Apart from oxalamide (OA) itself which is very important in many branches of industry [
In these studies BHEOA was subject to hydroxyalkylation with EC, and the obtained hydroxyethoxy derivatives were used for obtaining polyurethane foams of the enhanced thermal stability.
BHEOA was synthesized according to procedure [
In a 100 cm3 three-necked round bottom flask 6.6 g (0.037 mole) BHEOA and the appropriate amount of EC (pure, Fluka, Switzerland) were placed to reach the molar ratio of reagents of 1 : 2–1 : 10 and 0.31–0.47 g potassium carbonate (4.14–12.42 g/mole BHEOA, 0.03–0.09 mole/mole BHEOA), or 0.28 g diazabicyclo[2.2.2]octane (DABCO) (7.6 g/mole BHEOA, 0.06 mole/mole BHEOA) was added. The reaction mixture was protected from moisture (by tube filled with magnesium sulfate) and stirred mechanically at 120, 140, or
Attempts of foaming the reactions products of BHEOA with EC were carried out in small 250 cm3 test cups at room temperature. To 5 g of hydroxyethoxy derivatives of OA, 0.1 g of surfactant (Silicon 5340, Houdry Hülls), 0.0–0.22 wt.-% of triethylamine (TEA) catalyst (pure, Avocado, Germany), and 2 wt.-% of water were added. After careful mixing of the components, a preweighed amount of
1H-NMR spectra of BHEOA and products of its reactions with EC were recorded with 500 MHz spectrometer (Bruker, Germany) in deuterated dimethyl sulfoxide (d6-DMSO) and hexamethyldisiloxane (HMDS).
IR spectra of BHEOA and products of its reactions with EC were recorded from a capillary film or KBr pellets on a PARAGON 1000 FT spectrometer (Perkin-Elmer).
GC-MS experiments were conducted with Hewlett Packard 6890N chromatograph equipped with 5973 Network mass detector and HP-5MS
Chromatographic analysis of by-products, that is, ethylene glycol (EG) and products of its consecutive reactions with EC and N-(2-hydroxyethyl)oxazolidinone (OXON), was performed with gas chromatograph HP 4890A (Hewlett Packard, Ringoes, NJ, US) with FID detector and HP1
MALDI ToF spectra of reaction products of BHEOA with EC were obtained on Voyager-Elite Perseptive Biosystems (US) mass spectrometer working at linear mode with delayed ion extraction, equipped with nitrogen laser working at 337 nm. The matrix was 2,5-hydroxybenzoic acid. The samples were diluted with methanol to 1 mg/cm3, followed by addition of 10 mg/cm3 NaI in acetone. Therefore, in some cases the molecular ion weights were increased by the mass of
Thermal analyses (DTG and TG) of hydroxyethoxy derivatives of OA were performed in ceramic crucible, at 20–
The following properties of hydroxyethoxy derivatives of OA have been determined: pycnometer density [
The following properties of foams were determined: apparent density [
The differential scanning calorimetry (DSC) measurements were made using a
In order to obtain higher hydroxyethyl derivatives with OA unit, reactions of BHEOA with a 2–10-molar excess of EC in the presence of potassium carbonate or DABCO as a catalyst at temperature 120–
Reaction conditions of BHEOA with EC.
