Process for preparing 1,3-diketones

Details Process for preparing 1,3-diketones Process for preparing 1,3-diketones

2000-07-31

2001-10-30

Richter, Johann (Department: 1621)

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

Organic compounds

Oxygen containing

C568S384000

Reexamination Certificate

active

06310258

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a process for preparing 1,3-diketones by thermal rearrangement of the corresponding isomeric enol esters, and also to an apparatus for carrying out the process.
BACKGROUND OF THE INVENTION
It is known from U.S. Pat. No. 2,395,800 that 1,3-diketones can be prepared by thermal rearrangement of the corresponding isomeric enol esters at a temperature of from 300° C. to 700° C. in a tube reactor, with the gaseous product mixture subsequently being condensed and the pure product being distilled off. A disadvantage is that free-radical mechanisms leading to undesirable by-products and to carbon formation proceed in reactions of this type and thus make it necessary to stop production for cleaning the reactor. These by-products reduce the selectivity and have to be separated off by distillation. DE-A2047320 (U.S. Pat. No. 3,794,686) describes a procedure in which a tetraalkyllead is added to the reaction mixture to prevent carbon deposition. The Derwent Abstract—JP-A63159337—describes the addition of water to improve the selectivity in the preparation of acetylacetone from isopropenyl acetate and at the same time, reduces the rate of carbon formation. However, a disadvantage is that the water thus introduced leads firstly to hydrolysis of the enol ester and secondly, to corrosion problems.
It is therefore an object of the invention to develop a process which gives a higher conversion at least equal selectivity and lower carbon formation without addition of promoters of water.
BRIEF DESCRIPTION OF THE INVENTION
The invention provides a process for preparing 1,3-diketones by means of thermal rearrangement of the corresponding isomeric enol esters in a tube reactor
1
at a temperature of from 350° C. to 700° C. and subsequent cooling and work-up of the reaction product by distillation, wherein the tube reactor
1
is not heated over its full length but only in a front section
1
a
which extends over a region from at least ¼ to at most ¾ of the total tube length, calculated from the reactor inlet, and the remaining unheated section
1
b
of the tube reactor
1
is thermally insulated or cooled.
The invention further provides an apparatus for carrying out the process comprising a tube reactor
1
having a front, un-insulated tube section
1
a
which extends over a region from at least ¼ to at most ¾ of the total tube length, calculated from the reactor inlet, and is provided with one or more heating elements
6
, and a downstream tube section
1
b
which is provided with cooling or insulation
2
and is connected via a transfer tube
3
to a column
4
and is also provided with a line
5
for the introduction of cooling liquid.


REFERENCES:
patent: 2395800 (1946-03-01), Boese et al.
patent: 3794686 (1974-02-01), Spes et al.
patent: 2 047 320 (1972-03-01), None
patent: 63-159337 (1988-07-01), None
Derwent Abstract corresponding to JP-A 63159337 AN 1988-224238[32].
“Conversion Of Ketone Enol Esters To Beta-Diketones By Intramolecular Thermal Rearrangement And By Intermolecular Acylations Using Boron Fluoride”, 1950, p. 3635-3642.

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