FORMAHUN U? In: PWIUMIEU malnnau. “In, an -,

 

IN THE MASS SPECTRUM 0f Z-METHOXYETHANOL

Thesis far Hm {Degree of M. S.
MICWGAN STfiTE UNK‘IERS-EW

Kesmit Rainshré W‘ay, if.

'i 965

 

ABSTRACT

FORMATION or THE PROTONATED METHANE ION, CH2,
IN THE MASS SPECTRUM or 2—MBTHOXYETHANOL

by Kermit Rainsford Way, Jr.

A doublet had been observed at m/e = 17 in the mass Spectrum of
2—methoxyethanol. It was suSpected that one of these peaks was due
to CH; although the ion had never before been seen in a methane-free
system. This study endeavored to identify the ion and to learn some-
thing about its formation.

Measurement of the exact mass of the ion showed that the ion was
CH2. This was confirmed by high reSolution Spectra which resolved
the multiplet at m/e = 17 in samples of 2-methoxyethanol which con-
tained small amounts of ammonia or methane—d1.

Pressure dependence studies indicatalthat this ion is being
formed by a unimolecular process rather than by an ion—molecule re—
action.

Isotopic labeling was done to determine from which part of the
molecule the ion was formed. The mass spectrum of 2-methoxy-13C—
ethanol indicated that the carbon came from the methyl group, while
mass spectra of 2-methoxyethanol—l,l-d2 and 2-methoxyethanol-d do not
indicate involvement of the labeled hydrogens. It was concluded that
the ion is formed from the methyl group and both hydrogens in the
C-2 position in the compound.

A mechanism involving cleavage between the C—1 and C-2 carbons
followed by further fragmentation of the C2H50+ ion (which is the base

peak in the Spectrum) to yield CH: was proposed:
[CH30C2H4OH]+ _——> [cnsocnz]+ + other fragments
[CHSOCH2]+

 

> CH; + co.

FORMATION OF THE PROTONATED METHANE ION, CH5+,

IN THE MASS SPECTRUM OF 2—METHOXYETHANOL

By

Kermit Rainsford Way, Jr.

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Chemistry

1965

ACKN OWLE TITMEN TS

The author wishes to express his appreciation to Dr. M. E.
Russell for his guidance throughout this undertaking. Thanks are
also expressed to Drs. G. J. Papenmeier and W. H. Reusch for supply-
ing the 2-methoxyethanol—d, and to Mr. A. Struck of Perkin—Elmer

Corporation for obtaining the high resolution mass spectra.

ii

TABLE OF CONTENTS

Page

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . l
I. Historical Background . . . . . . . . . . . . . . . 1

II. Objectives of the Present Study . . . . . . . . . . 13
EXPERIMENTAL........................lb
I. Instruments . . . . . . . . . . . . . . . . . . . . lb

II. Chemicals . . . . . . . . . . . . . . . . . . . . . lb
III. Method of Exact Mass Measurement . . . . . . . . . 18
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . 19
I. Identification of the Ion . . . . . . . . . . . . . 19

II. Pressure Dependence Studies . . . . . . . . . . . . 23
III. Isotopic Studies . . . .V. . . . . . . . . . . . . 23
CONCLUSIONS AND DISCUSSION . . . . . . . . . . . . . . . . . 28
POSSIBLE FURTHER STUDIES . . . . . . . . . . . . . . . . . . 30
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . 32

APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . 36

iii

Table

II.

III.

LIST OF TABLES

Page
. . .. . . . + .
Data on ion-molecule reactions lDVOlVlng the CH5 ion . 5
- A .. ,... +. . .
Heat of Iormation or the CH5 ion and the prOton
affinity of methane . . . . . . . . . . . . . . . . . 8

Determination of the exact mass of the m/e = 17 peak . 20

iv

LIST OF FIGURES

Figure ' Page

1. High resolution spectrum of the multiplet at m/e 17
in 2-methoxyethanol with added ammonia . . . . . . . . 2l

2. High resolution Spectrum of the multiplet at m/e l?
in 2-methoxyethanol with a small amount of added

methane-d o o o o o o o o o o o o o o o o o o o o o o 22

Intensity of the m/e 17 peak as a function of pressure 2h

Intensity of the m/e 17 peak as a function of pressure 25

Peaks at m/e = 17, 18, and 19 in 2-methoxy—13C—ethanol . 26

QUIE’K»

. Peaks at m/e 17, 18, and 19 in unlabeled 2—methoxy—
ethanOl 0 O O O O O O O O O I O O O O O O O O O O O O O 26

Peaks at m/e

N

17, 18, and 19 in 2-methoxyethanol-l,l-d2 26

ll

8. Peaks at m/e 17, 18, and 19 in 2—methoxyethanol-d . . 26

LIST OF APPENDICES

Appendix Page
1. Mass Spectrum of 2-Methoxyethanol . . . . . . . . . . 37
2. Preliminary Determination of Appearance Potentials

for Selected Ions in the Mass Spectrum of 2—Methoxy-

ethanOl O O O O O C O O O O O C O O O O O O O 0 O O O 38
3. Pressure Dependence of Some Ions in the Mass

Spectrum of 2-Methoxyethanol . . . . . . . . . . . . . 39
b. Infrared Spectrum of 2—Methoxyethanol . . . . . . . . hO

vi

INTRODUCTION

I. Historical Background

Early History

 

+
The ion CH5 has been observed readily in the mass Spec—

trometer and has also been postulated in radiation chemistry mechan-
isms. In every case reported, the ion has been formed by an ion—
molecule reaction in which methane, either the molecule or one of
the ions therefrom, constituted at least one of the reactants.

