Synthesis of some new phthalazines and their evaluation as corrosion inhibitors of steel

Article abstract of DOI:10.3184/174751914X14116480062198

A convenient synthesis has been achieved of 11 substituted phthalazines starting from the condensation of 2-(p-toluoyl)benzoic acid with hydrazine and some of its simple congeners, H2NNHR. Four of the phthalazines showed activity as inhibitors of the corr

Full text of DOI:10.3184/174751914X14116480062198

JOURNAL OF CHEMICAL RESEARCH 2014
VOL. 38 OCTOBER, 617–621
RESEARCH PAPER 617
Synthesis of some new phthalazines and their evaluation as corrosion
inhibitors of steel
Magdy M. Hemdan*, Sherif M. Taha, Adel M. Gabr and Mohamed Y. Elkady
Department of Chemistry, Faculty of Science, Ain Shams University, 11566 Abbasia, Cairo, Egypt
A convenient synthesis has been achieved of 11 substituted phthalazines starting from the condensation of 2-(p-toluoyl)benzoic
acid with hydrazine and some of its simple congeners, H2NNHR. Four of the phthalazines showed activity as inhibitors of the
corrosion of steel immersed in 5 M HCl solutions.
Keywords: 2‑p‑(toluoyl)benzoic acid, hydrazine derivatives, phthalazine derivatives, corrosion inhibitors
Addition of an inhibitor remains a necessary procedure to secure
the metal against attack in chemical cleaning and pickling to
remove mill scales from metallic surfaces. Inhibitors should
be effective even under severe conditions such as concentrated
HCl at temperature up to 60 °C.1–3 Organic compounds rich
in heteroatoms such as sulfur, nitrogen and oxygen generally
exhibit the best protection against corrosion. They are adsorbed
in metals by displacing water molecules on the surface, thereby
blocking either cathodic, anodic or both reactions, and forming
a compact barrier film.4–6
of compound 2a in dry acetonitrile with phosphorus
pentasulfide in the presence of a catalytic amount of
triethylamine gave the phthalazin‑1(2H)‑thione derivative 3
in a good yield as illustrated in Scheme 1. The structures of
compounds 2a–d and 3 (and all the others described below)
were characterised by their microanalytical and spectral data.
Thus, their IR spectra showed bands corresponding to NH,
C=O and C=N as well as a band for C=S in case of 3. Further
support for the assigned structures of compounds 2 and 3 was
gained from their
1H NMR spectra, which exhibit signals
Phthalazine derivatives have been tested as corrosion
inhibitors7 of copper in 1 M H2SO4 using electrochemical
polarisation and weight loss techniques. This study monitored
the evolution of the inhibitory effect of the phthalazine
derivatives according to their constitutions. The development
of new synthetic methods for the efficient preparation of
heterocycles containing a phthalazine ring fragment is therefore
an interesting challenge. Therefore, a number of methods have
been reported for the synthesis of phthalazine derivatives.8–10
In the present investigation, 11 new phthalazine derivatives
were prepared starting from the reaction of 2‑(p-toluoyl)
benzoic acid with hydrazine and some of its derivatives
H2NNHR and their corrosion inhibition properties were
evaluated by weight loss measurements of steel immersed in
5 M HCl solutions at room temperature.
characteristic for aliphatic and aromatic protons in addition to
NH protons in the downfield region which were exchangeable
with D2O. Moreover, their mass spectral data are in accord with
their proposed structures as they show the molecular ion peaks
as well as some of the important fragmentation peaks. The
formation of compounds 2a–d can be explained on the basis of
the cyclocondensation of hydrazine derivatives with the acid 1.
