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Infra-red spectroscopy of benzo(α)phenoxazines
Bpeotrcchimica Acta1967,~ol.23A,pp.2175 to2183.PergamonPremLM.PrintedinNorthemIreland
I&a-red
of benzo (a >phenoxazines
spectroscopy
V. STU~KA,
V. &&NEK
and Z. STRANSKP
Institute of organic-, analytical- and physioal chemistry, Faculty of Natural Soiences Palacki University, Olomouc, Czechoslovakia (Received18 October1966) Abstract-The purpose of this paper is to assign some specific vibrational bands at 1700-1000 cm-1 to molecular vibrations of the basic benzo(a)phenoxazine skeleton, and to describe the position of the vibrational bands of some substituents attaohed to this skeleton. In addition, the effect of the electronic behaviour of the substituents on the frequency of the carbonyl vibrations of benzo(a)phenoxazoneswas determined and the possible electronic interactions in the individual moleculeswere discussed. The compounds investigated are of the types I, II, and III, where R1-Ra are the individual substituents. All the substanceswere synthetized for use aa acid-base indicators for aqueous and anhydrous media and as oxidation reduction indicators.
‘I
“\,\ ad?
,=I RI
0
0
m
II
INTR~DUOTI~N i&a-red spectra of substituted phenoxazones have been studied in some detail by MTJSSEN and MATHIES [11, CORBETT [2],and by other workers [3-51. They assign the absorption band in the region 1661-1630 cm-l to the carbonyl vibration of phenoxazone, the band at 1622-1585 cm-l to the C-N valence vibration, and the absorption bands in the region 1225-1150 cm-l s,re assumed to be due to the C-C, C-N and O-ring vibrations. The bands in the region 1595-1490 cm-l are attributed by them to the skeleton C=C valence vibrations of the quinoid and aromatic systems, and the band at 1215-1150 is ascribed to the Y C-O vibration of the oxazine ring. BUTEN~DT et al. [6] report the infra-red spectra of a number of substituted benzo(a)phenoxazones and pyridinophenoxazones. The spectra of these compounds show several characteristic bands in the region 1653-1515 cm-l. The intense bands THE
[l] H. Muss0 and H. MAITHIES, Ber. 90, 1814 (1957). [2] J. F. CORBETT, ii’peckochim. Acta 21, 1411 (1965). [3] H. Muss0 and H. BEECKEN, Ber. 94, 585 (1961). [4] G. W. CAVILL,~. S. CLEZY and F. B. WHITFIELD, Tetrahedron 12, 139 (1961). [5] A. BUTENANDT, E. BIEKERT and G. NEUBERT, Liebig Ann. 602, 72 (1957). [6] A. BUTENANDT, E. BIEKERT and W. SCHAFER, _&big8 Ann. 692. 134 (1960.) [7] J. F. CORBETT, 6’pectrochim. Acta 21, 1081 (1965). [S] H. Musso, E. D~~PP and J. KUEILS,Chem. Ber. 98, 3937 (1965). 2175
2810 -
[II] [ll] 1121 [13]
9.dimethylemino-SH-benzo(a)phenoxezone-(5)
9-diethylamino-5H-benzo(a)phenoxazone-(5)
I)-dimethylamino-SH-benzo(a)phenoxeoniumchloride
5-8mino-9-diethylamino-9H-be~o(a)phenoxezoniumsulphste 6-amino-9-dimethyl~mino-9H-benzo(a)phenoxazonium ahloride 6-anilino-9-dimethylrtmino-6H-benzo(a)phenoxazime
b-(3-methykmilino)-9-dimethylamino-SH-benzo(a)phenoxazoniumohloride 5-(bmethylanilino)-9-dimethylamino-5H-benzo(a)phenoxazime 5-(4-nitroanilino)S-dimethylemino-SH-benzo(a)phenoxezoniumchloride 6-(4-hydroxytmilino)-9-dimethylemino-SH-benzo(~)phenoxazoniumchloride 6-(3-aarboxyanilino)-9-dimethylamino-SH-benzo(a)phenoxazoniumohloride 5-(4-oarboxyaniliio)-9-dimethylamino-9H-benzo(a)phenoxezoniumchloride 5-(3-chloranilino)-9-dimethylemino-H9-benzo(a)phenoxazoniumchloride b-(Cbromanilino)O-dimethylamino-SH-benzo(a)phenoxaziniumohloride 5-(4-iodsnilino)-9-dthylamino-SH-benzo(a)phenoxszoniumchloride
V
VI
VII
VIII
XI
XIX
XVIII
XVII
XVI
xv
XIV
XIII
XII
X
2810
[16]
[lS]
[16]
2810
2810
-
2810
[16]
[16]
2910
[16]
2807
2805
[16] [16]
2810
2803
[16]
[15]
2808
-
[lo]
6-ethoxy-BH-benzo(o)phenoxazone-(9)
IV
[14]
-
[9]
5-amino-SH-benzo(a)phenoxazone-(9).HCl
III
IX
-
[9]
S-hydroxy-SH-benzo(a)phenoxazone.(g)
II
-
[9]
9H-benzo(a)phenoxaeone-(9)
I
-
-
-
-
-
-
-
-
-
-
-
-
-
1616
1616
1625
1660
1620
1638
1640
1640
1640
1640
1640
1640
1630
1635
1630
1631
1630
1632
1600 1.580 1595 1580 1590 1575
1680
1580
1600 1690 1590
1695s 1680 1590 1680 16908 1670 1690
1585 1578 1590 1670 1580
1632 1636
1580
1685
1635
1590
-
1610 1570 1684
1638
-
-
1550
1653
1540
1552
1555
1558
1545
1554
1540
1550
1542
1640
1550
1550
1550
1658
1560
1551
1567
1517 1490 1510
1520
1505 1489 1620 1493 1507 1495 1516 1504 1520 1606s 1510
1510
1506
1610 1490 1510 1490 1510 1490 1489
1507
1610 1490 1510 1490 1490
1326 1290 1328 1296 1320 1288 1325 1298 1325 1290