The first observation of this ion which has been reported was
by Eltenton (1,2) in l9hO. The ion was rediscovered in the period
l9hO-l9b6 by Nier (3). However, at the time neither of these dis-
coveries was published.

The first published report of the CH; ion appeared in 1952
when Tal'roze and Lyubimova (b,5) noted its appearance in the mass
Spectrum of methane at increased pressure. Shortly thereafter,
Stevenson and Schlissler (2,6) (unaware of Tal'roze's work) referred
to Eltenton's unpublished results in a communication on ion-molecule
reaction rates.

Alekseevskii, Tal'roze and Shelyapkin (7) confirmed the identity
of CH; by resolving the multiplet at m/e = 17 using high resolution
techniques. Field, Franklin and Lampe (8) also confirmed the appear-
ance of this ion during a study of the high pressure mass Spectrum

of methane.

Mass Spectrometric Systems

 

In addition to the formation of CH; in the electron impact

Spectrum of methane by the reaction

CH: + CH4 -—> CH; + CH3
there have been several other systems in which this ion has been
observed.

Wagner, Wadsworth, and Stevenson (9) compared the cross section
of formation of cnso: and CD4H+ in the mass spectrum of mixed CH4
and CD4. They found that the cross section of formation for CHSD:
was only one-sixtieth of that predicted if the H and D were randomly
arranged. Therefore, they concluded that the activated complex was
loosely bound (CH4-CD4)+ rather than tightly bound CZH4DI. Derwish
g}_§l. (10) saw evidence that the m/e = 19 peak in the Spectrum of
this mixture may be due to CD3H+ from the reaction of CD: + CH4.
If this is true in whole or in part, it would add more support to
the loosely bound complex.

In a very high pressure study (300 u), Field, Franklin and
Munson (11) report some evidence for the reactions

CH3+ + CH4 -——> [C2H:]+

in addition to the usual production of CH; in the methane spectrum.
They also note the decomposition of CH; by collision with CH4 in the
analyzer tube.

Several studies have been conducted of systems in which a methane
molecule or ion reacts with something other than another methane.

Munson, Field and Franklin (12) have done a study of the systems CH4

3

and H2, CH4 and D2, and CD4 and H2. They conclude that the CH;—
type ions can be formed by the reaction of CH: with either H2 or
of CH4 with H3. It will be noted that the latter is a termolecular
reaction since the formation of H; is bimolecular. They also found
that the reaction of CH: with D2 produced CH4D+ but very little
CHSD: indicating that the activated complex for this reaction was
loosely bound, similar to Wagner EE_El°'S findings for the (CH4-CD4)+
complex. Previous to this there had been some disagreement as to
whether or not the reaction

on: + H2 -——-> CH; + H
(or the corresponding reaction with either reactant deuterated) took
place. Tal'roze and Frankevitch (13) reported the reaction but
Lampe and Field (1h,lS) had been unable to observe it.

Lampe and Field (1h) have also found the ion CD4H+ in the mass
spectrum of mixtures of CD4 with CH4, CZHG, C3H8, iso-CaHlo, CH3C1,
NHS, HZS and HCl.

Mass spectrometry using photoionization rather than ionization
by electron impact is comparatively rare. However, CH; was observed
by Cook and coworkers (16) during a study of photoionization-induced

ion-molecule reactions.

Quantitative Studies

 

There are several review articles available on the mass spectrometry
of ion—molecule reactions (17,18,19,20,21) of which perhaps the best
introduction to the subject is the one by Stevenson (19). It is not

our present purpose to explore ion-molecule reactions in detail.

b

However, all of the mass spectrometric studies of the CH; ion have
been ion—molecule studies. Therefore, a large amount of the data
relating to this ion is in the form of reaction cross sections and
rate constants. These data have been collected in Table I. In such
studies the neutral product(s) must be inferred although sometimes
their nature is obvious. Also, it is not known whether the ion or
atom is transferred in some cases such as reaction 1. In this table
we have used brackets around both reactants with the charge outside
the brackets in cases where it was not determined which species was
ionic and which was neutral. In the reference column, the year is
also included for convenience in examining the data. The voltage
gradient indicated in the Comments column is the reported gradient
in the ionization region, i.e. the draw-out potential. The entry
"thermal" indicates that the data apply to ions possessing only
thermal velocities. Table II contains a similar tabulation of values
for the enthalpy of formation of CH; and the proton affinity of methane.

A few studies have been conducted which do not lend themselves
to tabular presentation. Cassuto (32) has studied thermal effects
on the formation of ions and concludes that there is no activation
energy (i 0.2 kca1./mole) for the reaction

CH: + CH4 ———> CH; + CH3 .

This is in agreement with Tal'roze's (13) postulate that a re-
action involving a significant activation energy barrier would be
undetectable. Melton and Hamill (33) have done careful appearance

c h o - ~ v - ° + o o
pOtentlal work on the same reaction and concluded that the CH4 is in

the ground state. Finally, vonKoch (3h) observed the reaction

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Table II. Heat of formation of the CH; ion and proton affinity of

methane.

