- Email: [email protected]
Analytical applications of thio. seleno and telluroethers
t l n a l 3 t i t a C h m m a ~It ta. 75 (1975)401-407 q-., Elsevier Scmntffic P u b h s l a m g C o m p a n y . A m ~ t e r d d m - P r m t c d m T h e N c t h e r l , m d s
ANA LYTICAL A PPLICATIONS
O F TI-! IO. S E L E N O A N D T E L L U R O E T H
PART V TITRIMETRIC DETERMINATION SODIUM ETHVLENE-BIS-(THIOGLYCOLATE)
LUIZ R M
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D v p a r t a m e n t o tie QuDmt a I'un,lamental. Islstttuto de QuDmc a, U m t ersulade tie S h e Paulo. S?to Prude ( B r , t z t l ) ( R e c e i v e d 8th A p r d 1974)
M a n y p a p e r s on tJtrlmetr~c m e t h o d s for v a r i o u s n o b l e m e t a l s h a v e b e e n p u b h s h e d ; m o s t o f these are b a s e d o n e l e c t r o m e m c t e c h n i q u e s , a n d the m r a n t s are u s u a l l y e l e c t r o g e n e r a t e d ~. Beam~sh ~ has p o i n t e d o u t t h a t the d e v e l o p m e n t of the m o r e classical t l t n m e t r i c t e c h m q u e s r e m a i n s ~ m p o r t a n t , p a r t i c u l a r l y for the a n a l y s t w h o m u s t w o r k wsth a m i n i m u m o f e q m p m e n t O n the basra o f results o b t a i n e d m a p r e v i o u s p a p e r z, a n e w m e t h o d for t h e d e t e r m i n a t i o n o f p a l l a d m m has been d e v e l o p e d b a s e d on visual ,'rod s p e c t r o p h o t o metric t l t r a t i o n s w R h d l s o d m r n e t h y l e n e - b t s ( t h l o g l y c o l a t e ) ( N a O O C . C H : . S . C z H , ~ . S C H 2 . C O O N a ) . T h e selectivity ideas o u t h n e d m p r e v i o u s p a p e r s : - s w e r e followed, a n d a g a i n c o n f i r m e d
Prehmmar y .stuthes T h e m m a l step was a s e a r c h for an m d z c a t o r t h a t w o u l d c o m p l e x pall,'tdlum m a s t r o n g acid m e d m m , to f o r m a s t a b l e c o l o u r e d c o m p o u n d T h e first a t t e m p t was m a d e with x y l e n o l o r a n g e , b e c a u s e a r e a s o n a b l e selectivity t o w a r d s p a l l a d m m m perchlorlc, s u l p h u r l c o r n i t r i c a c i d s m e d i u m has been c k u m e d a P a l l a d m m s o l u t i o n s c o n t a m m g c o n c e n t r a t e d perchl0rzc acid were w a r m e d ( __+60°C) u n t d a red colour appeared. However. no sharp end-points were observed, even when an a u x i h a r y i n d i c a t o r w a s used, ,'rod n o s a t i s f a c t o r y r e p r o d u c l b f l t t y c o u l d be a c h i e v e d . N l t r o s o - R salt has also b e e n r e p o r t e d 9'' as a r e a s o n a b l y selective r e a g e n t for c o l o r l m e t r l c p a l l a d i u m d e t e r m i n a t i o n . Recently, this r e a g e n t w a s u s e d in a c i d i c o r a l k a l i n e m e d m m t°, for p a l l a d m m d e t e r m i n a t i o n s . In the p r e s e n t w o r k , a s h a r p c h a n g e f r o m red to g r e e m s h y e l l o w was o b t a i n e d w h e n d r o p s o f N a 2 E B T G s o l t m o n were a d d e d to an a c i d i c s o l u t i o n o f the p a l l a d m m - m t r o s o - R salt c o m p l e x : g o o d r e p r o d u c l b l h t y was also o b t a i n e d , w i t h i n the h m l t a t l o n s o f these semiq u a n t ~ t a t t v e e x p e r i m e n t s . F u r t h e r tests s h o w e d t h a t dwect t l r a t l o n o f t e t r a c h l o r o p a l l a d a t e with N a ~ E B T G was p o s s i b l e w h e n m t r o s o - R salt served as t h e I n d i c a t o r EXPERIMENTAL
Apparatus A B e c k m a n s p e c t r o p h o t o m e t e r m o d e l B a n d a specially d e s i g n e d 7.0-cm cell ° were u s e d for s p e c t r o p h o t o m e t r i c titrat~ons
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Reaqent Stat;tlttrd palladnon solutum G r a y , m e t r i c ~ t a n d a r d J z a t m n w~th d t m e t h y l g l y o x m l e w a s used for tile p a l l a d m m c h l o r s d e s o l u u o n (0 I M m h y d r o c h l o r i c acsd). which c o n t a i n e d 1 142 m g Pd m l Soltlttons ot chver.se tons S t o c k s o l u t z o n s c o n t a i n i n g 40 m g P t ( I V ) m l - ' a n d p l a t i n u m g r o u p met.'tl s o l u t m n s (25.0 m g M e m l - ~ ) w e r e p r e p a r e d f r o m their c h l o r i d e s m 0.1 M h y d r o c h l o r i c acid T h e o t h e r c a U o n s w e r e used as s o l u t i o n s o f lhe~r m t r a t e s c o n t a i n i n g ca. 25 mg m i - ~ m 0.1 M n~tnc ,~c~d F o r s o l u t i o n s o f arllons, s o d i u m salts were p r e p a r e d in t h e s a m e c o n c e n t r a t i o n s Standard N a : E B T G solutum S o d lure ethylene-bzs( t h ] o g l y c o l a re) ( N a : E B T G ) was o b t a i n e d as p r e v i o u s l y r e p o r t e d 2. D r y i n g at 130"C for 24 h p r o d u c e d no c h a n g e m rn:lss, a n d the K a r l F m h e r m e t h o d s h o w e d t h a t n o w a t e r o f c r y s t a l l t z a t ] o n wa~ p r e s e n t . After e x p o s u r e for 14 h to 70".f, r e h t ] v e ht, m l d l t y , the s a m p l e dtd n o t increase m m a s s T h e p u r i t y w a s d e t e r m i n e d by p a s s i n g the s o d m m salt throt, gh a c a t m n - e x c h a n g e resin ( M e r c k I) a n d t i t r a t m g the free acid with st.'mdard s o d m m h y d r o x i d e s o h m o n . A p u r i t y a b o v e 9 9 . 