Kinetics of the base fragmentation of a model of lignosulfonate

Abstract

Lignin, a random polymer of phenylpropane units' is one of the major structural components of wood. During bisulfite and acid sulfite pulping lignin is converted into polymeric lignosulfonate. Lignosulfonate is the major component of spent sulfite pulping liquor (SSL). SSL generally constitutes a source of pollution and as such it presents an environmental problem. SSL is, however, also a potential source of chemical raw materiaL2 Thus the chemistry of lignosulfonates has been extensively investigated with a view to their commercial exploitation. The base fragmentation of lignosulfonate has been the subject of considerable attention.3 While initial studies on the base fragmentation of lignosulfonate were aimed a t their desulfonation, it was later found that vanillin and acetaldehyde were also pr0duced.~-6 The sulfonic acid group appeared to be essential for aldehyde production. Model-compound studies showed that the aldehydes originated from the guaiacylglycerin-P-guaiacylether-a-sulfonate structure present in lignosulfonate.',6 Model compounds 1 and 2 (as barium salts) of the guaiacylglycerin-P-guaiacylether-a-sulfonate of lignosulfonate produced on base fragmentation 71.3% vanillin, 58.1% acetaldehyde, 73.9% guaiacol, and 53% veratric aldehyde, 60% acetaldehyde, 73% guaiacol, respectively.'.6 From these and other results7 it was concluded that the fragmentation of 1 and 2 proceed via initial elimination of guaiacol ( 3 ) rather than by direct substitution; of the possible elimination pathways (Scheme l), pathway (a) was chosen. Strong arguments were raised against the possibility of pathway (b), which is characterized by the formation of an ally1 alcohol. Recently, the isolation of the stereoisomers (4)8 from the base treatment of the lignosulfonate model compound (2) prompted a reinvestigation of this mechanism.8 In this study it was ascertained that pathway (b) is indeed possible. Yield studies as a function of reaction time of the decomposition of model compound (2) and of the formation and decomposition of (4) as well as of subsequent products were also presented. We have used these yield studies as regards the mechanism presented8 to investigate the kinetic behavior of the reactions involved. The treatment carried out on (2) was with 2.5N NaOH a t the boiling point and the yields in function of reaction time were obtained by HPLC.8 Guaiac ylgl ycerin-o-guaiacylethera-sulfonateThe initial part of the system in question can be summarized as a system of two parallel reactions, namely The total rate of the decomposition of (2), thus the total decomposition in the sum of eqs. (I) and (II!, follows a first-order kinetic law and is defined by a first-order rate constant k , , ,~ = kz = 1.155 X s-l (high precision)

On the chemistry, behavior, and cure acceleration of phenol–formaldehyde resins under very alkaline conditions

“…The values of the secondary interactions (sum of van der Waals, H-bonds, electrostatic and torsional contributions), between each of the PF oligomers and the surface of a schematic model of the surface of a crystallite of Cellulose 11, have already been reportedss",'2 and were obtained according to established molecular mechanics methods. [13][14][15] The computational methods and constrained and noncon- strained force fields used have already been extensively reported.8~'~-'~ The results obtained are shown in Table 11.…”