WO2013121017A1

WO2013121017A1 - Process and equipment for the preparation of halocarboxylic acid alkyl esters

Info

Publication number: WO2013121017A1
Application number: PCT/EP2013/053119
Authority: WO
Inventors: Lothar Ott; Thomas Gruetzner; Constanze FRANZKE; Hilke-Marie Lorenz; Jens-Uwe Repke; Oliver Litzmann
Original assignee: Lonza Ltd
Priority date: 2012-02-17
Filing date: 2013-02-15
Publication date: 2013-08-22

Abstract

Provided is a reactive distillation and equipment to obtain a compound of formula (II) Hal-CH₂-A-C(O)-OR, wherein Hal is halogen selected from F, CI, Br or I, A denotes a bond or a divalent spacer selected from alkylene and arylene groups, and R is C_1-4 alkyl group.

Description

Process and equipment for the preparation of halocarboxylic acid alkyl esters

The present invention relates to a process and equipment for the preparation of halocarboxylic acid alkyl esters.

Background Art

Halocarboxylic acid alkyl esters and cyanocarboxylic acid alkyl esters are both important building blocks in the agrochemical and pharmaceutical industry. Typically, cyanocarboxylic acid alkyl esters such as alkyl cyanoacetates are produced starting from the corresponding halocarboxylic acid metal salts, for example sodium chloroacetate, which react with a cyanide to give the corresponding cyanocarboxylic acid salts such as sodium cyanoacetate. The acid is set free by mixing, for example, with sulphuric acid and is esterified with the desired alcohol. Alternatively,

esterification of a halocarboxylic acid is the first step which is optionally followed by a cyanidation step. A broad variety of esterification reactions of carboxylic acids with lower alcohols is known in the art. A reactive distillation for the preparation of methyl acetate using Katapak^®-S for structured column packing, wherein the ester is withdrawn as an overhead product, is known from Chemie Technik, 29, 2000, 42-45.

DE-A-19539962 discloses a continuous process for the esterification of chloroacetic acid with a lower alcohol in the presence of an acidic catalyst, wherein the product is withdrawn from the vapour phase of the reaction as an ester-water mixture which separates into two phases. The starting acid and the acidic catalyst are contained in the bottom of the reaction vessel. DD-A-97416 discloses a process for the continuous preparation of methyl monochloroacetate by reacting monochloroacetic acid and methanol in the liquid phase in a reactor vessel, wherein the vapour is distilled and the product is withdrawn at about the middle of the distillation column, while the column head stream is withdrawn and divided into two parts, one of which is reintroduced into the system at the column head while the other one is introduced directly into the reactor vessel. DD-A-97416 also refers to several prior art processes wherein methyl monochloroacetate is obtained by reacting monochloroacetic acid with methanol in the presence of concentrated mineral acids, by reaction with dimethylsulfate or by transesterification of higher esters.

EP-A-0 315 096 discloses the preparation of monochloroacetic acid Ci_-4 alkyl esters by reacting a melt of monochloroacetic acid comprising a catalyst with a Ci_-4 alcohol and removing product and reaction water as an azeotrope by distillation.

EP-A-0 424 861 discloses the reaction of a C2-5 carboxylic acid, preferably an aliphatic C2-5 carboxylic acid, and a Ci_-4 alcohol in the presence of a catalyst in a reactive distillation column, wherein an azeotrope of reaction consisting of water and ester is withdrawn as an overhead product.

EP-A-0 999 206 discloses the preparation of 2-ethyl-hexyl monochloroacetate by reacting monochloroacetic acid with 2-ethyl-hexan-1 -ol in the presence of sulphuric acid, water and toluene. The product is downstream processed by washing with aqueous NaHCO₃ solution and vacuum distillation. EP-A-0 999 206 further discloses the preparation of alkyl cyanoacetates by reacting the corresponding alkyl monochloroacetates with HCN in the presence of a tertiary alkylamine. Although EP-A-0 999 206 claims that cyanidation can be carried out without solvent, all examples have been carried out in the presence of acetonitrile as a solvent.

EP-A-0 999 206 also refers to DE-A-1 951 032 and EP-A-0 032 078 which also discloses cyanidation in the presence of acetonitrile as a solvent.

