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Preparation of ethylene glycol oligomers—II
Eur. Polym. J. Vol. 18, pp. 541 to 544, 1982 Printed in Great Britain. All rights reserved
0014-3057/82/060541-04503.00/0 Copyright © 1982 Pergamon Press Ltd
PREPARATION OF ETHYLENE GLYCOL OLIGOMERS--II H. H. TEO, R. H. MOBBS and C. BOOTH Department of Chemistry, University of Manchester, Manchester, M 13 9PL, U.K.
Abstract--Procedures are described for the preparation of oligomeric ethylene glycols HO[CHzCH20]:,H, x = 10, 15, 20, 25, 35 from the monosodium salt and the ditosylate of pentaethylene glycol. The melting points of the oligomers are higher than those of comparable materials prepared hitherto.
INTRODUCTION We have described [1] the synthesis of pure n o n a e t h ylene glycol by the reaction of the m o n o s o d i u m salt of triethylene glycol with the ditosylate of triethylene glycol [2] in solution in tetrahydrofuran. A small a m o u n t of less pure pentadecaethylene glycol was also isolated from the preparation. The crystallinity of the two glycols and their dimethyl ethers has been investigated [3], as has the crystallinity of a series of di-n-alkyl ethers of nonaethylene glycol [4]. In order to extend this work, we have prepared pentadecaethylene glycol starting from pentaethylene glycol. This has necessitated some changes in reaction conditions. Also, since small a m o u n t s of valuable higher oligomers were by-products of reaction, purification by short path distillation was not possible. We have found preparative scale gel filtration, with Sephadex LH-20 packing and ethanol solvent, to be very satisfactory for purification of the oligomers. EXPERIMENTAL
Materials Analar pyridine (BDH) was stirred over calcium hydride (2 days), boiled under reflux (3 hr) and then distilled (b.p. 114~115 °) onto, and stored over, type 4A molecular sieve (Union Carbide). Tetrahydrofuran (BDH) was stirred over calcium hydride (16 hr), boiled under reflux (2 hr) and then distilled onto, and stored over, type 4A molecular sieve. Analar methanol (BDH) was distilled from magnesium methoxide onto, and stored over, type 4A molecular sieve. Dichloromethane (Hopkin and Williams) was distilled. Pentaethylene glycol (Columbia Organic Chemical Co.) was used as received. Purity was checked by GLC [1] and found to exceed 98%-wt. Fractional distillation [1] was attempted but did not improve the purity. Sodium metal (BDH) was used without further purification. Toluene-p-sulphonyl chloride (BDH, 62g) was dissolved in chloroform (70 cm3), cliluted with petroleum ether (b.p. 4(~60 , 600cm3), stirred with decolourising charcoal and filtered. The clear solution was concentrated by rotary evaporation (to 150 cm 3) and slowly cooled to room temperature. The crystalline product (42 g) was filtered off and dried in vacuum.
Procedures Pentaethylene glycol ditosylate. Separate solutions of pentaethylene glycol (25.0g, O.105mol) in dry pyridine * x = nominal chain length in oxyethylene units. 541
(250cm 3) and of toluene-p-sulphonyl chloride (80.61 g, 0.423 tool) in dry pyridine (250 cm 3) were cooled to - 2 0 :, before being combined and stirred under dry Nz at - 2 0 (117 hr). The resultant mixture was added to ice and water (1 dm 3, vigorously stirred) and the mixture was extracted with dichloromethane (8 × 500cm3). After concentration (rotary evaporation to 1.5 dm 3) the dichloromethane solution was washed successively with hydrochloric acid (6 tool dm -3, 3 × 500 cm3), aqueous ammonium chloride (sat., 2 × 500cm3), distilled water (500cm3), and dried (NazSO4). Filtration of the solution followed by rotary evaporation yielded a viscous oil (54.77 g, 95~ yield) which was subsequently dried completely in a vacuum desiccator (PEns). The i.r. spectrum (NaCI) showed bands at 1175, 1190 cm- 1 (--O3SC6H4CH3) and no bands at 3200-3600cm-t (--OH). The ~H-NMR spectrum (CDCI3) showed resonances at 7.5-7.6z (--CH3), 5.8-6.5r (--CH2--) and 2.2-2.7 z (Ar-H) with associated integration in accord with the expected structure. (Analysis. Calculated for Cz4H34OIoS2: C, 52.750,0; H, 6.23°,;,: S, 11.72°/o. Found: C, 53.0°0: H, 6.3~o; S, 12.0~o). A second similar preparation gave pure pentaethylene glycol ditosylate in similar yield (94°,0). Oligomeric glycols. Dry methanol (63.2 g, 1.98 mol) was added to Na (5.90 g, 0.257 mol) under dry N 2. The mixture was gently reftuxed for 0.7 hr and then cooled, under N2, in ice-water. Pentaethylene glycol (184.1 