DE1543062C - - Google Patents

Description

The process is therefore preferably carried out in the presence of a quaternary ammonium compound general formula

R ¹ -N-R ⁴

R ³

carried out in which R ¹ and R ^{2 are} identical or different as above and are methyl, ethyl, isopropyl, n-propyl or isobutyl groups, R ^{3 is} an alkyl or cycloalkyl group, R ^{4 is} an alkyl group and X is an anion and in which optionally two of the radicals R ² , R ³ and R ⁴ can be connected directly or via at least one nitrogen, oxygen or sulfur atom to form a non-aromatic ring and in which furthermore optionally a third of the radicals R ² , R ³ and R ⁴ with this ring ■ can be linked directly or via at least one further nitrogen, oxygen or sulfur atom to form a non-aromatic bicyclic ring system;

"Alkyl" here also includes alkenyl and alkynyl radicals, in particular alkenyl radicals with a double bond in a position other than the vicinal position to the to understand quaternary nitrogen atom. However, the presence of the double bond does not bring about any special advantages, therefore, are saturated alkyl groups preferable.

The alkyl radicals R ³ and / or R ⁴ , which can be the same or different, can be short or long, for example with 1 to 24 carbon atoms and more, the upper limit being given by the fact that the compound must be appreciably soluble in the reaction medium .

The alkyl group can be branched and also carry certain non-alkyl substituents in the carbon chain. However, aromatic substituents must not be in the position to the quaternary nitrogen _/ . Benzyl is therefore ^{unsuitable as R 3} or R ⁴ , but the («- methyl - /? - phenyl) ethyl radical can be used. In general, however, no further improvement is achieved by substitution at R ³ or R ⁴ , and among the substituents, the less polar groups, which are inherently closer to the straight chain alkyl group, are better than polar groups. Acetylcholine is more effective than choline itself.

The salt must be soluble in water or in acrylonitrile; high solubility is preferable. at larger amounts of water are anions of inorganic acids, e.g. B. chloride or bromide, satisfactory. However, when small amounts of water are used, organic anions, e.g. B. p-toluenesulfonate, which are more soluble in acrylonitrile, cheaper.

A particularly suitable salt is tetraethylammonium p-toluenesulfonate. Further preferred salts are trimethylcetylammonium bromide and tetramethylammonium p-toluenesulfonate and trimethyl-ethyl-ammonium bromide.

The effective amount of the salt in the reaction medium varies within wide limits. The Advantages of the invention, i. H. the suppression of the formation of propiononitrile, at concentrations achieved between 0.5 and 50 parts by weight of the peralkylated salt per 100 parts by weight of acrylonitrile, but Concentrations between 3 and 30 parts by weight of the salt per 100 parts by weight of reaction mixture are preferable because of their greater effectiveness.

If appropriate, certain inorganic salts can be added to the reaction mixture as accelerators will. Such accelerators are z. B. chromium compounds such as chromium chloride or sodium chromate. The amount of accelerator used can be varied within wide limits, e.g. B. between 1 and 50 parts per million parts of the reaction mixture. In tests with careful removal of all analytically measurable amounts of accelerator (cf. especially Example 23) However, found that the presence of the same for the successful completion of the procedure according to the Invention is not essential.

The amount of water can vary within wide limits.

Relatively small amounts of water, e.g. B. only 1 mole to 10 moles of acrylonitrile are effective and give good yields at high acrylonitrile concentrations. It can also contain less than 1 mole of water However, monitoring is more difficult as the water increases in the reaction could deplete quickly and form a yellow by-product. An increased water content makes it easier the removal of the by-product salts produced by the neutralization of the alkali metal, and it it is therefore beneficial to use considerably more water, about 3 to 20 moles of water per mole of acrylonitrile. If cetyltrimethylammonium bromide is used, a ratio of about 3.8 mol of water per mol of acrylonitrile, which during the reaction to about 12.5 mol of water per mol Acrylonitrile increases, shown to be effective and convenient for removal of the by-product. It has also been found that at low water concentrations, products with a higher molecular weight Can be formed, probably hydrotrimers and hydrotetramers of acrylonitrile. The formation of these undesirable products is suppressed if the water content of the reaction mixture is increased, especially at concentrations ions of 29 or more moles of water per mole of acrylonitrile. A higher water content, e.g. B. of 39 moles Water per mole of acrylonitrile which increases to a ratio of at least 72: 1 during the reaction, has been found to be effective and suppresses the formation of undesirable by-products with a high level of

Molecular weight. . . ■■ ...

When using higher water concentrations

the aqueous phase can separate from the organic acrylonitrile / adipic dinitrile phase. This prevents however, the reaction does not and further facilitates the separation of the inorganic neutralization product, e.g. B. sodium bicarbonate, from the reaction mixture, and also not the temperature monitoring, since the excess water is the drainage a suddenly occurring heat of reaction supported. In general, the amount of water is related not critical to the course of the procedure.

The advantages of the invention, in particular the suppression of the reaction leading to propiononitrile, are particularly pronounced under neutral or alkaline reaction conditions. The pH should be . but not be significantly more alkaline than the pH value at which cyanoethylation occurs, which is about

5 6

9.5 is the case. It has been found, however, that a certain concentration in the course of the process does not Easily check lower, but still sufficient, suppression. Depending on the reaction conditions are the reaction leading to propiononitrile also has low concentrations, d. H. less than 0.1% sodium, takes place in an acidic medium. With regard to the mercury, it has proven useful if one issued that the addition of cetyltrimethylammo- 5 excessive heat generation can be avoided nium bromide is said to contribute to the formation of propionitrile itself.

a pH value of -1 slightly reduced, while temperatures suitable for the reaction are

