Introduction Of Sulfonic Acid Groups Research Articles

Thermodynamically Stable Functionalization of Microporous Aromatic Frameworks with Sulfonic Acid Groups by Inserting Methylene Spacers.

Porous aromatic frameworks (PAFs) are an auspicious class of materials that allow for the introduction of sulfonic acid groups at the aromatic core units by post-synthetic modification. This makes PAFs promising for proton-exchange materials. However, the limited thermal stability of sulfonic acid groups attached to aromatic cores prevents high-temperature applications. Here, we present a framework based on PAF-303 where the acid groups were added as methylene sulfonic acid side chains in a two-step post-synthetic route (SMPAF-303) via the intermediate chloromethylene PAF (ClMPAF-303). Elemental analysis, NMR spectroscopy, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy were used to characterize both frameworks and corroborate the successful attachment of the side chains. The resulting framework SMPAF-303 features high thermal stability and an ion-exchange capacity of about 1.7 mequiv g-1. The proton conductivity depends strongly on the adsorbed water level. It reaches from about 10-7 S cm-1 for 33% RH to about 10-1 S cm-1 for 100% RH. We attribute the strong change to a locally alternating polarity of the inner surfaces. The latter introduces bottleneck effects for the water molecule and oxonium ion diffusion at lower relative humidities, due to electrolyte clustering. When the pores are completely filled with water, these bottlenecks vanish, leading to an unhindered electrolyte diffusion through the framework, explaining the conductivity rise.

Revealing the mechanisms of lignin modification by phenolic additives during pre-hydrolysis treatment and its effects on enzymatic hydrolysis

Condensed lignin formed during eucalyptus woodchip pre-hydrolysis adversely affects subsequent enzymatic saccharification, and phenolic additives are popular lignin condensation inhibitors. The goal of this project was to reveal the mechanisms of lignin modification by phenolic additives during woodchip pre-hydrolysis and its effects on subsequent enzymatic saccharification. The HSQC and 31P NMR analyses confirmed that resorcinol with three electrophilic substitution of active sites could act as a cross-linking agent to promote the formation of condensed lignin, whereas 2-naphthol and sodium 2-naphthol-7-sulfonate could block benzyl carbocations and reduce the formation of condensed lignin. Interestingly, the introduction of sulfonic acid groups increased the electrostatic repulsion between enzyme and lignin as well as increased the hydrophilicity of lignin, thereby greatly reducing non-productive adsorption and physical obstacle effects. Sodium 2-naphthol-7-sulfonate as an efficient benzyl carbocations scavenger reduced the non-productive adsorption and physical obstacle effects of lignin by 82.4% and 13.3%, respectively.

Study on the Effect of Main Chain Molecular Structure on Adsorption, Dispersion, and Hydration of Polycarboxylate Superplasticizers.

Polycarboxylate ether (PCE) with different main chain structures was prepared by aqueous solution free radical polymerization using unsaturated acids containing sulfonic acid groups, acrylamide groups, and carboxyl groups and isoprenyl polyoxyethylene ether (IPEG). The molecular structure was characterized by infrared spectroscopy and gel chromatography, while adsorption, dispersion, and hydration properties were studied using a total organic carbon analyzer, rheometer, and isothermal microcalorimeter, respectively. The results show that the adsorption process of PCE on cement particles is spontaneous physical adsorption. The adsorption forces are mainly electrostatic interaction, and hydrogen bonding. The introduction of sulfonic acid groups and polycarboxylic acid groups reduces the initial adsorption amount of PCE but can accelerate the adsorption rate of PCE on cement and increase the adsorption amount at the adsorption equilibrium. The introduction of acrylamide groups in the PCE main chain is beneficial to the initial dispersion of PCE and can reduce the plastic viscosity of cement slurry. PCE can delay the hydration of cement. The introduction of acrylamide groups and dicarboxylic acid groups in the PCE main chain helps prolong the induction period of cement hydration, while the introduction of sulfonic acid groups is not conducive to its retarding effect.

