2.

3. 4. 5. 6.

7. 8.

G. F. B u r y a , L. D . A b r a m o v i c h , L. R. A n d r e e v a , A. K. E r e m i n , and M. I. Vinnik, Izv. Akad. Nauk SSSR, Ser. Khim., 304 (1978). G. F. B u r y a , L. D. A b r a m o v i c h , L. R. A n d r e e v a , A. K. E r e m i n , and M. I. Virmik, Izv. Akad. Nauk SSSR, Ser. Khim., 556 (1978). L. L. Kuznetsov and B. V. Gidaspov, Zh. Org. Khim., 1___0,263 (1974). L. L. Kuznetsov and B. V. Gidaspov, Zh. Org. Khim., 10, 541 (1978). S. P a t a i (editor), The C h e m i s t r y of the Amino Group, I n t e r s c i e n c e , New Y o r k - L o n d o n (1968). G. L. Panchenko and V. P. L e b e d e v , C h e m i c a l Kinetics and C a t a l y s i s [in Russian], Izd. Mosk. Univ. (1961). D. V. Bonthorpe, E. D. Hughes, and D. L. H. Williams, J. Chem. Soc., 5349 (1964).

REACTION

OF

CARBONYL

PRESENCE

OF

PHASE

COMPOUNDS

TRANSFER

IN THE

CATALYSTS

COMMUNICATION 1. THE ALKYLATION OF ACETONE BY 1-CHLORO-3-ME THYL-2-BUTENE I. A . E s i k o v a , B. A . R u d e n k o ,

UDC 541.128:66.095.253:547.284.3

V. F . K u c h e r o v , a n d S. S. Y u f i t

The alkylation of acetone by 1 - c h l o r o - 3 - m e t h y l - 2 - b u t e n e (prehnylchloride, PC) in a t w o - p h a s e s y s t e m (organic solvent - 50% aqueous solution of NaOH or KOH) containing a phase t r a n s f e r c a t a l y s t ( t e r t i a r y a m m o n i u m salt, Q+X- [1]) is u s e d in the industrial p r e p a r a t i o n of 2 - m e t h y l - 2 - h e p t e n - 6 - o n e (methylheptenone, MH), a key compound in the s y n t h e s i s of f a t - s o l u b l e vitamins and p e r f u m e s . Under i n d u s t r i a l conditions, the s y n t h e s i s p r o c e e d s through the following r e a c t i o n s [2]: CHs

CH3

\c = o ~

l CHsCCH~CCH a diac~tone alcohol~ DAA

CHs

OH

0

(,}Ipc Ctls \ CHf'

CH s

\

/ EH~

(4)I

CH~ \ C=CHCHzCH~CCH3 C=CHCCH s mesityl oxide, MO il

(MID 6

0

CHs \

C=CHCH~ \

CH3 \ / C=CHCH~ / EHj

I1

CH~/

/ \CHCCII~ / Ii

o

Dfl$opcntcnyl acetone, DIPA

CH3

CH~ / CH~CH=C / \ C=CCOCII3 CII~ isopentenyl-B-me~ityl oxide, (IB)

+ CH3

\

f CHz

/

/ CH~CH=C

CCHCOCH3

\

CH.~ CH~

Isopcntenyl-a-mesityl oxide (la)

In dilute alkaline solution, PC can also h y d r o l y z e to y , y - d i m e t h y l a l l y l alcohol (DMAA) and i s o m e r i z e to the t e r t i a r y chloride (TC), which can in turn, pass o v e r to dimethylvinylcarbinol (DMVC). N. D. Z e l i n s k i i Institute of Organic C h e m i s t r y , A c a d e m y of Sciences of the USSR, Moscow. T r a n s l a t e d i'rom ! 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. 1468-1474, July, 1979, Original a r ticle s u b m i t t e d F e b r u a r y 24, 1978.

