KR100529685B1 - Preparation of Aromatic Hydroxycarboxylic Acids - Google Patents

Abstract

Alkali metal aryloxides can be dried quickly by removing water during melting of the aryloxides. Such dry aryloxides are useful as chemical intermediates. Molten alkali metal salts can be prepared quickly, which when acidified yields the corresponding aromatic hydroxycarboxylic acids. Aromatic hydroxycarboxylic acids are useful as chemical intermediates and as monomers of polymers. Solid metal aryloxides, even when pasted, can stir the contents and react with carbon dioxide in a reactor that makes the reaction faster than conventional methods.

Description

Preparation of Aromatic Hydroxycarboxylic Acid {Preparation of Aromatic Hydroxycarboxylic Acids}

The present invention relates to a process for drying alkali metal aryloxides and / or reacting with carbon dioxide. The method is useful for the preparation of aromatic hydroxycarboxylic acids.

Aromatic hydroxycarboxylic acids are used not only as chemical intermediates for the synthesis of drugs and antibacterial agents but also as monomers for the preparation of polyesters. For example o-hydroxybenzoic acid (OHBA, salicylic acid) is used, for example, as a chemical intermediate for the preparation of aspirin, while p-hydroxybenzoic acid (PHBA) is used for the preparation of parabens and also as a monomer in the preparation of polyesters. do. The compounds can be prepared using alkali metal aryloxides.

Alkali metal aryloxides are generally prepared by the reaction of aryl hydroxy compounds such as phenols with alkali metal containing bases such as sodium or potassium hydroxide. This can be done in the presence of water and water is also produced during the reaction.

The aryloxides are useful as chemical intermediates in various chemical processes, such as the Kolbe-Schmitt method for preparing hydroxycarboxylic acids (see, for example, AS Lindsey et al., Chem. Rev. , Vol. 57, pp. 583-620 (1957)). In some of the above processes it is desirable to essentially remove all the water from the aryloxide. This is typically done by applying a vacuum to the aryloxide and / or heating the solid aryloxide (or aryloxide, which is initially an aqueous solution, eventually becoming a solid) while passing through an inert dry gas. However, it would be beneficial to improve the drying method since it is quite time consuming and expensive.

Alkali metal aryloxides can be converted to free hydroxy acids by drying and then reacting with carbon dioxide to form (usually) dialkali metal salts of aromatic hydroxycarboxylic acids and react with strong acids such as sulfuric acid. This is usually done by exposing the powdered alkali metal aryloxide to carbon dioxide for a long time in a device that can expose a new solid surface for reaction with CO ₂ by grinding the solid (or the resulting paste formed during the reaction). All. Of commercial interest is therefore an improved carboxylation process for the Kolbe-Schmidt reaction.

Canadian Patents 881,906 and US Pat. No. 3,554,264 describe a process for drying alkali metal phenates in a spray drying column in which a drying gas is passed through the column at 250 to 500 ° C. There is no mention as to whether the temperature of the alkali metal phenoxide reaches above the melting point of this phenoxide and whether the dry phenoxide is still liquid.

Summary of the Invention

The method of the present invention for drying an alkali metal aryl oxide includes finally removing water from the alkali metal aryl oxide while the alkali metal aryl oxide is in a molten state.

The process of the invention for the production of dialkali metal salts of aromatic hydroxycarboxylic acids also comprises contacting the alkali metal aryloxide and carbon dioxide at a temperature near or above the melting point of the alkali metal aryloxide.

Another method of the invention for preparing dialkali metal salts of aromatic hydroxycarboxylic acids

(a) finally removing water from the alkali metal aryloxide while the alkali metal aryl oxide is in the molten state,

(b) contacting the alkali metal aryloxide with carbon dioxide while stirring at or near the melting point of the alkali metal aryl oxide.

The present invention also provides a process for preparing an aromatic hydroxycarboxylic acid using a Kolbe-Schmidt reaction of a metal salt of an aromatic hydroxy compound with carbon dioxide, in which a paste is produced during the reaction, wherein the contents are stirred and a sufficient free volume is present. A gas that can pass through the reactor relatively freely and come into contact with the solid and / or liquid components present,

Provided that sufficient agitation is achieved such that the average residence time of the non-gaseous reactants in the reactor is less than about 2 hours;

At least 80 mole percent of the metal salt of the aromatic hydroxy compound is reacted with carbon dioxide in the reactor;

Disclosed and claimed is an improved production process, characterized in that the reaction with said carbon dioxide is carried out at an absolute atmosphere of about 0.8 to 2 atmospheres in a reactor equipped with a gas outlet.

1 is a schematic diagram of an apparatus used in Examples 1 and 5 to 7;

FIG. 2 is a freezing point diagram of this system which also shows the boiling point of the solution at various water pressures for the potassium phenoxide-water system.

