CA1166649A

CA1166649A - Process for the production of n,o-disubstituted urethanes

Info

Publication number: CA1166649A
Application number: CA000385293A
Authority: CA
Inventors: Hans-Josef Buysch; Heinrich Krimm; Wolfgang Richter
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1980-09-19
Filing date: 1981-09-04
Publication date: 1984-05-01
Also published as: DE3035354A1; EP0048371B1; JPS5782361A; ZA816484B; EP0048371A3; DE3161792D1; EP0048371A2; ES8206452A1; AU7523581A; BR8105975A; ES505616A0

Abstract

Mo-2276 LeA 20,586 A PROCESS FOR THE PRODUCTION OF
N,O-DISUBSTITUTED URETHANES
ABSTRACT OF THE DISCLOSURE
N,O-disubstituted urethanes are produced by reacting a primary amine with a dialkyl carbonate in the presence of a catalyst. Suitable catalysts include neutral and basic compounds of lead, titanium and zirconium. The urethanation reaction is desirably carried out at a temperature in the range of 80 to 250°C.
The N,O-disubstituted urethanes produced by this process are particularly useful as starting materials in processes for the production of isocyanates.

LeA 20,586

Description

Mo-2276 -1- LeA 20,586 A PROCESS FOR THE PRODUCTION O~
N,~-DrSUBS~ITUTE~ URETHANES
.
BACKGROUND OF THE INVENTION
This invention relates to a process for the production of N,O-disubstituted urethanes. Specifically, it relates to a process for the production of N,O-disubstituted ùrethanes in which primary amines are reacted with dialkyl carbonates.
It is known that amines can be reacted with carbonic acid esters to form urethanes. According to U.S. Patent No. 3,763,217, Lewis acids and uranium compounds may be used as catalysts for this purpose.
However, in addition to urethane formation, these compounds also catalyze alkylation of the amines by the carbonic acid esters, so that considerable quantities of N-alkylated amines are formed. This alkylation increases rapidly with increasing reaction temperature while urea formation (another secondary reaction) in-creases with increasing reaction time. Consequently, the range of acceptable reaction times and temperatures is limited. The above-described catalysts are typically used in quantities of about 10% by weiyht although in many cases larger quantities may be required. Since Lewis acids form complexes with amines, i~ is virtually impossible to recover these catalysts intact.
Two catalysts which have been found to yield relatively satisfactory results are uranium trioxide (UO3~ and uranium tetrachloride (UC14). These compounds must be used in quantities of about 10% by weight and 3a require both a reaction temperature of 80C and long reaction times. Uranium compounds are not commercially LeA 20,586 - -; 116~649 desirable catalyts, however, because of the danger of radioactive contamination and the extensive and costly safety precautions which must be taken.
In another process for the production of N-aryl O-alkyl urethanes, alkali metal compounds (particularly sodium compounds) are used to catalyze the reaction of aromatic amines with dialkyl carbonates (see Japanese ~ patent application as laid open 090,478). These ; alkali metal compounds which are used in at least equimolar quantities (based on the amine) are removed from the reaction environment by neutralization with acids and cannot therefore be recovered and reused.
Consequently, this process is also commercially impractical.
SUMM~RY OF THE INVENTION
It is an object of the present invention to provide a process for the production of N,0-disubstituted urethanes.
It is a further object of the present invention to provide a process for the production of N,0-di-substituted urethanes in which substantially all of the reactant amine is converted to urethane without the formation of a substantial amount of ureas.
It is also an object of the present invention to provide a process for the production of N,O-disubstituted urethanes which re~uires a shorter reaction time than prior art processes.
These and other obiects which will be apparent to those skilled in the art are accomplished by reacting a primary amine with a dialkyl carbonate in the presence of a catalyst. Appropriate catalysts ' include neutral and basic compounds of lead, titanium and zirconium. It has now surprisingly , ~ , Le~ 20,SB6 ' , 4~

