Note: Descriptions are shown in the official language in which they were submitted.
CA 02524052 2005-10-28
ESTERS OF PHOSPHORUS-OXYGEN ACIDS. THESE ESTERS
COMPRISING ALKOXY GROUPS. AND THEIR USE AS CORROSION
INHIBITORS AND FLAMEPROOFING AGENTS
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 ~aikaline 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 Pike containing an alkaline binder system.
Steel reinforcements embedded irr 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 uncon-oded steel itself. Accordingly, stresses
form in the
concrete that can lead to cracks or to breaking off of whole fragments.
Considerable
e~nomic 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 olio, dissolved Ca(OH)2 and 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 CO~ in the pores results,
inter olio, in
the formation of insoluble CaC03 and the pH of the pore irvater falls to
values below 9.
However, at these pH values, the passivation layer on the~stesl becomes
ineffective.
The effect of the passivation Payer 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 COZ or 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 iri
many cases.
PF 54495
CA 02524052 2005-10-28
2
' 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 phosphoric acids or
phosphoric
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 phosphoric 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, 8. Malric, Construcfion Repair, JulylAugusf 1997" or in US
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 Na2P03F can be used as a
'
migrating con-osion inhibitor. US 5,071,579 also discloses the combined use of
Na2P03F together with~a phosphoric acid of the formula R~R~N(CH2P03HZ)z~, (n=
0 or
1). However, sodium fluorophosphate is hydrolyzed in water and forms insoluble
calcium salts with Ca(OH)2 dissolved in the pore water. Phosphoric 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
CA 02524052 2005-10-28
PF 54495
(A) R3_NR4k-L~CH2)~ PO(OR')~ORZ)lm
or
3
(B) I(R'C)(RZC)Cp-(CI"~2)r, ~m-NR4k-R5-NR4k-~-(CHZ)o-PO(OR~)(CR2))m
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 R', R2 and, if appropriate, R3 is a(koxy of the
formula
-[CH2-CHRs-O],R', where I is from 2 to 30 and Rg and R' are each H or CH3,
and, where they are not alkoxy groups, R' and R2 are straight-chain or
branched
C,- to Cs-alkyl,
and, where it is not an alkoxy group, R3 is straight-chain or branched,
unsubstituted or substituted C~- to C2o-alkyl or aryl,
~ R4 is H or straight-chain or branched C~- to Cs-alkyl and
~ R5 is a divalent bridging group.
In a second aspect of the present invention, alkoxy-comprising ester salts of
phosphorus-oxygen acids of the formula
(C) R3-NR4k-[(CHz)n-PO~OR')(OM)Jm
or
) [(M~)~R'~)~P-(~%H2)n ~r~ NR4k-R5-NR4k~[-(CHz)r; PO(OR')(~M)~m
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 R' and, if appropriate, R3 is alkoxy of the
formula -
[CHZ_CHRs-O],R', where I is from 2 to 30 and Rs and R' are each H or CH3,
and, where it is not an alkoxy group, R' is straight-chain or branched C~- to
Cs-
alkyl,
PF 54495
CA 02524052 2005-10-28
4
and, where it is not an alkoxy group, R3 is straight-chain or branched,
unsubstituted or substituted C,- to C2o-alkyl or aryl,
~ R4 is H or straight-chain or branched C,- to C6-alkyl and
~ RS is a divalent bridging group, and
~ . M is at least one ration 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)2 solution and
form no
sparingly soluble precipitates. Furthermore, the solubility of the monoester
salts in
Ca(OH)2 solution 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
(A) R3-NR4k-I(CHz)n-PO(OR~)(OR2)~m,
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
I(R~O)(R20)OP-(CI"Iz)r, ~m NR4k-RS-NR4k-[-(CHZ)~ PO(OR~)(OR2)Jm~
PF 54495
CA 02524052 2005-10-28
in which two nitrogen atoms are linked to one another via a group RS and 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
5 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)~ PO(OR')(ORz) group is
linked to a
nitrogen atom.
At least one of the~radicals R', RZ and, 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-CHRs-O],R', where I is from 2 to
30 and
. R6 is H andlor CH3., Rs is preferably H, i.e. the alkoxy group is a
polyoxyethylene group.
