Polyacetal Carboxylates

This invention relates to novel polyacetal carboxylates useful as complexing agents and detergency builders.

The property possessed by some materials of improving detergency levels of soaps and synthetic detergents and the use of such materials in detergent compositions is known. Such cleaning boosters are called "builders" and such builders permit the attainment of better cleaning performance than is possible when so-called unbuilt compositions are used. The behavior and mechanisms by which builders perform their function are only partially understood. It is known that good builders must be able to sequester most of the calcium and/or magnesium ions in the wash water since these ions are detrimental to the detergency process. However, it is difficult to predict which class of compounds possess useful combinations of builder properties and which compounds do not because of the complex nature of detergency and the countless factors which contribute both to overall performance results and the requirements of environmental acceptability.

Sodium tripolyphosphate (STP) has been found to be a highly efficient cleaning and detergent builder and this compound has been widely used for decades in cleaning and detergent formulations. Indeed, millions of pounds of STP are used each year in cleansing formulations because of its superior builder qualities. However, because of the recent emphasis on removing phosphates from detergent and cleaning compositions for environmental reasons, the detergent and cleaning industry is now looking for materials suitable for use as builders which do not contain phosphorus, and which are environmentally acceptable.

A large number of materials which do not contain phosphorus have been evaluated for use in detergent and cleaning formulations as a builder, but all of these materials suffer one or more disadvantages, usually either poor builder properties or poor biodegradability. As an example, U.S. Pat. No. 3,692,685 discloses salts of oxydisuccinic acid and carboxy methyl oxysuccinic acid as detergent builders and U.S. Pat. No. 3,708,436 discloses a mixture of polymeric maleic anhydride with sodium nitrilotriacetate or STP. Numerous U.S. Pat. Nos., such as 3,704,320, disclose ether carboxylates as detergency builders and several references, such as 3,764,586 and 3,308,067, disclose polymeric, aliphatic polycarboxylic acids having certain specific structural relationships useful as builders.

Despite the advances taught in these and other references in the prior art to find a cleaning and detergency builder which does not contain phosphorus, all of these materials suffer from one or more disadvantages. Of the above-mentioned materials, those that are biodegradable are not equivalent to STP in builder performance, and of those that are equivalent to STP in builder performance, they are usually biodegradable only with great difficulty. Inorganic builders other than STP are generally not satisfactory for use as a builder in detergent formulations because of their poor builder properties. Sodium aluminum silicates, commonly known as zeolites, have been proposed for use in detergent formulations since they are able to soften water by removing calcium ions; however, they are not very effective in removing magnesium ions from water. Moreover, it is clear that such water-insoluble, clay-like materials have the potential problem of producing a sediment in the cleaning solution and the resulting waste waters.

Thus, it can be seen that there is a need for a new class of materials with builder properties equivalent to STP, which does not contain phosphorus, which is water-soluble, and which achieves environmental acceptability by being readily biodegradable. Now, according to the present invention, there is provided a new class of polyacetal carboxylates which are useful to provide builders that are equal to, if not superior to, STP and which will depolymerize rapidly in a non-alkaline medium to form low molecular weight components which are readily biodegradable.

These and other advantages are achieved by a polyacetal carboxylate having the following empirical formula: ##STR2## wherein M is selected from the group consisting of alkali metal, ammonium, tetra-alkyl ammonium groups and alkanol ammonium groups having from 1 to about 4 carbon atoms in the alkyl chain; and n averages at least 4.

Broadly described, the compositions of the present invention can be prepared by bringing together under polymerization conditions an ester of glyoxylic acid and a polymerization initiator. The resulting polyacetal carboxylate can then be attached to chemically stable end groups to stabilize the polyacetal carboxylate against rapid depolymerization in alkaline solution. To form a polyacetal carboxylate suitable for use as a chelant and as a detergency builder, the polyacetal carboxylate ester can be converted to the corresponding polyacetal carboxylate salt.

For the purposes of this invention, the term "rapid depolymerization in alkaline solution" as it is used in the specification and claims, shall mean that in an aqueous solution of 0.5 molar sodium hydroxide containing 10 grams per liter of polyacetal carboxylate, the average chain length of the polyacetal carboxylate will be reduced by more than 50 percent, as determined by Proton Magnetic Resonance, after 1 hour at 20.degree. C.

