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Substituent effects in p-substituted 3-t-butyl-1,5-diarylverdazyls
72rrdwdron.
Pcrgamon
Vol. 26. pp. 4853 IO 4857.
SUBSTITUENT
Press 1970.
Priolcd
in Great Brium
EFFECTS IN p-SUBSTITUTED 1,5-DIARYLVERDAZYLS’ F. A.
3-T-BUTYL-
NEUGEBAUER
Max-Planck-lnstitut fiir Medizinische Forschung, (Receioed in the UK 10 June 1970; Acceptedfor
Heidelberg,
West Germany
publication
2 July 1970)
Abstract--A series of verdazyls with electron donating and electron withdrawing substituents and the corresponding verdazylium salts were prepared. The substituent effects on ESR and UV spectra are discussed in the light of Walter’s hypothesis of radical systems.
ACCORDING to Walter’s hypothesis’ of substituent effects in free radicals, verdazyls should be classified as 0 radicals, because they contain the same structural elements as hydrazyls. Radicals of class 0 (for opposite effects of donor and acceptor substituents) should exhibit behaviour consistent with the Hammett relationship, and donor and acceptor substituents should shift both the ESR hyperfine splitting constants and the first UV absorption maximum in opposite directions. Because of difficulties in preparing and studying most series of free radicals only a few investigations have been made over a wide enough range of substituents or measured properties to form a conclusive picture of radical behaviour. This lack of experimental data and the exceptional stability of the verdazyls prompted us to prepare a series of p-substituted 3-t-butyL2,5diarylverdazyls. N-N’ \ -CT
H N=N’
CHIO, BF,
N-N
-CT
CH, N=;’
\
/
N-3: CH,O, B-
-C!
\
II
I
. N-N;
\ CH,
Ill
R R
N-N KH,),C-Ct
IIIa IlIb
\ CH,
IIIC
IIId IIIe HIf
T&N’ 111
NO, CN COOCH, H CH, OCH,
m.p. (dec) 195-196” 204-205” 13&131” 108-10!T5 120-122” 86 87”
R
The verdazyls IIIa-f, especially Illa-c with electron withdrawing substituents, were obtained by modifying a general verdazyl preparation procedure.3 The cyclization of formazan I with paraformaldehyde in the presence of BF3 in unpolar solvents (CHC13, 4853
F. A. NEUGEBAUER
4854
R N-N
IVa IVb IVC IVd IVe IVI
\ (CH,),C-C;
CH,
FeCI;
N&j’
IV
NO, CN COOCH, H CH, OCH,
m.p. (dec) 169-170”
168-169” 175176” 16>1MPs 150-151” 151-152”
R
benzene) yields the verdazylium salt II, which is readily reduced by formaldehyde in basic medium to give the verdazyl III. The verdazylium-FeCl, salts IVa-f were prepared by oxidation of the verdazyls IIIa-f with FeC1,.4 The ESR nitrogen splitting constants of the verdazyls IIIa-f are summarized in Table 1. The spectra consist of 9 groups, which are not further resolved in detail. Fig 1 gives as an example the ESR spectrum of IIId. The assignment of the nitrogen splittings was done by comparison with ESR data of other verdazyls, including some which were labelled with 15N.6 The values in Table 1 show that only relatively small changes of aNL’ are obtained by varying the p-substituents of the phenyl rings. However, the observed shifts obey a Hammett relationship consistent with the classification of the radicals in class 0. \ L
/p-N (C"3)pC\~_N,
Vl JI i
\CH 2
‘r
, GAUSS
0\-/ FIG 1. First
derivative
ESR spectrum
of 3-t-butyl-1,5diphenylverdazyl solution.
IIId in benzene
The UV absorption data of the verdazyls IIIa-f are summarized in Table 2. The first absorption band of these radicals is near 700 rnp, which is typical for verdazyls.3 Substitution of IIId, both by electron withdrawing substituents (IIIa+c) and by electron donating substituents (IIIe, f), results in a bathochromic shift of the first band of IIId from 672 rnh a result not expected for radicals of type 0.’
