Mass Spectrometric Analysis of Aliphatic Amides J. A. GlLPlN Specfroscopy laboratory, The Dow Chemical Co., Midland, Mich.
b
The mass spectra of 35 aliphatic amides have been tabulated and correlated. The amides are divided into three classes: primary, secondary, and tertiary. Fragmentation and rearrangement ions typifying each of the classes are noted, in addition to spectral characteristics common to all three classes of the aliphatic amides. These observations are utilized for prediction and characterization of molecular structure.
C
of the mass spectra of the aliphatic amides permits an additional type of compound to be more rapidly and reliably characterized in regard to its molecular structure. Previous correlations of this type for the aldehydes ( d ) , esters ( 5 ) , alcohols (S), ketones ( I I ) , halogens (IO), acids (Y), and sulfides and mercaptans (8) have provided valuable information TI hich facilitates the elucidation of molecular structure using mass spectral data. The mass spectra of 35 aliphatic aniides are tabulated and correlated. Fragmentation and rearrangement ions nhich are useful in structural identification are discussed. ORRELATION
R-cH-cH~-~-cH~-
The spectra were obtained on a 90" sector mass spectrometer ( I ) , nhich had a 200" C. heated inlet system ( 2 ) . The amides were the purest available either commercially or by synthesis. S o attempts ton ard further purification were made. RESULTS
The aniides are classified as
( 7 ), ( 51 R-C-XH,
secondary
R-(2-SH-R'
( 8 - I 2f
CH(CH8\2-P CHdT+ (m/e 30) This 7 n / e 30 rearrangement ion is comparable to rearrangenient ions observed in aliphatic amine spectra (6). Tertiary Amides. T h e sgectra of the tertiary amides
(
0-
R-d-K(
P)
are given in Table 111. The major contributions in the spectra of the tertiary amides are correlated with the rearrangement ions VOL 31, NO 5 . M A Y 1959
935
Table I. Mass Spectra of Primary Amides
Form
Acet
Molecular weight 45 59 Source. EK EK m/e 1 23 15 27 12 2 10 7 28 29 28 2 30 0.9 2 31 1 3 41 0 . 3 16 42 28 2 43 57 12 44 27 76 100 2 45 ... 55 0.1 56 57 0.1 58 0.2 59 100 4 60 71 72 73 74 85 86 87 88 99 100 101 114 115 116 127 128 129 141 142 143 156 157 169 170 171 184 185 197 198 199 212 213 226 227 240 241 255 283 100 100 Pd 0 . 6 5 0.57 S/Stale
-
- -
Propion
nIsoButyr butyr
nValer
73
87 EK
101 EK
D
87
EK
1 2 0.7 14 20 8 5 9 5 12 4 4 14 26 1 0.9 1 2 0.1 0.5 0.1 0.6 17 32 13 1 5 2 9 10 30 60 11 3 38 100 64 100 5 3 6 2 rn 7 8 6 3 0.4 0.9 2 0.2 0 . 2 11 18 0.2 0.6 0.7 1 100 26 3 100 0.7 3 0.1 3 ... 0.2 8 6 I1 78 40 19 __ -_ _. 56 1 2 3 3 ... 0.1 0.1 ... ,.. 3 3 4 3 3 23 0.2 1 2 ...
1
14
-
-
-
...
0.8 0.6
56
3
0.85
0.59
23 0.69
0.6 0.99
TriP Iso- methyl Methylvaler acet Capro valer Non
y-tert- y-sec-
butyl capro
butyl Do- Hex* capro decan decan Stearb
101
