preparación de placas y columnas de silica con agno3

8/9/2019 preparacin de placas y columnas de Silica con AgNO3

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E L S E V I E R

Journal of Chromatography A, 715 (1995) 372-375

JOURN L OF

CHROM TOGR PHY

Short communication

M o d i f i e d a n d c o n v e n i e n t p r e p a r a t i o n o f s i l i c a i m p r e g n a t e d

w i t h s i l v er n i t ra t e a n d i t s a p p l i ca t io n t o t h e s ep a ra t io n o f

s t ero id s a n d t r i t erp en es

Tong-Shuang Li*, Ji-Tai Li, Hui-Zhang Li

Department o f Chem istry, Hebei U niversity, Baoding 0 71002, Hebei Province, China

First received 12 January 1995; revised manuscript received 23 May 1995; accepted 24 May 1995

A b s t r a c t

Modified and convenient procedures are repo rted for the preparation of flash columns and thin-layer

chromatographic plates using silic a impregnated with silver nitrate. The application o f this ads orb ent to the

sep ara tion of steroids and triterpenes is also repo rted.

1 . I n t r o d u c t i o n

I n c o n n e c t i o n w i t h o u r r e s e a r c h o n t h e s y n -

t h e s i s o f s t e r o id a l a n d t r i t e r p e n o i d a l b i o l o g ic a l

m a r k e r s [ 1 - 5 ] , t h e s e p a r a t i o n o f o l e fi n ic h y d r o -

c a r b o n s w a s f r e q u e n t l y n e c e s s a r y . S i l i c a g e l

i m p r e g n a t e d w i t h s i lv e r i o n s h a s b e e n s u c c e s sf u l-

l y u s e d i n th e s e p a r a t i o n o f u n s a t u r a t e d c o m -

p o u n d s b y th i n -l a y er ( T L C ) a n d c o l u m n c h r o m a -

t o g r a p h y [ 6 - 2 3 ] . H o w e v e r , n o s i g n i f i c a n t m o d i -

f i c a ti o n o f t h e p r e p a r a t i o n o f th i s k in d a d s o r b e n t

h a s b e e n i n t r o d u c e d . T h e r e p o r t e d p r o c e d u r e s

[8 ,15 ,18 ,20 ,21 ,23 ] fo r t he p rep a ra t i o n o f s i li ca

i m p r e g n a t e d w i t h s i l v e r n i t r a t e i n v o l v e t h e a d d i -

t i on o f s i l ve r n i t ra t e so lu t ion to s i l i ca and d ry ing

t h e m i x t u r e u n d e r r e d u c e d p r e s s u r e i n a r o t a r y

e v a p o r a t o r . W h e n t h e s e p r o c e d u r e s w e r e r e -

p e a t e d i n o u r l a b o r a t o r y , h o w e v e r , t h e r e w e r e

a l w a y s p r o b l e m s a s a b o u t o n e t h i rd o f th e

a d s o r b e n t r o s e u p t h e c o n d e n s e r o f t h e

e v a p o r a t o r . T h e r e f o r e , t h e r o t a r y e v a p o r a t o r

h a d t o b e c l e a n e d a n d r e a s s e m b l e d a n d t h e y i e l d

o f t h e a d s o r b e n t w a s o n l y a r o u n d 7 0 .

T L C p l a t e s c o a t e d w i t h s i l i c a i m p r e g n a t e d

w i t h s i l v e r i o n s , p r e p a r e d b y l i t e r a t u r e

[ 6 , 7 , 1 0 , 1 1 ] m e t h o d s h a v e t h e d e f e c t t h a t t h e

a d s o r b e n t i s n o t s t r o n g e n o u g h a n d m i g h t b e

d e s t r o y e d b y s p r a y in g a g e n t s o r b y h e a t i n g , a n d

a ll t h e p l a t e s m u s t b e u s e d w i t h i n 1 w e e k a s

o t h e r w i s e t h e y b e c o m e d a r k .

W e r e p o r t h e r e m o d i f i e d a n d c o n v e n i e n t p r o -

c e d u r e s f o r t h e p r e p a r a t i o n o f f la s h c o l u m n s a n d

T L C p l a t e s u s i n g s i l i c a i m p r e g n a t e d w i t h s i l v e r

n i t r a t e a n d t h e i r a p p l i c a t i o n t o t h e s e p a r a t i o n o f

s t e r o i d s a n d t r i t e r p e n e s .

2 . E x p e r i m e n ta l

2 1 Preparation of TLC plates coated with

silica impregnated with silver nitrate

* Corresponding author.

A 10 2 .5 cm TLC p la t e coa t ed wi th s i l i ca ge l

0021-9673/95/$09.50 (~) 1995 Elsevier Science B.V. All rights reserved

S S D I

0021-9673(95)00619-2


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T. S. L i et a l. / J. C h r o m a t o g r . A 7 1 5 ( 1 9 9 5 ) 3 7 2 - 3 7 5 373

6 0 ( M e r c k ) w a s d e v e l o p e d o n c e w i th an a q u e o u s

s o l u t i o n o f s il v e r n it r a t e ( 2 . 0 g ) i n d i s t i l le d w a t e r

( 5 m l ) . T h e p l a t e w a s t h e n d r i e d a n d a c t i v a t e d

w i t h a h e a t g u n f o r 2 m i n . S i l v e r n i t r a t e c o n s t i -

t u t e d a r o u n d 2 5 o f t h e a d s o r b e n t . T h e p l a t e

c a n b e u s e d a s u s u a l an d t h e m o v e m e n t o f

s o l v e n t w a s u s u a l l y c o n t r o l l e d a t 2 c m f r o m t h e

u p p e r e d g e .

