2. The fact that the rate of alkylation changes with a change in the PC-to-acetone ratio and with the introduction of toluene into the system could be the result of changes in the solubility of the catalyst, or the ion pair, in the organic phase. 3. The differences in the effect of NaOH and KOH on the alkylation reaction have been explained, as has the suppression of PC hydrolysis under two-phase catalysis. 4. The usual temperature effects o f the aldol condensation c a r r y over to catalysis in two-phase systems. fl-Elimination with the formation of mesityl oxide requires the action of a phase-transfer catalyst. LITERATURE 1. 2. 3. 4. 5. 6.

CITED

M. Makosza, A. Patchornik, and D. Seebach, Modern Synthetic Methods, Schweizarischer Chemisher Gebund, Zurich (1976}. I . S . Aul'chenko, L. A. Kheifits, T. I. Konstantinova, and T. P. Cherkasova, Maslozhir. Promst., No. 12, 24 {1975}. V . A . Yakovlev, Kinetics of Enzyme Catalysis [in Russian], Nauka (1965). G . I . Mikulin (editor}, Problems in the Physical Chemistry of Solutions of Electrolytes [in Russian], Khimiya, Leningrad (1968}. K . P . Mishchenko and G. M. Poltoratskii, Problems in the Thermodynamics and Structure of Aqueous and Nonaqueous Solutions of Electrolytes [in Russian], Khimiya, Leningrad (1968}. V . V . Kafarov {editor}, Handbook of Solubilities [in Russian], Vol. 2, Book 1, Izd. Akad. Nauk SSSR (1962}, p. 85.

REACTIONS OF P H A S E

OF

CARBONYL

TRANSFER

COMPOUNDS

IN T H E P R E S E N C E

CATALYSTS

COMMUNICATION 2. STUDY OF THE CH-ACIDITY OF MONOCARBONYL COMPOUNDS THROUGH CNDO/BW QUANTUM CHEMICAL CALCULATIONS Faustov, S. S. Y u f i t , a n d I. A. E s i k o v a V.

I.

UDC530.145:543.241.5:541.128-547.384

The rate and direction of an organic reaction is often determined by the energy of heterolytie C - H bond rupture (i.e., by the acidity) and the structure of the earbanion resulting from this process. The data on CHacidities are too limited to give direct information on carbanion st ruct ures, the principal factor in fixing the initial stages of the reaction [1]. Quantum chemical methods can be used to determine both the energy of proton detachment from the CH-acid, and the structure of the carbanion resulting from this process. These methods give the energy of the gas-phase reaction; passage of the ion into solution requires that account be taken of solvation effects. Experiment shows that there is a correlation between AHd, the enthalpy of deprotonation, and AHs, the enthalpy of solvation, in a s e r i es of related compounds; moreover, the o r d e r of acidities of the ketones is the same in DMSO and in the gaseous phase [2]. The present work is a study of the acidities of the monocarbonyl compounds: acetone (1), methyl ethyl ketone (II), and mesityl c~ide (IID by semiempirical CNDO/BW quantum chemical calculations [3]. The possibility of using CNDO/BW methods for determining CH-aeidities and anion geometries was demonstrated by calculations on ethane, ethylene~ acetylene, and the anions resulting from deprotona~ion of these compounds. The work on the neutral molecules and anions was c a r r i e d out by complete optimization of geometries,* assuming invariance of the local symmetries of the methyl and methylene groups (C3v and Cs, * The computations were c a r r i e d out by a program developed by K. Ya. Burshtein and modified for optimization of the geometry by the method of variable metrization [4]. N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimieheskaya, No. 7, pp. 1474-1479, July, 1979. Original a r ticle submitted February 22, 1978.