Engineering sulfuric acid-pretreated biochar supporting MnO2 for efficient toxic organic pollutants removal from aqueous solution in a wide pH range

Manganese dioxides (MnO2) and biochar materials are both desirable candidates for environmental remediation of toxic organic pollutants (TOPs) in water due to wide availability and environmental-friendly. In practical application, however, MnO2 suffers from low redox activity owing to deprotonation, while biochar is subject to limited removal capacity. Herein, a difunctional engineering sulfuric acid-pretreated biochar supporting MnO2 composite (MBC-A) was firstly synthesized and optimized to remove various TOPs from aqueous solution. Specifically, sulfuric acid not only served as an active agent to improve the specific surface area of biochar for improvement of adsorption capacity and more MnO2 loading, but also facilitated the introduction of sulfonic acid groups (-SO3H) as an internal proton reservoir to inhibit inactivation of MnO2 due to deprotonation in alkaline. Thanks to adsorption and oxidation, MBC-A showed excellent removal capacity (214.9 mg/g) and fast reaction kinetics (360 min) for tetracycline (TC), exceeding precursor and other materials reported in literature. Importantly, the effective operation pH range of MBC-A was broadened to 1–13 with the help of buffering capacity of –SO3H groups. The dominant driving force of adsorption were π-π interaction and hydrogen bond; while reactive oxidative species were mainly ascribed to singlet oxygen (1O2), hydroxyl radical (·OH) and reactive Mn3+. The possible reactive sites and pathway were investigated by combining experimental results with density functional theory (DFT) calculation. Further, the results of multiple cyclic runs, removal in real river water and toxicity assessment demonstrated well reusability, high environmental security, and excellent practical applicability of MBC-A.

Catalytic Hydrogenation of CO2 to Formate Using Ruthenium Nanoparticles Immobilized on Supported Ionic Liquid Phases.

Ruthenium nanoparticles (NPs) immobilized on imidazolium-based supported ionic liquid phases (Ru@SILP) act as effective heterogeneous catalysts for the hydrogenation of carbon dioxide (CO2 ) to formate in a mixture of water and triethylamine (NEt3 ). The structure of the imidazolium-based molecular modifiers is varied systematically regarding side chain functionality (neutral, basic, and acidic) and anion to assess the influence of the IL-type environment on the NPs synthesis and catalytic properties. The resulting Ru@SILP materials contain well-dispersed Ru NPs with diameters in the range 0.8-2.9nm that are found 2 to 10 times more active for CO2 hydrogenation than a reference Ru@SiO2 catalyst under identical conditions. Introduction of sulfonic acid groups in the IL modifiers results in a greatly increased turnover number (TON) and turnover frequency (TOF) at reduced metal loadings. As a result, excellent productivity with TONs up to 16100 at an initial TOF of 1430 h-1 can be achieved with the Ru@SILP(SO3 H-OAc) catalyst. H/D exchange and other control experiments suggest an accelerated desorption of the formate species from the Ru NPs promoted by the presence of ammonium sulfonate species on Ru@SILP(SO3 H-X) materials, resulting in enhanced catalyst activity and productivity.

Janus sulfonated graphene oxide nanosheets with excellent interfacial properties for enhanced oil recovery

In this article, we prepared Janus sulfonated graphene oxide nanosheets (JSGO) by a facile method for large-scale production. Unlike previous single-sided modifications of graphene oxide (GO), the smart JSGO nanofluid that can automatically find oil was obtained by modifying the double sides of GO. Benefiting from the introduction of sulfonic acid groups, JSGO had outstanding dispersity and stability under extreme conditions. Furthermore, JSGO exhibited excellent interfacial properties due to its amphiphilic characteristic. On the one hand, JSGO can reduce interfacial tension by 71% and form a strong interfacial film at the oil–water contact, achieving piston displacement with high sweep efficiency. On the other hand, JSGO had a strong ability in wettability reversal that can turn the hydrophobic surface into completely hydrophilic. These excellent properties of JSGO nanofluid contributed to obtaining an additional 18.4% recovery factor at low concentration (100 mg/L) and low injection volume (0.3 pore volume). As a result of the simple preparation, high performance, and excellent dispersion stability of JSGO nanofluid, it can be utilized as a chemical agent to enhance oil recovery in the harsh environment of reservoirs.

