Method for reducing the chlorine content of organomonophosphites using dimethylaminobutane, triethylamine or triethanolamine

Abstract

The invention relates to a universally applicable method for reducing the chlorine content of organomonophosphites using dimethylaminobutane or triethylamine.

Claims

1. A process for reducing the chlorine content in an organomonophosphite of one of the general formulae I, II, III, IV, V, VI, VII, VIII, IX and X: ##STR00020## ##STR00021## ##STR00022## where the radicals R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.21, R.sup.22, R.sup.23, R.sup.24, R.sup.25, R.sup.31, R.sup.32, R.sup.33, R.sup.34, R.sup.35, R.sup.41, R.sup.42, R.sup.43, R.sup.44 and R.sup.45 are selected each independently from: H, (C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl, and R.sup.10 is (C.sub.1-C.sub.12)-alkyl; and T is selected from: CH.sub.3, CF.sub.3, CH.sub.2C.sub.6H.sub.5; and Q is selected from: (C.sub.1-C.sub.12)-alkyl-, C(CH.sub.3).sub.3; and V is selected from: CH.sub.2CH.sub.2COCH.sub.3, C(CH.sub.3).sub.3, CH.sub.6H.sub.5; and W is selected from: -Me, CH.sub.2CH.sub.3, CH.sub.2CH.sub.2CH.sub.3, CH.sub.2-cyclo-C.sub.3H.sub.5, CH(CH.sub.3).sub.2, -cyclo-C.sub.6H.sub.11, C(CH.sub.3).sub.3, CH.sub.2C.sub.6H.sub.5, CH.sub.2C.sub.6H.sub.3-2,4-(CH.sub.3).sub.2; and X and Y are each independently selected from: (C.sub.1-C.sub.12)-alkyl, (C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.1-C.sub.12)-alkyl-(C.sub.6-C.sub.20)-aryl; and Z is selected from: (C.sub.1-C.sub.12)-alkyl-, (C.sub.6-C.sub.20)-aryl-, (C.sub.6-C.sub.20)-aryl-(C.sub.6-C.sub.20)-aryl-; and the alkyl, cycloalkyl, and aryl groups mentioned may be substituted; comprising the process steps of: a) partly or fully dissolving the organomonophosphite in a first solution comprising a first solvent selected from aromatics, alcohols, acetone, ethyl acetate, acetonitrile, ether, water; where the first solution comprises dimethylaminobutane or triethylamine or triethanolamine; c) the purified organomonophosphite is precipitated.

2. The process as claimed in claim 1, which comprises the additional process step of: b) introducing the first solution into a second solution comprising a second solvent selected from aromatics, C.sub.5-C.sub.10-alkanes, alcohols, acetone, ethyl acetate, acetonitrile, ether, water.

3. The process as claimed in claim 1, wherein the first solution comprises dimethylaminobutane.

4. The process as claimed in claim 1, wherein the first solvent is selected from: ethyl acetate, anisole, ortho-xylene, toluene, acetone, methanol, ethanol, propanol, isopropanol, acetonitrile, water.

5. The process as claimed in claim 1, wherein the first solvent is toluene.

6. The process as claimed in claim 2, wherein the second solvent is selected from: ethyl acetate, anisole, ortho-xylene, toluene, acetone, methanol, ethanol, propanol, isopropanol, acetonitrile, tetrahydrofuran, diethyl ether, glycol, C.sub.5-C.sub.10-alkanes, water.

7. The process as claimed in claim 2 , wherein the second solvent is acetonitrile.

8. The process as claimed in claim 2, wherein the second solution comprises dimethylaminobutane or triethylamine.

9. The process as claimed in claim 1, wherein the organomonophosphite is dissolved fully in the first solution in process step a).

10. The process as claimed in 1, wherein the purified organomonophosphite has a chlorine content of <200 ppm.

11. The process as claimed in claim 2, wherein the second solution is brought to a temperature in the range from 10 C. to 80 C. before the first solution is introduced into the second solution in process step b).

12. The process as claimed in claim 1, wherein the organomonophosphite has one of the general formulae I, II, III and IV: ##STR00023##

13. The process as claimed in claim 1, wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 are each independently selected from: H, (C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl; and W is CH.sub.3; and Q is C(CH.sub.3).sub.3.

