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N-chlorophthalimide as a new oxidant for direct titrations in aqueous acetic acid medium
Trrhro. Vol 32. No Il. pp 1067-1068, 19X5 Printed in Great Brua~n
0039-9140/x5 $3 00 + 0.00 Pergamon Prerr Lki
N-CHLOROPHTHALIMIDE AS A NEW OXIDANT DIRECT TITRATIONS IN AQUEOUS ACETIC ACID MEDIUM
FOR
N. JAYASREE and P. INDRASENAN* Department (Received
of Chemistry, 16 April
University
of Kerala.
1984. Revised 27 May
Trivandrum-695034,
India
1985. Accepted 5 June 1985)
Summary-A stable new oxidimetric titrant, N-chlorophthalimide in anhydrous acetic acid, is proposed for direct titrations of a variety of simple and complex reductants such as As(III), Sb(III), Fe(II), ferrocyanide, iodide, ascorbic acid, hydroquinone, hydrazme, phenylhydrazine, benzhydrazide, isomcotinic acid hydrazide, semicarbazide, thiourea, amhne, phenol, oxine and its metal complexes, and anthranilic acid and its metal complexes.
In continuation of our work on organic oxidimetric titrants for use in non-aqueous or partially aqueous media,le5 we introduce N-chlorophthalimide (NCP). Solutions of NCP in anhydrous acetic acid are more stable than those of dibromamine-T,’ chlorbromamine-T,’ dihalohydantoin? and dichloramine-T.6 The solid compound is also stable for at least three months. Here we report on the application of NCP as an oxidimetric titrant for direct titrations of 31 reductants in aqueous acetic acid medium. EXPERIMENTAL
also needed. For Fe’+, 2 ml of 2M hydrochloric acid and 2 ml of orthophosphoric acid were required. For thiourea, addition of 0.5 g of sodium acetate was found to be essential. Near the equivalence point the solution was sttrred for 30 set after each addition of the titrant (0. I ml) to ensure a steady potential. The equivalence points were located as reported earlier,4,6 and the titrations continued until there was no sigmlicant change in potential on further addition of titrant. Direct visual titrations. The reductant solution was prepared in the same way as for the corresponding potentiometric titration and the indicator was added. A blank titration was done in each case but no blank correction was found necessary. RESULTS AND DISCUSSION
NCP was prepared by chlorination of phthalimide by the method given in the literature.’ It is practically insoluble in water, but soluble in acetic acid (I 9. I g/kg at 32 ) and common organtc solvents. An approximately 0 1N (0.05M) solution was prepared by dissolving 9 g of dry NCP in 1 litre of anhydrous acetic acid. This solution is sensitive to light and heat so was kept m an amber-coloured bottle. The solution was fairly stable, its strength remaining unchanged for the first 4 days and then decreasing by 0. I”,, per day. For accurate work, daily \tandardizatmn by the iodometric method used for the hdloamtdes’ ’ is recommended. Rcducrcmrs. The reductants used were of analyticalreagent grade. Standard solutions ( -0.1 N) of the 17 common reductants (Table I) were prepared in appropriate solvents as described earlier.’ ’ The oxmates of Mg’+, AIZ+. Mn”. Fe’+, Co’+. Nir+. Cu’+. Zn’+ and Cd” (Table 2) were prepared by standard methods.‘,’ Standard solutions ( -0.1 N) of these complexes were prepared in 2M hydrochloric acid. These reductant solutions were also analysed by standard methods.‘.“’ N-Chlorophthalimide,
Direct porentromelric wratlons. The apparatus and procedure described earlier’,4 were used. The reaction mixture in the titration cell was diluted to 50 ml with water and acetic acid to give 50’!,, v/v aqueous acetic acid medium. Addition of potassium bromide (0.5 g) was found to be essential for all the reductants except iodide. For Sb(II1) and hydrazine. addition of 2 ml of 2M hydrochloric acid was
*Author
for correspondence.