g, 0.773mol) was poured rapidly (60 secl into the vigorously stirred sodium methoxide solution at 0 °. The mixture was stirred at room temperature (0.7 hr), before the methanol was distilled off in a stream of dry N2 (bath temperature 90-112 °, pressure ambient to 0.5 mmHg) leaving a viscous yellow liquid. To this stirred liquid at 25 ° was added (3 min) a solution of pentaethylene glycol ditosylate (70.33 g, 0.129 mol) in tetrahydrofuran (660cm3l. The flask was shielded from light and the mixture was stirred (room temperature, 289 hr). The white precipitate of sodium tosylate (49 g, 98.5~o yield) was filtered off. Tetrahydrofuran was removed by rotary evaporation, and a clear yellow liquid resulted which crystallised on standing at room temperature. Distilled water (300 cm 3) was added to the residue and the faintly cloudy mixture was gently refluxed (2.5 hr). Upon cooling the solution was brought to pH ~- 6 (HCI, 3 tool dm -3, about 7 cm 3) and extracted with dichloromethane (10 x 200 cm3). The combined organic extracts were washed with aqueous sodium carbonate (10~o w/v, 2 x 50cm 3) and the aqueous washings re-extracted with dichloromethane (6 × 100 cm3). Finally the combined organic extracts were washed with distilled water (25 cm3), dried (Na2SO4), and the solvent evaporated to yield a mixture of oligomeric glycols* (x = 5, 10, 15, 20, 25, 35:93.34g). Subsequent continuous extraction (dichloromethanet of the combined aqueous phases, followed by
H.H. TEO et al.
542 ~'---A----'FB..J--C
I
D---~-.---E-----~-F~O-.r-.-r;
',
;
I
f _~3.5
-0
~n x
0 0
_¢
~O
3.0
,.~
11+.
1!+
+~
%
2'.2
z~o V/dm +
Fig. I. Refractive index difference (arbitrary scale) vs elution volume for preparative size exclusion (gel filtration) chromatography of l~he,oligomer mixture. The fractions A-I are indicated.
evaporation of solvent from the organic extract, yielded practically pure pentaethylene glycol (98.31 g). Separation of oligomeric glycols. The crude product was separated into its components by preparative scale size exclusion (gel filtration) chromatography. Two Sephadex LH-20 columns (length 80cm, diameter 5.0cm) were used* with ethanol at 20 ° and 0.85 c m 3 rain-z flow rate (short stroke pump, Metering Pumps Ltd). Elution volumes were measured by a 3 cm 3 syphon; detection was by differential refractometry (Waters Associates Model R403). Injection of sample (9 g in 40 cm 3 ethanol) was by interruption of the solvent stream, via a 4-port valve, and pumping in solution at the same flow rate (0.85 cm 3 min- t). Fractions were collected as indicated on the chromategram shown in Fig. 1. Combined fractions were : A, 0.25 g, mainly x = 35; B, 0.21 g, x = 25, 35; C, 4.17g, mainly x = 2 5 ; D, 1.11g, mainly x = 2 0 , some x = 15, 25; E, 46.81 g mainly x = 15; F, 14.79g, mainly x = 15, some x = 10; G, 1.63 g, mainly x = 10, some x = 15; H, 0.58 g, x = 5, 10; I, 22.94g, mainly x = 5; total, 92.49g, 99.1~o recovery. Fractions A-G were rechromatographed and recombined one or more times to obtain combined fractions of oligomers as follows: x = 35, 0.16g; x = 25, 4.07 g; x = 20, 0.10 g; x = 15, 57.93 g; x = 10, 0.51 g; total, 62.77 g, 91~ recovery of fractions A-G. RESULTS
AND
DISCUSSION
The preparation of pentaethylene glycol ditosylate has not been reported previously. Initial small scale experiments using pentaethylene glycol and toluene-psulphonyl chloride at 0 ° in fairly concentrated solution in pyridine (much as described for the preparation of triethylene glycol ditosylate [1]) gave variable and poor yields. Eventually the toluene-p-sulphonyl chloride was recrystallised, the reaction temperature was reduced to - 2 0 °, and the dilution was increased so as to maintain a homogeneous solution. Yields in the range 9 0 - 9 5 ~ were then regularly obtained. The procedure for the reaction between pentaethylene glycol ditosylate and the monosodium salt of pentaethylene glycol was similar to that described earlier [1] for the preparation of nonaethylene glycol. The mole ratio glycol/methoxide was increased (7.7 compared with 2.9) in an attempt to minimise disodium salt formation. Also the reaction time was lengthened (about 12 days compared with about 5 days) * A separation with two columns of diameter 2.5 cm and with injection of 3 g of sample (in 20 c m 3 ethanol) was useful but less convenient. t The yields are based on the incorporation of one ditosylate residue (pentadecamer) or two ditosylate residues (pentacosamer) into the product.