1372

0568-5230/79/2807-1372 $07.50 9 1980 Plenum Publishing Corporation

TABLE 1. Enthalpies of G a s - P h a s e Deprotonation, AH d (ev), for Model C o m pounds

l

-~c

Method

Compound 2I~

C2H4

CNDO/BW Experiment

t6,33 t6,9

t6,18

Nonempirical computation [6 ]

t9,77

C2H~

t5,88 t6,7 * t6,1 t5,0 t9,00 " i7,40

*values obtained u~ng CzHzradical electron affipities calculated by various methods [5].

r e s p e c t i v e l y ) throughout. The g a s - p h a s e acidities of ethane and acetylene w e r e d e t e r m i n e d f r o m the known values of the e n e r g y of homolytic C - H bond r u p t u r e and the e l e c t r o n affinity of the r e s u l t i n g r a d i c a l s [5]. None m p i r i c a l SCF calculations in extended STO 4-31 G and STO 6-31 G b a s e s [6] have a l r e a d y been c a r r i e d out on each of these t h r e e compounds. C o m p a r i s o n of the c a l c u l a t e d C H - a c i d i t i e s showed that the deprotonation energy should change u n i f o r m l y in p a s s i n g f r o m one of these compounds to another (Table 1), just as is found to be the c a s e e x p e r i m e n t a l l y . In c o m p a r i s o n with the m e a s u r e d values of the energy of proton detachment, the values obtained by the n o n e m p i r i c a l calculations a r e s y s t e m a t i c a l l y high, and those obtained by the s e m i e m p i r i c a l calculations s y s t e m a t i c a l l y low, the r e s u l t s obtained through the C N D O / B W method being c l o s e s t to the exp e r i m e n t a l . G e o m e t r i c a l p a r a m e t e r s for the neutral m o l e c u l e s c a l c u l a t e d by the two methods a r e consistent among t h e m s e l v e s [3, 6] and a g r e e with the m e a s u r e d values [3]; the anion g e o m e t r i e s a r e unknown, but the r e s u l t s of t r e a t m e n t by the two methods a r e c o n s i s t e n t t h e r e as well (Table 2). Only in the c a s e of the C = C and C -=C bond lengths is t h e r e a m a r k e d difference in the r e s u l t s obtained by the two m e t h o d s , the values given by the C N D O / B W calculations being c o n s i s t e n t l y high by 0.04 A [3] Since the p r o b l e m of ketone acidities is c l o s e l y tied up with k e t o - e n o l t a u t o m e r i s m , the calculations w e r e extended to the enol f o r m s of acetone (HI) and m e s i t y l oxide (IV), and to the fl- (V) and the a - (VI) f o r m s of the k e t o - t a u t o m e r . Calculations w e r e a l s o made on the c a r b a n i o n s (VII) and (XVI).

sCH, \ Ct------0t / CH3 ,

aCHs 1

4CHt \ C'-----rs / CH3 s

*CH.~ \ C'--s //' CHz

Hs~C \

eCHt

Hs'C

\

J

C~ I 4CH %

~

/

6CH3

/ Cs

II , ~C \

C'--0~H

CH3

CH~

8

(I)

(II)

Ha7%

(III)

3

(IV)

(V)

eCHa C5

HaSt

\C=O / CHs (VI)

\C~---0' e.C/H, (VII)

/

II

CH \ C=O / eCHt

(Xli)

I CH,

H3~C

CHa

C

CHa elHc

@CH~

I CH~

HsC N

Cx=O ~

/

\ C~--oz* / 4CHt (vm) H~C

C(CH,), e~

\ /

C=O

CHs

(xm)

CH~ ~ \

/

C II CH \ C=O /

\C=0 CH3/ (IX)

"C=O / CH~ (X)

HsC

CHs \

CH~ I CH,

J

C eCIH \ C=O /

CHs

CH s

(XlV)

(xv)

\C=O eC/H, (xI)

H~C

CH~ \

/

J

C ' CH II

C--O -~

CHs

(xvx)

The ions (VI1) and (VIII) could be thought of as arising from the deprotonation of a C atom in (1), or an 0 atom in (111), while the ions (IX)-(Xl) are possible results of proton detachment in (II). Onlythe most characteristic types of deprotonation w e r e c o n s i d e r e d in the m e s i t y l oxide i s o m e r s , possible d i f f e r e n c e s in the proton a c i d ities of the two 7 - m e t h y l groups of (V) being neglected, for instance. The calculations on (D-(VIID w e r e

1373

TABLE 2. Calculations on the Geometry of the Ethane, E t h y l e n e , and Acetylene Anions by C N D O / B W Methods and by the N o n e m p i r i cal Method of [6] (in parentheses) a

