IR absorption spectra of zinc organophosphates

I R ABSORPTION SPECTRA OF ZINC ORGANOPHOSPHATES *

YE. I. MARKOVA,G. N. KUZ'MI~A, L. G. KHA~AXOVA, V. V. S~.R and P. I. SA2¢I~ A. V. Topchiev I n s t i t u t e of Petrochemical Synthesis, U.S.S.R. A c a d e m y of Sciences

(Received 19 July 1974) THIS paper is concerned with a study of IR absorption spectra of zinc organophosphates of different structures, of which the main structural groups are as follows: RO RO

S

\f P

RO/ \S--Zn--

\/

/\

S P

R RO

\/

R

\/ /\

S--Zn--

R

S

RO

P

/ RO

S p S--Zn--

\/

0 p

/\ \O--Zn--

RO

O--Za--

where R represents hydrocarbon radicals. Some zince organophosphates are active anti-oxidizing agents. The synthesis of salts is described in another study [1]. As a result of investigating this series of compounds absorption bands could be almost fully assigned to vibrations of main structural groups of molecules and some relations established between structure, the type of spectra and the efficacy of compounds as anti-oxidizing agents. UR-20 and Perkin-Elmer-180 spectrophotometers were used to obtain I R spectra of compounds studied. Table 1 shows frequencies of bond stretching vibrations of main structural groups: for salts of dialkyldithiophosphorie acids Zn--S, P--S(Zn), P = S , P--O(C); for salts of dialkylmonothiophosphorieacids P = S , P--O(C),P--O(Zn); for salts of dialkylphosphoric acids P--O(C), P--O(Zn), P = O . I n addition to compounds shown in Table 1, spectra were obtained for zinc dialkyldithiophosphates with different hydrocarbon radicals of aliphatie series ranging from CH3 to CsHn and bis-(O,O-di-n-butylthiophosphoryl)-disulphide (Table 2). * lqeftekhimiya 15, No. 2, 311-318, 1975. 55

14 15 16 17 18 19

13

12

11

10

9

7 8

6

5

4

3

2

1

No. of compound

Zinc di-n-butyldithiophosphate Zinc di-is obutyldithiophosphate Zinc di-isobutyldithiophosphonate Zinc di-isobutyldithiophosphinate Zinc di-2-e thylhcxyldithiophosphate Zinc di-n-hexadecyldithiophosphate Zinc diphenyldithiophosphatc Zinc di-n-butylmono thiophosphate Zinc di-isobutyimonophosphate Zinc di-isobutylmonothiophosphinate Zinc di-2-ethylhexylmonothiophosphate Zinc di-n-hexadecyimouothiophosphatc Zinc diphcnylmonothiophosphatc Zinc di-n-butyiphosphatc Zinc di-isobutyiphosphate Zinc di-isobutyiphosphinate Zinc di-2-ethylhexylphosphate Zinc di-n-hexadecylphosphate Zinc diphenylphosphatc

l~ame

[(n-CºH,0hP(O)0]ffiZn [(iso-C,Hg0)sP(0)0]2Zn [(iso-C,H.)2P( 0)0]aZn [(CuH~,0)2P(0)0]~Zn [(n-C1.Ha~0)~P(0)0]zZn [(CaH60),P(0)0]sZn

[(C6Hs0)aP(S)0]=Zn

[(n-CIeHssO)=P(S)0],Zn

[(CaH~,0)iP(S)0],Zn

[(iso-C,H0)~P(S)0],Zn

[(iso-C,H,0),P(S)0J~Zn

[(C.H60)~P(S)S]ffiZn [(n-C4H.0)ffiP(S)SJ~Zn

[(n-CleH.sO)IP(S)S],Zn

[(CsH~,0)IP(S)S]aZn

[(iso-C,H.),P(S)S]~Zn

(iso-C,Ho0)C4HgP(S)S]=Zn

(tso-C4H.0),P(S)S]=Zn

(n-C4H.0)sP(S)S]ffiZn

Formula

338

326

314

308, 322

S-Zn

515,

524,

537,

536,

495

556

540,

543

563

556,

547

P-S(Zn)

562

590

627,

617,

628,

562,

625,

616,

582,

620,

650,

650

648

653

583

624

625 650

675

670

605

640

668

665

P=S

940, 970 1010, 1020 1043, 1063

1038, 1080 1030, 1065

910, 970

1000, 1085

985, 1020, 1050

1020, 1060

905, 920 982, 1033, 1075

1000

980-1040

980--1030

i000-1030

985-- 1030

P-O(C)

