ANALYTICAL CHEMISTRY
934 Component Analyses. Table X illustrates the analyses of three different blends of 1-butanol and 1-octanol, and the analysis of a four-component CS to CS alcohol blend. Such analyses are straightforward when no unknown interfering compounds are present. ACKNOWLEDGiVIENT
Table IX.
Mass Spectral Type Analyses of CS to Ce Alcohols (Calibration data include all alcohols above C,) Blend 1 KO. of
Primary, normal andy-branched 42+56+70+ Primary,@-branched 43 57 71 45 59 73
+ + + .. .. .. + +
n e la d a ,y r y1
The authors wish to acknowledge the help of A. F. Logar, B. 31. Thames, and Joseph Malli.
LITERATURE CITED
+
Matrix: Z 42+56+70+ Z 43+57+71+ z 45+59+73+
Bloom, E. G., Rfohler, F. L., Tengel, J. €I., Wise, C. E . , J . Research hratZ. Bur. Standards
alcohols in blend
Mass peaks
Type
Table
...
...
...
I
.
5 2
Primary P\-ormal and y-branched 8-branched 1379 897 918 1848 102 173
(1949).
Friedel, R. A., Sharkey, A. G., Jr., Humbert, C. R., A A ~ L . CHEM.21,1572 (1949). Friedman, L., Turkevlch, J., J . Am. Chem. SOC.74, 1666 (1952). Happ, G. P., Stewart, D. W., Ibid., 74, 4404 (1951). Kinney, I. W., Jr., Cook, G. L., ANAL.CHEM.24, 1391 (1952). hfcnlurry, H. L., Thornton, V.,J . Chem. Phys. 19, 1010 (1951). Mohler, F. L., Williamson, L., Dean, H. M., J . Research Natl. Bur. Standards 4 5 , 2 3 5 (1950)
O’Neal, RI. J., J r . , Wier, T. P.. Jr.. AXAL.CHEM.23, 830 (1951). Sharkey, A. G., Jr., Shultz, J. L., Friedel, R. A , , ANAT..CHEM. 28. 934 (1956).
5 2 0
72.4 75.4 27.6 22.4 0.0 2 2
Secondary and Tertiary 218 856 2270
X. Mass Spectral -4nalyses of Alcohol Synthetic Blends
Volume % Blend A
I-Butanol
I-Octanol
31.3 30.4 31.8
68 7 69.6 68.2
M.S. 2
71.7 71.7 71.0
28.3 28 3 29 0
Syn. M.S. 1 M.S. 2
88.0 89.7 87.9
12.0 10.3 12.1
Syn.
M.S. 1
Blend
M.S.2 €3
Syn.
M.S. 1 Blend C
(1951).
Friedel, R. .i.,Logar, A. F., Shultz, J. L., A p p l . Spectroscopv 6 , No. 5, 24 (1952). Friedel, R. A , , Sharkey, 4. G., Jr., ANAL.CHEM.28, 940 (1956). Friedel, R. A , . Sharkey, A. G , Jr., J . Chem. Phys. 17, 584
64.2 65.0 21.7 18.6 14.1 16.4
.
41, 129 (1948)
Brown, R. A., American Society for Testing Rlaterials, Committee E-14, Mass Spectrometer IIeeting, Yew Orleans, La., May 1954. Brown, R. A4., AXAI,.CHEM.23,439 (1951). Brown, R. A., Young, W. S., Ibid., 26, 1653 (1964). Collin, J., Bull. soc. chim. Belges 63, 500 (1954). Cummings, C. S., Bleakney, W., Phys. Rev. 58, 787 (1940). Eden, hi., Burr, B. E., Pratt, A. W.. ANAL. Cmar. 23, 1735
Blend 2
No, of Fo7 lume % alcohols Syn. Anal. in blend Syn. Anal.
Blend D
Syn. M.S.