4855
Substituent effects in p-substituted 3-t-butyl-1,Sdiarylverdazyls TABLE I. ESR HYPERFINE SPLITTING CONSTANIS (gauss) OF THE VERDAZYLS
IIIa IIIb IIIC IIId IIIe IIIf
NO, CN COOCH, H CH, OCH,
4.9 52 54 5,9 6.2 6.5
6.0 60 6.0 59 5.9 59
Ma-f IN BENZENE sownoN
0.83 088 090 1 1.05 1.10
Verdazyls have an odd number of both n-electrons and methine groups and can be considered to be polymethine cyanine radicals of the genera1 type V.’ V
X-N
A-x
+B
X-rj
n = 1.3.5
N-N’
III
_ &’
N-N .
CI
’ 6‘c’ 1.’ ‘/\ N-N
-C’
\\N_Nx
\
\
TABLE 2. UV ABSORPTION DATA OF THE VERDAZYLS llla-fm
IIIa IIIb IIIC IIId IIIe IIIf
NO, CN COOCH, H CH, OCH,
275 279 243 258 245
/
(4.23), (421X (412), (419), (4.25).
287s 293 280 290s
364 (4*21), 348 (4.23). 350 (3-69), 320 (3.73). 335 338
(4.30X (436), (4.38). (4.05), (4.15), (4.18),
420 422 333 380
DIOXANESOLUTION
527 (4+M), 435s (4Q7), 440s (4-05X 373 (368),
(4.21), (4.02), (4U4), (3.88),
704 690 690 672 679 690
(3.93) (390) (3.91) (3.77) (3.80) (3.81)
The C-6 bridge in the verdazyls connects the cyanine chain to form a 6-membered ring system and fixes the cyanine system in a cis-cis arrangement. One would expect for electrically neutral polymethine cyanines that, generally, each enlargement of the x-system, of X in V, e.g. by substitution, should result in a bathochromic shift of the first X--R*band, an effect actually observed in the verdazyl series III. The bathochromic shifts in the series III are simply a consequence of the enlargement of the conjugated system by substitution, which stabilizes the first excited state to a greater extent than the ground &ate and therefore lowers the excitation energy nearly independently from the electron donating or electron accepting power of the substituents. The x-system is also influenced in the sense ofan enlargement by substitution at C-3 (the meso position of the polymethine cyanine system). In 3-R- 1,5diphenylverdazyls dissolved in dioxane one observes the following increasing bathochromic shift depending on the nature of R : H : 658 rnp (log E 3.72) < C(CH,), ; 672 (3.77) < CH, ; 680 (3.75) < C6H5 ; 720 (3066)~ < p-CBH40CH,; 732 (3.62)4 < p-CBH4N0,; 734 (3.61).4 VI
\ /
N-N&&J’ \
+a
\+
/
I
N=N,=N-NC
4856
F. A. NEUGERAUER
Similarly, the verdazylium salts IV can be considered to be azacyanine cations of the general formula VI, in which two -CR= groups are replaced by -N=. Again the C-6 bridge connects the cyanine chain to form a &membered ring system in a cis-cis arrangement. In cyanine cations electron donating substituents shift the absorption maxima considerably to longer wavelengths, while electron withdrawing substituents yield only small effects. The UV data of the verdazylium salts IVa-f, summarized in Table 3, show this trend clearly. Each substitution of the system IV by R results in a bathochromic shift of the first II--R*band, and the bathochromic shift is significantly larger if the substituent is an electron donating one. TABLE 3. UV ABSORPTION DATAOFTHE
R IVa IVb WC IVd IVe IVf
NO, CN COOCH, H CH, OCH,
&.