1125 1115 1050, 1078 1110 1133 1110

1168,1200

1183, 1220

1159

1100

1153

1150

P - O(Zn)

Bond-stretching vibration frequencies of structural groups, cm -1

1185 1116, 1145 1200 1220 1200, 1218

1200

P=O

T A B L E 1. B O N D S T R E T C H I N G V I B R A T I O N F R E Q U E N C I E S OF S T R U C T U R A L GROUPS OF ZINC O R G A N O P H O S P H A T E S

0"60

--0-12

0.82 -- 0.60 -- 2-60 --

-- 2-60

-

-0.12 --0"82

- 2.60

-1.66

- 0"60

-0.82

~F

O

IR absorption spectra of zinc organophosphates

57

TABLE 2. BOND STRETCHINGVIBRATIONFREQUENCIESO1~ STRUCTURALGROUPSOF ZINC DIALKYLDITHIOPHOSPHATES :No. o f

• compound

Formula

[(CH.0),P(S)S],Zn [(CzI-Is0)~P(S)S]zZn [(n-C3H,0)2P(S)S],Zn [(iso-C.H,0),P(S)S],Zn [(n-C,H,O),P(S)S],Zn [(iso-C,H,O),P(S)S],Zn

[(n-C,H~OhP(S)S],Zn [(n-C6H~.0hP(S)S],Zn [n-C,H.0),P(S)]~Sa

Bond-stretching vibration frequency of structural groups, cm-~ Zn-- S P - - S(Zn) P=S 320 316 308, 322 314

311 --

515 525 545 537 547 536, 556, 550 550 420, 500,

590 523

611, 645, 667 616, 643, 658 666 640, 658 665 650, 668 670 665 650

Z~F --0-240 --0.425 - - O. 640 - - O- 600 --0-820 --0.600 --0,780 - - O' 640 - - 0' 820

A large number of studies were published (mainly in recent years) concerning I R spectra of organophosphoric acids and esters [2, 3]. There are relatively few papers dealing with I R spectra of corresponding salts and the description of spectra in these papers is normally confined to determining two-to-three typical bands. There are some conflicting results in the literature in connection with the assigning of the frequency of metal--sulphur bond stretching vibrations. These results were obtained using spectra of various metal dithiophosphates, dithiocarbamates, xanthates and dithiurates: nickel, cobalt, copper, lead and palladium salts were examined in most studies. I t was pointed out in these studies t h a t absorption due to the metal--sulphur bond takes place within a wide range (100-500 cm -1) [4-6]. Frequencies at 280, 390 cm -1 arc due to the bond stretching vibration of zinc--sulphur. In this study absorption bands due to bond stretching vibrations of zinc-sulphur were determined by comparing spectra of zinc dialkyldithiophosphates (Table 2, Nos. 1-8) obtained in the region of 150-400 cm -1 and a compound of a structure similar to t h a t of salts but free from metal--bis-(O,O-dibutylthiophosphoryl)-disulphide (Table 2, No. 9). Figure 1 shows spectra of the compounds studied. In the spectra there are absorption bands typical of both salts and a compound free from zinc at 200-290 cm -1 and 340-400 cm -1. In the region of 290-340 cm-1 absorption bands are observed which are only typical of spectra of salts, in the spectrum of disulphide there is no absorption in this region. The range at 290-340 cm -1 is attributed to absorption of the zinc--sulphur bond stretching vibration. Assigning absorption bands to vibrations of P--S(Zn) and P : S does not involve difficulties since most information published is related to these vibrations [2, 3, 8]. In spectra of compounds studied these bands are in the ranges of 495-590 and 582-675 cm -1, respectively. In m a n y instances vibrations are characterized by two bands. For salts of zinc di-isobutyl- and di-2-ethylhexyl-

58

YE. I. HARKOVAet al.

dithiophosphates in the region of P--S(Zn) vibrations three bands are even observed (Table 1, Nos. 2 and 5). I t should be noted t h a t absorption bands of the vibration of zinc diphenyldithiophosphate group (495 cm -i) and the absorption band of P----S in salts of dialkylthiophosphinic acids (Table 1, Nos. 4 and 10) are not within these ranges; in these compounds the band is considerably desplaced to the low-frequency region and approximates the P--S(Zn) band. There is considerable information in the literature about the position of the absorption band of the P--0(C) group, but chiefly for esters and acids V, cm " !

