US20060289833A1

US20060289833A1 - Esters of phosphorus-oxygen acids, these esters comprising alkoxy groups, and their use as corrosion inhibitors and flameproofing agents

Info

Publication number: US20060289833A1
Application number: US10/555,426
Authority: US
Inventors: Helmut Witteler; Fernandez Gonzalez; Gerhard Wagenblast
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2004-05-03
Filing date: 2004-05-03
Publication date: 2006-12-28

Abstract

The invention relates to esters or ester salts of phosphorus-oxygen acids, these esters or ester salts comprising alkoxy groups, and to the use of compounds of this type as corrosion inhibitors, particularly in alkaline media, and as flameproofing agents.

Description

The present invention relates to alkoxy-comprising esters or ester salts of phosphorus-oxygen acids. It furthermore relates to the use of such compounds as corrosion inhibitors, in particular in alkaline medium.
The use of phosphoric or phosphonic acid derivatives for corrosion protection is known in principle. Frequently, however, phosphoric or phosphonic acid derivatives or the hydrolysis products thereof form insoluble or sparingly soluble salts with various opposite ions, e.g. Ca²⁺, in aqueous alkaline media, so that they can be used only to a limited extent in such media.
An alkaline medium may be, for example, concrete, mortar and the like or finishes, coating systems or the like containing an alkaline binder system.
Steel reinforcements embedded in concrete are also not completely protected from corrosion but may corrode in the course of time. As a result of the corrosion of the steel reinforcement, the strength thereof and hence the strength of the concrete are reduced. Moreover, the corrosion products, for example iron oxides or hydrated iron oxides, have a larger volume than the uncorroded steel itself. Accordingly, stresses form in the concrete that can lead to cracks or to breaking off of whole fragments. Considerable economic damage is caused by corrosion of reinforced concrete.
The corrosion of the steel reinforcement is a substantially diffusion-controlled process. Water and oxygen can diffuse into the pores of the concrete. Pore water comprises, inter alia, dissolved Ca(OH)₂and has, in intact concrete, a pH of about 13. At this pH, steel reinforcements embedded in concrete are protected from corrosion by a passivation layer. The diffusion of atmospheric CO₂in the pores results, inter alia, in the formation of insoluble CaCO₃and the pH of the pore water falls to values below 9. However, at these pH values, the passivation layer on the steel becomes ineffective. The effect of the passivation layer can also be adversely affected or eliminated by chloride ions. Chloride ions can penetrate into the concrete, for example through contact of the concrete with sea water or deicing compositions.
The amount of penetrating CO₂or chloride is smaller when particularly dense, concrete having few pores is used. However, the penetration cannot be completely prevented in this way either. Moreover, when the structure of the concrete changes, so do its properties, which is frequently undesirable depending on the intended use. The possibility of using concrete having few pores is therefore not feasible in many cases.
It is therefore known that corrosion inhibitors, for example nitrites, amines, alkanolamines, mixtures thereof with inorganic or organic acids or phosphate esters, can be added to fresh concrete. It is also known that phosphonic acids or phosphonic acid derivatives can be used for corrosion protection in concrete. DE-A 36 29 234 discloses the addition of salts, in particular sodium salts of various alkylphosphonic acids, as an additive to concrete and mortar mixtures. GB-A 2 248 612 and JP-A-03-159945 disclose amino- or hydroxyl-containing phosphonic acids as an additive for concrete.
In addition to the corrosion-protecting treatment of fresh concrete, the question regarding the protection of old concrete frequently arises in practice. For this purpose, the concrete can be chipped off or blasted off on the surface and the steel reinforcement exposed. The steel reinforcement can then be treated with corrosion inhibitors and finally covered again with concrete. This method is used especially in serious cases if the structure of the concrete is already irreversibly damaged.
It is furthermore known that the surface of hardened reinforced concrete can be treated with a migrating corrosion inhibitor. This technique is disclosed, for example, in “M. Haynes, B. Malric, Construction Repair, July/August 1997” or in U.S. Pat. No. 5,071,579. For this purpose, a solution of the inhibitor is applied or sprayed several times in succession on the surface, the inhibitor migrating into the surface. The further diffusion into the interior down to the steel reinforcement is usually supported by the repeated application of water to the surface. It is known that Na₂PO₃F can be used as a migrating corrosion inhibitor. U.S. Pat. No. 5,071,579 also discloses the combined use of Na₂PO₃F together with a phosphonic acid of the formula R_nR_lN(CH₂PO₃H₂)_2-n(n=0 or 1). However, sodium fluorophosphate is hydrolyzed in water and forms insoluble calcium salts with Ca(OH)₂dissolved in the pore water. Phosphonic acids, too, form insoluble calcium salts. A considerable part of the superficially applied corrosion inhibitors thus does not reach the steel reinforcement at all and accordingly also cannot display any action. The inhibitors must therefore be used in large amounts. This is uneconomical and moreover the concrete is contaminated by undesired components as a result.
It is an object of the present invention to provide improved corrosion inhibitors which are particularly suitable for use in an alkaline medium and which in particular form no insoluble or sparingly soluble calcium salts.
We have found that this object is achieved by alkoxy-comprising esters of phosphorus-oxygen acids of the formula
R³—NR⁴ _k—[(CH₂)_n—PO(OR¹)(OR²)]_m (A)
or
[(R¹O)(R²O)OP—(CH₂)_n—]_m—NR⁴ _k—R⁵—NR⁴ _k—[—(CH₂)_n—PO(OR¹)(OR²)]_m (B)
where

