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Synthesis of polynitroalcohols by nucleophilic addition of butadiene–styrene nitrooligomer to acetaldehyde
European Polymer Journal 38 (2002) 2413–2422 www.elsevier.com/locate/europolj
Synthesis of polynitroalcohols by nucleophilic addition of butadiene–styrene nitrooligomer to acetaldehyde M.S. Karaivanova *, S.Z. Mitev University ‘‘Prof. Dr. As. Zlatarov’’, 8010 Bourgas, Bulgaria Received 18 December 2001; received in revised form 1 May 2002; accepted 3 May 2002
Abstract Two types of secondary polynitroalcohols (PNA) were prepared by AN -reaction of butadiene–styrene nitrooligomer (BSNO) and acetaldehyde. The corresponding yields were 58–64% and 25–33%. The reaction was conducted in water– ethanol solution in the presence of alkaline base as catalyst at temperatures from 40 to 60 °C, for 3.5–4 h. Introduction of hydroxyethyl groups by AN -reaction of BSNO to acetaldehyde increased the polarity and thermal stability of PNA as compared to BSNO. By using IR spectroscopy and liquid absorption chromatography on silica gel, PNA were found to be polyfunctional compounds, that contained structurally and functionally heterogeneous fractions. The quantitative functional composition of the first PNA type as well as their main fractions were determined by evaluating the relative content of nitro-, carbonyl and hydroxyl groups in the products. PNA are considered to be starting materials for the preparation of polynitrourethanes and salts of N-containing sulphonic acids. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polynitroalchohol; Nitrooligomer; AN -reaction; Fractions; IR spectroscopy; Chromatography
1. Introduction Polynitroalcohols (PNA), based on nitrooligomers and aldehydes as starting materials are interesting compounds because of their high reactivity, surfactant properties and their application as additives for rubber compositions [1]. PNA are obtained by a two-step synthesis including nitration of elastomers, model and waste vulcanisates [2–4] and subsequent interaction of the obtained nitrooligomers with aldehydes. Primary PNA have been prepared from nitrooligomers on the basis of natural rubber and formaldehyde by AN -reaction [5] in aqueous medium with alkaline [6] or acidic catalysts [7]. The reaction was carried out in organic solvents such as ethanol, 1,4-dioxane and tetrahydrofurane in the presence of alkaline bases [8]. The
*
Corresponding author. Fax: +359-2-623475. E-mail address: [email protected] (M.S. Karaivanova).
kinetics was studied by the polarographic method [9]. Two kinds of PNA were obtained from polyisoprene and polybutadiene nitrooligomers by the reaction with formaldehyde in the presence of alkaline catalysts [10]. PNA were synthesized from butadiene–styrene nitroligomer and formaldehyde [11,12] in aqueous or organic solvent medium by using alkaline bases or alkaline carbonates as catalysts. Their quantitative functional composition was also determined. The AN -reaction of the above mentioned nitrooligomers with aldehydes was found to be similar to the reaction between nitroalkanes and carbonyl compounds, studied by Henry and widely described in a number of publications [13–16]. PNA were obtained by interaction of 2-nitroethane and 2-nitropropane with formaldehyde, acetaldehyde and propanal at pH ¼ 4–5 [17]. Bromonitroalcohols were synthesized from bromonitromethane and C1 –C8 aldehydes at pH ¼ 4–7 [18]. Fluoronitroalcohols and fluoronitroalkenes were synthesized starting from the corresponding aldehydes or ketones and nitroalkanes [19].
0014-3057/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 2 ) 0 0 1 3 8 - 6
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The aim of the present work was to study the nucleophilic addition––AN -reaction of nitrooligomer derived from butadiene–styrene rubber with acetaldehyde in aqueous-ethanol solution and in the presence of alkaline bases as catalysts in order to prepare PNA. Another purpose of the study was to determine both the functional and fragmentary composition of PNA and their thermal stability.
2. Experimental 2.1. Butadiene–styrene rubber Bulex 1500 (a product of the Petrochemical Plant, Bourgas, Bulgaria), contained 23–25% styrene and had a number-average molecular weight M n ¼ 59 000 and weight-average molecular weight M w ¼ 2 97 000, which corresponded to the coefficient of polydispersity of 5 [11]. 2.2. Synthesis of butadiene–styrene nitrooligomer Butadiene–styrene nitrooligomer (BSNO) was obtained by nitration of butadiene–styrene rubber Bulex 1500 (BSR) with 65% nitric acid at 60 °C, for 4 h in solution of dichloroethane. The mass ratio of rubber to HNO3 was 1:3 respectively [11]. 2.3. Synthesis of PNA starting from butadiene–styrene nitrooligomer and acetaldehyde in water–alcohol solution in the presence of alkaline hydroxide as a catalyst 10 g of BSNO were dissolved in 200 ml 2% aqueous solution of potassium or sodium hydroxide by heating up to 40 °C and stirring in a 1 l thermostated reactor, equipped with a stirrer, thermometer, dropping funnel and reflux condenser. The temperature was increased to 50 °C and then 5 g (6.4 ml) of freshly distilled acetaldehyde were dissolved in 50 ml ethanol and were gradually added for 3.5 h by continuous agitation. The solution was stirred for another 0.5 h under the same conditions. Consequently, the reaction mixture was neutralized with 10% hydrochloric acid until pH ¼ 6 was reached. Finally the sample assigned as PNA-1-C2 was gradually precipitated. The product PNA-1-C2 was separated and purified by precipitation of 15% acetone solution in 3 l distilled water. The product (6 g, 60%) was soluble in acetone, 1,4-dioxane, tetrahydrofurane and ethylacetate. The filtrate was evaporated under vacuum (0.011 MPa) until a solid residue was obtained. The precipitate was further subjected to extraction with acetone and then the second product PNA-2-C2 , (2.3 g, 23%) was isolated. The latter was soluble in acetone and water.
2.4. Analysis of PNA Elemental analysis was carried out by using a Perkin– Elmer instrument. The thermal analysis was performed on derivatograph OD-102 (Hungary) within the temperature range of 20–600 °C at a heating rate of 6 K/ min. The sample weight was 50–100 mg and the analyses were conducted in an air static atmosphere. A metaloceramic crucible of 9 mm diameter with Pt and Pt/Th thermocouples was employed for the samples. 1 H-NMR spectra were obtained by using a 250 MHz spectrometer in a solution of (CD3 )2 CO. The IR spectra were recorded for samples prepared as potassium bromide pellets (1 mg/300 mg) with potassium ferricyanide as an internal standard on a Specord M 80 instrument. The content of aliphatic nitro-, carbonyl, and secondary hydroxyl groups in the PNA were determined using the base line and internal standard techniques with respect to two standard compounds from the corresponding IR spectra detected under the same conditions [11]. The typical characteristic absorption bands were employed from the IR spectra of the standards: 2-nitro-2ethyl-1,3-propanediol (mas NO2 1546 cm1 and mC–O–(H) 1056 cm1 ) and 10-nonadecanone (mC@O 1728 cm1 ) and also mCBN 2116 cm1 from the IR spectrum of the internal standard––potassium ferricianide. The absorption A and, subsequently, the ratio R ¼ Ax =Ast were calculated, where Ax was the absorptions of the corresponding functional group of PNA-1-C2 and Ast was the absorption mCBN at 2116 cm1 of the internal standard respectively. The content of the functional groups was determined by comparing their Rvalues to the corresponding R-values of the two standards. The chromatographic fractional separation of polynitroalcohol samples (1 g) was carried out in a glass column of 15 mm internal diameter and 550 mm length. The column was filled with 36 g silica gel (Fluka, 35–70 mesh) according to the ‘‘wet’’ method [11].