VERDAZYLILJMSALTS IVa-f
IN FORMIC ACID
in mp (log e)
290 (440). 340s 348 350 349 365 410
(3.84). (3.86) (3,86), (3.88). (3.93). (4.03),
512 512 513 503 525 564
(4.29) (428) (4.32) (4.19) (4.22) (4.31)
The UV data of the verdazyls do not fullil the specifications for 0 radicals. It seems to us that the combination of UV and ESR data as specifications for the classification of radicals is problematic, since the spin density distribution is a property of the ground state, whereas the optical transitions correspond to the energy differences between the ground state and excited states of the molecule. The effect observed in the model compounds for 0 radicals, that donor and acceptor substituents in the I-picryl-2,2diarylhydrazyl series shift the UV absorption in opposite directions,’ might be the result of the strong dipoles in these molecules, in which an extremely strong electron acceptor, the picryl group, is combined with a donator system varied by substitution. The only conclusion which can be drawn to date from the available data is that in many p-substituted radical systems s- lo dominant ESR hyperfine splitting constants satisfactorily follow the Hammett relationship, a general feature of radicals which is not restricted to radicals of type 0. Lotta and Taft’ ’ have found Hammett-like substituent effects for the nitrogen hyperfine splitting constant in N,N-dimethylaniline cation radicals, from their structure typical S radicals. EXPERIMENTAL 3-t-Butyl-l,5-bis(4-nirrophenyl)verdozyl (Illa). Paraformaldehyde (0.5 g) in CHCI, (20 ml) + BF,-ethyletherate (2 ml) were stirred for 5 min; a soln of 3-t-butyl-1,5-bis(4-nitrophenyl)formaxan (1 g)” in CHCI, (100 ml) was added and the mixture stirred for 1 hr. The mixture was cooled to Cl’and kept at this temp while 38 % aqueous formaldehyde (10 ml) and afterwards 2N NaOH (25 ml) were added Stirring was continued for 30 min. The mixture was washed several times with Hz0 and evaporated in vacuum. The residue yielded from acetone-MeOH black crystals (085 g) m.p. 195-196” (dec). (Found : C, 56.38; H, 4.98 ; N, 22.10. CL8Hi9N601 requires: C, 56.39; H, 500; N, 21.92%). 3-t-Butyl-1,5-bis(4-cyanophenyl)verdazyl (IIIb). Paraformaldehyde (0.5 g) + CHCI, (20 ml) + BF,ethyletherate (2 ml); 3-t-butyl-1,5-bis(4cyanophenyl) formazan (1 g)” in CHCI, (100 ml); 38% aqueous formaldehyde (IO ml) and 2N NaOH (25 ml) were treated as above (Illa) Crystallized twice from acetoneMeOH green black crystals (0.76 g) m.p. 204-205” (dec) were obtained. (Found : C, 70-14; H, 5.67 ; N, 24.47. C 20H IP N 6 requires: C. 69.95; H, 5.58; N, 24.47 %).
Substituent effects in p-substituted 3-t-butyl-l.Sdiarylverdaxyls
4857
3-t-Buty&l,5-bis(4-metho~ycorbonylphenyl)oerdozyl (Ilk). Paraformaldehyde(O5 g) + benxene(20 ml) + BFz-ethyletherate (2 ml); 3-t-butyl-1.5-bis(Cmethoxycarbonylphenyl~orma~ (10 g)12 in benzene (100 ml); 38 % aqueous formaldehyde (IO ml) and 2 N NaOH (25 ml) were treated as above (IIIa). The residue was chromatographed on AI,Oz (Brockmann) to give upon elution with benzene from MeOH dark green crystals (@56 g) m.p. 130-131” (dec). (Found: C, 64.74; H, 6.17; N, 13.72. C2zHzsN404 requires: C, 64.53; H, 6.15; N, 13.68%). 3-t-Bury/-1.5-diphenyluerdazyl (IIId). Paraformaldehyde (1 g) + CHCI, (50 ml) + BF,-ethyletherate (10 ml); 3-t-butyl-1,5diphenylformaxan (5a g)s in CHCI, (150 ml); 38% aqueous formaldehyde (20 ml) + 2 N NaOH (100 ml) were treated as above (111~).The residue was chromatographed on AI,O, (Woelm basic) to give upon elution with cyclohexane from hexane dark green prisms (3.3 g) m.p. 108-109” (dec). (Found: C, 73.92; H, 7.24; N, 19.28. CIsH2iNI requires: C. 73.68; H, 7.22; N, 19.10%). 