- n is an integer from 0 to 10,
- m+k=2 and m is 1 or 2 and k is 0 or 1,
- at least one of the radicals R¹, R²and, if appropriate, R³is alkoxy of the formula —[CH₂—CHR⁶—O]_lR⁷, where l is from 2 to 30 and R⁶and R⁷are each H or CH₃,
- and, where they are not alkoxy groups, R¹and R²are straight-chain or branched C₁- to C₆-alkyl,
- and, where it is not an alkoxy group, R³is straight-chain or branched, unsubstituted or substituted C₁- to C₂₀-alkyl or aryl,
- R⁴is H or straight-chain or branched C₁- to C₆-alkyl and
- R⁵is a divalent bridging group.

In a second aspect of the present invention, alkoxy-comprising ester salts of phosphorus-oxygen acids of the formula
R³—NR⁴ _k—[(CH₂)_n—PO(OR¹)(OM)]_m (C)
or
[(MO)(R¹O)OP—(CH₂)_n—]_m—NR⁴ _k—[—(CH₂)_n—PO(OR¹)(OM)]_m (D)
were found, where

- n is an integer from 0 to 10,
- m+k=2 and m is 1 or 2 and k is 0 or 1,
- at least one of the radicals R¹and, if appropriate, R³is alkoxy of the formula —[CH_2-CHR⁶—O]_lR⁷, where l is from 2 to 30 and R⁶and R⁷are each H or CH₃,
- and, where it is not an alkoxy group, R¹is straight-chain or branched C₁- to C₆-alkyl,
- and, where it is not an alkoxy group, R³is straight-chain or branched, unsubstituted or substituted C₁- to C₂₀-alkyl or aryl,
- R⁴is H or straight-chain or branched C₁- to C₆-alkyl and
- R⁵is a divalent bridging group, and
- M is at least one cation selected from the group consisting of alkali metal, alkaline earth metal or ammonium ions.

