Process for producing nitrile

A nitrile having formula (2): EQU RC.ident.N (2) PA1 wherein R represents a substituted or unsubstituted alkyl, alkenyl, aralkyl or aryl group having 3 to 20 carbon atoms, is produced by a process, which comprises heating an aldoxime having formula (1): EQU RCH.dbd.NOH (1) wherein R is as defined above, at 80 to 250.degree. C. in the presence of a catalyst (A) of an alkali metal or alkaline earth metal salt of a saturated or unsaturated mono- or dicarboxylic acid having 2 to 20 carbon atoms while removing product water from the reaction system by distillation.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a convenient process for producing a
 nitrile which is useful as a perfume or as a raw material for the
 synthesis of perfumes, medicines, and the like in high yields.
 2. Description of the Background
 It is known that a nitrile can be prepared from a corresponding aldoxime by
 dehydration in the presence of a basic catalyst such as sodium hydroxide
 or potassium hydroxide (see WO 93/02046). According to this technique, an
 aldoxime is heated in the presence of the basic catalyst while product
 water is removed by distillation from the reaction system to give a
 nitrile in high yield. However, when this technique is applied to an
 aldoxime having a geometric isomer, such as
 3,7-dimethyl-2,6-octadienoxime, the result is that the cis-trans ratio of
 the nitrile product is different from that of the raw oxime because of
 isomerization that has taken place during dehydration for unknown reasons,
 failing to provide a nitrile with the desired physical properties.
 SUMMARY OF THE INVENTION
 Accordingly, one object of the present invention is to provide a process of
 producing a nitrile, which achieves a high yield, suppresses isomerization
 that accompanies production of a nitrile having an alkenyl group, and is
 extremely advantageous from economic considerations in production.
 Briefly, this object and other objects of the present invention as
 hereinafter will become more readily apparent can be attained by a process
 for producing a nitrile represented by formula (2):
EQU RC.ident.N (2)
 wherein R represents a substituted or unsubstituted alkyl, alkenyl. aralkyl
 or aryl group having 3 to 20 carbon atoms, comprising heating an aldoxime
 represented by formula (1):
EQU RCH.dbd.NOH (1)
 wherein R is as defined above, at 80 to 250.degree. C. in the presence of
 an alkali metal or alkaline earth metal salt of a saturated or unsaturated
 mono- or dicarboxylic acid having 2 to 20 carbon atoms as a (dehydration)
 catalyst (hereinafter referred to as catalyst A) thereby distilling
 product water from the reaction system.
 According to the invention, a nitrile can be produced in a high yield while
 suppressing isomerization that accompanies its formation where the nitrile
 has an alkenyl group. Therefore, the process of the invention is extremely
 advantageous from the standpoint of manufacturing economy.
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 In formulae (1) and (2), the group represented by R contains 3 to 20 carbon
 atoms, preferably 6 to 14 carbon atoms. Suitable alkyl groups, as R,
 include heptyl, nonyl, undecyl, lauryl and myristyl. Suitable alkenyl
 groups, as R, include those having two or more double bonds such as
 2,6-dimethyl-1,5-heptadienyl and 2,6-dimethyl-5-heptenyl. Suitable aralkyl
 groups, as R, include 2-phenethyl and 2-styryl. Suitable aryl groups, as
 R, include phenyl, methylphenvl and dimethylphenyl. Of these, R preferably
 represents an alkenyl group which provides a conjugated system in the
 resulting nitrile, such as 2,6-dimethyl-1,5-heptadienyl group or 2-styryl.
 The group, as R, is preferably unsubstituted. However, the groups may be
 substituted with substituents which include cyano, hydroxyl, alkoxy,
 nitro, alkoxycarbonyl, amido, halogen and phenyl.
 The aldoxime (1) raw material of the process of the present invention is
 obtained by, for example, reacting a corresponding aldehyde and an
 inorganic salt of hydroxylamine in a conventional manner.
