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Title:
NITROSAMINE/NITRITE INHIBITION IN TERTIARY ALKYLAMINE OXIDE COMPOSITIONS
Document Type and Number:
WIPO Patent Application WO/2015/104673
Kind Code:
A9
Abstract:
The invention relates to a method for the production of tertiary amine oxides with and prevented and/or reduced nitrosamine formation and/ or reduced nitrite formation, comprising the steps of: during or after the production of the aforementioned tertiary amine oxide, adding a mixture comprising a polyamino methylene phosphonate of formula (I) wherein n=2-1500, M is hydrogen or a cation selected from alkali metals, alkaline earth metals and ammonium, and the R groups are the same or different from one another with at least one R group different from CH2PO3M2 and selected from the following classes: 1) CH2PO3M2, 2) CH2R', wherein R'=CH2OH; CHOHCH3; CHOHCH2Cl or CHOHCH2OH, 3) (CH2)nSO3M, wherein n=3 or 4, 4) CH2CH2R", wherein R"=CONH2, CHO, COOR1, COOX or CN, wherein R1 =CH3 or C2H5, wherein X is hydrogen or an alkali metal or ammonium cation. The invention also relates to tertiary amine oxide composition with improved nitrosamine contents and/or nitrite contents; as well as use of the aforementioned polyamino methylene phosphonates as nitrosamine inhibitor and/or as nitrite inhibitor

Inventors:
DE RYCKE, Daisy Sofie (Keuzelingsstraat 29, Kluisbergen, B-9690, BE)
UYTTERSPROT, Katrijn (Fierensveld 14, Erpe-Mere, B-9420, BE)
TAELMAN, Marie Claire Leona Hilda (Lindestraat 2, Wortegem-Petegem, B-9790, BE)
VEHENT, Dirk Cyriel (Daknam-Dorp 3, Lokeren, B-9160, BE)
Application Number:
IB2015/050149
Publication Date:
January 07, 2016
Filing Date:
January 08, 2015
Export Citation:
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Assignee:
EOC SURFACTANTS NV (Durmakker 35, Evergem, B-9940, BE)
International Classes:
C07C291/04; C11D1/75; C11D3/36
Attorney, Agent or Firm:
BRANTSANDPATENTS BVBA (ASSOCIATION 503) (Pauline Van Pottelsberghelaan 24, Ghent, B-9051, BE)
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Claims:
CLAIMS

A method for the production of tertiary amine oxides with prevented and/or reduced nitrosamine formation and/or reduced nitrite formation, comprising the steps of:

during or after the production of the afore-mentioned tertiary amine oxide, addin of a polyamino methylene phosphonate of formula (I)

wherein n=2-1500,

M is hydrogen or a cation selected from alkali metals, alkaline earth metals and ammonium, and the R groups are the same or different from one another with at least one R group different from CH2PO3M2 and selected from the following classes:

2) CH2R' R'=CH2OH; CHOHCH3; CHOHCH2CI or CHOHCH2OH;

3) (CH2)nS03M wherein n = 3 or 4

4) CH2CH2R" wherein R"=CONH2, CHO, COOR1, COOX or CN;

where R1=CH3 or CH2H5;

wherein X is hydrogen or an alkali metal or ammonium cation.

Method according to claim 1, wherein the tertiary amine oxide is selected from the list cocamine oxide, cocamidopropylamine oxide, laurylamidopropyiamine oxide, lauramine oxide, myristamine oxide, lauryl/myristylamidopropylamine oxide, decylamine oxide.

Method according to claim 1 or 2, wherein the tertiary amine oxide is produced within a reaction time of 50 hours when a reaction temperature of 50 °C is used; and within a reaction time of 30 hours, preferably less than 25 hours, when a reaction temperature of 70 °C is used.

Method according to one of the preceding claims, wherein n=2-50.

Method according to one of the preceding claims, wherein when n=2, at least two R groups differ from CH2PO3M2.

