982 R E C E I L (1958) 77

547.26118 : 542.938 : 615.7771.779

CHEMICAL. STUDIES ON INSECTICIDES VII 1)

Dipole moments of some esters of phosphoric and phosphorothioic acid

BY J. A. A. KETELAAR, H. R. GEJRSMANN * ) and F. HARTOG * * )

Laboratory for General and Inorganic Chemistry of the University of Amsterdam

In order to compare the partial bond moments of "energy rich" and other phosphorus acid esters dipole moments of a number of esters have been determined from dielectric constant measurements.

Literature values of dipole moments of phosphorus acid derivatives are also presented.

Introduction. To increase our knowledge of the nature of phosphorus acid esters,

especially with regard to the property called the "energy rich" phos- phate bond, the differences of a number of partial *bond moments of these esters were calculated from the dipole moments of ester molecules.

Tihe results were compared with partial bond moments of carboxylic esters and ethers. The dipole moments of the phosphorus acid esters were determined from dielectric constant measurements of solutions of the esters in benzene and dioxan.

Although the calculation of partial bond moments of relatively large molecules based on a static geometry of the molecule is a fairly crude approximation from a physical viewpoint, it is estimated that some of the errors of such calculations cancel out when differences of bond moments are considered.

A refinement of partial bond moment calculation of phosphoric esters has 'been given by Arbusow * ) , but as the molecules considered here are more complicated than those considered by this author we did not follow this procedure.

* ) Present address: KoninklijkejShell Laboratorium. Badhuisweg, Amsterdam-N. *) Present address: Centraal Laboratorium der Staatsmljnen. Geleen.

I) Chemical studies on Insecticides VI. J. A. A. Ketelaar and H. R. Gersmann; Rec. Trav. Chirn. in press: H. 4. Gersmann, Thesis Amsterdam (1956).

:) B. A. Arbusow, et el.. Isvest. Akad. Nauk. S.S.S.R. Otdel Khim Nauk. 1950, 237; 1952. 795; 1954, 812

Chemical studies on insecticides VZZ. 77 (1958) RECUEIL 983 ~~

Calculation of partial bond moments.

In order to be able to calculate partial bond moments, a number of assumptions have to be made: 1 ) It is assumed that a molecule (RO)3P0 has the symmetry C3v

and that this symmetry, a s well as the bond angles, are the same for different esters. The value which is obtained for the (O=P-0) angle from the calculation should not be identified with a chemical bond angle but with an angle between two partial bond moments (fig. 1 ).

0 Figure 1

Vectorial diagram of partial moments in a molecule XaPO with X an ester group OR or SR. The directions of the dipole moment vectors am not identical with the P-0 directions because of the bond angle at rhe 0-atom and of the possible rotations within the ester group.

2) A constant P=O moment. From the infrared spectra which will be presented in the IXth paper of this series * ) it can be seen that the phosphoryl stretching frequency shows a variation from 1275 cm--1 to 1305 cm--' for the compounds studied here. Although it is impossible to give exact values for the double bond character in these cases a s the P+-O- and P=O distances are not known, it may be expected that the partial P=O bond moment will not vary by more than 0.1-0.2 D for the compounds studied here.

For the actual calculation we study the series of compounds ( RiO) ,PO dipole ,moment ( A ) , (R,O) a( R,O) PO (B) , (R,O) (R,O),PO (C) and (R,O),PO I( D) .

* ) Chemical studies on Insecticides IX to be published.

984 J. A. A. Ketelaar, H. R. Gersmann and F. Hartog.

Other designations are:

The ,following equations are then obtained: P P -+ 0 = 1'0 PPORI = Pi PPOR? = /+ L PPO PPOR = B

1 ) + 3 pi COS = A

3) [PO + ( 2 p1 + pup) cos 8 1 2 + [ p 1 - p 2 1 2 sin2 8 = c2 4 ) [PO + (PI + 2 p 2 ) cos 8 1 2 + [ p z - PI12 sin2 8 = D2

2 ) p~ + 3 p2 cos 8 = B

These equations are dependent but the values (pi -A) and 8 can be derived.

5 ) cos / ?= & ( A - B ) / 1 / 9 C 2 - 3 3 2 - 6 6 B (from 1 . 2 and 3) 6 ) c o s b = & (A-B) /1 /9D2-332-6BA (from 1 , 2 and 4 ) 7) Ip l -p21 = I /D2-1 /3B2-2 /3AB=Idp\ ( f rom 1 , 2 and 6)

8) '(from 1, 2 and 5) It is obvious that the most reliable values for /? and LIP can be expected for molecules with large differences in dipole moment. The calculation of the dipole moment was carried out with the aid of the Debye formula. Although slightly better values for the dipole moments can be obtained with other somewhat more complicated formulae (see e.g. Scholte 3) ) the more simple equation of Debye was preferred for two reasons. 1 ) For comparisons to be made in this investigation, differences of

dipole moments are more important than the ,absolute values them- selves.

2) Most of the other investigators in this field also used the Debye equation and better comparisons will thus be possible.

