PREPARATION OF CIS-2-ALKENOIC ACIDS

Abstract

A process for the preparation of cis-2-alkenoic acid or an alkali metal salt thereof, comprising rearranging 1,3-dibromo-2-alkanone in an alkaline environment in the presence of a catalytically effective amount of an alkali metal salt of cis-2-alkenoic acid, and isolating from the reaction mixture cis-2-alkenoic acid, either in the form of the free acid or in the form of the alkali metal salt.

Claims

1. A process for the preparation of cis-2-alkenoic acid or an alkali metal salt thereof, comprising rearranging 1,3-dibromo-2-alkanone in an alkaline environment in the presence of a catalytically effective amount of an alkali metal salt of cis-2-alkenoic acid, and isolating from the reaction mixture cis-2-alkenoic acid, either in the form of the free acid or in the form of the alkali metal salt.

2. A process according to claim 1, comprising gradually adding the 1,3-dibromo-2-alkanone to a reaction vessel which was previously charged with an alkaline aqueous solution of Na.sub.2CO.sub.3, K.sub.2CO.sub.3, or a mixture thereof and a catalytically effective amount of an alkali metal salt of cis-2-alkenoic acid, at elevated temperature.

3. A process according to claim 1, comprising separating the reaction mixture into aqueous and organic phases, and working-up the aqueous phase, to recover therefrom cis-2-alkenoic acid, either in the form of the free acid or in the form of the alkali metal salt.

4. A process according to claim 3, wherein the aqueous phase is worked-up by washing with an organic solvent, followed by phase separation, to obtain a purified aqueous phase.

5. A process according to claim 1, wherein the reaction mixture is optionally diluted with water and washed with an organic solvent, followed by phase separation, to obtain a purified aqueous phase.

6. A process according to claim 4, further comprising acidifying the purified aqueous phase to obtain a biphasic medium, comprised of a heavy, salt-containing aqueous phase, and a light organic phase consisting essentially of the cis-2-alkenoic acid in the form of the free acid.

7. A process according to claim 1, wherein the cis-2-alkenoic acid is of the formula RCHCHCOOH wherein R is a straight alkyl chain CH.sub.3(CH.sub.2).sub.n, with 3n10.

8. A process according to claim 7, wherein the 1,3-dibromo-2-alkanone is selected from the group consisting of: ##STR00010##

9. A process according to claim 1, wherein the 1,3-dibromo-2-alkanone, used in the rearrangement reaction, is a crude 1,3-dibromo-2-alkanone obtained by the steps of: brominating the corresponding 2-alkanone in concentrated hydrobromic acid by the addition of elemental bromine, whereby 1,3-dibromo-2-alkanone is formed in the reaction mixture alongside 3,3-dibromo-2-alkanone; maintaining the reaction mixture over a hold time adjusted to maximize the interconversion of 3,3-dibromo-2-alkanone to 1,3-dibromo-2-alkanone; and collecting the crude 1,3-dibromo-2-alkanone.

10. A process according to claim 9, wherein the 2-alkanone is selected from the group consisting of 2-heptanone, 2-octanone, 2-nonanone, 2-decanone and 2-undecanone.

11. A process according to claim 9, wherein the hold time is adjusted to reach not less than 65% (GC, area %) of 1,3-dibromo-2-alkanone.

12. A process according to claim 1, wherein the catalytically effective amount of the alkali metal salt of cis-2-alkenoic acid is up to 10 mol % based on 1,3-dibromo-2-alkanone.

13. A process according to claim 3, wherein a minor portion of the aqueous phase is removed before or after the aqueous phase is worked-up, and is used to supply the catalytically effective amount of alkali metal salt of cis-2-alkenoic acid in a rearrangement reaction of the corresponding 1,3-dibromo-2-alkanone.

14. A process according to claim 1, wherein the catalytically effective amount of the alkali metal salt of cis-2-alkenoic acid is supplied to the rearrangement reaction in the form of aqueous solution recovered from an earlier rearrangement reaction.

15. A process according to claim 1, wherein the 1,3-dibromo-2-alkanone is 1,3-dibromo-2-decanone, such that the cis-2-alkenoic acid is cis-2-decenoic acid.

