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The salts of organic phosphorus acids—I
J. Inorg. Nu¢I. Chem., 1959, Vol. 9, pp. 150 to 154. Pergamon Press Ltd. Printed in Northern Ireland
THE
SALTS OF ORGANIC
PHOSPHORUS
ACIDS--I
THE INFRA-RED SPECTRA OF SALTS OF DI-n-BUTYL PHOSPHATE T. D. SMITH Chemistry Department, The Royal College of Science and Technology, Glasgow (Received 12 June 1958)
Abstract---The infra-red spectra of a number of salts of di-n-butyl phosphate have been recorded and the results interpreted from a consideration of the interaction of the various groups in the di-n-butyl phosphate radical with the metal ion.
THE infra-red spectra of di-n-butyl phosphate, its silver salt and those of a number of similar aliphatic and aromatic phosphorus acids have been recorded by BELLAMY and BEECHER.tl~ These authors pointed out that the usual position of the band for the P = O group in the 1200-1300 cm-x region, t2~ vanishes in all cases on formation of the silver salts and is replaced by a band in the 1050--1100 cm-1 region which was tentatively ascribed to the ionic phosphate vibration. Another assignment noted was that of the P O--C vibration to the 1030 cm-1 region which may be regarded as arising essentially from the O--C link of the P - - O - - C skeleton whereas a band at 980 cm-~ arises from the P--O link. The present investigation was carried out to determine the influence of the metal ion on the infra-red spectra of salts of di-n-butyl phosphate with a view to assessing the interaction of the various groups of the di-n-butyl phosphate radical with the metal ion concerned. EXPERIMENTAL
The di-n-butyl phosphates of sodium, barium, lithium, manganese (II), copper (II) and nickel (II), were made by adding, in slight excess, their carbonates to an aqueous solution of dibutyl phosphate. Evaporation on a water bath after filtration yielded waxy deposits of the salt which were recrystallized. The Iemaining salts were relatively insoluble in water and were prepared by direct precipitation from an acidified nitrate solution of the metal ion. The resulting precipitates were washed with water, alcohol and finally a little ether and dried over phosphorus pentoxide for several weeks. The infra-red spectra of the di-n-butyl phosphates in Nujol suspension were recorded on a Grubb-Parsons double beam instrument Model $4, with a rock-salt prism. A selection of the spectra obtained is shown in Fig. 1 and detailed by Table 1. RESULTS AND DISCUSSION
1242-1124 cm-1 region. Bands due to the bonded P ~ O group have been assigned to this region occurring in the ease of di-n-butyl phosphate tl~ at 1220 cm-1. On salt formation a band persists in this region though its position is dependent on the metal ion present, the positions being shown by Table 1. In the sodium salt the band appears at the highest frequency being shifted from the position at 1220 cm-1 due to the tXl L. J. BELLAMYand L. BEECHER, J. Chem. Soc. 728 (1953). ~2~C. I. MEYRICKand H. W. THOMPSON,J. Chem. Soc. 225 (1950). 150
The salts of organic phosphorus acids--I
151
release of the P~-O group from hydrogen bonding. In the barium and lithium salts the band is virtually in the same position. With the manganese salt a small shift to lower frequency occurs, the shift becoming more pronounced at nickel. It is proposed TABLE I
Metal salt
Sodium Barium Lithium Manganese (I1) Copper (II) Nickel (lI) Lead (II) Mercury (II) Mercury (I) Aluminium Lanthanum Yttrium Cerium (IlI) Iron (II1) Cerium (IV) Thorium Bismuthyl Zi rconyl Uranium (VI)
Position of P==O band (cm-1)
1242 1227 1242,1212 1220 1227 1190 1190 1130 1183 1183 1176 1190 1170 1163 1156 1183 1124 1124
that this shift is due to the participation of the P~---O group in bonding to the metal ion such that group represented as P = O - - + M e ~n appears. This tendency to form such a bond is then shown to some degree by the other metal ions with large shifts being shown in the lanthanum, ferric, eerie, mercuric, bismuthyl and uranyl salts, where the metal ion involves an ever increasing participation in bonding to the P ~ O group. 909-730 cm-1 region. The bands exhibited by the free acid in this region are very weak. However, those exhibited by the sodium and barium salts are intense. In the lithium salts these bands are diminished in intensity though little altered in position. This tendency is continued in most of the other salts being very weak in the zirconyl salt and almost non-existent in the uranyl salt. The aluminium and lanthanum salts show relatively strong bands in this region in contrast to the di-n-butyl phosphates of yttrium and cerium (IlI). It is proposed that the appearance of these strong bands for the sodium and barium salts is due to the P - - O - group. The loss in intensity of these bands in the remaining salts may be due to the formation of an electrostatic link with an increasingly covalent character which reaches a m a x i m u m in the uranyl salt where the P - - O - - U O ~ ~ bond is of the same order of covalency as the P - - O - - H bond resulting in the almost complete disappearance of the bands in this region. 1099-9524 cm * region. This region contains bands whose positions show little variation with change in the metal ion content of the salts, also in many cases the
152
T . D . SMITH Absorbance
5000
..