I-Pentano
I-Hexanol
I-Heptanol
40.6 39.2
30 0 30.3
19.7
19.6
1-Octanol 9.7
10 9
(19) Washburn, H. W., in “Physical Methods in Chemical Analysis,” p. 592, W. G. Berl, ed., Academic Press, New York, 1950. RECEIVEDfor review November 5 , 1955. Accepted March 20, 1956. Presented a t Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, P a . , March 1952. Contribution of Branch of Coal-to-Oil Research, Bureau of Mines, Region V, Bruceton, P a .
Mass Spectra of Ketones A. G. SHARKEY, JR., J. L. SHULTZ, and R. A. FRIEDEL Bureau
of Mines,
U. S. Department of Interior,
Bruceton,
Mass spectra of 42 ketones, ranging in molecular weight from 58 (2-propanone) to 198 (2-tridecanone), have been obtained. Fragmentation peaks can be correlated with molecular structures. Three or more rearrangement peaks are found in the spectra of all aliphatic ketones. Rearrangement peaks from higher molecular weight ketones appear at the parent masses of lower molecular weight ketones. In many instances these pealis are more intense than the parent peaks of the lower molecular weight ketones and can cause errors in analysis of mixtures. Empirical ru1,es have been derived relating fragmentation peaks and rearrangement peaks to molecular structures, and analytical procedures for identifying pure ketones are illustrated.
C
ORRELATIONS of mass spectra have been carried out on various classes of hydrocarbons (1, 2, 6, IO, 12, I S ) .
Happ and Stewart (9) have studied aliphatic acids and Friedel
Pa.
and Sharkey (6) have correlated spectra of acetals. The mass spectra of ketones have been investigated in an effort to extend the usefulness of the mass spectrometer in analyzing oxygenated products from synthetic liquid fuels processes. Information has been obtained concerning peculiarities in the mass spectra of ketones that could lead to analytical errors. The 42 ketones examined range from 2-propanone to 7-tridecanone. PROCEDURE
Mass spectra were obtained on a Consolidated Model 21-103 mass spectrometer equipped with a modified Charlet-type (3) mercury-orifice system. A4constant volume pipet (0.00068 cc. ) was used to introduce all samples. Rlicromanometer ressure measurements were found to be in error for the higher getones. These errors have been discussed in another paper on alcohols (8); data in the tables are therefore given in terms of peak height per unit of liquid volume introduced (volume sensitivities). Thus, spectral peak heights for various ketones are directly comparable. Calculated sensitivity factors on the basis of divisions per micromole are also given in Tables I, 11, and 111. Compounds were used as obtained, without further purification; infrared and mass
V O L U M E 28, NO. 6, J U N E 1 9 5 6
935
.. .. .. , . .
m
00
i
L2,
x, C
ti,*,
- c ?N EmN 3
mh-
m
c'6ioL ria1.1
. . . . . . . . . .. .. .. .. .. .. .. : : : : : . . . . . . .
: : : :
k
?d.? L ? 0 * C L. ,* ? em-
*
. . . . . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
L1
ti N
ANALYTICAL CHEMISTRY
1;
J 3
g
m i
-2
e. m. 0. c, '3. mmm d c 0-3
1.3c h L?
L?
L?
. T
mi Ji . u2 u3
V O L U M E 28, NO. 6, J U N E 1 9 5 6
937
spectra show no contamination by alcohols, acids, esters, or aldehydes. CORRELATIOh OF MASS SPECTRA WITH MOLECULAR STRUCTURES
Aliphatic, cyclic, and aromatic ketones have been investigated. The correlation study 1s based mainly on 35 aliphatic ketones. They are classified ax methyl, ethyl, propyl, etc., on the basis of R1, the smaller alkyl group 111 R1-CO-R2. Not all major fragmentation peaks result from simple bond rupture. Several rearrangenicnt peaks, resulting from rearrangement of atoms in t h e niolecde ion before and during fragmenta-
tion, appear in the spectra of all the aliphatic ketones investigated. Results of the correlation study are therefore divided into two parts-normal fragmentation and rearrangement peaks. NORMAL FRAGMENTATION PEAKS
Aliphatic Ketones. Tables I, 11, and I11 summarize all major fragmentation peaks and molecular structure correlations. Several empirical rules can be derived from an inspection of these tables. For the aliphatic ketones, major fragmentation peaks are produced by splitting on either side of the carbonyl group. LOSP of the smaller hydrocarbon group, R1, results in the first major
Table 111. Mass Spectra of Aromatic and Cyclic Ketones Compound
Cyclic A-ML
Sourceb
Carbons Molecular weight Mass
Cyclopenta E 5 84
Cyclohexa F 6 98
Me-cyclohexyl K 8 126
E 7 112
Phenyl methyl
Bromatic Propyl benzyl
Isopropyl benzyl
E
x
x
8 120
11 162
11 162
n-Heptane P 7 100
Chsrge 296 e 616 1230d 169d 5.5
538 259 143d 3.6 12.6 460 501 1200 l58d 16.2 1.5
39 41 42 43 44 45
347 633 312 57.1d 4.3 0.8
50 51
55.8 47.0
33.5 38.6
55 56 57 58 59
1460/ -
1330f 150
67 68 69 70 71
4.3 0.9
73 74 75 76 77 78 79 82 83 84 85 86 87 89 90 91 97 98 99 100 105 106
471 29.5 1.9
...