14. The process as claimed in claim 1, where Z is: ##STR00024## and where R.sup.11, R.sup.12, R.sup.13, R.sup.14, R.sup.15, R.sup.16, R.sup.17, R.sup.18 are each independently selected from: H, (C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl, -halogen, COO(C.sub.1-C.sub.12)-alkyl, CONH(C.sub.1-C.sub.12)-alkyl, (C.sub.6-C.sub.20)-aryl-CON[(C.sub.1-C.sub.12)-alkyl].sub.2, CO(C.sub.1-C.sub.12)-alkyl, CO(C.sub.6-C.sub.20)-aryl, COON, OH, SO.sub.3H, SO.sub.3Na, NO.sub.2, CN, NH.sub.2, N[(C.sub.1-C.sub.12)-alkyl].sub.2.

Description

EXAMPLE 1

: Synthesis of (XI)

(1) Reaction Scheme

(2) ##STR00009## ##STR00010##
Introduction of the BOC Group:

(3) ##STR00011##

(4) In a 2 l Schlenk flask, 400 mmol (143.8 g) of 3,3-di-tert-butyl-5,5-dimethoxy-(1,1-biphenyl-2,2-diol and 40 mmol (4.8 g) of N,N-dimethylaminopyridine (DMAP) were dissolved in 900 ml of CH.sub.2Cl.sub.2. Subsequently, at room temperature, 400 mmol (88 g) of di-tert-butyl dicarbonate were dissolved in 280 ml of CH.sub.2Cl.sub.2, transferred to a 500 ml dropping funnel and added dropwise to the biphenol/DMAP solution at 32 C. within one hour. The solution was stirred at room temperature overnight. The next morning, the solvent was removed under reduced pressure. The slightly waxy, reddish residue was admixed with 800 ml of n-heptane and stirred overnight. This gave a white residue which was filtered off, washed twice with 50 ml of n-heptane and then dried. The target product was obtained as a white solid (161.6 g, 84%). .sup.1H NMR (toluene-d.sub.8): 95% and further impurities.

Reaction of tert-butyl (3,3-di-tert-butyl-2-hydroxy-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate with phosphorus trichloride

(5) ##STR00012##

(6) In a 250 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 12 g (0.026 mol) of tert-butyl (3,3-di-tert-butyl-2-hydroxy-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate were dissolved by stirring in 120 ml of dried toluene and 12.8 ml (0.091 mol) of triethylamine.

(7) In a second 500 ml Schlenk flask, 100 ml of dried toluene were first stirred together with 8.1 ml (0.091 mol) of phosphorus trichloride. Subsequently, the phosphorus trichloride-toluene solution was added dropwise to the previously prepared carbonate-amine-toluene solution at room temperature within 30 minutes. On completion of addition, the mixture was heated to 80 C. for 30 minutes and cooled to RT overnight.

(8) The next morning, the mixture was filtered, the solids were washed with 50 ml of dried toluene, and the filtrate was concentrated to dryness. The target product was obtained as a solid (13.1 g, 89%). .sup.31P NMR (202.4 MHz, toluene-d.sub.8): 203.2 and 203.3 ppm (100%).

Reaction of tert-butyl (3,3-di-tert-butyl-2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate with 3,3,5,5-tetramethyl-(1,1-biphenyl)-2,2-diol

(9) ##STR00013##

(10) In a 1 l Schlenk flask which had been repeatedly evacuated and filled with inert gas, 24.7 g (0.044 mol) of tert-butyl (3,3-di-tert-butyl-2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate were dissolved in 400 ml of acetonitrile.

(11) In a second Schlenk flask (1 l) which had been repeatedly evacuated and filled with inert gas, 10.8 g (0.044 mol) of 3,3,5,5-tetramethyl-(1,1-biphenyl)-2,2-diol were dissolved by stirring in 200 ml of acetonitrile and 13.1 ml (0.011 mol) of dried triethylamine. Subsequently, the chlorophosphite solution was slowly added dropwise to the biphenol-triethylamine solution and the mixture was stirred overnight.

(12) The mixture was then filtered and the residue was washed twice with 15 ml of acetonitrile.

(13) The filtrate was concentrated under reduced pressure until a solid precipitated out. The latter was filtered and dried. The target product (XI) was obtained as a white solid (28.5 g, 87%). .sup.31P NMR (202.4 MHz, toluene-d.sub.8): 139.4 ppm (98.5%).

EXAMPLE 2

Synthesis of (XII)

Reaction of ter-butyl (3,3-di-tert-butyl-2-hydroxy-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate with 2-chloro-4,4,5,5-tetraphenyl-1,3,2-dioxaphospholane

(14) ##STR00014##

(15) In a 250 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 9.1 g (0.021 mol) of 2-chloro-4,4,5,5-tetraphenyl-1,3,2-dioxaphospholane were dissolved in 75 ml of dried toluene.

