Preparation of 2,4-hexadiyne-1,6-diol

Process for the preparation of 2,4-hexadiyne-1,6-diol of the formula I EQU HO-CH.sub.2 -CH.sub.2 -C.ident.C-.ident.C-CH.sub.2 -OH (I) by the reaction of diacetylene of the formula II EQU H-C.ident.C-C.ident.C-H (II) with formaldehyde of the formula III EQU H.sub.2 C=O (III), in the presence of a silver catalysts, in which the reaction is carried out in the presence of a polar organic solvent at temperatures ranging from 0.degree. to 150.degree. C. and under pressures ranging from 0.01 to 10 bar.

The present invention relates to a process for the preparation of 
2,4-hexadiyne-1,6-diol by the reaction of diacetylene with formaldehyde in 
the presence of a polar solvent and catalytic amounts of a silver 
catalyst. 
DE-A 877,453 and DE-A 869,053 each disclose a process for the preparation 
of 2,4-hexadiyne-1,6-diol by the reaction of aqueous formaldehyde solution 
with diacetylene in the presence of Ag catalysts. Only low conversions of 
diacetylene are found when using an apparatus as described in Example 1 of 
DE-A 877,453 in a safe-to-handle dilution for diacetylene (DE-A 4,137,011 
) giving a very unsatisfactory reaction rate (comparative example A). The 
mode of operation described in DE-A 877,453 to improve the diacetylene 
yield (condensation and recycling of unconverted and degassed diacetylene) 
is impracticable on an industrial scale for reasons of safety. 
It is thus an object of the present invention to overcome the 
aforementioned drawbacks. 
Accordingly, we have found a novel and improved process for the preparation 
of 2,4-hexadiyne-1,6-diol of the formula I 
EQU HO-CH.sub.2 -C.ident.C-C.ident.C-CH.sub.2 -OH (I), 
by the reaction of diacetylene of the formula II 
EQU H-C.ident.C-C.ident.C-H (II), 
with formaldehyde of the formula III 
EQU H.sub.2 C=O (III), 
in the presence of silver catalysts, wherein the reaction is carried out in 
the presence of a polar solvent at temperatures ranging from 0.degree. to 
150.degree. C. and under pressures ranging from 0.01 to 10 bar. 
The process of the invention can be carried out as follows: 
The formaldehyde III, optionally in water or in aqueous solution (formalin 
solution), can be placed in a vessel with a polar solvent in the presence 
of from 0.001 to 5 wt % and preferably from 0.005 to 2 wt % and more 
preferably from 0.01 to 1 wt % of a silver catalyst, and the diacetylene 
bubbled into it at temperatures ranging from 0.degree. to 150.degree. C. 
and preferably from 20.degree. to 130.degree. C. and more preferably from 
70.degree. to 110.degree. C. and pressures ranging from 0.01 to 1.4 bar 
and preferably from 0.1 to 1.2 bar and more preferably at atmospheric 
pressure (standard pressure). 
Suitable silver catalysts usually comprise elementary, metallic silver or 
Ag.sym. salts, in particular silver or silver oxide on inert supports such 
as aluminum oxide or silicon dioxide. 
The present process is particularly suitable for utilizing 
diacetylene-containing partial streams, such as commonly occur in 
industrial plant during separation of the cracked gas coming from the 
dissociation of hydrocarbons under the conditions of acetylene synthesis 
(Ullmann's Encycl. Of Indust. Chem., 5th Edition, A1, 1985 ). The mixtures 
of higher acetylenes (HA) which are formed partly as gas and partly as 
liquid can likewise be used in the process of the invention. 
The gas mixture coming from the plant for working up cracked gas generally 
has an operating temperature which is slightly higher than ambient 
temperature. Preliminary separation, at ambient temperature, of readily 
condensable gaseous components in separating vessels disposed in the 
reactor inlet line improves the purity of the crude product. 
The reaction may be carried out batchwise or, preferably, continuously in 
the gas phase or, preferably, in the liquid phase. Processes which are 
known to achieve good gas distribution in liquids, are advantageously used 
when using a gaseous partial stream, involving, for example, the use of 
equipment such as gassing rings, perforated trays, pressure-gassing 
equipment, spray reactors, or absorber towers. Suitable polar solvents are 
lactams, for example, pyrrolidones such as N-methylpyrrolidone, lactones, 
for example, lactones having 5 to 8 ring members such as butyrolactone, 
esters, for example, C.sub.1 -C.sub.20 alkyl carboxylates such as methyl 
formate, methyl acetate, methyl propionate, ethyl formate, ethyl acetate 
and ethyl propionate, acid amides, for example, dialkyl formamides such as 
dimethyl-formamide, alcohols, for example, C.sub.1 -C.sub.20 alkanols such 
as methanol and ethanol, alkylated ureas or glycol ethers such as ethylene 
glycol diethyi ether. 
2,4-hexadiyne-1,6-diol I is one possible starting point for 
hexane-1,6-diol, which is an important intermediate for the production of 
polyesters, polyurethanes, adhesives, pharmaceuticals and textile 
auxiliaries.