6.4
0.3
... ...
...
...
... ... ... ...
0.8 22.5
P 5280
29.3 1.5
25.14 3.1 0.6
, . .
...
... ...
32.0 44.8
21.0 41.5
llld
1120f 498
1.0
59.4 14.3 14.1 0.5 3.7
106 19.8 36 9; 270 7.4 1.8
38.4 9.0 9.4 48.1 6.2 2.0
57.8 56.9 11.0 298/ 10.5 5.4
234 496
16.1 29.7
21.1 38.8
9.1 14.8
9.8 6.8 4.1 0.9 0.6
8.0 5.4 3.5 0.7 4.3
124 281 506 20.7
0.6 1.6 4.6 6.5
0.5 0.7 2.8 16.9 148 e
4.3 1.3 7.7 190 481
...
17.6
...
260d 38.24 2.1
6.0 0.6 0.7
1070/ 33.0 0.9
...
1.3 1.9 1.3
2.9 1.4 2.1
16.6 71.2 41.1 49.5 1090 114 6.1
3.3 4.6 3.2 2.8 35.9 7.8 0.9
8.5 6.0 4.1 3.5 43.3 9.6 1.7
... ...
1.5 7.5 3.0 4.2 4.6 3.2 11.5 ‘3.8 25.3
0.7 2.3 2.4
0 4 1.3 1.3 0.7 1.0 1.1 11.6 8.4 171
...
...
1.5 1.7 6.1
5.3 90.8 5.0 0.8 0.3
...
... 22.9
P 422
28.0 0.7
. .4.. 6
2.1 33.3
7.5 224 159 12.8 2.4
117 608 102 59.2d 3.3 0.7
...
... ...
1.7
51.4 9.9 0.3
,..
... ... ...
...
...
18.0 5.9 16.5
...
...
... ...
P 277
119 120
...
...
...
125 126
...
... ...
2.5
30.5d 12.9d 4.5d
...
1.1 0.9
4.3
81.9h 6.6
...
1.0 3.9 0.3
*l
1.1
0.9 0.6 7.5 4.7 87.8
1.5
...
0.7 0.8
...
...
32.0 30.7
40.9 34.5
...
... ...
...
P 397
...
...
1260f~h 95.5 1.1
...
...
1.6h 0.4
0.4 0.4
1.7 0.3
162 ... ... ... ... P 26.0 Eens. of base peak (div. per pmole) 144 155 163 124 147 198 a Suffix “-anone” omitted. b E = E a s t m a n Kodak C o . ; Ii = Paul Kletzke, Lacrosse, Tvis F = Fisher Co.; P = Phillips Petroleum Co. c Peak height in divisions per liquid yolume (0.00068 c c . ) ; see nyheptane reference spectrum. d Rearrangement peaks. P a r e n t mass minus Rz (larger hydrocarbon group attached to carbonyl group). f Base peak, most intense peak in spectrum. U Parent peaks indicated by P. h P a r e n t mass minus R I (smaller hydrocarbon group attached t o carbonyl group).