Anion t 2 CHz--CHz @

Symmetry group C,

C'C2 1,539(i,55i); C'H 1,120(t,097); C2H 1,i23(i,t14); C~C2H103,7(i06,6); C2C~H115,9(113,4); HC2H 102,t (i04,7)

C,

CC 1,384(1,350); CH~ 1,t25(1,1t0); CH2 1,tt8(t,099); CH3 1,i15(i,090); CCH~ 109,4(t06,7); CCH2 i31,0 (i26,0); CCHa t22,8(t22,2)

1

2

II

H\o o/ H/~=~| 3 HC:C~

Bond lengrtm,A; valence angle,s,deg

C~

CC 1,278(1,23i) ; CH i,095(1,057)

extended to include optimization of all bond lengths and valence angles. The torsional angles of the C - C H 2 bends in the carbanion center w e r e optimized in the calculations on (VII) and (VIII), and the angles of rotation of the methylene and hydroxyl groups in the r e s p e c t i v e calculations on (VII) and (III). The calculations on the other anions w e r e extended to optimization of all CC and CO bond lengths, all skeletal valence angles, and the coordinates of all H atoms bound to carbanion centers. The coordinates of the remaining H atoms w e r e a s s u m e d to be the s a m e as for the neutral molecule. All C - H bond lengths w e r e calculated for the hindered conformation. The c a r b o n skeleton of derivatives (I)-(III) was a s s u m e d to be planar; the s t r u c t u r e of (V) was developed for the c i s s o i d c o n f o r m a t i o n with a 38 ~ double bond rotation [7]; this same value of the angle between the planes containing the double bonds was also a s s u m e d to the calculations on (IV), (VI), and (XIII)-(XVI). Calculations on (1) and (HI) showed the k e t o - t a u t o m e r to be m o r e stable than the enol f o r m s by 11.4 k c a l / mole, a figure in good a g r e e m e n t with 13.9 • 2 k c a l / m o l e , the experimentally d e t e r m i n e d difference in the heats of f o r m a t i o n of the two t a u t o m e r s in the gaseous phase [8]. This difference in the heats of formation of the two f o r m s falls to 8.2 k c a l / m o l e in the liquid phase, the OH group being m o r e strongly solvated than the CO group. Since enol ionization involves loss of a hydroxyl group proton, it is to be expected that the difference in the energies of solvation of (VII) and (VIII) would be negligibly small in c o m p a r i s o n / w i t h the difference in the energies of solvation of (I) and (III). The results on optimization of the g e o m e t r i e s a r e shown in Table 3, while the atomic c h a r g e s and the CO and CC bond resonance energies in acetone and its derivatives [11] are given in Table 4. It is c l e a r that the calculations give a good r e p r o d u c t i o n of carbonyl compound g e o m e t r i e s , at l e a s t in the c a s e of (1). The calculated C = C bond length in (III), 1.41 A, is obviously high, but it has already been pointed out the double and triple bend lengths d e t e r m i n e d by the C N D O / B W method a r e usually high by 0.04/~. Of the two possible acetone anions, only (VII) c o r r e s p o n d s to a minimum on the potential energy s u r face, w ~ i e (VIII) p a s s e s , without b a r r i e r , over into (VII). The fact that the C1C4 bond in (VII) is shortened by 0.04 A, while the CO bend is lengthened by 0.01 A, would s e e m to indicate the f o r m a t i o n of a delocalized H~C\ H2c~C~ O s t r u c t u r e . CompariSon of resonance bond e n e r g i e s , which fix the e l e c t r o n density distribution and thus give a m e a s u r e of the d e g r e e of double-bondedness [11], shows, however, that the C1C4 bend of (VIII) is still a single bond, and the CO bond a double bend. The calculated height of the b a r r i e r for rotation around the CIC 4 bond is 2.9 k c a l / m o l e , which is of the o r d e r c h a r a c t e r i s t i c for single bonds. It was interesting to c o m p a r e the atomic c h a r g e s in the neutral acetone t a u t o m e r s and in the anion (VII) (cf. Table 4). The O atoms of the neutral compounds (i) and (HI) w e r e found to c a r r y high negative c h a r g e s , just as was to be expected. The excess negative c h a r g e is markedly delocalized in the anion, a part of it being located on the C 4 atom with the g r e a t e r f r a c t i o n c a r r i e d by the O atom, just as in the c a s e of the neutral c o m pound. At f i r s t glance this would s e e m to be inconsistent with the s t r u c t u r a l f o r m u l a shown as (VII) in the s c h e m e , since this apparently entails localization of the excess c h a r g e on the C 4 atom. C o m p a r i s o n of the atomic c h a r g e s in (I) and (VII) shows, however, that the excess c h a r g e localized on the C 4 atom of the anion is considerably higher than the excess c h a r g e localized on any of the atoms of (VII), not even excepting the O atom, just as r e q u i r e d by the s t r u c t u r a l formula. Although such a c h a r g e distribution would p e r m i t alkylation at both the C atom and the O atom, the latter p r o c e s s would be hindered, at least in low-polarity solutions, by counterion coordination with the O atom. Methyl ethyl ketone differs f r o m acetone insofar as the molecule has three nonequivalent C atoms, each with its own c h a r a c t e r i s t i c acidity, i.e., each with its own heterolytic C - H bond rupture energy. The calculations showed (ef. Table 4) that the g a s - p h a s e stabilities of the various anion f o r m s of (II) fell off in the o r d e r