7 " . was f o u n d O n the basts o f these results N a z E B T G was c o n s i d e r e d to be a p r i m a r y s t a n d a r d A s u i t a b l e a m o u n t was w e i g h e d a n d t h e m o l a n t y w a s c h e c k e d b y the m e t h o d used for t e s t i n g the p u r i t y Nttro~o-R Salt A n a q u e o u s 0.02 M s o l u t m n w a s p r e p a r e d lsolatton o f i,alladzmn complex'. S o d m m e t h y l e n e - b t s ( t h m g l y c o l a t c ) ( 5 59 g. 22 m m o l e ) w.'m d t s s o l v e d m 240 ml o f w a t e r : to thin s o l u t m n were a d d e d 15 ml o f 70°;, p e r c h l o n c acsd a n d . w t t h c o n t m u o u ~ stirring. 250 ml o f h y d r o c h l o r t c acid s o l u t i o n c o n t a i n i n g 1.77 g. o f P d C I z (10 m m o l e ) After 24 h. the yellow crystals f o r m e d were filtered o f f ( y ~ e l d 6 30 g. 90.°,,: m . p 177-183 C ( d e c o m p ) . A n a l y t i c a l results, c a l c u l a t e d for ( H O O C . C H z . S . C z H 4 . S . C H . , C O O H ) , P d (CIO,~)CI.21-1:O ( m w . = 6 9 7 9 0 ) , 2065';~, C. 3 5'~.,, H. 18.4"-, S. 5 15'L', H z O . f o u n d 20 4'~;, C. 3 3'~,, H. 18.1'~,,, S. 4 85'>,, t-lzO ( K a r l F m c h e r m e t h o d ) T h e a b s o r p t i o n s p e c t r a o f the c o m p o u n d m o l a t e d a n d o f t h a t o b t a i n e d m a p r e v i o u s m v e s t t g a t m n z w e r e sdenucal, s h o w i n g a m a x i m u m at 290 nm. T a b l e I p r e s e n t s s o m e selected i r a n d R.'~m,m b a n d s T A BLI'- I SELECTED
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R e ¢ ' o m m e l l d e d pl ocedlll'~., /or" t'l',lltll llll'tllloll T o I0.00 ml o f s a m p l e ~olutlon ( w h i c h Maould bc 0.1 M in h y d r o c h l o r i c a c i d ) c o n t a i n i n g 5 70-31.0 m g of P d ( l l ) . a d d 3.0 ml o f 70",, p e r c h l o r l c acid Ariel a d d i n g 10 d r o p s o f 0.02 M n , t r o s o - R salt. stw a n d wa~t for I m m until a clear red c o l o u r a p p e a r s T i t r a t e ,,lowly with 5 . 1 0 - z M N a , E B T G s o l u t m n until thc red colot, r c h a n g e s to y e l l o w - g r e e m s h In the pre,,ence o f t u n g s t d t e , e n o u g h solid cRrtc acid ~hould be a d d e d to clea~ a n y p r e c i p i t a t e If ~r~d~tlm(IV) is present, e n o u g h sol~d ascorb~c acid s h o u l d be a d d e d R e c o n i l l l e l l d e d pl'occ?thll e Jot" ~pec l r o p l l o l o l l l e t p t i ttlrrlltoll~ Tr.'mSfel 25.00 ml o r t h e s a m p l e s o l u t i o n c o n t a l n , n g 2.50-10.05 nag o f p a l l a d m m ( i l ) ( w h l c h s h o u l d b e 0 ! M m h y d r o c h l o r ~ c a c ~ d ) to a t t t r d t i o n vessel A f t e r a d d m g 14.0 ml o f 70';~, p e r c h l o n c acid a n d 10 ml of w a t e r (final v o l u m e 60 nal). stw a n d a d j u s t the w a v e l e n g t h 7 to 510 nm. W i t h the sensitivity ;rod slit k n o b s , a d j u s t thc t r a n s m R t a n c e value to 63",,,. W R h the a d d i t i o n o f 10 d r o p s o f 0 02 M n~troso-R salt soluUon, the t r a n s m i t t a n c e v a l u e d r o p s , a n d after a few m i n u t e s r e m a i n s c o n s t a n t T H r a t e w~th 0 01 M N a z E B T G s o l u t i o n a d d i n g 0.25-mi p o r t i o n s T h e t r a n s m i t t a n c e values m c r e a s c a n d . a f t e r .'~ c e r t a i n v o l u m e has been a d d e d , b e c o m e c o n s t a n t D u r i n g the t~trat~on thc scn,,itlVlty s h o u l d bc s u i t a b l y c h a n g e d If i r i d i u m (IV) i~ present. a d d 4.0 ml o f an a q u e o u s I';h s o l u t i o n o f dscorb~c acid a n d 17.0 ml o f w a t e r Establish the e n d - p o i n t by p l o t t i n g t r a n s m i t t a n c e ret,,u., v o l u m e RESULTS [/'i'~,IlCII ttlPottotl~ F~//ec ! o / ¢lCldll) F o r t he s t u d y o r t he effect,, o f itcldlty ,tnd o f t h e n l t r o s o - R salt c o n c e n t r a t i o n , a n a r b i t r a r y c o n c e n t r a t , o n o f pallad~t,m. I 0 0 nag m l - ' . was selected A t t e m p t s to a d a p t the a c i d i t y used by S h a m w a n d S c h w a r t z V - - p H ca 2 with acetic or h y d r o c h l o ~ l c a c t d - - f a ~ l e d , b e c a u s e o f i n d m t l n c t e n d - p o i n t s W i t h increase o f a c x d l t y ( p e r c h l o r J c acid), the e o l o u r c h a n g e b e c a m e s h a r p , the best final a c i d c o n c e n t r a t i o n w a s f o u n d to be 2.5 M R e p l a c e m e n t o f p c r c h l o l l e acid by s u l p h u r l c or nitric acid at the s a m e c o n c e n t r a t i o n di d not give a clear c o l o u r c h a n g e , as s o m e t u r b i d i t y a p p e a r e d w h e n N a : E B T G wits a d d e d . E / / e c t e l nttroso-R sah c'o~:cet:trutton T I t r a t l o n s were r u n wRh i - I 5 d r o p s of a q u e o u s 0.02 /9/ n l t r o s o - R salt s o l u t i o n s T h e best results, with regard to c l e a r a n d ~cproduc,ble e n d - p o i n t s , were obt.'uned with 10 d r o p s , w h e n the m r a n t a d d i t i o n rate was I d r o p per 3 s. With m o r e t h a n 10 d r o p s o f i n d , c a t o r , s h a r p a n d r e p r o d v c l b l e e n d - p o i n t s were o b t a i n e d , p r o v i d e d t h a t the t R r a n t addR~on r a t e was decreased E / / e c t o~ chhn'ul,, ctmce~tratu,n Spcc,al a t t c n t , o n w a s given to th,s effect b e c a u s e p a l l a d i u m is n o r m a l l y prcscnt a s [PdCI.~]: - ,n a q u e o u s s o l u t , o n s . P a l l a d , t , m c h l o r , d e s o l u t i o n s COllta,nlng ra. 5 0 ing o f palladlt, m per I 0 0 0 ml a n d v a r , a b l c c h l o r t d c concentr.'ltlons at 2.5 M a c , d , t y were t,tratcd. C h l o r i d e c o n c c n t r a t t o n ~ h i g h e r t h a n 8.0 i 0 - : M g:,vc low results Optooal Imuje o/ palladltnpa S a m p l c s c o n t a i n i n g 5 0 - 3 1 nag o f p a l l a d i u m m a c o n s t a n t v o l u m e , a t fixed ac~dRy a n d with convrolled c h l o r i d e c o n c e n t r a t i o n s were an.'dyscd by the r e c o m m e n d e d p r o c e d u r e T h e results .are s h o w n m f a b l e !I. the 3 |Ill I a v e r a g e r e c o v e r y w a s 100 I'.',~, a n d the s t a n d a r d d e v m t l o n was /'~ ,.,..,/,,