P 24.0
... ... ... ...
,..
, . .
... ...
P 244
.
... ...
1.1
...
0.9
0.4 1.8 21.0 1.1
... ... , . .
... P is6 ...
...
3.1h
...
267 611 272
1.2 1.8 0.8
111 112
...
547 125 562 11.6 0.9
2.4 1.1 2.7 1.4 2.7
...
...
17.0 3.3
303 562 97 81 835 20.0 17.7
44.1 12.4 15.6 0.5 4.9
166 126 43.8 8.6 332d
... ...
333 579 328
67.2 31.3 16.0d
31.6 68.8 126 161 16.4
...
...
304 96.1 l54d 3.4 4.3
15.7 11.3 328 273 22.1
... ...
482 295 237d 8.1 10.4
156
200
938
ANALYTICAL CHEMISTRY
fragment ion in the spectrum below the parent mass. Loss of the larger hydrocarbon group, R2, also results in a major peak. This fragment is either the base (most intense) or over 40% of the base peak intensity for the methyl, ethyl, n-propyl, and butyl types. Three of five isopropyl-type ketones investigated are exceptions and have less intense parent-minus-Rz peaks. Mass 43 is the base peak for all of the methyl type and for all but six of the 24 other aliphatic ketones. The exceptions are three ketones of the ethyl type, one of the propyl type, and two of the butyl type. Two exceptions probably result from the symmetry of the molecules, three involve loss of the larger hydrocarbon group by splitting a t the carbonyl group, and one results from rearrangement Isotope peaks also indicate that masses 43, 57, etc , result from parent-minus-R? fragments for the methyl, ethyl, etc., types. For the methyl ketones, mass 44 is less than 2.9% of the 43 peak. Mass 43 cannot result entirely from the structure (C-C-C)+ and may be mainly the fragment ions (C-C-)+ from parentI'
0 minus-Rz. For the first five of the seven ethyl ketones, the isotope values show that mass 57 consists largely of (C-C-C) +
I
0 ions, which are also parent-minus-RZ fragments. For eight out of 11 propyl ketones and one of three butyl ketones, peaks 71 and 85, respectively, are shown by isotope measurements to arise partly from parent-minus-R? fragmentation. Aromatic and Cyclic Ketones. The mass spectra of four ryclic and three aromatic ketones were obtained (Table 111). Although this is an insufficimt number to provide the hasis for a correlation study, certain features of these spectra
Table IV.
should be noted. The three aromatic ketones (propyl benzyl, isopropyl benzyl, and phenyl methyl) have peaks resulting from fragmentation a t the carbonyl group, similar to the aliphatic ketones. Aromatic-type fragmentation peaks are also in these spectra. The four cyclic ketones investigated shorn a characteristic fragmentation pattern similar to that of the corresponding hydrocarbon, but different from that of the ketones described previously. Strong peaks result from the loss of the following masses from the parent molecule: 28, 29, 42, and 43. Mass 55 is the base peak, and parent peaks have usable intensities for all four cyclic ketones. REARRANGEMENT PE4KS
