Quantitative Analysis of the Etherification Degree of Phenolic Hydroxyl

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Quantitative analysis of the etherification degree of phenolic hydroxyl groups in oxyethylated lignins: Correlation of selective aminolysis with FTIR spectroscopy Lars Passauer, Katrin Salzwedel, Marlene Struch, Nadine Herold, and Joern Appelt ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01495 • Publication Date (Web): 03 Oct 2016 Downloaded from http://pubs.acs.org on October 9, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Quantitative analysis of the etherification degree of phenolic hydroxyl groups in oxyethylated lignins: Correlation of selective aminolysis with FTIR spectroscopy

Lars PassauerΨ,*, Katrin Salzwedel‡, Marlene StruchΓ, Nadine HeroldΩ, Jörn AppeltΘ

Ψ

Dresden Institute of Wood Technology – Institut für Holztechnologie Dresden

gemeinnuetzige GmbH, Zellescher Weg 24, 01217 Dresden, Germany

‡

International Graduate School, Technische Universitaet Dresden, Markt 23, D-02763 Zittau,

Germany

Γ

Institute of Food Chemistry, Leibniz University Hanover, Callinstr. 5, 30167 Hannover,

Germany

Ω

Faculty of Wood Science and Technology, University of Applied Science, Alfred-Moeller-

Str. 1, 16225 Eberswalde, Germany

Θ

Thünen Institute of Wood Research, Leuschnerstr. 91b, 21031 Hamburg, Germany

*Corresponding author Email: [email protected] Phone: +49 351 4662 369 FAX: +49 351 4662 211

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract PEGylated or oxyethylated lignins (OEL) have recently become a hot topic as precursors for novel lignin based and sustainable materials or active substances such as hydrogels, aerogels, carbogels, dispersants, and surfactants. Since functional properties of OEL and the resulting materials are strongly affected by the degree of oxyethylation (DOE) of phenolic hydroxyl groups (OHphen), analytical techniques for its determination are crucial. OELs with different levels of modification were obtained by reacting lignins from different pulping procedures with varying amounts of poly(ethylene) glycol-α,ω-diglycidyl ether (PEGDGE). Parent lignins and OELs were characterized by means of selective aminolysis that is subsequent preacetylation and selective deacetylation of aromatic acetates of preacetylated lignin/OEL with pyrrolidine. The reaction product 1-acetyl pyrrolidine was quantified using GC/FID. DOE of OEL, obtained by subtraction of OHphen content before and after lignin oxyethylation, was found to be in the range between 53.4 % and 70.0 %. Selective aminolysis has been shown to be very accurate for OEL analysis but is very time consuming. Thus it was the aim to investigate the extent to which FTIR features of acetylated lignin and OEL relate to OHphen contents and DOE of OEL as obtained by aminolysis. Strong linear correlations (R2 = 0.94 … 0.97) were found between OHphen contents of lignin/OEL and IR vibrations related to phenolic and aliphatic acetoxy groups. The results demonstrate that, with appropriate calibration, FTIR spectroscopy combined with sample preacetylation is a promising tool for a rapid and accurate determination of the DOE of OELs.

Keywords Biorenewable materials, Lignin ethers, Hydrogels, Structure-property relations, Phenolic hydroxyl groups, Etherification degree


Page 2 of 34

Page 3 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction Lignin – a main constituent of the plant cell wall - is the second most abundant natural and biorenewable polymer on earth.1 More than 50 Mt of technical lignins per year are produced as byproducts of pulp and paper manufacturing and second-/third-generation biorefineries.2 While those lignins have been mainly used for energy generation, depolymerization of lignin to fine chemicals and accordingly its processing to innovative materials is therefore of essential interest to improve the overall performance of biomass processing units and to convert lignin in high value-added products. Less known but promising approaches is using lignin as feedstock for bio-based surfactants and dispersants,3,4 hydrogels,5,6 aerogels7 and carbon aerogels.8-10 A promising route to obtain such intriguing materials is the etherification of lignin with monofunctional epoxidized PEG derivatives3,4 or simultaneous oxyethylation and crosslinking of lignin with bifunctional epoxidized PEGs namely poly/oligo(ethylene glycol)-α,ω-diglycidyl ethers, PEGDGE.4,11,12 For this, an activation of lignin in aqueous sodium hydroxide is performed in order to convert phenolic substructures of lignin into reactive phenolates. The latter can act as nucleophiles attacking the C2 atom of terminal epoxide moieties in PEGDGE (Scheme 1, structure 1). HO

Lignin

R

Lignin 2x

R

R

1

O

R

O

O

2

2

OH

-2OH-

Lignin OH

O

O

O

R1

Lignin

n

1

R1

O

n

2

+

1x

O

2H2O

O 2

OH 2H2O

R

-OH-

R1

O

n

2

O

O

3 R1 = OCH3

R2 = H; OCH3

OH

Scheme 1: Suggested reaction scheme for the oxyethylation of lignin with PEGDGE (1) under the formation of crosslinked (2) and not crosslinked OEL domaines (3) Due to the ring tension of oxiranes, cleavage of the respective C-O bond proceeds. The resulting alkoxide intermediate (not shown) is readily converted into the corresponding 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

secondary hydroxyl in β-position of the newly formed phenol ether bond (2, 3). Besides crosslinked structures (2) the formation of phenols etherified with oxyethylene glycol moieties might occur (3). Following this approach, OEL with hydrogel character were obtained from pine kraft lignin,11 spruce and beech organosolv lignin,6,11 birch acetic acid lignin,12 and wheat straw alkali lignin. Because of various beneficial features such as high water absorption capacity, high water retention and water release, mechanical stiffness, and biodegradability, OELs are suitable as water storing biomaterials, e.g., for agricultural applications and soil rehabilitation.6,11,13 Due to a more-step solvent exchange by replacing water by aqueous ethanol or acetone of decreasing water content and subsequent supercritical CO2 extraction of the resulting alco/organogels, OEL hydrogels can be successfully converted into the corresponding aerogels performing surface areas up to 120 m2g-1, bulk densities low as 0.15 g cm-3 and thermal conductivities of about 50 mW m-1 K-1.7 Hence, these materials are promising candidates for applications including, e.g., adsorption, filtration, light-weight constructions and thermal insulation.7 A pyrolytic conversion of OEL based aerogels into carbon aerogels which have been suggested as high surface adsorbents, catalysts and high surface electrodes in supercapacitors9 is under investigation.7,10 Since functional properties of respective OEL based materials such as swellability, water retention, mechanical stiffness and biodegradability of hydrogels, porosity, specific surface, thermal conductivity and sorption characteristics of aerogels and carbogels are strongly affected by crosslinking/oxyethylation degrees of the gels,6,7,10-13 analytical techniques for the determination of their DOE are crucial but not yet routinely performed. Because oxyethylation of lignin is mainly due to the etherification of phenolic substructures of lignin with PEG derivatives, the chemical reaction is indicated by decreasing OHphen contents of the reaction products.14 Thus, subtraction of OHphen contents before and after oxyethylation of lignin is assumed to yield the DOE of the resulting OEL. Free phenolic 4 ACS Paragon Plus Environment

