A composition useful for treating aqueous systems comprising a naphthylamine polycarboxylic acid having the formula: ##STR1## wherein X is CO.sub.2 H or SO.sub.3 H, Y is H, C.sub.1 to C.sub.6 alkyl, CO.sub.2 H or SO.sub.3 H, R is H, C.sub.1 to C.sub.6 alkyl, CO.sub.2 R' or COR', R' is C.sub.1 to C.sub.6 alkyl, n is an integer from 1 to 20, and water soluble salts thereof.

FIELD OF THE INVENTION 
The present invention is directed to certain novel compositions which are 
useful in the field of water treatment, and more specifically to certain 
novel naphthylamine polycarboxylic acids and to a method of preventing the 
formation of scale on surfaces in contact with an aqueous system and/or a 
method of inhibiting corrosion of ferrous-based metals in contact with an 
aqueous system. 
BACKGROUND OF THE INVENTION 
Most industrial aqueous systems contain alkaline earth metal cations, such 
as calcium, magnesium, and the like, as well as numerous anions such as 
bicarbonate, carbonate, sulfate, and the like. When the concentration of 
the various combinations of cation and anions exceed the solubility of 
their reaction products, precipitates tend to form until the product 
solubility concentrations are no longer exceeded. As these reaction 
products precipitate on the surfaces of the aqueous systems, they form 
what is known as scale. The precipitation of calcium carbonate is by far 
the most common form of scale in industrial aqueous systems. This occurs 
when the ionic product of calcium and carbonate exceeds the solubility of 
the calcium carbonate and a solid phase of calcium carbonate forms. 
The formation of scale in industrial aqueous systems represents a major 
problem since it reduces heat transfer efficiency on heat exchanger 
surfaces, increases corrosion problems and reduces flow of the water 
through the system. The addition of inorganic and, more recently, all 
organic polyphosphonates to these aqueous systems is known to inhibit 
scale formation. These compositions are generally added to the system in 
substoichiometric amounts to the scale forming salt and are known to those 
in the art as threshold inhibitors. Threshold inhibition describes the 
phenomenon whereby a sub-stoichiometric amount of a scale inhibitor can 
stabilize a solution from precipitation. Threshold inhibition generally 
takes place under conditions where a small amount, e.g. 1 ppm to 100 ppm 
of an additive, will stabilize the solution which contains many orders of 
magnitude greater concentration of scale forming salts. 
Iron and iron-based metal-containing alloys, such as mild steel, are 
well-known materials used in constructing the apparatus of aqueous 
systems. In these systems water circulates, contacts the ferrous-based 
metal surface, and may be concentrated, such as by evaporation, of a 
portion of the water from the system. Even though such, metals are readily 
subject to corrosion in such environments, they are used over other metals 
due to their strength and availability. 
It is known that various materials which are naturally or synthetically 
occurring in the aqueous systems, especially systems using water derived 
from natural resources such as seawater, rivers, lake and the like, attack 
ferrous-based metals. The term "ferrous-based metals", as used herein 
refers to any ferrous-containing metals. Typical devices in which the 
ferrous-based metal parts are subject to corrosion include evaporators, 
single and multi-pass heat exchangers, cooling towers, and associated 
equipment and the like. As the system water passes through or over the 
device, a portion of the system water evaporates causing a concentration 
of the dissolved materials contained in the system. These materials 
approach and reach a concentration at which they may cause severe pitting 
and corrosion which eventually requires replacement of the metal parts. 
Various corrosion inhibitors have been previously used. 
Chromates and inorganic phosphates or polyphosphates have been used in the 
past to inhibit the corrosion of metals which is experienced when the 
metals are brought into contact with water. The chromates, though 
effective, are highly toxic and, consequently, present handling and 
disposal problems. Phosphates are nontoxic. However, due to the limited 
solubility of calcium phosphate, it is difficult to maintain adequate 
concentrations of phosphates in many instances. The polyphosphates are 
also relatively non-toxic, but tend to hydrolyze to form orthophosphate 
which in turn, like phosphate itself, can create scale and sludge problems 
in aqueous systems (e.g. by combining with calcium in the system to form 
calcium phosphate). Moreover, where there is concern over eutrophication 
of receiving waters, excess phosphate compounds can provide disposal 
problems as nutrient sources. Borates, nitrates and nitrites have also 
been used for corrosion inhibition. These too, can serve as nutrients in 
low concentrations, and/or represent potential health concerns at high 
concentrations. 
In addition, environmental considerations have also recently increased 
concerns over the discharge of other metals, such as zinc, which 
previously were considered acceptable for water treatment. 