Aliphatic Ketones. Important rearrangement peaks occur in the mass spectra of all aliphatic ketones investigated (Tables I and 11). These peaks appear a t masses corresponding to the parent mass of the lower molecular weight ketones and to the parent masses plus one. Therefore, rearrangement peaks from higher ketones could cause considerable analytical difficulty. Table IV summarizes the rearrangement peak intensities after correction for isotopes and gives the percentage of total ion current resulting from rearrangement. The total rearrangement values range from almost 28% down to less than 1%. The 12 ketones having the highest percentage of total ion current in rearrangement peaks have mass 58 (2-propanone parent mass) as the major rearrangement peak. Evidence, other than the infrared spectra mentioned previously, was obtained to rule out impurities as the source of these peaks. For all higher mass ketones, mass 36 either m-as not present or limited the possible 2-propanone impurity to 3 % . Masses 58 and 50 in the spectrum of 2-heptanone n-ere investigated ex-
Rearrangement Peaks in Mass Spectra of Aliphatic Ketones Odd Mass Series ___
Even Mass Series Compound Llethyl type 2-Propanone 2-Butanone 2-Pentanone 3-Methyl-Z-butanone ?-Hexanone 3-Methyl-2-pentanone 4-11Zethyl-2-pentanone 2-Heptanone 5-Methyl-%hexanone 2-Undecanone E t h y l type 3-Pentanone 3-Hexanone 2-Methyl-3-pentanone 3-Heptanone 3-Octanone fi-Methyl-3-heptanone 3-Nonanone Isopropyl type 2-Methyl-3-hexanone 2,4-Dimethyl-3-pentanone 2-Methyl-3-heptanone 2-Methyl-3-octanone 2.6-Dimethyl-3-heptanone 2-Nethyl-3-nonanone
Butyl t y p e 2,6-Dimethyl-4-heptanone 5-Decanone 5-Undecanone Pentyl type 2-Met hyl-5-decanone 2-Methyl-5-undecanone 6-Dodecanone Hexyl type 7-Tridecanone a b
58 4833 12'7'b 3.7 803 9.6 622 1070 827 509
2.4 1.1 2.8 10.7 4.6 8.2 12.6 3.2 4.7 18.7 9,3 11.6 10.3
72 ,..
3995 __ ...
...
9.2 255 8.6 19.6 12.3 4.2
3.8 27.2 1.5
284 403 427 540
2.8 2.6 2.3 6.0 4.6
1.3
...
113 389 446 520 431
0.8 10.1 12.1 2.4
368 494 3 53
7.7 34.5 18.1
359 132 104 17.9
86
100
114
,..
... ...
... ... ...
...
287a -
...
...
... , . .
3 . .5 10 3 1.3 , . .
...
0.4
154, ... ... ...
3.7 4.7
...
...
..
...
..
... ...
2.0
... ... ...
45 5.4
59
73
87
101
...
,..
...
...
... ...
, . .
...
...
30.8 116 60.0 42.2 136 14.8 36.3 20.0 7.7
2.6 62.3 9.9 14.2 7.0 20.4 149 166 149
4.6 8.0 9.0 9.1 18.7 18.9 14.0
5,2 4.4 24.4 19.9 17.5 28.5 28.2
4.4 10.4 3.9 50.9 62.9 70.0
0.5 0.4 6.6 12.8 5.1 1.5
10.4 13.8 15.5 10.6 0.1 11.9
33.2 22.3 87.8 31.0 40.5 23.3
9.0 12.0 3.6 11.5 6.0 7.9
3.1 1.9 4.7 10.3 13.8 13.5
7.8 0.5 2.7 2.9
2.3 3.0 0.9
3.9 4.7 1.1 2.1 1.4 0.6
...
...
...
9.5 '14.2 9.6
' -4.' 8 5.3 0.6 10.4
4.1 0.5 95.7 139 254 166
4.0 30.8 0.4 8 8 7.8 3.7
,..
5.8
...
10.8 7.8 18.1 10.5 10.7
1.8 8.9 20.4 7.1 10.3
8 0 3.3 7.7 3.4 4.8
0 4 3.8 32.5 41.5 39.6
...
16.0 115
...
1.7
0.4 3.1
... ... .. ...
5.4
... ...
6.3 6.1
...
Percentage of Total Ion Current in Rearrangement Peaks 0.14 0.87 61 1.4 16.9 8.2 11.9
-9-7. _1
2.2 3.9 7 1
li.8 27.5
13.1 3.9 9.8
7.1 6.2 1.2 7.8
...
30.6 47.4 45.7
23.8 2.4
...
13.2 7.9 4.8
41.2 56.5 34,s
0.7 2.3 0.9
11.3 2.3 1.3
4.5 20.6 18.9
7.8 15.2 15.4
39.3 6.7 10.3
16.8 7.7 10.8
7.3
5.9 2.6 3.8
117 47.4 27.1
2.1 0.7 1.9
0.8
8.2
49.9 3.4 10.2
0.7
6.6
1.2
3.0 7.3 8.4
15.5 14.4 12.5
1.4
1.3
1.6
...
