linear curves do not provide more accurate readings and because additional effort is needed to prepare these curves, the nonlinear plots included in this reilort are used for analysis. ACKNOWLEDGMENT
The authors thank Louis 0. Raether for the interest he has shown in this
work and for providing the copolymer samples used as standards. LITERATURE CITED
(1) Bovey, F. A., Anderson, E. W., Douglass, D. C., J . Chem. Phys. 39,
1199 11963'1. (2) Chen, H.'Y., ANAL.CHEM.34, 1134 (1962). ( 3 ) Drushel, H. Y., Iddings, F. A,, Ibid., 35, 28 (1963).
(4) Holdsworth, R . S. (to IJnited States Rubber Company), U. S. Patent 2,956,973 (Oct. 18, 1960). ( 5 ) Perry, S. G., J . Gas Chromalog. 2, 54 (1964). (6) Porter, R. S., Nicksic, S. W., Johnson, J . F.. ANAL.CHEM.35. 1948 11963). ') Senn, w. L., Jr., Anal. Cham. A c t a 29, 505 (1963). RECEIVEDfor review June 25, 1964. Accepted July 27, 1964.
Mass Spectrometry of Naturally Occurring Alkenyl Phenols and Their Derivatives J. L. OCCOLOWITZ' Department of Supply, Defence Standards laboratories,
b The mass spectra of naturally occurring alkenyl phenols and derived alkyl phenols and methyl ethers have base peaks resulting from fission p to the benzene ring with the rearrangement of one hydrogen atom. The ratio of the intensity of this rearranged peak to the one resulting from pfission without rearrangement increases with the number of oxygen functions on the benzene ring, this behavior is attributed to resonance stabilization of the rearranged ion b y the participation of cyclohexadienetype structures. The m/e of the base peak and the molecular ion enable the number of phenolic groups and the length and degree of unsaturation of the alkenyl side chain to b e found. The application of mass spectrometry to the analysis of some naturally occurring compounds and their ozonolysis products is described.
A
are found widely in the family Anucardiaceae and constitute the physiologically active components of poison ivy ( 8 ) , cashew nutshell oil (Q),and Japanese lac (7). Recently an active resorcinol derivative has been found in the family Gymnospermeae (6). I n all of these compounds found, to date, the alkenyl side chain is unbranched and is meta to a t least one phenolic hydroxyl group. Usually the compounds occur as mixtures of alkenyl phenols each with the same chain length but varying degrees of unsaturation in the side chain, and analysis of the mixture involves the separation of each component. Mass spectrometry, as shown here, has proved to be a rapid method for determining the number of constituents LKENYL PHENOLS
1 Present address, Department of Chemistry, AZassachusetts Institute of Technology, Cambridge, hIass.
P. 0.Box 50,
Ascot Vale, Vic., Australia
and their degree of unsaturation. Because of its sensitivity it can also detect the presence of minor constituents often missed in conventional analysis. From the spectrum the number of phenolic hydroxyl groups, the molecular weight, and hence the length and degree of unsaturation of the side, chain, or strictly the sum of rings and double bonds, can be found. KO direct information regarding the position of unsaturation is available from the spectrum, except perhaps in the case of pure monoolefins, however ozonolysis products can be identified and this information used in determining the position of unsaturation. KO study of the fragmentation of alkenyl phenols under electron impact has been made to date, but the fragmentation of alkyl benzenes has been extensively studied and a review has recently appeared ( I ) . The principle fissions of these compounds occur p to the benzene ring to give the tropylium ion
EXPERIMENTAL
Spectra were determined on an Atlas CH4 mass spectrometer using an inlet temperature of 200' C., unless otherwise specified ionizing electron energy was 70 e.v. The ozonolysis of the C. auriculata Hook methyl ethers and the isolation of the resulting aldehydes was carried out as described in (6). DISCUSSION OF SPECTRA
Table I1 lists the base peak for a number of the samples examined, here p-fission with the rearrangement of a hydrogen atom gives an ion whose composition is the same as the corresponding 0-substituted toluene. From the m / e of the base peak it is possible to calculate the number of substituent hydroxyl or methoxyl groups. Molecular ions of 5 to 10% of the base peak enable the length and degree of unsaturation of the side chain to be found. Table I lists the intensities (base peak 100%) of the rearranged (RCH3+) and the tropylium ion (RCH2+)for a number
C7H7,m/e
or alternatively by rearrangement, via a postulated four- ( I ) or six-membered (4)transition complex, of a hydrogen atom to give the even m / e ion at 92e.g.,
91
of alkenyl and alkyl phenols and ethers, and alkyl benzenes. For the long chain alkyl benzene the ratio RCH3+/RCH2+ is about 1.2 to 1, adding an oxygen function to the benzene ring meta to the L
c; H
C,Hs,m/e 92 The ratio of the intensities 92/91 increases with the increase in chain length (Table I). Fragmentation of the side chain by other mechanisms gives predominantly ions of the type PhC,H2,+ which occur a t odd masses.
