DE2503114C3 - Process for the preparation of N- (α-alkoxyethyl) carboxamides - Google Patents

Description

mean,

with alcohols of the general formula (II)

R ⁴ (OH) "

CH, - CH ₃

where R ^{5 is} hydrogen or an alkyl group with 1 to 6 carbon atoms, in particular hydrogen or the methyl group, by electrolysis with alcohols of the general formula (V)

R ⁶ OH

(V)

where R ^{6 is} an alkyl group with 1 to 6 carbon atoms, in particular the methyl group, in the presence of tetraalkyl (Alkyi = Ci to C _b -) ammonium tetrafluoroborate (s) and / or hexafluorophosphate (s) as conductive salt (s) in a concentration of about 0.01 to about 2.0 mol / l at temperatures from ^{-10 to + 100 0} C to Na-Alkoxyiithylveibindungen of the general formula (VI)

R ⁵ -C N

CH-CH ₃

OR ⁶

(Vi)

in which R ⁵ and R ^{6 have} the aforementioned meanings, characterized in that an amount of at least 2.5 Faradays / mol of N-ethylcarboxamide (IV) is used in the electrolysis.

It is known carboxamides alkylated on the nitrogen with the help of alcohols electrochemically to the corresponding Ν-Λ-alkoxyalkylcarboxamides implement (DE-OS 21! 3 338). In this case, carboxamides alkylated on the nitrogen are the general formula (I)

R ¹ -C N

R ²

CH ₂

(I)

wherein
R ¹

R ^{4 is} an alkyl or alkylene group with 1 to 6 carbon atoms or a cycloalkyl or cycloalkylene group with 4 to 7 carbon atoms and
ii π 1 or 2

mean,

electrolyzed in the presence of a conductive salt at temperatures between +10 and lüOC.

2 (i The main electrolyte salts used are those whose cation is the ammonium, an alkali, alkaline earth or tetraalkylammonium ion with Cr to C alkyl groups, the nitryl or nitrosyl ion and their anion the nitrate or chloride ion or oxygen in complex-

2-, more federal form with P, Cl, Br or] as the central atom or F in complex-bound form with P, B, Ti, Sb, As, Sn or Si as the central atom. So are called Conductive salts, especially ammonium or alkali nitrate, ammonium or alkali hexafluorophosphai, -hexafluo-

iii rotitanate, -hexafluorosilicate, -hexafluoroanlimonate, -hexafluoroarsenate, tetrafluoroborate, trifluorostannate or perchlorate, tetraalkylammonium tetrafluoroborate or tetraalkylammonium chloride with Cr to Cb-alkyl groups called.

j-> In the mentioned DE-OS it is said that it is as has proven advantageous not to carry out the electrolysis until the reactants have been completely converted, because the cell voltage increases due to the product formation, whereby the material and energy yield decrease.

■ in Therefore, in the procedure of this DE-OS only Amounts of electricity not used above 2.4 Faraday / mol carboxylic acid amide.

In the tracking of the subject of the DE-OS underlying inventive concept has now been

4> found that with a very special type of Starting compounds and when using very specific supporting electrolyte salts from the group of in the DE-OS named compounds higher amounts of electricity through the reaction mixture /: can be passed,

• ν · without decreasing the material yield; yes it can be done here even achieve an extraordinary increase in the material yield. The increase in the material yield brings the Another advantage with it that the reaction mixture is then much easier to work up, then knows only little

·> ■■ or there is no starting product at all.

The subject of the invention is a process for the electrochemical alkoxylation of secondary N-ethylcarboxamides of the general formula (IV)

Hydrogen, an alkyl group with 1 to 6 carbon atoms or an aryl group with 6 to 10

Carbon atoms,
R ^{2 is} hydrogen, an alkyl group with 2 to 6

C atoms or
R ¹ and R ² together by an alkylene group having 2 to 6 carbon atoms or an alkyl substituted

R ⁵ - C - N

(IV)

O 'CII ₁ -CH ₃

where R ^{5 is} hydrogen or an alkyl group with 1 to 6

C atoms, especially H or the methyl group. means by electrolysis with alcohols of general Formula (V)

R ⁶ OH

(V)

where R ^{b is} an alkyl group with 1 to ό carbon atoms - especially the methyl group - in the presence of tetraalkyl (alkyl = Ci to Cö-JAmmoniumtetrafluoroborat (s) and / or -hexafluorophusphat (v.-n) as a conductive salt (. 'n) in a concentration of about 0.01 to about 2 mol / l at temperatures from - 10 to + 100' C to Na-Alkoxyäthylcarbonsäureamiden of the general formula (VI)

R ⁵ —C —Nl '

(Vl)

CH-CIl,

OR ⁶

in which R ⁵ and R ^{b have} the aforementioned meanings; the process is characterized in that an amount of current of at least 2.5 Faraday / mole of N-ethylcarboxamide (IV) is used in the electrolysis.

