2068
A. J. HAAGEN-SMIT AND R. SIU
Vol. 66
Conversion of *Galactose Diethyl Mercaptal into Ethyl p-D-Galactofuranoside with Mercuric Chloride and Cadmium Carbonate.-A mixture of D-galactose diethyl mercaptal (5.0 g., 1 mold cadmium carbonate (6.0 g., excess) and mercuric chloride (9.2g., 2 moles) in 100 cc. of absolute ethanol was stirred vigorously for two hours at room temperature and the product isolated as described above for the isolation of ethyl 0-D-galactofuranoside. The crystalline material was found to be a mixture of D-galactose diethyl mercaptal and ethyl P-D-galactofuranoside. When the reaction time was extended to six hours at room temperature, only ethyl 0-D-galactofuranoside was isolated, in approximately 50% yield.
diethyl monothioacetal to yield ethyl &Dgalactofuranoside and With o-galactose diethyl monothioacetal pentaacetate to yield D-galactose diethyl acetal pentaacetate. 5. Mercuric chloride and yellow mercuric oxide in methanol reacted with D-glucose Sethyl O-methyl monothioacetal to give a practically quantitative yield of the sirupy methyl P-D-glucofuranoside of Haworth and co-workers, herein characterized by a crystalline tetracarbanilate. Summary 6. Mercuric chloride and yellow mercuric 1. D-G~UCOX S-ethyl 0-methyl monothioace- oxide in ethanol reacted with D-galactose diethyl tal exhibited a simple mutarotation a t 25' in monothioacetal to give a practically quantitative methanol containing 0.05% hydrogen chloride yield of the crystalline ethyl 8-D-galactofuranoand exhibited a complex mutarotation in 0.05% side. D-Galactose diethyl acetal was stable toaqueous hydrochloric acid. Ethyl a-thio-D-gluco- ward these reaction conditions. 7. The above data indicate that D-gluCOSC furanoside was isolated as a final product in both S-ethyl 0-methyl monothioacetal, at least in this cases. 2 . Similar mutarotation phenomena were ex- anomeric form, is not the probable intermediate hibited by D-galactose diethyl monothioacetal. in the formation of ethyl a-thio-D-gluco+ranoside D-Galactose was isolated as a final product in the from D-glUCOSe diethyl mercaptal but that the mixed acetal is the probable intermediate in the aqueous medium. 3. Ethyl fl-D-galactofuranoside was not de- formation of ethyl 8-D-gahctofuranoside from tectably hydrolyzed by 0.05yohydrochloric acid D-galactose diethyl mercaptal. These deductions are in accord with the postulations of Pacsu and at 25'. 4. Mercuric chloride and cadmium carbonate Green. in absolute ethanol reacted with D-galactose COLUMBUS, OHIO RECEIVED SEPTEMBER 1, 1944
[CONTRIBUTION FROM THE WILLIAM G. KERCWOFF LABORATORIES OF THE BIOLOGICAL SCIENCES OF THE CALrPORNIA ISSTITUTE OF TECHNOLOGY AND THE EMERGENCY RUBBER PROJECT, BUREAU OF PLANT INDUSTRY, U. S.DEPARTMENT OF AGRICULTURE ]
Chemical Investigations in Guayule. I. Essential Oil of Guayule, Parthenium argentatum, Gray BY A. J. HAAGEN-SMIT AND R.SIU' Aside from the identification of a-pinene by Alexander,2very little is known about the essential oil of the guayule rubber plant. This meager chemical knowledge could not furnish a sound basis for the understanding of the injurious effects of the oil on rubber, of its role in the plant, and of its possibilities as a by-product in the guayule rubber industry. The following investigation was carried out to fill this gap in the chemical knowledge of the oil. The oil was obtained from the steam distillation of fresh guayule plants. Two-thirds of the total oil was obtained after one and one-half hours of steam distillation. About 25y0 more was obtained with an additional one and one-half hours. After four and one-half hours further steam distillation gave only a negligible amount of oil. The oil obtained after three hours of steam dis( 1 ) The authors greatly appreciate the hearty cooperation aiid keen interest of Dr A C Hiidreth and Dr H Traub during the course of this work The help of Dr J Kircliner IS also gratefully acknowledged ( 2 ) Alexander, Ber , 44, 2 3 2 0 (1911)
tillation emitted an odor suggestive of decomposition. For this reason later steam distillations were carried out for only two and one-half hours, yielding about 80% of the total oil. According to Table I, the leaves possess the highest essential oil content on a fresh weight basis (1.04%), followed next by the flowers, then the bark. Only a small amount of oil can be obtained from the wood. TABLEI ESSENTIAL OIL CONTENT OF DIFFERENT PARTS OF GUAYULE PLANT
THE
Part of plant
Fresh wt. of tissue in g.
