Field of Invention

The invention relates to processes for preparing secondary and tertiary amines and more particularly to processes for preparing mixed secondary and tertiary amines having high purity.

Background

Mixed secondary amines (i.e., secondary amines having different organic groups attached to the nitrogen) and mixed tertiary amines (i.e., tertiary amines having at least two different groups attached to the nitrogen) are known compounds which have many uses in which it is detrimental to have them contaminated with substantial amounts of by-products, such as the primary and/or tertiary amines which are typically co-produced when the secondary amines are synthesized or the tertiary amines which are different from the desired mixed tertiary amines but are typically co-produced with them. Contamination of amine products with amine by-products is quite common and occurs when they are prepared in the absence of any liquid medium, in an aqueous medium, or in an organic solvent. One case in which this contamination is a particular problem is in the preparation of mixed secondary amines corresponding to the formula RCH ₃ NH in which R is an alkyl group containing 6-24 carbons. Another case in which this contamination is a particular problem is in the preparation of mixed tertiary amines corresponding to the formula RR'CH ₃ N in which R and R' are the same or different alkyl groups containing 6-24 carbons. Both the symmetrical and the asymmetrical mixed tertiary amines formed in conventional syntheses are contaminated with substantial amounts of tertiary amines in which all of the organic groups attached to the nitrogen are the same; and the asymmetrical amines, i.e., those in which R and R' are different, are further contaminated with such large amounts of the symmetrical amines produced with them that they are apt to constitute less than 50% of the amine product.

U. S. Patent 3,471,562 (Wakeman et al.) discloses a process for prepari a mixed tertiary amine by (1) reacting one molar proportion of an alkyl bromide wi eight molar proportions of methylamine in an amount of isopropanol constituti somewhat more than 50% of the weight of the reaction mixture to form a salt of mixed secondary amine, (2) removing excess methylamine and isopropanol, (3) addi caustic soda solution to free the amine salt thus formed, and (4) adding a second m of the alkyl bromide in an equal amount of isopropanol and reacting it with th secondary amine to form the tertiary amine.

The reason for the use of a large excess of the amine in the Wakema et al. process is not explained, but the patentees' utilization of an alcoholic solve is the probable explanation. It is ordinarily necessary to increase the amine/alkyl halid ratio in such a reaction to achieve a yield of secondary amine comparable to wh is obtained with a lower amine/alkyl halide ratio when the reaction is conducted i the absence of an organic solvnt. U. S. Patent 2,870,207 (Niederhauser et al.) discloses the use of hydrogen halide acceptor, such as sodium hydroxide or a molar excess of the amin reactant, in an alkenyl halide/alkylamine or alkyl halide/alkenylamine reactio conducted to prepare a secondary amine in which both of the organic groups attache to the nitrogen contain 12-24 carbons. U. S. Patent 3,780,107 (Polanskyj et al.) teaches a continuous proces for preparing long-chain amines by reacting long-chain alkyl halides with a 2-500 mola excess of a normally liquid alkyl-, alkylene-, or alkanolamine containing 2-6 carbons

Summary of Invention

It has now been found that mixed secondary amines can be prepare with minimal co-formation of primary and/or tertiary amines by reacting (A) one mola proportion of an alkyl bromide corresponding to the formula RBr in which R is a alkyl group containing 6-24 carbons with (B) at least seven molar proportions o methylamine in the absence of an organic solvent.

The mixed secondary amines thus obtained can then be converted int mixed tertiary amines having high purity by reacting a product of the secondary amin

synthesis with an alkyl bromide corresponding to the formula R'Br in which R' is an alkyl group containing 6-24 carbons.

Detailed Description

Alkyl bromides which are utilizable in the synthesis of the secondary amines include, e.g., the hexyl, 2-ethylhexyl, octyl, 2-ethyloctyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, docosyl, and tetracosyl bromides. Because of the interest in products that can be formed from them, the preferred bromides are ordinarily those in which the alkyl groups are primary alkyl groups, most of which (i.e., at least 75%, preferably at least 90% of which) are linear. Mixtures of the alkyl bromides are also utilizable when desired.

As already mentioned, the amount of methylamine employed in the reaction with the alkyl bromide must be such as to provide a methylamine/alkyl bromide mol ratio of at least 7/1 in the reaction mixture in order to minimize the co-formation of primary and/or tertiary amines. The production of by-products is further minimized as this ratio is increased, and there is no maximum to the amount of methylamine that may be used. However, since the use of more than about 13-15 mols of methylamine per mol of alkyl bromide does not appear to effect further reductions in by-product formation, it is usually preferred to employ the reactants in a methylamine/alkyl bromide mol ratio of about 13-15/1. Although the reaction between the alkyl bromide and methylamine may be conducted at ambient temperatures, it proceeds more rapidly at elevated tempera¬ tures and is most commonly conducted at a temperature of about 20-250 ° C, preferably about 135-170 * C, under autogenous pressure. Either a batch or a continuous process may be used in reacting the alkyl bromide and methylamine, but a continuous process is generally preferred.