6.Ce ;l

EEL?

p--s

6¢0600620 c . . . . ~

~

[

580

0

550 5¢0

~

/ z 520 V/~ff

-

300~_IV 2OO

300 FIG. 1

z/go u,cm-I

300

0

I

/ . . 0 - -I

S Zn I

t

i

r

I

t

I

O.Zl 0"8 1"2 l-O

I

I

I

I

c t

2.0 2-4 o"f

Fro. 2

FIG. 1. Spectra of zinc bis-[O,O-dibutylthiophosphoryl]-disulphide and dialkyldithiophosphates in the 150-400 cm-1 region: 1--[(n-C4H~0)~P(S)]zS6 2--[(n-C4HgO)~, ,P(S)S]~Zn; 3--[(iso-C,H,O)20(S)S]2Zn; 4--[(C~HsO)a.P(S)S]2Zn; 5--[(CHsO)2P(S)S]2Zn. FIG. 2. Dependence of the position of absorption bands in IR spectra of zinc dithiophosphates on 2:~ of substituents at the phosphorus atom. Frequency of absorption bands, era-': S--Zn (I) in salts. [(C,H,O)~P(S)S]~Zn (A); [(C,H,O)C,H,P(S)S]2ZN (B); [(Call,),, ,P(S)S]2Zn (C); P--S (Zn) (II a, b) in the same salts; P = S (III, a, b) in the same salts; P--S (Zn), (IV, V) and P = S (points in the frame) in salts; 1--[(CHa0)~P(S)SJ~Zn; 2-[(C2HsO)~P(S)S]2Zn; 3-- [(n-CaHT0)2P(S)S]2Zn; 4-- [(iso-C3HTO)~P(S)S]2Zn; 5-[(n-C4HgO)2P(S)S]2Zn; 6 --[(iso-C4HgO)~ .P(S)S]2Zn; 7-- [(n-CsHllO)2P(S)S]2Zn; 8-- [(n-C.H130)2P(S)S]2Zn. [2, 3]. For salts the relevant assignment (968-1012 cm -1) was made only in one study using spectra of metal dialkyldithiophosphates [8]. For other types of salts shown in Table 1 there is no information available. For all the salts studied with one exception {Table 1, No. 6), the absorption band of P--O(C) is represented by a doublet, or triplet; it has a considerable width of the order of 40-100 cm -1. For this reason it is difficult to observe any variation in the

IR absorption spectra of zinc organophosphates

59

b a n d according to the structure of salts; some shift is only observed to the high frequency region for salts containing oxygen. The band of P--O(C) for the salts studied is in the range of 905-1085 cm -1. There is little information available in connection with the position of the absorption band of P--O(Zn). Assigning was only made [9] for zinc dimethyl a n d diethylmonothiophosphates (1070-1120 cm-1). No results have been obtained for salts of dialkylphosphoric acids. A comparative study of spectra T A B L E 3. E F F E C T OF SUBSTITITEI~TS A T T H E P H O S P H O R U S ~.TOlY~ O1~ T H E T I O N B A N D S Ii~ I R

No. of compound

S H I F T OF A B S O R P -

SPECTR.4. OF ZII~C DIBI~TYLPHOSPH.A-TES A.I~D D I B U T Y L P H O S P H I I ~ A T E S

Shifts of absorption band, cm -1 Formula

2:~F

2

[(iso-C4HsO)~P(S)SI~Zn

--0.60]

4

[(iso-G,I-Ig)BP(S)S]2Zn

--2.60J

9

[(iso-C,H90) 2P(S)O]~Zn

--0.60~

10

[(iso-C,Hg)2P(S)O]IZn

-- 2.

