Infrared Absorption Spectra of Methylenedioxy and Aryl Ether Groups LINDSAY H. BRIGGS and LAWRENCE D. COLEBROOK Auckland University College, Auckland, New Zealand
HENRY M. FALES and WILLIAM C. WILDMAN Laboratory of Chemistry of Natural Products, National Heart Institute, Bethesda,
Methylenedioxy, methoxy, and ethoxy groups attached to the aromatic nucleus exhibit 12, 10, and nine major bands associated with these respective groups. Most of them are common to all three groups. The analytical value of the bands for the detection of the groups is discussed.
F
the original observation by one of the authors (9, 12) that compounds containing methylenedioxy groups exhibit characteristic maxima :tt about 1040 to 1020 and 943 to 935 cm.-' in their infrared spectra, a more detailed examination of the spectrum of this group has been made on 100 compounds. The ability to recognize this group by infrared spectroscopy m-ould be of value because the chemical test for this group sometimes fails through an intense coloration produced by some other part of the molecule (6). For comparison, an examination was made on a number of analogous odimethoxy compounds and other methoxy compounds. Spectra were also studied for a limited number of aromatic ethoxy compounds. OLLOWIKG
EXPERIMENTAL
Infrared absorption spectra from 5000 to 700 cm.-l were obtained with either a Beckman Model IR-2 or Perkin-Elmer Model 21 spectrophotometer, both equipped with sodium chloride optics. Measurements in the 3000-cm. region were obtained with the former instrument equipped with a lithium fluoride prism or with a Beckman Model IR-3 spectrophotometer equipped with sodium chloride optics. The solvent notations are given in Table I . METHYLENEDIOXY C O M P O U N D S
The spectrum of liquid methylenedioxybenzene, determined with a sodium chloride prism in the region from 3330 to 700 cm.-' and with a lithium fluoride prism in the region from 5000 to 2500 cm.-l, and that of veratrole are illustrated in Figure 1. From a comparison of these spectra and those
904
ANALYTICAL CHEMISTRY
Md.
of 99 other methylenedioxy compounds (Table I) it may be concluded that the methylenedioxy group attached to the aromatic ring exhibits 12 major bands associated with this group-viz,, very strong bands a t about 1480, 1250, 1040, and 926 cm.-'; strong bands a t about 3010, 2960, 2910, 2780, 1360, and 1130 crn.-'; a medium band a t about 1400 cm.-l; and a weak band a t about 719 cm.-l The 3300- to 2500-Cm.- 1 Region. The methylene fragment of the methylenedioxy group would be espected to give rise to a doublet due to resonance interaction between the two C H bonds, not far removed from that of a normal &CHI-C group, the members of which occur a t 2924 and 2857 cm.-' (4). Two bands which occur in the region from 3000 to 2700 cm.-l are assigned to this mode of vibration. The strong band a t 2778 cm.-l in the methylenedioxybenzene spectrum, which occurs in all other methylenedioxy compounds within the range from 2801 to 2770 cm.-l, is considered t o be the upper band of this doublet. T'i'hen compounds are measured in the liquid state. in carbon tetrachloride solution, or in potassium bromide, this is a very sharp band; it is replaced by a broad band a t 2817 to 2770 cm.-l in hexachlorobutadiene mulls. It occurs beyond the normal range of C-H stretching vibrations and therefore is diagnostic for the methylenedioxy group. Absorption due to the -CH2N or -CHO groups, if present in the molecule, may obscure this band. The strong band a t 2890 cm.-1 in the methylenedioxybenzene spectrum is probably the lower member of the doublet. A band within the limits from 2941 to 2890 cm.-l occurs in all methylenedioxy compounds, but is of no diagnostic value alone as it occurs within the normal range of aliphatic C H stretching vibrations. Difficulty may be experienced in detecting these bands with a sodium chloride prism in some instruments, but this is obviated by the use of a lithium fluoride prism. Bands also occur a t 3012 and 2985
cm.-' in the methylenedioxybenzene spectrum, beyond the range expected for aromatic C-H frequencies. Usually, but not invariably, these two bands also occur in other methylenedioxy compounds a t about 3000 and 2960 cm.-l, similar in position to the bands of methoxy compounds (discussed belon-). The 1600- to llOO-Cm.-' Region. The very strong band a t 1477 em.-* in the methylenedioxybenzene spectrum occurs in all methylenedioxy compounds and may be assigned to aliphatic C-H bending. A medium band due to C-H bending of normal methylene compounds that occurs in the same region renders this band of little analytical value for detecting the pre,qence of the methylenedioxy group. The medium band a t 1401 em.-' in the methylenedioxybenzene spectrum occurs in many other methylenedioxy compounds within the range from 1427 to 1391 em.-'. The band, however, is weak in many cases and absent in others. Because normal methylene groups also give rise to a band in this region. it is of little diagnostic value. A sharply defined, strong band occurs in the spectrum of methylenedioxybenzene a t 1361 em.-', and in the spectra of many other methylenedioxy compounds within the range from 1376 to 1350 em.-' The band is of varying intensity, from weak t o strong, and is absent in five compounds. It may occur in other compounds containing a normal C-CH2-C group but is absent in methoxy compounds and, for this reason, may be analytically important. The presence of the aromatic C-0 linkage in aromatic methylenedioxy compounds would be expected t o give a band due to the stretching vibration in the same region as that of aromatic and unsaturated ethers a t about 1250 cm.-l ( 3 ) . I n fact, every methylenedioxy compound exhibits a very strong band in the region from 1266 to 1227 cm.-1, assignable to this vibration. I n some cases the single peak may appear as a strong doublet. Where both methylenedioxy and aromatic ether groups occur in the same molecule,
Table 1.