1374

TABLE 3. Bond Lengths and Valence Angles in Acetone and Its D e r i v a t i v e s Calculated by C N D O / B W Methods

t

Bondlengths,A

Colnpoun

c'o 2

I

c'o~

I j

(I) * I t,20(1,22) (III) 1,29 (VII) 1,21

t,54(t,55)1,571,53

[ __ Valence angles,dog

C'G4

C~C,C ~

C3C,0 ~

1t9(119,6) tl0 112

] 1,501'4tt'54(1'55) I t20131t22(120'8)

*gx~mental values, taken from [10]. shown in parentheses. TABLE 4. Atomic C h a r g e s * and R e s o n a n c e Bond E n e r g i e s for A c e tone and Its D e r i v a t i v e s Calculated by C N D O / B W Methods Atomic charges

Resonance bond energies, eV

Compound

(I) (m) (vH)

+0,482 +0,404 +0,528

O2

C3

-0,5t5 -0,570 -0,685

-0,155 -0,110 -0,147

C~

-0,t55 -0,337 -0,496

C,O ~

C,C 3

CLC4

24.4 t812 23,3

14,4 14.6 1311

14,4 20,2 15,2

*Numeration as for the reaction scheme. TABLE 5. Values of AH d (ev), the Enthalpy of Ketone D e p r o t o n a tion (I)

iI

(II)

Method d

(u

CNDO/BW calc. Experimental [12]

(V)

9 anion

t6,04 t5,78 [ll

I (IX) i

B

(X)

(XI)

t5,09 15,97

15,28 16,03

I

I

(XII)

(XIII)

{XVI)

