CA1312623C - Process for preparing 1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid - Google Patents

Abstract

05-21(6906)A ABSTRACT There is disclosed an improved process for preparing 1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid wherein the reaction mixture has a solids concentration of above about 60%, by weight whereby the amount of by-product fumarate is reduced.

Description

~ 3 ~ 3 -1- 05-21(6906)A

This invention relates to an improved process for making ether carboxylic acids and more particularly to processes for makin~ ether carboxylates prepared by a calcium ion catalyzed reaction in alkaline medium of maleic acid salt and a carboxylate salt containing a reactive hydroxyl group. Such reactions are of the type typically referred to as Michael condensation reactions.
Polycarboxylic acids have long been known to be useful, usually in the salt form, as detergent builders or sequestrants. Also, ether carboxylates useful as metal sequestering and detergent builders have been known and are most desirable for their beneficial effects in laundering applications.
While many carboxylate compounds in the prior art have utility as a builder or sequesterant in laundry detergent formulations, it has been found that certain ether carboxylates are more attractive and cost effective for such utility. In the field of detergent builders and se~uesterants for laundry detergent formulations low cost of the components is extremely important because it is in a very competitive market. While many ether carboxyla-te compounds have been found to be useful there is needed more economical manufacturing processes whereby such compounds can be economically produced in large volume.
One example of ether carboxylates is a mixture of polycarboxylic acids or salts thereof, particularly the sodium salts, of l-hydroxy-3-oxa-1,2,4,5-pentane -tetracarboxylic acid (HOPTC) and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid (DOOHC) which is highly useful in detergent formula-tions as a sequesterant or builder. This mixture is .~

~3~2~23 -2- 05-21 ( 6906 )A

prepared by reaction of a combination of D,L-tartrate salts with maleate salts catal~zed by calcium ions.
The production of builders or sequesterants for the detergent industry usually involves large 5 volumes of materials. Also, the reaction of oryanic materials generally provides by-products unwanted or undesired and cost is incurred for their removal.
The unwanted by-produc-ts often become waste products requiring disposal thereby presenting environmental issues. It is therefore desired to have processes for manufacture which reduce or eliminate by-product disposal re~uirements and associated costs, particu-larly in large scale production such as is encountered in the production of builders or sequesterants for use in detergent formulations.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided a process for preparin~ HOPTC and DOOHC
by the reaction of the salts of maleic acid and a tartaric acid (solids content~ said reaction catalyzed by calcium ions and conducted under alkaline conditions wherein unwanted fumarate by-product is reduced. Such reduction is achieved by concentrating the reaction mixture to a solids content of above 60%, by weight, prior to initiation of the reaction. More preferably, the reaction mixture is concentrated by removal of water to a range of from about 62% to about 70% and more particularly to about 62% to about 65% solids.
While the process of this invention achieves the objective of reduc~d by-product formation in the ranges of solids content as noted above, it is most desired to operate the process of this invention in the preferred range 65% solids content or below because calcium tartrate has been found -to precipitate in smaller crystals at higher solids content concentra-tion. While small crystals are not less pure, ~3:~ 2~3 -3- 05-21 ( 6906 )A

processin~ steps such as fil-tration, etc. become more difficul-t with smaller crystals.
various embodiments oE -this invention may be employed to achieve the concen-tra-tion of the reaction mixture which has been found to provide advantageous reduction of by-product. In one embodiment concentra-tion of the reaction mix-ture is provided by holding the reaction mix-ture for a period of time at moderate temperature while sweeping the reactor with an inert gas such as air to remove water. In another embodiment, the reaction mixture is heated to an elevated temp-erature such as the reaction tempera-ture or even boiling prior to adding the required amount of base -to initiate a reaction thereby removing water at a more rapid rate. I-t is preferred to subjec-t the reaction mixture to reduced pressure -to achieve efficient concentra-tion oE the reaction mixture prior to adding -the re~uired amount of base to initiate the reaction.
Because there are provided various recycle systems whereby unreac-ted starting materials are recovered and reused in subsequen-t reactions process efficiency is maintained even at high reactor solids concentration.
DETA I LED DE S CR I PT I ON OF THE I NVENT I ON
Calcium catalyzed reactions for the produc-tion of ether carboxylates are known. A typical example of such a process is disclosed in U.S.Patent 4,663,071 to Bush et al.