9568-5239/79/2807-1367507.50

0 1 9 8 0 Plenum Publishing C o r p o r a t i o n

i367

c. molcllirel: 2

8

J

8

I

~C 180

i

I

160

J

I

/~0

I

I

I

fZO

100

I

I,

8o

I

i

60 50

I

50 ~

Fig. 1

60

IXO

180 rnin

Fig. 2

Fig. 1. C h r o m a t o g r a m of a p r e p a r e d mixture: 1) Isoprene; 2) acetone; 3) PC; 4) MO; 5) 2,4dichloro-2-methylbutane; 6) C13H28; 7) (H); 8) MH; 9) unidentified product; 10) DAA; 11) 2c h l o r o - 2 - m e t h y l - 4 - b u t a n o l ; 12) (Ic~); 13) (Ifl); 14) DIPA. Fig. 2. Kinetic c u r v e s for the formation of various alkylation products: 1) PC; 2) MH; 3) DIPA; 4) (Ic~ + Ifl) (10 g 50% aqueous NaOH solution, 0.001 mole TEBA, 0.05 mole PC, 0.25 mole acetone, 40~ The p r e s e n t w o r k is a study of the kinetics of these reactions. EXPERIMENTAL The PC used here was a purified industrial product. All of the experiments w e r e c a r r i e d out with its 59-60~ (110 mm) boiling fraction which contained 80% PC, 20% TC, and a c e r t a i n amount Of the dichloride (2,4-dichloro-2-methylbutane, DC). Tests showed that the TC neither i s o m e r i z e d nor e n t e r e d into the alkylation r e a c t i o n during the kinetic experiments. Exact compositions w e r e obtained by c h r o m a t o g r a p h i c analysis. The values of the kinetic p a r a m e t e r s w e r e the s a m e , r e g a r d l e s s of whether they w e r e obtained with 97% PC (PMR data) o r with an 80%O mixture. The acetone was an Analytical Grade m a t e r i a l which had been dried over K2CO3 and redistilled; the MH, DAA, and M O w e r e purified by distillation; boiling points, ~ MH, 75-76 (25 mm); MO, 131; DAA, 165-166. The KOH and NaOH w e r e cp grade m a t e r i a l s , and the H20 w e r e distilled. The catalyst, t r i e t h y l b e n z y l a m m o n i u m chloride (TEBA), was synthesized by the usual m e t h o d s . E x p e r i ments c a r r i e d out under standard conditions (5 g NaOH, 5 g H20 , 0,23 g TEBA, and 5 g PC, at 40~ were used to determine whether AS was f o r m e d f r o m the PC. Since neither isoprene nor the h y d r o l y s i s products could be detected after 1.5 h of reaction, f o r w a r d and r e v e r s e T C - P C i s o m e r i z a t i o n was eliminated f r o m account. The kinetic experiments w e r e c a r r i e d out in a t h e r m o s t a t e d (~ I~ hydrogenation duck r e a c t o r with rapid agitation. Into this r e a c t o r was introduced 5 g of NaOH, 5 ml of H20 , and 0.23 g of TEBA; the mixture was brought up to the working t e m p e r a t u r e , shaken until the alkali dissolved, and the acetone, PC~ and s t a n d a r d C13H28 introduced. The solubility of the organic components in the aqueous l a y e r was neglected in calculating the concentrations. Samples w e r e periodically withdrawn f r o m the r e a c t o r for d i r e c t c h r o m a t o g r a p h i c analysis. The r e a c t i o n mixture was analyzed on a K h r o m - 4 c h r o m a t o g r a p h equipped with a flame ionization detector and p r o g r a m m e d for heating at 6 d e g / r n i n over the range f r o m 20 to 200~ the column, 2.4 x 0.4 cn] in dimensions, was made of glass and was packed with 15% Reoplex-400 on 0.2-0.25 m m C h r o m a t o n N-AW. Quantitative analyses w e r e c a r r i e d out with the aid of previously d e t e r m i n e d calibration coefficients, using t r i decane (C13H28) as an internal standard (Fig. 1). The a c c u r a c y of the analytic determinations was • The value of W 0, the r e a c t i o n rate at time z e r o , was d e t e r m i n e d by a N e w t o n - G r e g o r y t r e a t m e n t of the kinetic curves for MH f o r m a t i o n [3] (Fig. 2). The a c c u r a c y of determination of the rate constant k n = W 0 / [PC]0 • 5-7%. DISCUSSION