15,28

t5,60

t4,99

(X) > (XD >> (IX). The acidity of the ~ - C H 3 group of (II) is a p p r o x i m a t e l y the s a m e as the acidity of this s a m e group in acetone itself. Although calculations of this type s y s t e m a t i c a l l y lead to low values of the d e p r o t o n a tion e n e r g y , the c o m p u t e d values of the CHB-grou p C H - a c i d i t i e s in (I) and (I1) w e r e in good a g r e e m e n t with the e x p e r i m e n t a l data (Table 5). The m o s t stable f o r m of m e s i t y l oxide, the conjugated f l - f o r m (V), is 5.0 k c a l / m o l e m o r e stable than the unconjugated a - f o r m (VI), and 14.3 k e a l / m o l e m o r e stable than the enol f o r m (IV). The s t a b l e ions of m e s i t y l oxide have s t r u c t u r e s (XII), (XIH), and (XV), while the ions with s t r u c t u r e s (XIV) and (XVI) a r e unstable and p a s s into (XV) through a b a r r i e r l e s s reaction. Among the stable anions, s t r u c t u r e s (XV) and (XIII) a r e e n e r g e t i c a l l y p r e f e r r e d . Some idea of the s t r u c t u r e s of the m e s i t y l oxide i s o m e r s and their anion can be obtained f r o m o p t i m i z a t i o n of the various g e o m e t r i e s (Table 6). H e r e , just as in the d e r i v a t i v e s of acetone, C N D O / B W methods tend to m i n i m i z e the difference between single and double bond lengths. Nonet h e l e s s , the values of the bond lengths and r e s o n a n c e bond e n e r g i e s obtained for (XV) (Table 7) leave no doubt that the c a l c u l a t e d s t r u c t u r e is actually that c o r r e s p o n d i n g to the c l a s s i c a l f o r m u l a of the r e a c t i o n s c h e m e . The e n e r g y of the unstable (XIV) s t r u c t u r e was e s t i m a t e d by a r b i t r a r i l y a s s u m i n g the dihedral angle for the CH~- group to be the s a m e as in the m o r e stable c o n f o r m a t i o n of (VII), with the b i s e c t o r plane failing in the plane of the c a r b o n a t o m skeleton. The s t r u c t u r e then c o r r e s p o n d s to f o r m u l a (XIV) and has an energy 10 k c a l / m o l e higher than that of s t r u c t u r e (XV). An e n e r g y difference of this o r d e r would a s s u r e b a r r i e r - f r e e rotation around the C - C H 2 bond with i s o m e r i z a t i o n to (XV). In other w o r d s , detachment of a proton f r o m the -/-CH 3 (V) group entails d i r e c t p a s s a g e into s t r u c t u r e (XV), and the s a m e is true of proton detachment f r o m the hydroxyl group of (IV). This r e s u l t points up the n e c e s s i t y of optimization of the g e o m e t r y in calculations on complex conjugated s y s t e m s . The protons of highest acidity in the molecule of (V) a r e those a s s o c i a t e d with the methine and 7 - m e t h y l groups. The high stability of (XIH) finds its natural explanation in the fact that the C a t o m of the anion c e n t e r is u n s a t u r a t e d and close to the CO group. The a - C H 3 group acidity is e s s e n t i a l l y the s a m e in (V) and in (I), the slight difference in deprotonation e n e r g i e s being p r o b a b l y due to incomplete o p t i m i zation of the s t r u c t u r e s of the methyl ethyl ketone and m e s i t y I oxide d e r i v a t i v e s . Thus the anion (XV) can be f o r m e d by d i r e c t deprotonation of any of the i s o m e r s f r o m (IV) to (VI), while the second m o s t stable anion

1375

T A B L E 6. Bond Lengths and Valence A n g l e s f o r M e s i t y l e n e Oxide I s o m e r s and T h e i r Anions C a l c u l a t e d by C N D O / B W Methods Bond lengths, A

Compound

(IV) (v)

(VI) (XII) (XIII) (XV)

C,O 2

C'C ~

C'O

C~C s

1.29 1'20 t,20 1,21 1,21 1,21

1,54 t,54 t ,54 t,53 t ,57 1,57

t,4t 1,54 t,53 1,42 t,56 t,56 i,58 t,4i t.54

i,~2

..I

Valence angies0 deg

CsC 6

CsC ~

C3C~C 4 CaC'O ~

C'C4C ~ C~C~C 6 C~C~C z

t,40 i,55 1,40 1,56 t,56 t,42

1,55 1,55 t,55 t,56 1,56 1,56

t28,8 t2t,8 t2t,3 t21,4 ii7,5 ti8,7

t31,7 t25,6 ii8,9 127,8 115,6 ii.q.6

t09,i 118,8 118,7 127,8 tt3,7 i 13,4

124,0 t21,8 t21,9 121,9 123,2 t29,2

t13,3 t2t,2 114,4 t2t,9 123,2 .t12,6

T A B L E 7. R e s o n a n c e Bond E n e r g i e s f o r M e s i t y l e n e Oxide and Its A n i o n D e r i v a t i v e s Cornpound

(IV) (V) (VI) (XII) (XIII) (XV)

Resonance bond ener its, eV ClO.~

C~C~

C,C4

C4C~

C5C~

C5Cr

t83 24,2 24,4 23,8 23,6 23,6

14~5 14,4 14,1 14,0 13,3 13.3

19,2 14,9 14,1 12,8 13.9 15.2

14.9 19,8 13,7 19,9 19,3 14.6

20.5 14.3' 20.6 13.9 13.9 t9.8

14,3 t4,3 t4,3 t4,0

I4,0 13,7

(XIII) c a n be o b t a i n e d only f r o m the f l - f o r m (V). A m o n g the c o m p o u n d s c o n s i d e r e d h e r e , the a c i d i t y i n c r e a s e s in the o r d e r : a c e t o n e , m e t h y l ethyl ketone, m e s i t y l e n e oxide.

