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Behaviour of 32P in crystalline aromatic phosphates
HORG.
HUCL.
CHEM.
L.ETTERS
Vol.
4,
pp.
585-590,
1968.
Pergamon Press.
Printed In
Great
Britain,
BEHAVIOUR OF 32p IN CRYSTALLINE AROMATIC PHOSPHATES O.~.Jovanovi6-Kova~evi6 Hot Laboratory of the Boris Kidri~ Institute of Nuclear Sciences, Beograd, Yugoslavia (29 June 19~)
Since the S z i l a r d - C h a l m e r s ently
p r o c e s s has been i n s u f f i c i -
investigated in organic phosphate systems, especially in
organic aromatic phosphates (1) we decided to collect data and compare the chemical behaviour of 32p in the crystalline aromatic monophenyl and diphenyl phosphates with its behaviour in the inorganic solid systems investigated (2-5). Experimental Materials - In addition to the target compounds - monophenyl phosphate (C6H50)P(0)(OH)2(MPP) and diphenyl phosphate (C6H50)2P(0)(OH)(DPP)
(Albright purissimum),
other phosphorus compounds were used All
the
phosphorus
in
other chemicals
Merck and
B.D.H. were
thirty
this investigation.
compounds were purified
before use by repeated crystalization
about
several times
or distillation. analitically
The pure.
Neutron irradiation - Samples of MPP and DPP (10-50 mg) in polythene or in sealed quartz ampoules were irradiated at a thermal neutron flux of 1.3xlO 13 n/cm2s
(irradiation
dose
lO 7 rad/h) without cooling and with cooling with dry ice for 2.5 minutes and 5 seconds, or at a flux of 2.8x10 l0
n/cm2s
(irradiation dose lO 5 rad/h) for 22 hours. Separation of 32p species - After irradiation in the reactor samples of ~ P and DPP were dissolved in water (I-IC mg/ml, 5°C) containing small amounts ( ~ O . l ~ of anions of 585
586
BEHAVIOUR OF "P
Vel. 4 He. 10
phosphorus oxyacids acting as isotope
carriers.
To p r o v e w h e t h e r g a s e o u s f o r m s o f recoil ratus
reaction,
32p a r e
produced in
q u a r t z a m p o u l e s were opened i n a s p e c i a l
in a nitrogen
a t m o s p h e r e and u n d e r a s t r e a m o f i n a c t i v e
p h o s p h i n e g a s . P h o s p h i n e was o x i d i z e d w i t h bromine o r t h o p h o s p h o r i c a c i d whose a c t i v i t y An a l i q u e t
appa-
of 5-10~
water
was s u b s e q u e n t l y
of the aqueous s o l u t i o n
to
checked. was s p o t t e d
on t h e c a t h o d e s i d e o f a Whatman 3 MM p a p e r (2xlO0 cm). Chemic a l forms of 3 ~
w e r e s e p a r a t e d by h i g h - v o l t a g e
under the following conditions:
electrolyte
electrophoresis
pH 3 . 7 - 96% 0 . 1 M
acetic acid and 4% 0.2 M sodium acetate, 80 V/cm, 3 ~UL/strip, 10°C, I00 minutes. Identification of 3 ~
species - After electrophoretic
separation the paper strips were sprayed with an acid ammonium molybdate solution (6). The identification was also carried out by studying the behaviour of ions in the process of oxidation and hydrolysis
(7) and by neutron activation analysis.