At a pH of 1.5, the ratio of between 10 and 35 ^° C., however, adipic acid dinitrile to propionic acid nitrile can also be used at even higher temperatures. Although above is significantly increased and the ratio increases gradually with increasing io 35 ° C, the propiononitrile content, the pH continues to rise until it reaches its optimum, such temperatures may be desirable, between pH values of 7 and 9.5. The avoidance of the formation of hydrooligomers at a higher rate according to the invention is therefore preferably to reduce the molecular weight, and also for reasons in the pH range from 1.5 to 9.5, in particular for chemical and engineering reasons. As for a particular at 7 to 9.5. Since with the hydrodimer 15 favorable heat transfer a noticeable temperature. Sation reaction with alkali metal amalgam continual difference in temperature between the reaction mixture and alkali metal hydroxide is formed, it is necessary to add an acid to the cooling water. This can be desirable through constant addition at over 35 ° C in order to carry out cooling of a strong acid, but can be avoided through generation of cold. The techdie in the maintenance of acid-base equi- 20 African scale applicable temperature range is therefore greater Klobuk especially at low water concentrations and is between 10 and 6O ⁰ C.
particularly careful monitoring, possibly because polymer formation is undesirable, f

wisely even require automatic control. in the method according to the invention in practical However, a weak acid can also be used. their alkali or alkaline earth salt is not added as such. Suitable inhibitors are polybasic is that it becomes an undesirable, above merization inhibitor as it is out of technology 9.5 lying pH. Known from economic polymerization of vinyl monomers Reasons are inorganic weak acids. A particularly suitable, preferred inhibitor to draw. One known convenient method is N, N-dimethyl-p-nitrosoaniline. A few to produce weak acids is the addition of 30 parts of this substance to a million parts of the monostruff Acid to a buffer, e.g. B. the addition of mers already suppress the formation of the polymer. Phosphoric acid to a sodium dihydrogen phosphate / The method according to the invention can be batch

Disodium hydrogen phosphate buffer system. be carried out wisely or continuously. At the

A favorable and preferred method for batch operation can be the reaction vessel, for. B. maintaining a pH value between 7 and 9.5 must be a closed vessel, which is preferably provided with the addition of carbon dioxide, where 'a suitable relatively flat bottom is provided, concentration of the gas in' the iR'eaktionsgefäß of the Creation of a large surface area for the amal to be maintained and the rate of dissolution thereby enabled. The vessel can still following the same in the reaction liquid, for. B. by stirring, parts or facilities: one or more is conveyed. An atmosphere of pure carbon is preferable for the inlet openings for the liquid reactant dioxide, since complicators and water as well as any cations that may be used are avoided, the accelerators for the peralkylated salt and that of the gaseous acrylonitrile from a voluminous polymerization inhibitor when recovered; an inlet for acidification ^. inert gas flow occur. A slightly above the substance, which if carbon dioxide is used for this. Atmospheric pressure is expedient, but can be used, expediently made of a dip tube, also higher and even lower pressures, with a porous gas distributor that is inserted into the . Immersed by reaction of the alkali hydroxide with the water-monomer phase; a cooling carbon dioxide in the presence of water in the reactor or a cooling jacket in contact with the ionic medium becomes alkali metal hydrogen carbonate in the aqueous and / or amalgam phase; a stir forms which precipitates. It can be in a convenient device which can be set to be disconnected the way, e.g. B. stirred by intermittent aqueous phase and / or the amalgam phase, filtering or by continuous filtering, for example, or separate stirring devices for each of the phases by circulating part of the reaction mixture; an outlet for the reactants and through a filter, so that contamination of the reac- preferably a separate outlet for the aqueous ionic mixture with large amounts of the neutral phase and to remove the precipitated re-ionization product is avoided. tralization product, e.g. B. Sodium hydrogen carbon

Instead of alkali metal amalgams, nat. · '

also use alkaline earth metal amalgams. In the continuous process, the reac-

Sodium ion partners with those for the desired continuous amigam, however, are of commercial use and potassium amalgam to be preferred as this 60 lhe reaction continuously eases the necessary proportions provided by large-scale processes. Part of the acrylonitrile / water phase that makes up the and contains the corresponding neutral- selected salt is continuously removed, Station by-products have a commercial value. the salt is separated off, for example by centrifugation,

The content of alkali or alkaline earth and the filtrate is again in the reaction vessel can amalgam returned from the saturation 6 ₅ also within wide limits. Another part or a division point up to very low concentrations of the filtrate is removed and worked up, vary. Since the amalgam around the desired hydrodimer and the non-amalgam decompose quickly under the process conditions, the starting materials required can be obtained. At a

7 8

continuous operation are the two after the addition, the flask was vigorously by hand Phases shaken horizontally lengthways through the reac-.

tion vessel passed, which is a pipe or a trough. The unreacted acrylonitrile was from the

can be. Accordingly, there is a falling con- reaction vessel distilled off under reduced pressure, concentration gradient of the alkali metal in the amalgam 5 The weight of the recovered acrylonitrile and an increasing concentration gradient of the was 13.11 g- The reaction vessel was opened three times Adipinsäuredinitrils from the inlet to the outlet of the with 20 ml of water each and five times with each Reaction vessel. Techniques for continuously washing 8 ml of methylene chloride. The watery one Process sequence, the phases in cocurrent phase was seven times with 8 ml of methylene or flow countercurrently through the reaction vessel, extracted io chloride. The combined methylene chloride are known per se. extracts were extracted twice with 15 ml of water

With both batch and continuous and the methylene chloride then over a water-based operation, the product is evaporated as follows in a bath. The residue was worked for 10 minutes: the liquid phases were separated from one another, ^{heated to 130 °} C. for a long time in order to drive off the remaining water, for example by decanting and removing the solid salt. The weight of the residue was, as described above, fractional distillation or 1.64 g. Gas chromatography and infrared analysis of the aqueous monomer / solvent extraction indicated that no propionic acid nitrile was present in the residue hadrodimer / cation salt phase in a per se known manner and that the product appeared to be pure adipic mode and recovery of the unused dinitrile. Subsequent liquid raw material. ao speed chromatography showed, however, that impurities

An advantage of the invention is the high yield reinigungen higher molecular weight, wahran adiponitrile, which up to 80 ° / ₀ and more scheinlich is dimers and trimers of acrylonitrile, in the acrylonitrile. Another advantage is that there were backlogs,
the high conversion of acrylonitrile. Another

Another advantage is that the reaction takes place in 25 minutes

Absence of an external electrical current in front of the proportion of the supplied acrylonitrile, which is in crude

is going. This is very useful as the amalgam was then converted to adipic acid dinitrile: 10.5%.
separately with a high electrochemical efficiency portion of the supplied acrylonitrile, which is in propion

and low voltage can be generated, no acid nitrile has been converted: Not detectable.
Diaphragm is required and the anodic reactivity of the supplied acrylonitrile which has been usefully recovered as acrylate for some other useful purpose: 86%.
can be applied, e.g. B. for the production of proportion of the crude adipinitrile with respect to

Chlorine. In addition, the sodium or the other can be the consumed acrylonitrile: 75%.
Alkali metal in the decomposition of the amalgam in proportion of the crude adipic dinitrile, based on

Another useful by-product converts the hydrogen available from the amalgam: will. 99.3%.

The explanation below is based on the purity of the crude adipic dinitrile: 60%.

play explained in more detail. Yield of pure adiponitrile, based on

on the acrylonitrile consumed: 45%.