been found that these lead, titanium and zircon-- ium compounds are particularly suitable catalysts for the production of N,O-disubstituted urethanes because when these catalysts are used, virtually no N-alkyl amines are present in the product (in contrast to the process disclosed in U.S. 3,763,217). These catalysts make i~ possible to use higher temperatures without promoting secondaxy reactions which temperatures shorten the reaction time. These catalysts also make it possible to continue the reaction until the amine has been completely converted without promoting the formation of ureas.
DETAILED DESCRIPT~ON OF THE INVENTION
The present invention relates to a process for the production of N,O-disubstituted urethanes in which primary amines are reacted with dialkyl carbonates in the presence of a catalyst. Appropriate catalysts are neutral or basic inorganic or organic compounds of lead, titanium or zirconium. The N,O-disubstituted urethanes obtained by the process of the present invention are particularly useful as starting materials for the production of organic isocyanates.
Amines suitable for use in the process of the present invention include any organic compound which contains at least one primary amino group and which is otherwise inert under the reaction conditions.
Organic compounds which contain only aromatically-bound amino groups are among the pre~erred amines. Particu-larly preferred starting materials for the process of the present invention are compounds corresponding to the formula:
Rl (NH2)_ LeA 20,586 and mixtures thereof, In the'above'fo'rmula,' R
- represents an aromatic hydrocarbon radical with a total of 6 to 15 carbon atoms optionally containing alkyl and/or halogen substituents and/or alkylene brid.ges (particularly methylene bridges) and n represents 1 or 2.
. Examples of suitable amines are aniline; _-, m-, p-toluidine; o-, m-, p-chloroaniline; o-, m-, p-bromoaniline; o-, m-, p-trifluoromethyl aniline;

2,4-, 2,6-, 3,4- and 3,5-dimethyl-, -dichloro-, -dibromo-and diethyl-aniline; p-tert.butyl àniline; m- and p-phenylene diamine; 2,4- and 2,6-diaminotoluene;
: a- and ~-naphthyl amine; 1,4-, 1,5-, 2,6- and 2,7-diaminonaphthalene; 2,4'-, 2,2'-, 4,4'-diaminodiphenyl methane; 3,3'-dimethyl-4,4'-diaminodiphenyl methane;

3,3'-dichloro-4,4'-diaminodiphenyl methane; 4,4'-diaminodiphenyl-2,2-propane; 4,4'-diaminodiphenyl ether; methylamine; ethylamine; isopropylamine; n-butylamine; isobutylamine;: cyclohexylamine; dodecylamine;:
1,4-tetramethylene diamine; 1',6-hexamethylene diamine;
2,2,4-trimethyl hexamethylene diamine; isophorone diamine; and 4,.4'-diaminodicyclohexyl methane.
Any dialkyl carbonate may be used as a starting material in the process of the present invention.
Such dialkyl carbonates include compaunds corresponding ' to the formula:
: R - o ~
/C = O

in ~hich LeA 20,586 ;i64~1 .

R and R represent the same or dif~erent alkyl radicals, which radicals preferably contain from l to