Method according to one of the preceding claims, wherein the amine oxide is produced by reaction of a tertiary amine with hydrogen peroxide in the presence of a mixture comprising 0,05 - 20,0% by weight, based on the weight of the amine, of (a) a carbonate or bicarbonate, and 0,05 - 5,0% by weight, based on the weight of the amine, of said polyamino methylene phosphonate (b).

7. Method according to one of the preceding claims, wherein at least a part of the polyamino methylene phosphonate (b) is added to the amine oxide before and/or after the production thereof; preferably before and after production.

8. A composition obtained according to one of the methods according to claims 1-7.

9. A composition comprising a tertiary amine oxide and a polyamino methylene hosphonate of formula (I)

wherein n=2-1500,

M is hydrogen or a cation selected from alkali metals, alkaline earth metals and ammonium; and the R groups are the same or different from one another with at least one R group different from CH2PO3M2 and selected from the following classes:

2) CH2R' R'=CH2OH; CHOHCH3; CHOHCH2CI or CHOHCH2OH;

3) (CH2)nS03M wherein n = 3 or 4

4) CH2CH2R" wherein R"=CONH2, CHO, COOR1, COOX or CN;

where R1=CH3 or CH2H5;

wherein X is hydrogen or an alkali metal or ammonium cation.

10. Composition according to claim 9, wherein the tertiary amine oxide is cocamidopropylamine oxide, laurylamidopropylamine or lauryl/myristylamidopropylamine.

11. Composition according to one of the preceding claims, wherein n=2-50.

12. Composition according to one of the preceding claims, wherein n=2 and at least two R groups differ from CH2PO3M2.

13. Composition according to one of the preceding claims, having a nitrosamine content below 500 ppb in a solution with a tertiary amine oxide solids content comprised between 36.0-38.0 Brix%, measured by gas chromatography in combination with a thermal energy analyzer (GC-TEA).

14. Composition according to one of the preceding claims, with an amido-amine content of maximum 1%, expressed in % by weight with respect to the total composition.

15. Composition according to one of the preceding claims, with a nitrite content of maximum 2000 ppb, measured by ion chromatography (IC).

16. Use of a polyamino methylene phosphonate of formula (I)

wherein n=2-1500,

M is hydrogen or a cation selected from alkali metals, alkaline earth metals and ammonium; and the R groups are the same or different from one another with at least one R group different from CH2PO3M2, and selected from the following classes:

2) CH2R' R'=CH2OH; CHOHCH3; CHOHCH2CI or CHOHCH2OH;

3) (CH2)nS03M wherein n = 3 or 4

4) CH2CH2R" wherein R"=CONH2, CHO, COOR1, COOX or CN;

where R1=CH3 or CH2H5;

wherein X is hydrogen or an alkali metal or ammonium cation

as inhibitor for preventing or suppressing nitrosamine formation and/or reduced nitrite formation in a tertiary amine oxide solution.

Description:
NITROSAMINE/NITRITE INHIBITION

IN TERTIARY ALKYLAMINE OXIDE COMPOSITIONS

TECHNICAL FIELD

The invention relates to the suppression/prevention of nitrosamine formation in tertiary alkylamine oxide compositions by means of special polyamino methylene phosphonates and related salts. The invention also relates to tertiary alkylamine oxide compositions with reduced contents of nitrosamine. More particularly, the invention relates to the field of surfactants which are sensitive to nitrosamine contamination. These polyamino methylene phosphonates and related salts have also shown to be effective for suppression of nitrite formation in the synthesis of tertiary alkyl amine oxides. BACKGROUND

It is known that nitrosamines, which are generally considered to be harmful, and nitrites, which can be precursors for nitrosamines, are present in amine oxide compositions. Typically, these contaminants are present in commercial amine oxide compositions at contents between 800 and 4000 ppb.

EP 0 608 793 discloses a method for the preparation of amine oxides by a reaction of an amine with hydrogen peroxide in the. presence of sodium bicarbonate and various nitrosamine/nitrite inhibitors, such as sodium diethylenetriamine pentakis- (methylenephosphonate) and sodium tetraethylenepentamine heptakis- (methylenephosphonate).