US-A-2985682 discloses the reaction of alkyl monohaloacetates with HCN in the presence of NH₃ which renders the process dangerous to be carried out on large scale. After 7 h a yield of only 50% is disclosed. RO-B-1 13554 discloses the reaction of monochloroacetic acid with a Ci_-4 alcohol in the presence of an acidic catalyst in a gas-liquid media at a temperature from 50 to 150 °C to obtain the respective ester, wherein the product is withdrawn from the vapour phase and cooled, followed by vacuum rectification of the raw ester. Although not explicitly disclosed, the ester is condensed and thus withdrawn from the vapour phase of the reaction .

RO-A-94544 discloses the preparation of alkyl monochloroacetates reacting a lower aliphatic alcohol with monochloroacetic acid in a reaction column, wherein the product is withdrawn from the column head which is heated to a temperature of from 15 to 20 °C above the boiling point of the respective ester-water azeotrope.

RO-A-83054 discloses the liquid-liquid extraction of Ci- esters of monochloroacetic acid, wherein water is added to the reaction mixture comprising sulphuric acid, monochloroacetic acid and the respective alcohol to recover the ester from the aqueous layer. WO-A-90/14328 discloses the reaction of glacial acetic acid and methanol in the presence of an acidic catalyst to obtain methyl acetate at the column head in a reactive distillation column having an extractive distillation section and a methyl acetate/acetic acid rectification section, wherein the acidic catalyst, water and methanol are withdrawn from the column bottom.

The prior art processes suffer from the drawback that separation of halocarboxylic acid alkyl esters from alcohols may cause problems during downstream processing due to emulsification. Moreover, removal of water from carboxylic acid alkyl esters is laborious because of azeotrope formation. Known processes wherein esters are withdrawn from the vapour phase, either as an overhead product or at an

intermediate distillation tray, are characterized by high energy consumption and in each case the product contains a certain amount of water. In the classical approach of ester preparation, where reaction and purification occur in different unit operations, the mineral acid used as a catalyst, due to the higher boiling point of the ester compared to the corresponding alcohol, remains in the ester-phase and has to be separated in an additional step. While the use of HCI as a mineral acid is an interesting option as it is also a side-product in the production of chloroacetic acid, use thereof leads to a complex downstream process due to the formation of azeotropic mixtures.

Processes using HCN and a base for the preparation of cyanocarboxylic acid alkyl esters such as 2-cyanoacetic acid ethyl ester suffer from the drawback of undesired side products due to the formation of polymeric HCN and cyanidation products such as 2-cyanosuccinic acid diethyl ester (DECS) and 2-cyano-2-ethoxycarbonylmethyl- succinic acid diethyl ester (TECP). Similar side products can be expected in the esterification of other acids. Formation of polymeric HCN firstly results in loss of HCN and secondly may also clog lines and equipment such as circulating pumps. Another side effect of polymeric HCN is discoloration of the products. Only about 50 ppm of polymeric HCN is sufficient to colorize the product dark brown to black. Furthermore, the formation of side products also reduces yields and complicates purification of the desired product.

Therefore, an object of the invention is to provide process and equipment for the preparation of a compound (halocarboxylic acid alkyl ester) of formula Hal-CH₂-A-C(O)-OR II, wherein Hal is a halogen atom selected from F, CI, Br and I, wherein A denotes a bond or a divalent spacer selected from alkylene and arylene groups, and wherein R is a Ci_-4 alkyl group, as an end product as well as an intermediate for the preparation of a corresponding compound (cyanocarboxylic acid alkyl ester) of formula

N≡C-CH₂-A-C(O)-OR I,

wherein A and R are as defined above, which overcomes the drawbacks of the known processes.

(1 )

Provided is a process for preparing a compound (halocarboxylic acid alkyl ester) of formula

Hal-CH₂-A-C(O)-OR II, wherein Hal is a halogen atom selected from F, CI, Br and I, wherein A denotes a bond or a divalent spacer selected from alkylene and arylene groups, and wherein R is a Ci_-4 alkyl group, by reacting a compound (halocarboxylic acid) of formula

Hal-CH₂-A-C(O)-OH III, wherein Hal and A are as defined above,

with a compound (alcohol) of formula

ROH IV,

wherein R is as defined above, in a reactive distillation column comprising a reaction zone, a separation zone and, optionally, an extraction zone, wherein said process comprises, from bottom to top:

(a) feeding said compound of formula IV into an reaction zone containing a

heterogeneous catalyst,

(b) feeding said compound of formula III above the reaction zone,

(c) removing said compound of formula II below the reaction zone of said reactive distillation column.