The secondary amine synthesis of the invention is one in which no organic solvent is used, and it may be accomplished by stirring a mixture of the alkyl bromide and methylamine at the desired reaction temperature in the absence of any additives until the reaction has been completed. However, since the reaction results in the formation of the secondary amine and hydrogen bromide, and the secondary amine

is thus produced in salt form when prepared in the absence of a hydrogen hali acceptor, it is sometimes desirable to conduct the reaction in the presence of hydrogen halide acceptor.

When a hydrogen halide acceptor is included in the initial reacti mixture, it may be any conventional alkaline hydrogen halide acceptor, such as sodiu hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, calcium oxid or the like; and it may be added to the reaction mixture in solid or aqueous for

The preferred hydrogen halide acceptors are the alkali metal hydroxides, mo preferably sodium hydroxide. The amount of hydrogen halide acceptor employed may be the minimu amount required to free the secondary amine from its salt, i.e., one mol per mol hydrogen bromide formed in the reaction; or an excess may be utilized. Howeve the amounts of hydrogen halide acceptor and any other material (such as wate introduced with it should not be such as to create too much interference between alk bromide/methylamine molecular contact. In the processes of the invention, the alk bromides, methylamine, and reaction products thereof should constitute at least 50 usually at least 55% of the weight of the reaction mixtures.

When the alkyl bromide/methylamine reaction is conducted in th absence of a hydrogen halide acceptor, the secondary amine product may be free from its salt by the post-addition of any of the solid or aqueous hydrogen halid acceptors mentioned above, conveniently after cooling the reaction mixture at the en of the reaction.

The mixed secondary amine formed by the process of the invention ma be isolated in any suitable conventional manner. For example, when it is in a soli mass, the mass can be filtered and then distilled; and, when it is in an aqueous syste it is generally recovered by phase separation followed by distillation.

In the preparation of a mixed tertiary amine by the process of th invention, an alkyl bromide may be mixed with an unisolated, crude secondary amin prepared by the above-described process; or the secondary amine may be isolated fro the reaction mixture before it is mixed with the alkyl bromide. The use of an isolate secondary amine is usually preferred in order to improve the purity of the tertiar

amine product.

The alkyl bromide which is reacted with the mixed secondary amine may be any of the alkyl bromides mentioned above as useful in the preparation of the secondary amine, and it may be the same as or different from the alkyl bromide used in synthesizing the secondary amine. In the preparation of the tertiary amine, the proportionation of the reactants does not have the criticality it has in the preparation of the secondary amine. The reactants are ordinarily employed in substantially stochiometic amounts, but an excess or deficit of either reactant may be used.

In the synthesis of the mixed tertiary amine, the conditions used for the reaction, the materials used to free the amine from its salt form, and the methods used to isolate the amine may be any of those described above as utilizable in the preparation of the mixed secondary amine.

The following examples are given to illustrate the invention and are not intended as a limitation thereof.

EXAMPLE I

Charge a two-liter stainless steel autoclave with 295g (1.34 mols) of 1- bromodecane and 584g (18.4 mols) of methylamine. Heat the reaction mixture to 135 ^β C and maintain that temperature for one hour while stirring. Cool, add 104.8g of 50% sodium hydroxide, and isolate the product. The amount of purified N- decylmethylamine obtained is 90% of the theoretical amount. Essentially all of the starting bromide is converted.

EXAMPLE II

Charge a two-liter stainless steel autoclave with 295g (1.34 mols) of 1- bromodecane and 584g (18.4 mols) of methylamine. Heat the reaction mixture to 135 ° C and maintain that temperature for one hour while stirring. Cool the reaction mixture and add 104.8g of 50% sodium hydroxide to free the N-decylmethylamine formed. Add 233g (1.21 mols) of 1-bromooctane to the reaction mixture, heat the mixture to 135 ^β C, and maintain that temperature for one hour while stirring. Cool, add more 50% sodium hydroxide to free the amine, and isolate the product. Analysis

shows the product to be about 96% N-octyl-N-decylmethylamine and 2-3% trialk amine.

In contrast to the highly pure product prepared in the preceding examp asymmetrical mixed tertiary amines prepared by known processes are contaminat with large amounts of symmetrical mixed tertiary amines as well as with trialkylamin as shown in the following comparative example.

COMPARATIVE EXAMPLE

Charge a two-liter stainless steel autoclave with 221.1 g (1.0 mol) of bromodecane, 193.1g (1.0 mol) of 1-bromooctane, and 36.0g (1.2 mols) of methylami Stir the reaction mixture at 150 ^β C for four hours, cool, and add 160g of 50% sodiu hydroxide to neutralize the hydrobromide salt. Analysis of the N,N-dial-kylmethylami component of the product shows it to contain N,N-dioc lmemylamine, N,N-didecylm thylamine, and N-octyl-N-decylmethylamine in a 25/25/50 distribution.