3333
2500
2000
1667
1429
1250
Cm-1
1111
1000
909
833
769
i
2
3
4
5
6
7
8 U
9
10
11
12
13
14
1111
1000
909
833
769
cm-1 714 3
9
10
11
12
13
l .,
Absorbance
5000
3333
2500
2000
1667
1429
2
3
4
5
6
7
I
1250
8 U
.,
3333
2500
2000
1667
1429
1250
1111
1000
909
B33
769
8
g
10
11
12
13
1250
11"11
1000
909
833
769
j 2
3
4
5
6
14
~-
Absorbance
5000
714 1
7
cm-I 714 4
14
U Absorbance
5000
3333
-,,--I"
2500
2000
1667
1429
Cm-- !
714 11
/
J 2
3
4
5
6
7
u
8,
9
10
11
12
1,3
14
The salts of organic phosphorus acids--I
Absorbanca 5000
3333
153
• 2500
2000
1667
1429
1250
cm-1
1000
1111
909
833
769
714 13
L
2
J
3
I
6
8
9
1250
1111
lO
11
12
13
I 14
1000
909
833
769
era-| 714
U
Absorbance
5000
i
3333
2500
2000
1667
1429
r 2
3
4
5
6
7
8 U
9
Absorbance
5000
10
11
12
13
1000
909
833
769
4
3333
2500
2000
1667
1429
14
•
1250
1111
cm-1
714
19
2
3
4
I 5
6
7
8
9
10
11
12
13
14
bl
F~G. 1. 1--Sodium di-n-butyl phosphate; 3--Lithium di-n-butyi phosphate; 4--Manganese (II) di-n-butyl phosphate; 11--Lanthanum di-n-butyl phosphate; 13--Cerium (III) di-n-butyl phosphate; 18--Zirconyl di-n-hutyl phosphate; 19~Uranium (VI) di-n-butyl phosphate.
154
T.D. SMITH
resolution of these bands is poor. The band which appears in the region 1010 cm -1 in the sodium and barium salts appears as a shoulder absorption in the manganese (II), copper (II), nickel (II), lead (II), mercury (II) and aluminium salts but disappears in the remaining spectra, whilst the general appearance of the bands for these remaining salts is very similar. The band in region 980 cm -1 persists in most of the salts studied; however in zirconyl dibutyl phosphate the band becomes almost indistinguishable whilst in uranyl dibutyl phosphate spectrum this band has disappeared. These two salts present exceptional behaviour which it is tentatively proposed is due to the interaction of the metal ion with the oxygen of the P - - O - - C group. The infra-red spectra studies here indicate that the simplest structure is that presented by the sodium and barium salts which involve an essentially ionic link with the P - - O - group. The other salts studied point to the covalent character which this link may assume and to the interaction of the P~-O group with the metal ion. Finally the possibility of bonding with the P - - O - - C group arises in the zirconyl and uranyl compounds.
Acknowledgements--Theauthor expresses his gratitude to Messrs. ALBRIGHTand WILSONLTD.for the supply 9f di-n-butyl phosphate and to Miss N. CARAMANDOfor recording the spectra.
