US-12617741-B2 - Method for the manufacture of α,β-unsaturated ketones

US12617741B2US 12617741 B2US12617741 B2US 12617741B2US-12617741-B2

Abstract

A method for the manufacture of an α,β-unsaturated ketone, which method comprises oxidizing an alkene having —CH 2 — adjacent a carbon-carbon double bond to α,β-unsaturated ketone by passing air or oxygen through a solution of the hydrocarbon containing a catalyst consisting of N-hydroxyphthalimide (NHPI) and cobalt diacetate tetrahydrate at standard temperature and pressure during a period of at least 12 hours.

Inventors

Nazaret RIVAS BASCÓN
Ricardo RODRIGUEZ FERROL
ANTONIO RUIZ SANCHEZ

Assignees

SYMRISE AG

Dates

Publication Date: 20260505
Application Date: 20210412
Priority Date: 20200422

Claims (13)

1 . A method for the manufacture of an α,β-unsaturated ketone, which method comprises oxidizing an unsaturated hydrocarbon having —CH2- adjacent a carbon-carbon double bond (“the alkene”), wherein the alkene is selected from the group of compounds consisting of: to α,β-unsaturated ketone by passing air or oxygen through a solution of the alkene containing a catalyst consisting of N hydroxyphthalimide (NHPI) and cobalt diacetate tetrahydrate, wherein the mole ratio of cobalt diacetate tetrahydrate to NHPI catalyst is from 1:4 to 1:6 and wherein the amount of NHPI catalyst is less than 15% mole equivalent of the alkene in solvent comprising one or more of methyl propyl ketone (MPK), methyl isopropyl ketone (MIPK), methyl butyl ketone (MBK) and methyl isobutyl ketone (MIBK) at standard temperature and pressure during a period of at least 12 hours.
2 . A method according to claim 1 , comprising passing air through the solution at standard temperature and pressure during a period of at least 12 hours.
3 . A method according to claim 1 , wherein the alkene has between 4 and 30 carbon atoms.
4 . A method according to claim 1 , wherein the alkene is a hemiterpenoid, a monoterpenoid or a sesquiterpenoid.
5 . A method according to claim 1 , wherein the alkene is valencene.
6 . A method according to claim 1 , wherein an amount of solvent from 0.75 to 9.0 liters per kilogram of the alkene is used.
7 . A method according to claim 1 , providing a conversion of the alkene greater than or equal to 70%.
8 . A method according to claim 1 , providing the α,β-unsaturated ketone substantially free from the corresponding alcohol.
9 . A method according to claim 1 , having a regioselectivity greater than 95%.
10 . A method according to claim 1 , further comprising quenching by water, extracting the α,β-unsaturated ketone into an organic solvent and washing the extract with 5 wt/wt % aqueous sodium hydroxide.
11 . A method according to claim 1 , wherein the α,β-unsaturated ketone is a fragrance compound.
12 . A method according to claim 11 , wherein the α,β-unsaturated ketone is nootkatone.
13 . A method according to claim 1 , adapted for manufacture of the α,β-unsaturated ketone on an industrial scale.

Description

The present invention is concerned with a method for the manufacture of α,β-unsaturated ketones (enones) by oxidation of alkenes. The method is suitable for use as an industrial process and has particular utility for the manufacture of α,β-unsaturated ketones of interest in the field of fragrances. The allylic oxidation of alkenes to enones is a chemical conversion that offers a direct route to high value products from chemical compounds which are readily available as bulk chemicals or otherwise obtained from renewable sources. Accordingly, the allylic oxidation of alkenes to enones has found widespread use for the preparation of agricultural, pharmaceutical and flavoring products. A wide variety of methods have been used (and are reviewed by Weidmann, V. and Maison, W. in “Allylic Oxidations of Olefins to Enones”, Synthesis 2013, 45 2201-2221). Amongst these, the most commonly used method for allylic oxidation of alkenes to enones involves the use of stoichiometric amounts of chromium (VI) reagents such as chromium (VI) oxide, t-butyl chromate, sodium chromate, sodium dichromate and complexes comprising chromium (VI) oxide (for example, with pyridines, pyrazoles or benzotriazoles). However, the method is complicated by a need for harsh reaction conditions to achieve acceptable conversion within suitable timescales and by difficulty in removing the chromium (VI) reagents from crude reaction product(s). Furthermore, the method is not particularly suitable for an industrial process because of the amounts of chromium (VI) reagents involved and environmental regulations restricting chromium-containing waste chemicals. Accordingly, industrial chemists have sought alternative methods for the allylic oxidation of alkenes to enones. These methods rely upon the use of a catalytic amount of chromium (VI) salt and/or other metal salt with stoichiometric amounts of oxidants such as t-butyl hydroperoxide, sodium perborate, potassium hydrogen persulfate. However, the catalytic methods tend not to offer a significant improvement over the stoichiometric methods. The need for harsh reaction conditions often remains as does the difficulty in removing the chromium (VI) salt and/or other metal salt from crude reaction products. Further, the catalytic methods do not lend themselves to an industrial process because the amounts of catalyst used tend to be high and challenge compliance with environmental regulations restricting chromium- or other metal-containing containing waste chemicals. NHPI is known to catalyze the oxidation of alkanes to a variety of oxygen-containing compounds, including alcohols, ketones and carboxylic acids, under relatively mild conditions. The NHPI catalyzed oxidation of alkanes generally requires heating to temperatures higher than 70° C. in the presence of oxygen at atmospheric pressure and one or more a metal co-catalyst, usually a cobalt (II) salt. The oxidation proceeds by a free-radical chain reaction for which NHPI acts as a radical promoter. A free-radical initiator generates phthalimido N-oxyl (PINO) radical by hydrogen abstraction from NHPI. In the propagation phase, the PINO radical abstracts a hydrogen atom from a C—H bond forming an alkyl radical R⋅. The alkyl radical is trapped by oxygen leading to an alkyl peroxyl radical ROO⋅ which abstracts hydrogen atom from NHPI to form alkyl hydroperoxide ROOH. When cobalt (II) salts are present, the initiator is thought to be Co(III)OO⋅ radical. The alkyl hydroperoxide ROOH formed in the propagation phase is decomposed to an alkoxy radical RO⋅ which abstracts hydrogen atom from NHPI to form an alkyl alcohol ROH. The method has been adapted for the oxidation of primary and secondary alkyl benzenes to phenols, aldehydes and ketones as well as for the oxidation of alcohols to aldehydes and ketones, the oxidation of alkynes to ynones and for the epoxidation of alkenes (see, for example, Ishii, Y., Sakaguchi, S. and Iwahama, T. in “Innovation of Hydrocarbon Oxidation with Molecular Oxygen and Related Reactions in Advances in Synthetic Catalysis, 2001, 343, 393-427). Aerobic oxidation (with air or oxygen) with NHPI offers an alternative method for the allylic oxidation of alkenes to enones. Such a method is of interest to industrial chemists because NHPI is non-toxic and easily prepared from phthalic anhydride and hydroxylamine. However, the use of NHPI as a catalyst for the aerobic oxidation of alkenes to enones has not generally proved to be successful. The polarity of NHPI and its limited operating temperature range (NHPI undergoes decomposition at temperatures higher than 80° C.) means that is often necessary to use large volumes of polar solvents (which are often toxic) for a solubilization of NHPI achieving an acceptable conversion. These solvents often complicate the isolation of reaction products. Therefore, recent methods for aerobic oxidation of alkenes to enones using NHPI are dominated by the use of co-oxidants and/or co-catalysts, such as ter