(16) In a second Schlenk flask (250 ml), 9.2 g (0.02 mol) of tert-butyl (3,3-di-tert-butyl-2-hydroxy-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate and 2.3 g (0.02 mol) of potassium tert-butoxide were dissolved in 75 ml of dried toluene while stirring.

(17) Subsequently, the carbonate/potassium tert-butoxide/toluene mixture was slowly added dropwise at room temperature to the chlorophosphite solution, and the mixture was stirred at room temperature overnight.

(18) Thereafter, the solvent was removed under reduced pressure. The resultant residue was stirred in 75 ml of dried acetonitrile for 5 hours. The solids were filtered, washed with dried acetonitrile and dried. The target product (XII) was obtained as a white solid (15.3 g, 90%). .sup.31P NMR (202.4 MHz, toluene-d.sub.8): 147.0 ppm (99%).

EXAMPLE 3

Synthesis of (XIII)

Reaction of tert-butyl (3,3-di-tert-butyl-2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate with 2,2-biphenol

(19) ##STR00015##

(20) In a 250 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 10.5 g (0.019 mol) of tert-butyl (3,3-di-tert-butyl-2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate were dissolved in 50 ml of degassed acetonitrile while stirring.

(21) In a second Schlenk flask (250 ml) which had been repeatedly evacuated and filled with inert gas, 3.6 g (0.019 mol) of 2,2-biphenol were dissolved in 40 ml of degassed acetonitrile and 6.3 ml (0.045 mol) of dried triethylamine while stirring. Subsequently, the chlorophosphite mixture was slowly added dropwise at room temperature to the biphenol/triethylamine solution, and the mixture was stirred at room temperature overnight. The resultant solids were filtered and dried. The target product (XIII) was obtained as a white solid (11.5 g, 90%). .sup.31P NMR (202.4 MHz, toluene-d.sub.8): 146.2 ppm (100%).

EXAMPLE 4

Synthesis of (XIV)

Reaction of tert-butyl (3,3-di-tert-butyl-2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate with 3,3,5,5-tetra-tert-butylbiphenol

(22) ##STR00016##

(23) In a 250 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 7.0 g (0.0125 mol) of tert-butyl (3,3-di-tert-butyl-2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate were dissolved in 100 ml of dried acetonitrile.

(24) In a second Schlenk flask (100 ml) which had been repeatedly evacuated and filled with inert gas, 5.1 g (0.0125 mol) of 3,3,5,5-tetra-tert-butylbiphenol were dissolved in 60 ml of dried acetonitrile and 4.2 ml (0.03 mol) of dried triethylamine while stirring. Subsequently, the biphenol-triethylamine solution was slowly added dropwise at room temperature to the chlorophosphite solution and the mixture was stirred overnight. A portion of the solvent was removed under reduced pressure. The precipitated solids were filtered off and dried. The target product (XIV) was obtained as a white solid (10.2 g, 91%). .sup.31P NMR (202.4 MHz, toluene-d.sub.8): 142.7 ppm (100%).

EXAMPLE 5

Synthesis of (XV)

Reaction of tert-butyl (3,3-di-tert-butyl-2-(dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate with 3,3-di-tert-butyl-5,5-dimethoxybiphenol

(25) ##STR00017##

(26) In a 250 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 7 g (0.0125 mol) of tert-butyl (3,3-di-tert-butyl-2-(dichlorophosphino)oxy)-5.5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate were dissolved in 100 ml of dried acetonitrile.

(27) In a second Schlenk flask (100 ml) which had been repeatedly evacuated and filled with inert gas, 4.5 g (0.0125 mol) of 3,3-di-tert-butyl-5,5-dimethoxybiphenol were dissolved in 60 ml of dried acetonitrile and 4.2 ml (0.03 mol) of degassed triethylamine. Subsequently, the biphenol-triethylamine solution was slowly added dropwise at 40 C. to the chlorophosphite solution, and the reaction mixture was heated to 80 C. and stirred at this temperature for 6 h. This was followed by hot filtration.

(28) A portion of the solvent was removed under reduced pressure. The precipitated solids were filtered off and dried. The target product (XV) was obtained as a white solid (10.5 g, 96%). .sup.31P NMR (202.4 MHz, toluene-d.sub.8): 140.9 ppm (95.2%) and further impurities (further impurities=PH compounds, oxide compounds, as yet incompletely converted chlorophosphite).

EXAMPLE 6

Synthesis of (XVI)

Reaction of tert-butyl (3,3-di-tert -2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate with 2,4-dimethylphenol

(29) ##STR00018##

(30) In a 500 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 6.8 g (0.012 mol) of tert-butyl (3,3-di-tert-butyl-2-((dichlorophosphino)oxy)-5,5-dimethoxy-[1,1-biphenyl]-2-yl)carbonate were dissolved in 100 ml of dried acetonitrile.