Description

[0040] FIGS. 1A, 1B and 1C are .sup.1H-NMR spectra of CDA of Example 1.

[0041] FIGS. 2A, 2B and 2C are .sup.1H-NMR spectra of CDA of Example 2.

[0042] FIGS. 3A, 3B and 3C are .sup.1H-NMR spectra of CUDA of Example 4.

[0043] FIGS. 4A, 4B and 4C are .sup.1H-NMR spectra of CNA of Example 5.

[0044] FIGS. 5A, 5B and 5C are .sup.1H-NMR spectra of COA of Example 6.

[0045] FIGS. 6A, 6B and 6C are .sup.1H-NMR spectra of CHA of Example 7.

EXAMPLES

[0046] Methods

[0047] GC: Gas-Chromatograph HP 7890A [0048] Method (CDA): Initial temp. 50 C., held 2 min, then raised to [0049] 280 C. at 10 C./min and held for 5 min, then raised to 300 C. at [0050] 10 C./min and held for 2 min. [0051] Injector: 250 C. [0052] Detector: 300 C. [0053] Split ratio: 1:40 [0054] Concentration of the product sample: 20 mg/ml DCM [0055] Injection amounts: 1 l sample [0056] Column: Agilent J&W Columns, HP-5, 30 m0.32 mm0.25 [0057] Part no. 19091J-413, Ser. No. USF302346H

[0058] .sup.1H-NMR Spectroscopy

[0059] Spectra were taken on an Avance III, 500 MHz instrument.

Example 1

Preparation of Cis-2-Decenoic Acid

[0060] Step 1:

[0061] Into a mixture of 2-decanone (200 g, 1.28 mol) and aq. 48% HBr (300 g), stirred and cooled to 10 C., was added bromine (410 g, 2.56 mol), dropwise over 2 h. The reaction started immediately with the start of the addition of the bromine and no accumulation of bromine was observed.

[0062] The reaction was exothermic and accompanied by the emission of HBr gas, just before the end of the addition of the bromine, which was absorbed in a scrubber.

[0063] Most of the reaction took place during the addition of the bromine and cooking at room temperature (20 C.) for 6 hours.

[0064] After standing overnight (15 h) at room temperature, without stirring, the composition of the reaction mixture stabilized. Partial conversion of the 3,3-dibromo-2-decanone (3,3-DBD) to the desired product, 1,3-dibromo-2-decanone (1,3-DBD), took place. To the reaction mixture was added water (160 g) at RT, with stirring for 30 min, and the phases were separated.

[0065] An aqueous phase (627 g) was obtained containing 50% HBr (d=1.51 g/ml) and crude DBD (404 g, d=1.43 g/ml). The concentration of 1,3-DBD in the crude product was 69.6% (GC, area %).

[0066] Step 2: An aqueous solution of K.sub.2CO.sub.3, in a concentration of 25% w/w, was prepared in a 1 L stirred reactor by the batchwise addition of K.sub.2CO.sub.3 (200 g) to water (600 g). The reaction was exothermic. To this solution was added a part of the aqueous phase (which contained CDA-K) of the reaction mixture (50 g) remaining from a previous run (named AP-RM; see comparative Example 3). The clear solution obtained was heated to 40 C. and crude DBD of step 1 (200 g) was added to it dropwise over 60 min. The progress of the reaction was monitored by GC and by the change in the pH. The reaction was completed by cooking at 50 C. for 3.0 h, with mechanical stirring.

[0067] It should be pointed out that without the addition of AP-RM, the reaction only starts spontaneously two hours after the addition of the crude DBD.

[0068] The end of the reaction was determined by the pH (drop in the pH from 13.3 to 9.3) and by GC analysis of the reaction mixture (disappearance of 1,3-DBD to 1%, area %). After completion of the reaction, cooling to RT and stopping the stirring, an organic phase appeared above the aqueous phase which contained unreacted 3-bromo-2-decanone (3-BD) and 3,3-DBD, and by-products formed by a condensation reaction of crude DBD. The phases were separated. The organic phase (39 g) was organic waste. 50 g of the aq. phase was taken for use in the next run.