Preferably the process is carried in a reactive distillation column, comprising a separation zone being located above the reaction zone, said separation zone providing a mass transfer surface, and optionally reactive distillation column further comprising, an extraction zone providing an additional mass transfer surface, said extraction zone being located between said reaction zone and said separation zone. (2)

In a preferred embodiment A is a bond or is selected from the group consisting of linear or branched Ci_-5 alkylene and Ce-ιο arylene groups, preferably is a linear

Ci-5 alkylene group. Preferably, the compound (halocarboxylic acid) of formula III is fed to the process below the separation zone and above the reaction zone, where the compound of formula III enters the reaction zone and reacts with the compound of formula IV to form the product of formula II (halocarboxylic acid alkyl ester). Conveniently, the compound of formula III is introduced in a liquid form, optionally heated and/or optionally in the presence of an inert solvent. In a preferred embodiment, for example in the reaction of 2-chloroacetic acid (compound of formula III, wherein Hal is chloro and A is a bond) and ethanol (compound of formula IV, wherein R is ethyl), the molar ratio of halocarboxylic acid to alcohol fed into the column is in the range of from 1 :1 to 1 :5, preferably of from 1 :1 to 1 :3, and more preferably of from 1 :1 .5 to 1 :2.

In a preferred embodiment the compound of formula III is a C2-5 halocarboxylic acid, more preferably a C2_-4 halocarboxylic acid. Examples of useful halocarboxylic acids are 2-haloacetic acids, 2- or 3-halopropionic acids, 2-, 3- or 4-halobutyric acids, 4-haloisobutyric acids, and 2-, 3-, 4- or 5-halopentanoic acids. Typically, the halocarboxylic acid is a monochloro- or monobromocarboxylic acid, in particular a monochlorocarboxylic acid. In a further preferred embodiment, the compound of formula III is selected from

2- chloroacetic acid, 2- or 3-chloropropionic acid, 2-, 3- or 4-chlorobutyric acid and 2-,

3- , 4- or 5-chloropentanoic acid, wherein 2-chloroacetic acid and 2- or

3-chloropropionic acid are particularly preferred. Most preferably the compound of formula III is 2-chloroacetic acid.

(3) Expediently, the compound of formula IV is a linear or branched Ci_-4 alkyl alcohol selected from the group consisting of methanol, ethanol, n-propanol, isopropyl alcohol, n-butanol, sec-butanol, isobutanol and te/t-butanol. Most preferably, the compound of formula IV is selected from methanol, ethanol and isopropyl alcohol. (4)

Also preferably, the compound of formula IV (alcohol) is fed into the reaction distillation column in the range from the lower half to the end of the reaction zone. (5)

More preferably the compound of formula IV is fed into the reaction distillation column in the range between the lower half and the lower third of the reaction zone.

Preferably, the compound of formula IV is introduced as a water/alcohol mixture. Preferably an alcohol/water mixture feed approx. contains the respective azeotropic alcohol/water ratio. The alcohol or the alcohol/water feed mixture may or may not be heated. A pre-heated alcohol or alcohol/water feed is preferred.

In a further embodiment, in the present process at standard conditions (1 bar) the boiling point of the alcohol (compound of formula IV) is lower, preferably at least 10 °C lower, than the boiling point of the corresponding product of formula II

(halocarboxylic acid alkyl ester) at standard conditions (1 bar atmospheric pressure). Thus the boiling point difference is at least 10 °C at standard conditions. More preferably, the boiling point difference at standard conditions is 20 °C or more, even more preferably 30 °C or more, and most preferably at least 40 °C. According to a further embodiment of the invention, the temperature in the reactive distillation column is controlled to maintain the liquid mixture in the bottom part of the distillation column at a temperature of at least about 10 °C above the boiling temperature of the alcohol, i.e., the boiling point of the alcohol at the respective pressure in the distillation column. Unreacted halocarboxylic acid and halocarboxylic acid alkyl ester resulting from the reaction between halocarboxylic acid and alcohol move to the bottom of the column forming part of the bottom stream. The reactive distillation column is heated at a temperature in a range between about 20 °C below to the boiling temperature at operating pressure of said halocarboxylic acid alkyl ester. More preferably, the temperature is controlled to maintain the reaction mixture within a temperature range of from about 10 °C below boiling temperature to boiling temperature of the alkyl halocarboxylic acid alkyl ester at standard conditions. Most preferably, the

