AND PIAMINES

This invention relates to the preparation of copper-diamine complexes and the corresponding diamines. More particularly, it relates to a method for preparing diamines in high yields and with a minimum of by-products, wherein a copper-diamine complex is obtained as an interme¬ diate.

Various diamines in which both nitrogen atoms are secondary or tertiary are useful as components of catalyst systems used to prepare polyphenylene oxides (also known as polyphenylene ethers) by the oxidative coupling of phenols. Among the diamines useful for this purpose as N,N' -di-t-bu- tylethylenediamine (hereinafter DBEDA) and N,N' -diphenyleth- ylenediamine. The polyphenylene oxides produced by the use of these catalysts are in wide use as constituents of engineering resins.

A method commonly used for the preparation of DBEPA and similar diamines is by the reaction of a primary amine such as t-butylamine with a dihaloalkane such as 1,2-dibromoethane. Another method, disclosed in U.S. Patent 4,160,785, is the hydrogenation of a dii ine formed by the reaction of a dialdehyde such as glyoxal with a primary amine such as t-butylamine. Both of these reactions form, in addition to the desired product, a number of by-products such as N,N' -di-t-butylpiperazine, N,N' -di-t-butylimidazoli- dine, t-butylaziridine and vinyl bromide. Many of these by-products are toxic, some are suspected carcinogens, and none display catalytic activity in the oxidative coupling reaction. Therefore, there is continued interested in developing methods of synthesizing such diamines.

U.S. Patent 3,914,266 describes the reaction of diamines of this type with cupric bromide to produce copper- diamine complexes which are also useful as catalyst consti¬ tuents for polyphenylene oxide preparation. In order to obtain the complexes by this method, of course, it is necessary first to prepare the diamine by one of the above- described methods. Thus, the preparation of the complexes is subject to the same disadvantages as the preparation of the diamines themselves. A principal object of the present invention, therefore, is to provide a new synthetic method for prepar¬ ing copper-diamine complexes and the corresponding diamines.

A furrher object is to provide a method for preparing the diamines using the copper-diamine complexes as intermediates.

A further object is to provide a preparation method which affords the desired product in high yields and with a minimum of by-products.

A still further method is to provide a new method for preparing materials useful as catalyst constituents in the oxidative coupling of phenols to polyphenylene oxides.

Other objects will in part be obvious and will in part appear hereinafter.

In one of its aspects, the present invention is a method for preparing a copper-diamine complex having the formula

wherein:

R is an ethyiene, trimethylene or C _ς , 1,2- or 1, 3-cycloalkylene radical which, if substituted, contains only phenyl substituents or tertiary alkyl substituents containing about 4-8 carbon atoms;

2

R is an alkyl radical containing up to about 8 carbon atoms or a phenyl radical; 3 R is hydrogen, an alkyl radical containing up to about 8 carbon atoms or a phenyl radical; and X is chlorine, bromine or iodine; said method comprising reacting a dihalide of the formula R 1X- with an amine of the formula R2NHR3 and at least one basic copper(II) compound in at least one alipha¬ tic or aromatic nitrile as diluent. The dihalide used in the method of this invention may be a dichloride, dibromide or diiodide, or a mixed dihali.de such as a chlorobromide. The R value therein may be an ethyiene, trimethylene or 1,2- or 1,3-cyclopentylene or cyclohexylene radical, or a corresponding phenyl- or t-alkyl-substituted radical such as phenylethylene, diphen- ylethylene, t-butylethylene, (3-rnethyl-3-pentyl)ethylene, (2, , -trimethyl-2-pentyl)ethyiene or 3-t-butyl-l,3-cyclo- hexylene. Preferably, the R radical contains at most one substituent, and more preferably it is unsubstituted. The ethyiene radical is especially preferred.

The amine may be primary or secondary and is 2 usually primary. The R value therein may be phenyl or an alkyl radical such as methyl, 1-propyl, 2-propyl, 1-butyl,

2-butyl, t-butyl or 2, ,4-trimethyl-2-pentyl. The t-alkyl

3 radicals and especially t-butyl are preferred. The R value is usually hydrogen but may be any of the radicals listed

2 for R . Thus, suitable amines include dimethylamine, diethylamine, 1-propylamine, 2-propylamine, t-butylamine,

1-pentylmethyiamine and 1-octylamine, with t-butylamine being particularly preferred because of its availability and the high utility of the diamine thus produced as a catalyst constituent. Illustrative basic copper(II) compounds which may be used in the method of this invention are cupric oxide, cupric sulfide, basic cupric acetate and basic cupric carbonate. It is strongly preferred that the copper com¬ pound be halide-free. Because of its availability and relatively low cost, cupric oxide is the preferred basic copper compound.