side chain increases this ratio to about 2 to 1, and adding an additional oxygen function again meta to the side chain results in a further increase to about 7 to 1. This increase in rearranged to nonrearranged ion ratio can be explained on VOL. 36, NO. 1 1 , OCTOBER 1964
2177
IO0
I
10.6
T
I
I
I
1
Figure 1 . 0. Spectrum of 5-(1O-pentadecenyl)resorcinol; b . Spectrum of 5-pentadecylresorcinol
the basis of oxonium ion stabilization of the methylene cyclohexadiene structure by the resonance
q g - ((-Jy* \
H
+ OR
OR
H
R = H o r CHS
Figure 2. Spectra of phenols from Grevillea pyramidalis; top: ionizing energy, 70 e.v.; bottom: ionizing energy, 9 e.v.
peak at 124 confirm the previously assigned formula. The impurity at m/e 346, as shown later, is caused by a higher homolog. The ion at m/e 222 corresponds to the fission of the side chain a t the 7 position-Le. p to the double bond with the rearrangement of one hydrogen atom-but no other isomers were available to establish whether this fission is diagnostic for the
for the mono-oxygenated ions and __ c-t
OR
+OR
for the di-oxygenated ions. Resonance stabilization by the participation of analogous structures is possible for hydrogen atom transfer to the other position ortho to the methylene group. 411 of the major ion peaks (6) in the spectrum of commercial p-nonyl phenol, a mixture of branched chain isomers, occur a t odd masses. This is to be expected because in contrast to the compounds having oxygen functions only meta to the side chain those having an ortho or para oxygen function can form the cyclohexadiene structure by direct p-fission without hydrogen rearrangement-e.g.,
OR position of unsaturation. However, the dimethyl ether gives an analogous spectrum with the ion a t m/e 222 now shifted to m/e 250 (2 X CH,) indicating that this preferred p-fission is also operative in this compound. Figure 2 shows the partial spectrum, taken a t ionizing electron energies of
Tab1e 1.
70 and 9 e.v., of an extract from G. pyramidalis containing a number of minor constituents. Because of the pronounced hydrogen rearrangement in the spectra of these compounds, it is not possible to conclude from the 70 e.v. spectrum whether the ions a t m/e 290 and 276 are caused by fragmentation or are molecular ions. Reduction of the electron energy to 9 e.v. has removed the ion a t 276 but has left the relative intensity of 290 almost unchanged, the latter ion is then a molecular ion and is probably a resorcinol derivative with a monounsaturated side chain of 13 carbon atoms. This was confirmed bv methylation when the spectrum using 8 e.v. ionizing electrons of the mixed ethers showed a corresponding ion at 318. The ions a t m/'e 332, 346, and 356 albo shift 28 mass units higher on methylation so can be assigned as unsaturated biphenols with side chains of 16, 17, and 18 carbon atoms, respectively.
Unrearranged (RCH2+) and Rearranged (RCH3+) Ions from Alkyl Benzenes, and Alkenyl Phenols, and Derivatives
RCHz+, 70
Compound c~.Hb-ciH~
100
RCHs-, % 55
17
100
RSO =(=J==-cH~ ,4n ortho effect would not be expected to operate as it would result in the expulsion of a saturated hydrocarbon molecule. The preference for the cyclohexadiene structure in the spectra of the meta compounds suggests that this structure would also be favored in the spectra of the ortho and para compounds rather than the alternative tropylium type structure. Figure 1, top, shows the spectrum of 6-(10-pentadecenyl) resorcinol deriL-ed from Grevillea pyramidalis (6) , the molecular ion at mle 318 and the base 2 178
ANALYTICAL CHEMISTRY
.
