Synthesis of tetraaza derivatives of benzoxazinophenothiazine

Article abstract of DOI:10.13005/ojc/310114

Tetraaza benzoxazinophenothiazine heterocyclic rings were synthesized and characterized. The key intermediate, 11-amino-6-chlorobenzo[a]-8,10-diazaphenoxazin-5-one was prepared by reaction of 4,5-diamino-6-hydroxypyimidine with 2,3-dichloro-1,4-naphthoquinone in anhydrous sodium carbonate. Whereas the parent tetraaza derivatives: 15-amino-8-bromo-6,9,12,14-tetraazabenzo[a][1,4]benzoxazino[3,2-c] phenothiazine, 9,15-diamino-6,8,12,14-tetraazabenzo[a][1,4]benzoxazino[3,2-c]pheno- thiazine and 15-amino-6,8,12,14-tetraazabenzo[a][1,4]benzoxazino[3,2-c]phenothiazine were synthesized by base catalyzed condensation reactions of 11-amino-6-chlorobenzo[a]-8,10-diazaphenoxazin-5-one with 2-amino-5-bromopyrazin-3-thiol, 4,6-diaminopyrimidine-5-thiol and 4-diaminopyrimidine-5-thiol respectively. The compounds are intensely coloured and are readily reduced with sodium dithionite to their leuco bases which can make them applicable as vat dyes. Their wash fastness, sublimation fastness and staining undyed fabric were evaluated.

Full text of DOI:10.13005/ojc/310114

ISSN: 0970-020 X
CODEN: OJCHEG
2015, Vol. 31, No. (1):
Pg. 133-139
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Synthesis of Tetraaza Derivatives of
Benzoxazinophenothiazine
BENJAMIN E. EZEMA1*, CHIDIMMA G. EZEMA2, JUDE I. AYOGU1,
DAVID I. UGWU 1 and EFETURI A. ONOABEDJE1
1Department of Pure and Industrial Chemistry,
Faculty of Physical Sciences, University of Nigeria, Nsukka, Nigeria.
2National Centre for Energy Research and Development, University of Nigeria, Nsukka, Nigeria.
*Corresponding author E-mail: Benjamin.ezema@unn.edu.ng
(Received: December 06, 2014; Accepted: January 09, 2015)
http://dx.doi.org/10.13005/ojc/310114
ABSTRACT
Tetraaza benzoxazinophenothiazine heterocyclic rings were synthesized and
characterized. The key intermediate, 11-amino-6-chlorobenzo[a]-8,10-diazaphenoxazin-5-one
was prepared by reaction of 4,5-diamino-6-hydroxypyimidine with 2,3-dichloro-1,4-naphthoquinone
in anhydrous sodium carbonate. Whereas the parent tetraaza derivatives: 15-amino-8-bromo-
6,9,12,14-tetraazabenzo[a][1,4]benzoxazino[3,2-c] phenothiazine, 9,15-diamino-6,8,12,14-
tetraazabenzo[a][1,4]benzoxazino[3,2-c]pheno- thiazine and 15-amino-6,8,12,14-
tetraazabenzo[a][1,4]benzoxazino[3,2-c]phenothiazine were synthesized by base catalyzed
condensation reactions of 11-amino-6-chlorobenzo[a]-8,10-diazaphenoxazin-5-one with 2-amino-
5-bromopyrazin-3-thiol, 4,6-diaminopyrimidine-5-thiol and 4-diaminopyrimidine-5-thiol respectively.
The compounds are intensely coloured and are readily reduced with sodium dithionite to their
leuco bases which can make them applicable as vat dyes. Their wash fastness, sublimation
fastness and staining undyed fabric were evaluated.
Key words: 2-Amino-5-bromopyrazin-3-thiol; 4,5-diamino-6-hydroxypyimidine;
4,6-diaminopyrimidine-5-thiol; 2,3-dichloro-1,4-naphthoquinone;
Leuco Base; Vat dye; alkaline hydrolysis; condensation reaction.
INTRODUCTION
sedatives, CNS depressants, tranquilizing agents,
antitumor,1 antibacterial, anthelminthic, spasmolytic,
2
The application of phenoxazine and
phenothiazine compounds and their derivatives in
drug, textile, agriculture and other related industries
has long been recognized. Phenoxazine and its
derivatives were found to show tremendous
pharmacological activities as antiepileptic,
anticancer and parasticidal agents.3 Other
applications include their use as antioxidants and
biological stains, 4 laser dyes, 5 acid-base indicators,
6
bromometric and stannometric indicators and
7
especially as chromophoric compound in host
guest artificial protonic antenna system.

