Article pubs.acs.org/IECR
Kinetics of the Cationization of Cotton Timothy S. De Vries,*,† Dan R. Davies,† Michelle C. Miller,‡ and William A. Cynecki‡ †
Core R&D, and ‡Dow Consumer & Industrial Solutions, The Dow Chemical Company, 1776 Building, Midland, Michigan 48674, United States S Supporting Information *
ABSTRACT: Cationic cotton has a greater affinity for reactive dyes than untreated cotton, providing economic and environmental advantages for the textile industry. The reaction by which a cationic group is appended to cotton suffers from a competing hydrolysis in the aqueous medium; the inefficiency of the cationization under desired processing conditions currently limits widespread application. A study of the kinetics of the competing processes provided insight into the mechanism of hydrolysis and of the reaction with cotton, enabled by high-throughput parallel reactors. The reaction kinetics and the dependences on temperature and catalytic NaOH are well-defined under a range of industrially useful conditions. The temperature profiles of the competing reactions are similar, and both have the same first-order dependences on [NaOH]. Changing the amount of excess catalytic base and the temperature are therefore not expected to have a significant effect on reaction efficiency but can be used to control the time required for a reaction to go to completion. A rationale for the enhancement of reaction efficiency by organic cosolvents is also described.
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cationization of cotton.5 Reaction of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHTAC) has been shown to proceed through an epoxide intermediate (2,3-epoxypropyltrimethylammonium chloride, EPTAC) which reacts with hydroxyl groups on cellulose, appending a cationic moiety (Scheme 2). The electrostatic forces between cationic fiber and anionic dye are thereby made attractive, not repulsive. Now the dyeing process can produce an equal or greater depth of shade and fastness in a shorter time with less wasted dye and fewer fabric rinses, and without the addition of salts to the dye bath.6 The shorter time can result in energy and water savings, adding to the benefits of a cleaner effluent. Cationization chemistry is not without its own problems. Exposure of the epoxide intermediate to the alkaline aqueous conditions necessary to effect reaction with cellulose also results in direct hydrolysis of intermediate 2 to diol 5. Some studies have focused on alternative reagents,5b but the reaction efficiency of CHTAC itself has been improved by replacing at least some of the solvent with a nonaqueous medium or reducing the amount of water used relative to the fabric being treated (low liquor-to-goods ratios).5b,7 The present study of the kinetics of competing reaction pathways from the simple and readily available CHTAC reagent (sold under the trade name EcoFAST CR 2000; EcoFAST is a trademark of The Dow Chemical Company) helps to elucidate the basis for these application improvements and enables the optimization of more industrially relevant applications in some cases.
INTRODUCTION Despite competition from synthetic alternatives, cotton remains a popular choice for clothing and other textiles. To meet the performance expectations of consumers, reactive dyes continue to gain market share for coloring cellulosic fabrics;1 it was estimated in 2011 that reactive dyes accounted for 23% of all dyes used on textiles worldwide, 38% of those used on cellulosic textiles.2 Reactive dyes derive their name from the covalent bond to cellulose formed during application (Scheme 1 shows Reactive Orange 16 as a representative reactive dye), enhancing washfastness in particular. However, most reactive dyes, which have highly conjugated aromatic chromophores, are solubilized into water by functionalizing with strongly acidic or anionic groups like sulfonic or carboxylic acids. The hydroxyl groups in cellulose have a pKa near that of water,3 meaning they are deprotonated to a large extent in the aqueous alkaline environment used for dyeing. This lends a negative charge to cellulosic fibers, which then repel the anionic dyes. The conventional solution to this problem has been the addition of salts to the dyebath to decrease the electrostatic repulsion, but this has led to environmental concerns in