3. Results and discussion The present work appears as a continuation of the work concerned with the AN -reaction of BSNO to formaldehyde and reported previously [11]. Butadiene–styrene rubber Bulex 1500 represents a random copolymer of nonuniform distribution of styrene fragments along the macromolecular chain. It is characterized by the coefficient of polydispersity of, approximately, 5. The starting BSNO, as the product of nitration of elastomer Bulex 1500, is polyfunctional and has a coefficient of polydispersity of 1.7 with random distribution of fragments containing different functional groups.
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The main reaction centers of BSNO that participate in the AN -reaction in the presence of alkaline catalysts are the a-hydrogen atoms, adjacent to the C-atoms bearing the secondary nitrogroups. This interaction takes place, according to the following pattern:
Two types of the secondary PNA, indicated as PNA1-C2 and PNA-2-C2 , were prepared. The reaction was carried out in aqueous-alkaline solution of potassium or sodium hydroxide. The alkaline bases initially converted BSNO in its aci-form in the ethanol solution of acetaldehyde. An excess of the latter (mass ratio with respect to BSNO) was added to BSNO in order to decrease the rate of aldol condensation. The process was performed in temperature range 40–60 °C, to reduce the rate of the side reactions. The first reaction product PNA-1-C2 was separated as a precipitate after acidification of reaction mixture and the second one was subjected to vacuum distillation to remove the water. The PNA-1-C2 yields were 50–60%, for PNA-1-C2 25–33% respectively. PNA-1-C2 yields slowly increased by raising the temperature from 40 to 60 °C (Fig. 1). The yields did not differ essentially, whether the acetaldehyde was gradually added for 30 min or the whole amount was added at the beginning of the reaction (Table 1, samples 8, 12). Both the types of secondary PNA had different elemental compositions (Tables 2 and 3). The PNA-1-C2 carbon content was higher as compared to the initial BSNO, due to the introduction of hydroxyethyl groups as a result of the AN -reaction. The carbon content of PNA-2-C2 was lower as a result from the increased con-
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centration of oxygen-containing groups. Based on the comparison of the carbon content of PNA found previously, the reactivity of BSNO with respect to acetaldehyde was considered to be lower than that of formaldehyde.
Fig. 1. Polynitroalcohol PNA-1-C2 yield as reaction time (BSNO to acetaldehyde, mass ratio ¼ 2:1, 60 °C, KOH as catalyst).
The IR spectrum of PNA-1-C2 was characterized by the mas , ms stretching vibrations for the aliphatic NO2 group at 1546 and 1360 cm1 respectively, mC@C at 1632 cm1 and mC@O at 1716 cm1 (Fig. 2, curve 1). The new
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Table 1 Yields of polynitroalcohols PNA-1-C2 , obtained from BSNO and acetaldehyde No.
Reaction time (h)
Temperature (°C)
BSNO:CH3 CHO (w.p.)
Catalyst
Yield (%)a
1 2 3 4 5 6 7 8b 9 10 11 12b 13 14
4 5 4 5 4 4 4 4 4 3 4 4 5 4
40 40 50 50 60 40 40 40 40 50 50 50 50 60
2:1 2:1 2:1 2:1 2:1 1:1 2:1 2:1 3:1 2:1 2:1 2:1 2:1 2:1
KOH KOH KOH KOH KOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH
54 55 56 58 64 60 55 53 50 50 54 55 53 65
a b
The yields of PNA-2-C2 : 25–33%. CH3 CHO is added in bulk at the beginning of the reaction.
Table 2 Elemental analysis of polynitroalcohols PNA-1-C2 , obtained from BSNO and acetaldehyde No.
Reaction time (h)
Temperature (°C)
Catalyst
C (%)
H (%)
N (%)
1 2 3 4 5 6 7 8a 9 Initial
1 2 3 4 5 6 4 4 4 BSNO
60 60 60 60 60 60 50 50 40
KOH KOH KOH KOH KOH KOH KOH KOH NaOH
56.32 56.26 57.38 56.01 57.74 57.82 56.82 57.64 60.42 51.19
5.30 5.28 5.76 5.94 5.96 5.73 5.63 5.94 5.93 5.20
8.06 8.03 7.94 7.80 7.47 7.51 8.34 8.45 7.31 10.50
a
The whole amount of CH3 CHO is added in bilk at the beginning of the reaction.
Table 3 Elemental analysis of polynitroalcohols PNA-2-C2 , obtained from BSNO and acetaldehyde No.
Reaction time (h)
Temperature (°C)
Catalyst
C (%)
H (%)
N (%)
1 2 3 4 5
3 4 5 5 6
50 50 50 40 60
NaOH NaOH NaOH KOH KOH
42.77 40.89 39.90 38.12 39.95
3.57 3.45 4.27 4.12 3.42
5.72 5.49 6.07 8.11 7.86
multiplet band at 1100, 1030 and 1000 cm1 , mC–O–H, was assigned to secondary hydroxyl group. The wide absorption band with high intensity in the 3700–3100 cm1 , showed the presence of OH-groups in the compounds with intramolecular hydrogen bonds [20]. The vibration mC–O–H for secondary hydroxyl group 1120– 1130 cm1 in PNA-1-C2 was shifted to the lower fre-
quencies, which was similar to the cyclohexanol bands, mC–O–H 995 and 1062 cm1 [21]. The vibration mas for the nitratester group at 1280 cm1 indicated lower intensity with respect to those of the BSNO starting material. The IR spectrum of the polynitroalcohol PNA-2-C2 (Fig. 2, curve 2) indicated some characteristic bands mas;s for aliphatic nitrogroup at 1550, 1380 cm1 , mas
M.S. Karaivanova, S.Z. Mitev / European Polymer Journal 38 (2002) 2413–2422
Fig. 2. IR spectra of PNA, obtained from BSNO and acetaldehyde (3 h, 60 °C, mass ratio 2:1): (1) PNA-1-C2 ; (2) PNA-2-C2 .
1280 cm1 for nitratester group with high intensity, mC@C at 1630 cm1 and mC@O at 1680 cm1 for conjugated ketone group [21]. The presence of hydroxyl group was proved by the stretching vibrations mC–O–H at 1090, 1050 cm1 and by the increased absorption in the range of 3200–2400 cm1 . According to the quantitative functional groups composition determined by IR spectroscopy (Table 4), the content of aliphatic nitrogroup in PNA-1-C2 was found to be 12.5–19.6%, and that of the ketone and secondary hydroxyl groups was 2.4–3.3% and 1.7–3.9% respectively. Prolonger reaction times resulted in a slow decrease of the NO2 ––groups content after the third hour, whereas the content of OH––groups increased up to 3.6% and the ketone groups content did not change essentially.