Any number of esters of glyoxylic acid can be used to prepare the polyacetal carboxylates of the present invention. Such esters can be made by the reaction of an alcohol containing from 1 to 4 or more carbon atoms with glyoxylic acid hydrate under conditions known to those skilled in the art. Thereafter, the ester hemiacetal can be converted to the corresponding aldehyde ester by any number of techniques known to those skilled in the art, such as the reaction of the ester hemiacetal with phosphorus pentoxide. The product of the above reaction is then polymerized by techniques known to those skilled in the art using an initiator in accordance with the following general formula: ##STR3## where E is an alkyl group having 1 to 4 carbon atoms.

This intermediate polyacetal carboxylate ester is then reacted at its termini with a reagent which produces a chemically stable end group to stabilize the polyacetal carboxylate against rapid depolymerization in alkaline solution. The stabilized polyacetal carboxylate is then reacted with a base, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like, using conventional saponification techniques to make a polyacetal carboxylate salt suitable for use as a builder and as a sequestrant. In those cases where greater water solubility is desired, the ammonium salt, tetra-alkyl ammonium or alkanol ammonium salt can be prepared from the alkali metal salt by conventional ion exchange techniques.

Any number of initiators can be used for the polymerization. Nonionic or ionic initiators provide satisfactory results. Suitable initiators include 2-hydroxy pyridine-H.sub.2 O complex; triethyl amine; boron trifluoride etherate; and the like. Even traces of hydroxide ion or cyanide ion will trigger the polymerization. Compounds such as diethylsodiomalonate or sodiomethylmalonate esters have been used with good results.

Any number of chemically reactive groups can be added to the polyacetal carboxylate termini to stabilize the polyacetal carboxylate against rapid depolymerization in an alkaline solution. It is only necessary that the chemically reactive group stabilizes the polyacetal carboxylate against rapid depolymerization in an alkaline solution, and the specific nature of the chemically reactive group is not important in the proper function of the polyacetal carboxylate in its intended use. As an example, suitable chemically stable end groups include stable substituent moieties derived from otherwise stable compounds such as: alkanes, such as methane, ethane, propane, butane and higher alkanes such as decane, dodecane, octadecane and the like; alkenes such as ethylene, propylene, butylene, decene, dodecene and the like; branched chain hydrocarbons, both saturated and unsaturated, such as 2-methyl butane, 2-methyl butene, 4-butyl-2,3-dimethyl octane and the like; aromatic hydrocarbons such as benzene, toluene, xylene and the like, cycloalkanes and cycloalkenes such as cyclohexane and cyclohexene and the like; alcohols such as methanol, ethanol, 2-propanol, cyclohexanol, phenols and the like; polyhydric alcohols such as 1,2-ethane diol, 1,4-benzene diol and the like; mercaptans such as methane thiol, 1,2-ethanedithiol and the like; ethers such as methoxyethane methyl ether, ethyl ether, ethoxy propane and cyclic ethers such as ethylene oxide, epichlorohydrin, tetramethylene oxide and the like; and carboxylate-containing compounds such as the alkali metal salts of carboxylic acids, the esters of carboxylic acids and the anhydrides. The above listing is intended to be instructive and is not intended to be limited since other chemically stable end groups that stabilize the polyacetal carboxylate against rapid depolymerization in alkaline solution will occur to those skilled in the art in view of the disclosure. Particularly suitable end groups include alkyl groups and cyclic alkyl groups containing oxygen: such as oxyalkyl groups like methoxy, ethoxy and the like; carboxylic acids such as --CH.sub.2 COOM, ##STR4## and the like; aldehydes, ethers and other oxygen-containing alkyl groups such as --OCHCH.sub.3 OC.sub.2 H.sub.5, --CH.sub.2 CH.sub.2 OH, --CH.sub.2 CH.sub.2 O).sub.1-4 H, ##STR5## and the like. In the above examples of suitable end groups, M is alkali metal, ammonium, alkanol amine, tetra-alkyl ammonium groups and alkanol ammonium groups having from 1 to about 4 carbon atoms in the alkyl chain, and R is hydrogen or alkyl group of 1 to 8 carbon atoms. As will occur to those skilled in the art in light of the present disclosure, the chemically stable end groups at the polyacetal carboxylate termini can be alike or unlike.