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s u l p h i d e , s u l p h t t e , t h l o s u l p h a t e a n d n i t r l t e can easi l y be e l i m i n a t e d wRh a q u a rcgta, w h i c h is u s e d In t h e c o m m o n e s t p r o c e d u r e s for d i s s o l u t i o n o f a l l o y s a n d m i n e r a l s . In th~s s t u d y , h m l t a t l o n s w e r e c a u s e d by t hc c o l o u r i n t e n s i t i e s o f s o m e i ons F o r R h ( l l l ) . R u ( I V ) , O s ( I V ) a n d C r ( l l l ) . t l t r a t l o n s w e r e i m p o s s i b l e , b u t t he i n t e r f e r e n c e o f I t ( I V ) w a s a v o t d c d by r e d u c t i o n w i t h a s c o r b l c actd In time case o f N I ( I I ) . C u ( I I ) , C o ( l l ) a n d F e ( l l l ) . t he d e t e r m m a U o n w a s feasible w h e n time P d ' M e r a t i o w a s i : 2 5 It wqs p o s s i b l e to d e t e r m i n e p a l l a d m m ( l l ) m time p r e s e n c e o f p l a t m u m ( l V ) o n l y w h e n t he r a t i o w as b c l o w 1:1 T a b l e !II gives t h e rcsult~ for the d e t e r m i n a t i o n o f p a l l a d m m in t h e p r e s e n c e o f d~verse ~ons. ~p~ctro[)/lOlt)tltt.,ll'tt
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T ~ b l e IV p r e s e n t s t h e results o b t a i n e d b y t h e r c c o m m c n d e d p r o c e d u r e . T h e a v e r a g e r e c o v e r y o b t . ' u n e d o v e r time r a n g e 2 4 - 1 0 m g o f p a l l : t d t u m w a s 100~/. a n d t h e s t a n d a r d d e v t a u o n w a s 0 18"/,,. T q b l e III gives t h e r e s u l t s for t he s p e c t r o p h o t o m e t r l c U t r a t l o n o f p a l l a d m m m the presence of diverse tons DISCUSSION
A l t h o u g h m a n y t~tr~metrlc m e t h o d s for time d e t e r m l n a u o n o f p a l l a d m m h a v e b e e n r e p o r t e d . B e a m l s h 'J~ h a s p o i n t e d o u t time s c a r c i t y o f a c c e p t a b l e m e t h o d s . M a n y a r e b a s e d o n t u r b l d l m e t m c a n d h e t e r o m e t r l c t l t r a t l o n s 13 ~4 p r e c l s t o n d a t a b e i n g i g n o r e d , in t he s e m e t h o d s , r i g o r o u s c o n t r o l o f e x p e r i m e n t a l d e t a d s is e s s e n u a l , a n d t h e restllts a r e e x t r e m e l y d e p e n d e n t o n t h e skill o f time o p e r a t o r , T w o m e t h o d s b a s e d o n E D T A b a c k - t l t r a t l o n s a r c satisf.'lctory w i t h r e g a r d to p r e c l s t o n d.'lta ~5 tt~. b u t b o t h a r e g r e a t l y limited b y i n t e r f e r e n c e s , T i t r a t l o n s wsth i o d i d e a r e a v a d a b l e ~7-2°, as a r e d i r e c t t l t r a t l o n s w i t h d i e t h y i d R h l o c a r b a m a t e 2t o r n h r o s o - R salt i o s o l u t t o n s , b u t t hes e p r o c e d u r e s a r e v e r y t e d i o u s ,
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Time p r o p o s e d vzsual a n d s p e c t r o p h o t o m e t r J c t J t r a t J o n s ttre q u i t e ettsfly d o n e . a n d t h e w t o l e r a n c e for " a s s o c m t e d i o n s " ( m a i n l y P t ( I V ) ) v, g o o d T h e r e p r o d u c i b d t t y is c o m p a r a b l e to t hat o f E D T A m e t h o d s a n d t h e c o n c e n t r a t i o n r a n g e o f ca. 40- [ 6 0 ltg P d ( l l ) m l - t is fawJy s u i t a b l e 'm Classwcal r e a s o n i n g for time c h o i c e o f i n d i c a t o r was n-npo,,slble b e c a u s e time c o n s t a n t s f o r t h e p a l l a d s t t m ( l i ) c o m p l e x e s w i t h the i n d i c a t o r a n d E B T G Iig.'md a r e t, n k n o w n H o w e v e r . t h e c h o i c e w~ts n o t c o m p l e t e l y e m p i r i c a l . T h e s t r u c t u r a l f o r m u l a for t h e [ n l t r o s o - R salt - P d ( i i ) ] c o m p l e x h a s n o t b e e n e l u c i d a t e d , but t h e m o l a r r d t m is known. Palladlt, m ( l l ) s h o u l d be bot, nd b y t he O , - - - ~ - O H a n d ~ C = O groups ( " h a r d " g r o u p s ) N a 2 E B T G I n a s t r o n g l y a c i d i c m e d i u m w,II h a v e time c . ' l r b o x y l l c •'tcld g r o u p s b l o c k e d , a n d shot, ld t h e r e f o r e act as a b t d e n t d t e IIgand formHmg a s t r o n g 5 - m e m b e r e d n n g with the t w o st, lpht, r a t o m s ( " s o f t " g r o u p s ) In ~everal tests, m w h , c h t h e P d ( n t t r o s o - R s a l t ) , w a s t a k e n as a p a r a m e t e r . Jt w a s verified th at u n d e r t h e s a m e a c i d c o n d i t i o n s , c t h y l t h l o g l y c o l l c acid a n d t h t o d l g l y c o h c ;icld ( o n e s u l p h u r a t o m ) did n o t d e c o l o r l z e t h e red c o m p l e x , w h e r e ; i s f l - e t h y l t h ~ o e t h y l e n e thloglycolsc acid and e t h y l e n e - b l s ( t h l o g l y c o i l c ) a c i d did The hypothesis, that c o m p lex es c o n t a i n i n g a r i ng w i t h t w o s u l p h u r a t o m s s h o u l d be s t r o n g e r t h a n time o t h e r s , w a s tht, s p a r t m l l y p r o v e d D e t e r m m a t z o n , , o f time f o r m a l c o n s t a n t s for p a l l a d m m ( l l ) a n d t h e f o u r m e n t l o n e ¢ ! h g a n d sy~tem~ a r c ,n p r o g r e s s T h e : t b s o r p t t o n s p e c t r u m o f t h e , s o l a t e d c o m p l e x d e m o n s t r a t e d t h a t t he m o l a r r a t i o L M e is 2 . 