently 
precise under the conditions used to form a satisfactory basis for the estimation of 
impurity, differences between duplicates ranging up to 0.6%. The refractive index 
threw little light on the variation in composition of the fractions. 
Redistillation of the best fractions to reveal a possible further lowering of the 
density was discouraged by the very ready polymerisation of the myrcene and was 
not attempted as the object of this work-to place closely and reliably the point 
for myrcene on the njd diagram-had been achieved. The gross uncertainty in the 
properties of other terpenes demands prior attention, though the preparation of 
a larger sample of pure myrcene will be attempted when fresh supplies of myrcene 
become available. 
Fractions 6 and 8 are regarded as being myrcene of 99.5-100% purity and 
the properties of myrcene are determined as d24
5 0.78 4 7  ; n2D
5 1. 4679; and E max
1.8 4 x 104 at ..\ = 22 4 . 5 mJL.
Comparison with previously described samples of myrcene (1) suggest that 
the material separated by Goldblatt and Palkin (5) of d� 0.7862 (corrected from
20° C. ) contained only about one to two per cent. of �-pinene andjor limonene as 
impurity. Most other samples described in the literature are grossly impure. It 
would appear from the literature that two substances are described under the name 
myrcene and these may be distinguished by the considerable difference in refractive 
index (1) . If it is assumed that the low refractive index of some samples of myrcene 
(1, 6, 7, 8) results from the presence of an a-form of myrcene then it is clear that 
only the �-form is present in the essential oil of M. cunninghamii unless the two
forms have exactly the same boiling points, a rather remote possibility, considering 
the properties of simpler hydrocarbons showing the same difference in structure. 
The ultraviolet absorption spectrum of the present sample of myrcene, in 
alcohol, shows a maximum at the same wavelength (224.5 mJL) as that found 
25 for a sample (d 4 0.7922 (corrected from 15° C. ) E = 1. 46 x 104) preparedmax 
by D r. T. F. West and described by Booker, Evans and Gillam (9) , but it has a
very much stronger absorption, E = 1.8 4  X 104, in agreement with its greatermax 
purity. Woodward (10) has put forward a rule for the position of absorption 
maxima of conjugated dienes, which leads to a calculated value of 222 mJL for the 
myrcene molecule but the measurements recorded here substantiate the difference 
of 2.5 mJL between the observed and calculated values and confirm the existence 
Qf " subtle constitutional factors which shift the maximum slightly towards that 
characteristic of one or other of the two component systems." 
EXPERIMENTAL. 
A volume of 164 ml. of myrcene-rich material obtained by fractionation of 
M. cunninghamii oil was rectified in a twenty plate still previously described (2)
at a pressure of 20 mm. The distillate was collected in 10 ml. fractions, 1 4 3 ml.
being taken off in all, the loss being partly due to the formation of polymer. The
refractive index showed comparatively little change throughout the distillation but 
the density of the early fractions and the last showed some variation. Fractions 
4 to 1 4  all had densities of d2! 0.78 5 4  or lower and 92 ml. were bulked
for redistillation in another still containing a one metre length of the packing 
described by Bower and Cooke (11) . This colurmi has been tested to a maximum 
THE PHYSICAL PROPERTIES OF PURE TERPENES 3 
efficiency of fifty-five plates when operated at total reflux under atmospheric 
pressure and has a hold up of approximately 2 ml. The rectification was 
carried out at 50 mm. pressure and with a reflux ratio of approximately thirty-five. 
Owing to the necessity of starting the still each day and allowing time for the 
establishment of equilibrium, the distillation extended over several days. Fractions 
4 and 7 were fractions obtained at the start of the third and fourth days and were
rejected as possibly containing autoxidised myrcene which may have formed in 
the receive:r; overnight despite the carbon dioxide atmosphere introduced on closing 
down the apparatus. Loss of myrcene through polymerisation in the pot was 
excessive and resulted in the premature appearance of material of high density 
in the distillate as shown by the higher density of fraction 9. 
· 
The various fractions showed no difference in boiling point (about 83° to 84°) 
which could be attributed to changes in composition rather than to pressure changes. 
The refractive indices were measured with a Pulfrich refractometer and the densities 
jn a pycnometer holding a little over three grams of myrcene. The temperature of 
the pycnometer bath was held at 25° C. to within a few hundredths of a degree 
using a checked thermometer. 
The diene estimations were carried out by a method similar to that of Kaufmann, 
Batles and Josephs (12) and Jones and Hancox (13). It was found that the time
(1 t hours) suggested by Kaufmann et al for complete reaction of the myrcene with
maleic anhydride in benzene solution was insufficient and that three hours in toluene 
on the water bath, was necessary for satisfactory results. 
The ultraviolet absorption of myrcene was measured in rectified spirits solution 
using a Beckmann DU spectrophotometer, the density and wavelength scales of 
which have been checked. 
REFERENCES. 
1. SuTHERLAND. Univ. of Q'ld. Papers (1948) I., No. 34. 
2. DAVENPORT, jONES AND SUTHERLAND. Univ. of Q'ld. Papers (1948) l., No. 36. 
:3. JoNES, LAHEY AND SuTHERLAND. Univ. of Q'ld. Papers (1949) I., No. 37. 
4. SUTHERLAND AND WILSON. To be published shortly. 
!l. J .A.C.S. 63, 3517 (1941). 
6. PALl{IN AND WELLS, J.A.C.S. , 55, 1552 (1933). 
7. PowER AND KLEBER. See Gildermeister and Hoffman "The Volatile Oils," 2nd Ed. I, 
p. 303 (1913). 
8. J .C . S .. 83. fi07 (1903). 
9 . .J.C.S., (1940), 1453. 
10. J . A.C . S. , 64, 73 (1942). 
11. I.E.C. Anal. Ed. 15, 290 (1943). 
12. Ber. '10, 908 (1937). 
13. Univ. of Q'ld. Papers (1939) I., No. 14. 


The physical properties of pure terpenes. Part 1, Myrcene

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The physical properties of pure terpenes. Part 1, Myrcene

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