LITERATURE 1. 2. 3. 4. 5. 6. 7. 8. 9. I0. ii. 12.

CITED

W . E . K e l l e r , Compendium of P h a s e - T r a n s f e r Reactions and Related Synthetic Methods, Fluka AG, CH9470, Buchs, Switzerland (1979). I . A . E s i k o v a and S. S, Yufit, Izv. Akad. Nauk SSSR, Ser. Khim., 507 (1980). A. W e i s s b e r g e r , E. P r o s k a n e r , J . A. Riddick, and E. E. Toops, Organic Solvents, 2nd ed., Wiley, New Y o r k (1955). M. Finkelstein, R. S. P e d e r s e n , and S. D. R o s s , J. Am. Chem. Soc., 8_~1,2361 (1969). V . A . Yakovlev, Kinetics of E n z y m e C a t a l y s i s [in Russian], Nanka, Moscow (1965), p. 64. S . S . Yufit and I. A. Esikova, Dold. Akad. Nauk SSSR, 26_~5, 358 (1982). M. L i s s e l and E. V. Dehmlow, Chem. B e r . , 114, 1210 (1981). A. B r a n d s t r S m , Adv. P h y s . Org. Chem., 1_55, 267 (1977). A. BrandstrSm, Preparative Ion Pair Extraction, Apotekarsocieteten, Stockholm 0974). L.P. Hammett, Physical Organic Chemistry, 2nd ed., McGraw-Hill, New York (1970). O.A. Reutov, I. P. Beletskaya, and K. P. Butin, CH-Aeids [in Russian], Nauka, Moscow (1980), p. 37. S.S. Yufit and I. A. Esikova, Izv. Akad. Nauk SSSR, Set. Khim., 515 (1980).

REACTIONS PHASE

OF

CARBONYL

TRANSFER

COMPOUNDS

IN THE

PRESENCE

OF

CATALYSTS.

COMMUNICATION 12. ROLE OF QUATERNARY AMMONIUM CATION IN 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

I. A.

Esikova

and

S. S. Yufit

UDC

541.124:541.128:66.095.253:547.284.3

We had e s t a b l i s h e d p r e v i o u s l y [1, 2] that the r a t e of alkylation of acetone (HA) by 1 - c h l o r o - 3 - m e t h y l - 2 butene (prenyl chloride RX) in a t w o - p h a s e catalytic s y s t e m is l i n e a r l y dependent on the concentration of RX in the organic p h a s e and the activity of OH- in the aqueous phase. Also, we investigated the solubility of b e n z y l t r i e t h y l a m m o n i u m chloride (TEBA-C1, QC1) in organic p h a s e s with v a r i o u s compositions [3] and its c o n v e r s i o n s under the actual conditions in acetone alkylation [2]. The w o r k we are r e p o r t i n g h e r e was a i m e d at d e t e r m i n i n g the r e a c t i o n o r d e r with r e s p e c t to acetone and investigating the influence of QC1 concentration in the organic phase and the type of solvent on the rate of acetone alkylation by prenyl chloride. EXPERIMENTAL The p r o c e d u r e s used in the kinetic studies and in the a n a l y s i s of the products, as well as the c h a r a c t e r istics of the original r e a c t a n t s , have been p r e s e n t e d in [1]. The method of Newton and G r e g o r y [4] was used in d e t e r m i n i n g the initial r a t e s (W~ of f o r m a t i o n of 2 - m e t h y l - 2 - h e p t e n - 6 - o n e (MH) in the alkylation of acetone by RX in toluene o r benzene in the p r e s e n c e of a 50% aqueous solution of NaOH and TEBA-C1. The values obtained f o r the total concentration of TEBA-C1 and TEBA-OH in the m i x t u r e s of acetone with benzene a f t e r t r e a t m e n t with the 50% aqueous caustic solution a r e p r e s e n t e d in Fig. 1. Studies of the influence of the HA c o n c e n t r a tion on W 0 w e r e p e r f o r m e d at 40~ in s y s t e m s containing 25 m l of an organic p h a s e with [RX] = 5 m o l e s / l i t e r , [HA] = 0.8-3.2 m o l e s / l i t e r , benzene, and 1 g of t r i d e c a n e (internal s t a n d a r d f o r GLC); the aqueous p h a s e c o n s i s t e d of 10 g of a 50% NaOH solution and 0.23 g of TEBA-C1. We also i n v e s t i g a t e d the influence of the T E B A - C I c o n centration on W 0 (Table 1). The influence of v a r i o u s solvents on the rate of MG f o r m a t i o n (Table 2) was i n v e s tigated at 40~ in s y s t e m s consisting of 25 ml of organic p h a s e plus an aqueous phase (5 g NaOH + 5 g H20). The concentration of acetone in the aqueous NaOH solution was d e t e r m i n e d f r o m the data of [5], which a r e d e s c r i b e d by ~he equation log [HA] = A + B . [NaOH]. The solubility of acetone in aqueous solutions of v a r i o u s concentrations is shown in Table 3. F r o m t h e s e data it follows that the solubility of AH in 50% aqueous NaOH cannot be g r e a t e r than 2 . 10 -2 m o l e / l i t e r .