Compoiinda
Stateb
Methylenedioxybenzene l-llethosy-2,3-methylenedioxybenzene*
L T
Piperonyl alcohol lithium fluoride prism
T
C
Sodium chloride prism
T
6-Bromopiperonyl alcohol
T
6-Phenylpiperonyl alcohol Piperonyl bromide 6-Bromopiperonyl bromide 6-Bromopiperonyl tert-butyl ether Piperonal
N
T T C L T
1,2-Dibromo-4,5-methylenedioxybenzene Piperonylic acid
T
a
2915 2882 2950w 2890
2770 1121 1032 920 in
3021 2967 2933 2899
3021 2994 2915 3012 2959 2899
2778 -. ._
a a 1124 1121
1477 1403 1351 1242 1481 1393 1362 1241
1117 1036 935 ni a 1040 935 719
m m 1255 1488 1399 1357 m m m m 1253 m 1418 m 1236
1122 1034 925 In 1117 1125 1040 934 721 1122 1028 920 725
2778
2841 2778
N
N H N
T
Piperonylamine hydrochloride N,N-Dimethyl-6-phenylpiperonglamine Homopiperonyl cyanide
N N K
m
1481
Isosafrole
T L T
1408
m
m m
1114 1034 930 723 1115 1036 933 723 1031 922
m
Ill7 1042 939 919 1121 1040 939
m
a
1379w 1238 1357w m a m 1242 1477 1410w m m a
m
1126 1041 935 m 1124 1036 934 m
1414 m 1245 m 2786 1441 1418 1357 1236
1121 1034 925 725 1122 1034 934 720 923
2786 1437 1395 1357 1244
1121 1041 929 717
1439
a
1353 1242
1122 1041 937 719
a
1351 1233 1193 1133 1045 930 ni 1353 1233 1198 1135 1045 929 716
S N
m 3012 2959 2915 2849 2793 1427 2899 m m
C C
1481 1486
a a
1484
a
L
T
x
K
2976 2924 2899
2786
3012 2959 2915 2857 2778 2941 2882 a
m a
cyclohexanol 2-(3’,4’-methylenedioxypheny1)cyclohexanone
C T
5-(3’,4’-methylenedioxyphenyl)-4nitrocyclohexene
N
m
C
N
1481 m
a
N
m
a
N
m
N
m
4-(3’,4’-methylenedioxyphenyl)-5nitro-1,2-cyclohexanediol 4-Amino-5-( 3’,4’-methylenedioxyphenyl)-l,2-~yclohexanediol N-( 6-amin0-3~4-methylenedioxybenzoyl )-p-methylaminophenyl benzoate N-( 6-benzalaniino-3,4-methylene-
m
1256 1242 2786 1449 1410 1366 1258 2985 2924 1244 m 1408 1351 1242 2915 2841 2801 m m m a
2976 2924 2899 2907
927 931 931 930
2793
C
i3-3,4-methylenedioxyphenyl-
1036 1036 1036 1042
1031 930 m
1235 2899
m
1406 m 1236 125 1404 1372 m 1477 a 1362 m 1490 a 1361 1242
C
Piperonylamine
2-( 3’,4’-methylenedioxypheny1)-
3012
T
K
Isomyristicin’
1130 1043 937 718 3012 2985 2890 2778 1477 1401 1361 123,i 3012 2959 2890 2849 2778 2941 1053 924 1493 a 1350 1250 1176 a 1031 1460
N C
S N
propionic acid Safrole
Band Frequency, C :m .
N C C
Piperonal 6-Nitropiperonal 6-Bromopiperonal dimethyl acetal*
6-Bromopiperonylie acid Myristicinic acid*
Methylenedioxy Compounds
2976 2954 2941 2882
dioxybenzoy1)-p-methylamino-
phenyl benzoate
2793
1357 1232 1198 1138 1049 939 717 1362 1264 1129 1031 921 m 1242 1355 m 1121 1031 930 m 1370 1244 1126 1040 938 m 1350 1361 1245 m 1036 935 m
1399w m a
1248 1238 1362 1238 m 1264 124i m 1247
1120 1035 930
m
1120 1038 935 m a 1040 930 m a
1040 930
m
1397 1361 1263 1248
a
1044 943
in
1397 1361 1263 1248
a
1044 943
m
Compounds marked * contain methylenedioxy and methoxy groups. K, potassium bromide; C, chloroform; T, carbon tetrachloride; S, carbon disulfide; N, Nujol; H, hexachlorobutadi-
* L, liquid film;
ene. c
b, broad; w, weak; s, strong; a, absent; m, masked.
(Continued on page 906) ~
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VOL. 29, NO. 6, JUNE 1957
905
Table I.
Compound" A'-( 4,5-methylenedioxy-2-nitrobenzoyl)-p-methylaminophenol
?\[ethyl a-methyl-3,4-methylenedioxycinnamate*
Methylenedioxy Compounds (Confinoed from puge
Stateb K H C
cu-?\IethyI-3,4-methylenedioxy-
cinnamyl acetate 2,3,6,7-Bis( methylenedioxy)-g, 10dihydroanthracene
Band Frequency, Cm. -Ic m a m 1258 2817
2786
H N
I