As a further example of the polyacetal carboxylates of the present invention wherein the end groups can be different, one end group can be a polymer, and particularly a polymer with an anionic charge, which permits one or more of the polyacetal carboxylates of the present invention to be appended to the polymer, or on the other hand, the polyacetal carboxylates of the present invention can be the part of a block copolymer having a polymer chain at each of the polyacetal carboxylate termini. Preferred polymers that are anionic or can be made anionic include: polymers of cellulose acetate, cellulose propionate, cellulose acetate butyrate, polyvinyl acetate, polyvinyl alcohol and the like. In the case of an anionic polymer, the polymer can be used to initiate the polymerization to form the polyacetal carboxylates wherein the polymer adds to the termini as one of the chemically stable end groups to stabilize that end of the polyacetal carboxylate against rapid depolymerization in an alkaline solution, and thereafter the other end of the polyacetal carboxylate can be stabilized with a compound such as ethylene oxide or the like, as described above.

In one embodiment of this invention, diethylsodiomalonate or sodiomethylmalonate is used as an initiator to form the polyacetal carboxylates. These compounds not only initiate the polymerization, but also the ester stabilizes some of the polyacetal carboxylate against rapid hydrolysis in an alkaline solution. These compounds can be prepared from the corresponding esters using sodium hydride in a solvent, such as tetrahydrofuran, by techniques known to those skilled in the art.

The number of repeating units, i.e., the average value of n, in the polyacetal carboxylate is important since the effectiveness of the polyacetal carboxylate salt as a chelant, sequestrant and cleaning and detergency builder is affected by the average chain length. Even when the polyacetal carboxylate averages four repeating units (i.e., n averages 4), the polyacetal carboxylate salt shows some effectiveness as a sequestrant, chelating agent and builder. Although there is no upper limit to the desired number of repeating units, which may average as high as 400, or even higher, there does not seem to be an advantage to having a polyacetal carboxylate with an average of more than about 200 repeating units. When the average number of repeating units exceeds about 100, significant improvement in sequestration, chelation and builder properties is not observed. Thus, it is preferred that the polyacetal carboxylate contain an average between about 10 and about 200 units, and even more preferred that the polyacetal carboxylate contains an average between about 50 and about 100 repeating units.

Some important factors believed to control the chain length include (1) the initiator concentration, (2) the temperature of the polymerization, (3) the purity of the starting materials, and (4) the presence of solvents and their levels. As will occur to those skilled in the art, the concentration of the initiator, solvents and their levels, and the temperature of the polymerization reaction are all interrelated and the desired chain length can easily be controlled by simple experimentation by controlling these variables. Generally speaking, the lower the temperature at the beginning of the polymerization, the higher the chain length. For example, when polymerization was initiated with one mole percent 2-hydroxy pyridine-H.sub.2 O complex at a temperature of -70.degree. C., the resulting polyacetal carboxylate contained 60 repeating units as determined by Proton Magnetic Resonance (PMR). On the other hand, when one mole percent 2-hydroxy pyridine-H.sub.2 O complex was used at about 20.degree. C., the resulting polyacetal carboxylate had only about 20 repeating units.

The polyacetal carboxylate of the present invention can also contain other polymer fragments, and accordingly, the polymer can be a linear homopolymer or copolymer, or it can be branched. To form a copolymer, the polyacetal carboxylate segments are polymerized with any number of copolymers known to those skilled in the art. It is only necessary that the copolymer does not cause the polyacetal carboxylate to rapidly depolymerize in alkaline solution.

It is important that the polyacetal carboxylate contain at least 4 repeating units in a copolymer to insure that the polyacetal carboxylate will effectively sequester calcium and magnesium ions and provide builder properties. It is preferred that the polyacetal carboxylate contain at least 10 repeating units, or more, say 50 or 100 repeating units, for the reasons described above.