We have furthermore found the use of the esters or ester salts as corrosion inhibitors, in particular migrating corrosion inhibitors for reinforced concrete.
Surprisingly, we have found that the novel diesters—what is meant is the number of ester groups per phosphorus atom—are very useful for corrosion protection. They are very particularly suitable for an alkaline medium, if appropriate media comprising calcium ions. The novel esters are soluble in saturated Ca(OH)₂solution and form no sparingly soluble precipitates. Furthermore, the solubility of the monoester salts in Ca(OH)₂solution is sufficient.
Even in an excess of NaOH and at elevated temperature, the diesters hydrolyze in an alkaline medium in general only very slowly to give the corresponding monoester salts. The further hydrolysis to give the free acids or the salts thereof takes place only to a minor extent under said conditions. The diesters themselves have a corrosion-inhibiting action. As a rule, the corrosion-inhibiting action of the corresponding monoester salts is higher. The monoester salts are liberated only gradually by hydrolysis. The diesters are masked corrosion inhibitors or corrosion inhibitors having a delayed or long-term action.
Regarding the invention, the following may be stated specifically.
The novel, alkoxy-comprising esters of phosphorus-oxygen acids are either diesters of the formula
R³—NR⁴ _k—[(CH₂)_n—PO(OR¹)(OR²)]_m, (A)
in which one or two phosphorus-oxygen acid groups and at least one further substituent are linked directly or indirectly to a nitrogen atom, or a bridged diester of the formula
[(R¹O)(R²O)OP—(CH₂)_n—]_m—NR⁴ _k—R⁵—NR⁴ _k—[—(CH₂)_n—PO(OR¹)(OR²)]_m, (B)
in which two nitrogen atoms are linked to one another via a group R⁵and in turn have one or two phosphorus-oxygen acid groups and, if appropriate, a further substituent.
Below, the term “diester” is intended to relate to the number of ester groups per phosphorus atom and hence denote compounds in which all phosphorus atoms present in the molecule have two ester groups each. Accordingly, the term “monoester” below is intended to denote compounds in which each phosphorus atom has an ester group or an OH or OM group. The novel diesters or monoesters are a phosphonic acid derivative where n is greater than 0, whereas they are a derivative of amidophosphoric acid where n is 0.
The index n in the formulae (A) and (B) is an integer from 0 to 10. Preferably, n is an integer from 0 to 3, particularly preferably 0 or 1, very particularly preferably 1.
The index m is 1 or 2 and the index k is 0 or 1, the sum of m+k being 2. Preferably, m and k are each 1, i.e. in each case only one —(CH₂)_n—PO(OR¹)(OR²) group is linked to a nitrogen atom.
At least one of the radicals R¹, R²and, if appropriate, R³(i.e. where the diester is compound (A)) is alkoxy. Suitable alkoxy groups are in particular polyoxyethylene or polyoxypropylene groups of the formula —[CH₂—CHR⁶—O]_lR⁷, where l is from 2 to 30 and R⁶is H and/or CH₃. R⁵is preferably H, i.e. the alkoxy group is a polyoxyethylene group. Preferably, l is from 3 to 20, particularly preferably from 5 to 15. R⁷is a CH group or H.
It is known to a person skilled in the art that such alkoxy groups are obtainable, for example, by oxyalkylation or starting from industrial polyglycols. Said values for l are thus average chain lengths, where the average value need not of course be a natural number but may also be any desired rational number.
The remaining radical or radicals R¹, R²and, if appropriate, R³(only for case (A)) which is or are not alkoxy is or are straight-chain or branched, unsubstituted or substituted alkyl. Optionally present substituents may be, for example, amino or OH. In particular, the substituents may be a terminal OH group.
R¹and/or R²is/are preferably C₁- to C₆-alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl or n-hexyl, preferably methyl or ethyl, very particularly preferably ethyl. A substituted alkyl group may be in particular 2-methoxyethyl.
R³is preferably C₁- to C₂₀-alkyl or aryl. It is preferably straight-chain or branched C₄- to C₁₂-alkyl. Examples of suitable groups comprise methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, n-hexyl, 2-ethylhexyl, n-heptyl, n-octyl, n-nonyl, n-decyl or n-dodecyl. Particularly preferred groups comprise n-propyl, n-butyl, n-octyl and 2-ethylhexyl. A substituted alkyl group may be in particular an ω-methoxyalkyl group, e.g. methoxyethyl. Aryl groups may be pure aryl groups, such as alkyl-substituted aryl groups, for example a —CH₂C₅H₆group.
If present, R⁴is H or straight-chain or branched, unsubstituted or substituted alkyl, preferably C₁- to C₆-alkyl. Particularly preferably, R⁴is H or methyl. A substituted alkyl group may be in particular 2-methoxyethyl.
No R³is present in the bridged compound (B), but instead a divalent bridging group R⁵which preferably has at least 2 carbon atoms. Said group may be in particular a group derived from aliphatic, alicyclic or aromatic hydrocarbons. Examples comprise 1,4-xylylene, 1,4-cyclohexylene or ethylidene groups which may also have heteroatoms or substituents.