Treatments of thione 3 with hydrazine derivatives such as
hydrazine hydrate, 2‑hydrazinopyridine, phenylhydrazine or
benzoyl hydrazine furnished phthalazine derivatives 5a–d
with evolution of H2S gas. Thus the formation of compounds
5a–d can be understood on the basis of addition of the free
NH2 group of the hydrazines to the C=S group of 3 to give
the non‑isolable adduct 4 followed by elimination of an H2S
molecule. A chemical proof for the structure of compounds
5a–d was obtained through their synthesis from hydrazines
and the chloro phthalazine derivative 6 prepared by reaction
of phthalazine derivative 2a with POCl3 as shown in Scheme 2.
The IR spectra of compounds 5, 6 showed absorption bands
correlated with υ(C=N) and υ (NH) for 5a–d in addition to
Results and discussion
The reaction of 2‑p‑(toluoyl)benzoic acid 1 with hydrazine and
some of its simple congeners H2NNHR afforded 2‑substituted‑
4‑(p-tolyl)phthalazin‑1(2H)‑ones 2a–d (Scheme 1). Refluxing
Ar
Ar
Ar
O
N
N
N
P2S5
NH2NHR
NH
COOH
R
1
O
S
3
2a-d
Ar = p-Me-C6H4
a) R = H,
c) R = 2-pyridyl,
b) R = Ph,
d) R = C(=S)NH2
Scheme 1
* Correspondent. E‑mail: mhemdan39@hotmail
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618 JOURNAL OF CHEMICAL RESEARCH 2014
Ar
Ar
Ar
N
N
N
N
NH2NHR
NH
NH
HS
NHNHR
S
NHNHR
4
3
5
Ar = p-Me- C6H4
a) R = H,
c) R = Ph
b) R = 2-pyridyl,
d) R = COPh
NH2NHR
Ar
Ar
Ar
N
N
N
N
POCl3
NH
N
O
OH
Cl
6
2a
Scheme 2
υ(C=O) for 5d. Their 1H NMR and MS spectra were consistent
with their proposed structures.
Data in Table 1 and Fig. 1 show that phthalazine derivatives
2c, 5a, 5c and 7 were protecting steel from corrosion. The
weight loss decreases and inhibition efficiency increases in the
presence of inhibitors. The studied inhibitors are N‑containing
compounds which may be protonated in the working acidic
media. Therefore, they easily reach the steel surface and are
at once adsorbed upon it. The reactivity of the ring atoms and
those of the substituents they carry are interlinked, and it is
a matter of conjecture whether to regard certain reactions as
chemical properties of the former or of the latter.11 In most
inhibition studies the formation of donor–acceptor surface
complexes between the electrons of an inhibitor and the
vacant d‑orbital of a metal is postulated.12–15 Nitrogen‑based
compounds are effective inhibitors for corrosion in aqueous
solutions.16 They adsorb through electrostatic interactions
between the positively charged nitrogen atom and the negatively
charged metal surface.17 The greater inhibition properties of
2c over the other phthalazines 5a, 5b and 7 is perhaps due to
an increased number of centres of adsorption on the inhibitor
molecule as well as the higher electron densities on both N‑3 of
the phthalazine ring 2c and that on the pyridyl N‑atom.
Refluxing of phthalazine derivative 5a with benzoyl chloride
in pyridine yielded triazolophthalazine derivative 7 in a one‑
pot reaction. Moreover, compound 7 was obtained through
boiling 5d in dry toluene for a long time. On the other hand,
reaction of 5a with acetylacetone afforded pyrazolophthalazine
derivative 9 also in a one pot reaction. The IR spectra of 7 and 9
showed absorption bands correlated with υ C=N and the absence
of absorption bands due to C=O and NH groups. Their 1HNMR
spectra displayed signals corresponding to aromatic and aliphatic
protons. Further confirmation of the assigned structures were
gained from their mass spectra which revealed the correct
molecular ion peaks and some abundant fragmentation peaks.
The mechanism of formation of compounds 7 and 9 can be
visualised as a cyclocondensation of the intermediate tautomeric
hydrazides (not isolated) as shown in Scheme 3.