1;3;5-( HOj&-C&-C, 1,3,5-(CH
Table II.
." ..
,H.1
17
100
Base Peak in the Spectra of Alkenyl and Alkyl Phenols and Ethers Conipound m/ e Composition 108
122 122 124 152 152
.oo
i l ro 14.5 1 I
I
I
I
I
a 2v)
Z
W
C
tIO
b 4 300 I
M A S S NUMBER
0
Figure 3c. Spectrum of hydrogenated high boiling fraction from cashew nutshell oil
Figure 3. a. Spectrum of low boiling fraction from cashew nutshell oil; b. spectrum of high boiling fraction
The mass spectrum of 5-pentadecyl resorcinol shown in Figure 1, bottom, shows the extensive hydrogen rearrangement occurring in this compound where each ion above m/'e 151 caused by fragmentation of the side chain occurs a t even mass. Metastable ions in the spectrum show that fragmentation occurs by the elimination of olefin molecules from both the molecular and fragment ions. The preference for even mass ions may be the stability of ions of the type
OH
which could be formed by the following mechanism
R
as aell as the base peak, which has n = 0, ions with n = 3 and to a lesser extent nith 12 = 6 are favored to give peak< a t nz e 166 and 208, respectively.
the presence of minor amounts of components with side chains of 17 carbon atoms a t masses 330 and 332. Also evident in the spectrum is an intense peak a t mle 120 which may be formed by fission of the ?-bond and the expulsion of a hydrogen atom to give a stable styrene-type structure. The spectrum of a higher boiling fraction is shown in Figure 3b. The appearance of an ion a t mle 124 indicates the presence of a small amount of biphenolic compound. Hydrogenation can be used to establish whether this ion is due to the molecular ions a t m/e 314 or 316 or a t 326,328, and 340. Figure 3c shows the partial spectrum of the hydrogenated fraction. The peak a t mie 320 corresponds to the saturated biphenol with a side chain of 15 carbon atoms and not the monophenol with a 16 carbon atom side chain which would occur a t m,/e 318, similarly the ion at m/e 332 is caused by a monophenolic component with a 17 carbon atom side chain. Thus in Figure 3b the ions a t 314 and 316 arise from tri- and diunsaturated biphenols with 15 carbon atom side chains and the ions a t 326, 328, and 330 from di-, tri-, and monounsaturated monophenols with 17 carbon atom side chain3. Figure 4 shows the spectrum of methylated phenols derived from
saturated resorcinol derivatives of the same chain length. To check the applicability of mass spectrometry to the analysis of a mixture of this type the mass spectrum of a fraction obtained from the distillation of commercial cashew nutshell oil was used to calculate the percentage of each component. I n the calculation it was assumed that the amount of each species was proportional to the intensity of the corresponding molecular ion. This assumption could lead to high results for the more unsaturated components. Figure 3a shows the spectrum of a lower boiling fraction from the distillation of commercial cashew nutshell oil. The formulas in this figure and in the figures following where they represent compounds u i t h unsaturated side chains give the average composition of the side chain as determined by hydrogenation. The base peak a t m e 108 shows the compounds to be monophenolic and the group of molecular ions between masses 296 and 304 show the presence of monophenols with none to four double bonds in a 15 carbon atom side chain. Table I11 compares the composition found by mass spectrometry with that previously obtained by chromatography of the methyl ethers (9). The mass spectrum also indicates
Table Ill.
