Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2001-04-25
2002-03-05
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
Reexamination Certificate
active
06353127
ABSTRACT:
The invention relates to a process for the preparation of &agr;-chloronitriles by reaction of cyanohydrins with phosgene.
&agr;-Chloronitriles of the formula I can be used as versatile intermediates in a number of reactions. Thus, for example, it is possible to obtain &bgr;-chloroamines by hydrogenation of the nitrile group. Acidic hydrolysis of the nitrile group gives &agr;-chlorocarboxylic acids, which are only obtainable by another method by chlorination of carboxylic acids. By exchanging the chlorine substituents it is possible to prepare a number of other secondary products.
The literature discloses a number of synthesis routes for the preparation of &agr;-chloronitriles. A frequently used process is the chlorination of nitrites in the &agr;-position. A variety of chlorine carriers are suitable for this purpose. For example, chlorination reactions which chlorine, sulfonyl chloride, alkali metal and alkaline earth metal hypochlorites and with alkali metal salts of N-chloroarylsulfonamides have been described.
However, these chlorination reactions have the disadvantage that &agr;,&agr;-dichloronitriles are formed in relatively large amounts as secondary products or even as the main product.
In another synthesis route for the preparation of &agr;-chloronitriles, cyanohydrins of the formula II are reacted with chlorine with substitution of their hydroxyl group.
Cyanohydrins can be readily synthesized by addition of hydrocyanic acid to aldehydes and ketones. Substitution of the hydroxyl group for a chlorine substituent can be carried out with a variety of inorganic reagents. The literature frequently describes the use of inorganic acid halides. Suitable compounds are, for example, phosphorus pentachloride, phosphorus trichloride and thionyl chloride.
Phosgene is particularly suitable since in a reaction of phosgene with cyanohydrins only carbon dioxide forms as secondary product, which escapes from the system in gaseous form. Furthermore, phosgene is a valuable chlorinating reagent, meaning that the reaction with phosgene is an economical route for the preparation of &agr;-chloronitriles. Since phosgene on its own is too unreactive for the reaction with cyanohydrins at suitable reaction temperatures and pressures, the reaction is usually carried out in the presence of a catalyst.
J4 9001 516 (DW 0740037211V) describes a process for the preparation of chloroacetonitrile by reaction of glycolonitrile with phosgene using dimethylformamide (DMF) as catalyst.
J. Chem. Soc. 1935, p. 1059 discloses the reaction of acetaldehyde cyanohydrin with phosgene in the presence of equimolar amounts of pyridine. In the reaction, as well as the carbonate which forms as the main product, the corresponding &agr;-chloronitrile is formed in 6% yield. As well as the small amounts of &agr;-chloronitrile, a disadvantage of this process is that because pyridine is used as auxiliary base, the hydrochloride of the base is produced as coupling product, which on a larger scale hinders work-up and disposal.
It is an object of the present invention to provide a process for the preparation of &agr;-chloronitriles which can be used for a large number of compounds by reaction of cyanohydrins of aldehydes and ketones with phosgene.
We have found that this object is achieved by a process for the preparation of &agr;-chloronitriles by reaction of cyanohydrins of aldehydes or ketones with phosgene using a catalyst, where the catalyst is a phosphine oxide.
The process has the advantage that it can be used for a large number of compounds. Low-cost phosgene can be used, meaning that the process according to the invention is an economical route for the preparation of &agr;-chloronitriles.
Furthermore, the only byproducts which forms is gaseous carbon dioxide, meaning that work-up of the reaction mixture is problem-free, or that the reaction discharge can be used directly, without work-up, for subsequent syntheses.
The process according to the invention produces &agr;-chloronitriles of the formula I. The radicals R
1
and R
2
can be arbitrary, provided they are inert toward phosgene. They correspond to the radicals R
1
and R
2
of the cyanohydrins used in the process according to the invention, which are discussed later and to which reference is made here.