1305 1250 1288 1260 1268 1250 1320 1298 1310 1268 1312 1280 1320 1273 1285 1267 1270
1300 1250 1313 1290s 1306 1262 1305
1310
Table 1. The characteristic absorption bands of benzo(a)phenoxazinesin i.r. spectra,
1200 1175 1199 1180 1199 1177
1195
1180
1200
1190
1180
1190
1191 1170 1190
1190
1205 1180 1198 1180 1200
1181
1195
1210 1197 -
1150
1150
1150
1153
1160
1160 1160 1165 1140 1163 1162 1170 1142 1160
1160 1142 1160 1140 1138
1150
1146
1120 1090 1120 1080 1120 1090 1120 1088
1085
1090
1110
1110 1076 1110
1105
1105
1113
1093
1107
1106 1097 1110
1112
1152 1154
1103
1107
1180 1142 1150
1008
1012
1OlE
1015
1015
1012
1008
1000
1000
999
998
1003
1010 994 1006
1000
1000
1008
998
998
[lOI [ll] [12] [13] [14] [la] [16] [ 171 [18] [I91 [20] [21]
s-9,
Dissertation,
-
2810
Ber. 86, 1807 (1903). Faculty of Natural Sciences, Palack
[21]
[20]
2810
2810
[20] [20]
2810
2808
[19] [20]
2815
2810
[18]
[18]
-
2810
[15] 1171
-
[la]
-
-
-
-
-
-
-
-
-
-
-
1635s
1632
1630
1630
1630
1632
1636
1632
1630
1630
1640
1612 1596
1583
1590 1580 1590 1574 1590 15’78 1595 1577 1590 1580% 1583
1580
1595 1580 1590
1495
1555
-
1555
1555
1565
1500 14908 1520 149Oa 1520 1490 1520 1492 1526 1500
1520 1495 1606
1605
1638
1568 1640s 1553 1546 1565
1500
1519
15658 1540 1550
1308 1265 1320 1290 1320 1300 1315 1270 1316 1270 1310 1270 1310 1270
1310 1260 1320 1290 1290 1160
1195 1205 1182 1190 1210 1190 -
1150
1200
1165 1142 -
1146
1150
1178
University, Olomouc 1966. F. THORPE, J. Chem. Sot. 91, 324 (1907). MELDOLA, Ber. 12, 2065 (1879). Miirr~~u and K. ULLMANN, Liebigs Ann. 999,90 (1896). STUZKA, Candidate’s Dissertation Paper, Faculty of Natural Scicncrs, University of J. E. Purkinje, Brno 1966. HIRSCH and F. KALCKHOFF, Ber. 23,2992 (1890). V. SrnZg~ and Z. STRBNSK~, Acta Univ. Palackiunae Olomuc. Rer. Nat. In press. R. NIET~KI and A. BOSSI, Ber. 25, 2994 (1892). Z. STRANSK+ and V. STUZKA, Mh. C&n. 96, 1555 (1964). Z. STEANSK?, P. CAPITA and E. HOLOVBKOV~, unpublished results. V. STUZKA, V. SIMANEK and E. RuZIEKA, C&m. Zvesti In press. H. EGQERS and H. DIECKMANN, B&hem. 2. 810,233 (1942).
V. J. R. R. V.
HEPP,
5.(2-aminopyridyl)-9-dimethylsmlno-SH-benzo(a)phenoxazonlumchloride 5-( 1-n&ylamino)-9-dimethylemllo-9H-benzo(u)phenoxezoniomchloride 2-hy~o~-9-dimethylemino-9H-benzo(a)phenox~zonlumohloride 2-hydroxy-5-anlllno-9-dimethylamino-5H-benzo(a)phenoxezlme. 2-hydroxy-6-(4-nitroaollino)-9-dlmethyl~mlno-5Hbenzo(a)phenoxazime 3-hydroxy-B-anilino-9-~methylamino-9H-benzo(a)phenourzoniumahloride 5-(4.sulphoanillno)-9-dll&hylamino-5H-benzo(a)phenoxazime potassium salt 5-(3-sulphoanilino)-9-dimethylamlno-6H-banzo(~)phenoxazine potassium a& 5-(6-sulpho.I-naftylamino)-9-dimethylamino-6Hbenzo(o)phenoxszime sodium salt EL(7-sulpho-l-naftylemino)-9-dimethylamino-5Hbenzo(o)phenoxszlme sodium salt 2,4-disulpho-9-dimethylamino-9H-benzo(a)phenoxszime potassium salt
[9] 0. FISCHERand E.
xxx
XXIX
XXVIII
XXVII
XXVI
xxv
XXIV
XXIII
XXII
XXI
:: xx
1120
1110 1080 1106 1080 1120
1086
1120 1090 1120
1012 99s 1000
-
1020
1015
1010
1015
2178
V. STUZKA,V. &ANEK
and Z. STF&NSK+
in the region 1653-1638 cm-l are assigned to carbonyl valence vibrations of differently substituted benzo(a)phenoxazones and the weaker band at 1612-1587 cm-l to C-N valence vibration. All the benzo(a)phenoxazones exhibit a sharp band at ~710 cm-l in the region of the out-of-plane vibrational deformations which, according to these authors, is characteristic for the condensed benzene nucleus localized in the position (a) at the phenoxazone skeleton. CORBETT [7] reports the infra-red spectra of fifteen derivatives of triphenodioxazines. He assigns the absorption bands in the region 1650-1100 cm-l to the C-N, C-C ring vibrations. The band between 1200-1160 cm-l is obviously associated with the asymmetric C-O-C vibration. Musso et al. [S] studied the displacement of the frequencies of infra-red bands of labeled triphenodioxazines and that of unlabeled triphenodioxazine. On the basis of the results obtained the bands in the spectrum were assigned as follows: vC=C aromat. 1579, 1573 cm-l, &=N 1527 cm-l, phenyl-0 1271, G-0 1178-1171 cm-l. EXPERIMENTAL The i&a-red spectra were recorded, using KBr-tablets, on Perkin-Elmer model 421, Infrascan Hilger & Watts and UR lo-Zeiss, Jena, instruments. The data are given in Tables 1 and 2. Table 2. The bands of carbonyl vibrations of benzo(a)phenoxazones Frequencies (cm-l)
Substituent
5-N+H, Q-NO, 9-H 5-H 5-O&H, &OH Q-N(CH,), Q-NGH,),
1660
1653* 1640 1638 1625 1620 1616 1616
* From Ref. [6].