134
EZEMA et al., Orient. J. Chem., Vol. 31(1), 133-139 (2015)
However, phenothiazines and their been found useful as antioxidants in lubricants and
derivatives are useful in medicine as antitussive fuels. 12
and antitumor agents, anticonvulsants,
8
tranquilizers, antipsychotics, antimalarial agents
The three-branched fused phenothiazine
and in the treatment of prion diseases 9, to mention ring of the type 1 13 has been known for more than a
but a few. In textile, paint and plastic industries, they century.The monoaza-, diaza- and triaza-analogues
are used as vat dyes and pigments 10; and in of benzoxazinophenothiazine rings of the types 2,
agricultural industries, as insecticides and 3, 4 14 have been known. The authors wish to report
nematodicides. 11 In petroleum industries, they have here the successful synthesis of tetraaza-analogue.
N
O
N
S
N
O
N
O
N
N
N
N
N
N
N
S
S
S
S
N
2N
1
2
4
3
EXPERIMENTAL
to give dirty brown precipitates which was filtered
and dried in a desiccator. Pure sample for analysis
The solvents were of analytical grade from were further recrystallized from aqueous DMF. M.p.
Sigma-Aldrich.
diaminopyrimidine,
hydroxypyrimidine
2-aminopyrazine,
4,6- > 300 oC; FT-IR (KBr):  max 3488, 3420 (NH2), 1589
4,5-Diamino-6- (C=C, C=N), 770 and 728 cm-1.
2,3-dichloro-1,4-
and
naphthoquinone were also products of Aldrich 4,6-Diamino-5-thiocyanatopyrimidine (10)
chemicals. Melting points were determined using 4,6-Diaminopyrimidine 9 (15.00 g, 14
electrothermal melting point apparatus in open mmol) was poured into a litre of three-necked flask
capillaries and were uncorrected. The reactions equipped with a reflux condenser, mechanical glass
were monitored with TLC and also the purity was stirrer and dropping funnel. Glacial acetic acid
o
ascertained with TLC. Infrared spectra were cooled to 18 C was added and the mixture was
recorded on FT-IR 8400S spectrophotometer using further cooled in an ice-salt bath. Sodium
KBr discs. Nuclear magnetic resonance spectra (1H- thiocyanate (22.00 g) was added with stirring while
o
o
NMR and 13C-NMR) were determined using Brucker maintaining the temperature at -5 C and 0 C.
300 MHz instrument; chemical shifts were reported Bromine (8.00 mL) was added in droplets from the
on (ppm) scale.
dropping funnel to the ice cooled mixture for over 1
h and stirring was continued for a period of 5 h
o
Elemental analysis was obtained on Heraous while maintaining the temperature near 0 C. The
rapid analyzer
2-Amino-5-bromopyrazin-3-thiol (8)
Procedure as reported in literature. 15
slurry was left overnight, water was added and
mixture warmed to 80 oC and filtered hot. The filtrate
was preserved and the orange residue extracted with
A mixture of 2-amino-3,5-dibromopyrazine acetic acid. The acetic acid extract was combined
6 (10 g, 42 mmole) and sodium hydrosulphide (4.86 with the preserved filtrate and neutralized with
g, 84 mmole) was poured in a 250 mL reaction flask concentrated ammonia while cooling and
attached to reflux condenser. Methanol (100 mL) maintaining the temperature below 30 oC. It was then
was added and the mixture was refluxed for 13 h in filtered and the residue recrystallized from methanol
water bath. A little amount of activated carbon was to give 4,6-diamino-5-thiocyanatopyrimidine as
added and the mixture boiled for additional 15 min. bright yellow solid, m.p.181-182 oC (lit. 183-184 oC)
It was then filtered and the filtrate was allowed to [15]; FT-IR (KBr):  max 3475, 3415 (NH2), 1579
cool. It was neutralized with dilute hydrochloric acid (C=C, C=N), 1160, 790 and 730 cm-1.