Much recent research has been concerned with the development of organic 
scale and corrosion inhibitors which can reduce reliance on the 
traditional inorganic inhibitors. Among the organic inhibitors 
successfully employed are numerous organic phosphonates. These compounds 
may generally be used without detrimentally interfering with other 
conventional water treatment additives. There is a continuing need, 
however, for safe and effective water treatment agents which can be used 
to control corrosion. 
Many of the organic scale inhibitors and corrosion inhibitors used in 
industrial aqueous systems (e.g. hydroxyethylidene diphosphonic acid) are 
themselves very sensitive to calcium hardness and prone to form deposits 
of their calcium salts. This limits the range of hardness in which such 
materials can be usefully applied as scale inhibitors or corrosion 
inhibitors. There is a continuing need for safe and effective water 
treating agents which can be used to control scale formation and to 
inhibit corrosion, particularly when substantial calcium carbonate is 
present in the system water. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide certain novel scale inhibiting 
compositions. 
It is another object of this invention to provide certain novel corrosion 
inhibiting compositions. 
It is another object of this invention to provide a method of treating 
aqueous systems to effectively inhibit or prevent the formation of scale 
deposits on surfaces in contact with the aqueous system. 
It is another object of this invention to provide a method of treating 
aqueous systems to effectively inhibit corrosion of ferrous metals in 
contact with the aqueous system. 
In accordance with the present invention, there have been provided certain 
novel naphthalene polycarboxylic acids having the formula: 
##STR2## 
wherein X is --CO.sub.2 H or --SO.sub.3 H, Y is H, C.sub.1 C.sub.6 alkyl, 
alkoxy, --CO.sub.2 H, or --SO.sub.3 H, R is H, C.sub.1 to C.sub.6 alkyl, 
COR' or CO.sub.2 R', R' is alkyl and n is an integer from 1 to 20 or water 
soluble salts thereof which are useful in water treatment. 
Also provided in accordance with the present invention, is a method of 
controlling the deposition of scale on surfaces in contact with an aqueous 
system which comprises adding to the system the above naphthalene 
polycarboxylic acids in an amount effective to inhibit scale formation. 
Also provided in accordance with the present invention, is a method of 
controlling corrosion on surfaces in contact with an aqueous system which 
comprises adding to the system the above naphthalene polycarboxylic acids 
in an amount effective to inhibit corrosion.

DETAILED DESCRIPTION 
The present invention is directed to certain novel naphthalene 
polycarboxylic acids and to a method of inhibiting the formation of scale 
in aqueous systems and to a method of inhibiting corrosion of ferrous 
based metals in contact with an aqueous system, which involves adding to 
the system naphthalene polycarboxylic acid as hereinafter described, in an 
amount effective to inhibit scale formation and/or to inhibit corrosion. 
The naphthalene polycarboxylic acids of the present invention can be 
represented by the following formula: 
##STR3## 
wherein X is --CO.sub.2 H or --SO.sub.3 H, Y is H, C.sub.1 to C.sub.6 
alkyl, alkoxy, --CO.sub.2 H or --SO.sub.3 H, R is H, C.sub.1 to C.sub.6 
alkyl, COR' or CO.sub.2 R', R' is C.sub.1 to C.sub.6 alkyl and n is an 
integer from 1 to 20, and water soluble salts thereof. In a preferred 
embodiment, X is SO.sub.3 H, Y is H, --CO.sub.2 H or --SO.sub.3 H and R is 
H or --CH.sub.3. The naphthalene polycarboxylic acids of this invention 
may also be used in the form of alkali metal salts and are usually in the 
form of the sodium salt. Other suitable water soluble salts include 
potassium, ammonium, lower amine salts, and the like. The free acids may 
also be used and all of the acidic hydrogens need not be replaced nor need 
the cation be the same for those replaced. Thus, the cation may be any one 
of or a mixture of NH.sub.4, Na, K, etc. The naphthylamine polycarboxylic 
acids are readily converted into the water soluble salts by conventional 
methods. 
The naphthylamine polycarboxylic acids of this invention, having the above 
formula wherein n is 1, may be prepared by reacting an epoxysuccinate or 
an admixture of an epoxysuccinate and a tartrate with a molar equivalent 
of an amine compound in an aqueous medium to form an alkali metal salt of 
an amino polycarboxylic acid. This procedure is more fully disclosed in 
U.S. Pat. No. 3,929,874 to Beerman et al, which is incorporated herein in 
its entirety. See also Y. Matsuzawa et al, Chemical Abstract 81. 77484m 
(1974), J. Oh-hashi et al, Chem. Soc Jap. 40, 2997 (1967) and H. Hauptmann 
et al, Chemical Abstracts 57, 16732g (1962) which are also incorporated 
herein by reference in their entirety. 
