UV S P E C T R A A N D E L E C T R O N I C P R O P E R T I E S

p a r a - S U B S T I T U T E D P H E N Y L D I A L K Y L A R S I N E S

A N D T H E I R O X I D E S

R . R . S h a g i d u l l i n , B. D. C h e r n o k a l ' s k i i , I . A . L a m a n o v a , A. S. G e l ' f o n d , a n d G. K h . K a m a i

OF

UDC 543.422.6 +547.242

There a re few sys temat ic data on the UV spect ra of organoarsenic compounds, and in par t icular , their a romat ic derivat ives , in the l i terature . According to the data of [1], in the case of triphenyl deriva- tives of elements of group VB, the unshared p-e lec t rons of the cent ra l atom interact s t rongly with the 7r- orbitals of benzene r ings. If, however, the centra l atom does not have such electrons, there is no resonance interaction. We studied the UV spect ra of a number of compounds:

o

X - - ~ - - A s R ~ and ~ J __ X--\~/AsR~

H = C~Hs, CsHT; X-----H, CH~, CI, Br, OCH3, N(CH~)~ and NO~

The data obtained are cited in Table 1. Figure 1 presents as an example the UV spec t rogram of p- tolyl- dipropylars ine oxide. The values of X, (nm) and log ~ in Table 1 are indicated for the maxima of the bands without a considerat ion of the fine s t ruc ture . The fi-bands a re intense, but they lie at the boundary of the working region of the instrument, and the positions of their maxima; just like the intensities, cannot be indicated exactly; Table 1 presents the limiting values that could be measured. The a -bands of the oxide are weak and have a fine s t ruc ture . The p-bands are most re l iably determined. Therefore the fur ther con- clusions will be based chiefly upon their considerat ion. As can be seen f rom Table 1, the p-bands appar- ently experience a tendency for a shift in the long-wave direction as we go f rom ars ines to oxides and f rom dioxane to aqueous acid solutions, but these differences are negligible. Xmax both of the a - and of the p- bands is success ive ly bathochromical ly shifted in the order cited in Table 1, with the exception of the p- band of the NO 2 derivative.

I00

89'

z~O

r ~

�9 ~ 20

#=~oz

1 d = 0.513

4a.

f0080 (c H~)71

~ CL -

* 0

ZO

, I I I I 1 I I 1 I i J . = - - . - - p f

ZOO 2ZO 2~0 280 2~0 n m . 20 4L0 GO 80 lO0 8~o, nmi

Fig. I Fig. 2 Fig. i. UV spectra of para-tolydipropylarsine oxide. C = 0.01 M; d) cuvette thickness.

Fig. 2. Graph of the dependence of AX on 5X0~: i) for ars ines; 2) for a r - sine oxides.

A. E. Arbuzov Institute of Organic and Physica l Chemist ry , Academy of Sciences of the USSR; S. M. Kirov Kazan' Chemical Engineering Institute. Trans la ted f rom Izvest iya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1490-1494, July, 1969. Original ar t ic le submitted June 3, 1968.

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TABLE 1

:ompound and solvent

X -- CGH4As (C~H~)2 in dioxane

X -- CsH4As (0) (C~Hs)~ in dioxane

X -- C6H4As (O) (C~Hs)~ in water

X -- CGH4As (0) (C2Hs)~ in 0,0i N HCI

M ono -substitu ted X - - CsH~ [21

* k in rim, sh - shoulder

X = H

245

;o 265

<200 214 260

<200 2t5 262

X = CHa

l g e k

- - ~200 4,3 I 223 3,2 244

-- <200 4,1 I 223 2,8 263

>3,8 <200 3 9 225 2,9 265

>4,0 1<200 4,0 227 3,0 265

3,87 206,: 2,3i 26i

lg a k lg r

-- <2c0 >I <200 4,| 225 I 227 3,6 250 252

>4A I<200 > <200 4,1 [ 225 [ 230 2,4 263 270

>/4,2 [<200 t~ <200 4,t [ 227 [ 232 2,7 265 I 265

]

>4,O 1<2oo I>/ <200 4,1 [ 230 I 235 2,6 265 / 27O

| 3,84 209,51 7} 210 2,33 263,51 S 1 26i

X = CI X = Br

Ig

>/4,3 I < 4,2 I 2,8

>t4,2 I < 4,2 2,8

>~4,1 I< 4,1 2,8

3,91 2,28

I X = OCH~ X = N (OHs)2 V = NO~ lAss i

i gnment X lg r X lg e h lg e

- - -- -- ~200 ~ , 4 ~ B-Band

:200 >~$,2 ~200 ~ 265 [I 4,0 ] p-Band 325 sh] 3,8 n-lr*, Band [3, 4]

~200 I>4, 3 I ~-Band 235 4,2 275 , p- Band

N340 sh 2,9 [ a-Band 275 3,2 3t0 260 I I I ~,21 :200 >~,2 1<200 I>I <200 1>4,o/ B-Ban~ 235 4,2 277 ]

~3~0 sh?! 2,6 : a-Band 270 3,0 ~320 sh ~[ 262 [ 4,0 ] p-Bana I !