With a few exceptions all the substances under investigation were prepared in our laboratory according to the literature given in Table 1. Phenoxazine was purified by conversion to an acetyl derivative [22] which on hydrolysis with sulphuric acid in ethanol yielded a substance having the m.p. 156-7%. Thionine and methylene Before use the substances were blue were supplied by the M/S N.E.-Lachema. recrystallized from benzene or toluene, and the substances 2 and 4 were purified by sublimation in vacuum. The purity of all the substances was controlled by combustion analysis and thin layer chromatography using alumina or silica gel. DISCUSSION The present paper reports the results of our study based on the assumption that the investigated benzo(a)phenoxazines have the generally assigned structures I, II, [22] A. BERNTRSEN, Ber. 20, 942 (1887).
lkfra-red speotroscopy ofbenzo(a)phenoxazines
2179
and III, respectively, where R represents the different substituents. Table 1 illustrates the frequencies of the band of the YC-H, N(CH,), groups and the frequencies of the bands of benzo(a)phenoxazines in the region 1700-1000 cm-l, which are attributable to all these compounds. The in&a-red spectrum of the basic skeleton having a quinoid carbonyl group in the position 6 or 9 exhibits one or two absorption bands at 1660-1616 cm-l (according to the type of substitution), i.e. one sharp band of high intensity and another sharp band of medium intensity. A correlation with the frequency of the band assigned to the C=O valence vibration is discussed (wide in&~). It must, however, be assumed that it is not a pure carbonyl vibration and that an association with other vC=C, 9-Dialkylamino substituted benzo(a)phenoxazines PC=N vibrations is possible. exhibit a sharp characteristic absorption band with a frequency at 1640-1630 cm-l. This band is also present in the spectrum of the 9-dialkylamino-benzo(a)phenoxazines. It appears, however, that an association particularly with the valence vibration of the exocyclic double bond C-N is possible. The intense band in the region 16001570 cm-l could not be assigned to any particular bond type as yet. In conjugated systems, for instance, in the case of benzo(a)phenoxazines, where the bonds C=C, C-N are present, the absorption bands in the region 1650-1470 cm-l can only be ascribed to valence vibrations of the whole heterocyclic skeleton. Substances with the benzo(a)phenoxazine skeleton exhibit characteristic absorption bands at 1600-1500 cm-l, the presence of which in the spectra of the unknown compounds is indicative of a benzo(a)phenoxazine structure. 1600-1570
cm-l
one or two sharp bands the absorption not vary,
intensity
of which does
1560-1540 cm-l
mostly one band the intensity of which is lower than that of the preceding band,
1520-1490
cm-l
one or two bands which differ markedly in intensity,
1330-1250 1210-1170 1160-1140 1120-1080
cm-l\ cm-l cm-l I cm-i)
several bands differing in intensity,
1120-998 cm-l
sharp band of medium intensity.
An attempt has been made to assign some of the absorption bands to the diphenylether vibration of the benzo(a)phenoxazine skeleton. This vibration exhibits a characteristic absorption band of high intensity. The conjugated systems show a band at 1276-1200 cm-l which is assigned to the asymmetric phenyl-0 valence vibration but can even be displaced to higher frequencies. The model compounds under investigation were phenoxazine and phenothiazonine salts-methylene blue and thionine. Phenoxazine exhibits two intense bands at -1295 cm-l and 1280 cm-l. The phenothiazonine salts have no band of higher intensity in the region 1300-1230 cm-l. The recorded benzo(a)phenoxazines (except for the benzo(a)phenoxazones-9) have one or two bands of higher intensity in the region 1295-1230 cm-l which obviously can be associated with the diphenylether vibration of the basic skeleton.
V. STTJZJCA, V. SIMBNEK and Z. STR~SK?
2180
Correlation of the carbonyl frequency in benzo(a)phenoxazones with the type of substitution
From the data obtained for benzo(a)phenoxazones it appears that the displacement of the band assigned to the carbonyl vibration is entirely due to electronegativity of the aubstituent in the position 5 or 9 of the basic skeleton. The C=O frequencies of the carbonyl bond which correspond to variously substituted benzo(a)phenoxazones have been illustrated in Table 2. A decrease in the electronegativity of the substituent is followed by a distinct displacement of the YC=O frequency to lower values. The vibration of the carbonyl group is easily affected because of its direct participation in the conjugation of the heteroaromatic system of the benzo(a)phenoxazones. The carbonyl frequency decreases considerably when the basic skeleton has an eleotropositive substituent with a lone pair of electrons in the position 5 or 9. This is apparently due to the positive mesomeric effect of the substituents which is active in the following order:
A in om-l
H
C,H,O-
0
-15
WA), -20
-24
-24
There exists a direct interaction between the lone pair of electrons of the substituents and the r-electrons of the benzo(a)phenoxazine skeleton, which gives rise to a relatively great condensation of the electrons of the carbonyl group. The structure of the molecule shows the participation of two possible mesomeric forms, namely IV and V, respectively.
Ip
P
STR.LNSK+[23] studied the polarographic half wave potentials obtained in the case of SH-benzo(a)phenoxazone-9 and 9-diethylamino-5H-benzo(a)phenoxazones-5, using 68 per cent ethanol as solvent (pH-value = 8). In his opinion the substitution by an electropositive diethylamino group involves a considerable displacement of the half wave potential to negative values. -0.15V
9H-benzo(a)phenoxazone-9
=1/z =
9-diethylamino-SH-benzo(a)phenoxazone-5
r1/2 = -0.46V
From the values obtained it appears that by substitution the reduction of benzo(a)phenoxaeone is rendered more difficult. This is indicative of a relatively insufficient number of electrons as compared to the C=O group of the unsubstituted benzo(a)phenoxazone. By electropositive substitution at position 9, the basic skeleton becomes an electron donor to the C=O group. This is in good agreement with the (231 F. KEHRMANN
and A. SAAUER, Z3er. 36, 475 (1903).