2-5 I 1B0
I
I Z00
I
I
220
Wcm~
Fig. 2. Logarithm of molecular weight vs elution volume of (tl ethylene glycol oligomers and (O) commercial polyethylene glycols 3000-400. in an attempt to increase the yield. In fact yieldst of pentadecamer (33~o) and pentacosamer (6~o) were very similar to those reported I-1] for the triplication of triethylene glycol in tetrahydrofuran, i.e. nonamer (30~) and pentadecamer (6~o).
Analytical size exclusion (gel permeation) chromatography (GPC) Six Styragel columns (length 1.2m, diameter 0.94cm, nominal pore sizes 5-8, 15-35, 20--50, 50, 50-200 and 70-200 nm) were used with tetrahydrofuran at 25 ° and 1 cm 3 min -1 flow rate. Detection was by differential refractometry (Optilab Multiref 901). Samples were injected at a concentration of 1 g d i n - 3 via a 2 cm 3 loop, The system was calibrated by use of commercial polyethylene glycols of known molecular weight (in the range 400-3000gmo1-1). The calibration data are shown in Fig. 2. A chromatogram of the oligomer mixture prior to separation (Fig. 3) indicates the resolution of the method. The chromatogram of eicosaethylene glycol (potentially the least pure of our samples), also shown in Fig. 3, is typical of the single narrow peaks recorded for the oligomeric glycols. Their peak elution volumes, marked on Fig, 2, are as expected. The resolution and sensitivity of the method allow the conclusion that the purity of the oligomeric glycols exceeds 99~o-Wt. Improved resolution is possible if the chromatograph is used in recycle mode (see appendix). Investigation of the pentadecamer in this way indicated a purity of 99.9~-wt or better. The other oligomeric glycols were not recycled. Io)
(b)
7 ,~5
,o 2~o
A
r
__) L__
2~s Wcm ~ z~o ,6
2oo Vlcm3 ~o
Fig. 3. Refractive index difference (arbitrary scale) vs elution volume for analytical size exclusion (gel permeation) chromatography of (a) the oligomer mixture and (b) purified eicosaethylene glycol (x = 20). The elution volumes of the various oligomers are indicated on chromatogram (a).
543
Preparation of ethylene glycol oligomers Infra-red spectroscopy Spectra were recorded by means of a Perkin-Elmer Model 577 spectrometer. Oligomers were dried by melt evacuation ( < 10 3 mmHg, several days) and a thin film, placed between dried CsBr plates, was mounted in a temperature controlled vacuum cell (Beckmann RIIC). The assembled cell was evacuated (50 c, 3 hr) immediately, and the spectrum of the melt quickly recorded. The spectra so obtained were almost identical to those of melts of commercial polyethylene glycol of similar molecular weight (600-1500gmol -x) dried similarly. There was no evidence of unsaturated or carbonyl groups, such as has been reported for other ethylene glycol oligomers [5]. The spectra of the solids, in the temperature range 25 ° to - 8 0 °, were recorded; they are discussed elsewhere [6]. Nuclear magnetic resonance spectroscopy Spectra (CDCI3) were recorded at 6 0 M H z by means of a Perkin-Elmer R12B spectrometer. Resonances were found at 6.3 r ( - - O - - C H 2 - - C H 2 - - O - - ) and 7.25 r (--OH). Mass spectrometry The mass spectrum of the pentadecamer was recorded by means of an AEI MS30 spectrometer. No molecular ion was obtained, but a peak at M + 1 (m/e = 679) was present arising perhaps, as suggested earlier [1], by proton abstraction from a small fragment. A pattern of fragments arising from successive loss of oxyethylene units from M + 1 was readily discernible. Differential scannin9 calorimetry (DSC) Melting endotherms were obtained by means of a Perkin Elmer DSC-1B. Carefully dried oligomers (about 10 mg) were sealed into AI pans, of the kind designed to contain volatiles, taking stringent precautions to exclude moisture. Samples were heated to 60-70 ° and then crystallised by cooling rapidly to 0 °. Starting at this temperature, samples were heated through the melting transition at several heating rate(s) in the range 1 - 1 6 K m i n -~. The melting endotherms of the oligomeric glycols were narrow single peaks. The width of an endothermic peak at half-height (ATe) is a useful indicator of purity since, at s = 0, this slaould be zero for a pure compound. It is appropriate to plot AT~ against s ~, as illustrated earlier [3]. The results, AT½ < 0.1K at s = 0, show that the purity of the samples exceeds 99~,-mol with the exception of the decamer (AT½ _~ 0.25, purity -~ 98°~,-mol). M eltiny point Melting points, defined as the temperature of disappearance of the last trace of crystallinity, were measured for small samples (5-10 mg) of the carefully dried oligomers sealed into capillary tubes in a dry box. These were immersed in a stirred oil bath, the temperature of which was raised slowly (0.1 K m i n - t) from a temperature 4-5 K below the melting point. Melting was observed through a telescope. The thermometer was calibrated against N P L standards.
