DE3240082A1 - Preparation of dialkyl carbonates - Google Patents

Abstract

The invention relates to a process for the preparation of dialkyl carbonates which is characterised in that a monohydric aliphatic alcohol is reacted with carbon dioxide at temperatures from 0 to 300 DEG C and at a pressure from 1 to 3000 bar in the presence of a catalyst and a molecular sieve.

Description

Production of dialkyl carbonates

It is known that carbon dioxide and aliphatic alcohols can be converted into the corresponding dialkyl carbonates with the aid of tin dibutyl alkoxides as catalysts with elimination of water. The reaction proceeds according to The yields of this reaction are low, since the esterification equilibrium is strongly on the side of the starting materials (see Yamazaki et al., Pol. Preprints, Amer. Chem. Soc., Div. Polym. Chem. 20 (1979) pages 146 to 149, or Japanese Offenlegungsschrift dated January 11, 1979 No. 79/3012).

The invention is an improvement of this method, the leads to higher yields.

The invention thus provides a method for producing Dialkyl carbonates, which is characterized is that one monohydric aliphatic alcohol at temperatures from 0 to 300ob under pressure from 1 to 3000 bar in the presence of a catalyst and a molecular sieve with Converts carbon dioxide.

For example, gaseous carbon dioxide is used as the carbon dioxide.

In general, autoclaves are used for this reaction the alcohol, the catalyst and the molecular sieve are brought with them for example, gaseous carbon dioxide can be filled to the desired pressure and then brought to the reaction temperature. The carbonate formed can be isolated by conventional methods after releasing the pressure and opening the autoclave will.

Monohydric aliphatic alcohols suitable for the process are linear primary alcohols, branched primary alcohols or secondary alcohols, in particular C1-C10 alkanols such as ethanol, methanol, propanol, isopropanol, butanol, hexanol, 2-ethylhexanol, 2-methylpropanol, 3-methylbutanol, amyl alcohol and butanol-2 as well C5-C10 cycloalkanols such as cyclohexanol.

Suitable catalysts according to the invention are, for example, compounds the 1st to 6th main and subgroups as well as the 7th and 8th subgroups of the periodic System of elements (see Hollemann-Wiberg, textbook the inorganic Chemie, 37-39, edition, Verlag Walter De Gruyter and Co., Berlin 1956).

Compounds of the 1st main group and 1st subgroup which are suitable according to the invention are both salt-like and covalent compounds of the metals of these groups of the periodic table such as LiBr, Butyllithium, LiCl, LiJ, NaOCH3, CuCl, AgOCO-CH3 Etc.

Compounds of the 2nd main group and 2nd subgroup which are suitable according to the invention are both salt-like and covalent compounds of the metals of these groups of the periodic table such as MgCl2, Be (O-CO-CH3) 2, Grignard compounds, ZnC12, ZnSO4, Mg (OC2H5) 2 etc.

Compounds of the 3rd main and i. Subgroup are in particular covalent compounds of the elements of these groups of the periodic Systems like B + O-C6H5) 3, B (C6H5) 3, Al (OR) 3, (R = more aliphatic or aromatic Hydrocarbon residue) etc.

Compounds of the 4th main group and 4th subgroup which are suitable according to the invention derive from the elements germanium, tin, lead, titanium and zirconium; Examples are orthotitanates (e.g. tetrabutyl orthotitanate), orthostannates (e.g. tetraphenyl orthostannate) Etc.

Compounds of the 5th main group and 5th subgroup which are suitable according to the invention are in particular covalent bonds of the elements of these groups of the periodic table such as amines (e.g. diazabicyclooctane), phosphines (e.g. triphenylphosphine, Tri-n-octylphosphine), phosphine oxides (e.g. triphenylphosphine oxide) etc.

Compounds of the 6th main group and 6th subgroup which are suitable according to the invention are both covalent and salt-like compounds of the elements of these groups of the periodic table except for oxygen such as thioethers (e.g. diphenyl sulfide).

Compounds of transition group 7 which are suitable according to the invention are both covalent as well as salt-like compounds of the elements of this group of the periodic Systems (e.g. manganese (II) acetate).

Compounds of transition group 8 suitable according to the invention are both covalent as well as salt-like compounds of the elements of this group of the periodic Systems (e.g. iron (III) acetylacetonate).

Preferred catalysts for the process according to the invention are combinations of the above-mentioned compounds, where electron donor and electron acceptor properties the catalyst combination must be coordinated, i.e. combinations of Electron donors and electron acceptors are to be used.

Examples of such combinations are aluminum alcoholates in combination with amines, phosphines, phosphites or Phosphine oxides, lithium salts in combination with orthotitanates or magnesium alcoholates in combination with thioethers.