3-t-Buryl-1,5_di-ptolylverdazyl (IlIe). Paraformaldehyde (1 g) + benzene (50 ml) + BFs-ethyletherate (5 ml); 3-t-butyl-1,5-di-ptolylformazan (2.5 g)12 in benxenc (100 ml); 38 % aqueous formaldehyde (20 ml) + 2 N NaOH (70 ml) were treated as above (Illa). From Me,OH green black crystals (2.1 g) m.p. 12@122” (dec) were obtained. (Found: C, 74.56; H, 764; N, 17.27.C2aHz5N1 requires: C, 74.72; H, 7.84; N, 17.43%). 3-t-Butyl-l.5-bis(4-nrerhoxyphenyl)oerdazyl (IlIt). 3-t-Butyl-1,5-bis(4-methoxyphenyl)fonnaxan (1 g)‘z + NaHSO, (3 g) + 38 % aqueous formaldehyde (5 ml) in dimethylformamide (50 ml) were stirred for 1 hr. cooled to O”,38 ‘A aqueous formaldehyde (5 ml) was added and then 2 N NaOH dropwise until the colour of the reaction mixture changed to green. The product was separated by addition of Hz0 and crystallized twice from ligroin yielding black prisms (068 g). m.p. 86-87” (de@. (Found: C, 68.28: H, 7.26; N, 15.80. C20H2SN402 requires: C, 67.96; H, 7.13; N, 15.88%). 3-t-Buryl-1,5-bis(4-nitrophenyl)oerdazyIiul-FeCl~ (IVa). Compound IIIa (200 mg) in HCOOH (5 ml) + FeCI, .6H 2O (0.5 g) in HCOOH (3 ml) yielded dark brown crystals (200 mg), m.p. 169-170” (deck (Found : C, 37.30; H, 3.32; Fe, 9.21 ; N, 14.16. C, sH ,&I,FeN,O, requires: C, 37.21; H, 3.30; Fe, 9.61; N, 1446%). 3-t-Butyl-1,5-bis(Ccyanophenyl)erdazylium-Fe& (IVb). From Illb. as above: dark brown crystals (150 mg), m.p. 168-169” (dec) separated. (Found: C, 44.29; H, 3.67; Fe, 10.45, N, 15.37. CzOH,&I,FeN, requires: C, 44.39; H. 3.54; Fe, 10.32; N, 15.53%). 3-t-Butyl-l,5-bis(Cn~e~ho~yywbonylpheny[)oerdazyliu~~-FeCI, (IVc). From 111~as above: dark brown crystals (180 mg), m.p. 175-176” (dec) separated. (Found: C, 43.75; H, 4.24; Fe, 892; N, 944. C,,H,,CI,FeN,O, requires: C, 43.52; H, 4.15; Fe, 9.20; N, 9.23%). 3-t-Bury/-1,5-di-prolyluerdazyliunl-FeC1, (IVe). From IIIe as above: dark brown crystals (120 mg), m.p. 15&151”(dec)separated.(Found: C&47; H,4.89; Fe, 10.99; N, 1082.C,,H,,CI,FeN,requires: C.4627; H. 4.85 ; Fe, 10.76; N, 1@79%). 3-t-Butyl-l,5-bi~4-methoxypheny[)verdazylium-FeCl4 (IVB. From IIIf as above: black crystals (140 mg). m.p. 151-152” (dec) separated. (Found: C, 43.72; H, 4.69; Fe, 9.82; N, 998. C to H 25 Cl 4 FeN,Oz requires: C, 43.59; H. 4.57; Fe, 10.13; N, 10.17%).
REFERENCES
’ Part 18 of verdaxyls. Part 17: F. A. Neugebauer and H. Trischmann, Polymer Letters 6,255 (1968) 2 R. I. Walter, J. Am. Chem. Sot. g& 1923, 1930 (1966) 3 R. Kuhn and H. Trischmann, Mh. C/tern. 95,457 (1964); R. Kuhn, F. A. Neugebauer and H. Trischmann, Ibid. 97,525 (1%6) * R. Kuhn, F. A. Neugebauer and H. Trischmann, Ibid. W, 1280 (1966) s F. A. Neugebauer and H. Trischmann, Liebigs Ann. 706,107 (1967) ’ F. A. Neugebauer, Mh. Chem. Ss, 23 1 (1967); Hobilitationsschrif, Heidelberg (1969)
’ S. Diihne, Z. Chemie5, 441. 448 (1965) s A. H. Maki and D. H. Geske, J. Am Gem. Sot. 83.1852 (1961); P. L. Kolker and W. A. Waters, J. Chem. Sot. 1136 (1964) ’ H. LeMaire, Y. Marechal, R. Ramasseul, and A. Rassat, Bull. Sot. Chim. Fr. 372 (1965) lo E. T. Strom, J. Am. Chem. Sot. gS, 2065 (1966) I’ B. M. Latta and R. W. Taft, Ibid. 89,5172 (1967) ’ 2 F. A. Neugebauer, Tetrahedron 26,4843 (1970)
Pcrgamon
Vol. 26. pp. 4853 IO 4857.