Catalysts which can be used are phosphine oxides, e.g. Trialkyl- and triarylphosphite oxides. They can be used as individual compounds or as mixtures of different phosphine oxides. Particularly suitable tri aryl-phosphine oxides are triphenylphosphine oxide and tri-p-halogenophenylphosphine oxides. Preferred trialkylphosphine oxides are those with C3- to C18-alkyl radicals, where the alkyl radicals can be identical or different, such as trihexyl-, tributyl-, trioctyl- and tri(2-ethylhexyl)phosphine oxide.
It is possible to use either solid or liquid phosphine oxides. Because they are easier to meter, liquid phosphine oxides are preferred. Very particular preference is therefore given to a liquid mixture of C
6
- to C
8
-trialkylphosphine oxides as catalyst, as sold, for example, under the trade name Cyanex® 923 by Cytec Industries Inc., N.J., USA.
The catalysts are generally used in an amount of from 0.5 to 5 mol %, preferably from 1 to 2.5 mol %, based on the cyanohydrin used.
Suitable cyanohydrins in the process according to the invention are cyanohydrins of the formula II. It is possible to use cyanohydrins of aldehydes or ketones, and the cyanohydrin of formaldehyde.
The radicals R
1
and R
2
can be arbitrary, provided they are inert toward phosgene.
Radicals containing NH, OH and SH groups are therefore excluded. R
1
and R
2
are generally independently of one another hydrogen, aliphatic, cycloaliphatic, aromatic or araliphatic radicals. These can be substituted with heteroatoms, or their carbon chains can be interrupted by heteroatoms. The aliphatic radicals can be branched or unbranched, as desired. They preferably contain from 1 to 12 carbon atoms. Examples of aliphatic radicals are methyl, ethyl, n-propyl, etc. Suitable cycloaliphatic radicals are preferably those having from 5 to 8 carbon atoms such as cyclopentyl or cyclohexyl. The aromatic radicals preferably have from 6 to 12 carbon atoms. The aromatic radicals can be unsubstituted or substituted by alkyl or aryl substituents or heteroatoms, as desired. The aromatic radicals are preferably mono- or disubstituted. Examples of aromatic radicals are phenyl and chlorophenyl. Suitable araliphatic radicals are preferably those having from 7 to 13 carbon atoms. An example of a preferred araliphatic radical is benzyl.
The cyanohydrins used are preferably the cyanohydrins of aldehydes (either R
1
or R
2
in formula II is H). Particular preference is given to the cyanohydrins of unbranched or branched aliphatic aldehydes, cyano-hydrins of unsubstituted aromatic aldehydes, in particular benzaldehyde cyanohydrin, or cyanohydrins of mono- or disubstituted aromatic aldehydes such as benzaldehyde or p-chlorobenzaldehyde.
The cyanohydrins used are obtainable by reaction of the corresponding aldehydes and ketones with hydrocyanic acid (hydrogen cyanide), as described, for example, by C. Grundmann in Houben-Weyl, 4th Edition, enlarged volume V, Part II, Chapter 2.1.3, page 413 to 414. According to this, the desired cyanohydrins are prepared by reaction of carbonyl compounds with hydrocyanic acid (=hydrogen cyanide). This equilibrium reaction is catalyzed, for example, by ion exchanger resins.
In a preferred embodiment, the reaction mixture comprising cyanohydrin obtained by the reaction of aldehydes or ketones with hydrocyanic acid is reacted directly, without prior isolation, with phosgene. It is therefore possible to dispense with work-up steps, thus making the process more economical.
The reaction according to the invention of the cyanohydrins with phosgene is generally carried out in an organic solvent inert toward phosgene. Preferred solvents are hydrocarbons. Particular preference is given to mono- or polysubstituted aromatic hydro-carbons, very particular preference to toluene, o-, m- or p-xylene or ch
Fischer Jakob
Henkelmann Jochem
Siegel Wolfgang
Stamm Armin
BASF - Aktiengesellschaft
Keil & Weinkauf
McKane Joseph K.
Murray Joseph
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