EZEMA et al., Orient. J. Chem., Vol. 31(1), 133-139 (2015)
135
4, 6-Diaminopyrimidine-5-thiol (11)
4,6-Diamino-5-thiocyanatopyrimidine 10
(250 mL) containing a solution of benzene (100
mL) and DMF (20 mL). The mixture was warmed in
a water bath for 45 min until complete dissolution.
1 1 - A m i n o - 6 - c h l o r o b e n z o [ a ] - 8 , 1 0 -
diazaphenoxazin-5-one 14 (2.89 g, 97 mmol) was
later added and the entire mixture was refluxed in
a water bath with continuous stirring for 11 h.
Benzene was distilled off and the slurry was poured
into water (600 mL) and warmed to dissolve the
inorganic material. It was filtered, washed with
water, recrystallized from aqueous acetone and
later treated with activated charcoal to yield 18 as
(12.00 g, 72 mmol) was added into a reaction flask
containing potassium hydroxide (40 g) water (100
mL).The mixture was refluxed in sand bath for 13 h
until ammonia gas ceased to evolve. Activated
carbon was added to the mixture and it was refluxed
for further 20 min, it was filtered hot and the filtrate
allowed cooling. It was neutralized with glacial
acetic acid in ice-salt bath while maintaining the
o
temperature below 10 C. It was filtered and the
residue recrystallized from methanol to give 4,6-
Diaminopyrimidine-5-thiol (11) as yellow crystals.
o
intense red powder. M. p. > 320 (dec.); IR (KBr):

max cm-1 3466, 3396 (NH2), 1598, 1472 (C=N, C=C).
FT-IR (KBr): 
3480, 3413 (NH2), 1590 (C=C,
max
C=N), 1140, 1080 780 and 735 cm-1.
1H-NMR (DMSO) ppm: 9.10 (H-7, s), 7.85-7.70 (m,
H1, H2, H3, H4), 6.90 (br, NH2); 13C-NMR (CDCl3)
ppm: 157.7, 153.0, 151.5, 148.1, 147.1, 145.8,
139.2, 137.6, 136.0, 134.4, 132.2, 130.6, 130.0,
119.5.
1 1 - A m i n o - 6 - c h l o r o b e n z o [ a ] - 8 , 1 0 -
diazaphenoxazin-5-one (14)
4,5-Diamino-6-hydroxypyrimidine 12 (2.0
g, 15 mmol) and anhydrous sodium carbonate (2.5
g, 23 mmol) were poured in a three-necked reaction
flask (250 mL). A solution of benzene (120 mL) and
DMF (15 mL) was added and the mixture was boiled
for 45 min until complete dissolution. 2,3-Dichloro-
1,4-naphthoquinone 13 (3.60 g, 15 mmol) was later
added and the mixture refluxed for 5 h in water
Analysis: Calculated for C18H8N7OSBr: (%):
C, 48.01, H, 1.79, N, 21.77, S, 7.12, Br, 17.75.Found:
C, 48.05, H, 1.77, N, 21.77, S, 7.12, Br, 17.76.
9,15-Diamino-6,8,12,14-tetraazabenzo[a][1,4]
benzoxazino[3,2-c]phenothiazine (22)
o
bath at 75-80 C. At the end of the reflux period,
4,6-Diaminopyrimidine-5-thiol 11 (2.0 g, 14 mmol)
was condensed with 11-Amino-6-chlorobenzo[a]-
8,10-diazaphenoxazin-5-one 14 (4.20 g, 15 mmol)
in presence of anhydrous sodium carbonate (1.67
g, 15 mmol) to give 9,15-diamino-6,8,12,14-
tetraazabenzo[a][1,4]benzoxazino[3,2-
c]phenothiazine as reddish brown powder. mp >
300o (dec.);FT-IR (KBr):max cm-1 3450, 3376 (2NH2),
1590, 1482 (C=N, C=C); 1H-NMR (DMSO) ppm: 8.35
(1H, s, H-7), 7.90-7.75 (m, H1, H2, H3, H4) and
6.91 (2NH2, s), 13C-NMR (CDCl3) ppm: 159.7, 157.0,
155.5, 152.1, 147.1, 138.8, 135.2, 126.6, 123.0,
121.4, 120.2, 119.6, 119.0, 118.7 .
benzene was distilled off and the slurry poured into
water (100 mL) and stirred to dissolve the inorganic
material. It was cooled overnight, filtered and the
residue was recrystallized from acetone after
treatment with activated carbon to give 11-amino-
6-chlorobenzo[a]-8,10-diazaphenoxazin-5-one 14
o
as deep orange powder; m.p. 290-291 C. FT-IR
(KBr): max 3470, 3339 cm-1, (NH2), 1655 (C=O),
1
1589, 1540 (C=C, C=N). H-NMR (DMSO) ppm:
7.80-7.70 (5H, m, Ar-H), 6.90 (s, NH2). 13C-NMR
(CDCl3) ppm: 191.3 (C=O), 168.7, 165.8, 161.3,
150.3, 148.3, 137.5, 134.1, 133.0, 131.2, 129.9,
137.8, 126.9, 116.5 .
Analysis: Calculated for C18H10N8OS: (%):
C, 55.95, H, 2.61, N, 29.00, S, 8.30,
Found: C, 55.97, H, 2.59, N, 29.03, S, 8.29.
Analysis: Calculated for C14H7N4ClO2: (%):
C, 56.30; H, 2.36; N, 18.76; Cl, 11.87.
Found: C, 56.32; H, 2.36; N, 18.74; Cl, 11.89.
15-Amino-6,8,12,14-tetraazabenzo[a]
[1,4]benzoxazino[3,2-c]phenothiazine (22)
4-Aminopyrimidine-5-thiol 11 (2.0 g, 15
General Procedure for the Preparations of the
Complex Compounds
2-Amino-5-bromopyrazin-3-thiol 8 (2.0 g,
97 mmol) and anhydrous sodium carbonate (1.0 g,
97 mmol) were poured in 3-necked reaction flask
mmol)
condensed
with
11-Amino-6-
chlorobenzo[a]-8,10-diazaphenoxazin-5-one 14
(4.69 g, 15 mmol) in the presence of anhydrous