101 115 115 157 171 171 199 255 283 A EK EK EK D D A A EK Relative Intensity 0.2 0.4 0.1 2 1 1 0.4 0.3 0.2 0.2 4 5 3 5 8 4 3 6 6 7 4 3 1 2 25” 4OC -34 -4 2 2 9 5 6 9 10 7 7 32 6 10 0.8 0.4 0.4 0.8 1 0.7 1 1 0.6 0.8 0.2 0.3 0.2 0.5 0.7 0.1 0.4 0.5 0.2 0.1 16 18 14 16 47 9 15 9 11 17 3 4 3 4 5 3 2 6 4 5 18 22 21 27 2 24 22 13 11 20 15 12 7 15 33 13 8 31 16 27 0.7 1 1 2 1 1 1 2 0.6 0.3 17 11 13 16 1 3 6 8 6 9 1 2 2 3 6 5 2 6 1 3 15 13 16 18 12 100 2 16 5 16 2 1 2 1 1 8 0.2 2 0.3 1 100 100 100 100 100 100 3 100 100 9 12 13 8 3 5 4 3 0 . 2 3 9 4 6 8 ... 0.1 2 2 2 4 46 34 44 44 0.5 . . . 18 33 27 7 10 8 10 9 3 ... 4 7 5 2 3 0.2 ... 0 . 2 0 . 5 0 . 3 0 . 2 0 . 6 0 . 8 1 2 0.3 ... 0.1 0.3 0.1 0.2 2 4 5 11 9 9 7 6 0.8 2 7 7 7 0.6 0.5 0.5 0.7 0.5 0.1 0.2 1 2 2 0.5 . . . . . . . . . . . . . . . 0.2 0.1 0.1 0.6 0.6 1 2 1 0.9 0.1 0.2 0.2 2 2 4 2 1 2 1 0.5 0.3 8 0.3 2 2 3 2 18 ... 0.5 0 . 4 0.3 27 5 7 6 0.4 0.6 4 21 3 2 3 6 0.6 0 . 5 11 0.5 1 0.2 0.8 2 0.7 1 ... 4 0.1 0.2 0.5 1 ... 0.2 5 7 9 ‘2’ 0.1 ... 2 3 3 0.3 . . . ... 0.2 0.4 1 0.2 . . . 2 1 1 2 0.1 0.6 0.9 ,.. 0.1 0.2 0.5 0.6 0.4 3 1 1 0.1 2 ... 1 0.7 0.5 0.9 0.3 0.1 . 0.2 1 ... ... 2’ 2 3 ... 0.7 0.7 0.8 0.8 0.5 ... 1 2 ... 0.8 1 0.1 1 3 4 0.3 2 1 0.6 0.9 4 1 1 0.4 2 1 0.6 0.3 0.4 5 0.2 1 3 0.6 4 2 18 0.5 0.6 0 . 9 0.5 0.7 1 3 4
D
-
~
0.98
1.0 4 . 8 8
0.86
1.2
0.96
0.69
0.33
0.22
0.12
a EK = Eastman Kodak; D = Dow Chemical Co. (compounds listed are not necessarily commercially available); A = Aldrich Chemical Co. b Some background contributing. Air background present. d P = molecular ion (parent eak). scale divisions A scale divisions toluene. S/Stal = mg. of A mg. of toluene 0
936
P
ANALYTICAL CHEMISTRY
previously noted for the primary and secondary amides. Two of the tertiary amides-A',Ndiethyl decanamide (a) and N,N-diethyl dodecanamide @)-give the most iptense peak in their spectra a t m/e 115. The formation of this rearrangement ion corresponds to cleavage of the carboncarbon bond beta to the carbonyl, accompanied by the rearrangement of a hydrogen atom to the amide portion of the molecule.
Table II.
Molecular weight Source. 15 27 28 29 30 31 41 42 43 44 45 55 56 57 58 59 60 71 72 73 74 85 86 87 88 99 100 101 114 115 116 128 129
(a) C 6 H ~ 3 - C H - ~ H ~ - ~ - ~ H ~ -
5
The majority of the remainder of the tertiary amides examined give the most intense peak in their spectra at masses corresponding to cleavage similar to that proposed in the case of the m/e 30 rearrangement ion of the secondary amides. I n other words, cleavage of the nitrogen-carbonyl carbon bond and one of the carbon-carbon bonds beta to the nitrogen atom, accompanied by the rearrangement of a hydrogen atom to the nitrogen-containing portion of the molecule, is consistent ITith the rearrangement ions observed. Several tertiary amides having different alkyl substitutions illustrate the formation of this rearrangement ion. (a) S,S-diethyl acetamide 0
6
C3HsN ( m / e 58) N,X-diethyl hexsnamide +
0
-6
C3HsN+ ( m / e 58) ( b ) 5,S-dibutyl acetamide
0
6 -C5H12N+ ( m / e 86)
EK
D
7 3 34 13 54 2 3
23 2
17 3 67 17 3 10 83
1 1 1
4 9
0.1 0.3 0.4 0.4 8 100
0.7 0.9 0.4 40
3
1 1
0.3 0.4 100 4
N-Butyl N-Isobutyl N-Butyl Acet Acet Octadecan 115 115 339
D EK Relative Intensity 4 10 4 6 0 8 13 5 100 100 2 3 7 3
-
-
11
4
59 48
34 19
D
143 156 157 170 171 184 185 197 198 199 212 213 226 227 239 240 241 268 282 -295 -311 -339 S/StOlC
D
4 3 4 4 100 4
0.3 3 7 8 13
P,
14 3 18 12 0.7 13
3 31 3
0.4
2
2
1
0.1 0.3 0.1 0.1 4
2
2 4 2 13 0.6
23 3
18 0.3
4 6
3 2 4
0.6
1
10
0.1 14 0.6
0 3 20 21
...
1
...
0
0.5 72
1
'
, .
3 7 3
0.1 ...
0 4 6 0 4 0 % 11
...
