Hexacyanoethane reacted readily with a number of active-hydrogen coni j)oiinds io give hydroqeii cyanide and tars. Experimental Sodium pent~ic?.ariiie!liaiii~Iei(21 g., 0.1s 111o1cj\ Y in a dry flask with 40 r n l . of c>.aiiogcn cliloride. .I alurninuni chloride (0.2 g . ) \va$ added, and t!ic 1n:s;ure was refluxed (wet-ice coiidenserj for Iialf a n liiiur. C>.aniigen chloride was then tlistiiled off at atmosplicric pressure,
crushed under benzene, and \v;islied n i t h herizctic u i i t i l t!ic n d i i n g s were no longer >-cllo\\-, i~i(1ic:itiiig ciiir~!ilet~removal of tetracyaiiiietli~ler~e.'!YIC> irisoliii)!e \ that remained i v n s pure 1 i e ~ a c ~ : t i i i ~ e : l i ~ iii .~i ~c ;i (li7,). Heuacyaiioetliane suliliines ahove 150' miti i n :L sealed capillary dec,imposes in the infrared spectrum has bands a t 4,40,
[ C O S T R I R r T I O X 1-0. 784 FROM THE C E S T R A L RESEARCH IIEPARTWEST, EXPERIMEYTAL Sr,4rIOX, ASD C o . , Isc,WILMISCTOS (38,D E L . ]
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P O V T DE S E l l O U R S
Chemistry of Tetracyanoethylene Anion Radical 13\, 0 . 11.. I Y r u s r m ,
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RECEIVED hf.4y 25, 1!%2 Tetracyanoethylene ( T C N E ) reacts readily with n ieLy of reazents i n c l a l i ~ i gm-tals, iodiles aril alip'iakic amines t o give tetracyanoethylene anion-radical ( T C S E j dcri i v s . Sar?risiiigly, T C N E also undergoes reacti ) I I w i t h cyanide ion to give T C S E _. Evidence that this reactim proceed:; thraugh the isolable peiitac).aiioet:ianide ha> been obtained through tracer studies.
Tetracyanoethylene (TCKE) is a strong T-acid, as evidenced by the large equilibrium values for its complex formation with organic T-bases In these charge-transfer complexes there is only 1)arti:i.l electron transfer, as shown by their diamagnetic character. In addition to forming compleucs of this type, T C K E also reacts with A vir:+- of reagents to form tetracyanoethylene a n i o n - r d i c d (TCh'E-) derivatives, as established froiii electron paramagnetic resonance studies For example, TCKE reacts with potassium,' $odium,? a l u r n i n ~ mmagnesiumd ,~ and copper3 a t room temperature to give the corresponding metal salts of TCNE-. T h e details of our earlier work are reported now together with a study of an unusual reaction of cyanide ion with T C N E to yield TCKE-. The latter reaction was studied in some detail, since i t presented a potential source of the cyano rxlical, which has been previously detected a s a reactive species of some high-energy processes.i Nore recently, the question of the existence of the cyano radical under other conditions h:ts been r2,ised in (1) R. E . Llerrifield a n d \V. I ) . l'lii!lips, J . :Ii?i. C (1938). I 2 ) T h e existence uf meia: tetr:icyanc~eth> lrnidcs was nized b y Pr\,f. i; I. U'eiisman. \Va~.liin;.t,.~i see \V. I ) . Phillips. J. C l < < , n e i l iinrl >, I 33, ti26 (1060) 0 \V LVeiistcr, n' l l a h l e r a n d R. l i . 1 4 7 0 (1960). ( 4 ) See, for example, J IT. TVhilr. .l. ( hci~? /'I?\,,..8, 7!l :lfJ4Llj; 8, 4.75! c1nroj.