Pyrene-based sulfonated organic porous materials for rapid adsorption of cationic dyes in water

ABSTRACT Porous organic polymers (POP) have gained attention because of their high specific surface area, porosity and their simplicity in synthesis, but for the most part, they are hydrophobic because of their organic backbone, making it difficult to expand their applications. Here, we have obtained poly(pyrene) porous organic polymers (PyPOP) through the polymerization of pyrene monomers catalysed by aluminium trichloride, which is a simple and inexpensive synthesis method. The sulfonated poly(pyrene) porous organic polymers (PyPOP-SO3H) obtained showed rapid adsorption of cationic dyes, especially malachite green (MG adsorption 1607 mg/g) and methylene blue (MB adsorption 1220 mg/g) in pH = 7 aqueous solution, room temperature. The results show that the Freundlich model is more in line with the adsorption process than the Langmuir model, whether for methylene blue or malachite green. In addition, the PSO kinetic model fits better than PFO kinetic model, whether it is for the adsorption of methylene blue or malachite green. The excellent adsorption performance of PyPOP-SO3H for cationic dyes may be due to the introduction of sulfonic acid groups, which not only increases the specific surface area but also allows better dispersion in water, increasing contact points and adsorption efficiency. This research expands the scope of exploration and application of POP.

Graphene oxide-naphthalene sulfonate blends as possible proton exchange membranes

This work presents a study on the preparation of novel self-assembling naphthalene sulfonate-functionalised graphene oxide membranes, whose analysis aims at assessing their potentiality as an alternative to perfluorinated proton conductors. Three different graphene oxide-to-naphthalene sulfonate molar ratios and two different process temperatures were combined to identify the most suitable conditions to perform an effective functionalisation. ATR-FTIR, Raman and EDX spectroscopies, thermogravimetric analysis, static contact angle evaluation and XRD aimed to point out the introduction of sulfonic acid groups (–SO3H) in the GO framework, while optical and scanning electron microscopies verified the good membrane uniformity. The evaluation of the ion exchange capacity (IEC) demonstrated the proton-exchanging ability of the prepared membranes. The most promising sample underwent water uptake (WU) and electrochemical impedance spectroscopy (EIS) tests to examine the dependence of its water sorption and proton conductivity with respect to relative humidity and temperature, in order to deepen the assessment of its feasibility as a possible future electrolyte in alternative energy generators. A preliminary investigation of the mechanical properties of the above-mentioned sample was performed as well to expand the characterisation of its behaviour.

Towards an understanding of the microstructure and interfacial properties of the ionic liquid/sulfuric acid catalyst in liquid-liquid reactions

Sulfonic-acid-functionalized Brønsted acidic ionic liquids (SFILs) have been considered as a promising dual solvent-catalyst for numerous applications. The bulk microstructure and interfacial characteristics of different kinds of SFILs and the corresponding SFIL/H2SO4 systems were investigated in this work using molecular dynamics (MD) simulations in terms of the SFILs possessing three anions (e.g. bisulfate, triflate, and bis(trifluoromethylsulfonyl)imide), different alkyl chain lengths, and different introduced position of the sulfonic acid groups (-SO3H). The introduction of the sulfonic acid groups is found to provide a strong hydrogen-bonding interaction site with both the HSO4− and H2SO4, making almost two order of magnitudes larger for average numbers of hydrogen bonds between different pairs. The introduction of sulfonic acid groups onto the shorter side chains contributes to stronger hydrogen-bonding interactions with both the HSO4− and H2SO4 than when introduced onto the longer side chains. The coordination numbers of the equivalent terminal carbon atoms of octyl chain and equivalent sulfur atoms of sulfonic acid groups are more than 4.5 and 2.5, respectively, which suggests that obvious nanostructured aggregation of the polar sulfonic acid groups, as well as nonpolar longer alkyl chains, exists in the pure SFILs and SFIL/H2SO4 systems. In addition, it is found that the ordering preference and interfacial orientation of the side chains and imidazole rings at gas-liquid interfaces are sharply changed following the addition of the sulfonic acid groups. The insights into the bulk structural and interfacial characteristics of the SFIL/H2SO4 systems obtained in this work may inform the design and optimization of novel SFILs for specific catalytic applications.