Page 4 of 34

Page 5 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


groups of chemically unmodified lignins can be quantitatively determined by various methods such as conductometric or potentiometric titration in aqueous or nonaqueous solutions,15 spectrophotometric determination (∆ε method) according to Goldschmid16 and AulinErdtman,17 oxidation of lignin with aqueous sodium periodate,18 lignin methylation with diazomethane,19

thioacidolysis

of

premethylated

preacetylated samples,21,22 FTIR techniques,23,24 1H and

lignin,20 13

selective

aminolysis

of

C NMR spectroscopy after sample

preacetylation25-28 and 31P NMR spectroscopy of lignins reacted with 1,3,2-dioxaphospholanyl chloride.29,30 The latter allows the quantification of primary and secondary aliphatic OH groups as well as guaiacyl and syringyl hydroxyls in lignin. Most of these methods have not yet been applied to highly modified lignins like OEL or have some disadvantages in this context. It is, e.g., not recommended to use the conventional ∆ε method to analyse highly modified lignins like OEL, because the derivatives contain new structures and the UV absorption character and extinction coefficients of the corresponding phenolic groups are unknown.15 Furthermore, it is uncertain which effect chemical degradation methods such as periodate oxidation may have on the structure of degradation products of the lignin derivatives. On the other hand, NMR techniques require expensive analysis equipment and only soluble lignins/lignin derivatives can be characterized quantitatively. Thus, it was the aim of this study (1) to test the suitability of Månsson´s method21,22 – originally developed for characterizing unmodified technical lignins and coveted as a reproducible measurement for lignin structure23- to determine free OHphen groups of OEL which could render this method applicable for the determination of the DOE of this lignin ethers, and (2) to investigate the extent to which FTIR spectra of acetylated OEL relate to OHphen contents and DEO of OEL as obtained by selective aminolysis. Because aminolysis is a very accurate but rather time consuming method, a FTIR technique would allow a quick, easy and reliable quantification of the etherification degrees of lignins/polyphenols modified



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

with PEGDGE/glycidylethers and resulting materials in routine laboratories equipped with a FTIR spectrometer.

Materials and Methods Lignins. Spruce organosolv lignins indicated as OSL 1-8 obtained by sodium hydroxide/ methanol/ anthraquinone pulping under varying cooking conditions, precipitated with sulphuric acid at pH 4 and with carbon dioxide at pH 9, respectively (former Organocell GmbH Munich, pilot plant Munich–Pasing, Germany); pine mix kraft lignins (KL) Indulin AT (purified) and Indulin C (with hemicellulose residues; both MeadWestvaco, USA). OSL 1 and Indulin AT were used for the preparation of OEL. All the other lignin types were included into this study to cover samples with a range of phenolic hydroxyls as wide as possible and to ensure a better statistical evaluation of the analytical data obtained. Prior to chemical treatment (preoxidation, oxyethylation, preacetylation), lignin samples were continuously stored in a desiccator over silica gel in darkness at 5°C. Chemicals. Hydrogen peroxide 30% (H2O2), pyrrolidine and poly(ethylene) glycol diglycidyl ether (PEGDGE, MW 526 g mol-1) were provided from Merck (Darmstadt, Germany) and Sigma Aldrich (Steinheim, Germany). Molecular sieve (3 Å, type 564), hydrochloric acid (37%), acetic anhydride (< 99%, Ac2O), phosphorus pentoxide (P2O5), dioxane (HPLC grade) and pyridine were purchased from Carl Roth (Karlsruhe, Germany). 1-acetyl pyrrolidine (AcPyr) was obtained from Frinton laboratories (Hainsport, New Jersey, USA). Propionyl pyrrolidine (ProPyr) was synthesized as described by Koch.31 4-acetoxy-3-methoxy benzaldehyde (AcO-MeO-BA) and 4-acetoxy benzoic acid methyl ester (AcO-BCOO-Me) were from the chemicals collection of the Institute of Plant and Wood Chemistry, TU Dresden, Germany. Pyridine was stored over freshly dried molecular sieve. Ac2O was freshly


Page 6 of 34

Page 7 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


distilled before use. All other chemicals were from highest purity and were used without further purification. Lignin preoxidation. Preactivation of Indulin AT (INDox) was accomplished with H2O2 in alkaline media: 10 g of lignin was dissolved in 16 ml 3.3 M aqueous NaOH solution at ambient temperature. After 24 h/48 h of stirring, 0.125 - 1.0 ml aq. H2O2 (5 %, v/v) was added drop-wise and the reaction mixture was stirred for another 24 h. Lignin oxyethylation. Derivatization of unmodified and preoxidized lignins was performed with PEGDGE as described earlier.11 Unmodified lignin was dissolved in 3.3 M aq. NaOH solution. After 24 h/48 h of vigorous stirring, 0.5 - 1.25 mmol of PEGDGE glig-1 were added drop-wise until the viscosity was drastically increased by gel formation. Preoxidized lignin was crosslinked by adding the same amount of PEGDGE immediately after oxidative treatment. The resulting gels were thoroughly washed and neutralized with deionized water and subsequently freeze dried. Table 1 gives an overview of OEL variants and selected parameters of sample preparation. Table 1: Selected parameters for OEL preparation and sample codes for modified lignins Raw material lignin/aq. stirring aq. H2O2 PEGDGE/lignin sample code NaOH ratio time 5% ratio (w/v) (h) (ml gLig-1) (mmol gLig-1) OSL 1 1:1.6 24 0.0125 0.5 OE-OSL-1 OSL 1 1:1.6 24 0.025 0.5 OE-OSL-2 OSL 1 1:1.6 24 0.1 0.5 OE-OSL-3 OSL 1 1:1.6 48 0.1 0.5 OE-OSL-4 OSL 1 1:1.6 24 0.1 1.0 OE-OSL-5 OSL 1 1:1.6 24 0.1 0.75 OE-OSL-6 IND 1:1.7 24 0.2 0.5 OE-IND-1 IND 1:3 24 0.2 1.0 OE-IND-2 IND 1:3 24 1.0 OE-IND-3 IND 1:3 24 1.25 OE-IND-4 OSL: organosolv lignin, IND: Indulin AT, OE-OSL: oxyethylated OSL, OE-IND: oxyethylated IND

Sample preacetylation. Acetylation of technical lignins and respective OEL variants was accomplished according to Glasser et al.32 (Scheme 2a). The reaction was carried out with 1 g lignin/OEL in a dry pyridine/Ac2O mixture (1:1) at ambient temperature under nitrogen. After 7 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 34

