HU208667B - Process for cleaning tertiary amines obtained by methnylation with formaldehyde - Google Patents

Abstract

Tert. amines of general formulan R1N(R)CH3 (1) (where R= a cyclohexyl R1=R or alkyl), prepd. by methylation with formaldehyde, are purified as follows: raw prods. are subjected to a preliminary distillation to remove methanol, formaldehyde and part of the water. 8-12C aryl alkanes and/or cycloalkyl-alkanes are added to the resulting mix at a 5-20 fold concn. based on the combined mass of residual water and/or formic acid present, as formates. This mixt. is boiled for 4-10 hrs. in this case with a stream of inert gas bubbling through and/or at reduced pressure. Fractions are continuously removed and condensed, which aryl and/or cyclo-alkyl alkanes are simultaneously recirculate

Description

The present invention relates to a process for the purification of tertiary amines of the formula I obtained by methylation with formaldehyde. In the formula (I), R is cyclohexyl or C 1 -C 6 straight or branched alkyl.

The so-called. fatty amines and their salts are industrially important compounds because they are basic, cationic and strongly adsorbed on various surfaces, altering their surface properties. Based on these properties, fatty amines are used as an additive for flotation, as a corrosion inhibitor in various oils, and as an excipient in the plastics industry.

A known and widely used process for the preparation of amines of the formula I is the N-methylation of the amines with 3537% aqueous formaldehyde. The reaction is carried out under pressure in the presence of hydrogen and a hydrogenation catalyst. The reaction is usually conducted in such a way as to achieve the fullest possible conversion of the starting amine and therefore excess formaldehyde is used. Some of the excess formaldehyde is hydrogenated to methanol and the other part is converted to formic acid and methanol by disproportionation. The formic acid formed forms a formate salt with the amine present and is incorporated into the reaction mixture. Depending on the methylation conditions, 0.1-10% by weight of the amine product may be present in its formate salt form. The formates are highly absorbent, which makes the reaction mixture more difficult to dehydrate than usual. The formate salts in the reaction mixture, depending on their amount, may precipitate out of solution in crystalline form, making processing difficult.

There are several methods known in the art for processing the reaction product of reductive N-methylation with formaldehyde. In some of the processes, only tertiary separation operations are used to separate the tertiary amines; such a solution is described, for example, in U.S. Pat. German patent specification. Alternatively, distillation is complemented by other operations to process the reaction product. For example, U.S. Patent No. 61,236,751. According to Japanese Patent Specification, tertiary amines are obtained by distillation with triethylene pentamine to improve the color or color stability of the tertiary amines. Japanese Patent Application No. 59199655 achieves the same effect using alkali metal hydroxides. No. 278,779. in the German Democratic Republic patent, phthalic anhydride is added to the reaction mixture to distillate the tertiary amine; this will improve the color of the separated tertiary amine, but may also remove the remaining primary and secondary amines. No. 7,905,987. Dutch Patent No. 4255,356; U.S. Pat.

No purification method has been described so far in the art whereby the reaction product of formaldehyde methylation can be purified from the formate salt and the product is practically anhydrous. Our aim was to develop such a procedure.

In our experiments, it was found that when the methylation reaction product - which, besides the desired tertiary amine, contains the formate salt of the amine, methanol, water, and unmodified formaldehyde, the remaining methanol, formaldehyde and some water were distilled off. Heat treatment with C12 -C12 alkylbenzenes and / or cycloalkylalkanes can completely remove the water, as well as the formic acid in its formate form, and recover the tertiary amine target product in high purity.

In the preparation of the reaction mixture by distillation, the mixture to be heat-treated contains 5-15% by weight of water in addition to the tertiary amine, besides the formate salt of the amine. The amount of formic acid bound in the formate form is 0.1 to 10% by weight, depending on the reaction conditions. The choice of water content is important for decomposition of the formate salt and removal of formic acid: For water contents below 5% and above 15%, formic acid removal cannot be completed.

The present invention therefore relates to a process for the preparation of tertiary amines of formula I in anhydrous and formic acid-free yarns.

According to the present invention, high purity tertiary amines of the formula I are prepared by the addition of 5 to 20 times the weight of the water and formic acid contained in C8-C12 alkylbenzenes or cycloalkylalkanes, based on the water and formic acid contained therein. a mixture of the appropriate compositions thereof. The resulting mixture is then refluxed for 4-10 hours and optionally 10-20 times the volume of the inert gas is bubbled through the mixture. The distillate from the batch distillation is continuously drained, after condensation, the water and formic acid in the separate phase are removed and the alkylbenzenes and cycloalkylalkanes are recycled.

The carbon number of the alkyl benzenes and cycloalkyl alkanes is selected depending on the boiling point of the tertiary amine to be purified. The amines having a boiling range of 160 to 220 ° C are C8-alkylbenzene or C8-cycloalkylalkane, or any mixture of such alkylbenzenes and / or cycloalkylalkanes. For amines having a spinning point above 220 ° C, C 9 -C 12 alkylbenzenes or cycloalkylalkanes, or any mixture thereof, are used. For high amines with a boiling point above 260 ° C, distillation is generally carried out under reduced pressure to provide milder conditions. The lower limit of the applicable pressure is 10 kPa.

