Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-07-13
2001-07-24
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S319000
Reexamination Certificate
active
06265618
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a process for the preparation of ketones. More specifically, this invention pertains to the preparation of ketones by contacting one or more carboxylic acids with a niobium catalyst at elevated temperatures.
BACKGROUND OF THE INVENTION
The synthesis of ketones by contacting carboxylic acids with various metal oxide catalysts at elevated temperatures is well-known. For example, in U.S. Pat. No. 4,754,074 Hussman describes a process for the generation of dialkyl ketones using manganese dioxide supported on alumina. The Hussman patent provides an excellent overview of the prior art up to about 1988 and provides a comparison of the various prior art catalysts useful in the generation of diethyl ketone from propionic acid. Active catalysts include oxides of lead, iron, zirconium, manganese, thorium, and neodymium, with zirconium and thorium being preferred prior to Hussman's discovery of the use of manganese on alumina catalyst.
In addition to the prior art described by Hussman, several additional prior art references describe the preparation of ketones from carboxylic acids. In German Patent 2,758,113 (1979), Froelich, et al. describe the use of thorium and/or zirconium oxides with anatase (TiO
2
) along with an optional additional support, such as alumina. German Patent 2,111,722 describes an improved process for the generation of ketones from carboxylic acids by the addition of steam to thorium oxide catalyzed processes. These processes and those described by Hussmann are conducted in the vapor phase. However, Japanese Patent 93/016419 (1983) departs from the normal vapor phase process and describes a liquid phase process using a zirconium oxide catalyst.
U.S. Pat. No. 5,808,148 (1998) discloses a process for the preparation of methacrylic acid by contacting formaldehyde and propionic acid in the presence of a niobium catalyst, preferably supported on silica. This process also produces very small amounts of diethyl ketone.
BRIEF SUMMARY OF THE INVENTION
We have discovered that catalysts comprising niobium are very efficient catalysts for the conversion of carboxylic acids to ketones, such as the generation of diethyl ketone from propionic acid. Our invention, therefore, provides a process for the preparation of a ketone by contacting at least one carboxylic acid with a niobium oxide catalyst at elevated temperatures in the substantial absence of formaldehyde. The present process is useful for the synthesis of a variety of ketones using a variety of carboxylic acids as starting material. We have found that when used in the process of this invention the catalyst is: (1) not subject to rapid deactivation, (2) most active after being operated for a number of hours, (3) demonstrates its best selectivity when operated for multiple hours, and (4) demonstrates its lowest rates immediately after reactivation. This contrasts markedly with the process in U.S. Pat. No. 5,808,148, which deactivates relatively rapidly, with a notable accompanying loss of selectivity, requiring frequent reactivation. Furthermore, the fastest rates obtained by the process of U.S. Pat. No. 5,808,148 occur immediately after reactivation.