some areas. The Chinese textile industry, one of the largest consumers of sodium sulfate, is estimated to have applied approximately 3.9 billion pounds in 2011, mostly to dyeing and printing.4 Removal of these salts and the large amounts of unreacted and hydrolyzed colorants remaining in the fabric necessitates numerous washes, often with heated water, such that washing and wastewater treatment can account for up to 50% of the cost of the reactive dyeing process.1 Enhanced equipment and wastewater purification can help prevent these salts from entering a textile mill’s watershed, but alternative approaches to reduce the salt requirement have long been explored. Some dye manufacturers produce modified versions of reactive dyes as low-salt (e.g., Cibacron’s LS range of dyes) or environmentally friendly (Remazol’s EF product line). Another decades-old approach still being pursued is the © 2014 American Chemical Society
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RESULTS AND DISCUSSION General Experimental Design. Collecting reaction rate data can be a very time-consuming process, and the Received: Revised: Accepted: Published: 9686
February 26, 2014 May 6, 2014 May 12, 2014 May 12, 2014 dx.doi.org/10.1021/ie500836n | Ind. Eng. Chem. Res. 2014, 53, 9686−9694
Industrial & Engineering Chemistry Research
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Scheme 1. Reaction of a Representative Reactive Dye with Cellulosics
Scheme 2. Cationization of Cellulosics with CHTAC
heterogeneous chemistry to be studied here, wherein a cotton swatch must be continuously moved through a bath, does not lend itself readily to in situ monitoring methods. The quenched aliquot method of collecting samples to analyze outside the reaction vessel seemed a better choice, and this also seemed amenable to high-throughput data collection. A workflow was developed using an open reactor, with five reaction wells heated to the desired temperature and mixed with an orbital shaker. The open reactor enables easy transfer of reagents into and aliquots out of the reaction mixtures using an automated liquid handler. Aliquots can be transferred to HPLC sample vials in a titer plate on the reagent deck at consistent, preset time points by adding delays to the protocol used to control the system’s automated liquid handler. The HPLC sample vials can be filled by the liquid handler with a dilute acidic quench, about 2 equiv of AcOH based on excess NaOH in the reaction vessel. This quench was chosen for stability of any remaining epoxide in the samples (30 min before use), with 0.8 mL/min of PIC solution as the
mobile phase. Diol 5 is observed by refractive index detector at 4.4 min; PhS(O)Me standard is observed by ultraviolet detector at 11.1 min. The peak areas for 5 were divided by the peak area for the standard and plotted vs (mmol 5/mg PhS(O)Me) for each data point. The data were fit to a linear function in Excel with a constraint that the y-intercept must be zero: (mmol 5/mg PhS(O)Me) = response factor·peak area for 5/peak area for PhS(O)Me. Raw data (HPLC peak areas) and calibration graph can be found in the Supporting Information. HPLC Calibration of 2,3-Epoxypropyltrimethylammonium Chloride (2). Due to its hydrolytic instability, samples of epoxide 2 were prepared freshly for HPLC calibration. Each sample was prepared by adding chlorohydrin 1 to 0.38 M NaOH (1 equiv, stock solutions prepared by diluting 5.0 M NaOH either with water or with a solution of 257 mg of PhS(O)Me in 1.000 L of water; details for each calibration sample in the Supporting Information) and mixing for 30 min at room temperature. An aliquot (0.2 mL) was quenched by addition to an HPLC sample vial containing 0.8 mL of 0.05 M AcOH in PIC solution. The samples were analyzed by HPLC using the conditions listed above. Epoxide 2 and small amounts of diol 5 are observed by refractive index detector at 5.3 and 4.4 min, respectively; PhS(O)Me standard is observed by ultraviolet detector at 11.1 min. The peak areas for 5 were converted to mmol 5 and subtracted from the amount of 1 added, giving mmol 2. The peak areas for 2 were then divided by the peak area for the standard and plotted vs (mmol 2/mg PhS(O)Me) for each data point. The data were fit to a linear function in Excel with a constraint that the y-intercept must be zero: (mmol 2/mg PhS(O)Me) = response factor·(peak area for 2/ peak area for PhS(O)Me). Raw data (HPLC peak areas) and calibration graph can be found in the Supporting Information. 