50
(n/*C
•
0
t,0
o 30 I
1o
I
I
20
30
I
X
1,0
Fig. 4. Melting point vs chain length x for ethylene glycol oligomers: (0) this work; (x) reference 1;(©) reference 2. Melting points were also defined by the position of the endothermic peak obtained by DSC (s = 2 K min-~). Correction was made for thermal lag [7] and the temperature scale of the calorimeter was calibrated by melting standard materials (range 29.0°-55.1 °). Melting points are listed below, Oligomer (x) Tin~° (oil bath) T,,/°(DSC)
10 -30.8
15 40.0 40.0
20 44.4
25 46.6 47.0
35 49.8 50.1
and are compared with literature values [1, 2] in Fig. 4. B6mer et al. have suggested that their relatively low values of T,, for x = 18 and 36 formed from nonaethylene glycol are due to by-products formed by elimination or cyclisation reactions which can occur when linking even numbers of units. Our results for x = 10 and 20 are inconsistent with this suggestion. Acknowledoements--We thank Mr D. R. Roy for help with the chromatography. The work was financed by the Science Research Council. REFERENCES
1. A. Marshall, R. H. Mobbs and C. Booth, Eur. Polym. J. 16, 881 (1980). 2. B. B6mer, W. Heitz and W. Kern. J. Chromat. 53, 51 (1970). 3. A. Marhsall, R. C. Domszy, H. H. Teo, R. H. Mobbs and C. Booth, Eur. Polym. J. 17, 885 (1981). 4. R. C. Domszy and C. Booth, Makromol. Chem., accepted for publication. 5. B. A. Mulley, Nonionic SurJactants (Edited by M. J. Schick). Arnold, London (1967). 6. H. H. Teo, A. Marshall and C. Booth, Makromolek. Chem., accepted for publication. 7. J. L. McNaughton and C. T. Mortimer, Int. Rev. Sci., Phys. Chem. Ser. 2 10, 1 (1975). 8. R. A. Henry, S. H. Byrne and D. R. Hudson, J. Chromat. Sci. 12, 197 (1974). APPE N D IX
Recycle Gel Permeation Chromatography We have used a recycle system based on the alternate pumping method [8]. In this method the sample does not have to pass through the pump and so peak spreading and skewing is minimised. Alternation of flow was achieved by means of a six-port valve [8]. A chromatogram of pentadecaethylene glycol obtained using the GPC system described earlier, but with 3 cycles,
544
H.H. TEO et al.
is shown in Fig. A1 (a). The chromatogram shows baseline shifts which are attributable to switching of the valve, and which effectively obscure any small peaks which might be present because of impurities. This problem can be overcome by using a detector which is less sensitive to changes in temperature, pressure and low molecular weight impurities. Pentadecaethylene glycol has no useful u.v. absorption. Consequently we have made use of an evaporative analyser (Clanor Instruments)* with the result shown Fig. Al(b). There are no baseline problems and the pentadecamer is seen to be pure (within the sensitivity of the method: probably +0.1%-wt.). * The eluant stream emerging from the columns is split into two equivalent streams (T junction with equivalent back pressure of 80 psi on each stream), one of which is led to the differential refractometer and, subsequently, a syphon (5 cm3), and the other to the evaporative analyser. In this analyser the eluant stream is atomised into an air stream, the solvent is evaporated, and the intensity of light scattered at 90 ° from the resulting solute aerosol is recorded.
f (a)
I
(b) I 300
I 320
I 340 V/cm 3
Fig. A1. Detector signal (arbitrary scale) vs elution volume for analytical size exclusion (gel permeation) chromatography with 3 cycles: (a) refractive index detector and (b) evaporative analyser.