Example ⁴ ° Example 2

A reaction vessel according to Example 1 was used

A closed 250 ml was used as the reaction vessel, which was flushed through with carbon dioxide

Erlenmeyer flask which had been ays- with a dropping funnel and into which two solutions were placed,

was armed. The reaction vessel also had a 45 The first solution contained 4.0 g of trimethylcetylammo-

tightly inserted tube for introducing carbon bromide and 0.43 mg chromium chloride (CiCl ₃ -

Dioxide and a water bath to the reaction 6H ₂ O) in 10.10 g of water. The second solution contained

to keep temperature approximately at 20 ⁰ C on. 20 μg N, N-dimethyl-p-nitrosoaniline in 8.17 g acrylic

A solution was prepared from 15.17 g of nitrile. In addition, 20 ml of mercury were poured into the

Acrylonitrile, 6.86 g tetraethylammonium-p-toluenesulfonation vessel added.

nat, 1.07 g water, 0.43 g chromium chloride (CrCl ₃ - There were 80 ml of sodium amalgam in a same

6H ₂ O) and 20 μg Ν, Ν-dimethyl-p-nitrosoaniline. Cell produced as in Example 1. It became a stream

This solution was added to the reaction vessel, 4.3 amps through the cell for 82 minutes

which contained 20 ml of mercury and which. directed. The amalgam was taken from the cell

had been flushed with carbon dioxide. It was 55 men, dried and placed in a dropping funnel

a slight overpressure of carbon dioxide stored during a nitrogen atmosphere. 1 ml of this amal-

the reaction is maintained in the vessel. > gams gave 2.57 mg of hydrogen. 41.5 ml of this amal-

60 ml of sodium amalgam were produced by gams were placed in the reaction chamber for 33 minutes

Electrolyze a 40% aqueous sodium vessel. During this time and beyond

Hydroxide solution between a platinum sheet anode for 60 minutes after the addition, the vessel became vigorous

cylindrical shape with a surface of 6.5 cm ² shaken by hand. The temperature was through

and a mercury cathode with a surface partial immersion of the reaction vessel (piston)

of 26 cm ² , with a current of 4 amps kept in a bath with tap water at 20 ⁰ C,

was turned. The amalgam was removed from the cell. The amalgam dropping funnel was removed, 20 ml

taken and dried. 1 ml of this amalgam 65 water in the flask and a »Dean-and-

yielded 1.22 mg of hydrogen, 25.6 ml of the amalgam Starke® apparatus attached to the flask. This

were in the reaction vessel for 20 minutes was then heated and 2.95 ml, i.e. 2.36 g, not

given. During this time and a further 7 minutes reacted acrylonitrile were in the »Dean-und-

ίο

Strong «apparatus recovered. The contents of the flask were transferred to a separatory funnel. The reaction vessel was washed three times with 10 ml of methylene chloride. The aqueous phase was extracted six times with 10 ml of methylene chloride. The methylene chloride was evaporated from the combined extracts and the residue was ^{heated to 130 °} C. for 10 minutes to drive off residual water. The weight of the residue was 5.65 g. Infrared and gas chromatography analysis indicated essentially pure adiponitrile that was free of propiononitrile, but oligomeric impurities were subsequently discovered by liquid chromatography.

Substance balance * ⁵

Proportion of the supplied acrylonitrile which was converted into crude adipic dinitrile: 67.9%.

Proportion of the supplied acrylonitrile in propionic acid nitrile was converted: Not detectable.

Proportion of the supplied acrylonitrile that is called acrylonitrile was recovered: 28.8%.

Proportion of the crude adipic dinitrile, based on the acrylonitrile consumed: 95.5%.

Proportion of the crude adipic acid dinitrile, based on the hydrogen available from the amalgam: 99%.

Purity of the crude adipic acid dinitrile: 65%.

Yield of pure adiponitrile, based on the acrylonitrile consumed: 62%.

Examples 3 to 20

A number of small-scale tests were carried out using a similar device to Example 1, but at about a quarter of the capacity. Purpose of the experiments was to find out to what extent the range of basic experimental parameters is critical. the obtained products were examined by gas chromatography and the main effect, namely the ratio determined from adipic acid dinitrile to propionic acid nitrile, d. i.e., it was the suppression of the Tested propionic acid nitrile formation and determined the formation of impurities and / or polymers. The amount of oligomeric impurities formed from the acrylonitrile was not detected.

The test results are summarized in Table 1. In this table are the concentrations of Reactants given in mol percent, with 100% the sum of water, acrylonitrile and. to the alkylated salt forms. The concentration of the acrylonitrile - not specified - is the remainder up to 100%. The concentration of small quantities of additives, such as accelerators and polymerization inhibitors, are in parts by weight per million parts of the reaction mixture of acrylonitrile, water and alkylated salt expressed. The relative proportions of the two main reaction products, adiponitrile and propiononitrile, are expressed in percent by weight.

Examples 3 and 4 show, for comparison, the yields that can be achieved without using the invention and show the large amount of propiononitrile formed. Examples 5, 6 and 7 show the suppression of the formation of propiononitrile in the presence of very small amounts alkylated salts according to the invention.

Examples 8 and 16 show the suppression of propiononitrile formation in the presence of different quaternary ammonium salts with different concentrations of the quaternary salt, the water, the acrylonitrile, the accelerator and the polymerization inhibitor. Examples 8 and 9 lie at the lower limit of the water concentration at which water depletion during the Reaction with simultaneous formation of a yellow by-product can just be avoided.

Examples 17 to 19 show the suppression of propiononitrile formation at somewhat lower levels Acrylonitrile to water ratios, d. H. at higher water concentrations, reducing the removal is facilitated by sodium hydrogen carbonate. In Example 19, the reaction mixture comprises two phases, namely an aqueous phase containing essentially all of the sodium hydrogen carbonate contains, and an organic acrylonitrile / Ädipinsäuredinitrilphase, which is practically free of sodium hydrogen carbonate.