CONCLUSIONS i. Quantum chemical CNDO/BW calculations with optimization of geometries have been carried out on the keto and enol forms of acetone, mesityl oxide, and methyl ethyl ketone, and on the earbanions resulting from various types of deprotonation in these compounds. 2. The keto forms of acetone and mesityl oxide are considerably more stable than the enol forms, while the enolate anions resulting through from hetorolytie rupture of the OH bond in the enol forms pass over into the keto form anions with zero activation energy. 3. The calculated gas-phase acidities of the compounds in question here increase in the order: acetone, methyl ethyl ketone, mesityl oxide. 4. Proton detachment from the T-CH3 group of the fl-form of mesityl oxide, from the secondary C atom of the o-form, or from the hydroxyl group of the enol form leads, in every case, to the same anion structure, namely an c~-form carbanion with an uneonjugated system of single and double bonds. This, and the anion resuiting from proton detachment from the ~-methine C atom of the fl-form~ are the most stable of the mesityl oxide carbanions. 5. The H atoms bound to the secondary C atom are the most acidic hydrogens in methyl ethyl ketone. The ~-CH3 group acidity is the same in each of the compounds covered by this work. LITERATURE CITED 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

1376

T . B . McMahon and P. Kebarle, J. Am. Chem. Soc., 98, 3389 (1976). E.M. Arnett, D. E. Johnson, L. E. Small, and D. Oaneea, Faraday Syrup. Chem. Sot., 10, 20 (1975). R . J . Boyd and M. A. Whitehead, J. Chem. Soe., D, 73 (1972). B.A. Murtagh and R. W. Sargent, Comput. J., 1__33, 185 (1970). V.N. Kondrat'eva (editor), Chemical Bond Rupture Energies. Ionization Energies and Electron Affinities [in Russian], Nauka (1974). A.C. Hopkinson and M. H. Lien, J. Chem. Phys., 67, 571 (1977). D. Izsak and R. J. Le Fevre, J. Chem. Soe., B, 251 (1966). S.K. PollaekandW. J. Hehre, J. Am. Chem. Soc., 99, 4845 (1977). R . P . Bell and P. W. Smith, J. Chem. Sot., B, 241 (1977). P.W. Allen, H. J. M. Bowen, L. E. Sutton, and O. Bastiansen, Trans. Faraday Soe., 48, 991 (1952).

11. 12.

THE

H. F i s c h e r and H. K o l l m a r , Theor. Chim. Acta, 16, 163 (1970). J . B . C u m m i n g and P. K e b a r l e , J. Am. Chem. Soc., 99, 5818 (1977).