SUBSTITUENT
Press 1970.
Priolcd
in Great Brium
EFFECTS IN p-SUBSTITUTED 1,5-DIARYLVERDAZYLS’ F. A.
3-T-BUTYL-
NEUGEBAUER
Max-Planck-lnstitut fiir Medizinische Forschung, (Receioed in the UK 10 June 1970; Acceptedfor
Heidelberg,
West Germany
publication
2 July 1970)
Abstract--A series of verdazyls with electron donating and electron withdrawing substituents and the corresponding verdazylium salts were prepared. The substituent effects on ESR and UV spectra are discussed in the light of Walter’s hypothesis of radical systems.
ACCORDING to Walter’s hypothesis’ of substituent effects in free radicals, verdazyls should be classified as 0 radicals, because they contain the same structural elements as hydrazyls. Radicals of class 0 (for opposite effects of donor and acceptor substituents) should exhibit behaviour consistent with the Hammett relationship, and donor and acceptor substituents should shift both the ESR hyperfine splitting constants and the first UV absorption maximum in opposite directions. Because of difficulties in preparing and studying most series of free radicals only a few investigations have been made over a wide enough range of substituents or measured properties to form a conclusive picture of radical behaviour. This lack of experimental data and the exceptional stability of the verdazyls prompted us to prepare a series of p-substituted 3-t-butyL2,5diarylverdazyls. N-N’ \ -CT
H N=N’
CHIO, BF,
N-N
-CT
CH, N=;’
\
/
N-3: CH,O, B-
-C!
\
II
I
. N-N;
\ CH,
Ill
R R
N-N KH,),C-Ct
IIIa IlIb
\ CH,
IIIC
IIId IIIe HIf
T&N’ 111
NO, CN COOCH, H CH, OCH,
m.p. (dec) 195-196” 204-205” 13&131” 108-10!T5 120-122” 86 87”
R
The verdazyls IIIa-f, especially Illa-c with electron withdrawing substituents, were obtained by modifying a general verdazyl preparation procedure.3 The cyclization of formazan I with paraformaldehyde in the presence of BF3 in unpolar solvents (CHC13, 4853
F. A. NEUGEBAUER
4854
R N-N
IVa IVb IVC IVd IVe IVI
\ (CH,),C-C;
CH,
FeCI;
N&j’
IV
NO, CN COOCH, H CH, OCH,
m.p. (dec) 169-170”
168-169” 175176” 16>1MPs 150-151” 151-152”
R
benzene) yields the verdazylium salt II, which is readily reduced by formaldehyde in basic medium to give the verdazyl III. The verdazylium-FeCl, salts IVa-f were prepared by oxidation of the verdazyls IIIa-f with FeC1,.4 The ESR nitrogen splitting constants of the verdazyls IIIa-f are summarized in Table 1. The spectra consist of 9 groups, which are not further resolved in detail. Fig 1 gives as an example the ESR spectrum of IIId. The assignment of the nitrogen splittings was done by comparison with ESR data of other verdazyls, including some which were labelled with 15N.6 The values in Table 1 show that only relatively small changes of aNL’ are obtained by varying the p-substituents of the phenyl rings. However, the observed shifts obey a Hammett relationship consistent with the classification of the radicals in class 0. \ L
/p-N (C"3)pC\~_N,
Vl JI i
\CH 2
‘r
, GAUSS
0\-/ FIG 1. First
derivative
ESR spectrum
of 3-t-butyl-1,5diphenylverdazyl solution.
IIId in benzene
The UV absorption data of the verdazyls IIIa-f are summarized in Table 2. The first absorption band of these radicals is near 700 rnp, which is typical for verdazyls.3 Substitution of IIId, both by electron withdrawing substituents (IIIa+c) and by electron donating substituents (IIIe, f), results in a bathochromic shift of the first band of IIId from 672 rnh a result not expected for radicals of type 0.’
