COMMUNICATIONS TO THE EDITOR
Oct. 20, 1962
3979
visible spectrum was obtained by treating pyrindine methochloride (obtained by passing an aqueous solution of (IIIb) through a Dowex 1 chloride (10) This work was supported by grants from the U. S. Public Health column) with alkali: Ak2x,rjNa0H220, 256, 320, Service and the Sational Science Foundation. 456 mp (log E = 3.53, 4.06, 3.56, 2.84). The specDEPARTMENT OF BIOLOGY ALICE J. ADLER trum was recorded rapidly as (Ib) readily decomMASSACHUSETTS INSTITUTE OF TECHNOLOGY CAMBRIDGE, MASSACHUSETTS ALEXANDERRIcn posed in aqueous solution, even at p H 8. Figure 1 shows the visible absorption spectrum RECEIVED AUGUST8, 1962 of (Ib) with a thousand-fold reduced E scale and that of the colored impurity in neat pyrindine THE TAUTOMERISM OF 5H-1-PYRINDINE with full e scale. Despite the different solvents, Sir : the two absorption bands are strikingly similar; Recently much interest' has centered on hetero- they have emax. values of 685 and 0.76, respectively. cyclic analogs of azulene, which were first described If it is assumed that N-methylation of (Ia) does forty years ago by Armit and Robinson.2 Such not alter the eman, of its visible band appreciably, compounds are iso-a-electronic with azulene with then at 20' 5H-1-pyrindine (11) contains 1.1 the heteroatom (N, 0, S) providing an electron pair parts per 1000 of the colored pseudoazulene instead of a (-CH=CH-) group; they are ex- tautomer (Ia) in equilibrium with it. This pected to resemble azulene in their ultraviolet and equilibrium can be shifted by dilution or freezing. visible absorption spectra and general aromatic It is noteworthy that N-methylation causes a properties. We wish to report evidence for the hypsochromic shift of 14 mp, but this may be due to existence of the parent pseudo-azulene3of the pyrin- the different solvents involved. dine group discussed by Armit and Robinson,z namely, 1H-1-pyrindine (Ia). prove useful for the study of natural ribonucleic acids. lo
N
R Ia,R=H b,R=Me
N
' I1
aN
1
-
R IIIa, R = H b,R=Me
rx I
I V
Robison4 prepared 5H-1-pyrindine (11) and noted that the freshly distilled liquid had an orange color which was discharged on dilution with organic solvents, and that a M solution in cyclohexane was completely transparent above 305 mp. This color was also discharged slowly by freezing the 350 400 450 500 550 600 , ~ that the material. Anderson, et ~ l . suggested A, mr. color was due to the presence of the tautomeric Fig. 1.-Full curve is for 1-methyl-1-pyridine (Ib) in pseudoazulene (Ia) . E value. Broken curve is for We have confirmed Robison's observations and 0 1 N NaOH; ordinate, neat 5H-1-pyridine a t 20' ; ordinate, 6 value. have obtained spectral evidence which suggests that the orange color of (11) is indeed due to the This estimate of approximately 0.1% of pseudopresence of (Ia) . Pyrindine (11) was left overnight azulene (Ia) in tautomeric equilibrium with (11) a t room temperature with a large excess of methyl has been confirmed by pKa measurements. The iodide. The residue, obtained by evaporation of latter compound has pKa 5.7 (determined potenthe excess methyl iodide, was crystallized from tiometrically) whereas (Ib) has pKa 8.7 (determethanol to give cream colored crystals (50%) mined spectroscopically7). If (Ia) is assumed to of pyrindine methiodide (IIIb), m.p. 248-250' have the same pKa as (Ib) (ApK, for N-methyla(dec.). Ana/. Calcd. for C9HloIN: C, 41.69; tion is normally8 about 0.2 unit), and if both tauH, 3.86; N, 5.41. Found: C, 41.30; H, 3.60; tomers (Ia) and (11) are assumed to have the same 3 , 5.27. A dark orange oil of 1-methyl - 1-pyrin- conjugate acid (IIIa), then i t follows*that the taudine (Ib) was obtained by treating (IIIb) with tomeric equilibrium constant is l o 3 in favor of (11). alkali; this material could not be isolated as i t Tautomerism between (11) and the other possible was converted rapidly into an infusible solid, 2,3-~yclopentenopyridine, 'TH-1-pyrindine has not insoluble in organic solvents. In this way i t re- been investigated. Comparison of the ultraviolet sembled its sulfur analog6 (IV) and differed from spectra of (II), and 3-vinyl~yridine'~ the more stable pseudoazulenes prepared by was not helpful. Anderson, et al.5 However, its ultraviolet and UNIVERSITY CHEMICAL LABORATORY ( 1 ) See, for example, D. Leaver, J. Smolicz and W. H. Stafford,
J . Chem. SOL.,740 (1962). (2) J. W. Armit and R . Robinson, J. Chem. SOL.,827 (1922). (3) Term originated by R . Mayer, see reference (6). (4) M. M. Robison, J . A m . Chem. SOL.,80, 6254 (1958). (5) A. G. Anderson, Jr., W. F. Harrison, R. G. Anderson and A. G. Osborne, ibid., 81, 1255 (1959). ( 6 ) R. Mayer, Anpew. Chem., 6 9 , 481 (1957); R . Mayer, J. Franke, V. HorSk, I. Hanker and R . Zahradnik, Telrahedvon Letters, Xo, 9. 289 (1961).
CAMBRIDGE, ENGLAND RECEIVED AUGUST15, 1962
C. B. REESE
(7) A. Albert and E. P. Serjeant, "Ionization Constants of Acids and Bases," Methuen and Co.,Ltd., London, 1962, pp. 69-92. (8) S. J. Angyal and C. L. Augyal, J. Chem. SOC.,1461 (1952). (9) D. W.Adamson, P. A. Barrett, I. W. Billinghurst and T. S. G. Jones, ibid., 2315 (1957). (IO) M. L. Swain, A. Eisner, C. F. Woodward and B. A. Brice, J.A m . Chem. Soc., 71, 1341 (1949).