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It is worth noting that the ketone groups content in PNA-1-C2 (2.7–3.3%) was higher as compared to that of BSNO (1.9%), probably, because of the partial hydrolysis of the nitratester groups. The nitrous and nitric acid esters are considered to be active centers for the formation of alcohols, aldehydes and ketones [22]. Regardless of the relatively mild conditions of AN reaction, some side reactions were considered to occur, too. Some PNA-1-C2 possessed lower content of NO2 groups and higher degree of unsaturation than BSNO (Table 4) which is associated with processes of denitration. Some polynitroalcohols PNA-2-C2 (Table 5), contained also conjugated C@O groups (mC@O 1680 cm1 ). At the same time, partial hydrolysis of the nitratester groups of PNA-1-C2 took place which was proved by the lower intensity of m 1280 cm1 band. One of the PNA-1-C2 prepared was characterized by its 1 H-NMR spectrum (Fig. 3) which included chemical shifts as follows: 4.3 ppm (methyne protone) bonded to secondary NO2 -group; 4.1 ppm for H-proton from secondary OH-group; 3.8 ppm (methyne proton bonded to the same group); strong peak of methyne proton from –CHPh 3.6 ppm and C–H protons from Ph– 7.3 ppm; chemical shift for –(CH2 )–n 1.3 ppm and pronounced chemical shift for C–H protons from CH3 -group 0.9 ppm, introduced as a result from the AN -reaction. The shift of H-protons of the terminal CH3 -group 0.9 ppm in the hydrocarbon chain of the initial BSNO was very slightly pronounced in the 1 H-NMR spectrum. The presence of methyne group (C–H), attached to the secondary NO2 -group in the 1 H-NMR spectrum of PNA-1-C2 (Fig. 3) showed that the AN -reaction between BSNO and acetaldehyde did not take place completely. The two types of the PNA studied were found to be polyfunctional and polydisperse compounds. The study
Table 4 Quantitative functional composition of polynitroalcohols (PNA-1-C2 ), obtained from BSNO and acetaldehyde (2:1 mass ratio) No.
Reaction time (h)
Temper ature (°C)
Catalyst
R¼ 2116 A1546 NO2 =ACN
NO2 (%)
R¼ 2116 A1716 CAO =ACN
C@O (%)
R¼ 2116 A1632 CAC =ACN
R¼ 2116 A1100 CAOAðHÞ2 =ACN
OH (%)
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 4 3 5 BSNOa standardb standardc
60 60 60 60 60 30 50 50 50 – – –
KOH KOH KOH KOH KOH KOH KOH NaOH NaOH – – –
0.5612 0.5811 0.5792 0.5129 0.3616 0.3600 0.5488 0.4474 0.4367 0.5859 0.8886 –
19.6 20.1 20.8 17.8 12.5 12.4 18.6 15.2 14.9 19.0 28.3 –
0.1950 0.1933 0.2286 0.2106 0.1796 0.2233 0.1677 0.1847 0.1331 0.1285 – 0.6954
2.9 2.8 3.3 3.0 2.6 3.2 2.4 2.7 2.0 1.9 – 10.1
0.1499 0.1435 0.1594 0.1548 0.1371 0.1486 0.1947 0.1705 0.1519 0.1286 – –
0.0376 0.0435 0.0634 0.0781 0.0820 0.0848 0/0435 0.0720 0.0735 – 0.4928 –
1.7 1.9 2.9 3.6 3.8 3.9 1.9 3.3 3.4 – 22.8 –
a as
m NO2 , 1550 cm1 . 2-nitro-2-ethyl-1,3-propanediol, mC–O–(H) 1050 cm1 and mas NO2 1546 cm1 . c 10-nonadecanone, mC@O 1728 cm1 . b
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Table 5 Characteristic absorption bands in IR-spectra of the main fractionsa of two types of PNA obtained from BSNO and acetaldehyde (40 °C, 4 h, mass ratio 2:1, KOH as catalyst) PNA
Fraction no.
mC@O
mC@C cC@C
mas;s NO2
mas ONO2
mas;s C–O–C
mC–O–(H)
PNA-1-C2
1b
–
–
–
2b
1716d
1280
PNA-1-C2
3
1716c
1630c
1280d
PNA-1-C2
4
1700
1620c
1550 1380 1550c 1380c 1550
1100c 1020 1100c 1020 –
3700–2600
PNA-1-C2
800 890c 1630d
1280
–
PNA-1-C2
5
–
1630c
1280
–
PNA-2-C2
1b
1710
800
1280
PNA-2-C2
2b
1710
1640
PNA-2-C2
3
1710
1640
1550 1380c 1550 1380d 1550 1380d 1550
1280d
1100 1020 1100 1020 –
PNA-2-C2
4
1680
1620
1280d
–
PNA-2-C2
5
1680
1620
– –
– –
1550 1380 1550 1380
1280
3700–2600 1100, 1020 3700–2600 1080 3700–2600 1100 – 3700–2600 1100–1050 3700–2600 1100c 3700–2600 1100c 3700–2600
a
Fraction No 6 of the both PNA was hygroscopic. mC–O–(H) was overlaped with mas;s C–O–C. c Intensive. d Weak. b
of the distribution of functional groups in the different oligomer fractions, was expected to give information about their composition and reactivity. The fractional separation of the initial BSNO [11] and the PNA was carried out by the liquid adsorption chromatography on silica gel. The samples obtained therefrom were divided into six fractions (Figs. 4 and 5). The second and the third ones, that were the main fractions for PNA-1-C2 , were eluated by mixture of chloroform and ethylacetate (volume ratio 1:1) and ethylacetate respectively. The second and the forth PNA-2-C2 fractions were eluated by ethylacetate and acetone–ethanol (volume ratio 1:2) respectively. The PNA-2-C2 polynitroalcohols were found to be more polar compounds than PNA-1-C2 . IR spectra of both polynitroalcohol (Table 5) fractions showed the presence of different functional groups. This was associated with the various reactivites of the starting BSNO fractions with respect to the AN reaction. The main fractions of PNA-1-C2 were distinguished not only by qualitative but also, by the quantitative functional compositions (Table 6). This is also related to the PNA-2-C2 fractions which had different elemental composition (Table 7). Some of them were hygroscopic
and this created certain difficulties for the quantitative determination of the main functional groups. The first fraction of PNA-1-C2 did not contain nitrogen and N-containing groups (Tables 5 and 6). The IR spectra showed the presence of strong band c@CH at 890 cm1 (895–885 cm1 ) for the terminal C@C bond [23]. The first and the second fractions were characterized by the strong vibrations ms C–O–C at 1100 cm1 (1150–1050 cm1 ) that were probably overlapped by mC–O–(H) for the secondary OH-group. Fractions 2–5 contained nitro- (mas;s 1546, 1360 cm1 ), C@C bonds (m 1620 cm1 ), nitratester- (mas 1280 cm1 ) and ketone groups (mC@O 1720 cm1 ). The hydroxyl groups were concentrated in the third main fraction (mas;s 1100, 1020 cm1 ) but they were not necessary present in all of the fractions studied. The PNA-2-C2 fractions were also polyfunctional products (Table 5). Ether groups were present in the first and the second fractions. Nitratester groups were absent in the fifth fraction. The fourth and the fifth fractions contained conjugated C@O groups and this caused shift of the band at 1720 cm1 towards 1680 cm1 [23]. All fractions contained hydroxyl groups which was also proved by their solubility in water and the pronounced surfactant properties.