The U.S. Pa-tent discloses a process for preparing a mixture of HOPTC and DOOHC referred to above. In such process the mixture is obtained by the reaction of maleic acid and tartaric acid salts.
This disclosure is a typical example of the reaction of maleic acid with tartaric acid said reaction being catalyzed by calcium ions and conducted in alkaline ,~

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medi~m. Such reactions are known in the art as Michael condensation reactions. It is typical of the Michael condensation reactions -to provide the most effective e~uilibrium state for -the production of the desired compound or mixture by control of the reactant ratio.
It has been found that D,L-tartaric acid salts possess different solubility characteristics than do either the D- or L- isomers such that the D,L- isomer conveniently precipitate from solution at a pH in the range of from about 7 to about 9.5 while the calcium salts of HOPTC and DOOHC remain in solution and can be purified for use as a builder combination in detergent formulations.
The recovery of unreacted maleate salts from calcium catalyzed reactions of maleic acid salts with salt of tartrate salts in alkaline medium is conveni-ently achieved by acidifying the reaction product so as to reduce the pH to within the range of about 4 to below about 6.
A particular advantage of the process of this invention, whereby unreacted maleate salt is recovered, is the abilit~ to regulate the reac-tant ratios more freely sirlce convenient recovery and recycle is possible. Loss of unreacted maleate salt is insignificant and its reco~ery economical, parti-cularly when maleic acid is employed to reduce the pH of the reaction product of the condensation reaction.
In accordance with one embodiment of this invention the unreacted D,L-tartrate and maleate starting materials are removed by precipitation ~rom the reaction mass prior to the removal of calcium from the system. Specifically, calcium D,L-tartrate and mono sodium malea-te are precipitated from the reac-tion mix-ture by adjustment of the p~l o~ the reaction ~3~ i$~

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solution in two steps. The precipitate of calcium D,L-tartrate and mono sodium maleate is then returned to a subsequent condensation synthesis reaction. It has been found that the small amounts of by-products such as malate and fumarate and residual amounts of HOPTC and DOOHC trapped in the precipitate are not deleterious to the use of this recycled precipitate in subsequent condensation synthesis reaction.
FORMATION OF HOPTC/DOOHC MIXTURES
The first step is the synthesis of HOPTC/DOOHC mix-tures by the reaction in aqueous medium of maleate and D,L-tartrate reactants comprising both monovalent cation and calcium salts of maleic acid and D,L-tartaric acid. As noted above, the total amount of maleate plus D,L-tartrate reactants in the aqueous reaction mixture will generally range from about ~0%
to about 70% by weight of the mixture, more preferably from about 55% to about 65% by weight. Calcium maleate is provided by first reacting maleic acid with calcium hydroxide or calcium carbonate the later preferably provided at least in part by recycle from earlier reactions. The D,L-tartrate is typically provided by epoxidation of maleic acid (from maleic anhydride) in the presence of a catalyst and hydrogen peroxide by known means followed by hydrolysis of the epoxide.
one portion of the D,L-tartaric acid employed in the synthesis reaction is -taken from the neutralized hydroxylation reaction product. Another portion of the needed D,L-tartrate is provided by the recycled calcium D,L-tartrate provided by earlier reactions as will be more fully described below.
The molar ratio of maleic acid -to D,L-tartaric acid in the reaction mixture provided from all the sources noted above will generally range from about 0.5:1 to 8:1, more preferably from about 0.8:1 to about 1.2:1. The ratio of reactants will control the ratio of HOPTC/DOOHC in the final product.

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As noted above the synthesis reaction takes place in the presence of a catalyst comprising calcium ions. To provide the necessary amount of calcium cation, several sources can be used. Calcium mal~ate, prepared from recycled calcium carbonate and maleic acid, may provide one calcium ion source. Previously used but unreacted calcium D,L-tartrate recovered in the process of this invention provides another major calcium ion source. Any additional needed calcium ions, usually a very small amount, is typically provided by an additional calcium ion source such as calcium hydroxide added either as a solid or as a slurry.
Other water soluble calcium salts can be employed, but calcium hydroxide possesses the additional advantage of supplying needed hydroxide ions. The total amount of calcium ion present provides a total molar ratio of calcium cation to maleate of 1:1. However, the amount of calcium cation can vary greatly and may be such that the ratio of moles of calcium cations to total moles of maleic and D,L-tartaric acids in solution can approach, but be less than 1.
The hydroxide o~ a monovalent cation is also essentially added to the reaction mixture as a source of alkalinity. This neutralizing agent is usually added in an amount such that the ratio of moles of monovalent cations to total moles of D,L--tartaric acid plus the moles of maleic acid minus the moles of calcium cations ranges from about 2.1:1 to about 3.8:1. More preferably this ratio ranges from about 2.2:1 to about 3.3:1. The monovalent cation-containing neutralizing agent can be any hydroxide which upon addition to water yields monovalent n~utralizing cations in solution. Such neutralizing agents include, for example, alkali metal, ammonium or substituted ammonium hydroxide. Sodium hydroxide is highly preferred.