1.1
4.4
0.9
0.1
5.8
6.5
Parent peak intensity. Peak height in divisions after isotope correction.
200 253 239
7.5 6.4
1.6
V O L U M E 2 8 , N O . 6, J U N E 1 9 5 6
939
tensively. Determinations of rate of leak on mass 58 (4, 7) in the spectrum of this compound eliminate 2-propanone as an impurity. The mass spectrum of the heart cut from a distilled sample of 2-heptanone showed the same intensity mass 58 and 59 peaks as the original sample. The even-mass rearrangement peaks form the series 58, 72, 86, ctc., n hile the odd-mass rearrangement peaks include masses 59, 73, 87, etc. Except for the propyl types, the most intense rearrangement peaks in each series for any particular ketone appear at adjacent mass units. As an example, mass 58 is the most intense even-mass rearrangement peak in the spectitun of 2-heptanone and corresponds to the parent mass of 2-propanone. In the odd-mass series of rearrangement peaks for this compound, mass 59 is the most intense peak. This fact might indicate that these t n o types of rearrangement peaks are formed by related processes. Rearrangement peaks appearing a t paierit masses of lower molecular weight ketones are in general more intense than rearrangement peaks in the odd-mass series and possibly more important analytically. The subsequent discus-ion will be limited to the even-mass series. The following rules can be given regarding rearrangement peaks of aliphatic ketones as classified according to methyl, ethyl, etc., types in the tables. Possible structures are indicated METHYL TYPE. The most intense rearrangement peak is
These observations regarding rearrangement peaks can be summarized as follows: The most intense rearrangement peak is mass 58, 72, or 86; many ketones have tn-o or more intense rearrangement peaks. Happ and Steaart (9), in their work on the mass spectra of aliphatic acids, concluded that the carboxyl carbon is included in the mass 60 rearrangement fragment. The mass 60 rearrangement fragment for the aliphatic acids is equivalent to the ketone rearrangement peak, mass 58. If we assume that the carbonyl group is involved in the mass of the ketone rearrangement ions, the most intense rearrangement fragment for each of the methylor ethyl-type ketones can result from a single bond break and the rearrangement of a Fingle hydrogen atom. However, this is not true for the range from n-propyl to hexyl types of ketones, where mass 58 is the major rearrangement peak. As a minimum, two bond ruptures and the changing of position of tn-o hydrogen atoms must be involved.
R-'-C-C--Cf
g-1 J
I
-R tLfI L-
With branching on a carbon adjacent to the carbonyl group, the above postulate would not hold, and a more complex mechanism n-ould be needed Less rearrangement occurs in such structures as seen from the data for the isopropyl ketones. More involved mas? 58, C-C-CZj-R, for 2-pentanonr and higher molecular methods of rearrangement, isomerization, and complete regroupII ing have been discussed by Langer (11). 0 L H Ketones having the highest percentage of total ion current in n eight ketones without branching, or v i t h branching beyond rearrangement peaks (Table IV) are methyl-type ketones, in the third carbon atom. Because of branching on the third carbon which a simple hydrogen-transfer mechanism is sufficient. atom, 3-methyl-2-butanone and 3-methyl-2-pentanoiie cannot Aromatic and Cyclic Ketones. The mass spectra of the three form the mass 58 rearrangement ion easily. 3 - M e t h y l - 2 - p ~ ~ aromatic ketones did not she\\- any important rearrangement I
r-
tanone forms the mass 72 rearrangement ion, C-C-C11
-C; 1
*L_
0 CL-H ETHYL TYPE Mass 72, C-C-C-C-
I1 0
t
- 1 -R is. the most intense r
Methyl type Straight chain and branched beyond 3rd carbon Branched o n 3rd carbona Ethyl type Straight chain and branched bevond 4th carbon n-PropG1 type Straight chain and branched beyond 4th carbona Isopropyl type With and without other branching Butyl t o hexyl types Straight chain and branchedc
x X X
I
X h X
K
x.i
Only one example of this structure. h Second most intense rearran ement peak. C Higher mass ketones studiecf did not include examples with branching on carbon adjacent t o carbonyl group. d Second most intense rearrangement peak for butyl type.