DETAILED DESCRIPTION
The present process comprises contacting at least one carboxylic acid with a niobium catalyst at elevated temperature in the absence, or substantial absence, of formaldehyde to produce at least one ketone. When using a single carboxylic acid to produce a single ketone, the carboxylic acid contains at least one &agr;-hydrogen atom, e.g., carboxylic acids having the general formula
(R
1
)(R
2
)CHCOOH (I)
wherein R
1
and R
2
are selected from hydrogen, alkyl, alkenyl, cycloalkyl, carbocyclic aryl and heterocyclic aryl. In addition to carboxylic acid reactant (I), a second carboxylic acid reactant may be utilized to prepare a mixture of ketones, including an unsymmetrical ketone. The second carboxylic acid reactant may have the general formula
R
3
COOH (II)
wherein R
3
is selected from alkyl, alkenyl, cycloalkyl, and carbocyclic and heterocyclic aryl. The ketone product or products obtained from the process have the general formulas
(R
1
)(R
2
)CHC(═O)CH(R
1
)(R
2
) (III)
and
(R
1
)(R
2
)CHC(═O)CR
3
(IV)
The alkyl radicals which R
1
, R
2
and R
3
may represent may be unbranched or branched, unsubstituted or substituted alkyl containing up to about 20 carbon atoms. Example of the substituents which may be present on the alkyl radicals include alkoxy, e.g. C
1
to C
4
alkoxy; halogen, e.g., chloro and bromo; and aryl, e.g., phenyl and tolyl. The alkyl radicals preferably contain up to 12 carbon atoms, and most preferably are unsubstituted alkyl containing up to about 6 carbon atoms. The alkenyl radicals which R
1
, R
2
and R
3
may represent also may be unbranched or branched, unsubstituted or substituted alkenyl containing up to about 20 carbon atoms. The cycloalkyl radicals may contain 5 to 7 ring carbon atoms and may be substituted with alkyl, e.g., C
1
to C
4
alkyl; alkoxy, e.g., C
1
to C
4
alkoxy; and/or halogen, e.g., chloro and bromo. The aryl radicals which R
1
, R
2
and R
3
may represent may contains up to about 10 carbon atoms such as phenyl; phenyl substituted with alkyl, e.g., C
1
to C
4
alkyl; alkoxy, e.g., C
1
to C
4
alkoxy; and/or halogen, e.g., chloro and bromo; naphthyl; and naphthyl substituted with alkyl, e.g., C
1
to C
4
alkyl; alkoxy, e.g., C: to C
4
alkoxy; and/or halogen, e.g., chloro and bromo. Carboxylic acid reactant (I) preferably contains at least two &agr;-hydrogen atoms, i.e., R
2
preferably is hydrogen. The reactant employed in the present process consists essentially of one or more carboxylic acids, i.e., the process is carried our in the absence of any amount of formaldehyde which would interfere with the production of ketone products. It will be apparent to those skilled in the art that the radicals represented by (R
1
)(R
2
)CH and R
3
may be the same or different.
The niobium catalyst used to effect the transformation of the carboxylic acids to ketones according to the present invention may be unsupported niobium oxide or, preferably, in the form of a supported catalyst comprising niobium oxide supported on a catalyst support material such as silica, alumina, and titania. These catalysts are well known and may be prepared by conventional techniques. For example, the generation of niobium-silica catalysts using a co-precipitation of silica and niobium oxide is described in U.S. Pat. No. 5,808,148 while an impregnation technique is described in H. Yoshida, T. Tanaka, T. Yoshida, T. Funabiki, and S. Yoshida,
Catalysis Today,
28, 79 (1996). Further, in J. C. Vedrine, G. Coudurier, A. Ouqour, P. G. Pries de Oliveira, and J. C. Volta,
Catalysis Today,
28, 3 (1996), methods for the generation of niobium-alumina catalysts as well as methods for the generation of pure niobium oxide are described. Alternatively, impregnation techniques for the generation of niobium oxide on alumina are described in J. G. Weissman,
Catalysis Today,
28, 3 (1996). The catalytically active niobium is believed to be present primarily as Nb
2
O
5
although other known oxides such as Nb
2
O
3
and NbO
2
may be present.
The amount of niobium in or on the catalysts useful in the present invention may vary from 1 weight percent Nb on supported catalysts to 70 weight percent niobium in the case of pure niobium (V) oxide. The preferred supported catalysts comprise about 5 to 35 weight percent niobium, based on the total weight of the catalyst, deposited on a catalyst support material such as silica, alumina, and titania. Silica is the preferred catalyst support.
The activity and/or selectivity of the above described, niobium catalysts may be enhanced by contacting the above catalysts with an inorganic basic compound to obtain a base-exchanged, niobium catalyst. Such base-exchanged, niobium catalysts are especially advantageous when the carboxylic acid feedstock or ketone product contains one or more groups sensitive to the condit
Crooks Courtney Ann
Wilson Bruce Edwin
Zoeller Joseph Robert
Blake Michael J.
Eastman Chemical Company
Gwinnell Harry J.
Richter Johann
Witherspoon Sikarl A.
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