EXAMPLES 
The diacetylene in the stream of gas before and after the reaction was 
detected by gas chromatography on a packed column (20 % of Reoplex 400 on 
Chromosorb PAW) using N.sub.2 as carrier gas (35 mL/min) and using FID 
detection. The concentrations are given in vol %. The concentration of the 
diacetylene as well as the content of substances in the product were 
determined using gas chromatography in liquid phase on a capillary column 
HP1 with the aid of a WLD detector. 
EXAMPLE 1 
A bubble-cap column having a diameter of 25 mm, a height of 1000 mm, and a 
glass frit (pore size 40 to 90 .mu.m) for distributing the gas introduced 
at the bottom of the column was filled with a bed of 150 g of catalyst 
rings (13.7% of elementary Ag on .alpha.-Al.sub.2 O.sub.3 -rings) and with 
a mixture of 100 g of formalin (36% strength) and 100g of 
N-methylpyrrolidone (NMP). 20 L/h of HA (higher acetylenes) gas were 
passed into the solution at a reaction temperature of 95.degree. C. Liquid 
components were condensed from the exhaust gas and recycled, dropwise, to 
the reaction. The concentration of hexadiyne diol rose as a linear 
function of time to a concentration of 9.3 vol % following a period of 
10h, this corresponding to a space-time yield of approximately 15 g of 
product per kilogram of catalyst per hour. Due to the low residual 
concentration of formaldehyde (&lt;5U%) the reaction rate then diminished. 
The average diacetylene depletion was approximately 10% during the first 
30 hours of the experiment. 
EXAMPLE 2 
A bubble-cap column having a diameter of 25 mm, a height of 1000 mm, and a 
glass frit (pore size 40 to 90 .mu.m) for distributing the gas introduced 
at the bottom of the column was filled with a bed of 150 g of catalyst 
rings (13.7% of elementary Ag on .alpha.-Al.sub.2 O.sub.3 -rings), and 200 
g of the solvent mixture stated (formalin was used in each case in the 
form of a 36% strength solution) and 150 g of catalyst (the table below 
indicates the amount of active material and support material) were placed 
in the column and 20 L/h of HA gas were introduced at 95.degree. C. The 
table lists the space-time yield of hexadiyne diol as a function of the 
solvent used for different catalysts. 
TABLE 
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Yields of hexadiyne diol for various solvents 
Ratio by Space-time Yield 
Solvent Mixture volume 
Catalyst [g product/kg (cat) .multidot. 
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h] 
water/hexane-1,6-diol 
1:1 15 wt % Ag/Al.sub.2 O.sub.3 
4 
water/butyrolactone 1:1 15 wt % Ag/Al.sub.2 O.sub.3 
5 
water/ethylene glycol monomethyl ether 
1:1 15 wt % Ag/Al.sub.2 O.sub.3 
2 
water/N-methylpyrrolidone 
1:3 15 wt % Ag/Al.sub.2 O.sub.3 
5 
water/dimethylformamide 
1:1 15 wt % Ag/Al.sub.2 O.sub.3 
6 
water/N-methylpyrrolidone 
1:1 10 wt % Ag/SiO.sub.2 
15 
water/N-methylpyrrolidone 
1:1 5 wt % AgO.sub.2 /Al.sub.2 O.sub.3 
5 
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COMATIVE EXAMPLE A 
A bubble-cap column having a diameter of 25 mm, a height of 1000 mm, and a 
glass frit (pore size 40 to 90 .mu.m) for distributing the gas introduced 
at the bottom of the column was filled with a bed of 150 g of catalyst 
rings (13.7% of elementary Ag on .alpha.-Al.sub.2 O.sub.3 -rings). 
Following the addition of 150 g of formalin (content of formaldehyde 36%) 
20 L/h of HA gas were passed into the solution at a reaction temperature 
of 95.degree. C. Entrained liquid components were condensed from the 
exhaust gas and recycled, dropwise, to the reaction. During a reaction 
period of 30 h the maximum diacetylene depletion was 20%. The average 
depletion was less than 10%. During this period of time the concentration 
of hexadiyne diol (I) formed rose to 1.3 vol %, this being equivalent to a 
space-time yield of 0.45 g per kilogram of catalyst per hour.