The duration of the treatment is determined by the boiling point of formic acid formate salt bound and the mixture to be treated. Higher (3-15 m%) formic acid content and higher source (above 220 ° C) 2

EN 208 667 Β dehydrate the mixture for a longer period of time, otherwise dehydrate and formic acid over a shorter period of time.

Using the process of the invention, the desired tertiary amine can be prepared essentially free of water and formic acid. Further distillation operation (s) may achieve a purity greater than 99%.

The process does not require complicated equipment, the purification process can be carried out in batches, the high purity tertiary amine can be recovered economically from the reaction mixture.

The invention is illustrated by the following non-limiting Examples.

Example 1

The reaction mixture prepared by cyclization of cyclohexylamine formaldehyde was pre-distilled from methanol and partially dehydrated. The resulting mixture was composed of:, Ν-dimethylcyclohexylamine 90.2%, other amines 0.4%, water%, formic acid 1.4%.

1000 g of the mixture was poured into the distillation apparatus and 800 g of xylene mixture (d = 0.865, starting point 137 ° C, final point:

It was heated at 143 ° C per hour) and the mixture of 15 dm ³ argon stream for 8 hours. The distillate was continuously drained, water and formic acid appearing in a separate phase after condensation were removed, and the xylene mixture was returned to the distillation apparatus. As a result, N-, N-dimethylcyclohexylamine, free from water and formic acid, was obtained. Using further distillation, the target product was obtained in a purity of 99.7%.

Example 2

The reaction mixture, which was prepared by methylation of dicyclohexylamine in formaldehyde, was pre-distilled from methanol and partially dehydrated. The resulting mixture was composed of N-methyldicyclohexylamine 85.4%, other amines 0.8%, water 10%, formic acid 3.8%.

1000 g of the mixture was added to the distillation apparatus. 1200 g of a C8-C11 alkylbenzene mixture (C8 fraction: 8.5 m%, Carbon fraction: 85.9%, C10 fraction: 5.1 m%, C11 fraction: 0.5 m) % d ₄ ⁾ = 0.874, starting boiling point: 145 ° C, ending point: 190 ° C), and the resulting mixture was refluxed for 12 hours with 12 dm ^{3 of} nitrogen. The distillate was continuously drained, after condensation, the water and formic acid in a separate phase were removed and the alkylbenzene mixture was returned to the distillation apparatus. Treatment resulted in water and formic acid-free N-methyldicyclohexylamine. Further purification by distillation provided the target product with a purity of 99.6%.

Example 3

The reaction mixture obtained by methylation of N- (n-hexyl) -cyclohexylamine with formaldehyde was pre-distilled from methanol and partially anhydrous. The mixture thus obtained had the following composition: N- (n-hexyl) -N-methylcyclohexylamine 87.2%, other amines

1.1%, water 7.5%, formic acid 4.2%.

1000 g of the mixture was added to the distillation apparatus. 1750 g of mesitylene were added and the mixture was heated under reflux for 10 hours. The distillate was continuously drained, after condensation, the water and formic acid present in the separate phase were removed and the mesitylene was returned to the distillation apparatus. As a result, N- (n-hexyl) -N-methylcyclohexylamine, free from water and formic acid, was obtained. Further distillation gave 99.2% purity of the target product.

Example 4

1000 g of the composition described in Example 1 was introduced into the distillation apparatus. 1000 g of methylcyclohexane were added and the resulting mixture was heated to reflux for 18 hours with 18 dm ^{3 of} nitrogen. The distillate was continuously removed, after condensation, the water and formic acid present in the separate phase were removed and the methylcyclohexane was returned to the distillation apparatus. As a result of the treatment, mentes, Ν-dimethylcyclohexylamine free of water and formic acid was obtained. Using further distillation, the target product was obtained in a purity of 99.6%.

Example 5

The procedure described in Example 2 was followed; with the difference that it is gas-free without boiling

It was carried out at 26.3 kPa for 6 hours. As a result, N- methyldicyclohexylamine free of water and formic acid was obtained. By further distillation, the target product was obtained in a purity of 99.4%.

Claims (3)

PATENT CLAIMS CLAIMS 1. A process for the distillation purification of tertiary amines of formula (I) formed by methylation with formaldehyde, wherein R represents a cyclohexyl group or a straight or branched alkyl group containing from 1 to 6 carbon atoms, wherein the tertiary amine crude product is previously distilled to remove methanol and formaldehyde. water, characterized in that it is present in the remaining mixture 5 to 20% by weight based on the combined weight of water and formic acid formated salt form, 5 to 20 times the amount of C 8-12 alkylbenzenes and / or cycloalkylalkanes and the resulting mixture, optionally by bubbling inert gas and / or At a pressure not greater than 10 kPa - boil for 4 to 10 hours under distillation EN 208 667 Β and condensation and recycling of alkylbenzenes and / or cycloalkylalkanes. Process according to claim 1, characterized in that C 8 -C 12 cyclohexylalkanes are used, optionally in a mixture. The process according to claim 1 or 2, characterized in that nitrogen gas is bubbled through the mixture at a rate of 10-20 times per hour during boiling.