12
os 0.1
11 2
7
2
G 20 0
0.6
3
4
31 6 1
0.3 1 11 1
0.7 100 8 "3
4 4
142
P b
N,N-dibutyl hexanamide
N-Methyl N-Methyl N-Ethyl Form Acet Acet 59 73 87
m/e
@-
n
Mass Spectra of Secondary Amides
0.9 2 1 4 1
4 0.8 1
3 0.6 2 3
2 0.4 2 2 0.4 2
100 -
100 -
0.49
0.98
72
11
11
0.70
0.68
0.98
1 2 2 2 2
0.45
E K = Eastman Kodak; D = Dow Chemical Co. (compounds listed are not necessarily commercially available). b P = molecular ion (parent peak). scale divisions A scale divisions toluene S/Stol = mg. of A mg. of toluene *
I
VOL. 31,
NO. 5, MAY 1959
937
Table 111. Mass Spectra of Tertiary Amides N,NK,KN,Y.VJ5N,K-Di- X,A'-Di- N,XN,NN,iVNJA7- N,KN,Smethyl methyl Diethyl Diethyl Dibutyl Diethyl Dipentyl Diethyl Dibutyl Dipentyl Diethyl Dioctyl Acet Acet hcet Hexan Hexan Dodecan Form -4cet Form Hexan Acet Decan
Molecular weight Source.
73 D
87 D
101 D
11 2 12 6 14 0.5 3 24 6
11 5
5 15 25
1
28 Cr
115 D
171 D
mle 15 27 28 29 30 31
1
8 0.5 2 19 46 100 23 2 2 0.2
ir
1
5
5 6 7 14 0 5
-
2 3 2
7 12 0.4 5 3 19 15 2 2 2 5 0.8 0.1
171 D
199 227 D EK Relative Intensity 2 2 0 3 16 5 4 3 -1 8 13 28 -8 6 25 3 1 0.6 0 1 11 22 15 6 5 15 47 13 41 32 16 29 r 2 0.5 13 5 9 4 9 5 7 S 3 100 11 54 4 5 0.6 4 49 0.3 13 -5 5 24 35 -5 5 8 30 1 8 5 2 0.4 1 10 25 13 7 8 17 0.5 3 0.5 0.6 0 1 8 40 47 100 3 -7 4 2 D 65 71 100 5 c d 5 0.3 0 1 0 2 0.3 33 30 35 3 4 5 0.4 ... 7 9 ' 36 1 1 4 0.7 ... 0.3 27 2 1 3 0.1 0.6 4 12 0.9 0.6 1 8 2 4 0.4 0.7 2 0.4 0.8 6 0.7 0.1
227 D
255 D
0 4 4
0.3 3
3 c
2
i
5 0 3
7 8 0.2 11
255 D 0.4 3 4 10 3 0.1 9
283 D 0 5
2 4 5 11 0 3 10 4 29 26 2 6 4 8 2 0 3 3 3 5
4 7 11 41 c 4 4 5 10 42 12 35 18 3 31 43 11 15 8 47 31 44 1 0.7 0.7 11 6 2 45 6 9 5 0 7 0 4 0.1 55 3 3 3 1 5 3 56 2 11 8 1 0.8 0.1 57 1 4 37 5 1 58 84 100 2 0.3 0.3 59 0.2 0.1 3 4 1 1 60 ... 2 1 8 0 2 4 3 13 71 0 5 0 5 0.3 8 0.1 ... 17 3 3 17 21 72 6 7 15 c 2 7 6 8 100 0.9 I 1 5 73 0.7 4 0.3 0.3 0.8 74 5 0.1 0 8 0 3 2 0 7 0 4 0 . 7 0 . 3 ... 85 3 0 8 10 7 8 36 3 100 100 , 0.2 86 9 0 4 6 2 -1 10 69 87 0.5 0.6 0.4 0.3 0.4 4 0 2 0 1 88 c 0.4 0.5 8 0 2 0.2 99 0.8 3 100 33 7 2 6 100 e 2 3 0.9 100 0 4 0.6 101 2 5 50 8 0 1 4 114 1 100 7 4 41 0.3 115 1 7 0 1 4 0.7 0.8 116 0.5 0.7 0.1 0 2 ... 127 6 24 29 21 23 128 0 9 8 5 4 3 129 0.2 0.1 0.1 0 5 141 100 6 16 4 2 ' 142 __ 11 1 3 0.9 0.2 143 1 0.1 0.2 0c . 4 ... 155 2 8 14 6 156 1 0.9 2 1 0.6 157 12 3 0.7 3 0.1 1TO 2 0.7 0.4 5 5 171 11 2 52 9 184 7 0.4 1 2 185 2 5 3 4 198 0.4 0.7 0.4 3 199 c 5 1 0.7 212 1 0.3 0.8 0.1 213 2 4 2 1 0.5 226 0.5 0.6 4 0.7 6 227 5 0.6 0.9 240 0.1 0.2 0.8 211 4 0.7 4 255 17 268 0.8 282 3 283 -296 -310 -330 3 4 4 4 6 6 100 69 100 41 5 8 Pb 0.53 0.38 0.57 0.45 0.79 0.66 0.38 0.95 0.84 0.62 0.29 0.71 S/Sd D = Dow Chemical Go. (compounds listed are not necessarily commercially available) ; E K = Eastman Kodak. b P = molecular ion (parent peak). scale divisions A scale divisions toluene S/Std = mg. of A mg. of toluene
-
5
/
938
ANALYTICAL CHEMISTRY
;
N,'VDioctyl Hexan
339 D 0.5 3 8 8 10 0.4 14 5 37 22 2
10 4 12 3 0.6 7 12 4
10 1
2 6 7 0 6 8 4 3 13 2 1
0.7 6 3 0.5 100 12 1 11
2 13 5 39 6
7 1
5 1 3 1
12 2 0.9 38 2 3 8 3 2 2 0.29
(c) N,N-dipentyl acetamide 0
6
CBHllPIj ( m / e 100) +
( d ) N,N-dioctyl hexanamide 0
6 --