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Fig. 3. 1 H-NMR spectra of polynitroalcohol PNA-1-C2 .
Fig. 4. Functional composition of PNA-1-C2 , obtained from BSNO and acetaldehyde (40 °C, reaction time 4 h, KOH as catalyst).
Fig. 5. Fractional composition PNA-2-C2 , obtained from BSNO and acetaldehyde (40 °C, reaction time 4 h, KOH as catalyst).
The chemical and molecular polydispersity of PNA-C2 results from the structure of butadiene–styrene copolymer and the origin of initial BSNO obtained by nitration. The nitration has complex character including destruction and oxidation which take place in every
occasions. For example the nitration was performed even under ‘‘soft’’ conditions. The PNA-C2 as products of AN -reaction have nature similar to that of BSNO. They are less heterogeneous due to the BSNO fractionation during the reaction and
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Table 6 Elemental analysis and functional compositiona of the main fractions of polynitroalcohol PNA-1-C2 (60 °C, 4 h, BSNO:CH3 CHO 2:1 mass ratio) Fraction
Color
Eluating system (vol. p.)
1
Light beige
2
Light yellow
3 4 Initial PNA-1-C2
Dark yellow Dark yellow Yellow
Benzene: chloroform ¼ 1:1 Chloroform: ethylacetate ¼ 1:1 Ethylacetate Acetone
C (%)
H (%)
N (%)
R¼ 2116 A1546 NO2 =ACN
NO2 (%)
R¼ 2116 A1716 C@O =ACN
C@O (%)
42.00
9.42
–
–
–
–
–
54.21 51.41 55.57 56.01
6.17 5.53 4.80 5.94
7.16 7.20 7.90 7.80
0.4943 0.3531 0.5111 0.5129
17.8 12.7 18.7 17.8
0.2525 0.2725 0.2628 0.2106
4.1 4.6 4.4 3.0
Fractions 5, 6 were hygroscopic and therefore, their functionally compositions was not determined. a With respect to 2-nitro-2-ethyl-1,3-propanediol and 10-nonadecanone.
Table 7 Elemental analysis of the main fraction of polynitroalcohol PNA-2-C2 (60 °C, 4 h, BSNO:CH3 CHO ¼ 2:1, mass ratio) Fractiona
Color
Eluating system (vol. p.)
C (%)
H (%)
N (%)
1 2 3 4 5 Initial PNA-2-C2
Light beige Light yellow Beige Dark yellow Dark yellow Yellow
Chloroform Ethylacetate Acetone Acetone:ethanol ¼ 1:2 Ethanol:water ¼ 2:1 –
46.12 39.80 35.50 35.45 35.10
6.59 4.07 3.51 3.86 3.36
5.48 8.37 4.05 3.88 –
40.50
4.81
8.11
a
Fraction 6 was a brown, hygroscopic substance.
the obtaining of some other reaction products. The PNA-C2 characterization was rather laborious. The determination of functional polydispersity of PNA-C2 had to be made for several reasons: for prognosis their reactivity with respect to some reagents, to assist the possibilities of their utilization as additives in polymer composition, etc. The thermal stability of both types of PNA was also studied. PNA-1-C2 started to decompose within 110– 130 °C in three stages (Fig. 6, curves 1–4). DTA indicated three exothermal effects at 200, 330 and 500 °C, respectively. The first one was similar to the exothermal effect of the initial BSNO at 195 °C (Fig. 6, curve 5) and was caused by the nitrogroup exothermal decomposition accompanied by 25% weight loss within 130–240 °C. Decomposition of the main hydrocarbon chain occurred within 250–400 °C with an exotherm maximum at 330 °C and additional weight loss of 30%. The destruction within the temperature range of 450–600 °C was accompanied by pronounced exothermal effects at 500 °C. PNA-1-C2 , obtained after 1 h reaction time had lowest thermal stability (Fig. 6, curve 1). The destruction took place at low rate within the temperature interval of 170–350 °C. This was probably due to the cross-linking
effects caused by the nitrogen oxide release. The prolongation of reaction time from 2 to 6 h resulted in a weak increase the thermal stability of PNA-1-C2 which was confirmed by the TGA scans. The decomposition of PNA-2-C2 started at 130 °C and exothermal effects on DTA were detected at 250, 310 and 545 °C (Fig. 6, curve 6). Thermal analysis studies indicated that the both types of PNA had a higher thermal stability than the initial BSNO. Their thermal stability was close to that determined for PNA-C1 in previous publication [11].
4. Conclusions (1) BSNO reacts with acetaldehyde by the a-hydrogen atoms attached to secondary nitrogroups. This AN reaction results in the formation of two types of polynitroalcohols (PNA-1-C2 and PNA-2-C2 ). The optimum yields of the latter are obtained at temperature 50–60 °C, reaction time of 3.5–4.5 h and BSNO:CH3 CHO ¼ 2:1 mass ratio, in water–alcohol solution of alkaline bases. (2) Both types of PNA are polyfunctional oligomers and contain aliphatic nitro-, ketone and secondary hydroxyl groups predominantly. The content of
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tion chromatography in accordance with the polarity of the corresponding fractions. (4) Both types of PNA are found to have a higher thermal stability as compared to the BSNO employed as starting material.
Acknowledgements The authors are thankful to Prof. Dr. Kolio Troev from Institute of Polymers––Bulgarian Academy of Science, Sofia, for interpretation of 1 H-NMR spectra.
References
Fig. 6. Thermal analysis of polynitroalcohols PNA-1-C2 , obtained from BSNO and acetaldehyde (60 °C, mass ratio 2:1): (1) 1 h; (2) 2 h; (3) 3 h; (4) 6 h; (5) initial BSNO; (6) 3 h.
functional groups in PNA-1-C2 have been determined by using IR-spectroscopy base line and the internal standard line method. (3) Both types of polynitroalcohol fractions are found to be heterogeneous in terms of their composition and chemical structure. This was confirmed by their fractional separation carried out by liquid absorp-
[1] Shalteva A, Nikolinski P, Karaivanova M, Litvin Kr. Khimia i Industria 1977;49(6):247–50 [in Bulgarian]. [2] Karaivanova M, Kostov V, Stoeva V. Acta Polym 1992; 43:77–81. [3] Mladenov I, Georgiev T. Short Contrib Bratislava, 3–6 July, 1970. In: Fifth IUPAC International Conference ‘‘Modification of Polymers’’, vol. 2, 1979. p. 217–21. [4] Tsaikova S, Bojadzhiev N, Mladenov I. J Prikl Khim 1985;11:2592–5. [5] Mladenov I, Karaivanova M. Sbornic Dokl Mezdunar Symp ‘‘Polymers 71’’, 10, Varna: Bulgaria, 1971. p. 246–53. [6] Mladenov I, Karaivanova M, Bojkov B. BG patent no. 17389, 25.04.1973. [7] Mladenov I, Karaivanova M, Bojkov B. BG patent no. 17132, 25.02.1973. [8] Mladenov I, Karaivanova M, Atanasov M. Ann High Inst Chem Technol, Bourgas 1973;10:169–77. [9] Karaivanova M, Boneva St, Kostov G. Sbornik Dokl Mezdunar Symp ‘‘Polymers 73’’, 12, Varna: Bulgaria; 1973. p. 336–45. [10] Karaivanova M. Ann High Inst Chem Technol, Bourgas 1978;12(2):81–8. [11] Karaivanova M, Mitev S, Stoeva V. Eur Polym J 1998; 34(9):1349–59. [12] Karaivanova M, Mitev S. BG patent no. 50434, 15.06.1994. [13] Sveigheimer MGA, Pjatakov NF, Novikov SS. Uspehi Khimii 1959;28(4):484–518 [in Russian]. [14] Kozlov NM, Burmistrov VI. Nitrospiritii i Ikh Proizvodnie, Kazan: Khimia: 1960 [in Russian]. [15] Sveigheimer MGA. Uspehi Khimii 1998;67(1):39–74 [in Russian]. [16] Perekalin VV, Sopova AS, Lipina ES. Nepredelnie Nitrosoedinenia. Peterbourg: Khimia; 1982. p. 39–42 [in Russian]. [17] Klager K. US patent no. 3024288, 1962. [18] Williams J. US patent no. 5075510, 1991. [19] Feuer H, Nelson A, editors. Nitro compounds––recent advances in synthesis and chemistry. Lafayette, IN, USA: Pardue University; 1990. p. 429–33. [20] Colthyp J. J Am Chem Soc 1950;74:1256. [21] Nakanisi K. In: Infrakrasnie spektri org soedinenii. Moscow: Mir; 1956. p. 149 [in Russian].