4855
Substituent effects in p-substituted 3-t-butyl-1,Sdiarylverdazyls TABLE I. ESR HYPERFINE SPLITTING CONSTANIS (gauss) OF THE VERDAZYLS
IIIa IIIb IIIC IIId IIIe IIIf
NO, CN COOCH, H CH, OCH,
4.9 52 54 5,9 6.2 6.5
6.0 60 6.0 59 5.9 59
Ma-f IN BENZENE sownoN
0.83 088 090 1 1.05 1.10
Verdazyls have an odd number of both n-electrons and methine groups and can be considered to be polymethine cyanine radicals of the genera1 type V.’ V
X-N
A-x
+B
X-rj
n = 1.3.5
N-N’
III
_ &’
N-N .
CI
’ 6‘c’ 1.’ ‘/\ N-N
-C’
\\N_Nx
\
\
TABLE 2. UV ABSORPTION DATA OF THE VERDAZYLS llla-fm
IIIa IIIb IIIC IIId IIIe IIIf
NO, CN COOCH, H CH, OCH,
275 279 243 258 245
/
(4.23), (421X (412), (419), (4.25).
287s 293 280 290s
364 (4*21), 348 (4.23). 350 (3-69), 320 (3.73). 335 338
(4.30X (436), (4.38). (4.05), (4.15), (4.18),
420 422 333 380
DIOXANESOLUTION
527 (4+M), 435s (4Q7), 440s (4-05X 373 (368),
(4.21), (4.02), (4U4), (3.88),
704 690 690 672 679 690
(3.93) (390) (3.91) (3.77) (3.80) (3.81)
The C-6 bridge in the verdazyls connects the cyanine chain to form a 6-membered ring system and fixes the cyanine system in a cis-cis arrangement. One would expect for electrically neutral polymethine cyanines that, generally, each enlargement of the x-system, of X in V, e.g. by substitution, should result in a bathochromic shift of the first X--R*band, an effect actually observed in the verdazyl series III. The bathochromic shifts in the series III are simply a consequence of the enlargement of the conjugated system by substitution, which stabilizes the first excited state to a greater extent than the ground &ate and therefore lowers the excitation energy nearly independently from the electron donating or electron accepting power of the substituents. The x-system is also influenced in the sense ofan enlargement by substitution at C-3 (the meso position of the polymethine cyanine system). In 3-R- 1,5diphenylverdazyls dissolved in dioxane one observes the following increasing bathochromic shift depending on the nature of R : H : 658 rnp (log E 3.72) < C(CH,), ; 672 (3.77) < CH, ; 680 (3.75) < C6H5 ; 720 (3066)~ < p-CBH40CH,; 732 (3.62)4 < p-CBH4N0,; 734 (3.61).4 VI
\ /
N-N&&J’ \
+a
\+
/
I
N=N,=N-NC
4856
F. A. NEUGERAUER
Similarly, the verdazylium salts IV can be considered to be azacyanine cations of the general formula VI, in which two -CR= groups are replaced by -N=. Again the C-6 bridge connects the cyanine chain to form a &membered ring system in a cis-cis arrangement. In cyanine cations electron donating substituents shift the absorption maxima considerably to longer wavelengths, while electron withdrawing substituents yield only small effects. The UV data of the verdazylium salts IVa-f, summarized in Table 3, show this trend clearly. Each substitution of the system IV by R results in a bathochromic shift of the first II--R*band, and the bathochromic shift is significantly larger if the substituent is an electron donating one. TABLE 3. UV ABSORPTION DATAOFTHE
R IVa IVb WC IVd IVe IVf
NO, CN COOCH, H CH, OCH,
&.