The bridging group is preferably alkylene of 2 to 20 carbon atoms, in which nonneighboring CH₂groups may also be substituted by O or N atoms. Examples comprise —(CH₂)₂—, —(CH₂)₄—, —(CH₂)₆—, —(CH₂)₈—, —(CH₂)₂—O—(CH₂)₂—, —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—, —(CH₂)₃—O—(CH₂)₄—O—(CH₂)₃—, —(CH₂)₃—O—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₃—, —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—, —(CH₂)₂—O—[(CH₂)₂—O—]_j(CH₂)₂—O—(CH₂)₂—, —(CH₂)₂—N—(CH₂)₂— and —(CH₂)₂—NR₆—(CH₂)₂—NR₆—(CH₂)₂— groups, where j is from 1 to 10 and R₆is alkyl, —(CH₂)_n—PO(OR¹)(OR²) or —(CH₂)_n—PO(OR¹)(OM).
Said groups are preferably —(CH₂)₂—, —(CH₂)₄—, —(CH₂)₆—, —(CH₂)₃—O—(CH₂)₄—O—(CH₂)₃—, —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂— or —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂— groups.
Among the various possible combinations of the radicals R¹to R⁷, a person skilled in the art makes a suitable choice according to the desired properties and the intended use. For carrying out the invention, it is sufficient if one of the radicals R¹and R²is alkoxy. Preferably, however, both R¹and R²are alkoxy.
Migrating corrosion inhibitors which have proven particularly useful are the following compounds:
(2-ethylhexyl)-N(CH₃)—(CH₂)—PO(O-alkoxy)(O-alkoxy),
(2-ethylhexyl)-N[—(CH₂)—PO(O-alkoxy)(O-alkoxy)]₂,
butyl-NH—PO(O-alkoxy)(O-alkoxy),
octyl-NH—PO(O-alkoxy)(O-alkoxy),
(2-ethylhexyl)-NH—PO(O-alkoxy)(O-alkoxy),
(2-ethylhexyl)-N(CH₃)—PO(O-alkoxy)(O-alkoxy),
(alkoxy)-NH—PO(O-alkoxy)(O-alkoxy),
(alkoxy-O)(alkoxy-O)OP—NH—(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—NH—PO(O-alkoxy)(O-alkoxy)
(2-methoxyethyl)₂N—CH₂—PO(O-alkoxy)(O-alkoxy),
(ethyl)₂N—CH₂—PO(O-alkoxy)(O-alkoxy),
(CH₂)₅N—CH₂—PO(O-alkoxy)(O-alkoxy),
In the novel ester salts
R³—NR⁴ _k—[(CH₂)_n—PO(OR¹)(OM)]_m (C)
and
[(MO)(R¹O)OP—(CH₂)_n—]_m—NR⁴ _k—R⁵—NR⁴ _k—[—(CH₂)_n—PO(OR¹)OM)]_m (D)
the radicals—if present—and indices have the meaning stated above in the description of the diesters. However, the ester salts have only one ester group per phosphorus atom. In the case of (D), R¹is always alkoxy; in the case of (C), either R¹or R³may be alkoxy, or R¹and R³together.
M is at least one cation selected from the group consisting of alkali metal, alkaline earth metal or ammonium ions. The ammonium ions may be in particular NH₄ ⁺, alkyl- or hydroxyalkyl-substituted ammonium ions, for example (HOCH₂CH₂)₃NH⁺, (HOCH₂CH₂)₂NH₂ ⁺, HOCH₂CH₂NH₃ ⁺ or HOCH₂CH₂N(CH₃)₂H⁺, or else tetraalkylammonium ions, for example tetramethylammonium or tetraethylammonium. Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺, Ce⁺⁺⁺, Al⁺⁺⁺, Zn⁺⁺ and NH₄ ⁺ are preferred. The above formulae represent only the case of monovalent cations for the sake of simplicity. A person skilled in the art can, however, readily derive therefrom the correct formulae for polyvalent cations.
The novel diesters of phosphorus-oxygen acids can be prepared, for example, starting from commercially available phosphonic esters, for example diethyl phosphonate.
An alkoxylated diester can be obtained therefrom by transesterification, by reacting diethyl phosphonate with the polyethylene glycol or polypropylene glycol desired in each case or the respective monoethers. The transesterification can be catalyzed, for example, by alkali metals, and ethanol liberated is distilled off.
It is of course also possible to start from phosphonic acid itself and to oxyalkylate it by methods known in principle to a person skilled in the art. In this case, alkoxy groups which still have a terminal OH group are obtained.
For n=0, the dialkoxy esters obtained can be reacted with the desired amine, for example ethylhexylamine. The reaction can be carried out in a manner known in principle in CCl₄and a tertiary amine as a catalyst. The use of diamines, such as ethylenediamine, results in bridged diesters (B). The use of aminopolyethylene or polypropylene glycol results in diesters which have an alkoxy group as R³.
Diesters in which n=1 can be obtained by aminomethylation of diethyl phosphonate or of the corresponding alkoxylated diester. Here, the phosphonic diester is reacted with formaldehyde, the desired amine and a suitable Brönsted acid.
Diesters in which n=2 can be prepared by addition of amines to vinylphosphonic esters and, for n>2, by free-radical addition of phosphonic diesters at double bonds (e.g. to allylamines for n=3) or the Arbuzov reaction with aminoalkyl bromides.
The ester-salts are preferably prepared by alkaline hydrolysis of the diesters, for example by heating the diesters in aqueous NaOH to temperatures of from 60 to 100° C. for from 2 to 12 hours, substantially only one ester group per phosphorus atom being hydrolyzed. The optimum conditions for the compound desired in each case can be determined by a person skilled in the art, if appropriate by means of only a few experiments. The monoester salts can also be formed in situ, by hydrolysis in the medium of use.