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[22] Topchiev A. Nitrovanie Uglevodorodov i drugikh Org Soedinenij. Moscow: Acad Nauk Russia; 1956 [in Russian].
[23] Spasov St, Arnaudov M. In: Prilozenie na spektroskopiata v organitchnata khimia. Sofia: Nauka i iskustvo; 1978. p. 110 [in Bulgarian].
Synthesis of polynitroalcohols by nucleophilic addition of butadiene–styrene nitrooligomer to acetaldehyde M.S. Karaivanova *, S.Z. Mitev University ‘‘Prof. Dr. As. Zlatarov’’, 8010 Bourgas, Bulgaria Received 18 December 2001; received in revised form 1 May 2002; accepted 3 May 2002
Abstract Two types of secondary polynitroalcohols (PNA) were prepared by AN -reaction of butadiene–styrene nitrooligomer (BSNO) and acetaldehyde. The corresponding yields were 58–64% and 25–33%. The reaction was conducted in water– ethanol solution in the presence of alkaline base as catalyst at temperatures from 40 to 60 °C, for 3.5–4 h. Introduction of hydroxyethyl groups by AN -reaction of BSNO to acetaldehyde increased the polarity and thermal stability of PNA as compared to BSNO. By using IR spectroscopy and liquid absorption chromatography on silica gel, PNA were found to be polyfunctional compounds, that contained structurally and functionally heterogeneous fractions. The quantitative functional composition of the first PNA type as well as their main fractions were determined by evaluating the relative content of nitro-, carbonyl and hydroxyl groups in the products. PNA are considered to be starting materials for the preparation of polynitrourethanes and salts of N-containing sulphonic acids. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polynitroalchohol; Nitrooligomer; AN -reaction; Fractions; IR spectroscopy; Chromatography
1. Introduction Polynitroalcohols (PNA), based on nitrooligomers and aldehydes as starting materials are interesting compounds because of their high reactivity, surfactant properties and their application as additives for rubber compositions [1]. PNA are obtained by a two-step synthesis including nitration of elastomers, model and waste vulcanisates [2–4] and subsequent interaction of the obtained nitrooligomers with aldehydes. Primary PNA have been prepared from nitrooligomers on the basis of natural rubber and formaldehyde by AN -reaction [5] in aqueous medium with alkaline [6] or acidic catalysts [7]. The reaction was carried out in organic solvents such as ethanol, 1,4-dioxane and tetrahydrofurane in the presence of alkaline bases [8]. The
*
Corresponding author. Fax: +359-2-623475. E-mail address: [email protected] (M.S. Karaivanova).
kinetics was studied by the polarographic method [9]. Two kinds of PNA were obtained from polyisoprene and polybutadiene nitrooligomers by the reaction with formaldehyde in the presence of alkaline catalysts [10]. PNA were synthesized from butadiene–styrene nitroligomer and formaldehyde [11,12] in aqueous or organic solvent medium by using alkaline bases or alkaline carbonates as catalysts. Their quantitative functional composition was also determined. The AN -reaction of the above mentioned nitrooligomers with aldehydes was found to be similar to the reaction between nitroalkanes and carbonyl compounds, studied by Henry and widely described in a number of publications [13–16]. PNA were obtained by interaction of 2-nitroethane and 2-nitropropane with formaldehyde, acetaldehyde and propanal at pH ¼ 4–5 [17]. Bromonitroalcohols were synthesized from bromonitromethane and C1 –C8 aldehydes at pH ¼ 4–7 [18]. Fluoronitroalcohols and fluoronitroalkenes were synthesized starting from the corresponding aldehydes or ketones and nitroalkanes [19].
0014-3057/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 2 ) 0 0 1 3 8 - 6
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The aim of the present work was to study the nucleophilic addition––AN -reaction of nitrooligomer derived from butadiene–styrene rubber with acetaldehyde in aqueous-ethanol solution and in the presence of alkaline bases as catalysts in order to prepare PNA. Another purpose of the study was to determine both the functional and fragmentary composition of PNA and their thermal stability.
2. Experimental 2.1. Butadiene–styrene rubber Bulex 1500 (a product of the Petrochemical Plant, Bourgas, Bulgaria), contained 23–25% styrene and had a number-average molecular weight M n ¼ 59 000 and weight-average molecular weight M w ¼ 2 97 000, which corresponded to the coefficient of polydispersity of 5 [11]. 2.2. Synthesis of butadiene–styrene nitrooligomer Butadiene–styrene nitrooligomer (BSNO) was obtained by nitration of butadiene–styrene rubber Bulex 1500 (BSR) with 65% nitric acid at 60 °C, for 4 h in solution of dichloroethane. The mass ratio of rubber to HNO3 was 1:3 respectively [11]. 2.3. Synthesis of PNA starting from butadiene–styrene nitrooligomer and acetaldehyde in water–alcohol solution in the presence of alkaline hydroxide as a catalyst 10 g of BSNO were dissolved in 200 ml 2% aqueous solution of potassium or sodium hydroxide by heating up to 40 °C and stirring in a 1 l thermostated reactor, equipped with a stirrer, thermometer, dropping funnel and reflux condenser. The temperature was increased to 50 °C and then 5 g (6.4 ml) of freshly distilled acetaldehyde were dissolved in 50 ml ethanol and were gradually added for 3.5 h by continuous agitation. The solution was stirred for another 0.5 h under the same conditions. Consequently, the reaction mixture was neutralized with 10% hydrochloric acid until pH ¼ 6 was reached. Finally the sample assigned as PNA-1-C2 was gradually precipitated. The product PNA-1-C2 was separated and purified by precipitation of 15% acetone solution in 3 l distilled water. The product (6 g, 60%) was soluble in acetone, 1,4-dioxane, tetrahydrofurane and ethylacetate. The filtrate was evaporated under vacuum (0.011 MPa) until a solid residue was obtained. The precipitate was further subjected to extraction with acetone and then the second product PNA-2-C2 , (2.3 g, 23%) was isolated. The latter was soluble in acetone and water.
