Inorganic Reactions in Organized Media - ACS Publications

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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 8, 2016 | http://pubs.acs.org Publication Date: February 12, 1982 | doi: 10.1021/bk-1982-0177.ch012

T h e H y d r o l y s i s of C h l o r o p h y l l a i n Detergentless Microemulsion M e d i a An Initial Study in the Development of a Kinetic Model for the Geologic Transmetalation Reactions of Porphyrins Found in Petroleum DAVID K. LAVALLEE, EUPHEMIA HUGGINS, and SHELLEY LEE Hunter College of the City University of New York, Department of Chemistry, New York, NY 10021 The most reasonable mechanism for the conversion of natural macrocylic complexes, the chlorophylls, hemes and hemins, to the nickel and oxovanadium porphyrins formed in petroleum appears to be a sequence of hydrolysis and metallation reactions. The chlo rophylls and natural metalloporphyrins are hydrophobic whereas the hydronium ion and typical aquated metal ions are hydrophilic so the hydrolysis and metallation reactions may have taken place in interphase regions. Results for the hydrolysis of chlorophyll a in detergentless microemulsion media consisting of toluene, water and 2-propanol show a rate law that is first order in chlorophyll a and second order in acid concentrations, +

rate= k [ch1 a] [H ] 3

2

-1

withk - 4.7xl0 m-2s at χ (toluene)= 0.411, χ (water) = 0.180 and χ (isopropanol) = 0.408, Τ = 25.0°C and I . 0.10 M over a range of 105 ink . The rate is strongly dependent on the con centration of toluene giving a relationship of k α [toluene]2.5 while there is no evident correlation of the rate with water or isopropanol concentrations. The reaction follows the same rate law for a variety of compositions within the microemulsion region and even for compositions for which the structure is no longer a microemulsion. obs

obs

Introduction Chlorophylls and iron porphyrins are prevalent in plant and animal matter whereas only nickel (as Ni (II)) and vanadium (as oxo vanadium V(IV), V 0) metalloporphyrins are found in petroleum. To determine a plausible reaction sequence for these conversions, we are studying hydrolysis and metallation reactions of metal com plexes of pheophytins (the demetallated ligands of chlorophylls) and of porphyrins. The pheophytins and metal pheophytinates, in cluding the chlorophylls and the most abundant natural porphyrins, are highly lipophylic and have very low solubilities in aqueous s

0097-6156/82/0177-0195$05.00/0 © 1982 American Chemical Society In Inorganic Reactions in Organized Media; Holt, Smith L.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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s o l u t i o n s . Common n a t u r a l forms of metal ions and the hydronium i o n a r e , o f course, h y d r o p h i l i c w i t h low s o l u b i l i t y i n nonpolar o r g a n i c s o l v e n t s . Since r e a c t i o n s of pheophytins and porphyrins w i t h a c i d and w i t h metal i o n s during the g e o l o g i c a l development of petroleum may have occurred at lipid-aqueous interphase regions; we have chosen to study r e a c t i o n s i n n o n i o n i c microemulsion media. In t h i s r e p o r t we d i s c u s s the h y d r o l y s i s of c h l o r o p h y l l a i n a medium c o n s i s t i n g of toluene, water and i s o p r o p a n o l .