N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. i, pp. 53-58, January, 1983. Original article submitted April 2, 1982. 0 5 6 8 - 5 2 3 0 / 8 3 / 3 2 0 1 - 0 0 4 1 $07.50 9 1983 Plenum Publishing C o r p o r a t i o n

41

T A B L E i. Influence of Benzylt r i e t h y l a m m e n i u m Chloride (QC1) C o n c e n t r a t i o n on Specific Rate of Acetone Alkylation (4 0~ toluene, [RX] = 2.1 m o l e s / l i t e r , v o l u m e of o r g a n i c p h a s e 25 m l , aqueous p h a s e 10 g 50% aqueous NaOH solution)

[QCll [

[AH]

kobs:=~-105, sec"1

moles/liter

0,0100 0,0154 0,020 0,025 0,005 0,0i0 0,020 0,025 0,040 0,082 0,005 0,0t0 0.020 O.025 0,040 0,005 O,OiO 0,020 0,040 0,050 0,065 0,t13 0

t1,t 16,1 t8,5 19,0 i3,0 21,0 32,0 35,0 41,0 41,0 22,0 36,0 48,0 50,0 55,O

5.9-6,2 7,6-7,9

9,4

tt,0

33,0

47,0 61,0 7~0 77,0 8t,0 8t,0

tt,0

0

T A B L E 2. Influence of V a r i o u s Solvents on R a t e of Alkylation of Acetone (HA) by 1 - C h l o r o - 3 - m e t h y l - 2 - b u t e n e (RX) (40~ [RX] = 2, [HA] = 6.4 m o l e s / l i t e r , volume of o r g a n i c p h a s e 25 ml, s o l v e n t 6 ml, aqueous p h a s e 10 g 50% NaOH solution, QC1 0.23 g)

Solvent

e

Benzene Toluene

2,8

2,37

Chloroform*

4,8

Acetonet

Acetonltrfle

Dimethylsulfoxide

WO-I04 ,

moles/l.secl Yield, %

20,7 37,5 49

6,5

7,0 t,84 . 7,74 3,0 5,0

38 42 t9 45 35 45

* A c c o m p a n i e d by addition of dilmloc a r b e n e to r e a c t i o n p r o d u c t . [HA] = 11 m o l e s / l i t e r .

AS a r e s u l t of HA d e p r o t o n a t i o n u n d e r the influence of NaOH, the enolate of a c e t o n e is f o r m e d , the c o n c e n t r a t i o n of the enolate being d e t e r m i n e d by the equation K e [AH] aoH_ [A-] =

ntt,O

(1)

w h e r e K e is the e q u i l i b r i u m c o n s t a n t of HA d e p r o t o n a t i o n u n d e r the influence of OH-; a OH- is the activity of the h y d r o x y l ion [6]; all2 O is the activity of w a t e r [6]; [HA] is the c o n c e n t r a t i o n of a c e t o n e in the aqueous c a u s t i c .