Example 20 shows the influence of a very high water content.

table

Reaction partner isaiz
Mole
percent Mole
percent
H ₂ O N, N-Di-
methyl-
p-nitroso-
aniline
ppm Cr ⁺⁺⁺
ppm Relative
(Weight:
Adipine
acid
dinitrile Reaction products Insoluble
polymer - Other
fleeting
Contaminants
worked example
No. Quaternary ammonium
connection 8th '5 17th r share
Percent)
Propion
acid
nitrile not fixed something 3 Without 83 placed (Comparison) 2 8th - 5 20th not fixed not fixed 4th Without but instead 80 placed placed (Comparison) whose tertiary American nottriethanolamine too given 0.1 8th - 50 70 low low 5 Cetyltrimethylammo- 30th crowd crowd nium bromide 0.1 8th - 3 74 low low 6th the same 26th crowd crowd 0.18 8th - 50 73 low low 7th Tetraethylammonium 27 crowd crowd p-toluenesulfonate

Table 1 (continued)

Reaction partner - Mole
percent Mole Ν, Ν-Di-
methyl- Cr * ■ + * ■ Reaction products Propionic
acid-
nitrile Insoluble Other
fleeting example
No. Quaternary ammonium salt Distearyldimethyl 5.7 percent
H _U O p-nitroso-
aniline
ppm ppm Relative share
(Weight percent) < ⁴ polymer Polluting
gung, connection ammonium chloride 8th 50 Adipine
acid
dinitrile low noticeable 8th the same Same as example 15 5.7 > 96 <1 crowd crowd 8th 25th 50 no low 9 the same the same 5.7 > 99 <1 crowd 16. 1 50 no very small 10 the same Like example 13 .10 > 99 <1 crowd the same 16 1 50 no very small 11th the same 5.7 > 99 not fixed crowd 16 1 5 adjustable no . very small 12th the same 1.0 > 99.7 <0.5 crowd 16 1 5 no very small 13th Cetyltrimethylammo- 2.5 > 99.5 <1 crowd nium bromide 16 1 5 no very small 14th Tetramethylammo- 5 > 99 <1. crowd nium p-toluenesulfonate 16 1 1000 no very small 15th the same 1 > 99 <1.5 crowd 16 1 5 no very small 16 4th > 98.5 <5 crowd 66 1 5 no very small 17th 5 > 95 5 crowd 81 1 5 ¹ no very small 18th 2.4 95 0.5 crowd 2.2 81 1 5 5 no no 19th 95.2 0.1 5 99.5 no no 20th 95

Example 21

Another experiment was carried out with larger amounts in order to determine the more precisely To allow the yield and purity of the product produced.

The reaction vessel consisted of a 5 liter "Pyrex" glass flask with three necks and one round Floor, with an outlet with a tap in the floor. The flask was sealed with a inserted immersion tube provided, which up to the vicinity of the bottom in the interior of the piston was sufficient so that the end of this tube would certainly get into the reaction mixture during operation was immersed. The dip tube was connected to a source of carbon dioxide. Through a neck of the flask a glass stir bar was passed through a sealed stuffing box. The second neck was with one SOO-ml separating funnel · connected as a storage container served for the amalgam, and the third neck, which served as the gas outlet line, had two liquid traps connected, which dipped in a mixture of dry ice and acetone and then in the Atmosphere. Around the upper half of the piston, an annular distributor was arranged, so that an adjustable cooling water flow could be directed over the outside of the piston.

The reaction mixture consisted of:

250 ml acrylonitrile,

250 ml water,

100 g cetyltrimethylammonium bromide,

5 mg CrCl ₃ -OH ₂ O,

0.20 mg Ν, Ν-dimethyl-p-nitrosoaniline,
150 ml of mercury.

This mixture was added to the flask and this was thoroughly flushed with carbon dioxide: Sodium amalgam, which had been prepared by electrolyzing NaOH solution for 16 hours at 4.5 amperes, was then slowly poured into the flask over a period of 90 minutes introduced. During this addition, the reaction mixture was vigorously stirred and stirring was continued for 15 minutes after the addition of the amalgam was complete. The addition of amalgam was interrupted when the precipitated sodium hydrogen carbonate made it difficult to stir the liquid properly. The temperature of the reactant was maintained below 35 ⁰ C.
The carbon dioxide inlet tube, agitation device, and amalgam inlet tube were then removed from the flask and 6N hydrochloric acid slowly added to the flask until most of the sodium bicarbonate had decomposed. The released carbon dioxide was passed through the cold traps immersed in dry ice and acetone. The mercury layer was then allowed to drain and the remainder of the bottle was transferred to a 5 liter round bottom flask. 500 ml of water were added and the pH was adjusted to about 7 by adding hydrochloric acid and ammonia. The flask was then fitted with a condenser and receiver for distillation, and the unreacted acrylonitrile was distilled off. After the distillate had distilled over at 100 ^° C. for 5 minutes, the distillation was interrupted. The volume of acrylonitrile in the collecting vessel and in the cold traps and the volume of water in the distillate collecting vessel were then measured.

The solution remaining in the bottle was then transferred into a separating funnel with a capacity of 11, and about 11 water was added. This solution was extracted five times with 100 ml of methylene chloride each time. The two phases separated for about an hour on the first extraction. Both later extractions, however, more and more stable emulsions were formed. It was necessary centrifuging them for a considerable time to achieve phase separation. The methylene chloride extract was washed four times with small amounts of water and then placed in a weighed bottle.

Volatiles were driven off under reduced pressure, and the remaining non-volatile Liquid was weighed. A sample of this liquid was analyzed by infrared spectroscopy and appeared to be pure adipic dinitrile. However, liquid chromatography revealed the presence of oligomeric impurities in this raw material.

Material balance

Supplied acrylonitrile ..: 250 ml

Reclaimed acrylonitrile ... 114.4 ml

Used acrylonitrile 135.6 ml

Crude adipic dinitrile recovered 109.3 g

Theoretical yield of adipic acid dinitrile, based on consumed Acrylonitrile 110.5 g

Yield of crude adipic dinitrile, based on consumed

Acrylonitrile 99.0 ° / ₀

Conversion of the supplied

Acrylonitrile .. 54.3%

. Degree of purity of raw adipine

acid dinitrile. 75%

Yield of pure adipic acid dinitrile, based on converted acrylonitrile 74%

B e i s ρ i e 1 22

The apparatus, reaction mixture, and procedure of Example 21 were used.

After the reaction, concentrated hydrochloric acid was added while the contents of the flask were kept stirring. A slight excess of hydrochloric acid was added over the amount required to neutralize the sodium hydrogen carbonate. The mercury was allowed to drain and the remaining solution was then transferred to a 1 liter flask. About 500 ml of water was added. The flask was fitted with a condenser and a receiver for distillation, and the unreacted acrylonitrile was distilled off. A cold trap was immersed in dry ice and acetone and connected to the outlet of the collecting vessel. The distillation was interrupted after the distillate had passed over ^{at 100 ° C. for 5 minutes.} The amounts of acrylonitrile in the collecting vessel and in the cold trap as well as the amount of water were determined.