The compound to be dried herein is an alkali metal aryloxide. Alkali metal means any one of lithium, sodium, potassium, cesium or rubidium. Potassium and sodium are preferred alkali metals and potassium is particularly preferred. Aryloxide means a monovalent anion of an Ar—O structure, wherein Ar is an aryl group or a substituted aryl group in which oxygen is bonded to a carbon atom of an aromatic ring. Useful aryl groups without intending to limit this generality are phenyl, 1-naphthyl, 2-naphthyl, 2-phenylphenyl, and 3-methylphenyl. Preferred aryl groups are phenyl, 2-phenylphenyl, and 2-naphthyl, with phenyl being more preferred and phenyl being particularly preferred.

Alkali metal allyloxides can be prepared by reaction of a strong base (which is stronger than an aryloxide anion) with Ar-OH, a corresponding aromatic hydroxy compound. Suitable bases are alkali metal hydroxides which are also usually relatively inexpensive. The reaction can be carried out by reacting the solid alkali metal hydroxide (which generally comprises some water) with the molten aromatic hydroxy compound in water or using an alkali metal hydroxide with an approximately equivalent equivalent of the aromatic hydroxy compound. For example, 45% of aqueous KOH can be reacted with phenol.

Drying herein means the removal of water from the alkali metal aryloxide. The final “dry” aryloxide preferably has a water content of less than 2000 ppm water, preferably less than 500 ppm water, more preferably less than 100 ppm water. In a typical drying process currently performed in the art, an aqueous solution of alkali metal aryl oxide is heated to remove by distillation or evaporation of water. Eventually the alkali metal aryloxide becomes too high and precipitates out of solution and the final drying step is carried out on solid aryloxide. While the water is removed, preferably an inert dry gas can be passed over the aryloxide or a vacuum is applied to the aryloxide, or both, to assist in water vapor removal.

In the drying process disclosed herein, the final drying step is performed at a sufficiently high temperature so that the alkali metal aryloxide can be melted. This means that the final drying (ie, "final" water is removed) is done near or above the melting point of the dry alkali metal aryloxide. In one drying method, the temperature of the aryloxide (and the accompanying water) constantly rises above the melting point of allyloxide. The aryloxides that can start off as water-containing one-phase liquids during this time are solid aryloxy if the solids change back to one-phase liquids as solids form and reach (or exceed) the melting point of the aryloxide. Draw, or it can be converted to solids and liquids. During this time an inert gas can be passed over the aryloxide and / or vacuum applied. Stirring solid or liquid aryloxides generally helps to speed up drying. The final removal of water occurs when the aryloxide melts.

Another method of carrying out drying is to heat a mixture of water and alkali metal aryloxide above the melting point of aryloxide under atmospheric or elevated pressure to ensure that sufficient water is present to maintain a single liquid phase. The temperature is lowered by the name of the melting point of the aryloxide so that the water can evaporate and drying is completed as above. Care must be taken to ensure that the liquid is sufficiently cooled by the evaporation of water so that a solid does not form during the final drying step.

The above discussion of dehydration of aryloxides is illustrated by the dehydration of potassium phenoxide associated with the dehydration shown in FIG. 2, and of the phase diagram. The figure was made by appropriate measurements in the laboratory, but the data were smoothed and the curves at various pressures were paralleled under the assumption that Henry's Law was followed at low partial pressures of water in the vapor phase. Therefore, all data in the figure should be regarded as an approximation. The solid line represents the freezing point of the potassium phenoxide / water system. The abscissa is the weight fraction of potassium phenoxide present (water is another part of the weight fraction) while the ordinate is the temperature in degrees Celsius. The solid line represents the boiling point of water in this system at the pressure indicated (0 psig or 0 kPag is atmospheric pressure). In this system, where the freezing point curve is above the boiling point of water, the system is present at 0 kPag (0 psig) and approximately 0.93 to 0.98 mass (weight) fraction of potassium phenoxide, so that the water evaporates from this system. As it becomes partially solid. If the mass (weight) fraction of potassium phenoxide is greater than about 0.98, the system becomes liquid as water is removed at 0 kPag (0 psig). However, if the system pressure is maintained above about 68.9 kPag (10 psig), the system will remain liquid even after the water is removed.

The drying process is made more economical by generally proceeding quickly to remove the last amount of water from the molten alkali metal aryloxide.

Of course, it is desirable that the alkali metal aryloxide does not decompose to a noticeable extent during drying (ie significantly stable above its melting point). The melting point of the alkali metal aryloxide is therefore preferably less than 400 ° C., more preferably less than about 350 ° C., particularly preferably less than about 320 ° C. The preferred minimum drying temperature is, as long as the melting point of the alkali metal aryl oxide is higher. Or 275 ° C. The temperature referred to during drying (of the last part) is the actual temperature of the alkali metal aryloxide itself. The melting point is measured by differential scanning calorimetry at a rate of 25 ° C. per minute and the melting point is considered as the extrapolated initial temperature of the melting endotherm.