42

TABLE 3. Concentrations of Acetone and E n o l ate of Acetone in Aqueous NaOH Solutions of Various Concentrations I

[HA] [51 [NaOH], %

5 10 20 30 40 45 50

aOH- [6]

0,9 2,55 8.54~ 35.4

~6

337 534

aH~O [6]

I

moles/liter

5,73 3.09 0,87 0,24 0,07 0,04 0,019

0,96 0,90 0,72 0,44 0,20 0,t3 0,09

INa+A-]

0,00029 0,00048 0,00057 0,00106 0,00338 0,00570 0,00610

The value of K e can be e s t i m a t e d f r o m the values of the dissociation constants of acetone and water, as Ke = KHA/KH20, HA @ H~O H

A-

@ H.~+O; KHA ~ 10-~~[7]

H20 -t- H20 ~- H~+O ~- OH-; KH.O = t.8.t0 -16 [7] The values of the concentrations of A- in the aqueous phase with different concentrations of NaOtt are p r e s e n t e d in Table 3, f r o m which it can be seen that in the p r e s e n c e of 50% NaOH, [A-] = 0.00610 m o t e / l i t e r with an initial concentration of HA in the aqueous phase 0.0190 m o l e / l i t e r . ~hus we can c o n s i d e r that approximately 30% of the ketone is enolized under these conditions.

DISCUSSION may

The mechanism be accomplished

OF

RESULTS

of ketone alkylation in the two-phase catalytic system includes a deprotonation stage that by several paths - either under the influence of the organic base QOH in the organic phase }I-Aorg 4- QO Ho,g ~-~QAorg @ H2Oaq

(D

or under the influence of the 50% aqueous NaOH solution in the aqueous phase, or at the interface HAaq -[- NaOHaq ~ NaAi~ HAi~

T NaOHaq ~- NaA~

~- H~Oaq

(I~D

@ H~Oaq

(I]~

The choice between reactions (ID and (HD is difficult; the choice between r e a c t i o n (I) and (IDor ( I I I ) c a n b e m a d e on the basis of the kinetic relationships in the alkylation. H reaction (D w e r e realized, the r e a c t i o n would be f i r s t - o r d e r with r e s p e c t to HAorg. If reaction (II) o r (HI) takes place, we should expect a linear dependence of the alkylation rate on the OH- activity and on the concentration of acetone in the aqueous phase. Owing to the low solubility of acetone in 50% aqueous NaOH (see Table 3), variation of the original [HA] in the organic phase does not change its concentration in the aqueous phase. Accordingly, the o r d e r of the alkylation r e a c t i o n under the condition that the deprotonation takes place through r e a c t i o n (ID should be z e r o . 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 acetone was d e t e r m i n e d f r o m the dependence of kob s = W0/[RX] on the original [HA] in the organic phase, in e x p e r i m e n t s in which p a r t of the acetone was r e p l a c e d by benzene. However, the addition of benzene to acetone leads to a reduction of the QCI concentration in the organic phase [3], and this lowers the alkylation r a t e (Fig. 2). F o r an analysis of the influence of [HA] on kob s, it is n e c e s s a r y ! to r e f e r the value of kob s to unit concentration of QC1. The value thus obtained is kob s = 1.8 9 10-3 l i t e r / m o t e . sec ([QX]org = [QC1]org + [QOH]org) and is also independent of [HA] inthe organic phase; i.e., 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 acetone is z e r o .

=Wo/[RX][QX]org

Thus, in the alkylation of acetone in the two-phase s y s t e m , the deprotonation p r o c e e d s in a c c o r d a n c e with r e a c t i o n (II), i.e., in the aqueous phase (or at the interface), and it is unrelated to the a p p e a r a n c e of QOH in the organic phase. This is consistent with p r e v i o u s r e s u l t s [1] indicating that the initial rate of acetone alkylation v a r i e s linearly with the activity of OH- in the aqueous phase. A study of the influence of the QC1 concentration on the alkylation rate has made it possible to c o n f i r m this conclusion. In a s y s t e m containing 50% aqueous caustic as the aqueous phase and a mixture of acetone with prenyl chloride ([HA] = 11 m o l e s / l i t e r ) as the organic phase, [QC1] was v a r i e d in such a m a n n e r that it did not e x c e e d the

43

1/k bs-105,moles/liter.see

r

[GF]§[0H~I~-ion/liter W0.105,moles/liter.sec

8,o /

3.2

6,o

.q,O~ O,!I

1.6

2~a

/

l

2

6

Ig

[HA],molesili~er

I

I

]

I

4ooz goo, o,aa6 .o,oos o,o~a

/#

[QX],moles/liter

Fig. 1

Fig. 2

-//

I

i

0

~0

I

I

I

I

gO i2O lgg 208

1/[QC1],liters/mole Fig. 3

Fig. 1. Concentration of (QC1 +QOH) in a c e t o n e / b e n z e n e m i x t u r e s at 19.5~ a f t e r shaking QC1 with 50% a q u e ous NaOH solution. QC1 2.3 g, organic phase 25 ml, aqueous phase 5 ml, p h a s e contact t i m e 4 rain. Fig. 2. Initial alkylation r a t e W 0 as a function of concentration (QC1 + QOtt) in organic phase. T e m p e r a t u r e 40~ solvent benzene, [RX] = 5 m o l e s / l i t e r ; c o n c e n t r a t i o n s [HA] in m o l e s / l i t e r a r e indicated by n u m b e r s at each data point. Fig. 3. Dependence of kobs =Wo/[RX] as a function of initial concentration of QC1 on r e c i p r o c a l coordinates. Concentrations of acetone and benzene, m o l e s / l i t e r : 1) 11 and 0; 2) 9.4 and 0.364; 3) 7.7 and 1.091; 4) 6.1 and 2.18. concentration of a s a t u r a t e d solution with r e s p e c t to QX ([QX]sa t = 0.115 m o l e / l i t e r [3]). It can be s e e n f r o m the data of Table 1 that with i n c r e a s i n g [QC1], the r e a c t i o n r a t e f i r s t i n c r e a s e s and then r e m a i n s constant. This s o r t of relationship indicates [8] that the f o r m a t i o n of 2 - m e t h y l - 2 - h e p t e n - 6 - o n e is p r e c e d e d by a r e v e r sible stage. Since the alkylation of acetone does not take place in the absence of QC1, it is evident that this r e v e r s i b l e stage is an exchange r e a c t i o n between NaA and QX, leading to the f o r m a t i o n of the organic ion p a i r QA, which then is alkylated by the I~X NaA Jr QX ~ QA + RX ~

kl

QA -t- NaX

ka RA +

QX

(IV) (V)

This is consistent with data obtained p r e v i o u s l y on the inhibition of aIkylation under conditions of i n t e r facial c a t a l y s i s by the addition of NaBPh 4, and is also consistent with the existence of an induction p e r i o d f o r c a t a l y s i s of the alkylation r e a c t i o n by t r i e t h y l a m t n e [2]. A workup of the r e s u l t s on the influence of [QCI] on kob s =W0/[RX] on d o u b l e - r e c i p r o c a l coordinates (Fig. 3) gives a s t r a i g h t line that is d e s c r i b e d by the equation 1

