Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From organic oxygen-containing reactant
Reexamination Certificate
2002-12-04
2004-12-21
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From organic oxygen-containing reactant
C528S480000, C528S495000, C528S488000, C528S501000, C528S503000, C558S276000, C558S265000
Reexamination Certificate
active
06833433
ABSTRACT:
The present invention relates to a new process for the production of aliphatic oligo-carbonate diols from aliphatic diols by a multistage transesterification with dimethyl carbonate (DMC) with an almost complete consumption of the carbonate that is used. The process according to the invention enables a particularly high-yield production of aliphatic oligocarbonate diols to be achieved starting from easily accessible DMC.
Aliphatic oligocarbonate diols have been known for a long time as important intermediate products, for example in the production of plastics, lacquers and adhesives, for example by reaction with isocyanates, epoxides, (cyclic) esters, acids or acid anhydrides. They can be obtained in principle from aliphatic diols by reaction with phosgene (e.g. DE-A 1 595 446), bis-chlorocarbonic acid esters (e.g. DE-A 857 948), diaryl carbonates (e.g. DE-A 1 915 908), cyclic carbonates (e.g. DE-A 2 523 352: ethylene carbonate) or dialkyl carbonates (e.g. DE-A 2 555 805).
Of the carbonate sources, diphenyl carbonate (DPC) belonging to the diaryl carbonates is of particular importance since aliphatic oligocarbonate diols of particularly high quality can be produced from DPC (e.g. U.S. Pat. No. 3,544,524, EP-A 292 772). In contrast to for example aliphatic carbonate sources, DPC reacts quantitatively with aliphatic OH groups so that, after removal of the phenol that is formed, all terminal OH groups of the oligocarbonate diol are available for reaction with for example isocyanate groups. In addition only very small concentrations of soluble catalyst are required, with the result that the latter can remain in the product.
The processes based on DPC have the following disadvantages however:
Only ca. 13% of the DPC remains in the product, the remainder being distilled off as phenol. Depending on the respective alkyl radical, a substantially higher proportion of the dialkyl carbonates remains in the subsequent product. For example, ca. 31% of the dimethyl carbonate (DMC) remains in the subsequent product, since the methanol that is distilled off has a substantially lower molecular weight than phenol.
Accordingly, due to the fact that high boiling point phenol (normal boiling point: 182° C.) has to be separated from the reaction mixture, only diols having a boiling point that is considerably above 182° C. can be used in the reaction in order to avoid the diol being unintentionally distilled off.
Dialkyl carbonates, in particular dimethyl carbonate (DMC), as starting components are characterised by a better availability on account of their ease of production. For example, DMC can be obtained by direct synthesis from MeOH and CO (e.g. EP-A 0 534 454, DE-A 19 510 909).
Numerous patent applications (e.g. U.S. Pat. No. 2,210,817, U.S. Pat. No. 2,787,632, EP-A 364 052) relate to the reaction of dialkyl carbonates with aliphatic diols:
It is known from the state of the art to mix aliphatic diols together with a catalyst and the dialkyl carbonate (e.g. diethyl carbonate, diallyl carbonate, dibutyl carbonate) and distil off the alcohol that is formed (ethanol, butanol, allyl alcohol) from the reaction vessel through a column. The higher boiling point, co-evaporated dialkyl carbonate is separated in the column from the lower boiling point alcohol and is recycled to the reaction mixture.
In contrast to DPC, dialkyl carbonates do not react quantitatively with aliphatic OH groups since the transesterification of two aliphatic alcohols involves an equilibrium reaction. Thus, after the removal of the alcohol that is formed a proportion of the desired terminal OH groups are present not as OH groups but as alkoxycarbonyl terminal groups (—OC(O)—OR2 group in formula I, wherein R2 denotes an alkyl radical and R1 denotes an alkylene radical).
