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Titrimetric determination of aminobenzoic acids
Tdmro,
0039-9140/85$3.00+ 0.00
Vol 32, No. 1, pp. 66-67, 1985
Pnnted in Great Britain
Pergamon Press Ltd
TITRIMETRIC
DETERMINATION ACIDS
OF AMINOBENZOIC
D. AWIN, F. M. EL-SAMMAN and H. ABDULAHED-MALALLA Department of Chemistry, College of Science, University of Mosul, Mosul, Iraq (Received
7 November
1983. Revised 14 May 1984. Accepted
19 June 1984)
Summary-A novel titrimetric method for determination of aminobenzoic acids is based on their reaction with excess of bromine to form N-bromo-2,4,6-tribromoaniline, which liberates an equivalent amount of iodine when treated with iodide. The method is applicable to the aminobenzoic acids in the range 0.1-5.0 mg, with a recovery ranging from 96 to 99.7% and a coefficient of variation of 0.2-2.0”/,, depending on the concentration level.
A method’ based on bromine substitution has been used for determination of aminobenzoic acids, excess of bromine being back-titrated. A titrimetric’ determination of as little as 2-30 mg has been reported for determination of aminobenzoic acids. The development of a sensitive, rapid and accurate titrimetric procedure based on the quantitative reaction of o-, m- and p-aminobenzoic acids with bromine was therefore undertaken. The bromination of aromatic amines proceeds only at the unoccupied ortho and para positions on the ring. However, in the presence of a large excess of bromine the substitution goes further, to form Nbromo-2,4,6_tribromoaniline, which can be reacted with excess of iodide to liberate equivalent amounts of iodine which can be titrated with thiosulphate. The suggested reactions are:
yH2
EXPERIMENTAL Reagents
All chemicals used were of analytical grade, and distilled water was always used. Aminobenzoic acid solutions. Aqueous solutions of each acid, with concentrations 0.1 and 1.Omg/ml, were prepared in 0.04M sodium hydroxide. Sodium thiosubhate solutions, 0.001 and 0.01 N. Standardized against potassium iodate solutions of similar normality. Solutions of bromine water (saturated) and formic acid (80%) were used. Procedure
In a 50-ml conical flask, place a suitable volume (1-5 ml) of sample solution containing 0.1-5.0 mg of o-, m- or p-aminobenzoic acid, dilute with water to about 15 ml, then add about 3 ml of bromine water. Stopper the flask and shake it for 5 min. Remove the stopper, add about 1 ml of formic acid solution, shake for 1 min, then add 1 ml of concentrated phosphoric acid and about 0.5 g of potassium iodide. Let the flask stand for 10 min, with occasional shaking, then titrate the liberated iodine with O.OlN thiosulphate, with starch as indicator (for less than 2 mg of aminobenzoic acid, use 0.001N thiosulphate). Run a blank determination. 1 ml of O.OlN thiosulphate = 0.6857 mg of aminobenzoic acid.
t;lHBr
Br
RESULTS AND DISCUSSION
NHBr
NH2
The bromination of aminobenzoic acids normally proceeds at the unoccupied ortho and pura positions, but preliminary studies confirmed that with a large excess of bromine the bromination goes further, to the amino group reacting to give the N-bromo derivative. Decarboxylation of the o- and p-isomers was confirmed by disappearance of the carboxylate band in the infrared spectrum. The bromination is complete within 5 min; longer reaction time has no effect on the results. The complete bromination requires 2-3 ml of saturated broCOOH CgH21Br3)
mine water, the excess of which is destroyed by addition of 1 ml of formic acid. Reduction of the N-bromo-2,4,6&ibromoanilines requires about 0.5 g of potassium iodide and takes
Br NHBr
t21
--
C6H2(Br31
NH-+
12+
Br-
Scheme 1. 66
67
SHORT COMMUNICATIONS
Table 1. Determination
of aminobenzoic acids (5 replicates)
Weight, mg Isomer
Taken
Mean found
Recovery, %
Coefficient of variation, %
Ortho
0.100 2.000 5.000 0.100 2.000 5.000 0.100 2.008 5.000
0.096 1.969 4.952 0.098
96.0 98.0 99.0 98.0 99.7 99.2 96.0 98.9 98.8
1.7 0.8 0.4 1.1 0.5 0.2 2.0 0.8 0.6
Meta Para
1.994 4.960 0.096 1.978 4.940
15-20 mm. This time can be shortened to 10 min by adding about 1 ml of concentrated phosphoric acid. The blank is in the range 0.05-0.10 ml of O.OlN thiosulphate. Compounds which can be brominated under the experimental conditions, e.g., cresolq3 toluidines4 and phenolq5 will interfere. Table 1 shows the recoveries and the coefficient of variation for the compounds studied.
REFERENCES 1. S. Siggia and J. G. Hanna, Quantitative Organic Analysis via Functional Groups, p. 565. Interscience, New York, 1979. 2. F. M. Albert, V. Cimpa, M. Valeau and E. R. Jercan, Rev. Roum. Chim., 1966, 11, 1443. 3. D. Amin and K. Y. Saleem, Intern. J. Environ. Anal. Chem., 1984, 17, 3.
H. Abdulahed-Malalla,
F. M. El-Samman and D. Amin, unpublished work. 5. D. Amin and W. A. Bashir, Talanta, 1984, 31, 283.
4.