I&e-red epeotrosoopyof benzo(a)phenoxazines
2181
observed displacement of the frequencies of the bands of the carbonyl vibration in benzo(a)phenoxazones having electropositive substituents in the position 5 or 9. In order to establish the effect produced by the basic skeleton on the frequency of the band of the carbonyl group, a comparison was carried out between the unsubstituted phenoxazone-3 and the benzo(a)phenoxazones, which differ in the position of the carbonyl group. Phenoxazone-3
C=O vibration
1650 cm-l (1)
1640 cm-l (2)
From the comparison it appears that the presence of another aromatic ring has a very small effect on the vC=O frequencies of the benzo(a)phenoxazone skeleton. The electronic interaction of the benzo(a)@enoxazine compoun,ds
The 9-dimethylamino-5-amino substituted derivatives of SH-benzo(a)phenoxazincs and 9-dimethylamino-5H-benzo(a)phenoxazones exhibit three absorption bands with frequencies at 2800-2816 cm-l, 2860-2870, 2910-2930 cm-l frequencies in the region of valence vibrations of the methyl- and alkyl groups. In the literature, the first band at ~2810 cm-l is assigned to the C-H valence vibrations of the nitrogen which is attached to the methyl (C-H of N(CH,),). If the lone pair of electrons of nitrogen is overlapping the aromatic r-electrons, then an increase in the order of the v&N bond is, observed which probably involves a significant loss of electrons from the nitrogen atom. This indicates a certain increase in the valence frequency of the C-H vibration. The bands in the region 2850-2930 cm-r might be assigned to the vibrations of the methyl group attached to a nitrogen atom having some positive charge. In the spectrum of methyl blue where the dimethylamino and the N(CH,), groups are without charge, the bands appear at 2815 cm-l 2860, and 2925 cm-l. The relatively different stages of the electrons of the dimethylamino group attached to the benzo(a)phenoxazine skeleton which give rise to the corresponding bands in the i&a-red spectrum at 2800-2930 cm-l lend themselves to quantitative interpretation which shows that a definite electron structure cannot be assigned to the molecule of the benzo(a)phenoxazines as yet. An attempt has been made to confirm the assignment of the absorption bands of the methyl group in the infrared to different resonance structures of the compounds under discussion on the basis of other physico-chemical data. The in&a-red spectrum of Meldol’s blue does not show a band at 2810 cm-l {substance 7) which is assigned to the YC-H vibration of the N(CH,), group. The structure of the compound is given by the appended formula VI. One may expect other mesomeric forms where the positive charge on the basic skeleton is delocalized. This seems to be, however, very unlikely with regard to the properties of the substituents in position 9.
2182
V. STIJZKA,V. &B&NEK and Z. STR~NSK+
In the electronic spectrum of this substance the absorption maximum of the visible band is observed at 668 nm (E = 27.6 x 103)using absolute ethanol as solvent [l3]. The introduction of a substituent with a lone pair of electrons into the position 5 of the basic skeleton (VII) appears to result in the development of an absorption band at ~2810 cm-l. This absorption indicates that even the second possible mesomeric structure VIII participates in the whole structure of the molecule_
XII
pm
In the electronic spectrum the coloured band is displaced to longer wavelengths: for instance the absorption maximum of 5-amino-9-dimethylamino-9H-benzo(a)phenoxazoniumchloride is displaced to 626 nm (E = 29.4 x 10s)[la],6-aniline-9dimethylamino-9H-benzo(a)phenoxazoniumchloride to 650 nm (E = 71.8 x 10s} [la]. This bathochromic and hyperchromic effect on the electronic band which is exhibited in the visible range by the amino- and aryl-amino substituted g&methylaminobenzo(a)phenoxazines can be accounted for by the different electronic nature of the substituents in the positions 6 and 9. At the one end of the chain of the conjugated double bonds is an electronegative substituent and at the other end is an electropositive substituent. Conjugation of the system may result in a modiflcation of the resonance of the electronic nature of these two substituents. The in&a-red spectra of the bases of benzo(a)phenoxazines show absorption bands at ~2860 and 2920 cm-l. In the general structural formula (IX) the presence of a positive charge on the nitrogen atom is not anticipated.
The existence of these bands (a determination of the intensity of the maxima mentioned above was not carried out) indicates the presence of resonance types with a distributed charge, i.e. the positive charge localized to a greater part at the dimethylamino group. The greater tendency of the positive charge to this group is In all probability, accounted for by the behaviour of the bases during protonization. the protonization of the compound proceeds from the nitrogen at the position 5 under a simultaneous rearrangement of the conjugation of the molecule to the effect that the positive charge is localized at the dimethylamino group. This finding is further confirmed by the magnitude of the G values in Hammett’s equation when a comparison of these values obtained for substituted anilines with those of the evaluated dyes
Infra-red spectroscopy of benzo(a)pbenoxazines
is carried out.
2183
anilines amounted to G = 3-2 [25,26]. the value G = l-6 for 5-arylamino derivatives and the value G = 1.6 for Meldol’s blue. JAFF~~[27] reports that the elongation of the chain between the activation centre and the substituent by an ethylene group is followed by a decrease in the value to approximately half of it. In view of the fact that the substituents in the meta and the para position of the arylamine group attached in the position 5 of the basic skeleton are localized too far from the dimethylamino group, the protonisation cannot be attributed to the dimethylamino group, and a protonisation at position 5 is anticipated. The decrease in this value of the substances under investigation as compared to that in case of the substituted anilines can be ,explained by the finding that some of the free energy is employed for the rearrangement of the chain of the conjugated double bonds in the molecule. STRBNSKP
The value for the substituted
[24] calculated
(241 Z. STRJINSK~, Candidate’s Dissertation Paper, Faculty of Natural Sciences, University of J. E. Purkinje, Brno 1966. [25] L. P. OTT, Physical OrganicChemidy. McGraw-Hill (1940). [26] N. F. HALL and M. R. SPRINKLE,J. Am. Chem. Sot. 54, 3469 (1932). f27] H. H. JAI&, Chem. Reve. 53, 191 (1963).
