WO1993013059A1

WO1993013059A1 - Stabilizing composition for s-substituted aldehydes, process for stabilizing aldehydes and stabilized aldehydes

Info

Publication number: WO1993013059A1
Application number: PCT/BR1992/000020
Authority: WO
Inventors: Marino Tadeu Fabi; José Carlos MORETTI
Original assignee: Rhodia S/A.
Priority date: 1991-12-26
Filing date: 1992-12-22
Publication date: 1993-07-08
Also published as: BR9105694A; CA2103796A1; CN1077708A; MX9207585A; JPH06506001A

Abstract

This invention relates to a stabilizing composition for S-substituted aldehydes with general formula (I) having 4-15 carbon atoms, where: R1 = C1-C5 alkyl, C6-C9 aryl, furfuryl, benzyl; R2 = H, R1; R3 = H, R1, characterized by the fact that it is based on a prototropic agent (A) in association with an 02 abstracting agent (B). The components are selected among: (A) aromatic or heterocyclic aromatic amines, such as pyridine, dimethylaniline, quinoline, etc., alcanolamines or non-aromatic cyclic amines, such as triethanolamine, N-methylmorpholine, etc., lactams, such as N-methyl pyrrolidone, etc. (B) substituted phenols or hydroquinones, such as p-t-butyl phenol, BHT, etc., acid or unsaturated antioxidant agents, as ascorbic acid or beta-carotene. The amount indicated of said composition is 500-1000 ppm, preferably 1000 ppm, and the (A)/(B) molar ratio is comprised between 5/95 and 50/50. The process for stabilizing S-substituted aldehydes provides for addition to the stabilizing composition to an aldehyde containing up to 300 ppm of water at a stabilization temperature of up to 50 °C. The temperature so which the aldehyde is subjected in the stabilization process is 25-100 °C, and the aldehydes may be in contact with carbon steel. The proposed (A)/(B) composition is efficient to stabilize aldehyde with a certain amount of H20 in the presence of carbon steel and at a 25-100 °C temperature.

Description

STABILIZING COMPOSITION FOR S-SUBSTITUTED ALDEHYDES, PROCESS FOR STABILIZING ALDEHYDES AND STABILIZED ALDEHYDES TECHNICAL FIELD

This invention relates to a stabilising composition for S-suhsti tuted aldehydes, such as beta-methyl-thiopropionic aldehyde (MTPA), in order to prevent deterioration of this product under varying temperature and moisture conditions, including in the presence or absence of carbon steel. It further concerns a stabilization process using the proposed stabilizing composition, as well as stabilized aldehyde.

BACKGROUND ART

Aldehydes subjected to storage usually absorbe 02, setting off a series of reactions characterizing product degradation. The state of the art has already proposed many alternatives for stabilizing aldehydes, such as addition of:

a) aromatic or aliphatic amines, such as pyridine, quinoline, dialkylarninees, preferably in an amount of 2000 ppm, including for the case of MTPA. Back in 1929, U.S. patent 1736747 already proposed the stabilization of aldehydes against oxidation by adding 1.2-diaminoethanes, for instance, 1.2- di(phenylamlno)ethane, in an amount of 0.25-1.0%. Patent JP 72 32963 discloses HTPA stabilization by adding pyridine, quϊnoline, collidine or lutidine, in an amont of 0.1%. Another Japanese patent, JP 49116017 (Nov/27/74) provides for MTPA stabilization by means of N,N-dialkylaniline in an amount of 0.2%. Finally, in 1945 U.S. patent 2381771 quinolines, particularly substituted dihydroqui nones, are proposed as antioxidants for rubbers, glues, petroleum and derivates (gasoline, aldehydes).

b ) allcanolamines

Authors Sagarin E., and H.M., in reference Perfumer, 46 (7), 33-5, 1944, cite the use of aIkanolamines for stabilizing aldehydes. They also suggest for the same purpose the use of alkyl-substituted phenols. Patent SU 568629 reveals formaldehyde stabilization for preventing formation of formic acid and methanol by adding triethanolamine in the amount of 0.25-0.534.

c) unsaturated tetrasubstituted compounds

Such stabilizers are cited in GB 075285 (1952).

d) composition based on a phenolic compound (phenols, naphthols, etc.) and an amine (pyridine, picoline, lutidine, collidine, quinoline or mixtures thereof), preferably a. system based on 4-methoκyphenol and pyridine at 1000 ppm, useful for S-substituted aldehydes such as MTPA, which composition is described in U.S. patent 4546205 (PI 8301502) of PENWALT CORP.

Stabilizing compositions proposed in the state of the art have many drawbacks, such as the fact that they contain toxic amines and a relatively low boiling point before aldehydes, and such compositions may even interfere in the distillation to which the product is subjected before being used in synthetic routes. The extent of such interference will depend on the relative molecular weight (and boiling point) ranges of product and stabilizer.

DISCLOSURE OF INVENTION

Broadly speaking, aldehyde decomposition is due to absorption of 02, followed by auto-oxidation, aldol condensations and in some cases thermal decompositions.

The main mechanisms of decomposition of 5-substituted aldehydes are:

a) auto-oxidation by way of absorption of 02 and contact with metal, with propagation by free radicals. b) aldol condensations in acid medium; cyclic tritαerizations a.nd polymerizations.

c) thermal decomposition reactions uncathaiyzed or cathalyzed by metals. In the case of non-stabilized MTPA, there occurs formation of methyl mercaptan, acrolein, water and ethylene from MTPA itself and decomposition products thereof.

d) nucleophilic additions and substitutions. In the case of MTPA, this occurs from the decomposition product methyl mercaptan, originating mercaptals and thioesters. e) decarbonylations, i.e., elimination of CO with formation of non-carbonyl ic organic sulfides.

These five types of reactions probably act jointly and by a chain process justify the great capacity for absorption of oxygen displayed by S-substituted aldehydes, such as MTPA, as compared with other carbonylic compounds, which makes it recommendable as antioxidant for vegetable oils (Journal Amer. Oil Chem. Soc, 1977, 54, p. 4-7). It should be stressed that oxygen, contact with metals and the thermal factor, either separately or jointly, are decisive causes for decomposition of S-substituted aldehydes.

The schemes below show, for example, possible routes for MTPA decomposition, based on gas chromatography analyses coupled with mass spectroscopy, under the following conditions:

l

SCHEME 2

A.1.1. - 02 ABSORPTION AND AUTO-OXIDATION: formation of an addition compound between 02 and MTPA, which is regulated by dissolution of 02 in organic medium. From that point onwards, either MTPA peroxyacid is formed, which leads to MTPA acid, or the reaction evolves to formation of free radicals, as mercaptide, which in turn leads to formation of di sulfides and heavy compounds.

A.1.2 - ALDOL CONDENSATIONS IN ACID MEDIUM: reactions catalyzed by acids, favored by the stability of MTPA enolic form. Dimers, trimers and polymers are formed:

A.1.3 - THERMAL DECOMPOSITION: reactions of MTPA and decomposition products thereof, significant at a > 65°C temperature. The presence of metals accelerates this type of reaction. This thermal decomposition displaces the equilibrium of A.1.1 and A.1.2 and causes reactions of the A.1.4 type, due to release of methyl mercaptan in the organic medium.

A.1.4 - ADDITIONS AND SUBSTITUTIONS: Methyl mercaptan causes formation of mercaptal and hemi thioacetal type addition compounds. Thioeter type compounds are formed through reactions with carboxylic acids present.

A.1.5 - DECARBONYLATIONS: the presence of mercaptans, particularly at high temperatures, facilitate aldehyde decarbonylations, as in the case of MTPA, and form corresponding organic sulfides.

The initial step for MTPA decomposition involves oxygen absorption, leading to auto-oxidation facilitated by the characteristics of great stability of MTPA enolic form. This is followed by aldol condensations in acid medium, catalyzed by the acidity resulting from the peroxyacid formed or the corresponding carboxylic acid itself. Thermically controlled decompositions leading to the formation of methyl mercaptan, acrolein and ethylene occur from MTPA just as it is and/or from MTPA peroxyacid.

MTPA thermal decomposition studies in an inert atmosphere indicate that at temperatures below 90 C mercaptan formation through heating is small. However. above 105°C thermal decomposition becomes a factor of great importance for the stability of this molecule. Experimental observations by the Applicant show that in an oxygen atmosphere the decomposition releasing methyl mercaptan is made much easier and occurs even at low temperature, probably due to the participation of peroxyacid in the process. BEST MODE FOR CARRYING OUT THE INVENTION

The invention relates to a stabilizing composition for

S-substituted aldehydes with the general formula (I):

R1 - S - CH - CH - CHO

I I

R2 R3 having 4-15 carbon atoms, where:

R1 = C1-C5 alkyl, C6-C9 aryl, furfuryl and benzyl

R2 = H, R1

R3 = H, R1

characterized by being based on a prototropic agent (A) in association with an 02 abstracting agent (B). Such A and B compounds may be chosen from:

TABLE A/B

A.1: an aromatic or B.1: a subtituted

heterocyclic aromatic phenol or hydroquinone, amine, such as pyridine, such as p-t-butylphenol dimethyllaniline. (PTBF), BHT (2,6 di- quinoline, 8-hydroκy- terbutyl, 4-methyl

quinoline, collidine, phenol)

picoline, lutidine A.2.: alcanolamines or B.2: acid or unsaturat- non-aromatic cyclic ed antioxidant agents, amines, such as tri- such as ascorbic acid etanolamine (TEA) (AA), beta-carotene

N-methyImorpholine

A.3 : lactarns, such as

N-methyl pyrrolidone

The stabilizing composition is made up by and A and B, except for the following two pairs: A = pyridine/B = p- t-butyl phenol and A = quinoline/B = p-t-butyl phenol. Preferably, the following stabilizing compositions are indicated:

More specifically, composition A/B may be TEA/AA.

The role of the prototropic agent A is eliminating acid centers responsible for additional aldol condensations, and agent B competes for 02, thus avoiding the triggering of undesirable reactions in S-substituted aldehyde.

The stabilizing composition for S-substituted aldehyde with formula (I) is characterized by the fact that it is ed in an amount of 500-1500 ppm, preferably 1000 ppm. The molar ratio of A/B components is comprised between 5:95 and 5:50. The preferred stabilizing composition is further TEA/AA at 1000 ppm, with 10%-50% AA in TEA.

The synergy of the stabilizing composition as regards the use of isolated amines was noted, as proposed in the state of the art (see table 1 of examples), with the stabilized S-substituted aldehyde appearing without the yellowish coloring typical of the existence of decomposition products. Upon submitting the stabilized aldehyde to chromatography analysis, few components are found to form by transformation of the existing aldehyde itself, and therefor stabilization is quite efficient. The stabilizing composition also does not interfere with subsequent handlings of the stabilized aldehyde, since A and B components remain in the distillation residue (see table 4 of examples).

It was also evidenced (see table 2 of examples) that the stabilization is efficient at varying temperatrues, for example, MTPA stabilized with TEA/AA and kept at 50°C for 15 days suffered a decrease of less than 2% during storage.

This invention also concerns a process for stabilizing S-substituted aldehydes with the formula (I) characterized by addition to said aldehyde of the A/B stabilizing compositon as described above.

INFLUENCE OF WATER CONTENT

The presence of water in S-substituted aldehyde or the compositon interferes with the stabilizing capacity of the A/B system added, mainly when the aldehyde has contact with metals or carbon steel, for under such conditions the amine type component A will release 0H- ions which will set off aldol condensations.

In the case of TEA, for instance, the following will occur in the presence of water: N (CH2CH2OH)3 + H2O HN⁺ (CH2CH2OH)3 + OH-

Aldol condensation reactions set off in an alcaline medium (particularly if there is carbon steel in such medium) are, for MTPA:

Thus, the presence of water either in S-substituted aldhyde or in the stabilizing composition must be minimum. The process for stabilizing S-substituted aldehydes with formula (I) is characterized by the fact the the aldehyde contains a maximum of 300 ppm of water, preferably less than 100 ppm, for stabilizing temperatures up to 50 °C.

In terms of application of S-substituted aldehyde in industrial process, addition is recommended at the time of its manufacture, after its initial distillation and transfer to containers, before water is formed as a decomposition product.

CARBON STEEL

Experimental observations showed that carbon steel exerts two distinct effects on S-substituted aldehydes: 1) at temperatures < 50° C: carbon steel stabilizes aldehyde in relation to the isolated action of oxygen, probably due to the steel surface capacity to abstract 02 from the medium. More particularly, for MTPA a compleκation of its enol may occur, which is responsible for the auto-oxidation exercised by metal ions.

2) at temperatures > 50° C: carbon steel contributes to aldehyde decomposition, specially in the presence of oxygen. In the case of MTPA, the methyl mercaptide or enol formed probably attack the steel surface and release Fe2+, Fe3+ and Mn2+ metal ions, which in turn catalyze the aldehyde oxidating composition.

The stabilizing process proposed for S-substituted aldehydes (I) is characterized by the aldehyde being or not being in contact with carbon steel.

The A/B stabilizing composition proposed decreases the decomposition of S-substituted aldehydes in the presence of carbon steel and at all temperatures tested (see examples, table 1A). The stabilizing process is used in aldehydes subjected to temperatures in the range of 25- 100°C.

S-substituted aldehydes with formula (I) are characterized by containing an A/B stabilizing composition as previously described. E X A M P L E S

STABILIZING SYSTEM 1) SYNERGIC ACTION OF STABILIZING SYSTEM

MTPA samples, whether stabilized or not, were weighed, packed into glass ampoules or "Parr pumps" (Teflon ampoules with carbon steel outer lining), closed and subjected to heating in a stove for definite periods of time, in amospheric air and absence of light. Samples were then analysed by oximation and/or gas chromatography for checking the stabilizing effect of substances mentioned in table A/B as well the synergic effect of composition A+B.

For comparative purposes, each test was confronted with a non-stabilized MTPA specimen subjected to the same kinetic conditions of heat treatment. Each test and each specimen were carried out in duplicate.

Samples were prepared by weighing in a analytical or microanalytical balance of the chemical agent (s) tested as stabilizer (s) in convenient contents, in the range of 1000 to 2500 ppm of stabilizer in MTPA. The tests were carried out at temperatures of 50°C, 80°C,and 120°C, in addition to room temperature. Methods of Analysis

Gas chromatography

Analyses by gas chromatography determined the chromatographic aspect of sample and the MTPA content by normalization at 100%.

Dosage by oximation

MTPA content was obtained through functional analysis by potentiometric method. Results

Table 1 below synthesizes the test conditions (time, temperature, amount of stabilizer) for each sample and relevant stabilizer, as well as:

- MTPA initial content

- MTPA content after the heating stage for a definite period of time

- sample coloring

- MTPA decomposition and stabilization rate

- GC chromatogram aspect stressing impurities formed. The relative formation rate of impurity of molecular weight 190 (MTPA crotomer) was chosen as indicative of MTPA decomposition.

- stabilization factor, defined as the quotient between the variation value of non-stabilized MTPA content and stabilized MTPA content.

Before everything, addition of ascorbic acid alone, despite being capable of absorbing oxygen powerfully, is not indicated for stabilizing aldehydes, since as it is and acid it would catalyze aldol condensation reactions. The synergic effect of A/B composition in HTPA stabilization as compared with application of substances individually is very clear, particularly amines such as pyridine, quinoline and dimethylanil ine, as was done in the state of the art. Besides, amounts in the A/B stabilizing sytem are lower than those recommended in the state of the art.

Stabilizer mass ratios of 1000, 2000 and 2500 ppm and molar ratios of 10%, 20% and 50% of ascorbic acid in TEA were tested for the stabilizing mixture. Triethanolamine is known to exhibit low toxidity, virtually no contribution to smell and a high boiling point (206°C at 15 mm Hg), higher than HTPA, which positively recommends it for industrial handling. 2) TEST WITH TEA/AA

Other more precise tests were carried out with tee TEA/AA stabilizing system.

Samples were prepared with mass and molar ratios as indicated below: 9.6 mg ascorbic acid (0.055 m mol) and 90.4 mg triethanolamine (0.603 m mol) to 100 ml HTPA - actual molar ratio used: 8.4% molar ascorbic acid to 91.6% molar triethanolamine.

Tests were carried ou 50, 80 and 100°C for heating

periods of up to 360 hours (15 days).

Data obtained are shown in table 2, where each value is an average of two test repetitions with good relative accuracy. HTPA content was

determined by GC and oximation. By way of information, there are also included data obtained at 50°C for HTPA contact with carbon steel in the presence and absence of a stabilizing system.

From Table 2, the efficient behavior of this stabilizing composition can be noticed. Thus, for MTPA with an 98.01% initial content, it is noted that the content (dosed by oximation) is kept virtually unchanged at 97% after a 15-day heating, while in the absence of stabilizer such content drops to 78% under the same thermal conditions.

The composition herein is effective for stabilizing HTPA at 50°C kept in contact with carbon steel.

PHYSICAL CHEMICAL DATA ON STABILIZATION:

Graph 1 shows the correlation of data in table 2, where in:

I STABILIZED MTPA AT 50°C

II NON-STABILIZED MTPA AT 50°C

III STABILIZED MTPA AT 80°C

IV NON-STABILIZED MTPA AT 80°C

V STABILIZED MTPA AT 100°C

VI NON-STABILIZED MTPA AT 100°C

It is noticed that there is a first order kinetic variation between MTPA contents and time values for 50 and 80°C temperatures. At 100°C the correlation is not linear, which suggests an interference of mechanisms, particularly decomposi on by heat, operating at this temperature and with little operation up to 80°C.

The calculation of initial speed constants at the three temperatures for non-stabilized and stabilized MTPA leads to data in Table 3.

TABLE 3

KINETIC DATA RELATIVE TO NON-STABILIZED AND STABILIZED MTPA - SPEED CONSTANTS (K) AT EACH TEMPERATURE

* Stabilizer: 10% molar Ascorbid Acid - Triethanol- amine at 1000 ppm. ** The K value is that of the pseudo-first order initial speed constant calculated between times zero and 67 hours in Table 2.

As from table 3, the calculation of activation energies for the two situations leads to the following values:

Activation energy - MTPA decomposition..10.5 Kcal/mol non-stabilized

Activation energy - MTPA decomposition..25.5 Kcal/mol stabilized

Thus, kinetically and thermodynamically, MTPA stabilization with the TEA/AA stabilizing composition is equivalent to an increase of two and half times in the magnitude of activation energy, which quantifies the degree to which this composition is blocked by the presence of stabilizer.

An extrapolation of data in tables 2 and 3 according to correlation log K = f (1/T) for 30°C enables calculation of speed constant at this temperature in K = 1.15 x 10^-5 hour for stabilized aldehyde. This value means a rate forecast for MTPA dropping less than 1% for 1-month storage under environmental conditions in the presence of stabilizer.

3 - EFFECT OF STABILIZING SYSTEM ON 5-SUBSTITUED ALDEHYDE DISTILLATION This test shows the mass distribution of TEA/AA stabilizing components in MTPA distillation in its light, distillate and residue fractions. Stabilizer monitoring was conducted by following up TEA, since the AA high boiling point authorizes the assumption that this component remains in the distillation residue.

The test was carried out by discontinuous distil laton in a 5 cm outer diameter, 65 cm high glass column fitted with 7 Teflon pierced plates.

5.97 liter C6210 g) MTPA at 90.0% recently distilled to which were added 5.58 g (990 ppm) TEA and 0.62 g (100 ppm) AA were distilled at 91°C and 39 mm Hg. A light fraction equivalent to 18% of total, 3 consecutive destillate fractions jointly adding up to 77.7% mass and a residue equivalent to 3.4% mass from total were collected.

TEA was potentiometrically dosed in each fraction using 0.01 N perchloric acid in acetic acid as titrant.

Concurrently, blank tests were carried out in specimens, which showed that the TEA dosage limit under such conditions is 10 ppm. The results obtained are shown in table 4:

:

* Not detected by potentiometric dosage.

From the above table it is noted that all of TEA under such conditions remains in the distillation residue, and therefore it is possible to foresee that the components of the proposed stabilizing composition will remain in the residue even during continuous operation.

CARBON STEEL

1) LONG DURATION TEST ON MTPA DECOMPOSITION: STABILIZING ACTION IN AN INERT ATMOSPHERE, IN THE PRESENCE AND ABSENCE OF CARBON STEEL, AT 37° C

A 120-day long test was carried out to determine MTPA decomposition at 37° C, in the presence and absence of carbon steel, and stabilizing system in an inert atmosphere.

Tridistilled MTPA under N2 (and kept in N2) with a 100% Initial content was packed in glass ampoules, either containing or not containing carbon steel test speciments, in an N2 saturated atmosphere. A stabilizing composition having 900 ppm TEA and 100 ppm AA was used. From the results shown in Tabele 3A below it is noticed that:

a) decomposition becomes important between 15 days and 1 month in storage at such temperature, which suggests a strong autocatalysis effect by decomposition products themselves.

b) stabilizing effect of the system: an average 7% decomposition in a 3-month storage as against a 17% average decomposition for the non-stabilized product during the same period.

c) MTPA stabilization in the presence of carbon steel.

TABLE 3A

LONG DURATION TEST ON MTPA DECOMPOSITION AND STABILIZING ACTION IN AN INERT ATMOSPHERE. IN THE PRESENCE AND ABSENCE OF CARBON STEEL - VALUES IN MTPA %

MTPA - distillation and redistillation on test preparation date.

Samples prepared in nitrogen environment - inert atmosphere.

Carbon steel 1020.

The method used for determining MTPA content was dosage by liquid chromatography (HPLC) through outer standardization.

Apparatus: HPLC - Varian 5010 or similar.

Column: Lichrosorb RP 18, length = 30 cm, inner diameter

= 0.4 cm.

Moving stage: acetroni tri le/H2O, 1:9 v/v

Discharge: 1.2 ml/min.

Detection: UV at 200 nm. Dilution of measured solution: 0.1% in acetonitrile.

Injection volume: 10 ul.

Retention time: about 8 min.

Integrator: HP 3390.

Dosage by outside standardizations The MTPA standard is obtained by bidisti 1 lation and conservation in N2 in a freezer, stabilized with 900 ppm TEA and 100 ppm AA.

2) MTPA BEHAVIOR IN THE PRESENCE OF COMMON OR STAINLESS STEEL IN ACCORDANCE WITH TEMPERATURE AND ACTION OF STABILIZING SYSTEM.

The same procedure was used, as already described under item 1) "KINERGIC ACTION OF STABILIZING SYSTEM" hereinabove. MTPA dosage was made by oximation and also by gas chromatography and liquid chromatography (see aspect of chromatogram).

In tests carried out in the presence of carbon steel, test specimens of the material were placed inside ampoules, which then were sealed and heated for a definite period. TEA/AA system was used at 1000 ppmm.

TABLE 1A

»

The data in table IA above show the double effect of steel on MTPAt

. T < 50° C: the drop in MTPA content and rate of formation of impurities, noticed via chromatogram, is considerably reduced when in contact with carbon steel, as compared with MTPA alone (39.9% absolute difference in content values at room temperature).

At room temperature MTPA content is the same in the presence or absence of carbon steel, under the action of stabilizer after 1080 hours (45 days).

. T > 50°C: steel has a strong positive effect on aldehyde decomposition. Experimentally it is noted that, after 360 hours at 80°C the MTPA content in the presence of carbon steel is 6.4%, while MTPA content when placed under the same heat conditions for the same period is 65.5%. At 100°C the effect is even more strongly marked. Under such conditions, stabilizer decomposition is efficient at 80° C. Stabilized MTPA content exhibits a higher value than non-stabilized MTPA when in the presence of carbon steel.

Therefore, the conclusion is that the stabilizer is efficient to block S-substi tυted aldehyde decomposition at varying temperatures in the presence of carbon steel.

WATER

1) MTPA decomposition test at 50 and 80° C in the presence of growing water contents and 1000 ppm of 90% TEAT - 10% AA mixture. Samples were analysed for MTPA content by high resolution liquid chromatography (HPLC) under already described conditions.

Table 2A shows the negative effect of water on stabilization at tested temperatures:

TABLE 2A

MTPA DECOMPOSITION AT 50°C AND 80° C IN TE PRESENCE OF GROWING WATER CONTENTS AND 1000 PPM OF 90% TRIETHANOLAMINE - 10% ASCORBIC ACID MIXTURE

MTPA CONTENT

- Initital MTPA content: 100.0%

- TEA - Trithanolamine (900 ppm); A.A.- Ascorbic Acid (100ppm).

- HPLC dosage by ouside standardization.

- Test carried out in nitrogen.

The values indicated correspond to two tests carried out concorrently.

2) MTPA decomposition test at 50°C in the presence of 1000 ppm water and 1000 ppm of 90% pyridine - 10% ascorbic acid stabilizing mixture.

As in the previous test, samples were analysed for MTPA content by chromatographic analysis under already described conditions. The effect of water and steel on MTPA is thus noted (table 4A).

TABLE 4A MTPA DECOMPOSITION AT 50°C IN THE PRESENCE OF 1000 PPM OF WATER AND 1000 PPM OF 90% PYRIDINE - 10% ASCORBIC ACID MIXTURE.

MTPA CONTENT

- MTPA initial content (HPLC): 100.02%.

- py (Pyridine at 900ppm): A.A. (Ascorbic Acid at 100ppm). - Test carried out under nitrogen.

Test indicated corresponed to tests carried out concurrently.

Claims

1) STABILIZING COMPOSITION FOR S-SUBSTITUTED ALDEHYDES

WITH THE GENERAL FORMULA (I):

R1 - S - CH - CH - CHO

R2 R3 having 4-15 carbon atoms, where:

R1 = C1-C5 alkyl, C6-C9 aryl, furfuryl, benzyl

R2 = H, R1

R3 = H. R1

characterized by being based on a prototropic agent (A) in association with an 02 abstracting agent (B).

2) STABILIZING COMPOSITION FOR S-SUBSTITUTED ALDEHYDES according to claim 1, characterized by the fact that component (A) is selected among

. aromatic or heterocyclic aromatic amines, such as pyridine, dimethylani line, quinoline, 8- hydroxyquinoline;

. alcanolamines or cyclic non-aromatic alcanolamines, such as triethanolamine (TEA), N-methylmorphol ine;

. lactams, such as N-methylpyrrol idone;

and component (B) selected among

. substituted phenols or hydroqui nones, such as p-t- butyl phenol (PTBP), BHT (2,6-ditertbutyl, 4- methylphenol);

. acid or unsaturated antioxidant agents, as ascorbic acid (AA) or beta-carotene;

except for compositions A/B = pyridine/PTBP and quinoline/PTBP.

3) STABILIZING COMPOSITION FOR S-SUBSTITUTED ALDEHYDES according to claims 1 and 2, characterized by the fact that the composition is preferably (A) TEA / (B) AA.

4) STABILIZING COMPOSITION FOR S-SUBSTITUTED ALDEHYDES according to any of the previous claims, characterized by the fact that it is added in an amount of 500 - 1500 pprn, preferably in an amount 1000 ppm. 5) STABILIZING COMPOSTION FOR S-SUBSTITUTED ALDEHYDES according to claim 4, characterized by the fact that the molar ratio between components (A) /(B) is comporised between 5/95 - 50/50. 6) STABILIZATION PROCESS FOR S-SUBSTITUED ALIPHATIC ALDEHYDES OF FORMULA (I), characterized by the fact the stabilizing composition (A)/(B) is added as described in claims 1 - 5.

7) STABILIZATION PROCESS FOR S-SUBSTITUTED ALIPHATIC ALDEHYDES OF FORMULA (I), according to claim 6, characterized by the fact the aldehyde i s anhydrous or contains an amount of water l ower than 300 ppm, preferably lower than 100 ppm, for stabilization temperatures up to 50°C .

8) STABILIZATION PROCESS FOR S-SUBSTITUTED ALDEHYDES OF FORMULA (I), according to claims 6 or 7, characterized by the fact that the temperature to which the aldehyde is subjected is 25-100°C.

9) STABILIZATION PROCESS FOR S-SUBSTITUTED ALDEHYDES OF FORMULA (I), according to claims 6 to 8, characterized by the fact that the aldehyde is in contact with carbon steel.

10) ALIPHATIC S-SUBSTITUTED ALDEHYDE OF THE GENERAL FORMULA (I):

R1 - S - CH - CH - CHO R2 R3 having 4-15 carbon atoms, where:

R1 = C1-C5 alkyl, C6-C9 aryl, furfuryI, benzyl;

R2 = H, R1;

R3 = H, R1.

characterized by the fact that it contains an A/B stabilizing composition as desdribed in claims 1 to 5 or that is stabilized according to process described in claims 6 to 9.