The amount of polyacetal carboxylate salt required to effectively complex the ions in a given system will depend to some extent on the particular polyacetal carboxylate salt being used and the particular metal or alkaline earth metal ion in the aqueous media. Because the polyacetal carboxylate of the present invention tends to depolymerize in acid media, effective complexing is limited to neutral or preferably basic solution. Optimum conditions and amounts of the polyacetal carboxylate salt to be used can readily be determined by routine experimentation.

The polyacetal carboxylate salts of the present invention are also useful as builders in detergent formulations. Since the pH of a detergent solution is usually between pH 9 and pH 10, the polyacetal carboxylate salt will not depolymerize rapidly when used as a detergent builder in aqueous solution at normal use concentrations (1 cup/washer), temperatures (10.degree.-60.degree. C.) and times (i.e., about 15 minutes) typical of United States home laundry practices. Generally, the use of the alkali metal salts, particularly the sodium salt, is preferred. However, in some formulations where greater builder solubility is required, the use of ammonium or alkanol ammonium salts may be desirable.

The detergent formulations will contain at least 1 percent by weight and preferably at least 5 percent by weight of the polyacetal carboxylate salt of this invention. In order to obtain the maximum advantages of the polyacetal carboxylate salts as builders, the detergent should preferably contain from about 5 percent to about 75 percent of these salts. The polyacetal carboxylate salts can be the sole detergency builder, or the polyacetal carboxylate salts can be utilized in combination with other detergency builders which may constitute from 0 to 95 percent by weight of the total builders in the formulation. By way of example, builders which can be employed in combination with polyacetal carboxylate salts of this invention include either water insoluble materials, such as sodium alumino silicates, commonly known as zeolites, or water soluble inorganic builder salts such as alkali metal polyphosphates, i.e., the tripolyphosphates and pyrophosphates, alkali metal carbonates, borates, bicarbonates and silicates and water soluble organic builders, including amino polycarboxylic acids and salts, such as alkali metal nitrilotriacetates, cycloalkane polycarboxylic acids and salts, ether polycarboxylates, alkyl polycarboxylates, epoxy polycarboxylates, tetrahydrofuran polycarboxylates, such as 1,2,3,4 or 2,2,5,5 tetrahydrofuran tetracarboxylates, benzene polycarboxylates, oxidized starches, aminotri(methylene phosphonic acid) salts, diphosphonic acid salts (e.g., the sodium salts of methylene diphosphonic acid or 1-hydroxy ethylidene 1,1-dimethylenephosphonic acid), and the like.

The detergent formulations will generally contain from 5 percent to 95 percent by weight total builder (although greater or lesser quantities may be employed if desired). The total amount of builder employed will be dependent on the intended use of the detergent formulation, other ingredients of the formulation, pH conditions, and the like. For example, general laundry powder formulations will usually contain from about 20 percent to about 60 percent builder; and machine dishwashing formulations will usually contain from about 60 percent to about 90 percent builder. Optimum levels of builder content as well as optimum mixtures of polyacetal carboxylate salts with other builders for various uses can be determined by routine tests in accordance with conventional detergent formulation practice.

The detergent formulations will generally contain a water soluble detergent surfactant, although the surfactant ingredient may be omitted from machine dishwashing formulations. Any water soluble anionic, nonionic, zwitterionic or amphoteric surfactant can be employed.

Examples of suitable anionic surfactants include soaps such as the salts of fatty acids containing about 9 to 20 carbon atoms, e.g., salts of fatty acids derived from coconut oil and tallow; alkylbenzene sulfonates--particularly linear alkylbenzene sulfonates in which the alkyl group contains from 10 to 16 carbon atoms; alcohol sulfates; ethoxylated alcohol sulfates, hydroxy alkyl sulfonates; alkyl sulfates and sulfonates; monoglyceride sulfates; acid condensates of fatty acid chlorides with hydroxy alkyl sulfonates; and the like.

Examples of suitable nonionic surfactants include alkylene oxide (e.g., ethylene oxide) condensates of mono and polyhydroxy alcohols, alkyl phenols, fatty acid amides, and fatty amines; amine oxides; sugar derivatives such as sucrose monopalmitate; long chain tertiary phosphine oxides; dialkyl sulfoxides; fatty acid amides, (e.g., mono or diethanol amides of fatty acids containing 10 to 18 carbon atoms); and the like.