temperature of the reaction mixture in the distillation column corresponds to the boiling temperature of the halocarboxylic acid alkyl ester produced. In the case of the reaction of 2-chloroacetic acid with ethanol (boiling point 78 °C), expediently the temperature at the bottom of the column is maintained the boiling temperature of ethyl chloroacetate of between 125 to 145 °C at standard conditions, preferably at about 145 °C. Advantageously the process of the invention is carried out at ambient pressure.

In the process of the invention, the halocarboxylic acid alkyl ester formed during the esterification step is removed below the reaction zone, i.e., as a bottom product. Advantageously, removal of the product from the bottom of the column instead of from the head avoids additional efforts to heat the whole column above the boiling temperature of the ester. This reduces the thermal stress imposed upon the product. Although all esters encompassed by the instant invention can be rectified by distillation, the overall energy, turnover, and purity balance of the present process is advantageous compared to the state of the art. Also provided is a process, wherein the compound of formula II obtained in the first reaction process (reactive distillation), optionally after further rectification, is directly fed in the second reaction process (cyanidation)

Withdrawal of the compound of formula II from the reactive distillation column can be carried out, either partially or completely, by (a) removing the gaseous or vapour phase between the reaction zone and the reboiler and/or (b) removing the

condensed phase from the reboiler.

Apparatus for carrying out the inventive reaction.

Further provided is an apparatus (reactive distillation column) suitable for carrying out the process for obtaining the compound of formula II,

comprising:

(i) a reaction zone containing a heterogeneous esterification catalyst, (ii) a separation zone providing a mass transfer surface and being located above said reaction zone, and, optionally

(iii) an extraction zone providing an additional mass transfer surface and being located between said reaction zone and said separation zone

(iv) at least one feed for supplying a compound (halocarboxylic acid) of formula

Hal-CH₂-A-C(O)-OH III wherein Hal and A are as defined above, said feed for supplying the compound of formula III being located below the separation zone and above the reaction zone,

(v) at least one feed for supplying a compound (alcohol) of formula

ROH IV, wherein R is as defined above, said feed for supplying the compound of formula IV being located within the reaction zone,

(vi) means for removing the compound of formula II below the reaction zone of the distillation column.

Expediently, the temperature of the bottom liquids are controlled such that it is not more than 20 °C below the boiling temperature of the compound of formula II under operating pressure. The reactive distillation may be a glass column or a metal column, for example made from a nickel-based alloy such as Hastelloy, such as a Hastelloy C22 column. The column comprises at least a reaction zone and a separation zone located above said reaction zone. The reaction zone, i.e., the zone where the compound of formula III reacts with the compound of formula IV, contains a heterogeneous catalyst, preferably a

heterogeneous esterification catalyst. A heterogeneous catalyst does need not be extracted from the bottom product and thus facilitates the process. The

heterogeneous catalyst may be a solid or solidified catalyst, i.e., a catalyst solidified by coating the catalytically active material on an inert solid support. Preferably, the catalyst is an acidic catalyst, and more preferably is a solid or solidified body selected from acidic clays, acidic zeolites, acidic ion exchange resins, and heteropoly acids. In a preferred embodiment the heterogeneous catalyst tends to show no or minimal leaching under the reaction conditions.

An example of preferred acidic clays is Fe³⁺-montmorillonite.

Examples of preferred acidic zeolites are H-ZSM-5, HY or H-Beta.

Examples of preferred acidic ion exchange resins are acidic resins available under

TM TM

the trade name Amberlyst , in particular Amberlyst resins selected from the group

TM TM TM TM

consisting of Amberlyst 131 , Amberlyst 15, Amberlyst 16, Amberlyst 31 ,

TM TM TM TM TM

Amberlyst 33, Amberlyst 35, Amberlyst 36, Amberlyst 39, Amberlyst 40,

TM TM TM

and Amberlyst 70. Most preferably the acidic Amberlyst resin is Amberlyst 36.