Run | Initial Molar Ratio | Amount of K2CO3 (mole K2CO3/mole OA) | Temp. ( | Time of Reaction (h) | Molar Ratio BHEOA : x in PostReaction Mixture (from Mass Balance) |
1. | 1 : 2 | 0.03 | 120 | — | |
2. | 1 : 2 | 0.06 | 140 | 5 | 1 : 1.87 |
3. | 1 : 2 | 140 | 11 | 1 : 1.74 | |
4. | 1 : 2 | 0.06 | 160 | 2 | 1 : 1.82 |
5. | 1 : 4 | 0.06 | 140 | 10 | 1 : 3.76 |
6. | 1 : 6 | 0.06 | 140 | 14 | 1 : 5.61 |
7. | 1 : 6 | 0.06 | 160 | 5 | 1 : 5.45 |
8. | 1 : 10 | 0.09 | 140 | 24.5 | 1 : 9.07 |
9. | 1 : 10 | 0.09 | 160 | 8 | 1 : 9.14 |
x: oxyethylene unit,
At the temperature of
Basing on the analysis of 1H-NMR spectra in the obtained products, it was found that with a 2-molar excess of EC there are secondary amide groups in a derivative’s structure. There is a signal at 8.5 ppm in the derivative’s spectrum (Figure
1H-NMR spectrum of the reaction product of BHEOA : EC 1 : 2 in the presence of 0.06 mole K2CO3/mole OA at
IR spectrum of the reaction product of BHEOA : EC 1 : 2 in the presence of 0.06 mole K2CO3/mole OA at
Further, in 1H-NMR spectrum of the product (Figure
Confirmation of such course of the reaction provides the presence (in spectrum of the post-reaction mixture BHEOA with a 2-mole excess of EC/Figure
An increase of the reaction temperature up to
In 1H-NMR spectra of the reaction products of BHEOA with a 2-molar excess of EC (Figure
The presence of ester groups is confirmed by analysis of IR spectrum (Figure
Furthermore, a band at 1122 cm-1 has appeared in the spectrum which is specific for C-O-C valence vibrations and demonstrates a distinctly easier course of the consecutive reactions in the hydroxyethyl groups with EC as compared to reactions of the secondary amide groups see Scheme
Signals at 8.0 and 8.5 ppm disappear only at a 6-molar or higher excess of EC (Table
1H-NMR spectra of the reaction product of BHEOA : EC : (a) 1 : 4 at
MALDI ToF spectrum of reaction product of BHEOA : EC 1 : 6 in the presence of 0.06 mole K2CO3/mole at
In IR spectra of products obtained at 6-molar or high or excess of EC bands at 1724 and 1268 cm-1 are still present, which indicates the presence of OA dimers and/or carbonate groups in the product’s structure. The actual structure of the product can be presented with a general formula (VII), where
MALDI ToF spectrography enabled an assessment of the composition of the obtained OA hydroxyethyl derivatives. The products obtained with a 6- and 10-molar excess of EC (Figures 4) consist of oligomers containing up to 10 and 14 oxyethylene units per mole of OA, respectively. No OA dimers in the post-reaction mixtures were found. MALDI ToF method cannot be used for confirmation of a presence of carbonate groups in the products because the molar mass of oxyethylene and carbonate units is 44 g/mol.
However, GC-MS analysis of the reaction products of BHEOA with EC exhibits dimerization of hydroxyethyl derivatives of OA, as it has evidenced the presence of N-(2-hydroxyethyl)oxazolidinone (OXON, VIII) in their composition, formed in the reaction of 2-aminoethanol with EC, similarly as in the reaction products of OA with EC (see Scheme
Quantity analysis of OXON by GC method enabled the assessment of dimerization contribution. The largest amount of OXON was formed in the post-reaction mixture obtained with a 2-molar excess of EC (Table
Percentage of by-products in reaction products of BHEOA with excess of EC.
Entry* | Initial molar | Percentage of OXON in post-reaction | Percentage of glycols in postreaction mixtures (wt.-%) | ||
ratio | Mixtures (wt.-%) | ||||
1. | 1 : 2 | 0 | 0 | 0 | 0 |
2. | 1 : 2 | 5.49 | 0 | 0 | 0 |
3. | 1 : 2** | 18.48 | 0 | 0 | 0 |
4. | 1 : 2 | 4.74 | 0 | 0 | 2.26 |
5. | 1 : 4 | 0 | 2.15 | 0 | 0 |
6. | 1 : 6 | 0 | 1.41 | 3.41 | 0 |
7. | 1 : 6 | 0 | 2.75 | 3.49 | 2.35 |
8. | 1 : 10 | 1.75 | 0 | 0 | 1.47 |
9. | 1 : 10 | 2.65 | 0 | 0 | 2.45 |
Due to the fact that in the products obtained with a 4- and 6-molar excess of EC, no presence of OXON was found; on the basis of spectral analysis, an explicit confirmation of contribution of carbonate groups in the structure of hydroxyalkylation products of BHEOA with EC can be provided. A signal at 4.2 ppm noted at 1H-NMR spectra originates from protons of the methylene groups at the carbonate group.
Furthermore, GC analysis of the post-reaction mixtures evidenced the presence of by-products poly (ethylene glycols) in their composition (Table
Thermogravimetric studies demonstrated enhanced thermal stability of the obtained hydroxyethoxy derivatives of OA. There is only one peak with the maximum at
Thermal stability of reaction products of BHEOA with EC.