Preferred alkali metal aryloxides are potassium phenoxide, sodium phenoxide, and potassium 2-naphoxide and potassium phenoxide is particularly preferred.

The drying process can be carried out in any vessel suitable for use with the relevant materials and at the relevant temperatures. Stainless steel is particularly suitable. If some of the drying air is done under pressure and / or vacuum, the container should be considered accordingly. It is desirable to be able to shake liquids and / or solids that may be present in the vessels to improve heat transfer and to promote the evaporation of water from the aryloxides. The vessels and their contents are prepared in the usual manner (e.g. Trademark, Dowtherm) heat transfer fluid (condensation vapor, such as from Dow Chemical Co., Midland, Mich.), May be heated electrically or with hot oil.

The resulting dry aryloxide can be cold solidified to be used in a typical Kolbe-Schmidt type process, or it can remain molten and react with CO ₂ to form a dialkali metal salt of aromatic hydroxycarboxylic acid.

The chemical reactions associated with Kolbe-Schmidt synthesis can be represented by the following schemes 1-3.

In the scheme, M is an alkali metal, and Ar is suitably an aryl, substituted aryl, substituted arylene, or arylene group. Scheme 1 is simply the formation of alkali metal aryloxides as described above for drying. “Dry” aryloxides generally react with CO ₂ to form dialkali metal salts of aromatic hydroxycarboxylic acids. The salt may then be acidified to form an aromatic hydroxycarboxylic acid (sometimes referred to herein as "our" aromatic hydroxycarboxylic acid, meaning it is not a salt).

As indicated above, the reaction of Scheme 2 was typically performed by exposing the solid alkali metal aryloxide to CO ₂ in the conventional temperature range. Generally some stirring or grinding forms are provided to expose all solids to CO ₂ . Although solid under the dialkali conditions of the desired aromatic hydroxycarboxylic acid, the aromatic hydroxy compound formed is often a liquid which eventually boils or evaporates in a CO ₂ (or other gas) stream. This reaction therefore often proceeds from solid powder to paste and from solid powder, and due to the difficulty in fully reacting the solid with the gas, this reaction needs to be done for a long time to complete the reaction.

It has now been found that even shorter reaction times can be obtained when the molten alkali metal aryloxide is reacted (contacted) with CO ₂ , especially with stirring. The initial material in this scenario is a liquid which generally turns into a paste as the solid dialkali metal salt of the aromatic hydroxycarboxylic acid and the liquid aromatic hydroxy compound are formed. It generally changes slowly to a dry solid as the aromatic hydroxy compound boils or is volatilized from the mixture.

Since it is preferable to react the alkali metal aryloxide in the molten state, the contact should be performed near or above the melting point of the alkali metal aryloxide. Generally, the resulting alkali metal salt of the aromatic hydroxycarboxylic acid is preferably at least 90 mol percent, or more preferably 98 mol percent of the reaction, since the final 20 mol percent of the reaction with CO ₂ is preferably cooled. Although the above is preferably performed near or above the melting point of the alkali metal aryloxide, it can be carried out below the melting point of the alkali metal aryloxide.

In contact with CO ₂ , it is of course preferred that the alkali metal aryloxide or any other material present in the process does not decompose to an appreciable degree (ie, is fairly stable at process temperature). Therefore, it is preferable that the melting point of the alkali metal aryl oxide is less than 400 ° C, more preferably less than about 350 ° C, particularly preferably less than about 320 ° C. Preferred minimum temperatures are either the melting point of the alkali metal aryloxide or 275 ° C. as long as it is higher.

Useful aryl groups in the reaction with CO ₂ are phenyl, 1-naphthyl, 2-naphthyl, 2-phenylphenyl, and 3-methylphenyl. Preferred aryl groups are phenyl, 2-phenylphenyl and 2-naphthyl, more preferably phenyl and 2-naphthyl, with phenyl being particularly preferred. Preferred alkali metal aryloxides are potassium phenoxide, sodium phenoxide, potassium 2-phenylphenoxide, potassium 2-naphoxide, more preferably potassium phenoxide and thallium 2-naphoxide, with potassium phenoxide being particularly preferred. . Preferred products (represented as their parent aromatic hydroxycarboxylic acids and originally produced as their alkali metal salts) are salicylic acid, p-hydroxybenzoic acid, 3-phenyl, -4-hydroxybenzoic acid, and 6-hydroxy-2- Naphthoic acid, with p-hydroxybenzoic acid being particularly preferred.