OF RESULTS

In o r d e r to show that the r e a c t i o n was not diffusionally controlled, experiments of 1 h duration w e r e c a r r i e d out at 50~ working at a 1 : 5 P C - t o - a c e t o n e ratio and varying the rate of agitation of the r e a c t o r . The 1368

c, mole/liter

a

I

0,5 a,j ~

~

~

x~

o,1 f

I

I

I

b

I

I,,,

2 TABLE 1. Effect of Acetone C o n c e n t r a tion on the Specific Rate of Methylheptenone F o r m a t i o n (10 g of 50% aqueous NaOH solution, 0.23 g TEBA, 40~

.,.61x.....,-0

ZO

/Ig

5g men

Fig. 3. Kinetic c u r v e s for the f o r marion of MH (1), and DAS (2), at various r a t e s of agitation (conditions as for Fig. 2): a) vigorous agitation; b) weak agitation.

Vol.of I [pc] ~Acetone] w0.104 mole/ kn = Wo/fPC]" 10s' organic Iphase, ml[ mole/liter iiter.sec seci9,0 i2,4. 20,4 24,3

] 7,8 "l 0,78 4,68 4,68 4,6 1,6 5,7 2,88

i,78 i,o i,06 1,33

I

2,28 2,33 2,32 2,34

yield of MH relative to the PC consumed was independent of the agitation rate over the interval f r o m 600 to 900 v i b / r a i n . Below this range, the y i e l d of MH fell, and the MH-to-DAS ratio changed (Fig. 3). Since the rate of alkylation was unaffected by the rate of agitation in the 500-600 v i b / r a i n range, the r e a c t i o n kinetics were not diffusionally controlled. F u r t h e r confirmation of this point was found in the fact that the activation energy had its n o r m a l value here. The effect of t e m p e r a t u r e on the rate of MH formation (37% NaOH, [acetone] = 9.44 m o l e / l i t e r ) was reflected in the values of kn = W 0 / [PC]0 = 1 . 0 . 1 0 -4 see -1 at 318~ and 3.76" 10 -4 sec -I at 3 3 1 ~ , which gave the value of E a, the activation energy, as 14.55 k c a l / m o l e . It can be seen f r o m Fig. 3 that the alkylation and aldol condensation w e r e differently affected by changes in the rate of agitation, and must t h e r e f o r e follow different m e c h a n i s m s . This difference could be due to the fact that t r a n s f e r of an enolate or hydroxyl anion into the organic phase is r e q u i r e d for alkylation but not for the aldol condensation. The fact that the rate of consumption of acetone r e m a i n e d unchanged during a 1.5 h reaction under standa r d conditions ([acetone] = 9.4, [PC] = 1.88 m o l e / l i t e r ) (39% conversion) indicates that one is concerned here with a p r o c e s s which is z e r o t h - o r d e r with r e s p e c t to acetone. The s a m e conclusion also followed f r o m the r e sults of experiments in which the concentration of acetone was v a r i e d in s y s t e m s containing an excess of PC (Table 1). In experiments involving a 10-fold, or better, excess of acetone, it was found that the initial rate of MH formation i n c r e a s e d linearly with the PC concentration, which indicates that the reaction was f i r s t o r d e r with r e s p e c t to this component (Table 2). Upon r e p l a c e m e n t of a part of the acetone by 6.5 ml of toluene [ P C - t o - a c e t o n e ratio, 1.54 : 5.93 m o l e / liter (Table 3)], the initial rate of MH formation, W0, took on the value 3 . 3 4 . 1 0 -4 mole / ( l i t e r " sec), while the value of kn r o s e to 2.2 9 10 -4 sec -1. Dilution with toluene d e c r e a s e d the equilibrium concentration of DAS and s u p p r e s s e d the f o r m a t i o n of MO, the r e s u l t being that (In) and (Ifi), the products f r o m MO alkylation, did not appear here. The o r d e r of the r e a c t i o n with r e s p e c t to the alkali was d e t e r m i n e d in a s e r i e s of experiments at 40~ Here the concentration of the NaOH in the aqueous phase was varied f r o m 15 to 25 moles / 1000 g H20: It was found that the specific r e a c t i o n r a t e , W0 / [ P C ] 0 , v a r i e d linearly with the OH- ion activity [4] (Table 4). T h i s was consistent with the o b s e r v a t i o n that the MH yield fell f r o m 51 to 8.5% when the concentration of alkali in