24 h 100 ml 0.1 N HCl was added. The product was isolated by filtration on a fritted filter funnel and washed repeatedly with 0.1 N HCl and deionized water until the filtrate was pyridine free and neutral. The product was subsequently dried in vacuum for 24 h at 40°C. Lignin and OEL acetylation was evaluated using FTIR spectroscopy. Disappearance of the OH stretching vibration between 3000 cm-1 and 3500 cm-1 was considered as an indicator for a homogeneous acetylation of hydroxyl groups. Phenolic OH group contents. OHphen contens of lignins and OEL were determined by selective aminolysis of preacetylated samples with pyrrolidine and quantification of the resulting AcPyr by gas chromatography (Scheme 2b) according to21. O

a

OH

O

CH3

N

+ R2

R

2Ac2O

+

20°C

R

1

OH R1 = OCH3

R

2

O O

4

R2 = H; OCH3

H3C

O

O

b

CH3

O

R

CH3

O

O O

+ R2

2AcOH

1

N

1

H

O O

20°C fast

+ R2

R

N

1

OH

O

5

H3C

CH3 6

O

c

CH3

O

+ R2

R OH

1

OH

O O

N H

20°C slow

+ R2

R

N

1

OH

5

O

CH3 6

Scheme 2: a) Acetylation of lignin with acetic anhydride (Ac2O) in pyridine, b) fast aminolysis of phenolic and c) slow aminolysis of aliphatic acetoxy groups (4) with pyrrolidine (5) under the formation of 1-acetyl pyrrolidine (6)

Prior to analysis, all preacetylated samples were stored in a dessicator over P2O5 under vacuum. The following GC conditions were applied: GC/FID autosystem PERKIN-ELMER; column: ROTICAP® - 5 MS; temperature program: 160°C, 4 min; injector: 230°C; detector: 260°C; carrier gas: He: 2 ml min-1; combustion gas: H2: 30 ml min-1 and synthetic air: 8 ACS Paragon Plus Environment

Page 9 of 34

310 ml min-1.The GC system was calibrated by aminolysis of AcO-MeO-BA and AcOBCOO-Me. The concentration of OHphen was calculated using a calibration curve with the ratio of the peak heights of AcPyr and ProPyr. The latter was used as internal standard. Chromatograms obtained were analyzed using the software TotalChromTM Workstation Version 6.3.1 (PERKIN-ELMER, Waltham, Massachusetts, USA). For each determination 14 time measurements were conducted. Measurements of each sample were done in duplicates. The quantitative formation of 1-acetylpyrrolidine (6) and the corresponding OHphen content vs. time of aminolysis is exemplarily depicted for two lignin types and their oxyethylated variants (Fig. 1). Within the observed time period a change from phenolic to aliphatic deacetylation occurred (Scheme 2c) and the amount of phenolic acetyl groups was determined by extrapolating the linear region of the curves, indicated as dark symbols, to zero as depicted. Linear regression of rates of formation of (6) in the range between 25 min and 60 min of aminolysis yielded models with R2 ≥ 0.94 for both lignin and OEL. OHphen peak area BK25_4 + MS8

8

8

a

7

y = 6.278 + 0.017x 2 R = 0.98

OHphen [%]

4 2

2

0 10

20

30

40

50

60

2 3 y = 2.99 + 0.010x 2 R = 0.96

1

1

0 0

4

2

1

y = 1.777 + 0.015x 2 R = 0.98

3

-1

-1

3

y = 6.252 + 0.008x 2 R = 0.94

5

AcPyr [mmol gLigAc]

3

5

1

4

6

OHphen [%]

6

b

7

4

AcPyr [mmol gLigAc]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0

0

70

0

Reaction time [min]

10

20

30

40

50

60

70

Reaction time [min]

Figure 1: a) Aminolysis (OHphen, AcPyr: 1-acetyl pyrrolidine) of acetylated variants of Indulin AT () and the oxyethylated counterpart OE-IND-4 () and b) acetylated spruce organosolv lignin OSL 1 () and OE-OSL-1 (); linear regions of the curves used for extrapolation are indicated (, ); single measurements Degrees of oxyethylation. Etherification degrees of phenolic hydroxyls in OEL were calculated according to Eq. 1 from the phenolic hydroxyl content before (OH୮୦ୣ୬ై౟ౝ ) and after lignin modification with PEGDGE (OH୮୦ୣ୬ోుై ): 9 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

‫ = ܧܱܦ‬ቆ1 −

ைு೛೓೐೙ೀಶಽ ைு೛೓೐೙ಽ೔೒

ቇ × 100

Page 10 of 34

Eq. 1

FTIR spectroscopy. FTIR spectra of parent lignins, OEL variants and their acetylated counterparts were recorded with a NICOLET iS5 FTIR spectrometer (THERMO FISHER SCIENTIFIC Inc., Waltham, MA, USA) equipped with a deuterated triglycin sulphate (dTGS) detector and using the ATR accessory kid id5. The spectra were measured in a spectral range from 4000 to 500 cm-1 and at a spectral resolution of 4 cm-1. For each spectrum 32 scans were added. For quantitative analysis, base-line correction and vector-normalization of the spectra was done between 1900 and 750 cm-1. Evaluation of the acquired spectra included integrating peak areas and peak intensities determined at the peak maxima of the respective bands was conducted using BRUKER´s OPUS software version 6 (BRUKER Instruments, Billerica, MA, USA). Graphical representation of the spectra was carried out using ORIGIN 8G (OiginLab Corp., Northampton, MA, USA). Data analysis. To correlate data from selective aminolysis and FTIR features of preacetylated lignins and OEL, simple and straight-forward linear regression analysis was performed using ORIGIN 8G.