15

[(iso-CaH,O),P(O)O]aZn

16

[(iso-G4Hg)P(O)O]BZn

S--Zn

-]-24

P--S P--S(Zn) P = O

--65

--67

P--O(Zn)

--39

--

--53

601

::°011

--35

--37

of the salts studied enabled us to assign absorption in the 1050-1220 cm -1 region to vibrations of the P--O(Zn) group in salts of monothio and oxy acids of phosphorus. Absorption bands of this group in spectra of phosphinates are arranged in the region of lower frequencies (1050-1078 cm -1) (Table 1, :No. 16) than in spectra of salts with phosphate groups (1110-1133 cm -1) (Table 1, :Nos. 14, 15, 17-19). The absorption band of P = O established mainly from spectra of organophosphoric acids and esters, according to results published, is in the 12001320 cm -1 region. For salts this band is shifted'by 70-80 cm -1 to the lowfrequency region [2, 3]. For zinc dialkylphosphates studied the absorption band of P = O is arranged in the 1185-1220 cm -1 region, for zinc dibutylphosphinate two bands are observed at 1116 and 1145 cm -1 (Table 1, No.

16). Tables 1 and 2 show results of assigning absorption bands for all the compounds studied. As noted previously, the position of bands varies more or less according to compound structure. Some of these relations have been noted previously in the literature. Thus, a study was made [10, ll] of the effect of the structure of hydrocarbon radicals in the P - - O - - R group and the type

60

YE. I.

~--tRKOVAet

al.

of metal on the position of absorption bands of P----S and P--S(Me). Results in Table 1 confirm that not only absorption bands of P----S and P--S(Me), but also other bands are shifted. It was interesting to try to establish the possible relation between bond stretching vibration frequencies of main bonds and some other values characterizing the compounds. Examples of similar relations are derived by the authors, when examining IR spectra of metal dialkyldithiocarbamates, between the frequency variation of C--S and C ~ S with a variation of the ionic radius of metals and frequencies of C--N and Me--S with a variation in the.electronegativity of metals [7]. On the other hand it was very interesting to connect the relations derived with the ability of zinc organothiophosphates to inhibit the radical-chain reaction of liquid-phase oxidation of hydrocarbons, i.e. with their anti-oxidizing ability. It has now been established that the mechanism of action of anti-oxidizing agents of the type of metal dialkyldithiophosphates involves (without considering secondary reactions) interaction with peroxide radicals and interaction with hydroperoxides. It has also been established that interaction with RO~ takes place at the thiol atom of sulphur ~ P - - S - - and during interaction with U ROOH rupture of the --S--Zn bond occurs [12]. Thus, the P - - S - - Z n group may be regarded as the reaction centre in zinc dialkyldithiophosphates when they function as anti-oxidizing agents and the salts studied may be attributed to a general type of ogranic compound of A\I~Z pentavalent p h o s p h o r u s B / X--Y'

in which the reaction takes place in

the lateral chain X - - Y [13]. It was shown [13, 14] that the Hammer equation is applicable to similar organophosphorus compounds and values of a F were derived for many substituents of A and ]3; this constant is a quantitative measure of the effect of substituents at the phosphorus atom on the reactivity of organophosphorus compounds. It is known that a F correlated with many physical properties of the molecule, for example half-wave values of polarographic reduction, ionization potentials, absorption frequencies of UV and IR spectra, etc. Nearest examples (as regards objects of investigation) of similar relations are the results obtained [15] when examining composite compounds of mercury dithiophosphates. In this study it was shown to be possible to correlate the total of constants of substituents (Z~) at the phosphorus atom with stability constants of composite mercury compounds with phosphorus dithionic acid and redox properties of these acids. For salts of organophosphorus acids no studies have been carried out to determine the dependence of spectroscopic results on the value of ~F. Figure 2 shows the dependence of the position of absorption bands VZn_S,