Evaluation of the synthesised phthalazines as corrosion
inhibitors
The corrosion inhibition tendency of the synthesised
phthalazines was tested by studying the weight loss of steel
coupons immersed in a solution of 5 M HCl throughout 100 h
of immersion at room temperature. The results of weight loss
of steel coupons with and without the addition of 0.02 M of
different inhibitors at 25, 50, 75 and 100 h of immersion in 5 M
HCl are summarised in Fig. 1.
Table 1 Inhibition activity (%I)a of four of the synthesised phthalazinesb
%I
Slopec
Compd
93.4
47.8
57.1
64.3
–
0.0904
0.5528
0.4748
0.5568
0.9236
2c
5a
5b
7
The inhibition efficiency (% I) was calculated from the
equation:
%I=Wfree –Winh /Wfree × 100
B
aFor definition of %I see text.
where Wfree and Winh are the weight loss without and with
inhibitor, respectively. Table 1 shows the inhibition efficiency
of the different inhibitors.
bSee Schemes 1–3.
cSlope refers to plots in Fig. 1.
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JOURNAL OF CHEMICAL RESEARCH 2014 619
Ar
Ar
Ar
N
N
N
N
NH
N
OH
O
Ph
N
HN
N
N
7
N
Ph
N
H
Ph
reflux
toluene
PhCOCl
Ar
Ar
N
N
N
N
NH
NH2
NH
NHCOPh
5d
5a
CH3COCH2COCH3
Ar
Ar
Ar
N
N
N
N
N
N
NH
N
NH
CH3
N
OH
N
O
N
H3C
CH3
H3C
CH3
H3C
8
9
Scheme 3
washed with light petroleum ether and recrystallised from a suitable
solvent to give compounds 2a–d.
Experimental
Melting points were determined in open capillary tubes on a
Gallenkemp melting point apparatus and are uncorrected. The
elemental analyses were carried out using a PerkinElmer 2400 CHN
elemental analyser. The IR spectra were recorded on PerkinElmer
Spectrum RXIFTIR system as KBr discs. 1H NMR spectra were
obtained on a Varian Gemini 200 MHz instrument in DMSO‑d6.
Chemical shifts (δ) are expressed in ppm downfield from TMS as
internal standard and coupling constants J in Hz. Mass spectra were
recorded on a Shimadzu GC‑MS, QP 1000 EX instrument operating
at 70 eV. TLC aluminium sheets coated with silica gel F254 (Merck)
were used to monitor the progress of all reactions and to assess the
homogeneity of the synthesised compounds.
4-p-Tolylphthalazin-1(2H)-one (2a): Colourless crystals; yield 86%;
m.p. 244–246 °C (EtOH); IR: 3297, 3154 (NH), 3001 (aryl‑H), 2900
(alkyl‑H), 1661 (C=O), 1620 (C=N) cm–1; 1H NMR: δ 2.43 (s, 3H, CH3),
7.10–8.22 (m, 8H, ArH), 11.72 (br s, 1NH exchangeable); MS m/z (%):
236 (M+., 80), 237 (M+. +1, 9), 238 (M+. + 2, 1), 235 (M+. –1, 100), 208
(M+. –CO, 7), 207 (11), 117 (22), 91 (37). Anal. calcd for C15H12N2O
(236.27); C, 76.25; H, 5.12; N, 11.86; found: C, 75.98; H, 4.93; N,
11.64%.
2-Phenyl-4-p-tolylphthalazin-1(2H)-one (2b): Pale yellow crystals;
yield 88%; m.p. 168–170 °C (EtOH); IR: 3067, 3031 (aryl‑H), 2917
(alkyl‑H), 1655 (C=O), 1589 (C=N) cm–1; 1H NMR: δ 2.41 (s, 3H, CH3),
7.21–7.89 (m, 13H, ArH); MS m/z (%): 312 (M+., 30), 313 (M+. +1, 7),
284 (M+.–CO, 2), 221 (1), 207 (4), 179 (13), 178 (14), 78 (12), 77 (100),
76 (13), 65 (15). Anal. calcd for C21H16N2O (312.36); C, 80.75; H, 5.16;
N, 8.97; found: C, 80.72; H, 4.87; N, 8.65%.
