Deguchi, Yasuo

Nishiguchi, Hiroaki

Takaki, Hideo

Watanabe, Kohji

Yamauchi, Jun

Kyoto University Research Information Repository

Title Synthesis of Stable Free Radicals : 2, 2, 6, 6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (1)Author(s)Watanabe, Kohji; Yamauchi, Jun; Takaki, Hideo; Nishiguchi,Hiroaki; Deguchi, YasuoCitationBulletin of the Institute for Chemical Research, KyotoUniversity (1970), 48(2-3): 88-95Issue Date1970-08-22URL http://hdl.handle.net/2433/76332RightType Departmental Bulletin PaperTextversionpublisherKyoto University Bull. Inst. Chem. Res., Kyoto Univ., Vol. 48, Nos. 3-4, 1970   Synthesis of Stable Free Radicals : 2, 2, 6, 6-Tetramethyl-4-         Hydroxypiperidine-1-Oxyl-4-Derivatives (1) Kohji WATANABE, Jun YAMAUCHI, Hideo TAKAKI*, Hiroaki NISHIGUCHI**                            and Yasuo DBGUCHI***                             Received April27, 1970    This report deals with the synthesis of the stable free radicals : 2, 2, 6, 6-tetramethyl-4- hydroxypiperidine-1-oxy1-4-derivatives : methyl-, ethyl-, isopropyl-, tert. butyl-, cyclohexyl-,  phenyl-.     These derivatives were synthesized by means of Grignard reaction. The spectra of  U. V. and I. R. for these compounds were also reported.    We have studied the static magnetic susceptibility and the ESR absorption spectra of many organic stable free radicals.1-3' 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (Fig. 1-a) and 2, 2, 5, 5-tetramethylpyrrolidine-l-oxyl (Fig. 1-b) are very stable free radicals. The derivatives of these radicals are also very stable and easily soluble in most solvents e. g. ether, benzene, alcohol and water. Accord-ingly, these radicals are studied in various aspects such as organic chemical, biochemical and physiochemical ones. We, expressly, have been interested in magnetic property of these radicals. One of the conclusions obtained is that 2, 2, 6, 6-tetramethyl-4-hydroxypiperidine-1-oxyl (TANOL) (Fig. 1-c), one of the H HH OH  \/\/  CC      H>C C<HH>C—C<HH>C C<H      CH3C113> C C <CH3 CH3< C C<CH3 CH3> C C <CH3    \N/\N/\N/  000    (a)(b)(c) OR OH                                    \/  CC    /\/ \      H>C C < HH-CKH      CH3\CH3CH3CH3              CH3'CH3               'CH3CH3~.) <CH3 00     (d)(e)                                       Fig. 1 * : Laboratory of Solid State Chemistry, Institute for     Chemical Research, Kyoto University, Uji, Kyoto. ** 1=I 105, : Fuculty of Science, Kyoto University, Kyoto. *** If, I=1 : Fuculty of General Education, Kyoto University, Kyoto. ( 88 )             2, 2, 6,  6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (1) hindered organic stable free radicals, is the one-dimensional Heisenberg antiferro-magnet according to the static magnetic susceptibility measurments4-5) and that the exchange antiferromagnetic interaction was large as compared with other organic stable free radicals. The precise determination of the crystallographic structure has been made by Lajzerowicz-Bonneteau,6' who found that crystals of TANOL are monoclinic and the molecules are associated with hydrogen bonds and form chains. The following problems, however, have not been clarified definitely : whether this one-dimensional magnetic interaction is along this chain or not and if the hydrogen bond bridged between the radical molecules might contribute to this magnetic interaction.    The ESR absorption spectra of 2, 2, 6, 6-tetramethylpiperidine-1-oxyl derivatives have been observed by Rassat et al.." Kreilick8> has observed not only the normal 3 hyperfine lines arising from "N but also 7 to 13 lines from the protons. In the ESR absorption spectra of 2, 2, 6, 6-tetramethylpiperidine-1-oxyl derivatives the hyperfine coupling constants of both 14N and protons in TANOL have been larger that those of 2, 2, 6, 6-tetramethyl-4-ketopiperidine-1-oxyl (Fig. 1-d) but the hyperfine structures of protons of these derivatives have not been clearly observed. On the other hand, only two of the derivatives of TANOL, i. e. methyl and ethyl derivatives, have been synthesized by Rassat et a1.71 and Rozantsev et al..