The remaining liquid in the flask was placed in a separatory funnel and the aqueous and organic phases were separated from one another. The organic phase was washed three times with 25 ml of saturated saline solution each time, then dissolved in about 150 ml of methylene chloride and washed twice with 50 ml of water. The wash extracts were added to the aqueous phase. The methylene chloride extract was placed in a weighed bottle. The volatile constituents were driven off under reduced pressure (70 ^° C. and 20 torr) and the remaining non-volatile liquid was weighed. ·
The aqueous layer was placed in a 3 liter beaker and the volume was made up to 1,500 ml with water. The pH was then adjusted to about 7 using concentrated ammonia. A solution of 100 g Na ₂ Cr ₂ O ₇ , which contained a filter aid, was then slowly added with vigorous stirring. The precipitated complex (see I. Renard, J. Pharm. BeIg. 7, pp. 403 to 408, 1952) was filtered off and washed once with water. The precipitate was dissolved in 300 ml of hot acetone and precipitated by slowly adding about 2 liters of water with stirring. The precipitate was filtered off. Both filtrates were extracted separately with six 50 ml portions of methylene chloride each time, and the extracts were pooled and placed in a weighed bottle. The volatile substances were driven off at reduced pressure (70 ^° C. and 20 torr) and the remaining non-volatile liquid was weighed.
Both amounts of the crude product were combined and a sample was examined by infrared analysis which indicated that it appeared to be essentially pure adiponitrile which was free of propiononitrile. However, liquid chromatography indicated that oligomeric impurities were present.

Material balance

Supplied acrylonitrile 250 ml

Recycled acrylonitrile .... 107.1 ml

Used acrylonitrile 142.9 ml

Theoretical adipic dinitrile yield based on acrylonitrile consumed _; 116.5 g

Total amount of won

crude adipic dinitrile 115.4 g

Yield of crude adipic acid dinitrile, based on acrylonitrile consumed. ■ 99.1%

Share of converted acrylic

nitrils .... '.... 57.2%

Purity of raw adipic acid

dinitrils 75%

Yield of pure adipic acid dinitrile, based on converted acrylonitrile 74%

Example 23

This experiment shows the reaction without the addition of an accelerator, using reactants from which the usual impurities had been carefully removed, d. That is, the reactants contained much smaller amounts of accelerators than one in commercially available reactants. The quaternary ammonium compound was replaced by two Umkrislal'isalionen cleaned. Simply distilled

Water and acrylonitrile were purified by distillation. Analytical grade mercury was used further purified by passing it three times in fine drops through a 90 cm high column analytically pure nitric acid.

The reaction mixture was composed of the following purified reagents:

10 g cetyltrimethylammonium bromide,
30 ml H ₂ O,
30 ml acrylonitrile,
0.06 mg Ν, Ν-dimethyl-p-nitrosoaniline,
50 ml of mercury.

All vessels for the preparation of the reagents and for the reaction were made with 20% hydrofluoric acid washed and carefully rinsed with double distilled water. The amalgam was made by electrolyzing a 50% aqueous sodium hydroxide solution (made from analytically pure sodium hydroxide) using mercury as the cathode.

The reaction vessel consisted of a 250 ml, three necked flask with one outlet exhibited on the ground. A dip tube was provided as a gas inlet for the carbon dioxide. The carbon dioxide gas outlet was connected to two cold traps immersed in a carbon dioxide-acetone bath, and a glass stirrer was also used, as was already described in Example 22.

The reaction vessel was flushed through with carbon dioxide. The aqueous-organic phase continued stirred and the amalgam was slowly added to the reaction vessel from a dropping funnel. the The flask was placed in a water bath to cool. The temperature of the reaction was below 35 ° C held. The amalgam addition was stopped after the precipitated sodium bicarbonate fell had made it difficult to stir the solution effectively. The carbon dioxide inlet was removed and concentrated hydrochloric acid slowly added to the solution from a dropping funnel until the sodium bicarbonate had been dissolved. The amalgam was drained and the remaining contents of the reaction vessel transferred to a flask. This was prepared for distillation, and the unreacted acrylonitrile was distilled over.

The liquid remaining in the flask was transferred to a separating funnel, and the organic Layer was separated. The latter was washed four times with saturated sodium chloride solution, and the wash extracts were added to the aqueous layer. . The volatiles were taking under reduced pressure from the washed organic layer, and the remaining, non-volatile The fabric was weighed.

The pH of the aqueous layer was adjusted to 7 with ammonia and distilled water was added to a volume of 400 ml. A solution of 10 g of Na ₂ Cr ₂ O ₇ in 50 ml of water, which solution contained a filter aid, was then slowly added with stirring. The precipitate formed was filtered off and washed several times with water. It was then dissolved in about 40 ml of acetone and precipitated by adding 500 ml of water. The precipitate was filtered off and washed several times. The filtrates and the wash extracts were combined and extracted six times with 50 ml of methylene chloride each time.

The volatiles were driven off by the extract and the remaining non-volatile liquid weighed. .

Both amounts of the product were analyzed according to Example 21.

Substance household

Supplied acrylonitrile 30.0 ml

ίο Recovered acrylonitrile 9.9 ml

Used acrylonitrile 20.1 ml

Theoretical yield of adipic acid dinitrile, based on consumed Acrylonitrile 16.4 g

Actual yield of crude

Adipic acid dinitrile -16.25 g

Percentage yield of crude
Adipic dinitrile, based on

. used acrylonitrile 99.1%

Conversion of the supplied

Acrylonitrile 67%

Purity of the crude adipic acid dinitrile, 75%

Yield of pure adipic acid dinitrile, based on converted acrylonitrile 74%

B e i s ρ i e 1 24

This example shows the use of an inorganic acid in the presence of a buffer solution. The experiment was carried out as in Example 1, but a 50 ml Erlenmeyer flask with a tightly inserted tube was used for supplying phosphoric acid. It became the following Mixture of reactants poured into the flask:

2 ml acrylonitrile,
0.6 g trimethylcetylammonium bromide,

0.5 ml H ₂ O,

0.19 g NaH ₂ PO ₄ -2 H ₂ O,
, 0.17 g Na ₂ HPO ₄ ,

5 mg CrCl ₃ -OH ₂ O,
2 μg N, N-dimethyl-p-nitrosoaniline,

5 ml Hg.

To the reaction mixture, 8 ml of amalgam prepared according to Example 1 was slowly added, and at the same time 10% phosphoric acid was added dropwise at such a rate that the solution remained at a pH between 7.0 and 8.0.
The reaction mixture was worked up as described in Example 1 and the adipic acid dinitrile was analyzed by gas-liquid chromatography. No propiononitrile could be found. The yield of the crude product, based on acrylonitrile, was better than 99%, the purity of the crude adipic dinitrile was better than 70%, ie the yield of pure adipic dinitrile was about 70%.