Wt.of oil
% of oil on fresh wt. basis
Leaves Flowers Bark
6,870 890 10,265 5,910 23,935
71.2 6.7 24.7 6.3 108.9
1.04 0.75
Wood
Total
in g.
.24
.I1 .45
When the entire guayule plant was steam distilled, the oil separating from the steam distillate
ESSENTIAL OILS OF GUAYULE PLANT
Dec., 1944
2069
was light yellow in color. It was slightly kuorotatory and contained only a small amount of acids and saponifiable matter. Some constants determined for the total oil from two-year old guayule plants (variety 593) from Salinas, California, are: dZ7.$0.8648,PD 1 . 4 7 7 4 , [ ~-2.70°, ~]~~~ saponification no. 10, acid no. 0.3, and Wijs iodine no. 153. This oil was carefully fractionated into 45 fractions, on which different physical measurements were made. The data are plotted in Fig. 1.' TABLE I1 BOILINGPOINT OF A SESQUITERPENE OIL FRACTION AT DIFFERENT PREssmso B. p.,
Preuure
OC.
20 P 60 250 P 63 600 u 67 3 mm. 87 17 mm. 120 143 mm. 182 746 mm. 234 Interpolation among these figures gave a boiling point of 60' at 20-25 p pressure and 125' at 20-22 mm. pressure. The difference of 125 60 or 6 5 O , therefore, was adopted as the abscissa spacing in Fig.1 between 51 O at 20-25 p and 51' at 20-22 mm.
-
Oag8t
I
I
I
I
I
I rcl
The fractionation curve of Fig. 1 shows 4 large groups. Their differences are also reflected in the behavior of the curves for the various physical constants. From the boiling point ranges, the carbon-hydrogen, and the Zerewitinoff analyses these four groups were shown to represent terpenes, oxygenated terpenes, sesquiterpenes and sesquiterpene alcohols, respectively. These I d 73 groups are present in the oil in the following procj portions: 72.6% terpenes, 5.8% oxygenated ter6 a penes, 9.3% sesquiterpenes, 6.3% sesquiterpene ti alcohols and 5.9% residue. .-0 The physical constants for the M e r e n t fractions suggest the absence of large amounts of known aliphatic terpene hydrocarbons and aliphatic sesquiterpene hydrocarbons in guayule * 0 essential oil. This is confirmed by thq analyses of the separate fractions. Fraction 2 was shown to be a-pinene from the carbon-hydrogen analyses, physical constants, 51 6171 46 66 88 106 126 and the mixed melting point of the nitrosochloride (at 21-22 mm.) (at 20-25 p) with the same derivative prepared from known Distillation temperature in 'C. a-pinene. Although Fraction 2 was levo-rotatory ( [LY]*~D -5.67'), it produced a nitrosochloride with Fig. 1.-Quantitative distribution and physical properties of different boiling fractions of guayule essential oil. the melting point of that of dl-a-pinene nitrosochloride. This suggests that most of the a-pinene Through the oxidation of Fraction 4 and the in guayule is dl-a-pinene, with a possible excess of identification of the oxidation product as norpinic the l-isomer. It is estimated from the fractionation curve that dl-a-pinene makes up 50 to 60% acid, &pinene was identified. The physical constanti, the carbon-hydrogen of the total essential oil of guayule. analysis, and the melting point of the tetra(3) In order to establish the correct abscissa spacing in Fig. 1 bromide of Fraction 9 are identical with those from between the boiling points of fractionations at different pressures, &-limonene. Although the tetrabromide from a sesquiterpene fraction was refluxed at various pressures. The results are given in Table 11. Fraction 9 gave no melting point depression when
A. J. HAAGEN-SMIT AND R. SIU
2070