THE
SALTS OF ORGANIC
PHOSPHORUS
ACIDS--I
THE INFRA-RED SPECTRA OF SALTS OF DI-n-BUTYL PHOSPHATE T. D. SMITH Chemistry Department, The Royal College of Science and Technology, Glasgow (Received 12 June 1958)
Abstract---The infra-red spectra of a number of salts of di-n-butyl phosphate have been recorded and the results interpreted from a consideration of the interaction of the various groups in the di-n-butyl phosphate radical with the metal ion.
THE infra-red spectra of di-n-butyl phosphate, its silver salt and those of a number of similar aliphatic and aromatic phosphorus acids have been recorded by BELLAMY and BEECHER.tl~ These authors pointed out that the usual position of the band for the P = O group in the 1200-1300 cm-x region, t2~ vanishes in all cases on formation of the silver salts and is replaced by a band in the 1050--1100 cm-1 region which was tentatively ascribed to the ionic phosphate vibration. Another assignment noted was that of the P O--C vibration to the 1030 cm-1 region which may be regarded as arising essentially from the O--C link of the P - - O - - C skeleton whereas a band at 980 cm-~ arises from the P--O link. The present investigation was carried out to determine the influence of the metal ion on the infra-red spectra of salts of di-n-butyl phosphate with a view to assessing the interaction of the various groups of the di-n-butyl phosphate radical with the metal ion concerned. EXPERIMENTAL
The di-n-butyl phosphates of sodium, barium, lithium, manganese (II), copper (II) and nickel (II), were made by adding, in slight excess, their carbonates to an aqueous solution of dibutyl phosphate. Evaporation on a water bath after filtration yielded waxy deposits of the salt which were recrystallized. The Iemaining salts were relatively insoluble in water and were prepared by direct precipitation from an acidified nitrate solution of the metal ion. The resulting precipitates were washed with water, alcohol and finally a little ether and dried over phosphorus pentoxide for several weeks. The infra-red spectra of the di-n-butyl phosphates in Nujol suspension were recorded on a Grubb-Parsons double beam instrument Model $4, with a rock-salt prism. A selection of the spectra obtained is shown in Fig. 1 and detailed by Table 1. RESULTS AND DISCUSSION
1242-1124 cm-1 region. Bands due to the bonded P ~ O group have been assigned to this region occurring in the ease of di-n-butyl phosphate tl~ at 1220 cm-1. On salt formation a band persists in this region though its position is dependent on the metal ion present, the positions being shown by Table 1. In the sodium salt the band appears at the highest frequency being shifted from the position at 1220 cm-1 due to the tXl L. J. BELLAMYand L. BEECHER, J. Chem. Soc. 728 (1953). ~2~C. I. MEYRICKand H. W. THOMPSON,J. Chem. Soc. 225 (1950). 150
The salts of organic phosphorus acids--I
151
release of the P~-O group from hydrogen bonding. In the barium and lithium salts the band is virtually in the same position. With the manganese salt a small shift to lower frequency occurs, the shift becoming more pronounced at nickel. It is proposed TABLE I
Metal salt
Sodium Barium Lithium Manganese (I1) Copper (II) Nickel (lI) Lead (II) Mercury (II) Mercury (I) Aluminium Lanthanum Yttrium Cerium (IlI) Iron (II1) Cerium (IV) Thorium Bismuthyl Zi rconyl Uranium (VI)
Position of P==O band (cm-1)
1242 1227 1242,1212 1220 1227 1190 1190 1130 1183 1183 1176 1190 1170 1163 1156 1183 1124 1124
that this shift is due to the participation of the P~---O group in bonding to the metal ion such that group represented as P = O - - + M e ~n appears. This tendency to form such a bond is then shown to some degree by the other metal ions with large shifts being shown in the lanthanum, ferric, eerie, mercuric, bismuthyl and uranyl salts, where the metal ion involves an ever increasing participation in bonding to the P ~ O group. 909-730 cm-1 region. The bands exhibited by the free acid in this region are very weak. However, those exhibited by the sodium and barium salts are intense. In the lithium salts these bands are diminished in intensity though little altered in position. This tendency is continued in most of the other salts being very weak in the zirconyl salt and almost non-existent in the uranyl salt. The aluminium and lanthanum salts show relatively strong bands in this region in contrast to the di-n-butyl phosphates of yttrium and cerium (IlI). It is proposed that the appearance of these strong bands for the sodium and barium salts is due to the P - - O - group. The loss in intensity of these bands in the remaining salts may be due to the formation of an electrostatic link with an increasingly covalent character which reaches a m a x i m u m in the uranyl salt where the P - - O - - U O ~ ~ bond is of the same order of covalency as the P - - O - - H bond resulting in the almost complete disappearance of the bands in this region. 1099-9524 cm * region. This region contains bands whose positions show little variation with change in the metal ion content of the salts, also in many cases the
152
T . D . SMITH Absorbance
5000
..