 

 

Heat of Formation Proton Affinity

 

No. AHf (CHE) P(CHA) Reference Comments
(kcal/mole) (kcal mole)
l 218 < AHf 5 23b 113 < P < 129 15(1959)
2 11b < P < 129 13,28(l958) Contradicts No. 3.
3 233-23h 113 lb(l9S7) Contradicted by No.
2; AHf(CD4H )
h 167 29(1962) By calculation
5 > 115 2(1955) One of first papers
6 173 30(1959) By calculation
7 161 31(1959) By calculation

 

9

CH: + CD4 ——> CD2H+ + D2 + CH3

in a charge exchange study. He feels this indicates all of the

bonds in CH; are of equal strength.

Miscellaneous Reports

 

Other workers (10,35) have noted the CH; ion in passing, al-
though the object of their study was something else. In addition,
the reaction

CH: + CH4 -——> CH; + CH3

has been used as a reference reaction in studies of hydrogen ab-
straction by cyanides (36), hydride transfer (37), and ion—molecule
reactions in methanol and ethanol (38). Two studies (22,25) used the
same reaction to test their pulse method of studying ion-molecule
reactions in the mass spectrometer, and Field and Lampe (26) used

the deuterium analog of this reaction in their study of the methane-
hydrogen sulfide system to determine the partial pressure of methane-

d4 when they felt their samples were not thoroughly mixed.

Radiation Chemistry

 

Knowledge of the CH; ion has also had an influence upon radia-
tion chemistry. TunitskiY and Kupriyanov (39) studied the mass spec-
trum of methane with the intention to apply this knowledge to radia-
tion chemistry processes. They found that the ions CH; and CZH; were
an order of magnitude more abundant than any other secondary ions in

the spectrum.

lO
Wexler and Jesse (27) studied consecutive ion-molecule reactions
in the mass spectrometer also with the intent of applying this knOwledge
to the radiolysis of methane. They found CH; to be very reactive and
suggested the reaction

+

CH; + CH4 ——-> czH5

although they admitted it to be endothermic. Ausloos and coworkers
(b0) consider the fate of the CH; ion to be rather in doubt. They
(bl) find evidence that the reaction of CH; with CH4 may be quenched
either by the products or by impurities in the system. Munson,
Franklin and Field (b2) support Ausloos' findings that this reaction
is probably negligible in the radiolysis of methane.

Several workers (b3,bb,b§) have postulated various mechanisms
that include the ion CH; (and usually also CH4T+) in the exchange of
T2 with CH4. It should be mentioned though, that a study by Munson,
Field and Franklin (12) offers some contrary evidence. The latter
feel CH: rather than CH; is involved.

Meisels, Hamill and Williams (b6) irradiated the krypton-
methane-iodine system and suggested that the CH; ion breaks up to
form H2 and CH3. The latter is detected as CHSI. In a later paper
(b7) on the krypton-methane system they conclude that CH; is neutral—

ized to form CH3 and possibly some CH2 radicals:

CH; + e' -——> CH3 + H2 and
CH; + e- ———> CH2 + H2 + H.

Ausloos and Lias (b8) feel that they have established proton (or
deuteron) transfer, during gamma ray irradiation, by the reaction

H; + CH4 > CH; + H2 .

 

11
The latter product is detected by transfer of a proton (or deuteron)
to cshe. In a later paper (b9) they indicate that CH; is one of the
most likely bimolecular products in the radiolysis and photolysis of
methane. They feel however, that the CH; is neutralized to form CH4

and H rather than CH3 and H2.

Rearrangements

 

A number of books (50,51,52,53) in recent years have been con—
cerned, in whole or in part, with fragmentation mechanisms in mass
spectrometry. The emphasis, however, has been to explain the major
peaks in the Spectrum without being concerned with minor ones (51).
At the same time small peaks at m/e = 17 and 18 may be ignored because
samples generally contain water impurity (Sb). These are perhaps
the reasons CH; has not been noted as a rearrangement peak in mass
spectra.

For a thorough discussion of fragmentation mechanisms, one is
referred to the references above. We shall only attempt to mention
a few points as they apply to the present work. The most important
feature both of ether Spectra and of alcohol spectra is B cleavage.1
(The same bond is B with respect to both groups in 2-methoxyethanol.)
Beyond this, and the fragmentation characteristic of the hydrocarbon
portion of the molecule, most of the Spectrum is characterized by

rearrangements.

 

1a cleavage is cleavage of the bond between the functional group
and the rest of the molecule. B cleavage is cleavage of the bond be-
tween the atoms which are a and B with respect to the functional
group, etc.

12
One of the rearrangements for oxygenacontaining compounds which
is more commonly proposed by Budzikiewicz et_§l. (52) is the rearrange-
ment of hydrogen through a five or Six member ring. In such a re-
arrangement, a (f (or y) hydrogen is transferred to the oxygen.

H

,0

CH2 H +

(EH2 [CHR _—> [CH2=CHR] + CH2=CH2 + H20
\

CH2

McLafferty (55) has proposed four member rings in which hydro—
gen is transferred from the B carbon to a heteroatom, such as O in
OH, to eliminate HZO. In a later book (53) he states that the four
membered ring is not well established, however, he expands upon pro-
posed mechanisms involving such rings.

These four membered rings are also accepted by other authors
(51,52) such as in explaining Momighy's (56) work on deutero—labeled
ethanol. However, a recent paper by Meyerson and Leitch (57) on the
mass spectra of hexanol with various positions labeled with deuterium
found most (91%) of the water eliminated to result from a six member
intermediate ring (l,b-elimination) and the remainder from smaller
rings which they feel is 1,3-elimination. Benz and Biemann (58) also
felt that the 1,2 mechanism was not well supported as a general
mechanism and studied the mass spectra of a series of deutero labeled
alcohols. They find that the Six member ring is by far the most
important.

