US2807585A - Inhibitor acid - Google Patents

Description

Patented Sept. 24, 1957 INHIBITOR ACID George S. Gardner, Elkins Park, and Albert J. Saukaitis, Wayne, Pa., assignors to American Chemical Paint Company, Ambler, Pa., a corporation of Delaware No Drawing. Application December 2, 1953, Serial No. 395,852

2 Claims. (Cl. 252-448) This application is a continuation-in-part of our earlier application, Serial Number 332,491, filed January 21, 1953, now abandoned.

The invention relates to inhibitors such as are useful in the art of controlling the attack of acids on metals and is particularly concerned with the provision of new and improved inhibitors and inhibitor formulations as well as to a method for producing the same.

Before reciting the objects of the invention we wish to point out that organic nitrogen bases, especially those that are derived from coal tar, are ofparticular value as inhibitors in acid pickling baths and that various organic nitrogen compounds have been used in the pickling art. The compounds most widely used and of the most value at the present time are the cyclic bases of the aromatic series such as pyridines, quinolines, acridines and certain of their derivatives. Other nitrogen ring compounds of value as inhibitors are such as those disclosed in United States Patent No. 2,010,562. Unfortunately, however, the supply, quality and uniformity of naturally occurring bases suitable for the manufacture of pickling inhibitors have always been variable and the industry has long felt a need for a source of supply based upon easily obtainable chemicals from which pickling inhibitors of the type referred to can be produced. The present invention makes this possible and at the same time provides new inhibitors and inhibitor formulations which are markedly improved both as to strength and as to useful length of life in the acid solutions in which they are employed.

With the foregoing in mind, the principal objects of the invention may be recited as residing in the provision of new inhibitors of greatly increased inhibiting power and of exceptionally long life, the provision of a simple and effective method for the production of such inhibitors, which method makes use of relatively inexpensive and readily available raw materials and, finally, the provision of inhibitors and a method of producing the same, which are capable of far more exact control than has heretofore been possible so that quality and uniformity are very much improved. 7

By way of background, it should be noted that Mannich and his co-workers have shown that it is possible to prepare piperidine derivatives by means of a modification of the reaction now known as the Mannich reaction. If one molecule of methylamine hydrochloride reacts with two molecules of formaldehyde and two molecules of acetone, a compound is obtained having the following structural formula:

No. l

O CH:

By making the reaction product alkaline in the cold, a condensation takes place, and a piperidine derivative is formed having the following structural formula:

wherein R is alkyl, arylalkyl, cyclo-alkyl, hydrogen or the group and R1 is alkyl, aryl, or aryl-alkyl. Typical examples of R are methyl, ethyl, isopropyl, n-propyl, n-butyl, nhexyl, n-octyl, benzyl, alpha naphthyl methyl, cyclohexyl and cyclopentyl. Suitable examples of R1 are methyl, ethyl, n-propyl, n-amyl, isobutyl, phenyl, naphthyl, benzyl, and alpha naphthyl methyl.

The present invention is based upon the discovery that the substituted piperidines of No. 3 and certain of their derivative are excellent pickling inhibitors. Some of them are soluble in the dilute acid pickling solutions. Others are insoluble and need to be emulsified or dispersed in the pickling medium.

As the result of extensive tests we have found that the compounds represented by No. 3 above, have considerable value as pickling inhibitors even without further treatment and that they may be used to advantage in the art of pickling metal. However, we have also discovered that the compounds represented by No. 3 above can be "converted by certain treatments to be described below so as to yield inhibiting materials which have a markedly greater value for this purpose than do the pure compounds represented by structural formula No. 3 above given. Their conversion may be accomplished by:

a. Heating b. By treating with a solution of an alkali, preferably hot.

In the former case (a) the inhibitor is formed directly while in the latter case (b) the inhibitor usually forms as a phase separate from the aqueous layer, which phase 65 may be separated by any convenient means such as a separatory funnel. However, if the inhibitor does not separate properly, extraction may be made with a waterimmiscible solvent such as chloroform. After extraction, of course, the inhibitor may be obtained simply by evaporation of the solvent.

We also wish to point out that it is not always necessary to use the pure compounds of Formula No. 3 above as a starting point for the preparation of the inhibitors because it is perfectly feasible to begin with a reaction mixture containing the materials represented by Formula No. 3. For example, as was indicated above, compounds of Formula No. 3 can be prepared by the reaction of a ketone, formaldehyde and an amine hydrochloride. The term amine hydrochloride as used in this connection is to be understood to include ammonium chloride, which readily enters into this reaction. After proper refluxing, the mixture is made alkaline and the basic material, containing compounds represented by Formula No. 3, may be extracted by means of a water immiscible solvent such as chloroform. The solvent may then be evaporated and the residue subjected to the action of heat or boiled with an alkaline solution. The final product, freed from aqueous liquid, constitutes the inhibitor. It has been found that other amine salts, such as nitrates, acetates, sulfates, etc., may be used in the preparation of the compounds of Formula No. 3.

