Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-10-03
2002-04-30
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S461000, C568S463000, C568S464000, C568S852000
Reexamination Certificate
active
06380443
ABSTRACT:
The present invention relates to a process for preparing 1,3-diols having 6 or more carbon atoms by means of the aldol reaction.
1,3-Diols having six or more carbon atoms in the basic skeleton are versatile starting materials in the chemical industry. They can be used, for example, in the production of polyesters, polyurethanes, coatings raw materials, dispersions and plasticizers.
Such materials include 1,3-diols having eight carbon atoms for example 2-ethylhexane-1,3-diol (EHD), 2,2-dimethylhexane-1,3-diol (DMHD), 2,2,4-trimethylpentane-1,3-diol (TMPD) and 2-ethyl-4-methylpentane-1,3-diol (EMPD). These materials are additionally used as insect repellents.
It is known from WO A 97/16401 that such 1,3-diols can be prepared by hydroformylation of an olefin to give the corresponding aldehyde, subsequent aldol reaction with a further aldehyde with addition of an aldol catalyst and subsequent hydrogenation.
Wo 95/07254 describes a process for producing EHD by base-catalyzed reaction of n-butyraldehyde (n-BA) in the presence of a phase transfer catalyst. The yield indicated there is about 56%.
The preparation of EHD by means of aldol addition is also described in JP 2040-333-A. Here, n-BA is reacted in the presence of NaOH or KOH in butanol to give a mixture of 2-ethyl-3-hydroxyhexanal, the dehydration product 2-ethylhexenal derived therefrom and higher-boiling aldol-like condensation products. The selectivity of this aldol reaction is 86% and the conversion achieved is about 58%. The resulting mixture is neutralized with acetic acid and subsequently subjected to catalytic hydrogenation over a Raney nickel catalyst.
JP-A 1299-240 describes a similar process in which sodium methoxide in butanol is used as catalyst.
U.S. Pat. No. 4,225,726 discloses the use of tin or tin oxide as catalyst for preparing the butyric ester of, for example, EHD.
However, the above-described processes have the following disadvantages:
The incomplete conversion of n-BA means that n-butanol is obtained as a significant by-product in the hydrogenation. Although n-BA could be separated off prior to the hydrogenation, this results in additional costs.
In addition, the known processes employ catalysts for the aldol reaction. If the aldol catalyst is still present in the subsequent steps, for instance a hydrogenation or distillation, the aldol addition product (2-ethyl-3-hydroxyhexanal when n-BA is used as starting material) can be redissociated; furthermore, 2-ethyl-3-hydroxyhexanal can also enter into yield-reducing secondary reactions. For this reason, complicated removal of the catalyst, for example by neutralization, washing and absorption, is necessary in this case in order to avoid losses in yield. The aldol catalyst can likewise impair the efficiency of the hydrogenation or even poison the hydrogenation catalyst.
The formation of the abovementioned dehydration product cannot be avoided in the presence of a catalyst and causes an additional loss in yield.
The route for preparing the diol via an ester, for example the preparation of EHD via the butyric ester described in U.S. Pat. No. 4,225,726, requires an additional process step. Although the saponification of the ester does give EHD, i.e. the desired diol, it also forms the acid component of the ester, e.g. butyric acid or a salt of butyric acid, as coproduct. The removal of such coproducts is once more associated with additional costs.
The aldol reaction also forms a series of by-products such as esters, ethers, aldoxanes, hemiacetals and acetals of the aldehyde which lead, after hydrogenation, to a broad spectrum of by-product. This in turn makes it considerably more difficult to isolate the pure diol by distillation.
It is an object of the present invention to provide a simple and inexpensive process for preparing 1,3-diols which, in particular, avoids or at least reduces the disadvantages of the abovementioned conventional processes.
We have found that this object is achieved by preparing 1,3-diols having 6 or more carbon atoms in a simple manner by thermal treatment of alkanals.