reactions involving mercuric cyanide. For example, reaction of mercuric cyanide with disilicon hexachloride gave cyanotrichlorosilane, and a mechanism involving the addition of the cyano radical to the Si-Si bond was sug.gested.3 In addition, reaction of mercuric cyanide with hexaphenylethane yielded cranotriphenyllr~ethane,but in this case i t is stated t h a t i t is not certain whether the reaction involved the cyano radical or the cyanide ion.F Reaction of Cyanide Ion with TCNE.--Although sodium c:;anide is essentially insoluble in acetonitrile,: rc-action with T C S E in acetonitrile solution occurs rapidly and exothermally a t room temperaturc to give S a i T C N E - in iO--S{!?{ yicld. Efforts t o demonstrate the presence of cyanogen (deri\-ed fro:?: dimerization of the potentially formed . C S ) were unsuccessfiil, and rio appreciable quantity of h>-drogeri cy-exide (potentially formed by abstraction of proton from the solvent by .CN) could be detectcc! whet! the reaction was conducted in the presciice of ether. I n addition, no polymerization occurred when T C X E was allowed to regct with S n C N in the presence of either styrene or methyl zcrylate, and efforts to isolate cyanosubstituted derivatives of these vinyl monomers were unsuccessful. On this basis it was concluded t h a t ,Chr ~ . - n s::ot formed as a direct product of t!ic reaction. .A
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T o establish t h a t the course of the reaction was of the *CS-to appear in the TCNE-* (and hence not affected by the presence of insoluble cyanide, in the isolated TCNE*). T o establish t h a t the equilibrium involved Nathe reaction was studied in a homogeneous system. Tetraethylammonium cyanide8 was synthesized for PCE and the reactants NaCN and T C N E , labeled this purpose and found to be readily soluble in T C K E was added t o acetonitrile containing acetonitrile. TCNE- was obtained in 85-95yo NaPCE. After 1.5 hours a t room temperature, yield from this cyanide and T C K E , regardless of NaPCE* was isolated, converted to TCT\;E-*, and the latter oxidized t o T C K E * having molar the order of addition of the reagents. However, the yield of TCXE- was found to be activity corresponding to complete equilibration of markedly dependent upon the concentration of the cyano groups. These results estab!isb equjT C N E . n'hen an excess of T C N E was used with libriuin A . sodium cyanide, the yield of TCNE- fell, and a new CN CX 1 1 cN compound having the composition XaCN.TCNE T C N E CN3 4 + 3C-C-CN + (rate was isolated b y diluting the acetonitrile solution (A) I / deter. with ether. nTth lYc excess T C N E , the yield of CN CN step) TCXE? was only 107c, and the yield of NaCX. T C N E adduct was 33Yo, The adduct was obtained C N CN NO CN C N 1 1 in 49% yield when a 10% excess of T C N E was + BC:-C@ ((CN)I?) used. This adduct was characterized as sodium I I CN C N penta~yanoethatiide~ (XaPCE) on the basis of its infrared spectrum, which showed strong absorption a t 4.31and 4.63 attributable to a substituted TCNE TCNE: malononitrile anion and the absence of absorption in the 5-6 p region attributable to C=C or C=N. Furthermore, in view of the insolubility of the In confirmation of the proposed structure, chlorina- ~ y a n i d e i, t~ appears that the equilibrium lies far to tion yielded chloropentacyanoethane, a white solid, the side of PCE. If C N - is the agent responsible m.p. 174-175' dec. for the conversion of P C E - to TCNE-, then stabilN a P C E was obtained as a slightly off-white solid ization ol solutions of P C E - by T C X E is underthat has moderate stability a t room temperature. stood readily. On heating t o 14Uo, i t is converted to TCNE- in The postulated reaction of PCE- with C N - is high yield together with cyanogen. Dissolution of unusual, since it involves not only attack of one N a P C E in acetonitrile a t room temperature re- anion on another a t modest temperature b u t also sults in immediate formation of