Solid heteropoly acids comprise solid and solidified heteropoly acids, i.e., heteropoly acids coated on an inert carrier. Examples of preferred heteropoly acids are tungstates (wolframates) or molybdates, for example those of formulae H Xⁿ⁺Mi₂O₄o, wherein X is Si or Ge and M is Mo or W, H₃Xⁿ⁺Mi₂O ₀, wherein X is P or As and M is Mo or W, and Η₆Χ2Μι₈Ο₆2, wherein X is P or As and M is Mo or W. Preferred heteropoly acids are, tungstates, wherein M is W. Preferred tungstates are selected from the group consisting of preyssler heteropoly acid catalysts such as H₁₄[NaP₅W₃oOi io]; Keggin structured heteropoly acids such as H₃[PW₁₂O₄₀],

H₄[SiW₁₂O₄₀];

and HstPW ThOsg]; and Dawson structured heteropoly acids such as a-H₆[P2W₁₈O62] , H₆[P2W₂iO₇i] (H₂O)₃, H₆[As₂W₂i O69] (H₂O) and H₂₁ [B₃W₃9Oi 3₂] . Each heteropoly acid optionally can be used with or without silica (S1O2), niobium pentoxide (Nb2Os), zirconia (ZrO2) or titania (TiO₂) carrier, such as H₃[PWi₂O₄o], Ho.5[Cs2.5PWi₂O₄o], H₄[SiWi₂O₄₀],

15% H3[PWi2O₄o] Nb2O_5j 15% H₃[PWi2O₄o] ZrO2 and 15% H₃[PWi2O₄o]/TiO2. The packing of the catalyst is designed to enable a reaction in a liquid film on the catalyst. Thus, the catalyst packing comprises enough space to establish a

continuous vapour phase in the reactive distillation column. Preferably the catalyst is comprised in compartments, for example in woven metal fabric bags, optionally further stacked or compiled in cages, for example in a structured catalytic packing such as Katapak™ SP, wherein the catalyst is located in the Katapak™-SP packing elements. According to a further preferred embodiment, the catalytic packing is divided into at least two sections to allow easy feeding of the starting compound feeds between said sections. Preferably, the separation zone contains a mass transfer surface.

A mass transfer surface to be used in the present invention can be for example a set of, optionally corrugated, metal plates column plates, a suitable particle filling providing a high surface, or said mass transfer surface can be provided by a porous or spongiform material. The material of said mass transfer surface preferably is heat resistant and chemically inert under the reaction conditions such as glass, ceramics, high temperature resistant polymer or metal, such as stainless steel. Said particles providing said mass transfer surface, can be for example coarsely broken or regularly shaped, filamentous pieces, such as Raschig rings, Pall rings, glass or metal fibers. In one embodiment the particles might be packed in cages or woven metal or glass fiber fabric sacs which facilitate handling such as packing or exchanging the material. In another embodiment the filling can be placed as an accretion on a column plate. In a preferred embodiment the body is a metal packing, comprising filamentous metal, optionally filled in cages or woven metal fabric sacs.

In the separation zone ester and acid condenses on the filling material and thus essentially do not leave the distillation column over the column head.

Optionally, the reactive distillation column may also comprise an extraction zone located between the reaction zone and the separation zone. The optional extraction zone also contains a mass transfer surface, which may be the same or different from that of the separation zone, to prevent formation of an ester-water heteroazeotrope.

Each of the reaction zone, the separation zone and the extraction zone can be divided into separated layers of adequate filling.

Starting the reaction in the reactive distillation column is carried out according to state of the art procedures.

In a preferred embodiment, the column is divided into a portion comprising a reaction zone containing the heterogeneous catalyst and a portion comprising a separation zone containing a mass transfer surface. The reaction zone is located in the lower part of the column and the separation zone is located above said reaction zone. An optional extraction zone, which preferably also contains a mass transfer surface, is located between the separation zone and the reaction zone. The separation zone can comprise bubble trays, bubble cap trays or sieve trays as mass transfer surface or further comprise material as described above. Preferably, the body of the reactive distillation column comprises columns with different inner diameters so that the portion of the column comprising reaction zone has a wider diameter than the portion comprising the separation zone and optional extraction zone. For example, for reacting about 300 to 350 Kg/h halocarboxylic acid (compound of formula III, wherein A is a bond and Hal is chloro) a suitable diameters of reaction zone and separation zone may be about 30 cm and 10 cm, respectively. Different sized portions of the column are particularly useful for the preparation of 2-chloroacetic acid alkyl esters. In any case, a narrower diameter of the separation zone has the advantage of increased contact between the liquid and vapour phase.

