Sulfided Catalysts and Fine Chemicals

139

M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals '0 1988 Elsevier Science Publishers B.V, Amsterdam - Printed in The Netherlands

SULFIDED CATALYSTS AND FINE CHEMICALS C. MOREAU, R. DURAND, P. GRAFF IN and P. GENESTE Laboratoire de Chimie Organique Physique et Cinetique Chimique Appliquees, U.A. CNRS 418, Ecole Nationale Superieure de Chimie, 8, Rue Ecole Normale 34075 Montpellier Cedex, France. ABSTRACT

Industrial hydrotreating sulfided catalysts have been shown to be efficient catalysts in some fundamental reactions in organic synthesis such as transformation of ketones, alcohols and amines into hydrocarbons or removal of protective groups like ketals and thioketals. Judicious functionalizations of organic substrates can make these catalysts applicable to synthesis of fine chemicals. INTRODUCTION

Sulfided catalysts have been widely used in synthesis and reactions of organic fuel

industry,

compounds

thus leading to

particularly

purpose of this paper

is

in

to use

their important application in

hydrotreating

processes

(ref.l)

and

the acquired knowledges

in this

field

order to consider the potential application of sulfided catalysts

the in

in other

important synthetic reactions in organic synthesis, particularly those leading to fine chemicals. The

two main chemical

reactions

occuring

in

hydrotreating

cesses over sulfided catalysts are hydrogenation and hydrogenolysis. differences of reacti vi ty have

been observed in these

two reactions

proLarge for

example, olefins are hydrogenated hundredfold faster than aromatics and C-S, C-Br or C-Cl bonds are also hundredfold easier to cleave than C-O or C-N bonds

(ref. 2).

resul ting

from

It is

thus

these

differences

possible

to

take

advantage

of reacti vi ty

to

of

the

develop

new

selecti vi ty synthetic

routes to organic compounds over sulfided catalysts. ORGANIC REACTANT + CATALYST

--7>

FINE CHEMICAL

In order to obtain products with high added values,

two different

approaches can be considered depending whether attention is focused onto the catalyst or onto the organic reactant. The goal will be the same in both approaches, i.e. improvement of conversion and/or of selectivity as compared to other

known

catalysts

processes.

The

first

in a given reaction

approach

is

to

operate

with

different

and the second one is to operate with a given

140 catalyst and

the question will

then be how to

functionalize

the

starting

material to yield the desired product. We will report in this paper some results or preliminary results illustrating these

two approaches with mono- or polyfunctionalized organic

reactants.

EXPERIMENTAL Experiments were

carried

out

in

a

0.3

litre

(Autoclave Engineers type Magne-Dri ve ) operating in a

stirred

batch mode.

autoclave Analysis

were performed on a Girdel 30 gas chromatograph equipped with a flame ionization detector using hydrogen as carrier gas and adequate capillary columns. Products were identified by comparison with authentic samples and/or by GC-MS analysis. The catalysts used were industrial Procatalyse HR 346 (3% NiO ; 14% and HR 306 (3% CoO ; 14% Mo0 ; 83% y-A1 presulfided Mo0 ; 83% Y -AI 20 3) 3 3 20 3) at atmospheric pressure using a fluidized-bed technique with a gas mixture of 15% H and 85% H by volume (gas flow: l20ml/min ; 400°C for 4h). 2 2S

RESULTS AND DISCUSSION Conversion of ketones alcohols and amines into hydrocarbons

Ketones : the conversion of ketones into the corresponding hydrocarbons is an important reaction in organic synthesis which often requires multistep procedures depending on the steric environment or the degree of conjugation of the carbonyl group. We have recently shown that this reaction is easily performed over an industrial a sulfided NiMo/A1

catalyst at 250°C and 40 bar 20 3 Sterically hindered ketones or conjugated ones are converted

H (ref. 3). 2 into their corresponding

hydrocarbons

wi thin

15 minutes

and

in

excellent

yields. Although the question was not exhaustively considered, this procedure could be of interest as compared to known homogeneous processes (Clemmensen, Huang-Mi n Lon catalysts

or Wolff-Kishner)

ones

over

supported

(ref.4 and 5) or unsupported sulfided catalysts (ref.6).

tion, some hydrocarbons chemicals.