The present invention accordingly provides a process for preparing 1,3-diols having 6 or more carbon atoms, which comprises the following steps:
a) provision of at least one alkanal having 3 or more carbon atoms,
b) thermal treatment of the alkanal in the absence of a basic catalyst,
c) hydrogenation of the aldol addition product formed in step b) to give the 1,3-diol, and
d) isolation of the 1,3-diol.
The process of the present invention starts out, as per step a), from at least one alkanal having three or more carbon atoms, in particular n-butyraldehyde and i-butyraldehyde. The alkanal can be provided by means of customary processes for preparing alkanals. The alkanal is preferably provided by means of the oxo process, in particular starting from ethylene or propylene. The oxo process is known, for example from Ullmann's Encyclopedia of Industrial Chemistry, Vol. A18, 321, 5
th
Edition. In the oxo process, the olefin is reacted with carbon monoxide and hydrogen in the presence of a transition metal catalyst, generally rhodium or cobalt, under superatmospheric pressure and at elevated temperature. In the case of olefins having 3 or more carbon atoms, the oxo process generally gives a mixture of isomers of the corresponding alkanal. Thus, for example, the oxo process starting from propylene gives a mixture of i-butyraldehyde (i-BA) and n-butyraldehyde (n-BA). Depending on the process conditions, the ratio of i-BA to n-BA can vary from about 50/50 to 5/95. The process of the present invention can be carried out starting from one alkanal or a mixture of two or more alkanals of any composition, with the alkanals preferably having from 3 to 10 carbon atoms.
In step (b), the alkanal is subjected to a thermal treatment in the absence of a basic catalyst as is customarily used for an aldol addition. In the thermal treatment, a thermally induced aldol addition occurs to form the corresponding aldol addition product. The thermal treatment is preferably carried out during a distillation or hydrogenation of the alkanal. The crude product obtained in the provision of the alkanal can, for example, be subjected to a distillation to purify the alkanal or to fractionate an alkanal mixture. In the distillation, as mentioned, a thermally induced aldol addition occurs to form the corresponding aldol addition product. This has a higher boiling point than the corresponding alkanal and therefore accumulates in the high-boiling fraction obtained in the distillation. In order to obtain the 1,3-diol, the high-boiling fraction has to be subjected to a hydrogenation. This is carried out under the conditions customary for the hydrogenation of alkanals, i.e. in the presence of a hydrogenation catalyst, for example as described in DE 12 69 605, in the liquid or gas phase. Examples of suitable catalysts are copper chromite, supported nickel, copper or cobalt catalysts which may be doped with, for example, Mo, Mn or Cr, with suitable support materials being, for example, silica, kieselguhr, carbon, zirconium oxide, silicon carbide and the like. Further suitable catalysts are catalysts comprising noble metals such as Pd, Pt or Rh. The pressure at which the hydrogenation is carried out is preferably in the range from 1 to 250 bar, in particular from 10 to 150 bar. The temperature is generally in the range from 50 to 250° C., in particular from 100 to 210° C. The high-boiling fraction comprising the aldol addition product is preferably hydrogenated together with the alkanal.
In a further embodiment, the thermal treatment is carried out during a hydrogenation of an alkanal. The hydrogenation is carried out under the abovementioned conditions, resulting in formation of the aldol addition product. This aldol addition product is at the same time reduced to the 1,3-diol. The hydrogenation of a pure alkanal gives the corresponding 1,3-diol, while hydrogenation of an alkanal mixture gives a mixture of the corresponding 1,3-diols.
In step c), the 1,3-diol is then isolated in a customary manner. This is prefer
Helf Volker
Kratz Detlef
Krokoszinski Roland
Rust Harald
Barts Samuel
BASF - Aktiengesellschaft
Keil & Weinkauf
Price Elvis O.
LandOfFree
Preparation of 1,3-diols does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preparation of 1,3-diols, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of 1,3-diols will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2911008