Results and Discussion Phenolic hydroxyl group contents and degrees of oxyethylation. OHphen contents of different lignins and OELs obtained by aminolysis and resulting DOE are summarized in Tab. 2. It is obvious that free phenolic hydroxyls significantly decreased after oxyethylation of both IND and OSL-1 (see also Fig. 1a, b). For unmodified technical lignins OHphen contents were in the range from 4.03 % (Indulin C) and 6.90% (OSL-7; Tab. 3), what is in good accordance with literature data.21,33 Aminolysis of acetylated OELs gave rise to OHphen contents between 1.83 % (OE-OSL-4) and 2.84 % (OE-OSL-1) which is assumed to depend on 1) the amount of PEGDGE used for lignin oxyethylation, 2) the lignin type and 3) 10 ACS Paragon Plus Environment

Page 11 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


if a preoxidation of lignin was conducted or not.6,11,34 It is notable that free OHphen of OEL could be analyzed with good consistence via aminolysis method. DOEs of OEL variants calculated using Eq. 1 were found to be in the range from 53.44 % - 70.0 %. Maximum DOEs of the variants OE-OSL-5 (70.0 %), OE-IND-2 (64.75 %) and OE-IND-4 (67.98 %) correspond with highest amounts of PEGDGE (1.0 and 1.25 mmol gLig-1, respectively) used for lignin modification. Table 2: Phenolic hydroxyl contents of lignins (OH୮୦ୣ୬ై౟ౝ ) and OEL variants (OH୮୦ୣ୬ోుై ) determined by aminolysis of lignin acetates and OEL acetates and resulting degrees of oxyethylation DOE of OEL Lignin sample OSL-1 OSL-1b OSL-2 OSL-3 OSL-3a OSL-5 OSL-6 OSL-7 OSL-8 OSL-8b IND AT IND C

OH୮୦ୣ୬ై౟ౝ [%] 6.09 6.08 4.59 5.45 5.44 6.18 5.34 6.90 5.59 5.18 6.09 4.03

OEL sample OE-OSL-1 OE-OSL-2 OE-OSL-3 OE-OSL-4 OE-OSL-5 OE-OSL-6 OE-IND-1 OE-IND-2 OE-IND-3 OE-IND-4

OH୮୦ୣ୬ోుై [%]

DOE [%]

2.84 2.41 2.43 2.73 1.83 2.35 2.47 2.15 2.42 1.95

53.44 60.49 60.16 55.25 70.0 61.48 59.51 64.75 60.26 67.98

FTIR spectroscopy of lignin, OEL, and acetylated samples. FTIR spectra of Indulin AT and its oxyethylated variant OE-IND-3 are exemplarily depicted in Fig. 2, whereas the assignments to the respective IR bands are summarized in Tab. 3. A number of dissimilarities are evident which are interpreted as a result of the oxyethylation of lignin with PEGDGE. Whereas the spectrum of kraft lignin is dominated from aromatic skeletal vibrations at 1590 cm-1 and 1510 cm-1 (non-conjugated guaiacyl units), aromatic C-H in-plane (1,030 cm-1) and out-of plane deformation vibrations at 855 cm-1 (syringyl units) and 815 cm-1 (guaiacyl units), δas(C-H) at 1460 cm-1 and 1450 cm-1, both related to methyl and methylene groups of the side chain and methoxy groups,35,36 new bands appear after oxyethylation. Vibrations at 1125 cm-1 and 1085 cm-1, assigned to υ(C-O-C) and δ(C-O),38 clearly indicate the introduction of oxyethylene groups into the lignin macromolecule. This is supported by 11 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 34

increased intensities of C-H vibrations at 2930 cm-1, 2870 cm-1, and 2835 cm-1 related to methylene groups in oxyethylene substituents in OEL and broad bands at 1215 and 940 cm-1 associated with (CH2) twisting, (CH2) rocking and υ(C-O-C) of oxyethylene chains.37,38 Secondary hydroxyls formed due to the ring opening of the epoxide (Scheme 1) were verified most likely by the intense band at 1085 cm-1 related to δ(C-O) in ethers and secondary alcohols.37 The decreased intensities of signals at 1510 and 815 cm-1 in the spectrum of OEIND-3, both typical for guajacyl units,35,39 are indicative for their etherification with PEGDGE but from this results it is not clearly evident to which extent an etherification of phenolic OH groups occurred.6

arom. ring

1590 υas(C-H)

2930

G ring

δ(C-O) sec. alcohols + OE

1510

1085

υs(C-H)

2870, 2835 υ(C-O-C)

r(CH2) +

in OE

υ(C-O-C) in OE

1125

940

b

a 3000

1750

1500

1250

1000

750

-1

Wave number [cm ]

Figure 2: FTIR spectra of a) Indulin AT and b) its oxyethylated counterpart OE-IND-3; G: guajacyl, OE: oxyethylene; relevant signals are indicated (G – guajacyl, OE – oxyethylene moieties)


Page 13 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Tab. 3: Positions and assignments of IR bands of lignin, oxyethylated lignin OEL and acetylated counterparts of both (Lig-OAc, OEL-OAc) Band position [cm-1] Band assignment Reference OEL, Lig-OAc,, Lignin OEL-OAc 2930 2935 w-m υas(C-H), side chain, OMe 35,39 2870 w-m υs(C-H), OEL ….. 37 2835 2835 sh υs(C-H), side chain, OMe 35,39 1765 s-vs υ(C=O) phenyl OAc 24,40 1740 s-vs υ(C=O) aliphatic OAc 24,40 1590 s 1585 s aromatic skeletal vibration 35,39 1515 s 1510 s aromatic skeletal vibration G 35,39 1460 m 1460 m δas(C-H), CH2, CH3 35,39 1450 m 1450 m δas(C-H) , CH2, CH3 35,39 38 1215 s t(CH2) twisting, OEL 1215 υ(CO-O) aliphatic OAc 36 1190 υ(CO-O) phenyl OAc 41 1150 δ(C-H) in-plane G 34 1125 δ(C-H) in-plane S 34 1125 vs υ(C-O-C) ether, OEL 24 1085 w 1085 vs δ(C-O) sec. alcohols, aliphatic ethers 35,37 1030 vs υ(C-O-C) ether, OEL 37 940 r (CH2) rocking, υ(C-O-C) ether, OEL 38 900 υ(C-C), phenyl OAc 41 δ(C-H) out-of-plane deformation in 2, 35,39 855 6 position of S δ(C-H) out-of-plane in 2, 5, 6 position 815 35,39 G Key to intensities and vibrations: vs: very strong; s: strong; m: moderate; w: weak; sh: shoulder; υ: stretching vibration, δ: deformation vibration, s: symmetrical, as: asymmetrical; S: syringyl, G: guajacyl, OMe: methoxyl

FTIR spectra of acetylated samples of lignin and OEL modified with different amounts of PEGDGE (Fig. 3) allow a more detailed consideration of the structural differences of both.,14,23 Overlaid profiles of the most significant bands are shown in Fig. 4. It is clearly visible that the intensities and intensity ratios of the signals at 1765 cm-1 and 1740 cm-1 related to C=O stretching vibration of phenolic and aliphatic acetates

24,40

significantly

changed after lignin oxyethylation. Decreasing intensities of υ(C=O)phen and increasing strength of υ(C=O)aliph after lignin modification are clearly indicative for the etherification of 13 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 34

phenolic hydroxyls with PEGDGE and the formation of new secondary OH groups (Scheme 1). The latter is due to the ring opening of the epoxide moieties of PEGDGE during the reaction with lignin (Scheme 1) and is in accordance with results from FTIR of nonacetylated lignin and OEL samples. The spectra of the preactetylated OEL variants modified with an increasing amount of PEGDGE are characterized by an intensity gradient of υ(C=O)phen in the order OE-IND-1 < OE-IND-2 < OE-IND-3 < OE-IND-4, but only marginal differences can be seen for the peak intensity of υ(C=O)aliph (Fig. 3 and 4). This indicates that at the modification of lignin with PEGDGE the crosslinking reaction - where one OHaliph/C9 (phenylpropane unit) is newly formed (Scheme 1, structure 2) - dominates in relation to the formation of noncrosslinked OEL domains containing oxyethylene glycol moieties with three new OHaliph/C9 (Structure 3). υ(C=O) OAcphen