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Su~ficient neutralizing agent which, in combination with calcium hydroxide, is added to the synthesis reaction mixture to insure that the reaction mixture is over-neutralized. Thus, the reaction mixture in the process of this invention will general-ly have a pH within the range of from about 8.5 to 13, more preferably from about 10.5 to about 12.5. The aqueous reaction mixture, after the appropria-te amounts of reactants, catalysts and n~utralizing agent are combined, is maintained at a temperature of from about 20C. to about 120C., preferably from about 70C. to about 95C. for a period of time sufficient to form a reaction product mixture containing the desired amounts of ~OPTC and DOO~C. Reaction times of from about 0.5 -to 50 hours, more preferably from about 1 to 4 hours, would generally be suitable for realiz-ing acceptable yields of the 2 components of the desired mixture. Reaction time is highly affected by temperature whereby higher temperature increases the rate of reaction. The mole ratio of reactants in the reaction mixture, that is, tartrate, maleate, calcium and free hydroxide is 1.1/1.0/0.85/0.50 respectively.
At completion of the reaction the mixture is quenched with water to cool it to a temperature in the range of 80C. Addition of water also improves the handling of the viscous reaction mass.
MONOSODIUM MALEATE AND D, L-TARTRATE PREC IP ITA~ION
The reaction mixture containing mixed salts of HOPTC and DOOHC also contains relatively large amounts of unreacted maleic and tartrate acid salt.
These salts are recovered and recycled to provide higher efficiency of utilization of this valuable raw material.
The recovery of these salts is achieved by a two step method of lowering of the pH of the reaction mixture whereby sodium hydrogen maleate or monosodium . ~, .

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maleate and calcium -tartrate precipitate. In the preferred embodiment the reaction mixture is cooled and diluted with water. An acidic material such as sulfuric acid, or an organic acid such as formic acid is combined with the reaction mixture in sufficient amount to bring the combined synthesis mass and acid to an initial pH in the range of from abou-t 6 to about 9, preferably slightly below 7. Then, with further addition of suitable acid the pH of the reaction mixture is relatively more rapidly acidified further to a pH in the range of from about 4.5 to below 6, preferably to about 4.8 -to about 5.2.
Any number of acidic materials can be employed to lower the pH of the reaction mixture.
Combinations of acidic materials may also be employed.
Typical examples of such acids are sulfuric acid, hydrochloric acid, nitric acid, formic, acetic, propionic, butyric and D,L-tartaric, carbonic, phosphoric, sulfonic, sulfurous, boric, phosphorous, adipic, benzoic, citric, fumaric, glycolic, malic, maleic, malonic, oxalic, succinic, sorbic, nitrilo-triacetic, long chain fatt~ acids, etc.
In the process of this invention, the acid substance may be added to the crude reaction mass.
Alternately, the reaction mass may be added to a heel containing the acid substance~ In a further process of this invention, the acid substance and the reaction mass may be added concurrently into a mixing vessel.
Sufficient water is added to the reaction mass and/or acid material so that the final concentration of desired ether carboxylate in the completed mixture is about ~0%.
Sufficient acid is added to reach a preferred pH of near 5.0 and the precipitated reaction mass is cooled to below 50~C., preferably from just above the freezing point of the mixture to about ~ 3 -9- 05 21(6906)A

40C. most practically to from about 20C. to about 30C. to obtain usable filtration rates in large scale production. In a preferred mode, cooling the reaction product from the 80C. reaction temperature to 65C.
over 30 minutes is ~ollowed by slow cooling to from about 30C. to about 40C. The suspension is then allowed to rest for about 30 minutes. The slurry is preferably cooled slowly with mild or slow agitation so as to grow particles which can be filtered in an appropriately short time. Other methods of acid addition such as are noted above can also be employed with appropriate adjustment of precipitation conditions.
In the process of this invention wherein HOPTC and DOOHC are produced it has been found that both unreacted starting acids, D,L-tartaric acid and maleic acid can be recovered in their salt ~orm.
Also, it has been found that the calcium salt of D,L-tartaric acid precipitates from the reaction mixture at a pH in the range of from about 7 to about 12 and is typically of smaller crys-tal habit than the maleate salt. However, according to this invention the two acid salts may be precipitated in a two step procedure which produces globular particles including both acid salts.
When a mixed acid solution is employed to precipitate tartrate and maleat~ in the process o~
this invention, the acids may be added either sequentially or concurrently. In one mode of operation, the reaction mass at a temperature of about 80C., is added to a heel of aqueous acid, typically formic acid, and then a solution of maleic acid is added to the partly neutralized reaction mass.
It has been found that when the pH of the reaction mixture is in the abo~e-stated range calcium D,L-tartrate precipitates when such mixture is diluted with water or cooled to a temperature in the 2 ~ ~ ~