The results of the titrations are given in Tables 1 (common reductants) and 2 (metal oxinates and anthranilates). NCP undergoes reduction according to the equation
co\ :I a a co\ NCI
+ n++
2e- =
:I
CO’
NH + CI-
co /
The reduction product was identified as phthalimide. The conditional redox potential in 5Og.gv/v aqueous acetic acid was found to be +0.996 V at 32’. The potential break in the potentiometric titrations is sharp and in the range IO&400 mV. The visual end-points are also very sharp. Quinoline Yellow was found the most suitable indicator for all but the Fe*+, ferrocyanide. hydroquinone and metal oxinate titrations, for which amaranth was better. Either of these indicators is suitable for most of the titrations. All the reductants react as reported earlier.‘~6 Except for the iodide titration, bromide must be added to increase the rate of reaction, and the rate of potential equilibration in the potentiometric titrations. Presumably bromine is formed and acts as a more reactive intermediate. For thiourea, the oxidation is still very slow. however, and sodium acetate must also be added.
SHORT COMMUNICATIONS
1068 Table
I, Titrtmetric
determination
of some common
Potentiometric
n*
Reductants
2 2
As(llI) Sb(II1) Fe(I1) Ferrocyamde Iodide Ascorbic acid Hydroquinone Hydrazine Phenylhydrazine Benzhydrazide Isomcotinic acid hydrazide Semtcarbazide Thiourea Aniline Phenol Oxine Anthramhc acid
Visual titrations Reduction found,t %
2 2 4 4 4 4
0.15-0.30 0.14-0.30 0.29-0.49 0.27-0.47 0.29-0.60 0.15-0.30 0.12-0.21 0.07-O. 13 0.07-O. 15 0.05-O. 13 0.07-O. 12
2.4 2.8 1.9 2.4 2.9 2.5 2.3 2.5 2.3 2.2 2.9
100.3 100.3 99.8 99.9 99.9 100.1 100.1 99.9 100.1 99.8 100. I
4 8 6 6 4 6
0.07-O. I3 0.03-0.08 0.04-o. IO 0.04-0.10 0.07-O. 14 0.03-0.09
I.7 2.8 1.5 2.8 2.4 2.6
100.2 100.1 100.0 99.9 100.1 100.0
I I I
with N-chlorophthahmide
titrations
Standard deviation, pmole
Range studied, mmole
reductants
Range studied, mmole 0.49-0.95 0.50-0.97 1 01-1.93 0 98-1.87
Standard deviation, pmole
Reductant f0und.t %
0.49-0.94 0.41-0.79 0.22-0.43 0.24-0.47 0.23-0.45 0.21-0.41
2.5 1.6 1.3 2.1 unsuccessful 2.6 2.0 0.1 1.0 2.1 1.7
99.9 100.0 100.1 100.0 100.1 100.0 100.0 100.0 100.0 100.1
0.25-0.49 0.13-0.26 0.140.29 0.15-0.29 0.26-0.50 0.21-0.41
1.6 2.0 2.1 1.2 1.8 6.7
100.0 100.0 99.9 100.0 99.9 100.0
*Equivalents of NCP per mole of reductant. tAverage of ten replicates.
Table 2. Titrimetric
determination
of some metal oxinates
Direct
potentiometric
Reductants
It*
Range studied, mmole
Mg(C,H,0N),.2H20 Al(C,H,GN), Mn(C,H,0N)2.2H,0
8 12 8 12 8 8 8 8 8 12 I2 I2 I2 I2
0.02-0.07 0.02-0.04 0.02-0.07 0.02-0.04 0.02-0.05 0.02-0.06 0.03-0.06 0.03-0.08 0.02-0.06 0.02-0.06 0.0220.06 0.02-0.05 0.02-0.05 0.02-0.06
Fe(C,H,ON), CO(C,H,ON)~.~H~O NI(C,H,ON),.~H~O Cu(C,H,0N),.2H20 Zn(C,H,0N)2 2H,O Cd(C,H,0N)Z.2H20 Mn(C,H,,0ZN)2 Ni(C:H,,O>N), Cu(C-H,,O:N), Zn(C‘,H,,O,N), C‘dtC-H,,O,N),
Standard devtation. pmole 2.3 1.3 0.1 2.2 2.7 2.7 2.9 1.5 2.5 2.6 3.1 3.8 2.9 3.7
and anthranilates
titrations Reductant found.? % 99.8 100.2 100.4 99.9 100.0 99.9 100.0 100.3 100.2 100.1 99.9 99.9 99.8 99.9
with N-chlorophthalimide Direct
Range studied, mmole 0.12-0.24 0.08-O. 16 0.13-0.26 0. I l-O.23 0.09-O. 18 0. I l-0.22 0.1&0.21 0.10-0.20 0.07-O. 15 0.07-O. 15 0.07-0.25 0.09-O. 19 0.07-O. I6
visual titrations Standard deviation, pmole 1.2 1.5 1.5 unsuccessful 2.0 1.3 2.0 0. I 01 01 01 17 1.9 1.8
Reductant found.? 0, ,‘” 100.0 100.0 100.0 100.1 99.9 100.0 100.0 100.0
100.0 100.0 100.0 100.0 99 9
*Fqu~v~dcnt~ of NCP per mole of reductant : 4~cragcof km rcphcates.
