Process for the preparation of silicon and aluminium N,N-dialkylcarbamates and their hydrolysis products

Abstract: Silicon and aluminium N,N-dialkylcarbamates are prepared by reacting a secondary amine and CO ₂ with respectively a silicon and an aluminium halide in a reaction medium consisting of an organic solvent. The respective hydrolysis products are obtained from said N,N-dialkylcarbamates by treatment with water in tetrahydrofuran.

Description: Field of the invention The present invention relates to a process for the preparation of silicon and aluminium organic derivates and their hydrolysis products. Prior Art Metal N-substituted carbamate salts are known as well as methods for their production. For example US-A-3,056,820 discloses a method for preparing substituted carbamate salts reacting a compound of formula M(NR₂) n with carbon dioxide wherein M is a metal, R is hydrogen or an organic radical and n is the valence of M, in a mineral oil solution to produce a greaselike gel containing said substituted carbamate salts, diluting said gel with a volatile hydrocarbon liquid to precipitate said salts, and separating and washing said precipitated salts. US-A-2,957,826 discloses a method for preparing a metal N-substituted carbamate-thickened grease. The described methods are complicated and involve expensive steps. Summary of the invention This invention relates to a new process for preparing N,N-dialkylcarbamates of general formula (I): M[O₂CNR₂] n where M is Si or Al, n is 4 when M is Si and 3 when M is Al, and R is a C₁-C₆ alkyl group, and for preparing the hydrolysis products of the compounds (I). The process for preparing the compounds (I) and their hydrolysis products is characterised by: a) reacting a secondary amine of formula R₂NH and CO₂ with an MX n halide in which M is Si or Al, X is Cl or Br, n is 4 when M is Si and 3 when M is Al and R is a C₁-C₆ alkyl group, in a reaction medium consisting of an organic solvent; b) filtering off the dialkylammonium halide which forms; c) precipitating the compound (I) by concentrating the filtered solution, and if necessary cooling and adding n-heptane; d) recovering the product (I) by filtration; and optionally e) dissolving the product (I) in tetrahydrofuran and hydrolyzing with water; f) recovering the hydrolysis product by filtration. Detailed description of the invention The characteristics and advantages of the silicon and aluminium N,N-dialkyl-carbamates of formula (I) and their hydrolysis products, and the process for preparing the compounds (I) and their hydrolysis products will be more apparent from the following detailed description. The compounds of formula (I) are prepared by reacting a secondary amine and CO₂ with an MX n halide as heretofore defined. To effect this reaction, a solution of MX n in an organic solvent is gradually added to a solution of R₂NH and CO₂ in an organic solvent. The organic solvent is chosen from the group comprising saturated aliphatic and aromatic hydrocarbons and is preferably toluene. The organic solvent has a water content of less than 50 ppm. The concentration of the secondary amine solution is between 0.5 and 5 moles/l and the concentration of the MX n solution is between 0.1 and 2 moles/l. The molar ratio of secondary amine to MX n used in the reaction is between 8 and 12. The MX n solution is added to the secondary amine solution under a CO₂ atmosphere. When the addition is complete the reaction mixture is kept stirring at a temperature of between 15°C and 30°C under a CO₂ atmosphere for a time of between 4 and 8 hours. On termination of the reaction the mixture consists of a colourless solution of (I) and a colourless solid consisting of dialkylammonium halide. The reaction mixture is filtered and the solution recovered. To recover (I) when M is Si, the solution is concentrated by evaporating the solvent at ambient temperature under reduced pressure, until a concentration of (I) of between 1 and 2 moles/l is obtained, then cooling to -30°C and adding n-heptane in a quantity of between 1 and 3 volumes per volume of solution while maintaining the temperature