ITMI962072A1 - PROCEDURE FOR THE PREPARATION OF AROMATIC URETHANES FROM NITROAROMATIC COMPOUNDS BY HETEROGENEOUS CATALYSIS - Google Patents

Description

MINISTRY OF UNIVERSITY AND SCIENTIFIC AND TECHNOLOGICAL RESEARCH DESCRIPTION

The present invention relates to a process for the preparation of aromatic urethanes by catalytic reductive cabonylation of nitroaromatic compounds with carbon monoxide and a compound containing at least one hydroxyl group which uses a particular catalytic system.

Aromatic urethanes (or carbamates) are generally used as intermediates useful for organic syntheses in the field of fine chemistry, for example for the preparation of substances useful in agriculture, and in the synthesis of aromatic isocyanates used in the preparation of polyurethanes. Among the urethanes, those of greatest interest, from a commercial point of view, are phenyl urethane and 2,4-toluene-urethane used in the preparation of methylenediphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) which are currently industrially produced by phosgenation of the corresponding diamines.

Catalytic carbonylation processes of aromatic nitro-derivatives with CO and an alcohol are known in the art.

Thus, for example, the process described in US patent 4,186,269 employs a catalytic system consisting of a noble metal such as Pd, Rh or Ru or its salt, a Lewis acid such as FeCl3 or SnCl4, and a tertiary amine such as for example triethylamine or pyridine.

The system consisting of palladium supported on carbon or alumina, anhydrous FeCl3 and pyridine is particularly effective, using molar ratios: pyridine / palladium = 130, starting pyridine / nitro derivative = 0.46 and FeCl, / Pd = 40.

The tertiary amine, used in large excess with respect to the metal, generally serves to increase the catalytic activity of the Pd / Lewis acid system and to minimize the corrosion of the synthesis reactor due to the presence of Lewis acid.

The use of considerable quantities of tertiary amine and Lewis acid presents considerable technical and economic problems relating to the recovery of the products and the recycling of the catalytic system, especially when operating on an industrial scale.

According to another process described in patent EP-169.650, a catalytic system is used consisting of a supported noble metal, an aromatic nitrogen bidentate chelator and a Bronsted acid.

This process substantially has the disadvantages deriving from corrosion problems due to the use of an excess of acid.

The object of the present invention is that of obtaining aromatic urethanes with high yields and selectivity by means of a simple, economical process which does not give rise to corrosion phenomena of the reactor, which is easy to industrialize and which does not present the disadvantages of the processes of the known art.

It has now been found that these results are achieved if the carbonylation reaction is carried out in the presence of a catalytic system consisting of a supported noble metal, an aromatic bidentate chelator and an acid salt consisting of a protonated nitrogen chelator and the anion of an acid with a pKa lower than 2.

This acid salt improves the activity and stability of the catalyst. Furthermore, the protonated nitrogen chelator in the presence of free chelants gives rise to a buffer solution which allows to maintain the concentration of the H <+> ions in solution at low and constant values over time, regardless of dilution. This allows a better reproducibility of the reaction and a reduction of the molar ratios between the reactants (palladium, chelator and protonated chelator).

Accordingly, an object of the present invention is a process for the preparation of aromatic urethanes by reaction of a nitroaromatic compound with carbon monoxide and a compound containing at least one hydroxyl group in the presence of a catalytic system consisting of: (1) a metal noble supported on inert supports;

(2) a nitrogen or phosphorus bidentate chelator (chel); and

(3) an acid salt having the general formula (I) (I)

where: chel 'represents a bidentate azo-tate chelator equal to or different from chel and A <-> is the anion of an acid with a pKa lower than 2.

The noble metal, for example Pd, Pt, Rh, Ru, preferably palladium (Pd), is used in supported form on inert porous supports.

Finely divided coal, silica, barium sulfate, alumina can be used as inert supports. Preferred for the purposes of the present invention are coal and barium sulfate.

Examples of nitrogenous bidentate chelators can be chosen from those of general formula (II)

(II) where: X and Y, the same or different from each other, represent a bridged organic group having at least three atoms in the bridge of which at least two are carbon atoms. When, in addition to the carbon atoms, the X and Y groups contain other atoms these are preferably nitrogen or oxygen atoms.

Preferred nitrogenous bidentate chelators according to the present invention are those in which the bridging groups X and Y are the same and contain from 3 to 10 atoms at least two of which are carbon atoms.

Examples of nitrogen chelators are:

2,2 '-bipyridyl (bipy); 4,4'-dimethyl-2,2'-bipyridyl (DM-bipy); 4,4'-diphenyl-2,2'-bipyridyl (DP-bipy); 5, 5'-dimethyl-2,2'-bipyridyl; 5-methyl-2,2'-bipyridyl; 6,6'-dimethyl-2,2'-bipyridyl; 1, 10-phenanthroline (phen); 4-methyl-1,110-phenanthroline; 5-methyl-1,110-phenanthroline; 4,7-dimethyl-1,110-phenanthroline; 3, 8-dimethyl-1,110-phenanthroline; 4,7-diphenyl-1,10-phenanthroline; 4,7-dichloro-1,110-phenanthroline; 3,4,7,8-tetramethyl-1,10-phenanthroline (TM-phen); 4,4'-dimethyl-5,5 '-dioxazole; 2,2'-bipyrimidine.

Phosphorated bidentate chelators are selected from those of general formula (III):

(H I)

where: R represents an alkyl radical with a number of carbon atoms from 2 to 4, a cycloalkylidene radical with a number of carbon atoms from 2 to 10 or an orthophenylene radical; R1-R4 equal or different from each other, each represent a C1-C10 alkyl radical, C3-C10 cycloalkyl radical or a C6-C12 aromatic radical optionally substituted with a C1-C4 alkyl or alkoxy radical.

Non-limiting examples of phosphorated bidentate chelators suitable for the purposes of the present invention are selected from: 1,3-bis- (diphenylphosphino) propane (DPPP), 1,3-bis (di-4-methoxy-phenylosphine) propane, 1,4 -bis (dicyclohexylphosphino) butane and 1,2-bis (diphenylphosphino) cyclohexane.

A is an essentially non-coordinating and non-esterifiable anion selected from hexafluorophosphate, tetrafluoroborate and hexafluoroantimoniate. Preferred is hexafluorophosphate (PF6-).

In the preferred embodiments of the present invention the acid salts (I) [phenH <+>] [PF6], [bipyH] [PF6], [TMe-phenH <+>] [PFfi], (4,7- DMe-phenH <+>] [PFtì <'>] and (4,7-DMe-bipyH <*>] [PF6 <">].

Preferred according to the present invention is [phenH <+>] [PF6].

Compounds of general formual (I) can be synthesized as white solids according to the following reaction:

Chel 'H <+> Cl NH4PF6 -> Chel' H <+> PF6 <-> + NH4C1

The catalyst is used in catalytic quantities generally comprised between 10 <-1> and 10 <-5> gram of metal atoms contained in the catalyst per mole of nitroaromatic compound.

Advantageous results are obtained by using quantities of catalyst ranging from 10 <-2> to 2. 10 <-3>.

The aromatic bidentate chelator (chel) is used in an amount such as to give a molar chel / metal ratio between 0.1: 1 and 20: 1, preferably between 1: 1 and 5: 1.

The acid salt (I) is used in such an amount as to give a molar ratio chelH <+> / metal comprised between 0.1: 1 and 20: 1, preferably between 1: 1 and 10: 1.

Nitroaromatic compounds usable in the process of the present invention can be selected from compounds containing at least one aromatic group in which a NO group is directly linked to a carbon atom of the aromatic ring. Examples of said compounds are: nitrobenzene, alkyl or alkoxy nitrobenzene, optionally substituted, dinitrobenzenes and polynitrobenzenes.

Particularly useful nitroaromatic compounds in the process of the present invention are, nitrobenzene, m-dinitrobenzene, 2,3-4-trinitrotoluene, 2,4-dinitrotoluene, 2, 6-dinitrotoluene and 4,4 '-dinitrodifenylmethane.

Compounds containing at least one hydroxyl group can be represented by the general formula R (OH) m where m is an integer between 1 and 4 and R represents an achyl, aryl, alkylaryl, arylachyl, cycloaliphatic group with a number of carbon atoms up to to 20, preferably up to 6, possibly substituted. Examples of compounds according to the general formula R (OH) m are primary, secondary or tertiary mono or polyhydroxylated alcohols, or mixtures thereof, optionally substituted with oxygen or one or more halogen atoms. Examples of monohydroxylated alcohols are, for example, ethanol, methanol, cicohexanol, CF3-CH2-OH, 2,6-dimethyl-4-heptanol, tert-amyl alcohol, tert-butyl, n-amyl, n-butanol, iso- butanol, n-propanol, iso-propanol, benzyl alcohol, chlorobenzyl, methoxybenzyl, methoxy ethanol, butoxy ethanol, phenol and cresols.

Examples of polyhydroxylated alcohols are selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and trimethylolpropane.

Preferred for the purposes of the present invention are methanol and ethanol since the urethanes obtained using these alcohols can be easily decomposed thermally to isocyanates.

Alcohol can be used in stoichiometric quantities with respect to the nitrogroups present in the nitroaromatic compound, but it is preferable to use alcohol in slight excess as it also acts as a solvent. An inert organic solvent can be used in combination with alcohol.

According to an embodiment of the process of the present invention, the reaction can be carried out in the presence of an anhydrifying agent. Examples of such agents are selected from 2,2'-dimethoxy propane, trialkyl orthoformates, zeolites. In this case the drying agents are used in quantities ranging from 1 to 10% by weight with respect to the alcohol.

Non-limiting examples of aromatic urethanes which can be prepared with the process of the present invention are: methyl-N-phenylurethane, butyl-N-phenyl urethane, pentyl-N-phenyl urethane, hexyl-N-phenyl urethane, 4,4'-methylenedimethyldiphenyl urethane, 2, 4-toluene urethane.

The process of the present invention can be carried out at temperatures between 25 and 200 ° C and at a pressure between 1 and 100 bar. Conveniently one operates at a temperature between 100 ° and 180 ° C and at a pressure between 10 and 60 bar.

The reaction time is a function of temperature and pressure. However, reaction times ranging from 1 to 5 hours are adequate.

The process according to the present invention can be carried out in batch, continuous or semi-continuous. At the end of the reaction the product is separated according to conventional techniques. For example, the reaction mixture is filtered to remove any metal or supported metal present, followed by a distillation to remove the excess alcohol until precipitation of the urethane.

The process according to the present invention allows to obtain aromatic urethanes with high re-se and selectivity. Furthermore, this process allows the recovery of palladium in the form of supported metal with yields higher than 99%. The catalyst, which keeps its activity unaltered, can be reused in subsequent carbonylation cycles for the preparation of aromatic urethanes.

In order to better understand the present invention, some illustrative but non-limiting examples are given.

Example 1

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

Molar ratios: Sub / Pd = 250; Chel / Pd chel 'H' / Pd = 2.

After having eliminated the air present in the autoclave by two washes with CO, 40 bars of carbon monoxide are charged at room temperature and subsequently heated to 160 ° C, under magnetic stirring. After 2 hours from the start of heating, the autoclave is cooled, the contents are filtered to remove the Pd / C and the solution is analyzed by gas chromatography.

There is a conversion of 99.6%, with a yield in methyl phenylurethane of 95%; the selectivity in urethane with respect to the reacted nitrobenzene is 95.4%.

Example 2

Into a 50 ml autoclave in stainless steel, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

Molar ratios: Sub / Pd = 250; Chel / Pd = 1,

that the HVPd = 2.

The reaction is carried out under the same conditions

operating procedures shown in example 1.

There is a conversion of 99.3%, with a yield

96% methyl phenylurethane; selectivity

in urethane with respect to the reacted nitrobenzene is of

96.6%.

Example 3

In a 50 ml stainless steel autoclave

bile, with Teflon coating, equipped with agitator

magnetic tore and heat exchange media,

are introduced:

Molar ratios: Sub / Pd = 250; Chel / Pd = 1,

chelHVPd = 1.

After eliminating the air present in the autoclave by means of two CO washes, 40 bars of carbon monoxide are loaded at room temperature and then heated to 160 ° C, under magnetic stirring.

After 2 hours from the start of heating, the autoclave is cooled, the contents are filtered to remove the Pd / C and the solution is analyzed by gas chromatography.

There is a conversion of 99.3%, with a yield in methyl phenylurethane of 94.7%; the selectivity in urethane with respect to the reacted nitrobenzene is 95.4%.

Examples 4-6 (Comparison)

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

Molar ratios: Sub / Pd = 250; Chel / Pd = 1, A-H <+> / Pd = 1.

One operates as in example 3, but using 2,6-bis-trifluoromethylbenzoic acid, 2,4,6-trimethylbenzoic acid and p-toluenesulfonic acid, instead of the protonated chelator [phenH <+>] [PF6-]. The results are reported in table 1

Table 1

With [p-TS] <-> = p-toluenesulfonate;

[2.6 (CF3), Bz] <-> - 2,6-bis-trifluoromethylbenzoate;

[2,4,6 (CH3) 2Bz] <-> = 2,4,6-trimethylbenzoate

Examples 7-10

Effect of the nature of the nitrogen chelator

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <2> moles),

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd), - chelating agent (chel) (8.IO <'5> moles),

- protonated chelator (chelH <*> PF6 -) (8.10 <'5> moles), 8 ml of methanol and

- 0.2 ml of 2,2'-dimethoxy-propane (DMP). Molar ratios: Sub / Pd 250; chel / Pd chel'H / Pd = 1.

The air present in the autoclave is removed with two CO washes, 40 bars of carbon monoxide are loaded at room temperature and then heated to 145 ° C, under magnetic stirring.

After 2 hours from the start of heating, the autoclave is cooled, the contents are filtered to remove the Pd / C and the solution is analyzed by gas chromatography. The results are reported in table 2.

Table 2

bipy = bipyridine

DMe-bipy = 4,4'-dlmethyl-bipyridine

phen = 1,10'-phenanthroline

ΤΜθ-phen = 3,4,7,8-tetramethyl-phenanthroline Examples 11-13

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles),

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd), - 0.012 g bipyridine (bipy) (8.10 <-5> moles),

- 0.024 g [bipyH <+>)] PF6] (8.10 <-5> moles),

- 8 ml of methanol e

- 0.2 ml of 2,2'-dimethoxy-propane (DMP).

Molar ratios: Sub / Pd = 250; Chel / Pd = 1, chel'H '/ Pd = 1.

The reaction is carried out with the same experimental procedure followed in Examples 7-10, but varying the temperature. The results are reported in table 3.

Table 3

Examples 14-16

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles),

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd), - 0.014 g 1,10'-phenanthroline (phen) (8.10 <-5> moles), - 0.026 g ( phenH <+>) (PFfi) (8.10 <-5> moles),

- 8 ml of methanol e

- 0.2 ml of 2,2'-dimethoxy-propane (DMP).

Molar ratios: Sub / Pd = 250; chel / Pd = 1, chel'H '/ Pd - 1.

The reaction is carried out with the same experimental procedure followed in Examples 7-10, but varying the temperature. The results are reported in table 4.

Table 4

Examples 17-21

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles)

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd) - bipyridine (bipy)

- [bipyH <+>] [PF6],

- 8 ml of methanol e

- 0.2 ml of 2,2'-dimethoxy-propane (DMP).

Molar ratio: Sub / Pd = 250.

The reaction is carried out with the same experimental procedure followed in Examples 7-10, but by varying the molar ratio between bipy / Pd and bipyHVPd.

The results are reported in table 5.

Table 5

Examples 22-24

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles),

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of

- 4,4'-dimethyl-bipyridine (DMe-bipy)

- [DMe-bipyH <*>] [PF6 <-> 1,

- 8 ml of methanol e

- 0.2 ml of 2,2'-dimethoxy-propane (DMP).

Molar ratio: Sub / Pd = 250.

The reaction is carried out with the same experimental procedure followed in Examples 7-10, but by varying the molar ratio between DMe-bipy / Pd and DMebipyH <+> / Pd.

The results are reported in table 6.

Table 6

Examples 25-30

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles),

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd), - 1,10'-phenanthroline (phen),

[phenH <+>] [PF6 <->)

8 ml of methanol e

- 0.2 ml of 2,2'-dimethoxy-propane (DMP).

Molar ratios: Sub / Pd = 250.

The reaction is carried out with the same experimental procedure followed in Examples 7-10, but by varying the molar ratio between phen / Pd / and phen-H <+> / Pd.

The results are reported in table 7.

Table 7

Examples 31-34

Into a 50 ml autoclave in stainless steel, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles),

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd), - 0.036 g 1,10'-phenanthroline (phen) (2 .10 <-4> moles), - 0.065 g [phenH <+>] [PF6] (2.10 <-4> moles),

- 8 ml of methanol e

- 2,2'-dimethoxy-propane (DMP).

Molar ratios: Sub / Pd = 250; phen / Pd = 2.5 and phenHVPd = 2.5.

The reaction is carried out with the same experimental procedure followed in example 30, but by varying the quantity of DMP. The results are reported in table 8.

Table 8

Examples 35-38

Effect of Reaction Time on Palladium Recovery

Into a 50 ml stainless steel autoclave, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles), - 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd), - 0.036 g 1,10'-phenanthroline (phen) (2 .10 <-4> moles), - 0.065 g [phenH] [PF6] (2.10 <-4> moles),

- 8 ml of methanol e

- 0.6 ml 2.2 '-dimethoxy-propane (DMP).

Molar ratios: Sub / Pd = 250; phen / Pd = 2.5 and phenHVPd = 2.5.

The reaction is carried out with the same experimental procedure followed in Examples 31-34, but varying the reaction times.

The results obtained from the analysis of palladium both in the reaction solutions and on the recovered solid (Pd / C) are reported in table 9.

Table 9

Example 39

Into a 50 ml autoclave in stainless steel, with Teflon coating, equipped with a magnetic stirrer and heat exchange means, are introduced:

- 2.46 g of nitrobenzene (2.10 <-2> moles),

- 170.2 mg of Pd / C at 5% of Pd (8.10 <-5> moles of Pd) recovered in Example 38,

- 0.036 g 1,10'-phenanthroline (phen) (2.10 <-4> moles), - 0.065 g (phenH) (PF6) (2.10 <-4> moles),

- 8 ml of methanol e

- 0.6 ml 2,2'-dimethoxy-propane (DMP).

Molar ratios: Sub / Pd = 250; phen / Pd = 2.5 and phenH '/ Pd = 2.5.

The reaction is carried out with the same experimental procedure followed in example 38.

There is a conversion of 95.4%, with a yield in methyl phenylurethane of 90%; the selectivity in urethane with respect to the reacted nitrobenzene is 94.3%. Also in this case the recovery of Pd / C is equal to 99.2%.

Claims (31)

Claims 1. Process for the production of aromatic urethanes by reductive carbonylation of nitroaromatic compounds with carbon monoxide and a compound containing at least one hydroxyl group which comprises carrying out the carbonylation reaction in the presence of a catalytic system consisting of: (a) a noble metal supported on inert supports; (b) a nitrogen or phosphorus bidentate ketant (chel); and (c) an acid salt of general formula (I) (I) where: chel 'represents a nitrogenous bidentate ketant equal to or different from chel and A' is the anion of an acid with pKa lower than 2. 2. The process according to claim 1, where the noble metal is selected from Pd, Pt, Rh, Ru. 3. The process according to claim 2, where the noble metal is Pd. 4. The process according to claim 1, wherein the inert support is selected from finely divided coal, silica, barium sulfate or alumina. 5. The process according to claim 4, where the support is carbon or barium sulfate. 6. The process according to claim 1, wherein the nitrogenous bidentate chelators are selected from those of general formula (II) (II) where X and Y, the same or different from each other, represent bridged organic groups having each at least three atoms in the bridge, of which at least two are carbon atoms. 7. The process according to claim 6, where when, in addition to the carbon atoms, the groups x and Y contain other atoms these are selected from oxygen or nitrogen. The process according to claim 7, wherein the nitrogenous bidentate chelators have the same bridging groups X and Y and contain from 3 to 10 atoms at least two of which are carbon atoms. 9. The process according to claim 6, wherein the nitrogenous bidentate chelators are selected from 2,2'-bipyridyl, 4, 4'-dimethyl-2,2'-bipyridyl, 4,4'-diphenyl-2,2'- bipyridyl, 5,5'-dimethyl-2,2'-bipyridyl, 5-methyl-2,2'-bipyridyl, 1,10-phenanthroline, 4-methyl-1, 10-phenanthroline, 5-methyl-1, 10 -phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 3,8-dimethyl-1, 10-phenanthroline, 4,7-diphenyl-1, 10-phenanthroline, 4,7-dichloro-1,10-phenanthroline , 3,4,7,8-tetramethyl - 1,10-phenanthroline, 4,4'-dimethyl-5,5'-dioxazole and 2,2'-bipyrimidine. 10 The process according to claim 1, where the phosphorated bidentate chelators are selected from those of general formula (III): (III) where: R represents an alkyl radical with a number of carbon atoms from 2 to 6, a cycloalkylidene radical with a number of carbon atoms from 2 to 10 or an orthophenylene radical; R1R4, the same or different from each other, each represent a C1-C10 alkyl radical, C3-C10 cycloalkyl radical or a C6-C12 aromatic radical optionally substituted with an alkyl or alkoxy radical 11. The process according to claim 10, wherein the phosphorated bidentate chelators are selected from 1,3-bis (diphenylphosphino) propane, 1.3 -bis (di-4-methoxy-phenylphosphine) propane, 1.4-bis (dicyclohexylphosphine) butane and 1,2-bis (diphenylphosphine) cyclohexane. 12. The process according to claim 1, where A <-> is selected from hexafluorophosphate, tetrafluoroborate and hexafluoroantimoniate. 13. The process according to claim 12, where A <-> is hexafluorophosphate. 14. The process according to claim 1, where the acid salt is selected from [phenH <+>] [PF6-], [TMe-phenH '] [PF5], (4,7-DMe-phenH <+>] [ PFg-], (4,7-DMe-bipyH <+> J [PF6-] and [bipyH <+>] fPF6]. 15. The process according to claim 1, characterized in that it additionally contains an anhydrifying agent selected from 2,2'-dimethoxy-propane, tri-alkyl-orthoformate and zeolites. 16. The process according to claim 15, characterized in that the anhydrifying compound is 2,2'-dimethoxy-propane. 17. The process according to claim 1, wherein the nitroaromatic compound is selected from compounds containing at least one aromatic group in which an N02 group is directly bonded to a carbon atom of the aromatic ring. 18. The process according to claim 17, wherein the nitroaromatic compound is selected from optionally substituted nitrobenzene, alkyl or alkoxy nitrobenzene, dinitrobenzenes, such as 2,4-dinitrotoluene and 2,6-dinitrotoluene, 4,4'-dinitrodifenylmethane and polynitrobenzenes . 19. The process according to claim 18, where the nitroaromatic compound is selected from nitrobenzene, m-dinitrobenzene, 2, 3-4-nitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene and 4,4'-dinitrodiphenylmethane. 20. The process according to claim 1, where the compounds containing at least one hydroxyl group are selected from those represented by the general formula R (OH) m where m is an integer between 1 and 4 and R represents an achyl, aryl, alkylaryl group , arylachyl, cycloaliphatic with a number of carbon atoms up to 20 possibly substituted. 21. The process according to claim 20, where the compounds of general formula R (0H) m are primary, secondary or tertiary mono or polyhydroxylated alcohols, or mixtures of these, optionally substituents with oxygen or one or more halogen atoms. 22. The process according to claim 20, where the monohydroxylated alcohols are selected from ethanol, methanol, cicohexanol, CF3-CH2-OH, 2, 6-dimethyl-4-heptanol, tert-amyl, terbutyl, n-amyl alcohol, n -butanol, iso-butanol, n-propanol, iso-propanol, benzyl alcohol, chlorobenzyl, methoxybenzyl, methoxy ethanol, butoxy ethanol, phenol and cresols. 23. The process according to claim 20, wherein the polyhydroxylated alcohols are selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol and trimethylolpropane. 24. The process according to claim 1, wherein the catalyst is used in catalytic quantities comprised between 10 <-1> and 10 <-5> gram of metal atoms contained in the catalyst per mole of nitroaromatic compound. 25. The process according to claim 24, characterized in that the quantity of catalyst is comprised between 10 <-2> and 2.10 <-3> gram of metal atoms contained in the catalyst per mole of nitroaromatic compound. 26. The process according to claim 1, characterized in that the amount of acid salt (I) used is such as to give a molar ratio of chelHVmetal comprised between 0.1: 1 and 20: 1. 27. The process according to claim 26, characterized in that the molar ratio of metal to HV is comprised between 1: 1 and 10: 1. 28. The process according to claim 1, characterized in that the quantity of aromatic bidentate chelator (chel) used is such as to give a molar chel / metal ratio between 0.1: 1 and 20: 1. 29. The process according to claim 28, characterized in that the molar ratio chel / metal is comprised between 1: 1 and 5: 1. 30. The process according to claim 1, characterized in that the reductive carbonylation reaction is carried out at a temperature of between 25 ° and 200 ° C and at a pressure of between 1 and 100 bar. 31. The process according to claim 30, characterized in that the temperature is between 100 and 180 ° C and the pressure does not exceed 60 bar.