[0069] In order to reduce the amount of impurities to a minimum, the remainder of the aqueous phase (950 g) was washed three times with dichloromethane (DCM, 3250 g).

[0070] After the washing stage, an aqueous phase was obtained containing cis-2-decenoic acid potassium salt (CDA-K), organic by-products, KBr and KHCO.sub.3. In order to obtain the crude cis-2-decenoic acid (CDA), the aqueous phase was acidified by the dropwise addition of aq. 32% HCl (193 g) over 1 h. During the acidification (final pH=1.1), CO.sub.2 (calculated at 63 g) was emitted.

[0071] After stopping the stirring, an aqueous phase (955 g) was obtained containing salts: KCl and KBr (heavy phase, d=1.19 g/ml) and wet crude CDA (light phase, 71 g, d=1.07 g/ml).

[0072] Evaporation of the DCM and lights from the wet CDA under vacuum (at T.sub.B=50 C.) gave crude CDA (50.5 g), which was analysed by GC and .sup.1H-NMR (see FIGS. 1A, 1B and 1C for .sup.1H-NMR spectra). The calculated yield of crude CDA was 68%, based on 1,3-DBD, or 46.8%, based on 2-decanone.

[0073] The purity of the crude CDA obtained was 88.2% (by GC area %). The main impurity in the crude product was 2-bromomethylidene nonanoic acid (BMNA): 8.8% (by GC, area %).

Example 2

Preparation of Cis-2-Decenoic Acid

[0074] Step 1:

[0075] Into a mixture of 2-decanone (400 g, 2.564 mol) and aq. 48% HBr (600 g), stirred and cooled to 10 C., was added bromine (800 g, 5 mol), dropwise over 5 h. The reaction started immediately with the start of the addition of the bromine and no accumulation of bromine was observed. The reaction was exothermic and accompanied by the emission of HBr gas, just before the end of the addition of the bromine, which was absorbed in a scrubber.

[0076] Most of the reaction took place during the addition of the bromine, and after standing overnight at room temperature, without stirring, the composition of the reaction mixture stabilized. Partial conversion of the 3,3-dibromo-2-decanone (3,3-DBD) to the desired product, 1,3-dibromo-2-decanone (1,3-DBD), took place. To the reaction mixture was added water (300 g) at RT, with stirring for 30 min, and the phases were separated.

[0077] An aqueous phase (1207 g) was obtained containing 49.5% HBr (d=1.51 g/ml) and crude DBD (789 g, d=1.42 g/ml). The concentration of 1,3-DBD in the crude product was 70.4% (GC, area %).

[0078] Step 2: An aqueous solution of K.sub.2CO.sub.3, in a concentration of 25% w/w, was prepared in a 2 L stirred reactor by the batchwise addition of K.sub.2CO.sub.3 (400 g) to water (1200 g). The reaction was exothermic. To this solution was added a part of the aqueous phase of the reaction mixture of CDA-K (50 g) remaining from a previous run. The clear solution obtained was heated to 40 C. and crude DBD (Step 1, 400 g) was added to it dropwise over 70 min. The progress of the reaction was monitored by GC and by the change in the pH. The reaction was completed by cooking at 40 C. for 1.0 h, then at 50 C. for 2.0 h, with mechanical stirring.

[0079] The end of the reaction was determined by the pH (drop in the pH from 12.7 to 9.6) and by GC analysis of the reaction mixture (disappearance of 1,3-DBD to 1%, area %). After completion of the reaction, cooling to RT and stopping the stirring, an organic phase appeared above the aqueous phase which contained unreacted 3-BD and 3,3-DBD, and by-products formed by a condensation reaction of crude DBD. The phases were separated. 50 g of the aq. phase was taken for use in the next run.

[0080] In order to reduce the amount of impurities to a minimum, the aqueous phase (1943 g) was washed three times with dichloromethane (DCM, 3500 g).

[0081] After the washing stage, an aqueous phase was obtained containing cis-2-decenoic acid potassium salt (CDA-K), organic by-products, KBr and KHCO.sub.3. In order to obtain the crude cis-2-decanoic acid (CDA), the aqueous phase was acidified by the dropwise addition of aq. 32% HCl (401 g) over 1 h. During the acidification (final pH=1.9), CO.sub.2 (calculated at 127 g) was emitted.