Table 1

R F values of steroids and triterpenes

Mixture R r Solvent

Cholesterol 0.37

Cholestanol 0.47

3/3-Acetoxycholest-5-ene 0.48

3/3-Acetoxycholestane 0.62

3/3-Acetoxycholest-8(14)-ene

3/3-Acetoxycholest-14-ene

0.42

0.27

4/3-Methylcholest-2-ene 0.43

4-Methylcholest-3-ene 0.33

4-Methylcholest-4-ene 0.55

Cholest-4-ene 0.68

Cholest-3-ene 0.57

Cholest-2-ene 0.54

Cholesta-3,5-diene 0.32

(20R)-Diacholest- 13(17)-ene

(20S)-Diacholest-13(17)-ene

4,4-Dimethylcholest-5-ene

4,5a-Dimethylcholest-3-ene

(20R)-4,4-Dimethyldiacholest- 13(17)-ene

(20S)-4,4-Dimethyldiacholest-13(17)-ene

Lupeol

Dihydrolupeol

Betulin

Dihydrobetulin

Lup-2-ene

/-Lup-3(4)-ene

y-Lup-3(5)-ene

Lupa-2,20(29)-diene

y-Lupa-3(4),20(29)-diene

19a(H)-28-Norlup-17-ene

19/3(H)-28-Norlup-17-ene

28-Norlup-16-ene

28-Norlup-17(22)-ene

0.46

0.61

0.35

0.64

0.46

0.61

0.42

0.53

0.39

0.50

0.34

0.50

0.29

0.37

0.46

0.82

0.70

0.51

0.38

Hexane-ethyl acetate

(3:1)

Hexane-diethyl ether

(10:1)

Hexane-diethyl ether

(5:1)

Hexane

Hexane-toluene

(10:1)

Hexane-toluene

(10:1)

Hexane

Hexane-tolucne

(10:1)


3 : 1 )


(2:1)

Hexane

Hexane-toluene

(10:1)

Hexane


3/4

374

T . - S . L i e t a l . / J . C h r o m a t o g r . A 7 1 5 ( 1 9 9 5 ) 3 7 2 - 3 7 5

2.2. Preparation o f sil ica impregnated with

si lver ni trate (10 ) fo r f lash column

chromatography

An aqueous solution of 5.5 g of silver nitrate

in 30 ml of distilled water was mixed with 50 g of

200-300-mesh silica and ground for 5 min in a

mortar. The mixture was then dried in an oven

at 150C for 1 h. The resulting powder was

almost white, stored in a beaker wrapped with

dark paper and dried over phosphorus pentoxide

in a vacuum desiccator. The adsorbent could be

stored for several months without significant

darkening or decrease in activity. Columns were

packed in the same way as ordinary silica col-

umns and wrapping with dark paper was not

necessary for flash chromatography. Most mix-

tures were separated by using 50 g of adsorbent

for each gram of mixture.

lupeol and betulin was usually checked by 1H

NMR spectroscopy, but now the evolution of

these hydrogenation reactions can be monitored

by silica-silver nitrate TLC. The fractions from

flash column chromatography on silica impreg-

nated with silver nitrate could also be checked by

this kind of TLC instead of GC.

In conclusion, very convenient and practical

procedures for the preparation of flash columns

and TLC plates using silica impregnated with

silver nitrate have been developed.

A c k n o w l e d g e m e n t

This work was supported by the State Educa-

tion Commission of China via a Research Grant

for Returned Chinese Scholars.

3 . R e s u l t s a n d d i s c u s s i o n

To prepare TLC plates coated with silica

impregnated with silver nitrate, 0.5, 1.0, 1.5, 2.0

and 3.0 g of silver nitrate in 5 ml of distilled

water were tried as development solvents. The

first three caused double fronts and the last led

to overloading with silver nitrate. Consequently,

a solution of 2.0 g of silver nitrate in 5 ml of

distilled water was adopted and thus silver ni-

trate constituted ca. 25% of the adsorbent. For

flash column chromatography, 10% silver nitrate

on 200-300-mesh silica was found to be efficient

enough for the separation of olefinic mixtures of

steroids and triterpenes.

Thirteen olefinic mixtures, containing 32 ster-

oids and triterpenes, were separated satisfactori-

ly by flash column chromatography on silica

impregnated with silver nitrate (10%), except for

the mixture of cholest-2-ene and cholest-3-ene.

The R F values of the 32 compounds obtained by

TLC are given in Table 1. The mixtures in Table

1 could not be separated by the usual TLC and

column chromatography on silica. TLC plates

prepared in this manner were mainly used for

analysis purposes. For example, the hydrogena-

tion of cholesterol, 3/3-acetoxycholest-5-ene,

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preparación de placas y columnas de silica con agno3

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