VERDAZYLILJMSALTS IVa-f
IN FORMIC ACID
in mp (log e)
290 (440). 340s 348 350 349 365 410
(3.84). (3.86) (3,86), (3.88). (3.93). (4.03),
512 512 513 503 525 564
(4.29) (428) (4.32) (4.19) (4.22) (4.31)
The UV data of the verdazyls do not fullil the specifications for 0 radicals. It seems to us that the combination of UV and ESR data as specifications for the classification of radicals is problematic, since the spin density distribution is a property of the ground state, whereas the optical transitions correspond to the energy differences between the ground state and excited states of the molecule. The effect observed in the model compounds for 0 radicals, that donor and acceptor substituents in the I-picryl-2,2diarylhydrazyl series shift the UV absorption in opposite directions,’ might be the result of the strong dipoles in these molecules, in which an extremely strong electron acceptor, the picryl group, is combined with a donator system varied by substitution. The only conclusion which can be drawn to date from the available data is that in many p-substituted radical systems s- lo dominant ESR hyperfine splitting constants satisfactorily follow the Hammett relationship, a general feature of radicals which is not restricted to radicals of type 0. Lotta and Taft’ ’ have found Hammett-like substituent effects for the nitrogen hyperfine splitting constant in N,N-dimethylaniline cation radicals, from their structure typical S radicals. EXPERIMENTAL 3-t-Butyl-l,5-bis(4-nirrophenyl)verdozyl (Illa). Paraformaldehyde (0.5 g) in CHCI, (20 ml) + BF,-ethyletherate (2 ml) were stirred for 5 min; a soln of 3-t-butyl-1,5-bis(4-nitrophenyl)formaxan (1 g)” in CHCI, (100 ml) was added and the mixture stirred for 1 hr. The mixture was cooled to Cl’and kept at this temp while 38 % aqueous formaldehyde (10 ml) and afterwards 2N NaOH (25 ml) were added Stirring was continued for 30 min. The mixture was washed several times with Hz0 and evaporated in vacuum. The residue yielded from acetone-MeOH black crystals (085 g) m.p. 195-196” (dec). (Found : C, 56.38; H, 4.98 ; N, 22.10. CL8Hi9N601 requires: C, 56.39; H, 500; N, 21.92%). 3-t-Butyl-1,5-bis(4-cyanophenyl)verdazyl (IIIb). Paraformaldehyde (0.5 g) + CHCI, (20 ml) + BF,ethyletherate (2 ml); 3-t-butyl-1,5-bis(4cyanophenyl) formazan (1 g)” in CHCI, (100 ml); 38% aqueous formaldehyde (IO ml) and 2N NaOH (25 ml) were treated as above (Illa) Crystallized twice from acetoneMeOH green black crystals (0.76 g) m.p. 204-205” (dec) were obtained. (Found : C, 70-14; H, 5.67 ; N, 24.47. C 20H IP N 6 requires: C. 69.95; H, 5.58; N, 24.47 %).
Substituent effects in p-substituted 3-t-butyl-l.Sdiarylverdaxyls
4857
3-t-Buty&l,5-bis(4-metho~ycorbonylphenyl)oerdozyl (Ilk). Paraformaldehyde(O5 g) + benxene(20 ml) + BFz-ethyletherate (2 ml); 3-t-butyl-1.5-bis(Cmethoxycarbonylphenyl~orma~ (10 g)12 in benzene (100 ml); 38 % aqueous formaldehyde (IO ml) and 2 N NaOH (25 ml) were treated as above (IIIa). The residue was chromatographed on AI,Oz (Brockmann) to give upon elution with benzene from MeOH dark green crystals (@56 g) m.p. 130-131” (dec). (Found: C, 64.74; H, 6.17; N, 13.72. C2zHzsN404 requires: C, 64.53; H, 6.15; N, 13.68%). 