If the solvent extraction just mentioned is not employed, after the reaction product is made alkaline (preferably by means of a strong alkali such as sodium hydroxide. potassium hydroxide, etc.) the mixture is heated, preferably boiled, for a period which may vary between several minutes and several hours. The final product, again freed from the aqueous layer, is the inhibitor.

In the above disclosure where we mention the use of heat for the conversion of the substituted piperidines of No. 3. We intend heating to a temperature of from 60 C. to 150 C. and a period of time varying from five minutes to twenty-four hours.

As already pointed out, the pure compounds of Formula No. 3 can be used to good advantage as pickling inhibitors and they may be used either as the crystalline compounds or as crude bases separated from the reaction mixture by means of a cold alkali treatment. Further, the pure compounds of the generic formula of No. 3 may be employed as the starting materials from which improved inhibitors may be prepared by means of heat treatment alone or by means of heat treatment, preferably boiling, in the presence of an alkali. Still further, as indicated above, in preparing our improved inhibitors we may apply the heat and/or alkali treatment to the reaction mixture used in preparing the compounds of the generic Formula No. 3. In other words, a mixture of a ketone, an amine hydrochloride and formaldehyde may be reacted and the reaction mixture treated with heat and/or an alkali and we prefer relatively long boiling with an alkali.

We will now give the following examples of ways in which our improved inhibiting materials may be prepared but before We do so we wish to introduce the following Table 1 which shows how the materials that were employed in the preparation of the inhibitors listed in Table 2 below fit into the generalized structural Formula No. 3 above:

The following are the examples which we wish to introduce:

iii)

Example A One mole of ammonium chloride, 5 mols. of acetone, and 3 mols. of aqueous formaldehyde solution (37% by weight), are mixed in a liter round-bottom flask equipped with condenser. The flask is heated gently, with refluxing, for 15 hours. At the end of this time 2.0 mols. of acetone are distilled off. The reaction mixture is cooled to 20 C., and a cool (20) solution of 1.25 mols. of NaOH in ml. water is added. The temperature of the reaction mixture is maintained at or below 20 C. After 15 minutes the base is shaken out with chloroform. The chloroform solution is evaporated to dryness in the air (not heat applied), and the brown resinous base material is dried 2 hours at 50 C. This resinous material, g., is inhibitor A of Table 2. (See below.)

Example B One mole of ammonium chloride, 5 mols. of acetone, and 3 mols. of aqueous formaldehyde solution (37% by weight), are mixed in a liter round-bottom flask equipped with condenser. The flask is heated gently, with refluxing, for 15 hours. At the end of this time 2.0 mols. of acetone are distilled oil. The reaction mixture is cooled to 40 C., and a solution of 1.25 mols. of NaOH in 100 ml. of water is added. The mixture is heated to boiling, with stirring, and is maintained under these conditions for four hours. At the end of this time the reaction mixture is poured into a separatory funnel. The waste liquor separates on the bottom and is removed. The viscous upper layer is washed with hot, concentrated, sodium chloride solution. After the washing, the black, viscous layer weighed grams. This material is inhibitor B of Table 2. (See below.)

Example C One mole of ammonium chloride, 3.0 mols. of methyl ethyl ketone, and 3 mols. of aqueous formaldehyde (37% by weight) are mixed in a liter round-bottom flask equipped with reflux condenser. The flask is heated gently, with refluxing, for 15 hours. At the end of this time the reaction mixture is cooled to 20 C. and treated with a cool solution of 1.25 mols. of NaOH in 100 ml. water. The mixture is heated to boiling, with stirring, and is maintained under these conditions for four hours. The whole reaction mixture is transferred to a separatory funnel, and the lower aqueous layer removed. The upper layer is washed with hot, saturated sodium chloride solution. The upper layer is now heated on a water bath for 8 hours to remove any excess methyl ethyl ketone. The resinous mass obtained, weighing 176 grams, is inhibitor C of Table 2. (See below.)