136
EZEMA et al., Orient. J. Chem., Vol. 31(1), 133-139 (2015)
sodium carbonate (1.67 g, 15 mmol) to give 15- fabrics were inserted into the separate solutions
a m i n o - 6 , 8 , 1 2 , 1 4 - t e t r a a z a b e n z o [ a ] followed by addition of glacial acetic (5.0 mL). The
[1,4]benzoxazino[3,2-c]phenothiazine as dark mixtures were refluxed with gradual increase in
purple brown powder mp > 320o (dec.). FT-IR (KBr): temperature and occasional agitation for further 1

max cm-1 3450, 3376 (NH2), 1598, 1472 (C=N, C=C). h. They were quickly cooled to room temperature
and the fabrics were removed and air-dried. Their
1H-NMR (DMSO) ppm: 8.70 (s, H-7), 8.55 wash fastness, stain on undyed fabric and
(s, H-9), 7.8-7.75 (m, H1, H2, H3, H4) and 6.50 (NH2, sublimation fastness based on the international
s), 13C-NMR (CDCl3) ppm: 159.7, 157.0, 155.5, geometric gray standard (1 for poor and 5 for
152.1, 147.1, 145.8, 143.2, 136.6, 133.0, 131.4, excellent respectively) were ascertained.
130.2, 129.6, 129.0, 119.7
RESULTSAND DISCUSSION
Analysis: Calculated for C18H10N8OS: (%):
C, 58.22, H, 2.44, N, 26.40, S, 8.63,
Found: C, 58.27, H, 2.44, N, 26.38, S, 8.67.
2-Aminopyrazine 5 was converted to 3,5-
dibromo-2-aminopyrazine 6 by treating with
bromine in acetic acid and sodium acetate. Refluxing
General Method of Dyeing with the Compounds 6 in methanol and sodium hydrosulphide for 13 h
14, 18 and 22 gave the sodium salt 7 which was then neutralized
The dye compounds (0.20 g) each were with glacial acetic acid to give 2-amino-5-
weighed into separate reaction flasks attached to bromopyrazin-3-thiol 8 as brownish ash powder. On
reflux condensers and thermometers. Acetone (60 the other hand, 4,6-diaminopyrimidine 9 was
mL) was added to the separate reaction mixtures thiocyanated with sodium thiocyanate dihydrate in
o
each and warmed in water bath to achieve glacial acetic and bromine at -5 C to give 4,6-
dissolution. Little volume of DMF (5.0 mL) was also diamino-5-thiocyanatopyrimidine 10. Alkaline
added to aid complete dissolution. Sodium dithionite hydrolysis of 10 in 40 % KOH followed by
(5.0 g) was later added and the mixtures refluxed neutralization with acetic acid gave 4,6-
for 2 h and allowed to cool to 40 oC. Pieces of rayon diaminopyrimidine-5-thiol 11 (scheme 1).
Br2/AcOH
NaOAc
N
Br
N
Br
Br
N
N
SNa
NH2
NaSH
MeOH
Br
N
N
SH
AcOH
N
5
NH2
N
6
NH2
NH2
7
8
N
NH2
SC
N
N
NH2
SH
N
NH2
(i)
KOH
NaSCN.H2O
AcOH/Br2
(ii)
N
N
AcOH
N
NH2
10
NH2
11
NH2
9
Scheme 1:
When 4,5-diamino-6-hydroxypyimidine 12 1H and 13C-NMR provided further support for the
1
was treated with 2,3-dichloro-1,4-naphthoquinone assigned structure. The H-NMR could not resolve
13 in anhydrous sodium carbonate and benzene/ the individual protons but gave multiplet at ppm 7.80-
DMF, the concomitant product 11-amino-6- 7.70 due to aromatic protons while the singlet at 6.90
chlorobenzo[a]-8,10-diazaphenoxazin-5-one 14 ppm was assigned to NH2. 13C-NMR gave prominent
was obtained as a deep orange solid. Elemental chemical shift at ppm 191.3 for C=O (scheme 2).
analysis agrees with the molecular formular
C14H7N4O2Cl. FT-Infrared spectrum gave bands at
Formation of compound 14 is proposed
3441, 3344cm-1for (N-H) and at 1675 cm-1 for (C=O). as follows (Scheme 3).

EZEMA et al., Orient. J. Chem., Vol. 31(1), 133-139 (2015)
137
2
NH2
O
3
4
1
NH2
11
12
N
NH2
OH
Cl
Cl
Na2CO3
N
10
+
N
C6H6/DMF
5
N
9
N
8
O
7
O
6
O
13
12
Cl
14
Scheme 2:
NH2
NH2
N
O
NH2
NH2
OH
NH2
N
Cl
Cl
NH2
..
(-)
-Cl
Na2CO3
N
+
N
O
N
O-
Na+
N
O
O
12
15
Cl
13
O
16
NH2
H
NH2
OH
N
-H2O
N
O
N
N
N
O
O
N
O
Cl
Cl
17
14
Scheme 3:
The presence of reactive halogen and
Structure 18 was assigned based on the
spectra and elemental analysis. The elemental
analysis was in agreement with the molecular
formula C18H8N7OSBr. The FT-infrared spectrum
gave bands at 3401, 3346 cm-1 (NH), 1598 and
1472 cm-1 (aromatic C=C, C=N).The chemical shifts
in the 1H-NMR at ppm 9.10 (H-7, s), 7.85-7.70 (m,
H-1, H-2, H-3, H-4), 6.90 (br, NH2) were in support
of structure 18. 13C-NMR gave further evidence of
the assigned structure. (Scheme 4)
carbonyl groups in compound 14 led to the
consideration of further extension of the conjugated
ring system. This was achieved by refluxing 11-
amino-6-chlorobenzo[a]-8,10-diazaphenoxazin-5-
one 14 with 2-amino-5-bromopyrimidine-3-thiol 8
in a basic medium of anhydrous sodium carbonate
for 11 h to furnish one of the tetraaza heterocycles
15-amino-8-bromo-6,9,12,14-tetraazabenzo[a]
[1,4]benzoxazino[3,2-c]phenothiazine 18 as an
intense red powder mp > 300 oC.
2
NH2
15
NH2
1
3
16
N
H2N
HS
N
N
N
O
Na2CO3
4
N
14
13
N
+
C6H6/DMF
Br
O
N
5
N
N
O
12 11
Cl
S
10
N 6
14
8
N
9
7
8
Br
16
Scheme 4:

138
EZEMA et al., Orient. J. Chem., Vol. 31(1), 133-139 (2015)
NH2
N
NH2
N
N
N
NH2
S
N
O
N
O
-
N
Cl
N
+
..
NH2
Br
O
O
Cl
S
N
19
14
N
20
Br
NH2
N
NH2
N
N
N
O
N
N
OH
- H2 O
O
N
H
N
S
S
N
N
N
N
Br
Br
18
21
Scheme 5: Product 18 was likely formed by the proposed mechanism
When 11-amino-6-chlorobenzo[a]-8,10- elemental analysis of 22 agreed with the molecular
diazaphenoxazin-5-one 14 was also treated with formular C18H10N8OS. 1H and 13C NMR gave further
4,6-diaminopyrimidine-5-thiol 11 in anhydrous support for the assigned structure. Compound 22
sodium carbonate, another tetraaza heterocycle exhibited proton chemical shifts signals in ppm as
9,15-diamino-6,8,12,14-tetraazabenzo[a][1,4] follows: 8.35 (s, H-7), 7.90-7.75 (m, H-1, H-2, H-3,
benzoxazino[3,2-c]pheno- thiazine 22 (R = NH2) H-4) and 6.79 (2NH2, br).
was obtained as reddish brown powder. The
NH2
NH2
N
NH2
N
N
O
N
N
O
S
R
Na2CO3
N
N
+
N
N
N
C6H6/DMF
O
S
N
Cl
R
14
11
22
R = NH2, H
Scheme 6:
NH2
N
NH2
N
NH2
S
N
N
O
N
N
+
N
..
NH2
-
O
O
Cl
N
O
S
R
Cl
N
23
14
R
N
24
NH2
N
NH2
N
O
N
N
OH
N
N
N
N
- H2O
N
N
H
N
O
S
R
S
R
N
22
25
22
R = NH2, H
Scheme 7: Formation of 22 follows the proposed mechanism as in scheme 7 below

EZEMA et al., Orient. J. Chem., Vol. 31(1), 133-139 (2015)
139
Table 1. Fastness properties of synthesized heterocyclic dyes
Dye no
Wash
fastness
Stain on undyed fabric
after washing (1-5)
Sublimation
fastness (1-5)
Stain on undyed fabric
after sublimation (1-5)
(1-5)
Rayon
Cotton
Rayon
Cotton
14
18
3
4
4-5
4
3
4
4
4
3-4
4-5
4-5
5
3
4
4
4
3
4
4
4
4
4-5
4-5
4-5
22(R=NH2)
22(R=H)
Again, treatment of 14 with
4-
They exhibited good to excellent shades on the
rayon fabric and showed excellent wash fastness
and good sublimation fastness based on the
international geometric gray standard (1 for poor
and 5 for excellent respectively) as presented in
the table.
aminopyrimidin-5-thiol gave 15-amino-6,8,12,14-
tetraazabenzo[a][1,4]benzoxazino[3,2-
c]phenothiazine 22 (R = H) as dark purple brown
powder:The elemental analysis of 22 (R = H) agreed
with the molecular formular C18H9N7OS. 1H and 13
C
NMR gave further support for the assigned structure.
The compound 22 exhibited the following protons
chemical shifts signals in ppm: 8.70 (s, H-7), 8.55
(s, H-9), 7.8-7.75 (m, H-1, H-2, H-3, H-4) and 6.50
(NH2, s) (scheme 6).
CONCLUSION
Tetraaza heterocyclic compounds were
synthesized and characterized by spectral and
elemental analysis. Their ease of reduction with
sodium hydrosulphide (sodium dithionite) makes
them applicable as vat dyes. Their wash fastness,
sublimation fastness and staining undyed fabric
were evaluated.
Dyeing of nylon fabric with synthesized dyes:
The new compounds are vat dyes and they
are applied in their reduced state. Dyeing was
carried out in the presence of sodium dithionite and
in aqueous solution of acetone/DMF/ acetic acid.
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