TCNE-. The the attack of C S - on a nitrile group. T o establish rate of this conversion is markedly lowered by the t h a t the latter reaction could occur under these addition of 1 mole per cent. of T C S E , and this in- conditions, the action of CY- on phenyltricyanohibitory effect is removed by the addition of CN-. rnethaneI2 was studied. This reaction in acetoniThese results suggest t h a t K a P C E is converted trile a t - GO" gave phenylmalononitrile anion in to TCNE- by C K - and t h a t the concentration of (jOy0yield C N - is appreciably lowered by the presence of C$HsC(CS).:+ CSC? --+ C6HjC(CS)r3 f [ ( C S ) , ? ] T C N E . These observations are in accord with a reversible reaction involving the formation of and on this basis it is believed t h a t the attack of K a P C E from T C K E and sodium cyanide as was cyanide on P C E - is feasible. By analogy, reaction of C K a with NaPCE would yield disodium tetraestablished by studies with radioactive cyanide. The reaction was conducted with IT-tagged cyanoethanediide [ S a e T C N E ] . In a separate exK C X and a ,'3.L'c:)excess of T C N E a t -30" to give periment i t wzs shown t h a t NaZTCNE, derived K P C E * which was isolated and converted to froin tetracyaiioetharie and sodium hydride, reacts TCNE-* by heating a t 1.4Oo. The latter was readily with T C N E to give TCKE- in high yield. oxidized with 7,+7,8,S-tetracyanoquinodimethanOn this basis, the reactions in Fig. 1 are postulated (TCN$))'O to give T C N E * and R i T C N Q - . for the conversion of T C K E to TCNE- with cyaT C N E was isolated by sublimation. Counting nide ion. No cyanogen, the expected by-product, was studies established that the molar activity of the isolat.ed TCT\;E* was ii.37, of the initial activity found in this study. However, it was shown th:tt of the W X - . I n a separate experiment it was cyanogen did not survive the reaction conditions. established that no exchange occurred between Thus, efforts to recover added cvanogen from the ' T N - and TCXE- under the reaction conditions. TCSE-SaCh--acetonitrile reaction system were Complete equilibration of I T S - with T C N E to unsuccessful. The reaction of T C N E with an equivalent of give KPCE* would require 7S.2Y0l1of the activity labeled potassium cyanide was examined a t 25' and ( 8 ) Ionic ct-anides t h a t are soluble in moderately polar organic 40'. Under these conditions, no K P C E was isoso!vents a r e of considerable synthetic interest. T h e prepnratian of lated and K'TCNE- was formed directly. tetraethylammonium cyanide was previously described (11. S . StromIf the reaction of CN- with T C N E were considholm, B e y . , 31, 2389 (1898)), b u t t h e compound was neither isolated nor characterized. See ftiotnote 2 2 for synthetic details. erably slower than the conversion of K P C E to ( e ) T h e structure of S a P C E has been further crinfirmed b y reaction K+TCKE?-, the TCSET formed would be exwith cyanripen chltiride t o give hexacyanoethanr ;S.Trofinienko a n i l +
1
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I3 C . RIcKusick, to be published) , l o ) 1). S. Acker, K S. Harder, I\. I: IIertler, X- l i a h l c r . I,. R. hlelby, R. E . nensC yields, o u ~ l y ,T ' ~C~N E reacts with a variety of metals a t respectively. room temperature to give metal TCNE- derivaAcidification of solutions of TCNE- gives all tives. For example, reaction of T C N E in acetoni- equimolar mixture T C N E and H y T C X E . Pretrile with copper yields CufTCXE-. In addition, sumably, the anion-radical is initially protonated lead also reacts readily to give Pb'+(TCSE-)?. to yield HTCKE., which disproportionates to the These compounds appear to have excellent stability observed products. l a to air in the solid state. TCNE- derivatives have been oxidized to Iodide ion also reacts with T C K E in acetonitrile T C N E by a variety of reagents. For laboratory to yield TCNE-. Free iodine is foriiied in this purposes, i,i,S,S-tetracyanoquinodirnethane