[0082] After stopping the stirring, an aqueous phase (2017 g) was obtained containing salts: KCl and KBr (heavy phase, d=1.19 g/ml) and wet crude CDA (light phase, 128 g, d=1.03 g/ml).

[0083] Evaporation of the DCM and lights from the wet CDA under vacuum (T.sub.B=50 C.) gave crude CDA (102 g), which was analyzed by GC, HPLC and .sup.1H-NMR (.sup.1H-NMR spectra in FIGS. 2A, 2B and 2C).

[0084] Based on the results, the purity of the crude CDA obtained was 89.7% (by GC area %) and 90.0% (by HPLC, area %). The calculated yield of crude CDA was 67% based on 1,3-DBD.

Example 3 (Comparative)

Preparation of cis-2-decenoic acid

[0085] Step 1 was carried out as in Example 1. The rearrangement reaction of Step 2, however, was carried out without the addition of the alkali metal salt of cis-2-alkenoic acid.

[0086] Step 2: An aqueous solution of K.sub.2CO.sub.3, in a concentration of 25% w/w, was prepared in a 1 L stirred reactor by the batchwise addition of K.sub.2CO.sub.3 (200 g) to water (600 g). The reaction was exothermic. The clear solution obtained was heated to 40 C. and crude DBD (200 g; obtained as previously described) was added to it dropwise over 60 min. The progress of the reaction was monitored by GC and by the change in the pH.

[0087] The mixture of aq. K.sub.2CO.sub.3 and crude DBD was stirred for 3 h at a temperature of 50 C. Based on the pH (unchanged at 13) and on GC, it was seen that no reaction had taken place.

[0088] Then suddenly, the temperature in the reactor started to rise spontaneously and reached 76 C. within ten minutes. The end of the reaction was determined by the pH (drop in the pH from 13.3 to 9.5) and by GC analysis of the reaction mixture (disappearance of 1,3-DBD to 1%, area %). The phases were separated, and 50 g of the aqueous phase was taken for use in the next run (i.e., the procedure of Example 1).

Example 4

Preparation of Cis-2-Undecenoic Acid

[0089] Step 1:

[0090] Into a mixture of 2-undecanone (218 g, 1.28 mol) and aq. 48% HBr (300 g), stirred and cooled to 10 C., was added bromine (410 g, 2.56 mol), dropwise over 3 h. The reaction started immediately with the start of the addition of the bromine and no accumulation of bromine was observed. The reaction was exothermic and accompanied by the emission of HBr gas, just before the end of the addition of the bromine, which was absorbed in a scrubber.

[0091] Most of the reaction took place during the addition of the bromine and cooking at room temperature (20 C.) for 3.5 hours. After standing overnight (16.5 h) at room temperature, without stirring, the composition of the reaction mixture stabilized. Partial conversion of the 3,3-dibromo-2-undecanone (3,3-DBUD) to the desired product, 1,3-dibromo-2-undecanone (1,3-DBUD), took place. To the reaction mixture was added water (160 g) at RT, with stirring for 30 min, and the phases were separated.

[0092] An aqueous phase (627 g) was obtained containing 50% HBr (d=1.50 g/ml) and crude DBUD (415 g, d=1.39 g/ml). The concentration of 1,3-DBUD in the crude product was 69.1% (GC, area %).

[0093] Step 2:

[0094] An aqueous solution of K.sub.2CO.sub.3, in a concentration of 25% w/w, was prepared in a 1 L stirred reactor by the batchwise addition of K.sub.2CO.sub.3 (200 g) to water (600 g). The reaction was exothermic. The clear solution obtained was heated to 40 C. and crude DBUD of Step 1 (200 g) was added to it dropwise over 20 min. The progress of the reaction was monitored by GC and by the change in the pH.

[0095] The mixture of aq. K.sub.2CO.sub.3 and crude DBUD was stirred for 1 h at a temperature of 50 C., for 1.5 h at a temperature of 60 C., and for an additional 1.5 h at a temperature of 70 C. Based on the pH (unchanged at 13) and on GC, it was seen that no reaction had taken place.