0014-3057/82/060541-04503.00/0 Copyright © 1982 Pergamon Press Ltd
PREPARATION OF ETHYLENE GLYCOL OLIGOMERS--II H. H. TEO, R. H. MOBBS and C. BOOTH Department of Chemistry, University of Manchester, Manchester, M 13 9PL, U.K.
Abstract--Procedures are described for the preparation of oligomeric ethylene glycols HO[CHzCH20]:,H, x = 10, 15, 20, 25, 35 from the monosodium salt and the ditosylate of pentaethylene glycol. The melting points of the oligomers are higher than those of comparable materials prepared hitherto.
INTRODUCTION We have described [1] the synthesis of pure n o n a e t h ylene glycol by the reaction of the m o n o s o d i u m salt of triethylene glycol with the ditosylate of triethylene glycol [2] in solution in tetrahydrofuran. A small a m o u n t of less pure pentadecaethylene glycol was also isolated from the preparation. The crystallinity of the two glycols and their dimethyl ethers has been investigated [3], as has the crystallinity of a series of di-n-alkyl ethers of nonaethylene glycol [4]. In order to extend this work, we have prepared pentadecaethylene glycol starting from pentaethylene glycol. This has necessitated some changes in reaction conditions. Also, since small a m o u n t s of valuable higher oligomers were by-products of reaction, purification by short path distillation was not possible. We have found preparative scale gel filtration, with Sephadex LH-20 packing and ethanol solvent, to be very satisfactory for purification of the oligomers. EXPERIMENTAL
Materials Analar pyridine (BDH) was stirred over calcium hydride (2 days), boiled under reflux (3 hr) and then distilled (b.p. 114~115 °) onto, and stored over, type 4A molecular sieve (Union Carbide). Tetrahydrofuran (BDH) was stirred over calcium hydride (16 hr), boiled under reflux (2 hr) and then distilled onto, and stored over, type 4A molecular sieve. Analar methanol (BDH) was distilled from magnesium methoxide onto, and stored over, type 4A molecular sieve. Dichloromethane (Hopkin and Williams) was distilled. Pentaethylene glycol (Columbia Organic Chemical Co.) was used as received. Purity was checked by GLC [1] and found to exceed 98%-wt. Fractional distillation [1] was attempted but did not improve the purity. Sodium metal (BDH) was used without further purification. Toluene-p-sulphonyl chloride (BDH, 62g) was dissolved in chloroform (70 cm3), cliluted with petroleum ether (b.p. 4(~60 , 600cm3), stirred with decolourising charcoal and filtered. The clear solution was concentrated by rotary evaporation (to 150 cm 3) and slowly cooled to room temperature. The crystalline product (42 g) was filtered off and dried in vacuum.
Procedures Pentaethylene glycol ditosylate. Separate solutions of pentaethylene glycol (25.0g, O.105mol) in dry pyridine * x = nominal chain length in oxyethylene units. 541
(250cm 3) and of toluene-p-sulphonyl chloride (80.61 g, 0.423 tool) in dry pyridine (250 cm 3) were cooled to - 2 0 :, before being combined and stirred under dry Nz at - 2 0 (117 hr). The resultant mixture was added to ice and water (1 dm 3, vigorously stirred) and the mixture was extracted with dichloromethane (8 × 500cm3). After concentration (rotary evaporation to 1.5 dm 3) the dichloromethane solution was washed successively with hydrochloric acid (6 tool dm -3, 3 × 500 cm3), aqueous ammonium chloride (sat., 2 × 500cm3), distilled water (500cm3), and dried (NazSO4). Filtration of the solution followed by rotary evaporation yielded a viscous oil (54.77 g, 95~ yield) which was subsequently dried completely in a vacuum desiccator (PEns). The i.r. spectrum (NaCI) showed bands at 1175, 1190 cm- 1 (--O3SC6H4CH3) and no bands at 3200-3600cm-t (--OH). The ~H-NMR spectrum (CDCI3) showed resonances at 7.5-7.6z (--CH3), 5.8-6.5r (--CH2--) and 2.2-2.7 z (Ar-H) with associated integration in accord with the expected structure. (Analysis. Calculated for Cz4H34OIoS2: C, 52.750,0; H, 6.23°,;,: S, 11.72°/o. Found: C, 53.0°0: H, 6.3~o; S, 12.0~o). A second similar preparation gave pure pentaethylene glycol ditosylate in similar yield (94°,0). Oligomeric glycols. Dry methanol (63.2 g, 1.98 mol) was added to Na (5.90 g, 0.257 mol) under dry N 2. The mixture was gently reftuxed for 0.7 hr and then cooled, under N2, in ice-water. Pentaethylene glycol (184.1 g, 0.773mol) was poured rapidly (60 secl into the vigorously stirred sodium methoxide solution