Annealing - A water bath at 45_+0.500 was used for ther~I
annealing, while for radiation annealing a about I0 Ci 6°0o
source with a radiation dose of the order of I0 @ rad/h was used. Measurement of 3 ~
activity - The activity of
bromine
water was measured with a @.M.end-window counter and the actlvi~y of the paper strips (2xl cm) with a well-type scintillation counter. Results and discussion The experiments have shown that in the systems investigated neither 3~-phosphlne nor a~y other gaseous product is formed. By u s i n g t h e above p r o c e d t u c e s f o u r g r o u p s o f 3 ~ - r e c o i l
products were identified (FI@. i):
Vol. 4, He. 10
BEHAVIOUR OF ,Zp
A
B CD
F F
6
N
I3KL
M
/4
0
587
P
R
E
"6
I
A
Oi~.*nce
(cm)
FIG. I Electrophoretic
h i s t o g r e -m o f a n ao.ueous s o l u t i o n
of monophe~71 phosphate (irrad.2.Sxl0I0 n/cm2s,22 h) a) Aromatic esters of orthophosphoric and or~hophosphorous acids (P-O-C bond)-%Tiphenyl Hhosphate (A) (C6Hs0)3PO , diHhe~71 phosphate (G) (C6Hs0)2P(O) (OH), monophe~71 phosphate (I) (C6Hs0)P(0) (OH) 2' %TIHhe~71 phosphite (B) (C6Hs0)3P , diphenyl phosphite (C) (C6Hs0)2HP0 and monophe~71 Hhosphite (J) (C6Hs0)EP(O) (OH) ; b) A r o m a t i c o r g a n o p h o s p h o r u s compounds w i t h P-C b o n d -
phe~71 phosphonlc acid (D) (C6HS)P(O) (OH) 2, diphe~71 phosphlnlc acid (E) (C6H5)2P(0)(OH) and monophe~71 phosphlnlc acid (K)
(C6Hs)HP(0)(OH); c) Aliphatic or~nophosphorus co~ounds-dimethyl phosphinic acid (F) (CH3)2P(0)(0H) and methyl phosphate (H)
(CH30)P(O)(OH)2; d) Inorganic compounds-orthophosphoric acid (Z) H3P04, pyrophosphoric acid (M) H4P207, hypophosphoric acid (N) H4P206, orthophosphorous acid (0) H3P03, pyrophosphorous acid (P) H4P205 and hypophosphorous acid (R) HsPO 2. The results obtained show that similarly to the phenomens in inorganic crystal phosphates the largest number of recoil 3 ~ atoms break the chemical bond with the parent mole-
588
BEHAVIOUR OF " P
YoL 4, No. 10
c u l e in aromatic phosphates as well, so that t h e experimental upper limit for retention does not exceed 12.7% of the total
activity of 3 ~ (~N.,'r, 1) ~ TAm
1
3 ~ Distribution in Orystalline MPP and I ~ under Different Oonditions of Irradiation
lrr~ltation . n/ea2s
Time
IWP
2,5 •
1,3xlo 13
2,5 • 5 •
2,8x].OlO
1,3]r.tO13
2,8x10lO
°0
ambient
Tote~l. 321: yiel4
P e r c e n t a g e of t o t a l 32!~ a c t i v i t y
conditions •
B
C
D
E
F
G
B
l
~
It"
L
M
N
0
3,6 4 , l 4,2 7,2 4,5 4,2
9,3 4,9 10,8 5,4 6,0
-78
2,3 4,2 5,4 6,0 4.6 3,7
5,3 3,4 12,7 5,1 5,5 12,7 4,8 3,8 ~
-78
2,4 3*9 4,0 4,9 4,1 3,2
P
R
6,9 5,8 2,8 11,7 2,7 5,9
OrpnA~ l n o r p n A o
64,2
35,8
2,4 7,0
58,2
43.,8
5.0 3,9
8,6 5,7 4,9 15,2 8,6 4,1 12,3 2,2 7,0
50,6
49,4
22 h
t,,bienl;
3,1 3,8 4,8 6,4 5,0 4,4
9,2 4,3
9,9 4,9 4,2
8,3 5,4 4,4 14.2 2,6 5,1
60,0
40,o
2.5 •
Aubient
4 . 9 6.7 6 . 6 6 . 9 4 . 9 4 . 6 1 1 . 4 3 . 7
7.2 4.4 7.2
8.5 5.2 2.9 7.7 2.9 4.3
68.5
31.5
2,5 •
-?8
3,7 5,6 4,8 5,7 5,0 4,3
9,8 3.5
8~9 8,2 9,0
8,2 5,6 4,0 7,4 l,O 5,3
68,5
31,5
5 •
-78
4,4 6.8 6,3 6,1 5,0 4,1
6,3 3,4
5,6 4,7 4,9
9,9 5,1 5,5 10,9 2,6 8,6
57,4
42,6
4,3 4,7 4,8 5,8 5,7 4,4
8,1 3,5
7,8 4,3 4,6
8,8 6,8 4,0 11423,8 7,4
58,0
42,0
22 h
Ambient
The appearance of two alipha~ic forms with a yield not exceeding 4.9% of the total 3 ~
activity can be ascribed to
the process of benzene ring breakage. The da%a that the yields of these forms negligibly vary with v a ~ n g ditions
in the reactor
imply that their
a s c r i b e d t o t h e gamma r a d i a t i o n ,
irradiation con-
foraation
but to the 3 ~
s h o u l d n o t be
recoil
ener~.