IR absorption spectra of zinc organophosphates

61

Vp-s¢zn;, Vp=s on the value of ~F for the compounds studied. In salt molecules alkoxyl RO and alkyl R groups are the nearest substituents at the phosphorus atom (A and B). Their effect on the position of absorption bands may be observed in the dithiophosphate--dithiophosphonate--dithiophosphinate series. For compounds with the same hydrocarbon radicals (Table 1, Nos. 2-4) a satisfactory linear relation is observed (Fig. 2, straight lines I-III). The number of compounds in the dialkyldithiophosphate--phosphonate--phosphinate series with the same R values is naturally confined to three compounds. Accordingly, lines I - I I I in Fig. 2 are drawn through three points. It should be noted that for all salts with isobutyl radicals in the P = S and P - - S region of bond stretching vibrations there are two bands of approximately identical intensity. Figure 2 shows results for both bands, IIa, b and IIIa, b, respectively. Linearity and a practically parallel arrangement of lines a and b suggests that these bands correspond to the same structural group. The position of bands of main bonds is not only influenced by the nearest surroundings of the phosphorus atom, but also in our ease the structure of the alkyl radical in alkoxy groups. Relations were plotted between Vzn-s, Vp-s, vp=s and the value of a F (Fig. 2, straight lines IV and V and points situated in the frame) for dialkyldithiophosphates shown in Table 2. I t was found t h a t there is a satisfactory linear relation between Vzn-s, Vp-sczn~ and a F. Values of Vp=s although change according to the structure of the radical (~F), no relation whatsoever has been established. In the Figure these points, which are arranged at random, are surrounded by a rectangular frame. I t is interesting to note that there are three bands in the spectrum of zinc di-isobutyldithiophosphate (Table 1, No. 2) in the region of P--S(Zn) vibrations, two of these at 556 and 590 cm -1 are situated on corresponding straight lines a and b (Fig. 2) and the third band of P--S(Zn), which is of the lowest frequency, at 536 cm -1 on straight line IV. This effect has not been explained so far. Results of Fig. 2 indicate that with an increase in the absolute value of a F absorption bands vf various structural groups behave differently. Bands of P----S and P--S(Zn) are displaced to the low frequency region (on changing substituents in the closest surroundings), as shown by straight fines II, I I I and of S--Zn (on changing substituents in the distant surroundings), as shown by line IV. A shift is observed to the high frequency region for bands of P--S(Zn) (on changing substituents in the distance), shown by line V and ~or S - - Z n (on changing substituents close by), shown by line I. Unfortunately, similar curves could not be plotted for phesphates containing one sulphur atom and free from sulphur because of the absence of salts of monothiophosphonic and phosphonic acids. We only compared the variation of positions of absorption bands of main bonds on changing from phosphates to phosphinates. Results for salts of all types of acid containing the same isobutyl radical are shown in Table 3.

{}2

YE. I. MAm~ovA~ al.

The following conclusions m a y be drawn from the information given in Table 3. On changing from phosphates to phosphinates all bands; except for bands of S--Zn, are shifted to the low frequency region. This proves t h a t the effect of the nearest surroundings at the phosphorus atom is the same both in salts of thioacids and in salts of oxy acids of phosphorus. The band of P - - S is displaced most and this applies to both dithio- and monothiophosphates. A comparison of salts of dithio-, monothio- and oxy acids of phosphorus shows that the effect of substituents somewhat varies. On changing from dithiophosphates to dithiophosphinates the shift of the P = S band is considerably greater than that of the P--S(Zn) band, 65 and 39 cm -1, respectively. In monothio salts the most considerable shift both for P = S bands and for P--O(Zn) b a n d s is observed at 67 and 53 cm -1. In oxy salts the effect of substituents is t h e weakest, the shift of P = O and P--O(Zn) bands is less marked than in other salts and is practically the same at 35 and 37 cm -1. The relation observed between the frequency variation and values of a F of substituents at the phosphorus atom and results in Table 3 suggest that for the salts examined the effect of substituents is transferred to all main bonds and therefore, to all characteristic bands. Therefore, in zinc salts studied of a general strueure

t

A\pfZ

the

B/ \X--Zn

e f f e c t of substituents at the phosphorus atom m a y be evaluated quantitatively by I R spectroscopy. The specific behaviour of the P = S band in dithiophosphates, i.e. the absence of linear relation between the position of the P-=S b a n d and a F of the substituent in distant surroundings is, apparently, due t o the fact that a d~--P~ conjugation exists between the sulphur and phosphor us atoms in the P = S group [16]. A s mentioned previously, the effect of metal dialkyldithiophosphates on liquid-phase oxidation of hydrocarbons is due to two reactions: interaction with peroxide radicals and hydroperoxides. The reaction with hydroperoxides is complex and takes place in several successive and parallel directions. The antioxidative activity of metal dialkyldithiophosphates also varies considerably according to the temperature at which the compounds are tested or used. It is therefore very difficult to obtain strictly quantitative results concerning the reactivity of salts studied as antioxidants. I t is well known, however, t h a t the induction period observed during oxidation of hydrocarbons in the presence of salts increases in the following order: dialkyldithiophosphates--dialkyldithiophosphonates--dialkyldithiophosphinates [15], i.e. in the order in which the absolute value of ar of closest substituents increases at t h e phosphorus atom. As shown by spectroscopic studies, bond-stretching vibration frequencies of main bonds vary successively in the same order. F u r t h e r investigations are required to derive more precise r elations between