The rate of reaction of the basic copper(II) compound depends to some extent on the proportion of avail¬ able surface area thereon. It is therefore preferred to use it in a form which has a high surface area. An example is "copper oxide wire", commercially available from Fisher Scientific Company.

Another essential feature of the method of this invention is the diluent, which is at least one aliphatic or aromatic nitrile such as acetonitrile, propionitrile, butyronitrile or benzonitrile. The saturated aliphatic nitriles and especially acetonitrile are preferred. Mix¬ tures of nitriles may be used but their use seldom provides any benefit. The method of this invention is typically conduct¬ ed by heating a mixture of the four above-described materi¬ als at a temperature typically in the range of about 50- 120°C, and preferably about 70-100°C, until the reaction is complete. Mixtures of this type are another aspect of the invention. When the diluent is acetonitrile, the reaction may be conveniently conducted at reflux since the boiling point of acetonitrile is about 82°C. The progress of the reaction can be visually followed by the disappearance of

the basic copper(II) compound as it is consumed. When consumption thereof has ceased, the reaction may be consid¬ ered to have proceeded as far as possible.

Isolation of the copper-diamine complex may be effected by crystallization from the reaction mixture by evaporating and/or cooling. If desired, the complex may be further purified by recrystallization or the like, but such further purification is generally unnecessary.

It will be apparent from formula I that the reaction theoretically involves two moles of amine, one mole of dihalide and an amount of basic copper compound contain¬ ing one gram-atom of copper. In practice, it is often advantageous to employ a slight excess of amine, typically about 2.1-2.5 moles per mole of dihalide. The reaction mix-cure typically comprises about 40-60% reactants, with the balance being diluent.

As is apparent from formula I, the diamine ligand in the copper complex has the formula

wherein R 1, R2 and R3 are as previously defined. This diamine may be liberated from the complex by reacting it with a stronger complexing agent for copper(II) than the diamine, and this reaction constitutes another aspect of the present invention.

Suitable complexing agents for preparation of the diamine include, in general, all compounds which complex more strongly with copper than the diamine. Such compounds include ammonium ion, cyanide ion, and chelating agents such

as ethylenediaminetetraacetic acid and its salts and r.irrii- otriacetic acid and its salts. The salts of ethylenedia¬ minetetraacetic acid, especially the alkali metal salts and most desirably the trisodium salt, are preferred. It is generally convenient to use an excess of complexing agent:, typically in solution in water and/or a relatively polar organic diluent. The liberated diamine may then be isolated and purified by conventional techniques.

The invention is illustrated by the following examples. All parts, percentages and proportions are by weight. Example 1

A mixture of 1.60 parts (20 mmol. ) of cupric oxide wire, 3.5 parts (48 mmol.) of t-butylamine, 3.76 parts (20 mmol.) of 1,2-dibromoethane and 10.7 parts of acetonitrile was heated to reflux under nitrogen, with vigorous stirring. Heating and stirring were continued for 20 hours, at which time all the cupric oxide had dissolved and an orange-brown precipitate had formed. The mixture was cooled to 25°C, whereupon additional solid precipitated. It was removed by filtration, washed with acetonitrile and dried under vacuum. There was obtained 2.0 grams of a product which was shown to be the copper( II)-DBEPA bromide complex by comparison witch an authentic sample. Further complex was obtained by evaporation of acetonitrile from the filtrate. Example 2

The copper(II )-DBEDA bromide complex prepared in Example 1 was added to an excess of a 10% solution of trisodium ethylenediaminetetraacetate in a water-ether mixture. The mixture was stirred until the solids disap¬ peared. After separation from the aqueous layer, the organic phase was analyzed by gas chromatography and shown to comprise PBEDA and N,N' -di-t-butylimidazolidine in a

ratio of 99:1. The PBEDA was isolated by evaporation of the ether.

Similar rreatment of the solid obtained in Example 1 by the evaporation of the acetonitrile yielded a product shown by analysis to contain DBEPA, N,N' -di-t-butylimidazol- idine and N,N' -di-t-butylpiperazine in a ratio of 90:5:3. Example 3

The procedure of Example 1 was repeated, substi¬ tuting benzonitrile for the acetonitrile and conducting the reaction at 85°C. When cupric oxide dissolution had ceased, the mixture was filtered; analysis of the residue showed that 94% of the cupric oxide had been consumed. Upon isolation of the complex and treatment with trisodium ethylenediaminetetraacetate as in Example 2, a product was obtained which was shown by nuclear magnetic resonance spectroscopy to be PBΞPA.