Typically the compound of formula III is fed into the reactive distillation column through an, optionally heated, inlet port located immediately below the separation zone and above the reaction zone. Within the column the compound of formula III predominantly moves down to reaction zone and reacts with the compound of formula IV, which is fed through an, optionally heated, inlet into the reaction zone where it is vapourized. Preferably, the feed of the compound of formula IV enters the reactive distillation column as low as possible while it should be avoided that the compound of formula directly enters the liquid in the bottom. In an industrial size facility, for example for esterification of 2-chloroacetic acid with ethanol, the height of the catalyst filled reaction zone preferably has a total length of about 6 to 10 m at a maximum liquid throughput of about 15 m³/m²h, with a height of the catalyst packing below the feed of the compound of formula IV being about 1 to 2 m and a height of the catalyst packing above the feed of the compound of formula IV being about 5 to 8 m. The separation zone typically has a length of about 2 to 3 m.

The compound of formula II resulting from the reaction of compound of formula III and compound of formula IV, and optionally, unreacted compound of formula III forms the bottom stream which is heated by a heating system connected to the bottom of the column. Preferably the heating system is a reboiler, for example designed as a thermosyphon reboiler (also known as calandrias, i.e. an evaporator with natural circulation) or a kettle reboiler (i.e. a forced circulation reboiler). Other reboiler types are also possible. Thermosyphon reboilers have the advantage of less maintenance compared to other reboilers. Thermosyphon and kettle reboilers reduce thermal strain on the product compared to direct heating such as, for example, direct heating of a distillation bladder. The heating system provides the thermal energy to evaporate the mixture in the column bottom and provides a constant pressure of vapour in the column. The reactive distillation column is heated at the bottom and optionally also comprises individually controllable means for adjusting the temperature along the column.

The compound of formula IV, having a lower boiling then the product of formula II, is distributed in the reaction zone of the reactive distillation column. Unreacted compound of formula IV further enters the optional extraction zone and finally the separation zone. Finally the compound of formula IV reaches the column head, where it leaves the process in a mixture together with water, which at least partially is formed during the reaction, as the main component of the head stream. Said mixture head stream comprising water and the compound of formula IV exits the column and is fed to a condenser, to condense the head stream. A fraction of the condensed head stream is reintroduced into the column head as a reflux stream. The remaining fraction of the condensed head stream is withdrawn as a withdrawal stream and may be further processed to recycle the compound of formula IV and/or water to the process. In a preferred embodiment, a fraction of water of the condensed head stream is removed in a subsequent column and the recovered compound of formula IV, optionally as an mixture of water and the compound of formula IV, is recycled to the reaction zone. The ratio of the split between reflux stream and withdrawal stream expediently is in a range of from 0.4:1 to 2:1 , preferably is in the range of from 0.6:1 to 1 .5:1 . In case of the esterification of 2-chloroacetic acid with ethanol, for example, the weight ratio most preferably is about 0.8:1 . In that system the reflux stream mainly consists of water and ethanol and comprises only minor amounts of the starting acid and the ester product of formula II.

At the top of reaction zone, a heteroazeotrope of water with compound of formula II may occur which can be prevented by inserting the optional extraction zone. In said optional extraction zone, the compound of formula II and the compound of formula III are condensed and are extracted from the vapour phase and reintroduced into the column by the respective feed. In a 2-chloroacetic acid/ethanol system an extraction zone is not necessary and a simple separation zone is likely sufficient to effectively reduce the amount of the compounds of formulae II and III to prevent them to escape the reactive distillation column as over head stream. The remaining head stream of the column comprises mainly water and alcohol.