TWO-ELECTRON

MOLECULAR

OXYGEN

OXIDATION

OF

COORDINATED

METHANOL WITH

BY

COPPER

IONS

S. O. T r a v i n , Yu. I. Skurlatov, N. V. G o r b u n o v a , a n d A. P . P u r m a l '

UDC 541.124:542.943.7:547.261

The Cu 2+ ion c a t a l y z e d oxidation of a s c o r b i c acid p r o c e e d s through a t w o - e l e c t r o n chain m e c h a n i s m of s u b s t r a t e oxidation which does not involve the f o r m a t i o n of either i n t e r m e d i a t e peroxides or s u b s t r a t e r a d i cals [1]. Since chain p r o p a g a t i o n p r o c e e d s through the r e a c t i o n of 02 with Cu(!0 [2], it has been s u g g e s t e d that a C u ( I ) - O 2 complex is f i r s t f o r m e d h e r e , and then e n t e r s into t w o - e l e c t r o n r e a c t i o n with the s u b s t r a t e . Studies of autooxidation kinetics [3-5] have shown that Cu(dipy)~ (I) (dipy = a , a ' - d i p y r i d y l ) c a n r e a c t with O2 to f o r m two different types of oxygen c o m p l e x e s : an oxygen adduct (dipy)2Cu+O2 [4] and a complex, with partial c h a r g e t r a n s f e r , r e s u l t i n g f r o m a m o n o m o l e c u l a r r e a r r a n g e m e n t of the l a t t e r (dipy)2CuO2+ (ID [5]. It s e e m e d of i n t e r e s t to study the r e a c t i v i t i e s of these two c o m p l e x e s , differing as they do in both the o r i e n t a t i o n of the 02 molecule r e l a t i v e to the Cu(1) ion and the d e g r e e of c h a r g e t r a n s f e r f r o m the Cu(I) to the 02 [3]. Methanol was c h o s e n as a model s u b s t r a t e since its oxidation by 02 is actively c a t a l y z e d by complexes of c o p p e r with o-phenanthroline, an analog of dipy [6]. Analysis of the data of [6] suggests that t h e r e should be a c o r r e l a t i o n between the r a t e of s u b s t r a t e oxidation, on the one hand, and the r a t e of the (I) - O2 reaction, on the other. P r e l i m i n a r y studies on the effect of CH3OH on the kinetics and m e c h a n i s m of the r e a c t i o n of (1) with O2 indicated [7] that (dipy)2Cu+O2 does not i n t e r a c t with CH3OH. Our investigation of the (I) - O 2 - C H 3 O H s y s t e m was t h e r e f o r e l i m i t e d to neutral solutions w h e r e f o r m a t i o n of the (dipy)2CuO2+ complex could be anticipated. EXPERIMENTAL

The kinetics of the i n t e r a c t i o n of (I) with 0 2 w e r e studied by the i n t e r m i t t e n t jet method [4, 7], optical homogeneity being a s s u r e d by mixing equal volumes of the O2 a n d Cu(dipy)~ solutions, each containing CH3OH at the s a m e concentration. A t i t r a t i o n method was followed in determining the s t o i c h i o m e t r y o f t h e r e a c t i o n [3]. Some of the e x p e r i m e n t s w e r e c a r r i e d out in s y s t e m s containing ~ 10 -6 m o l e / l i t e r of c a t a l a s e , the a i m t h e r e being to p r e v e n t oxidation of (I) and CH3OH by the hydrogen peroxide resulting f r o m the 02 reduction [8]. The p r o c e d u r e followed in p r e p a r i n g the solutions, of compound (I) and the c h a r a c t e r i s t i c s of the various r e a g e n t s have been d e s c r i b e d in [9]. The e x p e r i m e n t s w e r e c a r r i e d out at 22~ The a c c u r a c y of d e t e r m i n a t i o n of 7, the h a l f - r e a c t i o n t i m e of the Cu(dipy)~, was 5-10%; that of the d e t e r m i n a t i o n of n, the Cu(dipy)~ s t o i c h i o m e t r i c oxidation coefficient, 3-5%. DISCUSSION OF RESULTS The stepwise variation of r with pH, both in pure water and in alcoholic solutions [4, 7], indicates the formation of two types of complexes in both cases: an adduct complex (dipy)2Cu+O2 and a partial charge transfer complex (dipy)2CuO2+ (H) [3]. In substrate-free aqueous solutions of pH greater than 4.5, the rate of reaction of (I) at high concentration is limited by the rate of formation of complex (If), the latter rapidly reacting with a second Cu(dipy)~ ion [3]. The introduction of CH3OH into the system reduced the rate of oxidation of (I). The increase in T observed over the initial segment of the ~ vs [CH3OH] curve (Fig. 1) could not have been due to a change in the physical properties of the medium, since these become significant only at alcohol concentration in excess of 3 mole/liter [7]. With the oxidation of CH3OH proceeding through a radical mechanism [I0], an increase in resulting from a change of the Cu(1) ion environment is observed only at [CH3OH] > 10% by volume. The effect of low concentrations of CH3OR on T suggested that (1) is at least partially regenerated in the reaction of (II)

Institute of C h e m i c a l P h y s i c s , A c a d e m y of Sciences of the USSR, Moscow. T r a n s l a t e d f r o m I z v e s t i y a Akademii Nauk SSSR, S e r i y a K h i m i c h e s k a y a , No. 7, pp. 1480-1484, July, 1979. Original a r t i c l e s u b m i t t e d F e b r u a r y 23, 1978.

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