= r/ C2 - xx2 - 2 / 3 AB

E x p e r i m e n t a l Dielectric constants were measured in a Cohen-Henriquez 4, type apparatus. Cali-

bration of the measuring condenser was carried out with dry nitrogen, benzene and chlorobenzene. Benzene (Analar B.D.H.) was distilled in a 20 plate column to con- stant dielectric constant and kept over sodium.

Chlorobenzene. distilled in the same way, was dried over anhydrous sodium sulphate.

Petroleum ether (b.p. 40"-60" C) was distilled and kept over sodium. Dioxan was purified according to the directions of V a n de Stolpe6) (€26 = 2.210,

na25 = 1.4198).

8 ) Th. G. Scholte, Diss. Leiden ( 1950). 4 ) P. Cohen Henriquet, Diss. Delft (1935); P. P. van Velden, Diss. Amsterdam

6 ) C. van de Stolpe, Diss. Amsterdam (1953). (1950): A. 1. Dekker, Diss. Amsterdam (19451.

Chemical studies on insecticides VII. 77 (1958) ,RECUEIL 985

Special care was taken to avoid moisture and errors due to induction or other electrical disturbances.

To determine the molecular polarisation of the various phosphate esters the di- electric constant of solutions of different concentrations of these esters was measured and the polarisation calculated by extrapolation to infinite dilution.

Benzene was used preferably as a solvent, but in some cases dioxan had to be employed because of poor solubility of the compounds in benzene.

By comparison of experimental results and also from a calculation based on the formula of Ross") it is probable that dipole moments derived from measurements in the above solvents will show no significant differences.

Indices of refraction of the solutions were measured with a pulhich rcfractometer using a sodium lamp. Densities were determined by pycnometer. All measurements were carried out a t 25".

Most of the compounds measured have already been described in the literature, but two esters were specially synthesized to obtain a more reliable value of 8:

00-Diphenyl 0-p-nitrophenyl-phosphorothioate (1):

0.5 mole of PSCk was added slowly with stirring to a solution of 0.5 mole of phenol in a small excess (10%) of sodium hydroxide. T h e temperature was kept between 10" and 20". After the addition, the emulsion which was obtained, separated into two layers. T h e organic layer was washed with distilled water, dried and distilled in vacuum (8b.p. 88"-89"/15 mm). The product was 0-phenyl phosphor* dichloridothioate (CdH,CI,PSO) (11).

A small residue of 0,Odiphenyl phosphorochloridothioate (C,,H,,CIPSO,) (111) was also obtained (a).

The dichloride I1 was then heated with an excess of phenol in alkaline medium at 90". At the end of the reaction ,part of the product solidified (b). Distillation of the organic layer obtained after filtration afforded some unreacted I1 and a solid residue (c). The crude monochloride. (a) + (b) + (c) , was recrystallised and thereby the pure compound I11 was obtained in 50% yield.

Compound 111 was then reacted with sodium nitrophenoxide as described pre- viously "). Compound I. thus obtained, had a m.p. after crystallisation from ethanol of 47".

Found Cal. for CisHi4NO5PS (387.36) : ,, 55.81: ,, 3.64; ,, 3.62: ,, 8.28: ,, 8.00

: C 55.7 ; H 3.6 : N 3.7 : S 8.0 : P 7.8

0-Phenyl 0.0-di-(p-nitrophenyl) phosphorothioate (IV) 0.1 mole of the dichloride (11) was reacted with 0.22 mole of sodium nitrophenate

in dioxan as described 7 , previously. After evaporation of the solvent, the product IV crystallised and was obtained pure after two crystallisations from ethanol, m.p. 85".

Found : C 50.1 : H 3.1 : N 6.5 ; S 7.2 : P 7.1 Calc. for C I S H I ~ N ~ O T P S (432.36) : ,, 50.00: ,, 3.03: ,, 6.48: ,, 7.42; ,, 7.16

Results and discussion.

Table I gives the measured dipole moments while the values of the

6 , 1. G. Ross, Proc. Phys. SOC. 63. 893 (1950). i, 1. A. A. Ketelaar and H. R. Gersrnann, J. Am. Chem. SOC. 72, 5777 (1950).

T a b l e I Dipole moments of some phosphoric and phosphorothioic esters

Name

.. -.

000-tr iphenyl phosphorothioatt 00-diphenyl 0-p-nitrophenyl phosphorothioate

0-phenyl OOdi( p-nitrophenyl) phosphorothioate

000-tri- (p-nitrophenyl) phosphorothioate

triethyl phosphate diethyl hydrogen phosphate diethyl phenyl phosphate triphenyl phosphate diethyl p-nitrophenyl phosphate (Paraoxon)

00-diethyl 0-p-nitrophenyl phosphorothioate (Parathion)

ethyldi- (p-nitrophenyl) phosphate

O-ethyl 0 0 - d i (p-nitrophenyl) phosphorothioate

Property

m.p. 47"

m.p. 85"

m.p. 174"

b.p. 110"-111" (24 mm) 98 yo ' * * )

n420,5 = 1.4761 *"*) m.p. 48-50"

> 97 yo ' * * * * )

> 99 yo * '***)

m.p. 134"

m.p. 125"

(R R i 0 R z 0

* ) Value obtained from the literature. * * ) Unreliable value owing to poor solubility. * * * ) Determined by titration. ' * * * ) Sample rcceived from Dr. D. K. Myers.