The novel diesters and monoester salts can be used as corrosion inhibitors. They are particularly-suitable for use in alkaline media, for example having a pH of from 8 to 13. They are furthermore particularly suitable for use in the presence of Ca²⁺ ions.
The novel diesters and monoester salts can be used as such for corrosion protection. For example, suitable derivatives can be sprayed or poured onto a metallic surface, if appropriate after gentle heating. They can also be added to other substances or mixtures, for example finishes, printing inks, mortar or concrete and can thus prevent corrosion on contact of said substances or mixtures with metals.
However, the diesters and monoester salts are preferably used in the form of suitable formulations which comprise at least one diester and/or one monoester salt, a suitable solvent and optionally further components.
Suitable solvents are in particular water or alcohols, such as methanol, ethanol, propanol, polyethylene glycol or alkylpolyethylene glycols. It is of course also possible to use mixtures of different solvents.
Formulations which comprise a predominantly aqueous solvent mixture are preferred. This is to be understood as meaning mixtures which comprise at least 50, preferably at least 65, particularly preferably at least 80, % by weight of water. Further components are water-miscible solvents. Examples comprise monoalcohols, such as methanol, ethanol or propanol, higher alcohols, such as ethylene glycol, glycerol or polyetherpolyols, and ether alcohols, such as butylglycol or methoxypropanol.
Depending on the type of corrosion inhibitor used and on the desired use, a person skilled in the art makes a suitable choice from among the solvents possible in principle.
A particularly preferred solvent is water.
The pH of the formulation is chosen by a person skilled in the art according to the desired use. The use of corrosion inhibitors in an aqueous alkaline medium, for example at a pH of from 8 to 13, is preferred.
The concentration of the corrosion inhibitors is established by a person skilled in the art according to the desired purpose. It is of course also possible to prepare concentrates, which are not diluted to the desired concentration until before the actual use on site.
It is also possible to use further corrosion inhibitors as a mixture with the novel inhibitors, provided that no disadvantageous effects occur.
The formulations comprising the novel corrosion inhibitors are applied in a suitable manner, for example by coating, spraying, printing or immersion, to the metal surface to be protected. The metal surfaces may be in general industrially customary materials selected from the group consisting of aluminum alloys and magnesium alloys, iron, steel, copper, zinc, tin, nickel, chromium and industrially customary alloys of these metals. Further examples comprise industrially customary metal coatings which may be produced by chemical or electrochemical methods, selected from the group consisting of zinc and its alloys, preferably metallic zinc, zinc/iron, zinc/nickel, zinc/manganese or zinc/cobalt alloys, tin and its alloys, preferably metallic tin, alloys of tin which comprise Cu, Sb, Pb, Ag, Bi and Zn, particularly preferably those which are used as solders, for example in the production and processing of circuit boards, and copper, preferably in the form in which it is used on circuit boards and metallized plastics parts.
The metal surfaces to be protected may also be metal particles or metal lamellae, for example aluminum flakes. Such metal effect pigments are used for a very wide range of purposes, depending on particle size. Relatively small particles are used as silver bronzes, for example in printing inks or finishes, while relatively large particles serve as corrosion protection pigments in finishes. The novel diesters and monoester salts can be added to the printing inks or finishes, or else the metal effect pigments are treated with a novel formulation prior to incorporation.
The novel diesters and monoester salts are particularly suitable for corrosion protection of reinforced concrete. On the one hand, they can be added to the fresh concrete. They can also be used for the renovation of old concrete, for example for the treatment of exposed steel reinforcement. They are also suitable as migrating corrosion inhibitors.
The novel compounds can of course also be used in other areas. They are also suitable, for example, as flameproofing agents.
The examples which follow illustrate the invention in more detail:
Starting Materials Used:
Pluriol® A 275E: methylpolyethylene glycol ether, M_w275 g/mol (BASF AG).
In the examples, the compound is referred to as methoxyhexaethylene glycol for the sake of simplicity. In fact, it is a mixture of various methylpolyethylene glycols having a mean value of 5.5 with a number of —CH₂CH₂O— units present.
For the experiments, it is also possible to use other methylpolyethylene glycol ethers having other average molecular weights M_w, e.g. Pluriol® A 350E (M_w350 g/mol) or Pluriol® A 500E (M_w500 g/mol).