3-t-Bury/-1.5-diphenyluerdazyl (IIId). Paraformaldehyde (1 g) + CHCI, (50 ml) + BF,-ethyletherate (10 ml); 3-t-butyl-1,5diphenylformaxan (5a g)s in CHCI, (150 ml); 38% aqueous formaldehyde (20 ml) + 2 N NaOH (100 ml) were treated as above (111~).The residue was chromatographed on AI,O, (Woelm basic) to give upon elution with cyclohexane from hexane dark green prisms (3.3 g) m.p. 108-109” (dec). (Found: C, 73.92; H, 7.24; N, 19.28. CIsH2iNI requires: C. 73.68; H, 7.22; N, 19.10%). 3-t-Buryl-1,5_di-ptolylverdazyl (IlIe). Paraformaldehyde (1 g) + benzene (50 ml) + BFs-ethyletherate (5 ml); 3-t-butyl-1,5-di-ptolylformazan (2.5 g)12 in benxenc (100 ml); 38 % aqueous formaldehyde (20 ml) + 2 N NaOH (70 ml) were treated as above (Illa). From Me,OH green black crystals (2.1 g) m.p. 12@122” (dec) were obtained. (Found: C, 74.56; H, 764; N, 17.27.C2aHz5N1 requires: C, 74.72; H, 7.84; N, 17.43%). 3-t-Butyl-l.5-bis(4-nrerhoxyphenyl)oerdazyl (IlIt). 3-t-Butyl-1,5-bis(4-methoxyphenyl)fonnaxan (1 g)‘z + NaHSO, (3 g) + 38 % aqueous formaldehyde (5 ml) in dimethylformamide (50 ml) were stirred for 1 hr. cooled to O”,38 ‘A aqueous formaldehyde (5 ml) was added and then 2 N NaOH dropwise until the colour of the reaction mixture changed to green. The product was separated by addition of Hz0 and crystallized twice from ligroin yielding black prisms (068 g). m.p. 86-87” (de@. (Found: C, 68.28: H, 7.26; N, 15.80. C20H2SN402 requires: C, 67.96; H, 7.13; N, 15.88%). 3-t-Buryl-1,5-bis(4-nitrophenyl)oerdazyIiul-FeCl~ (IVa). Compound IIIa (200 mg) in HCOOH (5 ml) + FeCI, .6H 2O (0.5 g) in HCOOH (3 ml) yielded dark brown crystals (200 mg), m.p. 169-170” (deck (Found : C, 37.30; H, 3.32; Fe, 9.21 ; N, 14.16. C, sH ,&I,FeN,O, requires: C, 37.21; H, 3.30; Fe, 9.61; N, 1446%). 3-t-Butyl-1,5-bis(Ccyanophenyl)erdazylium-Fe& (IVb). From Illb. as above: dark brown crystals (150 mg), m.p. 168-169” (dec) separated. (Found: C, 44.29; H, 3.67; Fe, 10.45, N, 15.37. CzOH,&I,FeN, requires: C, 44.39; H. 3.54; Fe, 10.32; N, 15.53%). 3-t-Butyl-l,5-bis(Cn~e~ho~yywbonylpheny[)oerdazyliu~~-FeCI, (IVc). From 111~as above: dark brown crystals (180 mg), m.p. 175-176” (dec) separated. (Found: C, 43.75; H, 4.24; Fe, 892; N, 944. C,,H,,CI,FeN,O, requires: C, 43.52; H, 4.15; Fe, 9.20; N, 9.23%). 3-t-Bury/-1,5-di-prolyluerdazyliunl-FeC1, (IVe). From IIIe as above: dark brown crystals (120 mg), m.p. 15&151”(dec)separated.(Found: C&47; H,4.89; Fe, 10.99; N, 1082.C,,H,,CI,FeN,requires: C.4627; H. 4.85 ; Fe, 10.76; N, 1@79%). 3-t-Butyl-l,5-bi~4-methoxypheny[)verdazylium-FeCl4 (IVB. From IIIf as above: black crystals (140 mg). m.p. 151-152” (dec) separated. (Found: C, 43.72; H, 4.69; Fe, 9.82; N, 998. C to H 25 Cl 4 FeN,Oz requires: C, 43.59; H. 4.57; Fe, 10.13; N, 10.17%).
REFERENCES
’ Part 18 of verdaxyls. Part 17: F. A. Neugebauer and H. Trischmann, Polymer Letters 6,255 (1968) 2 R. I. Walter, J. Am. Chem. Sot. g& 1923, 1930 (1966) 3 R. Kuhn and H. Trischmann, Mh. C/tern. 95,457 (1964); R. Kuhn, F. A. Neugebauer and H. Trischmann, Ibid. 97,525 (1%6) * R. Kuhn, F. A. Neugebauer and H. Trischmann, Ibid. W, 1280 (1966) s F. A. Neugebauer and H. Trischmann, Liebigs Ann. 706,107 (1967) ’ F. A. Neugebauer, Mh. Chem. Ss, 23 1 (1967); Hobilitationsschrif, Heidelberg (1969)
’ S. Diihne, Z. Chemie5, 441. 448 (1965) s A. H. Maki and D. H. Geske, J. Am Gem. Sot. 83.1852 (1961); P. L. Kolker and W. A. Waters, J. Chem. Sot. 1136 (1964) ’ H. LeMaire, Y. Marechal, R. Ramasseul, and A. Rassat, Bull. Sot. Chim. Fr. 372 (1965) lo E. T. Strom, J. Am. Chem. Sot. gS, 2065 (1966) I’ B. M. Latta and R. W. Taft, Ibid. 89,5172 (1967) ’ 2 F. A. Neugebauer, Tetrahedron 26,4843 (1970)