[0096] Next, to the reaction mixture was added a part of the aqueous phase of the reaction mixture of CDA-K (10 g) dropwise over 15 min. At the end of the addition, the temperature in the reactor started to rise and reached 82 C. within 10 min. This mixture was then stirred for an additional 2 h at 70 C.

[0097] The end of the reaction was determined by the pH (drop in the pH from 13 to 10) and by GC analysis of the reaction mixture (disappearance of 1,3-DBUD to 1%, area %).

[0098] In order to reduce the amount of impurities to a minimum, the reaction mixture (960 g) was washed three times with dichloromethane (DCM, 3250 g) at RT. It should be mentioned that the first phase separation was slow.

[0099] After the washing stage, an aqueous phase was obtained containing cis-2-undecenoic acid potassium salt (CUDA-K), organic by-products, KBr and KHCO.sub.3. In order to obtain the crude cis-2-undecenoic acid (CUDA), the aqueous phase was acidified by the dropwise addition of aq. 32% HCl (132 g) over 1 h. During the acidification, CO.sub.2 was emitted.

[0100] After stopping the stirring, an aqueous phase (762 g) was obtained containing salts:

[0101] KCl and KBr (heavy phase, d=1.15 g/ml) and wet crude CUDA (light phase, 53 g, d=1.07 g/ml) which was analysed by GC and .sup.1H-NMR (see FIGS. 3A, 3B and 3C for .sup.1H-NMR spectra). The purity of the crude CUDA obtained was 89.6% (by GC area %). The main impurity in the crude product was 2-bromomethylidene decanoic acid (BMDA): 5.2% (by GC, area %).

[0102] Evaporation of the DCM and lights from the wet CUDA under vacuum (at T.sub.B=50 C.) gave crude CUDA (35 g).

[0103] It is seen that in this Example, a small amount of alkali metal salt of a homologue acid (CDA-K) was used to advance the preparation of CUDA. The aqueous phase obtained containing cis-2-undecenoic acid potassium salt (CUDA-K), with an insignificant amount of CDA-K, can be used to supply, for the next run, a catalytically effective amount of CUDA-K to be added to the alkaline K.sub.2CO.sub.3 solution before the slow addition of the crude DBUD starts, to ensure an efficient, manageable reaction.

Example 5 (Comparative)

Preparation of cis-2-nonenoic acid

[0104] Step 1: Into a mixture of 2-nonanone (from Sigma-Aldrich; 182 g, 1.28 mol) and aq. 48% HBr (300 g), stirred and cooled to 10 C., was added bromine (410 g, 2.56 mol), dropwise over 3 h. The reaction started immediately with the start of the addition of the bromine and no accumulation of bromine was observed. The reaction was exothermic and accompanied by the emission of HBr gas, just before the end of the addition of the bromine, which was absorbed in a scrubber.

[0105] Most of the reaction took place during the addition of the bromine and cooking at room temperature (20 C.) for 2.0 hours. After leaving overnight (17 h) at room temperature, with stirring, the composition of the reaction mixture stabilized. Partial conversion of the 3,3-dibromo-2-nonanone (3,3-DBN) to the desired product, 1,3-dibromo-2-nonanone (1,3-DBN), took place. To the reaction mixture was added water (160 g) at RT, with stirring for 30 min, and the phases were separated.

[0106] An aqueous phase (624 g) was obtained containing 50% HBr (d=1.50 g/ml) and crude DBN (382 g, d=1.47 g/ml). The concentration of 1,3-DBN in the crude product was 70.6% (GC, area %).

[0107] Step 2:

[0108] An aqueous solution of K.sub.2CO.sub.3, in a concentration of 25% w/w, was prepared in a 1 L stirred reactor by the batchwise addition of K.sub.2CO.sub.3 (200 g) to water (600 g). The reaction was exothermic. The clear solution obtained was heated to 46 C. and crude DBN from Step 1 (191 g) was added to it dropwise over 45 min. The progress of the reaction was monitored by the change in the pH and the T.sub.R.

[0109] Based on the pH (unchanged at 13) and on GC, it was seen that no reaction had taken place during the addition of the crude DBN. Immediately after the addition of the crude DBN, the pH started to go down and the T.sub.R started to go up.