Suitable constituent materials for the CO ₂ reaction are the same as described above for the drying of the alkali metal aryloxide. Useful types of devices for this reaction include ribbon blenders, LIST-CRP and LIST ORP manufactured by LIST AG (Arisdorf, Switzerland), and littleford Day, Inc. Available in various sizes manufactured by Florence, KY, or Reactotherm RT manufactured by Krauss-MafferVerfahrenstechnik Gmbh (Munich, Germany). The reaction can be carried out batchwise, semicontinuously or continuously. For example a modified screw conveyor reactor can be used. Screw conveyor reactors are known in the art (see, eg, Ullmann's Encyclopedia of Industrial Chemistry, Vol. B4, Trial, VCH Verlagagesellschaft, Weinhem, 1992, p. 111- edited by B. Elvers et al. 112]. These are generally used for reactions involving solids and pharmaceuticals. By deformed screw conveyor reactor is meant a reactor, or equivalent thereof, in which sufficient free volume is present such that gas can be contacted with the solid and / or liquid components present through the reactor relatively freely. Such reactors may be equipped with single or multiple rotary shaft (s), or other stirring aids such as high speed choppers. Equivalent means that a liquid and / or solid reactant can be moved through the reactor at a moderate rate (giving the desired residence time) while at the same time a new atmosphere of solid and / or liquid is contained in the gas atmosphere (in this case containing CO ₂ ). It means any reaction device that can be exposed to. It should also have a sex ratio for adding one or more gases at one or more points through the reaction vessel along the reaction vessel, preferably any excess gas added to the system, and / or any product generated during the process There should also be a doorway to remove volatiles. If a "threaded" conveyor reactor is used, the "screw" of the reactor need not be a solid screw, but may be a segmented screw having an opening space between the screw shaft and the periphery of the screw. The screw shaft or stirrer shaft is hollow at the center so that heat transfer fluid or CO ₂ and / or other gases can pass therethrough. In the case of CO ₂ and / or other gases, holes exist in the axis (s) to allow the gas to pass through and contact the reaction mass.

As described above, reacting CO ₂ with 2 equivalents of alkali metal aryloxide yields 1 equivalent of the dialkali metal salt of aromatic hydroxycarboxylic acid and 1 equivalent of the original aromatic hydroxy compound, substantially aromatic hydroxy The compound is generally at its process temperature above its melting point and forms a paste with the alkali metal salt formed and the solid (below its melting point) alkali metal aryloxide. The paste formation makes the mixing of CO ₂ and the starting alkali metal aryl oxide difficult, thus slowing down the reaction. It is also believed that the reactivity of the alkali metal aryl oxide and CO ₂ is reduced in the presence of free aromatic hydroxy compounds.

The formation of the paste is believed to be due to a long overall process cycle, typically several hours or more, experienced in typical commercial Kolbe-Schmidt methods such as ball mills. In order to overcome the above problem, a reactor equipped with a stirrer for stirring the contents is preferable. The stirrer and stirrer driving force (ie, the power for the stirrer) should be strong enough to mix the contents of the reactor, especially in the reaction on the paste, so that a relatively fast reaction rate with CO ₂ is maintained. Reactors as described above (when reacting molten alkali metal aryloxides) are suitable, and modified screw conveyor reactors (see above) are preferred reactor types. Suitable strained screw conveyor reactors of this series are LIST-CRP and LIST ORP, manufactured by LIST AG (Arisdorf, Switzerland) and are available in a variety of sizes. Another suitable type of reactor is Reactotherm RT manufactured by Krauss-Maffei Verfahrenstechnik Gmbh (Munich, Germany).

The reactor should also be equipped with facilities for adding one or more gases at one or more points along or through the screw conveyor system, particularly preferably all excess gas added to the system, and / or process There should also be a doorway to remove all volatiles produced during the process.

Preferably, the stirrer of the reactor is essentially self-cleaning (ie, it does not remain in the reactor for an excessive amount of time where essentially any material that can stick to the screw or tub surface is wiped off or otherwise removed from the surface). As mentioned above, the driving force of the reactor is strong enough to constantly mix the solids and / or liquids with the gas phase in the reactor by overcoming any interference that may be caused by solids or any paste that may form inside the reactor. The reaction rate of CO ₂ should not be limited.

Since most Kolbe-Schmidt reactions must be carried out at elevated temperatures, there should generally be a means to heat the reactor. Such means are known to those skilled in the art and include steam or other condensed vapors, hot liquids, electric heat and the like.

The reaction can be carried out batchwise, semibatch or continuously and preferably the process is carried out continuously. Also preferably, the solid alkali metal aryloxide is fed at the first end of the reactor and continuously passes through the reactor to the second end of the reactor, leaving the reactor at the second end of the reactor. Preferably at least some CO ₂ is added at the second end of the reactor to move towards the first end of the reactor (preferably against the movement of solids and liquids in the reactor). Further CO ₂ may be added at other points along the reactor. Preferably of CO ₂ added The amount is from about stoichiometric amount (the amount required to react with the added metal aryloxide) to about 5 times the stoichiometric amount, more preferably about 2 to 4 times the stoichiometric amount.

