and the mixture was allowed to stand overnight. The crude
product (19.0 g, 74%) was vacuum filtered and washed well with
diethyl ether and air dried to constant weight. Recrystallisation
was carried out by dissolving the total product in boiling
methanol (125 cm3), treating it with activated charcoal and
allowing the filtrate to cool to room temperature by standing
for 2 h. Purified material (5.5 g, mp 149–152 ЊC with decom-
position) was recovered by vacuum filtration and air drying.
Further material (4.5 g) was recovered by increasing the filtrate
volume to 250 cm3 with diethyl ether and standing the solution
overnight at room temperature.
Method B.—Crude product was obtained by reacting phthal-
ic anhydride and 1,2-diaminobenzene (0.2 mol of each) in
DMF according to the procedure of Young.2 This material was
then further purified from methanol as described in Method A
above. Literature melting points given are 147Њ–150 ЊC 2 and
151–152 ЊC.19 Analysis, found: C, 65.78; H, 4.4; N, 10.83. Calc.
for C14H12N2O3: C, 65.62; H, 4.72: N, 10.93%.
Kinetic measurements
All kinetic work was carried out using a Perkin Elmer λ 5
double beam UV–VIS spectrophotometer with a water heated
sample cell and the appropriate reaction medium in the refer-
ence cell. A flow of heated water was maintained with a Grant
thermostatted heater and pump operating in a separate bath.
Temperatures (±0.2 ЊC) were determined by direct measure-
ment of the cuvette contents using a thermocouple and cross
checks made with a mercury thermometer. Each run was con-
ducted in a conventional 1 cm stoppered quartz cuvette con-
taining ca. 2.5 cm3 of solution. Cuvettes containing the reaction
solvent were allowed to equilibrate for at least 10 min in the
spectrometer before the addition of reactant. Reactants were
introduced to the cuvettes by preparing saturated solutions of
the compounds in absolute ethanol at room temperature and
then adding an appropriate volume (typically 10–50 µl) to
give the required initial absorbance. Cuvettes were stoppered
and rapidly inverted 2–3 times before data collection was start-
ed. The wavelength used was dependent on the pH of the buffer
employed in the study and this is made clear in the discussion.
At each pH the appropriate wavelength was determined from a
full spectrum of both product(s) and reactant.
N-(2-Aminophenyl)phthalimide (B). Dilute 2 HCl (20 cm3)
was heated to 65–70 ЊC in a 50 cm3 conical flask with magnetic
stirring. Solid N-(2-aminophenyl)phthalamic acid (1.30 g) was
added directly to the flask and stirring continued until a clear
solution was obtained. After a few minutes more stirring, a
white precipitate appeared and after 8 min ice was added to
bring the temperature to 25 ЊC. The white solid was either fil-
tered off as the hydrochloride of N-(2-aminophenyl)-
phthalimide (0.50 g, 33.5%, mp 240–245 ЊC, lit.,10 values 253–
255 ЊC and 272 ЊC), or neutralised in suspension with 0.880
aqueous NH3 to give a yellow solid which was N-(2-amino-
phenyl)phthalimide (0.30 g, 33.1%, mp 182–4 ЊC, lit.,2 194–
195 ЊC). For kinetic work the crude compound was recrystal-
lised from ethanol to give material with a melting point of 192–
193 ЊC. Analysis, found: C, 70.29; H, 4.05; N, 11.54. Calc. for
C14H10N2O2: C, 70.58; H, 4.23; N, 11.76%.
1,2-Benzoylenebenzimidazole (11H-isoindolo[2,1-a]benzimid-
azol-11-one). N-(2-Aminophenyl)phthalamic acid (2.0 g) was
placed in a 100 cm3 beaker and heated to its melting point on an
electric hotplate. The temperature was gradually raised until
sublimation occurred and the product was collected by closing
the beaker with a glass petri-dish cooled by standing a small
flask of cold water on top of it. Bright yellow needles of 1,2-
benzoylenebenzimidazole (0.80 g, 46.5%, mp 215–220 ЊC, lit.,2
214–215 ЊC) were collected in this way.
2-(2-Carboxyphenyl)benzimidazole (C). N-(2-Aminophenyl)-
phthalamic acid (1a≡A, 10.0 g) was refluxed for 1.5 h in 1
aqueous HCl (100 cm3). The solution was then cooled to room
temperature and neutralised with 0.880 aqueous NH3,
whereupon a white solid was precipitated. The mixture was
allowed to stand at room temperature overnight before the
crude product (6.5 g, 70%) was filtered under vacuum and
washed with water before drying. Pure material (mp 262–
263 ЊC) was obtained by repeated recrystallisation of small
samples from ethanol. Note, considerable variation in reported
mp has been observed (cf. 245 ЊC,2 271.5 ЊC 10 and 270 ЊC 20).
Analysis, found: C, 70.37; H, 4.01; N, 11.51. Calc. for
C14H10N2O2: C, 70.58; H, 4.23; N, 11.76.
Acknowledgements
The author thanks the Royal Society of Chemistry for a per-
sonal research grant that has made much of the kinetic work
possible. Thanks are also due to Martin Gilligan, Sartaj Kahl-
on, Maniha Gul, Maria Rodruigez-Sol and Kath Shelley.
References
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Buffer solutions
All mineral acid solutions (0.1 HCl and 2 H2S04) were
prepared from AnalaR grade materials and other buffer solu-
tions (citric acid–Na2HPO4) were prepared directly from McIl-
vaine’s table of Standard Buffers.21 All pH values were checked
before use by employing a glass electrode and were found to be
as stated in the table (±0.1). Where buffer dilution experiments
were conducted, the stock buffers (HCl–KCl, acetic acid–
acetate and formic acid–formate) were made to a total ionic
strength of 0.1 and a series of dilutions made with 0.1 KCl.
Again, the pH was measured before use.
Paper 6/06699B
Received 30th September 1996
Accepted 14th January 1997
982
J. Chem. Soc., Perkin Trans. 2, 1997