2.4. Analysis of PNA Elemental analysis was carried out by using a Perkin– Elmer instrument. The thermal analysis was performed on derivatograph OD-102 (Hungary) within the temperature range of 20–600 °C at a heating rate of 6 K/ min. The sample weight was 50–100 mg and the analyses were conducted in an air static atmosphere. A metaloceramic crucible of 9 mm diameter with Pt and Pt/Th thermocouples was employed for the samples. 1 H-NMR spectra were obtained by using a 250 MHz spectrometer in a solution of (CD3 )2 CO. The IR spectra were recorded for samples prepared as potassium bromide pellets (1 mg/300 mg) with potassium ferricyanide as an internal standard on a Specord M 80 instrument. The content of aliphatic nitro-, carbonyl, and secondary hydroxyl groups in the PNA were determined using the base line and internal standard techniques with respect to two standard compounds from the corresponding IR spectra detected under the same conditions [11]. The typical characteristic absorption bands were employed from the IR spectra of the standards: 2-nitro-2ethyl-1,3-propanediol (mas NO2 1546 cm1 and mC–O–(H) 1056 cm1 ) and 10-nonadecanone (mC@O 1728 cm1 ) and also mCBN 2116 cm1 from the IR spectrum of the internal standard––potassium ferricianide. The absorption A and, subsequently, the ratio R ¼ Ax =Ast were calculated, where Ax was the absorptions of the corresponding functional group of PNA-1-C2 and Ast was the absorption mCBN at 2116 cm1 of the internal standard respectively. The content of the functional groups was determined by comparing their Rvalues to the corresponding R-values of the two standards. The chromatographic fractional separation of polynitroalcohol samples (1 g) was carried out in a glass column of 15 mm internal diameter and 550 mm length. The column was filled with 36 g silica gel (Fluka, 35–70 mesh) according to the ‘‘wet’’ method [11].
3. Results and discussion The present work appears as a continuation of the work concerned with the AN -reaction of BSNO to formaldehyde and reported previously [11]. Butadiene–styrene rubber Bulex 1500 represents a random copolymer of nonuniform distribution of styrene fragments along the macromolecular chain. It is characterized by the coefficient of polydispersity of, approximately, 5. The starting BSNO, as the product of nitration of elastomer Bulex 1500, is polyfunctional and has a coefficient of polydispersity of 1.7 with random distribution of fragments containing different functional groups.
M.S. Karaivanova, S.Z. Mitev / European Polymer Journal 38 (2002) 2413–2422
The main reaction centers of BSNO that participate in the AN -reaction in the presence of alkaline catalysts are the a-hydrogen atoms, adjacent to the C-atoms bearing the secondary nitrogroups. This interaction takes place, according to the following pattern:
Two types of the secondary PNA, indicated as PNA1-C2 and PNA-2-C2 , were prepared. The reaction was carried out in aqueous-alkaline solution of potassium or sodium hydroxide. The alkaline bases initially converted BSNO in its aci-form in the ethanol solution of acetaldehyde. An excess of the latter (mass ratio with respect to BSNO) was added to BSNO in order to decrease the rate of aldol condensation. The process was performed in temperature range 40–60 °C, to reduce the rate of the side reactions. The first reaction product PNA-1-C2 was separated as a precipitate after acidification of reaction mixture and the second one was subjected to vacuum distillation to remove the water. The PNA-1-C2 yields were 50–60%, for PNA-1-C2 25–33% respectively. PNA-1-C2 yields slowly increased by raising the temperature from 40 to 60 °C (Fig. 1). The yields did not differ essentially, whether the acetaldehyde was gradually added for 30 min or the whole amount was added at the beginning of the reaction (Table 1, samples 8, 12). Both the types of secondary PNA had different elemental compositions (Tables 2 and 3). The PNA-1-C2 carbon content was higher as compared to the initial BSNO, due to the introduction of hydroxyethyl groups as a result of the AN -reaction. The carbon content of PNA-2-C2 was lower as a result from the increased con-
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centration of oxygen-containing groups. Based on the comparison of the carbon content of PNA found previously, the reactivity of BSNO with respect to acetaldehyde was considered to be lower than that of formaldehyde.
Fig. 1. Polynitroalcohol PNA-1-C2 yield as reaction time (BSNO to acetaldehyde, mass ratio ¼ 2:1, 60 °C, KOH as catalyst).
The IR spectrum of PNA-1-C2 was characterized by the mas , ms stretching vibrations for the aliphatic NO2 group at 1546 and 1360 cm1 respectively, mC@C at 1632 cm1 and mC@O at 1716 cm1 (Fig. 2, curve 1). The new
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Table 1 Yields of polynitroalcohols PNA-1-C2 , obtained from BSNO and acetaldehyde No.
Reaction time (h)
Temperature (°C)
BSNO:CH3 CHO (w.p.)
Catalyst
Yield (%)a
1 2 3 4 5 6 7 8b 9 10 11 12b 13 14
4 5 4 5 4 4 4 4 4 3 4 4 5 4
40 40 50 50 60 40 40 40 40 50 50 50 50 60
2:1 2:1 2:1 2:1 2:1 1:1 2:1 2:1 3:1 2:1 2:1 2:1 2:1 2:1
KOH KOH KOH KOH KOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH
54 55 56 58 64 60 55 53 50 50 54 55 53 65
a b
The yields of PNA-2-C2 : 25–33%. CH3 CHO is added in bulk at the beginning of the reaction.
Table 2 Elemental analysis of polynitroalcohols PNA-1-C2 , obtained from BSNO and acetaldehyde No.
Reaction time (h)
Temperature (°C)
Catalyst
C (%)
H (%)
N (%)
1 2 3 4 5 6 7 8a 9 Initial
1 2 3 4 5 6 4 4 4 BSNO
60 60 60 60 60 60 50 50 40
KOH KOH KOH KOH KOH KOH KOH KOH NaOH
56.32 56.26 57.38 56.01 57.74 57.82 56.82 57.64 60.42 51.19
5.30 5.28 5.76 5.94 5.96 5.73 5.63 5.94 5.93 5.20
8.06 8.03 7.94 7.80 7.47 7.51 8.34 8.45 7.31 10.50
a
The whole amount of CH3 CHO is added in bilk at the beginning of the reaction.
Table 3 Elemental analysis of polynitroalcohols PNA-2-C2 , obtained from BSNO and acetaldehyde No.
Reaction time (h)
Temperature (°C)
Catalyst
C (%)
H (%)
N (%)
1 2 3 4 5
3 4 5 5 6
50 50 50 40 60
NaOH NaOH NaOH KOH KOH
42.77 40.89 39.90 38.12 39.95
3.57 3.45 4.27 4.12 3.42
5.72 5.49 6.07 8.11 7.86
multiplet band at 1100, 1030 and 1000 cm1 , mC–O–H, was assigned to secondary hydroxyl group. The wide absorption band with high intensity in the 3700–3100 cm1 , showed the presence of OH-groups in the compounds with intramolecular hydrogen bonds [20]. The vibration mC–O–H for secondary hydroxyl group 1120– 1130 cm1 in PNA-1-C2 was shifted to the lower fre-
quencies, which was similar to the cyclohexanol bands, mC–O–H 995 and 1062 cm1 [21]. The vibration mas for the nitratester group at 1280 cm1 indicated lower intensity with respect to those of the BSNO starting material. The IR spectrum of the polynitroalcohol PNA-2-C2 (Fig. 2, curve 2) indicated some characteristic bands mas;s for aliphatic nitrogroup at 1550, 1380 cm1 , mas
M.S. Karaivanova, S.Z. Mitev / European Polymer Journal 38 (2002) 2413–2422
Fig. 2. IR spectra of PNA, obtained from BSNO and acetaldehyde (3 h, 60 °C, mass ratio 2:1): (1) PNA-1-C2 ; (2) PNA-2-C2 .