Optionally, an inert gas such as nitrogen may also be added to the reactor. Excess C0 ₂ and / or inert gas may help reduce paste formation in the reactor by assisting in the removal of aromatic hydroxy compounds, which are by-products formed during the reaction. As described above, it is believed that the presence of the aromatic hydroxy compound reduces the reaction rate between the alkali metal aryloxide and the CO ₂ , and therefore, the removal of the aromatic hydroxy compound is thought to further shorten the overall process time.

It is also known that many Kolbe-Schmidt reactions are carried out at temperatures above the boiling point of many of the aromatic hydroxy compounds used. Thus, many aromatic hydroxy compounds can be removed by simple evaporation in many cases as long as there is an outlet on the reactor, even without adding excess CO ₂ and inert gas to the reactor. The heat of reaction can be used to help evaporate the free aromatic hydroxy compound, further reducing circulation time and further improving thermal efficiency.

The average residence time of the alkali metal aryloxide (or its reaction product with CO ₂ ) in the reactor is less than about 1.5 hours, more preferably less than about 1 hour, particularly preferably less than about 0.5 hour, very preferably Less than about 0.25 hours is preferred. Less than 2 hours, or any of the above times, at least 80 mole percent, more preferably at least 90 mole percent, particularly preferably at least 95 mole percent, most preferably at least 98 mole percent of the original alkali metal aryloxy Degas is preferred to react with CO _2. Retention in a batch reactor simply means the reaction time for the batch. Average residence time in semi-batch and continuous reactors has its general meaning.

Preferably the interior of the reactor is at an atmospheric pressure of ± 20.0 kPa (0.2 bar). Pressures above ambient pressure minimize leakage of atmospheric gases such as oxygen or moisture into the reactor. It can be costly and difficult to produce an industrial reactor in which such gases do not pass.

Preferably the alkali metal is sodium or potassium, more preferably potassium. Preferred aryloxide anions for the process in a stirred reactor are the same as those listed above for the process comprising drying and / or reacting the molten alkali metal aryloxide.

Example 1

This embodiment was carried out in the apparatus shown schematically in FIG. The method is a CRP-6 batch reactor in which nitrogen or carbon dioxide can be passed through a flow meter (2) and connected to valves (19) and (20) from a nitrogen cylinder (3) and a CO ₂ cylinder (4), respectively. It was carried out in (1). The amount of carbon dioxide passing through the reactor 1 was measured by finding out the mass loss of the CO ² cylinder 4 on the scale 5. Reactor 1 was heated by circulating hot oil system 6 (including heater 7). Volatile material was removed by passing through a dust filter (8) and into a condensate (9). A weighable condensation liquid was then flowed through the valve 17 to the receiver 10 to determine the amount of condensate recovered. Condenser 9 provides water / glycol recycle in the manner illustrated. Vacuum is established through the trap and the discharge / vacuum pump as illustrated. Throughout the drawings various thermometers "T1" and pressure gauges "P1" help to monitor this process. The reactor 1 is installed on the stand 18. Another useful coupling valve 21 is illustrated in the figure.

4.16 kg of Pelletized Potassium Hydroxide (KOH, available from JT Baker company, "Baker analyzed ACS grade (KOH of 85% by weight minimum assay, the rest of which is mostly water)) is a high temperature oil system (as illustrated in the accompanying drawings). 6), loaded into List, Inc.'s CRP-6 twin screw mixing machine (CRP-6 batch reactor (1)), equipped with a steam outlet (12), and two gas inlets (13), (14). The entire system was evacuated to 1.3 kPa pressure and a total of three times nitrogen gas was recharged to atmospheric pressure to remove oxygen from KOH and the atmosphere of this system, followed by 5.97 kg of weakly bound crystalline phenol (PhOH, Lancaster Chemical Co.). Purchased from.) Was charged to the mixer through a charging inlet at the top of the steam outlet 12. The mixer was turned on for about 5 minutes to allow phenol crystals to drop into reactor 1, and the system was brought to a pressure of about 2.7 kPa. Empty and three times more nitrogen Recharge to atmospheric pressure to remove all oxygen introduced with phenol, where cooling water was fed to the condenser 9, the control point of the hot oil heater 7 was increased from room temperature to 225 ° C, and the mixer agitator drive force was adjusted. The mixer speed was 75 and 94 RPM, respectively, on the slow and fast shafts of the CRP-6 batch reactor 1, approximately 0.28 m ³ / hour nitrogen sweeping gas (at STP) during the heating portion of the experiment. Most of the swept nitrogen was injected onto the side of the reactor 1 closest to the drive linker.The temperature of the internal thermocouple in this unit was approximately At 120 ° C., the contents were determined by the inventors of a solution of potassium phenoxide (PhOK) in water (introduced with KOH and the phenol and potassium hydroxide to form phenoxide and water). It was melted in a will that all of) visible through the clear liquid visible glass 15 on the end of (furthest CRP-6 batch reactor (1 from the gear drive) which considered) released from the response. When the contents temperature reached approximately 160 ° C. the solution began to boil and water began to collect in the receiver 10. Very vigorous nasal passages were observed throughout the solution volume when the solution temperature reached approximately 180 ° C. The viscosity of the solution increased rapidly with increasing process temperature and at a temperature of about 190 ° C. the solution began to solidify. Once solidification was complete the glass of water was significantly slowed and the control point of the hot oil heater 7 increased to 325 ° C. Heating continued with slow release of water. When the process temperature reached 280 ° C., the solid began to melt to produce a clear melt of potassium phenoxide comprising a small amount of dissolved water. The heating oil temperature controller (not illustrated) was adjusted to 310 ° C. when the process temperature was 290 ° C. and the nitrogen sweeping flow was increased to 0.56 m ³ / hour. The increased nitrogen flow continued for 15 minutes during which an additional 0.064 kg of water was collected (2.57 kg of water collected in total).