It seems that five or six membered transition states are the

most likely to be formed when such are possible. However, in other

13
ions where this is not possible, a smaller ring can also transfer
hydrogen across the molecule.

In addition to transfer of a single hydrogen there are instances
where transfer of two or more hydrogens occurs. Beynon (50) mentions
examples such as the C2H502+ ion at m/e = 61 from a-methylpropyl
ethanoate, the H30+ion from 2-propanol, and the NH: ion from many
nitrogen containing compounds. In fact, the NH: peak in the spectrum
of trimethyl hydrazine is cited as being 11 per cent of the base peak

in the spectrum.
II. Objectives of the Present Study

We noted the presence of a doublet at m/e = 17 in the mass spec-
trum of 2-methoxyethanol. One peak was assumed to be OH+ from water
impurity and/pr the hydroxyl group in the compound.. The other peak
was thought to be CH; since ammonia was believed to be absent (also
it is doubtful that our instrument could resolve 0H+-NH§) and the
peak was much too intense to be an isotopic variation of either 0+
or CH: at m/e = 16.

Our study attempted to verify that the ion, CH; was present in
the mass spectrum 0f 2-methoxyethanol, to determine whether or not
this was being formed by an ion—molecule reaction, and (particularly
if it were not an ion-molecule reaction product) to determine hy

isotopic labeling how the ion is formed.

EXPERIMENTAL
I. Instruments

Most of this study was conducted on a Consolidated Electro-
dynamics Corporation mass Spectrometer,Mode1 21-103C. This model
instrument is described elsewhere (59). The samples were admitted
through the gas inlet with a normal reservoir pressure of about 70
to 80 microns. The usual ionizing electron beam was 10 microamps
at 70 volts; the instrument was Operated with the narrow collector
slit (0.18 mm), high sensitivity and focused. A magnet current of
about 0.23b amps allowed the range m/e = 12 through m/e = 80 to be
covered in one scan.

A tungsten filament was used for all experiments except those
involving the isotopically labeled 2—methoxyethanol. For these, a
different Isatron (ion source) with a rhenium filament was used.
Additional Spectra were taken of peaks of interest while operating
non-focused with increased ionizing and magnet currents to im-
prove the resolution.

The high resolution Spectra were obtained for us on a double-
focussing Hitachi mass spectrometer, model RMU—6D, through the courtesy

of the Perkin-Elmer Corporation.
II. Chemicals

2-Methoxyethanol, CH3092H40H, unlabeled

 

 

The unlabeled 2-methoxyethanol was Fisher Certified Reagent

lb

IS
dried at least twelve hours over anhydrous calcium sulfate (non—
indicating "Drierite"). This was analyzed with a gas chromatograph
containing a hydrogen flame detector. Analyses were made using a
Silicone column at 90—950 and a PDBAS, HMDS treated 60/80 Chrom. N.
Column (phenyldiethanolamine on hexamethyldisilazane treated white
diatomaceous earth from Wilkens Instrument and Research, Inc.) at
1250 C. No impurities were detected using sensitivities capable of

detecting impurities in the order of one part per thousand.

2—Methoxy-13C-ethanol,13CH39§2H40H

 

2—Methoxyethanol with a labeled methyl group was prepared using
a Williamson synthesis (60).

13CH3I + NaOC2H4OHi———> 13CH3OC2H4OH

The amount of each reactant was modified to reduce side products
such as 1,2-dimethoxyethane and yet favor complete use of the
iodomethane-13C. A solution was prepared by dissolving 1.5 g of
sodium in 25 ml of cooled 1,2-dihydroxyethane (redistilled, b.p.
9b—96OC at ll mm Hg). To 8 ml of this solution was added about

0.50 g of iodomethane—13C (ST-63.8% C-13 from Merck, Sharp and Dohme
of Canada, Ltd.). This was allowed to react about five hours, a
little water was added to react with the remaining organosodium salt,
and a crude distillation was done using semi-micro apparatus. The
fraction boiling 103-12800 was further purified by preparative gas
Chromatography using a Carbowax 20M column (from Wilkens Instrument

and Research, Inc.) at 126-1300C.

.16

The gas Chromatographic separation was done in several small
batches. An infrared Spectrum of the product of one such run was
taken on a Beckman infrared spectrophotometer, Model IR-8. This
Spectrum was compared with similar Spectra taken of unlabeled 2-meth-
oxyethanol from a commercial source (Fisher Certified Reagent) and
from a preparation equivalent to the labeled preparation except that
ordinary iodomethane was used. The only difference between these
three spectra was a possible shift of the 1120 cm_1 ether vibration
by about 6 cm-1 in the labeled compound. This may be an isotope
effect or it may be of instrumental nature Since such a small shift
is near the detection limit of the instrument. There seems though
to be little doubt of the identity of the compound.