1369

TABLE 2. Effect of the Initial Concentration of 1C h l o r o - 3 - methylbutene-2 (PC) on the Rate of MH F o r mation (10 g 50% aqueous NaOH solution, 0.001 mole TEBA, 40~ [PC]

[[Acetone]W0.104,mole/

mole/liter

TABLE 3. Buildup of P r o d u c t s f r o m the Reaction of PC and Acetone in the P r e s e n c e of Toluene (10 g 50% aqueous NaOH solution, 0.001 mole TEBA, [PC] = 1.54 m o l e / l i t e r , [acetone] = 5.9 m o l e / l i t e r , 6.5 m l toluene, 26 ml organic phases 4O~

(liter-sec) e, min

0,374 0,42i 0,435 0,49i 0,509 0,795 i,t t,15

i2~5 i2,6 i2,4 i2,3 i2,4 1i,6 ii,3 t0,8

'

mole/liter

3,1

3,t8 2,0 2,66 i,75 4,42 6,94 7,51

0 25 60 120 i80 240 300

0,296

0,o~6

0,765

0,O52 0,069 0,071 0,066

0,535 0,603 0,678

o,o~

O,O825 0,0863 0.0985 0,t04 0,t22

the aqueous phase was r e d u c e d f r o m 50 to 28%. This reduction in the alkali concentration also markedly inc r e a s e d the PC hydrolysis. The substitution of KOH for the NaOH had very little effect on the r a t e of MH f o r mation. The fact that the initial rate of MH f o r m a t i o n v a r i e d linearly with the NaOH activity in the aqueous phase (aOH-) suggested that the alkylation s c h e m e must involve the r e v e r s i b l e deprotonation of acetone under the action of the alkali. Although this r e a c t i o n can take place either at the w a t e r - o r g a n i c phase interface or in the aqueous phase itself, it involves only those acetone molecules which pass into the aqueous phase. Although PC hydrolysis proceeds readily in dilute solution, it a l m o s t certainly does not o c c u r in conc e n t r a t e d alkaline solutions (->33%) where the w a t e r is completely bound up in hydration of the NaOH and KOH molecules [4, 5]. Differences between the KOH and the NaOH a r i s e because of changes in the activity of the w a t e r in the c o u r s e of the reaction. Since w a t e r is evolved in the alkylation p r o c e s s , the alkali concentration falls to 36% by the time the reaction is completed. The H20 activity changes, at the s a m e time, its value, rising to ~ 0.45 in the KOH solution to ~ 0.25 in the NaOH solutions [4] (effects f r o m salt formation a r e not c o n s i d e r e d here). Thus NaOH solutions should be used if h y d r o l y s i s effects a r e to be avoided. It is generally true that organic compounds tend to be sparingly soluble in 50% aqueous alkali solutions. A study of the data on the solubility of acetone in c o n c e n t r a t e d aqueous NaOH solutions, and the solubility of NaOH in acetone [6], suggests that the concentration of acetone in the aqueous l a y e r s of the s y s t e m under disc u s s i o n here must be quite low, r e g a r d l e s s of whether the compound enters the l a y e r through dissolution, adsorption, or enolate formation, C o