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range of from about at least above freezing to about 70C. The reaction mixture is typically diluted with water in amounts up to about 200 percent by weight.
Greater dilution may be accomplished but additional amounts o~ water are not beneficial due to increased solubility or the salts being precipitated and also would probably require removal later. Dilution of the reaction mixture by about 30 to about 80 percent, by weight, is typical and usually both cooling and dilution are employed to provide maximum amount of tartrate precipitation.
In the process of this invention, there is employed, in conjunction with the above-noted stepwise reduction of pH, the use of crystal seeding whereby small particles of calcium tartrate/monosodium maleate recovered from previous production of mixtures of HOPTC and DOOHC are added to the reaction mixture.
Thus, when the temperature of the reaction mixture is first reduced to about 80C. by diluting the reaction mixture as noted above, crystals of calcium tartrate/
sodium maleate from a previous batch are introduced into the reaction mixture. Amounts of crystals in the range of up to about 30 percent of the expected weight of the fresh precipitate may be added. When crystals are employed from the previous filter cake there is provided seed crystals of monosodium maleate. These crystals dissolve leaving calcium tartra-te. However, the dissolved monosodium tartrate buffers the solution to a pH of about 6. When the pH is reduced in the second step dissolved monosodium maleate begins to precipitate below about 5.~.
Following the addition of crystals, the pH
of the reaction mixture is then slowly reduced by combining the reaction mixture with acid to provide a reaction mixture having a pH in the range of about 7 to about 9 without prior seeding as described above.

:~3~23 ~ 05-21~906)A

However, with seedin~ as noted above it is more preferable to reduce the pH of the reaction mixture in the first step of pH reduction to from about 6 to about 7. While lowering the pH of the reaction mixture i~ is also cooled to a temperature in the range of from above the freezing point of the mixture to about 50C. It has been surprisingly found that, in the second step of pH reduction when the pH of the reaction mixture is reduced rapidly, or over a brief period of time, for example up to about one minute to about 10 minutes, unexpectedly large agglomerates of the combined salts of calcium tartrate and monosodium maleate are created. Throughout pH reduction, cooling is required to maintain the temperature of the reaction mixture in the desired range of from above freezing to about 35C. As noted above, the reaction mixture is held for about 30 to about 40 minutes after final pH
reduction to allow crystal formation. It is preferred to allow a short rest period between steps whereby -the reaction mixture, at a pH above about 6, rests for about 10 minutes before the second step of pH reduction is performed. The larger agglomerates are more easily separated from the reaction mixture.
Removal of the precipitated acid salt may take any form practical and typically is performed by continuously drawing the slurry from the precipitator to a belt or drum filter or centrifuge. Other forms of removal such as decantation, etc. may also be employed. The filtrate contains the ether carboxylate in salt form. In a preferred embodiment the filtrate is transferred to another precipitator for removal of the calcium cations in the form of calcium carbonate.
In the production the HOPTC/DOOHC mixture filter cake is discharged and, in one embodiment, reslurried with water. The slurry is ~ecycled directly or indirectly to the synthesis reactor to supply a -12- 05-2.1(6906)A

