Ring Transformation of Tetrahydropyran into Piperidine over

49 Ring Transformation of Tetrahydropyran into Piperidine over Dealuminated L-Zeolites YOSHIO ΟΝΟ, ANAND HALGERI, MASAMICHI ΚΑΝΕΚΟ, and KOU HATADA

Downloaded by FUDAN UNIV on March 10, 2017 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0040.ch049

Department of Chemical Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan 152

ABSTRACT The reaction of tetrahydropyran with ammonia to give piperidine has been studied over L-zeolites. Dealumination of the zeolite enhanced the ring conversion. The reaction kinetics was determined and the reaction mechanism was proposed. The effects of dealumination on the thermal stability and the acidic property were also studied. Introduction R e c e n t l y , we have r e p o r t e d t h a t s y n t h e t i c z e o l i t e s are v e r y e f f e c t i v e c a t a l y s t s f o r t h e r i n g c o n v e r s i o n o f l a c t o n e s and c y c l i c e t h e r s i n t o t h e c o r r e s p o n d i n g l a c t a m s and c y c l i c i m i n e s i n t h e p r e s e n c e o f ammonia Ç1-5). I t s h o u l d be n o t e d t h a t t h e hydrogen form o f L - z e o l i t e ( H L ) shows h i g h e r s e l e c t i v i t y t h a n t h e hydrogen form o f Y - z e o l i t e ( H Y ) f o r t h e c o n v e r s i o n o f c y c l i c e t h e r s i n t o i m i n e s . F o r examples, t e t r a h y d r o f u r a n i s c o n v e r t e d i n t o p y r r o l i d i n e o v e r HL a t 350°C w i t h a y i e l d o f 53 % and a t a s e l e c t i v i t y o f 91 % ( 4 ) . However, t h e y i e l d and t h e s e l e c t i v i t y f o r t h e c o n v e r s i o n o f t e t r a h y d r o p y r a n i n t o p i p e r i d i n e was n o t v e r y s a t i s f a c t o r y (4_) . H e r e , we r e p o r t t h a t t h e d e a l u m i n a t i o n o f Lz e o l i t e enhances t h e c a t a l y t i c a c t i v i t y and t h e s e l e c t i v i t y for the ring transformation of tetrahydro pyran i n t o p i p e r i d i n e . The k i n e t i c s o f t h e r e a c t i o n i s s t u d i e d and a r e a c t i o n mechanism i s p r o p o s e d . The thermal s t a b i l i t y o f dealuminated L - z e o l i t e s are s t u d i e d b y means o f X - r a y and i n f r a r e d s p e c t r o s c o p y . The a c i d i c p r o p e r t i e s o f d e a l u m i n a t e d N H 4 L a r e a l s o s t u d i e d by i n f r a r e d s p e c t r o s c o p y and by t h e use o f 596 Katzer; Molecular Sieves—II ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

49.

ΟΝΟ E T A L .

Ring Transformation of Tetrahydropyran

597

Hammett i n d i c a t o r s . Experimental M a t e r i a l s . The s t a r t i n g z e o l i t e i s KL z e o l i t e from t h e L i n d e D i v i s i o n o f U n i o n C a r b i d e Corp. The c h e m i c a l a n a l y s i s o f t h e z e o l i t e gave t h e c o m p o s i t i o n of Kg^^Alg ^Si27,6°72' ^ 2°· exchange was p e r f o r m e d w i t h aqueous s o l u t i o n s o f ammonium c h l o r i d e . D e a l u m i n a t i o n o f KL was c a r r i e d out i n a f o l l o w i n g manner. KL (20 g) was added t o 300 ml o f aqueous H^EDTA o f v a r i o u s c o n c e n t r a t i o n and t h e m i x t u r e was r e f l u x e d . The p a r t o f t h e s u p e r n a t a n t l i q u i d was d r i e d up and t h e r e s i d u e was c a l c i n e d a t 600°C t o get w h i t e powder o f a l u m i n a , w h i c h was t h e n d i s s o l v e d i n n i t r i c a c i d . Aluminum c o n t e n t o f t h e s o l u t i o n was d e t e r m i n e d as t h e o x i n e complex by measuring t h e absorbance a t 380 nm. The p o t a s s i u m e x t r a c t e d was d e t e r m i n e d by flame photometry. The amount o f t h e aluminum e x t r a c t e d and t h a t o f t h e p o t a s s i u m e x t r a c t e d were almost e q u i v a l e n t . Thus, t h e c h e m i c a l r e a c t i o n i n v o l v e d i n the d e a l u m i n a t i o n may be w r i t t e n by a f o l l o w i n g equation.