B e i s ρ i e 1 25

Magnesium amalgam was made by shaking mercury with an excess of magnesium chips in a separating funnel and draining the amalgam thus formed. The amalgam

309 623/188

was prepared and handled under a nitrogen atmosphere. This amalgam was then used instead of the sodium amalgam in a hydrodimerization reaction of acrylonitrile according to Examples 3 to 20. The quaternary ammonium salt was cetyltrimethylammonium bromide (1 mole percent), the water content 16 mole percent, the N, N-dimethyl-p-nitrosoaniline content 1 part per million and the Cr +++ content 5 parts per million. The crude reaction product appeared due to the infrared analysis of more to exist as a 99 ° / ₀ adiponitrile. However, liquid chromatography indicated oligomeric impurities. No propiononitrile was found in the crude product. The yield of the crude product based on the amount consumed

Acrylonitrile was better than 99% ^and the purity of the crude product was better than 70%. Therefore the yield of pure adipic acid dinitrile was about 70%. However, the reaction rate was somewhat slower than when using sodium amalgam.

B e i s ρ i e 1 e 26 to 69

Another series of small tests was carried out, which corresponded to Examples 3 to 20, to determine the effectiveness of other compounds which have alkylated cations. the Results are shown in Table 2 and expressed in the same manner as in Examples 3 until 20.

. . . Reaction partner • 2J ' Ν, Ν, Ν, Ν ', Ν', Ν'-hexamethyl- Mole
percent Table . 2 N, N-Di-
methyl- ppm Reaction products Propionic
acid-
nitrile 53 U.N Other amounts Salt capable of forming alkylated cations 1,3-propylenediammonium iodide 10 p-nitroso-
aniline
ppm 5. Relative share
(Weight percent) <! soluble
polymer Contaminants
worked at
game connection Tetramethylphosphonium iodide Mole 1 Adipine
acid
dinitrile 10 No. Trimethyl (ethyl) ammonium Trimethyl (p-tolyl) ammonium
iodide
Trimethyl (benzyl) ammonium 5 percent
H ₂ O 5 > 99 <1 26th bromide iodide _: 20th 1 - small amount Trimethyl (n-propyl) ammonium 10 5 > 99 <1 27 bromide 30th 1 - small amount Trimethyl (n-butyl) ammonium • 5 5 > 99 <1 28 bromide 35 1 - very Trimethyl (isoamyl) ammonium 5 5 > 99 <1 small amount 29 bromide 40 1 - small amount Trimethyl (n-amyl) ammonium 4.1 1 > 99 <! 30th bromide 3.6 40 1 5 <1 - small amount Trimethyl (n-decyl) ammonium 1 > 99 small amount 31. Ul U 111 IU.
Trimethyl (cyclopentyl) ammo 4.7 40 5 > 99 <1 32 nium bromide 25th 1 - - Trimethyl (cyclohexyl) ammo 3.7 5 > 99 <1 33 nium bromide 32 1 - small amount Trimethyl (l-phenyl-2-propyl) - 5.0 5 > 99 <1 34 ammonium iodide 5.0 47 1 5 58 - very low Acetylcholine bromide 4.3 1 5 > 99 11th small amount 35 Choline chloride 32 1 42 - 36 Ν, Ν, Ν ', Ν'-Tetramethylpipe- 3.0 32 5 89 21 37 razinium iodide 32 1 - very Ν, Ν-dimethylmorpholinium 3.5 5 79 <2 small amount 38 iodide 56 1 Ν, Ν, Ν, Ν ', Ν', Ν'-hexamethyl- > 98 39 ethylenediammonium dibromide 49 [(CH ₃ ) ₃ N ⁺ . 4.5 5 3 CH ₂ CH ₂ N ⁺ (CH ₃ ) J 2Br- 1 small amount Ν, Ν'-dimethyltriethylenedi- 97 40 ammonium iodide 32 , CH ₂ CH ₂ . CH ₃ N ⁺ (- CH ₂ CH ₂ -) N ⁺ CH ₃ 2.3 5 CH ₂ CH ₂ 1 small amount 2.4 5 47 OO 41 3.9 40 1 5 - very low 4.7 1 5 90 very low yield 42 33 1 High ratio of adipine 43 39 acid dinitrile: propionic acid 44 33 nitrile, however large pollution

Table 2 (continued)

Reaction partner it salt
Mole
percent Mole
percent
H ₂ O N, N-Di-
methyl-
p-nitroso-
aniline
ppm Cr +++
ppm Reaction products Relative
(Weight
Adipine
acid
dinitrile r share
percent)
Propion
acid
nitrile U.N
soluble
polymer Other
fleeting
Contaminants
worked 1 small amount small amount at
game
No. capable of forming alkylated cations
connection 4.3 33 ι - -5 25th 75 very 45 Girard's reagent T-trimethyl small amount 1 - ■ small amount (hydrazidomethyl) ammonium ChIoHd (CHj) ₃ ⁺ NCl- · CH ₂ · 4th - - - CO - NHNH ₂ 8.8 23 1 5 99 1 - small amount 46 Dimethyl (diethyl) ammonium
iodide
Dimethyl (di-n-propyl) ammo
nium iodide
Dimethyl (di-n.-butyl) ammonium 4.6 33 1 5 91.5 8.5 large 1 - - 47 iodide 5.0 24 1 5 40 60 small amount 48 Dimethyl (di-n-decyl) ammonium
iodide
Methyl (triethyl) ammonium iodide 2.5 small amount small amount Methyl (diethyl) (n-propyl) - 2.9 56 1 5 89 11th - small amount 49 ammonium bromide 6.6 20th 1 5 > 99 <1 small amount 57 small amount small amount 50 Methyl (tri-n-propyl) ammonium 4.8 25th 1 5 > 99 <1 - 1 small amount 51 iodide 55 - small amount Methyl (n-propyl) (di-n-butyl) - 5.0 32 1 5 87 13th small amount - 52 ammonium iodide Methyl (tri-n-butyl) ammonium 4.4 33 1 5 66 34 - small amount ⁵³ iodide N-methyl-N-ethyl piperidinium-
_y iodid
N-methylpyridinium iodide 5.2 24 1 5 38 62 medium middle 54 quality 4.4 33 1 5 99 1 - - 55 4.8 33 1 5 extremely low yield 56 Adipic acid dinitrile, no Propionic acid nitrile. Blue _; N-methylquinoline uniiodide Color that is in the light effect faded too N-methylisoquinolini u mjodide original light yellow 3.6 39 1 5 very low yield. color 57 changes to dark brown 3.7 30th 1 5 extremely low yield 58 N, N'-dimethyl-2-methyl- Adipic acid dinitrile, no pyrazinium iodide Propionic Acid Nitrile .. Color N, N'-dimethyl-3,3'-dipyridi- changes to dark brown lium iodide 4.1 39 1 5 very low yield. color 59 changes to dark brown 1.6 76. 1 5 extremely low yield 60 Adipic acid dinitrile. Blueness Stearyl pyridinium bromide Color that is in the light light yellow effect changes Triethyl (n-propyl) ammonium 4.3 10 1 5 large amount of propionic acid 61 bromide nitrile. Color formation as with Triethyl (n-butyl) ammonium Example 60 bromide 4.4 33 1 5 99 62 Triethyl (n-decyl) ammonium bromide 4.0 39 1 5 99 63 Diethyl (di-isobutyl) ammonium iodide 4.1 39 1 . 5 96 64 Ethyl (tri-n-propyl) ammonium bromide 4.2 33 1 5 99 65 Ethyl (tri-n-butyl) ammonium
iodide
Triethylsulfonium iodide Tetra (n-butyl) ammonium iodide 3.9 39 1 5 97.5 66 6.4 33 1 5 43 67 5.0 33 1 5 99 68 5.0 33 1 5 45 69