portion o~ the required D,L-tartrate and maleate salts. Pxeferably the recovered maleate salt and/or D,L-tartrate salt is slurried with water and mixed with calcium maleate for recycle into the synthesis reaction.
CALCIUM CARBONATE PRECIPI TATION
After removal of the insoluble acid salt or salts as described above, the ~iltrate from such operation is recovered and purified for use as deter-gent builder. In a preferred embodiment, calcium is removed either batchwise or preferably continuously.
Typically, the filtrate from the above-mentioned step is pH adjusted with a base, preferably sodium hydroxide, as it is being fed into a calcium carbonate precipitator to bring the pH of the solution into a range of from about 10 to about 12, preferably from about 10 to about 10.5. The pH adjustment may be performed either in the precipitator or in a separate vessel if desired.
The pH adjusted material is maintained in -the range of from about 75C. to about 110C., preferably at about 90C. to 100C. Concurrently a solution o~ a basic carbonate, preferably sodium carbonate, preferably at a concen-tration of about 25%, is added to the precipi-tator to provide an overall mole ratio of carbonate to calcium o~ 1.3:1.
Alternatively, calcium carbonate is removed by increasing the mole ratio of carbonate ion to calcium ion without change in pH.
Although this invention is described with respect to carbonate precipitation using the preferred sodium cation, it is to be understood that other suitable cations may also be employed to obtain precipitation of calcium carbonate. Other cations useful in the process of this invention include potassium, ammonium or organo substituted ammonium.
Other salts may be employed to obtain the calcium ~3~ 2~
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carbonate precipitate and includes sodium bicarbonate and mixtures of carbonates and bicarbonates.
During the precipitation of calcium carbonate it is preferred that watex is continuously removed from the slurry to maintain the concentration of the organic acid salts in the range of from about 30% to about 50% by weight. Filtration of the precipitated calcium carbonate may take any form practical and typically is performed by continuously drawing the slurry from the precipitator to a centrifuge or to a belt or drum filter. The filtrate contains the desired ether carboxylate mostly as the alkaline salt along with minor amounts of raw material and by-products.
In the preparation of HOPTC/DOOHC mixtures, the by-products comprise typically less than ~0% by weight of the HOPTC and DOOHC present.
The wet cake from the separation is mechani-cally reslurried with water to form an approximately 50% calcium carbonate slurry for recycle to the synthesis reac-tion. The recovered carbonate may be added directly to the ether carboxylate synthesis reactor or together with recovered, unreacted tartrate and maleate. Preferably, the recovered calcium carbonate is converted to calcium maleate in a separate vessel before return to the synthesis reaction.
CALCIUM MALEATE FORMATION
Before introduction into the synthesis reaction, the calcium carbonate precipitate obtained from the product as described above is preferably converted to calcium maleate by reac-t.ion with maleic acid. Prefera~ly, the maleic acid is prepared in situ. In one embodiment, the maleic acid is prepared by charging molten maleic anhydride to water heated to 65C. to 75C. After hydrolysis of the maleic anhydride to maleic acid is complete, the slurry of calcium carbonate solids is added at a rate slow 2 .-~ 2 ?3 -14- 05-21(6906)A

enough to avoid uncontrolled foaming due to the evolution of carbon dioxide. During the addition of calcium carbonate the reaction mass is heated to a temperature in the range of from about 90C. to about 100C. and preferably to about 95C.
In the production of HOPTC and ~OOHC it is preferred that calcium D,L-tartrate and monosodium maleate slurry obtained from the tartrate/maleate removal step is added to the calcium maleate while heating to a boil at atmospheric pressure. The mixture is held at boiling for about 15 minutes to ensure conversion of all of the calcium carbonate to the maleate. The mixture is then charged to the synthesis reactor for the preparation of additional HOPTC and DOOHC. During transfer to the synthesis reactor water may be evaporated to reduce volume.
Although the above described process follows a particular scheme, it is obvious that other schemes or flow charts may also be followed. For example, hold tanks, mixing tanks and transfer tanks may be employed which are not described above. Other variations will occur to those knowledgeable in the art.
EXTRACTION
The filtrate obtained from the procedure to remove calcium carbonate is purified by extraction with methanol and water. Such purification in the production of HOPTC and DOOHC mixtures is shown in U.S. Patent 4,633,071 referred to above.
According to such patent the solution obtained after removal of calcium carbonate is thoroughly mixed with methanol. After settling, two layers ~orm because the desired solution of HOPTC and DOOHC is less soluble in methanol than the impurities to be removed. The undesired solution is decanted and stripped of residual methanol. The residue is dissolved in water and extracted again with methanol.

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After purification the product is concentrated so as to provide the desirable concentra-tion of ether carboxylate solution fox use as detergent builder or sequestrant. The concentrated material 5 may also be dried by ~ny typical means such as by spray drying, etc. to provide granular or particulate material which is the form traditionally employed.
To further illustrate the process of the present invention there is desGribed below non limiting preferred em~odiments. In the following examples all percentages are by weight unless otherwise noted.