at 0 °. The mixture was stirred at room temperature (0.7 hr), before the methanol was distilled off in a stream of dry N2 (bath temperature 90-112 °, pressure ambient to 0.5 mmHg) leaving a viscous yellow liquid. To this stirred liquid at 25 ° was added (3 min) a solution of pentaethylene glycol ditosylate (70.33 g, 0.129 mol) in tetrahydrofuran (660cm3l. The flask was shielded from light and the mixture was stirred (room temperature, 289 hr). The white precipitate of sodium tosylate (49 g, 98.5~o yield) was filtered off. Tetrahydrofuran was removed by rotary evaporation, and a clear yellow liquid resulted which crystallised on standing at room temperature. Distilled water (300 cm 3) was added to the residue and the faintly cloudy mixture was gently refluxed (2.5 hr). Upon cooling the solution was brought to pH ~- 6 (HCI, 3 tool dm -3, about 7 cm 3) and extracted with dichloromethane (10 x 200 cm3). The combined organic extracts were washed with aqueous sodium carbonate (10~o w/v, 2 x 50cm 3) and the aqueous washings re-extracted with dichloromethane (6 × 100 cm3). Finally the combined organic extracts were washed with distilled water (25 cm3), dried (Na2SO4), and the solvent evaporated to yield a mixture of oligomeric glycols* (x = 5, 10, 15, 20, 25, 35:93.34g). Subsequent continuous extraction (dichloromethanet of the combined aqueous phases, followed by
H.H. TEO et al.
542 ~'---A----'FB..J--C
I
D---~-.---E-----~-F~O-.r-.-r;
',
;
I
f _~3.5
-0
~n x
0 0
_¢
~O
3.0
,.~
11+.
1!+
+~
%
2'.2
z~o V/dm +
Fig. I. Refractive index difference (arbitrary scale) vs elution volume for preparative size exclusion (gel filtration) chromatography of l~he,oligomer mixture. The fractions A-I are indicated.
evaporation of solvent from the organic extract, yielded practically pure pentaethylene glycol (98.31 g). Separation of oligomeric glycols. The crude product was separated into its components by preparative scale size exclusion (gel filtration) chromatography. Two Sephadex LH-20 columns (length 80cm, diameter 5.0cm) were used* with ethanol at 20 ° and 0.85 c m 3 rain-z flow rate (short stroke pump, Metering Pumps Ltd). Elution volumes were measured by a 3 cm 3 syphon; detection was by differential refractometry (Waters Associates Model R403). Injection of sample (9 g in 40 cm 3 ethanol) was by interruption of the solvent stream, via a 4-port valve, and pumping in solution at the same flow rate (0.85 cm 3 min- t). Fractions were collected as indicated on the chromategram shown in Fig. 1. Combined fractions were : A, 0.25 g, mainly x = 35; B, 0.21 g, x = 25, 35; C, 4.17g, mainly x = 2 5 ; D, 1.11g, mainly x = 2 0 , some x = 15, 25; E, 46.81 g mainly x = 15; F, 14.79g, mainly x = 15, some x = 10; G, 1.63 g, mainly x = 10, some x = 15; H, 0.58 g, x = 5, 10; I, 22.94g, mainly x = 5; total, 92.49g, 99.1~o recovery. Fractions A-G were rechromatographed and recombined one or more times to obtain combined fractions of oligomers as follows: x = 35, 0.16g; x = 25, 4.07 g; x = 20, 0.10 g; x = 15, 57.93 g; x = 10, 0.51 g; total, 62.77 g, 91~ recovery of fractions A-G. RESULTS
AND
DISCUSSION
The preparation of pentaethylene glycol ditosylate has not been reported previously. Initial small scale experiments using pentaethylene glycol and toluene-psulphonyl chloride at 0 ° in fairly concentrated solution in pyridine (much as described for the preparation of triethylene glycol ditosylate [1]) gave variable and poor yields. Eventually the toluene-p-sulphonyl chloride was recrystallised, the reaction temperature was reduced to - 2 0 °, and the dilution was increased so as to maintain a homogeneous solution. Yields in the range 9 0 - 9 5 ~ were then regularly obtained. The procedure for the reaction between pentaethylene glycol ditosylate and the monosodium salt of pentaethylene glycol was similar to that described earlier [1] for the preparation of nonaethylene glycol. The mole ratio glycol/methoxide was increased (7.7 compared with 2.9) in an attempt to minimise disodium salt formation. Also the reaction time was lengthened (about 12 days compared with about 5 days) * A separation with two columns of diameter 2.5 cm and with injection of 3 g of sample (in 20 c m 3 ethanol) was useful but less convenient. t The yields are based on the incorporation of one ditosylate residue (pentadecamer) or two ditosylate residues (pentacosamer) into the product.