J

Km

1

kob~--k~ [Nah] + ~ [Nai] [QCI] -k-t - W-~ - - k~.,

(2)

k---- k2 [NaAI

This is p o s s i b l e only under the condition that [NaA] << [QX]. The p r e s e n c e of a s u b s t a n t i a l e x c e s s of NaOH in the aqueous phase and of AH in the organic phase e n s u r e s that Na+A - will be s t a t i o n a r y during the entire p r o c e s s ; h e r e , [A-Na +] = 6 9 10 -3 m o l e / l i t e r . A c o m p a r i s o n of [A-Na +] in the aqueous p h a s e and [QX] in the organic p h a s e shows that they a r e e i t h e r s i m i l a r o r differ by an o r d e r of magnitude. This m e a n s that the condition [A-Na +] << [QX] is r e a l i z e d only at the interface; obviously, in an exchange r e a c t i o n p r o c e e d i n g i n t e r f a c i a l l y , the only ion p a i r s Na+A - that will take p a r t will be those located at the s u r f a c e of the aqueous phase. Thus, f o r the f i r s t t i m e , d i r e c t kinetic evidence has been obtained

44

TABLE 4. Values of kap p and K m , a p p in S y s t e m s Containing Different Amomlts of Acetone and Toluene Cohen., moles/liter acetone

toluene

1t 9,4 7,7 6,1

0 0,364 1,09t 2,182

k

"10 5 , aPsePc'l

Km app'i0 3, moles/llter

8,7 71,4 62,5 45,9

7,9 tt,29 t9,56 27,8

Km,ap p (1 + [I]/K I' ).103moles/liter

l/k

"I

aPP

~g

"10"3 see

J0 20

~ , 5 ~ f0~ "

~

TI

I

T r

I

z

to

l

z,o

[I], moles/liter

I

~

r

r

I

i

40

~

I

I

I

I,o

i

f

i

d

I

I

2,o

~ A-...L-L.

J,O

[I], m oles//iter

Fig. 4. Dependence of 1 / k a p p on c o n c e n t r a t i o n of toluene (I).

Fig. 5. Dependence of K m , a p p on concentration of toluene (I).

that the f o r m a t i o n of the organic ion p a i r p r o c e e d s interfacially, and that the kinetics of aikylation a r e not d e t e r m i n e d by t r a n s f e r of QOH to the organic p h a s e and deprotonation of the HA u n d e r the influence of QOH. This m e a n s that r e a c t i o n (I) e i t h e r does not take p l a c e at all or that it does not d e t e r m i n e the alkylation ldnetics. The s a m e type of dependence of kob s on [QX] is m a i n t a i n e d if p a r t of the acetone is r e N a c e d by toluene; h o w e v e r , this does lower the r e a c t i o n r a t e , in p r o p o r t i o n to the amount of toluene in the s y s t e m . Since 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 acetone is z e r o , the o b s e r v e d effect can be explained by an "inhibiting" effect of toluene. On double r e c i p r o c a l coordinates (Fig. 3), bundles of lines a r e obtained, i n t e r s e c t i n g at a c o m m o n point; this indicates m i x e d - t y p e inhibition by toluene [8]. In our case, " m i x e d inhibition" a s s u m e s a r e v e r sible bonding of QX and QA by toluene, leading to the c o r r e s p o n d i n g solvate c o m p l e x e s , the p o s s i b i l i t y of f o r m a tion of which was shown in [9-111. This p r o d u c e s changes in both kap p and K m , a p p

kapp --~ "i @ [I]/KI'

~hn,app =

K m ( t @ [~]/KI) I & [I]/KI'

(4)

!

H e r e , K I = [QX][I]/[QXI] and K I = [QA][I]/[QAI]; I t s t o l u e n e ; Q X I and QAI are c o m p l e x e s of toluene with QX and Q A, r e s p e c t i v e l y . Data f o r s y s t e m s containing different a m o u n ~ of toluene were analyzed g r a p h i c a l l y to d e t e r m i n e K m , a p p and kap p (Table 4). An mlalysis of the dependence of 1 / k a p p on [I] (Fig. 4) and of Km,app(1 + [I]/K~) on [I] I (Fig. 5) gave the values K I = 2.45 and K I = 0.395 m o l e / l i t e r . Since g r e a t e r dissociation constants of the complex c o r r e s p o n d to l o w e r stability, we can c o n s i d e r that QX is bound by toluene m o r e strongly than is QA. This can be explained by the g r e a s lipophilicity of QA and by the f a c t that C1- is s o l v a t e d by toluene b e t t e r than is A-. If the solvent added to the organic s y s t e m is not an a r o m a t i c h y d r o c a r b o n , but r a t h e r a solvent that does not have mW inhibiting effect, the r a t e of alkylation should not be lowered, but the side p r o c e s s e s in which acetone p a r t i c i p a t e s should be r e t a r d e d [1]. In Table 2 we have l i s t e d the yields and initial r a t e s of HA a l k y l a tion by p r e n y l chloride. It will be noted that t h e s e quantities a r e not dependent on the d i e l e c t r i c constant (~) of the solvent, and this indicates that the i n c r e a s e in the d e g r e e of d i s s o c i a t i o n of the ion p a i r s with i n c r e a s i n g e , which m u s t lead to a d e c r e a s e in the concentration of the ion p a i r s as a r e s u l t of the i n c r e a s e in f r a c t i o n of