Preferably, I is from 3 to 20, particularly preferably from 5 to 15. R' is 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 I 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 R', RZ and, 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 substituerits may be, for example, amino or OH. (n
particular,
the substituents may be a terminal OH group.
R' and/,or RZ islare preferably C~- 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.
R3 is preferably C~- to C2o-alkyl or aryl. It is preferably straight-chain or
branched C4- to
~ C,Z-alkyl. Examples of suitable groups comprise methyl, ethyl, n-propyl,
isopropyl, n-
PF 54495
CA 02524052 2005-10-28
6
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 w-methoxyalkyl
group, e.g.
methoxyethyl. Aryl groups may be pure aryl groups, such as alkyl-substituted
aryl
groups, for example a -CH2C5Hs group.
If present, R4 is H or straight-chain or branched, unsubstituted or
substituted alkyl,
preferably C~- to C6-alkyl. Particularly preferably, R4 is H or methyl. A
substituted alkyl
group may be in particular 2-methoxyethyl.
No R3 is present in the bridged compound (B), but instead a divalent bridging
group R5
which 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 CH2 groups may also be Substituted by O or N atoms. Examples
comprise -(CHz)r, -(CHZ)a-, -(CH2)s-, -(CH2)s-, -(CH2)2-O-(CH2)2-,
-(CH2)z-O-(CHZ)a-O-(CHz)z-, -(C'H2)3-O-(CH2)4-O-(CH2)3-s
-(CHZ)s-O-(CHZ)2-O-(CH2)z-O-(CH2)s-. -(Ci"IZ)2-~-(CHz)z-O-(CHZ)z-O-(CHZ)2-,
-(CHz)z-O-[(CHz)z-O ~i(CHZ)2-O-(CHZ)2-~-(CHz)z-HN-(CHZ)2- and -(CHZ)rNRs-
(CH2)r
NR6-(CHZ)2- groups, where j is from 1 to 10 and Rs is alkyl, -(CHZ)~
PO(OR')(OR2) or .
-(CHZ)~ PO(OR')(OM).
Said groups are preferably -(CH2)2-, -(CHZ)4-, -(CH2)s-, -(CH2)3-O-(CH2)4-O-
(CH2)3-,
. -(CHZ)rO-(CHZ)i-O-(CH2)z- or-(CHZ)2-O-(CHz)z-O-(CHZ)Z-O-(CH2)2- groups.
Among the various possible combinations of the radicals R' to R', 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
R' and R2 is
alkoxy. Preferably, however, both R' and R2 are alkoxy.
Migrating corrosion inhibitors which have proven particularly useful are the
following
compounds:
(2-ethylhexyl)-N(CH3)-(CHZ)-PO(O-alkoxy)(O-alkoxy),
(2-ethylhexyl)-N[-(CHz)-PO(O-alkoxy)(O-alkoxy)]2,
butyl-NH-PO(O-alkoxy)(O-alkoxy),
octyl-NH-PO(O-alkoxy)(O-alkoxy),
(2-ethylhexy!)-NH-PO(O-alkoxy)(O-a(koxy),
(2-ethylhexyl)-N(CH3)-PO(O-alkoxy)(O-alkoxy),
PF 54495
CA 02524052 2005-10-28
7
(al koxy)-N H-PO (O-al koxy)(O-al koxy),
(alkoxy-O)(alkoxy-O)OP-NH-(CHZ)2-O-(CHz)2-O-(CH2)Z-NH-PO(O-alkoxy)(O-alkoxy).
(2-methoxyethyl)ZN-CHZ-PO(O-alkoxy)(O-alkoxy),
(ethyl)zN-CH2-PO(O-alkoxy)(O-alkoxy),
(CH2)5N-CHZ-PO(O-alkoxy)(O-alkoxy),
(alkoxy-O)(alkoxy-O)OP\N( ~2)ZN-CHZ-PO(O-alkoxy)(O-alkoxy),
(CH2)2
In the novel ester salts
(C) R3-NR4k-[(CH2)~ PO(OR')(OM)]m
and
(D) ((MO)(R'O)OP-(CHZ)~ Jrt; NR4k-R5-NR4k-[-(CH2)~ PO(OR')(OM))rt,
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), R' is always ~alkoxy;:in the case of (C), either R'
or R3 may be
alkoxy, or R' and R3 together.