The main oxidants
advantages
reported
and the more tttrations.
earlier’”
of
NCP are
rapid equilibration
il~k,lo~~/c,c/Kc~r,1(‘,11~~Weare thankful the University of Kerala for awardmg to one of us (N.J ).
over its greater
the
similar stability
in potentiometric
to the authorities of a research fellowshtp
REFERENCES I. C G. R Nair and P Indrdsenan. Tulm/u. 1976.23,239. 2. K. D Mahilamony and P. Indrasenan. rhrd.. 1981. 28, 627.
3. M. P. Radhamma and P. Indrasenan, ihid.. 1983,30,49. 4. P. Indrasenan and M. P. Radhamma, Indian J. C/tern.. 1983. 22A, 729. 5. M. P. Radhamma and P. Indrasenan, J. Indian C/tern. Sot., 1984. 61, 464 6. T. J. Jacob and C. G. R. Natr. Talunfu, 1972, 19, 347 7. E. H. Rodd (ed.), Chemisryv o/ Carhon Compounris. Vol. 1118. Elsevier, Amsterdam, 1956. 8. C Duval. Inorganic Thermogrurimrrrrc Analysrs, 2nd Ed , Elsevier, Amsterdam. 1963. 9. A. I Vogel. A Te.\-t Book of Quantltatrve Inorganic Anol~~s, 3rd Ed., Longmans. London. 1964. 10. I. M. Kolthoff, R. Belcher. V. A. Stenger and G. Matsuyama. Vo/umerric Anu/ysis. Vol. III. Interscience, New York. 1957.
0039-9140/x5 $3 00 + 0.00 Pergamon Prerr Lki
N-CHLOROPHTHALIMIDE AS A NEW OXIDANT DIRECT TITRATIONS IN AQUEOUS ACETIC ACID MEDIUM
FOR
N. JAYASREE and P. INDRASENAN* Department (Received
of Chemistry, 16 April
University
of Kerala.
1984. Revised 27 May
Trivandrum-695034,
India
1985. Accepted 5 June 1985)
Summary-A stable new oxidimetric titrant, N-chlorophthalimide in anhydrous acetic acid, is proposed for direct titrations of a variety of simple and complex reductants such as As(III), Sb(III), Fe(II), ferrocyanide, iodide, ascorbic acid, hydroquinone, hydrazme, phenylhydrazine, benzhydrazide, isomcotinic acid hydrazide, semicarbazide, thiourea, amhne, phenol, oxine and its metal complexes, and anthranilic acid and its metal complexes.