Examples of possible N-ethylcarboxamide starting materials (IV) are:
N-ethylformamide, N-ethyl acetamide, N-ethyl propionamide, N-ethyl butyramide, etc .; N-ethylformamide and N-ethyl acetamide are preferred.

Suitable alcohols (V) are:

Methanol, ethanol, n-propanol, isopropanol, n-butanol. sec-butanol etc .; methanol and ethanol are preferred, especially methanol.

The conductive salts used for the electrolysis process according to the invention are tetraalkylammonium tetrafluoroborate and hexafluorophosphate. The alkyl groups in these salts are, in particular, those with 1 to 6 C atoms, preferably methyl and ethyl groups, are possible. The tetramethylammonium salts are particularly preferred. The following salts are mentioned by way of example:

Tetramethylammonium tetrafluoroborate,
Tetraethylammonium tetrafluoroborate,
Tetraäthylariimoniumhexafluorophosphai,
Tetra (n-butyl) ammonium hexafluorophosphate
Etc.;

the preferred conductive salts are tetramethylammonium tetrafluoroborate and tetraethylammonium tetrafluoroborate, especially tetramethylammonium tetrafluoroborate. The conductive salts can be used either individually or as a mixture.

The concentration of conductive salt in the electrolysis solution should be about 0.01 to about 2.0 mol / l, preferably about 0.02 to about 1.0 mol / l.

It is possible to carry out the electrochemical alkoxylation according to the invention both batchwise and to be carried out continuously.

In the discontinuous process, the electrolysis can, for example, be carried out in the manner shown in the figure Electrolysis cell (1) are run. It is provided with a tightly closing lid (2) through which the Power supply lines for the electrodes (3) and (4) are guided, and in which the openings (5) for the inlet the electrolysis solution. (6) for the discharge of the gas and for a thermometer (9). The opening for the discharge of the gas can be fitted with a reflux condenser be provided, in which evaporating parts of the electrolysis mixture can be re-condensed. The electrolytic cell is encased and can be connected to a heating or heating system through the inlet (7) and outlet nozzles (8) Be connected to the coolant circuit. The temperature of the electrolysis solution is about a Thermometer (9) or a thermal sensor monitored. The two electrodes (3) (anode) and (4) (cathode) are at a distance of 0.5 to 50 mm. preferably between 1 and 15 mm, arranged to one another. Meshes or sheets are used as electrode material Palladium or platinum sou ie metal electrode coated with precious metal ^ preferably titanium electrodes, mixed oxide coated metal electrodes (as anodes), preferably titanium anodes are used. The net-shaped design of the electrodes is particularly advantageous, because hydrogen gas formed during the electrolysis can be discharged from these more easily and through the resulting gas flow also the uniform dichroic mixing de: electrolysis solution is promoted. The vertical arrangement of the electrodes can also be replaced by a horizontal one It is also possible to arrange several pairs of electrodes, as is the case above all in the block-like one Combination of angled or non-angled capillary gap electrodes with and without vibration of the Electrodes has proven itself. During the electrolysis, the solution is passed through a stirrer, e.g. B. Magnetic stirrer (10). or by pumping, especially with the block-like combinations vigorously mixed.

If the process is operated continuously, there is another in the cover (2) of the electrolysis vessel (1) Opening provided for continuous pumping of the electrolysis solution. From the circulated Part of the electrolysis solution is separated off for product processing. After checking the content of the electrolysis solution for the ratio of desired reaction product to starting material z. B. with the help of a nuclear magnetic resonance spectroscopy Determination method, the solution is worked up in a known manner. Those recovered in the distillation Starting materials, after they have been adjusted to the molar ratio used, are together with the required amount of the conductive salt of the continuously pumped electrolysis solution metered in again.

The electrolysis is normally carried out at normal pressure. But it can also be reduced Pressure operated.

Work is to avoid the formation of explosive gas mixtures of hydrogen and air with the addition of an inert gas, such as. B. nitrogen, advantageous.

According to the invention, the electrolysis solution consists of an alcoholic solution of an N-monoethylcarboxamide in the molar ratio of N-Monoäthylcarbonsäureamid to alcohol of about 1 to 1 to 1 to 100, preferably from about 1 in 2 to 1 in 60, in particular from about 1 in 5 to 1 in 50, in the one Conductive salt is dissolved.