1765

υ(C=O) OAcaliph

υ(CO-O)

OAcaliph

1740

1215

υ(CO-O) OAcphen δ(C-C) OAcphen

1190

900

60 min US 12.5 mmol PEGDGE

e

IA_US_15

60 min US + H

d 10 mmol PEGDGE IA_US_01

60 min US

c10 mmol PEGDGE IA_US_04

Fenton-ox. b 7.5 mmol PEGDGE IA_F_01

a Indulin AT 3000

1750

1500

1250

1000

750

-1

Wave number [cm ]

Figure 3: FTIR spectra of preacetylated samples from a) Indulin AT and its oxyethylated counterparts b) OE-IND-1, c) OE-IND-2, d) OE-IND-3, and e) OE-IND-4; relevant signals are indicated (OAcphen – phenolic acetoxy, OAcaliph – aliphatic acetoxy)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Intensity [-]

Page 15 of 34

0.10

0.10

0.08

0.08

0.06

0.06

0.04

0.04

0.02

0.02

0.020

0.015

0.010

0.00

0.005

0.00

1800

1750

1700 -1

1650

0.000 1300

1250

1200

1150

925

900

-1

Wave number [cm ]

Figure 4: Overlaid profiles of selected IR bands of preacetylated samples from Indulin AT (black) and its oxyethylated counterparts OE-IND-1 (red), OE-IND-2 (blue), d) OE-IND-3 (green), and OE-IND-4 (orange) Accordingly, intensities of signals at 1190 cm-1 and 1215 cm-1, related to υ(CO-O) in phenolic37 and aliphatic acetates,41 respectively, change in the same manner as υ(C=O)phen and υ(C=O)aliph. Thus, the intensity ratio I1190/I1215 of acetylated lignins and OEL is assumed as a suitable and powerful indicator to quantify free phenolic OH groups of lignin and lignin derivatives like OEL as it was described for the aliphatic and aromatic IR ester bands of acetylated milled wood and organosolv lignins at 1745 and 1765 cm-1.23,24 Correlation of phenolic hydroxyl contents with features in FTIR spectra. In order to verify this assumption, intensity ratios I1765/I1740 and I1190/I1215 from the IR spectra of acetylated lignins and OEL were plotted against OHphen contents of the respective samples determined by aminolysis. Strong correlations were found between both IR indices and OHphen contents of technical lignins and the respective OEL variants with coefficients of determination R2 > 0.95 (Fig. 5a, b; Tab. 4.). It thus appears that a) the intensity ratio of the bands at 1765 cm-1 and 1740 cm-1 is not only suitable for the determination of phenolic hydroxyls of technical lignins but also for the analysis of highly modified lignin derivatives like OEL; b) the evaluation of the intensity



ratio I1190/I1215 as novel approach for the quantitative analysis of the OHphen content of lignin and lignin derivatives. Interestingly, same relations were found for the intensity I900 and more distinctive for the peak integral A900 of the IR band at 900 cm-1 (Fig. 5c, d), attributed to υ(C-C) in phenolic acetates.41 Linear regression of these two IR parameters with OHphen contents from aminolysis yielded coefficients of determinations R2 ≥ 0.94 (Tab. 4). This signal is regarded as a more effective and powerful indicator for the quantification free phenolic hydroxyls, particularly when samples with low OHphen contents were analyzed as it is the case for OEL. If so, signals related to aliphatic acetoxy groups (1740 and 1215 cm-1) can overlap the bands associated to phenolic acetates (1765 and 1190 cm-1).23 Hence, band resolution techniques, e.g., deconvolution, decimation, or derivatization of the spectra and, therefore, further analytical work may be required. Those additional steps omit when I900 or A900 is evaluated. 1.4 1.4

a

y = 0.3656 + 0.1923 x

2

2

R =0.97

R =0.96

1.4 1.4

Gleichung

y = a + b*x

Gewichtung

Keine Gewichtu ng

I1190/I1215 [-]

I1765/I1740 [-]

b

1.6 1.6

y = 0.24 + 0.1564 x

1.2 1.2

0.04415

Fehler der Summe der Quadrate

1.0 1.0

Kor. R-Quadrat

I1765I1740

0.8 0.8

1.20.97062 Wert 1.2

Standardfehler

Schnittpunkt mit 0.23995 der Y-Achse

0.02647

Steigung

0.00593

0.15635

Gleichung Gewichtung

1.0 1.0

Fehler der Summe der Quadrate Kor. R-Quadrat

0.6 0.6

0.8 0.8 Lignin OEL

0.4 0.4 11

22

3 3

55 44 OHphen [%]

66

33

5 44 5 OHphen [%]

6 6

77 A910 88 Lineare Anpassung von A910

0.6 0.6

c

0.025 0.025

d 0.5 0.5

y = -0.00047 + 0.0037 x 2

y = -0.0849 + 0.0917 x 2

R =0.97

R =0.94

0.4 0.4

0.015 0.015

Gleichung Gewichtung

A900 [-]

0.020 0.020


0.010 0.010

Kor. R-Quadrat

0.3 0.3

y = a + b*x

Keine Gewichtung Gleichung

4.86767E-5

Gewichtung

0.2 0.2 0.94275 Wert Schnittpunkt mit der Y-Achse

I910

0.005 0.050 0.000 0.000

I1190I1215

Lignin OEL

0.4 0.6 7 8 11 2 7 I9108 2 Lineare Anpassung von I910

0.030 0.030

I900 [-]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 34

0.1 0.1

Steigung

Lignin OEL


Standardfehler

-4.68906E-4

8.78913E-4

0.00367

1.96942E-4

Kor. R-Quadrat

Lignin OEL

A910

0.0 0.0 11

22

3 3

55 44 OHphen [%]

66

7 7

8 8

11

2 2

33

5 44 5 OHphen [%]

6 6

77

88

Figure 5: Correlations of a) the intensity ratio I1765/I1740, b) the intensity ratio I1190/I1215, c) the peak intensity I910 and d) the peak area A910 with phenolic OH group contents of various 16 ACS Paragon Plus Environment

Page 17 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lignins () and their oxyethylated counterparts () determined by selective aminolysis; regression parameters for linear fits of scatter plots are listed in Tab. 4