Composition of C,i Monophenols from Commercial Cashew Nutshell Oil
APPLICATIONS
Comrnm4al cashew nutshell oil has been found by chemical analysis (9) to consist of a mixture of saturated, mono,di-, and tri-un*aturated monophenols with side cahains of 15 carbon atoms together with maller amounts of un-
4
Component Saturated Mono-unsaturated Di-unsaturated Tri-unsaturated Tetra-unsaturated
mle
304 302 300 298 296
Per cent Column Mass spectrometry chromatography 4 7 45 20 25 3
VOL. 3 6 , NO. 1 1 , OCTOBER 1964
45 20 31 0
2179
2t-
$-
v,
Z
"I-
C
Figure 5 a . Spectra of methyl ethers from Campnosperma auriculata Hook
~,~D.W..H.~F CHJC H,),CHO , 300'
'
'
l= 3
d
MASS NUMBER Figure 5b. Spectra of 2,4-dinitrophenylhydrazones of steam volatile aldehydes from ozonolysis of C. auriculata Hook methyl ethers Figure 4. a. Spectra of methyl ethers from Pentaspadon officinalis Holmes; b. hydrogenated methyl ethers from P. officinalis Holmes; c. spectrum of anilides derived from steam involatile aldehydes from ozonolysis of P. officinalis Holmes methyl ethers
Pentaspadon oflcinalis Holmes. Chemical examination had identified two monophenolic constituents with side chains of 17 carbon atoms, one unsaturated and the other diunsaturated, and established, the position of unsaturation ( 3 ) . As well as these components a t m/e 344 and 342, respectively, the mass spectrum shows ions a t m l e 340 and 338 which are probably caused by the presence of tri-, and tetra-unsaturated components, an ion a t m ' e 318 which does not shlft on hydrogenation (Figure 4b) is then caused by the presence of the saturated monomethyl ether with a side chain of 15 carbon atoms. The absence of an ion a t m'e 150 shows the absence of biphenolic componentu. The qpectrum of the hydrogenated methyl ethers (Figure 4b) shows practically only one molecular ion, m/e 346, corresponding to the qaturated compound with a side chain of 17 carbon atoms, this fact together with the simplicity of the spectrum indicates that only one structural type is present and confirms the identity of the tetra-, and triunsaturated materials in the original material.
21 80
ANALYTICAL CHEMISTRY
> t VI
w z
Figure 5c. Spectra of steam involatile residue from ozonolysis of C. auriculata Hook methyl ethers
Figure 4c shows the mass spectrum of the recrystallized anilides obtained from the acids resulting from the oxidation of the steam involatile aldehydes from the ozonolysis of the methyl ethers (3). Only one anilide is present, molecular ion a t m,'e 325, corresponding to the acid with an 8 carbon atom side chain. Hence. most of the unsaturation in the mixture occurs between the C-8 and the terminal carbon atom of the side chain and each compound has a common 8-9 double bond. As a final example of the application of mass spectrometry to the analysis of this type of compound, some work done on the methyl ethers derived from Campnosperma auriculata Hook ( 2 ) is described. These compounds were found to be monophenolic with side chains of 19 carbon atoms and the material
shoF ed unsaturation equivalent to one double bond per mole (2) The mass spectrum (Figure 50) confirms this result as the base peak occurs at m e 122 and the molecular ion a t 372. In addition there are hmaller peak. at m e 368, 388, 400, and 402 indicating the presence of compounds s i t h side chains of 18, 20, and 21 carbon atoms, reqpectivelv I t i s not powble to assign the poqition of unsaturation although the ion at m e 276 suggests the presence of a 14-15 double bond (pfi-ion) Preliou. nork had shown (6) that the mass ipectra of 2.4-dinitrophen~1hjdrazones of qhorter chain length aliphatic aldehj des and of w-phenyl aldehydes ga\e suffinentl, intense molecular ions for their identification. Figure 5b shoas the partial mas< spectrum of the 2,4-dinitrophenvlh~dra-
zones of the steam volatile aldehydes and Figure 5c of the steam-involatile residue obtained from the ozonolysis of C. auriculata Hook methyl ethers. Because of the possibility of side reactions during ozonolysis only conjugate pairs of aldehydes-i.e., with the sum of the n’s equal to 16, corresponding to a total chain length of 19 carbon atoms--are used to establish the position of unsaturation. The data presented in Figure 5b and 5c permit one to establish the position of the double bond in the major components as summarized in Table IV. The intensities of the molecular ions from the 2,4-dinitrophenylhydrazones vary markedly with chain length, as might be expected the compounds of shorter length give relatively more abundant molecular ions and are thermally more stable. ACKNOWLEDGMENT
The author is indebted to J. A. Lamberton of the Commonwealth Scientific and Industrial Research
Table IV.