The bottoms stream, which optionally is essentially free of water and the compound of formula IV and thus mainly comprises the compound of formula II and optionally some unreacted compound of formula III and/or high boiling by-products, exits the reactive distillation column at the bottom of the column. The molar ratio of compound of formula II (halocarboxylic ester) to compound of formula III (halocarboxylic acid ratio) can be increased with the length of the column. Preferably, the column length is sufficient to reduce the amount of remaining the compound of formula III in the lower part of the column to nearly zero. The bottom stream exiting the column may be divided into a reboiler stream and a crude stream of the compound of formula II. The reboiler stream is heated in an external heating system and is reintroduced into the column through a line either by natural or by forced circulation. The stream of crude compound of formula II is subjected to further downstream processing through line. The crude product stream preferably is withdrawn from the column in a manner not to negatively affect the circulation stream.

At the top of the reactive distillation column, an mixture mainly comprising the compound of formula IV and water, is withdrawn through and fed to a further rectification column, for example a stainless steel column operated at ambient pressure, in order to recycle the compound of formula IV to the process. The bottom residue of the rectification column, after purification of the compound of formula II, can be disposed. The crude product of compound of formula II, mainly comprising the desired ester and some unreacted compound of formula III is withdrawn from the bottom of the rectification column and is charged to a further rectification column, for example a stainless steel column preferably operated under vacuum conditions, for example at a pressure from 300 to 500 mbar, for further product purification. The fraction containing for example unreacted halocarbocylic acid, by-products and impurities, such as di- or trihalogenated acids and respective esters, can be removed through while the purified compound of formula II is removed from the head of the column as an end product or as an intermediate for use in further reactions.

Depending on the residual amount of unreacted compound of formula III, optionally further rectification means as known to the skilled person, such as flash evaporator or further distillation columns, can be introduced in the downstream processing. While esterification is an equilibrium reaction in which the compound of formula III cannot be fully converted into the respective compound of formula II, it has been found that the process of the invention using reactive distillation allows the

equilibrium to be shifted towards the formation of the product. Therefore, a high conversion preferably at least 80%, particularly preferred at least 90% regarding the halocarboxylic acid can be obtained. In a further preferred embodiment, depending on the length of the active part of the reactive distillation column and the product flow, a conversion up to >99% can be reached. Moreover in the present reactive distillation the formation of by-products is significantly reduced. In the substantial absence of water and compound of formula IV in the raw product stream the complexity of the working-up procedure in the reactive distillation is reduced compared to solvent based esterification. Less equipment is required and less cost is foreseen due to the equipment. The present reaction set up uses the advantage of solvent based reaction, reaction in liquid phase, i.e. in the liquid film established around the catalyst bodies, and the advantage of good separation of low and high boilers in gaseous reaction and also avoids emulsion formation which often occurs in solvent

esterification.

The use of a heterogeneous catalyst eliminates the separation requirement in the case of a homogeneous catalyst in batch or continuous reaction. Due to the formation and presence of azeotropes, the separation of the reaction mixture from water and/or alcohol is very difficult in the case of the conventional procedure, where the ester is withdrawn or condensed from the vapour phase. With the present reactive distillation including withdrawal of essentially water free compound of formula II, optionally together with some compound of formula III, from the bottom, the problem of azeotrope separation can be overcome. Separation of compounds of formulae II and III by distillation can be difficult in the presence of water due to formation of azeotropes, especially in the additional presence of compound of formula III. The desired compound of formula II can be withdrawn at the bottom of the column although it has a lower boiling point than the corresponding compound of formula II which was initially fed to the column. Compared to batch mode the average residence time can be roughly shortened by a factor of about 2, i.e. the time for reacting the same acid amount in continuous column mode including separation from catalyst can be shortened from about 120 min to about 50 to 60 min.

In most cases it is only necessary to heat the column bottom and due to the moderate temperatures, the instant esterification process saves energy compared to the state of the art processes with head stream withdrawal.

Since the used compound of formula III, such as 2-chloroacetic acid, always has a higher boiling point than the compound of formula II, such as ethyl 2-chloroacetate, the boiling point of the compound of formula II is the measure to control the bottom temperature of the reactive distillation column, causing the compound of formula III to move down the column and to pass the reaction zone where the compound of formula II, such as ethyl 2-chloroacetate, is formed. Only a minor amount of the compound of formula III can go up the column together with water and the compound of formula IV vapour to pass the separation zone. Even less compound of formula III will leave the column over head. This simplifies work up and recycling of unreacted ethanol and raises the conversion of the acid in the process. Examples:

Example 1 :

Chloroacetic acid (compound of formula III, wherein A is a bond and Hal is CI) was molten in a heated tank. During the trial the tank was refilled with molten acid.