2

-Si-0

K

O-Si-

I

X

I

I

o

n

-Si-OH HO-Si-

+ Ηι» · E D T A — -

Al -Si-o'

Η

0-Si-

+ KAl-EDTA (1)

-Si-OH HO-SiI

I

The d e a l u m i n a t e d KL was exchanged w i t h aqueous ammonium c h l o r i d e t o o b t a i n d e a l u m i n a t e d N H 4 K L zeolites. C a t a l y t i c Reaction. Reaction of tetrahydrofuran and ammonia was c a r r i e d out i n a f i x e d bed t y p e r e a c t o r under continuous flow c o n d i t i o n s at atmospheric p r e s s u r e . P r i o r t o r e a c t i o n , t h e c a t a l y s t s were h e a t e d i n an a i r stream a t 460°C f o r 180 min and t h e n i n an ammonia stream a t r e a c t i o n t e m p e r a t u r e f o r 30 m i n . T e t r a h y d r o p y r a n ( T H P ) was pumped i n t o p r e h e a t i n g zone o f the r e a c t o r by a m i c r o f e e d e r . The p r o d u c t s were c o l l e c t e d i n a c o l d t r a p m a i n t a i n e d a t -100°C. The main p r o d u c t s e p a r a t e d by f r a c t i o n a l d i s t i l l a t i o n was p i p e r i d i n e , s i n c e t h e i n f r a r e d spectrum agreed w i t h t h a t o f t h e pure compound. The r e a c t i o n p r o d u c t s were a n a l y z e d b y a gas chromatograph w i t h a hydrogen flame i o n i z a t i o n d e t e c t o r . The a n a l y t i c a l column was a 4 mm χ 2 mm s t a i n l e s s s t e e l t u b i n g packed w i t h PEG-6000

Katzer; Molecular Sieves—II ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

MOLECULAR

598

on S h i m a l i t e F. attempted.

SIEVES—Π

I d e n t i f i c a t i o n o f b y p r o d u c t s was not

I n f r a r e d Spectrum. I n f r a r e d measurements were conducted i n a p r e v i o u s l y d e s c r i b e d m a n n e r ( 6 ) , a l l o w i n g the t h i n sample w a f e r s t o be h e a t e d under vacuum o r e q u i l i b r a t e d w i t h p y r i d i n e v a p o r . The samples were compressed under 600 kg/cm i n t o 20 mm-diameter d i s k s . S p e c t r a were r e c o r d e d a f t e r c o o l i n g t h e sample t o room temperature. F o r measurements i n t h e l a t t i c e v i b r a t i o n s (400-1400 c m " ) , t h e N u j o l method was used. 2


1

A c i d i t y Measurement. The a c i d i c c h a r a c t e r o f t h e z e o l i t e s was d e t e r m i n e d by t h e B e n e s i method by use o f n - b u t y l a m i n e as a t i t e r and Hammett i n d i c a t o r s . Z e o l i t e s were h e a t e d f o r 2 h r a t 500°C p r i o r t o t h e measurements. R e s u l t s and D i s c u s s i o n E f f e c t o f D e a l u m i n a t i o n on R i n g C o n v e r s i o n . I n T a b l e 1, t h e a c t i v i t y and t h e s e l e c t i v i t y f o r t h e r i n g conversion of tetrahydropyran i n t o p i p e r i d i n e of the o r i g i n a l and t h e d e a l u m i n a t e d z e o l i t e s a r e summarized. L i k e t h e i n i t i a l z e o l i t e , t h e d e a l u m i n a t e d KL w h i c h does not have some c a t i o n exchange o f Κ w i t h NH^ i s i n a c t i v e f o r t h i s r i n g t r a n s f o r m a t i o n . D e a l u m i n a t e d HL Table 1

E f f e c t o f d e a l u m i n a t i o n on a c t i v i t y and s e l e c t i v i t y f o r the r i n g conversion of tetrahydropyran into piperidine

catalyst

Si/Al

KL

3.2

11

0

0

KL

4.8

15

0

0

HL

3.2

24

14

58

HL

6.0

25

20

80

HY

2.4

15

5

33

HY

4.7

26

17

65

total conversion(%)

piperidine y i e l d (%)

selectivity (*)


49.

ΌΝΟ E T A L .