These alkoxycarbonyl terminal groups are unsuitable for further reaction with for example isocyanates, epoxides, (cyclic) esters, acids or acid anhydrides. The reaction is therefore completed by applying a vacuum in order to de-cap and remove the alcohol that is formed. The reaction mixtures are normally heated and stirred in vacuo in order to achieve this objective, although the quality of oligocarbonate diols that can be achieved is not as good as is obtained by reaction with DPC.
EP-A 0 364 052 describes for example a process in which a degree of utilisation of the terminal OH groups of only ca. 97% is achieved at 200° C. and under a vacuum of ca. 50 Torr (ca. 66 mbar). Even under considerably more drastic conditions the degrees of utilisation of the terminal OH groups can be increased only insignificantly. At 1 Torr (ca. 1.3 mbar) degrees of utilisation of only ca. 98% are achieved (EP-A 0 798 328).
The use of dimethyl carbonate (DMC) to produce aliphatic oligocarbonate diols has been known only for a fairly short time despite its good accessibility (e.g. U.S. Pat. No. 5 171 830, EP-A 798 327, EP-A 798 328, DE-A 198 29 593).
When using DMC to produce oligocarbonate diols low boiling point azeotropic DMC-methanol mixtures are formed that contain, depending on the pressure, ca. 20 to 30 wt. % of DMC (ca. 30 wt. % at normal pressure). A relatively large effort and expenditure is required to separate these azeotropic mixtures into methanol and DMC (e.g. membrane separation). The DMC that is azeotropically distilled off is accordingly lost to the reaction and is no longer available for a complete conversion. The lost DMC therefore has to be replenished by additional fresh DMC.
In EP-A 0 358 555 and U.S. Pat. No. 4,463,141 it is for example in addition simply recommended to take into account, during the weighing in, the amount of DMC that is azeotropically distilled off.
In EP-A 0 798 328 the corresponding diol component is reacted with DMC accompanied by distillation of the azeotropic mixture. The subsequent de-capping takes place under vacuum distillation, whereby under very drastic vacuum conditions (I Torr, ca. 1.3 mbar) degrees of utilisation of the terminal OH groups of ca. 98% can be achieved (EP-A 0 798 328: Table 1). No details of the remaining azeotropic mixture and the loss of the DMC are given.
EP-A 798 327 describes a two-stage process in which a diol is first of all reacted with an excess of DMC with distillation of the azeotropic mixture to form an oligo-carbonate whose terminal OH groups are completely inaccessible, being methoxycarbonyl terminal groups. After removal of the catalyst and distillation of the excess DMC in vacuo (65 Torr, 86 mbar), the oligocarbonate diol is obtained in a second stage by adding further amounts of the diol and a solvent (e.g. toluene) as entrainment agent for the methanol that is formed. Solvent residues then have to be distilled off in vacuo (50 Torr, 67 mbar). The degree of utilisation of the terminal OH groups according to this process is only ca. 97%. The disadvantage of this process is that it is complicated due to the use of a solvent and due to the multiple distillation, low degree of utilisation of the terminal OH groups, as well as the very high DMC consumption.
In DE-A 198 29 593 a diol is reacted with DMC, the methanol that is formed being distilled off. This publication does not give any details of the overall azeotropic distillation procedure, apart from a single mention of the word “azeotrope” in the Table “Flow chart of the process according to the invention”. Claim 1c states that the molar ratio of methanol to DMC in the distillate is between 0.5:1 and 99:1. The DMC content in the methanol that is distilled off is accordingly between 85 wt. % and 2.8 wt. %. As a detailed analysis shows (see below), in DE-A 198 29 593 DMC is in fact also used in excess and is distilled off azeotropically. Accordingly, ca. 27.8% of the DMC that is used is lost.
As Comparison Example 1 shows (see below), DMC contents in the distillate of less than 20% can be achieved only at high catalyst concentrations (ca. 0.15% Ti(O-iPr)
4
, corresponding to ca. 250 ppm Ti) and very long reaction times. At these high catalyst concentrations the catalyst cannot be left in the product after the end of the reaction, but has to be neutrali
Laue Jörg
Schlemenat Andreas
Tillack Jörg
Witossek Herbert
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Truong Duc
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