Examples of suitable zwitterionic surfactants include derivatives of aliphatic quaternary ammonium compounds such as 3-(N,N-dimethyl-N-hexadecylammonio) propane-1-sulfonate and 3-(N,N-dimethyl-N-hexadecylammonio)-2-hydroxy propane-1-sulfonate.

Examples of suitable amphoteric surfactants include betains, sulfobetains and fatty acid imidazole carboxylates and sulfonates.

It will be understood that the above examples of surfactants are by no means comprehensive and that numerous other surfactants are known to those skilled in the art. It will be further understood that the choice and use of surfactants will be in accordance with well understood practices of detergent formulation. For example, anionic surfactants, particularly linear alkylbenzene sulfonates, are preferred for use in general laundry formulations, whereas low foaming nonionic surfactants are preferred for use in machine dishwashing formulations.

The quantity of surfactant employed in the detergent formulations will depend on the surfactant chosen and the end use of the formulation. In general, the formulations will contain from 5 percent to 50 percent surfactant by weight, although as much as 95 percent or more surfactant may be employed if desired. For example, general laundry powder formulations normally contain 5 percent to 50 percent, preferably 15 percent to 25 percent surfactant. Machine dishwashing formulations normally contain about 0.5 percent to about 5 percent surfactant. Liquid dishwashing formulations normally contain about 20 percent to about 45 percent surfactant. The weight ratio of surfactant to builder will generally be in the range of from 1:12 to 2:1.

In addition to builder and surfactant components, detergent formulations may contain fillers such as sodium sulfate and minor amounts of bleaches, dyes, optical brighteners, soil anti-redeposition agents, perfumes and the like.

In machine dishwashing compositions, the surfactant will be a low-foaming nonionic surfactant which will constitute 0 to 5 percent of the formulation.

It is to be noted that when the alkali ammonium or alkanol ammonium salts of polyacetal carboxylates are used as builders, they will be used generally in an alkaline medium. When the polyacetal carboxylate salts are used at a pH of 7 or below, the polyacetal carboxylate depolymerizes. Thus, the polyacetal carboxylate salts of the present invention, when used as builders, will be effective for chelating, sequestering and as detergency and cleaning builders, but when an aqueous solution containing the polyacetal carboxylate salt is discharged into a sewer or other waste water system, the polyacetal carboxylate salt will soon depolymerize into small fragments which are readily biodegradable.

This invention is illustrated by, but not limited to, the following Examples wherein all percentages are by weight unless otherwise noted.

To a 50 milliliter single-necked, round-bottomed reaction flask equipped with a magnetic stirrer was added 10 grams (0.114 mole) of freshly distilled methyl glyoxylate and 4 milliliters of methylene chloride. The temperature of the flask and the contents was lowered to about 0.degree. C., and 0.5 milliliters of 0.05 molar sodium diethyl methylmalonate was added to initiate polymerization. The flask was kept in an ice bath, and when the temperature returned to 0.degree.-2.degree. C., (about 45 minutes) 0.18 milliliter trifluoroacetic acid (1.5 mole percent) and 3.5 milliliters of ethyl vinyl ether was added to the mixture. The mixture was stirred at room temperature overnight. About 2 milliliters of 1 molar NaOH solution was added to the mixture and the volatiles were removed under vacuum. Then 12 milliliters of 2.5 molar NaOH was added. The mixture was stirred at about 0.degree. C. for about 5 hours and then heated to about 40.degree. C. for about 24 hours. The methanol and residual solvents were removed by rotary evaporation. The solution was concentrated to about 15 percent, precipitated in about 100 milliliters of methanol and stirred for 30 minutes. The precipitate was recovered by filtration and dried. The precipitate was then redissolved in distilled water, precipitated into methanol, stirred and recovered by filtration. The yield was about 74.8 percent. Analysis of the product, including the chain length, by Proton Magnetic Resonance (PMR) Spectra Analysis, showed that the product was a mixture, mostly a polymer having the following formula: ##STR6## where n averages 40, and a minor amount of ##STR7##

The procedure of Example I was repeated except that the temperature of initiation was varied. The result of this variation of the temperature of initiation on the chain length as determined by the average value of n is shown in the following tabulation.

