Synthesis and non-linear optical and redox properties of 6-nitro-6′-piperidyl-2,2′-bisbenzothiazole: A new type of push-pull molecules

Article abstract of DOI:10.1016/j.tet.2003.11.020

The present paper describes the synthesis, the non-linear optical and redox properties of 6-nitro-6′-piperidyl-2,2′-bisbenzothiazole, the first described member of a new family of push-pull structures based in the 2,2′-bisbenzothiazole.

Full text of DOI:10.1016/j.tet.2003.11.020

Tetrahedron 60 (2004) 285–289
Synthesis and non-linear optical and redox properties of
6-nitro-60-piperidyl-2,20-bisbenzothiazole: a new type of
push–pull molecules
a
Francisco Lopez-Calahorra, Mariano Martınez-Rubio, Dolores Velasco, Enric Brillas
a
a
b
,
*
´
´
´ `
and Lluıs Julia
c
a
´
Departament de Quımica Organica, Universitat de Barcelona, c/ Martı i Franques, 1-11, 08028 Barcelona, Spain
Departament de Quımica Fısica, Universitat de Barcelona, c/ Martı i Franques, 1-11, 08028 Barcelona, Spain
`
´
`
b
´
´
´
`
c
´ ` ` ´
Departament de Quımica Organica Biologica, Institut d’Investigacions Quımiques i Ambientals de Barcelona (CSIC), c/ Jordi Girona,
18-26, 08034 Barcelona, Spain
Received 28 May 2003; revised 14 October 2003; accepted 11 November 2003
Abstract—The present paper describes the synthesis, the non-linear optical and redox properties of 6-nitro-60-piperidyl-2,20-
bisbenzothiazole, the first described member of a new family of push–pull structures based in the 2,20-bisbenzothiazole.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Our research on new organic materials includes an interest
in new molecules with non-linear optical (NLO) properties1
and other dipolar moment-dependent properties. Organic
molecules with large delocalized p-electron systems are
good candidates for the display of large non-linear
responses.2 The main factor involved in presenting such
properties is the presence and nature of electron-donating
and -accepting groups. Furthermore, the extension and kind
of conjugation path is crucial for the transfer of charge
between the substituents in the presence of electric fields. A
number of factors prompted us to sy0nthesize and study the
properties of 6-nitro-60-piperidyl-2,2 -bisbenzothiazole (1):
(a) 0our experience in the chemistry of benzothiazoles and
2,2 -bisbenzothiazoles,3 (b) the scarce mention in the
literature of related systems,4 (c) the high thermal stabilities
of systems derived from benzothiazole, characteristic very
adequate for possible technological applications of this
molecules, and (d) the good theoretical value for b(0)
(34£10230 esu) predicted for 1,5 similar to the described6
Scheme 1 shows the synthetic path followed to prepare 1.
The strategy was to prepare the two benzothiazoles
conveniently functionalized and link both by a coupling
reaction. The first half of the molecule was prepared from
4-(N-piperidyl)aniline. The problem of the construction of
substituted benzothiazoles consists in the formation of the
corresponding 2-aminothiophenol from the adequate ani-
line. Several procedures7 for performing this process are
known but in general the yields are low, the manipulation
difficult, or the methods incompatible with various func-
tional groups. The only method that proved adequate in our
case is the one described by Levkoev et al.8 This method
consists in reacting aniline and sodium thiosulfate in an
oxidative medium. The second half-molecule was prepared
by means of a standard Sandmeyer reaction9 from
commercial 2-amino-6-nitrobenzothiazole. Finally, the
coupling reaction was done via reaction of the organozinc
derivative of 6-(N-piperidyl)benzothiazole with the above
bromoderivative.10 The yields from this reaction are never
high and the fo0rmation of some amount of the symmetric
compound 6,6 -di(N-piperidyl)2,20 bisbenzothiazole in
unavoidable.
for
4-(N,N-dimethylamino)-nitrostilbene
(DANS)
(b(0)¼55£10230 esu.
After preparing the desired compound, we studied its non-
linear optic behavior by means the EFISH method, which
permitted the calculation mb(0) from the experimental value
of mb by using a simple two-level model.11 The low
solubility of 1 in the common organic solvents prevented us
from determining the dipolar moment, m; hence in this
Keywords: 2,20-Bisbenzothiazole; Synthesis; Push–pull molecules; Non-
linear optical properties; Redox properties.