Tab. 4: Regression parameters for linear fits Y = a + bX obtained after plotting OHphen contents from aminoylsis vs. specific FTIR parameters, where Y is the FTIR value, X is OHphen, a is the Y-intercept, b is the slope, R2 is the coefficient of determination, SD is the standard deviation; the sample volume n is 22 FTIR value a) I1765/I1740 (intensity ratio) b) I1190/I1215 (intensity ratio) c) I900 (intensity) d) A900 (peak area)

a

b

SD

R2

0.2400 0.3656 -0.0005 -0.0085

0.1564 0.1923 0.0037 0.0917

0.0470 0.0653 0.0022 0.0273

0.971 0.963 0.943 0.971

The compliance of OHphen contents of lignins and OEL counterparts determined by aminolysis with values calculated from FTIR calibration models (Tab. 4) is shown in Fig. 6. Although the samples are very heterogeneous regarding their free phenolic group contents, the plots are satisfactory. Using the FTIR parameters I1765/I1740, I1190/I1215, I900 and A900, linear regressions gave similar results with absolute standard errors (SEs) ± 0.28 - 0.40 % (Tab. 5). This is in accordance with findings of Faix et al.,42 who applied simple regression analyses based on the bands at 1765 and 1740 cm-1 for the characterization of milled wood lignins with a more narrow OHphen content between 1 and 3 % (SE = 0.35 %). In the current work, better results (SE = 0.28 and 0.29 %) were obtained for the analysis of samples with a wider range of OHphen contents (1.8-6.9 %) using A900 and I1765/I1740 for calibration and calculation by FTIR. Thus, this FTIR method for the determination of OHphen contents and DOEs of OEL can be established and based on different IR bands ascribed to vibrations of phenolic and aliphatic acetate groups of preacetylated OEL and the corresponding parent lignins.



8

a

I1765/I1740

7 6 5 4 3 2

b

I1190/I1215

7 OHphen [%] calculated by FTIR

OHphen [%] calculated by FTIR

8

6 5 4 3 2

1

1 1

2

3 4 5 6 OHphen [%] by aminolysis

7

8

1 1

8

2 2

5 33 44 5 66 OHphen [%] by aminolysis

77

88

8

c

I900

6 5 4 3 2 1

d

A900



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 34

6 5 4 3 2 1

1

2


7

8

1

2


7

8

Figure 6: Correlation plots of OHphen contents of various lignins () and their oxyethylated counterparts () determined by aminolysis vs. the results calculated from FTIR parameters: a) the intensity ratio I1765/I1740, b) the intensity ratio I1190/I1215, c) the peak intensity I910 and d) the peak area A910; regression parameters and the standard errors for linear fits are summarized in Tab. 5

Tab. 5: Regression parameters for linear fits Y = a + bX obtained after plotting OHphen contents from aminoylsis vs. OHphen contents calculated by FTIR, where a is the Y-intercept, b is the slope, R2 is the coefficient of determination, SE is the standard error; the sample volume n is 22 FTIR calculation a) I1765/I1740 (intensity ratio) b) I1190/I1215 (intensity ratio) c) I900 (intensity) d) A900 (peak area)

a

b

SE

R2

0.0511 0.0469 0.0473 0.0494

0.9916 0.9919 0.9832 0.9918

0.2924 0.3226 0.4086 0.2838

0.972 0.966 0.946 0.974

Conclusion In this study it was shown that the DOE of OEL can be determined by preacetylation and subsequent selective aminolysis of phenolic acetates before and after lignin oxyethylation. Moreover, strong correlations between OHphen contents of parent lignin/OEL obtained by 18 ACS Paragon Plus Environment

Page 19 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


aminolysis and IR signals of preacetylated lignin and OEL counterparts with varying DOE were found. Thus intensities, intensity ratios, and integrated areas of IR bands related to aliphatic and phenolic acetates can be used to generate calibration models for the FTIR spectroscopic determination of actual OHphen contents and to quantify DOE values of OEL. In addition to the conventional FTIR approach using the ratio of the IR ester bands at 1765 and 1740 cm- for OHphen determination of unmodified lignins, we demonstrated for the first time that 1) this approach is also suitable for the characterization of highly modified lignin derivatives like OEL, 2) the ratio I1215/I1190 of the CO-O stretching vibrations of aliphatic and phenolic acetates and 3) the maximum intensity and the integrated peak area of the C-C stretching vibration of phenolic acetates at 900 cm-1 are suitable IR spectroscopic measures for a rapid and reliable determination of free OHphen and the DOE of phenolic substructures of OEL after its preacetylation. Using the peak area of the signal with its maximum intensity at 900 cm-1 is the most effective approach with an absolute standard error of 0.28 %. The easily performed method will bring new insights into structure-function relations of OEL based materials and other classes of modified lignins and related natural compounds like tannins, flavones, and other polyphenols. More precise results of FTIR analysis of OEL and related materials can be expected when multivariate techniques like multiple linear regression, principal component analysis or partial least-squares approaches were applied what will be the subject of further investigations.

Notes The authors declare no competing financial interest.

Acknowledgements 19 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The authors are grateful to Technische Universitaet Dresden for supporting this study.

References (1) Dimmel, D.R. In Lignin and lignans: Advances in chemistry. Heitner, C.; Dimmel, D.R.; Schmidt, J.A., Eds.; CRC Press: Boca Raton, 2010; pp 1-10. (2) Podschun, J.; Stücker, A.; Saake, B.; Lehnen, R. Structure-function relationship in the phenolation of lignins from different sources. ACS Sustainable Chem. Eng. 2015, 3, 2526−2532. (3) Uraki, Y.; Koda, K.; Yamada, T.; Oikawa, C.; Aso, T. Novel functions of non-ionic, amphiphilic lignin derivatives. In Functional materials from renewable resources. Liebner, F.; Rosenau, T., Eds.; ACS Symposium Series 1107, American Chemical Society: Washington, 2012; pp 243-254. (4) Lin, X.; Zhou, M.; Lou, H.; Yang, D.; Oiu, X. Synthesis, structure, and dispersion properties of a novel polyoxyethylene ether from kraft lignin and poly(ethylene glycol). ACS Sustainable Chem. Eng. 2014, 2, 1902–1909 (5) Thakur, V. K.; Thakur, M. K. Recent advances in green hydrogels from lignin: a review. Int. J. Biol. Macromol. 2015, 72, 834−847. (6) Passauer, L. Highly swellable lignin hydrogels: Novel materials with interesting properties. In Functional materials from renewable resources. Liebner, F.; Rosenau, T., Eds.; ACS Symposium Series 1107, American Chemical Society: Washington, 2012; pp 211-228. (7) Perez-Cantu, L.; Liebner, F.; Smirnova, I. Preparation of aerogels from wheat straw lignin by cross-linking with oligo(alkylene glycol)-α,ω-diglycidyl ethers. Microporous Mesoporous Mat. 2014, 195, 303-310.