3333
2500
2000
1667
1429
1250
Cm-1
1111
1000
909
833
769
i
2
3
4
5
6
7
8 U
9
10
11
12
13
14
1111
1000
909
833
769
cm-1 714 3
9
10
11
12
13
l .,
Absorbance
5000
3333
2500
2000
1667
1429
2
3
4
5
6
7
I
1250
8 U
.,
3333
2500
2000
1667
1429
1250
1111
1000
909
B33
769
8
g
10
11
12
13
1250
11"11
1000
909
833
769
j 2
3
4
5
6
14
~-
Absorbance
5000
714 1
7
cm-I 714 4
14
U Absorbance
5000
3333
-,,--I"
2500
2000
1667
1429
Cm-- !
714 11
/
J 2
3
4
5
6
7
u
8,
9
10
11
12
1,3
14
The salts of organic phosphorus acids--I
Absorbanca 5000
3333
153
• 2500
2000
1667
1429
1250
cm-1
1000
1111
909
833
769
714 13
L
2
J
3
I
6
8
9
1250
1111
lO
11
12
13
I 14
1000
909
833
769
era-| 714
U
Absorbance
5000
i
3333
2500
2000
1667
1429
r 2
3
4
5
6
7
8 U
9
Absorbance
5000
10
11
12
13
1000
909
833
769
4
3333
2500
2000
1667
1429
14
•
1250
1111
cm-1
714
19
2
3
4
I 5
6
7
8
9
10
11
12
13
14
bl
F~G. 1. 1--Sodium di-n-butyl phosphate; 3--Lithium di-n-butyi phosphate; 4--Manganese (II) di-n-butyl phosphate; 11--Lanthanum di-n-butyl phosphate; 13--Cerium (III) di-n-butyl phosphate; 18--Zirconyl di-n-hutyl phosphate; 19~Uranium (VI) di-n-butyl phosphate.
154
T.D. SMITH
resolution of these bands is poor. The band which appears in the region 1010 cm -1 in the sodium and barium salts appears as a shoulder absorption in the manganese (II), copper (II), nickel (II), lead (II), mercury (II) and aluminium salts but disappears in the remaining spectra, whilst the general appearance of the bands for these remaining salts is very similar. The band in region 980 cm -1 persists in most of the salts studied; however in zirconyl dibutyl phosphate the band becomes almost indistinguishable whilst in uranyl dibutyl phosphate spectrum this band has disappeared. These two salts present exceptional behaviour which it is tentatively proposed is due to the interaction of the metal ion with the oxygen of the P - - O - - C group. The infra-red spectra studies here indicate that the simplest structure is that presented by the sodium and barium salts which involve an essentially ionic link with the P - - O - group. The other salts studied point to the covalent character which this link may assume and to the interaction of the P~-O group with the metal ion. Finally the possibility of bonding with the P - - O - - C group arises in the zirconyl and uranyl compounds.
Acknowledgements--Theauthor expresses his gratitude to Messrs. ALBRIGHTand WILSONLTD.for the supply 9f di-n-butyl phosphate and to Miss N. CARAMANDOfor recording the spectra.