In continuation of our work on organic oxidimetric titrants for use in non-aqueous or partially aqueous media,le5 we introduce N-chlorophthalimide (NCP). Solutions of NCP in anhydrous acetic acid are more stable than those of dibromamine-T,’ chlorbromamine-T,’ dihalohydantoin? and dichloramine-T.6 The solid compound is also stable for at least three months. Here we report on the application of NCP as an oxidimetric titrant for direct titrations of 31 reductants in aqueous acetic acid medium. EXPERIMENTAL
also needed. For Fe’+, 2 ml of 2M hydrochloric acid and 2 ml of orthophosphoric acid were required. For thiourea, addition of 0.5 g of sodium acetate was found to be essential. Near the equivalence point the solution was sttrred for 30 set after each addition of the titrant (0. I ml) to ensure a steady potential. The equivalence points were located as reported earlier,4,6 and the titrations continued until there was no sigmlicant change in potential on further addition of titrant. Direct visual titrations. The reductant solution was prepared in the same way as for the corresponding potentiometric titration and the indicator was added. A blank titration was done in each case but no blank correction was found necessary. RESULTS AND DISCUSSION
NCP was prepared by chlorination of phthalimide by the method given in the literature.’ It is practically insoluble in water, but soluble in acetic acid (I 9. I g/kg at 32 ) and common organtc solvents. An approximately 0 1N (0.05M) solution was prepared by dissolving 9 g of dry NCP in 1 litre of anhydrous acetic acid. This solution is sensitive to light and heat so was kept m an amber-coloured bottle. The solution was fairly stable, its strength remaining unchanged for the first 4 days and then decreasing by 0. I”,, per day. For accurate work, daily \tandardizatmn by the iodometric method used for the hdloamtdes’ ’ is recommended. Rcducrcmrs. The reductants used were of analyticalreagent grade. Standard solutions ( -0.1 N) of the 17 common reductants (Table I) were prepared in appropriate solvents as described earlier.’ ’ The oxmates of Mg’+, AIZ+. Mn”. Fe’+, Co’+. Nir+. Cu’+. Zn’+ and Cd” (Table 2) were prepared by standard methods.‘,’ Standard solutions ( -0.1 N) of these complexes were prepared in 2M hydrochloric acid. These reductant solutions were also analysed by standard methods.‘.“’ N-Chlorophthalimide,
Direct porentromelric wratlons. The apparatus and procedure described earlier’,4 were used. The reaction mixture in the titration cell was diluted to 50 ml with water and acetic acid to give 50’!,, v/v aqueous acetic acid medium. Addition of potassium bromide (0.5 g) was found to be essential for all the reductants except iodide. For Sb(II1) and hydrazine. addition of 2 ml of 2M hydrochloric acid was
*Author
for correspondence.
The results of the titrations are given in Tables 1 (common reductants) and 2 (metal oxinates and anthranilates). NCP undergoes reduction according to the equation
co\ :I a a co\ NCI
+ n++
2e- =
:I
CO’
NH + CI-
co /
The reduction product was identified as phthalimide. The conditional redox potential in 5Og.gv/v aqueous acetic acid was found to be +0.996 V at 32’. The potential break in the potentiometric titrations is sharp and in the range IO&400 mV. The visual end-points are also very sharp. Quinoline Yellow was found the most suitable indicator for all but the Fe*+, ferrocyanide. hydroquinone and metal oxinate titrations, for which amaranth was better. Either of these indicators is suitable for most of the titrations. All the reductants react as reported earlier.‘~6 Except for the iodide titration, bromide must be added to increase the rate of reaction, and the rate of potential equilibration in the potentiometric titrations. Presumably bromine is formed and acts as a more reactive intermediate. For thiourea, the oxidation is still very slow. however, and sodium acetate must also be added.
SHORT COMMUNICATIONS
1068 Table
I, Titrtmetric
determination
of some common
Potentiometric
n*
Reductants
2 2
As(llI) Sb(II1) Fe(I1) Ferrocyamde Iodide Ascorbic acid Hydroquinone Hydrazine Phenylhydrazine Benzhydrazide Isomcotinic acid hydrazide Semtcarbazide Thiourea Aniline Phenol Oxine Anthramhc acid
Visual titrations Reduction found,t %
2 2 4 4 4 4
0.15-0.30 0.14-0.30 0.29-0.49 0.27-0.47 0.29-0.60 0.15-0.30 0.12-0.21 0.07-O. 13 0.07-O. 15 0.05-O. 13 0.07-O. 12
2.4 2.8 1.9 2.4 2.9 2.5 2.3 2.5 2.3 2.2 2.9
100.3 100.3 99.8 99.9 99.9 100.1 100.1 99.9 100.1 99.8 100. I
4 8 6 6 4 6
0.07-O. I3 0.03-0.08 0.04-o. IO 0.04-0.10 0.07-O. 14 0.03-0.09
I.7 2.8 1.5 2.8 2.4 2.6
100.2 100.1 100.0 99.9 100.1 100.0
I I I
with N-chlorophthahmide
titrations
Standard deviation, pmole
Range studied, mmole
reductants
Range studied, mmole 0.49-0.95 0.50-0.97 1 01-1.93 0 98-1.87
Standard deviation, pmole
Reductant f0und.t %
0.49-0.94 0.41-0.79 0.22-0.43 0.24-0.47 0.23-0.45 0.21-0.41
2.5 1.6 1.3 2.1 unsuccessful 2.6 2.0 0.1 1.0 2.1 1.7
99.9 100.0 100.1 100.0 100.1 100.0 100.0 100.0 100.0 100.1
0.25-0.49 0.13-0.26 0.140.29 0.15-0.29 0.26-0.50 0.21-0.41
1.6 2.0 2.1 1.2 1.8 6.7
100.0 100.0 99.9 100.0 99.9 100.0
*Equivalents of NCP per mole of reductant. tAverage of ten replicates.