1 . F r o m t h e i r a n d R a m a n s p e c t r a ( T a b l e !). o n e ma,~ c o n c l u d e t h a t t he o b s e r v e d f o u r f u n d a m e n t a l p e r c h l o r : t t e b a n d s , wsth t e t r a h e d r a l s y m m e t r y , a g r c e Wlt]l e a r l i e r r e s u l t s 22 o n t h e i oni c n a t u r e o f t h a t ~on. M o r e o v e r . time fact t h a t all f r c q u e n c l e s a r e dct~ve m R a m a n s p e c t r o s c o p y a n d o n l y the ~3 a n d ~,, f r e q u e n c i e s m ~ r s p e c t r o s c o p y c o n f i r m s t h e i n t e r p r e t a t i o n . T h c C--S. s y m m e t r i c a n d a s y m m e t r i c C O O s t r e t c h i n g f r e q u e n c i e s m N a , E B T G .and ~n t h e a c i d d g r e e w ; t h e a r l i e r r e s u l t s a3 T h e p a l l a d ~ t ~ m - s u l p h t , r c o o r d i n a t i o n m t h e ~solated c o m p l e x w a s e v i d e n c e d b y t h e fact t h a t t h e C - S s t r e t c h , r i g f r e q u e n c y ~s sh~ftcd t o l o w e r w ~ v e n u m b e r s , c o m p a r e d w i t h t he free a c , d a n d sis s o d i u m salt zz. A n o t h e r fact t h a t s e e m s t o c o n f i r m thss asst, m p t , o n is t h e m t e n s e b a n d at 325 c m - t m t he R a m a n s p e c t r u m . in ( P d C I z . 2 R . S C z H . , S R) c o m p l e x e s z'= :-~. t h e P d - S s t r e t c h i n g f r e q u e n c y wits a l s o o b s e r v e d m time r a n g e 3 1 0 - 3 4 0 c m - ~ . A c o m p a r i s o n o f t he ~. a n d ~, C O 0 f r e q u e n c i e s o b t a i n e d f or t he ~solated c o m p l e x . N a : E B T G a n d t he f r e e a c i d i n d i c a t e s th at th e c a r b o x y h c grot, p s a ~ e i n t a c t m time p a l l a d i u m c o m p l e x A n o t h e r p o i n t ~n f a v o u r o f thin. is t h e i n t e n s e ~nd w~dc a b s o r p t i o n m the r a n g e 2 3 0 0 - 3 6 0 0 e r a with v a r i o u s m a x i m a T h i s ss c h a r a c t e r i s t i c for t h e C O O H g r o u p r e v o l v e d ,n h y d r o g e n b o n d a s s o c m t ~ o n z~' Time s u p p o r t r e c e i v e d fiorn time C o n s e l h o N , l c l o n a l d e P c s q u m a ( R i o d e J a n e l r o ) a n d time F u n d a ~ f i o de A m p a r o ~t pe~qul,,a (Silo P i t u l o ) is g r a t e f u l l y itck n o w l e d g e d . SUMMARY
P a l l a d l u n a s o l u t i o n s ctln be t l t r a t e d v i s u a l l y a n d s p e c t r o p h o t o m e t r z c a l l y w i t h s o d i u m e t h y l e n e - b l s ( t h l o g l y c o l a t e ) T i t r a t J o n s w e r e d o n e in 2 5 M p e r c h l o r t c aci d with n l t r o s o - R sltlt as i n d i c a t o r . P a l l ; l d l u m w a s d e t e r m i n e d ~n t h e r a n g e 5 0 - 3 0 m S
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(v~sual t ~ t l a t ~ o n ) a n d 2 0 - 1 0 m g ( s p c c t r o p h o t o m e t r ~ c tztrat~on), tho tolcr.'tncc Ior d~vcrsc ~ons ,s g o o d . part~ct,l~rly w|th the spcctrophotomctr~c end-point T h e probable structure o f the isolated c o m p l c x ~ g w c n . REFERENCFS I 2 3 4 5 6 7 8 9 IO II 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
F E Bemnt~h l a h l n l t l 13 (1966)IO~;3 L R M PttombodndG Ohxc~r,i Nelo, Imll ( I r o n Itl,I 7 ~ ( 1 9 7 5 ) 391 L R M P I I o m b o ,-Inal C h l m Ic Ill 46 (1969) I qR L R M PJtombo. ,,l#ltll Chilli ~It Ill, 62 (1972) I0"~ L R M P l l o m b o d n d E Q Cdrl,lV, O lah#nttl 21 ( 1 9 7 4 ) 9 6 5 P B S w e c t s e r dnd G E Brlt, ker IHtll ( h t , m 25 (1953) 253 J S h a m l r dnt.t A Sh'.l, drtF. FtlhlHtt#. 8 ( 1961 ) 330 M 0101110 Hldl Cht'lH StJt Jtlp ~6(196"~) 889 F E B c m n . s h T h v 4 n a l l l l t a l C h v m # s l l i r~l t h e Ntd~h. A l e t a l s P c r g , , m o n . Oxt't~rd 1966 (d) p 441, (b) pp 68. Io9 130. ( c ) p p 324 334 ( d ) p 341 O W R o l l i n s dnd M M O I d h d m ,Dial C h t , m 43 ( 1971 ) ,"~6 ,"~ F E Bedmlgh Tt#hlllla. 14 (1971) 991 R F" G o d d u dnd D N H u m e ,I;Itll C h c m 2 6 ( 1 9 5 4 ) 1740 M B o b t c N k y dnd B M d y c r . /llltll (. h i m ,'It t¢l, 15 (1956) 164 M B o b t c N k y ,llld J Er,,cn,,tdtltcr ,|Hill (.hilt! A I I t l 16 (1957) 479 W N M,It.No~,m d n d II O K r l c g e /llltll C ' h v n l . 27 (It)55) 535 T A Klhh F F G d o l ,rod T M S u r , m y c ( , l a s Itt, m D I n s livo~llad. 34 (1969) 42 ~, C h v m Ihst 74 ( 1971 ) 9323 R Kcr,,tlng ,,Iml ( ' h e m P h a l m g7 ( 1 9 5 3 ) 2 5 R H A t k m , , o n . ,IHcdl ~t ( L o n t h m ) . "79 (1954) "~6N R H A t k m , . o n R N R h o d d ,|nd R G L o m c l l A n a l t s t ( L C n l d t m ) 8 0 ( 1 9 5 5 ) 8 3 g R H A t k m , , o n dnd R N R h o d d . r'hltll Ch¢,pll 28 (1956) 535 'vV B P o l l d r d . , I m l l l s t ( L t m d t m ) 6 7 ( 1 9 4 2 ) IN4 B J II,lth,lwdy dnd A E Undcrh~ll d C h t . m StJt L¢IHdt,I. ( 1961 ) ~1091 J P o d l d h a ,rod J P o d l , d l o ~ d . lll¢lrgl C'IHIH *ltltl 5 ( 1971 ) 41 "~ G E C o d t e ' , dnd C P d r k m J Cht.nl StJt L m l d r m ( 1 9 6 3 ) 4 2 1 J Plu~,Cu~, ,Ind A D We~tl,lnd, J C h v m S o t L o m h m . ( 1 9 6 5 ) 5371 L J Belldmy /hh'gl#;t¢,s m i ~ l ; t H t , d Grol~p I'tvtlHt, nt I. M e l h u c n . L o n d o n , 196g. p 270
ANA LYTICAL A PPLICATIONS
O F TI-! IO. S E L E N O A N D T E L L U R O E T H