mixed with the tetrabromide from dl-limonene, Fraction 9 showed a dextro-rotation, [u]"D -t25.76'. This may be explained by an excess of the d-isomer in the guayule plant. About lo(% of the weight of the oil WCLS thus qhown l o be limonene. The largest sesquiterpene fractioii, which makes up about 8% by weight of the total oil, was identified as cadinene. The chemical composition and the physical constants for Fraction 29 agree very closely with those given by Henderson and Robertson for cadinme. The dihydrochlor ide gave the same melting point as that of cadinene dihydrochloride. Hydrogenation of Fraction 29 demonstrated the presence of two double bonds. This indicated a bicyclic structure for an empirical formula of C15H24. 'The ethylenic linkages were shown to be isolated by their non-reactivity toward sodium and alcohol and also toward maleic anhydride. Selenium dehydrogetiatiw of the oil gave an aromatic hydrocarbon, the picrate of which had the Same empirical forniula arid melting point a5 cadalelie picrate, which 15 obtained from cadinene under similar wlidition~. Selenium dehydrogen,ition of Fraction 26 produced S-guajazulene, which w;ts identified by its picrate, m. 11. 120-3211.50,its styphnate, in. p. 105.3-106.5", and its absorption spectrum. The melting points rccordeti i n litcr,tture for the picrate and the styphilate .m 10b-IO'io .ind I'LI--122', respectively. According to I'ldttnerb the absorption spectrum of S-guajazulene is characterized by 3 strong bands a t 608, 661 and 732 mp, and weak bands at 556, 577, G 3 1 and 699 mp. The absorption spectrum of the azulene obtained from the dehydrogenation of Fraction 26 (Fig. 21, shows maxima at the same places. The formation of S-pajazulene in the selenium rlchyclrogenation I
560 640 720 Wave length in mp. Fig. 2.-Absorption spectrum of guayule azulene. 480
(4) Henderson ahd Robertson, J . C h e m . Soc., 196, 1993 (1924). ( 5 ) Ruzicka and Haagen-Srnit. 1Iei.d. C h i n ? . i1c:a. 14, 110.1 (1931) it;] l*l;ittrier, ibid.. 2 4 , L'nor?(1!111:
Vol. 66
of guayule oil is interesting in view of the work of Iiuzicka and Haagen-Smit.' These workers obtained a blue S-guajazulene on dehydrogenation of guajol with sulfur and a violet Se-guazulene with selenium. Furthermore, picrates of the two azulenes gave distinctively different melting points of 121-122' and 11-2-115', respectively. The fact that the physical constants of Fraction 26 agree very well with those for guajene, a sesquiterpene which can also be dehydrogenated to S-guazulene, suggests a guajene-like nucleus in Fraction 26. This fraction makes up Z(r, of the oil. A sesquiterpene alcohol, which is identical or closely related to elemol, C15H260, was found in Fraction 39. The empirical formula and the physical constants agree very well. Fraction 39 gave eudalene upon selenium dehydrogenation, as is the case with elemol. One active hydrogen was shown by the Zerewitinoff analysis, thereby suggesting the presence of an alcoholic group The failure of this group to react with phthalic anhydride and with carbon bisulfide to form a xanthogenate showed it to be a tertiary one. This is also the case with elemol. Further like elemol, there were found two ethylenic linkages in the guayule oil fraction. About 4y0of the oil is made up of this compound. One of the oxygenated terpene fractions was shown to be probably E-phellandral. Good agreement exists between the physical constants of Fraction 20 and those of I-phellandral Also, the 2,4-dinitrophenylhydrazoneprepared from Fraction 20 showed the same melting point as that recorded in the literature for phellandral. Only 3 of the maxima in the fractionation curve of Table V remain unidentified a t present. These arc Fractions 7, 1.5 arid 41. Inasmuch as this project had to be interrupted, the information obtained so far on these fractions will be given i n this p p e r and conclusions as to their nature will be drawn, as much as available evidences permit. Fraction '7.