Examples 70 and 71 were run to examine the effect of elevated temperatures on the proportion of to investigate formed propionic acid nitrile.

Example 70

The experimental set-up corresponded to that of Example 23, but with commercially available, uncleaned Chemicals were used. The reaction mixture consisted of

12 g cetyltrimethylammonium bromide, 15 ml acrylonitrile,
30 ml water,
0.6 mg CrCl ₃ -OH ₂ O,
60 μg - Ν, Ν-dimethyl-p-nitrosoaniline, 20 ml mercury

The reaction was carried out as in Example 23. Samples were taken from the reaction mixture at intervals during the reaction and examined for adipic acid dinitrile, propionic acid nitrile and acrylonitrile by gas chromatography. The temperature the reaction was kept constant at 40 ± 2 ° C. throughout the experiment. There were achieved the following results:

Composition of the reaction mixture (percent by weight)

Acrylonitrile Adipic acid dinitrile Propionic acid nitrile 83%
51.5%
39% 17%
48%
60% 0.1%
0.45%
1.0%

This example shows the slight increase in the formation of the undesired propiononitrile higher temperatures. It can also be seen that for the initial lower conversions, the The proportion of propiononitrile was significantly lower.

Example 71

The above example was repeated, but maintaining the temperature throughout the reaction was held at 50 ± 2 ° C. The following results were achieved:

Composition of the reaction mixture (percent by weight).

Acrylonitrile Adipic acid dinitrile Propionic acid nitrile 88%
72%
50.5%
34% 12%
27%
47.5%
61.5% not detectable
0.8%
2%
4.5%

This example shows the further increase in the formation of propionic acid at higher temperatures and again the lower propiononitrile content at lower conversions.

B e i s ρ i e 1 e 72 to 80

Examples 72 to 80 show the influence of the pH values on the course of the reaction, with pH values between 1.5 and 9.5 is carried out in the presence and absence of quaternary ammonium salts. Examples 72 to 80 were carried out as follows: The reaction was carried out in a closed, from a jacket surrounded glass vessel with a capacity of 350 ml, which has three necks and was provided with a glass stirrer. The amalgam produced according to Example 1 was passed through the reaction vessel at a controlled rate by means of inlet and outlet lines located in the bottom of the reaction vessel, ao whereby a 0.5 cm mercury layer was maintained. The temperature was 32 ± 3 ° C. For runs 72 through 74, the pH of the solution was increased during the addition of the amalgam kept at 1.5 to 2.5 by the dropwise addition of 11 η hydrochloric acid, in the presence of thymol blue was worked as an indicator. For Examples 75 to 77 the reaction was carried out at pH carried out from 4 to 5 using a 0.1 M phosphate buffer and with neutralization during the reaction by adding concentrated hydrochloric acid in the presence of bromocresol green as Indicator.

For Examples 78-80, the reaction was carried out at pH 8.2 ± 0.5 in the presence a dicarbonate buffer carried out as described in Example 1. The device instructed Dip tube to introduce the carbon dioxide.

Examples 72, 75 and 78 show, for comparison, the response in the absence of a quaternary Salt. Examples 73, 76 and 79 show the reaction in the presence of 30 g of triethylmethylammonium p-toluenesulfonate, and Examples 74, 77 and 80 show the reaction in the presence of 30 grams of trimethylcetylammonium bromide. On 100 ml of water that has the pH control criteria given above and optionally containing the quaternary ammonium salts, the following reagents were also used added: 13.2 g acrylonitrile, 0.012 mg Ν, Ν-dimethylp-nitrosoaniline and 10 ml of mercury. After the completion of the reaction, the reaction mixture became removed from the reaction vessel, and a sample thereof was checked for residual acrylonitrile, propiononitrile and adipic acid dinitrile analyzed by gas chromatography. Examples 74, 77 and 80 were then the higher-boiling nitriles are removed and extracted from the rest of the solutions, as in Example 23 is described. In Examples 72, 73, 75, 76, 78 and 79, the higher boiling nitriles were from the The remainder of the solution was removed as in Example 1. A portion of each extract was then gas chromatographed analyzed to determine the percentage of adipic dinitrile.

The impurities in the extract, as determined by difference, appear to be higher hydrooligomers of acrylonitrile with the exception of adiponitrile.

The results are shown in Table 3.

table

example
No. Quaternary ammonium salt PH R <
(C.
Adipic acid saktionsproduk
Weight percent
Propionic .te
t) Higher
Hydro conversion
of the supplied
Acrylonitrile
(Ol \ dinitrile acid nitrile oligomers ν lot 72
(Comparison)
73 no 14.7 79.8 5.5 70 Triethylmethylammonium 46.3 48.7 5.0 69 74 p-toluenesulfonate '1.5 to 2.5 Trimethylcetylammonium 77.2 11.4 11.4 96 75 bromide (Comparison) no 14.0 81.1 4.9 61 76 Triethylmethylammonium 36.5 54.5 9.0 68 77 p-toluenesulfonate '4 to 5 ■ Trimethylcetylammonium 67.3 15.4 17.3 92 78 bromide (Comparison) no 7.7 86.9 5.4 53 79 Triethylmethylammonium 8.2 61.4 32.8 5.8 78 80 p-toluenesulfonate ± Trimethylcetylammonium 0.5 75.7 5.4 18.9 86 bromide

Examples 81 to 86

Examples 81 to 86 demonstrate the effect of increasing the water to acrylonitrile ratio the proportion of the higher hydrooligomers in the raw product.