3,3′-Oxybis(N,N,N-trimethyl-2-hydroxypropanaminium) Dichloride (6). Trimethylammonium chloride (1.87 g, 19.6 mmol) was suspended in 90 mL of chloroform and heated to 40 °C. With stirring, diglycidyl ether (1.00 mL, 8.6 mmol) was added in two portions about 7 min apart. After stirring for 24 h, the mixture was cooled to room temperature and the solvent removed by rotary evaporation. The resulting oil was dissolved in ∼5 mL of hot isopropyl alcohol, and acetonitrile was added until the solution became cloudy (∼25 mL). After cooling slowly, a white crystalline powder formed and was collected by vacuum filtration, an inverted funnel feeding nitrogen gas over the Büchner funnel to minimize water 9692
dx.doi.org/10.1021/ie500836n | Ind. Eng. Chem. Res. 2014, 53, 9686−9694
Industrial & Engineering Chemistry Research
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AcOH solution; row C: 400 μL of mobile phase + 400 μL AcOH solution; row D: 200 μL of mobile phase + 600 μL AcOH solution; row E: 800 μLof AcOH solution. Five 40 mL vials were placed in a 72-well reactor with orbital shaker in positions A1−E1, and the reactor was warmed to 30 °C and shaken at 180 rpm. To each was added water via an automated liquid handler (A1, 16.47 mL; B1, 14.39 mL; C1, 10.22 mL; D1, 6.05 mL; E1, 1.89 mL), 1.2 M NaOH (A1, 3.53 mL; B1, 5.61 mL; C1, 9.78 mL; D1, 13.95 mL; E1, 18.11 mL), and finally a solution of 1 (3.280 g of 65.4 w/w% 1 in water + 30 mL of a solution of 257 mg PhS(O)Me in 1.000 L water, 5.00 mL added to each vial). The liquid handler’s syringe was rinsed between addition of NaOH and EcoFAST CR 2000, and before every aliquot transfer. An aliquot (200 μL) was transferred from each of the reaction vessels A1−E1 to HPLC sample vials A1−E1 about 10 min after the final reagent was added to each reaction vial. Immediately following an aliquot transfer, with the syringe tip still in the aliquot vial, 400 μL was aspirated and then immediately dispensed, repeating once, to mix. After a delay, the transfer and mixing sequence was repeated to quench aliquots in HPLC sample vial positions A2−E2 at 20 min after the start of the reaction, in positions A3−E3 at 40 min, A4−E4 at 60 min, A5−E5 at 80 min, A6−E6 at 120 min, A7−E7 at 160 min, A8−E8 at 200 min, and A9−E9 at 240 min. These quenched aliquots were analyzed by HPLC using the conditions described above. Diol 5 is observed by refractive index detector at 4.4 min, epoxide 2 at 5.3 min, and chlorohydrin 1 at 8.7 minnot typically observed. The peak areas for 2 and 5 were plotted vs time for each data point. The
absorption by the hygroscopic material. A small sample was taken for analysis and demonstrated to be isomerically pure. The remainder (0.35 g, 13% y) was dissolved in water; HPLC analysis showed a peak at 18.7 min consistent with the byproduct observed in kinetics experiments. 1H NMR (d6DMSO): δ5.84 (dd, J = 5.5, 2.3 Hz, 2H), 4.25 (m, 2H), 3.35− 3.61 (m, 8H), 3.21 (s, 18H). 13C NMR (CDCl3) δ73.67, 68.43, 64.58, 53.91. HPLC Calibration of 3,3′-Oxybis(N,N,N-trimethyl-2hydroxypropanaminium) Dichloride (6). To a 5 × 9 HPLC titer plate was added 45 HPLC sample vials (positions labeled A1−E9). To each was added via an automated liquid handler 400 μL of PIC solution and 400 μL of a solution of 0.1 M acetic acid (200 μL of AcOH in 35 mL of PIC solution). Five 40 mL vials were placed in a 72-well reactor with orbital shaker in positions A1−E1, and the reactor was warmed to 50 °C and shaken at 180 rpm. To A1−D1 was added water via the automated liquid handler (A1, 19.69 mL; B1, 16.47 mL; C1, 10.02 mL; D1, 3.57 mL); to E1 was added a solution of diol 5 (stock solution: 1878 mg of 64.7 w/w% 5 in water + 19 mL water; 10.00 mL added to E1), and to each was added 1.2 M NaOH (A1, 2.81 mL; B1, 3.53 mL; C1, 4.98 mL; D1, 6.43 mL; E1, 4.98 mL) and finally a solution of 1 (stock solution: 3.280 g of 65.4 w/w% 1 in water + 30 mL of a solution of 257 mg PhS(O)Me in 1.000 L water; A1, 2.50 mL; B1, 5.00 mL; C1, 10.00 mL; D1, 15.00 mL; E1, 10.00 mL). The liquid handler’s syringe was rinsed between additions of 5, NaOH, and 1, and before every aliquot transfer. An aliquot (200 μL) was transferred from each