The conductive salt is added after the alcoholic solution has been produced. The chronological order however, it can also be changed.

Water does not have to be completely excluded from the electrolysis because of its low moisture content

do not affect the reaction flow according to the invention.

The process can be in terms of energy or The material yield can be optimized by the fact that the conversion of the N-monoethylcarboxamide is very high. z. B. over 99%. is driven, which is also very beneficial to! ic work-up of the electrolysis solution affects. Electrolysis is therefore generally carried out until practically all of the starting material is obtained is implemented. so that its later separation from the reaction product is unnecessary.

After checking the desired tightness the electrolysis current is switched off, the electrolysis discharge is freed from the l.eitsal / and in known Way, preferably worked up by distillation. The reaction product of the electrolysis is with a Nuclear magnetic resonance spectroscopic determination method examined for purity.

The working temperature chosen for the electrolysis is a temperature below the boiling point of the alcohol and above the melting point of the electrolysis solution. In general, temperatures from -10 to + 100 ^° C., preferably from 0 to 60 ° C., are used.

The current density will be between 2 and 100 A / dm- '. preferably between 4 and 80 A / dm ² . Lower current densities are also possible, but they slow down product formation.

The N-valkoxyethylcarboxamides produced by the electrochemical process according to the invention are valuable intermediates for the production of N-vinylcarboxamides. which can be converted to water-soluble polymers with a wide range of application properties (cf. L ¹ Ilmanns Encyclopadie der Techn. Chemie. 3rd edition. Vol. 14, pages 261-264).

The process of the invention is illustrated in more detail by the following examples.

The inventive examples are then followed by 2 comparative examples A and B. which show that the special effect achieved by the invention - d. ι. so primarily the improved yield - actually critical of the application of an increased amount of electricity to the electrolysis, especially the in the starting compounds mentioned in DE-OS 21 13 338 in the presence of only very specific ones as well in the mentioned DE-OS occurring electrolyte salts bound and is therefore surprising.

In Comparative Example A, N-methylacetamide - a starting compound for the process of DE-OS 21 13 338th but not also for the process of present application - in methanol in the presence of a used for the inventive method Electrolyte salt (tetramethylammonium tetrafluoroborate) electrolyzed. After passing a sirome amount of 2.4 Faraday / mole of N-methylacetamide, a good yield of N-methoxymethyl-acetamide is achieved (Material yield 74.3% of theory); when passing a higher amount of electricity (4.0 Faraday / mol N-Methyijcetamid) the yield is considerably lower (52.0%).

In Comparative Example B, N-ethylformamide - a starting compound for both the process of DE-OS 21 13 338 and that of the present Invention - in the presence of the process of DE-OS 21 13 338th but not for the process of present avoidance of possible conductive salt potassium hexafluorophosphate electrolyzed in methanol. at Applying an amount of electricity of 4.0 Faraday / mol N-ethylformamide became a material benefit N-a-methoxyethylformamide of only 30.1% d. Th. Received. In the comparable example 7 of DE-OS (same starting material and conductive salt) is the yield after passing through an amount of electricity of about 2 Faraday (= about 1 current equivalent) / mole of N-ethylformamide 52.1% of theory. Th.

The one in Comparative Example B compared to Example 7 of DE-OS 2113 338 mentioned Quantity ratio of starting material to methanol (in comparative example B was relatively more methanol used) is due to the use of higher currents; one to Example 7 of DE-OS corresponding amount of methanol would because of the main reaction as well as the side reactions of the methanol not sufficient for a reasonably proper electrolysis with the higher amount of electricity used. A higher amount of conductive salt applied in accordance with the aforementioned example 7 would result in one lead to an even lower yield result.

example 1

lii an electrolytic cell corresponding to the figure of about 380 ml content with lid and reflux condenser a mix of

91.4 g of N-ethylformamide and

200.3 g of methanol

filled, in the 2.45 g of Ttrameihylammoniumietrafluoroborat are dissolved as conductive salt. Three concentrically arranged platinum mesh cylinders with 225 meshes per cm and with a 15. 30 or 50 mm diameter at 100 mm Height immerse as electrodes in the solution. The outer and inner electrodes are connected in parallel and serve as anode, the cathode is in the middle between the two. The temperature during electrolysis is kept at 40 C. The stirring is carried out by a magnetic stirrer with 30 to 35 revolutions per minute Minute. After switching on the electrolysis direct current the anode current density is 5 A / dm-. After an amount of electricity of 7,075 Faradays per mole of N-ethylformamide has gone through. the power is switched off. The calculated mean voltage is 18.7 volts.