A reactive distillation column with an inner diameter of 50 mm was used. The column was made of glass and the internals (Sulzer Katapak SP1 :1 filled with Amberlyst 36 and Sulzer BX) from alloy steel. The column without extraction zone was used.

Column set up from top to bottom:

0.40 m Sulzer^® BX, a feed inlet for compound of formula III, 1 .20 m Sulzer^® Katapak SP1 :1 , a feed inlet for compound of formula IV, a 0.80 m Sulzer^® Katapak SP1 :1 , and a reboiler.

For reaction start up, the column was fed via the acid feed tube with hot water. The reboiler was started after a sufficient level of water was reached in the bottom. When the column reached a temperature of 100 °C over total height the acid feed was switched from water to chloroacetic acid and the ethanol flow was started as well. The column was operated with a feed stream of 4.57 kg/h chloroacetic acid

(compound of formula III, wherein Hal is chloro and A is a bond) and 2.86 kg/h ethanol (compound of formula IV, wherein R is ethyl) with azeotropic concentration. A reflux ratio of 0.9 and a heating duty of 2000 W have been used. After 5 h a stationary temperature profile was observed. Within further 4 h, samples from top and bottom showed that a stationary state was reached. Finally, a temperature of 134 °C was observed in the reboiler and 78.9 °C at the top. The conversion of chloroacetic acid was 33.1 %. The assay measured of the compound of formula II was 85wt%.. Example 2:

Example 1 was repeated with a feed of chloroacetic acid (compound of formula III, wherein A is a bond and Hal is CI) of 3.1 kg/h and a feed of ethanol (compound of formula IV with R is ethyl) of 3.14 kg/h. At a bottom temperature of 154 °C a conversion of 46.1 % was observed. The assay measured of the compound of formula II was 82wt%.

Claims

Claims:

1 . A process for producing a compound of formula

Hal-CH₂-A-C(O)-OR II wherein Hal is a halogen atom selected from F, CI, Br and I, wherein A denotes a bond or a divalent spacer selected from alkylene and arylene groups, and wherein R is a Ci_-4 alkyl group,

by reacting a compound of formula

Hal-CH₂-A-C(O)-OH III wherein Hal and A are as defined above

with a compound of formula

ROH IV

wherein R is as defined above, in a reactive distillation column comprising, from bottom to top, a reaction zone, a separation zone and, optionally, an extraction zone, wherein said process comprises:

(a) feeding said compound of formula IV into a reaction zone containing a heterogeneous catalyst,

(b) feeding said compound of formula III above the reaction zone,

2. The process of claim 1 , wherein A is a bond or is a divalent spacer selected from the group consisting of linear or branched Ci_-5 alkylene and C-6-10 arylene groups, preferably is a linear Ci_-5 alkylene group. The process of claims 1 or 2 wherein the compound of formula IV is a linear or branched Ci_-4 alkyl alcohol selected from the group consisting of methanol, ethanol, n-propanol, isopropyl alcohol, n-butanol, sec-butanol, isobutanol and te/t-butanol.

The process of any of claims 1 to 3, wherein the compound of formula IV is fed into the reaction distillation column between the lower half to the end of the reaction zone.

The process of any of claims 1 to 3, wherein the compound of formula IV is fed into the reaction distillation column between the lower half and the end of the reaction zone.

An apparatus suitable for carrying out the process of claim 1 to 5, said apparatus comprising:

(i) a reaction zone containing a heterogeneous esterification catalyst,

(ii) a separation zone providing a mass transfer surface and being located above said reaction zone, and, optionally,

(iii) an extraction zone providing an additional mass transfer surface and being located between said reaction zone and said separation zone,

(iv) at least one feed for supplying a compound of formula

Hal-CH₂-A-(CO)-OH III, wherein Hal and A are as defined above, said feed for supplying the compound of formula III being located below the separation zone and above the reaction zone,

(v) at least one feed for supplying a compound of formula

ROH IV,

wherein R is as defined above, said feed for supplying the compound of formula IV being located within the reaction zone,