Antifouling and High Flux Sulfonated Polyamide Thin-Film Composite Membrane for Nanofiltration

A new sulfonated aromatic diamine monomer, potassium 2,5-bis(4-aminophenoxy)benzenesulfonate (BAPBS), was synthesized and employed to develop a series of thin-film composite (TFC) nanofiltration membranes with trimesoyl chloride (TMC) on a polysulfone (PSF) substrate by an interfacial polymerization (IP) technique. The TFC membrane performed a high water flux of 72.8 L m–2 h–1 and a rejection of 92.5% to Na2SO4 at 0.6 MPa. The surface hydrophilicity of the as-prepared sulfonated polyamide (SPA) membrane was greatly improved by the introduction of sulfonic acid groups, as confirmed by the much reduced contact angle value. Moreover, the membrane also exhibited good antifouling ability with water flux recovery ratio (FRR) and total flux decline ratio (DRt) of about 88% and 18%, respectively. Molecular dynamics simulation was investigated to obtain an in-depth understanding of the transport behaviors of water molecules through the SPA polymers. The results clearly illustrated that the diffusion coefficient of...

Novel sulfonated thin-film composite nanofiltration membranes with improved water flux for treatment of dye solutions

In this paper, two types of novel sulfonated aromatic diamine monomer, 2,5-bis(4-amino-2-trifluoromethyl-phenoxy)benzenesulfonic acid (6FAPBS) and 4,4′-bis(4-amino-2-trifluoromethyl-phenoxy)biphenyl-4,4′-disulfonic acid (6FBABDS), were synthesized and used to prepare the thin-film composite (TFC) nanofiltration (NF) membranes. Two series of sulfonated TFC NF membranes were prepared on a microporous polyphenylsulfone (PPSU) support membrane through an interfacial polymerization technique with trimesoyl chloride (TMC) solution and amine solutions containing 6FAPBS/6FBABDS and piperazine (PIP), and their properties including chemical composition, membrane morphology and hydrophilicity of the active layer were characterized by ATR-IR, XPS, SEM and contact angle measurement. After that, these resultant membranes were employed to perform dye treatment experiments with aqueous solutions of rhodamine B and methyl orange. The membranes prepared under the optimum condition showed an increase in the water flux by improving surface hydrophilicity which was enhanced by the presence of sulfonated aromatic diamine monomers without compromising the rejection of dyes. The introduction of sulfonic acid groups plays a major role in water permeation and rejection of dyes during TFC NF separation process.

Adsorptive potential of sulfonated poly(glycidylmethacrylate)-grafted cellulose for separation of lysozyme from aqueous phase: Mass transfer analysis, kinetic and equilibrium profiles

Lysozyme (LYZ) adsorption onto poly(glycidylmethacrylate)-grafted cellulose having sulfonate functional group (PGMA-g-Cell-SO 3H) was investigated. PGMA-g-Cell-SO 3H was prepared by graft copolymerization of glycidylmethacrylate (GMA) onto cellulose in the presence of ethyleneglycoldimethacrylate as cross linker using α,α′-azobisisobutyronitrile as initiator followed by the introduction of sulfonic acid groups through ring opening reaction of epoxide group in grafted GMA with sodium sulfite–isopropanol–water mixture. The adsorbent was characterized by means of FTIR, SEM, XRD and BET analysis. The maximum value of LYZ adsorption was found to be 74.93 and 96.21 mg/g for an initial concentration of 150 and 200 mg/L, respectively, at pH 6.0. The batch adsorption process followed pseudo-second-order kinetics and the equilibrium was achieved within 3 h. The kinetic data were also analyzed using external and intraparticle diffusion models. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. Equilibrium isotherm data were well fitted with the Langmuir isotherm with maximum adsorption capacity of 141.67 mg/g at 30 °C. Thermodynamic study revealed an endothermic adsorption process. All of the adsorbed LYZ was eluted completely by 0.2 M CH 3COOH solution. Results obtained from repeated adsorption/desorption process showed that PGMA-g-Cell-SO 3H can be used for the separation of LYZ from aqueous solutions.