After working up the electrolysis solution in a known manner, 95.0 g of N- (α-methoxyethyl) formamide are obtained (Kp. 66-67 "C / 1.3 mbai ·;» ·· '= 1.4370). This corresponds to a material yield of 73.7% and a current efficiency. 20.8%. The current yield increases as expected with the larger Stronimengc a lower value than the material yield.

In Examples 6 and 7 of DE-OS 21 13 338. according to which N-ethylformamide is also electrolyzed with CHiOH, but with only about 2.4 (Example 6) or 2 (Example 7) Faraday per mole of acid amide and using other Leitsalzc (NH ₄ NOi or KPF ”) only material yields of 40.7 (Example 6) or 52.1% of theory were obtained.

Example 2

The following are electrolyzed in the same way as in Example 1:

131.5 g (= 1.8 mol) of N-ethylformamide and

288.4 g (= 9.0 mol) of methanol

in the presence of 90 g (= 0.018 mol) of tetramethylammonium tetrafluoroborate as conductive salt. Here, however, the current is switched off after an amount of current of 4,073 Faraday per mole of N-ethylformamide has passed. The calculated mean cell voltage is 1 92 volts.

Working up the electrolysis solution yields 160.2 g (= 1.554 mol) N- (i \ -Methoxyethyl) -formamide: this corresponds to a material yield of 86.3% and a current yield of 42.3%.

Example 3

In an electrolytic cell according to the figure of A mixture of about 70 ml with a lid with a reflux condenser is made

10.54 g (= 0.121 mol) of N-ethyl acetamide and

38.77 g (= 1.210 moles) of methanol

filled, in which 1.95 g (= 0.121 mol) of tetramethylammonium tetrafluoroborate are dissolved as conductive salt. The temperature during the electrolysis is kept at 40 ° C. Stirring is carried out using the magic stirrer with 30 to 35 revolutions per minute. After switching on the elec- trolysis system, the anode current density is 5 A / dm- '. After going through an amount of stroin of 3 Faradays per mole of N-Äihvlaeetamide. the Slroin is switched off. The calculated initial cell voltage is 32.3 volts. After processing the Electrolysis solution in a known manner is obtained 12.3 g N- (v-methoxyethyl) acetamide (boiling point 71-73 ° C / 0.9 mbar). That corresponds to a painterial yield of 86.8 "/ o and a Stromausbeutc of 57.8.

Example 4

In the same way as in Example 3, an electrolysis cell with a capacity of approx. 380 ml
63.2 g N-Älhylacetamid and

232.6 grams of methanol

in the presence of 1.95 g of tramethylammonium tetrafluoroborate electrolyzed as conductive salt: however, it is now double the line curve. so 6.0 Faraday per Moles of N-ethylacetamide. passed through the cell. The mean cell voltage is calculated as 19.0 full. the Work up the F.lekirolysclösung in a known manner yields 71.2g N - (\ - Metlii> xvälhvl) aectamid. Corresponding a material output of 83.7% and a current efficiency of 27.9%. Despite increasing the transmitted Stroniniengc from 3 to 6 Faraday per Mole of N-ethylacetamide never drops the material yield away. but remains constant. As expected, the current yield decreases.

Example 5

In an electrolysis cell as shown in the figure with a volume of about 70 ml with a lid and reflux condenser a mix of

9.5 g ethyl formamide and

48.2 g n-butanol

filled in, in which 4.38 g of tetra-n-butylammonium tetrafluoroborate are dissolved as conductive salt. Two concentrically arranged platinum mesh cylinders with 225 meshes per cm ² with 15 or 30 mm diameter and 50 mm height are immersed in the solution as electrodes. The outer electrode serves as the anode, the inner one as the cathode. The stirring is carried out by means of a magnetic stirrer at 30 to 35 revolutions per minute. After switching on the electrolysis direct current, the anode current density is 5 A / dm ² . The temperature during the electrolysis is kept at 40 ° C.

After an amount of current of 5.34 Faradays per mole of N-Ethyiformamide has gone through. will the Power switched off The calculated mean cell voltage is 39.1 volts.

After working up the electrolysis solution in known

Thus, 8.3 g of N - (. ^ - n-butoxyethyl) formamide are obtained (Bp. 75 ° C / 0.1 mbar m '= 1.4328). That corresponds to a Material yield of 44.0% and a current efficiency

-, from 16.5%.