Background While crude o i l c o n s i s t s mainly of hydrocarbons which have undergone s i g n i f i c a n t chemical changes t h a t reduce t h e i r u t i l i t y as chemical records of the g e o l o g i c h i s t o r y of the o i l formation p r o c e s s , there are a l s o some s t a b l e components of o i l that have p e r s i s t e d l a r g e l y i n t a c t f o r very l o n g p e r i o d s - the metalloporp h y r i n s . The porphyrin s p e c i e s commonly found i n o i l s are vanadyl and n i c k e l complexes of mainly d e o x o p h y l l o e r y t h r o e t i o p o r p h y r i n , deoxophylloerythin, and e t i o p o r p h y r i n I I I (or mesoetioporphyrin)see Figure 1 (2, 2Ù · The s i m i l a r i t y of these porphyrins to the common porphyrins found i n p l a n t s and animals, c h l o r o p h y l l and p r o t o p o r p h y r i n IX (the p o r p h y r i n found i n hemoglobin, myoglobin and many p l a n t and animal cytochromes) shown i n Figure 2, was one of the e a r l y i n d i c a t o r s of the o r i g i n of crude o i l . Along the f a c t that most o i l occurs i n formation with sedimentary rock, the presence of porphyrins provides very strong evidence f o r the o r i g i n o f o i l b e i n g vegetable and animal matter that has been chemically transformed by the e f f e c t s of temperature and pressure over long p e r i o d s o f time. Metalloporphyrins are very s t a b l e compounds, p e r s i s t i n g a t temperatures of two hundred degrees C e l s i u s w i t h changes o f organic s u b s t i t u e n t s on the p e r i p h e r y o f the macrocycle but with r e t e n t i o n of the b a s i c m a c r o c y c l i c s t r u c t u r e . They have apparently s u r v i v e d from the o r i g i n a l d e p o s i t i o n o f organic m a t e r i a l m i l l i o n s o f year ago. As s t a t e d by Constantinides and A r i c h ( 4 ) : The problem of the o r i g i n o f the metal-porphyrins i s c l o s e l y r e l a t e d to t h a t of the o r i g i n o f petroleum and i s one of the most b a s i c and i n t e r e s t i n g questions of petroleum geochemistry. The most probable c o n c l u s i o n seems to be t h a t the n i c k e l and vanadium porphyrin complexes are formed by metal exchange r e a c t i o n s from animal and/or p l a n t metabolic pigments such as hemoglobin and c h l o r o p h y l l . These comments have been a m p l i f i e d by Hodgson, Baker and Peake (5): Among the multitude o f compounds o c c u r r i n g i n petroleum there are few which are unique. Of these, the p o r p h y r i n com-

In Inorganic Reactions in Organized Media; Holt, Smith L.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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0-CH2-CH-Ç-C H33 l6

CH

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Figure 2. Structures of chlorin and porphyrin molecules found in plant and animal matter. Several different chlorophylls have the same basic ring structure but different peripheral substituents.



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pounds are d i s t i n c t i v e , o f f e r i n g some hope of d e f i n i n g more c l e a r l y the genesis o f petroleum. Although there are many p o s s i b l e s t r u c t u r e s f o r p o r p h y r i n s , only a l i m i t e d number occur i n petroleum. However, these few may have had both an a c t i v e and a p a s s i v e r o l e to p l a y i n the development of crude o i l from i t s source b i o g e n i c m a t e r i a l . The p a s s i v e r o l e played by the pigments was that i n which the p r e c u r s o r molecules underwent a s e r i e s of systematic changes u n t i l they became the s t a b l e and e a s i l y recognizable t r a c e compounds of crude o i l . In an a c t i v e sense, the developing pigments may have had a s u r f a c t a n t r o l e to p l a y d u r i n g the m o b i l i z a t i o n , m i g r a t i o n and accumulation o f crude o i l hydrocarbons. The transformation o f porphyrin precursors to porphyr i n s , as w e l l as the occurrence o f these compounds i n poss i b l e petroleum source m a t e r i a l s and i n petroleum, have cons i d e r a b l e geochemical s i g n i f i c a n c e i n the h i s t o r y of the o r i g i n and accumulation of petroleum. The range of concentrations of porphyrins i n o i l i s q u i t e l a r g e - from about 1 ppm i n some l i g h t o i l s e s p e c i a l l y i n Texas and Oklahoma to n e a r l y 2000 ppm i n h e a v i e r crudes from Venezuela (and as h i g h as 0.4 % by weight i n some o i l shales) ( 6 ) , w i t h the common c o n c e n t r a t i o n of 100-400 ppm. Because o f the h i g h e x t i n c t i o n c o e f f i c i e n t s (^10^ I f ^ cm ) of both f r e e porphyrins and p o r p h y r i n complexes and the very s t r o n g f l u o r e s c e n c e o f f r e e porphyr i n s (obtained by t r e a t i n g the metalloporphyrins w i t h a c i d ) low concentrations of porphyrins can be q u i t e r e a d i l y determined. The r a t i o of vanadium to n i c k e l i n the p o r p h y r i n f r a c t i o n can be determined a c c u r a t e l y by common techniques such as atomic a b s o r p t i o n spectrometry. Large c o l l e c t i o n s of such data are a v a i l a b l e (7 - 10). Attempts have been made to c o r r e l a t e the vanadium to n i c k e l r a t i o s (which vary from e s s e n t i a l l y a l l vanadium to l e s s than 10% vanadium) w i t h age of the crude o i l and l i m i t e d success - g e n e r a l l y w i t h deposits i n the same r e g i o n - has been achieved ( 5 ) . Further e l u c i d a t i o n of the t r a n s m e t a l l a t i o n mechanism may provide more i n formation f o r purposes of c o r r e l a t i o n w i t h h i s t o r y of an o i l deposit. I t may be found as a r e s u l t of these i n v e s t i g a t i o n s that temperature of pH i s important i n determining the type of m e t a l l o porphyrin as w e l l as metal i o n a v a i l a b i l i t y . In modelling s t u d i e s of the chemical transformations of c h l o r o p h y l l and protoporphyrin IX to the porphyrins found i n o i l s , more a t t e n t i o n has been given to the o r g a n i c chemistry - the changes of s u b s t i t u e n t s a t the periphery of the p o r p h y r i n r i n g than to the way i n which these s p e c i e s came to be vanadium and n i c k e l complexes. The presence of the i s o c y c l i c r i n g i n deoxophyll o e r y t h r o e t i o p o r p h y r i n and deoxophylloerythrin p o i n t s to c h l o r o p h y l l as p r e c u r s o r w h i l e the s t r u c t u r e of e t i o p o r p h y r i n (or mesoporphyr i n ) makes hemin ( c h l o r o p r o t o p o r p h i n a t o i r o n ( I I I ) ) a l i k e l y precurs o r . The conversion of the c h l o r i n r i n g system found i n c h l o r o -