Into a round bottom 1ask equipped with a thermometer, addition funnel, condenser and mechanical stirrer there were placed 39.4g of maleic anhydride and 200g of water. The mixture was heated to 70C.
to form maleic acid to which was added 50.lg of calcium carbonate. Then wet filter cake, 350g, from a previous run together with 100g of water were added to the flask. The w~t cake contained the following in weight percent:
Disodium meso tartrate - O.3~1 Calcium D,L-tartrate - 19.62 Disodium Malate - 1.27 HOPTC - 13.24 DOOHC - 0.7 Monosodium Maleate - 15.71 After addition of wet cake 62.95g of D,L-tartaric acid and 550g of disodium tartrate solution obtained by hydrolysis of epoxysuccinate were added to the reaction. This mixture was heated to 90C. with stirring. Air was swept through the reactor to remove about 760g of water during a period 35 of 70 minutes after the reaction mass reached 90C.
Then 127.9g of sodium hydroxide, 50% solution, was -16- 05-21(6906)A

added to the mixture. Heating at 90C. was continued for another 90 minutes. The reaction mixture was quenched with 126g of water to reduce the organic solids content from 65% to 54% thereby cooling the reaction mass from 90C. to about 80C. The resulting mixture, a clear solution, was then divided into 2 parts with Portion A containing 566g and Portion B
containing 280g.
A
Into this portion of the reaction mixture 40g of ~ilter cake from a previous reaction containing both calcium tartrate and sodium hydrogen maleate together with 160g of watex were added and the reaction -mass held at 60C. After holding for 10 minutes at that,temperature formic acid was added over 20 minutes to lower the p~ to 5.9. After reducing the pH the reaction mixture was cooled to 35C. over 30 minutes.
The reaction mixture was then held at 35C. for an additional 30 minutes. A sample was taken for a filtration rate test (A-l). Th~n a 40% maleic acid solution was added to adjust the pH to 4.85 over a period of about 5 minutes and the system again held at 35C. for an additional 30 minutes. Another sample was taken (A-2).
B
In this portion of the reaction mixture there were added 15g of calcium tartrate filter cake as described above in Part A together with 80g of water. The diluted reaction mixture was then cooled to 35C. Then formic acid was added over a period of 20 minutes to adjust the pH to 6. The reaction mixture at the lower pH value was held at 35C. for 45 minutes and a sample taken for a filtra-tion rate test (B-1). A 40% maleic acid solution was added to adjust the p~ to 4.8 with relatively rapid addition and the system held at 35C. for an additional ~3~2 ~

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30 minutes. Another sample was taken for a filtration rate test ~B-2). The results of -these tests are presented below in Table I. As shown in Table 1, the filtration rates of both samples in Part B are much lower than the samples in Part A. This is believed to be due to the addition of greater amounts of crystal seed material from the previous filter cake in Part A.
The filtration rate reported in Table I below was measured at a cake thickness of 12.7 mm.
TABLE I
Sample A-l A-2 B-l B-2 pH during filtration 5.9 4.85 6.0 4.8 Filtration rate423711,407 1263 3259 liters/hr/meter2 The filtrates were analyzed to determine their components. The results of the analyses are shown in Table II below. The results indicate that the maleate salt is mostly removed from the system at the lower pH even though maleic acid is employed to 20 acidify the reaction mixture.
TABLE II
Analyses A-l A-2 B-1 B-2 Disodium tartrate 2.2 1.9 2.0 1.6 Disodium malate O.3 0.3 0.O O.O
Disodium maleate4.6 0.7 4.3 0.5 Disodium fumarate 1.1 1.2 1.1 1.O
HOPTC 21.0 21.5 20.4 20.0 DOOHC 3.2 3.3 3.1 3.3 ~L3~2$2~
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(Prior Art) A sodium tartrate solution, 385 g (analysis below), diluted with 115 g. water was charged to a 2 liter 4-necked reactor fitted with a mechanical stirrer, condenser, thermometer and addition funnel. In a separate vessel, maleic anhydride, 92.5 g, was mixed with 200 g. of water and heated to 60C. to form maleic acid. Then 47 ~. of calcium carbonate was added to form calcium maleate. This mixture was then added to the reactor containing the sodium tartrate solution. Calcium tartrate filter cake from a previous reaction, 275 g. (analysis below) was then charged to the reactor. 50% sodium hydroxide, 173 g, and D,L-tartaric acid, 49.5 g, were also added to the reactor. The analyses of these materials are given below in Table III.
TABLE III
COMPONENT SODIUM TARTRATE CALCIUM TARTRATE FINA~
(WEIGHT %)SOLUTIONFILTER CAKEREACTION CHARGE
Tartrate 29.6 42.1 23.9 Malate 0.9 0.4 0.4 Maleate 7.3 2.7 15.2 Fuma~ate 0.5 0.7 0 3 HOPTC --- l1.1 2.5 DOOHC --- 1.1 0.2 The mole ratio of reactants at the start of the reaction was tartrate/maleate/calcium/hydroxide = 1.3/1.0/0.9/l.O.
The reaction mixture was stirred at 120 rpm and heated at 90~3C. for three hours while sweeping air across the reaction to remove water from the system. [Final total solids concentration was 60- 65%.] At the end of the reaction, 185 g. of water was added to quench the reaction. Then 45 g of 1312~?~
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88% formic acid and 60 g water was added and khe reaction mixture allowed to cool to room temperature.
The final pH after the addition of formic acid was 5.2.
After filtration to remove the crystallized calcium tartrate and sodium hydrogen maleate, the filtrate was analyzed and the results shown below in Table IV.