1280 cm1 for nitratester group with high intensity, mC@C at 1630 cm1 and mC@O at 1680 cm1 for conjugated ketone group [21]. The presence of hydroxyl group was proved by the stretching vibrations mC–O–H at 1090, 1050 cm1 and by the increased absorption in the range of 3200–2400 cm1 . According to the quantitative functional groups composition determined by IR spectroscopy (Table 4), the content of aliphatic nitrogroup in PNA-1-C2 was found to be 12.5–19.6%, and that of the ketone and secondary hydroxyl groups was 2.4–3.3% and 1.7–3.9% respectively. Prolonger reaction times resulted in a slow decrease of the NO2 ––groups content after the third hour, whereas the content of OH––groups increased up to 3.6% and the ketone groups content did not change essentially.
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It is worth noting that the ketone groups content in PNA-1-C2 (2.7–3.3%) was higher as compared to that of BSNO (1.9%), probably, because of the partial hydrolysis of the nitratester groups. The nitrous and nitric acid esters are considered to be active centers for the formation of alcohols, aldehydes and ketones [22]. Regardless of the relatively mild conditions of AN reaction, some side reactions were considered to occur, too. Some PNA-1-C2 possessed lower content of NO2 groups and higher degree of unsaturation than BSNO (Table 4) which is associated with processes of denitration. Some polynitroalcohols PNA-2-C2 (Table 5), contained also conjugated C@O groups (mC@O 1680 cm1 ). At the same time, partial hydrolysis of the nitratester groups of PNA-1-C2 took place which was proved by the lower intensity of m 1280 cm1 band. One of the PNA-1-C2 prepared was characterized by its 1 H-NMR spectrum (Fig. 3) which included chemical shifts as follows: 4.3 ppm (methyne protone) bonded to secondary NO2 -group; 4.1 ppm for H-proton from secondary OH-group; 3.8 ppm (methyne proton bonded to the same group); strong peak of methyne proton from –CHPh 3.6 ppm and C–H protons from Ph– 7.3 ppm; chemical shift for –(CH2 )–n 1.3 ppm and pronounced chemical shift for C–H protons from CH3 -group 0.9 ppm, introduced as a result from the AN -reaction. The shift of H-protons of the terminal CH3 -group 0.9 ppm in the hydrocarbon chain of the initial BSNO was very slightly pronounced in the 1 H-NMR spectrum. The presence of methyne group (C–H), attached to the secondary NO2 -group in the 1 H-NMR spectrum of PNA-1-C2 (Fig. 3) showed that the AN -reaction between BSNO and acetaldehyde did not take place completely. The two types of the PNA studied were found to be polyfunctional and polydisperse compounds. The study
Table 4 Quantitative functional composition of polynitroalcohols (PNA-1-C2 ), obtained from BSNO and acetaldehyde (2:1 mass ratio) No.
Reaction time (h)
Temper ature (°C)
Catalyst
R¼ 2116 A1546 NO2 =ACN
NO2 (%)
R¼ 2116 A1716 CAO =ACN
C@O (%)
R¼ 2116 A1632 CAC =ACN
R¼ 2116 A1100 CAOAðHÞ2 =ACN
OH (%)
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 4 3 5 BSNOa standardb standardc
60 60 60 60 60 30 50 50 50 – – –
KOH KOH KOH KOH KOH KOH KOH NaOH NaOH – – –
0.5612 0.5811 0.5792 0.5129 0.3616 0.3600 0.5488 0.4474 0.4367 0.5859 0.8886 –
19.6 20.1 20.8 17.8 12.5 12.4 18.6 15.2 14.9 19.0 28.3 –
0.1950 0.1933 0.2286 0.2106 0.1796 0.2233 0.1677 0.1847 0.1331 0.1285 – 0.6954
2.9 2.8 3.3 3.0 2.6 3.2 2.4 2.7 2.0 1.9 – 10.1
0.1499 0.1435 0.1594 0.1548 0.1371 0.1486 0.1947 0.1705 0.1519 0.1286 – –
0.0376 0.0435 0.0634 0.0781 0.0820 0.0848 0/0435 0.0720 0.0735 – 0.4928 –
1.7 1.9 2.9 3.6 3.8 3.9 1.9 3.3 3.4 – 22.8 –
a as
m NO2 , 1550 cm1 . 2-nitro-2-ethyl-1,3-propanediol, mC–O–(H) 1050 cm1 and mas NO2 1546 cm1 . c 10-nonadecanone, mC@O 1728 cm1 . b
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Table 5 Characteristic absorption bands in IR-spectra of the main fractionsa of two types of PNA obtained from BSNO and acetaldehyde (40 °C, 4 h, mass ratio 2:1, KOH as catalyst) PNA
Fraction no.
mC@O
mC@C cC@C
mas;s NO2
mas ONO2
mas;s C–O–C
mC–O–(H)
PNA-1-C2
1b
–
–
–
2b
1716d
1280
PNA-1-C2
3
1716c
1630c
1280d
PNA-1-C2
4
1700
1620c
1550 1380 1550c 1380c 1550
1100c 1020 1100c 1020 –
3700–2600
PNA-1-C2
800 890c 1630d
1280
–
PNA-1-C2
5
–
1630c
1280
–
PNA-2-C2
1b
1710
800
1280
PNA-2-C2
2b
1710
1640
PNA-2-C2
3
1710
1640
1550 1380c 1550 1380d 1550 1380d 1550
1280d
1100 1020 1100 1020 –
PNA-2-C2
4
1680
1620
1280d
–
PNA-2-C2
5
1680
1620
– –
– –
1550 1380 1550 1380
1280
3700–2600 1100, 1020 3700–2600 1080 3700–2600 1100 – 3700–2600 1100–1050 3700–2600 1100c 3700–2600 1100c 3700–2600
a
Fraction No 6 of the both PNA was hygroscopic. mC–O–(H) was overlaped with mas;s C–O–C. c Intensive. d Weak. b
of the distribution of functional groups in the different oligomer fractions, was expected to give information about their composition and reactivity. The fractional separation of the initial BSNO [11] and the PNA was carried out by the liquid adsorption chromatography on silica gel. The samples obtained therefrom were divided into six fractions (Figs. 4 and 5). The second and the third ones, that were the main fractions for PNA-1-C2 , were eluated by mixture of chloroform and ethylacetate (volume ratio 1:1) and ethylacetate respectively. The second and the forth PNA-2-C2 fractions were eluated by ethylacetate and acetone–ethanol (volume ratio 1:2) respectively. The PNA-2-C2 polynitroalcohols were found to be more polar compounds than PNA-1-C2 . IR spectra of both polynitroalcohol (Table 5) fractions showed the presence of different functional groups. This was associated with the various reactivites of the starting BSNO fractions with respect to the AN reaction. The main fractions of PNA-1-C2 were distinguished not only by qualitative but also, by the quantitative functional compositions (Table 6). This is also related to the PNA-2-C2 fractions which had different elemental composition (Table 7). Some of them were hygroscopic
and this created certain difficulties for the quantitative determination of the main functional groups. The first fraction of PNA-1-C2 did not contain nitrogen and N-containing groups (Tables 5 and 6). The IR spectra showed the presence of strong band c@CH at 890 cm1 (895–885 cm1 ) for the terminal C@C bond [23]. The first and the second fractions were characterized by the strong vibrations ms C–O–C at 1100 cm1 (1150–1050 cm1 ) that were probably overlapped by mC–O–(H) for the secondary OH-group. Fractions 2–5 contained nitro- (mas;s 1546, 1360 cm1 ), C@C bonds (m 1620 cm1 ), nitratester- (mas 1280 cm1 ) and ketone groups (mC@O 1720 cm1 ). The hydroxyl groups were concentrated in the third main fraction (mas;s 1100, 1020 cm1 ) but they were not necessary present in all of the fractions studied. The PNA-2-C2 fractions were also polyfunctional products (Table 5). Ether groups were present in the first and the second fractions. Nitratester groups were absent in the fifth fraction. The fourth and the fifth fractions contained conjugated C@O groups and this caused shift of the band at 1720 cm1 towards 1680 cm1 [23]. All fractions contained hydroxyl groups which was also proved by their solubility in water and the pronounced surfactant properties.