at -30°C. The product (I) in which M is Si thus precipitates, and is separated by filtration under a CO ₂ atmosphere. To recover (I) when M is Al, the solution is evaporated to dryness under reduced pressure, the residue taken up in n-heptane and the product separated by filtration. To hydrolyze the compound (I), this is dissolved in anhydrous tetrahydrofuran and then treated with H ₂ O. The compound (I) is dissolved in the tetrahydrofuran under an atmosphere of dry argon, the quantities used being such as to obtain a concentration of (I) in the tetrahydrofuran which ranges from 0.05 to 2 moles/l. H ₂ O is added to the solution in such a quantity as to obtain a molar ratio of H ₂ O to M of between 2 and 4. This reaction is conducted at ambient temperature for 0.5-2 hours while keeping the mixture stirred. The hydrolysis product is a colourless solid which is recovered by filtration. The compounds (I) are soluble in both aromatic and aliphatic hydrocarbons, and are very sensitive to atmospheric moisture, by which they hydrolyze rapidly. The hydrolysis products of the compounds (I) find important use in the production of very pure zeolites, with the introduction of the cations of interest. The following examples of the preparation of the compounds according to the invention are given by way of non-limiting illustration. EXAMPLE 1 SiCl ₄ (5 ml; 0.043 moles) dissolved in anhydrous toluene (100 ml) is added slowly under a carbon dioxide atmosphere to a solution of 35.5 g (0.485 moles) of diethylamine MHEt ₂ in anhydrous toluene (200 ml). After stirring for 5 hours at a temperature of 23°C in a CO ₂ atmosphere, the reaction mixture comprised a colourless solution and a colourless solid consisting of diethylammonium chloride. The reaction mixture was filtered under CO ₂ and the solution was recovered, for which the chloride test was found negative, and was concentrated under reduced pressure (10⁻² Torr) to a volume of 30 ml, and cooled to about -30°C. This treatment resulted in the partial crystallization of the silicon N,N-diethylcarbamate, which was recovered as a colourless solid by filtration and dried at 20°C under reduced pressure to obtain 5.7 g of product. After cooling the toluene solution, resulting from the filtration, to about -30°C and adding 30 ml of n-heptane, a further 12.45 g of product were recovered, to give an overall yield of 86% on the silicon tetrachloride used. The product was analyzed for silicon content by combustion and for carbon dioxide content by decomposing with 20% sulphuric acid and measuring the volume of the gas evolved. Analysis: % found (calculated values for C ₂₀ H ₄₀ N ₄ O ₈ Si being given in parentheses): Si, 5.7 (5.7); CO ₂ , 32.9 (35.7). The compound has an intense IR band at 1710 cm ⁻¹ due to the coordinated carbamate grouping. The ¹ H-NMR spectrum shows two resonances corresponding to absorption of the methylene and methyl groups bonded to the nitrogen of the carbamate group, Si[O ₂ CN(CH ₂ CH ₃ ) ₂ ] ₄ EXAMPLE 2 Example 1 is repeated, using diisopropylamine in place of the diethylamine. Silicon N,N-diisopropylcarbamate, Si[O ₂ CNPr ₂ ] ₄ , was obtained and was analyzed for its silicon and carbon dioxide content as indicated in Example 1. Analysis: % found (calculated values for C ₂₈ H ₅₆ N ₄ O ₈ Si being given in parentheses): Si, 4.2 (4.6); CO ₂ , 26.8 (29.1). CO ₂ :Si molar ratio = 4.1. EXAMPLE 3 The silicon N,N-diethylcarbamate, Si[O ₂ CNEt ₂ ] ₄ , obtained in Example 1 (2.47 g; 5.01 mmoles) was dissolved in anhydrous tetrahydrofuran (100 ml) under a dry argon atmosphere and treated with 0.36 g (20.0 mmoles) of H ₂ O at ambient temperature. A colourless suspension immediately formed and was kept stirring for 1 hour after which it was filtered under argon. The resultant finely divided colourless solid was dried for 12 hours under reduced pressure (about 10 ⁻² Torr) at ambient temperature. 