PART V TITRIMETRIC DETERMINATION SODIUM ETHVLENE-BIS-(THIOGLYCOLATE)
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D v p a r t a m e n t o tie QuDmt a I'un,lamental. Islstttuto de QuDmc a, U m t ersulade tie S h e Paulo. S?to Prude ( B r , t z t l ) ( R e c e i v e d 8th A p r d 1974)
M a n y p a p e r s on tJtrlmetr~c m e t h o d s for v a r i o u s n o b l e m e t a l s h a v e b e e n p u b h s h e d ; m o s t o f these are b a s e d o n e l e c t r o m e m c t e c h n i q u e s , a n d the m r a n t s are u s u a l l y e l e c t r o g e n e r a t e d ~. Beam~sh ~ has p o i n t e d o u t t h a t the d e v e l o p m e n t of the m o r e classical t l t n m e t r i c t e c h m q u e s r e m a i n s ~ m p o r t a n t , p a r t i c u l a r l y for the a n a l y s t w h o m u s t w o r k wsth a m i n i m u m o f e q m p m e n t O n the basra o f results o b t a i n e d m a p r e v i o u s p a p e r z, a n e w m e t h o d for t h e d e t e r m i n a t i o n o f p a l l a d m m has been d e v e l o p e d b a s e d on visual ,'rod s p e c t r o p h o t o metric t l t r a t i o n s w R h d l s o d m r n e t h y l e n e - b t s ( t h l o g l y c o l a t e ) ( N a O O C . C H : . S . C z H , ~ . S C H 2 . C O O N a ) . T h e selectivity ideas o u t h n e d m p r e v i o u s p a p e r s : - s w e r e followed, a n d a g a i n c o n f i r m e d
Prehmmar y .stuthes T h e m m a l step was a s e a r c h for an m d z c a t o r t h a t w o u l d c o m p l e x pall,'tdlum m a s t r o n g acid m e d m m , to f o r m a s t a b l e c o l o u r e d c o m p o u n d T h e first a t t e m p t was m a d e with x y l e n o l o r a n g e , b e c a u s e a r e a s o n a b l e selectivity t o w a r d s p a l l a d m m m perchlorlc, s u l p h u r l c o r n i t r i c a c i d s m e d i u m has been c k u m e d a P a l l a d m m s o l u t i o n s c o n t a m m g c o n c e n t r a t e d perchl0rzc acid were w a r m e d ( __+60°C) u n t d a red colour appeared. However. no sharp end-points were observed, even when an a u x i h a r y i n d i c a t o r w a s used, ,'rod n o s a t i s f a c t o r y r e p r o d u c l b f l t t y c o u l d be a c h i e v e d . N l t r o s o - R salt has also b e e n r e p o r t e d 9'' as a r e a s o n a b l y selective r e a g e n t for c o l o r l m e t r l c p a l l a d i u m d e t e r m i n a t i o n . Recently, this r e a g e n t w a s u s e d in a c i d i c o r a l k a l i n e m e d m m t°, for p a l l a d m m d e t e r m i n a t i o n s . In the p r e s e n t w o r k , a s h a r p c h a n g e f r o m red to g r e e m s h y e l l o w was o b t a i n e d w h e n d r o p s o f N a 2 E B T G s o l t m o n were a d d e d to an a c i d i c s o l u t i o n o f the p a l l a d m m - m t r o s o - R salt c o m p l e x : g o o d r e p r o d u c l b l h t y was also o b t a i n e d , w i t h i n the h m l t a t l o n s o f these semiq u a n t ~ t a t t v e e x p e r i m e n t s . F u r t h e r tests s h o w e d t h a t dwect t l r a t l o n o f t e t r a c h l o r o p a l l a d a t e with N a ~ E B T G was p o s s i b l e w h e n m t r o s o - R salt served as t h e I n d i c a t o r EXPERIMENTAL
Apparatus A B e c k m a n s p e c t r o p h o t o m e t e r m o d e l B a n d a specially d e s i g n e d 7.0-cm cell ° were u s e d for s p e c t r o p h o t o m e t r i c titrat~ons
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A c a h b r a t e d 10.00-ml s e m ] m ~ c r o - b u r e t t e was used for vasual .'rod spectrop h o t o r n e t r [ c t~trat~ons I n f r a r e d s p e c t r a were t a k e n m K B r d ~ k s o r N u j o l mulls on a P e r k m E l m e r s p e c t r o p h o t o m e t e r m o d e l 333. R a m a n spectra w e r e o b t a i n e d f r o m the s o h d s u b s t a n c e (pastille). w i t h a J a r r e i I - A s h s p e c t r o p h o t o m e t e r m o d e l 25.
Reaqent Stat;tlttrd palladnon solutum G r a y , m e t r i c ~ t a n d a r d J z a t m n w~th d t m e t h y l g l y o x m l e w a s used for tile p a l l a d m m c h l o r s d e s o l u u o n (0 I M m h y d r o c h l o r i c acsd). which c o n t a i n e d 1 142 m g Pd m l Soltlttons ot chver.se tons S t o c k s o l u t z o n s c o n t a i n i n g 40 m g P t ( I V ) m l - ' a n d p l a t i n u m g r o u p met.'tl s o l u t m n s (25.0 m g M e m l - ~ ) w e r e p r e p a r e d f r o m their c h l o r i d e s m 0.1 M h y d r o c h l o r i c acid T h e o t h e r c a U o n s w e r e used as s o l u t i o n s o f lhe~r m t r a t e s c o n t a i n i n g ca. 25 mg m i - ~ m 0.1 M n~tnc ,~c~d F o r s o l u t i o n s o f arllons, s o d i u m salts were p r e p a r e d in t h e s a m e c o n c e n t r a t i o n s Standard N a : E B T G solutum S o d lure ethylene-bzs( t h ] o g l y c o l a re) ( N a : E B T G ) was o b t a i n e d as p r e v i o u s l y r e p o r t e d 2. D r y i n g at 130"C for 24 h p r o d u c e d no c h a n g e m rn:lss, a n d the K a r l F m h e r m e t h o d s h o w e d t h a t n o w a t e r o f c r y s t a l l t z a t ] o n wa~ p r e s e n t . After e x p o s u r e for 14 h to 70".f, r e h t ] v e ht, m l d l t y , the s a m p l e dtd n o t increase m m a s s T h e p u r i t y w a s d e t e r m i n e d by p a s s i n g the s o d m m salt throt, gh a c a t m n - e x c h a n g e resin ( M e r c k I) a n d t i t r a t m g the free acid with st.'mdard s o d m m h y d r o x i d e s o h m o n . A p u r i t y a b o v e 9 9 . 