[0110] The end of the reaction was determined by the pH (drop in the pH from 13.3 to 9.1) and by GC analysis of the reaction mixture (disappearance of 1,3-DBN to 1%, area %). The phases were separated. The organic phase (42.6 g) was organic waste.

[0111] In order to reduce the amount of impurities to a minimum, the aqueous phase (948 g) was washed three times with dichloromethane (DCM, 3250 g).

[0112] After the washing stage, an aqueous phase was obtained containing cis-2-nonenoic acid potassium salt (CNA-K), organic by-products, KBr and KHCO.sub.3. In order to obtain the crude cis-2-nonenoic acid (CNA), the aqueous phase was acidified by the dropwise addition of aq. 32% HCl (227 g) over 1 h. During the acidification, CO.sub.2 was emitted.

[0113] After stopping the stirring, an aqueous phase (978 g) was obtained containing salts: KCl and KBr (heavy phase, d=1.19 g/ml) and wet crude CNA (light phase, 51 g, d=1.02 g/ml) which was analysed by GC and .sup.1H-NMR (see FIGS. 4A, 4B and 4C for .sup.1H-NMR spectra). The purity of the obtained CNA was 92.0% (by GC, area %).

[0114] Evaporation of the DCM and lights from the wet CNA under vacuum (at T.sub.B=50 C.) gave crude CNA (46.6 g).

Example 6 (Comparative)

Preparation of cis-2-octenoic acid

[0115] Step 1: Into a mixture of 2-octanone (from Sigma-Aldrich; 164 g, 1.28 mol) and aq. 48% HBr (300 g), stirred and cooled to 10 C., was added bromine (410 g, 2.56 mol), dropwise over 3 h. The reaction started immediately with the start of the addition of the bromine and no accumulation of bromine was observed. The reaction was exothermic and accompanied by the emission of HBr gas, just before the end of the addition of the bromine, which was absorbed in a scrubber.

[0116] Most of the reaction took place during the addition of the bromine and cooking at room temperature (20 C.) for 2.5 hours. After leaving overnight (15 h) at room temperature, with stirring, the composition of the reaction mixture stabilized. Partial conversion of the 3,3-dibromo-2-octanone (3,3-DBO) to the desired product, 1,3-dibromo-2-octanone (1,3-DBOO), took place. To the reaction mixture was added water (160 g) at RT, with stirring for 30 min, and the phases were separated.

[0117] An aqueous phase (636 g) was obtained containing 50% HBr (d=1.51 g/ml) and crude DBO (358 g, d=1.54 g/ml). The concentration of 1,3-DBO in the crude product was 71.0% (GC, area %).

[0118] Step 2:

[0119] An aqueous solution of K.sub.2CO.sub.3, in a concentration of 25% w/w, was prepared in a 1 L stirred reactor by the batchwise addition of K.sub.2CO.sub.3 (200 g) to water (600 g). The reaction was exothermic. The clear solution obtained was heated to 49 C. and crude DBO from Step 1 (182 g) was added to it dropwise over 1 h. The progress of the reaction was monitored by the change in the pH and the T.sub.R.

[0120] Based on the pH (unchanged at 13) and on GC, it was seen that no reaction had taken place during the addition of the crude DBO. Immediately after the addition of the crude DBO, the pH started to go down and the T.sub.R started to go up.

[0121] The end of the reaction was determined by the pH (drop in the pH from 13.7 to 9.3) and by GC analysis of the reaction mixture (disappearance of 1,3-DBO to 1%, area %).

[0122] Before starting the washings, water (75 g) was added to the reaction mixture (982 g). In order to reduce the amount of impurities to a minimum, the reaction mixture was washed four times with dichloromethane (DCM, 4250 g).

[0123] After the washing stage, an aqueous phase was obtained containing cis-2-octenoic acid potassium salt (COA-K), organic by-products, KBr and KHCO.sub.3. In order to obtain the crude cis-2-octenoic acid (COA), the aqueous phase was acidified by the dropwise addition of aq. 32% HCl (178 g) over 1 h. During the acidification, CO.sub.2 was emitted.