° It is reported that their ESR absorption spectra including the proton hyperfine lines have been observed only in TANOL.    We have synthesized several 4-alkyl and 4-aryl derivatives of TANOL (Fig. 1-e) in order to investigate the effect of the substituted group on the hydrogen bond formation in the crystal and the ESR absorption spectra in solution. The obser-vation of these hyperfine structures of protons will result in the evidence of direct interaction of an unpaired electron on the NO group with the protons, because these compounds have no it system except the NO group. Furthermore, we might expect that the hydroxyl and 4-substituted groups would affect the hyperfine coupling constants of 14N and protons. In the present paper we shall report synthetic methods and properties of radicals thus obtained.                           EXPERIMENTAL (1) Preparation of the substances was as follows :    a) 2, 2, 6, 6-tetramethyl-4-ketopiperidine was synthesized following the same process as that of Leonard et al..10' In a 1-1. three -necked flask was placed 500 g. (8.62 moles) of acetone and 160 g. of crashed calcium chloride and passed ammonia for 30 minutes. More ammonia was introduced for 15 minutes period at intervals of 3 hours for 3 days. The mixture was allowed to stand at room temperature. It was poured into 250 ml of 50 % sodium hydroxide. The upper layer was decanted from the heavy white sludge of calcium hydroxide which was then rinsed with ether. The combined ether layers were dried over potassium carbo-nate and distilled to give 120 g. yellow liquid, boiling 75-105715 mmHg. Careful fractionation of this material through a short column gave 85 g. 2, 2, 6, 6-tetra- methyl-4-ketopiperidine, yielding 12.8 %, lit. 20%,10)b. p. 95-102°/13 mmHg, lit. ( 89 )                                 K. WATANABE et al.  O  u                                                CCH3CaCl2H'l GH       (a) 3 CH3>C + NH3 .............. CH3H3                                       CH3 C/<CH3                                              N H                                                2, 2, 6, 6-tetramethyl-4-ketopiperidine                                             (triacetonamine) OH OH \/ CC          H> C C GHLiA1H4H> CC GH     (b)CHaCH3CH3CH3      CH3-'GCH3CH3C NC<CH3 HH                                                2, 2, 6, 6-tetramethyl-4-hydroxypiperidine OR OH \/ CC      H / HH   H (c)CH3C C GC3+RMgXCH3> C C GH3          CH3-'NC—CH3CH3`1\1'GCH3 HH                                                2, 2, 6, 6-tetramethyl-4-hydroxypiperidine-                                                  4-derivativesH2O2 (d) AmineNa2WO4Nitroxide Radical                                  EDTA-Na2    0R OH \/   CC      H/\HH/\H         cf. CHCCGC3+RMgX> CH3 C C GH3 CHaCGCH3CH3CNCGCH3 OO                                                2, 2, 6, 6-tetramethyl-4-hydroxypiperidine-                                               4-derivatives                                           (TANOL-4-derivatives)                                               R—: methyl", ethyl')                                     Fig. 2 102-105°/18 mmHg,101 m. p. 35.0-36.0°, lit. 34-36°.10) (These boiling point and melting point are not corrected.)    (b) 2, 2, 6, 6-tetramethyl-4-hydroxypiperidine was snythesized following the same process as that of Rassat et al..') In a 300-ml three-necked flask equipped with a reflux condenser and dropping funnel, both protected by drying tube, was placed a suspension of 2.5 g. (0.07 mole) of litium aluminum hydride in 100 ml of anhydrous ether. The mixture was stirred with a mechanical sealed stirrer. A solution of 10 g. (0.06 mole) of 2, 2, 6, 6-tetramethyl-4-ketopiperidine in 100 ml of ( 90 )             2, 2, 6,  6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (1) anhydrous ether is added at such a rate as to maintain gentle reflux. The mix-ture was then stirred and heated under reflux for 6 hours. The heater was replaced by an ice bath. 2.5 ml of water was added slowly with vigorous stirring. Stirring was continued for 30 minutes after the addition of water was complete. A cold solution of 2.5 ml of 15 % sodium hydroxide was added at once, filtered with suction and solid was washed with several portions of ether. After the ether was removed from the filtrates, the residue was recrystallized from benzene, yielding 35.5 % (3.6 g.), lit. 39.4 %,7) m. p. 128.5-130.0°, lit. 128.5-129°."     (c) 2, 2, 6, 6-tetramethyl-4-hydroxypiperidine-4-derivatives were synthesized by means of Grignard reaction. In a 100-ml three-necked flask was placed 1.6 g. (0.07 mole) of magnesium turnings and 20 ml of anhydrous ether. The stirring was started, and a solution of 7.9 g. (0.06 mole) of isopropyl bromide (or methyl bromide, ethyl bromide, tert. butyl bromide, cyclohexyl bromide or phenyl bromide) in 20 ml of anhydrous ehter was then added. The reaction was practi-cally complete when all the halides had been added, but the reaction mixture was refiuxed on a heater for 30 minutes longer. The flask was cooled and a solution of 5 g. (0.03 mole) of 2, 2, 6, 6-tetramethyl-4-ketopiperidine in 20 ml of anhydrous ether was slowly added to the reacting mixture. After the 2, 2, 6, 6-tetramethyl-4-ketopiperidine had been added, the flask was heated on a heater and stirring was continued for 4 hours, and then left to stand over night. After removal of ether the solid reacting mass was dissolved with cooling in 15 hydrogen chloride, then saturated with sodium hydroxide and extracted with ether. The combined ether extracts were dried with potassium carbonate and ether removed, the residue was recrystallized from petroleum ether, yielding 50-70 %. Methyl-derivative : m. p. 78.0-79.0°. Ethyl-derivative : m. p. 65.0-66.0°, lit. 66.6°.91 isoPropyl-derivative : m. p. 45-50° (This compound may be contaminated by trace of the initial ketone but it does not matter, because we can separate the ketone with column chromathography as ketone radical on next step.) tert. Butyl-derivative : m. p. 135.0-136.5°. cycloHexyl-derivative : m. p. 92.5-93.5°. Phenyl-derivative : m. p. 135.0-136.5°, lit. 130°.10)    (d) TANOL and its derivatives were synthesized following the same process as that of Rozantsev et al..') 0.1 g. of ethylenediaminetetraacetic acid disodium salt, 0.1 g. of sodium tungstate, 50 ml of water and 15 ml of 30 % hydrogen peroxide were added to 0.05 mole of 2, 2, 6, 6-tetramethyl-4-hydroxylpiperidine or its derivatives in 50 ml of methanol. The mixture was stirred for 2 days and then saturated with potassiun carbonate and extracted with ether and the extracts combined and dried with potassium carbonate. After removal of ether the residual solid or oil were recrystallized from petroleum ether or benzene, or were redis-solved in a little ether, isolated by chromathography on aluminium oxide and recrystallized from petroleum ether or benzene, yielding 70-80 %. TANOL : m. p. 72.0-72.5°, lit. 71.5°.7' Methyl-TANOL : m. p. 103.5-104.5°, lit 104°." Ethyl-TANOL : m. p. 67.5-68.5°, lit. 67-68°.9' isoPropyl-TANOL : orange red plate from n-hexane ; m. p. 88.5-89.5°, Anal.  Calcd. for Ci2H24NO2 : C, 68.24 ; H, 11.29 ; N, 6.54. Found : C, 67.84 ; H, 11.61 ; ( 91 )                                 K. WATANABE et  al.   N, 6.58.     tert. Butyl-TANOL : orange red needle from n-hexane ; m. p. 150.0-150.5°, Anal.   Calcd. for C,3H2,NO2 : C, 68.34 ; H, 11.48 ; N, 6.13. Found : C, 68.41 ; H, 11.92 ;   N, 6.02. cycloHexy-TANOL : orange red needle from n-hexane ; m. p. 110.5-111.5°, Anal.   Calcd. for C,5H28NO2 : C, 70.82 ; H, 11.10 ; N, 5.51. Found : C, 70.53 ; H, 11.40 ;   N, 5.74. Phenyl-TANOL : orange leaf from benzene ; m. p. 119.5-120.5°, Anal. Calcd. for C,5H22NO2 : C, 72.54 ; H, 8.93 ; N, 5.64. Found : C, 72.75 ; H, 9.39 ; N, 5.84. (2) Ultraviolet absorption spectra TANOL : ,i =240 mp (s =1260) (dioxane), 2=239 mu (6=1720) (methanol) 7' Methyl-TANOL : 2,..