45

free A-, does not play any significant role, even though, according to the data of Br~[ndstrSm [12], the rate of C-alkylation of carbonyl compounds depends on the concentration of the ion pair. The result that we have obtained may reflect the fact that the alkylation of the organic ion pair can take place both in the bulk organic phase and directly on the interface. CONCLUSIONS i. In the alkylation of acetone by l-chloro-3-methyl-2-butene in a two-phase system in the presence of a 50% aqueous NaOH solution and benzyltriethylammonium chloride, the deprotonation of the acetone takes place in the aqueous phase or at the interface, and the deprotonation is not related to transfer of the OH- ion to the organic phase. The reaction is zero-order with respect to acetone. 2. On the basis of the influence of the benzyltriethylammonium chloride concentration on the rate of acetone alkylation, it has been established that the formation of 2-methyl-2-hepten-6-one is preceded by a reversible reaction between the acetone enolate and the catalyst at the interface. 3. Toluene lowers the alkylation rate as a result of reversible bonding of the catalyst and the organic ion pair; the catalyst is bonded approximately 6 times more strongly than is the organic ion pair. 4. Changing the solvent has very little effect on the rate of formation of 2-methyl-2-hepten-6-one; this indicates that there is no relationship between the process rate and the dielectric constant of the solvent. LITERATURE i. 2. 3. 4. 5. 6. 7. 8. 9. i0. ii. 12.

46

CITED

I.A. Esikova, V. F. Kucherov, B. A. Rudenko, and S. S. Yufit, Izv. Akad. Nauk SSSR, Ser. Khim., 1468 (1979). I.A. Esikova and S. S. Yufit, Izv. Akad. Nauk SSSR, Set. Khim., 1996 (1981). S.S. Yufit and I. A. Esikova, Izv. Akad. Nauk SSSR, Ser. Khim., 2693 (1981). V.A. Yakovlev, Kinetics of Enzyme Catalysis [in Russian], Nauka, Moscow (1965), p. 64. V.V. Kafarov (editor), Handbook of Solubilities [in Russian], USSR Academy of Sciences Press, Moscow (1962), Book I, p. 85. G.I. Mikulin (editor), Problems in Chemical Physics of Electrolyte Solutions [in Russian], Khimiya, Leningrad (1968). O.A. Reutov, I. P. Beletskaya, and K. P. Butin, CH-Acids [in Russian], Nauka, Moscow (1980). I.V. Berezin and A. L. Klesov, Practical Course in Chemical and Enzyme Kinetics [in Russian], Moscow University Press, Moscow (1976), p. 79. A.J. Cornish-Bowden, Principles of Enzyme Kinetics, Butterworths, Woburn, Mass. (1976). K.P. Mishchenko and G. M. Polteratskii, Problems in the Thermodynamics and Structure of Aqueous and Nonaqueous Electrolyte Solutions [in Russian], Khimiya, Moscow (1968), p. 271. I.A. Esikova and S. S. Yu~it, Zh. Fiz. Khim. B, 30, 106 (1982). A. Br~adstr~m, Acta Chem. Scand. B, 30, 203 (1976).