Example D One mole of cyclohexylamine hydrochloride, 4.0 mols. of acetone, and 2.0 mols. of aqueous formaldehyde (37% by weight), are mixed in a liter round-bottom flask equipped with condenser. The flask is heated gently, with refluxing for 15 hours. At the end of this time, 2.0 mols. of acetone are distilled oil. The reaction mixture is cooled to 20 C., and a cool solution of 1.25 mols. NaOH in 100 ml. water is added. The reaction mixture is now heated to boiling, with stirring, for four hours. After this boiling operation has been completed, the whole reaction mixture is transferred to a separatory funnel, and the resinous material separated from the lower aqueous layer. The resinous material is used without any washing, and weighs 178 g. This is inhibitor D of Table 2. (See below.)

Example E 30 g. of l-methyl, 4-hydroxy, 4-phenyl, 5 benzoyl piperidine, are boiled over night with a solution of g. of NaOH in 200 ml. water. The product is 25 g. of a brown resinous material, and is inhibitor E of Table 2. (See below.)

Example F 0.5 mol. ammonium chloride, 1.0 mol. benzalacetone, and 1.0 mol. aqueous formaldehyde are mixed in a reaction flask, and refluxed for hours. The cool reaction mixture is treated with a solution of 30 g. of NaOH in 50 ml. water, and the mixture boiled for 3 hours. After settling in a separatory funnel, the upper layer of inhibitor is separated from the lower aqueous layer. The inhibitor, 85 g., is inhibitor F of Table 2. (See below.)

Example G This is pure l-n-butyl, 3 benzoyl, 4-hydroxy, 4-phenyl piperidine, prepared according to Plati, Schmidt, and Wenner. This is inhibitor G of Table 2. (See below.)

Example H This is pure l-benzyl, 3-benzoyl, 4-hydroxy, 4-phenyl piperdine, prepared according to Plati, Schmidt, and Wenner. This is inhibitor H of Table 2. (See below.)

Example I Example I 3.0 mols. of acetone, 3.0 mole. of aqueous formaldehyde solution (37%), and 1.0 mol. of NHtCl were reacted under reflux over night. The solution was cooled, and 100 ml. of reagent grade NH4OH solution added. The solution was stirred and heated (75 C.) for 4 hours. At the end of this time, the solution was cooled, and 300 ml. of chloroform added, with shaking. The chloroform was separated, and an additional 200 ml. of chloroform added, with shaking. The total separated chloroform was evaporated on a water bath. The total residue, 110 g., is inhibitor J of Table 2. (See below.)

That there is a profound change in the chemical structure of the 4-hydroxy piperidine of Figure 3 on treatment with alkalies or by heating without alkalies, in accordance with any one of the foregoing examples, is evidenced by important changes in physical properties, such as appearance, solubility, infra-red absorption spectrum, etc. The inhibitors which are formed are highly complex compounds characterized by the presence of carbon, oxygen, hydrogen and nitrogen; they are bases capable of reacting with mineral acids to form salts; they are soluble in methyl alcohol or chloroform and are substantially insoluble in water containing sodium hydroxide while having considerable solubility in water acidulated with hydrochloric acid.

The inhibitors of the various examples given above were tested and evaluated according to the following table:

TABLE NO. 2

Inhibition, Inhibitor Starting measured specimen materla Method of preparation of inhibitor as lfitln We 8 gJItJ/hr.

A V Crude base separated from reaction 8. 6

mixture by means of cold alkali and 01101;. B V Crude base separated from reaction 1.9

. mixture by means of boiling alkali (4 hours). 0 I 3. 7 D II do 2. 5 E III Pure material boiled with NaOH 1. 0

solution 4 hours, then separated. F IV Orude bass separated from reaction 2. 2

mixture by means of boiling alkali (3 hours). G VI Platl, Schmidt and Wanner, J. Org. 42. 8

Chem, 14, 873-878 (1949). H VII 12. 6 I V Base separated by means of NaOH 2. 4

solution, 5 minutes, at 0. Then heated 8 hours at C. in absence of NaOH. .1 V NHAOH solution added to reaction 6. 7

mixture; heated to 75 0., 4 hrs. Product extracted with chlororm. Blnnk No inhibitor 105.6

The inhibitor test used to evaluate the inhibitors referred to in Table No. 2, just above, is as follows: 0.05 gram of the compound or mixture are dissolved or suspended in a mixture of 20 milliliters 66 B. sulfuric acid, 1 milliliter C. P. (23 B.) hydrochloric acid and milliliters water. The solution was heated to 180 F. and aged for two hours. After the ageing, a weighed test strip of hot rolled steel, previously pickled in 1:1 hydrochloric acid solution at room temperature for 10 minutes, was immersed in the test solution for 30 minutes, the temperature of the test solution being maintained at 180 F. The strip was then removed from the test solution, rinsed in water, alcohol dried and weighed. The loss in weight expressed as grams/sq. ft./hour was reported as noted in the table above. The blank was run in a similar fashion except that no inhibiting material or compound was added to the test solution.

