-CO-NH-CO- group in cyclic imides. Hydrolysis of the compound with dilute acid or alkali releases 1 mole of ammonia. The aziridine ring in the molecule can be deter- mined by acidinletric titration after addition of sodium thio- sulfate [5] . The compound is readily soluble in water and on potentiometric titration with 0.1 N NaOH requires 1 mole of sodium hydroxide to neutralize its acidic imide hydrogen. Its aqueous solution has a neutral reaction hence the compound is here probably in the form of an intramolecuiar salt (5). On melting, the compound undergoes an exothermic reac- tion to form a strongly cross-linked infusible polymer, which

C-C' H, II

0

is insoluble in organic solvents but swells readily in water; this polymer is hydrolysed by prolonged heating with acids and alkalies and decomposes at 30OoC. N,N'-Polymethylenebismaleimides with the bridging ele- ments -(CH2)6-, -(CH2)12-, and - C G H ~ - C H ~ - C & - add on two molecules of aziridine in the same way to give two sirupy products and a crystalline compound that melts at 123- 126 "C. On prolonged heating polymerization occurs.

Received: June 3rd, 1965 [ Z 101836 IE1 German version: Angew. Chem. 77, 718 (1965)

111 M . Semonsky and A . Cerrzy, Chem. Listy 47, 281 (1953). 121 J. Cason, Org. Syntheses Coll. Vol. 3, 169 (1955). 131 J. Samberh and F. Grundschober, Swiss Patent Applications 1508/64 (Dec. loth, 1964). [4] The analogous reaction of maleic esters has been observed by H. Bastian et al., German Patent 849407 (Aug. Sth, 1944). It has also been found that piperidine also adds onto the C=C double bond of maleimide: P. 0. Tawny, R . H . Snyder, P . P . Conger, K . A. Leibbrand, C. H. Stiteler, and A. R . WiNiams, J. org. Chem- istry 26, 21 (1961). [51 E. Allen and W. Seaman, Analytic. Chem. 27, 540 (1955).

Cyclotrirnethine Dyes Derived from Squaric Acid

By Prof. Dr. A. Treibs and Dip1.-Chem K. Jacob

Organisch-Chemisches Institiit der Technischen Hochschule Munchen (Germany)

~,2-Dihydroxycyclobutenedione or squaric acid ( I ) [I, 21 can be condensed with highly reactive pyrroles 131 to give red- violet dyes which are similar to the cyclotrimethine dyes [4]. Owing to the acidity of squaric acid ( I ) , which is still maintained in thedye bridge, the dyes are intramolecular salts, whereas the dipyrrylmethine and dipyrrylpolymethine dyes known to date are salts of dye bases.

Judging from their mode of formation, elemental composi- tion, and infrared and ultraviolet absorption speclra, the new dyes should have the betaine structure (2), which is stabilized by resonance. The positions and intensities of the absorptjon bands of the new dyes in particular correspond to

the salt form of the trimethine and cyclotrimethine dyes with five- toeight-membered carbo- and heterocyclic rings [4,5]. The carbonyl absorption in the infrared is at an extremely long wavefength (1620 cm-1) owing to the peculiar bonding ar- rangement. The possibility of the existence of a tautomeric form (3) of (2) cannot be excluded; the yellow to red solu- tions given by the dyes in alkali are probably derived from the form (3). NMR measurements to decide this question could not yet be carried out because of the poor solubility of the new dyes. The dyes (2u) and (2b) are de- colorized rather rapidly by solutions of amines in ethanol. With (2a) this reaction is not merely salt formation, for the regeneration of the dye with acid occurs very slowly. Pyrrole, N-methylpyrrole, and pyrrole derivatives with both z-positions free give only blue to blue-green insoluble poly- mers by polycondensation; these probably have the formula

(3) (41

(4). Dyestuffs are also formed with 2-substituted indoles, but indole itself undergoes secondary reactions. Phenols and pyrroles have many reaction features in common. Thus phloroglucinol also condenses smoothly with squaric acid. The resultatet deep red-violet crystalline dyestuff proba-

OH OH OH

b H 0 d H

bly has the structure (5) or a tautomeric polar form of it. The presence of a polar form is not excluded by the position of the absorption due to the carbonyl group on ?he four-membered ring at 1635 cm-1. Methylation or acetylation dispels the dye character of ( 5 ) completely. Resorcinol also gives rise to a dye with squaric acid, but phenol does not and can therefore be used as solvent for the reactions described. Synthesis of (2u) : 2,4-Dimethylpyrrole i s condensed Rith squaric acid in a molar ratio of 2:l in ethanol by heating at 70°C or by prolonged standing at 20°C with catalytic amounts of perchloric acid. The violet crystals of (2a) are ob- tained in 65 04 yield after washing with ethanol, water, ethanol, and ether, and are recrystallized from chlorofoIm. These crystals release 1 mole of water of crystallization at 90 "C in vacuum and then melt at 240-250°C (decomp.); the ultra- violet spectrum of (2a) in chloroform has A,,, = 550mp (5 = 1.2~105); its infrared spectrum in KBr has VNH at 3230 cm-1 (w) and vco at 1635 (vs) and 1610 cm-1 (vs). Synthesis of (5): Quadratic acid is refluxed for 4 h with a lwo- fold molar amount of phloroglucinol in a twentyfold amount of acetic acid. The dye staits to crystallize from the hot solu- tion and is obtained in 67p/,y ield; it is recrystallized from boiling glacial acetic acid; m.p. 340- 345'C. (decomp.) 161; infrared spectrum in KBr: vo~=3300-2950 cm-I (s); vco= 1635 cm-l (s); vco(?)=I585 cm-1 (s). On drying at 95°C in vacuum the dye loses 0.5 mole of acetic acid of crystal- lization.

Received: June 8th. 1965 [ Z 998/824 IEI German version: Angew. Chem. 77,680 (1965)

[I] J. D. Park, S. Cohen, and J. R . Lacher, I. Amer. chem. SOC. 81, 3480 (1959); 84, 2919 (1962). 121 G. Maahs, Angew. Chern. 75, 982 (1963); Angew. Chem. internat. Edit. 2, 690 (1963). [3] A. Treibs and G. Fritz, Liebigs Ann. Chem. 611, 162 (1957). 141 A.Treibs and E.Herrmann, Liebigs Ann. Chem. 589,207 (1954: [ 5 ] A. Treibs and R . Zimmer-Galler, Hoppe-Seylers 2. physiol. Chem. 318, 12 (1960). 161 Determined on a hot metal block according to A. Treibs and R . Zimmer-Galler, Chem. Ber. 93, 2547 (1960).

694 Angew. Chem. interndt. Edit. 1 Vol. 4 (1965) I No. 8