TABLE IV
Com~onent Weight %
disodium tartrate 1.8 disodium malate 0.6 disodium maleate 0.4 disodium fumarate 2.0 HOPTC 28.0 DOOHC 5.7 Total diacids, 4.8% or 14.2% of ~OPTC ~ DOOHC
Fumarate, 2.0% or 5.9% of HOPTC+DOOHC
This example shows the use of a 'istandard"
procedure for the synthesis of HOPTC~DOOHC that employs recycle of a previously produced filter cake 0 of calcium tartrate and sodium hydrogen maleate.

The procedure of Example 1 was repeatd except that after all the charges were added the reaction mixture was held at 78~3C. for 1.5 hours while removing the excess water by sweeping with air.
When the reaction mixture had reacted 60-65% solids level it was heated to 85C. and held for an additional hour. The reaction was treated as in Example 1.
Final pH was 5Ø The filtrate was analyzed as shown below in Table V.

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TABLE V
Component Weight %
disodium tartrate 1.3 disodium malate 0.4 disodium maleate 0.4 disodium fumarate 1.0 HOPTC 24.1 DOOHC 5.1 Total diacids, 3.1% or 10. 6% of HOPTC+DOOHC
Fumarate, 1.0% or 3.4% of HOPTC~DOOHC
This example shows that a significant reduction of fumarate content is achieved by concentrating the reaction mixture at a lower temperature prior to heating to the desired reaction temperature.

This example demonstrates the disadvantage of cooling the reaction mixture before reducing the pH
by combining the mixture with acid. A reaction mixture obtained in accordance with the procedure of Example 1 was obtained and divided into four equal portions of 180g, then each was querlched with 40g of water. A heel comprising 10g of formic acid, 88%, and 40g of water was prepared for each portion.
A
One portion of the reaction mixture at 52C. was added to the acid heel thereby lowering the pH of the mix~ure to about 6.9 while cooliny continued over a period of about 32 minutes. Cooling was then continued until the reaction mixture and the combined heel reached about 34C. The maleic acid mixture, 40%, was then added over a period of about 5 minutes with continued cooling to maintain the reaction mixture at about 34C. and lowering the pH to 5Ø

~t~

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Globular precipitate formed and the mixture was then filtered to recover the precipitate.
B
The reaction mixture was cooled to 43c.
before being added to the heel. The combined heel and reaction mixture was further cooled to a temperature of about 30C. during combination which produced a p~ of about 7.1 after holding at the noted temperature and pH for about 10 minutes. Maleic acid was then added to the solution over a period of 6 minutes lowering the pH to 5Ø The resulting mixture was then filtered to recover the precipitate.
The filtration rate of each precipitate was measured during filtration and the results appear in Table III below.

TABLE VI
Cake Thickness - mm Filtration Rate - liters/hr/M2 A B
9.5 2770.3 1751.~
12.7 2077.7 1495.1 15.8 1670.7 1197.7 The data in Table III above indicates that combining the reaction mixture with ~he acid heel at 5 higher temperature improves the filtration rates.

A reaction mixture obtained in accordance with the procedure of Example 1, 360g, was quenched with 80g of water and cooled to about 80C. An acid heel was prepared by combining 23g of 88% formic acid and 80g of water. Into this heel was charged the quenched reaction mixture; however, the pH was lowered, with cooling to about 35C. as it was combined with the acid heel in the one step whereby the pH of the combination reached about 6.3. Maleic acid, 40%, was added over a period of one hour r~sulting in a -22- 05-21 ( 6906 )A

final pH of 5Ø Cooling was continued for an addi-tional one hour and 40 minutes to obtain a final temperature of 32C. The precipitate was recovered by filtration and the filtration rates at the varying filter cake thicknesses are reported below.
TABLE VII
Cake Thickness - mm Filtra-tion Rate - liters/hr/M2 9.5 1222 . 2 12 . 7 937 1015.8 774 By comparing the data presented in Tables II and IV the improvement in product by means of reduced by-product formation in accordance with this invention is clearly shown.
There has been described a novel process of general application for the production of ether carboxylates. While the process has been described with reference to specific compounds no intention is made by such reference to limit the scope of this invention unless expressly stated. Various modifica-tions may be made in the materials and sequence of process steps as well as process combinations which are adapted to suit the various reactants and products without departing from this invention.