Because of the carcinogenicity of nitrosamines, pressure increasingly grows to reduce their contents. Improved methods of analysis allow to determine contents of ATNC (Apparent Total Nitrosatable Content) expressed as NNO lower than 50 ppb "total NNO" and wherein nitrite, expressed as "total NO", is the sum of the nitrosamines and volatile nitrites. Consequently, the search is also started for methods to prevent the formation of these contaminants, or to suppress them as far as possible.

The present invention aims to find a solution for at least some of the abovementioned problems. The invention aims to improve the final specifications of tertiary alkyl amine oxide products and to reduce the content of by-products. Process improvements should be economically feasible, i.e. in terms of cost and reaction time.

SUMMARY

The invention provides a solution thereto by providing an improved method of synthesis for amine oxide compositions. Also, the invention relates to compositions with reduced contents of nitrosamine and use of an inhibitor to reduce nitrosamine contents. The inhibitor can be used for the suppression of nitrite content.

In a first aspect, the invention provides a method for the production of tertiary alkyl amine oxides with prevented and/or reduced nitrosamine formation and/or reduced nitrite formation, comprising the steps of:

during or after the production of the aforementioned tertiary alkyl amine oxide, adding a mixture comprising

(a) a carbonate or bicarbonate and

(b a polyamino methylene phosphonate of formula (I)

wherein n=2-1500,

M is hydrogen or a cation selected from alkali metals, alkaline earth metals and ammonium,

and the R groups are equal or different from one other with at least one R group different from ChhPC l^ and selected from the following classes:

1) CH 2 P0 3 M 2

2) CH 2 R' R'=CH 2 OH; CHOHO ; CHOHCH 2 CI or CHOHCH2OH;

3) (CH2) n S0 3 M wherein n = 3 or 4

4) CH 2 CH 2 R" wherein R"=CONH 2 , CHO, COOR1, COOX or CN;

where R1=CH 3 or CH 2 H 5 ;

wherein X is hydrogen or an alkali metal or ammonium cation. The inventors have found that with this mixture, the final specifications of tertiary alkyl amine oxides could be improved. By the improvement of the final specifications is particularly meant, the content of nitrosamines of an amine oxide composition and/or its colour stability. Preferably, also the nitrite content is reduced as a result of the use of formula (I) compound.

In a second aspect, the invention provides a composition obtained according to a method of the invention.

Compositions with reduced nitrosamine contents were obtained by the presence of the mixture. An advantage of the compositions is their stability over longer periods of time. Stability refers to the colour stability and/or stability of the content of nitrosamines. Additionally, the content of nitrite may also be reduced.

In a third aspect, the invention provides a composition comprising a tertiary alkyl amine oxide, a carbonate or bicarbonate and a polyamino methylene phosphonate of formula (I) as described above. The tertiary alkylamine oxide compositions, in particular cocamidopropylamine oxide compositions, meet stricter final specifications in regard to nitrosamines and amido- amine residual content. Preferably, this is also the case for the nitrite content.

In a fourth aspect, the invention provides the use of the aforementioned polymethylene phosphonates for preventing or suppressing nitrosoamine formation in a tertiary alkyl amine oxide solution. Aforementioned polymethylene phosphonates can also be used for reducing the content of nitrite in a tertiary alkylamine oxide solution.

The use of the aforementioned polymethylene phosphonates has proven to be very advantageous to stabilize tertiary alkylamine oxide compositions. Strict final specifications in terms of nitrosamines and amido-amine residual content are attainable without sacrificing reaction time. Using polymethylene phosphonates as aforementioned, in the synthesis of tertiary alkyl amine oxide compositions offers as an advantage that nitrite formation is reduced.

Further improvements have been set out in the dependent claims. DETAILED DESCRIPTION OF THE INVENTION

Unless defined otherwise, all terms used in the description of the invention, including technical and scientific terms, have the meaning as commonly understood by the skilled person in the technical field of the invention. For a better assessment of the description of the invention, the following terms are explained explicitly.