0039-9140/85$3.00+ 0.00
Vol 32, No. 1, pp. 66-67, 1985
Pnnted in Great Britain
Pergamon Press Ltd
TITRIMETRIC
DETERMINATION ACIDS
OF AMINOBENZOIC
D. AWIN, F. M. EL-SAMMAN and H. ABDULAHED-MALALLA Department of Chemistry, College of Science, University of Mosul, Mosul, Iraq (Received
7 November
1983. Revised 14 May 1984. Accepted
19 June 1984)
Summary-A novel titrimetric method for determination of aminobenzoic acids is based on their reaction with excess of bromine to form N-bromo-2,4,6-tribromoaniline, which liberates an equivalent amount of iodine when treated with iodide. The method is applicable to the aminobenzoic acids in the range 0.1-5.0 mg, with a recovery ranging from 96 to 99.7% and a coefficient of variation of 0.2-2.0”/,, depending on the concentration level.
A method’ based on bromine substitution has been used for determination of aminobenzoic acids, excess of bromine being back-titrated. A titrimetric’ determination of as little as 2-30 mg has been reported for determination of aminobenzoic acids. The development of a sensitive, rapid and accurate titrimetric procedure based on the quantitative reaction of o-, m- and p-aminobenzoic acids with bromine was therefore undertaken. The bromination of aromatic amines proceeds only at the unoccupied ortho and para positions on the ring. However, in the presence of a large excess of bromine the substitution goes further, to form Nbromo-2,4,6_tribromoaniline, which can be reacted with excess of iodide to liberate equivalent amounts of iodine which can be titrated with thiosulphate. The suggested reactions are:
yH2
EXPERIMENTAL Reagents
All chemicals used were of analytical grade, and distilled water was always used. Aminobenzoic acid solutions. Aqueous solutions of each acid, with concentrations 0.1 and 1.Omg/ml, were prepared in 0.04M sodium hydroxide. Sodium thiosubhate solutions, 0.001 and 0.01 N. Standardized against potassium iodate solutions of similar normality. Solutions of bromine water (saturated) and formic acid (80%) were used. Procedure
In a 50-ml conical flask, place a suitable volume (1-5 ml) of sample solution containing 0.1-5.0 mg of o-, m- or p-aminobenzoic acid, dilute with water to about 15 ml, then add about 3 ml of bromine water. Stopper the flask and shake it for 5 min. Remove the stopper, add about 1 ml of formic acid solution, shake for 1 min, then add 1 ml of concentrated phosphoric acid and about 0.5 g of potassium iodide. Let the flask stand for 10 min, with occasional shaking, then titrate the liberated iodine with O.OlN thiosulphate, with starch as indicator (for less than 2 mg of aminobenzoic acid, use 0.001N thiosulphate). Run a blank determination. 1 ml of O.OlN thiosulphate = 0.6857 mg of aminobenzoic acid.
t;lHBr
Br
RESULTS AND DISCUSSION
NHBr
NH2
The bromination of aminobenzoic acids normally proceeds at the unoccupied ortho and pura positions, but preliminary studies confirmed that with a large excess of bromine the bromination goes further, to the amino group reacting to give the N-bromo derivative. Decarboxylation of the o- and p-isomers was confirmed by disappearance of the carboxylate band in the infrared spectrum. The bromination is complete within 5 min; longer reaction time has no effect on the results. The complete bromination requires 2-3 ml of saturated broCOOH CgH21Br3)
mine water, the excess of which is destroyed by addition of 1 ml of formic acid. Reduction of the N-bromo-2,4,6&ibromoanilines requires about 0.5 g of potassium iodide and takes
Br NHBr
t21
--
C6H2(Br31
NH-+
12+
Br-
Scheme 1. 66
67
SHORT COMMUNICATIONS
Table 1. Determination
of aminobenzoic acids (5 replicates)
Weight, mg Isomer
Taken
Mean found
Recovery, %
Coefficient of variation, %
Ortho
0.100 2.000 5.000 0.100 2.000 5.000 0.100 2.008 5.000
0.096 1.969 4.952 0.098
96.0 98.0 99.0 98.0 99.7 99.2 96.0 98.9 98.8
1.7 0.8 0.4 1.1 0.5 0.2 2.0 0.8 0.6
Meta Para
1.994 4.960 0.096 1.978 4.940
15-20 mm. This time can be shortened to 10 min by adding about 1 ml of concentrated phosphoric acid. The blank is in the range 0.05-0.10 ml of O.OlN thiosulphate. Compounds which can be brominated under the experimental conditions, e.g., cresolq3 toluidines4 and phenolq5 will interfere. Table 1 shows the recoveries and the coefficient of variation for the compounds studied.
REFERENCES 1. S. Siggia and J. G. Hanna, Quantitative Organic Analysis via Functional Groups, p. 565. Interscience, New York, 1979. 2. F. M. Albert, V. Cimpa, M. Valeau and E. R. Jercan, Rev. Roum. Chim., 1966, 11, 1443. 3. D. Amin and K. Y. Saleem, Intern. J. Environ. Anal. Chem., 1984, 17, 3.
H. Abdulahed-Malalla,
F. M. El-Samman and D. Amin, unpublished work. 5. D. Amin and W. A. Bashir, Talanta, 1984, 31, 283.
4.