599


and d e a l u m i n a t e d HY a r e more a c t i v e t h a n t h e o r i g i n a l HL and HY, r e s p e c t i v e l y . I n t h e case o f HL, a s e l e c t i v i t y o f 80 % c a n be a t t a i n e d . As d e s c r i b e d i n a p r e v i o u s paper (4_) , n o n - c r y s t a l l i n e s o l i d s l i k e a l u m i n a or s i l i c a - a l u m i n a g i v e much l e s s s e l e c t i v i t y . Since d e a l u m i n a t e d HL gave a r e a s o n a b l y good s e l e c t i v i t y , an e f f o r t was made t o f i n d t h e optimum r e a c t i o n c o n d i t i o n s w i t h u s e o f d e a l u m i n a t e d HL as a c a t a l y s t . Time Course o f t h e R e a c t i o n . F i g u r e 1 shows a t y p i c a l time course o f t h e r e a c t i o n over dealuminated HL. The r e a c t i o n c o n d i t i o n s a r e as f o l l o w s ; r e a c t i o n t e m p e r a t u r e 350°C, c a t a l y s t w e i g h t 3.5 g, ΝΗτ/ΤΗΡ=7, W/F=26 g-cat·hr/mole. A t t h e s e r e a c t i o n c o n d i t i o n s , a p i p e r i d i n e y i e l d o f 22 % w i t h a s e l e c t i v i t y as h i g h as 80 % was o b t a i n e d . F u r t h e r , i t i s note worthy that t h e r e i s no s i g n o f d e a c t i v a t i o n o f t h e c a t a l y s t w i t h i n 7 hr. E f f e c t o f R e a c t i o n Temperature. The e f f e c t o f t h e r e a c t i o n t e m p e r a t u r e on t h e c a t a l y t i c a c t i v i t y o f d e a l u m i n a t e d HL was examined and t h e r e s u l t s were i l l u s t r a t e d i n F i g u r e 2. The t o t a l c o n v e r s i o n o f t e t r a h y d r o p y r a n i n c r e a s e s w i t h t h e r e a c t i o n temperature, while the y i e l d of p i p e r i d i n e increases with the r e a c t i o n t e m p e r a t u r e up t o 350°C, b u t f a l l s down o v e r 370°C. I t can be c o n c l u d e d t h a t t h e optimum r e a c t i o n t e m p e r a t u r e l i e s around 350°C. The s e l e c t i v i t y t o p i p e r i d i n e remains as h i g h as 80 % a t t h i s t e m p e r a t u r e . K i n e t i c s of the Reaction. R e a c t i o n k i n e t i c s was examined i n t h e t e m p e r a t u r e range o f 310-350°C i n a low W/F c o n d i t i o n (13.8 g-cat·hr/mole). F i g u r e 3 shows t h e e f f e c t o f t h e p a r t i a l p r e s s u r e o f ammonia (PNH3^ ^ reaction rate. I t i s clear that the reaction rate i s the f i r s t order w i t h respect t o t h e p a r t i a l pressure o f ammonia. The dependence o f t h e r a t e on t h e p a r t i a l pressure of tetrahydropyran(Pj ) i s shown i n F i g u r e 4. The r a t e depends m a r k e d l y on when PTHP0.2 atm. I n t h i s r e g i o n , t h e r a t e (τ; mole/hr·g^catj c a n be e x p r e s s e d as f o l l o w s , o

n

t

i e

H p

r - k Ρ Μ μ

(P

T H P

> 0.2 atm)

(2)

The v a l u e s o f t h e f i r s t o r d e r r a t e c o n s t a n t , k, c a l c u l a t e d from t h e s l o p e o f F i g u r e 3 a r e 0.52, 1.02 and 2.02 m o l e / h r - g - c a t a t 310, 330 and 350°C, r e s p e c t i v e l y . From t h e dependence o f t h e r a t e c o n s t a n t on r e a c t i o n


600

MOLECULAR SIEVES—II

I 80

u • •

£60 c AO !

20


Figure 1. Variation of the conversion of > tetrahydropyran (A), the yield of piperi 3 ο dine (O), and the selectivity (•) with time on stream

Figure 2. Variation of the conversion of tetrahydropyran (Δ), the yield of piperi dine (O), and the selectivity (•) with reaction temperature. W / F = 26 g-cathr/mole F /F P = 7. NH3

TH

Figure 3. The dependence of the reaction rate on the partial pressure of ammonia, V = 0.125 atm THP

~D—O-O-O-

2 3 A 5 6 Time on stream (hr)

300 320 340 360 380 A00 Reaction temperature ( C) e

Partial pressure of NH (atm) 3


49.

ΌΝΟ E T A L .