A portion of the same labeled compound used for the mass Spectra
was analyzed by gas chromatography similarly to the preparative runs.
Impurities (as detected by a thermal conductivity cell) appear to be
less than one part in one thousand. Anhydrous calcium sulfate was
added as a drying agent to the sample vial from which the compound
was introduced into the mass Spechxmmter. The material was determined

mass Spectrometrically to be about 56 percent labeled.
2-Methoxyethanol-l,l—d2, CH30CHZED;OH

2-Methoxyethanol with deuterium labelling on the C-1 carbon was
prepared by a three step synthesis:

HNo3
CHSOCZH40H ———> CH3OCH2C00H

CHSOCHZCOOH ________s> CH300H2COOC2H5

LiAlD4

CHSOCHZCOOCZHS > CH300H2CD20H

17

The oxidation with nitric acid followed a well known organic
method (61). The esterification also followed a conventional method
(62) but was modified by the substitution of b-methylbenzenesulfonic
acid for sulfuric acid and by omitting the washings but separating
the product with two distillations. The reduction of the ethyl ester
with lithium aluminum deuteride (63) (from Metal Hydrides, Inc.) was
done under helium atmOSphere using solvent ether which had been dis-
tilled from lithium aluminum hydride directly into the reaction ves-
sel and separatory funnel.

The product (b.p. 120-12300) was determined mass Spectrometrically
to be at least 97 percent dideuterated and was dried with anhydrous

calcium sulfate shortly before being used.

2-Methoxyethanol-d,CH39§ZH4OD

 

2-Methoxyethanol with deuterated hydroxyl was obtained from
Drs. G. J. Papenmeier and W. H. Reusch and had been prepared by ex-
change of unlabeled CH30C2H4OH with D20. It was dried by repeated
trap to trap distillation between traps containing fresh anhydrous
calcium sulfate and was analyzed mass Spectrometrically to be about

20 percent deuterated.

Ammonia,»NH;

 

The ammonia was Matheson anhydrous ammonia dried over sodium.

Methane-d, CHSD

 

The mondeuterated methane was from Merck and Co., Ltd. and was

used as received.

18

III. Method of Exact Mass Measurement

An exact measurement of the mass of the ion at m/e - 17 was made
by measuring the accelerating voltages needed to focus peaks m/e = 15,
l6, l7, l8, and 19 on the collector slit. This was done by measuring
the voltage across a voltage divider circuit (consisting 01 fixed re-
sistors) in the instrument with a millivolt potentiometer (Leeds and
Northrup Catalog No. 8691). The voltage measured was nominally one
four thousandth the actual accelerating voltage.

In a magnetic mass Spectrometer the accelerating voltage is re-
lated to the mass of the ion by

m/e = k/V,

where the proportionality constant, k, includes the strength of the
magnetic field, etc. The values of k were determined from the
measured voltages for the peaks at m/e = 15, l6, l8, and 19. From
the average of these values and the voltage for the peak at m/e = 17,
the exact mass was calculated. All of the measurements were repeated

for each trial. The results are Shown later.

RESULTS
I. Identification of the Ion

The identification of the ion at m/e = 17 was based both upon
measurement of the mass of the ion and upon the resolved peaks in
high resolution spectra containing intentional impurities. The
results of the mass measurements performed as described earlier are
shown in Table III, together with the calculated mass of some ions
of the same nominal mass based on the atomic weights given by Beynon
and Williams (6b) and considering the mass of the electron.

A high resolution Spectrum of 2-methoxyethanol containing a
small amount of ammonia is shown in Figure 1. It is quite apparent
that there is another peak present besides 0H+ and those from ammonia.
If this other peak is CH}, the NH; peak would be expected to fall
about 65 percent of the distance from the 0H+ peak to the CH; peak.
Inspection of the figure shows this to be the case.

A similar high resolution spectrum of 2-methoxyethanol contain-
ing some methane-d1 is shown in Figure 2. The mass separation of the
CH3D+ and the CH; peaks is one part in eleven thousand. This is ap—
proximately equal to the expected resolution of the mass Spectrometer
used. The figure shows a partially resolved peak on the high mass
side of CH3D+. This is where it is expected.

Several other combinations of carbon and hydrogen isotopes also
have a mass of 17. or these, the most likely is 13CH:. Since the

natural abundance of 13C is 1.1% of 12C, the 13CH: peak must be about

19

20

Table III. Determination of the exact mass of the m/e = 17 peak.

 

 

 

Trial Mass Found Ion Calculated
Mass
1 17.0h35 0H+ 17.0022
2 17.0377 NH3+ 17.0260
3 17.011311 1301f 17.03111
b 17.0bbl CH3D+ 17.0370
5 17.0337 CH5+ 17.0386
Average 17.0b05 (i 0.0038)*

 

 

 

 

 

*-
Average DeV1atlon.

21

 

 

 

 

 

__J

 

 

c 21D

 

CH

 

Figure 1.

High resolution Spectrum of the multiplet at Nye
in 2-methoxyethanol with added ammonia.

1?

 

22

 

ou"

cusp"

 

 

 

 

 

 

 

 

Figure 2. High resolution Spectrum of the multiplet at m/e - 17

in 2—methoxyethanol with a small amount of added methane-d.

23
one percent of the 12CH: peak at m/e = 16. Actually the m/e = 17
peak is about eighty percent of the 1‘ZCH: peak. Other isotopic vari—
ati ons such as 170 or deuterated ions would be expected to be even

less abundant. Therefore, we feel that the lon ln queStlon ls CH5.

II. Pressure Dependence Studies

Studies were made of the intensity of the CH; ion as the sample
reservoir pressure (which is proportional to the pressure in the ion
SOLLFCQ) was varied. Figures 3 and b Show these data fortmm>runs (separ-
atxad by four months time) plotted as peak intensity XE' pressure and
as; peak intensity XE' (pressure)2. It is easily seen that a linear
Tnnessure dependence for the formation of this ion exists. This means
ifllat the ion, CH; is not being formed by an ion-molecule reaction
(tnnich requires dependence on the square of the pressure) and is, to

(mar knowledge, the first time it has been so Seen.
III. Isotopic Studies

Since the CH; ion in the 2-methoxyethanol Spectrum is apparently
I"OI‘med by an intramolecular process, we desired to know from which
PaITt of the molecule this ion is formed. Spectra were taken of
2“methoxyethanol with the atoms in various positions isotopically
lalbeled. The pertinent portions of these spectra are Shown in
F1 gures 5, 6, 7, and 8.