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p h y l l (one s a t u r a t e d double bond i n one of the four p y r r o l e r i n g s ) to the p o r p h y r i n system ( a l l unsaturated p y r r o l e s ) i s r e a d i l y accomplished by quinones (11). Similarly, bacteriochlorophylls, i n which two p y r r o l i c double bonds have been s a t u r a t e d , can a l s o be converted r e a d i l y to porphyrins. The other organic r e a c t i o n s that l e a d to the porphyrins found i n o i l i n c l u d e s a p o n i f i c a t i o n of e s t e r s u b s t i t u e n t s , s a t u r a t i o n o f v i n y l groups, r e d u c t i o n o f formyl and a c e t y l groups, r e d u c t i o n of carbonyl groups and dec a r b o x y l a t i o n of a c i d groups ( 6 ) . From the nature of these r e a c t i o n s and the known p r o p e r t i e s of decaying organic matter, the l o c a l environment during the development of o i l i s presumed to be reducing. Of the metal ions commonly a v a i l a b l e from ground water and sedimentary rock that can r e a c t w i t h porphyrins i n contact w i t h water, two have d i f f e r e n t o x i d a t i o n s t a t e s under normal a e r o b i c c o n d i t i o n s and under reducing c o n d i t i o n s . These are i r o n and vanadium - two metal ions which are thought to be very imp o r t a n t i n the conversion o f porphyrin and c h l o r o p h y l l s i n animal and vegetable matter to the vanadium and n i c k e l porphyrins found i n petroleum. Under reducing c o n d i t i o n s of the type presumed f o r petroleum development, i r o n i s expected to e x i s t as Fe(II) and vanadium as V ( I I I ) (vanadium(II) i s such a powerful reducing agent that i t would be expected to reduce organic compounds whereas V ( I I I ) near n e u t r a l pH i s only a m i l d recuding agent). Other metal i o n s that are reasonably abundant and c o u l d p l a y a r o l e i n n a t u r a l t r a n s m e t a l l a t i o n r e a c t i o n s are C u ( I I ) , N i ( I I ) , Z n ( I I ) , and *fti(II) . M e t a l l a t i o n and T r a n s m e t a l l a t i o n

