48 Thermal Rearrangement and Condensation of O,O-Dimethyl-O-phenylphosphorothionate HERBERT TEICHMANN Zentralinstitut für Organische Chemie der Akademie der Wissenschaften der DDR, DDR1199 Berlin-Adlershof, GDR
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GERHARD SCHRAMM Orthopädische Klinik der Medizinischen Akademie, Erfurt, DDR-50 Erfurt, GDR
I t i s now more than three decades that d i a l k y l arylphosphorothionates such as parathion and p a r a thion-methyl took a dominant r o l e among organophosphorus p e s t i c i d e s . Owing to o c c a s i o n a l i n c i d e n t s i n production and h a n d l i n g , v a r i o u s e f f o r t s have been made in the past to e l u c i d a t e the thermal behaviour of such compounds ( c f . (1, 2, 3) and references c i t e d t h e r e i n ) . However, our knowledge of the r e a c t i o n s involved i s still f a r from being s a t i s f a c t o r y . With the aim of a better understanding of the thermal r e a r r a n gement and decomposition processes i n t h i s c l a s s of commercially h i g h l y important substances, the thermolysis of (MeO)2(PHO)PS (I) as a model compound has been reexamined. In the temperature range of 1 2 5 - 1 4 0 ° C two periods c l e a r l y can be d i s t i n g u i s h e d . During the first one which consumes about 70% of the t o t a l r e a c t i o n time, only 30% conversion of the thionate I takes p l a c e . So f a r the decrease of I follows an a u t o c a t a l y t i c law and corresponds quite w e l l to the increase of the i s o meric S-methyl t h i o l a t e I I . In the shorter and exothermic second p e r i o d i s o m e r i z a t i o n of I soon comes to completion. Here, however, the t h i o l o isomer II also r a p i d l y decomposes a f t e r reaching a maximum conc e n t r a t i o n of about 65%. The final product, free from I and I I , c o n s t i t u t e s a water s o l u b l e , hygroscopic substance of unchanged elemental composition, e x h i b i t ing strong a c i d i c r e a c t i o n and containing Me3^ions ( about h a l f o f the t o t a l s u l f u r ) and condensed phosphates. An i d e n t i c a l product i s obtained from pure I I a f t e r a much shorter heating time. The t h i o n o - t h i o l o rearrangement I-^II i s c a t a l y zed by II as w e l l as by decomposition products of I I : Me2S induces an 0 - d e a l k y l a t i o n / S - r e a l k y l a t i o n sequence ( 4 ) , and Me3S® acts as an a l k y l a t i n g agent s u p e r i o r 0097-6156/81/0171-0235$05.00/0 © 1981 American Chemical Society In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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to I or I I j S-alkylation of I-analogues with R3O® i n stead of s a l t s t o form c r y s t a l l i n e trialIroxyalkylthiophosphonium s a l t s and dealkylation of them by Me2S to y i e l d II-analogues has been demonstrated before (5.» 6). Relative reaction times u n t i l t o t a l loss of I a% 135°C are (hours, approximately)1 with out catalyst 7; i n the presence of 1 equivalent of I I or of 0,06 equivalents of Me3S® SbClôP 2; i n the pre sence of 0,06 equivalents of Me2S 1; removing Me2S by passing through a stream of N2 18· Further evidence for c a t a l y s i s by I I arose from crossing experiments
(1).
Soon a f t e r t o t a l isomerization of I the decompo s i t i o n of i t s isomer I I also i s completed. The con version of I I into the f i n a l mixture of i o n i c substan ces consists of two basic steps: dealkylation by Me2S to form the S-methyl-O-phenylphosphorothiolate anion I I I (eq. 3), and nucleophilic attack at phosphorus by the anion I I I t o give a S-methyl diphosphate which i s O-dealkylated to IV by the leaving group MeS® (eq. 1 ) . 0
es u
0 0 ^c£) 0 0 M u + MeS~κ , ι > MeO-P-0-P-SMe * ^O-P-0-P-SMe + Me S OPh OPh OPh OPh (1) IV
^ TT +11
M
0-P-SMe OPh III
M
2
Preparative application of t h i s condensation p r i n c i p l e has been shown (8) to y i e l d , e.g., 83°/> diphenyldiphosphate from I I and (MeO)(PhO)POOK after 5 hours r e f l u x i n BU2O. Analogous condensation of I I with IV or even higher condensed phosphorothiolate anions would enable a stepwise formation of longer chains. The Me2S produced i n every single condensation step must consume an equivalent amount of 0-methylester functions because no sulfur i s l o s t . Therefore, a f t e r isomerization of I , one h a l f of I I i s required for sulfonium s a l t formation, and a reasonable s t o i chiometry of the II-conversion r e s u l t s from the sum of equations (2) and (3). Since by reaction (3) a large supply of anion I I I i s offered, I I I w i l l be the dominant nucleophile f o r condensation with I I , and one may expect a large number of chains, i . e . , a low average condensation degree b. TLC on DEÂE c e l l u l o s e with 0.2 m HC1 permits the i o n i c species to be separated and thus the course of the thermolysis t o be followed. Besides an i n i t i a l t i n y uncertain spot (obviously (MeO)(PhO)P02® accord ing to Rp value), four different compounds emerge suc cessively: I I I , a f t e r i t IV, and f i n a l l y the s u l f u r -
In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
TEiCHMANN A N D S C H R A M M
48.