The preparation of the naphthalene polycarboxylic acids of this invention 
having the above formula wherein n is from 2 to 20 is analagous to U.S. 
Pat. No. 4,654,159 which is incorporated herein in its entirety. In 
general, the naphthalene polycarboxylic acids are prepared by treating an 
epoxysuccinate or an admixture of an epoxysuccinate and a tartrate 
together with the n=1 compound from the above procedure with an alkaline 
calcium compound in an aqueous media to form the alkali metal and/or 
calcium salts of an ether hydroxypolycarboxylate and optionally separating 
the salts from the aqueous media. 
In accordance with this invention, the formation of scale in an aqueous 
system, particularly calcium carbonate scale, may be inhibited by adding 
the naphthalene polycarboxylic acids of the above formula, wherein n is 
greater than 2, or their water soluble salts, to the aqueous system in an 
amount effective to either inhibit the formation of scale or to remove 
scale deposits which may already be present in the system. The precise 
dosage of the scale inhibiting agents of this invention depends to some 
extent on the nature of the aqueous system in which it is to be 
incorporated i.e., the amount of hardness causing and scale forming 
compounds present in the system, and the degree of protection desired, as 
well as the degree of scale which may be deposited in the system. The 
compositions of this invention are preferably added to the system in 
substoichiometric amounts to the scale forming salt and accordingly, are 
known to those skilled in the art as threshold inhibitors. Threshold 
inhibition describes the phenomenon whereby a sub-stoichiometric amount of 
a scale inhibitor can stabilize a solution from precipitation. Threshold 
inhibition generally takes place under conditions where a small amount 
i.e. 1 to 100 ppm of an additive will stabilize the solution which 
contains many orders of magnitude greater concentration of scale forming 
salts. Thus, in general, the amount of naphthalene polycarboxylic acid 
added to the system can be from about 0.1 ppm to 1000 ppm and is 
preferably 0.1 ppm to 100 ppm and is most preferably in the range of from 
0.5 to 10 ppm. The exact dosage amount required with respect to a 
particular aqueous system can be readily determined in conventional 
manners which are known to those of ordinary skill in the art. 
The naphthalene polycarboxylic acids of this invention have also been found 
to be effective for inhibiting corrosion of ferrous-based metals which are 
in contact with an aqueous system. Thus, in accordance with this aspect of 
the invention, corrosion of ferrous-based metals which are in contact with 
an aqueous system may be inhibited by adding to the system a naphthalene 
polycarboxylic acid having the above-described formula, wherein n is 1 or 
2, in an amount effective to inhibit corrosion. 
The scale inhibiting compositions of this invention are particularly 
suitable for use in aqueous systems having a high degree of hardness and 
have exhibited a high degree of insensitivity to relatively high 
concentrations of both magnesium and calcium. It is considered an 
important feature of this invention, that the claimed compositions be 
calcium insensitive. Calcium sensitivity refers to the tendency of a 
compound to precipitate with calcium ions in solution. The calcium 
insensitivity of the claimed compositions permits their use in aqueous 
systems having water with relatively high hardness. The test for calcium 
insensitivity of a compound, as used in this application, involves a cloud 
point test (hereinafter the CA500 cloud point test) where the compound is 
added to hard water containing 500 ppm calcium ion (as CaCO.sub.3) which 
is buffered at pH 8.3 using 0.005 M borate buffer and which has a 
temperature of 60.degree. C. The amount of compound which can be added to 
the solution until it becomes turbid (the cloud point) is considered to be 
an indicator of calcium insensitivity. 
The calcium insensitive compounds of this invention have cloud points of at 
least about 25 ppm as determined by the CA500 cloud point test, and 
preferably have cloud points of at least about 40 ppm. 
The aqueous systems which may be advantageously treated in accordance with 
the polymers of this invention include, but are not limited to cooling 
water systems such as e.g. cooling towers, desalinization units, gas 
scrubbers, as well as to boiler systems and other recirculating water 
systems where scale deposits are known to form. 
The compounds of this invention may be used in combination with other water 
treatment components customarily employed in the aqueous system including, 
but not limited to other scale inhibitors, corrosion inhibitors, biocides, 
dispersing agents, antifoaming agents, oxygen scavengers, sequestering 
agents, and the like and mixtures thereof. 