The catalysts suitable according to the invention are used in amounts of 10 3 to 5 mol%, preferably from 0.1 to 3 mol%, based on moles of each used alcohol used, and this applies both to the use of individual Catalysts as well as catalyst combinations. The molar ratio of the types of catalysts in the catalyst combinations can vary between 1: 3 and 3: 1 and is for example at 1: 1.

Preferred catalysts are Sn, Zr and Ti compounds of the general formula where R1 is C1-C18 alkyl or C6-C20 aryl, R2 is C1-C18 alkyl, C6-C20 aryl or C2-C18 acyl, x is halogen, SH, = 0/2 or = S / 2 and n1, n2, n3 and n4 are integers from 0 to 4, the sum of n1 + n2 + n3 + n4 each being 4.

In particular, for Me = Sn n1 = 1 or 2 and for Me = Ti or Zr n3 = 4.

Particularly preferred catalysts are, for example, dialkyltin dialkoxides such as dibutyltin dibutylate or dibutyltin dilaurate / tetrapropyl orthozirconate and Tetrabutyl orthotitanate.

The molecular sieves to be used according to the invention are known (see for example DE-OS 2,350,327, column 3, lines 28 to 65 and Ullmann's Encyclopedia der technical chemistry, 4th edition, vol. 17, pages 9 to 18, Verlag Chemie, Weinheim 1979).

Particularly suitable molecular sieves are zeolites, their channels Have a diameter of 3 to 4 i.

The process can be carried out with or without a solvent or diluent will. All solvents or diluents are inert to the reaction Liquids suitable.

For the process one can use carbon dioxide pressures from 1 bar to 3000 bar, use in particular from 1 bar to 1000 bar, preferably 10 bar are used up to 500 bar and very particularly preferably 25 bar to 300 bar.

In general, temperatures from 0 to 300 ° C. can be used. However, the reaction temperatures are preferably between 100 and 220 ° C., particularly preferred temperatures are between 130 and 1800C.

The reaction times can be between 2 and 100 hours, in particular between 10 and 60 hours and in particular between 24 and 48 hours.

The amount of molecular sieve to be used for the process according to the invention must be dimensioned in such a way that that the split off in the reaction Water can be bound. It can also be a little more or a little less than that The amount of molecular sieve required for water binding is used.

A special variant of the process consists in the implementation Carried out in several stages, preferably up to five stages, after each In the second stage, the reaction solution is separated from the molecular sieve and replaced with fresh molecular sieve is moved.

Example 1 An aliphatic alcohol (25 g 2-ethylhexanol = 193.5 mmol) was with a catalyst (3.3 g dibutyltin dilaurate = 5.5 mmol / v 3 mol%) and a dehydrating substance (50 g molecular sieve 4 i) in a 200 ml Given laboratory autoclave. By repeatedly pressing in carbon dioxide followed by The air was removed by venting. Then 55 bar C02 were injected, shaken several times for mixing and the autoclave at 1600C for 66 hours tempered. The autoclave was then allowed to cool down and excess CO2 was drained off and the proportion of carbonate formed is determined by gas chromatography. The amount of di (2-ethylhexyl) carbonate was 22.2% (area%).

Example 2 Amounts used as in Example 1. A 250 ml laboratory autoclave used. The reaction temperature was 2200C, the Response time 18 hours.

The yield was 20.2%.

Example 3 1.25 g of 2-ethylhexanol (= 9.6 mmol), 0.083 g Dibutyltin dilaurate (= 0.14 mol ~ 1.5 mol%) and 2.5 g molecular sieve 3 i are used. A 10 ml high-pressure autoclave was used, onto which 3000 bar CO2 was injected became. The reaction temperature was 2000 ° C. and the reaction time was 42 hours. the Yield was 16.6%.

Example 4 Amounts used as in Example 1. It was e-in 200 ml laboratory autoclave used. After each 18 hours of reaction time at 1600C the reaction was interrupted, the reaction solution from the molecular sieve separated, treated with fresh molecular sieve and again injected CO2. To 4 reaction cycles, the carbonate yield was 60.1%.

Example 5 (comparative example) 12.5 g of 2-ethylhexanol (= 96 mmol) and 2.7 g of dibutyltin dilaurate (= 4.5 mmol = 4.7 mol%) were mixed with 50 ml of xylene and 10.3 g of N, N'-dicyclohexylcarbodiimide (= 50 mmol) in a 250 ml laboratory autoclave used. The reaction solution was under a CO2 pressure of 45 bar for 66 hours at room temperature touched. The carbonate yield was 8.1%.

Example 6 (comparative example) Amounts used as under example 5. A 200 ml laboratory autoclave was used. The reaction temperature was 80 ° C. and the reaction time was 66 hours. 4% carbonate was obtained.