I&a-red
of benzo (a >phenoxazines
spectroscopy
V. STU~KA,
V. &&NEK
and Z. STRANSKP
Institute of organic-, analytical- and physioal chemistry, Faculty of Natural Soiences Palacki University, Olomouc, Czechoslovakia (Received18 October1966) Abstract-The purpose of this paper is to assign some specific vibrational bands at 1700-1000 cm-1 to molecular vibrations of the basic benzo(a)phenoxazine skeleton, and to describe the position of the vibrational bands of some substituents attaohed to this skeleton. In addition, the effect of the electronic behaviour of the substituents on the frequency of the carbonyl vibrations of benzo(a)phenoxazoneswas determined and the possible electronic interactions in the individual moleculeswere discussed. The compounds investigated are of the types I, II, and III, where R1-Ra are the individual substituents. All the substanceswere synthetized for use aa acid-base indicators for aqueous and anhydrous media and as oxidation reduction indicators.
‘I
“\,\ ad?
,=I RI
0
0
m
II
INTR~DUOTI~N i&a-red spectra of substituted phenoxazones have been studied in some detail by MTJSSEN and MATHIES [11, CORBETT [2],and by other workers [3-51. They assign the absorption band in the region 1661-1630 cm-l to the carbonyl vibration of phenoxazone, the band at 1622-1585 cm-l to the C-N valence vibration, and the absorption bands in the region 1225-1150 cm-l s,re assumed to be due to the C-C, C-N and O-ring vibrations. The bands in the region 1595-1490 cm-l are attributed by them to the skeleton C=C valence vibrations of the quinoid and aromatic systems, and the band at 1215-1150 is ascribed to the Y C-O vibration of the oxazine ring. BUTEN~DT et al. [6] report the infra-red spectra of a number of substituted benzo(a)phenoxazones and pyridinophenoxazones. The spectra of these compounds show several characteristic bands in the region 1653-1515 cm-l. The intense bands THE
[l] H. Muss0 and H. MAITHIES, Ber. 90, 1814 (1957). [2] J. F. CORBETT, ii’peckochim. Acta 21, 1411 (1965). [3] H. Muss0 and H. BEECKEN, Ber. 94, 585 (1961). [4] G. W. CAVILL,~. S. CLEZY and F. B. WHITFIELD, Tetrahedron 12, 139 (1961). [5] A. BUTENANDT, E. BIEKERT and G. NEUBERT, Liebig Ann. 602, 72 (1957). [6] A. BUTENANDT, E. BIEKERT and W. SCHAFER, _&big8 Ann. 692. 134 (1960.) [7] J. F. CORBETT, 6’pectrochim. Acta 21, 1081 (1965). [S] H. Musso, E. D~~PP and J. KUEILS,Chem. Ber. 98, 3937 (1965). 2175
2810 -
[II] [ll] 1121 [13]
9.dimethylemino-SH-benzo(a)phenoxezone-(5)
9-diethylamino-5H-benzo(a)phenoxazone-(5)
I)-dimethylamino-SH-benzo(a)phenoxeoniumchloride
5-8mino-9-diethylamino-9H-be~o(a)phenoxezoniumsulphste 6-amino-9-dimethyl~mino-9H-benzo(a)phenoxazonium ahloride 6-anilino-9-dimethylrtmino-6H-benzo(a)phenoxazime
b-(3-methykmilino)-9-dimethylamino-SH-benzo(a)phenoxazoniumohloride 5-(bmethylanilino)-9-dimethylamino-5H-benzo(a)phenoxazime 5-(4-nitroanilino)S-dimethylemino-SH-benzo(a)phenoxezoniumchloride 6-(4-hydroxytmilino)-9-dimethylemino-SH-benzo(~)phenoxazoniumchloride 6-(3-aarboxyanilino)-9-dimethylamino-SH-benzo(a)phenoxazoniumohloride 5-(4-oarboxyaniliio)-9-dimethylamino-9H-benzo(a)phenoxezoniumchloride 5-(3-chloranilino)-9-dimethylemino-H9-benzo(a)phenoxazoniumchloride b-(Cbromanilino)O-dimethylamino-SH-benzo(a)phenoxaziniumohloride 5-(4-iodsnilino)-9-dthylamino-SH-benzo(a)phenoxszoniumchloride
V
VI
VII
VIII
XI
XIX
XVIII
XVII
XVI
xv
XIV
XIII
XII
X
2810
[16]
[lS]
[16]
2810
2810
-
2810
[16]
[16]
2910
[16]
2807
2805
[16] [16]
2810
2803
[16]
[15]
2808
-
[lo]
6-ethoxy-BH-benzo(o)phenoxazone-(9)
IV
[14]
-
[9]
5-amino-SH-benzo(a)phenoxazone-(9).HCl
III
IX
-
[9]
S-hydroxy-SH-benzo(a)phenoxazone.(g)
II
-
[9]
9H-benzo(a)phenoxaeone-(9)
I
-
-
-
-
-
-
-
-
-
-
-
-
-
1616
1616
1625
1660
1620
1638
1640
1640
1640
1640
1640
1640
1630
1635
1630
1631
1630
1632
1600 1.580 1595 1580 1590 1575
1680
1580
1600 1690 1590
1695s 1680 1590 1680 16908 1670 1690
1585 1578 1590 1670 1580
1632 1636
1580
1685
1635
1590
-
1610 1570 1684
1638
-
-
1550
1653
1540
1552
1555
1558
1545
1554
1540
1550
1542
1640
1550
1550
1550
1658
1560
1551
1567
1517 1490 1510
1520
1505 1489 1620 1493 1507 1495 1516 1504 1520 1606s 1510
1510
1506
1610 1490 1510 1490 1510 1490 1489
1507
1610 1490 1510 1490 1490
1326 1290 1328 1296 1320 1288 1325 1298 1325 1290
1305 1250 1288 1260 1268 1250 1320 1298 1310 1268 1312 1280 1320 1273 1285 1267 1270
1300 1250 1313 1290s 1306 1262 1305
