M a y s , 193s
A
[CONTRIBUTION FROM THE
DEPARTMENT OF CHEMISTRY,
Azo Compounds. BY
SEVEN-hlE:MBERED C Y C L I C L I Z 0 C O M P O U N D
2317
POLYTECHNIC IXSTITUTE OF BROOKLYX]
A Seven-membered Cyclic Azo Compound
c. G. O V E R B E R G E R AND JOSEPH c. L O h I B A R D I N 0 2 RECEIVED NOVEMBER 13, 1957
The seven-membered cyclic azo compound 3,7-diphenyl-1,2-diaza-l-cycloheptene ( I ) has been prepared. Spectral and kinetic properties of I support the postulated cis nature of the azo link in a seven-membered ring. The decompoiiition of I gave mixtures of cis- and trans-1,2-diphenylcyclopentane and 1,5-diphenyl-l-pentene, the products expected from nonstereospecific combination or disproportionation of the 1,5-diphenyl-1,5-pentadiyl biradical. At lower decomposjtion temperatures, isomerization of I to the cyclic hydrazone, 3,7-diphenyl-1,2-diaza-2-cycloheptene(I\'), was found to compete with normal thermal decomposition. A reason for previous3 unsuccessful attempts to prepare I is offered.
As part of a continuing program to synthesize tion between 1,4-diphenyl-1,3-butadie11e and azocyclic azo compounds which would thermally de- dicarboxylic ester followed by hydrogenation and compose to give moderately active biradicals in saponification. The product, a six-membered cysolution, we have synthesized the seven-membered clic azo compound, 3,6-diphenyl-3,4,5,6-tetrahydrocyclic azo compound 3,7-diphenyl-1,2-diaza-lpyridazine, exhibited an abnormal azo absorption, cycloheptene (I). A,, 387 mp, log E 2.89, which is attributed to the CH2 cis configuration forced on the azo bond. / \ A compound of type I with only one phen:yl group also has been prepared recently by a similar meth~d.A ~ five-membered cyclic azo co-mpound prepared by a Diels-Alder reaction of cyclopentak=N I diene with azo-dicarboxylic ester has been deThe small ring size of I forces a cis configuration scribeda; however, no spectral or kinetic data on on the azo link and enables a comparison of the this interesting bicyclic azo compound were respectral and kinetic data of I with linear, trans-azo ported.8 Two eight-membered cyclic azo comcompounds of similar structure. It was also of p o u n d ~ 'also ~ ~ ~have been reported. The eightinterest to study the decomposition products of membered cyclic azo analog of I exhibitslb Xmax such a cyclic azo compound in order to compare the 368 mp, log E 1.65; the interpretation of these relative amounts of coupled and disproportionated values is under investigation. The absorption for products from biradicals of this type with those of the eight-memberedlb analog of I (at 368 :mp) lies monoradicals in solution. almost midway between a trans, acyclic azo abThe chemistry of large, cyclic, bis-azo compounds sorption (355 m ~ and ) ~the absorption of a. cis-azo previously has been studied by Overberger and link in the six- and seven-membered rings (387 L a ~ k i n . These ~ large (24, 28) membered bis-azo and 389 mp). These data would indicate that an compounds can exist with a trans-azo configura- eight-membered cyclic azo compound is the smalltion and comparison of spectral and kinetic data est ring which will permit the azo link to relieve support a trans-azo link. For example, the 24- some of the strain associated with a cis-azo Iconfigumembered cyclic bis-azo compound, 3,12,15,24- ration. Larger rings (24,28-membered) have azo tetraphenyl - 1,2,13,14 - tetraaza - 1,13 - cyclo- bonds which assume the more stable trans configutetra~osadiene~ exhibits an azo absorption at 360 ration. mp, log E 2.06 and decomposes a t 110.8' with a rate This paper will report the synthesis, kinetic and constant of 7.6 X 10-5 sec.-l. Similarly the spectral properties and decomposition products trans, acyclic azo compound azo-1-phenylethane ex- of the seven-membered cyclic azo compound (I). h i b i t ~an ~ absorption maximum a t 355 mp, log E A. Preparation of the Azo Compound.--Previ1.77 and decomposes a t 110.3" with a rate constant ous unsuccessful attempts to synthesize I provided a of 16.9 X sec.-l. A smaller cyclic azo com- starting point. Thus, Overberger and M onagle3 pound (6-, 7- or 8-membered) should require a cis reported the synthesis of the precursor hydrazine, configuration for the azo link. Recently, a six- 3,7-diphenyl-l,2-diazacycloheptane (111); however, membered cyclic compound of type I has been its apparently anomalous oxidation behavior sugprepared by Cohen, et u Z . , ~ by a Diels-Alder reac- gested that I11 was of unusual stability or that I (1) (a) This is the 2 1 3 in a series of papers concerned with the was of high instability. These workers eniployed preparation and decomposition of azo compounds. For the previous the following sequence of reactions in an attempt to paper in this series, see C. G. Overberger, J . G. Lombardino and R. G . synthesize I. 79, 6430 (1957). (b) For a preliminary report Hiskey, THIS JOURNAL, Compound I11 was reported3 as a liquid. whose of this work, see C . G. Overberger, J. G. Lombardino, I. Tashlick and R. G. Hiskey, ibid., 79, 2662 (1957). infrared spectrum exhibited an N-H stretching (2) This paper comprises a portion of a dissertation presented by frequency. Analysis of 111 supported a hydrazine Joseph G. Lombardino in partial fullillment of the requirements for the structure, but when a variety of methods were emdegree of Doctor of Philosophy in the Graduate School of the Polyployed3 in an effort to oxidize I11 to the a~ L,O comtechnic Institute of Brooklyn. (3) c. G . Overberger and J. J. Xionagle, TEIS.JOURNAL,78, 4470 pound I, none was successful. Only bromine in ( 1 956). aqueous acid gave a reaction, yielding the unex(4) C. G. Overberger and Xi. Lapkin, ibid., 77, 4651 (1955). (5) S. G. Cohen, S. J. Groszos and D. R. Sparrow, ;bid., 72, 3947 (1950). ( 6 ) S . C C u h e n , S. Hsiau, k