EXAMPLE 1

Preparation of di(methylhexaethylene glycol) phosphite

Diethyl phosphite (12.8 g, 0.093 mol) and Pluriol A 275 E (50 g, 0.186 mol) are initially taken together in a 500 ml flask. After the addition of potassium (20 mg, 0.5 mmol) as a catalyst, the reaction mixture is heated to 170° C. and EtOH formed is distilled off under atmospheric pressure. The remaining EtOH is evaporated at 20 mmHg. The yield is 95-98%.
By using other polyethylene glycol ethers having a higher or lower molecular weight, phosphonic esters having other ester groups can be obtained.
In an alternative method of preparation, di(methylhexaethylene glycol) phosphite is also prepared by direct ethoxylation of phosphonic acid.

EXAMPLE 2

Preparation of 2-ethylhexylphosphoramide di(methylhexaethylene glycol) ester

62.0 g (0.092 mol) of the di(methylhexaethylene glycol) phosphite obtained according to example 1 are dissolved in a 1:1 CCl₄/CH₂Cl₂(185 ml) mixture, and 2-ethylhexylamine (11.9 g, 0.092 mol) is added (R³in the above formula is 2-ethylhexyl). Finally, triethylamine (9.28 g, 0.092 mol) is added dropwise. The white triethylammonium hydrochloride powder is filtered off and the solvent is distilled off. 2-Ethylhexylphosphoramide di(methylhexaethylene glycol) ester is obtained as a transparent liquid in a yield of 76% (based on synthesis method of F. R. Atherton, A. R. Todd, J. Am. Chem. Soc., (1947), 674, ibid. (1945), 660).
Other compounds obtainable according to the method of example 1 can also be used as the phosphonic ester. Instead of 2-ethylhexylamine, other amines can also be used.

EXAMPLE 3

Preparation of di(methylhexaethylene glycol) N-methyl-N-2-ethylhexylaminomethyl-phosphite

Di(methylhexaethylene glycol) phosphite (0.1 mol) is added dropwise in the course of 1 hour to a mixture of N-methyl-2-ethylhexylamine (14.3 g, 0.1 mol), formaldehyde (8.21 g, 36.5% strength solution, 0.1 mol) and o-phosphoric acid (4.89 g, 85% strength, 5% by weight) while cooling at −11° C. Thereafter, the reaction mixture is heated to 90° C. and kept at this temperature for 3 hours.
Instead of the o-phosphoric acid, it is also possible to use an acidic ion exchanger, for example Amberlyst 36Dry, in an amount of 1% by weight, based on the total amount, as a catalyst. Other compounds obtainable according to example 1 may also be used as the phosphonic ester. Instead of 2-ethylhexylamine, other amines may also be used. With the use of primary amines, the corresponding dimer is also formed in addition to the above product. This is shown below by way of example for the use of octylamine.

EXAMPLE 4

Preparation of di(hydroxyhexaethylene glycol) N-methyl-N-2-ethylhexylaminomethyl-phosphite