Identification of Ketones from ;\rase Spectral Characteristics
lfaj or Identification ~~~~~~~~~~~~~t Possible Mass Position o i carbonyl Branching compounds 72 Loss of mass 29 indicates smaller group is Straight chain or branched 3-Nonanoneb or 142 Cz; rearrangement mass 72 indicates beyond 4th carbon branched C P ethyl group. 170 155 h-0 second 58 Loss o i mass 15 indicates methyl group: Possibly branched beyond 2-Undecanoneb or major peak rearrangement peak mass 58 supports 3rd carbon branched C11 methyl type. 128 85 71 86 Loss of mass 43 indicates smaller group is Branched in 2-position 2-Methyl-3-heptanone D Ca: rearrangement peak mass 86 indicates or doubly branched C8 isopropyl t y p e . 142 99 . 71 58 a n d 86 Loss of mass 43 indicates smaller group is Straight chain or branched 4-Xonanone or branched (less intense) Ca: rearrangement masses 58 a n d 86 beyond 4 t h carbon C Q (7-methyl-4-octaindicate n-propyl type. none) b First and second major peaks below parent mass. Denotes actual compound.
M$!zFMass $:r
a b
Correlation of Ketone Structure with Rearrangement Peaks
-H
rearrangement peak for 3-heptanone and higher molecular weight ethyl-type ketones PROPYL A N D ISOPROPYL TYPES. Mass 86 is the most intense rearrangement peak of isopropyl-type ketones, starting with 2-methyl-3-heptanone. Mass 58 is the most intense rearrangement peak for n-propyl-type ketones, mass 86 being second most intense. BUTYLTO HEXYL TYPES. Mass 58 is the most intense rearrangement peak for all ketones of these types. All higher even-mass rearrangement peaks are less than 15% of the ma\58 intensity.
Table TI.
Table V.
Fragment Massesa First Second 113 85
940
ANA
peaks. One or more rearrangement peaks (masses 29, 43, and 5 7 ) were found in the spectra of the four cyclic ketones. IDENTIFICATION OF UNKIVOWN KETONE
Analytical Significance of Rearrangement Peaks. Both normal fragmentation and rearrangement peaks can be useful in identifying an unknown ketone. It is apparent that ions corresponding in ma88 t o parent peaks of low molecular neight ketones, but resulting from high molecular weight ketones, can lead to erroneous analyses. For methyl, propyl, butyl) and higher types without branching on a carbon atom adjacent t o the carbonyl group, mass 58 rearrangement peak intensities are more than 20% of the 2-propanone parent sensitivity. The values shown in Table IV for the above ketones range from about twice the 2-propanone sensitivity down to one fifth, a i t h the majority near 80%. A similar chance exists for confusing higher mass ethyl-type ketones v i t h 2-butanone. For 3-heptanone and higher molecular weight ethyl types, the sensitivity is 70% or more of the 2-butanone sensitivity. It should be possible to determine the molecular weight of any ketone through 2-undecanone from the relatively intense parent peaks of these compounds. The empirical rules, as stated in the discussion of normal fragmentation, should aid in determining the mass of each of the two hydrocarbon groups attached t o the carbonyl group. Rearrangement peaks will in many instances verify these side-chain mass assignments. Even more important, rearrangement peaks should aid in determining the position of branching. Table V summarizes useful information obtained from rearrangement peaks. Four evamples of the identification of ketones are given in Table VI, utilizing normal fragmentation and the information contained in Table V.
L Y T I C A L C H E M 16 T R Y
Identification of straight-chain ketones should be relatively easy. I n many cases branching can be determined, especially if the branching is on the smaller hydrocarbon group. Although positive identification cannot always be made, the choice is limited to two or three possibilities. ACKNOWLEDGMENT
The authors Rish to acknonledge the asmtance of A. F. Logar, B. M. Thames, and Joseph Malli in obtain~ngthe mass spectra. LITERATURE CITED
Bloom, E. G., Nohler, F. L., Tengel. J. H., Kise, C. E., J . Research A'atl. B u r . Standards 41, 129 (1948).