Page 20 of 34

Page 21 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8) Leitner, S.P.; Paulik, C.; Weber, H. From lignin aerogels to carbogels. Book of abstracts. European Workshop of Lignocellulosics and Pulp 2014, Seville, Spain (9) Grishechko, L.I., Amaral-Labat, G.; Szczurek, A.; Fierro, V.; Kuznetsov, B.N.; Celzard, A. Lignin–phenol–formaldehyde aerogels and cryogels. Microporous Mesoporous Mat. 2013, 168, 19–29. (10)

Passauer, L.; Takano, T.; Perez, L.; Smirnova, I.; Malinina, V., Kepplinger, R.;

Wieland, M.; Rosenau, T.; Liebner, F. Lignin-based hydrogels, aerogels and carbon aerogels. Book of abstracts. 17th International Symposium on Wood, Fiber, and Paper Chemistry 2013, Vancouver, Canada. (11)

Passauer, L.; Liebner, F.; Fischer, K. Preparation and physical characterization of

strongly swellable oligo(oxyethylene) lignin hydrogels. Holzforschung 2011, 65, 309-317. (12)

Nishida, M., Uraki, Y., Sano, Y. Lignin gel with unique swelling property. Biores.

Technol. 2003, 88, 81–83. (13)

Passauer, L.; Hallas, T.; Bäucker, E.; Ciesielski, G.; Lebioda, S.; Hamer, U.

Biodegradation of hydrogels from oxyethylated lignins in model soils. ACS Sustainable Chem. Eng. 2015; 3, 1955-1964. (14)

Passauer, L.; Struch, M.; Schuldt, S.; Appelt, J.; Schneider, Y.; Jaros, D.; Rohm, H.

Dynamic

moisture

sorption

characteristics

of

xerogels

from

water-swellable

oligo(oxyethylene) lignin derivatives. ACS Appl. Mater. Interfaces 2012, 4, 5852-5862. (15)

Zakis, G.F. Functional Analysis of lignins. Tappi Press: Atlanta, 1994; pp 33-43.

(16)

Goldschmid, O. Determination of phenolic hydroxyl content of lignin preparations by

ultraviolet spectrophotometry. Anal. Chem. 1954, 26, 1421-1423. (17)

Aulin-Erdtman, G. Spectrographic contributions to lignin chemistry. V. Phenolic

groups in spruce lignin. Sven. Papperstidn. 1954, 57, 745-760. (18)

Adler, E.; Hernestam, S.; Walldén, I. Estimation of phenolic hydroxyl groups in

lignin. I. Periodate oxidation. Sven. Papperstidn. 1958, 61, 640-647. 21 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(19)

Björkmann, A.; Person, B. Studies on finally divided wood. Part 4. Some reactions of

the lignin extracted by neutral solvents from Picea abies. Svensk. Papperstidn. 1957, 285292. (20)

Lapierre, C. Determining lignin structure by chemical degradations. In Lignin and

lignans: Advances in chemistry. Heitner, C.; Dimmel, D.R.; Scmidt, J.A.,Eds.; CRC Press: Boca Raton; pp 11-48. (21)

Månsson, P. Quantitative determination of phenolic and total hydroxyl groups in

lignins. Holzforschung 1983, 11, 143-146. (22)

Månsson, P. Selective deacetylation of aromatic acetates by aminolysis. Tetrahedron.

Lett. 1982, 23, 1845-1846. (23)

Faix, O.; Böttcher J.H. Determination of phenolic hydroxyl group contents in milled

wood lignins by FTIR spectroscopy applying partial least squares (PLS) and principle components regression (PCR). Holzforschung 1993, 47, 45-49. (24)

Wegener, G.; Strobel C. Bestimmug der phenolischen Hydroxylgruppen in Ligninen

und Ligninfraktionen durch Aminolyse und FTIR-Spektroskopie. Holz Roh. Werkst. 1992, 50, 417-420 (in German). (25)

Lundquist, K. Proton 1H NMR spectroscopy. In Methods in lignin chemistry. Lin, S.Y.

and Dence, C.W., Eds.; Springer: Heidelberg, 1992; pp 242-249. (26)

Ludwig, C.H.; Nist, B.J.; McCarthy, J.L. Lignin. XIII. The high resolution nuclear

magnetic resonance spectroscopy of protons in acetylated lignin. J. Am. Chem. Soc. 1964, 86, 1196-1202. (27)

Ludwig, C.H.; Nist, B.J.; McCarthy, J.L. Lignin. XII. The high resolution nuclear

magnetic resonance spectroscopy of protons in compounds related to lignin. J. Am. Chem. Soc. 1964, 86, 1186-1196. (28)

Robert, D. Carbon-13 nuclear magnetic resonance spectrometry. In Methods in lignin

chemistry. Lin, S.Y. and Dence, C.W., Eds.; Springer: Heidelberg, 1992; pp 250-273. 22 ACS Paragon Plus Environment

Page 22 of 34

Page 23 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(29)

Argyropoulos, D.S. Quantitative phosphorus-31 NMR analysis of six soluble lignins.

J. Wood Chem. Technol. 1994, 14, 65-82. (30)

Argyropoulos, D.S. Quantitative phosphorus-31 NMR analysis of lignins, a new tool

for the lignin chemist. J. Wood Chem. Technol. 1994, 14, 45-63. (31)

Koch, C.J. Asymmetrische Synthese von 1-Aminocyclobutancarbonsäuren. PhD

Dissertation, LMU Munich, Germany, 2002 (in German). (32)

Glasser, W.; Davé, V.; Frazier, C.E. Molecular weight distribution of (semi-)

commercial lignin derivatives. J. Wood Chem. Technol. 1993, 13, 545-549. (33)

Zier, N. Strukturelle Merkmale eines Organosolv-Lignins bei Variation der

Aufschlussparameter. PhD Dissertation, Technische Universität Dresden, 1996 (in German). (34)

Passauer, L.; Liebner, F.; Fischer, K. Activation of pine kraft lignin by Fenton-type

oxidation for cross-linking with oligo(oxyethylene) diglycidyl ether. Holzforschung 2011, 65, 319-326. (35)

Faix, O. Classification of lignins from different botanical origin by FT IR

spectroscopy. Holzforschung 1991, 45, 21-27. (36)

Hergert, H.L. Infrared spectra of lignin. In Lignins: Occurrence, formation, structure

and reactions. Sarkanen, L.V.; Ludwig, H.C., Eds.; Wiley: New York, 1970; pp 267-297. (37)

Socrates, G. Infrared and Raman characteristic group frequencies, 3rd ed.; John Wiley

& Sons, 2001. (38)

Yoshihara, T.; Tadokoro, H; Murahashi, S. Normal vibrations of the polymer

molecules of helical conformation. IV. Polyethylene oxide and polyethylene-d4 oxide. J. Chem. Phys. 1964, 41, 2902-2911. (39)

Hergert, H.L. Infrared spectra of lignin and related compounds. II. Conifer lignin and

model compounds. J. Organ. Chem. 1960, 25, 405-413.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(40)

Faix, O.; Argyropoulos, D.; Robert, D.; Neirinck, D. Determination of hydroxyl

groups in lignins: Evaluation of 1H-,

13

C-,

31

P-NMR, FTIR and wet chemical methods.