At this point the CRP-6 batch reactor 1 was filled approximately 60% with molten / dehydrated phenoxide. The nitrogen sweeping gas stream was terminated and there was introduced a carbon dioxide stream at a flow rate indicated as 1.68 m ³ / hour (measured by flowmeter calibrated for air at STP). The carbon dioxide stream was divided into two streams. One is introduced into the vapor space above the phenoxide at the end of the reactor (1) furthest from the drive end, while the second stream is slightly below the surface of the phenoxide at the end of the reactor (1) closest to the drive linkage. Introduced. Approximately two thirds of carbon dioxide was introduced through the gear drive nearest exit, while about one third was introduced through the other exit. It was observed that what was previously a transparent melt through the thorn glass 15 immediately after the introduction of carbon dioxide gas became cloudy. Carbon dioxide gas was fed at this rate over a period of 80 minutes during which time a total 4.3 kg (weight measured on a digital balance) was charged to the CRP-6 batch reactor (1). The process temperature was relatively constant at 290 ° C. (+/− 2 ° C.) during carbon dioxide charging. Phenol was collected relatively slowly in receiver 10 for the first approximately 40 minutes upon carbon dioxide charge (a total of 0.97 kg of phenol was collected during this time) and the phenoxide melt became increasingly cloudy but still looked like a weak solid slurry. After about 40 minutes of carbon dioxide flow, the material in the CRP-6 reactor (1) began to take shape of the wet paste and the phenol collection rate also began to rise, and hydraulic pressure was needed to maintain a fixed speed on the mixer stirrer. Further 0.74 kg of phenol was collected as a stirrer hydraulic pressure returned to the same value seen during the initial portion of the carbon dioxide stream over the next 10 minutes (total 1.71 kg obtained). Shortly thereafter, the paste seen through the visible glass 15 of the CRP-6 batch reactor 1 appeared to be dried, and an instant burst of very large phenol release was observed. After 70 minutes of carbon dioxide flow, a total of 2.79 kg of phenol was collected and the product dipotassium p-hydroxybenzoate appeared as a dry / weakly bound powder and phenol release was significantly reduced. Over the next 10 minutes essentially no additional phenol was collected and the process was terminated. The carbon dioxide gas injection was replaced with 0.28 m 3 / hour nitrogen gas (measured by flowmeter 2 calibrated for air at STP), the control of the hot oil heater 7 adjusted to 10 ° C., and cooling the circulation Oil was provided. Over the next 90 minutes, the process temperature decreased to 45 ° C. At this time the mixer stirrer was stopped, the nitrogen sweep gas flow was stopped, and the circulating oil flow was stopped. The reactor end plate was removed and the powdered product was transferred for further testing. A total of 6.67 kg of solid was transferred from the mixer (1). Most of the solids (approximately 6.40 kg) were in the form of free flowing creamy powders, while some 0.27 kg were recovered as lumps in the vapor discharge line.

Powders were analyzed by high pressure liquid chromatography using appropriate compounds for calibration. The potassium salt was converted to the free compound before analysis. The analysis showed that 61.14 weight percent PHBA (equivalent to 94.87 weight percent dipotassium salt in the original sample) and 0.39 weight percent phenol (0.56 weight percent potassium phenoxide in the original sample) (based on the weight of the original sample) ) Is present. 4-hydroxyisophthalic acid or salicylic acid was not detected at all.

