Process for the preparation of substituted cycloketones

Details Process for the preparation of substituted cycloketones Process for the preparation of substituted cycloketones

1998-12-18

2001-04-24

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S343000, C568S361000, C560S129000, C560S248000, C560S252000

Reexamination Certificate

active

06222076

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a novel process for the preparation of hydroxyalkyl- and acyloxyalkyl-substituted cycloketones by free-radical addition of hydroxyalkenes and acyloxyalkenes respectively to cyclic ketones.
BACKGROUND OF THE INVENTION
The general type of the reaction is already known from DE-B 21 36 496; it is generally carried out in the presence of organic peroxides (e.g. di-tert-butyl peroxide). In this case, the initial charge is for example an excess of cyclododecanone (at least 4 moles per mole of alkene), and to this is added, over the course of 6 hours, a mixture of allyl alcohol and di-tert-butyl peroxide (10-20 mol %, based on alkene) at 140-150° C.
Although, in principle, free-radical reactions of this type take place in a few minutes, with this discontinuous method the allyl alcohol is added very slowly in order to suppress, as far as possible, secondary reactions which lead to polymeric material.
Despite this slow addition, considerable amounts of polymeric byproducts form. A further disadvantage is the poor space-time yield which results because of the long metering time.
The object of the present invention was thus to largely avoid these disadvantages.
DETAILED DESCRIPTION OF THE INVENTION
It has now been possible to achieve the aforementioned object by carrying out the free-radical addition of oxoalkenes to cycloketones in the presence of organic peroxides as free-radical initiators in a continuous process.
Surprisingly, it has been found that by using a continuous procedure, a residence time in the reactor of preferably only from 30 to 80 minutes suffices to obtain a high space-time yield with only small amounts of polymeric byproducts.
The invention thus provides a process for the preparation of compounds of the formula
in which
R
1
to R
3
independently of one another are hydrogen, methyl or ethyl,
R
4
is hydrogen or C
1
-C
8
-acyl,
n is an integer from 6 to 10 and
m and p independently of one another are zero or 1,
by reacting a cyclic ketone of the formula
in which
n is as defined above,
with an alkenol or alkenol ester of the formula
in which
R
1
-R
4
, m, n and p are as defined above,
in the presence of a free-radical initiator, characterized in that the process is carried out continuously.
The following may for example be mentioned as substituted cycloketones according to the invention:
Cyclic ketones for the process according to the invention can for example be the following:
Alkenols for the process according to the invention can for example be the following: vinyl acetate, 2-methyl-2-propen-1-ol, isopropenyl acetate, 3-buten-1-ol, 2-methyl-3-buten-1-ol, allyl alcohol, allyl acetate and 3-methyl-3-buten-ol.
Free-radical initiators for the process according to the invention can for example be the following: cumene hydroperoxide, peroxy esters, such as for example tert.-butyl peroxypivalate, peroxy dicarbonates, such as for example di-(2-ethylhexyl)-peroxydicarbonate, and azo compounds, such as for example 2,2′-azo-bis (4-methoxy-2,4-dimethylvaleronitrile).
The resulting hydroxyalkyl ketones III can be converted, using acid catalysts, to cyclic enol ethers, as are already described in DE-B 21 36 496. These bicyclic enol ethers are in turn very good starting materials for preparing fragrances.
The temperature during the process according to the invention can be from 80 to 200° C., depending on the free-radical initiator used; if the particularly preferred di-tert-butyl peroxide is used, the preferred reaction temperature is from 130 to 1 80° C.
It is advantageous to choose the pressure range such that a homogeneous reaction can take place so that, where appropriate, also readily boiling starting components, such as, for example, allyl alcohol, can be used which have a boiling point below the reaction temperature required for the free-radical initiator. A preferred pressure range is, for example, from 3 to 50 bar. The process is particularly preferably carried out at a pressure of from 10 to 30 bar.
A further advantage of this continuous process is that the excess starting components can be continually distilled off from the product and returned to the reaction process.
In addition, this procedure makes it possible to introduce the starting materials and the catalyst at various positions along the reaction tube in order in this way to vary the procedure depending on the sensitivity and reactiveness of the feed materials or to always keep one component in large excess. This can reduce secondary and consecutive reactions.
The continuous method is associated with a significant increase in the space-time yield; it is thus far superior to the conventional discontinuous process.


REFERENCES:
patent: 3856815 (1974-12-01), Hopp et al.

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