The inhibitors which We have described lend themselves exceptionally well to inhibitor formulations. As is well known in this art, quite often it is desirable (in order to formulate inhibitor compounds of the highest possible value and greatest utility for present day commercial practice) to use the primary inhibitor or principal inhibitor with other materials which, for the sake of brevity, will be called herein adjuncts." For instance, some inhibitor formulations may be made by incorporating therein wetting agents, bone tar oil, high boiling coal tar bases, both cyclic and heterocyclic, foam producing materials, etc. Additionally, the most important inhibitor formulations of the present invention are those embodying the primary reaction product in admixture with sulfur-bearing compounds such as thiocyanates and thioureas, including both alkyl or aryl substituted thioureas. Especially good results are usually obtained when the admixtures are heated. Specific examples of such inhibitor formulations are as follows:

FORMULATION 1 Sulfuric acid 66 B -.ml.. 49.8

In a separate container the sulfuric acid and the water are mixed and cooled to 40 C. The reaction product of Example B is dissolved in this acid mixture and the solution cooled to 30 C. The muriatic acid is then added and the solution heated to 80 C. At this point the thiourea is added and the solution heated to 100 C. This temperature is maintained for one hour. At the end of the hours heating, the admixture is allowed to cool. The cooled admixture is an extremely strong longlasting inhibitor formulation.

The inhibitors of the present invention are primarily useful in the art of pickling and cleaning metal especially where the acids employed consist of dilute solutions of non-oxidizing mineral acids such as sulphuric, hydrochloric and phosphoric acids as well as solutions of acid salts such as acid sulphate and the like. The typical example is the pickling of iron and steel articles such as sheets, forgings, bars, wire and other articles at various stages of their manufacture. Naturally the composition of these pickling or metal treating solutions, their temperature of use and other factors vary with different operations but in every instance the primary function of the solution is to remove undesirable incrustations from the metal while at the same time restraining the attack of the acids upon the exposed metal and thereby to conserve both acid and metal and to prevent or minimize damage such as hydrogen embrittlement, burning, or overpickling. The quantity of the inhibitor to be used, naturally, will vary depending upon any given set of conditions but those skilled in the art of pickling can easily determine the proportions to be employed. The invention is entirely independent of quantities except, of course, that a sufficient quantity should be employed to produce a useful result and in this connection, because of the improved character of our new inhibitors, it is frequently possible to reduce the quantity of inhibitor which may be required for any particular operation.

We claim:

1. An acid corrosive to metals containing, as an inhibiting agent, the reaction product formed by heating at temperatures of from 60 C. to 150 C. for a period of time of from five minutes to twenty-four hours a substituted 4hydroxy piperidine having the general formula:

wherein R is from the class consisting of alkyl and cycloalkyl radicals containing no more than eight carbon atoms, aryl-alkyl radicals in which the aryl moiety contains no more than eleven carbon atoms, hydrogen, and

0H CH:

ll CHr-C-C 2 /CH: N

at temperatures of from C. to C. for a period of time of from five minutes to twenty-four hours, the said reaction product being present in the acid in an amount sufficient to materially retard the attack of the acid on basis metal.

References Cited in the file of this patent UNITED STATES PATENTS 2,010,562 Parkes Aug. 6, 1935 2,499,283 Robinson Feb. 28, 1950 2,604,451 Rocchini July 22, 1952 2,630,368 Wachter et al. Mar. 3, 1953 OTHER REFERENCES Beilstein: Handbook of Organic Chemistry (Springer), 2d. sup. vol. 21, page 412.

Plati et al.: Journal of Organic Chemistry, vol. 14, pages 543-549 (1949).

Plati et al.: Journal of Organic Chemistry, vol. 14, pages 873-878 (1949).

Blicke et al.: Journal of the American Chemical Society, vol. 64, pages 451-454.

Mannich et al.: Arcbiv der Pharmazie, vol. 1926, page 66.

Claims (1)

1. AN ACID CORROSIVE TO METALS CONTAINING, AS AN INHIBITING AGENT, THE REACTION PRODUCT FORMED BY HEATING AT TEMPERATURES OF FROM 60*C. TO 150*C. FOR A PERIOD OF TIME OF FROM FIVE MINUTES TO TWENTY-FOUR HOURS A SUBSTITUTED 4-HYDROXY PIPERIDINE HAVING THE GENERAL FORMULA: