DONALD S. ACKERAND WALTERR. HERTLER
3370 [CONTRIBUTION No. 665 FROM
THE
V O l . 84
CENTRAL RESEARCH DEPARTMENT, EXPERIMENTAL STATIOS, E. I. DU PONTDE NEMOURS AND C O . , INC., \vILMINGTON
98, DEL.]
Substituted Quinodimethans. I. Preparation and Chemistry of 7,7,8,8-Tetracyanoquinodimethan BY DONALD s. ACKER4 N D WALTERR. HERTLER RECEIVED MARCH15, 1962 7,7,8,8-Tetracyanoquinodimethanhas been synthesized from the condensation product of 1,4-cyclohexanedione and rnalononitrile. Tetracyanoquinodimethan is easily reduced to an anion-radical or to p-phenylenedimalononitrile. T h e latter has served as the intermediate in a synthesis of 7,7,8,8-tetrakis-(metho~ycarbon~-l)-quinodimethan.These quinodimethans readily undergo 1,6-addition reactions.
The recent discovery of tetracyanoethylene' and general investigation of negatively substituted the demonstration of its versatile chemistry2 quinodimethans. This first paper on the chemisprompted us to explore the chemistry of other struc- try of these compounds reports the synthesis, tures containing the highly electronegative cyano characterization and 1,6-addition reactions of group. Of particular interest are those struc- TCNQ and tetrakis-(methoxycarbony1)-quinoditures in which the double bond of tetracyano- methan. ethylene is replaced by a conjugated system. The Synthesis of TCNQ.-Malononitrile readily conquinodimethan ring system was selected as one denses with 1,4-cyclohexanedione to give 1,4-bis(dicyanomethylene)cyclohexane (I Ia) . Condensawhich should lend itself to investigation. Although the literature on quinodimethans is 0 quite extensive, only relatively few have been C, N sufficiently stable to permit isolation and charac+ C\H2 terization. X11 of the quinodimethans which are CN stable in the monomeric form a t room temperature 0 have aromatic substituents on carbons 7 and S, the best known example being tetraphenyl-p-quinoNC, ,CN N C H CN NC, ,CN NC, ,CN dimethan. Quinodimethan itself polymerizes very C C C C '' readily and can be kept monomeric in the condensed phase only in dilute solution and at very low temperature^.^ No stable quinodimethans with other functional groups on the a-carbon atoms have been reported. In our investigations, i,i,S,S-tetracyanoquinodiniethan (I, TCNQ) has been prepared and found IIa IIb I I11 to exhibit several exceptional properties. Of particular interest is the ease with u hich this compound tion in benzene solution apparently gives a mixaccepts one electron to form stable anion-radical ture of I I a and I I b since even the most highly range (204derivatives. The solid state properties of these purified material melted over a (io derivatives are remarkable, many being charactcr- 210°j, and there is absorption in the infrared a t ized by exceptionally low electrical resistivities.,j 3030 cm.-' which is best attributed to the unsatuNo quinodimethan anion-radicals have been pre- rated CH stretching frequency. However, if the viously reported, although sevcral quinodimethans condensation is carried out in aqueous solution, a including tetrapheriylquinoditnethatliaii have been high yield of IIa, m p . 2l6-2lZ'io. is obtained diconverted to cztioii-radicals.fi In no case have rectly from the reaction mixture. Treatment with these cation radica!s been isolated in the solid pyridine and either N-bromosuccinimide or brostate. The novelty and unusual solid state proper- mine gives TCNQ in excellent yields. Other ties of the TCKQ anion-radical have led us into a oxidizing agents such as selenium dioxide have been used to eiTect this conversion to TCNQ, ( 1 ) T L Cairns, R A Car ni. U . I ) . Cuffman, V. A . Engelhardt, but the yields have been poor. R E . Heckert. E . I. Little. G. hlcGeer. R C. hIcKusick, W. J , Properties of TCNQ.- 'l'etracyanoquinodiMiddleton, R . 31 Scribner, C \V. 'l'heobald and €1. E Winberg, methan, m.p. 293.3-296", isa rust-colored, crystalline J . A m Chrin. S O L ,8 0 , P77,i (1'9381 solid which can be sublimed a t temperatures above ( 2 ) ( a ) W J . >liddleton, R . li. Heckert. I