1310
Table 1. The characteristic absorption bands of benzo(a)phenoxazinesin i.r. spectra,
1200 1175 1199 1180 1199 1177
1195
1180
1200
1190
1180
1190
1191 1170 1190
1190
1205 1180 1198 1180 1200
1181
1195
1210 1197 -
1150
1150
1150
1153
1160
1160 1160 1165 1140 1163 1162 1170 1142 1160
1160 1142 1160 1140 1138
1150
1146
1120 1090 1120 1080 1120 1090 1120 1088
1085
1090
1110
1110 1076 1110
1105
1105
1113
1093
1107
1106 1097 1110
1112
1152 1154
1103
1107
1180 1142 1150
1008
1012
1OlE
1015
1015
1012
1008
1000
1000
999
998
1003
1010 994 1006
1000
1000
1008
998
998
[lOI [ll] [12] [13] [14] [la] [16] [ 171 [18] [I91 [20] [21]
s-9,
Dissertation,
-
2810
Ber. 86, 1807 (1903). Faculty of Natural Sciences, Palack
[21]
[20]
2810
2810
[20] [20]
2810
2808
[19] [20]
2815
2810
[18]
[18]
-
2810
[15] 1171
-
[la]
-
-
-
-
-
-
-
-
-
-
-
1635s
1632
1630
1630
1630
1632
1636
1632
1630
1630
1640
1612 1596
1583
1590 1580 1590 1574 1590 15’78 1595 1577 1590 1580% 1583
1580
1595 1580 1590
1495
1555
-
1555
1555
1565
1500 14908 1520 149Oa 1520 1490 1520 1492 1526 1500
1520 1495 1606
1605
1638
1568 1640s 1553 1546 1565
1500
1519
15658 1540 1550
1308 1265 1320 1290 1320 1300 1315 1270 1316 1270 1310 1270 1310 1270
1310 1260 1320 1290 1290 1160
1195 1205 1182 1190 1210 1190 -
1150
1200
1165 1142 -
1146
1150
1178
University, Olomouc 1966. F. THORPE, J. Chem. Sot. 91, 324 (1907). MELDOLA, Ber. 12, 2065 (1879). Miirr~~u and K. ULLMANN, Liebigs Ann. 999,90 (1896). STUZKA, Candidate’s Dissertation Paper, Faculty of Natural Scicncrs, University of J. E. Purkinje, Brno 1966. HIRSCH and F. KALCKHOFF, Ber. 23,2992 (1890). V. SrnZg~ and Z. STRBNSK~, Acta Univ. Palackiunae Olomuc. Rer. Nat. In press. R. NIET~KI and A. BOSSI, Ber. 25, 2994 (1892). Z. STRANSK+ and V. STUZKA, Mh. C&n. 96, 1555 (1964). Z. STEANSK?, P. CAPITA and E. HOLOVBKOV~, unpublished results. V. STUZKA, V. SIMANEK and E. RuZIEKA, C&m. Zvesti In press. H. EGQERS and H. DIECKMANN, B&hem. 2. 810,233 (1942).
V. J. R. R. V.
HEPP,
5.(2-aminopyridyl)-9-dimethylsmlno-SH-benzo(a)phenoxazonlumchloride 5-( 1-n&ylamino)-9-dimethylemllo-9H-benzo(u)phenoxezoniomchloride 2-hy~o~-9-dimethylemino-9H-benzo(a)phenox~zonlumohloride 2-hydroxy-5-anlllno-9-dimethylamino-5H-benzo(a)phenoxezlme. 2-hydroxy-6-(4-nitroaollino)-9-dlmethyl~mlno-5Hbenzo(a)phenoxazime 3-hydroxy-B-anilino-9-~methylamino-9H-benzo(a)phenourzoniumahloride 5-(4.sulphoanillno)-9-dll&hylamino-5H-benzo(a)phenoxazime potassium salt 5-(3-sulphoanilino)-9-dimethylamlno-6H-banzo(~)phenoxazine potassium a& 5-(6-sulpho.I-naftylamino)-9-dimethylamino-6Hbenzo(o)phenoxszime sodium salt EL(7-sulpho-l-naftylemino)-9-dimethylamino-5Hbenzo(o)phenoxszlme sodium salt 2,4-disulpho-9-dimethylamino-9H-benzo(a)phenoxszime potassium salt
[9] 0. FISCHERand E.
xxx
XXIX
XXVIII
XXVII
XXVI
xxv
XXIV
XXIII
XXII
XXI
:: xx
1120
1110 1080 1106 1080 1120
1086
1120 1090 1120
1012 99s 1000
-
1020
1015
1010
1015
2178
V. STUZKA,V. &ANEK
and Z. STF&NSK+
in the region 1653-1638 cm-l are assigned to carbonyl valence vibrations of differently substituted benzo(a)phenoxazones and the weaker band at 1612-1587 cm-l to C-N valence vibration. All the benzo(a)phenoxazones exhibit a sharp band at ~710 cm-l in the region of the out-of-plane vibrational deformations which, according to these authors, is characteristic for the condensed benzene nucleus localized in the position (a) at the phenoxazone skeleton. CORBETT [7] reports the infra-red spectra of fifteen derivatives of triphenodioxazines. He assigns the absorption bands in the region 1650-1100 cm-l to the C-N, C-C ring vibrations. The band between 1200-1160 cm-l is obviously associated with the asymmetric C-O-C vibration. Musso et al. [S] studied the displacement of the frequencies of infra-red bands of labeled triphenodioxazines and that of unlabeled triphenodioxazine. On the basis of the results obtained the bands in the spectrum were assigned as follows: vC=C aromat. 1579, 1573 cm-l, &=N 1527 cm-l, phenyl-0 1271, G-0 1178-1171 cm-l. EXPERIMENTAL The i&a-red spectra were recorded, using KBr-tablets, on Perkin-Elmer model 421, Infrascan Hilger & Watts and UR lo-Zeiss, Jena, instruments. The data are given in Tables 1 and 2. Table 2. The bands of carbonyl vibrations of benzo(a)phenoxazones Frequencies (cm-l)
Substituent
5-N+H, Q-NO, 9-H 5-H 5-O&H, &OH Q-N(CH,), Q-NGH,),
1660
1653* 1640 1638 1625 1620 1616 1616
* From Ref. [6].