Example 7 (comparative example) Amounts used as under example 5. Reaction in 200 ml laboratory autoclave. Reaction temperature 1200C, reaction time 9 hours. Yield of carbonate 7.3%.

Example 8 There were 40.45 g of n-butanol (= 545.65 mmol), 1.61 g of dibutyldimethoxy tin (= 5.46 mmol% = 1 mol%) and 50 g molecular sieve 3 i in a 200 ml laboratory autoclave mixed with 55 bar CO2. The reaction time was 91 hours, the reaction temperature 1550C. The yield of di (n-butyl) carbonate was 22.0% (areas *).

Example 9 10.0 g of n-heptanol (= 86.05 mmol) and 1.27 g of dibutyldimethoxytin were obtained (= 4.30 mmol = 5 mol%) with 50 ml xylene and 50 g molecular sieve in a 250 ml autoclave mixed with 55 bar CO2. The reaction temperature was 1550 ° C. and the reaction time 50 h. The yield of di (n-heptyl) carbonate was 19.4% (area%).

Example 10 quantities as under 9). 9.62 g of cyclohexanol were used as alcohol (= 96.08 mmol) were used. The reaction time was 91 hours, the reaction temperature 1550C. The yield of di (cyclohexyl) carbonate was 4.0% (area%).

Example 11 There were 25 g of 2-ethylhexanol (= 191.97 mmol) in 50 ml Xylene, 50 g molecular sieve 3 2 and 2.84 g zirconium propylate (= 8.67 mmol = 4.5 mol%) mixed with 55 bar CO2 in the 200 ml laboratory autoclave. The reaction time was 69h, the reaction temperature 155 ° C. 6.15% of di (2-ethylhexyl) carbonate were obtained (Area%).

Example 12 There were 12.5 g of 2-ethylhexanol (= 95.98 mmol) in 50 ml xylene, 50 g molecular sieve 3 2 and 4.40 g tetrabutyl orthotitanate in a 200 ml laboratory autoclave mixed with 55 bar CO2. After 53 hours at 150 ° C., 9.1% di (2-ethylhexyl) carbonate were obtained preserved (area%).

Example 13 Quantities and procedure as under 11. As a catalyst 7.25 ml of 20% solution of dibutylaluminum hydride (= DiBAH) in toluene / 2.28 g triphenylphosphine (= 8.7 mmol = 4.5 mol%) are used. After a reaction time of 42 h 4.0% di (2-ethyl-hexyl) carbonate were obtained.

Example 14 Quantities and procedure as under 12. As a catalyst 3.6 ml of 20% solution of DiBAH in toluene / 1.35 g of triphenyl phosphite (= 4.34 mmol = 4.5 mol%) used.

After a reaction time of 93 hours, the yield of di (2-ethylhexyl) carbonate was 3.0%.

Example 15 Quantities and procedure as under 12. As a catalyst 3.6 ml of 20% solution of DiBAH in toluene / 0.44 g of triethylamine (= 4.34 mmol = 4.5 mol%) are used. After a reaction time of 75 hours, the carbonate yield was 2.0%.

Claims (9)

Claims "". ~ 1. Process for the preparation of dialkyl carbonates, characterized in that a monohydric aliphatic alcohol is used at temperatures from 0 to 3000C and at a pressure of 1 to 3000 bar in the presence of a catalyst and a molecular sieve is reacted with carbon dioxide. 2. The method according to claim 1, characterized in that as Molecular sieves using zeolites. 3. The method according to claims 1 and 2, characterized in that the implementation is carried out in several stages 4. The method according to claims 1 to 3, characterized in that the reaction is carried out at pressures of 1 to 1000 bar performs. 5. The method according to claim 4, characterized in that at The reaction is carried out at pressures from 10 to 500 bar. 6. The method according to claims 1 to 5, characterized in that the reaction is carried out at temperatures from 100 to 2200C. 7. The method according to claim 6, characterized in that at The reaction is carried out at temperatures from 130 to 1800C. 8. The method according to claims 1 to 7, characterized in that the catalysts are Sn, Zr and Ti compounds of the general formula can be used, in which R1 is C1-C18 alkyl or C6-C20 aryl, 2 is C1-C18 alkyl, C6-C20 aryl or C2-C18 acyl, X is halogen, SH, = 0/2 or = S / 2 and n1 , n2, n3 and n4 are integers from 0 to 4, the sum of n1 + n2 + n3 + n4 each being 4. 9. The method according to claim 8, characterized in that as catalysts of the general formula, those are used in which Me = Sn and n1 = 1 or 2 where Me = Ti and n3 = 4 or where Me = Zr and n3 = 4.