or heterogeneous

such as

terpenes

(C

l OH1 6)

metal

In addi-

can be regarded as fine

Alcohols : alcohols are more rapidly converted into hydrocarbons than their parent ketones under the same operating conditions (ref.3). For alcohols and ketones where a second function capable of being hydrogenated is present on

141 the starting materials (diphenylmethanol, benzophenone), hydrogenation of the aromatic rings does not compete with the removal of the carbonyl or hydroxyl groups. Amines : As for ketones and alcohols, the conversion of amines

into the cor-

responding hydrocarbons generally requires

Heterogeneous

multistep

methods.

catalysts have been recently used to achieve the one-step reduction of amines into hydrocarbons, Ni/Al (ref.7) and Pt/Si0 (ref.S). The latter catalyst 203 2 does not work when the amino group is connected to a tertiary position whereas a sulfided NiMo/A1

catalyst is efficient whatever the type of connec20 3 tion as we have shown recently (unpublished results).

Removal of protective groups The

removal

of

protective

1,3-oxathiolanes II or 1, 3-dioxolanes

groups

such

as

1,3

dithiolanes

I,

III has received much less attention

over sulfided catalysts.

However, protection and deprotection of functional groups are often required in organic synthesis. It has been also shown that ketones which are not easily converted into hydrocarbons under standard procedures can be transformed into 1,3-dithiolanes and then desulfurized as

illustrated below

(ref. 9) for the conversion of 4-twistanone into twistane.

'----f-H H

142 Over a sulfided CoMo/A1 catalyst, known for its hydrogenolytic 20 3 properties higher than those of a NiMo/A1 catalyst, the transformation of 20 3 the 0-0, O-S and S-S ketals into hydrocarbons is achieved within 10 to 30 minutes at 150°C under 40 bar hydrogen pressure. The most important feature served in the removal of

° and

is

the difference

in selectivity ob-

S atoms which could lead to an interesting new

synthetic route to benzylalkylethers. New synthetic route to benzylethylether We have attempted to use the differences in selectivity observed in the removal of 0- and S- atoms in order to lead to benzylethylether. Benzyl ethers are generally not easily available from standard procedures (ref. 10).

We have

shown

that

benzylethylether

athiolane over a sulfided CoMo/A1

The scheme with k

reaction

3 = 2 x 10-

20 3

proceeds

is

obtained

from

phenyl-1,3-ox-

catalyst at 100°C and 40 bar H 2.

through

a

consecutive

3 -1 min. = 0.5 x 10-

kinetic

and k 2 1 tion conditions have not been optimized to improve the selectivity.

be expected that the mixed O,S ketal IV should be a

reaction

(g.cat. )-1. The reacIt could

better starting material

O-Et

Ph-C/

H'S-R IV

as due to entropic considerations between cyclic and acyclic systems. New synthetic route to imines Imines are generally synthesized from lac tames lithium aluminium hydride.

by

reduction with

In order to avoid the use of this material which

is not easy to handle in large quantities we have carried out this reaction over a variety of hydrogenating catalysts such as NiMo/A1

20 3

'

NiW/ A1 203

'

143 Pt0

' Ni Raney or Wilkinson catalyst. All these catalysts were found to be 2 unselective in the conversion of the substituted lactame :

r"\-R "N~H

/

~,

H

0: I

R'

Keeping in mind that

° and

N atoms behave similarly in hydrotreat-

ing reactions, we have thus selectively replaced the

° atom

by S atom by us-

ing Lawesson' s reagent to operate under milder experimental conditions.

At

the present time the desired transformation has been achieved on aNi-Raney catalyst at OOC, and the two-step synthesis remains an attractive route synthesis of imines. On the other hand a sulfided NiMo/A1 removes

the S-atom but also cleaves the C-N bond.

to

catalyst easily

20 3 A sulfided CoMo/ A1

catalyst would be probably a better catalyst.

203

CONCLUSIONS In spite of the extensive work in organic synthesis over sulfided catalysts,

their selective properties can make

them

sui table

for

a

large

number of reactions where different functional groups are present. Some novel aspects have thus been presented here, particularly in the removal of protective groups which could be of greater interest because of the use of 1,3-dithiolanes as insecticides (ref. 11) and in strategies of synthesis to yield fine chemicals.

ACKNOWLEDGEMENTS The experiments.

authors

thank

C.Gauthier,

J.L.Pirat

and

N.Zmimita

for

144

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