(31) In a second Schlenk flask (250 ml) which had been repeatedly evacuated and filled with inert gas, 6 g (6 ml; 0.048 mol) of 2,4-dimethylphenol were dissolved in 100 ml of dried acetonitrile and 5 g (7 ml; 0.059 mol) of degassed triethylamine. Subsequently, the biphenol-triethylamine solution was slowly added dropwise at room temperature to the chlorophosphite solution and the mixture was stirred at room temperature overnight and cooled in an ice bath the next morning.

(32) A portion of the solvent was removed under reduced pressure. This formed a slime-like solution which solidified after prolonged drying. The target product (XVI) was obtained as a white solid (11.8 g, 62%). .sup.31P NMR (202.4 MHz, toluene-d.sub.8): 139.1 ppm (92.8%) and further impurities (further impurities=PH compounds, oxide compounds, as yet incompletely converted chlorophosphite).

EXAMPLE 7

Synthesis of bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphate

(33) ##STR00019##

(34) A 250 ml Schlenk flask with magnetic stirrer, attachment, dropping funnel and reflux condenser was initially charged with 22.5 g (0.1 mol) of 2,4-di-tert-butyl-6-methylphenol (4,6-di-tert-butyl-ortho-cresol), and heated to 55 C. in order to melt the phenol. 0.13 ml (0.0015 mol) of dried degassed dimethylformamide was added to the melt. Subsequently, 5.7 ml (0.065 mol) of phosphorus trichloride were added dropwise within 2 hours. After the addition had ended, the reaction mixture was heated to 140 C. within 3 hours and stirred at this temperature for 1 hour. Then the mixture was stirred at 130 C. under reduced pressure for 1 hour. Thereafter, the clear yellow-orange melt obtained (=bis(2,4-di-tert-butyl-6-methyl) phosphochloridite) was cooled down to 80 C. overnight and diluted with 75 ml of degassed petroleum (80-110 C.). After the solution had been cooled down to 5 C., 9.1 ml (0.0665 mol) of degassed triethylamine were added within 15 minutes. Subsequently, within 2 hours, 4.4 ml (0.075 mol) of dried and degassed ethanol were added dropwise, in the course of which the temperature did not rise above 5 C. This mixture was warmed gradually to room temperature overnight while stirring.

(35) The next morning, the precipitated triethylamine hydrochloride was filtered off and the filtrate was concentrated under reduced pressure. This gave a white residue which was recrystallized in 60 ml of degassed ethanol. The product was thus obtained in a yield of 73.9% (19.03 g) as a white solid in 98% purity by LC-MS.

(36) Chlorine Reduction

EXAMPLE 8

Chlorine Reduction of (XI)

(37) a) toluene-DMAB/acetonitrile-DMAB

(38) In a 500 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 10 g of crude ligand (XI) having an initial chlorine level of 5.7% by weight were heated to 105 C. in 40 ml of degassed toluene and 10 ml of N,N-dimethylaminobutane with stirring.

(39) A second 500 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas was initially charged with 90 ml of degassed acetonitrile and 10 ml of N,N-dimethylaminobutane, while stirring. Thereafter, the ligand/toluene/amine solution was added dropwise at room temperature to the acetonitrile-amine solution while stirring within a couple of minutes. In order to hold back the insoluble solid fraction, dropwise addition took place through a frit.

(40) After the clear solution had been stirred for 12 hours, the solvent was removed under reduced pressure. Thereafter, the resulting solid was admixed with 40 ml of degassed acetonitrile and stirred at room temperature for 12 hours. The mixture was subsequently filtered and dried. The product was obtained in 67% yield (5.9 g).

(41) NMR result: 100% P 139.3 ppm (toluene-d8).

(42) Result of duplicate Wickbold chlorine determination: 65/65 mg/kg (ppm)

(43) For accuracy, the chlorine levels were analyzed in a duplicate determination.

(44) b) toluene-DMAB/acetonitrile

(45) In a 2 l Schlenk vessel which had been repeatedly evacuated and filled with inert gas, 115.6 g of crude ligand (XI) having an initial chlorine level of 5.7% by weight were heated to 105 C. in 460 ml of degassed toluene and 100 ml of N,N-dimethylaminobutane, with stirring, and stirred at this temperature for about 10 minutes.

(46) For further work-up, the mixture was cooled to room temperature and filtered through a frit.