 Catalyst A employed in the present process, i.e., an alkali metal or
 alkaline earth metal salt of a saturated or unsaturated mono- or
 dicarboxylic acid having 9 to 20 carbon atoms, includes the sodium,
 potassium or magnesium salt of a monocarboxylic acid, such as acetic acid,
 propionic acid, stearic acid or oleic acid; and a sodium or potassium salt
 of a dicarboxylic acid, such as oxalic acid or maleic acid. Preferred
 salts include the alkali metal or alkaline earth metal salts of an
 aliphatic carboxylic acid. From economic considerations, an alkali metal
 salt of a lower fatty acid having 2 to 5 carbon atoms is preferred, with
 sodium acetate or potassium acetate being particularly preferred. These
 compounds can be used either individually or in a combination of two or
 more.
 Catalyst A can be used in combination with another basic catalyst more
 basic than catalyst A, as long as the trans/cis ratio of the product
 nitrile is not adversely affected. The other basic catalyst that can be
 used in combination with catalyst A (hereinafter referred to as catalyst
 B) includes an alkali metal or alkaline earth metal hydroxide or an alkali
 metal or alkaline earth metal alkoxide having 1 to 6 carbon atoms, such as
 sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium
 methoxide or potassium methoxide. The molar ratio of catalysts B to A is
 preferably 3 or less, still preferably 2 or less, particularly preferably
 1.0 or less. A preferred lower limit of the catalysts B to A molar ratio
 is 0.2.
 In order to achieve an improved yield of the nitrile (2), catalyst A is
 preferably used or a combination of catalysts A and B in a total amount of
 0.1 to 50% by weight, particularly 0.1 to 5% by weight, based on the
 aldoxime (1).
 The reaction is conducted by heating the aldoxime at 80 to 250.degree. C.,
 preferably 80 to 200.degree. C., still preferably 100 to 170.degree. C. At
 temperatures below 80.degree. C., the reaction rate is low for industrial
 production. At temperatures above 250.degree. C., the nitrile decomposes
 to thereby causing a reduction in yield.
 The means for removing water produced during the reaction by distillation
 is not particularly limited. For example, water can be driven out of the
 reaction system efficiently by azeotropic distillation using a solvent
 capable of forming a constant-boiling azeotrope with water or by vacuum
 distillation by decompression.
 Solvents which form a constant-boiling azeotrope with water thereby
 enabling the removal of water from the system include benzene, toluene,
 xylene, chlorobenzene, heptane, methyl isobutyl ketone and ethyl acetate.
 The vacuum distillation is preferably conducted by continuously removing
 the product water or product water with nitrile by distillation while
 continuously feeding the aldoxime (1) to a solution of the above-described
 catalysts in a high-boiling solvent under reduced pressure at the reaction
 temperature. The high-boiling solvent must have a higher boiling point
 than the product nitrile (2). Such solvents include liquid paraffin and
 alkylbenzenes.
 The reaction by which the nitrile (2) is obtained from the aldoxime (1) is
 usually conducted under atmospheric pressure under which the product water
 is removed by azeotropic distillation using the azeotropic solvent or
 under reduced pressure of 27 kPa or less, particularly 8 kPa or less,
 where the product water is removed by vacuum distillation in the presence
 of the high boiling solvent. The resulting crude nitrile is purified by
 distillate on, column chromatography or a similar means to isolate the
 desired nitrile (2).
 In the present invention, the cis-trans ratio of the unsaturated alkenyl
 group R changes very little from the raw aldoxime to the product nitrile.
 The rate of change in ratio (=((trans/cis ratio of raw oxime)-(trans/cis
 ratio of product nitrile))/(trans/cis ratio of raw oxime)) is preferably
 0.10 or less.

The present invention will now be illustrated in greater detail with
 reference to Examples, but it should be understood that the invention is
 not construed as being limited thereto.
 EXAMPLE 1
 A flask was charged with 50 g of 3,7-dimethyl-6-octenoxime, 2 g of sodium
 acetate, and 25 ml of toluene, and the mixture was stirred at reflux at
 126.degree. C. for 2 hours while azeotropically distilling the product
 water together with toluene. After cooling to 30 to 40.degree. C., the
 reaction mixture was neutralized with acetic acid, toluene was removed by
 evaporation, and the residue was distilled to give 44.0 g of a fraction
 (90.degree. C./0.67 kPa). Analysis on the fraction revealed that
 3.7-dimethyl-6-octenonitrile having a purity of 94.5% had been produced in
 a yield of 93.0% at a conversion of 99.0% and a selectivity of 94.0%. The
 conversion and the selectivity were calculated as follows.