It was shown in the systems investigated, as well aa in incrganic orthophosphates (2-5) ,that the irradiation conditions considerably influence the final distribution of 3 ~
in
dif-
ferent ionic forms (TABLE I).
"The yields given in the tables are average values of 5 independent determinations. The standard deviation is 10-15%.
Vel. 4, 14o. 10
BEHAVIOUR OF ,2p
589
The results presented in TABLE 2 have shown that isothermal annealing leads to an increase in the retention and to the oxidation reactions which result in the decreased yield of 3~-hypophosphorous-- and monophen~l phosphinic acids and increased yield of 32p-orthophosphorous and phe~71 phosphonic acids. These results are in good agreement with those in the literature concerning the annealing in some inorganic systems. TABLE 2 32p Distribution in Crystalline MPP and DPP after Postirradiation Treatments
Postirradiation
Total 3 ~ ~ield
Percentage of total 3 ~ activity
treatment
A
B
C
D
E
F
G
H
I
J
K
R
8.1 2.7 3.3 15.1
0.3
6.4
64.1
35.9
9.2 2.2 3.1 18.9
0.4
1.9
64.3
35.7
9.8 3.4 3.9 14.4 2.1 3.0 19.7
1.2
2.2
57.4
42.6
4.3 6.0 4.5 6.6 4.9 4.6 10.8 3.9
9.9 5.7 6.4
8.5 5.1 2.9 10.6
0.7
4.6
67.6
32.4
At 45°C, 8 d (irrad. 1.3xi013 n/cm2s,2.5 m,-78°C)
5.1 4.5 3.7 8.0 5.1 4.7 10.2 4.0
8.5 5.5 5.9 i1.4 4.2 3.5 12.4
0.3
3.0
65.2
34.8
6°Co 104 rad/~8 d (irrad. 1.3xlO 13 n/cm2s,2.5 m,-Te°C)
4.8 3.9 3.4 8.7 5.0 4.6 10.3 4.1
9.0 4.9 5.3 12.9 4.1 3.3 12.8
0.6
2.3
64.0
36.0
4.1 5.6 4.9 6.9 4.3 3.8 ii.O 4.7 10.7 3.5 4.6
At 45°Cp 8 d 1 (irrad. 1.3xi0 3 n/cm2s, 2.5 m,-78°C
3.9 2.9 2.4 8.8 4.3 3.9 12.6 4.2 13.4 3.6 4.3
6°Co 104 rad/h{ 8 d (irrad. 1.3x10 3 n/cm2s,2.5 m,-78°C)
3.8 2.8 2.9 7.I 5.3 4.6
DPP A-~-22°C, 8 d (irr@d. i. 3xlO 13 n/cm2s,2°5 m,-78°C)
9.2 4.6
L
M
N
0
Orphic Inorjani~
P
MPP A-~--22°C,8 d (irrmd. 1.37.1013 n/cm2s,2.5 m,-78°0)
Comparison of the results given in TABLE I with those in TABLE 2 imply t h a t
in the investigated aromatic phospha-
tes, still during irradiation in the reactor, there occurs thermal and, probably to a certain extent, radiation annealing too.
BEHAVIOUR OF ':P
590
Vei. 4, Me. 10
Acknowledgements The a u t h o r w i s h e s to e x p r e s s h e r s i n c e r e g r a t i t u d e to
Prof. Dr.G.W.Wittig, Prof. Dr.L.Horner, Dr.W.Reiss, Dr.F.Kra~ovec, Dr.A.J.Speziale, Dr.M.Halmannand Dr.G.Schrader for their kind supply of rare phosphorus compounds.
References I. 0.~rbacher and K.Philipp, Z.Phyeik.0hem. (~eipzig) A 179,
263 (1937) 2. W.F.Libby, J.Am.Chem.Soc., 62, 1930 (1940). 3. A.H.W.Aten Jr., H.v.d.S~ra~ten and P.Riesebos, Science,
IA5, 267 (1952). 4. 7 . . 1 i n d n e r and G . H a r b o t t l e , O h e m . E f f e c t e N u c l . T r a n s f o r m . , p .