-This small maximum in the fractionation curve is probably caused by the presence ( J f a small amount of an easily oxidizable terpene. Carbon-hydrogen analyses after different lengths of time of standing gave varying oxygen content Immediately after fractionation, the oil fraction analyzed 86.84% carbon, ll.66Y0 hydrogen and 1.50% oxygen. Fraction 15.-The formation of a 2,4-dinitrophenylhydrnzorit. showed this fraction t o he a carbonyl coiiil)ound. Its boiling point indicates d Clo compciuiid. SLolecular refractivity calculd tions suggest a monocyclic compound. This fraction makes up about 2% of the oil, experimental MD,46.0; calcd A I D for monocyclic CloHlsO, 46.2. Fraction 41.-Combustion analyses suggest an empirical formula of CI6H260. The oxygen is present as an alcoholic group, as shown by the (7
l < i i , ~ d ,i i i t l
lit,*,.ot
hmlt i b d
14, 1 1 0 1 ( I ' j J I )
Zerewitinoff active hydrogen analysis. Failure of the hydroxyl group to react with phthalic anhydride and with carbon bisulfide to form xanthogenate indicates a tertiary alcoholic group. The compound in question is, therefore, a tertiary sesquiterpene alcohol. Furthermore, selenium dehydrogenation of the oil resulted in the formation of an azulene. The presence of such a carbon skeleton in the sesquiterpene alcohol is thereby indicated. This alcohol makes up about 3% of the total oil. Thus, about 90% of the essential oil of guayule is identified as cyclic compounds. This is in support of the belief that the terpenaceous compounds are not intermediates in the formation of rubber in the plant.8 If the terpene compounds are considered as rubber precursors, it is hardly to be expected that these intermediary compounds would be cyclic in nature, which would necessitate the difficult task of breaking the carbon-to-carbon bonds so that they can again polymerize in a straight chain manner into rubber. While both terpenes and rubber can be resolved into isopentane units, which indicates a similarity in their mode of formation in the plant, it has never been demonstrated that these originate from a common precursor. The often irregular build up and the cyclization tendencies of the terpene precursor as contrasted to the aliphatic regularity of the rubber molecule speak against a common precursor. It may be that rubber has its origin in polyoses like starch and inulin, while the terpenes are derived in a similar way from simpler sugars as postulated by Emde.g
Experimental Part Fractionation of Guayule Essential Oil.-The essential oil was obtained from the steam distillation for two and one-half hours of two-year old guayule plants (Parthe&m argentaturn, Gray, variety 593). These had been grown in the William Bryan tract of Salinas, California, and were harvested in the fall. The oil was separated from the water of the steam distillate and dried over anhydrous sodium sulfate. The oil was first fractionated by means of an 8-inch helices column into the 11 fractions given in Table 111-IV. TABLE 111-IV FRACTIONATION OF GUAYUI.E ESSENTIAL OIL PRELIMINARY Fraction
1 2
3 4 5 6 7 8 9 10 11 Total
207 1
ESSENTIAL OILS OF GUAYULEPLANT
Dec., 1944
Pressure
21 mm. 21 mm. 21 mm. 21 mm. 8~ 8c( 8 P
8r 8r 8r Residue
1'>istn. temp., "C.
Wt. in K.
54-58 58-62 62-66 66-70