Example 6

In an electrolytic cell as in Example 5 is a

in mixture of

23.3 g of N-ethyl propionic acid amide and
36.9 g of methanol

filled, in the 0.37 g of tetramethylammonium tetrafluoroborate are dissolved as conductive salt. After switching on

ti of the electrolysis strony is the anode current density 2 A / dii) '. The temperature during electrolysis will be kept at 40 ° C. Stirring is carried out by means of a magnetic stirrer at 30 to 35 revolutions per minute. After an amount of electricity of 4.06 Faraday per mole

2Ii N-ethylpropionic acid amide has gone through. the power is switched off. The calculated mean cell voltage is 54.9 V. After the electrolysis solution has been worked up in a known manner, 24.4 g of N- (ix-methoxyethyl) propionic acid camide (melting point) are obtained.

? -, ^{29-32 C} C. η = 1.4333). This corresponds to a material yield of 80.7% and a current bulge of 40.4%.

Example 7

^V

In an electrolytic cell as in Example 5 is a Mix of

18.3 g N-Äthylformaniid and
40.1 g of methanol

j ·. filled, in which 0.83 g of tetra-n-propylammonium hexafluorophosphate are dissolved as a conductive salt. After switching on the electrolytic current, the anode current density is 5 A / dm- ¹ . The temperature is kept at 40 ^° C. Stirring is done using a 30 to 35 magnetic stirrer

in revolutions per minute. After going through an amount of electricity of 6 Faraday per mole of N-ethylformamide is. the power is switched off. The calculated mean cell voltage is 34.2 V. After working up the electrolysis solution is obtained in a known manner

4i 19.6 N- (A-methoxyethyl) formamide. Corresponding a material yield of 76.0% and a current efficiency of 25.3%.

Comparative example A.

In an electrolysis cell according to comparative example 1 DE-OS 2113 338 of 150 ml content is a mixture of

56.9 g of N-methylacetamide and

49.9 g of methanol

electrolyzed. in which 1.25 g of tetramethylammonium tetrafluoroborate are dissolved as Leitsa'z. After an amount of current Q of a) 2.4 or b) 4.0 Faraday per mole of N-methylacetamide has passed, the experiment is terminated. After the electrolyte salt has been removed, the electrolysis discharge is analyzed. The data and yields of the experiments are summarized in the table. Mean:

/ = Cell current.
^ U = mean cell voltage,
M = material yield

based on the amide used.
S = current efficiency.

9 scdalon
L.
(V) 25th 03 114 IO S. No. l-leklroly
(Λ) 313 Q
Ii-VMi) I) Coupon product M. 61.9 a 3.4 2.4 CII ₁ CNHCh ₂ OCH, 74.3

if O

i 'b 3.2 364 4.0 52.0 26.0

[| based on the theoretically required amount of charge as a conductive salt (as in Example 7 of the above-mentioned DE-OS

| ge of 2 Faraday per mole of amide. π 21 13 338) are solved. After passing through a current

!! . . amount O = 4 Faraday per mole of N-ethylformamide

Ü. ergleichsbeispicl B _the attempt aborted. After removing the duct

B The electrolysis discharge is analyzed in an electrolysis unit according to Comparative Example 1. The data

I of DE-OS 21 13 338 of 150 ml content is a and yields are in the table of the data and

a 'Mixture of -' <> Yields of Example 7 of DE-OS 21 13 338

h 56.8 g of N-ethylformamide (EF) and compared. /, U, / V / and S have the same thing

fj! 49.9 g of methanol Meaning as in Comparative Example A.

|. | electrolyzed, in the 1.43 g of potassium hexafluorophosphate

Theatrical Version cn -,OH KIM- ,, lilcktrolysciUilen Q License product M. S. / a (IVMoI) (%) (%) Ig) IgI 181 (Λ) (V)

56.8 49.9 1.43 2.6 29.6 4.0 30.1 15.1

CH,

HCNHCH

Il \

O OCH,

Example 7 of 37.4 16.4 9.4 --9, (I 2.0 "52.1 52.1

DE-OS 21 13 338

For this purpose I sheet drawings

Claims (1)

Claim: Process for electrochemical alkoxylation of secondary N-Äihylcarbonsäureamiden der general formula (IV) R ⁵ -C N (IV) Alkylene group with 2 to 6 carbon atoms and Cr to Cr alkyl groups are connected.
R ^{1 is} hydrogen or an alkyl group with 1 to 6 Carbon atoms