"A", "an" and "the" refer in this document to both the singular and the plural, unless the context clearly implies otherwise. For example, "a segment" means one or more than one segment.

Where "about" or "about" are used in this document with a measurable quantity, a parameter, a time period or moment in time, and the like, then variations are meant of +/-20% or less, preferably +/- 10% or less, more preferably +/-5% or less, even more preferably or less, to the extent that such variations apply in the described invention. It should, however, be understood that the value of the quantity in which the term "about" or "around" is used, is itself specifically disclosed.

The terms "comprise", "comprising", "consist of", "consisting of", "provided with", "contain", "containing", "include", "including", "encompass", "encompassing" are synonyms and are inclusive or open terms which indicate the presence of what follows, and which do not exclude or prevent the presence of other components, features, elements, members, steps, known from and described in the prior art. The quoting of numerical intervals by endpoints includes all integers, fractions and/or real numbers between the endpoints, these endpoints included.

Surprisingly, it has been found that specific polyamino methylene phosphonate derivatives were able to reduce nitrosamine formation and/or nitrite formation much more than what was previously possible with other inhibitors. Therefore, these polyphosphonates that can be applied for nitrosamine reduction, are the main subject of the present invention.

In general, such compounds can be the derivatives of polyamino methylene phosphonates of the following general formula : M2O3PH2C CHoPOjMa (I)

wherein n is an integer comprised between 2 and 1500, preferably between 2 and 50, more preferably 2, the endpoints included; M2 may be hydrogen or a suitable cation such as an alkali metal, alkaline earth metal or ammonium, and each R group may be the same or different and is preferably selected from the following classes: 1. CH2PO3M2 wherein M is hydrogen or a suitable cation such as alkali metal or ammonium;

CH 2 R' wherein R'=CH 2 OH; CHOHCH 3 ; CHOHCH2CI or CHOHCH 2 OH;

(CH2) n S0 3 M wherein n = 3 or 4 where M is hydrogen or a suitable cation such

as alkali metal or ammonium;

4. CH2CH2R" wherein R"=CONH 2 , CHO, COOR1, COOX or CN;

where R1=CH 3 or CH 2 H 5 ;

wherein X is hydrogen or a suitable cation such as alkali metal or ammonium;

yet at least one of the substituents R should be different from the methylene phosphonated group, i.e. other than CH2PO3M2.

These polyamino methylene phosphonate compounds are described in WO 2005/073130, US 7659315 and EP 1 525 206.

Methods of preparation for these phosphonates are known. They can be prepared by means of a phosphonomethylation reaction of a polyamine or polyamine mixture, by means of a Mannich reaction as follows:

HCI II

-NH + HCHO + h PO -NCH 2 P{OH) 2

The phosphonomethylation reaction of amines according to Mannich is described in the literature, as, for example, by Moedritzer and Irani in J. Organic Chem. 31 (5), of phosphorous acid and hydrochloric acid. The reaction mixture thus obtained is heated under reflux with addition of formaldehyde. The reaction time usually ranges between 1 and 5 hours.

Suitable polyamino methylene phosphonate derivatives of formula (I) for use in the present invention are Hydrodis WP20, WP40 and Hydrodis Hydrodis WP56, available at Giovanni Bozzetto S.p.A, Italy. Hydrodis WP20 exhibits an inhibitory effect on the formation of nitrosamines. Additional tests have shown that Hydrodis WP40 and Hydrodis WP56 exhibit an even better inhibitory effect. Further research has shown that these compounds also have a favourable effect since nitrite formation is suppressed.

By the term "inhibitory effect", "inhibition" as used herein, is meant that the additive has an impact on the formation of nitrosamines, wherein the formation of nitrosamines is prevented and/or suppressed.

The inhibitory effect was unexpected since a good effect was rather expected to occur with monomers, rather than with oligomers or polymers as is the case in the present phosphonates. A further advantage is the compatibility with the catalyst carbonate or bicarbonate. No negative impact on the colour of the end product was found.