Reaction of 2-(p-toluoyl)benzoic acid 1 with hydrazines to give
phthalazines 2a–d; general procedure
A solution of 2‑(p-toluoyl)benzoic acid 1 (2 mmol) in dry toluene
(30 mL) and an equivalent amount of hydrazine hydrate, phenyl
hydrazine, 2‑pyridyl hydrazine or thiosemicarbazide was refluxed for
3–4 h. The solid product formed during the reaction was filtered off,
2-(Pyridin-2-yl)-4-p‑tolylphthalazin-1(2H)-one (2c): Yellow crystals;
yield 76%; m.p. 164–166 °C (EtOH); IR: 3100 (aryl‑H), 2932 (alkyl‑H),
1666 (C=O), 1583 (C=N) cm–1; 1H NMR: δ 2.40 (s, 3H, CH3), 7.34–8.04
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620 JOURNAL OF CHEMICAL RESEARCH 2014
160
B
5a
140
5b
7
120
2c
100
80
60
40
20
0
-20
0
20
40
60
80
100
time (hr)
Fig. 1 Extent of corrosion of steel coupons by four phthalazines (0.02 M) in 5 M HCl determined as weight loss W (g cm–2)/h. W, the weight loss of steel
coupons was determined after 25, 50, 75 and 100 h; B, a steel coupon without addition of inhibitors.
(m, 10H, ArH), 8.41–8.45 (m, 1H, ArH), 8.61–8.64 (m, 1H, ArH); MS
m/z (%): 313 (M+., 72), 299 (4), 298 (12), 285 (M+. –CO, 17), 284 (25),
255 (14), 235 (35), 178 (27), 176 (21), 135 (13), 91 (6), 78 (100), 77 (23).
Anal. calcd for C20H15N3O (313.35); C, 76.66; H, 4.82; N, 13.41; found:
C., 76.47; H, 4.60; N, 13.47%.
1-(Pyridin-2-yl)-2-(4-p-tolylphthalazin-1-yl)hydrazine (5b): Yellow
crystals; yield 66%; m.p. 298–300 °C (EtOH); IR: 3286, 3130 (NH),
3083, 3021 (aryl‑H), 2946 (alkyl‑H), 1612, 1587 (C=N) cm–1; 1H NMR:
δ 2.44 (s, 3H, CH3), 6.91–8.01 (m, 10H, ArH), 8.82–8.84 (m, 2H, ArH),
12.72 (br. s, 2NH exchangeable); MS m/z (%): 327 (M+., 93), 326 (M+.
+1, 18), 312 (18), 311 (58), 297 (42), 234 (67), 163 (12), 91 (88), 78 (100),
77 (41). Anal. calcd for C20H17N5 (327.38); C, 73.37; H, 5.23; N, 21.39;
found: C, 73.41; H, 4.97; N, 21.18%.
1-Oxo-4-p-tolylphthalazine-2(1H)-carbothioamide (2d): Colour‑
less crystals; yield 72%; m.p. 224–226 °C (EtOH); IR: 3296, 3154
(NH), 3041 (aryl‑H), 2901 (alkyl‑H), 1660 (C=O), 1559 (C=N)
1
cm–1; H NMR: δ 2.49 (s, 3H, CH3), 4.49, 7.22 (two br. s, 2H, NH2,
1-Phenyl-2-(4-p‑tolylphthalazin-1-yl)hydrazine (5c): Yellow crystals;
yield 86%; m.p. 298–300 °C (toluene); IR: 3211, 3156 (NH), 3091
exchangeable), 7.35–8.62 (m, 8H, ArH); MS m/z (%): 295 (M+., 19), 269
(44), 236 (38), 222 (44), 167 (40), 67 (25), 65 (63), 64 (100). Anal. calcd
for C16H13N3OS (295.36); C, 65.06; H, 4.44; N, 14.23; found: C, 64.73;
H, 4.16; N, 13.87%.