Holzforschung 1994, 48, 387-394. (41)

Panicker, C.Y.; Varghese, H.T.; Madhavan, V.S.; Mathew, S.; Vinsova, J.; van

Alsenoy, C.; Sheena Mary, Y. FT-IR, FT Raman, and computational calculations of 4chloro-2-(3-chlorophenyl carbamoyl) phenyl acetate. J. Raman. Spec. 2009, 40, 21762186. (42)

Faix, O.; Grünwald, C.; Beinhoff, O. Determination of phenolic hydroxyl group

content of milled wood lignins (MWD´s) from different botanical origins using selective aminolysis, FTIR, 1H NMR, and UV spectroscopy. Holzforschung 1992, 40, 273-280.


Page 24 of 34

Page 25 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For Table of Contents Use Only

Quantitative analysis of the etherification degree of phenolic hydroxyl groups in oxyethylated lignins: Correlation of selective aminolysis with FTIR spectroscopy Lars Passauer, Katrin Salzwedel, Marlene Struch, Nadine Herold, Joern Appelt

Synopsis A reliable analytical approach for the determination of the etherification degree of oxyethylated lignins for functional materials from renewable sources is presented.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

ACS Paragon Plus Environment

Page 26 of 34

Page 27 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


HO

Lignin

R

Lignin 2x

R1

R O

R

O

2

2

OH

Lignin

2

OH

O

O

O

Lignin

n

1

OH 2H2O

R

O 2

-OH-

R1

O

O

3 R1 = OCH3

R1

O

n

2

O

-2OH-

+

1x

O

2H2O

R1

O

R2 = H; OCH3


OH

n

a 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

O


OH

Page 28 of 34

CH3

O N

+ R2

R

2Ac2O

+

20°C

R

1

OH R1 = OCH3

R

2

1

O O

4

R2 = H; OCH3

H 3C

O

O

b

CH 3

O

R

2

CH3

O

O O

+ R

2AcOH

N

1

H

O O

20°C fast

+ R2

R

N

1

OH

O

5

H 3C

CH 3 6

O

c

CH3

O

+ R2

R OH

1

OH

O O

N H

20°C slow

+ R2


5

R OH

N

1

O

CH3 6

Page 29 of 34

OHphen peak intens INDera_C + IA_US_15a

OHphen peak area INDera_C + IA_US_15a

a

7

b

7

4 y = 6.278 + 0.043x 2 R = 0.98

4 2

3

3

5 4

2

3

1

y = 1.777 + 0.0379x 2 R = 0.98

1

-1

-1

2

2

y = 1.959 + 0.0154x 2 R = 0.98

1

Schn t mit Achs Steig

B

AcPyr [mmol gLigAc]

3

5

4

y = 6.627 + 0.015x 2 R = 0.95

6

OHphen [%]

6

OHphen [%]

Gleichung y = a Gewichtun Kein g Fehler der 0 Summe der Quadrate Kor. R-Qua

8

8

AcPyr [mmol gLigAc]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


1

Gleichung

Gewichtung


Kor. R-Qua

G

0

0 0

10

20

30

40

50

60

70

0

0 0

10

20

30

40

50

Reaction time [min]

Reaction time [min]


60

70


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

arom. ring

1590 as(C-H)

2930

Page 30 of 34

(C-O)

G ring

sec. alcohols + OE

1510

1085

s(C-H)

2870, 2835 (C-O-C)

r(CH2) +

in OE

(C-O-C) in OE

1125

940

b

a 3000

1750

1500

1250 -1

Wave number [cm ] ACS Paragon Plus Environment

1000

750

Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


(C=O)

(C=O)

(CO-O)

OAcphen

OAcaliph

OAcaliph

1765

1740

1215

(CO-O)

OAcphen (C-C)

1190

OAcphen

900

e

60 min US 12.5 mmol PEGDGE IA_US_15

60 min US + H2O2-ox.

d 10 mmol PEGDGE IA_US_01

60 min US

c 10 mmol PEGDGE IA_US_04

Fenton-ox.

b 7.5 mmol PEGDGE IA_F_01

a Indulin AT 3000

1750

1500

1250

1000

-1

Wave number [cm ]


750


Intensity [-]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

0.10

0.10

0.08

0.08

0.06

0.06

0.04

0.04

0.02

0.02

0.00

0.00 1800

1750

1700 -1

Wave number [cm ]

1650

Page 32 of 34

INDalt 0.020 IAF01 IAUS01 IAUS04 IAUS15 0.015 BK254 MS8 MS19 MS23 0.010 MS24

INDalt IAF01 IAUS01 IAUS04 IAUS15 BK254 MS8 MS19 MS23 MS24

0.005

0.000

1300

1250

1200 -1

Wave number [cm ]


1150

925

900

Page 33 of 34

a

b

1.6

I1190/I1215 [-]

1.4

I1765/I1740 [-]

1.4 1 2 3 1.2 4 5 6 7 1.0 8 9 10 0.8 11 12 13 14 0.6 15 16 17 0.4 18 1 19 20 21 22 0.030 23 24 25 0.025 26 27 0.020 28 29 30 0.015 31 32 33 0.010 34 35 36 0.050 37 38 39 0.000 40 1 41 42


1.2

1.0

0.8

0.4 2

3

4

5

6

7

1

8

2

3

4

5

6

7

8

0.6

c

d 0.5

I900 [-]

A900 [-]

0.4 0.3 0.2 0.1

2

3

4 5 OHphen [%]

6

7

8

0.0 ACS Paragon 1 Plus2 Environment 3 4 5 OHphen [%]

6

7

8

ACS Sustainable Chemistry & Engineering 8

a

I1765/I1740

7 6 5 4 3 2

6 5 4 3 2

1

1 1

2


7

11

8

8

2 2

3 55 6 3 44 6 OHphen [%] by aminolysis

7 7

88

8

c

I900

7

d

A900 7



b

I1190/I1215

7



8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Page 34 of 34

6 5 4 3 2 1 1

2


7

8

6 5 4 3 2

1 ACS Paragon 1 Plus2Environment 3 4 5 6 OHphen [%] by aminolysis

7

8

Quantitative Analysis of the Etherification Degree of Phenolic Hydroxyl

Recommend Documents