Reactions

S e v e r a l d i f f e r e n t sequences of r e a c t i o n s may be p o s t u l a t e d f o r the conversion of the magnesium complexes of pheophytins ( c h l o r o p h y l l s ) and i r o n complexes of protoporphyrin IX and r e l a t e d porphyrins (hemes and hemins) i n t o the n i c k e l and vanadium porphyr i n s found i n petroleum. One p o s s i b l e reason f o r the i s o l a t i o n of only the n i c k e l and oxovanadium metalloporphyrins i s that only they were r e s i s t a n t to degradation. While s t u d i e s o f Hodgson do i n d i c a t e t h a t complexation o f vanadium and n i c k e l do impart added thermal s t a b i l i t y to porphyrins (12), B e r e z i n has found that comp l e x a t i o n of other metal ions such as c o b a l t and copper a l s o imp a r t s added thermal s t a b i l i t y (13, 14). In a d d i t i o n , Hodgson's study i n d i c a t e s t h a t r e l a t i v e l y l i t t l e thermal degradation o f the metalloporphyrins has taken p l a c e i n most crude o i l s (which would l e a d to unbound vanadium and n i c k e l ) . One would expect that i f l i t t l e degradation o f these metalloporphyrins has occurred, complete disappearance of other metalloporphyrins by thermal degradation i s an unreasonable assumption. A second type o f mechanism would be the r e d u c t i v e or o x i d a t i v e d e m e t a l l a t i o n o f intermediate m e t a l l o p o r p h y r i n s , a l l o w i n g n i c k e l and vanadium to complex. From the e l e c t r o c h e m i s t r y of porp h y r i n s , and s o l u t i o n s t u d i e s i n v o l v i n g o x i d i z i n g and reducing



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agents, (15) however, i t would appear that the only metalloporphyr i n s which are i n v o l v e d i n petroleum maturation that would be s u s c e p t i b l e to d e m e t a l l a t i o n under m i l d c o n d i t i o n s by t h i s mechanism are oxovanadium porphyrins (16), which are, i n f a c t , one of the two types of complexes found. I t would appear then that none of the intermediate species would be a f f e c t e d by t h i s mechanism. A t h i r d general mechanism i s d i r e c t t r a n s m e t a l l a t i o n i n which a metal atom d i s p l a c e s a metal atom that i s bound to a porphyrin or pheophytin l i g a n d . I t could not be necessary f o r n i c k e l or vanadium to d i r e c t l y d i s p l a c e the magnesium of c h l o r o p h y l l s or the i r o n of hemes of hemins but a s e r i e s of t r a n s m e t a l l a t i o n reactions could occur f o r which the termination steps i n v o l v e d the n i c k e l and vanadium r e a c t i o n s . The k i n e t i c s of t r a n s m e t a l l a t i o n react i o n s of s e v e r a l metalloporphyrins have been i n t e r p r e t e d i n terms of such a d i r e c t displacement mechanism (17, 18, 19). The h i g h r e a c t i v i t y of copper (II) as the d i s p l a c i n g metal i o n i n these r e a c t i o n s and r e l a t i v e l y low r e a c t i v i t y of n i c k e l (II) i m p l i e s that a t l e a s t some copper porphyrin complexes should be observed i n petroleum. In a d d i t i o n , the d i r e c t (or a s s o c i a t i v e ) mechanism for t r a n s m e t a l l a t i o n has only been p o s t u l a t e d f o r cases i n v o l v i n g m e t a l l o p o r p h y r i n s i n which the metal i o n i s s i g n i f i c a n t l y outof-plane (Hg(II), P b ( I I ) , Cd(II) and Zn(II)) and which are a l s o of low s t a b i l i t y w i t h respect to a c i d h y d r o l y s i s . An a l t e r n a t i v e mechanism f o r t r a n s m e t a l l a t i o n i s one which i n v o l v e s a c i d c a t a l y z e d d i s s o c i a t i o n followed by competitive m e t a l l a t i o n (20, 21, 22). In t h i s process, the metal i o n i n the metalloporphyrin i s d i s p l a c e d by protons. At r e l a t i v e l y low a c i d concentrations (pH >_ 4) expected f o r ground waters and most environments of developing petroleum d e p o s i t s , the predominant form of the demetallated porphyrins and pheophytins would be the n e u t r a l f r e e base. The metal ions i n the v i c i n i t y of these f r e e base species could then compete w i t h each other to form complexes. The h y d r o l y s i s - competitive complexation sequence would be repeated u n t i l the metal i o n or ions which are most r e s i s t a n t to a c i d h y d r o l y s i s have bound a l l the a v a i l a b l e l i g a n d s . The s t a b i l i t i e s of metalloporphyrins toward displacement of the metal i o n by a c i d were reported many years ago by Caughey and Corwin (23) and i t was found that a c i d d i s s o c i a t i o n r a t e s were i n the q u a l i t a t i v e order N i ( I I ) < Cu(II) < Co(II) « Z n ( I I ) . From a number of q u a l i t a t i v e s t u d i e s F a l k and Buchler have constructed a s t a b i l i t y s e r i e s f o r r e s i s t a n c e to a c i d d i s s o c i a t i o n as : N i ( I I ) > Co(II) > Cu(II) > Fe(II) > Zn(II) > M ( n ) w i t h no mention of oxovanadium complexes (24, 25) . Although the r e l a t i v e l y h i g h s t a b i l i t y of N i ( I I ) porphyrins toward a c i d displacement might be taken as presumptive evidence i n support of the i n d i r e c t t r a n s m e t a l l a t i o n sequence i n v o l i n g a c i d h y d r o l y s i s , data o f B e r e z i n and Drobysheva must a l s o be considered. B e r e z i n and Drobysheva have s t u d i e d a c i d h y d r o l y s i s of metal complexes of pheophytin a i n mixed solvent systems of e t h a n o l , g l a c i a l a c e t i c a c i d and s u l f u r i c a c i d . They suggest a s t a b i l i t y order of F e ( I I I ) > Cu(II)> g