1
(aryl‑H), 2963 (alkyl‑H), 1631, 1587 (C=N) cm–1; H NMR: δ 2.43 (s,
3H, CH3), 5.8, 6.11 (br. s, 2H, NH exchangeable), 6.97–7.87 (m, 11H,
ArH), 8.78–8.0 (m, 2H, ArH); MS m/z (%): 326 (M+., 30), 280 (21), 279
(26), 269 (35), 176 (35), 166 (31), 146 (83), 139 (44), 95 (26), 91 (22),
60 (100). Anal. calcd for C21H18N4 (326.39); C, 77.28; H, 5.56; N, 17.17;
found: C, 76.89; H, 5.49; N, 17.06%.
4-p-Tolylphthalazine-1(2H)-thione (3): A mixture of compound 2a
(2 mmol), a few drops of triethylamine and phosphorus pentasulfide
(4 mmol) in dry toluene (30 mL) was refluxed for 1 h. The reaction
mixture was cooled, and the solid that formed was filtered off and
recrystallised to give compound 3as yellow crystals; yield 88%; m.p.
230–232 °C (EtOH); IR: 3143 (NH), 3073 (aryl‑H), 2938 (alkyl‑H),
N′-(4-p-Tolylphthalazin-1-yl)benzohydrazide (5d): Yellow crystals;
yield; 83%; m.p.>300 °C (EtOH); IR: 3317, 3268 (NH), 3056 (aryl‑H),
1
2960, 2915 (alkyl‑H), 1703 (C=O), 1656, 1605 (C=N) cm–1; H NMR:
1
1644, 1562 (C=N), 1177 (C=S) cm–1; H NMR: δ 2.44 (s, 3H, CH3),
δ 2.44 (s, 3H, CH3), 7.53–8.70 (m, 13H, ArH), 10.60, 11.50 (br. s, 2H,
NH exchangeable); MS m/z (%): 354 (M+., 6), 337 (M+.–OH, 11), 336
(M+.– H2O, 36), 241 (1), 240 (3), 106 (9), 105 (100), 78 (9), 77 (87), 51
(58). Anal. calcd for C22H18N4O (354.40); C, 74.56; H, 5.12; N, 15.81;
found: C, 74.30; H, 4.78; N, 15.58%
1-Chloro-4-p-tolylphthalazine (6): In a 100 mL round‑bottomed
flask compound 2a (1 g) was heated with POCl3 (10 mL) on a boiling
water bath for 5 h. The cooled reaction mixture was poured into ice/
cold water, and then extracted with diethyl ether. Evaporation of diethyl
ether under vacuum gave a solid product that was recrystallised to give
compound 6: Yellow crystals; yield 81%; m.p. 150–152 °C (toluene); IR:
3030 (aryl‑H), 2909 (alkyl‑H), 1662, 1601 (C=N) cm–1; 1H NMR: δ 2.43
(s, 3H, CH3), 7.37–7.71 (m, 6H, ArH), 7.97–8.83 (m, 2H, ArH); MS m/z
(%): 254 (M+., 100), 256 (M+. +2, 29), 165 (4), 163 (17), 117 (28), 91 (77),
67 (27). Anal. calcd for C15H11ClN2 (254.71); C, 70.73; H, 4.35; N, 11.00;
found: C, 70.43; H, 4.14; N, 10.79%.
7.35 (d, 2H, J=7.8 Hz), 7.49 (d, 2H, J=8.0 Hz), 7.72–7.76 (m, 1H,
ArH), 7.89–7.98 (m, 2H, ArH), 8.82 (d, 1H, J=9.0 Hz), 14.55 (br s,
1NH exchangeable); MS m/z (%): 252 (M+., 3), 251 (M+. –1, 14), 219
((M+. –SH, 10), 161 (17), 117 (12), 91 (38), 76 (51), 64 (39), 53 (100).