M.S. Karaivanova, S.Z. Mitev / European Polymer Journal 38 (2002) 2413–2422
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Fig. 3. 1 H-NMR spectra of polynitroalcohol PNA-1-C2 .
Fig. 4. Functional composition of PNA-1-C2 , obtained from BSNO and acetaldehyde (40 °C, reaction time 4 h, KOH as catalyst).
Fig. 5. Fractional composition PNA-2-C2 , obtained from BSNO and acetaldehyde (40 °C, reaction time 4 h, KOH as catalyst).
The chemical and molecular polydispersity of PNA-C2 results from the structure of butadiene–styrene copolymer and the origin of initial BSNO obtained by nitration. The nitration has complex character including destruction and oxidation which take place in every
occasions. For example the nitration was performed even under ‘‘soft’’ conditions. The PNA-C2 as products of AN -reaction have nature similar to that of BSNO. They are less heterogeneous due to the BSNO fractionation during the reaction and
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Table 6 Elemental analysis and functional compositiona of the main fractions of polynitroalcohol PNA-1-C2 (60 °C, 4 h, BSNO:CH3 CHO 2:1 mass ratio) Fraction
Color
Eluating system (vol. p.)
1
Light beige
2
Light yellow
3 4 Initial PNA-1-C2
Dark yellow Dark yellow Yellow
Benzene: chloroform ¼ 1:1 Chloroform: ethylacetate ¼ 1:1 Ethylacetate Acetone
C (%)
H (%)
N (%)
R¼ 2116 A1546 NO2 =ACN
NO2 (%)
R¼ 2116 A1716 C@O =ACN
C@O (%)
42.00
9.42
–
–
–
–
–
54.21 51.41 55.57 56.01
6.17 5.53 4.80 5.94
7.16 7.20 7.90 7.80
0.4943 0.3531 0.5111 0.5129
17.8 12.7 18.7 17.8
0.2525 0.2725 0.2628 0.2106
4.1 4.6 4.4 3.0
Fractions 5, 6 were hygroscopic and therefore, their functionally compositions was not determined. a With respect to 2-nitro-2-ethyl-1,3-propanediol and 10-nonadecanone.
Table 7 Elemental analysis of the main fraction of polynitroalcohol PNA-2-C2 (60 °C, 4 h, BSNO:CH3 CHO ¼ 2:1, mass ratio) Fractiona
Color
Eluating system (vol. p.)
C (%)
H (%)
N (%)
1 2 3 4 5 Initial PNA-2-C2
Light beige Light yellow Beige Dark yellow Dark yellow Yellow
Chloroform Ethylacetate Acetone Acetone:ethanol ¼ 1:2 Ethanol:water ¼ 2:1 –
46.12 39.80 35.50 35.45 35.10
6.59 4.07 3.51 3.86 3.36
5.48 8.37 4.05 3.88 –
40.50
4.81
8.11
a
Fraction 6 was a brown, hygroscopic substance.
the obtaining of some other reaction products. The PNA-C2 characterization was rather laborious. The determination of functional polydispersity of PNA-C2 had to be made for several reasons: for prognosis their reactivity with respect to some reagents, to assist the possibilities of their utilization as additives in polymer composition, etc. The thermal stability of both types of PNA was also studied. PNA-1-C2 started to decompose within 110– 130 °C in three stages (Fig. 6, curves 1–4). DTA indicated three exothermal effects at 200, 330 and 500 °C, respectively. The first one was similar to the exothermal effect of the initial BSNO at 195 °C (Fig. 6, curve 5) and was caused by the nitrogroup exothermal decomposition accompanied by 25% weight loss within 130–240 °C. Decomposition of the main hydrocarbon chain occurred within 250–400 °C with an exotherm maximum at 330 °C and additional weight loss of 30%. The destruction within the temperature range of 450–600 °C was accompanied by pronounced exothermal effects at 500 °C. PNA-1-C2 , obtained after 1 h reaction time had lowest thermal stability (Fig. 6, curve 1). The destruction took place at low rate within the temperature interval of 170–350 °C. This was probably due to the cross-linking
effects caused by the nitrogen oxide release. The prolongation of reaction time from 2 to 6 h resulted in a weak increase the thermal stability of PNA-1-C2 which was confirmed by the TGA scans. The decomposition of PNA-2-C2 started at 130 °C and exothermal effects on DTA were detected at 250, 310 and 545 °C (Fig. 6, curve 6). Thermal analysis studies indicated that the both types of PNA had a higher thermal stability than the initial BSNO. Their thermal stability was close to that determined for PNA-C1 in previous publication [11].
4. Conclusions (1) BSNO reacts with acetaldehyde by the a-hydrogen atoms attached to secondary nitrogroups. This AN reaction results in the formation of two types of polynitroalcohols (PNA-1-C2 and PNA-2-C2 ). The optimum yields of the latter are obtained at temperature 50–60 °C, reaction time of 3.5–4.5 h and BSNO:CH3 CHO ¼ 2:1 mass ratio, in water–alcohol solution of alkaline bases. (2) Both types of PNA are polyfunctional oligomers and contain aliphatic nitro-, ketone and secondary hydroxyl groups predominantly. The content of
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tion chromatography in accordance with the polarity of the corresponding fractions. (4) Both types of PNA are found to have a higher thermal stability as compared to the BSNO employed as starting material.
Acknowledgements The authors are thankful to Prof. Dr. Kolio Troev from Institute of Polymers––Bulgarian Academy of Science, Sofia, for interpretation of 1 H-NMR spectra.
References
Fig. 6. Thermal analysis of polynitroalcohols PNA-1-C2 , obtained from BSNO and acetaldehyde (60 °C, mass ratio 2:1): (1) 1 h; (2) 2 h; (3) 3 h; (4) 6 h; (5) initial BSNO; (6) 3 h.
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