Aldehydes from the Ozonolysis of C. Auriculata Hook Methyl Ethers and Structure of C19 Components
Steam volatile
_ aldehyde _ 2,4-D.N.P.H. of
CHa(CH2)nCHO mle n 238 266 294 322
1
3 5 7
Steam involatile aldehyde ~ rn-CHaO-CeH4(CH,),CHO mle n 346 318 290 262
15 13 11 9
Organization, Melbourne, for some of the samples studied. LITERATURE CITED
(1) Grubb, H. M., Meyerson, S.,“Mass Spectrometry of Organic Ions,” F. W. McLafferty, ed., Chap. 10, Academic Press, New York, 1963. (2) Lamberton, J. A., Australian J . Chem. 12, 224 (1959). (3) Ibid., 12, 234 (1959). ( 4 ) McLafferty, F. W., ANAL. CHEM. 31, 2072 (1959).
(R R-( R-( R-( R-(
=
Compound m-CHaO-Ce.H4-)
CHz),,-CH=CH-CHzCHa CH,),,-CH=CH-( CHz)aCHa CH2)ii-CH=CH-( CH2)SCHa CHz)s-CH=CH-( CH2)vCHa
( 5 ) Occolowitz, J. L., unpublished data, Defence Standards Laboratories, Australia, 1963. (6) Occolowitz, J. L., Wright, A. S., Australian J . Chenc. 15, 858 (1962). (, 7,) Sunthankar. W. F.. Dawson. C. R..’ J . Am. Chern.‘ SOC.76; 5070 (1954). ( 8 ) Symes, W. F., Dawson, C. R., Ibid., 76, 2959 (1954). ( 9 ) Ibid., 75,4952 (1953).
RECEIVEDfor review May 21, 1964. Accepted July 29, 1964.
Separation of Isotopic Position Isomers of Tritium-Labeled Olefins by Gas Chromatography SIR: While isotopic substitution in a molecule causes relatively small physicochemical differences, these variations are nevertheless large enough to encourage attempts at separation and analysis through the powerful techniques of gas chromatography. Earlier results from several laboratories have demonstrated the separation of the various isotopic forms of molecular hydrogen, of multi-deuterated from fully protonated compounds, and of mono-tritiated from fully protonated hydrocarbon. (6). R e now report the gas chromatographic separation of inonotritiated forms of olefinic hydrocarbons, differing from each other only in the intramolecular location of the tritium atom. This separation technique readily permits the rapid, nondestructive determination of the intramolecular isotopic distributions of these compounds. Our first attempts a t separations of isotopic position isomers have been directed toward the olefinic hydrocarbons. The earlier experiments of Cvetanovic, Duncan, and Falconer (1) have demonstrated hydrogen isotope effects on hgN03-ethylene glycol
columns sufficient for the resolution of CzHzDzor CzD4 from C2H4,and for other similar olefinic pairs (1). Since CzHzDz and CzD4 emerge 7.5y0and 15% later than C2H4, the substitution of a single deuterium or tritium atom in an olefinic position was expected to increase the retention time by about 4 and 7y0, respectively. The progressive lengthening of retention time by increasing deuterium substitution has in fact been used as the basis for the separation and analysis of the various isotopic ethylenes, C2H,D4-,, and in similar separations of the isotopic allenes ( 2 ) . On the other hand, since all alkanes emerge very rapidly from such columns, little or no isotope effect mas anticipated for tritium in alkyl positions. The separation mechanism is dependent both on the relative solubilities of the olefins in ethylene glycol, and on the equilibrium constants for the Ag+olefin complexes (4). I n the present experiments, however, the Ag+-complex equilibria are the dominant effect, and the isotopic separations depend upon isotope effects in these equilibria. The chemical reactions of the hot tritium atoms forined in nuclear re-
actions have been studied with a wide variety of mono-olefin hydrocarbons ( 7 ) . Invariably, the radioactive olefins smaller than the reacting parent olefin have been those expected from the decomposition by C-C break of the excited free radical formed in the initial hot reaction, as in Equations 1 and 2 :
T*
+ R-CHz-CH=CH-R’
+
R - C H ~ ~ H C H T R ~(1)
-
RCH~CHCHTR~
RCHZCH=CHT
+ R’
or
R
+ CHz=CHCHTR’
(2)
For example, propylene-t is forined in the reactions of tritium with each of the isomeric butenes. However, from Equations l and 2 , the propylene-t niolecules expected from trans-(or cis-)butene-2, isobutene, and butene-1 can be seen to be CHsCH=CHT, CH3CT=CH,, and CH,TCH=CH2, respectively. If decomposition of the excited radical occiir5 by C-H bond break, then labeled VOL. 36, NO. 1 1 , OCTOBER 1964
2181