The present invention relates to a process for the production of tertiary alkyl amine oxides with prevented and/or reduced nitrosamine formation and/or nitrite formation, comprising the steps of: during or after the production of the aforementioned tertiary alkyl amine oxide, adding a polyamino methylene phosphonate of formula (I)

n

wherein n=2-1500,

M is hydrogen or a cation selected from alkali metals, alkaline earth metals and ammonium,

and the R groups are the same or different from one another with at least one R group different from CH2PO3M2 and selected from the following classes: 1) CH2PO3M2

2) CH 2 R' R'=CH 2 OH; CHOHCH3; CHOHCH2CI or CHOHCH 2 OH;

3) (CH2) n S0 3 M wherein n = 3 or 4

4) CH2CH2R" wherein R"=CONH 2 , CHO, COOR1, COOX or CN;

where R1=CH 3 or CH 2 H 5 ;

wherein X is hydrogen or an alkali metal or ammonium cation.

In a preferred embodiment, n=2-50. In a preferred embodiment, n is equal to 2 and at least two R-groups differ from CH2PO3M2. In a preferred embodiment, the amine oxide is produced by reaction of a tertiary alkyl amine with hydrogen peroxide in the presence of a mixture comprising 0,05 to 20 percent by weight, based on the weight of the amine, of (a) a carbonate or bicarbonate, and (b) 0,05 to 5 percent by weight, based on the weight of the amine, of afore-mentioned polyamino methylene phosphonate. More preferably, the mixture comprises 0,075-2 percent by weight, most preferably 0.10-0.30 percent by weight of carbonate or bicarbonate (a).

More preferably, the mixture comprises 0,5-1 percent by weight, most preferably 0.1-0.3 percent by weight of afore-mentioned polyamino methylene phosphonate

(b). Most preferably, 0,1-0,3% of carbonate or bicarbonate (a) and 0,1-0,3% of aforementioned polyamino methylene phosphonate (b) is used.

Preferably, 0,1% inhibitor is used, expressed with respect to the amido-amine or amine raw material for the preparation of the tertiary alkylamine oxide.

Carbonate or bicarbonate is a preferred catalyst for the conversion of a tertiary alkylamine with the aid of hydrogen peroxide to a tertiary alkylamine oxide. These catalysts are compatible with the use of afore-mentioned polyamino methylene phosphonate inhibitor.

In a preferred embodiment of a method according to the invention, the tertiary alkylamine oxide is selected from the list cocamine oxide (chemical name: cocodimethylamine oxide), cocamidopropylamine oxide (chemical name: cocoamidopropyldimethylamine oxide), laurylamidopropylamine oxide (chemical name: laurylamidopropyldimethylamine oxide), lauramine oxide (chemical name: lauryl/myristylamidopropylamine oxide (lauryl/myristylamidopropyldimethylamine oxide, decylamine oxide (decyldimethylamine oxide) Mixtures of oxides from the list are also possible.

In a preferred embodiment of a method according to the invention, the tertiary alkyl amine oxide is cocamidopropylamine oxide (chemical name: cocoamidopropyldimethylamine oxide).

The structural formula for cocamidopropylamine is as follows, as shown by means of formula (II), wherein R represents a C8 to C18 alkyl.

(Π) Cocamidopropylamine oxide is a non-ionic surfactant. This substance is characterized by its activity as foaming agent and foam stabilizer, as antistatic agent, as mild conditioner, and is also used for the build-up of viscosity. This substance is classified under the non-ionic surfactants and is mainly used in household dishwasher liquids, for the cleaning of hard surfaces, in chlorine bleaches, in toilet cleaners and cleaning products for cars. It is also applied in cosmetics, and mainly in body and facial cleansers and shampoos.

The synthesis of cocoamidopropylamine oxide is known. A method to produce this active substance is the reaction of cocamidopropylamine with hydrogen peroxide using sodium bicarbonate as catalyst. Hydrogen peroxide is added to a reaction mixture having a pH lower than 9 so that the peroxide would not dissolve.

