METHOD FOR THE PRODUCTION OF UNBRANCHED ACYCLIC OCTACTRIENES
The invention relates to the preparation of one or more unbranched acyclic octatriene(s) by dimerization of 1,3-butadiene in the presence of a catalyst comprising a carbene ligand and an element of transition group VIII of the Periodic Table of the Elements as metal.
1 . A process for preparing linear octatrienes from 1,3-butadiene or 1,3-butadiene-containing hydrocarbon mixtures, wherein the dimerization of the 1,3-butadiene is carried out in the presence of a secondary alcohol and a base, and a complex of a metal of transition group eight of the Periodic Table of the Elements having at least one carbene of the structure L
where R1 and R2=C 1 -C 3 -alkyl radical and R3 and R4=H or C 1 -C 3 -alkyl radical, with the radicals R1 and R2 or R3 and R4 being able to be identical or different, as ligand is used as catalyst.
2 . The process as claimed in claim 1 , wherein the catalyst comprises 1,3-bis(2,6-diisopropylphenyl)-4,5-dimethyl-2-dehydro-3-hydroimidazole (structural formula L1) as carbene ligand.
3 . The process as claimed in claim 1 , wherein a catalyst having palladium or nickel as metal is used.
4 . The process as claimed in claim 1 , wherein alkoxides are used as base.
5 . The process as claimed in claim 1 , wherein alkali metal hydroxides are used as bases.
6 . The process as claimed in claim 1 , wherein isopropanol is used as secondary alcohol.
7 . The process as claimed in claim 1 , wherein cyclohexanol is used as secondary alcohol.
8 . The process as claimed in claim 1 , wherein the carbene of the structure L and the metal complex derived therefrom are generated in situ from an imidazolium salt of the general structure S
where R1 and R2=C 1 -C 3 -alkyl radical and R3 and R4=H or C 1 -C 3 -alkyl radical, with the radicals R1 and R2 or R3 and R4 being able to be identical or different, and a metal compound.
9 . The process as claimed in claim 8 , wherein the carbene 1,3-bis(2,6-diisopropylphenyl)-4,5-dimethyl-2-dehydro-3-hydroimidazole and the metal complex derived therefrom are generated in situ from a 1,3-bis(2,6-diisopropylphenyl)-4,5-dimethyl-3-hydroimidazolium salt of the general structure S1 and a metal compound.
10 . The process as claimed in claim 1 , wherein a butadiene-containing C 4 fraction is used as starting material.
11 . The process as claimed in claim 1 , wherein the concentration of the catalyst, formally reported in ppm (mass) of metal based on the total mass, is from 0.01 ppm to 1000 ppm.
12 . The process as claimed in claim 1 , wherein the ratio (mol/mol) of carbene L to metal is set in the range from 0.01/1 to 250/1.
13 . The process as claimed in claim 1 , wherein at least one further ligand is present in addition to the carbene ligand.
14 . The process as claimed in claim 13 , wherein at least 1,1,3,3-tetramethyl-1,3-divinyldisiloxane is present as a further ligand in addition to the carbene ligand.
15 . The process as claimed in claim 13 , wherein the ratio of the at least one further ligand to the carbene ligand L is preferably from 0.1:1 to 10:1.
16 . A mixture of octatrienes prepared by the process as claimed in claim 1 .
17 . (canceled)
18 . A carbene complex catalyst which is a ligand complex of a metal of transition group eight of the Periodic Table of the Elements which has at least one carbene of the structure L,
where R1 and R2=C 1 -C 3 -alkyl radical and R3 and R4=H or C 1 -C 3 -alkyl radical, with the radicals R1 and R2 or R3 and R4 being able to be identical or different, as ligand.
19 . A process for preparing linear octenes comprising hydrogenating the mixture of octatrienes as claimed in claim 16 .
20 . Linear octenes produced by a process comprising hydrogenating the mixture of octatrienes as claimed in claim 16 .