7 " . was f o u n d O n the basts o f these results N a z E B T G was c o n s i d e r e d to be a p r i m a r y s t a n d a r d A s u i t a b l e a m o u n t was w e i g h e d a n d t h e m o l a n t y w a s c h e c k e d b y the m e t h o d used for t e s t i n g the p u r i t y Nttro~o-R Salt A n a q u e o u s 0.02 M s o l u t m n w a s p r e p a r e d lsolatton o f i,alladzmn complex'. S o d m m e t h y l e n e - b t s ( t h m g l y c o l a t c ) ( 5 59 g. 22 m m o l e ) w.'m d t s s o l v e d m 240 ml o f w a t e r : to thin s o l u t m n were a d d e d 15 ml o f 70°;, p e r c h l o n c acsd a n d . w t t h c o n t m u o u ~ stirring. 250 ml o f h y d r o c h l o r t c acid s o l u t i o n c o n t a i n i n g 1.77 g. o f P d C I z (10 m m o l e ) After 24 h. the yellow crystals f o r m e d were filtered o f f ( y ~ e l d 6 30 g. 90.°,,: m . p 177-183 C ( d e c o m p ) . A n a l y t i c a l results, c a l c u l a t e d for ( H O O C . C H z . S . C z H 4 . S . C H . , C O O H ) , P d (CIO,~)CI.21-1:O ( m w . = 6 9 7 9 0 ) , 2065';~, C. 3 5'~.,, H. 18.4"-, S. 5 15'L', H z O . f o u n d 20 4'~;, C. 3 3'~,, H. 18.1'~,,, S. 4 85'>,, t-lzO ( K a r l F m c h e r m e t h o d ) T h e a b s o r p t i o n s p e c t r a o f the c o m p o u n d m o l a t e d a n d o f t h a t o b t a i n e d m a p r e v i o u s m v e s t t g a t m n z w e r e sdenucal, s h o w i n g a m a x i m u m at 290 nm. T a b l e I p r e s e n t s s o m e selected i r a n d R.'~m,m b a n d s T A BLI'- I SELECTED
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R e ¢ ' o m m e l l d e d pl ocedlll'~., /or" t'l',lltll llll'tllloll T o I0.00 ml o f s a m p l e ~olutlon ( w h i c h Maould bc 0.1 M in h y d r o c h l o r i c a c i d ) c o n t a i n i n g 5 70-31.0 m g of P d ( l l ) . a d d 3.0 ml o f 70",, p e r c h l o r l c acid Ariel a d d i n g 10 d r o p s o f 0.02 M n , t r o s o - R salt. stw a n d wa~t for I m m until a clear red c o l o u r a p p e a r s T i t r a t e ,,lowly with 5 . 1 0 - z M N a , E B T G s o l u t m n until thc red colot, r c h a n g e s to y e l l o w - g r e e m s h In the pre,,ence o f t u n g s t d t e , e n o u g h solid cRrtc acid ~hould be a d d e d to clea~ a n y p r e c i p i t a t e If ~r~d~tlm(IV) is present, e n o u g h sol~d ascorb~c acid s h o u l d be a d d e d R e c o n i l l l e l l d e d pl'occ?thll e Jot" ~pec l r o p l l o l o l l l e t p t i ttlrrlltoll~ Tr.'mSfel 25.00 ml o r t h e s a m p l e s o l u t i o n c o n t a l n , n g 2.50-10.05 nag o f p a l l a d m m ( i l ) ( w h l c h s h o u l d b e 0 ! M m h y d r o c h l o r ~ c a c ~ d ) to a t t t r d t i o n vessel A f t e r a d d m g 14.0 ml o f 70';~, p e r c h l o n c acid a n d 10 ml of w a t e r (final v o l u m e 60 nal). stw a n d a d j u s t the w a v e l e n g t h 7 to 510 nm. W i t h the sensitivity ;rod slit k n o b s , a d j u s t thc t r a n s m R t a n c e value to 63",,,. W R h the a d d i t i o n o f 10 d r o p s o f 0 02 M n~troso-R salt soluUon, the t r a n s m i t t a n c e v a l u e d r o p s , a n d after a few m i n u t e s r e m a i n s c o n s t a n t T H r a t e w~th 0 01 M N a z E B T G s o l u t i o n a d d i n g 0.25-mi p o r t i o n s T h e t r a n s m i t t a n c e values m c r e a s c a n d . a f t e r .'~ c e r t a i n v o l u m e has been a d d e d , b e c o m e c o n s t a n t D u r i n g the t~trat~on thc scn,,itlVlty s h o u l d bc s u i t a b l y c h a n g e d If i r i d i u m (IV) i~ present. a d d 4.0 ml o f an a q u e o u s I';h s o l u t i o n o f dscorb~c acid a n d 17.0 ml o f w a t e r Establish the e n d - p o i n t by p l o t t i n g t r a n s m i t t a n c e ret,,u., v o l u m e RESULTS [/'i'~,IlCII ttlPottotl~ F~//ec ! o / ¢lCldll) F o r t he s t u d y o r t he effect,, o f itcldlty ,tnd o f t h e n l t r o s o - R salt c o n c e n t r a t i o n , a n a r b i t r a r y c o n c e n t r a t , o n o f pallad~t,m. I 0 0 nag m l - ' . was selected A t t e m p t s to a d a p t the a c i d i t y used by S h a m w a n d S c h w a r t z V - - p H ca 2 with acetic or h y d r o c h l o ~ l c a c t d - - f a ~ l e d , b e c a u s e o f i n d m t l n c t e n d - p o i n t s W i t h increase o f a c x d l t y ( p e r c h l o r J c acid), the e o l o u r c h a n g e b e c a m e s h a r p , the best final a c i d c o n c e n t r a t i o n w a s f o u n d to be 2.5 M R e p l a c e m e n t o f p c r c h l o l l e acid by s u l p h u r l c or nitric acid at the s a m e c o n c e n t r a t i o n di d not give a clear c o l o u r c h a n g e , as s o m e t u r b i d i t y a p p e a r e d w h e n N a : E B T G wits a d d e d . E / / e c t e l nttroso-R sah c'o~:cet:trutton T I t r a t l o n s were r u n wRh i - I 5 d r o p s of a q u e o u s 0.02 /9/ n l t r o s o - R salt s o l u t i o n s T h e best results, with regard to c l e a r a n d ~cproduc,ble e n d - p o i n t s , were obt.'uned with 10 d r o p s , w h e n the m r a n t a d d i t i o n rate was I d r o p per 3 s. With m o r e t h a n 10 d r o p s o f i n d , c a t o r , s h a r p a n d r e p r o d v c l b l e e n d - p o i n t s were o b t a i n e d , p r o v i d e d t h a t the t R r a n t addR~on r a t e was decreased E / / e c t o~ chhn'ul,, ctmce~tratu,n Spcc,al a t t c n t , o n w a s given to th,s effect b e c a u s e p a l l a d i u m is n o r m a l l y prcscnt a s [PdCI.~]: - ,n a q u e o u s s o l u t , o n s . P a l l a d , t , m c h l o r , d e s o l u t i o n s COllta,nlng ra. 5 0 ing o f palladlt, m per I 0 0 0 ml a n d v a r , a b l c c h l o r t d c concentr.'ltlons at 2.5 M a c , d , t y were t,tratcd. C h l o r i d e c o n c c n t r a t t o n ~ h i g h e r t h a n 8.0 i 0 - : M g:,vc low results Optooal Imuje o/ palladltnpa S a m p l c s c o n t a i n i n g 5 0 - 3 1 nag o f p a l l a d i u m m a c o n s t a n t v o l u m e , a t fixed ac~dRy a n d with convrolled c h l o r i d e c o n c e n t r a t i o n s were an.'dyscd by the r e c o m m e n d e d p r o c e d u r e T h e results .are s h o w n m f a b l e !I. the 3 |Ill I a v e r a g e r e c o v e r y w a s 100 I'.',~, a n d the s t a n d a r d d e v m t l o n was /'~ ,.,..,/,,