The scale inhibitors of this invention may be added to the system by any 
convenient mode, such as by first forming a concentrated aqueous solution 
of the naphthalene polycarboxylic acids or their water soluble salts, 
preferably containing between 1 and 50 total weight percent of the 
compound, and then feeding the concentrated aqueous solution to the 
aqueous system at some convenient point. In many instances the scale 
inhibitors may be added to the make-up or feedwater lines through which 
water enters the system. Typically, an injector calibrated to deliver a 
predetermined amount periodically or continuously to the makeup water is 
employed. 
Without further elaboration, it is believed that one skilled in the art, 
using the preceding detailed description can utilize the present invention 
to its fullest extent. 
The following examples are provided to illustrate the invention in 
accordance with the principles of this invention, but are not to be 
construed as limiting the invention in any way except as indicated in the 
appended claims. All parts and percentages are by weight unless otherwise 
indicated. 
EXAMPLE 1 
A solution of disodium epoxysuccinate (9.7g, 55 mmol) in 38 ml water was 
placed in a flask under a nitrogen atmosphere. 
5-Amino-2-naphthalenesulfonic acid (11.2g, 50 mmol) and potassium 
hydroxide (3.4g, 61 mmol) were added to the solution. The pH of the 
resulting solution was adjusted to 9 by the addition of 0.4g 3N 
hydrochloric acid. The resulting mixture was heated to reflux for 23 
hours. Examination of the reaction product by proton NMR showed it 
contained N-2-(6-sulfonaphthyl)hydroxyaspartic acid (ANS-HS) contaminated 
by a very minor amount of tartaric acid. 
EXAMPLE 2 
A solution of disodium epoxysuccinate (9.7g, 55 mmol) in 38 ml water was 
placed in a flask under a nitrogen atmosphere. 
7-Amino-1,3-naphthalenedisulfonic acid monopotassium salt (17.1g, 50 mmol) 
and potassium hydroxide (3.2g, 57 mmol) were added. After adjusting the pH 
of the solution to 9 with 0.5g 3N hydrochloric acid, it was heated to 
reflux for 24 hours. Examination of the reaction product by proton NMR 
showed that it contained N-2-(6,8-disulfonaphthyl)-hydroxyaspartic acid 
(ANDS-HS) contaminated by a minor amount of tartaric acid. 
EXAMPLE 3 
N-2-(6,8-disulfonaphthyl)-hydroxyaspartic- acid (1.0 mmol) was reacted with 
disodium epoxysuccinate (17.6g, 100 mmol) by heating these two reactants 
together with calcium hydroxide (1.1g, 15 mmol) in 27 ml water for 17 
hours at 60-65.degree. C. and then for 5 hours at about 75.degree. C. 
During this time the reaction was kept under a nitrogen atmosphere. 
Examination of the product by proton and carbon NMR showed that the 
desired product had been formed. The average value of "n" of the 
polyepoxysuccinate portion of the product (as illustrated below) was 
determined by carbon NMR to be 9.8. 
##STR4## 
EXAMPLE 4 
N-2-(6,8-disulfonaphthyl)-hydroxyaspartic acid (5.0 mmol) was reacted with 
disodium epoxysuccinate (17.6g, 100 mmol) by heating these two reactants 
together with calcium hydroxide (1.1g, 15 mmol) in 27 ml water for 16 
hours at 56-58.degree. C. and then for 5 hours at about 70-75.degree. C. 
During this time the reaction was kept under a nitrogen atmosphere. 
Examination of the product by proton and carbon NMR showed that the 
desired product had been formed. The average value of "n" of the 
polyepoxysuccinate portion of the product (as illustrated below) was 
determined by carbon NMR to be 5.2. 
##STR5## 
EXAMPLE 5 
Two representative compounds of this invention were evaluated for their 
effectiveness in inhibiting corrosion in aqueous systems using an Aerated 
Solution Bottle test according to the following procedure and used a 
standard corrosive water having the following composition: 
______________________________________ 
Standard Corrosive Water 
______________________________________ 
12.8 mg/l 
CaCl.sub.2 
110.7 mg/l 
CaSO.sub.4 --2H.sub.2 O 
54.6 mg/l 
MgSO.sub.4 
75.7 mg/l 
NaHCO.sub.3 
______________________________________ 
Mild steel coupons (4.5 in..times.0.5 in.) were immersed in 15% 
hydrochloric acid for 15 minutes, then rinsed sequentially in saturated 
sodium bicarbonate solution, distilled water and isopropanol, dried and 
stored in a desiccator. They were weighed prior to use in the corrosion 
test. 