TR absorption spectra of zinc organophosphates

63

t h e structure, optical characteistics of o r g a n o p h o s p h a t e s a n d their r e a c t i v i t y as antioxidants. SUMMARY

1. A spectroscopic s t u d y was m a d e of zinc o r g a n o p h o s p h a t e s . F o r this p u r p o s e a b s o r p t i o n b a n d s were assigned to v i b r a t i o n s of m a i n s t r u c t u r a l groups of S - - Z n , P - - S ( Z n ) , P----S, P - - O ( C ) , P - - O ( Z n ) a n d P----O atoms. 2. I t was f o u n d t h a t a m o n g the salts studied the effect of n e a r e s t (RO a n d R) a n d d i s t a n t (R in RO) s u b s t i t u e n t s t r u c t u r e a t t h e p h o s p h o r u s a t o m is t r a n s m i t t e d to all the m a i n bonds. T h e linear relationship b e t w e e n the position of b a n d s of S - - Z n , P - - S ( Z n ) a n d P----S b o n d s a n d % o f s u b s t i t u e n t s a t t h e p h o s p h o r u s a t o m p r o v e s t h a t it is possible to e v a l u a t e q u a n t i t a t i v e l y b y I R s p e c t r o s c o p y t h e effect of s u b s t i t u e n t s a t the p h o s p h o r u s a t o m on the r e a c t i v i t y of c o m p o u n d s . REFERENCES

1. G. N. KUZ'MINA, V. V. SH'ER and P. I. SANIN, Neftekhimiya 10, 465, 1971 2. Ye. M. POPOV, M. I. KABACHNIK and L. S. MAYANTS, Uspckhi khimii 30, 846, 1961 3. L. BELLAMI, Novyye dannye po I K spektram slozhnykh molekul (New Results Concerning I R Spectra of Complex Molecules). Mir, Moscow, 1971 4. M. R. HUNT, A. G. KRUGER, L. SMITH and G. W. WINTER, Austral. J. Chem. 24, 53, 1971 5. D. M. ADAMS and J. B. CORN]ELL, J. Chem. Soe. A, 6, 1299, 1968 6. D.M. ADAMS and J. B. CORNELL, J. Chem. Soe. A, 3, 884, 1967 7. Ye. I. MARKOVA, I. V. SHKHIYANTS, V. V. SHER and P. I. SANIN, Neftekhimiya 13, 294, 1973 8. J. ROCKETT, Appl. Spectroscopy 2, 39, 1962 9. Ye. I. MATROSOV, Kand. dis., In-t elementoorgan, soyed. AN SSSR (Candidate's Thesis. Institute of Hctero-organie Compounds, U.S.S.R. Academy of Sciences), Moscow, 1965 10. K. I. ZIMINA, G. G KOTOVA, P. I. SANIN, V. V. SHER and G. N. KUZ'MINA, ~eftekhimlya 5, 629, 1965 11. G. I. BOLOTOVA, G. G. KOTOVA, K. I. ZIMINA and V. I. ISAGULYANTS, Zh. prikl, khimii 38, 1580, 1965 12. V. V. SHER, Ye. I. MARKOVA, L. G. KHANAKOVA, G. N. KUZ'MINA and P. I. SANIN, Neftekhimiya 13, 876, 1973 13. M. I. KABACttNIK, Tr. I I konf. po khimii i primeneniyu fosfororganieheskikh soyedinenii (Proceedings of the 2nd Conference on the Chemistry and Use of Organophosphorus Compounds). Nauka, Moscow, 1962 14. T. A. MASTRYUKOVA and M. I. KABACI-INIK, Uspekhi khimii 38, 1751, 1969 15. V. F. TOPOROVA, P. A. CHERKASOV, M. I. SAVEL'YEVA and A. N. PUDOVIK, Zh. obshch, khimii 40, 1043, 1970 16. T. A. MASTRYUKOVA, Tr. IV konf. po khimii i primeneniyu fosfororganicheskikh soyedinenii (Proceedings of the 4th Conference on the Ohemistry and Use of Organophosphorus Compounds). l~auka, Moscow, 1972