[0124] After stopping the stirring, an aqueous phase (938 g) was obtained containing salts: KCl and KBr (heavy phase, d=1.18 g/ml) and wet crude COA (light phase, 44 g, d=1.00 g/ml) which was analysed by GC and .sup.1H-NMR (see FIGS. 5A, 5B and 5C for .sup.1H-NMR spectra). The purity of the COA obtained was 89.6% (by GC, area %).

[0125] Evaporation of the DCM and lights from the wet COA under vacuum (at T.sub.B=50 C.) gave crude COA (41.3 g).

Example 7 (Comparative)

Preparation of cis-2-heptenoic acid

[0126] Step 1: Into a mixture of 2-heptanone (from Sigma-Aldrich; 146 g, 1.28 mol) and aq. 48% HBr (300 g), stirred and cooled to 10 C., was added bromine (410 g, 2.56 mol), dropwise over 3 h. The reaction started immediately with the start of the addition of the bromine and no accumulation of bromine was observed. The reaction was exothermic and accompanied by the emission of HBr gas, just before the end of the addition of the bromine, which was absorbed in a scrubber.

[0127] Most of the reaction took place during the addition of the bromine and cooking at room temperature (20 C.) for 4.5 hours. After standing overnight (17 h) at room temperature, with stirring, the composition of the reaction mixture stabilized. Partial conversion of the 3,3-dibromo-2-heptanone (3,3-DBH) to the desired product, 1,3-dibromo-2-heptanone (1,3-DBH), took place. To the reaction mixture was added water (160 g) at RT, with stirring for 30 min, and the phases were separated.

[0128] An aqueous phase (631 g) was obtained containing 50% HBr (d=1.52 g/ml) and crude DBH (351 g, d=1.60 g/ml). The concentration of 1,3-DBH in the crude product was 72.6% (GC, area %).

[0129] Step 2:

[0130] An aqueous solution of K.sub.2CO.sub.3, in a concentration of 25% w/w, was prepared in a 1 L stirred reactor by the batchwise addition of K.sub.2CO.sub.3 (200 g) to water (600 g). The reaction was exothermic. The clear solution obtained was heated to 49 C. and crude DBH from Step 1 (173 g) was added to it dropwise over 1 h. The progress of the reaction was monitored by the change in the pH and the T.sub.R.

[0131] Based on the pH (unchanged at 13), it was seen that no reaction had taken place during the addition of the crude DBH. Immediately after the addition of the crude DBH, the pH started to go down and the T.sub.R started to go up.

[0132] The end of the reaction was determined by the pH (drop in the pH from 13.5 to 9.3) and by GC analysis of the reaction mixture (disappearance of 1,3-DBH to 1%, area %). After completion of the reaction, cooling to RT and stopping the stirring, an organic phase appeared above the aqueous phase which contained unreacted 3-BH and 3,3-DBH, and by-products formed by a condensation reaction of crude DBH. The phases were separated. The organic phase (24 g) is organic waste.

[0133] Before starting the washings, water (50 g) was added to the reaction mixture (948 g). In order to reduce the amount of impurities to a minimum, the diluted reaction mixture (998 g) was washed three times with dichloromethane (DCM, 3250 g).

[0134] After the washing stage, an aqueous phase was obtained containing cis-2-heptenoic acid potassium salt (CHA-K), organic by-products, KBr and KHCO.sub.3. In order to obtain the crude cis-2-heptenoic acid (CHA), the aqueous phase was acidified by the dropwise addition of aq. 32% HCl (193 g) over 1 h. During the acidification, CO.sub.2 was emitted.

[0135] After stopping the stirring, an aqueous phase (1014 g) was obtained containing salts: KCl and KBr (heavy phase, d=1.18 g/ml) and wet crude CHA (light phase, 45 g, d=1.00 g/ml) which was analysed by GC and .sup.1H-NMR (see FIGS. 6A, 6B and 6C for .sup.1H-NMR spectra). The purity of the CHA obtained was 95.6% (by GC, area %).

[0136] Evaporation of the DCM and lights from the wet CHA under vacuum (at T.sub.B=50 C.) gave crude CHA (44 g).