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s u l p h i d e , s u l p h t t e , t h l o s u l p h a t e a n d n i t r l t e can easi l y be e l i m i n a t e d wRh a q u a rcgta, w h i c h is u s e d In t h e c o m m o n e s t p r o c e d u r e s for d i s s o l u t i o n o f a l l o y s a n d m i n e r a l s . In th~s s t u d y , h m l t a t l o n s w e r e c a u s e d by t hc c o l o u r i n t e n s i t i e s o f s o m e i ons F o r R h ( l l l ) . R u ( I V ) , O s ( I V ) a n d C r ( l l l ) . t l t r a t l o n s w e r e i m p o s s i b l e , b u t t he i n t e r f e r e n c e o f I t ( I V ) w a s a v o t d c d by r e d u c t i o n w i t h a s c o r b l c actd In time case o f N I ( I I ) . C u ( I I ) , C o ( l l ) a n d F e ( l l l ) . t he d e t e r m m a U o n w a s feasible w h e n time P d ' M e r a t i o w a s i : 2 5 It wqs p o s s i b l e to d e t e r m i n e p a l l a d m m ( l l ) m time p r e s e n c e o f p l a t m u m ( l V ) o n l y w h e n t he r a t i o w as b c l o w 1:1 T a b l e !II gives t h e rcsult~ for the d e t e r m i n a t i o n o f p a l l a d m m in t h e p r e s e n c e o f d~verse ~ons. ~p~ctro[)/lOlt)tltt.,ll'tt
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T ~ b l e IV p r e s e n t s t h e results o b t a i n e d b y t h e r c c o m m c n d e d p r o c e d u r e . T h e a v e r a g e r e c o v e r y o b t . ' u n e d o v e r time r a n g e 2 4 - 1 0 m g o f p a l l : t d t u m w a s 100~/. a n d t h e s t a n d a r d d e v t a u o n w a s 0 18"/,,. T q b l e III gives t h e r e s u l t s for t he s p e c t r o p h o t o m e t r l c U t r a t l o n o f p a l l a d m m m the presence of diverse tons DISCUSSION
A l t h o u g h m a n y t~tr~metrlc m e t h o d s for time d e t e r m l n a u o n o f p a l l a d m m h a v e b e e n r e p o r t e d . B e a m l s h 'J~ h a s p o i n t e d o u t time s c a r c i t y o f a c c e p t a b l e m e t h o d s . M a n y a r e b a s e d o n t u r b l d l m e t m c a n d h e t e r o m e t r l c t l t r a t l o n s 13 ~4 p r e c l s t o n d a t a b e i n g i g n o r e d , in t he s e m e t h o d s , r i g o r o u s c o n t r o l o f e x p e r i m e n t a l d e t a d s is e s s e n u a l , a n d t h e restllts a r e e x t r e m e l y d e p e n d e n t o n t h e skill o f time o p e r a t o r , T w o m e t h o d s b a s e d o n E D T A b a c k - t l t r a t l o n s a r c satisf.'lctory w i t h r e g a r d to p r e c l s t o n d.'lta ~5 tt~. b u t b o t h a r e g r e a t l y limited b y i n t e r f e r e n c e s , T i t r a t l o n s wsth i o d i d e a r e a v a d a b l e ~7-2°, as a r e d i r e c t t l t r a t l o n s w i t h d i e t h y i d R h l o c a r b a m a t e 2t o r n h r o s o - R salt i o s o l u t t o n s , b u t t hes e p r o c e d u r e s a r e v e r y t e d i o u s ,
406
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Time p r o p o s e d vzsual a n d s p e c t r o p h o t o m e t r J c t J t r a t J o n s ttre q u i t e ettsfly d o n e . a n d t h e w t o l e r a n c e for " a s s o c m t e d i o n s " ( m a i n l y P t ( I V ) ) v, g o o d T h e r e p r o d u c i b d t t y is c o m p a r a b l e to t hat o f E D T A m e t h o d s a n d t h e c o n c e n t r a t i o n r a n g e o f ca. 40- [ 6 0 ltg P d ( l l ) m l - t is fawJy s u i t a b l e 'm Classwcal r e a s o n i n g for time c h o i c e o f i n d i c a t o r was n-npo,,slble b e c a u s e time c o n s t a n t s f o r t h e p a l l a d s t t m ( l i ) c o m p l e x e s w i t h the i n d i c a t o r a n d E B T G Iig.'md a r e t, n k n o w n H o w e v e r . t h e c h o i c e w~ts n o t c o m p l e t e l y e m p i r i c a l . T h e s t r u c t u r a l f o r m u l a for t h e [ n l t r o s o - R salt - P d ( i i ) ] c o m p l e x h a s n o t b e e n e l u c i d a t e d , but t h e m o l a r r d t m is known. Palladlt, m ( l l ) s h o u l d be bot, nd b y t he O , - - - ~ - O H a n d ~ C = O groups ( " h a r d " g r o u p s ) N a 2 E B T G I n a s t r o n g l y a c i d i c m e d i u m w,II h a v e time c . ' l r b o x y l l c •'tcld g r o u p s b l o c k e d , a n d shot, ld t h e r e f o r e act as a b t d e n t d t e IIgand formHmg a s t r o n g 5 - m e m b e r e d n n g with the t w o st, lpht, r a t o m s ( " s o f t " g r o u p s ) In ~everal tests, m w h , c h t h e P d ( n t t r o s o - R s a l t ) , w a s t a k e n as a p a r a m e t e r . Jt w a s verified th at u n d e r t h e s a m e a c i d c o n d i t i o n s , c t h y l t h l o g l y c o l l c acid a n d t h t o d l g l y c o h c ;icld ( o n e s u l p h u r a t o m ) did n o t d e c o l o r l z e t h e red c o m p l e x , w h e r e ; i s f l - e t h y l t h ~ o e t h y l e n e thloglycolsc acid and e t h y l e n e - b l s ( t h l o g l y c o i l c ) a c i d did The hypothesis, that c o m p lex es c o n t a i n i n g a r i ng w i t h t w o s u l p h u r a t o m s s h o u l d be s t r o n g e r t h a n time o t h e r s , w a s tht, s p a r t m l l y p r o v e d D e t e r m m a t z o n , , o f time f o r m a l c o n s t a n t s for p a l l a d m m ( l l ) a n d t h e f o u r m e n t l o n e ¢ ! h g a n d sy~tem~ a r c ,n p r o g r e s s T h e : t b s o r p t t o n s p e c t r u m o f t h e , s o l a t e d c o m p l e x d e m o n s t r a t e d t h a t t he m o l a r r a t i o L M e is 2 . 