 Conversion (%)=((weight of charged oxime)-(weight of recovered
 oxime))/(weight of charged oxime).times.100
 Selectivity (%)=(mole number of produced nitrile)/(mole number of converted
 oxime).times.100
 EXAMPLE 2
 A flask was charged with 30 g of liquid paraffin and 6 g of sodium acetate.
 The mixture was heated to 150.degree. C. while stirring, and the inner
 pressure was reduced to 6.7 kPa. 3,7-Dimethyl-6-octenoxime was fed into
 the flask at a rate of 100 g/hr for 2 hours, followed by aging under the
 same conditions for 30 minutes. A 172 g amount of a nitrile fraction was
 obtained together with a small amount of water. Analysis on the fraction
 revealed the production of 3,7-dimethyl-6-octenonitrile with a purity of
 93.5%, a yield of 90.0%, a conversion of 99.0%, and a selectivity of
 91.0%.
 EXAMPLE 3
 A reaction was carried out in the same manner described in Example 2,
 except that sodium acetate was replaced with 4 g of potassium acetate. A
 nitrile fraction (170 g) was obtained together with a small amount of
 water. Analysis on the fraction revealed the production of
 3,7-dimethyl-6-octenonitrile with a purity of 93.0%, a yield of 88.0%, a
 conversion of 99.0%, and a selectivity of 89.0%.
 EXAMPLES 4 AND 5
 A nitrite fraction was obtained in the same manner described in Example 1,
 except that the catalysts and the raw oximes shown in Table 1 below were
 used. The reaction results are also shown in the table.
 TABLE 1
 Produced Yield Conversion
 Selectivity
 Example Raw Oxime Catalyst Nitrile (%) (%)
 (%)
 4 3-phenyl- potassium 3-phenyl- 86 99
 87
 propanoxime stearate propano-
 nitrile
 5 3-phenyl-2- potassium 3-phenyl-2- 79 99
 80
 propenoxime oxalate propeno-
 nitrile
 EXAMPLE 6
 Into a flask were placed 30 g of liquid paraffin and 4 g of potassium
 acetate. The mixture was heated to 150.degree. C. while stirring, and the
 inner pressure was reduced to 6.7 kPa. 3,7-Dimethyl-2,6-octadienoxime
 having a trans/cis ratio of 1.2 was fed into the flask at a rate of 100
 g/hr for 2 hours, followed by aging under the same conditions for 30
 minutes. A 170 g amount of a nitrile fraction together with a small amount
 of water was obtained. Analysis on the fraction revealed that
 3,7-dimethyl-2,6-octadienonitrile having a purity of 94.0% and a trans/cis
 ratio of 1.8 in a yield of 90.0% was obtained.
 EXAMPLE 7
 A nitrile fraction (177 g) was obtained together with a small amount of
 water in the same manner described in Example 6, except that 4 g of
 potassium acetate was replaced with 2.7 g of potassium acetate and 0.8 g
 of sodium hydroxide. Analysis on the fraction revealed the production of
 3,7-dimethyl-2,6-octadienonitrile having a purity of 94% and a trans/cis
 ratio of 1.17 in a yield of 93%.
 COMATIVE EXAMPLE 1
 A nitrile fraction (170 g) was obtained together with a small amount of
 water in the same manner described in Example 6, except that potassium
 acetate was replaced with the same weight of sodium hydroxide. Analysis on
 the fraction revealed the production of 3, 7-dimethyl-2,6-octadienonitrile
 having a purity of 94.0% and a trans/cis ratio of 0.76 in a yield of
 90.0%.
 According to the process of the present invention, a nitrile can be
 produced in a high yield, by suppressing the isomerization that
 accompanies production of a nitrile having an alkenyl group, which is
 extremely advantageous from the viewpoint of economic considerations in
 production.
 The disclosure of Japanese priority application Hei. 11-155729 filed Jun.
 2, 1999 is hereby incorporated by reference into the present application.
 While the invention has been described in detail and with reference to
 specific examples thereof, it will be apparent to one skilled in the art
 that various changes and modifications can be made therein without
 departing from the spirit and scope thereof.