Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Patent
1996-05-16
1997-07-08
Bond, Robert T.
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
540451, 546243, 548553, C07D20108
Patent
active
056462778
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel process for preparing cyclic lactams by reacting amino carbonitriles with water in the presence of catalysts.
U.S. Pat. No. 4,628,085 discloses the reaction of 6-aminocapronitrile with water in the gas phase on acidic silica gel at 300.degree. C. The reaction takes place quantitatively with an initial selectivity of 95% to produce caprolactam, but the productivity and selectivity are found to decline rapidly. A similar process is described in U.S. Pat. No. 4,625,023, in which a highly diluted gas stream composed of 6-aminocapronitrile, adiponitrile, ammonia, water and carrier gas is passed over a silica gel catalyst bed and a copper/chromium/barium/titanium oxide catalyst bed. Caprolactam is obtained with a selectivity of 91% and a conversion of 85%. In this case too there is rapid inactivation of the catalyst.
U.S. Pat. No. 2,301,964 relates to the uncatalyzed conversion of 6-aminocapronitrile to caprolactam in aqueous solution at 285.degree. C. The yields are below 80%.
FR-A 2 029 540 describes a process for cyclization of 6-aminocapronitrile to caprolactam, using catalysts, which are metallic Zn or Cu powder, or oxides, hydroxides, halides, cyanides of rubidium, lead, mercury or elements with an atomic number of from 21 to 30 or 39 to 48. These catalysts are used as suspended catalysts in stirred autoclaves operated batchwise. Caprolactam is obtained in yields of up to 83%. However, there are problems in complete removal of the catalysts from the required caprolactam because the latter may form compounds with the soluble constituents of the metals used, or extremely fine particles may be produced by mechanical agitation.
It is an object of the present invention to provide a process for preparing cyclic lactams by reacting amino carbonitriles with water in the presence of catalysts which does not entail the disadvantages described above, provides high yields and selectivities and allows continuous operation.
It was furthermore intended to keep the amount of catalyst used as small as possible. In addition, it was intended to avoid the separation problems occurring in a suspension procedure, whether by complexation of the soluble constituents of the catalyst with components of the reaction mixture or due to extremely fine particles resulting from the high mechanical stress during agitation.
We have found that this object is achieved by carrying out the reaction in liquid phase in a fixed bed reactor in the presence of heterogeneous catalysts which have no soluble constituents under the reaction conditions. The heterogeneous catalysts are located in a fixed bed through which the reaction mixture flows continuously in a downward or upward direction.
Preferred embodiments of the process according to the invention are evident from the dependent claims.
The starting materials employed in the process according to the invention are amino carbonitriles, preferably those of the general formula I ##STR1## where n and m are each 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and n+m total at least 3, preferably at least 4.
R.sup.1 and R.sup.2 can, in principle, be substituents of any type, it merely being necessary to ensure that the required cyclization is unaffected by the substituents. R.sup.1 and R.sup.2 are preferably, independently of one another, each C.sub.1 -C.sub.6 -alkyl, C.sub.5 -C.sub.7 -cycloalkyl or C.sub.6 -C.sub.12 -aryl.
Particularly preferred starting compounds are amino carbonitriles of the general formula 6-aminocapronitrile.
In the process according to the invention, the amino carbonitriles described above are reacted with water in liquid phase using heterogeneous catalysts to give cyclic lactams. Use of amino carbonitriles of the formula I results in the corresponding cyclic lactams of the formula II ##STR2## where n, m, R.sup.1 and R.sup.2 have the abovementioned meanings. Particularly preferred lactams are those where n is 0 and m is 4, 5 or 6, in particular 5 (in the latter case, caprolactam is obtained).
The reaction is carried out in liquid phase at, in general, f
REFERENCES:
patent: 2301964 (1942-11-01), Martin
patent: 4625023 (1986-11-01), Mares et al.
patent: 4628085 (1986-12-01), Mares et al.
Fuchs Eberhard
Witzel Tom
BASF Aktiengellschaft
Bond Robert T.
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