Anal. calcd for C15H12N2S (252.33); C, 71.40; H, 4.79; N, 11.10; found:
C, 71.11; H, 5.12; N, 10.88%.
General procedure
A solution of compounds 3 or 6 (2 mmol), in dry toluene (30 mL)
and an equivalent amount of hydrazine hydrate, 2‑pyridylhydrazine,
phenylhydrazine or benzoyl hydrazine was refluxed for 1 h. The solid
product that formed after cooling, was filtered off, then washed with
light petroleum ether and recrystallised from a suitable solvent to give
compounds 5a–d.
1-(4-p-Tolylphthalazin-1-yl)hydrazine (5a): Orange crystals; yield
77%; m.p. 266–268 °C (toluene); IR: 3382 (NH), 3068, 3021 (aryl‑H),
2920 (alkyl‑H), 1621, 1569 (C=N) cm–1; 1H NMR: δ 2.44 (s, 3H, CH3),
4.40 (br. s, 2H, NH2 exchangeable), 7.35–7.68 (m, 6H, ArH), 8.84 (d,
2H, J=7.4 Hz), 11.9 (br. s, 1NH exchangeable); MS m/z (%): 250 (M+.,
2), 249 (M+.–1, 1), 230 (7), 209 (3), 172 (16), 141 (13), 91 (4), 83 (100),
55 (69). Anal. calcd for C15H14N4 (250.3); C, 71.98; H, 5.64; N, 22.38;
found: C, 71.72; H, 5.38; N, 22.04%.
3-Phenyl-6-p-tolyl-[1,2,4]triazolo[3,4-a]phthalazine (7): A mixture of
compound 5a (2 mmol) and benzoyl chloride (2 mmol) in dry pyridine
(20 mL) was refluxed for 4 h. The reaction mixture was left to cool,
and then poured onto an ice/HCl mixture. A brown precipitated was
obtained which was filtered off and recrystallised to give compound 7.
Compound 7 was also prepared by refluxing 5d in dry toluene for 7 h
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JOURNAL OF CHEMICAL RESEARCH 2014 621
and was obtained as pale brown crystals; yield 82%; m.p. 198–200 °C
(toluene); IR: 3056 (aryl‑H), 2960, 2913 (alkyl‑H) 1656, 1605 (C=N)
cm–1; 1H NMR: δ 2.1 (s, 3H, CH3), 6.90–7.01 (m, 8H, ArH), 7.24–7.32)
m, 5H, ArH); MS m/z (%): 336 (M+., 5), 337 (M+.+1, 1), 222 (5), 167 (1),
165 (6), 103 (68), 77 (100), 76 (34), 65 (10). Anal. calcd for C22H16N4
(336.39); C, 78.55; H, 4.79; N, 16.66; found: C, 78.78; H, 4.61; N,
16.38%.
References
1
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4
5
6
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of compound 5a (2 mmol) and acetyl acetone (2 mmol) in dry toluene
(30 mL) was refluxed for 6 h. The reaction mixture was left to cool.
The solid product that formed was filtered off and recrystallised
to give compound 9: Yellow crystals; yield; 80%; m.p. 278–280 °C
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7
8
9
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cm–1; H NMR: δ 2.1 (s, 3H, CH3), 2.73 (s, 6H, 2 CH3), 7.00 (s, 1H,
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278 (2), 234 (40), 219 (69), 205 (26), 190 (59), 178 (21), 91 (100), 65 (59).
Anal. calcd for C20H18N4 (314.38); C, 76.41; H, 5.77; N, 17.82; found: C,
76.31; H, 5.57; N, 17.63%.
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Received 8 September 2014; accepted 14 September 2014
Paper 1402872 doi: 10.3184/174751914X14116480062198
Published online: 17 October 2014
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