In another preferred embodiment of a method according to the invention, the tertiary alkylamine is laurylamidopropylamine or lauryl/myristylamidopropylamine.

Laurylamidopropylamine has a structural formula as shown by formula (II) wherein R is a C12 alkyl residue. In lauryl/myristylamidopropylamine, the R part is a C12/C14 alkyl residue, i.e. the number of hydrocarbon atoms in the alkyl tail is 12/14.

Tertiary alkyl amines can act as precursors for the formation of nitrosamines. Once formed, they are stable and cannot be dissolved easily. The ease with which nitrosamines are formed, is dependent on the structure of the compound, the nature of the medium and the possible presence of a catalyst.

In a preferred embodiment, the tertiary alkylamine oxide is produced within a reaction time of 50 hours when a reaction temperature of 50 °C is used; and within a reaction time of 30 hours, preferably less than 25 hours, when a reaction temperature of 70 °C is used. Limiting the reaction time has an economic relevance. An increase in the reaction temperature and thus shortening the reaction time is not evident, since nitrosamine formation mostly increases at elevated temperatures.

In a preferred embodiment, at least a part of afore-mentioned polyamino methylene phosphonate derivate is added to the amine oxide before and after the production thereof (pre and post-synthesis addition).

In a preferred embodiment, the polyamino methylene phosphonate derivate was obtained by means of a two-step reaction :

step 1 : reaction of N,N'-bis(2-amino-ethyl)ethane-l,2- diamine(triethylenetriamine) (I) with ethylene oxide (II) in a weight ratio

(I)/(II) 1.659/1;

step 2: phosphono methylation of the product obtained in step 1 with formaldehyde and H3PO3 according to reaction (A)

-NH + HCHO + H3PO3 ~» -NHCH 2 PO(OH) 2

wherein the weight ratio of the product obtained in step 1 / formaldehyde/phosphorous acid is 1/0,05376/1,430;

wherein the P31-NMR analysis of the thus obtained product shows that at least 90% of the amino groups in step 2 were phosphonomethylated.

In a second aspect, the invention relates to compositions directly obtained according to a method of the invention.

In a further aspect, the invention relates to a composition comprising a tertiary alkylamine oxide, and a polyamino methylene phosphonate of formula (I)

R R 2O 3 PH 2 C CH2PO3 2 (!) wherein n=2-1500,

M is hydrogen or a cation selected from alkali metals, alkaline earth metals and ammonium,

and the R groups are the same or different from one another with at least one

R group different from CH2PO3M2 and selected from the following classes:

2) CH 2 R' R'=CH 2 OH; CHOHCH 3 ; CHOHCH2CI or CHOHCH 2 OH;

3) (CH2) n S0 3 M wherein n = 3 or 4

4) CH2CH2R" wherein R"=CONH 2 , CHO, COOR1, COOX or CN;

where R1=CH 3 or CH 2 H 5 ;

wherein X is hydrogen or an alkali metal or ammonium cation. Preferably, in a composition according to the invention, n=2-50. When n=2, preferably at least two R groups differ from CH2PO3M2.

In a preferred embodiment of a composition according to the invention, the nitrosamine content is under 500 ppb and preferably lower than 100 ppb. For the measurement, gas chromatography in combination with a thermal energy analyzer (GC-TEA) is used. In measurements using this technique, the so-called apparent total N-nitroso compounds (ATNC) are determined by a chemical denitrosation and detection of the released dinitrogen(mono)oxide and reported in terms of dinitrogen(mono)oxide (nitrous oxide, NNO) in pg/kg (ppb). This content is also determined by denitrosation of an N-nitrosodiisopropanolamine (NDiPLA) calibration standard.

In a preferred embodiment of a composition according to the invention, the nitrite content is less than 2000 ppb, measured by ion chromatography (IC). Compositions obtained without the use of an inhibitor according to the invention have a nitrite content higher than 2000 ppb. Cocamidopropylamine oxide is a substance which is already being used in detergent applications, but by reducing the toxicity profile, it will allow this substance to also be used in cosmetic applications, in which the contact with the human body is the most relevant. In another preferred embodiment, the tertiary amine oxide is laurylamidopropylamine or lauryl/myristylamidopropylamine.

In a final aspect, the invention provides the use of the aforementioned polyamino methylene phosphonates, for preventing or suppressing nitrosoamine and the formation in a tertiary amine oxide solution. Afore-mentioned polyamino methylene phosphonates act as inhibitors of nitrosamine formation.

In an additional final aspect, the invention provides the use of the afore-mentioned polyamino methylene phosphonates, for suppressing the formation of nitrite in a tertiary amine oxide solution. Afore-mentioned polyamino methylene phosphonates act as inhibitors of nitrite formation.

In what follows, the invention is described with reference to non-limiting examples which illustrate the invention, and which should not be intended or interpreted as to limit the scope of the invention.

EXAMPLES

General method for cocamidopropylamine oxide

To a three-neck flask of 1000 ml, demi-water and citric acid were added. The acid was added in order to keep the pH of the reaction mixture below 9. Subsequently, cocamidopropylamine and hydrogen peroxide were added. The reaction mixture was heated to a desired temperature of either 50 °C or 70 °C. Upon reaching the desired reaction temperature, sodium bicarbonate was added. The pH of the reaction mixture is maintained between 7,0 and 7,5. If necessary, NaOH is added. The final product has a dry matter content of between 36,0 and 38,0 Brix%.

In the examples described below, different additives were tested for their ability to inhibit the formation of nitrosamines. Each time, during the reaction, an amount of inhibitor was added which corresponds to 0,1% by weight of the amount of added amido-amine raw material. The resulting compositions were listed in Table 1. The nitrosamine content was determined with the aid of a chemical denitrosation technique and measurement with a thermal energy analyzer. The detection limit of the method used was 50 pg total content of N-nitroso compounds/kg .

The amido-amine residual content was determined in the final product obtained. The amine oxide was converted to amide by reflux with acetic acid anhydride whereby the amido-amine does not react. A sample is then diluted with methanol and injected onto an Ultimate 3000 high pressure liquid chromatograph. The separation took place on a reversed-phase Luna 3 U CN 100 A and the detection was done with a UV detector. The amido-amine concentration was determined using a calibration curve and standards.

Example 1 (samples 1 and 2V. polyamine methylene phosphonate To the reaction mixture, the polyamino methylene phosphonate Hydrodis WP20 was added, in an amount of 0,1 percent by weight on amido-amine. This resulted in a low content of nitrosamines. All this could be achieved within a relatively short reaction time. Example 2 (samples 3 and 4) : no additive

In a comparative test, no additive was added. This resulted in a higher content of nitrosamines and free amido-amine residual content. Example 3 (samples 5 and 6) : DTPA Na

In a comparative test, 0, 1 percent by weight, with respect to the amido amine, of diethylene triamine pentaacetic acid (DTPA Na) was added. By using this additive, it was, at 50 °C reaction temperature, not possible to obtain a final specification below 0,3% of amido-amine residual content within an acceptable reaction time. Increasing the reaction temperature to 70 °C made this possible, yet the colour of the final product became unacceptably high, i .e. above 100 Apha.

Example 4 (samples 7 and 81 : DTPMP

In a comparative test, diethylenetriamine penta(methylene phosphonic acid) (DTPMP) was added. The specifications related to colour and the residual content of amido-amine were achieved. At a reaction temperature of 50 °C, a long reaction time was required for this. Both samples showed an excessive content of nitrosamines. The additive is insufficiently able to inhibit the formation of nitrosamines. Example 5 (samples 9 and 10) : EDTA

In a comparative test, ethylenediaminetetraacetic acid (EDTA) was added. The specifications related to colour and the residual content of amido-amine were achieved . At a reaction temperature of 50 °C, a long reaction time was required for this. Both samples showed an increased content of nitrosamines compared to the Hydrodis 20WP additive. The additive is insufficiently able to inhibit the formation of nitrosamines.