Claims (20)

1. In a process for preparing mixtures of 1-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid which comprises (1) reacting in an alkaline reaction medium the salts of maleic acid and tartaric acid in the presence of calcium ion catalyst, the improve-ment comprising providing a reaction mixture, having a solids content in excess of 60% by weight prior to reaction.

2. The process of Claim 1 wherein the solids content of the reaction mixture is in the range of from about 62% to about 70%, by weight of the mixture.

3. The process of Claim 2 wherein the solids content is about 62% to about 65%.

4. The process of Claim 1 wherein the reaction mixture is concentrated by means of holding the mixture below the reaction temperature and sweeping the reaction vessel with an inert gas.

5. The process of Claim 1 wherein the reaction mixture is subjected to reduced pressure to remove water.

6. The process of Claim 4 wherein the inert gas is air.

7. The process of Claim 1 wherein the reaction mixture is concentrated by raising the temperature to about the reaction temperature prior to the addition of calcium ion catalyst to the mixture.

8. The process of Claim 7 wherein the reaction mixture is subjected to reduced pressure.

9. The process of Claim 2 wherein the reactor is swept with air to remove water vapor.

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10. A process for preparing a mixture of the alkali metal of l-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid which comprises the steps of:
(a) forming an aqueous reaction mixture compris-ing above about 60% by weight of both calcium and monovalent cation salts of maleic acid and tartaric acid, said mixture corresponding to the over-neutralized mixture which is formed by combining:
(i) maleic and tartaric acids in a maleic to tartaric molar ratio of from about 0.5:1 to about 8:1;
(ii) a source of calcium cations in an amount such that the molar ratio of calcium to tartaric acid ranges from about 0.1:1 to 2.0:1 with the ratio of moles of calcium to total moles of maleic and tartaric acid being less than 1; and (iii) a neutralizing agent comprising a hydroxide of a monovalent cation in an amount such that the ratio of moles of monovalent cation to moles of maleic acid plus moles of tartaric acid minus moles of calcium ranges from about 2.1:1 to 3.8:1.
(b) maintaining said aqueous reaction mixture at a temperature of from about 20°C to 120°C
for a time period sufficient to form a reaction product mixture of said l-hydroxy-3-oxa-1,2,4,5-pentane tetracarboxylic acid salts and 3,6-dioxa-1,2,4,5,7,8-octane hexacarboxylic acid salts;

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(c) lowering the pH of reaction mixture of step (b) to the range of from about 4.5 to about 5.5 and cooling the mixture to precipitate calcium tartrate and monosodium maleate in two steps wherein the pH is first reduced to a range of from about above 6 to about 9 and then lower the pH
relatively rapid whereby unreacted starting acids are precipitated in large particle size;
(d) removing the precipitate from the reaction mixture formed in step (c) and recycling it to step (a) to prepare additional amounts of reaction product;
(e) treating the reaction mixture from step (d) with a carbonate or bicarbonate whereby calcium carbonate precipitates;
(f) removing the calcium carbonate from the reaction mixture of step (e) and recycling it to step (a) to prepare additional amounts of reaction product; and (g) recovering and purifying the reaction mixture from step (f).

11. A process of Claim 10 wherein the calcium carbonate recovered in step (f) is reacted with maleic acid prior to recycle to step (a) to form calcium maleate.

12. A process of Claim 11 wherein the precipitate of step (c) is combined with the calcium carbonate and sufficient maleic acid to convert the monosodium maleate to calcium maleate.

13. A process of Claim 12 wherein the carbonate is an alkali metal carbonate.

14. A process of Claim 13 wherein the alkali metal is sodium.

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15. A process of Claim 13 wherein the bicarbonate is sodium bicarbonate.

16. A process of Claim 10 wherein the pH of the filtrate of step (d) is in the range of from 9 to 11 before combining with the carbonate.

17. A process of Claim 10 wherein the mole ratio of carbonate to calcium in step (d) is 1.3:1Ø

18. A process of Claim 10 wherein the neutralizing agent is sodium hydroxide.

19. A process of Claim 10 wherein the solids concentration of the reaction mixture is in the range of from about 62% to about 70%.

20. A process of Claim 19 wherein the concentration of the solids concentration in the reaction mixture is about 62% to about 65%.