Example 2

One liter of 316 stainless steel resin canister (purchased from Lab Glass Supplies) equipped with three perforated glass tops was charged with 131.8 g of potassium hydroxide (KOH) pellet (analytical value> 85%). Once the pellet was filled, the filling funnel was replaced with a condenser tube and a condensate receiver to ensure that any condensable vapor produced in the resin bottle was condensed and collected in the receiver to prevent entry into the resin bottle. The KOH pellets were evacuated to 700 Pa pressure and refilled with nitrogen to remove oxygen from KOH. The resin container was suspended on the molten liquid metal bath during this time, and it was observed that sufficient heat diffused into the steel vessel and the KOH pellets began to melt. 500 g of molten phenol was then charged into a dropping funnel arranged to allow direct release into the process vessel through one of the holes in the top. Some of the molten phenol was charged during the process. Initially a very vigorous reaction was observed and the remaining phenol was very slowly charged with vigorous mechanical stirring of the vessel contents provided. The total KOH charged was completely melted / dissolved by the completion of the phenol filling. After the phenol filling was complete, the dropping funnel was removed and replaced by a bleed tube connected to house nitrogen. The molten metal bath was raised so that about 40% of the height of the resin barrel was covered by the liquid metal. Even if the metal bath temperature controller was adjusted to 170 ° C, the heat of reaction between phenol and KOH raised the metal bath temperature to 205 ° C. The adjustment point of the molten metal bath temperature control apparatus rose to 220 degreeC. Milky condensate was collected as the heating proceeded. The condensate changed from milky white to transparent as the process temperature was named for the bath temperature. The molten metal bath temperature controller adjustment point rose to 240 ° C. and the jog itself rose to cover 80% or more of the height of the resin container with the liquid metal. The liquid metal bath temperature controller adjustment point rose to 300 ° C. over the next 30 minutes and held the bath at this temperature for about 1 hour while slowly sweeping nitrogen to help remove water. The metal bath was then lowered out of contact with the resin barrel and its heater was turned off. The temperature of the liquid in the resin barrel was 266 ° C. as measured by thermocouple. After removing the thermocouple, the resin container was allowed to flow a small amount of nitrogen when cooled to room temperature. 304 g of liquid was collected in a condensate receiver. The recovered solid was found to contain 1.1% water as measured by Karl Fisher titration.

Example 3

40 g of sodium hydroxide pellets were charged to the same 1 liter stainless steel resin pail as described in Example 2, evacuated to less than 400 Pa and replenished with nitrogen to 3 times atmospheric pressure to remove oxygen. 100.0 g of weakly bound crystalline phenol was then charged to a container filled with nitrogen through a powder funnel. The vessel was then evacuated to 6.6 kPa and recharged to twice the atmospheric pressure to remove oxygen. Nitrogen gas bleed was established across the vessel, condenser and condensate receiver to help remove volatiles from the reactants. The molten liquid metal bath held at 200 ° C. was then raised to cover 80% of the longitudinal height of the stainless steel resin barrel. The bath temperature control was adjusted to 318 ° C. and the mechanical stirrer was turned on. Water and excess phenol boiled as the crude, resin barrel, and reaction mass were heated. The metal bath temperature reached 318 ° C. after about 35 minutes. Further heating was continued for 20 minutes and the molten metal bath was then lowered and its heater was turned off.

The vessel was cooled to near room temperature and then opened to inspect the contents. A visual inspection showed that most of the vessel contents melted at the end of the experiment, although clearly a small fraction was in the form of icing powder. Differential scanning calorimetry on the material of the molten phase showed a clear melting point at 272 ° C. Essentially no change was seen in the DSC traces after heating sodium phenoxide to 180 ° C. and holding in a vacuum oven for several hours.

Example 4

66.0 g of potassium hydroxide pellets were charged to the same 1 liter stainless steel resin pail as described in Example 2, evacuated to below 400 Pa and refilled with nitrogen to three times the atmospheric pressure to remove oxygen. 144.2 g of weakly bound crystalline 2-naphthol was then charged to a container filled with nitrogen through a powder funnel. The vessel was then evacuated to 6.7 kPa and refilled to twice the atmospheric pressure to remove oxygen. Nitrogen gas bleed was established across the vessel, condenser and condensate receiver to help remove volatiles from the reactants. The molten liquid metal bath held at 200 ° C. was then raised to cover 80% of the longitudinal height of the stainless steel resin barrel. The bath temperature control was adjusted to 318 ° C. and the mechanical stirrer was turned on. Water and excess phenol boiled as the crude, resin barrel, and reaction mass were heated. The metal bath temperature reached 318 ° C after about 30 minutes. Further heating was continued for 20 minutes and the molten metal bath was then lowered and its heater was turned off.

The vessel was cooled to near room temperature and then opened to inspect the contents. Visual inspections showed that essentially all container contents were melted at the end of the heating time. Differential scanning calorimetry on recovered potassium 2-naphthoxide showed a clear melting point at 243 ° C.

Example 5

In the above example, similar to the apparatus shown in Fig. 1 was used except that there were no scales (5) and (11) for weighing the added CO2 or phenol recovered.

2.7 kg of potassium hydroxide and 4.0 kg of phenol were added to the CRP-6 batch reactor 1 under nitrogen and the reactor 1 was placed under vacuum followed by ambient pressure of nitrogen and nitrogen purge. The reactor was started to heat and the two stirrer shafts were adjusted to rotate at 30/37 rpm followed by 53/67 rpm. Water was distilled off during this time. When the contents temperature reached 255 ° C., vacuum was applied for 25 minutes to remove the final traces of water. At this point a powder was present in reactor 1.

CO2 was then added at a rate of 1.99 to 2.26 m 3 / hour (70 to 80 SCF / hour) for 72 minutes (excluding the two short times when the phenol plug is formed in the condenser 10) at a reactor content temperature of 255 ° C Added. Also added was 0.5 m3 / hour (20 SCF / hour) of nitrogen during the first 37 minutes of CO2 addition. Except for two short periods of time when there was a plug in the condenser 10, the pressure in the reactor 1 was approximately ambient pressure. Immediately after the addition of CO2, the reaction mass was pasted and then gradually dried powder as CO2 addition proceeded. Immediately after the CO2 addition and almost simultaneously with the reaction material pasting, the driving force consumption by stirrer driving also peaked. Subsequent driving force consumption gradually decreased. Product analysis is shown in Table 1.

Example 6

This example performs drying and reaction with CO ₂ at 272 to 274 ° C. with a CO ₂ flow rate of 2.26 m 3 / hour (80 SCF / hour) for 58 minutes (no plug in this system) and nitrogen flow during CO 2 addition. It carried out exactly the same as Example 5 except not having. The observations during the CO2 addition were similar to those of Example 5. Product analysis is shown in Table 1.

Example 7

The examples were drying and reaction with CO ₂ at 269-271 ° C., reactor contents temperature, drying under a nitrogen flow of 0.57 m 3 / hour (20 SCF / hour) and CO ₂ addition for 2.26 m 3 / It was done exactly the same as Example 5 except that it was done at time (80 SCF / hour). The observations during the CO2 addition were similar to those of Example 5. Product analysis is shown in Table 1.

Table 1

The yield in the table is expressed as a percentage of the original total sample, where the compound was present as its alkali metal salt. Practical analysis was performed using a suitable standard by high pressure liquid chromatography (HPLC) on the free compound (ie after acidifying the compound). "Total salt" is based on recalculations using HPLC analysis results for the total amount of samples found by this analysis. "It is thought that the lost material is potassium (heavy) carbonate and possibly other inorganic salts." N / D "in the table means no detection.

Claims (15)

In the process for producing an aromatic hydroxycarboxylic acid using the Kolbe-Schmidt reaction of alkali metal aryloxide and carbon dioxide, in which a paste is formed during the reaction, In the reactor where the contents are stirred and sufficient free volume is present so that gas can pass relatively freely through the reactor and come into contact with the solid and / or liquid components present, the alkali metal under absolute pressure of about 0.8 to 2 atmospheres. Reaction with the carbon dioxide at or near the melting point of the aryloxide, Provided that the reaction takes place in the absence of a reaction medium, Sufficient agitation is achieved such that the average residence time of the non-gaseous reactants in the reactor is less than about 2 hours; At least 80 mole percent of the alkali metal aryloxides in the reactor react with carbon dioxide; Improved manufacturing method characterized in that the unreacted gas is discharged from the reactor. The method of claim 1, wherein the alkali metal aryloxide is potassium phenoxide, sodium phenoxide, potassium 2-phenyl-phenoxide or potassium 2-naphoxide. The method of claim 1, wherein the alkali metal aryloxide is potassium phenoxide. The method of claim 1 wherein the alkali metal aryloxide has a melting point of less than about 320 ° C. 5. The method of claim 1, wherein the process is performed at a temperature of about 275 ° C. or higher. The process of claim 1 wherein excess carbon dioxide or an inert gas or both are added to the reactor. The method of claim 1 wherein the process is carried out continuously. The method of claim 1 wherein the process is carried out in a batch reaction. The method of claim 1, wherein the carbon dioxide is added to flow opposite to the movement of the solid in the reactor. The method of claim 1, wherein at least 95 mole percent of the alkali metal aryloxide is reacted with the carbon dioxide in the reactor. The method of claim 1, wherein the total pressure is ambient atmospheric pressure 0.2 0.2 bar. The method of claim 1 wherein said alkali metal is sodium or potassium. The method of claim 1 wherein the alkali metal is potassium. The method of claim 1 wherein the aromatic hydroxy compound is removed during the process. The method of claim 1, wherein said average residence time is less than about 1.0 hour.