Table 2. Titrimetric
determination
of some metal oxinates
Direct
potentiometric
Reductants
It*
Range studied, mmole
Mg(C,H,0N),.2H20 Al(C,H,GN), Mn(C,H,0N)2.2H,0
8 12 8 12 8 8 8 8 8 12 I2 I2 I2 I2
0.02-0.07 0.02-0.04 0.02-0.07 0.02-0.04 0.02-0.05 0.02-0.06 0.03-0.06 0.03-0.08 0.02-0.06 0.02-0.06 0.0220.06 0.02-0.05 0.02-0.05 0.02-0.06
Fe(C,H,ON), CO(C,H,ON)~.~H~O NI(C,H,ON),.~H~O Cu(C,H,0N),.2H20 Zn(C,H,0N)2 2H,O Cd(C,H,0N)Z.2H20 Mn(C,H,,0ZN)2 Ni(C:H,,O>N), Cu(C-H,,O:N), Zn(C‘,H,,O,N), C‘dtC-H,,O,N),
Standard devtation. pmole 2.3 1.3 0.1 2.2 2.7 2.7 2.9 1.5 2.5 2.6 3.1 3.8 2.9 3.7
and anthranilates
titrations Reductant found.? % 99.8 100.2 100.4 99.9 100.0 99.9 100.0 100.3 100.2 100.1 99.9 99.9 99.8 99.9
with N-chlorophthalimide Direct
Range studied, mmole 0.12-0.24 0.08-O. 16 0.13-0.26 0. I l-O.23 0.09-O. 18 0. I l-0.22 0.1&0.21 0.10-0.20 0.07-O. 15 0.07-O. 15 0.07-0.25 0.09-O. 19 0.07-O. I6
visual titrations Standard deviation, pmole 1.2 1.5 1.5 unsuccessful 2.0 1.3 2.0 0. I 01 01 01 17 1.9 1.8
Reductant found.? 0, ,‘” 100.0 100.0 100.0 100.1 99.9 100.0 100.0 100.0
100.0 100.0 100.0 100.0 99 9
*Fqu~v~dcnt~ of NCP per mole of reductant : 4~cragcof km rcphcates.
The main oxidants
advantages
reported
and the more tttrations.
earlier’”
of
NCP are
rapid equilibration
il~k,lo~~/c,c/Kc~r,1(‘,11~~Weare thankful the University of Kerala for awardmg to one of us (N.J ).
over its greater
the
similar stability
in potentiometric
to the authorities of a research fellowshtp
REFERENCES I. C G. R Nair and P Indrdsenan. Tulm/u. 1976.23,239. 2. K. D Mahilamony and P. Indrasenan. rhrd.. 1981. 28, 627.
3. M. P. Radhamma and P. Indrasenan, ihid.. 1983,30,49. 4. P. Indrasenan and M. P. Radhamma, Indian J. C/tern.. 1983. 22A, 729. 5. M. P. Radhamma and P. Indrasenan, J. Indian C/tern. Sot., 1984. 61, 464 6. T. J. Jacob and C. G. R. Natr. Talunfu, 1972, 19, 347 7. E. H. Rodd (ed.), Chemisryv o/ Carhon Compounris. Vol. 1118. Elsevier, Amsterdam, 1956. 8. C Duval. Inorganic Thermogrurimrrrrc Analysrs, 2nd Ed , Elsevier, Amsterdam. 1963. 9. A. I Vogel. A Te.\-t Book of Quantltatrve Inorganic Anol~~s, 3rd Ed., Longmans. London. 1964. 10. I. M. Kolthoff, R. Belcher. V. A. Stenger and G. Matsuyama. Vo/umerric Anu/ysis. Vol. III. Interscience, New York. 1957.