is a reaction, and excess iodide usually has been used preferred reagent, since metal i,i,S,S-tetracyanoas a scavenging agent for iodine by formation of the quinodirnethanides are insoluble and stable. triiodide ion. The .odium and lithium derivatives Thus, the T C N E formed can be separated froin the can be prepared readily in this manner from the oxidant by filtration or sublimation. Silver tricorresponding iodides. .ilkylaiiiiiioniuin iodides fluoroacetate is also an excellent oxidizing agent, also react readily with T C N E in acetonitrile to giving T C N E in high yield. Bromine and chlorine give the corresponding ammonium TCNE- deriv- also react with TCXE- to give T C N E although iii atives, as established from rpectral aiialyses. lower yields. Tertiary aliphatic amines also react with 'TCNE Physical Properties of TCNE---Charactcrizain acetonitrile to give ammonium T C S E - coin- tion of TCNE- derivatives has been facilitated by pounds. In this respect T C N E further resembles spectroscopic studies. The infrared spectrunl, T,i,S,S-tetracyanoquinodimethan. lo The source of determined in potassium bromide, is markedly simthe proton has not been established, b u t it is pre- ple, showing absorption a t 4.33, 4.58 and '7.33 p . sumably derived from the ainine.'l (13) T h e resistivities of t h e T C S E ' derivatives a r e much higher Reaction of a moderately strong Lewis base with h a n those of t h e correiponding derivatives of 7,7,8.8-tetracvano~juinuT C N E in the presence of an equimolar quantity of tdirnethan (see reierence of f o o t n o t e 1.1). tetracyanoethane ( H 2 T C S E ) yields onium T C N E T (16) \'v' J. hliddleton, E. I.. Little, 13. TI. Coffrnan a n d V , A Ilngelderivatives readily. For example, 1,4-diazabicyclo- h a r d t , J . A m ( ' h n z . S O L .8, 0 , 2786 (1958) (17) C. I,, IXckinson, 1) \V. Wiley a n d B. C . LIcKubick, ibigl., [ 2.2.2loctane in acetonitrile with TCSE-H:TCNE
__
82, 6134 (l'J60). (18) An alternate mechanism, proposed by I ) . E Paul, 1) l . i i i k i n a n d S . I. Weissrnan tibid., 78, 116 ( ) ) for reaction c i i aroniatic H o n e v e r , we d o n o t wish to d r a w further conclusions i r v m thebe studies ion radicals with water, is f o r t h e HTC t o capture an d e c t r m f r i m because uf experimental l i r n i t a t i o n ~ T h e yield of T C S E - ia 65T C S I C 7 giving H T C N E - a n d T C X E . h second groton;rtiun t h e n SOc+, a n d it would he diRicult t < ) t h e rflecl u[ side rcnctioiis introducing activity i n t o TCNII-'complete5 t h e reaction t o give HnTCNE a n d T C S E , l!l) A l t h o u ~ h T C S E and 7 . 7 . 8 . 8 - i e r r a c y a n r ~ i ~ u i n ~ ~ d i m e th-ticalS L I I I J ) ~ ~ wxs prelinred b y recrystallization from :icetonitrile. Tlie identity o f the product \\-as coiifirinerl by the infrctred spectruiri. Anal. Culctl. for C6K4Cs: C , C7.fil; S,21.47. 1 ~ 1 ) u n d : C, 2 i . 8 8 ; S,21.47. Lithium Tetracyanoethylenide Ti) :t suspension of 5.00 g. (39.0 inmoles) of TCY-E in 200 nil. of dry ether was added 4.50 g. (33.G mimiles) of lithium iodide in 10 nil. of acetonitrile. The mixture was stirred 2 hours mid filtered t o give LiTTCIL7ET (1.50 g., 3355) identified by its infrared spectrum. B n a l . Calcd. for C&.,Li: C, 53.38; S, 41.51. Found: C, 53.88; S,41.10. Lead Tetracyanoethy1enide.-.2 solution of 1.50 g. (11.7 minoles) of T C S E was stirred with 1.15 g. ( 5 . 5 2 mmoles) of fresh le:rd filings in 50 nil. of acetonitrile for 24 hours at room temperature: Pb++(TCSE-)? ( 2 . 3 2 g., 90"; ) was isolated by filtratioii. A n aiial!-tical s:rrnple was dried a t 80' (0.3 I I I I I I . ~ . The infrared spectruiu identified the product as P b - - + ( T C S E T L . A n a l . Calcd. fix CI:S,Pb: C . f'31.07: S, 24.18; l'b, 44.72. FoLlnd: C, 31 .19; K , 24.01; I'b, -44.fiO. N-Methylquinolinium Tetracyanoethylenide.2B-Quinoline inct!iii)dide ( 2 . 7 g . , 10.0 nirnoles) w:i? dissirlvetl i n 200 inl. ( ~ ixiiliiig f iiictliylciie clilririclc. :iri