2-5 I 1B0
I
I Z00
I
I
220
Wcm~
Fig. 2. Logarithm of molecular weight vs elution volume of (tl ethylene glycol oligomers and (O) commercial polyethylene glycols 3000-400. in an attempt to increase the yield. In fact yieldst of pentadecamer (33~o) and pentacosamer (6~o) were very similar to those reported I-1] for the triplication of triethylene glycol in tetrahydrofuran, i.e. nonamer (30~) and pentadecamer (6~o).
Analytical size exclusion (gel permeation) chromatography (GPC) Six Styragel columns (length 1.2m, diameter 0.94cm, nominal pore sizes 5-8, 15-35, 20--50, 50, 50-200 and 70-200 nm) were used with tetrahydrofuran at 25 ° and 1 cm 3 min -1 flow rate. Detection was by differential refractometry (Optilab Multiref 901). Samples were injected at a concentration of 1 g d i n - 3 via a 2 cm 3 loop, The system was calibrated by use of commercial polyethylene glycols of known molecular weight (in the range 400-3000gmo1-1). The calibration data are shown in Fig. 2. A chromatogram of the oligomer mixture prior to separation (Fig. 3) indicates the resolution of the method. The chromatogram of eicosaethylene glycol (potentially the least pure of our samples), also shown in Fig. 3, is typical of the single narrow peaks recorded for the oligomeric glycols. Their peak elution volumes, marked on Fig, 2, are as expected. The resolution and sensitivity of the method allow the conclusion that the purity of the oligomeric glycols exceeds 99~o-Wt. Improved resolution is possible if the chromatograph is used in recycle mode (see appendix). Investigation of the pentadecamer in this way indicated a purity of 99.9~-wt or better. The other oligomeric glycols were not recycled. Io)
(b)
7 ,~5
,o 2~o
A
r
__) L__
2~s Wcm ~ z~o ,6
2oo Vlcm3 ~o
Fig. 3. Refractive index difference (arbitrary scale) vs elution volume for analytical size exclusion (gel permeation) chromatography of (a) the oligomer mixture and (b) purified eicosaethylene glycol (x = 20). The elution volumes of the various oligomers are indicated on chromatogram (a).
543
Preparation of ethylene glycol oligomers Infra-red spectroscopy Spectra were recorded by means of a Perkin-Elmer Model 577 spectrometer. Oligomers were dried by melt evacuation ( < 10 3 mmHg, several days) and a thin film, placed between dried CsBr plates, was mounted in a temperature controlled vacuum cell (Beckmann RIIC). The assembled cell was evacuated (50 c, 3 hr) immediately, and the spectrum of the melt quickly recorded. The spectra so obtained were almost identical to those of melts of commercial polyethylene glycol of similar molecular weight (600-1500gmol -x) dried similarly. There was no evidence of unsaturated or carbonyl groups, such as has been reported for other ethylene glycol oligomers [5]. The spectra of the solids, in the temperature range 25 ° to - 8 0 °, were recorded; they are discussed elsewhere [6]. Nuclear magnetic resonance spectroscopy Spectra (CDCI3) were recorded at 6 0 M H z by means of a Perkin-Elmer R12B spectrometer. Resonances were found at 6.3 r ( - - O - - C H 2 - - C H 2 - - O - - ) and 7.25 r (--OH). Mass spectrometry The mass spectrum of the pentadecamer was recorded by means of an AEI MS30 spectrometer. No molecular ion was obtained, but a peak at M + 1 (m/e = 679) was present arising perhaps, as suggested earlier [1], by proton abstraction from a small fragment. A pattern of fragments arising from successive loss of oxyethylene units from M + 1 was readily discernible. Differential scannin9 calorimetry (DSC) Melting endotherms were obtained by means of a Perkin Elmer DSC-1B. Carefully dried oligomers (about 10 mg) were sealed into AI pans, of the kind designed to contain volatiles, taking stringent precautions to exclude moisture. Samples were heated to 60-70 ° and then crystallised by cooling rapidly to 0 °. Starting at this temperature, samples were heated through the melting transition at several heating rate(s) in the range 1 - 1 6 K m i n -~. The melting endotherms of the oligomeric glycols were narrow single peaks. The width of an endothermic peak at half-height (ATe) is a useful indicator of purity since, at s = 0, this slaould be zero for a pure compound. It is appropriate to plot AT~ against s ~, as illustrated earlier [3]. The results, AT½ < 0.1K at s = 0, show that the purity of the samples exceeds 99~,-mol with the exception of the decamer (AT½ _~ 0.25, purity -~ 98°~,-mol). M eltiny point Melting points, defined as the temperature of disappearance of the last trace of crystallinity, were measured for small samples (5-10 mg) of the carefully dried oligomers sealed into capillary tubes in a dry box. These were immersed in a stirred oil bath, the temperature of which was raised slowly (0.1 K m i n - t) from a temperature 4-5 K below the melting point. Melting was observed through a telescope. The thermometer was calibrated against N P L standards.