Entry | Initial molar ratio OA : EC | Temperature of max. decomposition ( | ||||
---|---|---|---|---|---|---|
1. | BHEOA | 230 | 250 | 265 | 270 | 270 |
2. | 1 : 6 | 160 | 180 | 220 | 260 | 250 and 360 |
3. | 1 : 10 | 90 | 160 | 190 | 240 | 220 and 350 |
4. | 1 : 10* | 90 | 160 | 210 | 290 | 250 and 350 |
5. | comp. 1 | 200 | 220 | 240 | 330 | 260 |
Parameters of foaming process.
Initial molar ratio BHEOA : EC in polyol | Composition (g/100 g of tetraol) | Foaming process | Properties of foams just prepared | ||||||
Composition | water | molar ratio OH : NCO | time (s) | ||||||
No. | |||||||||
1 : 6 | 1. | 200 | 2 | 0.50 | 1 : 1.57 | 36.5 | 18 | 0 | rigid |
1 : 10 | 2. | 212 | 2 | 0.50 | 1 : 2.31 | 17 | 7 | 0 | rigid |
a:
c: Time of Creaming: the time elapsed from the moment of mixing to the start of volume expansion.
d: Time of Expanding: the time from the start of expansion to the moment of reaching the sample final volume.
e: Time of Drying: the time from reaching by the sample its final volume to the moment of loosing its surface adhesion to powdered substances.
Thermal analysis of the reaction product of BHEOA : EC 1 : 10 in the presence of 0.06 mole K2CO3/mole OA at
Some selected physical properties of the obtained products in the reaction of BHEOA with the excess of EC were investigated and it was found that while increasing the temperature refractive index, density and surface tension decrease linearly and the viscosity in exponential mode (Figure
Physical properties of reactions products of BHEOA with EC in function of temperature.
The obtained products of hydroxyalkylation of BHEOA with 6- and 10-molar excess of EC were foamed using MDI, water as foaming agent and TEA as a catalyst, carrying out the foaming in small laboratory scale.
Foams of the highest thermal stability were achieved from polyol obtained from BHEOA and the 6-molar excess of EC (EC6) with 0.5 wt.-% contribution of TEA (Table
Apparent density of foams obtained with contribution of EC6 and EC10 is within 31–38 kg/m3 (Table
Properties of foams.
Kind of polyol | Comp. | Density (kg/m3) | Water uptake (wt.-%) | Linear dimension change after heating at | |||||||
after 5 min | after 3 hrs | after 24 hrs | length | width | thickness | ||||||
after 20 hrs | after 40 hrs | after 20 hrs | after 40 hrs | after 20 hrs | after 40 hrs | ||||||
EC6 | 1. | 37.79 | 3.80 | 9.39 | 9.63 | 0.00 | 1.17 | 0.00 | 0.00 | 0.39 | 0.19 |
EC10 | 2. | 30.86 | 4.92 | 9.66 | 11.71 | 2.15 | 3.01 | 1.39 | 1.74 | 0.00 | 0.00 |
The lowest water uptake (9.6 wt.-%) after a 24-hour exposure in water at room temperature is displayed by foams obtained from ployol EC6 (Table
Thermogravimetric studies of the obtained polyurethane foams confirm their enhanced thermal stability; a 5% weight loss occurs not before temperatures
The foams hold for 30 days at the temperature of 150 and
Compressive strength of polyurethane foams (MPa).
Kind of polyol | Comp. no. | Compressive strength | Increase of Compressive Strength in (%) after exposition in temperature ( | |
150 | 175 | |||
EC6 | 1. | 0.14 | 112 | 5 |
EC10 | 2. | 0.16 | 115 | 2 |
In the reactions of
The obtained oligomers are accompanied by insignificant amount of by-products: poly(ethylene glycols) and N-(2-hydroxyethyl)oxazolidinone.
The obtained hydroxyethoxy derivatives of oxalamide are characterized by the enhanced thermal stability and show physical properties of typical polyols used for manufacturing polyurethane foams.
The polyurethane foams obtained with the contribution of hydroxyethoxy derivatives of oxalamide are characterized by good stability of dimensions, enhanced thermal stability.