= 239-242 mp (s/M=4960) (cyclohexane)7' Ethyl-TANOL : 2.=227 mp, 235 nip (n-heptane)3' OO 3 -         .I- 250300 550 my250 B 300550 my                  A         isoPropyl-TANOLtert. Butyl-TANOL     ).ma=242 mo (s/M=1970) (n-hexane)2>„ax=242 mit (s/M=2070) (n-hexane) .7 .55                              O O •33 .I 250  500350 mp250 D 300350 mu       CycloHexyl-TANOLPhenyl-TANOL Amax= 241 mpe (s/M=1890) (n-hexane)2.a.x=241 m ft (s/M=2560), 2s =245 mp, 2,=.250 m~c, 2.s°256 mu, 2,=262 mfe. (n-hexane)                                       Fig. 3 (3) Infrared absorption spectra TANOL : 3620(OH) or 3430-3450(OH) cm-' (CC14) 1240 cm-' (CS2).7' Methyl-TANOL : 3500(OH), 1310, 1200, 1090, 960, 905, 810 cm-' (nujo1J.71 Ethyl-TANOL : 3445 cm-' (broad band), 3605 cm-' (narrow band)5'    In Fig. 3, little difference is found in the spectra of TANOL and its deriva-tives. And in Fig. 4, the broad band between 3400 and 3600 cm-' indicates the ( 92 )            2, 2, 6,  6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (1) S------------------------------------------------------------------------------ r r~           Jn/S r/.'                      if/aIJ~l v It.I I , ,^1 1 , f I I I I I 1 I 1 I 1 i 1 I----------------------------------------------------------------------------- 4000300015001000 500 cm-1                                A                            TANOL (KBr) I------------------------------------------------------------------------ I '11\ lr 1.(1----'                                                  v--/ ! , [V, ..                                         .,,                                    ,,, II III I I I I1I I 40003000115001000 500 cm-1                               B                           isoPropyl-TANOL [KBr)-----------------------------------SS--------------------------------------------------------------------------------------------- n 1 L r II ) .11 J . r 5 ^ 1 1 1 f I 1S S I tip I I I I I I I 1 I  4000300015001000 500 cm-1                            C                           tert. Butyl-TANOL [KBr)( 93 )                                  K. WATANABE et  al.  }---------------------------------------------------------------------- 4000300015001000500 cm-' D                            cycloHexyl-TANOL CKBr)          k-Y-\\)1\ 41, \lifINIPI  1 ^} II I I 1 Ili I I 1 I I------------------------------------------------------ 4000300015001000500 cm-I E Phenyl-TANOL CKBr)                                    Fig. 4 formation of hydrogen bonds in TANOL and all its derivatives.ESR absorption spectra were also observed in TANOL and all its derivatives.    We are now analysing the ESR absorption spectra and measuring temperature dependence of static magnetic susceptibility of these radicals. These results will be published in succeeding papers.                           REFERENCES   (1) J. Yamauchi, H. Nishiguchi, K. Mukai, Y. Deguchi and H. Takaki : Bull. Chem. Soc.      Japan, 40, 2512 (1967).   (2) K. Mukai, H. Nishiguchi, K. Ishizu, Y. Deguchi and H. Takaki : Bull. Chem. Soc. Japan,      40, 2731 (1967).   (3) K. Mukai : Bull. Chem. Soc. Japan, 42, 40 (1969).   (4) Yu. S. Karimov : Soc. Phys. JETP Letter, 8, (5) 145 (1968).   (5) J. Yamauchi, T. Fujito, E. Ando, H. Nishiguchi and Y. Deguchi : J. Phys. Soc. Japan,      25, 1558 (1968). (94)           2, 2, 6,  6-Tetramethyl-4-Hydroxypiperidine-1.Oxyl-4-Derivatives (1) (6) J. Lajzerowicz-Bonneteau : Acta cryst. B 24, 196 (1968). (7) R. Briere, H. Lemaire et A. Rassat : Bull. Soc. Chim. France, 11, 3273 (1965). (8) R. W. Kreilick : J. Chem. Phys., 46, 4260 (1968). (9) R. G. Rozantsev and M. B. Neiman : Tetrahedron, 20, 131 (1964). (10) H. K. Hall : J. Amer. Chem. Soc. 79, 5443 (1953). (11) C. H. Clarke and F. Francis : Ber. 45, 2060 (1912). ( 95 )

Synthesis of Stable Free Radicals : 2, 2, 6, 6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (1)

Title ESR Studies of Stable Free Radicals : 2, 2, 6, 6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (II)Author(s)Watanabe, Kohji; Yamauchi, Jun; Takaki, Hideo; Nishiguchi,Hiroaki; Deguchi, YasuoCitationBulletin of the Institute for Chemical Research, KyotoUniversity (1971), 48(6): 264-268Issue Date1971-03-24URL http://hdl.handle.net/2433/76348RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityBull. Inst. Chem. Res., Kyoto Univ., Vol. 48, No. 6, 1970           ESR  Studies of Stable Free Radicals 2,2,6,6-Tetramethyl-4-I1ydroxypiperidine-l-                Oxyl-4-Derivatives (II)              Kohji WATANABE*, Jun YAMAUCfH*, Hideo TAKAKI*, Hiroaki NISHZGUCHI** and Yasuo DEGUCHI***                                Received October 21, 1970      The ESR absorption spectra of 2,2,6,6-tetramethyl-4-hydroxypiperidine-l-oxyl-4-derivatives  have been observed at room temperature. The substitution at 4-position have not evidently  affected to the hyperfine interaction.     Organic stable free radicals such as 2,2,5,5-tetramethylpyrrolidine-1-oxyl (Fig. 1-a) and 2,2,6,6-tetramethylpiperidine-l-oxyl (TADIN) (Fig. 1-b) have already studied by many investigators with use of the ESR or magnetic susceptibility tech-nique.'-') The ESR absorption spectra of TADIN derivatives have been observed by Rassat et al.' Kreilickz' has observed not only the normal 3 hyperfine lines arising from 14N but also 7 to 13 lines from the protons. The observation of these hyperfine structure of protons will result in the evidence of direct interaction of an unpaired electron on the NO group with the protons, because these compounds have no 7r system except the NO group. However, in the ESR absorption spectra of these series, they have obtained a lower resolved spectrum of 2,2,6,6-tetramethyl-4-ketopiperidine-l-oxyl (TAAO) (Fig. 1-c) compared with those of 4-substituted TADIN derivatives.    We might expect that the 4-substituted groups would affect the hyperfine coupling constants of 14N and protons. Only two of the 4-substituted derivatives, i.e. methyl H H               CZ}        HZVNHCHH~C/C,C/HHCC7H   CH,H~NHH~NH       ~CCr,      CH,~CH,,ICH,CH3, I,CH3      NNCH.C CCC CH3 v/ 'CH, OI OO     (a)(b)(c)                                           Fig. 1. k r 7 -_, 11fr , As: 33 f : Laboratory of Solid State Chemistry, Institute for Chemical     Research, Kyoto University, Uji, Kyoto. ** NT' : Faculty of Science, Kyoto University, Kyoto. *** {'i p Faculty of General Education, Kyoto University, Kyoto. ( 264 )           ESR of  2,2,6,6-Tetramethyl-4-Hydroxypiperidine-l-Oxyl-4-Derivatives (2) R~/OH                  HiC/C~C H                     HH R: H(TANOL), Methyl, Ethyl,                        CH3,,~CH3iso-Propyl, tert. Butyl,                         CH3~C\r~~CH,cyclo-Hexyl, Phenyl0                                     Fig. 2. and ethyl derivatives of 2,2,6,6-tetramethyl-4-hydroxypiperidine-l-oxyl (TANOL) (Fig. 2) have been studied by Rassat et al.' and Rozantsev et al..4'    In their ESR absorption spectra the proton hyperfine lines have been observed only in TANOL. In the present paper we report ESR absorption spectra of 4-sub-stituted TANOL derivatives in order to clarify the effect of 4-substituted groups on the hyperfine coupling constants of 14N and protons. Furthermore, as we have observed an anomalous line alternation in the ESR absorption spectra of TAAO and methyl-TANOL, we should like to discuss the mechanism of this phenomena.    Preparation of the samples was previously reported in this bulletin." In case of the observation of the ESR absorption spectra the solvent was well purified, de-hydrated and degassed by the ordinary method.s° An aqueous solution of peroxyl-amine disulfonate was used as a standard for the magnetic field. All the ESR absorp-tion spectra were observed with ME-3X type spectrometer of Japan Electron Optics Laboratory Co., Ltd., equipped with 100 KHz field modulation.    We have observed the similar ESR absorption spectra in all TANOL derivatives and one of them shown in Fig. 3.     The triplet splitting in Fig. 3-a arises from a nitrogen nuclear spin (I=1).     Therefore the hyperfine components in Fig. 3-b can be attributed to the hyperfine interaction of protons. Taking into account the molecular framework in Fig. 2, one can easily estimate that the nine lines are due to hyperfine interaction of 12 methyl 10G, 1G ,      (a)(b)            (a) The ESR absorption spectrum of Ethyl-TANOL in THE solution                    at room temperature under low resolution.             (13) One of the three 14N lines under high resolution.                                           Fig. 3. (265)            K.  `VATANABE, J. YAMAUCHI, H. TAKAKI, H. NISHIGUCHI and Y. DEGUCHI            Table I. Hyperfine Coupling Constants of 14N (AN) and Protons* (Agi)                for TANOL and its Derivatives. (in gauss)         SampleAN AN        TANOL15.5 0.43           Methyl-TANOL15. 1 0. 38          Ethyl-TANOL15. 1 0. 34            iso-Propyl-TANOL15.3 0.41             tert. Butyl-TANOL15.2 0.42             cyclo-Hexyl-TANOL15.2 0.41          Phenyl-TANOL15.2 0.41                * methyl protons                               j     f, 1 „yip' io 40 Fig. 4Stereomodel f TANOL protons; possible line intensities are 1 : 12 : 16 : 220 : 495 : 792 : 924 : 792 : 495 : 220 : 66 : 12 : 1. The coupling constants obtained in tetrahydrofuran (THF) solution are summarized in Table I.    As seen from Table I, 4-substituted groups of TANOL derivatives have little influence on the '4N and proton's hyperfine coupling constants and play no important role in the spin density distribution. Namely, an unpaired electron is almost localized on the NO group masked by the four methyl groups(Fig. 4), which may cause large stability of these radicals. Thus, we have concluded that the ESR absorption spectra of both hyperfine coupling constants of "N and of protons were not affected by 4-substituted groups.    On the other hand, we have observed an interesting temperature dependence of ESR absorption spectra on crude TAAO and methyl-TANOL, which are shown in Fig. 5.    The spectrum at low temperature which suggests an existence of two radical species coalesces into simple three lines at room temperature. These line shape variation lead to some chemical exchange phenomena occurred sometimes in solution.     We presume this phenomenon, on the one hand, that there are the exchange of (266 )ESR of  2,2,6,6-Tetramethy1-4-Hydroxypiperidine-l-O l-4-llerivatives (2) 15 c ,5 G, -10 °c , -50 c Fig. 5. Typical ESR absorption spectra of methyl-TANOL in THF. (267)            K. WATANABE, J. YAMAUCHI, H. TAKAKI, H.  NISHIGUCHI and Y. Danuc II                           N + -N- F ' -N- -I- -N-       O HO                                        Fig. 6. molecular frameworks between boat-form and chair-form. On the other hand, equilibrium of two different species such as an aminoxyl radical and an amino radical (Fig. 6) exist.    We are now investigating these mechanism in more detail. These results will be published elsewhere.                             REFERENCES (1) R. Briere, H. Lemaire et A. Rassat, Bull. Soc. Chim. France, 11, 3273 (1965). (2) R. W. Kreilick, J. Chem. Phys., 46, 4260 (1968). (3) J. Yamauchi, T. Fujito, E. Ando, H. Nishiguchi and Y. Deguchi, J. Phys. Soc. Japan, 25, 1558     (1968). (4 ) M. B. Neiman, E. G. Rozantsev and Yu. G. Mamedova, Nature, 200, 256 (1963). (5) K. Watanabe, J. Yamauchi, H. Nishiguchi, Y. Deguchi and H. Takaki: Bull. Inst. Chem. Res.,      Kyoto Univ., 48, 88 (1970). (6) Y. Deguchi, Bull. Chem. Soc. Japan, 35, 910 (1962). (268 )

ESR Studies of Stable Free Radicals : 2, 2, 6, 6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (II)

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Synthesis of Stable Free Radicals : 2, 2, 6, 6-Tetramethyl-4-Hydroxypiperidine-1-Oxyl-4-Derivatives (1)

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