The desired amount or corrosion inhibitor was dissolved in 850 ml of the 
standard corrosive water listed above. The solution was heated in a 
thermostatted bath at 55.degree. C. After the temperature had equilibrated 
the pH of the solution was adjusted to 8.5. Two coupons were suspended in 
the solution and air was passed into the solution at 250 ml/min. After 48 
hours, the coupons were removed and cleaned with steel wool, rinsed, 
dried, and weighed again. The rate of corrosion was calculated from the 
weight loss and was expressed in mils per year (mpy). The results are 
shown in the following table. 
TABLE 1 
______________________________________ 
Dosage ppm 
Corrosion Rate (mpy) 
______________________________________ 
Blank -- 70 
ANS-HS 200 3.0 
100 46 
ANDS-HS 200 2.9 
100 48 
*AHNS-HS 250 -- 
200 32 
150 44 
______________________________________ 
*N-2-(5-hydroxy-7-sulfonaphthyl)-hydroxy aspartic acid. 
EXAMPLE 6 
Calcium sensitivity test determines the tendency of a chemical to 
precipitate with calcium ions in solution. 
Calcium insensitivity is considered an important feature of this invention 
because it allows the compound of this invention to be used effectively in 
water of relatively high hardness. The test for calcium insensitivity of a 
compound as used in this application involves a cloud point test where the 
compound is added to a hard water containing 500 ppm calcium ion (as 
CaCO.sub.3) which is buffered at pH 8.3 using 0.005 M borate buffer and 
has a temperature of 60.degree. C. The amount of compound which can be 
added until the solution becomes turbid (the cloud point) is considered to 
be an indicator of calcium sensitivity. The calcium insensitive compounds 
of this invention have cloud points of at least about 25 ppm as determined 
by this specific test. 
Formation of the co-precipitates of calcium with polyacrylic acid, 
polymethacrylic acid and polymaleic acid were at cloud points of 4 ppm, 6 
ppm, and 12 ppm, respectively. This result indicated that polyacrylic 
acid, polymethacrylic acid and polymaleic acid were very sensitive to 
calcium hardness and prone to form calcium polymer precipitates at low 
treatment concentrations. In contrast, the naphthalene polycarboxylic 
acids, as illustrated in Table 1, were relatively insensitive to calcium 
with cloud points at 40 and 77 ppm, respectively. 
TABLE 2 
______________________________________ 
Calcium Sensitivity 
Treatment Cloud Point (ppm) 
______________________________________ 
Polyacrylic Acid 
4 
Polymethacrylic Acid 
6 
Polymaleic Acid 12 
Product of Example 3 
40 
Product of Example 4 
77 
______________________________________ 
EXAMPLE 7 
Threshold inhibition test measures the ability of a chemical to inhibit 
calcium carbonate formation. 
Laboratory tests for calcium carbonate threshold inhibitors were performed 
under the following water conditions: water containing 283 ppm Ca.sup.+2, 
184 ppm Mg.sup.+2 and 423 ppm HCO.sub.3.sup.- (all as CaCO.sub.3). The 
test solution was prepared in a 1000 ml beaker and 5 ppm of the additive 
being tested was added to the above water. The final volume of the 
solution was made up to 800 ml. The solution was stirred with a magnetic 
stir bar and heated by a stainless steel immersion heater to 130.degree. 
F. The pH of the solution was monitored and adjusted at pH 7.15 with the 
addition of dilute HCl. On achieving the required temperature, 0.1 N NaOH 
was added at a rate of 0.32 ml/minute using a syringe pump. 
The pH was monitored and recorded during the titration. A decrease or 
plateau in pH reading is observed when calcium carbonate starts to 
precipitate. This point is termed the critical pH (pH.sub.c). An effective 
threshold inhibitor will raise the critical pH, compared to the blank, and 
require more base (hydroxide) to reach pH.sub.c. Results are summarized in 
Table 3. 
As shown in Table 3, naphthalene polycarboxylic acid is an effective 
calcium carbonate threshold inhibitor. Also apparent from the data in 
Table 3 is the general unpredictability of the effectiveness of similar 
additives for threshold inhibition when viewed on the basis of chemical 
structure alone. Clearly the effectiveness of the compositions of this 
invention in providing calcium carbonate threshold inhibition was 
comparable to polymaleic acid and polyacrylic acid and yet the results 
were far superior to polymethacrylic acid which is structurally similar to 
these compounds. 
TABLE 3 
______________________________________ 
Threshold Inhibition 
Critical pH 
Meq. OH.sup.- /Liter 
Additive pH.sub.c to pH.sub.c 
______________________________________ 
Blank 8.12 0.91 
Polymaleic Acid 9.12 2.79 
Polyacrylic Acid 
9.33 3.62 
Polymethacrylic Acid 
8.93 1.78 
Product of Example 3 
9.32 3.33 
Product of Example 4 
9.19 2.78 
______________________________________