485, I.A.~.A., Vienn~ (1961). 5. R . F . O . O l a r i d g e and A.G.Maddock, T r a n s . F a r a d a y S o t . ,
59,
935 (1963). 6. C.S.Hanee and T.A.Isherwood, Nature, 164, 1107 (1949). 7. B.Blaser and K.H.Worms, Z.Anorg.Allgem.Ohem., 300, 229 (1959);ibid. 301, 18 (1959).
HUCL.
CHEM.
L.ETTERS
Vol.
4,
pp.
585-590,
1968.
Pergamon Press.
Printed In
Great
Britain,
BEHAVIOUR OF 32p IN CRYSTALLINE AROMATIC PHOSPHATES O.~.Jovanovi6-Kova~evi6 Hot Laboratory of the Boris Kidri~ Institute of Nuclear Sciences, Beograd, Yugoslavia (29 June 19~)
Since the S z i l a r d - C h a l m e r s ently
p r o c e s s has been i n s u f f i c i -
investigated in organic phosphate systems, especially in
organic aromatic phosphates (1) we decided to collect data and compare the chemical behaviour of 32p in the crystalline aromatic monophenyl and diphenyl phosphates with its behaviour in the inorganic solid systems investigated (2-5). Experimental Materials - In addition to the target compounds - monophenyl phosphate (C6H50)P(0)(OH)2(MPP) and diphenyl phosphate (C6H50)2P(0)(OH)(DPP)
(Albright purissimum),
other phosphorus compounds were used All
the
phosphorus
in
other chemicals
Merck and
B.D.H. were
thirty
this investigation.
compounds were purified
before use by repeated crystalization
about
several times
or distillation. analitically
The pure.
Neutron irradiation - Samples of MPP and DPP (10-50 mg) in polythene or in sealed quartz ampoules were irradiated at a thermal neutron flux of 1.3xlO 13 n/cm2s
(irradiation
dose
lO 7 rad/h) without cooling and with cooling with dry ice for 2.5 minutes and 5 seconds, or at a flux of 2.8x10 l0
n/cm2s
(irradiation dose lO 5 rad/h) for 22 hours. Separation of 32p species - After irradiation in the reactor samples of ~ P and DPP were dissolved in water (I-IC mg/ml, 5°C) containing small amounts ( ~ O . l ~ of anions of 585
586
BEHAVIOUR OF "P
Vel. 4 He. 10
phosphorus oxyacids acting as isotope
carriers.
To p r o v e w h e t h e r g a s e o u s f o r m s o f recoil ratus
reaction,
32p a r e
produced in
q u a r t z a m p o u l e s were opened i n a s p e c i a l
in a nitrogen
a t m o s p h e r e and u n d e r a s t r e a m o f i n a c t i v e
p h o s p h i n e g a s . P h o s p h i n e was o x i d i z e d w i t h bromine o r t h o p h o s p h o r i c a c i d whose a c t i v i t y An a l i q u e t
appa-
of 5-10~
water
was s u b s e q u e n t l y
of the aqueous s o l u t i o n
to
checked. was s p o t t e d
on t h e c a t h o d e s i d e o f a Whatman 3 MM p a p e r (2xlO0 cm). Chemic a l forms of 3 ~
w e r e s e p a r a t e d by h i g h - v o l t a g e
under the following conditions:
electrolyte
electrophoresis
pH 3 . 7 - 96% 0 . 1 M
acetic acid and 4% 0.2 M sodium acetate, 80 V/cm, 3 ~UL/strip, 10°C, I00 minutes. Identification of 3 ~
species - After electrophoretic
separation the paper strips were sprayed with an acid ammonium molybdate solution (6). The identification was also carried out by studying the behaviour of ions in the process of oxidation and hydrolysis
(7) and by neutron activation analysis.