*
Corresponding author. Tel.: þ34-93-4021252; fax: þ34-93-3397878;
e-mail address: flopezcalahorra@ub.edu
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.11.020

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F. Lopez-Calahorra et al. / Tetrahedron 60 (2004) 285–289
286
Scheme 1. Reagents and conditons. (i) Na2S2O3·5H2O, K2Cr2O7, AcOH, 0 8C, 8 h, r.t. ovemigth, 34%. (ii) NaNO2, CuBr, HBr 48%. (iii) Bu–Li, anh. ZnCl2,
CuI.
paper the experimental results are expressed as mb
(375£10248 esu) and mb(0) (276£10248 esu) in CH2Cl2
(l¼1.9 mm, static electric field¼5 kV). Our calculated
theoretical value for b(0) is 34£10230 esu, and for m is
8.3£10218 esu; consequently, the theoretically estimated
value for mb(0) is 283£10248 esu. The concordance
between this value and the experimental one is excellent,
showing that the semiempirical method (AM1-RHF) used is
very adequate in this kind of molecules.
were obtained using DMF as solvent, indicating a large
stability of the radical anion 1z2 and the dianion 122 in
both media. For the oxidation of the same solutions, their
cyclic voltammograms exhibited an anodic irreversible
peak either in DMF or in CH2Cl2 for v,50 mV s21. At
higher scan rates in CH2Cl2 solution, its associated
cathodic peak was already observed, the process behaving
1$1zþþe2 as a quasi-reversible one-electron redox pair
((Epa2Epc)¼0.12 V at v¼200 mV s21) with a standard
potential E o¼0.95 V vs SSCE (Fig. 1b). These results
indicate the electron accepting and donating ability of 1,
the radical cation species being of much lower stability
than the radical anion.
To study the redox properties of 1, we applied two
complementary techniques: cyclic voltamperommetry and
EPR.
As can be seen in Figure 1a, the cyclic voltammogram for
the reduction of 1 in CH2Cl2 solution with tetrabutylammo-
nium perchlorate (0.1 M) as electrolyte on Pt at 25 8C
displayed two consecutive quasi-reversible one-electron
redox couples, with standard potentials Eo1¼21.07 V and
Eo2¼21.46 V vs SSCE (NaCl-saturated calomel electrode).
Both peaks had the same cathodic and anodic heights and
showed an increasing difference between their correspond-
ing anodic and catodic peak potentials (Eap2 Epc) from
0.10 V at a scan rate (n) of 20 mV s21 to 0.17 V at
n¼200 mV s21. They can be ascribed to the equilibrium
processes 1þe2$1z2 and 1z2þe2$122. Similar results
The above cyclic-voltammetric behavior was confirmed by
electron paramagnetic resonance (EPR) spectroscopy. So,
while 1z2 was easily detected by chemical reduction (see
Section 4), we were not able to detect 1zþ.
To characterize the EPR spectrum of 1z2, we had previously
registered the spectra of the radical anions ch0emically
derived from 6-nitrobenzothiazole (2) and 2,2 -bisben-
zothiazole (3). A multiplet of lines (g¼2.0052; peak to
peak linewidth, DHpp¼0.2 G) of a very stable radical was
obtained when a degassed DMSO solution of 2 was treated
with potassium t-butoxide at room temperature (Fig. 2a).
Figure 1. Cyclic voltammograms for the (a) reduction and (b) oxidation of a 1 mM 1 solution in CH2Cl2 with 0.1 M tetrabutylammonium perchlorate at
200 mV s21 and at 25 8C on a 0.093 cm2 Pt electrode. Initial potential: (a) 20.50 V, (b) 0.50 V. Reversal potential: (a) 21.800 V, (b) 1.200 V.

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F. Lopez-Calahorra et al. / Tetrahedron 60 (2004) 285–289
287
Figure 2. (a) EPR spectrum of 2z2 in DMSO solution at room temperature. (b) Computer simulation with the values given in Table 1.
The intensity of the lines slightly increased with short
periods of ultraviolet irradiation.
