[ CONlRIBUTION FROM THE GEORGE HERBERT JONES LABORATORY, THEUNIVERSITY
O F CHICAGO]
The “Isomerism” of N-Substituted Maleimides BY WILLIAMR. RODERICK’ RECEIVED SEPTEMBER 27, 1956 I\-(~-Methoxyphenyl)-tnaleimide and N-(p-ethoxyphenyl)-maleimidehave been prepared by dehydration of the corresponding maleamic acids with phosphorus pentoxide and with acetic anhydride, the former imide also by vigorous dehydration with acetyl chloride. These imides are both yellow, and the normal or symmetrical structure is indicated. The compounds designated in the literature as the corresponding white unsymmetrical maleimides have been shown t o be a chloro-n’-(9-methoxypheny1)-succinimide and a-chloro-N-(p-ethoxyphenyl)-succinimide,respectively. Both have been prepared by addition of hydrogen chloride t o the respective maleimides, the former also by dehydration of the maleamic acid with acetyl chloride. Attempts t o prepare N-(p-ethoxyphenyl)- and S-(p-nitropheny1)-isomaleimideswere unsuccessful.
Flett and Gardner state that the existence of the maleimides in both a symmetrical and unsymmetrical form has been shown clearly only in the case of the alkoxy-phenyl derivatives.2 Piutti3 prepared N-(9-methoxypheny1)-maleimide and N-(pethoxypheny1)-maleiniide, each in both a yellow and a white form which he designated as having the symmetrical and unsymmetrical structures I and 11, respectively. This assignment was 0 0
/-
H ---C-C
‘I I
I-I--C-C
H-C- I I
\o
HC-C‘
HC-C’
~\ I/ OH HC-C
HC--C
1
>o
n IIIb
IIIa
drolyzed to a certain extent, and the p-anisidine thus liberated is responsible for the violet color with ferric chloride. The acid may, therefore, be assumed to have the usual amic structure IV. 0
/
IL
I‘ ‘OH HC---C -”/-
OR
0
‘‘confirmed” by measurement of their absqrption spectra in the visible region (2000-6500 A,), in I\‘ which the spectra showed the expected diff e r e n ~ e . ~ The yellow (symmetrical) compound was obtained by Piutti by dehydration of the maleamic 0 acid with phosphorus pentoxide ; the white com1 pound (designated by Piutti as the unsymmetrical Dehydration of the N-(p-methoxypheny1)-maleform) was obtained by dehydration with acetyl chloride, a method previously employed in the amic acid (IV, R = CH3) with phosphorus pentoxpreparation of the i~ophthalimides.~Because of ide in toluene gave a yellow compound; gentle discrepancies between this reported isomerism and heating of the acid with acetyl chloride in acetone that obtaining in the case of the phthalimides, and gave a white compound. On strong heating of the also because it was anticipated that the infrared acid with acetyl chloride, a yellow compound idenabsorption spectra in the carbonyl region would tical with that from the phosphorus pentoxide deprobably be sufficient to enable structural assign- hydration was obtained. However, the infrared absorption spectra, while showing some differences, ments, it was decided to repeat Piutti’s work. The N- (p-methoxypheny1)-maleamic acid had were identical in the carbonyl region; since the been reported to give a violet color with ferric spectra of the phthalimides and isophthalimides chloride, this being interpreted as evidence for an are significantly different in this region,I this idenenolic structure I I I a or I I I b for the acid.6 It was tity was interpreted as evidence for the same type found that neither the crude nor recrystallized acid of imide linkage in both the yellow and white conigives a color with ferric chloride, but that on boiling pounds. Characterization of these compounds then rein aqueous ethanol for one minute, the acid is hyvealed that the white dehydration product does not ( I ) Standard Oil Foundation (Indiana) Fellow, 1955-1966. decolorize aqueous permanganate and that i t con(2) L. H. Flett and W. H. Cardner, “Maleic Anhydride Derivatives,” John Wiley and Sons, Inc., Xew York, N. Y . , 1952, p . 108. tains halogen, thus indicating addition of hydro(3) A. Piutti, A t t i . veale accad. Lincei, Classe sci. 3 s . mat. e nut., 151 gen chloride to the double bond of the maleimide to 18, 11, 312 (1909); C.A , , 4 , 2451 (1910). form a-chloro-N-(p-methoxypheny1)-succinimide (4) A. Piutti and E. de’Conno. M e i n . reaie accad. Lincei, Classe sci. (V, R = CH3). The literature reports a similar 5 s . mat. e ?zQ~.. [5] 8 , 793 (1911). ( 5 ) (a) S . Hoogewerff and pi. A van Dorp, Rec. Irau. r h i m . . 13, 93 addition of hydrogen chloride during the prepara( l a g s ) , (1,) c j . M. I. Shrrrill, F, L. Schaeffer and E. P. Shoyer, THIS tion of maleanil by dehydration with acetyl chloJ O U R N A L , 60, 474 (19%). \ 3
l5l ( I ; ) .\, rillit;,A ~ t i Y P , L / ~ i. i i i i , i f Lu(ii. Cirisse s ~ il i s . mut. e mi., 1 7 , I . ti:l5 (1908).