of the reaction vessels A1−E1 to HPLC sample vials A1−E1 about 10 min after the final reagent was added to each reaction vial. Immediately following an aliquot transfer, with the syringe tip still in the aliquot vial, 400 μL was aspirated and then immediately dispensed, repeating once, to mix. After a delay, the transfer and mixing sequence was repeated to quench aliquots in HPLC sample vial positions A2−E2 at 100 min after the start of the reaction, in positions A3−E3 at 120 min, A4−E4 at 140 min, A5−E5 at 160 min, A6−E6 at 200 min, A7−E7 at 240 min, A8−E8 at 280 min, and A9−E9 at 320 min. These quenched aliquots were analyzed by HPLC using the conditions listed above. Diol 5, epoxide 2, and dimer 6 are observed by refractive index detector at 4.4, 5.3, and 18.7 min, respectively; PhS(O)Me standard is observed by ultraviolet detector at 11.1 min. The peak areas for epoxide 2 were converted to mmol 2 and peak areas for diol 5 were converted to mmol 5 using the calibration determined above, and these were subtracted from the amount of 1 added, giving mmol dimeric byproduct 6 formed in the reaction by mass balance (assuming no other byproducts form). The peak areas for 6 were then divided by the peak area for the standard and plotted vs (mmol 6/mg PhS(O)Me) for each data point. The data were fit to a linear function in Excel with a constraint that the yintercept must be zero: (mmol 6/mg PhS(O)Me) = response factor·(peak area for 6/peak area for PhS(O)Me). Raw data (HPLC peak areas) and calibration graph can be found in the Supporting Information. General Procedure for Monitoring the Hydrolysis of 2 to 5. To a 5 × 9 HPLC titer plate was added 45 HPLC sample vials (positions labeled A1−E9). To each was added via an automated liquid handler varying amounts of PIC solution and of a solution of 0.4 M acetic acid (800 μL of AcOH in 35 mL of PIC solution) as follows: Row A: 700 μL of mobile phase + 100 μL AcOH solution; row B: 600 μLof mobile phase + 200 μL
loss of 5 was fitted to an exponential curve: Peak area = y0·e−k′·t. The observed rate constants (k′) were plotted against [NaOH]excess and the data fit to a linear function with a constraint that the y-intercept must be zero: k′ = k· [NaOH]excess. Representative HPLC chromatogram, raw data (HPLC peak areas), extracted rate constants, and graphical representations of the concentrations over time for reactions at different temperatures (30−70 °C) can be found in the Supporting Information. General Procedure for Monitoring Cotton Cationization to 4. To a 5 × 9 HPLC titer plate was added 45 HPLC sample vials (positions labeled A1−E9). To each was added via an automated liquid handler varying amounts of PIC solution and of a solution of 0.4 M acetic acid (800 μL of AcOH in 35 mL of PIC solution) as follows: Row A: 640 μL mobile phase + 160 μL AcOH solution; row B: 480 μL mobile phase + 320 μL AcOH solution; row C: 320 μL mobile phase + 80 μL AcOH solution; row D: 160 μL mobile phase + 640 μL AcOH solution; row E: 800 μL AcOH solution. Five 40 mL vials were placed in a 72-well reactor with orbital shaker in positions A1−E1, each charged with cotton (TestFabrics Style #419, Bleached and Mercerized Cotton, 1 swatch of about 15 × 15 cm, ∼2.6 g, cut into four strips and rolled to fit into vial), and the reactor was warmed to 30 °C and shaken at 180 rpm. To each was added via the automated liquid handler water (A1, 17.55 mL; B1, 16.55 mL; C1, 15.55 mL; D1, 14.55 mL; E1, 13.55 mL), a solution of 1 (3.283 g of 65.4 w/w % 1 in water + 30 mL of a solution of 257 mg of PhS(O)Me in 1.000 L of water, 5.00 mL added to each vial), and 1 equiv NaOH (1.45 mL of 1.2 M NaOH in each vial). After a short delay to allow formation of epoxide, excess NaOH was added as a 5 M solution (A1, 1.00 mL; B1, 2.00 mL; C1, 3.00 mL; D1, 9693