Brown, R. A,, ANAL.CHEY.23, 430 (1951). Charlet, E. hl., Consolidated Engineering Corp., Pasadena, Calif., hlass Spectrometer Group Kept. 74 (1950). Eden, M., Burr, B. E.. Pratt. -1.IT.. -1.v.i~. CHEM.23, 1735 (1951)
F., Shulta. J. L . . I p p l . Spectroscopy 6 , No. 5, 24 (1952). Friedel, R. A,, Sharkey, A. G., Jr.. .LYAL. CHEM. 28, 940 Friedel, R. A., Logar. (1956).
Friedel, R. h.,Sharkey, -1.G., Jr.,J . Chem. P h y s . 17, 584 (1949).
Friedel, R. A , , Shulta. J. L., Sharkey. -1.G . , J r . , ABAL.CHEM. 28, 926 (1956).
Happ, G. P., Stewart, D. X-., J . A n i . C h e w . Soc. 74, 4404 (1952). Kinney, I. W., Jr., Cook, G . L.. ah-.^^. CHEM.24, 1391 (1952). Langer, dlois, J . P h y s . & Colloid Chern. 54, 618 (1950). O'Keal, SI. J., Jr., \Vier, T. P., J r . , ASAL. CHEM.23, 830 (1951). Washburn, H. W., in "Physical lIethod.5 in Chemical Analysis," p. 592. W. G. Berl. ed.. -1cademic Press, New York, 1950. RECEIVED for review Sovember 5 , 195.5. -4ccepred hIarch 20, 1956. Presented a t A S T M E-14 Committee l l e e t i n g on l l a j s Spectrometry, New Orleans, L a . , May 1954. A contribution from t h e Central Experiment Station, Bureau of Mines, Rruceton, P a .
Mass Spectra of Acetal-Type Compounds R. A. FRIEDEL and A. G. SHARKEY, JR. Bureau o f M i n e s ,
U. S. D e p a r t m e n t o f t h e Interior, Bruceton, Pa.
.\lass spectra of various acetals have been determined and correlated with molecular structure, and the analytical applications are discussed. Evidence for the temporary existence of hemiacetals in the vapor state has been found in the form of anomalous mass peaks which appear in spectra of mixtures of oxygenated conipounds. The decomposition of hemiacetals in the vapor phase is a first-order reaction; specific reaction rate constants for the decompositions have been measured by following decreases in spectral peak heights with time. Analytical interference by unstable hemiacetals can be circumvented b: proper procedure.
MASS
ectra of mixtures of Oxygenated compounds frequently -p produce mass peaks that are not attributable to common alcohols, acids, aldehydes, or the like. Some of these peaks are at odd masses and are, therefore, fragmentation peaks. They are consistently two mass units higher than fragmentation peaks from other oxygenated compounds. T o produce such peaks, the oxygenated hydrocarbons must contain two oxygen atoms and no unsaturated bonds. Acetals and hemiacetals are logical possibilities. Mixtures of aldehydes and alcohols produce hemiacetals, most of which are rather undable at room temperature ( 1 , 6).
A series of acetals of formaldehyde, xetaldehyde, and propionaldehyde was investigated to correlate mass spectra and to use the data for analyzing mixtures of oxygenated compounds. The general formula of the acetals is
H OR: R1-C
'/ \
OR? where R1 is hydrogen for diosymethane.; (formais) from the reaction of formaldehyde yith alcohols, or CH, for dioxyethanes (acetals) from the reaction of acetaldehydp with alcohols, or C2H6for dioxypropanes (propionale) froni the reaction of propionaldehyde with alcohols. EXPERIMEYTAL
Spectra were run on a Consolidated 21-103 mass spectrometer equipped s i t h a Consolidated micronirinometer. Effusion rate measurements were made with valve open to the mass spectrometer leak. The effusion rate TTith n-butane was the reference for calculation of apparent molecular weights For the calculation of specific reaction rate constants, the curves obtained for mass spectral peak heights decreasing n*ith time were corrected for normal decay of peak heights.
