Isolation of &agr;-ethynyl carbinols by distillation

Details Isolation of &agr;-ethynyl carbinols by distillation Isolation of &agr;-ethynyl carbinols by distillation

1999-12-06

2001-11-13

Richter, Johann (Department: 1621)

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

Organic compounds

Oxygen containing

C568S874000, C568S876000, C568S879000

Reexamination Certificate

active

06316680

ABSTRACT:

The present invention relates to a process for isolating &agr;-ethynyl carbinols from the liquid reaction mixture from the addition of acetylene onto &agr;,&bgr;-unsaturated carbonyl compounds by distillation, and also a use of the process for the isolation of vinylbutynol.
&agr;-Ethynyl carbinols are addition products of acetylene onto &agr;,&bgr;-unsaturated carbonyl compounds. In order to reduce the tendency of the carbonyl compound to polymerize during the addition reaction, alkali metal acetylides or alkaline earth metal acetylides are generally used as reagent at a low temperature in a dipolar aprotic solvent. Thus, it has been found to be usefull to use a mixed sodium-magnesium acetylide complex or lithium acetylide. The lithium acetylide complex can either be prepared directly in an ether, in which case the additional use of a complexing agent, for example dimethyl sulfoxide or dimethylacetamide, as described in U.S. Pat. No. 3,576,889, is advisable, or the lithium acetylide is prepared in liquid ammonia and the ammonia is subsequently replaced by an ether, corresponding to the process proposed in CH-A-642 936. The reaction with the carbonyl compound is carried out at low temperatures; CH-A-642 936 recommends temperatures in the range from −30 to 20° C., preferably from −20 to 10° C. After the addition reaction, the resulting &agr;-ethynyl carbinolate is hydrolyzed. To work up the product mixture on a laboratory scale, CH-A-642 936 describes drying of the ether phase using sodium sulfate and subsequent distillation using a Vigreux column.
Processes for working up the product mixture from the addition reaction of acetylene onto &agr;,&bgr;-unsaturated carbonyl compounds on an industrial scale are not known to date. Problems are firstly the high hazard potential (the decomposition energy of &agr;-ethynyl carbinols is above 1000 J/g) and secondly the recovery of &agr;-ethynyl carbinols from water-containing mixtures, since &agr;-ethynyl carbinols generally distill off together with water as heteroazeotropes which do separate into two phases but with only a slightly different composition.
In the case of batch distillations, as are described, for example, in CH-A-642 936, there is also an increased hazard potential due to the accumulation of the easily decomposed &agr;-ethynyl carbinols in the bottom of the column.
It is an object of the present invention to provide an industrial-scale, continuous distillation process for isolating &agr;-ethynyl carbinols, which has good economics and ensures a high level of safety when carrying out the process.
We have found that this object is achieved in a process for isolating &agr;-ethynyl carbinols from the liquid reaction mixture from the addition of acetylene onto &agr;,&bgr;-unsaturated carbonyl compounds by distillation by
a) carrying out the distillation continuously,
b) introducing the feed stream in the middle section of a distillation column,
c) azeotropically distilling off the major part of the water with solvent at the top of the column and
d) taking off the target product &agr;-ethynyl carbinol below the feed point to the column.
It has been found that the major part of the water in the liquid reaction mixture from the addition of acetylene onto &agr;,&bgr;-unsaturated carbonyl compounds can be removed azeotropically together with the solvent at the top of the distillation column, thus solving the problem of the separation of the water/&agr;-ethynyl carbinol azeotrope which cannot be carried out directly.
In the addition reaction with acetylene, it is possible in principle to use any &agr;,&bgr;-unsaturated carbonyl compound of the formula
where R
1
and R
4
are each hydrogen or an unbranched or singly or multiply branched aliphatic C
1
-C
10
-radical or an unsubstituted or singly or multiply aliphatically substituted alicyclic C
3
-C
10
-radical or R
1
and R
4
are together an aliphatic C
1
-C
4
-radical which joins both parts of the molecule and R
2
and R
3
are each hydrogen or an aliphatic C
1
-C
3
-radical. Preference is given to using acrolein, methyl vinyl ketone, mesityl oxide, &bgr;-ionone, pseudoionone, citral or cyclopentenone as &agr;,&bgr;-unsaturated carbonyl compounds.
The addition reaction is carried out in a known manner, using an alkali metal acetylide or alkaline earth metal acetylide as reagent at low temperature in a dipolar aprotic solvent. For example, a mixed sodium-magnesium acetylide complex or lithium acetylide can be used. The lithium acetylide complex can be prepared in a known manner either directly in an ether, in which case additions of a complexing agent such as dimethyl sulfoxide, dimethylacetamide or dimethylformamide are advisable, or the lithium acetylide is prepared in liquid ammonia and the ammonia is subsequently replaced by an organic solvent, in particular by an ether. Organic solvents suitable for carrying out the present work-up process are all those which form an azeotrope with water that has a boiling point which is at least 5° C., preferably at least 10° C., lower than that of the &agr;-ethynyl carbinol or that of the azeotrope of the &agr;-ethynyl carbinol with water. These include, in particular, ethers such as diethyl ether, tetrahydrofuran or isopropyl ether and also aliphatic, cycloaliphatic or aromatic hydrocarbons, for example pentane, cyclohexane or toluene, and alcohols, in particular butanol.
A typical reaction mixture from the addition of acetylene onto &agr;,&bgr;-unsaturated carbonyl compounds has the following composition:
&agr;-ethynyl carbinol:
from 2 to 40% by weight, preferably from 5 to
20% by weight,
water:
from 0.1 to 10% by weight, preferably from 1 to
5% by weight,
high boilers:
from 0 to 5% by weight,
intermediate boilers:
from 0 to 2% by weight,
balance:
solvent.
High boilers with reference to the present invention are oligomers and polymers of the &agr;,&bgr;-unsaturated carbonyl compound; they have virtually no vapor pressure.
Intermediate boilers are predominantly substances having a boiling point which is above the boiling point of the respective &agr;-ethynyl carbinol. Intermediate boilers can be, for example, by-products which are formed by reaction of the &agr;,&bgr;-carbonyl compound with the &agr;-ethynyl carbinol.
In the process of the present invention, the liquid reaction mixture from the addition of acetylene onto &agr;,&bgr;-unsaturated carbonyl compounds is fed continuously into the middle section of a distillation column, i.e. the distillation column used according to the present invention has a stripping section.
The target product &agr;-ethynyl carbinol is taken off below the feed point to the column. If the purity requirements are only moderate or if the levels of intermediate and high boilers to be separated off are low, the target product can be taken off at the bottom. However, the target product is generally taken off at a side offtake, preferably at the second to fifth theoretical plate, counted from the bottom.
The distillation column is essentially not subject to any restrictions in respect of construction. In principle, it is possible to use any vacuum distillation column, with preference being given to columns having separation-active internal fittings in the form of structured packing. Particular preference is given to columns which have structured packing in the middle and lower sections and in their upper section have trays, preferably from two to three trays; a droplet precipitator can be provided at the top of the column. Particularly in the case of small boiling point differences between the solvent/water azeotrope and the &agr;-ethynyl carbinol/water azeotrope, the distillation column can also be configured as a dividing wall column.
The preferred operating conditions for the distillation column are:
pressure: from 10 mbar to 1 bar absolute, preferably from 100 to 700 mbar, number of theoretical plates: from 5 to 50, preferably from 7 to 20, particularly preferably from 8 to 15.
In order to be able to carry out condensation using cooling water, it is advantageous to reduce the pressure at the top of t

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