M is at least one ration 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 (HOCHzCH2)3NH+,
(HOCH2CH2)2NH2'", HOCH2CH2NH3+ or HOCHZCH2N(CH3)2H+, or else
. tetraalkylammonium ions, for example tetramethylalmmonium or
tetraethylammonium.
Na+, K', Mg'+,. Ca++, Ce+++; AI+++, Zn+'' and NH4'' are preferred. The above
formulae
represent only the case of monovalent rations for the sake of simplicity. A
person
skilled in the art can, however, readily derive therefrom the correct formulae
for
30. polyvalent rations. . .
The novel diesters of phosphorus-oxygen acids can be prepared, for example,
starting
from commercially available phos,phonic 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.
. CA 02524052 2005-10-28
PF 54495
8
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 CCI4 and a tertiary amine as a catalyst. The use of diarnines,
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 Bronsted 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.
PF 54495
CA 02524052 2005-10-28
9
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.
25.
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, zinclnickel,
zinclmanganese or
zinclcobalt 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.
CA 02524052 2005-10-28
PI= 54495
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
5 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.
10 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 ofd 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:
PluriolO A 275E. : methylpolyethylene glycol ether, Mw 275 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 -CHZCH20- units present.
For the experiments, it is also possible to use other methylpolyethylene
glycol ethers
having .other average molecular weights MW, e.g. Pluriol~ A 350E (MW 350
g/mol) or
Pluriol~ A 500E (MW 500 g/mol).
Example 1:
Preparation of di(methylhexaethylene glycol) phosphite
o K.(Cat.) o
~O~H O~ . + . ~O~O _EH~ ~O~O.H O~O
Diethyl phosphite (12.8 g, 0.093 mol) and P(uriol A 275 E (50g, 0.186 mol) are
initially
taken together° in a 500 ml flask. After the addition of potassium (20
mg, 0.5 mmol) as a
PF 54495
CA 02524052 2005-10-28
11
' 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,
phosphoric esters having other ester groups can be obtained_
In an alternative method of preparation, di(methyihexaethylene glycol)
phosphate is also
prepared by direct ethoxylation of phosphoric acid.
Example 2:
Preparation of 2-ethylhexylphosphoramide di(methylhexaethylene glycol) ester
CHZCH2/ CCIa O
NH ~ Et~N II
3 Z .~ H~P~ORS ~ HN5 O OR,
ORz Et3N HCI + CHCI3 R Rz
-
62.0 g (0.092 mol) of the di(methylhexaethylene glycol) phosphate obtained
according
to example 1 are dissolved in a 1:1 CChlCH2C12 (185 ml) mixture, and 2-
ethylhexylamine (11.9 g, 0.092 mol) is added (R3 iri 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 phosphoric ester. Instead of 2-ethylhexylamine, other amines can also
be used.
Example.3:
Preparation of di(methylhexaethylene glycol) N-methyl-N-2-
ethylhexylaminomethyl-
phosphite
0
H~C~NH + H.P~OR' -1- CHZO . Hue,.,. H~C~N~p-ORS
R ORZ . R3 O~ .
Di(methylhexaethylene glycol) phosphate (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,
PF 54495
CA 02524052 2005-10-28
12
' S% 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.
o , ~ o o°Hi\ o
NHZ + H~P~pR~ .~. CHZO ~, HN~p-ORZ -E ~O P'ORZ'
Octyl ORi Octyi ORi O~ R,
Example 4:
Preparation of di(hydroxyhexaethylene glycol) N-methyl-N-2-
ethylhexylaminomethyl-
phosphite
o . o
H'C~IJH .f. ~P~OH .H CH2~--a HzC~N~P~OH
R' H OH R' OH
A
p H c ~o
H~C~N~p-OH U s ~ ~N P~OR~
R3 OH
A . ~ ~ B
1 st 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 I
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.
PF 54495
CA 02524052 2005-10-28
13
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-
s 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 3'P,'H and '3C-
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 x 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 [%J = [(dMo -dM)l( dMa)J~ 7 00.
dMo: Loss of mass of the metal sheet without corrosion inhibitor
dM; Loss of mass of the metal sheet with addition of corrosion inhibitor.
Test solution: Demineralized water, 0.03 moll NaCI, 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
CA 02524052 2005-10-28
PF 54495
14
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.
Expetiments 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.
CA 02524052 2005-10-28
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