(47) The resulting filtrate was then concentrated to dryness under reduced pressure. Thereafter, the solid obtained was admixed with 290 ml of degassed acetonitrile, stirred for 15 minutes at 78 C., cooled to room temperature again and stirred at room temperature overnight. In the morning, the solid was filtered off, rinsed with 50 ml of degassed acetonitrile, and dried. The product was obtained in 61.8% yield.

(48) NMR result: 100% P 139.3 ppm (toluene-d8).

(49) Result of duplicate Wickbold chlorine determination: 75/80 mg/kg (ppm)

(50) c) toluene-DMAB/acetonitrile

(51) In a 2 l Schlenk vessel which had been repeatedly evacuated and filled with inert gas, 189.6 g of crude ligand (XI) having an initial chlorine level of 1.1% by weight were heated to 105 C. in 760 ml of degassed toluene and 165 ml of N,N-dimethylaminobutane, with stirring, and stirred at this temperature for about 10 minutes.

(52) For further work-up, the mixture was cooled to room temperature and filtered through a frit.

(53) The resulting filtrate was then concentrated to dryness under reduced pressure, admixed with 475 ml of degassed acetonitrile, stirred at 75 C. for 15 minutes and then cooled back down to room temperature with stirring overnight. In the morning, the solid was filtered off, rinsed with 50 ml of degassed acetonitrile, and dried.

(54) The product was obtained in 86% yield (160 g).

(55) NMR result: 100% P 139.3 ppm (toluene-d8).

(56) Chlorine result according to Wickbold: <10 mg/kg (ppm)

(57) d) work-up using toluene/methanol/triethanolamine (comparative example)

(58) In a 100 ml Schlenk flask which had been repeatedly evacuated and filled with inert gas, 10.06 g of (XI) having an initial chlorine level of 1.1% by weight were weighed out and admixed with 45 ml of degassed toluene. This suspension was heated to 102 C. and left with stirring for 20 minutes. During this time, the major fraction dissolved. Only a few particles were insoluble. Subsequently, the slightly turbid solution was subjected to hot filtration, and the clear filtrate was concentrated to dryness under reduced pressure at room temperature.

(59) The next morning, 150 ml of degassed methanol and 15 ml of degassed triethanolamine were added to the solid residue from the concentrated filtrate, and stirring was carried out for 3 hours.

(60) This gave a white suspension. The solid was subsequently isolated by filtration and dried.

(61) The product was obtained in 98% yield (9.8 g).

(62) NMR result 100% P 139.3 ppm (toluene-d8).

(63) Chlorine result according to Wickbold: 120 mg/kg (ppm)

EXAMPLE 9

Chlorine Reduction of (XV)

(64) a) work-up using degassed ethanol+1% degassed water+5% degassed DMAB at 0 C.

(65) For work-up, 300 ml of degassed ethanol and 15 ml of degassed N,N-dimethylaminobutane were initially added with stirring to the crude ligand (XV) with an initial chlorine level of 1.3% and the mixture was stirred for 2 h. Thereafter, 3 ml of degassed DI water were added and the mixture was cooled to 0 C. and stirred for 2 h. The solid was then isolated by filtration, rinsed twice with 40 ml of cold, degassed ethanol, and dried.

(66) Result of duplicate Wickbold chlorine determination: 20/20 mg/kg (ppm)

(67) Yield: 68.01 g corresponding to 68.9%.

(68) b) work-up using water/acetonitrile/N,N-dimethylaminobutane (10:10:1)

(69) For further work-up, the crude ligand (XV) with an initial chlorine level of 1.3 wt % was dissolved with stirring in 40 ml of degassed ACN and 4 ml of degassed N,N-dimethylaminobutane (5%).

(70) This was followed by overnight stirring at RT. Initial precipitation was observed after about 1 h. In the morning, 40 ml of degassed DI water were added to the mixture. The mixture was stirred for 30 minutes. Then the solid was isolated by filtration, washed with a little degassed water, and dried.

(71) Result of duplicate Wickbold chlorine determination: 50/55 mg/kg (ppm)

(72) Yield: 16.6 g corresponding to 64.02%.

(73) TABLE-US-00001 TABLE 1 Chlorine levels Chlorine level, average value 1st solvent 1st base 2nd solvent 2nd base [ppm] 8a) toluene DMAB acetonitrile DMAB 65 8b) toluene DMAB acetonitrile 77.5 8c) toluene DMAB acetonitrile <10 8d)* toluene methanol triethanolamine 120 9a) ethanol DMAB H.sub.2O 20 9b) acetonitrile DMAB H.sub.2O 52.5 *comparative example DMAB: dimethylaminobutane

(74) The examples above show that by virtue of the use dimethylaminobutane it was possible to lower the chlorine level to a value of less than 100 ppm.