:200 ~4,2 <200 [> <200 I>~4,0 B-Band 240/ 4 2 I 293 ] , 260 [ 3,9 I

cr Bana 2 01 300 shil: ~34o sh:] 2,6

2171 3,8 242151I : 268,5 t 3,S9/ 269[ 3,i7 290sI~] c~rBand : 235 sh?',[5l [ 3,18 / p-Band

In [2] it was shown o n t h e b a s i s of e x t e n s i v e m a t e r i a l that t h r e e a b s o r p t i o n bands a r e o b s e r v e d in the UV s p e c t r a of m o n o - and d i - s u b s t i t u t e d b e n z e n e d e r i v a t i v e s , a s s o c i a t e d wi th the p r e s e n c e of an a r o m a t i c r ing: a r e l a t i v e l y weak l o n g - w a v e band - a ( s e c o n d a r y a c c o r d i n g to t h e i r t e r m i n o l o g y ) , fo l lowing in w a v e - l eng th an i n t e n s e band - p { f i r s t p r i m a r y ) , and the s h o r t e s t wave i n t e n s e band - fl ( s econd p r i m a r y ) . F o r the p - b a n d , a r e l a t i o n s h i p to the a b i l i t y of the s u b s t i t u e n t s to dona te o r a c c e p t e l e c t r o n s in the i n t e r a c t i o n with the b e n z e n e r i n g was d e t e c t e d . Both o r t h o - o r i e n t e r s ( e l e c t r o n dono r s ) and m e t a - o r i e n t e r s (which a t - t r a c t e l e c t r o n s f r o m the r ing) can be a r r a n g e d in a s e r i e s a c c o r d i n g to the amount of the sh i f t of the m a x i - m u m of the f i r s t p r i m a r y band . In p a r a - d e r i v a t i v e s , fo r two i d e n t i c a l l y o r i e n t e d g r o u p s , Xmax of the f i r s t p r i m a r y band is on ly a l i t t l e sh i f t ed r e l a t i v e to the l o n g e s t wave of the c o r r e s p o n d i n g bands of the m o n o - d e r i v a t i v e s . F o r c o m p l i m e n t a r y s u b s t i t u e n t s (one dona t ing , the o t h e r a t t r a c t i n g ) , the m o s t s u b s t a n t i a l b a t h o c h r o m i c sh i f t of the band is o b s e r v e d . In th i s c a s e it is r e l a t e d to the v a l u e s of 5~.0i of the sh i f t of the c o r r e s p o n d i n g m o n o - d e r i v a t i v e s f r o m the va lue 180 n m b y the fo l lowing funct ion

6zo' 5~" (n) )~max-- 180 ~ - - nm.

24.05 '

According to this functionl at fixed 6X0', for complimentary substituents there is a direct proportionality between; A = A.ma x_ 180 and 610". Subsequently this principle was considered theoretically [6]. The func- tion (A) was derived for hydroxyl solvents. For arsines we do not have any data for water; therefore we shall use the results obtained for solutions in dioxane. On the basis of the small difference in the para- meters in the spectra for the two solvents among oxides, of which we spoke above, we may assume that for arsines as well this has no effect on the conclusions. If ~ve plot AA. along the Y-axis, and 6X 0" of the varying substituents [2] along the X-axis (Table 2), then we obtain graphs for arsines and arsine oxides (Fig. 2).

According to the data of [2], ortho-orienters are arranged in the following series with respect to the value of AX: CH 3 < Cl < Br < OH < OCH 3 < NH 3 < O-; meta-orienters are arranged in the following series:

NH3+< SO2NH 2 < CO 2- --CN< CO2H < COCI-I 3 < CHO < NO 2.

All our substituents X, with the exception of NO 2, belong to the first series, and all the points ob- tained, with the exception of NO 2, fit rather well on straight lines 1 and 2 (we should mention that the dif- ference between them is small). From this it follows that the AsR 2 and As(O)R 2 groups fall in the series of meta-orienters, i.e., acceptors of electrons with respect to the benzene ring. Since the electronegativity of the As atom is less than that of the C atom (2.10 and 2.60 according to Pauling, respectively), for com- pounds of trivalent arsenic the only mechanism explaining the effect noted can be pTr- d~r conjugation. It is natural to assume that the same is also the case for oxides.

From all the aforementioned it may be concluded that the contribution of structures of the type 0

1382

T A B L E 2

I X tI I CH, CI Br 0CHa N (CHa)~ NO.

I

+ far?~ 127 I

AX o sines 43 45 50 55 95 80

* In [2] no value of 6),0 for the dimethylamino grouP is cited, We took a value for N(CH~)s: 5No = 242 [g] - 180 = 62 nm.

T A B L E 3

Para- substituent

CHa C1 Br O CHa N(CHsh

Incre- ment 6

t0 10 t5 26 85

! XP +5 [ A=Xexp-Xcalc

CsHsAsRz . of arsines I

217 +}-,6 2t7 +8 222 +5 232 ? 292 ?