1st Stage: Synthesis of the Phosphonic Acid
The phosphonic acid A is synthesized in a first reaction stage on the basis of the synthesis method of K. Moedritzer, R. R. Irani, J. Org. Chem. (1966), 1603-1607, according to the above equation.
2nd Stage: Ethoxylation of the Phosphonic Acid
N-Methyl-N-2-ethylhexylaminomethylphosphonic acid (238 g, 1 mol) is suspended in 2 l of toluene, and 14 equivalents of ethylene oxide (616 g, 14 mol) are slowly metered in at 50° C. and 1-1.5 bar. The solvent is separated from the product (B) under reduced pressure.
General Method for Hydrolysis of the Diesters to Give the Monoesters
Di(methylpolyethylene glycol) dialkylaminomethylphosphites or alkylphosphoramide di(methylpolyethylene glycol) esters (0.05 mol) are initially taken in a 100 ml four-necked flask having a thermocouple, temperature regulator, coil condenser and bubble counter. The product is diluted with demineralized water (37.0 g). Sodium hydroxide solution (50%, 8 g, 0.1 mol) is then added dropwise in the course of about 10 minutes, the temperature increasing to not more than 32° C. After complete addition, heating is effected slowly to a reflux temperature of 100-105° C. and the reaction mixture is kept at this temperature for 8 hours. The product is characterized by ³¹P, ¹H and ¹³C-NMR.
Under these conditions, only monohydrolysis product can be detected.
Use of the novel compounds as a corrosion inhibitor in an alkaline medium:
General Working Method:
The metal test sheets (2 cm×5 cm, steel 1.0037) are pretreated by cathodic alkaline degreasing and subsequent electrolytic derusting.
The samples are covered with a test solution for 7 days and the loss of mass of the metal test sheet is then determined. The corresponding corrosion inhibitor is added to the test solutions. A comparative experiment is carried out in each case using the same metal sheet and the same test solution but without addition of the corrosion inhibitor.
The corrosion protection efficiency is obtained by comparison of the loss of mass of the metal sheet tested with and without corrosion inhibitor.
Efficiency [%]=[(ΔM ₀ −ΔM)/(ΔM ₀)]·100.
ΔM₀: Loss of mass of the metal sheet without corrosion inhibitor
ΔM: Loss of mass of the metal sheet with addition of corrosion inhibitor.
Test solution: Demineralized water, 0.03 mol/l NaCl, brought to pH 10 with KOH
Concentration of the corrosion inhibitor in the solution: 1% by weight in each case.
Table 1 shows the corrosion protection efficiency of different novel corrosion inhibitors. A zero sample and a sample containing the conventional corrosion inhibitor monoethanolamine are also run as comparative experiments.
Behavior of the Novel Corrosion Inhibitors in Concrete:
General Working Method:
For testing the migration behavior of the novel corrosion inhibitors, concrete sheets 75 mm long, 20 mm wide and 4 mm thick are used. As in the case of thin-layer chromatography, the concrete sheets are placed perpendicularly in a test solution comprising in each case 10% by weight of the novel corrosion inhibitors in water so that they dip about 1 cm into the solution at the lower edge. In order to prevent evaporation of the test solution, the tests are carried out in a closed vessel, for example a glass jar of suitable size which has a snap-on cover. After 1 day, the test solution has migrated upward to the upper edge of the sheet.
For analysis, a sample is broken off from the upper third of the concrete sheet after one day and is ground, and the phosphorus content is analyzed. The phosphorus content of an untreated concrete sheet was subtracted in each case.

Experiments with 3 different novel compounds were carried out. The results are listed in table 2 and show that the novel compounds have good migration behavior.

TABLE 1


Efficiency of the novel corrosion inhibitors in an alkaline medium

		Hydrolyzed
		to the
	Corrosion inhibitor	monoester	Efficiency
No.	(concentration in each case 1% by weight)	salt	Formula	[%]


Example 5	Product of di (2-methoxyethyl)amine, formaldehyde and di(methylhexaethylene glycol) phosphite (according to example 3)	Yes		65

Example 6	As for example 5	No		30

Example 7	Product of octylamine and di(methylhexaethylene glycol) phosphite (according to example 2)	Yes		92

Example 8	Product of butylamine and di(methylhexaethylene glycol) phosphite (according to example 2)	Yes		73

Example 9	Product of N-methyl-2-ethylhexylamine and di(methylhexaethylene glycol) phosphite (according to example 2)	Yes		75

Example 10	As for example 9	No		39

Comp.	No inhibitor		—	0
example 1
Comp.	Monoethanolamine inhibitor		HO—CH₂—CH₂—NH₂	10
example 2

TABLE 2


P analyses after carrying out migration test in concrete

			P content
No.	Corrosion inhibitor	Formula	[mg/100 g]


Example 11	Product of di(2-methoxyethyl)amine, formaldehyde and di(methylhexaethylene glycol) phosphite		55