This spectrum (Fig. 2b) was simulated12 using the hyperfine
splitting (hfs) values showed in Table 1, and was attributed
to 2z2. The assignment of hfs values to the different nuclei
in the molecule was verified by molecular orbital calcu-
Figure 3. (a) EPR spectrum of 3z2 in DMSO solution at room temperature.
(b) Computer simulation with the values given in Table 1.
lations, using the semiempirical MINDO/3 method as
shown also in Table 1.
Anion radicals from thiazolyl derivatives have already been
detected and well characterized by EPR;13 however, as far
as we know, no spectra of the reduced species from
benzothiazolyls have been reported to date. Our attempts to
generate the anion radical from the parent compound
benzothiazole or from 6-morpholinebenzothiazole, a ben-
zothiazole with a secondary amine as substituent, were
unsuccessful. Therefore, the presence of an electron with-
drawing group such as the nitro group is necessary to
facilitate the electron transfer reaction and to stabilize the
corresponding charged species.
one radical species. As in the case of 2,20-bisthiazole, the
free rotation around C–C bond is hindered in the neutral
molecule, and the energy barrier to rotation expected for the
anion radical should be larger considering the partial double
bond character, similar as it is suggested in 2,20-bisthiazole
by Pedully et al.13 The consequence is the presence of only
one isomer in solution.
When a degassed solution of 6-nitro-60-(N-piperidy)-2,20-
bisbenzothiazole (1) (,1022 M) in THF–DMSO (1:1) with
an excess of potassium t-butoxide was irradiated with UV
light, a symmetric multiplet of lines centered at g¼2.0048
was detected by EPR (Fig. 4a). This radical species was
stable and was attributed to 1z2. One of the simulations
which roughly fits to the experimental spectrum (Fig. 4b)
was performed by using the following hfs values in gauss:
a(N)¼6.87, a(N)¼2.87, a(1H)¼2.20, a(1H)¼1.94,
a(3H)¼0.9, DHpp¼0.7 G. Values from other nuclei in the
molecule should be less than the linewidth. As before, the
presence of only one radical species suggests only one
isomer in solution at room temperature.
Similarly, when degassed DMSO solution of 2,20-bisben-
zothiazole (3), treated with potassium t-butoxide, were
prolonged irradiated (1 h) with UV light a persistent
multiplet of very narrow lines (g¼2.0043; DHpp¼0.09 G)
was detected by EPR (Fig. 3a). This spectrum (Fig. 3b) was
simulated by using the hfs values displayed in Table 1 and
was attributed to 3z2. As before, the assignment was
performed by MINDO/3.0 Two different conformations
could be expected for 2,2 -bisbenzothiazole, however the
spectrum at room temperature revealed the presence of only
Table 1. Experimental and calculated hyperfine coupling constants (a) for radical anions derived from 6-nitrobenzothiazole (2) and 2,20-bisbenzothiazole (3)
a (exp)a
a (theor)b
a (exp)a
a (theor)b
2z2
1.7(N3)
614
511
1175
670
898
3z2
684
806
718
791
672
0.85(N6)
2.02(H2)
0.85(H4)
0.85(H5)
1.28(H7)
3.34(N3,N30)
2.16(H4,H40)
0.56(H5,H50)
1.88(H6,H60)
0.28(H7,H70)
1110
a
In Gauss.
Arbitrary units.
b

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F. Lopez-Calahorra et al. / Tetrahedron 60 (2004) 285–289
288
4.1.2. Synthesis of 6-(N-piperidyl)benzothiazole. Dihy-
drogensulfate of N-(4-aminophenyl)piperidine (1.59 g,
4.25 mmol) and sodium thiosulfate pentahydrate (2.04 g,
8.23 mmol) were dissolved in 18% aqueous solution of
acetic acid (3.2 mL) at 0 8C. A solution of potassium
dichromate (411 mg, 1.40 mmol) in diluted acetic acid
(6.5%, 8.3 mL) was added for 1 h. The reaction mixture was
stirred in an ice bath for 8 h and overnight at room
temperature. The formed precipitate was filtered, washed
with water, suspended in formic acid (15 mL) and heated
under reflux for 3 h. The formic acid was removed, the
residue diluted with water (15 mL), neutralized with sodium
bicarbonate and extracted with methylene chloride. The
solvent was removed and 6-(N-piperidyl)benzothiazole
(305 mg, 34%) was isolated as a white solid by column
chromatography over silicagel, eluting with CH2Cl2–
EtOOCCH3 9:1; mp 87–88 8C; TLC (SiO2, CH2Cl2–
EtOOCCH3 9:1); Rf¼0.34; IR (KBr): n¼2935, 2854
(C–H st.); 1600, 1542 (arom.); 1480, 1383 (thiazole);
Figure 4. (a) EPR spectrum of 1z2 THF–DMSO (1:1) solution at room
temperature. (b) Computer simulation with the values given in the text.
3. Conclusion
We report the first synthesis of 6-nitro-60-(N-piperidy)-2,20-
bisbenzothiazole, a new push–pull molecule. This molecule
shows good NLO properties and a dual, oxidative and
reductive, three-stage single-electron redox character. It
shows a quite stable radical anion detected by EPR. Related
to this radical anion, the first EPR spectra of radical anions
derived from bisbenzothiazoles is also described
1
1237 (C–N st.); 940, 876, 824 (Car–H) cm21; H NMR
(200 MHz, CDCl3, TMSint): d¼8.72 (s, H6, 1H), 7.93 (d, H4,
J3–4¼9.2 Hz, 1H), 7.34 (d, H1, J1–3¼2.2 Hz, 1H), 7.17
(dd, H3, J1–3¼2.2 Hz, J3– 4¼9.2 Hz, 1H), 3.19 (t, H8,
J8–9¼5.4 Hz, 4H), 1.71 (sc, H9, J8–9¼5.4 Hz, 4H), 1.59 (sc,
H10, 2 H) ppm; 13C NMR (50 MHz, CDCl3): d¼150.49
(C6), 146.50 (C5), 135.21 (C7), 123.30 (C4), 117.83 (C3),
107.11 (C1), 51.32 (C8), 25.81 (C9), 24.20 (C10) ppm; MS
(70 eV, CI, NH3): m/z: 219 [Mþ1]þ.
4. Experimental
4.1. General
¨
Melting points were determined using a Kofler apparatus
provided with a Reichert Thermovar microscope and are
uncorrected. TLC was carried out on SiO2 (Alugram SIL
G/UV254 Macherey–Nagel 0.25 mm) and spots were
located with UV light. Flash chromatography was carried
out on SiO2 (Silica Gel 60 A CC, Merck). Organic extracts
were dried over anhydrous MgSO4, and solutions were
evaporated under reduced pressure with a rotatory evapor-
ator. IR spectra were recorded on a Nicolet 510 FT-IR
spectrometer. NMR spectra were measured with Varian
Gemini-200 (200 MHz) and Varian Unity-300 (300 MHz)
spectrometers; data are given in d/ppm, referenced to TMS
4.1.3. Synthesis of 2-bromo-6-nitrobenzothiazole. 2-
Amino-6-nitrobenzothiazole (5 g, 25.6 mmol) was mixed
under vigorous stirring with 85% phosphoric acid (23 mL)
at 50 8C. The solution was cooled to 220 8C and a solution
of sodium nitrite (1.91 g) and water (2.2 mL) was slowly
added. After 1 h, the resulting suspension was poured over a
solution of cuprous bromide (4.51 g, 31.4 mmol) in 48%
hydrobromic acid (25 mL) at room temperature and
mechanically stirred. After 1 h, the mixture was heated at
40 8C for 2 h, diluted to a final volume of 500 mL and
extracted repeatedly with methylene chloride. The organic
layer was dried over anhydrous magnesium sulfate, the
solvent removed and 2-bromo-6-nitrobenzothiazole (4.66 g,
70%) isolated as an orange solid; mp 202–204 8C dec. (lit.
206–7 8C); TLC (SiO2, CH2Cl2); Rf¼0.46; IR (KBr):
n¼3100 (Car–H st.); 1601, 1568 (sis. arom.); 1510
(Car–NO2 st. as.); 1344 (Car–NO2 st. si.); 884, 843,
751 (Car–H) cm21; 1H NMR (200 MHz, CDCl3, TMSint):-
1
for H NMR, to CDCl3 (77.0 ppm) for 13C NMR and J
values are given in Hz. Mass spectra were measured in
chemical impact (CI, NH3) mode with a Hewlett–Packard
5988A spectrometer, or with a Fisons VG-Quattro spec-
trometer. The samples were then introduced into a matrix of
2-nitrobenzyl alcohol for FAB analysis and subjected to
bombardment with cesium atoms.
d
1, J1–3¼1.2 Hz, 1H), 8.35 (dd, H3, J1–3¼1.2 Hz,
4.1.1. Electron spin resonance of radical anions from 6-
nitro-60-piperidyl-2,20-bisbenzothiazole (1), 6-nitroben-
zothiazole (2) and 2,20-bisbenzothiazole (3). (a) Prep-
aration of the samples: solutions of 1, 2 and 3 (1022 M) in
dimethylsulfoxide in a quartz tube were degassed by
bubbling argon while an excess of dimethylsulfoxide
solution of potassium t-butoxide was added. These colored
solutions were introduced into the cavity of the spectrometer
at room temperature and their spectra were registered while
irradiated with light from a high-pressure mercury lamp
(500 W).
¼8.76 (d, H
J3–4¼9.2 Hz, 1H), 8.08 (d, H4, J3–4¼9.2 Hz, 1H) ppm; 13
C
NMR (75 MHz, CDCl3): d¼155.89 (C5), 145.33 (C2),
144.67 (C7), 137.69 (C6), 123.19 (C4), 122.14 (C3), 117.37
(C1) ppm.; MS (70 eV, CI, CH4): m/z¼259, 261 [MþHþ].
4.1.4. Synthesis of 6-nitro-60-piperidyl-2.20-bisbenzothia-
zole. 6-(N-piperidyl)benzothiazole (2.40 g, 11.0 mmol) was
dissolved in anhydrous tetrahydrofurane (35 mL) under
inert atmosphere and at 2100 8C. Over this solution butyl-
lithium (7,5 mL 1.6 M in hexane, 12.0 mmol) was slowly
added. After addition, the mixture was stirred in the same
condition for further 20 min and anhydrous zinc chloride
(1.67 g, 12.2 mmol) in anhydrous tetrahydrofurane (15 mL)
was added. The reaction mixture was maintained for 40 min
and 2-bromo-6-nitrobenzothiazole (2.90 g, 11.2 mmol),
(b) EPR spectra were recorded with a Varian E-109
spectrometer working in the X band. Determinations of
the g values of the radicals were made with DPPH
(g¼2.0037) as standard.

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F. Lopez-Calahorra et al. / Tetrahedron 60 (2004) 285–289
289
´
thanks Dr Belen Villacampa for the experimental determi-
nation of NLO properties.
dichlorobis(triphenylphosphine)palladium(II)
(488 mg,
0.70 mmol) and cuprous iodide (353 mg, 1.85 mmol) were
added in this order and in solid state. The mixture was
heated for 15 h at 50 8C. The solvent was removed, and the
residue was treated with hydrochloric acid (250 mL 0.1 M).
The aqueous layer was extracted repeatedly with methylene
chloride, the organic layer dried with anhydrous magnesium
sulfate, filtered and the solvent was removed. 6-nitro-60-
piperidyl-2.20-bisbenzothiazole was isolated as a red solid
(1.41 g, 32%) by column chromatography over silicagel,
eluting with CH2Cl2–EtOOCCH3 in a gradient from 10:0 to
9:1. The product was purified for elemental analysis by
sublimation at 280 8C and 0.5 mm Hg; mp 298–300 8C;
TLC (SiO2, CH2Cl2–EtOOCCH3 30:1); Rf¼0.48; IR (KBr):
n¼3115 (Car–H st.); 2937, 2860 (C–H st.); 1603, 1546 (sis.
arom.); 1517 (Car–NO2 st. as.); 1453, 1383 (thiazol); 1337
(Car–NO2 st. si.); 1229 (C–N st.); 895, 858, 814 (Car–H)
References and notes
´ ´
1. (a) Dıaz, J. L.; Villacampa, B.; Lopez-Calahorra, F.; Velasco,
´
D. Tetrahedron Lett. 2002, 43, 4333. (b) Dıaz, J. L.;
´
Villacampa, B.; Lopez-Calahorra, F.; Velasco, D. Chem.
Mater. 2002, 14, 2240.