Figure 5 (operating conditions: nonfocused, Slow scan, 85 pa
iOnizing current, P

inlet = 60 mlcrons) shows very definitely that a

chCH; peak is present at m/e = 18 in 2-methoxy-13C-ethanol. This is

Peak Intensity (arbitrary units)

27

24

2b

 

 

 

A A l A A

 

0 l.0 2.0 3.0 4.0 0.0 00

o -2 o
Pin1€t(mlcrons x 10 )(Clrcles)

2 ' 2 -5
Pinlet(mlcrons X 10 )(squares)

Figure 3. Intensity of the m/e = 17 peak as a function of
pressure.

Peak Intensity (arbitrary units)

60

25

 

V

 

 

A + A A

2.0 40 0.0 0.0 ”.0 I20

. ‘1 .
Pinlet(mlcrons x 10 )(Clrcles)
P

2 - 2 ‘3
inlet(mlcrons x 10 )(squares)

Figure b. Intensity of the m/e = 17 peak as a function of

pressure.

 

 

 

 

JL 111.

l7 l8 l9

 

 

 

Fig. 5. Peaks at m/e =

l7,

l8, and 19 in 2-methoxy-

13C-ethanol.

 

 

.7 citrus

 

 

 

Fig. 7. Peaks at m/e =
18, and 19 in 2-methoxy-
ethanol—1,1-d2.

17,

 

 

 

 

 

Asia __

9

 

Fig. 6. Peaks at m/e = 17,
18, and 19 in unlabeled
2emethoxyethanol.

 

 

 

 

 

b“Aw—(19‘

17 18

 

Fig. 8. Peaks at m/e = l7,
l8, and 19 in 2-methoxy-
ethanol—d.

27
not seen in the unlabeled compound, Figure 6 (operating conditons:

same except Pi = 6b microns). The large Size of the higher mass

nlet
side of the m/e = 17 doublet is the sum of 13CH: and 12CH2.
Figure 7 (Operating conditions: focused, slow scan, 10 Ba ion-

. = 5b microns) of 2—methoxyethanol—l,l-d2 Shows

izin current P.
g ’ inlet

no significant difference in the CH; peak from the unlabeled compound
in Figure 6. Due to the very high percentage of deuterium (over
97 percent) one would expect the CH; peak to become very small as
well as a second peak at m/e = 18 or 19 to appear if one or both of
the hydrogens on the C-1 carbon were involved. The peaks due to
water impurity do, of course, vary between samples; also the m/e = 19
peak is diminished.

Figure 8 (operating conditions: nonfocused, slow scan, 85 pa

ionizing current, P = 83 microns) Of 2-methoxyethanol-d also

inlet
Shows no significant difference from Figure 6. Although the per-
centage of labeling is much smaller than in the other compounds

(about 20 percent) it is still large enough that the CH4D+ ion, if

present, would be plainly visible.

CONCLUSION AND DISCUSSION

This study indicates that the ion CH; can be observed in systems
which do not include methane and that it is present in the mass
Spectrum of pure 2-methoxyethanol. Further, the ion is formed by a
mechanism which iS unimolecular. Calculation Shows that with rate
constants in the order of 10-9 cm3 molecule-1 sec-1 and the usual
pressure in the ionization region, a bimolecular reaction will have
a half-life in the order Of milliseconds while unimolecular fragmenta—
tion processes have half-lives in the order Of microseconds. There-
fore this could not be a rate limiting, unimolecular step followed
by a fast bimolecular step.) Isotopic labeling indicates that the
ion is formed from the methoxy— carbon and the five hydrogens around
the ether oxygen.

As noted earlier, much of the discussion of alcohol and ether
Spectra is based on B Cleavage and rearrangements through five or
Six member rings. Such a ring mechanism would lead to the formation
of the CH; ion from the hydrogens on C-l rather than from C-2 as
found in the present study.

One would, however, expect from the fragmentation mechanisms of
both ethers and alcohols that the C-C bond in the parent ion would
break most easily. This is confirmed by the intense base peak at
m/% = b5. (The spectra Of methoxy-13C-ethanol and methoxyethanOl—1,1-
(12 further support this assignment.) It is possible that the ion

+ . . a . .. . . +
C3i5 13 formed by a rearrangement and Iragmentatlon of the lon CZH50 :

28

29

 

[CH3OC2H4OH]+ > [CHSOCH2]+ + other fragments

[CH OCH 1* > CH+ + CO
3 2 5

 

Such a mechanism would be energetically favored by the formation of
the molecule C0. However, it is only a supposition. A search for

a metastable ion at m/e = 6.b would support this proposition. A

Scan which was made of the low mass region Showed nothing from m/e = b
through m/e = 10. However, the detection Of a metastable peak places
a requirement upon the rate as well as the mechanism, its absence

does not preclude the proposed mechanism.

A preliminary, uncalibrated set of appearance potential measure—
ments is Shown in Appendix 2. The values of 0.b volts for m/e = b5
and 5.1 volts for m/e = 17 do not contradict the proposed mechanism
since a precursor ion should have an appearance potential lower than
its fragments. Such data do limit the possible choices of precursor
ions.