Annealing - A water bath at 45_+0.500 was used for ther~I
annealing, while for radiation annealing a about I0 Ci 6°0o
source with a radiation dose of the order of I0 @ rad/h was used. Measurement of 3 ~
activity - The activity of
bromine
water was measured with a @.M.end-window counter and the actlvi~y of the paper strips (2xl cm) with a well-type scintillation counter. Results and discussion The experiments have shown that in the systems investigated neither 3~-phosphlne nor a~y other gaseous product is formed. By u s i n g t h e above p r o c e d t u c e s f o u r g r o u p s o f 3 ~ - r e c o i l
products were identified (FI@. i):
Vol. 4, He. 10
BEHAVIOUR OF ,Zp
A
B CD
F F
6
N
I3KL
M
/4
0
587
P
R
E
"6
I
A
Oi~.*nce
(cm)
FIG. I Electrophoretic
h i s t o g r e -m o f a n ao.ueous s o l u t i o n
of monophe~71 phosphate (irrad.2.Sxl0I0 n/cm2s,22 h) a) Aromatic esters of orthophosphoric and or~hophosphorous acids (P-O-C bond)-%Tiphenyl Hhosphate (A) (C6Hs0)3PO , diHhe~71 phosphate (G) (C6Hs0)2P(O) (OH), monophe~71 phosphate (I) (C6Hs0)P(0) (OH) 2' %TIHhe~71 phosphite (B) (C6Hs0)3P , diphenyl phosphite (C) (C6Hs0)2HP0 and monophe~71 Hhosphite (J) (C6Hs0)EP(O) (OH) ; b) A r o m a t i c o r g a n o p h o s p h o r u s compounds w i t h P-C b o n d -
phe~71 phosphonlc acid (D) (C6HS)P(O) (OH) 2, diphe~71 phosphlnlc acid (E) (C6H5)2P(0)(OH) and monophe~71 phosphlnlc acid (K)
(C6Hs)HP(0)(OH); c) Aliphatic or~nophosphorus co~ounds-dimethyl phosphinic acid (F) (CH3)2P(0)(0H) and methyl phosphate (H)
(CH30)P(O)(OH)2; d) Inorganic compounds-orthophosphoric acid (Z) H3P04, pyrophosphoric acid (M) H4P207, hypophosphoric acid (N) H4P206, orthophosphorous acid (0) H3P03, pyrophosphorous acid (P) H4P205 and hypophosphorous acid (R) HsPO 2. The results obtained show that similarly to the phenomens in inorganic crystal phosphates the largest number of recoil 3 ~ atoms break the chemical bond with the parent mole-
588
BEHAVIOUR OF " P
YoL 4, No. 10
c u l e in aromatic phosphates as well, so that t h e experimental upper limit for retention does not exceed 12.7% of the total
activity of 3 ~ (~N.,'r, 1) ~ TAm
1
3 ~ Distribution in Orystalline MPP and I ~ under Different Oonditions of Irradiation
lrr~ltation . n/ea2s
Time
IWP
2,5 •
1,3xlo 13
2,5 • 5 •
2,8x].OlO
1,3]r.tO13
2,8x10lO
°0
ambient
Tote~l. 321: yiel4
P e r c e n t a g e of t o t a l 32!~ a c t i v i t y
conditions •
B
C
D
E
F
G
B
l
~
It"
L
M
N
0
3,6 4 , l 4,2 7,2 4,5 4,2
9,3 4,9 10,8 5,4 6,0
-78
2,3 4,2 5,4 6,0 4.6 3,7
5,3 3,4 12,7 5,1 5,5 12,7 4,8 3,8 ~
-78
2,4 3*9 4,0 4,9 4,1 3,2
P
R
6,9 5,8 2,8 11,7 2,7 5,9
OrpnA~ l n o r p n A o
64,2
35,8
2,4 7,0
58,2
43.,8
5.0 3,9
8,6 5,7 4,9 15,2 8,6 4,1 12,3 2,2 7,0
50,6
49,4
22 h
t,,bienl;
3,1 3,8 4,8 6,4 5,0 4,4
9,2 4,3
9,9 4,9 4,2
8,3 5,4 4,4 14.2 2,6 5,1
60,0
40,o
2.5 •
Aubient
4 . 9 6.7 6 . 6 6 . 9 4 . 9 4 . 6 1 1 . 4 3 . 7
7.2 4.4 7.2
8.5 5.2 2.9 7.7 2.9 4.3
68.5
31.5
2,5 •
-?8
3,7 5,6 4,8 5,7 5,0 4,3
9,8 3.5
8~9 8,2 9,0
8,2 5,6 4,0 7,4 l,O 5,3
68,5
31,5
5 •
-78
4,4 6.8 6,3 6,1 5,0 4,1
6,3 3,4
5,6 4,7 4,9
9,9 5,1 5,5 10,9 2,6 8,6
57,4
42,6
4,3 4,7 4,8 5,8 5,7 4,4
8,1 3,5
7,8 4,3 4,6
8,8 6,8 4,0 11423,8 7,4
58,0
42,0
22 h
Ambient
The appearance of two alipha~ic forms with a yield not exceeding 4.9% of the total 3 ~
activity can be ascribed to
the process of benzene ring breakage. The da%a that the yields of these forms negligibly vary with v a ~ n g ditions
in the reactor
imply that their
a s c r i b e d t o t h e gamma r a d i a t i o n ,
irradiation con-
foraation
but to the 3 ~
s h o u l d n o t be
recoil
ener~.