50
(n/*C
•
0
t,0
o 30 I
1o
I
I
20
30
I
X
1,0
Fig. 4. Melting point vs chain length x for ethylene glycol oligomers: (0) this work; (x) reference 1;(©) reference 2. Melting points were also defined by the position of the endothermic peak obtained by DSC (s = 2 K min-~). Correction was made for thermal lag [7] and the temperature scale of the calorimeter was calibrated by melting standard materials (range 29.0°-55.1 °). Melting points are listed below, Oligomer (x) Tin~° (oil bath) T,,/°(DSC)
10 -30.8
15 40.0 40.0
20 44.4
25 46.6 47.0
35 49.8 50.1
and are compared with literature values [1, 2] in Fig. 4. B6mer et al. have suggested that their relatively low values of T,, for x = 18 and 36 formed from nonaethylene glycol are due to by-products formed by elimination or cyclisation reactions which can occur when linking even numbers of units. Our results for x = 10 and 20 are inconsistent with this suggestion. Acknowledoements--We thank Mr D. R. Roy for help with the chromatography. The work was financed by the Science Research Council. REFERENCES
1. A. Marshall, R. H. Mobbs and C. Booth, Eur. Polym. J. 16, 881 (1980). 2. B. B6mer, W. Heitz and W. Kern. J. Chromat. 53, 51 (1970). 3. A. Marhsall, R. C. Domszy, H. H. Teo, R. H. Mobbs and C. Booth, Eur. Polym. J. 17, 885 (1981). 4. R. C. Domszy and C. Booth, Makromol. Chem., accepted for publication. 5. B. A. Mulley, Nonionic SurJactants (Edited by M. J. Schick). Arnold, London (1967). 6. H. H. Teo, A. Marshall and C. Booth, Makromolek. Chem., accepted for publication. 7. J. L. McNaughton and C. T. Mortimer, Int. Rev. Sci., Phys. Chem. Ser. 2 10, 1 (1975). 8. R. A. Henry, S. H. Byrne and D. R. Hudson, J. Chromat. Sci. 12, 197 (1974). APPE N D IX
Recycle Gel Permeation Chromatography We have used a recycle system based on the alternate pumping method [8]. In this method the sample does not have to pass through the pump and so peak spreading and skewing is minimised. Alternation of flow was achieved by means of a six-port valve [8]. A chromatogram of pentadecaethylene glycol obtained using the GPC system described earlier, but with 3 cycles,
544
H.H. TEO et al.
is shown in Fig. A1 (a). The chromatogram shows baseline shifts which are attributable to switching of the valve, and which effectively obscure any small peaks which might be present because of impurities. This problem can be overcome by using a detector which is less sensitive to changes in temperature, pressure and low molecular weight impurities. Pentadecaethylene glycol has no useful u.v. absorption. Consequently we have made use of an evaporative analyser (Clanor Instruments)* with the result shown Fig. Al(b). There are no baseline problems and the pentadecamer is seen to be pure (within the sensitivity of the method: probably +0.1%-wt.). * The eluant stream emerging from the columns is split into two equivalent streams (T junction with equivalent back pressure of 80 psi on each stream), one of which is led to the differential refractometer and, subsequently, a syphon (5 cm3), and the other to the evaporative analyser. In this analyser the eluant stream is atomised into an air stream, the solvent is evaporated, and the intensity of light scattered at 90 ° from the resulting solute aerosol is recorded.
f (a)
I
(b) I 300
I 320
I 340 V/cm 3
Fig. A1. Detector signal (arbitrary scale) vs elution volume for analytical size exclusion (gel permeation) chromatography with 3 cycles: (a) refractive index detector and (b) evaporative analyser.