4 carbon atoms. Particularly preferred dialkyl carbonates for the process of the present invention are those compounds corresponding to the above general formula -in which R2 and R3 represent the same saturated, un-substituted alkyl radic~l containing from l to 4 carbon atoms. It is also possible, although less preerred, to use cyclic carbonates corresponding to the above general formula, in which R2 and R3 together represent an alkylene radical containing a total of from 3 to 6 car-bon atoms andwhich, together with the carbonate radical, form a heterocyclic ring having at least 6-members. The term "dialkyl carbonate" as used herein should therefore be understood to include cyclic carbonates of this type.
Typical examples of dialkyl carbonates suitable to the process of the present invention are dimethyl, dieth~l, di-n-propyl, diisopropyl, di-n-butyl, diiso-butyl and methyl ethyl carbonate as well as cycliccarbonates, such as trimethylene carbonate and 2,2-dimethyl trimethyle~e carbonate.
Catalysts suitable to the process of the present invention are compounds of lead, zirconium and preferablY
of titanium, which show a neutral or basic reaction..
in aqueous solution or suspension. These catalysts are preferably compounds which do not contain any ionically-bound halogen or halogen bound to the metal atoms. Suitable compounds include: the hydroxides, oxides, carbonates and organic acid salts of lead, titanium and zirconium. The preferred catalysts are the salts of these metals formed from organic acids. Preferred catalysts are the salts of sulfonic acids such as benzene sulfonic acid, toluene sul~onic acid, chlorobenzene sulfonic acid, phenol sulfonic LeA 20,586 ;649 acid; salts of phosphonic acids such as benzene pho~-phonic acid, toluene'phosphonic acid, chlorobenzene' phosphonic acid, methoxy benzene phosphonic acid. Par-ticularly preferred catalysts are the'salts of car-boxylic acids such as formates, acetates, propionates,butyrates, laurates, stearates, benzoates, adipates, maleates,fumarates, succinates and sabacates, and alcoholates r such as methylates, ethylates, isopropylates, butylates, and iso-octylates of the above-mentioned metals.
The catalyst is used in the process of the present invention in a quantity which is from 0.01 to 6 wt. %, preferably from 0.05 to 5 wt. %, and most preferably from 0.1 to 3 wt. ~, based on the reaction mixture.
The reaction temperature should be in the range from 80 to 250C, preferably from 100 to 200C.
The process may be carried out under normal pressure or at elevated pressure. Elevated pressure should be applied in cases where low-boiling reactants are to be reacted at temperatures above their boiling point.
In the process of the present invention, the reactantæ are generally used in quantities such that there is at least one mole of dialkyl carbonate for each gram equivalent of amino groups of the amine. The reactants may be used in stoichiometric amounts. The reaction proceeds in accordance with the following equation:
RNH2 + ~R'O)2CO ~ RNHCOOR' + R'-OH
in ~hich the radicals R and R' represent the neutral 3~ radicals o~ the reactants. The urethane is virtually the sole reaction product. It may, however, be LeA 20,586 116f~i649 advantageous to use up to a 3~-fold molar excess of carbonic acid esters because'these'esters act'as solvents for sparingly soluble starting materials and speed up completion of the reaction. The alcohol formed is generally distilled off during the reaction.
Where dialkyl carbonates of relatively high-boiling alcohols (particularly cyclic carbonates) are used, the alcohol component is preferably separated off by fractional distillation after the reaction according to the present invention. The products obtained by the process of the present invention may be purified by distillation after their production.
The products obtained by the process of the present invention correspond to the formula:
Rl (NH-CO-O-R2) in which Rl, R2 and n are as defined above. These products represent valuable starting materials in the production of isocyanates. Such'isocyanates are produced by the'r'mally splitting the N,O-disubstituted urethanes of the present invention into the'isocyanate and alcohol on which they are based. Appropriate techniques for such thermal splitting are known to those in the art.
The products formed by splitting are immediately ~eparated. The products obtained by the process of the present invention are also valuable intermediates for the production of pesticides.
Having thus described our invention, the Pollowing examples are given by way of illustration.
The percentages given in these examples represent percen'tages by weight.

LeA 20,586 64~

EXAMoel.ES
EXAMPL~ 1 A mixture of 31 g (0.33 mole) of aniline, 118 g (1 mole) of diethyl carbonate and 1~5 g of titanium tetrabutylate was heated to boiling point in a 50 cm long metal-coated Vigreux column. The ethanol which formed distilled off during this heating. The sump temperature was 130 to 140C. After 6 to 7 hours, the conversion was complete and a stoichiometric quantity of ethanol had been eliminated. The reaction mixture was worked up by fractional distillation in vacuo.
After first runnings of diethyl carbonate, N-phenyl-O-ethyl urethane (melting point: 46 to 47C) was obtained at 90-93/0.1 mbar in a yield of 52 g (96% of the theoretical yield). No N-ethylaniline was detected.

93 g (1.0 mole~ of aniline, 174 g (1.0 mole~
of dibutyl carbonate and 2 g of zirconium tetrapropylate were heated to boiling point in a column and butanol was distilled off. After 5 to 6 hours, the reaction was complete and the sump temperature had risen to 190C. The reaction product which crystallized on cooling was recrystallized in ligroin. 172 g of N-phenyl-O-butyl urethane, corresponding to a yield of 89% of the theoretical yield (melting point 60-61C) were recovered.

93 g (1 mole) of aniline, 356 g (3 moles) of diethyl carbonate and 5 g of lead acetate were heated to hoiling and ethanol was separated off through a column at a sump temperature of 135 to 136C. Slowly precipitating diphenyl urea was left in the reaction mixture. After 6 hours, the temperature was increased LeA 20,586 64~

g to 180C using a pressure ve~sel` and maintained at that leveI for 5 hours. ~rac~ional distilla~ion yielded N-phenyl-O-ethyl urethane in an amount which was 96%
of the theoretical yield. No N-ethyl aniline was detected.