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N i ( I I ) > Co(II) > Zn(II) (13, 14, 26, 27). Considering the conc e n t r a t i o n s of metal ions which r e a c t w i t h porphyrins and pheop h y t i n s that are t y p i c a l o f groundwater ( i n ppm) Fe(0.23), Mn(0.009), Cu(0.007), Ni(0.004) and V(0.001), i n sedimentary rock such as graywackes and s h a l e , r e s p e c t i v e l y (Fe(3.84x10*, 4.8x10*), Mn (750,850), Cu(45,45), Ni(40,68) and V(67,120)) and i n marine sediments ( l i k e those o f s h a l e , a l l data from reference 28), and r e a c t i o n r a t e s t y p i c a l l y found i n homogeneous s o l u t i o n s (29^, 30, 31) one would expect to f i n d Cu(II) porphyrins i n petroleum i f Berezin's order dominated the t r a n s m e t a l l a t i o n sequence. Several i n t e r e s t i n g p o s s i b i l i t i e s f o r u n r a v e l i n g the present ambiguities e x i s t . I t i s q u i t e p o s s i b l e that the r e l a t i v e a c i d s t a b i l i t i e s f o r a s e r i e s of metal ions as pheophytin complexes and as porphyrin, complexes are indeed very d i f f e r e n t and the c r u c i a l t r a n s m e t a l l a t i o n h y d r o l y s i s r e a c t i o n s occurred a f t e r the pheophytins had been converted to porphyrins. Another i n t e r e s t i n g p o s s i b i l i t y to e x p l a i n the absence o f Cu(II) porphyrins i n petroleum i s t h a t the h y d r o l y s i s and m e t a l l a t i o n r e a c t i o n s d i d not take p l a c e i n homogenous s o l u t i o n but i n interphase regions and that the k i n e t i c s of these r e a c t i o n s are s i g n i f i c a n t l y d i f f e r e n t from those i n homogeneous s o l u t i o n . Herein we r e p o r t on the f i r s t stage o f our i n v e s t i g a t i o n o f t h i s aspect of the d e v e l opment of a k i n e t i c model f o r the metalloporphyrin transmetallat i o n sequence f o r the formation o f the complex found i n petroleum: the h y d r o l y s i s o f c h l o r o p h y l l i n a d e t e r g e n t l e s s microemulsion medium. Results and