601


t e m p e r a t u r e , t h e a c t i v a t i o n energy was c a l c u l a t e d t o be 24.7 k c a l / m o l e . E s s e n t i a l l y t h e same e x p r e s s i o n has been o b t a i n e d f o r i n g c o n v e r s i o n o f t e t r a h y d r o f u r a n i n t o p y r r o l i d i n e , though t h e a c t i v a t i o n energy t o t e t r a h y d r o f u r a n i s 17 k c a l / m o l e . E f f e c t o f KL on i t s Thermal S t a b i l i t y . The change i n t h e s t r u c t u r e o f KL w i t h d e a l u m i n a t i o n was s t u d i e d by i n f r a r e d s p e c t r o s c o p y and X - r a y d i f f r a c t i o n . A new OH band a t 3700 cm" appears a f t e r d e a l u m i n a t i o n and t h e i n t e n s i t y o f t h e band i n c r e a s e s w i t h i n c r e a s i n g d e a l u m i n a t i o n . The OH band i s c o n s i d e r e d t o be due t o t h e Si-OH groups formed by t h e r e a c t i o n ( 1 ) . P i c h a t e t al.(7J) showed t h a t t h e 608 cm' band due t o t h e v i b r a t i o n o r d o u b l e D-6 r i n g s was a good measure for the c r y s t a l l i n i t y of the z e o l i t e s . The i n t e n s i t y o f 608 cm" band d e c r e a s e s w i t h i n c r e a s i n g d e a l u m i n a tion. Thus, t h e d e a l u m i n a t i o n o f L - z e o l i t e l e a d s t o the d e s t r u c t i o n o f z e o l i t e framework. The same c o n c l u s i o n i s a l s o drawn from t h e X - r a y d i f f r a c t i o n . The i n t e n s i t i e s of d i f f r a c t i o n l i n e s decrease w i t h d e a l u m i n a t i o n . C a l c i n a t i o n o f t h e samples a t 460°C f o r 1 h r l e a d s t o f u r t h e r decay o f t h e c r y s t a l s t r u c t u r e . 1


1

1

A d s o r p t i o n o f P y r i d i n e on D e a l u m i n a t e d KL. P y r i d i n e was adsorbed a t 100°C f o r 1 h r on d e a l u m i n a t e d KL. The i r band due t o t h e p y r i d i n e m o l e c u l e i n t e r a c t i n g w i t h p o t a s s i u m c a t i o n s was o b s e r v e d around 1440 cm" . B u t , no bands o f p y r i d i n e adsorbed on a c i d i c centers are observed. The OH band a t 3700 c m does n o t r e a c t w i t h p y r i d i n e . Thus, t h e OH groups formed by r e a c t i o n (1) have no a c i d i c c h a r a c t e r . 1

= 1

A c i d i c P r o p e r t i e s o f D e a l u m i n a t e d NH^L. The i n f r a r e d spectrum o f t h e NH^ form o f d e a l u m i n a t e d Lz e o l i t e (NH4.3QK2 j A l ^ ^ ) i n v e s t i g a t e d as a f u n c t i o n o f t h e e v a c u a t i o n * t e m p e r a t u r e . The d e s o r p t i o n o f w a t e r and ammonia t a k e s p l a c e i n almost t h e same manner as i n t h e case o f o r d i n a r y NH^L z e o l i t e , w h i c h has been r e p o r t e d p r e v i o u s l y (7). The sample e v a c u a t e d a t 460°C showed bands a t 3640, 3280 and 2600 cm' , w h i c h a r e q u i t e s i m i l a r t o t h o s e o b s e r v e d i n o r d i n a r y NH^L ( 7 ) . The o n l y d i f f e r e n c e between d e a l u m i n a t e d and o r d i n a r y NH^L i s t h e p r e s e n c e o f 3700 cm" band i n t h e f o r m e r , w h i c h i s a s c r i b e d t o SiOH groups formed b y t h e r e a c t i o n w

a

s

1

1

(1).

A f t e r t h e sample was e v a c u a t e d a t 460°C, i t was exposed t o p y r i d i n e v a p o r a t 100°C f o r 30 m i n , and t h e n e v a c u a t e d a t 200°C f o r 1 h r . Then, t h e bands a t 3640, 3280 cm d i s a p p e a r e d , b u t t h e band a t 3700 cm" 1