Example 12	As for example 11, partly hydrolyzed with NaOH		52

Example 13	Product of butylamine and di(methylpolyethylene glycol) phosphite		40

Claims

1. A corrosion inhibitor which comprises an alkoxy-comprising ester of phosphorus-oxygen acids of the formula

R³—NR⁴ _k—[(CH₂)_n—PO(OR¹)(OR²)]_m (A)
or
[(R¹O)(R²O)OP—(CH₂)_n—]_m—NR⁴ _k—R⁵—NR⁴ _k—[—(CH₂)_n—PO(OR¹)(OR²)]_m (B)

and/or

analkoxy-comprising ester salt of phosphorus-oxygen acids of the formula

R³—NR⁴ _k—[(CH₂)_n—PO(OR¹)(OM)]_m (C)
or
[(MO)(R¹O)OP—(CH₂)_n—]_m—NR⁴ _k—R⁵—NR⁴ _k—[—(CH₂)_n—PO(OR¹)(OM)]_m (D)

where

n is an integer from 0 to 10,

m+k=2 and m is 1 or 2 and k is 0 or 1,

at least one of the radicals R¹, R²and, if appropriate, R³is alkoxy of the formula —[CH₂—CHR⁶—O]_lR⁷, where l is from 2 to 30 and R⁶and R⁷are each H or CH₃,

and, where, they are not alkoxy groups, R¹and R²are straight-chain or branched, unsubstituted or substituted C₁- to C₆-alkyl,

and, where it is not an alkoxy group, R³is straight-chain or branched, unsubstituted or substituted C₁- to C₂₀-alkyl or aryl,

R⁴is H or straight-chain or branched, unsubstituted or substituted C₁- to C₆-alkyl

R⁵is a divalent bridging group, and

M is at least one cation selected from the group consisting of alkali metal, alkaline earth metal or amnionium ions.

2. The inhibitor according to claim 1, wherein the corrosion inhibitor is used in an alkaline medium.

3. The inhibitor according to claim 1, wherein the medium is an aqueous medium.

4. The inhibitor according to claim 1, wherein n is 0 or 1.

5. The inhibitor according to claim 1, wherein k and m are each 1.

6. The inhibitor according to claim 1, wherein l is from 3 to 20.

7. The inhibitor according to claim 1, wherein R⁶is H.

8. An alkoxy-comprising ester salt of phosphorus-oxygen acids of the formula

where

n is an integer from 0 to 10,

m+k=2 and m is 1 or 2 and k is 0 or 1,

at least one of the radicals R¹and, if appropriate, R³is alkoxy of the formula —[CH₂—CHR⁶—O]_lR⁷, where l is from 2 to 30 and R⁶and R⁷are each H or CH₃,

and, where it is not an alkoxy group, R¹is straight-chain or branched, unsubstituted or substituted C₁- to C₆-alkyl,

R⁴is H or straight-chain or branched, unsubstituted or substituted C₁- to C₆-alkyl and

R⁵is a divalent bridging group, and

M is at least one cation selected from the group consisting of alkali metal, alkaline earth metal or ammonium ions.

9. An alkoxy-comprising ester of phosphorus-oxygen acids of the formula

where

n is an integer from 0 to 10,

m+k=2 and m is 1 or 2 and k is 0 or 1,

least one of the radicals R¹, R²and, if appropriate, R³is alkoxy of the formula —[CH₂—CHR⁶—O]_lCH₃where l is from 2 to 30 and R⁶is H or CH₃,

and, where they are not alkoxy groups, R¹and R²are straight-chain or branched, unsubstituted or substituted C₁- to C₆-alkyl,

R⁵is a divalent bridging group.

10. The inhibitor according to claim 2, wherein n is 0 or 1.

11. The inhibitor according to claim 10, wherein k and m are each 1.

12. The inhibitor according to claim 11, wherein l is from 3 to 20.

13. The inhibitor according to claim 12, wherein R⁶is H.

14. The inhibitor according to claim 11, wherein l is from 5 to 15 and n is 1.

15. The inhibitor according to claim 1, wherein R¹or R²is 2-methoxyethyl.

16. The inhibitor according to claim 1, wherein R⁴is H, methyl or 2-methoxyethyl.

17. The alkoxy according to claim 9, wherein R⁴is H, methyl or 2-methoxyethyl.