93 g of aniline, 356 g of diethyl carbonate and 3 g of zirconium tetrapropylate were heated for 25 hours at 130-134C, ethanol being split off. Fractional distillation yielded N-phenyl-O-ethyl urethane in an amount ~hich was 85~ of the theoretical yield. A
small fraction (1.5%) of the aniline used was converted into N-ethyl aniline.

15 I The procedure described in Example 1 was repeated ¦ using lead oxide as the catalyst. The reaction time was 22 hours. The catalyst was removed by treatment with 20 g of a sulfonated crosslinked polystyrene and the reaction product was worked up by distillation. 48 g of N-phenyl ethyl urethane melting at 48 to 49C
were obtained. tyield: 88% of the theoretical yield) 24 g (0.33 mole) of n-butylamine, 118 g (1 mole) of diethyl carbonate and 1.7 g of titanium tetrabutylate were reacted in the same manner as described in -45~

Example 1. Ater a reaction time'of 72, hours,,the reaction product was worked up by distillation.
24 g of N-n-butylethyl urethane were obtained at 93-95C/ll Torr. nD = 1.4292. Yield- 50~ of the theoretical yield (based on the n-butyl amine). The dibutyl urea formed as a secondary product was converted to N-butyl ethyl urethane by continued heating of the, reaction mixture. The yield of N-butyl ethyl urethane, based on the butyl amine was substantially quan,titative., 30.5 g (0.25 m~le) of 2,4-tolylene diamine, 118 g (1 mole) of diethyl carbonate and 2 g of titanium tetrabutylate were heated for 40 hours to reflux temperature in a 50 cm microcolumn while 23.5 g of ethanol were distilled off at 78 to 79C. 32 g of polyurea of the tolylene diamine were filtered off and the filtrate concentrate was distilled at up to 80C/10 Torr. Recrystallization from toluene gave 17 g of 2,4,-tolylene-his-ethyl urethane melting at 136 to 137C. YieId: 26% of the theoretical yield, based on m-tolylene diamine used.
The polyurea obtained in addition to the bis-urethane was converted into m-tolylene-bis-ethyl urethane by continued heating of the reaction mixture, so that a bis-urethane yield of from 94 to 97% of the theoretical yield (based on the tolylene diamine) was ultimately obtained.

13.8 g (0.1 mole) of 4,4'-diaminodiphenyl methane,,69.6 g (0.4 molel of dibutyl carbonate and 2 g of titanium tetrabutylate were heated to boiling point in a small column, n-butanol being split off. After LeA 20,586 11~6649 heating for 12 hours at lgO-195C, the'reaction product was separated from the'prec'ipitated polyurea by dissolution in methylene chloride and filtration.
After the solvent and excess dibutyl carbonate were distilled off in vacuo, 4,4'-methylene diphenyl-bis-.
butyl urethane (melting point 112-113C from toluene/
. ligroin) in a yield of 6.8 g (corresponding to 17%
of the theoretical yield) remained as residue.
Further reaction of the polyurea'in accordance with the procedure described in Example 9 by heating with dibutyl carbonate in the presence of titanium tetrabutylate increased the yield of 4,4'-methylene diphenyl-bis-butyl urethane to between 90 and 95%
of the theoretical yield.

LeA 20,586

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the production of N,O-di-substituted urethanes by reacting a primary amine with a dialkyl carbonate in the presence of a catalyst which is a neutral or basic compound of lead, titanium or zirconium.

2. The process of Claim 1 in which monoamines or polyamines containing aromatically-bound primary amino groups or mixtures thereof are used as the primary amine.

3. The process of Claim 1 in which the primary amine is a compound or mixtures of compounds corresponding to the formula:
R1-(NH2)n in which R1 represents an aromatic hydrocarbon radical with a total of 6 to 15 carbon atoms optionally containing alkyl and/or halogen substituents and/or alkylene bridges, and n = 1 or 2,

4. The process of Claim 1 in which the dialkyl carbonate is a compound corresponding to the formula:

in which R2 and R3 may be the same or different and each represents a saturated aliphatic hydrocarbon radical containing from 1 to 4 carbon atoms.

5. The process of Claim 1 in which the catalyst is a carboxylic acid salt of lead, titanium or zirconium.

LeA 20,586