1 . F r o m t h e i r a n d R a m a n s p e c t r a ( T a b l e !). o n e ma,~ c o n c l u d e t h a t t he o b s e r v e d f o u r f u n d a m e n t a l p e r c h l o r : t t e b a n d s , wsth t e t r a h e d r a l s y m m e t r y , a g r c e Wlt]l e a r l i e r r e s u l t s 22 o n t h e i oni c n a t u r e o f t h a t ~on. M o r e o v e r . time fact t h a t all f r c q u e n c l e s a r e dct~ve m R a m a n s p e c t r o s c o p y a n d o n l y the ~3 a n d ~,, f r e q u e n c i e s m ~ r s p e c t r o s c o p y c o n f i r m s t h e i n t e r p r e t a t i o n . T h c C--S. s y m m e t r i c a n d a s y m m e t r i c C O O s t r e t c h i n g f r e q u e n c i e s m N a , E B T G .and ~n t h e a c i d d g r e e w ; t h e a r l i e r r e s u l t s a3 T h e p a l l a d ~ t ~ m - s u l p h t , r c o o r d i n a t i o n m t h e ~solated c o m p l e x w a s e v i d e n c e d b y t h e fact t h a t t h e C - S s t r e t c h , r i g f r e q u e n c y ~s sh~ftcd t o l o w e r w ~ v e n u m b e r s , c o m p a r e d w i t h t he free a c , d a n d sis s o d i u m salt zz. A n o t h e r fact t h a t s e e m s t o c o n f i r m thss asst, m p t , o n is t h e m t e n s e b a n d at 325 c m - t m t he R a m a n s p e c t r u m . in ( P d C I z . 2 R . S C z H . , S R) c o m p l e x e s z'= :-~. t h e P d - S s t r e t c h i n g f r e q u e n c y wits a l s o o b s e r v e d m time r a n g e 3 1 0 - 3 4 0 c m - ~ . A c o m p a r i s o n o f t he ~. a n d ~, C O 0 f r e q u e n c i e s o b t a i n e d f or t he ~solated c o m p l e x . N a : E B T G a n d t he f r e e a c i d i n d i c a t e s th at th e c a r b o x y h c grot, p s a ~ e i n t a c t m time p a l l a d i u m c o m p l e x A n o t h e r p o i n t ~n f a v o u r o f thin. is t h e i n t e n s e ~nd w~dc a b s o r p t i o n m the r a n g e 2 3 0 0 - 3 6 0 0 e r a with v a r i o u s m a x i m a T h i s ss c h a r a c t e r i s t i c for t h e C O O H g r o u p r e v o l v e d ,n h y d r o g e n b o n d a s s o c m t ~ o n z~' Time s u p p o r t r e c e i v e d fiorn time C o n s e l h o N , l c l o n a l d e P c s q u m a ( R i o d e J a n e l r o ) a n d time F u n d a ~ f i o de A m p a r o ~t pe~qul,,a (Silo P i t u l o ) is g r a t e f u l l y itck n o w l e d g e d . SUMMARY
P a l l a d l u n a s o l u t i o n s ctln be t l t r a t e d v i s u a l l y a n d s p e c t r o p h o t o m e t r z c a l l y w i t h s o d i u m e t h y l e n e - b l s ( t h l o g l y c o l a t e ) T i t r a t J o n s w e r e d o n e in 2 5 M p e r c h l o r t c aci d with n l t r o s o - R sltlt as i n d i c a t o r . P a l l ; l d l u m w a s d e t e r m i n e d ~n t h e r a n g e 5 0 - 3 0 m S
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407
(v~sual t ~ t l a t ~ o n ) a n d 2 0 - 1 0 m g ( s p c c t r o p h o t o m e t r ~ c tztrat~on), tho tolcr.'tncc Ior d~vcrsc ~ons ,s g o o d . part~ct,l~rly w|th the spcctrophotomctr~c end-point T h e probable structure o f the isolated c o m p l c x ~ g w c n . REFERENCFS I 2 3 4 5 6 7 8 9 IO II 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
F E Bemnt~h l a h l n l t l 13 (1966)IO~;3 L R M PttombodndG Ohxc~r,i Nelo, Imll ( I r o n Itl,I 7 ~ ( 1 9 7 5 ) 391 L R M P I I o m b o ,-Inal C h l m Ic Ill 46 (1969) I qR L R M PJtombo. ,,l#ltll Chilli ~It Ill, 62 (1972) I0"~ L R M P l l o m b o d n d E Q Cdrl,lV, O lah#nttl 21 ( 1 9 7 4 ) 9 6 5 P B S w e c t s e r dnd G E Brlt, ker IHtll ( h t , m 25 (1953) 253 J S h a m l r dnt.t A Sh'.l, drtF. FtlhlHtt#. 8 ( 1961 ) 330 M 0101110 Hldl Cht'lH StJt Jtlp ~6(196"~) 889 F E B c m n . s h T h v 4 n a l l l l t a l C h v m # s l l i r~l t h e Ntd~h. A l e t a l s P c r g , , m o n . Oxt't~rd 1966 (d) p 441, (b) pp 68. Io9 130. ( c ) p p 324 334 ( d ) p 341 O W R o l l i n s dnd M M O I d h d m ,Dial C h t , m 43 ( 1971 ) ,"~6 ,"~ F E Bedmlgh Tt#hlllla. 14 (1971) 991 R F" G o d d u dnd D N H u m e ,I;Itll C h c m 2 6 ( 1 9 5 4 ) 1740 M B o b t c N k y dnd B M d y c r . /llltll (. h i m ,'It t¢l, 15 (1956) 164 M B o b t c N k y ,llld J Er,,cn,,tdtltcr ,|Hill (.hilt! A I I t l 16 (1957) 479 W N M,It.No~,m d n d II O K r l c g e /llltll C ' h v n l . 27 (It)55) 535 T A Klhh F F G d o l ,rod T M S u r , m y c ( , l a s Itt, m D I n s livo~llad. 34 (1969) 42 ~, C h v m Ihst 74 ( 1971 ) 9323 R Kcr,,tlng ,,Iml ( ' h e m P h a l m g7 ( 1 9 5 3 ) 2 5 R H A t k m , , o n . ,IHcdl ~t ( L o n t h m ) . "79 (1954) "~6N R H A t k m , . o n R N R h o d d ,|nd R G L o m c l l A n a l t s t ( L C n l d t m ) 8 0 ( 1 9 5 5 ) 8 3 g R H A t k m , , o n dnd R N R h o d d . r'hltll Ch¢,pll 28 (1956) 535 'vV B P o l l d r d . , I m l l l s t ( L t m d t m ) 6 7 ( 1 9 4 2 ) IN4 B J II,lth,lwdy dnd A E Undcrh~ll d C h t . m StJt L¢IHdt,I. ( 1961 ) ~1091 J P o d l d h a ,rod J P o d l , d l o ~ d . lll¢lrgl C'IHIH *ltltl 5 ( 1971 ) 41 "~ G E C o d t e ' , dnd C P d r k m J Cht.nl StJt L m l d r m ( 1 9 6 3 ) 4 2 1 J Plu~,Cu~, ,Ind A D We~tl,lnd, J C h v m S o t L o m h m . ( 1 9 6 5 ) 5371 L J Belldmy /hh'gl#;t¢,s m i ~ l ; t H t , d Grol~p I'tvtlHt, nt I. M e l h u c n . L o n d o n , 196g. p 270