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(4) Suresh, B.; Funada, C. Sodium Sulfate. CEH Marketing Research Report; Chemical Economics Handbook; SRI Consulting: Zurich, August 2012; pp 771.1000A−771−1002Q. (5) (a) Rupin, M. Dyeing with Direct and Fiber Reactive Dyes. Text. Chem. Color. 1976, 8, 54. For leading references to more recent work, see: (b) Hashem, M.; Hauser, P.; Smith, B. Reaction Efficiency for Cellulose Cationization Using 3-Chloro-2- Hydroxypropyl Trimethyl Ammonium Chloride. Textile Res. J. 2003, 73, 1017. (c) Hasani, M.; Westman, G.; Potthast, A.; Rosenau, T. Cationization of Cellulose by Using N-Oxiranylmethyl-N-Methylmorpholinium Chloride and 2Oxiranylpyridine as Etherification Agents. J. Appl. Polym. Sci. 2009, 114, 1449. (6) Hauser, P. J. Reducing Pollution and Energy Requirements in Cotton Dyeing. Textile Chemist and Colorist & American Dyestuff Reporter 2000, 32, 44. (7) (a) Cold pad batch application was also used in a glycidyl stearate modification of cotton: Muresan, E. I.; Balan, G.; Popescu, V. Durable Hydrophobic Treatment of Cotton Fabrics with Glycidyl Stearate. Ind. Eng. Chem. Res. 2013, 52, 6270. (b) A variation of steam pad batch application was used to treat fabrics with N-halamine epoxides: Liang, J.; Chen, Y.; Ren, X.; Wu, R.; Barnes, K.; Worley, S. D.; Broughton, R. M.; Cho, U.; Kocer, H.; Huang, T. S. Fabric Treated with Antimicrobial N-Halamine Epoxides. Ind. Eng. Chem. Res. 2007, 46, 6425. (8) Hauser, P.; Tabba, A. North Carolina State University, Raleigh, NC. Unpublished work, 2004. (9) One equivalent of base was used up in all reactions to form epoxide 2 from chlorohydrin 1. The relevant [NaOH] for these studies was therefore based on subtracting the amount of 1 added from the amount of NaOH added and then dividing by the reaction volume, giving [NaOH]excess. (10) Anslyn, E. V.; Dougherty, D. A. Transition State Theory and Related Topics. Modern Physical Organic Chemistry; University Science Books: Herndon, VA, 2006; p 365.
4.00 mL; E1, 5.00 mL). The liquid handler’s syringe was rinsed between additions of EcoFAST CR 2000 and NaOH, and before every aliquot transfer. An aliquot (200 μL) was transferred from each of the reaction vessels A1−E1 to HPLC sample vials A1−E1 about 10 min after the final reagent was added to each reaction vial. Immediately following an aliquot transfer, with the syringe tip still in the aliquot vial, 400 μL was aspirated and then immediately dispensed, repeating once, to mix. After a delay, the transfer and mixing sequence was repeated to quench aliquots in HPLC sample vial positions A2−E2 at 20 min after the start of the reaction, in positions A3−E3 at 40 min, A4−E4 at 60 min, A5−E5 at 80 min, A6−E6 at 120 min, A7−E7 at 160 min, A8−E8 at 200 min, and A9−E9 at 240 min. These quenched aliquots were analyzed by HPLC using the conditions listed above. Diol 5 is observed by refractive index detector at 4.4 min, epoxide 2 at 5.3 min, chlorohydrin 1 at 8.7 minnot typically observed, and dimer 6 at 18.7 min; PhS(O)Me standard is observed by ultraviolet detector at 11.1 min. The peak areas for 2, 5, and 6 were divided by the peak area for the standard and plotted vs time for each data point. The data were fit to the model described above (eqs 2−5), using the rate constants determined by hydrolysis alone as a starting point for k1. Raw data (HPLC peak areas), extracted rate constants, calculated percentages of NaOH on cotton, and graphical representations of the concentrations over time for reactions at different temperatures (30−70 °C) can be found in the Supporting Information.
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ASSOCIATED CONTENT
S Supporting Information *
NMR spectra of 5 and 6, representative HPLC chromatograms, and kinetics data tables. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: 989-638-8318. E-mail:
[email protected]. Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank Joseph Deavenport (Dow Chemical), Patrick Brutto (Dow Chemical), William Miles (Dow Chemical), and Peter Hauser (North Carolina State University) for helpful discussions and Adham Tabba (North Carolina State University) for the hydrolysis study which helped define a good starting point for this work.
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REFERENCES
(1) Choudhury, A. K. R. Dyeing of Cellulosic Fibres. Textile Preparation and Dyeing; Science Publishers: Enfield, NH, 2006; pp 491−627. (2) Janshekar, H.; Suresh, B.; Inoguchi, Y. Dyes. CEH Marketing Research Report; Chemical Economics Handbook; SRI Consulting: Zurich, May 2011; pp 520.5000A−520.5008W. (3) Saric, S. P.; Schofield, R. K. The Dissociation Constants of the Carboxyl and Hydroxyl Groups in Some Insoluble and Sol-Forming Polysaccharides. Proc. R. Soc. London, Ser. A 1946, 185, 431−447. 9694
dx.doi.org/10.1021/ie500836n | Ind. Eng. Chem. Res. 2014, 53, 9686−9694