It was shown in the systems investigated, as well aa in incrganic orthophosphates (2-5) ,that the irradiation conditions considerably influence the final distribution of 3 ~
in
dif-
ferent ionic forms (TABLE I).
"The yields given in the tables are average values of 5 independent determinations. The standard deviation is 10-15%.
Vel. 4, 14o. 10
BEHAVIOUR OF ,2p
589
The results presented in TABLE 2 have shown that isothermal annealing leads to an increase in the retention and to the oxidation reactions which result in the decreased yield of 3~-hypophosphorous-- and monophen~l phosphinic acids and increased yield of 32p-orthophosphorous and phe~71 phosphonic acids. These results are in good agreement with those in the literature concerning the annealing in some inorganic systems. TABLE 2 32p Distribution in Crystalline MPP and DPP after Postirradiation Treatments
Postirradiation
Total 3 ~ ~ield
Percentage of total 3 ~ activity
treatment
A
B
C
D
E
F
G
H
I
J
K
R
8.1 2.7 3.3 15.1
0.3
6.4
64.1
35.9
9.2 2.2 3.1 18.9
0.4
1.9
64.3
35.7
9.8 3.4 3.9 14.4 2.1 3.0 19.7
1.2
2.2
57.4
42.6
4.3 6.0 4.5 6.6 4.9 4.6 10.8 3.9
9.9 5.7 6.4
8.5 5.1 2.9 10.6
0.7
4.6
67.6
32.4
At 45°C, 8 d (irrad. 1.3xi013 n/cm2s,2.5 m,-78°C)
5.1 4.5 3.7 8.0 5.1 4.7 10.2 4.0
8.5 5.5 5.9 i1.4 4.2 3.5 12.4
0.3
3.0
65.2
34.8
6°Co 104 rad/~8 d (irrad. 1.3xlO 13 n/cm2s,2.5 m,-Te°C)
4.8 3.9 3.4 8.7 5.0 4.6 10.3 4.1
9.0 4.9 5.3 12.9 4.1 3.3 12.8
0.6
2.3
64.0
36.0
4.1 5.6 4.9 6.9 4.3 3.8 ii.O 4.7 10.7 3.5 4.6
At 45°Cp 8 d 1 (irrad. 1.3xi0 3 n/cm2s, 2.5 m,-78°C
3.9 2.9 2.4 8.8 4.3 3.9 12.6 4.2 13.4 3.6 4.3
6°Co 104 rad/h{ 8 d (irrad. 1.3x10 3 n/cm2s,2.5 m,-78°C)
3.8 2.8 2.9 7.I 5.3 4.6
DPP A-~-22°C, 8 d (irr@d. i. 3xlO 13 n/cm2s,2°5 m,-78°C)
9.2 4.6
L
M
N
0
Orphic Inorjani~
P
MPP A-~--22°C,8 d (irrmd. 1.37.1013 n/cm2s,2.5 m,-78°0)
Comparison of the results given in TABLE I with those in TABLE 2 imply t h a t
in the investigated aromatic phospha-
tes, still during irradiation in the reactor, there occurs thermal and, probably to a certain extent, radiation annealing too.
BEHAVIOUR OF ':P
590
Vei. 4, Me. 10
Acknowledgements The a u t h o r w i s h e s to e x p r e s s h e r s i n c e r e g r a t i t u d e to
Prof. Dr.G.W.Wittig, Prof. Dr.L.Horner, Dr.W.Reiss, Dr.F.Kra~ovec, Dr.A.J.Speziale, Dr.M.Halmannand Dr.G.Schrader for their kind supply of rare phosphorus compounds.
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