In Examples 81, 82 and 83, the apparatus, the execution of the experiments, the work-up and analysis as in Example 80, except that 100 g of water, 30 g of cetyltrimethylammonium bromide,

0.015 mg Ν, Ν-dimethyl-p-nitrosoaniline and acrylonitrile in the molar amounts indicated in Table 4 were used. Examples 84, 85 and 86 were made Performed in substantially the same manner in a semi-industrial scale continuous glass reaction vessel, with the collected Reaction mixture had about 5 liters volume after the end of the experiment. The results that show the reduced proportion of higher hydrooligomers at higher water-acrylonitrile ratios, are summarized in Table 4.

table

Molar ratio 1 Reaction product (weight percent) Propionic
acid nitrile Higher
Hydro
oligomers conversion example
No. Water too
Acrylonitrile 1 Adipic acid
dinitrile 0.5 36.5 of acrylonitrile
(7o) 81 8.2: 1 1 63 5.4 18.9 75 82 22.2 1 75.7 8.0 13.0 87 83 38.9 1 79 1.7 23.9 50 84 23.2 74.4 11.7 8.1 - 85 52 80.2 15.0 1.7 - 86 70 83.3 -

209 547/541

Claims (2)

1 2 claims suppresses the formation of propiononitrile and leads to a high conversion if, in counter 1. Process for the reductive dimerization of wart of the organic specified below Acrylonitrile to adiponitrile works by means of an alkali cation. or alkaline earth algams in an aqueous medi- 5 The invention now relates to a method for reducing to, characterized in that tiven dimerization of acrylonitrile to adipic acid the reaction in the presence of peralkylated quaternitrile by means of an alkali or alkaline earth amalgam ner ammonium or phosphonium or in an aqueous medium, which is characterized by tertiary sulfonium salts at a temperature is characterized by the fact that the reaction is carried out in the presence from 10 to 60 ⁰ C carries out. io peralkylated quaternary ammonium or phosphorus 2. The method of claim 1, characterized overall phonium- or tertiary sulfonium at a indicates that one carries out the reaction at a temperature of 10 to 60 ⁰ C. Carries out a pH of 1.5 to 9.5. The addition of these salts is in particular 3. The method according to claim 1 or 2, characterized in that the undesired full Hygemarked, that one is in the presence of tetra- 15 dration of the double bond, whereby propionic acid alkylammonium salts works that produce minitrile is avoided. at least three of the alkyl groups from lower al- Particularly effective are the peralkylated quaternary phatic residues exist. natural ammonium salts. Pyridinium salts are in this 4. The method according to any one of claims I respect significantly less effective than saturated to 3, characterized in that a 20 heterocyclic quaternary compounds, for. B. Pipe Aqueous Solution of 0.1 to 10 mole percent of a ridinium or piperazinium salt. quaternary ammonium salt is used. The method is therefore preferably used in counter was a peralkylated quaternary ammonium running salt. Salts in which the quaternary 25 nitrogen atom is part of a ring structure of aromatic character, do not belong to the invention The hydromerization of acrylonitrile to adipine according to the quaternary salts to be used. she Acid dinitrile according to the equation would be intense in the presence of the amalgam QH __ QiT Q ^ Color, which changes again on contact with air 2CH = CHCN + 2H-> ■ I ~ * ³ ° pale or change. ² γή rir γ · μ ^ ^{s seems} ' that the special effect of the quater- ² * - ^H 2 tN natural ammonium compounds on the geometry is based on Knunyants and Vyazankin of the quaternary ammonium ions, which arguably (Bull. Acad. Science U.S.S.R. 1957, pp. 238 to 240) must be such that this geometrically corresponds to the have been described, which can pack together as reducing agent 35 reducing surface, a mercury amalgam and an alkali metal and as that the access of unwanted molecules or Medium used strong hydrochloric acid, which contains the acrylic ion, i. H. of acrylonitrile or water or nitrile in dilute solution. With this hydrated hydrogen ion, for reducing System, adipic dinitrile could be produced, but surface area was avoided or reduced. It leaves A considerable part of the acrylonitrile in 40 has been shown on the basis of molecular models that the Converted to propionic acid nitrile; this made the highly effective tetraethylammonium and cetyl processes uneconomical. trimethylammonium ions densely on an upper It is also from the French patent surface can pack, while tetra-n-butyl and 1,328,327 known that the formation of propionic acid methyltri-n-butylammonium ions, which is known as weninitrile can be suppressed if the procedure 45 ger have proven effective because of the three carried out by means of electrochemical reduction or there are four butyl residues in between. In this process, an electric current releases neighboring ions that are large enough to from a separate anode by a solution of that the hydrated hydrogen ions have access to Acrylonitrile that have come into contact with a cathode's surface. The more effective cations which has a hydrogen overpotential, 50 therefore appear to be among the tetraalkylammonium is greater than that of copper, to be found in a water compound which has at least two Substance ion concentration and, in the case of an acrylonitrile, carry short alkyl radicals that are the same or different concentration above 10% passed through. In and methyl, ethyl, propyl, isopropyl and isodiesers Patent specification also shows the advantages that butyl radicals can be. those with the use of certain aliphatic and hetero- 55 ^ - Quaternary ammonium salts improve the cyclic amine salts, quaternary ammonium salts definition above essentially the ratio of and other salts in the case of the direct elec- adipic acid dinitrile to propionic acid nitrile in the product, troiytic method can be obtained. As for, however, education remains a desirable goal Page 8 column 2 of this patent is executed to push back so far from propiononitrile that this is in clear contrast to the indirect contamination, which is not returned as an impurity in the end product the production of sodium amalgam can be kept through. There are conversions to electrochemical reduction of the sodium salt and propionic acid nitrile of less than 20% and possibly the following mere contact of a solder down to 1% is desirable. There was singing of the olefin with the sodium amalgam. found that particularly low propionitrile conversion It has now been found that the hydro-65 boys in the presence of quaternary ammonium dimerization of acrylonitrile take place through alkali metal compounds, which contain certain proportions of amalgam without external electrical current to high short-, medium- and long-chain alkyl substituents Yields of adipic dinitrile, too low.