Colour stability (Examples 1 and 2)

In addition to a positive influence on nitrosamines, it was also found that a method according to an embodiment of the invention results in compositions which exhibit a less pronounced increase in colour during storage at 30 °C. The products are less yellow with respect to compositions without the use of an inhibitor or even with respect to compositions with another inhibitor. This improved colour stability is an important advantage. The compositions are processed in compositions in which colour is an important aspect.

Example 6: long term stability at room temperature

After a storage time of 10 months, measurements were again carried out on a sample produced according to the description in example 1. The results are shown in Table 2. Only a slight increase was observed in colour and nitrosamine content. This indicates an improved storage stability of a tertiary amine oxide stabilized with polyamino methylene phosphonate.

Table 2: Long-term storage stability

Example 7: Production Test

As a comparative test, a production batch of cocamidopropylamine oxide was produced with and without inhibitor. As catalyst, sodium bicarbonate was used. As inhibitor, Hydrodis WP20 was used. The production batches were kept separately in the factory. Samples were taken on which the nitrosamine content was determined by GC-TEA. The results are summarized in Table 3. These show that because of the use of the inhibitor, the nitrosamine content in the final product is significantly lower, in comparison with the previously used method; more particularly, lower than 300 ppb with respect to nearly 800 ppb.

Example 8: Production test at various temperatures In this test, cocamidopropylamine oxide was produced at various temperatures. Other parameters such as duration of reaction, catalyst, inhibitor were kept constant. The reaction temperature was varied. The results show the temperature dependence of the nitrosamine formation. The reaction temperature is preferably kept below 70 °C, more preferably below 60 °C.

Table 4: Production test at various tem eratures

Table 1 : Summary of the synthesis tests with candidate inhibitors and the measurement results on the compositions

/ = not measured

5 Table 3 : Production test with inhibitor Hydrodis WP 20

Example 9 : Suppression of nitrosamine and nitrite formation

Lauramine oxide (chemical name: lauryldimethylamine oxide) was made without or with inhibitor Hydrodis WP20, a poiyamino methylene phosphonate according to formula I, commercially available at Bozetto. 0.13% of Hydrodis WP20 was added, expressed with respect to the amount of amine used. Tmax was not higher than 50 °C. Reaction time was maximum 17h.

The nitrite content was measured using ion chromatography. The nitrosamine content was measured with the aid of a chemical denitrosation technique and measurement with a thermal energy analyzer.

Table 5: Production batches of lauryl amine oxide without stabilizer

Table 6: Production batches of lauryl amine oxide with Hydrodis WP20 stabilizer

Reaction Inhibitor Nitrite nitrosamine

Batch Tmax duration (h) (%) (ppb) (ppb NNO)

1 65,5 12,5 0,13 568 < 17

2 61,4 13 0,13 320 < 17

3 64,9 13,5 0,13 763 <17

4 not

64,5 14 0,13 738 measured

5 not

66,2 17 0,13 739 measured Example 10: suppression of nitrite formation

Lauramine oxide was made without or with inhibitor Hydrodis WP56, a polyamino methylene phosphonate according to formula I, commercially available at Bozetto. In the case of the addition of stabilizer, 0.15-0.31% of Hydrodis WP56 was used, expressed with respect to the amount of amine used. The reaction time was 10-12 hours. The maximum temperature was 66-78°C.

With respect to synthesis batches without stabilizer (Table 5), the content of nitrite is clearly lower in batches wherein stabilizer was used in the synthesis (Table 7). The nitrite content was determined by ion chromatography.

Table 7: Production batches of lauryl amine oxide with Hydrodis WP56 stabilizer

Reaction

Batch Tmax duration (h) Inhibitor (%) Nitrite (ppb)

11 70,8 10 0,31 492

12 78 12 0,31 286

13 68,7 0,31 491

14 66,9 0,31 417

15 66,8 0,31 206

16 66,7 0,15 761

17 67,3 0,15 733