2. (a) Chemla, D. S.; Zeiis, J. Nonlinear Optical Properties of
Organic Molecules and Crystals; Academic: New York, 1987.
(b) Prasad, P. N.; Williams, D. J. Introduction to Nonlinear
Optical Effects in Molecules and Polymers; Wiley: New York,
1991. (c) Zeiss, J. Molecular Non Linear Optics: Materials,
Physics and Devices; Academic: New York, 1994. (d) Nalwa,
H. S.; Miyata, S. Nonlinear Optics of Organic Molecules and
Polymers; CRC: New York, 1997.
1
cm21; H NMR (300 MHz, CDCl3, TMSint): d¼8.83 (d,
H8, J8–10¼2.4 Hz, 1H), 8.34 (dd, H10, J8–10¼2.4 Hz,
J10–11¼8.7 Hz, 1H), 8.13 (d, H11, J10–11¼8.7 Hz, 1H), 7.94
(d, H4, J3–4¼9.0 Hz, 1H), 7.28 (d, H1, J1–3¼2.4 Hz, 1H),
7.19 (dd, H3, J1–3¼2.4 Hz, J3–4¼9.0 Hz, 1H), 3.32 (t, H15,
J15–16¼5.4 Hz, 4H), 1.73 (sc, H16, J15–16¼5.4 Hz, 4H),
1.65 (sc, H17, 2 H); 13C NMR (75 MHz, CDCl3): d¼167.46
(C12), 157.28 (C13), 155.37 (C6), 151.50 (C9), 146.67 (C5),
145.37 (C2), 138.73 (C14), 135.81 (C7), 124.52 (C11), 123.68
(C4), 122.03 (C10), 118.42 (C8), 117.95 (C3), 105.49 (C1),
50.19 (C15), 25.62 (C16), 24.23 (C17) ppm; UV (CH2Cl2):
´
3. Lopez-Calahorra, F.; Rubires, R. Tetrahedron 1995, 51, 9713,
and references therein cited.
4. (a) Sun, S.-S. J.; Dalton, L. R.; Yang, Z.; Spangler, C. W.; He,
M. Polym Preprints 1995, 36, 584. (b) Liu, Y.; Liu, K.; Kong,
X.; Min, X.; Liu, C. Teoret. Exp. Chem. 2000, 36, 303.
5. Our AM1-RHF calculations.
6. Marder, S.; Beretan, D.; Cheng, L. Science 1991, 252, 103.
7. (a) Warburton, W. Chem. Rev. 1957, 57, 1011–1020. (b) Ast,
M.; Bogert, M. Rec. Trav. Chim. 1935, 54, 917–930.
8. Levkoev, I.; Sveshnikov, N.; Gorbacheva, I.; Barvyn, N. J.
Gen. Chem. USSR, Eng. Ed. 1990, 24, 2027–2034.
9. Todesco, P. E. Bull, Sc., Fac. Chim. Ind. Bologna 1965, 223,
107–129.
lmax (nm)/1 (M21 cm21)¼450/2,6£104, 347/1,0£104,
´
302/1,5£104; MS-FAB(þ): m/z¼396 (Mzþ); elemental
analysis: found C: 57.55%, H: 3.94%, N: 14.20%, S:
16.12%, C19H16N4O2S2 requires C: 57.57%, H: 4.07%, N:
14.13%, S: 16.17%).
10. (a) Pelter, A.; Rowlands, M.; Clements, G. Synthesis 1987,
51–53. (b) Negishi, E.; King, A.; Okukado, N. J. Org. Chem.
1977, 42, 1821–1823.
Acknowledgements
11. Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1991, 252, 103.
12. Spectra were simulated following the WINSIM program
provided by D. Dulog, Public EPR Software Tools, National
Institute Of Environmental Health Sciences, Bethesda Md,
1996.
This research was supported by the Spanish Ministerio de
´
Educacion y Cultura, grants PB96-1491 and BQU2000-
0789-C02-02, and the Generalitat de Catalunya, grant
´
1996SGR 00094. r. M. Martınez thanks the Ministerio de
Educacion y Cultura for a fellowship. The authors also
13. Pedulli, G. F.; Zanirato, P.; Alberti, A.; Tiecco, M. J. Chem.
Soc., Perkin Trans. II 1975, 293–298.
´