Randomly Sulfonated Liquid Crystalline Polymers Containing Triad Mesogen of Butylene Terephthalate

A thermotropic liquid crystalline polymer (LCP) containing a terephthaloyl bis(4-oxybenzoyl) (Triad) rigid moiety and a butylene terephthalate flexible unit was solution-polymerized and was subsequently partly sulfonated. It was found that the introduction of sulfonic acid groups to the LCP did not change the position of the DSC peak for the nematic-to-isotropic transition of the LCP (T n-i). However, the sulfonation induced a peak related to the melting of crystalline phase of the Triad domains (T m(T)). When the acid groups of the sulfonated LCP were neutralized with NaOH, the T n-i DSC peak shifted to lower temperatures with a strong decrease in its size, but the T m(T) DSC peak did not change its position strongly. Furthermore, a new peak for the melting of crystalline phase of the butylenes domains (T m(BT)) appeared at much lower temperatures. The above results suggested that the sulfonation introduced ionic characters to the TLCP polymer successfully; as expected, it changed the liquid crystalline characters of the TLCP significantly.

Grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticle and carbon black surfaces

AbstractThe surface grafting of hyperbranched cyclotriphosphazene polymer onto silica nanoparticles and carbon black was investigated. The grafting of hyperbranched cyclotriphosphazene polymer onto these surfaces was achieved by the repeated reactions of hexachlorocyclotriphosphazene with hexamethylenediamine from surface amino groups and sodium carboxylate groups, respectively. The percentage of grafting onto silica and carbon black surfaces exceeded 760 and 390%, respectively. However, it proved difficult to achieve the theoretical growth of cyclotriphosphazene polymer from these surfaces because of steric hindrance. The introduction of sulfonic acid groups was successfully achieved by the reaction of terminal chlorophosphazene groups of the hyperbranched polymer‐grafted silica and carbon black with sulfanilic acid. The content of sulfonic acid groups introduced onto silica and carbon black surfaces was 4.98 mmol/g and 5.70 mmol/g, respectively. The sulfonated cyclotriphosphazene polymer‐grafted carbon black was extremely hydrophilic, yielding stable colloidal dispersions in polar solvents. The sulfonated cyclotriphosphazene polymer‐grafted silica and carbon black showed ionic conductivity, with the conductance increasing exponentially with increasing relative humidity and temperature. This study may offer important leads in the application of silica nanoparticles and carbon black in polymeric membranes for fuel cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4218–4226, 2008

Surface-modified carbon black for As(V) removal

This paper reports the results of the adsorption performance of As(V) removal by a commercial carbon black and its H 2SO 4-modified form in a single-ion situation. The influence of different process parameters and the physicochemical principles involved were studied in detail. Acid modification caused morphological changes in the virgin carbon black as evidenced by BET surface area measurements and SEM study. FTIR spectra showed the introduction of sulfonic acid group in the parent carbon due to H 2SO 4 treatment. TGA analysis revealed higher weight loss characteristics of the modified carbon, demonstrating the creation of functional groups. The point of zero charge (pH pzc) of the modified carbon black is highly acidic (3.5) compared to commercial carbon black (6.4). It directly infers the generation of acidic functional moieties in the carbon black. The adsorption experiments were carried out following batch equilibrium techniques. The kinetics and thermodynamics of adsorption were investigated to unveil the mechanism and nature of the adsorption process, respectively. The kinetic parameters of different models were calculated and discussed. The kinetics of adsorption can be expressed by a pseudo-second-order model and intraparticle diffusion was not the rate-determining step. Dependence of pH on adsorption showed maximum metal uptake in the range of 4–5 and inferred surface complexion as the principal mechanism of adsorption. The equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin–Kaganer–Radushkevich (DKR) isotherm equations and the corresponding isotherm parameters were calculated and discussed in detail.

Pore Size Effect on Improvement of Surface Proton Conductivity for Three-Dimensionally Ordered Macroporous Silica Composite Membrane

A composite membrane composed of a three-dimensionally ordered macroporous (3DOM) silica matrix and a proton conducting polymer electrolyte was prepared. The proton conductivity of the composite membrane was successfully improved by introduction of sulfonic acid groups on the 3DOM silica surface. On decreasing pore size of the 3DOM silica matrix, a greater improvement of proton conductivity was observed. ( pore) or ( pore) improvement was attained for the composite membranes filled with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) polymer. These values are two orders of magnitude larger than those expected from the amount of sulfonic acid groups introduced on the 3DOM silica surfaces. This result suggests a formation of new proton conducting paths by an interaction between sulfonic acid groups on the 3DOM silica surface and those in the AMPS polymer electrolyte.