n v e r s e l y , the alkali dissolves to only a limited extent in the acetone. The fact that organic molecules a r e "salted out" by the alkali and pass to the s u r f a c e of the aqueous l a y e r would in itself account for the inhibiting effect of s u r f a c e - a c t i v e substances (SAS) in alkylation reactions [2]. Those SAS which are neither catalysts o r inhibitors reduce the r e a c t i o n rate, occupying a part of the o r g a n i c - a q u e o u s interface, despite the fact that the interfacial a r e a i n c r e a s e s . All of this suggests that the catalysts may act through desorption of the organic anions f r o m the s u r f a c e of the aqueous phase. This is also indicated by the fact that a l t e r a t i o n of the volume of this phase has little effect on the alkylation rate (cL also [2]). The fact that the r e a c t i o n is z e r o t h - o r d e r with r e s p e c t to acetone in s y s t e m s containing an excess PC is readily understood if it is a s s u m e d that it is only those molecules which a r e soluble in the 50% alkali s o l u tion, and a r e converted to Na acetone derivatives, which come into play here. According to the data of [6], a 27% aqueous NaOH solution will dissolve 1.1% of its own weight of acetone, i.e., 10 g of a 50% aqueous NaOH solution would dissolve no m o r e than 0.1 g of acetone, and possibly much less. F r o m this it would follow that our determinations of the o r d e r of the alksTlation r e a c t i o n with r e s p e c t to acetone w e r e always c a r r i e d out in s y s t e m s in which the aqueous phase was s a t u r a t e d with the ketone. As a r e s u l t the rate of alkylation did not v a r y with the acetone concentration of the organic phase, and the r e a c t i o n appeared formally to be z e r o t h - o r d e r with r e s p e c t to the acetone. Cation exchange between the Na-derivative of acetone and the c a t a l y s t could lead to the f o r m a t i o n of an i o n - p a i r , soluble in the organic l a y e r , which could be alkylated to MH by the t)C, the r e s u l t being that the r e action would appear to be f i r s t - o r d e r with r e s p e c t to the l a t t e r component 1370

TABLE 4. Effect of the Aqueous Alkali Solution on the Alkylation Rate Constant (5 ml H20 , 0.001 mole TEBA, [PC] = 1.76 m o l e / l i t e r , [acetone] = 9.44 m o l e / l i t e r , 26 ml organic phase, 40~ OH'ion ] OH" activity ] " / " " mole/1000 aetivi~coef-' molell000 fieient [4] g Hz0 - mo~ nter g H20

[NaOtt],

27 37 50

I0 t5 25

3,22 ~7t 28,0

I

32,2 t45,5 700

29,8 t27,2 538,4

kn" I04,

1 t

SeC" i

0,3 t,0 4,98

CHaCOCHaorg ~-~ CHzCOCH3aq -~ NaOH ~ [CHaCOCH3]- Na~q + H20 QX + Na0H ;2 QOH + NaX [CH3COCH~]- Na~q + QOH ~ [CHaCOCH2]-Qorg+ -~ NaOIt [CHaCOCH~]- Qorg+ + ttX org* -> CI-I3COCH2Rorg+ QX CH3COCHag