Some other features relating to highly rearranged ions were also
noted in this study. The H30+ ion, which was also found to be uni—
molecular (See Appendix 3) shifted in large part to m/e = 20 and 21
in the Spectrum of 2-methoxyethanol-l,l-d2. This indicates some
mechanism other than a five or six membered ring is Operating. The
CH50+ ion at m/e = 33 in methyl ethers is believed (5b) to be a re—
arrangement although this portion Of the Spectrum was not covered in
our pressure dependence work. This peak is also at least partially
shifted to m/e = 3b and 35 in the Spectrum of the dideuterated compound.

Here,though, the dataeme insufficient to propose a mechanism.

POSSIBLE FURTHER STUDIES

A search could be made for a metastable ion at m/e = 6.b by taking
Spectra at various ionizing voltages. The appearance of such a peak
which shifts to m/e = 7.0 for 2—methoxy—13C—ethanol or to m/e = 7.7
for 2-methoxyethanOl-2,2—d2 but is not affected by isotopic labeling
at C-1 or at the hydroxyl would give considerable support to the
proposed mechanism. In addition to varying the ionization voltage,
one could increase the sensitivity of the mass spectrometer by using
a vibrating reed electrometer or an electron multiplier for ion de—
tection. One might also adapt Scan averaging techniques (such as has
recently been introduced by varian Associates, Palo Alto, California
for NMR Spectroscopy) to mass Spectrometry to detect a very broad
low intensity, metastable peak.

Another investigation which might be more fruitful than the
Search for metastable peaks would be the examination of the peaks
at m/e = 17 in other Compounds, particularly methyl ethers such as
methoxyethane and 1,2-dimethoxyethane. Perhaps CH; ions being formed
from these compounds have heretofore been overlooked as 0H+ or have
been covered by 0H+ from water impurity.

A study which might prove very interesting is the study of the
intensity Of highly rearranged ions Such as CH; with ionization energy.
Chupka (65) has suggested that an ion such as our rearrangement CH;
ion should be very persistent in low ionization voltage spectra. This
is because it would take longer for an ion to fragment if it is at

lower energy and such additional time would be favorable toward a

30

31
highly rearranged ion. It is interesting to note in Appendix 3 that
the ions H20+ and H30+ are also formed by unimolecular mechanisms.
While it is conceivable that the H20+ peak is due to a constant per-
centage of impurity in the sample, the H30+ ion must be another re-
arrangement ion. Appendix 2 indicates that this also may be quite
persistent at low ionizing voltages.

With an instrument of higher resolution, one could learn much
more about the fragmentation of this compound from the spectrum of
isotopically labeled molecules. For instance, if one were trying to
determine which carbon is used to form the 00+ ion in the present
study he would be in difficulty. First, it is not known what per-
centage of the peak is C0+, what percentage is C2H4+ and what per-
centage is due to other contributions such as 12C13CH4. More important
however, the peak at m/e = 29 is so much larger than the peak at
m/e = 28 that the addition of 13C0+ to the unresolved peak would add
an insignificant increment to its Size. Using sufficiently high
resolution, one could see the peak due to each of these ions and the

problem would cease to exist.

10.

11.

12.

13.

1b.
15.
16.

17.

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Tal'roze, V. L. and A. L. Lyubimova, DOkl. Akad. Nauk. SSSR,

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Lampe, F. W., J. L. Franklin, and F. H. Field in Progress in Re—
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32

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Graw-Hill Book Company, Inc., New York, 1963, Chap. 13.

 

Durup, J., Les Reactions Entre Ions Positifs et Molecules en
Phase Gazeuse, Gauthier-Villars, Paris, 1960.

 

 

Melton, C. E. in Mass Spectrometry of Organic Ions, F. W.
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Tal'roze, V. L. and E. L. Frankevitch, Izv. Akad. Nauk SSSR, Otd.
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Frankevitch,E.lL.and V.L. Tal'roze, Doklady Akad. Nauk. SSSR, £2,
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in Charge Exchange Collisions with Positive Ions. Ion—Molecule

Reactions of Methane." AD 603 091, 6 April 196b.

Field, F. H., H. N. Head, and J. L. Franklin, J. Am. Chem. Soc.,
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53.

Sb.

3b

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Meisels, G. G., W. H. Hamill and R. R. Williams, Jr., J. Chem.
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9

Beynon, J. H., Mass Spectrometry and its Applications to Orggnic
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Biemann, K. MassySpectrometry Organic Chemical Applications,
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Budzikiewicz, H., C. Djerassi, and D. H. Williams, Inteppretation
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55.

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63.

6b.

65.

35

McLafferty, F. W., in Determination of Organic Structures by
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Methods of Analysis, 3rd. edition, D. van Nostrand Company, Inc.,
New York, 1958, p. 285.

 

 

Murray, A., III, and D. L. Williams, Organic Synthesis with
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Powell, S. G. E. H. Huntress, and E. B. Hershberg in Organic
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Natelson, S. and S. Gottfried in Organic Synthesis, Coll. Vol.
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Brown, W. G. in Organic Reactions, Vol. VI, R. Adams et al.
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Beynon, J. H. and A. E. Williams, Mass and Abundance Tables for
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1963. p. vii.

 

 

Chupka, W. A., private communication.