With a few exceptions all the substances under investigation were prepared in our laboratory according to the literature given in Table 1. Phenoxazine was purified by conversion to an acetyl derivative [22] which on hydrolysis with sulphuric acid in ethanol yielded a substance having the m.p. 156-7%. Thionine and methylene Before use the substances were blue were supplied by the M/S N.E.-Lachema. recrystallized from benzene or toluene, and the substances 2 and 4 were purified by sublimation in vacuum. The purity of all the substances was controlled by combustion analysis and thin layer chromatography using alumina or silica gel. DISCUSSION The present paper reports the results of our study based on the assumption that the investigated benzo(a)phenoxazines have the generally assigned structures I, II, [22] A. BERNTRSEN, Ber. 20, 942 (1887).
lkfra-red speotroscopy ofbenzo(a)phenoxazines
2179
and III, respectively, where R represents the different substituents. Table 1 illustrates the frequencies of the band of the YC-H, N(CH,), groups and the frequencies of the bands of benzo(a)phenoxazines in the region 1700-1000 cm-l, which are attributable to all these compounds. The in&a-red spectrum of the basic skeleton having a quinoid carbonyl group in the position 6 or 9 exhibits one or two absorption bands at 1660-1616 cm-l (according to the type of substitution), i.e. one sharp band of high intensity and another sharp band of medium intensity. A correlation with the frequency of the band assigned to the C=O valence vibration is discussed (wide in&~). It must, however, be assumed that it is not a pure carbonyl vibration and that an association with other vC=C, 9-Dialkylamino substituted benzo(a)phenoxazines PC=N vibrations is possible. exhibit a sharp characteristic absorption band with a frequency at 1640-1630 cm-l. This band is also present in the spectrum of the 9-dialkylamino-benzo(a)phenoxazines. It appears, however, that an association particularly with the valence vibration of the exocyclic double bond C-N is possible. The intense band in the region 16001570 cm-l could not be assigned to any particular bond type as yet. In conjugated systems, for instance, in the case of benzo(a)phenoxazines, where the bonds C=C, C-N are present, the absorption bands in the region 1650-1470 cm-l can only be ascribed to valence vibrations of the whole heterocyclic skeleton. Substances with the benzo(a)phenoxazine skeleton exhibit characteristic absorption bands at 1600-1500 cm-l, the presence of which in the spectra of the unknown compounds is indicative of a benzo(a)phenoxazine structure. 1600-1570
cm-l
one or two sharp bands the absorption not vary,
intensity
of which does
1560-1540 cm-l
mostly one band the intensity of which is lower than that of the preceding band,
1520-1490
cm-l
one or two bands which differ markedly in intensity,
1330-1250 1210-1170 1160-1140 1120-1080
cm-l\ cm-l cm-l I cm-i)
several bands differing in intensity,
1120-998 cm-l
sharp band of medium intensity.
An attempt has been made to assign some of the absorption bands to the diphenylether vibration of the benzo(a)phenoxazine skeleton. This vibration exhibits a characteristic absorption band of high intensity. The conjugated systems show a band at 1276-1200 cm-l which is assigned to the asymmetric phenyl-0 valence vibration but can even be displaced to higher frequencies. The model compounds under investigation were phenoxazine and phenothiazonine salts-methylene blue and thionine. Phenoxazine exhibits two intense bands at -1295 cm-l and 1280 cm-l. The phenothiazonine salts have no band of higher intensity in the region 1300-1230 cm-l. The recorded benzo(a)phenoxazines (except for the benzo(a)phenoxazones-9) have one or two bands of higher intensity in the region 1295-1230 cm-l which obviously can be associated with the diphenylether vibration of the basic skeleton.
V. STTJZJCA, V. SIMBNEK and Z. STR~SK?
2180
Correlation of the carbonyl frequency in benzo(a)phenoxazones with the type of substitution
From the data obtained for benzo(a)phenoxazones it appears that the displacement of the band assigned to the carbonyl vibration is entirely due to electronegativity of the aubstituent in the position 5 or 9 of the basic skeleton. The C=O frequencies of the carbonyl bond which correspond to variously substituted benzo(a)phenoxazones have been illustrated in Table 2. A decrease in the electronegativity of the substituent is followed by a distinct displacement of the YC=O frequency to lower values. The vibration of the carbonyl group is easily affected because of its direct participation in the conjugation of the heteroaromatic system of the benzo(a)phenoxazones. The carbonyl frequency decreases considerably when the basic skeleton has an eleotropositive substituent with a lone pair of electrons in the position 5 or 9. This is apparently due to the positive mesomeric effect of the substituents which is active in the following order:
A in om-l
H
C,H,O-
0
-15
WA), -20
-24
-24
There exists a direct interaction between the lone pair of electrons of the substituents and the r-electrons of the benzo(a)phenoxazine skeleton, which gives rise to a relatively great condensation of the electrons of the carbonyl group. The structure of the molecule shows the participation of two possible mesomeric forms, namely IV and V, respectively.
Ip
P
STR.LNSK+[23] studied the polarographic half wave potentials obtained in the case of SH-benzo(a)phenoxazone-9 and 9-diethylamino-5H-benzo(a)phenoxazones-5, using 68 per cent ethanol as solvent (pH-value = 8). In his opinion the substitution by an electropositive diethylamino group involves a considerable displacement of the half wave potential to negative values. -0.15V
9H-benzo(a)phenoxazone-9
=1/z =
9-diethylamino-SH-benzo(a)phenoxazone-5
r1/2 = -0.46V
From the values obtained it appears that by substitution the reduction of benzo(a)phenoxaeone is rendered more difficult. This is indicative of a relatively insufficient number of electrons as compared to the C=O group of the unsubstituted benzo(a)phenoxazone. By electropositive substitution at position 9, the basic skeleton becomes an electron donor to the C=O group. This is in good agreement with the (231 F. KEHRMANN
and A. SAAUER, Z3er. 36, 475 (1903).