Alkylation in s y s t e m s containing e x c e s s acetone is m o r e rapid, by a whole o r d e r of magnitude, than alkylation in s y s t e m s containing an e x c e s s of PC. R e p l a c e m e n t of a p a r t of the acetone by toluene also tends to r e t a r d the alkylation p r o c e s s . This could r e f l e c t changes in the solubiIity of the c a t a l y s t (salts o r hydrides), or the o r ganie ion p a i r , in the organic l a y e r . S i m i l a r effects in solutions of t e t r a a l k y l a m m o n i u m s a l t s in benzene have been d e s c r i b e d in [5]. The alkylation of acetone can be a c c o m p a n i e d by various side r e a c t i o n s , principally those shown as (2) (3), and (4) in the r e a c t i o n s c h e m e . Although dealkylation (reaction 2) is unavoidable h e r e , the CH acidities of the ce-CH 3 groups of IVlH and acetone being of the s a m e o r d e r of magnitude, it is, to a c e r t a i n d e g r e e , cont r o l l e d by the difference in the MH and acetone concentrations and by the difference in the a d s o r p t i o n of these compounds on the s u r f a c e of the aqueous alkali solution. In g e n e r a l , the DIPA yield is only 10-15% of the yield of MH. The f o r m a t i o n of DAS c e a s e s a f t e r 5-10 rain, and the c o n c e n t r a t i o n of the compound r e m a i n s constant f r o m then until the end of the reaction. The initial r a t e of DAS f o r m a t i o n under s t a n d a r d conditions (WDAS) was 4.2" 10 -a mole / ( l i t e r . sec). Under these s a m e conditions, the value of W0MH was 0.264.10 -3 mole / ( l i t e r . sec) (initial PC concentration, 0.421 m o l e / l i t e r ) . The e q u i l i b r i u m concentration of DAS i n c r e a s e d with a r e duction in t e m p e r a t u r e . Thus with 37% aqueous alkali solution its value r o s e f r o m 0.14 m o l e / l i t e r at 58~ to 0.23 m o l e / l i t e r at 40~ Since the DAS c o n c e n t r a t i o n r e m a i n e d constant to the end of the r e a c t i o n , while the PC c o n c e n t r a t i o n fell to z e r o , it was r e a s o n a b l e to a s s u m e that the m e a s u r e d quantity was actually the equil i b r i u m DAS concentration. The position of the point of e q u i l i b r i u m is d e t e r m i n e d by the t e m p e r a t u r e and the c o n c e n t r a t i o n of the alkali in the aqueous phase. A reduction in the t e m p e r a t u r e was found to i n c r e a s e the DAS concentration, which would be expected f r o m the fact that aldoI condensation r e a c t i o n s a r e highly e x o t h e r m i c . This r e a c t i o n can be readily s u p p r e s s e d by the addition of toluene, aldol condensations differing in this r e s p e c t f r o m alkylation r e a c t i o n s . By i t s e l f the f o r m a t i o n of DAS has no effect on the r a t e of PC consumption but the compound can undergo r e a c t i o n (4) to f o r m the highly r e a c t i v e MO which i t s e l f alkylates to give the and fi f o r m s of i s o p e n t e n y l m e s i t y l oxide [(Ic~), (Ifl)]. C o n s i d e r a b l e amounts of PC might be c o n s u m e d in these r e a c t i o n s ; aside f r o m a reduction in the DAS concentration, t h e r e is no m e a n s of controlling these p r o c e s s e s other than that of s e l e c t i n g a different c a t a l y s t , fi-elimination and MO f o r m a t i o n requiring the p r e s e n c e of TEBA in the s y s t e m . The authors would like to thank A. A. Bakhtinov, I. I. Sidorov, L S. Aul'chenko, and L. A. Kheifits for useful d i s c u s s i o n s of this w o r k and for having furnished the prehnylehloride and the compounds needed for c h r o m a t o g r a m i n t e r p r e t a t i o n , and T. I. Konstantinova for help with the GL c h r o m a t o g r a p h i c a n a l y s e s . CONCLUSIONS 1. The r a t e of alkylation of acetone by prehnylchloride (PC) i n c r e a s e s l i n e a r l y with an i n c r e a s e in the OH- ion activity and the PC concentration. The fact that the r e a c t i o n a p p e a r s to be z e r o t h o r d e r with r e s p e c t to acetone is due to the deprotonation of acetone in the aqueous phase, the r e s u l t being that the acetone c o n c e n t r a t i o n in the 50% NaOH solution is that c o r r e s p o n d i n g to s a t u r a t i o n , r e g a r d l e s s of the original ketone content of the s y s t e m . 1371

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.

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