APPENDICES

36

Mass Spectrum of 2-Meth0xyethan01

APPENDIX 1

 

~_'—

 

Normalized

 

m/e Normalized Probable m/e . .. Probable
Inten51qy. Identlty . Inten51ty Identlty
1* 2.56 H1 L2 1.7h C2H20+
2* 0.19 H2+ b3 8.6b C2H30+
12 0.b2 C+ bu 1.51 C2H4O+
13 1.07 CH+ L5 100 C2H50+
1b 3.77 CH2+_ ~b5 metastable 2 _
15 27.5 CH3+ b6 3.88 i(&c2H50*)
16 0.680 CH,+ b7 5.b6 C2H7O+
17 0.560 CH;(&QH+) b8 0.13 i
18 ~0.7 H20+ b9 0.017 i
19 1.81 H30+ 55 0.0b1 031130+
~19 metastable 2 56 0.0b2 C3H4O+(or C202+)
2b 0.036 C2+ 57 0.169 C,H,0*(or C202H+)
25 0.21b C2H+ 58 2.50 C3H6O(Or C2H202+)
26 1.69 C2H2+ ~58 metastable ?
27 6.72 C2H3+ 59 0.232 C3H70(0r C2H302+)
28 2.32 C0+ 6/Or 02H,* 60 0.1b' 02H,02+
29 26.5 CHO+(& C2H5+?) 61 0.11b CZHSOZ
~29 metastable 2 69 0.0bb C3H02+'
30 1.9b CHZO+ 70 0.022 C3H202+
31 23.b CH30+ 72 0.135 C3H402+
32 0.73 i a 02+ 73 0.039 C3H502+
33 0.9h CH50+ 7b 0.031 C3H602+
36 0.015 C3+ 75 0.165 C3H702+
37 0.166 C3H+ 76 5.b0’ parent
39 0.076 C3H3+ _ 77 »0.202 1
b0 0.0b8 020+ 0r 03H,+ 78 0.027 1
b1 0.3b8 C2H0+

 

 

 

 

 

 

 

*m/e = 1 thru 11 based on only one copy of the spectrum.

37

APPENDIX 2

Preliminary Determination of Appearance Potentials for Selected Ions
in the Mass Spectrum of 2-Methoxyethanol

These appearance potentials are the result of a single, uncali-
brated determination and should only be considered approximate. Due
to the Complete lack of calibration (the values reflect the reading
of the "ionizing voltage" meter on the instrument) they should be con—
sidered merely as ordinal numbers. Some discrepancies due presumably
to scatter are obvious.

The criteria for selection of ions was to report those ions between
m/e = 12 and m/e = 76 which, a) at No volts produced a deflection of
at least 10 percent of full scale on the most sensitive galvanometer
(m/e = 17 produced 37 per cent), b) at 10 volts produced a deflection
of at least 1 percent of the deflection at b0 volts, and c) at 10 volts
produced a deflection of a least 1 percent of full Scale on the most

sensitive galvanometer (m/e = 17 produced 9.6 percent).

 

 

 

m/e Volts m/e Volts
15 7.5 33 b.2
16 8.0 bl b.6
17 . 5.1 b2 10.5
18 inconclusive b3 5.6
19 6.7 at 5.3
26 15.2 b5 0.b
27 9.3 ' b6 0.2
28 21.7 117 < O
29 6.2 58 0.7
30 ' 9.2 “ 59 2.0
31. 5.0 76 0.0
32 6.2

 

 

 

 

 

38

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w.H suocco No.0 ab.o oo.H No.a No.0 cd.o ad.o stucco
com c.wma Owes Owes oosm oooN ooo.NoH ombca Omam H.4Nm
ca m.mcm coca mmb oaaa oaaa ooo.o~ .... comm a.HOm

a.m as.md oama mwm am: .amm Aoom.mmiv Oman mob Om.mm
o.m No.64 was d.mc was c.6d ..... was man cm.mm
m.~ amm.s mew a.am c.mm c.ms csam as: mma. ma.ma
are 2833 $an rows are are ass fines CBS sectors

NH u wwm. owsmmowa 0H n mme ma uiw\e NH u w\s pa u w\s ma u w\e 4H n mks ma u m\a unannoum

newness _

 

 

Hocmcposxocpoa-m

1|L

 

.muonsdc magma 03¢ cmmzpon oocopomwwv

Hflmsm m mcmpcww mo>Ho>cH HmUnH pom compoonuoo one mcmxms Oocwm poppmom manmuopmmcoo.zonm Op OopOOQXO.On

canon umppma 0:5 .oococcoaop 003mmuna poppo Ocooow m upmnpmSHHH Op Edupooam ocwcpos 02p cw com Mao 030

Mo cowpmcHEpouuU m mm powwoaop owad

.wpwc: zumupwnum cm 0pm Ompnoaou mopwmcopcm meQ 05H

.MOOHSmHL

OOHQ 0p pom: memo one mm oawp 08mm 030 pm coxmp numb oococcoaop unannoua meow Ooppoaop mum soaom

.aocmcpostSOOzim mo Edppooam wmm: one cm mCOH meow mo oocopcoaom ousmmoum

m xHszmmd

39

APPENDIX A

Infrared Spectrum of 2-Methoxyethanol

 

 

Frequency (cm-1) Peak
7b0 medium
770 medium broad
830 strong
880 strong
960 weak
1010 strong
1050 . very strong
1120 very strong
1190 strong with Shoulder
1220 medium
1360 strong
1b00 medium
1b50 strong with shoulder
2710 weak
2810 strong
2880 very strong
2920 very strong
2990 strong
3b60 broad strong
3600 medium

 

A0

 

"711M (T; 11131111711 NT if“