CoH?oN ( m / e 142) +
AMIDE IDENTIFICATION
An unknown aliphatic amide may be characterized by its mass spectrum as follon s : 1. The peak a t highest mass in the spectrum designates the molrcular M right of the amide. 2. If the most intense ion current in the spectrum corresponds to the C,H2,+Ji0 series (m/e 59, 115, etc.). this is a molecular ion or a rearrangement ion corresponding to cleavage of the carbon-carbon bond beta to the carbonyl group, accompanied b y the rearrangement of a hydrogen atom. K h e n n = 2 and m / e 59 (not a molecular ion) is the most intense peak in the spectrum, a primary amide is necessitated. When n is greater than
2, either a secondary or tertiary amide is indicated, and additional information may be obtained from the C,H2,+2S series (see 3). 3. If the most intense ion current in the spectrum falls in the C,H2,+& series ( m / e 30, 58, 86, 100, 142, etc.), the rearrangement ion can be correlated with cleavage of the nitrogen-carbonyl carbon bond and the carbon-carbon bond beta to the nitrogen atom, accompanied by hydrogen rearrangement to the nitrogen-containing fragment. A maximumm/e30peak (n = 1) designates a secondary amide. A maximum contribution in the C,H2,+2S series, when n is greater than 1, indicates, in general, a tertiary amide. The study of tertiary amides was limited by the availability of conipounds to cases where the alkyl substitutions on the nitrogen atom were identical. I n the cases examined, a masiniuni spectral contribution in the C,HZn+.S series when n = 3 designates a n S,A'diethyl amide; n = 5 , a n N.S-dibutj1 amide; n = 6, a n .Y,S-dipentyl amide: and n = 9, a n S,S-dioctyl amide. The mass-to-charge ratios used for amide identification, particularly in the CnH2n+2Kseries, are also characteristic of other types of structures; therefore, relatively pure compounds should be used 13hen the above rules are applied for characterization of the amides.
ACKNOWLEDGMENT
The author extends sincere thanks to
R. S. Gohlke, V. J. Caldecourt, and F. IT. hfclafferty for aid and advice in the preparation of this manuscript. LITERATURE CITED
V. J., AXAL. CHEM.27, 1670 (1955). (2) Caldecourt, 1'. J., ASTM Committee E-14, Conference on Mass Spectrometry, Sew Orleans, La., M a y 1954. ( 3 ) Friedel, R. *4., Shultz, J. L., Sharkey, A. G., Jr., AKAL.CHEM.28, 926 (1956). (4) Gilpin, J. A., Mclafferty, F. W., Ibid., 29,990 (1957). (5) Gohlke, R. S., McLafferty, F. W., ASTM Committee E-14, Conference on Mass Soectrometrv. San Francisco, Calif., Maf 1955. (6) Gohlke, R. S., McLafferty, F. IT., The Dow Chemical Co., blidland, Mich., unpublished work. (7) Happ, G. P., Steward, D. W., J . A m . Chem. SOC.74, 4404 (1952). (8) Levy, E. J., ASTM Committee E-14, Conference on Mass Spectrometry, Sew York, S . Y., May 1957. (9) Mclafferty, F. K., ANAL. CHEM. 28, 306 (1956). (10) hIcLafferty, F. K., ASTM Conimittee E-14, Conference on Mass Soectrometrv. San Francisco. Calif.. Xfay 1955. (11) Sharkey, A. G., Jr., Shultz, J . I,., Friedel, R. &4.,ilzr.4~. CHEJI. 28, 934 (1956). ( 1 ) Caldecourt,
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I
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