Preparation and solubility of water–methanol mixtures in sulfonated poly(etherketone) containing a cardo‐ring structure

AbstractThe preparation and solubility of water–methanol mixtures in sulfonated (1,3‐dihydro‐3‐oxoisobenzofuran‐1,1‐diyl‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenyleneoxy‐1,4‐phenylene) (C‐PEK) was systematically studied. The sulfonation was carried out by reacting C‐PEK with 98% sulfuric acid at 60°C. This reaction obeys a first‐order reaction mechanism up to 4 h. The sulfonic acid group was uniformly dispersed in a sulfonated C‐PEK (SC‐PEK) membrane. The introduction of sulfonic acid groups in C‐PEK could increase polymer segmental gaps because of the size of a bulky sulfonic acid group or decrease polymer segmental gaps as a result of polar interactions. The former effect is dominant for SC‐PEK with low sulfonic acid content, whereas the latter occurs for SC‐PEK with high sulfonic acid content. The uptake of pure water or an aqueous methanol solution (e.g., 3, 5, and 10 wt % methanol concentration) in the sulfonated C‐PEK membranes increases with increasing sulfonic acid group content. However, the sulfonated C‐PEK with high sulfonic acid content selectively sorbs water rather than methanol in the membrane. This suggests that the sulfonated C‐PEK membrane could prevent crossover of methanol through the membrane and has potential as a polymer electrolyte for the direct methanol fuel cell. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1113–1123, 2006

Enhancement on proton conductivity of inorganic–organic composite electrolyte membrane by addition of sulfonic acid group

A proton-conducting porous silica matrix for composite membranes was prepared by introduction of sulfonic acid groups on the surface. The surface modification of pores in the porous silica membrane was performed by using 3-mercaptopropyltrimethoxysilane (SH oxidation method) or 1,3-propanesultone (direct reaction method). The sulfonated silica matrix exhibited high proton conductivity of 6.0×10−3 S cm−1 at 60 °C under 90% relative humidity. This value was about 400 times higher than that of unmodified silica matrix. The proton conductivity of the composite membrane filled by a proton-conducting gel polymer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), was considerably enhanced by using the sulfonated silica matrix.

Crosslinked Organic/Inorganic Hybrid Proton Exchange Polymeric Membranes

ABSTRACTA general, efficient and experimentally simple method for the synthesis of covalently crosslinked class II hybrid polymers based on PolyEtherEtherKetone (PEEK) with a high degree of sulfonation (DS = 0.8) was performed. The synthetic strategy foreseen two steps: the first one, direct sulfonation, led to the introduction of sulfonic acid groups and to the formation of sulfone bridges among repeat units. The second step, lithiation and silylation, led to the formation of covalent bonds between the organic backbone and Si(OH)3 moieties. The materials were characterized by 1H NMR Spectroscopy, ATR/FTIR Spectroscopy, Thermogravimetric Analysis (TGA) and Mass Spectrometry. Preliminary proton conduction measurements in dry conditions were performed. The introduction of silicon groups in the system improved thermal stability.

Enzymatic modification of kraft lignin through oxidative coupling with water-soluble phenols.

The aromatic polymer lignin can be modified through promotion of oxidative coupling between phenolic groups on lignin and various phenols. The reaction is initiated by an oxidation of both components, e.g., by using the oxidoreductases laccase or peroxidase. Coupling between phenolic monomers and lignin has previously been studied by the use of radio-labeled phenols. In this study, incorporation of water-soluble phenols into kraft lignin, using laccase as catalyst, was investigated. Several phenols with carboxylic or sulfonic acid groups were used as markers for the incorporation. The modified lignin was isolated and the amount of phenol incorporated was characterized by means of titration, quantitative 1H-NMR, and quantitative 31P-NMR after modification with 2-chloro-4,4,5,5-tetramethyl-1,2,3-dioxaphospholane. Only a few of the phenols studied were found to be incorporated into lignin. When the phenol guaiacol sulfonate was incorporated into kraft lignin, the lignin became water-soluble at pH 2.4 and a low ionic strength due to the introduction of sulfonic acid groups. The content of sulfonic acid groups in the product was 0.5-0.6 mmol/g lignin. A lower amount of 4-hydroxyphenylacetic acid was incorporated under similar conditions.