I&e-red epeotrosoopyof benzo(a)phenoxazines
2181
observed displacement of the frequencies of the bands of the carbonyl vibration in benzo(a)phenoxazones having electropositive substituents in the position 5 or 9. In order to establish the effect produced by the basic skeleton on the frequency of the band of the carbonyl group, a comparison was carried out between the unsubstituted phenoxazone-3 and the benzo(a)phenoxazones, which differ in the position of the carbonyl group. Phenoxazone-3
C=O vibration
1650 cm-l (1)
1640 cm-l (2)
From the comparison it appears that the presence of another aromatic ring has a very small effect on the vC=O frequencies of the benzo(a)phenoxazone skeleton. The electronic interaction of the benzo(a)@enoxazine compoun,ds
The 9-dimethylamino-5-amino substituted derivatives of SH-benzo(a)phenoxazincs and 9-dimethylamino-5H-benzo(a)phenoxazones exhibit three absorption bands with frequencies at 2800-2816 cm-l, 2860-2870, 2910-2930 cm-l frequencies in the region of valence vibrations of the methyl- and alkyl groups. In the literature, the first band at ~2810 cm-l is assigned to the C-H valence vibrations of the nitrogen which is attached to the methyl (C-H of N(CH,),). If the lone pair of electrons of nitrogen is overlapping the aromatic r-electrons, then an increase in the order of the v&N bond is, observed which probably involves a significant loss of electrons from the nitrogen atom. This indicates a certain increase in the valence frequency of the C-H vibration. The bands in the region 2850-2930 cm-r might be assigned to the vibrations of the methyl group attached to a nitrogen atom having some positive charge. In the spectrum of methyl blue where the dimethylamino and the N(CH,), groups are without charge, the bands appear at 2815 cm-l 2860, and 2925 cm-l. The relatively different stages of the electrons of the dimethylamino group attached to the benzo(a)phenoxazine skeleton which give rise to the corresponding bands in the i&a-red spectrum at 2800-2930 cm-l lend themselves to quantitative interpretation which shows that a definite electron structure cannot be assigned to the molecule of the benzo(a)phenoxazines as yet. An attempt has been made to confirm the assignment of the absorption bands of the methyl group in the infrared to different resonance structures of the compounds under discussion on the basis of other physico-chemical data. The in&a-red spectrum of Meldol’s blue does not show a band at 2810 cm-l {substance 7) which is assigned to the YC-H vibration of the N(CH,), group. The structure of the compound is given by the appended formula VI. One may expect other mesomeric forms where the positive charge on the basic skeleton is delocalized. This seems to be, however, very unlikely with regard to the properties of the substituents in position 9.
2182
V. STIJZKA,V. &B&NEK and Z. STR~NSK+
In the electronic spectrum of this substance the absorption maximum of the visible band is observed at 668 nm (E = 27.6 x 103)using absolute ethanol as solvent [l3]. The introduction of a substituent with a lone pair of electrons into the position 5 of the basic skeleton (VII) appears to result in the development of an absorption band at ~2810 cm-l. This absorption indicates that even the second possible mesomeric structure VIII participates in the whole structure of the molecule_
XII
pm
In the electronic spectrum the coloured band is displaced to longer wavelengths: for instance the absorption maximum of 5-amino-9-dimethylamino-9H-benzo(a)phenoxazoniumchloride is displaced to 626 nm (E = 29.4 x 10s)[la],6-aniline-9dimethylamino-9H-benzo(a)phenoxazoniumchloride to 650 nm (E = 71.8 x 10s} [la]. This bathochromic and hyperchromic effect on the electronic band which is exhibited in the visible range by the amino- and aryl-amino substituted g&methylaminobenzo(a)phenoxazines can be accounted for by the different electronic nature of the substituents in the positions 6 and 9. At the one end of the chain of the conjugated double bonds is an electronegative substituent and at the other end is an electropositive substituent. Conjugation of the system may result in a modiflcation of the resonance of the electronic nature of these two substituents. The in&a-red spectra of the bases of benzo(a)phenoxazines show absorption bands at ~2860 and 2920 cm-l. In the general structural formula (IX) the presence of a positive charge on the nitrogen atom is not anticipated.
The existence of these bands (a determination of the intensity of the maxima mentioned above was not carried out) indicates the presence of resonance types with a distributed charge, i.e. the positive charge localized to a greater part at the dimethylamino group. The greater tendency of the positive charge to this group is In all probability, accounted for by the behaviour of the bases during protonization. the protonization of the compound proceeds from the nitrogen at the position 5 under a simultaneous rearrangement of the conjugation of the molecule to the effect that the positive charge is localized at the dimethylamino group. This finding is further confirmed by the magnitude of the G values in Hammett’s equation when a comparison of these values obtained for substituted anilines with those of the evaluated dyes
Infra-red spectroscopy of benzo(a)pbenoxazines
is carried out.
2183
anilines amounted to G = 3-2 [25,26]. the value G = l-6 for 5-arylamino derivatives and the value G = 1.6 for Meldol’s blue. JAFF~~[27] reports that the elongation of the chain between the activation centre and the substituent by an ethylene group is followed by a decrease in the value to approximately half of it. In view of the fact that the substituents in the meta and the para position of the arylamine group attached in the position 5 of the basic skeleton are localized too far from the dimethylamino group, the protonisation cannot be attributed to the dimethylamino group, and a protonisation at position 5 is anticipated. The decrease in this value of the substances under investigation as compared to that in case of the substituted anilines can be ,explained by the finding that some of the free energy is employed for the rearrangement of the chain of the conjugated double bonds in the molecule. STRBNSKP
The value for the substituted
[24] calculated
(241 Z. STRJINSK~, Candidate’s Dissertation Paper, Faculty of Natural Sciences, University of J. E. Purkinje, Brno 1966. [25] L. P. OTT, Physical OrganicChemidy. McGraw-Hill (1940). [26] N. F. HALL and M. R. SPRINKLE,J. Am. Chem. Sot. 54, 3469 (1932). f27] H. H. JAI&, Chem. Reve. 53, 191 (1963).