) Determined by the method of Ketelaor et a/. . Anal. G e m . 24, 646 (1951) .....

X

S

S

S

S

0 0 0 0

0

s

0

S

-

-

Solvent

benzene

dioxan

dioxan

dioxan

benzene benzene benzene benzene

benzene

benzene

benzene

dioxan

dipole- moment

in Debye-

units

2.58

4.52

4.78

3.33

3.00 2.32 3.34 2.79

5.30

4.98

6.0 *')

4.97

Chemical studies on insecticides VII. 77 (1958) RECUEIL 987

T a b l e I1

Values of fi obtained from the series:

(CaHaO) 3PS. ( C~HGO) 2 (p-NOzCoH40) PS. (pN02CoH40) 3PS 86" (CoH60) 3PS, (CaHaO) (p-NO2C6H40) 2PS. (p-NOnCoH40) 3PS I 86"

T a b l e I11

Differences of partial bond moments

RiOX - RnOX

C~HGOP - CoHaOP CoHaOH - CZHGOH CaHaOC2Ha - C O H ~ O C ~ H G

CoHaOC-CHx A0 - C~HBOC P \CH3

p-NO2CoH40P - CoHjOP p-NOnCoH40H - CoHriOH

lAul

1.60 0.18

' 0.15

0.3 1

3.60 3.51

~

p-NOnCoH4OCHs - CoHaOCH3 3.55

p-N0zCeH~0H - CZHGOH 3.33 p-NOnCoH40P - C2HaOP 1 4.27

p-N02CoH40CH~ - CnHsOCHs i 3.60

O=P-OR angle p! obtained for different series of esters are compiled in table 11. T h e value of LIP for the partial phosphate bonds as well as for the corresponding ethers and ester are given in table 111. A feature of these results is the value of nearly 90° for angle /?.

Comparison of the dipole moment of the different "tri" esters (RO),P(O) . . . ( S ) proves that this vector angle is indeed a physical reality (fig. I ).

Our calculation resulted in two values of p, either 8 8 O or 9 2 O . T h e following argument makes it plausible that cos should be

positive: The partial P-0 and P-0-aryl moments are directed from the

electropositive phosphorus atom towards the negative oxygen and aryl groups respectively: the dipole moment of tri (p-nitrophenyl ) phosphate is larger than that of triphenyl phosphate.

This is only possible i f cos p is positive, Table 111 illustrates the charge effects of partial bond moments. The

988 J . A. A. Keteleer. H. R. Gersmenn and P. Hertog,

T a b l e IV

Dipole moments of phosphorus ac.id derivatives compiled from the literature *) 8 )

C3H7 iso-€aH~

GHo CaH6

C2Ha (RO) zHPO R = CH3

CaH7 is0-CaH.r

. . . - n

R=CH3 - ZZHGP (0) (H) (OR)

LHaP (S) (OC3H7)Z (n) i H s P (0) (CCls) OR

R = CHR

ZZHSP(S) (OGH6)z

....................... X l s P (0) (OGHa) z (R0)3PO R =

CIUHZI

- C3H7

CH3 C2Hs

. . . . . . . . . . . . . . . . . . . . .

1 .oo 2.40 1.41

I .66- 1.70 1 .83 1.96 1.99 1.98 1.92 1.59 2.94 3.08 3.15 3.08 3.17 3.88

2.93 0.65 1.39 4.31 4.74 4.83 2.95

2.83 -2.52

3.17-3.42 3.22 2.95

3.15-3.29 3.25 3.02 3.07 3.09 2.85 3.05 2.89 2.91

(2.94) 2.99 3.04 3.18 3.08 2.79

(2.79) 2.58

R. J. W. le Feure. “Dipolemornents” (Methuen 1948): C. P. Smyth, et el., J. Am. Chem. SOC. 62, 1219 (1940): L. Maletaste, Gazz. Chim. ital. 76, 182 (1946); A. E. Arbusow. et el., Doklady, acad. Nauk. S.S.S.R. 81, 507 (1952): G. Speroni. Chimica e industria 33, 543.

Chemical studies on insecticides VIZ. 77 (1958) RECUEIL 989

larger difference between aliphatic and aromatic phosphate esters as compared with corresponding carboxylic esters indicates a larger dis- placement of charge from the phosphorus atom towards the aromatic group ( "energy rich" bond).

Tihis charge effect is obviously larger than the electron localising effect of the electropositive phosphorus atom on the aromatic system, which tends to decrease the partial moment.

Table IV gives values of dipole moments of phosphorus acid derivatives from the literature.

(Received November 1st 1958).