602

M O L E C U L A R SIEVES—II

r e m a i n e d , i n d i c a t i n g t h a t t h e f o r m e r OH group are a c i d i c and t h a t t h e l a t t e r i s n o t . The p r e s e n c e o f t h e band at 2600 cm" shows t h a t t h e p y r i d i n i u m i o n s t h u s formed are hydrogen-bonded w i t h l a t t i c e oxygen. A d s o r p t i o n of p y r i d i n e l e a d s t o the appearance o f a band at 1550 cm" , indicative for pyridinium ions. The i n t e n s i t y o f t h e band i s p l o t t e d as a f u n c t i o n of t h e exchange degree by NH^ per u n i t c e l l f o r o r d i n a r y and d e a l u m i n a t e d z e o l i t e s ( F i g u r e 5 ) . The i n t e n s i t y o f 1550 cm" band of t h e d e a l u m i n a t e d N H 4 L i s s t r o n g e r t h a n t h a t of o r d i n a r y N H 4 L i f samples o f t h e same exchange l e v e l are compared. The i n c r e a s e i n t h e number o f a c i d c e n t e r s by d e a l u m i n a t i o n i s a l s o d e m o n s t r a t e d by t i t r a t i o n w i t h n - b u t y l a m i n e . Hammett i n d i c a t o r s w i t h H© v a l u e s of 3.3, 1.5 and -3.0 are used. The r e s u l t s are g i v e n i n F i g u r e 6. I n t h e case o f o r d i n a r y NH^L, o n l y p a r t o f H i o n s i n t r o d u c e d i s e f f e c t i v e as a c i d i c c e n t e r s . Though t h e same can be s a i d a l s o o f d e a l u m i n a t e d NH^L, the f r a c t i o n o f H i o n s e f f e c t i v e f o r t h e a d s o r p t i o n o f n - b u t y l a m i n e i s much l a r g e r t h a n t h a t found f o r N H 4 L . The e x t e n t o f t h e i n c r e a s e i s more pronounced f o r c e n t e r s o f s t r o n g e r a c i d i t y (H =-3.0). T h i s i n c r e a s e i n a c i d i t y and the s t r e n g t h of a c i d might be r e s p o n s i b l e f o r t h e enhanced c a t a l y t i c a c t i v i t y f o r r i n g conversion of tetrahydropyran i n t o p i p e r i d i n e . 1

1


1

+

+

o

R e a c t i o n Mechanism. I n p r e v i o u s p a p e r s ( 3 , 4 ) , we have p r o p o s e d a mechanism f o r t h e r e a c t i o n o f t e t r a h y d r o f u r a n and ammonia, i n c l u d i n g B r o n s t e d a c i d s as a c t i v e c e n t e r s . S i n c e e s s e n t i a l l y the same k i n e t i c s was found a l s o f o r t h e r i n g c o n v e r s i o n o f t e t r a h y d r o p y r a n , we assume t h e f o l l o w i n g r e a c t i o n mechanism i s o p e r a t i v e f o r the r e a c t i o n .

(3)

+ H

H

H

(rate determing)(5)

+ H

H

H

3


ΟΝΟ E T A L .

Partial pressure of THP (atm)


603


Figure 4. The dependence of the re action rate on the partial pressure of tetrahydropyran, P = 0.625 atm NH3

Figure 5. The change in the absorhance of 1550 cm hand with H* content per unit cell. Ordinary HL, (O); dealuminated HL, 1

H/u.c.

Figure 6. The change in the acidity with H content per unit cell. Solid marks for ordinary HL and open marks for dealuminated HL. +

H/u.c.


604

MOLECULAR

Ο

SIEVES—Π

C6)

H0

+

2

fast

Η H Η Ammonia may r e a c t w i t h B r o n s t e d s i t e s ; 3

NH

+ Η

3

J

..

·»

NH

(7)

4

From t h e above mechanism, t h e f o l l o w i n g r a t e i s obtained,


k K

ι

K

C

+

P

P

l 2 H ' THP NH

• K

I

C

I K )P +

expression

2

T

H

P

+

3

K P 3

N

H

3

Ο

where C u i s t h e s u r f a c e c o n c e n t r a t i o n o f B r o n s t e d s i t e s e f f e c t i v e f o r t h e r e a c t i o n . I f Κ·^(I+K2)Ρχ^Ρ 1 + K P , Eq.(8) i s r e d u c e d t o 3 ο +

3

> >

N H

le K/} CTJ+ r

P

" 1 + K

C 9 )

NH N H

2

3

Eq. (9) agrees w i t h o b s e r v e d r a t e e x p r e s s i o n . Comparison o f Eq.(1) w i t h Eq.(9) g i v e s t h e f o l l o w i n g relation. k K~ C „ + = 2_H_ (10) 1 + κ k

o

b

s

2

I f one assumes K relation.

Ring Transformation of Tetrahydropyran into Piperidine over

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