Discussion

H o l t , Barden, and coworkers have r e c e n t l y reported the charact e r i z a t i o n of d e t e r g e n t l e s s microemulsion media c o n s i s t i n g of toluene, water and 2-propanol and hexane, water and 2-propanol (32, 33, 34). In developing pseudophase diagrams f o r these sys-r terns, they have i d e n t i f i e d regions of s t a b l e w a t e r - i n - o i l microemulsions. Since i s o p r o p a n o l which i s present i n the interphase r e g i o n i s a l s o q u i t e s o l u b l e i n both water and hydrocarbons, the s t r u c t u r e o f these microemulsions i s much l o o s e r , w i t h a greater average thickness o f molecules, than i s t y p i c a l of microemulsions formed w i t h detergents. R e i s e r and H o l t have shown that metall a t i o n o f a f r e e base p o r p h y r i n (tetraphenylporphyrin) occurs r e a d i l y i n the d e t e r g e n t l e s s w a t e r - i n - o i l microemulsion media we have used i n t h i s study (35). When they added other s u r f a c t a n t s t o t h i s medium, they found l i t t l e e f f e c t w i t h n o n i o n i c and a n i o n i c s u r f a c t a n t s but l a r g e r a t e enhancements w i t h c a t i o n i c s u r f a c t a n t s , i n sharp c o n t r a s t w i t h r e s u l t s p r e v i o u s l y found by L e t t s and Mackay f o r o i l - i n - w a t e r microemulsion media (36) and by Lowe and P h i l l i p s i n aqueous m i c e l l a r media (37). Hambright has a l s o r e p o r t e d m e t a l l a t i o n r a t e s f o r porphyrins i n aqueous media c o n t a i n i n g Tween 80 (38). To avoid the profound i n f l u e n c e that i o n i c detergents can have, we have decided to employ a nonionic medium.



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As y e t , no k i n e t i c data have been reported f o r the m e t a l l a t i o n o f pheophytinates o r f o r the h y d r o l y s i s o f metal pheophytinates o r metalloporphyrins i n w e l l - c h a r a c t e r i z e d microemulsion media. For t h i s study, we prepared toluene, water, 2-propanol micro emulsions i n which c h l o r o p h y l l a ( e x t r a c t e d from f r e s h spinach, 39) was d i s s o l v e d i n toluene and p e r c h l o r i c a c i d and l i t h i u m p e r c h l o r a t e (to maintain the i o n i c s t r e n g t h a t 0.10M) were d i s s o l v e d i n the aqueous phase. K i n e t i c s were monitored by observ i n g changes i n the v i s i b l e absorption spectrum w i t h a convention a l o r a stopped-flow spectrophotometer, as appropriate, and the temperature was c a r e f u l l y maintained a t 25.0°C. A l l k i n e t i c runs were p s e u d o - f i r s t - o r d e r w i t h the c h l o r o p h y l l a concentration a t l e s s than 10 T L In a l l cases, the change i n absorbance c o r r e sponded t o a f i r s t - o r d e r process f o r s e v e r a l h a l f - l i v e s . A t y p i c a l p l o t i s shown as F i g u r e 3. As reported p r e v i o u s l y (39), at a s i n g l e microemulsion composition o f χ (toluene) = 0.411, χ (H 0) - 0.180 and χ (2-propanol) - 0.403^ the dependence o f the observed r a t e on a c i d concentration was second order over f o u r orders o f magnitude o f r a t e ( f r o m k = 1,0 t o 10"*). The data of B e r e z i n , e t . a l . (13, 14, 26, 27) have i n d i c a t e d n o n - i n t e g r a l behavior f o r a c i d c a t a l y z e d h y d r o l y s i s o f other metal pheophytin ates and the nature o f the s o l v e n t systems used (eg e t h a n o l , g l a c i d a c e t i c a c i d ) have o f t e n made determination o f the hydrogen i o n a c t i v i t y tenuous and the range o f a c i d concentrations s t u d i e d were g e n e r a l l y very r e s t r i c t e d . More extensive s t u d i e s o f a c i d c a t a l y z e d d i s s o c i a t i o n have been performed w i t h metalloporphyrins, i n c l u d i n g Z n ( I I ) , ^ ( I I ) , C d ( I I ) , F e ( I I ) and F e ( I I I ) complexes (29, 40, 45). The r a t e laws a t h i g h a c i d are t y p i c a l l y second order b u t a t low a c i d , t h i r d order r a t e laws have been observed. For example, f o r the a c i d c a t a l y z e d h y d r o l y s i s o f one o f c l o s e s t analogues to the petroleum porphyrins, e t i o p o r p h i n a t o z i n c ( I I ) . the r a t e law observed by Hambright and coworkers(41) i s : 2

o b s

r a t e =

Inorganic Reactions in Organized Media - ACS Publications

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