The procedure of Example I was repeated except different initiation temperatures were used to provide a series of samples having different chain lengths, as measured by PMR. These samples were tested for sequestration function using the procedures described by Matzner et al ("Organic Builder Salts as Replacements for Sodium Tripolyphosphate", TENSIDE DETERGENTS, 10 No. 3, pages 119-125) 1973. The sequestration of calcium ions and magnesium ions (as a percent of STP performance) as a function of chain length is shown below:

Thus, it can be seen that a sequestration performance plateau of 120-127 percent of STP was reached at a chain length between about 45 and about 70, but only a small increase in performance occurred at greater chain lengths.

The biodegradation of three of the samples from Example V was measured by diluting one part of an activated sewerage sludge with about 10 parts of river water, and adding a known amount of the polymer to the diluted sludge. The biodegradation is determined by measuring the CO.sub.2 evolution from the diluted sludge. The results are presented in the following tabulation:

The evolution of carbon dioxide indicated that the polymer was comparable to materials known to be completely biodegradable, but as will occur to those skilled in the art, other end groups may affect the rate of biodegradation.

To a 500 milliliter single-necked round-bottom reaction flask equipped with a magnetic stirrer, 100 grams (1.1 moles) of freshly distilled methyl glyoxylate and 40 milliliters of methylene chloride were added. The temperature of the flask and the contents was lowered to about 0.degree. C. and 5 milliliters of 0.05 molar sodium diethyl methylmalonate was added to initiate polymerization. The flask was kept in an ice bath and when the temperature returned to 0.degree.-2.degree. C. (about 45 minutes) two milliliters of trifluoroacetic acid (1.5 mole percent) and 35 milliliters of ethyl vinyl ether was added to the mixture. The mixture was stirred at room temperature overnight.

The following morning the reaction mixture was treated with 200 milliliters of a 1:1 mixture by volume of benzene and hexane. The contents were stirred vigorously for about 1 minute and the layers were then allowed to separate. The bottom, nearly water-white layer containing the polymeric acetal carboxylate ester was separated from the solvent. The benzene/hexane mixture containing the color-producing impurities was discarded.

To the polymeric acetal carboxylate ester cooled to 0.degree. C. in an ice bath was then added 120 milliliters of 10 molar sodium hydroxide with vigorous stirring. The heat of reaction raised the temperature to about 45.degree. C. Stirring was continued for about one hour. The white polymeric acetal carboxylate sodium salt precipitated and was recovered by filtration. The precipitate was washed once with diethyl ether and dried. The yield was 73 percent.

About 4.4 grams (0.05 mole) of methyl glyoxylate was diluted with about 1.5 milliliters of methylene chloride, and the temperature was reduced to about -10.degree. C. Then about 1.2 mole percent boron trifluoride diethyl etherate was added to the methyl glyoxylate solution. After about 30 minutes, 0.01 mole ethylene oxide was added and allowed to react at about 22.degree. C. for about 34 hours. The resulting stabilized polymer was hydrolyzed using 2.5 molar NaOH as in Example I. Analysis by PMR showed that the yield was about 73 percent. The average mole ratio of polyacetal carboxylate segments to oxyethylene groups was about 8.4 to 1.

Sequestration performance of the polymer as determined by the procedure of Example V showed that the salt was about 78 percent of STP performance.

Using the general procedure of Example I, about 50 grams of unstabilized polymer is prepared by polymerizing methyl glyoxylate using a trace of 10 normal sodium hydroxide as initiator. The resulting polymer is diluted with sufficient methylene chloride to permit stirring at 0.degree. C. Then, 5 gram portions were taken and separately stabilized using a variety of chemically stable end groups. The reagent and the catalyst employed to provide chemically stable end groups, the time and temperature of adding the end groups, and the identification of the end groups are shown in Table 1 for the general structure ##STR8##

Although the invention has been described in terms of specified embodiments which are set forth in considerable detail, it should be understood that this is by way of illustration only and that the invention is not necessarily limited thereto since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.