(in water) I0 xides I

224 I +1 224 +3 229 -}-3 239 --4 299 --22

a r i s i n g as a r e s u l t of P~r- d~ con juga t ion is m o s t s u b s t a n t i a l in the e x c i t e d s t a t e (the p - b a n d is a s s i g n e d to a A t g - Btu t r a n s i t i o n ) .

It is a l so i n t e r e s t i n g to no te tha t the sh i f t s of the p - b a n d c a u s e d by s u b s t i t u e n t s in the s e r i e s of a t - s i n e s and t h e i r ox ides a r e ana logous to the sh i f t s in the c o r r e s p o n d i n g d e r i v a t i v e s of a r o m a t i c k e t o n e s . Thus , the i n c r e m e n t s of s u b s t i t u t i n g g r o u p s w e r e found in [7] fo r a p p r o x i m a t e d e t e r m i n a t i o n s of the p - band of a r o m a t i c k e t o n e s . M o r e o v e r , fo r m o s t of the compounds t hey gave a g r e e m e n t wi th the e x p e r i m e n - t a l da t a wi th in 5 nm. The u s e of t h e s e i n c r e m e n t s fo r the i n v e s t i g a t e d s e r i e s a l so shows r a t h e r good a g r e e - men t , wi th t h e excep t ion of the d i m e t h y l a m i n o g r o u p (Tab l e 3).

S ince the k e t o - g r o u p is a p r o n o u n c e d m e t a - o r i e n t e r , the da ta c i t e d m a y be c o n s i d e r e d as an add i t i ona l c o n f i r m a t i o n ~hat the i n t e r a c t i o n of the AsR 2 and As(O)R 2 g r o u p s wi th an a r o m a t i c s u b s t i t u e n t m a y be of the s a m e n a t u r e .

5X 0 of the AsR 2 and As(O)R 2 g r o u p s , found by c a l c u l a t i o n a c c o r d i n g to f o r m u l a (A), f r o m the da ta of T a b l e 1, fo l lowed by a v e r a g i n g , a r e equa l to 34.3 and 35.8 r im, r e s p e c t i v e l y . In [8] ana logous p r o p e r t i e s of p h o s p h o r u s - c o n t a i n i n g g r o u p s w e r e no ted .

E X P E R I M E N T A L

The s y n t h e s i s of the compounds was r e p o r t e d in [9]. The s p e c t r a w e r e o b t a i n e d on an S F - 4 s p e c t r o - p h o t o m e t e r . S p e c t r o s c o p i c a l l y p u r e d ioxane , w a t e r , and a 0.01 N s o l u t i o n of h y d r o c h l o r i c a c id w e r e u s e d as the s o l v e n t s . The c o n c e n t r a t i o n s w e r e v a r i e d ~10 -2 M. A s a m p l e s p e c t r u m , c i t ed in F ig . 1, was r e - c o r d e d on an S F - 8 t w o - b e a m r e c o r d / n g i n s t r u m e n t .

The a u t h o r s would l i ke to thank G. M. D o r o z h k i n a fo r h e r p a r t i c i p a t i o n in the e x p e r i m e n t .

CONCLUSIONS

1. The UV s p e c t r a of a n u m b e r of p a r a - s u b s t i t u t e d p h e n y l d i a l k y l a r s i n e s and t h e i r ox ides w e r e s tud ied .

2. T h e d i e t h y l a r s i n y l and d i e t h y l a r s i n e g r o u p s b e h a v e as m e t a - o r i e n t e r s , in a c c o r d with the concep t of p a r t i c i p a t i o n of the d - o r b i t a l s of the As a t o m in con juga t ion .

1.

2. 3. 4. 5.

LITERATURE CITED

C. N. Rao , J . R a m a c h a n d r a n , and A. B a l a s u b r a m a n i a n , Canad . J . C h e m . , 3_).9, 171 (1961). L. Doub and J . M. Vandenbe l t , J . A m e r . Chem. Soc . , 6...99, 2714 (1947). W. R. C a l l e n and B. R. G r e e n , J . Ino rgan . Nucl . C h e m . , 27, 641 (1965). B. I. S t epanov , A. I. Bokanov, and B. A. K o r o l e v , T e o r e t . i ]~kspe r im . K h i m i y a , 4 , 354 (1968). O r g a n i c E l e c t r o n i c S p e c t r a l Da ta , O. H. W h e e l e r and L. A. Kap lan ( e d i t o r s ) , Vol. 111, 1956-1957, I n t e r s c i e n c e P u b l i s h e r s , New Y o r k - L o n d o n - S y d n e y (1966), pp. 58, 163.

1383

6,

7.

8.

9.

Ph. E. Stevenson, J . Molec. Spect rosc . , 1._~5, 220 (1965). A. I. Scott, Interpretat ion of the Ultraviolet Spectra of Natural Products , Pergamon P r e s s , Oxford (1964), p. 109. E. N. Tsvetkov, M. M. Makamatkhanov, and M. I. Kabachnik, Teore t . i ~ksper im. Khimiya, 3 , 824 (1967). B. D. Chernokal'skii, A. S. Gel'fond, and G. Kh. Kamai, Zh. Obshch. Khim., 37, 1396 (1967).

1384