Ο,Ο-Dimethyl-O-phenylphosphorothionale
237
Ο Ο Ο ιι II a ^O-P-SMe• O-P-SMe η MeO-P-SMe + Ο-Ρ OPh OPht OPh II III Ο Ο ιι II n O-P-SMe + n Me^S" η MeO-P-SMe + n Me2S OPh OPh II III Ο Ν
n Me S 2
(2)
(3)
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0
Ο
Ο © Θ " c O-P-SMe O-P-SMe + Ο-Ρ— + n Me^S OPh OPh b III (4) b = a + c = n
0 2n MeO-P-SMeOPh II
Ο
Θ
Ν
0
P
h
free diphosphate V and triphosphate VI. By P-NMR spectroscopy exactly the same components are identi f i e d . Phosphorus determinations in isolated spots of the f i n a l product are in l i n e with values obtained from integration of NMR signals (see table). 31
III IV 7
VI \\ ^ ;
Table: Thermolysis of I at 135°C, composition of f i n a l product $> of total Ρ * 3 1 Ρ (ppm) 1) from T K from P-NMR 15 14 1 s 29 62 65 P 12Î72(d);pB-18,05(d) ) 11 9 -18,26 ,x 12 13 pA-18,20(d);P -29,14(t) in CH C1 ) P bond to SMe; Jpp 26,4 Hz P terminal P; Jpp 17,7 Hz A
2
B
5
5
2
1
A
Hydrolytic s t a b i l i t y of the condensed species decreases i n the series V>VI >IV; the latter could not be isolated but was identified unambiguously by its hydrolysis products (eq. 5 , b = 1) in two dimen0
Η
0 - P — O-P-SMe + H 0-
OPh
2
v OPh
0
0
0
Η
fp-o OPh
θ
+
b = 2: V b = 3 : VI
M
O-P-SMe 1 OPh
+ 2 H® (5)
III
In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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PHOSPHORUS
CHEMISTRY
sional TLC as w e l l as i n 31p-NMR spectra. Higher con densed t h i o l o oligophosphates must be regarded to be extremely sensitive to moisture and to act as precur sors of V and VI. I f the thermolysis temperature i s allowed to r i s e to 180°C and above, evolution of Me2S takes place with sulfur l o s s up to 60$· Simultaneously the content of V and VI and of other unidentified conden sation products increases markedly at the expense of IV· l o s s of Me3S® approximately p a r a l l e l s that of t h i o l o ester groups, however*, no MeO groups are detec table i n the H-NMR spectra. From these r e s u l t s one must conclude that the uncharged t h i o l o sulfur w i l l p r e v a i l over the anionic oxygen functions as nucleo phile toward the Me3S© ion (eq. 6); the r e s u l t i n g θ
0 M 0-P— OPh
0 0 ι -P-SMe + Me S' -y^Me-f-O-P- 0-P-SMe OPh OPh OPh 0 II
3
Me S 2
b
(6) V
0 θ
0 il
M
0-P-SMe, 0-P OPhJb OPh L
Me S 2
+ 2 Me S
-μο-Ρ-
2
OPhJb+1 L
monomeric (b = 0) or oligomeric metaphosphate species open an alternative route for building up condensed phosphates even a f t e r t o t a l consumption of I I . Literature
cited
1. H i l g e t a g , G.; Schramm, G.; Teichmann, H . J. P r a k t . Chem. 1959, 8, 73. 2. Teichmann, Η . ; Lehmann, G. Sitzungsber. DAW Berlin Kl. Chem., Geol., B i o l . 1962, No. 5. 3. E n g e l , R. R . ; L i o t t a , D . J. Chem. Soc. C 1970, 523. 4. H i l g e t a g , G . ; Teichmann,H. Angew. Chem. i n t e r n a t . Edit. 1965, 4, 914. 5. Teichmann, H.; H i l g e t a g , G . Chem. B e r . 1963, 96, 1454. 6. Schulze, J. T h e s i s , Humboldt U n i v e r s i t y B e r l i n , 1971. 7. Teichmann, H . Angew. Chem. i n t e r n a t . E d i t . 1965, 4, 993. 8. H i l g e t a g , G . ; K r ü g e r , M . ; Teichmann, H . Z . Chem. 1965, 5, 180. RECEIVED July 7, 1981.
In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