0.401 g were obtained with a yield of 90.3% based on the silicon content of the product. Analysis: % found (calculated values for [NH ₂ (C ₂ H ₅ ) ₂ ] ₂ Si ₈ O ₁₇ .3H ₂ O, C ₈ H ₃₀ N ₂ O ₂₀ Si ₈ given in parentheses): C, 14,2; 12.9 (13.7); H, 3.8; 3.6 (4.3); N, 3.1; 3.3 (4.0); Si, 31.7 (32.1). EXAMPLE 4 Example 3 was repeated using a H ₂ O:Si molar ratio of 2. A finely divided colourless product was obtained, of appearance similar to the product of Example 3. The product had the following analytical composition: C, 15.0%; H, 4.2%; N, 4.0%. EXAMPLE 5 30 ml (21.66 g; 214 mmoles) of NH(iC ₃ H ₇ ) ₂ are dissolved in 200 ml of anhydrous toluene at atmospheric pressure under carbon dioxide. 5.05 g of AlBr ₃ (18.9 mmoles) are then added and the resultant suspension is stirred at ambient temperature for 7 hours. After filtering off the di-isopropylammonium hydrobromide which forms, the carbamate solution is evaporated to dryness under reduced pressure. The residue is taken up in n-heptane (30 ml), the resultant suspension is filtered and the aluminium dialkylcarbamate which collects on the filter is dried under a mechanical pump (ca. 10 ⁻¹ mmHg) for 2 hours. 4.3 g of product are obtained with a yield of 49.5%. The colourless microcrystalline product has good solubility in aromatic hydrocarbon solvents, moderate solubility in saturated hydrocarbon solvents and good solubility in CCl ₄ . Elemental analysis: found % (calculated values for Al[O ₂ CN(C ₃ H ₇ ) ₂ ] ₃ , C ₂₁ H ₄₂ AlN ₃ O ₆ given in parentheses): C, 53.0 (54.9); H, 8.9 (9.2); Al, 6.0 (5.9); CO ₂ , 27.3 (28.7); N, 8.4 (9.1). The product is very sensitive to atmospheric moisture. The infrared band (in polychlorotrifluoroethylene) shows absorption bands at 2960, 2930, 2880, 1620, 1550 f, 1500 f.

Claims: A process for preparing N,N-dialkylcarbamates of general formula (I): M[O₂CNR₂] n where M is Si or Al, n is 4 when M is Si and 3 when M is Al, and R is a C₁-C₆ alkyl group, and the respective hydrolysis products, characterised by: a) reacting a secondary amine of formula R₂NH and CO₂ with MX n in which R, M and n have the aforesaid meaning, and X is Cl or Br, in a reaction medium consisting of an organic solvent; b) filtering off the dialkylammonium halide which forms; c) precipitating the compound (I) by concentrating the filtered solution, and if necessary cooling and adding n-heptane; d) recovering the product (I) by filtration; and optionally e) dissolving the product (I) in anhydrous tetrahydrofuran and hydrolyzing with water; f) recovering the hydrolysis product by filtration. A process as claimed in claim 1, characterised in that said solvent is chosen from the group consisting of saturated aliphatic and aromatic hydrocarbons. A process as claimed in claim 2, characterised in that said solvent is toluene. A process as claimed in claim 1, characterised in that said organic solvent has a water content of less than 50 ppm. A process as claimed in claim 1, characterised in that the molar ratio of the secondary amine to the MX n used in the reaction is between 8 and 12. A process as claimed in claim 1, characterised in that the reaction between the secondary amine, CO₂ and MX n is conducted at a temperature of between 15°C and 30°C in a CO₂ atmosphere for a time of between 4 and 8 hours. A process as claimed in claim 1, characterised in that said precipitation of the compound (I) when M is Si is effected by concentrating said filtered solution to a compound (I) concentration of between 1 and 2 moles/l, then cooling to -30°C and adding n-heptane in a quantity of between 1 and 3 volumes per volume of solution, while maintaining the temperature at -30°C. A process as claimed in claim 1, characterised in that said hydrolysis of the compound (I) is conducted at a compound (I) concentration in tetrahydrofuran of between 0.05 and 2 moles/l, with a molar ratio of H₂O to M of between 2 and 4. A process as claimed in claim 1, characterised in that said hydrolysis of compound (I) is conducted at ambient temperature for 0.5-2 hours under stirring.

Inventors: BELLI DELL AMICO DANIELA, CALDERAZZO FAUSTO, DELL INNOCENTI MICHELA, BELLI DELL' AMICO, DANIELA, CALDERAZZO, FAUSTO, DELL'INNOCENTI, MICHELA
Applicants: CONSIGLIO NAZIONALE RICERCHE, CONSIGLIO NAZIONALE DELLE RICERCHE
Application year: 1990
Main classification: C07F5
IPC codes: C07F7, C07F5